AU2011203119A1 - Human monoclonal antibodies to programmed death 1(PD-1) and methods for treating cancer using anti-PD-1 antibodies alone or in combination with other immunotherapeutics - Google Patents

Abstract

HUMAN MONOCLONAL ANTIBODIES TO PROGRAMMED DEATH 1(PD-1) AND METHODS FOR TREATING CANCER USING ANTI-PD-1 ANTIBODIES ALONE OR IN COMBINATION WITH OTHER IMMUNOTHERAPEUTICS 5 Abstract The present invention provides isolated monoclonal antibodies, particularly human monoclonal antibodies, that specifically bind to PD-1 with high affinity. Nucleic acid molecules encoding the antibodies of the invention, expression vectors, host cells 1a and methods for expressing the antibodies of the invention are also provided. Immunoconjugates, bispecific molecules and pharmaceutical compositions comprising the antibodies of the invention are also provided. The invention also provides methods for detecting PD-1, as well as methods for treating various diseases, including cancer and infectious diseases, using anti-PD-1 antibodies. The present invention further provides is methods for using a combination immunotherapy, such as the combination of anti-CT LA 4 and anti-PD-1 antibodies, to treat hyperproliferative disease, such as cancer. The invention also provides methods for altering adverse events related to treatment with such antibodies individually.

Description

S&F Ref: 832495D1 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Ono Pharmaceutical Co., Ltd., of 1-5, Doshomachi 2 of Applicants: chome, Chuo-ku, Osaka-shi, Osaka, 5418526, Japan Medarex, Inc., of 707 State Road, Princeton, New Jersey, 08540, United States of America Actual Inventor(s): Alan J. Korman Bing Chen Mohan Srinivasan Josephine M. Cardarelli Mark J. Selby Changyu Wang Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Human monoclonal antibodies to programmed death 1(PD-1) and methods for treating cancer using anti-PD-1 antibodies alone or in combination with other immunotherapeutics The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(5380365_1) DESCRIPTION HUMAN MONOCLONAL ANTIBODIES TO PROGRAMMED DEATH 1 (PD-1) AND METHODS FOR TREATING CANCER USING ANTI-PD-1 ANTIBODIES ALONE OR IN COMBINATION WITH OTHER IMMUNOTHERAPEUTICS Technical Field S The present invention relates generally to immunotherapy in the treatment of human disease and reduction of adverse events related thereto. More specifically, the present invention relates to the use of anti-PD-I antibodies and the'use of combination immunotherapy, including the combination of anti-CTLA-4 and anti-PD-i antibodies, to treat cancer and/or to o decrease the incidence or magnitude of adverse events related to treatment with such antibodies individually. BAcki-ound of the Invention The protein Programmed Death 1 (PD-1) is an inhibitory member of the CD28 family of receptors, that also includes CD28, CTLA-4, ICOS and BTLA. PD-1 is expressed on S activated B cells, T cells, and myeloid cells (Agata et al., supra; Okazaki et al. (2002) Curr. Opin. Inununol. 14: 391779-82; Bennett et al. (2003) JImmunol 170:711-8). The initial members of the family, CD28 and ICOS, were discovered by functional effects on augmenting T cell proliferation following the addition of monoclonal antibodies (Hutloff et aL. (1999) Nature 397:263-266; Hansen etaL. (1980) Immunogenics 10:247-260). PD-i was discovered ko through screening for differential expression in apototic cells (Ishida et aL. (1992) EABO J. 11:3887-95).. The other members of the family, CTLA-4, and BTLA were discovered through screening for differential expression in cytotoxic T lymphocytes and THI cells, respectively. CD28, ICOS and CTLA-4 all have an unpaired cysteine residue allowing for horriodiiefization. In contrast, PD- is suggested to.exist as a monomer, lacking:the 93 unpaired cysteine residue characteristic in other CD18 family.members. The PD-I gene is a 55 kDa type I transmembrane protein that is part of the Ig gene superfamily (Agata et al. (1996) Int hnnninol 8:765-72). PD-I contains a membrane proximal immunoreceptor tyrosine inhibitory motif.(ITIM) and a membrane distal tyrosine based switch motif (ITSM) (Thomas, M.L. (1995) JExp Med 181:1953-6; Vivier, E and 30 Daeron, M (1997) Ininuinol Today .1:286-91). Although structurally similar to CTLA-4, PD-1 lacks the MYPPPY motif that is critical for B7-1 and B7-2 binding. Two ligands for PD-I have. been identified, PD-L1 and PD-L2, that have been shown to downregulate T cell activation upon binding to PD- I (Freeman -et al. (2000) JExp Med 192:1027-34; Latchman et al. (2001) Nat Innnunol 2:261-8; Carter et a. (2002) Eurt JIhinol32:634-43). Both PD as LI and PD-L2 are B7 homologs that bind to PD-1, but do not bind to other CD28 family members. One ligand for PD-I, PD-LI is abundant in a variety of human cancers (Dong et.aL. 1 (2002) Nat. Med 8:787-9). The interaction between PD-1 and PD-LI results in a decrease in tumor infiltrating lymphocytes, a decrease in T-cell receptor mediated proliferation, and immune evasion by the cancerous cells (Dong et al. (2003) J Mol. Med 81:281-7; Blank et aL. (2005) Cancer Immunol. Immunother. 54:307-314; Konishi et al. (2004) Clin Cancer Res. 5 10:5094-100). Immune suppression can be reversed by inhibiting the local interaction of PD 1 with PD-Li, and the effect is additive when the interaction of PD-1 with PD-L2 is blocked as well (Iwai et al. (2002) Proc. Nat'l. Acad Sci. USA 99:12293-7; Brown et al. (2003) J. Immunol. 170:1257-66). PD-1 is an inhibitory member of the CD28 family expressed on activated B cells, T to cells, and myeloid cells (Agata et al., supra; Okazaki et al. (2002) Curr Opin Immunol 14: 391779-82; Bennett et al. (2003) JImmunol 170:711-8). PD-1 deficient animals develop various autoimmune phenotypes, including autoimmune cardiomyopathy and a lupus-like syndrome with arthritis and nephritis (Nishimura et al. (1999) Immunity 11:141-51; Nishimura et al. (2001) Science 291:319-22). Additionally, PD-1 has been found to play a role in k5 autoimmune encephalomyelitis, systemic lupus erythematosus, graft-versus-host disease (GVHD), type I diabetes, and rheumatoid arthritis (Salama et al. (2003) JExp Med 198:71-78; Prokunina and Alarcon-Riquelme (2004) Hum Mol Genet J3:R143; Nielsen et al. (2004) Lupus 1:510). In a murine B cell tumor line, the ITSM of PD-1 was shown to be essential to block BCR-mediated Ca 2 -flux and tyrosine phosphorylation of downstream effector ao molecules (Okazaki et al. (2001) PNAS 98:13866-71). Accordingly, agents that recognize PD-1, and methods of using such agents, are desired. Disclosure of the Invention The present invention provides isolated monoclonal antibodies, in particular human a s monoclonal antibodies, that bind to PD-I and that exhibit numerous desirable properties. These properties include, for example, high affinity binding to human PD-1, but lacking substantial cross-reactivity with either human CD28, CTLA-4 or ICOS. Still further, antibodies of the invention have been shown to modulate immune responses. Accordingly, another aspect of the invention pertains to methods of modulating immune responses using 30 anti-PD-1 antibodies. In particular, the invention provides a method of inhibiting growth of tumor cells in vivo using anti-PD-1 antibodies. In one aspect, the invention pertains to an isolated monoclonal antibody, or an antigen binding portion thereof, wherein the antibody exhibits at least one of the following properties: (a) binds to human PD-I with a KD of 1 x 107 M or less; (b) does not substantially bind to human CD28, CTLA-4 or ICOS; (c) increases T-cell proliferation in an Mixed Lymphocyte Reaction (MLR) assay; (d) increases interferon-gamma production in an MLR assay; (e) increases IL-2 secretion in an MLR assay; 2 (f) binds to human PD-I and cynomolgus monkey PD-1; (g) inhibits the binding of PD-Li and/or PD-L2 to PD-1; (h) stimulates antigen-specific memory responses; (i) stimulates antibody responses; (j) inhibits tumor cell growth in vivo. Preferably the antibody is a human antibody, although in alternative embodiments the antibody can be, for example, a murine antibody, a chimeric antibody or humanized antibody. In more preferred embodiments, the antibody binds to human PD-i with a KD of 5 x 10~ M or less, binds to human PD-i with a KD of 1 x 10-8 M or less, binds to human PD-1 1o with a KD of 5 x 10~9 M or less, or binds to human PD-I with a KD of between 1 x10' 8 M and 1 x 10 0 M. In another embodiment, the invention provides an isolated monoclonal antibody, or antigen-binding portion thereof, wherein the antibody cross-competes for binding to PD-I with a reference antibody comprising: IS (a) a human heavy chain variable region comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7; and (b) a human light chain variable region comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14. In various embodiments, the reference antibody comprises: . (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 1; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 8; or the reference antibody comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: as 2; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 9; or the reference antibody comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 3; and 3 0 (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 10; or the reference antibody comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 4; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 35 11; or the reference antibody comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 5; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 12; or the reference antibody comprises: 3 (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 6; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 13; or the reference antibody comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 7; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 14. In another aspect, the invention pertains to an isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a heavy chain variable region that is the product of or derived from a human VH 3-33 gene, wherein the antibody specifically binds PD-1. The invention further provides an isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a heavy chain variable region that is the product of or derived from a human VH 4-39 gene, wherein the antibody specifically binds PD-1. The invention further provides an isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a light chain variable region that is the product of or derived from a human VK L6 gene, wherein the antibody specifically binds PD-1. The invention further provides an isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a light chain variable region that is the product of or derived from a human VK LI 5 gene, wherein the antibody specifically binds PD-1. In a preferred embodiment, the invention provides an isolated monoclonal antibody, or an. antigen-binding portion thereof, comprising: (a) a heavy chain variable region of a human VH 3-33 gene; and (b) a light chain variable region of a human VK L6 gene; fS wherein the antibody specifically binds to PD-1. In another preferred embodiment, the invention provides an isolated monoclonal antibody, or an antigen-binding portion thereof, comprising: (a) a heavy chain variable region of a human VH 4-39 gene; and (b) a light chain variable region of a human VK L15 gene; wherein the antibody specifically binds to PD-1. In another aspect, the invention provides an isolated monoclonal antibody, or antigen binding portion thereof, comprising: a heavy chain variable region that comprises CDR1, CDR2, and CDR3 sequences; and a light chain variable region that comprises CDR1, CDR2, and CDR3 sequences, wherein: (a) the heavy chain variable region CDR3 sequence comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35, and conservative modifications thereof; 4 (b) the light chain variable region CDR3 sequence comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56, and conservative modifications thereof,. and (c) the antibody specifically binds to human PD-1. S Preferably, the heavy chain variable region CDR2 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28, and conservative modifications thereof, and the light chain variable region CDR2 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, and conservative modifications to thereof Preferably, the heavy chain variable region CDR1 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, and conservative modifications thereof, and the light chain variable region CDR1 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, and conservative IS modifications thereof. In yet another aspect, the invention provides an isolated monoclonal antibody, or antigen-binding portion thereof, comprising a heavy chain variable region and a light chain variable region, wherein: (a) the heavy chain variable region comprises an amino acid sequence that is at least 20 80% homologous to an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7; (b) the light chain variable region comprises an amino acid sequence that is at least 80% homologous to an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14; 2s (c) the antibody binds to human PD-I with a KD of 1 x 10- 7 M or less; and (d) the antibody does not substantially bind to human CD28, CTLA-4 or ICOS. In a preferred embodiment, the antibodies additionally comprise at least one of the following properties: (a) the antibody increases T-cell proliferation in an MLR assay; 30) (b) the antibody increases interferon-gamma production in an MLR assay; or (c) the antibody increases IL-2 secretion in an MLR assay. Additionally or alternatively, the antibody may comprise one or more of the other features listed above. In preferred embodiments, the invention provides an isolated monoclonal antibody, or s antigen-binding portion thereof, comprising: (a) a heavy chain variable region CDR1 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21; (b) a heavy chain variable region CDR2 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28; 5 (c) a heavy chain variable region CDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 29,-30, 31, 32, 33, 34 and 35; (d) a light chain variable region CDR1 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42; 5 (e) a light chain variable region CDR2 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49; and (f) a light chain variable region CDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56; wherein the antibody specifically binds PD-1. (o A preferred combination comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 15; (b) a heavy chain variable region CDR2 comprising SEQ BD NO: 22; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 29; (d) a light chain variable region CDR1 comprising SEQ ID NO: 36; (e) a light chain variable region CDR2 comprising SEQ ID NO: 43; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 50. Another preferred combination comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 16; (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 23; 20 (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 30; (d) a light chain variable region CDR1 comprising SEQ ID NO: 37; (e) a light chain variable region CDR2 comprising SEQ ID NO: 44; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 51. Another preferred combination comprises: )3 (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 17; (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 24; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 31; (d) a light chain variable region CDR1 comprising SEQ ID NO: 38; (e) a light chain variable region CDR2 comprising SEQ ID NO: 45; and 30 (f) a light chain variable region CDR3 comprising SEQ ID NO: 52. Another preferred combination comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 18; (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 25; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 32; (d) a light chain variable region CDR1 comprising SEQ ID NO: 39; (e) a light chain variable region CDR2 comprising SEQ ID NO: 46; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 53. Another preferred combination comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 19; 6 (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 26; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 33; (d) a light chain variable region CDR1 comprising SEQ ID NO: 40; (e) a light chain variable region CDR2 comprising SEQ ID NO: 47; and 5 (f) a light chain variable region CDR3 comprising SEQ ID NO: 54. Another preferred combination comprise: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 20; (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 27; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 34; 10 (d) a light chain variable region CDR1 comprising SEQ ID NO: 41; (e) a light chain variable region CDR2 comprising SEQ ID NO: 48; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 55. Another preferred combination comprises: (a) a heavy chain variable region CDRI comprising SEQ ID NO: 21; S (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 28; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 35; (d) a light chain variable region CDR1 comprising SEQ ID NO: 42; (e) a light chain variable region CDR2 comprising SEQ ID NO: 49; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 56. Other preferred antibodies of the invention, or antigen-binding portions thereof; comprise: (a) a heavy chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4,'5, 6 and 7; and (b) a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14; 2$ wherein the antibody specifically binds PD-1. A preferred combination comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 1; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 8. 30 Another preferred combination comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 2; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 9. Another preferred combination comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 3; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 10. Another preferred combination comprises: 7 (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 4; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 11. £ Another preferred combination comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 5; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 12. ICo Another preferred combination comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 6; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 13. is Another preferred combination comprises: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 7; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 14. _X) The antibodies of the invention can be, for example, full-length antibodies, for example of an IgGI or IgG4 isotype. Alternatively, the antibodies can be antibody fragments, such as Fab or Fab'2 fragments, or single chain antibodies. The invention also provides an immunoconjugate comprising an antibody of the invention, or antigen-binding portion thereof, linked to a therapeutic agent, such as a cytotoxin QS or a radioactive isotope. The invention also provides a bispecific molecule comprising an antibody, or antigen-binding portion thereof, of the invention, linked to a second functional moiety having a different binding specificity than said antibody, or antigen-binding portion thereof. Compositions comprising an antibody, or antigen-binding portion thereof; or 30 immunoconjugate or bispecific molecule of the invention, and a pharmaceutically acceptable carrier, are also provided. Nucleic acid molecules encoding the antibodies, or antigen-binding portions thereof, of the invention are also encompassed by the invention, as well as expression vectors comprising such nucleic acids and host cells comprising such expression vectors. . Moreover, the invention 35 provides a transgenic mouse comprising human immunoglobulin heavy and light chain transgenes, wherein the mouse expresses an antibody of the invention, as well as hybridomas prepared from such a mouse, wherein the hybridoma produces the antibody of the invention. In yet another aspect, the invention provides a method of modulating an immune response in a subject comprising administering to the subject the antibody, or antigen-binding 8 portion thereof, of the invention such that the immune response in the subject is modulated. Preferably, the antibody of the invention enhances, stimulates or increases the immune response in the subject. In a further aspect, the invention provides a method of inhibiting growth of tumor cells S in a subject, comprising administering to a subject a therapeutically effective amount of an anti PD-i antibody, or antigen-binding portion thereof. The antibodies of the invention are preferred for use in the method although other anti-PD-1 antibodies can be used instead (or in combination with an anti-PD-1 antibody of the invention). For example, a chimeric, humanized or fully human anti-PD-1 antibody can be used in the method of inhibiting tumor o growth. In a further aspect, the invention provides a method of treating an infectious disease in a subject, comprising administering to a subject a therapeutically effective amount of an anti PD-1 antibody, or antigen-binding portion thereof The antibodies of the invention are preferred for use in the method although other anti-PD-1 antibodies can be used instead (or in s combination with an anti-PD-1 antibody of the invention). For example, a chimeric, humanized or fully human anti-PD-I antibody can be used in the method of treating an infectious disease. Still further, the invention provides a method of enhancing an immune response to an antigen in a subject, comprising administering to the subject: (i) the antigen; and (ii) an anti 20O PD-I antibody, or antigen-binding portion thereof; such that an immune response to the antigen in the subject is enhanced. The antigen can be, for example, a tumor antigen, a viral antigen, a bacterial antigen or an antigen from a pathogen. The antibodies of the invention are preferred for use in the method although other anti-PD-1 antibodies can be used instead (or in combination with an anti-PD-1 antibody of the invention). For example, a chimeric, as~ humanized or fully human anti-PD-1 antibody can be used in the method of enhancing an immune response to an antigen in a subject. The invention also provides methods for making "second generation" anti-PD-1 antibodies based on the sequences of the anti-PD-1 antibodies provided herein. For example, the invention provides a method for preparing an anti-PD-I antibody comprising: 30 (a) providing: (i) a heavy chain variable region antibody sequence comprising a CDR1 sequence that is selected from the.group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, and/or a CDR2 sequence that is selected from the group consisting of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28; and/or a CDR3 sequence that is selected from the group consisting of SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35; or (ii) a light chain variable region 36 antibody sequence comprising a CDRi sequence that is selected from the group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, and/or a CDR2 sequence that is selected from the group consisting of SEQ ED NOs: 43, 44, 45, 46, 47, 48 and 49, and/or a CDR3 sequence that is selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56; 9 (b) altering at least one amino acid residue within at least one variable region antibody sequence, said sequence being selected from the heavy chain variable region antibody sequence and the light chain variable region antibody sequence, to create at least one altered antibody sequence; and (c) expressing the altered antibody sequence as a protein. Other features and advantages of the instant invention will be apparent from the following detailed description and examples which should not be construed as limiting. The contents of all references, GenBank entries, patents and published patent applications cited throughout this application are expressly incorporated herein by reference. Brief Description of the Drawinge Figure 1A shows the nucleotide sequence (SEQ ID NO: 57) and amino acid sequence (SEQ ID NO: 1) of the heavy chain variable region of the 17D8 human monoclonal antibody. The CDRI (SEQ ID NO: 15), CDR2 (SEQ ID NO: 22) and CDR3 (SEQ ID NO: 29) regions are delineated and the V, D and J germline derivations are indicated. Figure 1B shows the nucleotide sequence (SEQ ID NO: 64) and amino acid sequence (SEQ ID NO: 8) of the light chain variable region of the 17D8 human monoclonal antibody. The CDRI (SEQ ID NO: 36), CDR2 (SEQ ID NO: 43) and CDR3 (SEQ ID NO: 50) regions are delineated and the V and J germline derivations are indicated. Figure 2A shows the nucleotide sequence (SEQ ID NO: 58) and amino acid sequence 2 O (SEQ ID NO: 2) of the heavy chain variable region of the 2D3 human monoclonal antibody. The CDR1 (SEQ ID NO: 16), CDR2 (SEQ ID NO: 23) and CDR3 (SEQ ID NO: 30) regions are delineated and the V and J germline derivations are indicated. Figure 2B shows the nucleotide sequence (SEQ ID NO: 65) and amino acid sequence (SEQ ID NO: 9) of the light chain variable region of the 2D3 human monoclonal antibody. 2S The CDR1 (SEQ ID NO: 37), CDR2 (SEQ ID NO: 44) and CDR3 (SEQ ID NO: 51) regions are delineated and the V and J germline derivations are indicated. Figure 3A shows the nucleotide sequence (SEQ ID NO: 59) and amino acid sequence (SEQ ID NO: 3) of the heavy chain variable region of the 4H1 human monoclonal antibody. The CDR1 (SEQ ID NO: 17), CDR2 (SEQ ID NO: 24) and CDR3 (SEQ ID NO: 31) regions 30 are delineated and the V and J germline derivations are indicated. Figure 3B shows the nucleotide sequence (SEQ ID NO: 66) and amino acid sequence (SEQ ID NO: 10) of the light chain variable region of the 4H1 human monoclonal antibody. The CDR1 (SEQ ID NO: 38), CDR2 (SEQ ID NO: 45) and CDR3 (SEQ ID NO: 52) regions are delineated and the V and J germline derivations are indicated. Figure 4A shows the nucleotide sequence (SEQ ID NO: 60) and amino acid sequence (SEQ ID NO: 4) of the heavy chain variable region of the 5C4 human monoclonal antibody. The CDR1 (SEQ ID NO: 18), CDR2 (SEQ ID NO: 25) and CDR3 (SEQ ID NO: 32) regions are delineated and the V and J germline derivations are indicated. 10 Figure 4B shows the nucleotide sequence (SEQ ID NO: 67) and amino acid sequence (SEQ ID NO: 11) of the light chain variable region of the 5C4 human monoclonal antibody. The CDRI (SEQ ID NO: 39), CDR2 (SEQ ID NO: 46) and CDR3 (SEQ ID NO: 53) regions are delineated and the V and J germline derivations are indicated. 5 Figure 5A shows the nucleotide sequence (SEQ ID NO: 61) and amino acid sequence (SEQ ID NO: 5) of the heavy chain variable region of the 4A1 1 human monoclonal antibody. The CDRI (SEQ ID NO: 19), CDR2 (SEQ ID NO: 26) and CDR3 (SEQ ID NO: 33) regions are delineated and the V and J germline derivations are indicated. Figure 5B shows the nucleotide sequence (SEQ ID NO: 68) and amino acid sequence 10 (SEQ ID NO: 12) of the light chain variable region of the 4A1 1 human monoclonal antibody. The CDR1 (SEQ ID NO: 40), CDR2 (SEQ ID NO: 47) and CDR3 (SEQ ID NO: 54) regions are delineated and the V and J germline derivations are indicated, . Figure 6A shows the nucleotide sequence (SEQ ID NO: 62) and amino acid sequence (SEQ ID NO: 6) of the heavy chain variable region of the 7D3 human monoclonal antibody. %5 The CDR1 (SEQ ID NO: 20), CDR2 (SEQ ID NO: 27) and CDR3 (SEQ ID NO: 34) regions are delineated and the V and J germline derivations are indicated. Figure 6B shows the nucleotide sequence (SEQ ID NO: 69) and amino acid sequence (SEQ ID NO: 13) of the light chain variable region of the 7D3 human monoclonal antibody. The CDR1 (SEQ ID NO: 41), CDR2 (SEQ ID NO: 48) and CDR3 (SEQ ID NO: 55) regions 20O are delineated and the V and J germline derivations are indicated. Figure 7A shows the nucleotide sequence (SEQ ID NO: 63) and amino acid sequence (SEQ ID NO: 7) of the heavy chain variable region-of the 5F4 human monoclonal antibody. The CDR1 (SEQ ID NO: 21), CDR2 (SEQ ID NO: 28) and CDR3 (SEQ ID NO: 35) regions are delineated and the V and J germline derivations are indicated. a5 Figure 7B shows the nucleotide sequence (SEQ ID NO: 70) and amino acid sequence (SEQ ID NO: 14) of the light chain variable region of the SF4 human monoclonal antibody. The CDRI (SEQ ID NO: 42), CDR2 (SEQ ID NO: 49) and CDR3 (SEQ ID NO: 56) regions are delineated and the V and J germline derivations are indicated. Figure 8 shows the alignment of the amino acid sequence of the heavy chain variable 30 region of 17D8, 2D3, 4H1, 5C4 and 7D3 with the human germline VH 3-33 amino acid sequence (SEQ ID NO: 71). Figure 9 shows the alignment of the amino acid sequence of the light chain variable region of 17D8, 2D3 and 7D3 with the human germline Vk L6 amino acid sequence (SEQ ID NO: 73). Figure 10 shows the alignment of the amino acid sequence of the light chain variable region of 4H1 and 5C4 with the human germline Vk L6 amino acid sequence (SEQ ID NO: 73). 11 Figure 11 shows the alignment of the amino acid sequence of the heavy chain variable region of 4A1 I and SF4 with the human germline VH 4-39 amino acid sequence (SEQ ID NO: 72). Figure 12 shows the alignment of the amino acid sequence of the light chain variable 5 region of 4A1 I and 5F4 with the human germline Vk L15 amino acid sequence (SEQ ID NO: 74). Figures 13 A-1 3B show the results of flow cytometry experiments demonstrating that the human monoclonal antibodies 5C4 and 4H1, directed against human PD-i, binds the cell surface of CHO cells transfected with full-length human PD-1. Figure 13A shows to the I 0 flow cytometry plot for 5C4. Figure 13B shows the .flow cytometry plot for 4H1. Thin line represents the binding to CHO cells and solid line represents the binding to CHO hPD-I cells. Figure 14 shows a graph demonstrating that the human monoclonal antibodies 17D8, 2D3, 4Hi, 5C4, and 4A1 1, directed against human PD-1, bind specifically to PD-1, and not to other members of the CD28 family. 5 Figures 15A- 15C show the results of flow cytometry experiments demonstrating that the human monoclonal antibodies 4H1 and 5C4, directed against human PD-1, binds to PD-i on the cell surface. Figure 15A shows binding to activated human T-cells. Figure 15B shows the binding to cynomolgous monkey T-cells. Figure 15C shows the binding to CHO transfected cells expressing PD-1. 20 Figures 16A-16C show the results of experiments demonstrating that human monoclonal antibodies against human PD-1 promote T-cell proliferation, IFN-gamma secretion and IL-2 secretion in a mixed lymphocyte reaction assay. Figure 16A is a bar graph showing concentration dependent T-cell proliferation; Figure 16B is a bar graph showing concentration dependent IFN-gamma secretion; Figure 16C is a bar graph showing 25 concentration dependent IL-2 secretion. Figures 17A-17B show the results of flow cytometry experiments demonstrating that human monoclonal antibodies against human PD-1 block the binding of PD-Li and PD-L2 to CHO transfected cells expressing PD-1. Figure 17A is a graph showing inhibition of binding of PD-Li; Figure 17B is a graph showing inhibition of binding of PD-L2. 30 Figure 18 shows the results of flow cytometry experiments demonstrating that human monoclonal antibodies against human PD-1 do not promote T-cell apoptosis. Figure 19 shows the results of experiments demonstrating that anti-PD-1 HuMabs have a concentration dependent effect on-IFN gamma secretion by PBMCs from CMV-positive donors when PBMCs were stimulated with a CMV lysate and anti-PD-1. Figure 20 shows the results of tumor growth experiments in a mouse model system demonstrating that treatment in vivo of mouse tumors with anti-PD-1 antibodies inhibits the growth of tumors. Figures 21A to 21D show the tumor volume over time in individual mice that were implanted with MC38 colon tumor cells (PD-L1~) and on the same day treated with one of the 12 following therapies: (A) mouse IgG (control), (B) anti-CTLA-4 antibody, (C) anti-PD-I antibody, and (D) anti-CTLA-4 antibody and anti-PD-I antibody. The mice received. subsequent antibody treatments on days 3, 6 and 10 as described in Example 13 and tumor volume was monitored over 60 days. 5 Figure 22 shows the mean tumor volume of the mice shown in Figure 21. Figure 23 shows the median tumor volume of the mice shown in Figure 21. Figures 24A to 24D show the tumor volume over time in individual mice that were implanted with MC38 colon tumor cells (PD-L 1) and one week later treated with one of the following therapies: (A) mouse IgG (control), (B) anti-CTLA-4 antibody, (C) anti-PD-I (0 antibody, and (D) anti-CTLA-4 antibody and anti-PD-i antibody. The tumor volume on the first day of treatment was about 315 mm 3 . The mice received subsequent antibody treatments on days 3, 6 and 10 as described in Example 14. Figure 25 shows the mean tumor volume of the mice shown in Figure 24. Figure 26 shows the median tumor volume of the mice shown in Figure 24. k5 Figure 27 shows the mean tumor volume over time in individual mice that were implanted with MC38 colon tumor cells (PD-L -) (day -7) and then treated on days 0, 3, 6 and 10 post-implantation (as described in Example 15) with one of the following therapies: (A) mouse IgG as a control (20 mg/kg, X 2 0 ) (B) anti-PD-1 antibody (10 mg/kg) and mouse IgG (10 mg/kg) (PioXio), (C) anti-CTLA-4 antibody (10 mg/kg) and mouse IgG (10 mg/kg) 20 (CioXio), (D) anti-CTLA-4 antibody and anti-PD-1 antibody (10 mg/kg each) (C 1 oPio), (E) anti-CTLA-4 antibody and anti-PD-1 antibody (3 mg/kg each) (C 3

P

3 ), and (F) anti-CTLA-4 antibody and anti-PD-1 antibody (1 mg/kg each) (C 1

P

1 ). Two groups of mice were treated with each antibody sequentially as follows: (G) anti-CTLA-4 antibody (10 mg/kg, day 0), anti-CTLA-4 antibody (10 mg/kg, day 3), anti-PD-1 antibody (10 mg/kg, day 6), and anti-PD 235 1 antibody (10 mg/kg, day 10) (CioCioPioPic); and (H) anti-PD-i antibody (10 mg/kg, day 0), anti-PD-I antibody (10 mg/kg, day 3), anti-CTLA-4 antibody (10 mg/kg, day 6), and anti-CTLA-4 antibody (10 mg/kg, day 10) (10 mg/kg, day 10) (PioPioCioCio). Figure 28 shows the mean tumor volume of the mice shown in Figure 27. Figure 29 shows the median tumor volume of the mice shown in Figure 27. 30 Figures 30A to 30F show the tumor volume over time in individual mice that were implanted with SA1/N fibrosarcoma cells (PD-LI) and one day later treated with one of the following therapies: (A) PBS (vehicle control), (B) mouse IgG (antibody control, 10 mg/kg), (C) anti-PD-1 antibody (10 mg/kg), (D) anti-CTLA-4 antibody (10 mg/kg), (E) anti-CTLA-4 antibody (0.2 mg/kg), and (F) anti-PD-i antibody (10 mg/kg) and anti-CTLA-4 antibody (0.2 9s mg/kg). The mice received subsequent antibody treatments on days 4, 7 and II as described in Example 16 and tumor volume was monitored over 41 days. Figure 31 shows the mean tumor volume of the mice shown-in Figure 29. Figure 32 shows the median tumor volume of the mice shown in Figure 29. 13 Figures 33A to. 33J show the tumor volume over time in individual mice that were implanted with SA1/N fibrosarcoma cells (PD-L1-) and then treated on days 7, 10, 13 and 17 post-implantation (as described in Example 17) with one of the following therapies: (A) PBS (vehicle control), (B) mouse IgG (antibody control, 10 mg/kg), (C) anti-CTLA-4 antibody 5 (0.25 mg/kg), (D) anti-CTLA-4 antibody (0.5 mg/kg), (E) anti-CTLA-4 antibody (5 mg/kg), (F) anti-PD-I antibody (3 mg/kg), (G) anti-PD-I antibody (10 mg/kg), (H) anti-PD-I antibody (10 mg/kg) and anti-CTLA-4 antibody (0.25 mg/kg), (I) anti-PD-1 antibody (10 mg/kg) and anti-CTLA-4 antibody (0.5 mg/kg), and (F) anti-PD-1 antibody (3 mg/kg) and anti-CTLA-4 antibody (0.5 mg/kg). The tumor volume on the first day of treatment was about 110 mm 3 . o0 Figure 34 shows the mean tumor volume of the mice shown in Figure 33. Figure 35 shows the median tumor volume of the mice shown in Figure 33. Figures 36A and 36B show the tumor volume over time in individual mice that were implanted with SA1/N fibrosarcoma cells (PD-L1i) and then treated on days 10, 13, 16 and 19 post-implantation (as described in Example 17) with one of the following therapies: (A) mouse ':5 IgG (antibody control, 10 mg/kg) or (B) anti-PD-1 antibody (10 mg/kg) and anti-CTLA-4 antibody (1 mg/kg). The tumor volume on the first day of treatment was about 250 mm 3 . Figure 37 shows the mean tumor volume of the mice shown in Figure 36. Figure 38 shows the median tumor volume of the mice shown in Figure 36. Figure 39 shows the mean and median percent tumor inhibition calculated from the 20 tumor volumes shown in Figures 33 and 36. Figures 40A to 40D show the tumor volume in BALB/c mice that were implanted subcutaneously with RENCA renal adenocarcinoma cells (PD-Li) (Murphy and Hrushesky (1973) J. Nat'l. Cancer Res. 50:1013-1025) (day -12) and then treated intraperitoneally on days 0, 3, 6 and 9 post-implantation with one of the following therapies: (A) mouse IgG .s (antibody control, 20 mg/kg), (B) anti-PD-1 antibody (10 mg/kg), (C) anti-CTLA-4 antibody (10 mg/kg), and (D) anti-PD-1 antibody (10 mg/kg) in combination with anti-CTLA-4 antibody (10 mg/kg). The tumor volume on the first day of treatment was about 115 mm 3 . Figure 41 shows binding of mouse PD-L2-Fc fusion protein to mouse PD-i (mPD-1) is blocked by anti-mPD-1 antibody 4H2 in a dose dependent manner. The binding is detected 30 by measuring fluorescence of FITC-labeled donkey-anti-rat IgG by ELISA. The greater the MFI (mean fluorescence intensity) the greater the binding. Figure 42 shows binding curves of anti-mPD-1 antibodies to immobilized iPD-1-Fc fusion protein by ELISA. Figure 43 shows the binding curve of rat anti-mPD-1.antibody 4H2.B3 to mPD-1 3s expressing CHO cells. ' Binding was detected with donkey-anti-rat IgG, FITC conjugated and measured by FACS (MFI). Figure 44 shows the binding curve of mPD-L1-hFc fusion protein to mPD-1 expressing CHO cells in the presence of increasing concentrations of anti-mPD-1 antibody - 14 4H2.B3. Binding was detected with goat-anti--human IgG, FITC conjugated and measured by FACS (MFI). Figure 45 shows the binding curves of rat anti-mPD-I antibody 4H2.B3 to mPD-1 expressing CHO cells as compared to chimeric rat:mouse anti-mPD-1 antibody 4H2. Figure 46 shows the binding curves of mPD-Li-hFc fusion protein to mPD-1 expressing CHO cells in the presence of increasing concentrations of either rat anti-mPD-1 antibody 4H2.B3 or chimeric rat:mouse anti-mPD-1 antibody 4H2. Figure 47 shows the mean tumor volume of tumor-free mice previously treated with anti-PD1 antibody and re-challenged with SA1/N fibrosarcoma cells (PD-Li-). Also shown (o is the mean tumor volume of naive mice (control, not previously challenged or treated) implanted with SA1/N fibrosarcoma cells. Figure 48 shows the tumor volume over time in individual mice, which survived tumor-free following implantation of MC38 colon tumor cells (PD-L1~) and treatment with anti-PD 1 antibody or a combination of anti-PD1 antibody with anti-CTLA-4 antibody), 15 re-challenged with lOx more MC38 colon tumor cells than the initial treatment. Also shown is the mean tumor volume of naive mice (control, not previously challenged or treated) implanted with MC38 colon tumor cells. Figure 49 shows the mean tumor volume of the mice shown in Figure 48. Figure 50 shows the mean tumor volume over time in individual mice that were 20 implanted with CT26 colon tumor cells. Figures 5 1A-B shows the results of experiments demonstrating that human monoclonal antibodies against human PD-1 promote T-cell proliferation and IFN-gamma secretion in cultures containing T regulatory cells. Figure 50A is a bar graph showing concentration dependent T-cell proliferation using HuMAb 5C4; Figure 50B is a bar graph showing 25 concentration dependent IFN-gamma secretion using HuMAb 5C4. Figures 52A-B shows the results of experiments demonstrating that human monoclonal antibodies against human PD-1 promote T-cell proliferation and IFN-gamma secretion in cultures containing activated T cells. Figure 51A is a bar graph showing concentration dependent T-cell proliferation using HuMAb 5C4; Figure 5iB is a bar graph showing 3o concentration dependent IFN-gamma secretion using HuMAb 5C4. Figure 53 shows the results of an antibody dependent cellular cytotoxicity (ADCC) assay demonstrating that human monoclonal anti-PD-I antibodies kill human activated T cells in an ADCC concentration-dependent manner in relation to the Fc region of the anti-PD-1 antibody. Figure 54 shows the results of a complement dependent cytotoxicity (CDC) assay demonstrating that human monoclonal anti-PD-1 antibodies do not kill human activated T cells in a CDC concentration-dependent manner. 15 Best Mode for Carrying Out the Invention In one aspect, the present invention relates to isolated monoclonal antibodies, particularly human monoclonal antibodies, that bind specifically to PD-1. In certain embodiments, the antibodies of the invention exhibit one or more desirable functional 5 properties, such as high affinity binding to PD-1, lack of cross-reactivity to other CD28 family members, the ability to stimulate T cell proliferation, IFN-y and/or IL-2 secretion in mixed lymphocyte reactions, the ability to inhibit binding of one or more PD-I ligands (e.g., PD-LI and/or PD-L2), the ability to cross-react with cynomolgus monkey PD-1, the ability to stimulate antigen-specific memory responses, the ability to stimulate antibody responses lo and/or the ability to inhibit growth of tumor cells in vivo. Additionally or alternatively, the antibodies of the invention are derived from particular heavy and light chain germline sequences and/or comprise particular structural features such as CDR regions comprising particular amino acid. sequences. In another aspect, the invention relates to the combined use of monoclonal antibodies that bind specifically to PD-I and monoclonal antibodies that bind I S specifically to CTLA-4. The invention provides, for example, isolated antibodies, methods of making such antibodies, immunoconjugates and bispecific molecules comprising such antibodies and pharmaceutical compositions containing the antibodies, immunconjugates or bispecific molecules of the invention. 20 In another aspect, the invention pertains to methods of inhibiting growth of tumor cells in a subject using anti-PD-1 antibodies. As demonstrated herein, anti-PD-1 antibodies are capable of inhibiting tumor cell growth in vivo. The invention also relates to methods of using the antibodies to modify an immune response, as well as to treat diseases such as cancer or infectious disease, or to stimulate a protective autoimmune response or to stimulate antigen .is specific immune responses (e.g., by coadministration of anti-PD-I with an antigen of interest). In order that the present invention may be more readily understood, certain terms are first defined. Additional definitions are set forth throughout the detailed description. The terms "Programmed Death 1," "Programmed Cell Death 1," "Protein PD-I," "PD 1," PD1," "PDCD1 ," "hPD-1" and "hPD-r' are used interchangeably, and include variants, 3c> isoforms, species homologs of human PD-1, and analogs having at least one common epitope with PD-1. The complete PD-i sequence can be found under GenBank Accession No. U64863. The terms "cytotoxic T lymphocyte-associated antigen-4," "CTLA-4," "CTLA4," "CTLA-4 antigen" and "CD152" (see, e.g., Murata, Am. J Pathol. (1999) 155:453-460) are 5 used interchangeably, and include variants, isoforms, species homologs of human CTLA-4, and analogs having at least one common epitope with CTLA-4 (see, e.g., Balzano (1992) Int. J Cancer Suppl. 2:28-32). The complete CTLA-4 nucleic acid sequence can be found under GenBank Accession No. Li5006. 16 The term "immune response" refers to the action of, for example, lymphocytes, antigen presenting cells, phagocytic cells, granulocytes, and soluble macromolecules produced by the above cells or the liver (including antibodies, cytokines, and complement) that results in selective damage to, destruction of, or elimination from the human body of invading 5 pathogens, cells or tissues infected with pathogens, cancerous cells, or, in cases of autoimmunity or pathological inflammation, normal human cells or tissues. A "signal transduction pathway" refers to the biochemical relationship between a variety of signal transduction molecules that play a role in the transmission of a signal from one portion of a cell to another portion of a cell. As used herein, the phrase "cell surface '0 receptor" includes, for example, molecules and complexes of molecules capable of receiving a signal and the transmission of such a signal across the plasma membrane of a cell. An example of a "cell surface receptor" of the present invention is the PD-i receptor. The term "antibody" as referred to herein includes whole antibodies and any antigen binding fragment (i.e., "antigen-binding portion") or single chains thereof. An "antibody" is refers to a glycoprotein comprising at least two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds, or an antigen-binding portion thereof. Each heavy chain is comprised of a heavy chain variable region (abbreviated herein as VH) and a heavy chain constant region. The heavy chain constant region is comprised of three domains, CHI, Cm and Cm. Each light chain is comprised of a light chain variable region (abbreviated herein as 20 VL) and a light chain constant region. The light chain constant region is comprised of one domain, CL. The VH and VL regions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDR), interspersed with regions that are more conserved, termed framework regions (FR). Each VH and VL is composed of three CDRs and four FRs, arranged from amino-terminus to carboxy-terminus in as the following order: FRI, CDR1, FR2, CDR2, FR3, CDR3, FR4. The variable regions of the heavy and light chains contain a binding domain that interacts with an antigen. The constant regions of the antibodies may mediate the binding of the immunoglobulin to host tissues or factors, including various cells of the immune system (e.g., effector cells) and the first component (Clq) of the classical complement system. 30 The term "antigen-binding portion" of an antibody (or simply "antibody portion"), as used herein, refers to one or more fragments of an antibody that retain the ability to specifically bind to an antigen (e.g., PD-1). It has been shown that the antigen-binding function of an antibody can be performed by fragments of a full-length antibody. Examples of binding fragments encompassed within the term "antigen-binding portion" of an antibody s5 include (i) a Fab fragment, -a monovalent fragment consisting of the VL, VH, CL and CHI domains; (ii) a F(ab') 2 fragment, a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region; (iii) a Fd fragment consisting of the VH and CHI domains; (iv) a Fv fragment consisting of the VL and VH domains of a single arm of an antibody, (v) a dAb fragment (Ward et aL, (1989) Nature 341:544-546), which consists of a 17 VH domain; and (vi) an isolated complementarity determining region (CDR). Furthermore, although the two domains of the Fv fragment, VL and VH, are coded for by separate genes, they can be joined, using recombinant methods, by a synthetic linker that enables them to be made as a single protein chain in which the VL and VH regions pair to form monovalent molecules (known as single chain Fv (scFv); see e.g., Bird et al. (1988) Science 242:423-426; and Huston et al. (1988) Proc. Nat/. Acad Sci. USA 5:5879-5883). Such single chain antibodies are also intended to be encompassed within the term "antigen-binding portion" of an antibody. These antibody fragments are obtained using conventional techniques known to those with skill in the art, and the fragments are screened for utility in the same manner as are oC intact antibodies. An "isolated antibody", as used herein, is intended to refer to an antibody that is substantially free of other antibodies having different antigenic specificities (e.g., an isolated antibody that specifically binds PD-I is substantially free of antibodies that specifically bind antigens other than PD-1). An isolated antibody that specifically binds PD-1 may, however, 15 have cross-reactivity to other antigens, such as PD-1 molecules from 9ther species. Moreover, an isolated antibody may be substantially free of other cellular material and/or chemicals. The terms "monoclonal antibody" or "monoclonal antibody composition" as used herein refer to a preparation of antibody molecules of single molecular composition. A 'aO monoclonal antibody composition displays a single binding specificity and affinity for a particular epitope. The term "human antibody", as used herein, is intended to include antibodies having variable regions in which both the framework and CDR regions are derived from human germline immunoglobulin sequences. Furthermore, if the antibody contains a constant region, 25 the constant region also is derived from human germline immunoglobulin sequences. The human antibodies of the invention may include amino acid residues not encoded by human germline immunoglobulin sequences (e.g., mutations introduced by random or site-specific mutagenesis in vitro or by somatic mutation in vivo). However, the term "human antibody", as used herein, is not intended to include antibodies in which CDR sequences derived from the W germline of another mammalian species, such as a mouse, have been grafted onto human framework sequences. The term "human monoclonal antibody" refers to antibodies displaying a single binding specificity which have variable regions in which both the framework and CDR regions are derived from human germline immunoglobulin sequences. In one embodiment, the 3,s human monoclonal antibodies are produced by a hybridoma which includes a B cell obtained from a transgenic nonhuman animal, e.g., a transgenic mouse, having a genome comprising a human heavy chain transgene and a light chain transgene fused to an immortalized cell. The term "recombinant human antibody", as used herein, includes all human antibodies that are prepared, expressed, created or isolated by recombinant means, such as (a) antibodies 18 isolated from an animal (e.g., a mouse) that is transgenic or transchromosomal for human immunoglobulin genes or a hybridoma prepared therefrom (described further below), (b) antibodies isolated from a host cell transformed to express the human antibody, e.g., from a transfectoma, (c) antibodies isolated from a recombinant, combinatorial human antibody 5 library, and (d) antibodies prepared, expressed, created or isolated by any other means that involve splicing of human immunoglobulin gene sequences to other DNA sequences. Such recombinant human antibodies have variable regions in which the framework and CDR regions are derived from human germline immunoglobulin sequences. In certain embodiments, however, such recombinant human antibodies can be subjected to in vitro 10 mutagenesis (or, when an animal transgenic for human Ig sequences is used, in vivo somatic mutagenesis) and thus the amino acid sequences of the VH and VL regions of the recombinant antibodies are sequences that, while derived from and related to human germline VH and VL. sequences, may not naturally exist within the human antibody germline repertoire in vivo. As used herein, "isotype" refers to the antibody class (e.g., IgM or IgGl) that is 1 S encoded by the heavy chain constant region genes. The phrases "an antibody recognizing an antigen" and "an antibody specific for an antigen" are used interchangeably herein with the term "an antibody which binds specifically to an antigen." The term "human antibody derivatives" refers to any modified form of the human 20 antibody, e.g., a conjugate of the antibody and another agent or antibody. The term "humanized antibody" is intended to refer to antibodies in which CDR sequences derived from the germline of another mammalian species, such as a mouse, have been grafted onto human framework sequences. Additional framework region modifications may be made within the human framework sequences. 2S The term "chimeric antibody" is intended to refer to antibodies in which the variable region sequences are derived from one species and the constant region sequences are derived from another species, such as an antibody in which the variable region sequences are derived from a mouse antibody and the constant region sequences are derived from a human antibody. As used herein, an antibody that "specifically binds to human PD-1" is intended to 30 refer to an antibody that binds to human PD-I with a KD of 1 x 107 M or less, more preferably 5 x 10-8 M or less, more preferably l x IO' M or less, more preferably 5 x 109 M or less. The term "Kassoc" or "K.", as used herein, is intended to refer to the association rate of a particular antibody-antigen interaction, whereas the term "Kdjj" or "K," as used herein, is intended to refer to the dissociation rate of a particular antibody-antigen interaction. The 35 term "KD", as used herein, is intended to refer to the dissociation constant, which is obtained from the ratio of K, to Ka (i.e,. KdKa) and is expressed as a molar concentration (M). KD values for antibodies can be determined using methods well established in the art. A preferred method for determining the KD of an antibody is by using surface plasmon resonance, preferably using a biosensor system such as a Biacore* system. 19 As used herein, the term "high affinity" for an IgG antibody refers to an antibody having a KD of 10~8 M or less, more preferably 10-9 M or less and even more preferably 1010 M or less for a target antigen. However, "high affinity" binding can vary for other antibody isotypes. For example, "high affinity" binding for an IgM isotype refers to an antibody S having a KD of 10 M or less, more preferably 10-8 M or less, even more preferably 10- M or less. The term "treatment" or "therapy" refers to administering an active agent with the purpose to cure, heal, alleviate, relieve, alter, remedy, ameliorate, improve, or affect a condition (e.g., a disease), the symptoms of the condition, or to prevent or delay the onset of io the symptoms, complications, biochemical indicia of a disease, or otherwise arrest or inhibit further development of the disease, condition, or disorder in a statistically significant manner. An "adverse event" (AE) as used herein is any unfavorable and generally unintended, even undesirable, sign (including an abnormal laboratory finding), symptom, or disease associated with the use of a medical treatment. For example, an adverse event may be iS associated with activation of the immune system or expansion of immune system cells (e.g., T cells) in response to a treatment. A medical treatment may have one or more associated AEs and each AE may have the same or different level of severity. Reference to methods capable of "altering adverse events" means a treatment regime that decreases the incidence and/or severity of one or more AEs associated with the use of a different treatment regime. 20 As used herein, "hyperproliferative disease" refers to conditions wherein cell growth is increased over normal levels. For example, hyperproliferative diseases or disorders include malignant diseases (e.g., esophageal cancer, colon cancer, biliary cancer) and non-malignant diseases (e.g., atherosclerosis, benign hyperplasia, benign prostatic hypertrophy). As used herein, "subtherapeutic dose" means a dose of a therapeutic compound (e.g., '25 an antibody) that is lower than the usual or typical dose of the therapeutic compound when administered alone for the treatment of a hyperproliferative disease (e.g., cancer). For example, a subtherapeutic dose of CTLA-4 antibody is a single dose of the antibody at less than about 3 mg/kg, i.e., the known dose of anti-CTLA-4 antibody. The use of the alternative (e.g., "or") should be understood to mean either one, both, or 30 any combination thereof of the alternatives. As used herein, the indefinite articles "a" or "an" should be understood to refer to "one or more" of any recited or enumerated component. As used herein, "about" or "comprising essentially of' mean within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the 5s measurement system. For example, "about" or "comprising essentially of' can mean within 1 or more than 1 standard deviation per the practice in the art. Alternatively, "about" or "comprising essentially of' can mean a range of up to 20%. Furthermore, particularly with respect to biological systems or processes, the terms can mean up to an order of magnitude or up to 5-fold of a value. When particular values are provided in the application and claims, 20 unless otherwise stated, the meaning of "about" or "comprising essentially of" should be assumed to be within an acceptable error range for that particular value. As described herein, any concentration range, percentage range, ratio range or integer range is to be understood to include the value of any integer within the recited range and, when s appropriate, fractions thereof (such as one tenth and one hundredth of an integer), unless otherwise indicated. As used herein, the term "subject" includes any human or nonhuman animal. The term "nonhuman animal" includes all vertebrates, e.g., mammals and non-mammals, such as nonhuman primates, sheep, dogs, cats, horses, cows chickens, amphibians, reptiles, etc. to Except when noted, the terms "patient" or-"subject" are used interchangeably. Various aspects of the invention are described in further detail in the following subsections. Anti-PD-1 Antibodies The antibodies of the invention are characterized by particular functional features or is properties of the antibodies. For example, the antibodies bind specifically to PD-1 (e.g., bind to human PD-I and may cross-react with PD-i from other species, such as cynomolgus monkey). Preferably, an antibody of the invention binds to PD-i with high affinity, for example with a KD of 1 x 10-7 M or less. The anti-PD-I antibodies of the invention preferably exhibit one or more of the following characteristics: (a) binds to human PD-1 with a KD of 1 x 10 7 M or less; (b) does not substantially bind to human CD28, CTLA-4 or ICOS; (c) increases T-cell proliferation in an Mixed Lymphocyte Reaction (MLR) assay; (d) increases interferon-gamma production in an MLR assay; (e) increases IL-2 secretion in an MLR assay; -(f) binds to human PD-1 and cynomolgus monkey PD-1; (g) inhibits the binding of PD-Li and/or PD-L2 to PD-1; (h) stimulates antigen-specific memory responses; (i) stimulates antibody responses; (j) inhibits tumor cell growth in vivo. 30 Preferably, the antibody binds to human PD-1 with a KD of 5 x 10~8 M or less, binds to human PD-I with a KD of 1 x 108 M or less, binds to human PD-I with a KD of 5 x 10~9 M or less, or binds to human PD-I with a KD of between 1 x 10- M and 1 x 10-10 M or less. An antibody of the invention may exhibit any combination of the above-listed features, such as two, three, four, five or more of the above-listed features. S Standard assays to evaluate the binding ability of the antibodies toward PD-1 are known in the art, including for example, ELISAs, Western blots and RIAs. The binding kinetics (e.g., binding affinity) of the antibodies also can be assessed by standard assays known in the art, such as by Biacore analysis. Suitable assays for evaluating any of the above-described characteristics are described in detail in the Examples. .21 Monoclonal Antibodies 17;D8, 2D3. 4H1. 5C4. 4AIl, 7D3 and 5F4 Preferred antibodies of the invention are the human monoclonal antibodies 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4isolated and structurally characterized as described in Examples 1 and 2. The VH amino acid sequences of 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 and 5F4 are S shown in SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7, respectively. The VL amino acid sequences of 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 are shown in SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14, respectively. Given that each of these antibodies can bind to PD-1, the VH and VL sequences can be "mixed and matched" to create other anti-PD-1 binding molecules of the invention. PD-i I C binding of such "mixed and matched" antibodies can be tested using the binding assays described above and in the Examples (e.g., ELISAs). Preferably, when VH and VL chains are mixed and matched, a VH sequence from a particular VHIVL pairing is replaced with a structurally similar VH sequence. Likewise, preferably a VL sequence from a particular VH/VL pairing is replaced with a structurally similar VL sequence. Accordingly, in one aspect, the invention provides an isolated monoclonal antibody, or antigen-binding portion thereof comprising: (a) a heavy chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7; and (b) a light chain variable region comprising an amino acid sequence selected from the 2c group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14; wherein the antibody specifically binds PD-1, preferably human PD-1. Preferred heavy and light chain combinations include: (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 1; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 8; '2. or (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 2; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 9; or (a) a heavy chain variable region comprising the amino acid sequence of SEQ IID NO: 30 3; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 10; or (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 4; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 11; or (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 5; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 12; or 22 (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 6; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 13; or (a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 5 7; and (b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 14. In another aspect, the invention provides antibodies that comprise the heavy chain and light chain CDR1s, CDR2s and CDR3s of 17D8, 2D3, 4111, 5C4, 4A1 1, 7D3 and 5F4, or combinations thereof. The amino acid sequences of the VH CDRis of 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 are shown in SEQ ID NOs: 15, 16, 17, 18, 19; 20 and 21, respectively. The amino acid sequences of the VH CDR2s of 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 are shown in SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28, respectively. The amino acid sequences of the VH CDR3s of 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 are shown in SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35, respectively. The amino acid sequences of the Vk CDR1s of 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 and 5F4 are shown in SEQ ID NOs: 36, 37, 38, 1 5 39, 40, 41 and 42, respectively. The amino acid sequences of the Vk CDR2s of 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 and 5F4 are shown in.SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, respectively. The amino acid sequences of the Vk CDR3s of 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 and 5F4 are shown in SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56, respectively. The CDR regions are delineated using the Kabat system (Kabat, E. A., et al. (1991) Sequences of :D Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242). Given that each of these antibodies can bind to PD-1 and that antigen-binding specificity is provided primarily by the CDR1, CDR2, and CDR3 regions, the VH CDR1, CDR2, and CDR3 sequences and Vk CDR1, CDR2, and CDR3 sequences can be "mixed and 25 matched" (i.e., CDRs from different antibodies can be mixed and match, although each antibody must contain a VH CDRI, CDR2, and CDR3 and a Vk CDR1, CDR2, and CDR3) to create other anti-PD-I binding molecules of the invention. PD-1 binding of such "mixed and matched" antibodies can be tested using the binding assays described above and in the Examples (e.g., ELISAs, Biacore analysis). Preferably, when VH CDR sequences are mixed 2o and matched, the CDR1, CDR2 and/or CDR3 sequence from a particular VH sequence is replaced with a structurally similar CDR sequence(s). Likewise, when Vk CDR sequences are mixed and matched, the CDR1, CDR2 and/or CDR3 sequence from a particular Vk sequence preferably is replaced with a structurally similar CDR sequence(s). It will be readily apparent to the ordinarily skilled artisan that novel VH and VL sequences can be created 35 by substituting one or more VH and/or VL CDR region sequences with structurally similar sequences from the CDR sequences disclosed herein for monoclonal antibodies antibodies 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 and SF4. Accordingly, in another aspect, the invention provides an isolated monoclonal antibody, or antigen-binding portion thereof comprising: 23 (a) a heavy chain variable region CDR1 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21; (b) a heavy chain variable region CDR2 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28; S (c) a heavy chain variable region CDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35; (d) a light chain variable region CDRI comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42; (e) a light chain variable region CDR2 comprising an amino acid sequence selected 10 from the group consisting of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49; and (f) a light chain variable region CDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56; wherein the antibody specifically binds PD-1, preferably human PD-1. In a preferred embodiment, the antibody comprises: ( s (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 15; (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 22; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 29; (d) a light chain variable region CDR1 comprising SEQ ID NO: 36; (e) a light chain variable region CDR2 comprising SEQ ID NO: 43; and o (f) a light chain variable region CDR3 comprising SEQ ID NO: 50. In another preferred embodiment, the antibody comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 16; (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 23; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 30; (d) a light chain variable region CDR1 comprising SEQ ID NO: 37; (e) a light chain variable region CDR2 comprising SEQ ID NO: 44; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 51. In another preferred embodiment, the antibody comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 17; 30 (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 24; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 31; (d) a light chain variable region CDRI comprising SEQ ID NO: 38; (e) a light chain variable region CDR2 comprising SEQ ID NO: 45; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 52. 35S In another preferred embodiment, the antibody comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 18; (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 25; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 32; (d) a light chain variable region CDR1 comprising SEQ ID NO: 39; 24 (e) a light chain variable region CDR2 comprising SEQ ID NO: 46; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 53. In another preferred embodiment, the antibody comprises: (a) a heavy chain variable region CDR1 comprising SEQ ID NO: 19; 5 (b) a heavy chain variable region CDR2 comprising SEQ ID NO: 26; (c) a heavy chain variable region CDR3 comprising SEQ ID NO: 33; (d) a light chain variable region CDRi comprising SEQ ID NO: 40; (e) a light chain variable region CDR2 comprising SEQ ID NO: 47; and (f) a light chain variable region CDR3 comprising SEQ ID NO: 54. \O Antibodies Having Particular Germline Sequences . In certain embodiments, an antibody of the invention comprises a heavy chain variable region from a particular germline heavy chain immunoglobulin gene and/or a light chain variable region from a particular germline light chain immunoglobulin gene. For example, in a preferred embodiment, the invention provides an isolated ':5 monoclonal antibody, or an antigen-binding portion thereof, comprising a heavy chain variable region that is the product of or derived from a human VH 3-33 gene, wherein the antibody specifically binds PD-1, preferably human PD-1. In another preferred embodiment, the invention provides an isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a heavy chain variable region that is the product of or derived from a human VH 4 'a-~ 39 gene, wherein the antibody specifically binds PD-1, preferably human PD-1. In yet another preferred embodiment, the invention provides an isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a light chain variable region that is the product of or derived from a human VK L6 gene, wherein the antibody specifically binds PD-1, preferably human PD-1. In yet another preferred embodiment, the invention provides an 215 isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a light chain variable region that is the product of or derived from a human VK L15 gene, wherein the antibody specifically binds PD-1, preferably human PD-1. In yet another preferred embodiment, the invention provides an isolated monoclonal antibody, or antigen-binding portion thereof, wherein the antibody: 30 (a) comprises a heavy chain variable region that is the product of or derived from a human VH 3-33 or 4-39 gene (which gene encodes the amino acid sequence set forth in SEQ ID NO: 71 or 73, respectively); (b) comprises a light chain variable region that is the product of or derived from a human VK L6 or L15 gene (which gene encodes the amino acid sequence set forth in SEQ ID NO: 72 or 74, respectively); and (c) specifically binds to PD-1. Examples of antibodies having VH and VK of VH 3-33 and VK L6, respectively, are 17D8, 2D3, 4H1, 5C4, and 7D3. Examples of antibodies having VH and VK of VH 4-39 and VK L15, respectively are 4AI 1 and 5F4. 25 As used herein, a human antibody comprises heavy or light chain variable regions that is "the product of' or "derived from" a particular germline sequence if the variable regions of the antibody are obtained from a system that uses human germline immunoglobulin genes. Such systems include immunizing a transgenic mouse carrying human immunoglobulin genes 5 with the antigen of interest or screening a human immunoglobulin gene library displayed on phage with the antigen of interest. A human antibody that is "the product of' or "derived from" a human germline immunoglobulin sequence can be identified as such by comparing the amino acid sequence of the human antibody to the amino acid sequences of human*germline immunoglobulins and selecting the human germline immunoglobulin sequence that is closest 10 in sequence (i.e., greatest % identity) to the sequence of the human antibody. A human antibody that is "the product of' or "derived from" a particular human germline immunoglobulin sequence may contain amino acid differences as compared to the germline sequence, due to, for example, naturally-occurring somatic mutations or intentional introduction of site-directed mutation. However, a selected human antibody typically is at 15 least 90% identical in amino acids sequence to an amino acid sequence encoded by a human germline immunoglobulin gene and contains amino acid residues that identify the human antibody as being human when compared to the germline immunoglobulin amino acid sequences of other species (e.g., murine germline sequences). In certain cases, a human antibody may be at least 95%, or even at least 96%, 97%, 98%, or 99% identical in amino acid 20 sequence to the amino acid sequence encoded by the germline immunoglobulin gene. Typically, a human antibody. derived from a particular human germline sequence will display no more than 10 amino acid differences from the amino acid sequence encoded by the human germline immunoglobulin gene. In certain cases, the human antibody may display no more than 5, or even no more than 4, 3, 2, or 1 amino acid difference from the amino acid sequence 25 encoded by the germline immunoglobulin gene. Homologous Antibodies In yet another embodiment, an antibody of the invention comprises heavy and light chain variable regions comprising amino acid sequences that are homologous to the amino acid sequences of the preferred antibodies described herein, and wherein the antibodies retain 30) the desired functional properties of the anti-PD-1 antibodies of the invention. For example, the invention provides an isolated monoclonal antibody, or antigen binding portion thereof; comprising -a heavy chain variable region and a light chain variable region, wherein: (a) the heavy chain variable region comprises an amino acid sequence that is at 35 least 80% homologous to an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7; (b) the light chain variable region comprises an amino acid sequence that is at least 80% homologous to an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14; and 26 the antibody exhibits one or more of the following properties: (c) the antibody binds to human PD-I with a KD of 1 x 10- M or less; (d) the antibody does not substantially bind to human CD28, CTLA-4 or ICOS; (e) the antibody increases T-cell proliferation in an MLR assay; 5 (f) . the antibody increases interferon-gamma production in an MLR assay; (g) the antibody increases 11-2 secretion in an MLR assay; (h) the antibody binds to human PD-i and cynomolgus monkey PD-1; (i) the antibody inhibits the binding of PD-Li and/or PD-L2 to PD-1; () the antibody stimulates antigen-specific memory responses; o (k) the antibody stimulates antibody responses; (1) the antibody inhibits tumor cell growth in vivo. In other embodiments, the VH and/or VL amino acid sequences may be 85%, 90%, 95%, 96%, 97%, 98% or 99% homologous to the sequences set forth above. An antibody having VH and VL regions having high (i.e., 80% or greater) homology to the VH and VL regions of 'a the sequences set forth above, can be obtained by mutagenesis (e.g., site-directed or PCR mediated mutagenesis) of nucleic acid molecules encoding SEQ ID NOs: 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69 and 70, followed by testing of the encoded altered antibody for retained function (i.e., the functions set forth in (c) through (1) above) using the functional assays described herein, As used herein, the percent homology between two amino acid sequences is equivalent to the percent identity between the two sequences. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % homology = # of identical positions/total # of positions x 100), taking into account the number of gaps, and the length of each gap, which need to be introduced for optimal alignment of the two sequences. The comparison of sequences and determination of percent identity between two sequences can be accomplished using a mathematical algorithm, as described in the non limiting examples below. The percent identity between two amino acid sequences can be determined using the algorithm of E. Meyers and W. Miller (Comput. AppL. Biosci., 4:11-17 (1988)) which has been M incorporated into the ALIGN program (version 2.0), using a PAM120 weight residue table, a gap length penalty of 12 and a gap penalty of 4. In addition, the percent identity between two amino acid sequences can be determined using the Needleman and Wunsch (J. Mol. Biol. 48:444-453 (1970)) algorithm which has been incorporated into the GAP program in the GCG software package (available at www.gcg.com), using either a Blossum 62 matrix or a PAM250 matrix, and a gap weight of 16, 14, 12, 10, 8, 6, or 4 and a length weight of 1, 2, 3, 4, 5, or 6. Additionally or alternatively, the protein sequences of the present invention can further be used as a "query sequence" to perform a search against public databases to, for example, identify related sequences. Such searches can be performed using the XBLAST program (version 2.0) of Altschul, et al. (1990) J Mol. Biol. 215:403-10. BLAST protein searches 27 can be performed with the XBLAST program, score = 50, wordlength = 3 to obtain amino acid sequences homologous to the antibody molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., (1997) Nucleic Acids Res. 25(17):3389-3402. When utilizing BLAST and Gapped S BLAST programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. (See www.ncbi.nlm.nih.gov). Antibodies with Conservative Modifications In certain embodiments, an antibody of the invention comprises a heavy chain variable region comprising CDRI, CDR2 and CDR3 sequences and a light chain variable region to comprising CDR1, CDR2 and CDR3 sequences, wherein one or more of these CDR sequences comprise specified amino acid sequences based on the preferred antibodies described herein (e.g., 17D8, 2D3, 4H11, 5C4, 4A1 1, 7D3 or 5F4), or conservative modifications thereof, and wherein the antibodies retain the desired functional properties of the anti-PD-I antibodies of the invention. Accordingly, the invention provides an isolated monoclonal antibody, or 5 antigen-binding portion thereof, comprising a heavy chain variable region comprising CDRI, CDR2, and CDR3 sequences and a light chain variable region comprising CDR1, CDR2, and CDR3 sequences, wherein: (a) the heavy chain variable region CDR3 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 29, 30, 20 31, 32, 33, 34 and 35, and conservative modifications thereof; (b) the light chain variable region CDR3 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequence of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56, and conservative modifications thereof; and the antibody exhibits one or more of the following properties: (c) the antibody binds to human PD-I with a KD of 1 x 10- M or less; (d) the antibody does not substantially bind to human CD28, CTLA-4 or ICOS; (e) the antibody increases T-cell proliferation in an MLR assay; (f) the antibody increases interferon-gamma production in an MLR assay; (g) the antibody increases 11-2 secretion in an MLR assay; (h) the antibody binds to human PD-i and cynomolgus monkey PD-1; (i) the antibody inhibits the binding of PD-Li and/or PD-L2 to PD-1; (j) the antibody stimulates antigen-specific memory responses; (k) the antibody stimulates antibody responses; (1) the antibody inhibits tumor cell growth in vivo. ,.5 -In a preferred embodiment, the heavy chain variable region CDR2 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28, and conservative modifications thereof; and the light chain variable region CDR2 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, and 28 conservative modifications thereof. In another preferred embodiment, the heavy chain variable region CDRI sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, and conservative modifications thereof; and the light chain variable region CDRI sequence 5' comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, and conservative modifications thereof As used herein, the term "conservative sequence modifications" is intended to refer to amino acid modifications that do not significantly affect or alter the binding characteristics of the antibody containing the amino acid sequence. Such conservative modifications include 03 amino acid substitutions, additions and deletions. Modifications can be introduced into an antibody of the invention by standard techniques known in the art, such as site-directed mutagenesis and PCR-mediated mutagenesis. Conservative amino acid substitutions are ones in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the is art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, seine, threonine, tyrosine, cysteine, tryptophan), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side ) chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). Thus, one or more amino acid residues within the CDR regions of an antibody of the invention can be replaced with other amino acid residues from the same side chain family and the altered antibody can be tested for retained function (i.e., the functions set forth in (c) through (1) above) using the functional assays described herein. 15 Antibodies that Bind to the Same Epitope as Anti-PD-I Antibodies of the Invention In another embodiment, the invention provides antibodies that bind to the same epitope on human PD-I as any of the PD-I monoclonal antibodies of the invention (i.e., antibodies that have the ability to cross-compete for binding to PD-I with any of the monoclonal antibodies of the invention). In preferred embodiments, the reference antibody for cross 0 competition studies can be the monoclonal antibody 17D8 (having VH and VL sequences as shown in SEQ ID NOs: 1 and 8, respectively), or the monoclonal antibody 2D3 (having VH. and VL sequences as shown in SEQ ID NOs: 2 and 9, respectively), or the monoclonal antibody 4H1 (having VH and VL sequences as shown in SEQ ID NOs: 3 and 10, respectively), or the monoclonal antibody 5C4 (having VH and VL sequences as shown in SEQ ID NOs: 4 s and 11, respectively), or the monoclonal antibody 4A1 1 (having VH and VL sequences as shown in SEQ ID NOs: 5 and 12, or the monoclonal antibody 7D3 (having VH and VL sequences as shown in SEQ ID NOs: 6 and 13, or the monoclonal antibody 5F4 (having VH and VL sequences as shown in SEQ ID NOs: 7 and 14, respectively). Such cross-competing antibodies can be identified based on their ability to cross-compete with 17D8, 2D3, 4H1, 5C4, 29 4A1 1, 7D3 or 5F4 in standard PD-I binding assays. For example, BlAcore analysis, ELISA assays or flow cytometry may be used to demonstrate cross-competition with the antibodies of the current invention. The ability of a test antibody to inhibit the binding of, for example, 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 or 5F4, to human PD-I demonstrates that the test antibody 5 can compete with 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 or 5F4 for binding to human PD-I and thus binds to the same epitope on human PD-1 as 17D8, 2D3, 4H1, 5C4, or 4A11. In a preferred embodiment, the antibody that binds to the same epitope on human PD-I as 17D8, 2D3, 4H1, 5C4, 4A11, 713 or 5F4 is a human monoclonal antibody. Such human monoclonal antibodies can be prepared and isolated as described in the Examples. \O Engineered and Modified Antibodies An antibody of the invention further can be prepared using an antibody having one or more of the VH and/or VL sequences disclosed herein as starting material to engineer a modified antibody, which modified antibody may have altered properties from the starting antibody. An antibody can be engineered by modifying one or more residues within one or '5 both variable regions (i.e., VH and/or VL), for example within one or more CDR regions and/or within one or more framework regions. Additionally or alternatively, an antibody can be engineered by modifying residues within the constant region(s), for example to alter the effector function(s) of the antibody. One type of variable region engineering that can be performed is CDR grafting. 20 Antibodies interact with target antigens predominantly through amino acid residues that are located in the six heavy and light chain complementarity determining regions (CDRs). For this reason, the amino acid sequences within CDRs are more diverse between individual antibodies than sequences outside of CDRs. Because CDR sequences are responsible for most antibody-antigen interactions, it is possible to express recombinant antibodies that mimic 25 the properties of specific naturally occurring antibodies by constructing expression vectors that include CDR sequences from the specific naturally occurring antibody grafted onto framework sequences from a different antibody with different properties (see, e.g., Riechmann, L. et al. (1998) Nature 332:323-327; Jones, P. et al. (1986) Nature 321:522-525; Queen, C. et al. (1989) Proc. Natl. Acad See. USA. 86:10029-10033; U.S. Patent No. 5,225,539 to Winter, 30 and U.S. Patent Nos. 5,530,101; 5,585,089; 5,693,762 and 6,180,370 to Queen etal.) Accordingly, another embodiment of the invention pertains to an isolated monoclonal antibody, or antigen-binding portion thereof, comprising a heavy chain variable region comprising CDR1, CDR2, and CDR3 sequences comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, SEQ ID NOs: 22, 23, 3S 24, 25, 26, 27 and 28, and SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35, respectively, and a light chain variable region comprising CDR1, CDR2, and CDR3 sequences comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, and SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56, respectively. Thus, such antibodies contain the VH and VL CDR sequences of 30 monoclonal antibodies 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 or 5F4 yet may contain different framework sequences from these antibodies. Such framework sequences can be obtained from public DNA databases or published references that include germline antibody gene sequences. For example, germline DNA 5 sequences for human heavy and light chain variable region genes can be found in the "VBase" human germline sequence database (available on the Internet at www.mrc cpe.cam.ac.uk/vbase), as well as in Kabat, E. A., et al. (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242; Tomlinson, I. M., et al. (1992) "The Repertoire of Human Germline 10 VH Sequences Reveals about Fifty Groups of VH Segments with Different Hypervariable Loops" J. Mo. Biol._227:776-798; and Cox, J. P. L et al. (1994) "A Directory of Human Germ-line VH Segments Reveals a Strong Bias in their Usage" Eur. J. Immunol. 24:827-836; the contents of each of which are expressly incorporated herein by reference. As another example, the germline DNA sequences for human heavy and light chain variable region genes 5 can be found in the GenBank database. For example, the following heavy chain germline sequences found in the HCo7 HuMAb mouse are available in the accompanying GenBank accession numbers: 1-69 (NG_0010109, NT_024637 and BC070333), 3-33 (NG_0010109 and NT_024637) and 3-7 (NG_0010109 and NT_024637). As another example, the following heavy chain germline sequences found in the HCol2 HuMAb mouse are available '- in the accompanying GenBank accession numbers: 1-69 (NG_0010109, NT_024637 and BC070333), 5-51 (NG_0010109 and NT_024637), 4-34 (NG_0010109 and NT_024637), 3 30.3 (AJ556644) and 3-23 (AJ406678). Preferred framework sequences for use in the antibodies of the invention are those that are structurally similar to the framework sequences used by selected antibodies of the 23 invention, e.g., similar to the VH 3-33 framework sequences (SEQ ID NO: 71) and/or the VH 4-39 framework sequences (SEQ ID NO: 73) and/or the VK L6 framework sequences (SEQ ID NO: 72) and/or the VK L15 framework sequences (SEQ ID NO: 74) used by preferred monoclonal antibodies of the invention. The VH CDR1, CDR2, and CDR3 sequences, and the VK CDR1, CDR2, and CDR3 sequences, can be grafted onto framework regions that have the identical sequence as that found in the germline immunoglobulin gene from which the framework sequence derive, or the CDR sequences can be grafted onto framework regions that contain one or more mutations as compared to the germline sequences. For example, it has been found that in certain instances it is beneficial to mutate residues within the framework regions to maintain or enhance the antigen binding ability of the antibody (see e.g., U.S. Patent AS Nos. 5,530,101; 5,585,089; 5,693,762 and 6,180,370 to Queen et al). Another type of variable region modification is to mutate amino acid residues within the VH and/or VK CDRI, CDR2 and/or CDR3 regions to thereby improve one or more binding properties (e.g., affinity) of the antibody of interest. Site-directed mutagenesis or PCR mediated mutagenesis can be performed to introduce tlie mutation(s) and the effect'on .31 antibody binding, or other functional property of interest, can be evaluated in in vitro or in vivo assays as described herein and provided in the Examples. Preferably conservative modifications (as discussed above) are introduced. The mutations may be amino acid substitutions, additions or deletions, but are preferably substitutions. Moreover, typically no S more than one, two, three, four or five residues within a CDR region are altered. Accordingly, in another embodiment, the invention provides isolated anti-PD-I monoclonal antibodies, or antigen-binding portions thereof; comprising a heavy chain variable region comprising: (a) a VH CDR1 region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, or an amino acid sequence io having one, two, three, four or five amino acid substitutions, deletions or additions as compared to SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21; (b) a VH CDR2 region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28, or an amino acid sequence having one, two, three, four or five amino acid substitutions, deletions or additions as compared to SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28; (c) a VH IS CDR3 region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35, or an amino acid sequence having one, two, three, four or five amino acid substitutions, deletions or additions as compared to SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35; (d) a VK CDR1 region comprising an amino acid sequence selected from the-group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, or an amino acid 2o sequence having one, two, three, four or five amino acid substitutions, deletions or additions as compared to SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42; (e) a VK CDR2 region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, or an amino acid sequence having one, two, three, four or five amino acid substitutions, deletions or additions as compared to SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 25 49; and (f) a VK CDR3 region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56, or an amino acid sequence having one, two, three, four or five amino acid substitutions, deletions or additions as compared to SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56. Engineered antibodies of the invention include those in which modifications have been 3 made to framework residues within VH and/or Vv, e.g. to improve the properties of the antibody. Typically such framework modifications are made to decrease the immunogenicity of the antibody. For example, one approach is to "backmutate" one or more framework residues to the corresponding germline sequence. More specifically, an antibody that has undergone somatic mutation may contain framework residues that differ from the germline 3S sequence from which the antibody is derived. *Such residues can be identified by comparing the antibody framework sequences to the germline sequences from which the antibody is derived. For example, Table 1 below shows a number of amino acid changes in the framework regions of the anti-PD-1 antibodies 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 that differ from 32 the heavy chain parent germline sequence. To return one or more of the amino acid residues in the framework region sequences to their germline configuration, the somatic mutations can be "backmutated" to the germline sequence by, for example, site-directed mutagenesis or PCR-mediated mutagenesis. 5 Amino acid changes may occur in the framework regions of anti-PD-1 antibodies that differ from the light chain parent germline sequence. For example, for 17D8, amino acid residue #47 (within FR2) of VK is an isoleucine whereas this residue in the corresponding VK L6 germline sequence is a leucine. To return the framework region sequences to their germline configuration, the somatic mutations can be "backmutated" to the germline sequence ~o by, for example, site-directed mutagenesis or PCR-mediated mutagenesis (e.g., residue #47 (residue #13 of FR2) of the VK of 17D8 can be "backmutated" from isoleucine to leucine). As another example, for 4A1 1, amino acid residue #20 (within FR1) of VK is a serine whereas this residue in the corresponding VK L15 germline sequence is a threonine. To return the framework region sequences to their germline configuration, for example, residue is #20 of the VK of 4A1 1 can be "backmutated" from serine to threonine. Such "backmutated" antibodies are also intended to be encompassed by the invention. The alignment of VH regions for 17D8, 2D3, 4H1, 5C4 and 7D3, against the parent germline VH 3-33 sequence is shown in Figure 8. The alignment of VH regions for 4A11 and 5F4 against the parent germline VH 4-39 sequence is shown in Figure 11. 33 Table 1. Modifications to antibodies 17D8, 2D3, 4H1, 5C4, 4Al 1, 7D3 and 5F4 from the heavy chain germline configuration. Anti-PD-i Amino acid Amino acid of Original amino acid of Ab position antibody germline configuration 17D8 10 D G 16 G R 27 V F 28 A T 78 M T 93 M V 2D3 10 D G 27 L F 30 T S 85 N S 98 T R 4H1 3 Y Q 84 T N 88 V A 98 S R 5C4 21 D S 23 K A 27 I F 80. F Y 98 T R 4A11 29 L I 79 Q H 98 V A 7D3 23 T A 24 T A 27 I F 70 L I .74 D N 97 V' A 98 T R 5F4 23 S T 29 L I 51 A G 77 R K Another type of framework modification involves mutating one or more residues within the framework region, or even within one or more CDR regions, to remove T cell 5 epitopes to thereby reduce the potential immunogenicity of the antibody. This approach is also referred to as "deimmunization" and is described in further detail in U.S. Patent Publication No. 20030153043 by Carr et al. In addition or alternative to modifications made within the framework or CDR regions, antibodies of the invention may be engineered to include modifications within the Fc region, 0. typically to alter one or more functional properties of the antibody, such as serum half-life, 34 complement fixation, Fc receptor binding, and/or antigen-dependent cellular cytotoxicity. Furthermore, an antibody of the invention may be chemically modified (e.g., one or more chemical moieties can be attached to the antibody) or be modified to alter its glycosylation, again to alter one or more functional properties of the antibody. * Each of these embodiments s is described in further detail below. The numbering of residues in the Fc region is that of the EU index of Kabat. In one embodiment, the hinge region of CHI is modified such that the number of cysteine residues in the hinge region is altered, e.g., increased or decreased. This approach is described further in U.S. Patent No. 5,677,425 by Bodmer et al. The number of cysteine o residues in the hinge region of CH1 is altered to, for example, facilitate assembly of the light and heavy chains or to increase or decrease the stability of the antibody. In another embodiment, the Fc hinge region of an antibody is mutated to decrease the biological half life of the antibody. More specifically, one or more amino acid mutations are introduced into the CH2-CH3 domain interface region of the Fc-hinge fragment such that the i s antibody has impaired Staphylococcyl protein A (SpA) binding relative to native Fc-hinge domain SpA binding. This approach is described in further detail in U.S. Patent No. 6,165,745 by Ward et al. In another embodiment, the antibody is modified to increase its biological half life. Various approaches are possible. For example, one or more of the following mutations can 20 be introduced: T252L, T254S, T256F, as described in U.S. Patent No. 6,277,375 to Ward. Alternatively, to increase the biological half life, the antibody can be altered within the CHI or CL region to contain a salvage receptor binding epitope taken from two loops of a CH2 domain of an Fc region of an IgG, as described in U.S. Patent Nos. 5,869,046 and 6,121,022 by Presta et al. 's In yet other embodiments, the Fc region is altered by replacing at least one amino acid residue with a different amino acid residue to alter the effector function(s) of the antibody. For example, one or more amino acids selected from amino acid residues 234, 235, 236, 237, 297, 318, 320 and 322 can be replaced with a different amino acid residue such that the antibody has an altered affinity for an effector ligand but retains the antigen-binding ability of W the parent antibody. The effector ligand to which affinity is altered can be, for example, an Fc receptor or the Cl component of complement. This approach is described in further detail in U.S. Patent Nos. 5,624,821 and 5,648,260, both by Winter et al. In another example, one or more amino acids selected from amino acid residues 329, 331 and 322 can be replaced with a different amino acid residue such that the antibody has S altered CIq binding and/or reduced or abolished complement dependent cytotoxicity (CDC). This approach is described in further detail in U.S. Patent Nos. 6,194,551 by Idusogie et al. In another example, one or more amino acid residues within amino acid positions 231 and 239 are altered to thereby alter the ability of the antibody to fix complement. This approach is described further in PCT Publication WO 94/29351 by Bodmer et al. 35 In yet another example, the Fc region is modified to increase the ability of the antibody to mediate antibody dependent cellular cytotoxicity (ADCC) and/or to increase the affinity of the antibody for an Fcy receptor by modifying one or more amino acids at the following positions: 238, 239, 248, 249, 252, 254, 255, 256, 258, 265, 267, 268, 269, 270, 272, 276, 5 278, 280, 283, 285, 286, 289, 290, 292, 293, 294, 295, 296, 298, 301, 303, 305, 307, 309, 312, 315, 320, 322, 324, 326, 327, 329, 330, 331, 333, 334, 335, 337, 338, 340, 360, 373, 376, 378, 382, 388, 389, 398, 414, 416, 419, 430, 434, 435, 437, 438 or 439. This approach is described further in PCT Publication WO 00/42072 by Presta. Moreover, the binding sites on human IgGl for FcyR1, FoyRI, FcyRiI and FcRn have been mapped and variants with io improve binding have been described (see Shields, R.L. et al. (2001) J. Biol Chem. 276:6591-6604). Specific mutations at positions 256, 290, 298, 333, 334 and 339 were shown to improve binding to FcyRIII. Additionally, the following combination mutants were shown to improve FpyRII binding: T256A/S298A, S298A/E333A, S298A/K224A and S298A/E333A/K334A. 1s In still another embodiment, the glycosylation of an antibody is modified. For example, an aglycoslated antibody can be made (i.e., the antibody lacks glycosylation). Glycosylation can be altered to, for example, increase the affinity of the antibody for antigen. Such carbohydrate modifications can be accomplished by, for example, altering one or more sites of glycosylation within the antibody sequence. For example, one or more amino acid '2C substitutions can be made that result in elimination of one or more variable region framework glycosylation sites to thereby eliminate glycosylation at that site. Such aglycosylation may increase the affinity of the antibody for antigen. Such an approach is described in further detail in U.S. Patent Nos. 5,714,350 and 6,350,861 by Co et al. Additionally or alternatively, an antibody can be made that has an altered type of L S glycosylation, such as a hypofucosylated antibody having reduced amounts of fucosyl residues or an antibody having increased bisecting GlcNac structures. Such altered glycosylation patterns have been demonstrated to increase the ADCC ability of antibodies. Such carbohydrate modifications can be accomplished by, for example, expressing the antibody in a host cell with altered glycosylation machinery. Cells with altered glycosylation machinery 30 have been described in the art and can be used as host cells in which to express recombinant antibodies of the invention to thereby produce an antibody with altered glycosylation. For example, the cell lines Ms704, Ms705, and Ms709 lack the fucosyltransferase gene, FUT8 (alpha (1,6) fucosyltransferase), such that antibodies expressed in the Ms704, Ms705, and Ms709 cell lines lack fucose on their carbohydrates. The Ms704, Ms705, and Ms709 FUT8' 'SS cell lines were created by the targeted disruption of the FUT8 gene in CHO/DG44 cells using two replacement vectors (see U.S. Patent Publication No. 20040110704 by Yamane et al. and Yamane-Ohnuki et a. (2004)BiotechnolBioeng 2:614-22). As another example, EP 1,176,195 by Hanai et al. describes a cell line with a functionally disrupted FUT8 gene, which encodes a fucosyl transferase, such that antibodies expressed in such a cell line exhibit 36 hypofucosylation by reducing or eliminating the alpha 1,6 bond-related enzyme. Hanai et al. also describe cell lines which have a low enzyme activity for adding fucose to the N acetylglucosamine that binds to the Fc region of the antibody or does not have the enzyme activity, for example the rat myeloma cell line YB2/0 (ATCC CRL 1662). PCT Publication 5 WO 03/035835 by Presta describes a variant CHO cell line, Lecl3 cells, with reduced ability to attach fucose to Asn(297)-linked carbohydrates, also resulting in hypofucosylation of antibodies expressed in that host cell (see also Shields, R.L. et al. (2002) J. Biol. Chem. 277:26733-26740). PCT Publication WO 99/54342 by Umana et al. describes cell lines engineered to express glycoprotein-modifying glycosyl transferases (e.g., beta(1,4)-N I acetylglucosaminyltransferase III (GnTIII)) such that antibodies expressed in the engineered cell lines exhibit increased bisecting GlcNac structures which results in increased ADCC activity of the antibodies (see also Umana et al. (1999) Nat. Biotech. 17:176-180). Alternatively, the fucose residues of the antibody may be cleaved off using a fucosidase enzyme. For example, the flcosidase alpha-L-fucosidase removes fucosyl residues from (S antibodies (Tarentino, A.L. et al. (1975) Biochem. 14:5516-23). Another modification of the antibodies herein that is contemplated by the invention is pegylation. An antibody can be pegylated to, for example, increase the biological (e.g., serum) half life of the antibody. To pegylate an antibody, the antibody, or fragment thereof, typically is reacted with polyethylene glycol (PEG), such as a reactive ester or aldehyde 20 derivative of PEG, under conditions in which one or more PEG groups become attached to the antibody or antibody fragment. Preferably, the pegylation is carried out via an acylation reaction or an alkylation reaction with a reactive PEG molecule (or an analogous reactive water-soluble polymer). As used herein, the term "polyethylene glycol" is intended to encompass any of the forms of PEG that have been used to derivatize other proteins, such as 23 mono (C1-C1O) alkoxy- or aryloxy-polyethylene glycol or polyethylene glycol-maleimide. In certain embodiments, the antibody to be pegylated is an aglycosylated antibody. Methods for pegylating proteins are known in the art and can be applied to the antibodies of the invention. See for example, EP 0 154 316 by Nishimura et al. and EP 0 401 384 by Ishikawa et al. 30 Methods of Engineering Antibodies As discussed above, the anti-PD-1 antibodies having VH and VK sequences disclosed herein can be used to create new anti-PD-1 antibodies by modifying the VH and/or VK sequences, or the constant region(s) attached thereto. Thus, in another aspect of the invention, the structural features of an anti-PD-1 antibody of the invention, e.g. 17D8, 2D3, 4H1, 5C4, 35S 4Al 1, 7D3 or 5F4, are used to create structurally related anti-PD-1 antibodies that retain at least one functional property of the antibodies of the invention, such as binding to human PD 1. For example, one or more CDR regions of 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 or 5F4, or mutations thereof, can be combined recombinantly with known framework regions and/or other CDRs to create additional, recombinantly-engineered, anti-PD-1 antibodies of the 37 invention, as discussed above. Other types of modifications include those described in the previous section. The starting material for the engineering method is one or more of the VH and/or VK sequences provided herein, or one or more CDR regions thereof. To create the engineered antibody, it is not necessary to actually prepare (i.e., express as a protein) an 5 antibody having one or more of the VH and/or VK sequences provided herein, or one or more CDR regions thereof. Rather, the information contained in the sequence(s) is used as the starting material to create a "second generation" sequence(s) derived from the original sequence(s) and then the "second generation" sequence(s) is prepared and expressed as a protein. to Accordingly, in another embodiment, the invention provides a method for preparing an anti-PD-1 antibody comprising: (a) providing: (i) a heavy chain variable region antibody sequence comprising a CDR1 sequence selected from the group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, a CDR2 sequence selected from the group consisting of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 'S 28, and/or a CDR3 sequence selected from the group consisting of SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35; and/or (ii) a light chain variable region antibody sequence comprising a CDR1 sequence selected from the group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, a CDR2 sequence selected from the group consisting of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, and/or a CDR3 sequence selected from the group consisting of SEQ ID NOs: 50, 20 51, 52, 53, 54, 55 and 56; (b) altering at least one amino acid residue within the heavy chain variable region antibody sequence and/or the light chain variable region antibody sequence to create at least one altered antibody sequence; and (c) expressing the altered antibody sequence as a protein. 23 Standard molecular biology techniques can be used to prepare and express the altered antibody sequence. Preferably, the antibody encoded by the altered antibody sequence(s) is one that retains one, some or all of the functional properties of the anti-PD-1 antibodies described herein, which functional properties include, but are not limited to: 3 0 (a) the antibody binds to human PD-1 with a KD of 1 x 10" M or less; (b) the antibody does not substantially bind to human CD28, CTLA-4 or ICOS; (c) the antibody increases T-cell proliferation in an MLR assay; (d) the antibody increases interferon-gamma production in an MLR assay; (e) the antibody increases 11-2 secretion in an MLR assay; 3 S (f) the antibody binds to human PD-1 and cynomolgus monkey PD-1; (g) the antibody inhibits the binding of PD-LI and/or PD-L2 to PD-1; (h) the antibody stimulates antigen-specific memory responses; (i) the antibody stimulates antibody responses; (j) the antibody inhibits tumor cell growth in vivo. 38 The functional properties of the altered antibodies can be assessed using standard assays available in the art and/or described herein, such as those set forth in the Examples (e.g., flow cytometry, binding assays). In certain embodiments of the methods of engineering antibodies of the invention, 5 mutations can be introduced randomly or selectively along all or part of an anti-PD-1 antibody coding sequence and the resulting modified anti-PD-1 antibodies can be screened for binding activity and/or other functional properties as described herein. Mutational methods have been described in the art. For example, PCT Publication WO 02/092780 by Short describes methods for creating and screening antibody mutations using saturation mutagenesis, synthetic 1o ligation assembly, or a combination thereof. Alternatively, PCT Publication WO 03/074679 by Lazar et al. describes methods of using computational screening methods to optimize physiochemical properties of antibodies. Nucleic Acid Molecules Encoding Antibodies of the Invention Another aspect of the invention pertains to nucleic acid molecules that encode the 15 antibodies of the invention. The nucleic acids may be present in whole cells, in a cell lysate, or in a partially purified or substantially pure form. A nucleic acid is "isolated" or "rendered substantially pure" when purified away from other cellular components or other contaminants, e.g., other cellular nucleic acids or proteins, by standard techniques, including alkaline/SDS treatment, CsCl banding, column chromatography, agarose gel electrophoresis and others well )0 known in the art. See, F. Ausubel, et al., ed. (1987) Current Protocols in Molecular Biology, Greene Publishing and Wiley Interscience, New York. A nucleic acid of the invention can be, for example, DNA or RNA and may or may not contain intronic sequences. In a preferred embodiment, the nucleic acid is a cDNA molecule. Nucleic acids of the invention can be obtained using standard molecular biology 25 techniques. For antibodies expressed by hybridomas (e.g., hybridomas prepared from transgenic mice carrying human immunoglobulin genes as described further below), cDNAs encoding the light and heavy chains of the antibody made by the hybridoma can be obtained by standard PCR amplification or cDNA cloning techniques. For antibodies obtained from an immunoglobulin gene library (e.g., using phage display techniques), nucleic acid encoding 20 the antibody can be recovered from the library. Preferred nucleic acids molecules of the invention are those encoding the VH and VL sequences of the 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 or 5F4 monoclonal antibodies. DNA sequences encoding the VH sequences of 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 are shown in SEQ ID NOs: 57, 58, 59, 60, 61, 62 and 63, respectively. DNA sequences 3S encoding the VL sequences of 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 are shown in SEQ ID NOs: 64, 65, 66, 67, 68, 69 and 70, respectively. Once DNA fragments encoding VH and VL segments are obtained, these DNA fragments can be further manipulated by standard recombinant DNA techniques, for example to convert the variable region genes to full-length antibody chain genes, to Fab fragment genes 39 or to a scFv gene. In these manipulations, a VL- or VH-encoding DNA fragment is operatively linked to another DNA fragment encoding another protein, such as an antibody constant region or a flexible linker. The term "operatively linked", as used in this context, is intended to mean that the two DNA fragments are joined such that the amino acid sequences encoded by $ the two DNA fragments remain in-frame. The isolated DNA encoding the VH region can be converted to a full-length heavy chain gene by operatively linking the VH-encoding DNA to another DNA molecule encoding heavy chain constant regions (CHI, CH2 and CH3). The sequences of human heavy chain constant region genes are known in the art (see e.g., Kabat, E. A., el al. (1991) Sequences of 10 Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242) and DNA fragments encompassing these regions can be obtained by standard PCR amplification. The heavy chain constant region can be an IgG1, IgG2, IgG3, IgG4, IgA, IgE, IgM or IgD constant region, but most preferably is an IgGI or IgG4 constant region. For a Fab fragment heavy chain gene, the VH-encoding DNA can be S operatively linked to another DNA molecule encoding only the heavy chain CHI constant region. The isolated DNA encoding the VL region can be converted to a full-length light chain gene (as well as a Fab light chain gene) by operatively linking the VL-encoding DNA to another DNA molecule encoding the light chain constant region, CL. The sequences of 2o human light chain constant region genes are known in the art (see e.g., Kabat, E. A., et al (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242) and DNA fragments encompassing these regions can be obtained by standard PCR amplification. The light chain constant region can be a kappa or lambda constant region, but most preferably is a kappa 23 _ constant region. To create a scFv gene, the VH- and VL-encoding DNA fragments are operatively linked to another fragment encoding a flexible linker, e.g., encoding the amino acid sequence (Gly 4 -Ser)3, such that the VH and VL sequences can be expressed as a contiguous single chain protein, with the VL and VH regions joined by the flexible linker (see e.g., Bird et al. 30 (1988) Science 242:423-426; Huston et al. (1988) Proc. Nail. Acad Sci. USA 85:5879-5883; McCafferty et al., (1990) Nature 348:552-554). Production of Monoclonal Antibodies of the Invention Monoclonal antibodies (mAbs) of the present invention can be produced by a variety of techniques, including conventional monoclonal antibody methodology e.g., the standard 35 somatic cell hybridization technique of Kohler and Milstein (1975) Nature 256: 495. Although somatic cell hybridization procedures are preferred, in principle, other techniques for producing monoclonal antibody can be employed e.g., viral or oncogenic transformation of B lymphocytes. 40 The preferred animal system for preparing hybridomas is the murine system. Hybridoma production in the mouse is a very well-established procedure. Immunization protocols and techniques for isolation of immunized splenocytes for fusion are known in the art. Fusion partners (e.g., murine myeloma cells) and fusion procedures are also known. 5 Chimeric or humanized antibodies of the present invention can be prepared based on the sequence of a murine monoclonal antibody prepared as described above. DNA encoding the heavy and light chain immunoglobulins can be obtained from the murine hybridoma of interest and engineered to contain non-murine (e.g., human) immunoglobulin sequences using standard molecular biology techniques. For example, to create a chimeric antibody, the O o murine variable regions can be linked to human constant regions using methods known in the art (see e.g., U.S. Patent No. 4,816,567 to Cabilly et al.). To create a humanized antibody, the murine CDR regions can be inserted into a human framework using methods known in the art (see e.g., U.S. Patent No. 5,225,539 to Winter, and U.S. Patent Nos. 5,530,101; 5,585,089; 5,693,762 and 6,180,370 to Queen et al.). S 5 In a preferred embodiment, the antibodies of the invention are human monoclonal antibodies. Such human monoclonal antibodies directed against PD-1 can be generated using transgenic or transchromosomic mice carrying parts of the human immune system rather than the mouse system. These transgenic and transchromosomic mice include mice referred to herein as HuMAb mice and KM miceTm, respectively, and are collectively referred to herein as 2C "human Ig mice." The HuMAb mouse* (Medarex, Inc.) contains human immunoglobulin gene miniloci that encode unrearranged human heavy (p and y) and x light chain immunoglobulin sequences, together with targeted mutations that inactivate the endogenous R and x chain loci (see e.g., Lonberg, et al. (1994) Nature 368(6474): 856-859). Accordingly, the mice exhibit reduced 15 expression of mouse IgM or 1c, and in response to immunization, the introduced human heavy and light chain transgenes undergo class switching and somatic mutation to generate high affinity human IgGK monoclonal (Lonberg, N. et al. (1994), supra; reviewed in Lonberg, N. (1994) Handbook ofExperimentalPharmacology 1.1:49-101; Lonberg, N. and Huszar, D. (1995) Intern. Rev. Immunol. 13: 65-93, and Harding, F. and Lonberg, N. (1995) Ann. N Y. 30 Acad Sci. 164:536-546). The preparation and use of HuMab mice, and the genomic modifications carried by such mice, is further described in Taylor, L. et al. (1992) Nucleic Acids Research 20:6287-6295; Chen, J. et al. (1993) International Immunology 5: 647-656; Tuaillon et al. (1993) Proc. Nati. Acad Sci. USA 20:3720-3724; Choi et aL (1993) Nature Genetics 4:117-123; Chen, J. et al. (1993) EMBO J. 2: 821-830; Tuaillon et al. (1994) J BS Immunol. 152:2912-2920; Taylor, L. et al. (1994)International Immunology 6: 579-591; and Fishwild, D. et al (1996) Nature Biotechnology 14: 845-851, the contents of all of which are hereby specifically incorporated by reference in their entirety. See further, U.S. Patent Nos. 5,545,806; 5,569,825; 5,625,126; 5,633,425; 5,789,650; 5,877,397; 5,661,016; 5,814,318; 5,874,299; and 5,770,429; all to Lonberg and Kay; U.S. Patent No. 5,545,807 to Surani et al.; 41 PCT Publication Nos. WO 92/03918, WO 93/12227, WO 94/25585, WO 97/13852, WO 98/24884 and WO 99/45962, all to Lonberg and Kay; and PCT Publication No. WO 01/14424 to Korman et al. In another embodiment, human antibodies of the invention can be raised using a mouse 5 that carries human immunoglobulin sequences on transgenes and transchomosomes, such as a mouse that carries a human heavy chain transgene and a human light chain transchromosome. Such mice, referred to herein as "KM mice T m ", are described in detail in PCT Publication WO 02/43478 to Ishida et al. Still further, alternative transgenic animal systems expressing human immunoglobulin io genes are available in the art and can be used to raise anti-PD-I antibodies of the invention. For example, an alternative transgenic system referred to as the Xenomouse (Abgenix, Inc.) can be used; such mice are described in, for example, U.S. Patent Nos. 5,939,598; 6,075,181; 6,114,598; 6, 150,584 and 6,162,963 to Kucherlapati et al. Moreover, alternative transchromosomic animal systems expressing human 5 immunoglobulin genes are available in the art and can be used to raise anti-PD-1 antibodies of the invention. For example, mice carrying both a human heavy chain transchromosome and a human light chain transchromosome, referred to as "TC mice" can be used; such mice are described in Tomizuka et al. (2000) Proc. Nat. Acad Sci. USA 97:722-727. Furthermore, cows carrying human heavy and light chain transchromosomes have been described in the art 20 (Kuroiwa et al. (2002) Nature Biotechnology 20:889-894) and can be used to raise anti-PD-I antibodies of the invention. Human monoclonal antibodies of the invention can also be prepared using phage display methods for screening libraries of human immunoglobulin genes. Such phage display methods for isolating human antibodies are established in the art. See for example: - U.S. Patent Nos. 5,223,409; 5,403,484; and 5,571,698 to Ladner et al; U.S. Patent Nos. 5,427,908 and 5,580,717 to Dower etal.; U.S. Patent Nos. 5,969,108 and 6,172,197 to McCafferty et al.; and U.S. Patent Nos. 5,885,793; 6,521,404; 6,544,731; 6,555,313; 6,582,915 and 6,593,081 to Griffiths et al. Human monoclonal antibodies of the invention can also be prepared using SCID mice 'o into which human immune cells have been reconstituted such that a human antibody response can be generated upon immunization. Such mice are described in, for example, U.S. Patent Nos. 5,476,996 and 5,698,767 to Wilson et al. Immunization of Human Ig Mice When human Ig mice are used to raise human antibodies of the invention, such mice as can be immunized with a purified or enriched preparation of PD-1 antigen and/or recombinant PD-1, or an PD-1 fusion protein, as described by Lonberg, N. et al. (1994) Nature 3(6474): 856-859; Fishwild, D. et al. (1996) Nature Biotechnology 14: 845-85 1; and PCT Publication WO 98/24884 and WO 01/14424. Preferably, the mice will be 6-16 weeks of age upon the 42 first infusion. For example, a purified or recombinant preparation (5-50 gg) of PD-I antigen can be used to immunize the human Ig mice intraperitoneally. Detailed procedures to generate fully human monoclonal antibodies to PD-1 are described in Example 1 below. Cumulative experience with various antigens has shown that $ the transgenic mice respond when initially immunized intraperitoneally (1P) with antigen in complete Freund's adjuvant, followed by every other week IP immunizations (up to a total of 6) with antigen in incomplete Freund's adjuvant. However, adjuvants other than Freund's are also found to be effective. In addition, whole cells in the absence of adjuvant are found to be highly immunogenic. The immune response can be monitored over the course of the ' o immunization protocol with plasma samples being obtained by retroorbital bleeds. The plasma can be screened by ELISA (as described below), and mice with sufficient titers of anti PD-1 human immunoglobulin can be used for fusions. Mice can be boosted intravenously .with antigen 3 days before sacrifice and removal of the spleen. It is expected that 2-3 fusions for each immunization may need to be performed. Between 6 and 24 mice are typically IS immunized for each antigen. Usually both HCo7 and HCol2 strains are used. In addition, both HCo7 and HCo12 transgene can be bred together into a single mouse having two different human heavy chain transgenes (HCo7/HCo 12). Alternatively or additionally, the KM mouse strain can be used, as described in Example 1. Generation of Hybridomas Producing Human Monoclonal Antibodies of the Invention 2C To generate hybridomas producing human monoclonal antibodies of the invention, splenocytes and/or lymph node cells from immunized mice can be isolated and fused to an appropriate immortalized cell line, such as a mouse myeloma cell line. The resulting hybridomas can be screened for the production of antigen-specific antibodies. For example, single cell suspensions of splenic lymphocytes from immunized mice can be fused to one-sixth 2s the number of P3X63-Ag8.653 nonsecreting mouse myeloma cells (ATCC, CRL 1580) with 50% PEG. Alternatively, the single cell suspensions of splenic lymphocytes from immunized mice can be fused using an electric field based electrofusion method, using a Cyto Pulse large chamber cell fusion electroporator (Cyto Pulse Sciences, Inc., Glen Burnie, MD). Cells are plated at approximately 2 x 10 5 in flat bottom microtiter plate, followed by a two .o week incubation in selective medium containing 20% fetal Clone Serum, 18% "653" conditioned media; 5% origen (IGEN), 4 mM L-glutamine, 1 mM sodium pyruvate, 5mM HEPES, 0.055 mM 2-mercaptoethanol, 50 units/ml penicillin, 50 mg/ml streptomycin, 50 mg/ml gentamycin and IX HAT (Sigma; the HAT is added 24 hours after the fusion). After approximately two weeks; cells can be cultured in medium in which the HAT is replaced with as HT. Individual wells can then be screened by ELISA for human monoclonal IgM and IgG antibodies. Once extensive hybridoma growth occurs, medium can be observed usually after 10-14 days. The antibody secreting hybridomas can be replated, screened again, and if still positive for human IgG, the monoclonal antibodies can be subcloned at least twice by limiting 43 dilution. The stable subclones can then be cultured in vitro to generate small amounts of antibody in tissue culture medium for characterization. To purify human monoclonal antibodies, selected hybridomas can be grown in two liter spinner-flasks for monoclonal antibody purification. Supernatants can be filtered and S concentrated before affinity chromatography with protein A-sepharose (Pharmacia, Piscataway, N.J.). Eluted IgG can be checked by gel electrophoresis and high performance liquid chromatography to ensure purity. The buffer solution can be exchanged into PBS, and the concentration can be determined by OD 280 using 1.43 extinction coefficient. The monoclonal antibodies can be aliquoted and stored at -80 *C. io Generation of Transfectomas Producing Monoclonal Antibodies of the Invention Antibodies of the invention also can be produced in a host cell transfectoma using, for example, a combination of recombinant DNA techniques and gene transfection methods as is well known in the art (e.g., Morrison, S. (1985) Science 229:1202). For example, to express the antibodies, or antibody fragments thereof, DNAs encoding 15 partial or full-length light and heavy chains, can be obtained by standard molecular biology techniques (e.g., PCR amplification or cDNA cloning using a hybridoma that expresses the antibody of interest) and the DNAs can be inserted into expression vectors such that the genes are operatively linked to transcriptional and translational control sequences. In this context, the term "operatively linked" is intended to mean that an antibody gene is ligated into a vector Z0 such that transcriptional and translational control sequences within the vector serve their intended function of regulating the transcription and translation of the antibody gene. The expression vector and expression control sequences are chosen to be compatible with the expression host cell used. The antibody light chain gene and the antibody heavy chain gene can be inserted into separate vector or, more typically, both genes are inserted into the same 25 expression vector. The antibody genes are inserted into the expression vector by standard methods (e.g., ligation of complementary restriction sites on the antibody gene fragment and vector, or blunt end ligation if no restriction sites are present). The light and heavy chain variable regions of the antibodies described herein can be used to create full-length antibody genes of any antibody isotype by inserting them into expression vectors already encoding .o heavy chain constant and light chain constant regions of the desired isotype such that the VH segment is operatively linked to the CH segment(s) within the vector and the VK segment is operatively linked to the CL segment within the vector. Additionally or alternatively, the recombinant expression vector can encode a signal peptide that facilitates secretion of the antibody chain from a host cell. The antibody chain gene can be cloned into the vector such I s that the signal peptide is linked in-frame to the amino terminus of the antibody chain gene. The signal peptide can be an immunoglobulin signal peptide or a heterologous signal peptide (i.e., a signal peptide from a non-immunoglobulin protein). In addition to the antibody chain genes, the recombinant expression vectors of the invention carry regulatory sequences that control the expression of the antibody chain genes in 44 a host cell. The term "regulatory sequence" is intended to include promoters, enhancers and other expression control elements (e.g., polyadenylation signals) that control the transcription or translation of the antibody chain genes. ' Such regulatory sequences are described, for example, in Goeddel (Gene Expression Technology. Methods in Enzymology 185, s Academic Press, 'San Diego, CA (1990)). It will be appreciated by those skilled in the art that the design of the expression vector, including the selection of regulatory sequences, may depend on such factors as the choice of the host cell to be transformed, the level of expression of protein desired, etc. Preferred regulatory sequences for mammalian host cell expression include viral elements that direct high levels of protein expression in mammalian cells, such as P- promoters and/or enhancers derived from cytomegalovirus (CMV), Simian Virus 40 (SV40), adenovirus, (e.g., the adenovirus major late promoter (AdMLP) and polyoma. Alternatively, nonviral regulatory sequences may be used, such as the ubiquitin promoter or p-globin promoter. Still further, regulatory elements composed of sequences from different sources, such as the SRc promoter system, which contains sequences from the SV40 early promoter is and the long terminal repeat of human T cell leukemia virus type 1 (Takebe, Y. et al. (1988) Mol. Cell. Biol. 8:466-472). In addition to the antibody chain genes and regulatory sequences, the recombinant expression vectors of the invention may carry additional sequences, such as sequences that regulate replication of the vector in host cells (e.g., origins of replication) and selectable 10 marker genes. The selectable marker gene facilitates selection of host cells into which the vector has been introduced (see, e.g., U.S. Pat. Nos. 4,399,216, 4,634,665 and 5,179,017, all by Axel et al.). For example, typically the selectable marker gene confers resistance to drugs, such as G418, hygromycin or methotrexate, on a host cell into which the vector has been introduced. Preferred selectable marker genes include the dihydrofolate reductase (DHFR) is gene (for use in dhfr- host cells with methotrexate selection/amplification) and the neo gene (for G418 selection). For expression of the light and heavy chains, the expression vector(s) encoding the heavy and light chains is transfected into a host cell by standard techniques. The various forms of the term "transfection" are intended to encompass a wide variety of techniques 3c commonly used for the introduction of exogenous DNA into a prokaryotic or eukaryotic host cell, e.g., electroporation, calcium-phosphate precipitation, DEAE-dextran transfection and the like. Although it is theoretically possible to express the antibodies of the invention in either prokaryotic or eukaryotic host cells, expression of antibodies in eukaryotic cells, and most preferably mammalian host cells, is the most preferred because such eukaryotic cells, and in as particular mammalian cells, are more likely than prokaryotic cells to assemble and secrete a properly folded and immunologically active antibody. Prokaryotic expression of antibody genes has been reported to be ineffective for production of high yields of active antibody (Boss, M. A. and Wood, C. R. (1985)Immunology Today 6: 12-13). Preferred mammalian host cells for expressing the recombinant antibodies of the 45 invention include Chinese Hamster Ovary (CHO cells) (including dhfr- CHO cells, described in Urlaub and Chasin, (1980) Proc. Nati. Acad Sci. USA 7:4216-4220, used with a DHFR selectable marker, e.g., as described in R. J. Kaufman and P. A. Sharp (1982) Mol. BioL 159:601-621), NSO myeloma cells, COS cells and SP2 cells. In particular, for use with NSO 5 myeloma cells, another preferred expression system is the GS gene expression system disclosed in WO 87/04462, WO 89/01036 and EP 338,841. When recombinant expression vectors encoding antibody genes are introduced into mammalian host cells, the antibodies are produced by culturing the host cells for a period of time sufficient to allow for expression of the antibody in the host cells or, more preferably, secretion of the antibody into the culture to medium in which the host cells are grown. Antibodies can be recovered from the culture medium using standard protein purification methods. Characterization of Antibody Binding to Antigen Antibodies of the invention can be tested for binding to PD-I by, for example, standard ELISA. Briefly, microtiter plates are coated with purified PD-i at 0.25 pg/ml in PBS, and IS then blocked with 5% bovine serum albumin in PBS. Dilutions of antibody (e.g., dilutions of plasma from PD-1-immunized mice) are added to each well and incubated for 1-2 hours at 37 0 C. The plates are washed with PBS/Tween and then incubated with secondary reagent (e.g., for human antibodies, a goat-anti-human IgG Fc-specific polyclonal reagent) conjugated to alkaline phosphatase for 1 hour at 37*C. After washing, the plates are developed with 20 pNPP substrate (1 mg/ml), and analyzed at OD of 405-650. Preferably, mice which develop the highest titers will be used for fusions. An ELISA assay as described above can also be used to screen for hybridomas that show positive reactivity with PD-i immunogen. Hybridomas that bind with high avidity to PD-i are subcloned and further characterized. One clone from each hybridoma, which 25 retains the reactivity of the parent cells (by ELISA), can be chosen for making a 5-10 vial cell bank stored at -140 *C, and for antibody purification. To purify anti-PD-I antibodies, selected hybridomas can be grown in two-liter spinner flasks for monoclonal antibody purification. Supernatants can be filtered and concentrated before affinity chromatography with protein A-sepharose (Pharmacia, Piscataway, NJ). Eluted IgG can be checked by gel electrophoresis and high performance liquid chromatography to ensure purity. The buffer solution can be exchanged into PBS, and the concentration can be determined by OD280 using 1.43 extinction coefficient. The monoclonal antibodies can be aliquoted and stored at -80 *C. To determine if the selected anti-PD-1 monoclonal antibodies bind to unique epitopes, 6 each antibody can be biotinylated using commercially available reagents (Pierce, Rockford, ]L). Competition studies using unlabeled monoclonal antibodies and biotinylated monoclonal antibodies can be performed using PD-i coated-ELISA plates as described above. Biotinylated mAb binding can be detected with a strep-avidin-alkaline phosphatase probe. 46 To determine the isotype of purified antibodies, isotype ELISAs can be performed using reagents specific for antibodies of a particular isotype. For example, to determine the isotype of a human monoclonal antibody, wells of microtiter plates can be coated with 1 [ig/ml of anti-human immunoglobulin overnight at 4 *C. After blocking with 1% BSA, the plates are S reacted with I Rg /ml or less of test monoclonal antibodies or purified isotype controls, at ambient temperature for one to two hours. The wells can then be reacted with either human IgGI or human IgM-specific alkaline phosphatase-conjugated probes. Plates are developed and analyzed as described above. Anti-PD-1 human IgGs can be further tested for reactivity with PD-1 antigen by Western (o blotting. Briefly, PD-I can be prepared and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis. After electrophoresis, the separated antigens are transferred to nitrocellulose membranes, blocked with 10% fetal calf serum, and probed with the monoclonal antibodies to be tested. Human IgG binding can be detected using anti human IgG alkaline phosphatase and developed with BCIP/NBT substrate tablets (Sigma ~s Chem. Co., St. Louis, Mo.). Immunoconjugates In another aspect, the present invention features an anti-PD-I antibody, or a fragment thereof, conjugated to a therapeutic moiety, such as a cytotoxin, a drug (e.g., an immunosuppressant) or a radiotoxin. Such conjugates are referred to herein as 20 "immunoconjugates". Immunoconjugates that include one or more cytotoxins are referred to as "immunotoxins." A cytotoxin or cytotoxic agent includes any agent that is detrimental to (e.g., kills) cells. Examples include taxol, cytochalasin B, gramicidin D, ethidium bromide, emetine, mitomycin, etoposide, tenoposide, vincristine, vinblastine, colchicin, doxorubicin, daunorubicin, dihydroxy anthracin dione, mitoxantrone, mithramycin, actinomycin D, 1 Z5 dehydrotestosterone, glucocorticoids, procaine, tetracaine, lidocaine, propranolol, and puromycin and analogs or homologs thereof. Therapeutic agents also include, for example, antimetabolites (e.g., methotrexate, 6-mercaptopurine, 6-thioguanine, cytarabine, 5 fluorouracil decarbazine), alkylating agents (e.g., mechlorethamine, thioepa chlorambucil, melphalan, carmustine (BSNU) and lomustine (CCNU), cyclothosphamide, busulfan, ZO dibromomannitol, streptozotocin, mitomycin C, and cis-dichlorodiamine platinum (II) (DDP) cisplatin), anthracyclines (e.g., daunorubicin (formerly daunomycin) and doxorubicin), antibiotics (e.g., dactinomycin (formerly actinomycin), bleomycin, mithramycin, and anthramycin (AMC)), and anti-mitotic agents (e.g., vincristine and vinblastine). Other preferred examples of therapeutic cytotoxins that can be conjugated to an ? antibody of the invention include duocarmycins, calicheamicins, maytansines and auristatins, and derivatives thereof. An example of a calicheamicin antibody conjugate is commercially available (Mylotargm; Wyeth-Ayerst). Cytoxins can be conjugated to antibodies of the invention using linker technology available in the art. Examples of linker types that have been used to conjugate a cytotoxin to 47 an antibody include, but are not limited to, hydrazones, thioethers, esters, disulfides and peptide-containing linkers. A linker can be chosen that is, for example, susceptible to cleavage by low pH within the lysosomal compartment or susceptible to cleavage by proteases, such as proteases preferentially expressed in tumor tissue such as cathepsins (e.g., cathepsins B, C, D). For further discussion of types of cytotoxins, linkers and methods for conjugating therapeutic agents to antibodies, see also Saito, G. et al. (2003) Adv. Drug Deliv. Rev. 55:199 215; Trail, P.A. etal. (2003) Cancer Immunol. Immunother. 52:328-337; Payne, G. (2003) Cancer Cell 3:207-212; Allen, T.M. (2002) Nat. Rev. Cancer 2:750-763; Pastan, I. and ' Kreitman, R. J. (2002) Curr. Opin. Investig. Drugs 1::1089-1091; Senter, P.D. and Springer, C.J. (2001) Adv. Drug Deliv. Rev. 53:247-264. Antibodies of the present invention also can be conjugated to a radioactive isotope to generate cytotoxic radiopharmaceuticals, also referred to as radioimmunoconjugates. Examples of radioactive isotopes that can be conjugated to antibodies for use diagnostically or '3 therapeutically include, but are not limited to, iodine, indium", yttrium' and lutetium'm. Method for preparing radioimmunconjugates are established in the art. Examples of radioimmunoconjugates are commercially available, including ZevalinTm (IDEC Pharmaceuticals) and BexxarTm (Corixa Pharmaceuticals), and similar methods can be used to prepare radioimmunoconjugates using the antibodies of the invention. '1o The antibody conjugates of the invention can be used to modify a given biological response, and the drug moiety is not to be construed as limited to classical chemical therapeutic agents. For example, the drug moiety may be a protein or polypeptide possessing a desired biological activity. Such proteins may include, for example, an enzymatically active toxin, or active fragment thereof such as abrin, ricin A, pseudomonas exotoxin, or 25 diphtheria toxin; a protein such as tumor necrosis factor or interferon-y; or, biological response modifiers such as, for example, lymphokines, interleukin-1 ("IL-1"), interleukin-2 ("IL-2"), interleukin-6 ("IL-6"), granulocyte macrophage colony stimulating factor ("GM-CSF"), granulocyte colony stimulating factor ("G-CSF"), or other growth factors. Techniques for conjugating such therapeutic moiety to antibodies are well known, see, 30 e.g., Amon et al., "Monoclonal Antibodies For Immunotargeting Of Drugs In Cancer Therapy", in Monoclonal Antibodies And Cancer Therapy, Reisfeld et al. (eds.), pp. 243-56 (Alan R. Liss, Inc. 1985); Hellstrom et al., "Antibodies For Drug Delivery", in Controlled Drug Delivery (2nd Ed.), Robinson et al. (eds.), pp. 623-53 (Marcel Dekker, Inc. 1987); Thorpe, "Antibody Carriers Of Cytotoxic Agents In Cancer Therapy: A Review", in ?S Monoclonal Antibodies '84: Biological And Clinical Applications, Pinchera et al. (eds.), pp. 475-506 (1985); "Analysis, Results, And Future Prospective Of The Therapeutic Use Of Radiolabeled Antibody In Cancer Therapy", in Monoclonal Antibodies For Cancer Detection And Therapy, Baldwin et al. (eds.), pp. 303-16 (Academic Press 1985), and Thorpe et al., 48 "The Preparation And Cytotoxic Properties Of Antibody-Toxin Conjugates", Immunol. Rev., 62:119-58 (1982). Bispecific Molecules In another aspect, the present invention features bispecific molecules comprising an 5 anti-PD-1 antibody, or a fragment thereof, of the invention. An antibody of the invention, or antigen-binding portions thereof, can be derivatized or linked to another functional molecule, e.g., another peptide or protein (e.g., another antibody or ligand for a receptor) to generate a bispecific molecule that binds to at least two different binding sites or target molecules. The antibody of the invention may in fact be derivatized or linkd to more than one other functional '0 molecule to generate multispecific molecules that bind to more than two different binding sites and/or target molecules; such multispecific molecules are also intended to be encompassed by the term "bispecific molecule" as used herein. To create a bispecific molecule of the invention, an antibody of the invention can be functionally linked (e.g., by chemical coupling, genetic fusion, noncovalent association or otherwise) to one or more other binding molecules, Is such as another antibody, antibody fragment, peptide or binding mimetic, such that a bispecific molecule results. Accordingly, the present invention includes bispecific molecules comprising at least one first binding specificity for PD-I and a second binding specificity for a second target epitope. In a particular embodiment of the invention, the second target epitope is an Fc 10 receptor, e.g., human FcyRI (CD64) or a human Fca receptor (CD89). Therefore, the invention includes bispecific molecules capable of binding both to FcyR or FcaR expressing effector cells (e.g., monocytes, macrophages or polymorphonuclear cells (PMNs)), and to target cells expressing PD-1. These bispecific molecules target PD-I expressing cells to effector cell and trigger Fc receptor-mediated effector cell activities, such as phagocytosis of 25 an PD-I expressing cells, antibody dependent cell-mediated cytotoxicity (ADCC), cytokine release, or generation of superoxide anion. . In an embodiment of the invention in which the bispecific molecule is multispecific, the molecule can further include a third binding specificity, in addition to an anti-Fc binding specificity and an anti-PD-1 binding specificity. In one embodiment, the third binding 30o specificity is an anti-enhancement factor (EF) portion, e.g., a molecule which binds to a surface protein involved in cytotoxic activity and thereby increases the immune response against the target cell. The "anti-enhancement factor portion" can be an antibody, functional antibody fragment or a ligand that binds to a given molecule, e.g., an antigen or a receptor, and thereby results in an enhancement of the effect of the binding determinants for the Fc receptor ,s or target cell antigen. The "anti-enhancement factor portion" can bind an Fc receptor or a target cell antigen. Alternatively, the anti-enhancement factor portion can bind to an entity that is different from the entity to which the first and second binding specificities bind.- For example, the anti-enhancement factor portion can bind a cytotoxic T-cell (e.g. via CD2, CD3, 49 CD8, CD28, CD4, CD40, ICAM-1 or other immune cell that results in an increased immune response against the target cell). In one embodiment, the bispecific molecules of the invention comprise as a binding specificity at least one antibody, or an antibody fragment thereof; including, e.g., an Fab, Fab', F(ab') 2 , Fv, or a single chain Fv. The antibody may also be a light chain or heavy chain dimer, or any minimal fragment thereof such as a Fv or a single chain construct as described in Ladner et al. U.S. Patent No. 4,946,778, the contents of which is expressly incorporated by reference. In one embodiment, the binding specificity for an Fcy receptor is provided by a o monoclonal antibody, the binding of which is not blocked by human immunoglobulin G (IgG). As used herein, the term "IgG receptor" refers to any of the eight y-chain genes located on chromosome 1. These genes encode a total of twelve transmembrane or soluble receptor isoforms which are grouped into three Fcy receptor classes: FcyRI (CD64), FcyRII(CD32), and FcyRIII (CD16). In one preferred embodiment, the Fcy receptor a human high affinity i s FcyRI. The human FcyRI is a 72 kDa molecule, which shows high affinity for monomeric IgG (108 - 10 9 M-). The production and characterization of certain preferred anti-Fcy monoclonal antibodies are described by Fanger et al. in PCT Publication WO 88/00052 and in U.S. Patent No. 4,954,617, the teachings of which are fully incorporated by reference herein. These 20 antibodies bind to an epitope of FcyRI, FcyRII or FcyRfI at a site which is distinct from the Fc y binding site of the receptor and, thus, their binding is not blocked substantially by physiological levels of IgG. Specific anti-FcyRI antibodies useful in this invention are mAb 22, mAb 32, mAb 44, mAb 62 and mAb 197. The hybridoma producing mAb 32 is available from the American Type Culture Collection, ATCC Accession No. HB9469. In other L S embodiments, the anti-Fcy receptor antibody is a humanized form of monoclonal antibody 22 (H22). The production and characterization of the H22 antibody is described in Graziano, R.F. et al. (1995) J. Immunol 155 (10): 4996-5002 and PCT Publication WO 94/10332. The H22 antibody producing cell line was deposited at the American Type Culture Collection under the designation HAO22CL1 and has the accession no. CRL 11177. -1o In still other preferred embodiments, the binding specificity for an Fc receptor is provided by an antibody that binds to a human IgA receptor, e.g., an Fc-alpha receptor (FcaRI (CD89)), the binding of which is preferably not blocked by human immunoglobulin A (IgA). The term "IgA receptor" is intended to include the gene product of one a-gene (FcaRI) located on chromosome 19. This gene is known to encode several alternatively spliced 15 transmembrane isoforms of 55 to 110 kDa. FcaRI (CD89) is constitutively expressed on monocytes/macrophages, eosinophilic and neutrophilic granulocytes, but not on non-effector cell populations. FcaRI has medium affinity (z 5 x 107 M-1) for both IgAl and IgA2, which is increased upon exposure to cytokines such as G-CSF or GM-CSF (Morton, H.C. et al. (1996) Critical Reviews in Immunology L6:423-440). Four FcaRI-specific monoclonal 50 antibodies, identified as A3, A59, A62 and A77, which bind FcaRI outside the IgA ligand binding domain, have been described (Monteiro, R.C. et al. (1992) J. Immunol. 148:1764). FccRI and FcyRI are preferred trigger receptors for use in the bispecific molecules of the invention because they are (1) expressed primarily on immune effector cells, e.g., 5 monocytes, PMNs, macrophages and dendritic cells; (2) expressed at high levels (e.g., 5,000 100,000 per cell); (3) mediators of cytotoxic activities (e.g., ADCC, phagocytosis); (4) mediate enhanced antigen presentation of antigens, including self-antigens, targeted to them. While human monoclonal antibodies are preferred, other antibodies which can be employed in the bispecific molecules of the invention are murine, chimeric and humanized 0 monoclonal antibodies. The bispecific molecules of the present invention can be prepared by conjugating the constituent binding specificities, e.g., the anti-FcR and anti-PD-1 binding specificities, using methods known in the art. For example, each binding specificity of the bispecific molecule can be generated separately and then conjugated to one another. When the binding 1S specificities are proteins or peptides, a variety of coupling or cross-linking agents can be used for covalent conjugation. Examples of cross-linking agents include protein A, carbodiimide, N-succinimidyl-S-acetyl-thioacetate (SATA), 5, 5'-dithiobis(2-nitrobenzoic acid) (DTNB), o phenylenedimaleimide (oPDM), N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP), and sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohaxane-1-carboxylate (sulfo-SMCC) (see e.g., 20 Karpovsky et al. (1984) J Exp. Med. 160:1686; Liu, MA et al. (1985) Proc. Natl. Acad Sci. USA 82:8648). Other methods include those described in Paulus (1985) Behring Ins. Mitt. No. 78, 118-132; Brennan etal. (1985) Science 229:81-83), and Glennie etal. (1987)J. Immunol. 139: 2367-2375). Preferred conjugating agents are SATA and sulfo-SMCC, both available from Pierce Chemical Co. (Rockford, IL). Ss When the binding specificities are antibodies, they can be conjugated via sulfhydryl bonding of the C-terminus hinge regions of the two heavy chains. In a particularly preferred embodiment, the hinge region is modified to contain an odd number of sulfhydryl residues, preferably one, prior to conjugation. Alternatively, both binding specificities can be encoded in the same vector and 30 expressed and assembled in the same host cell. This method is particularly useful where the bispecific molecule is a mAb x mAb, mAb x Fab, Fab x F(ab') 2 or ligand x Fab fusion protein. A bispecific molecule of the invention can be a single chain molecule comprising one single chain antibody and a binding determinant, or a single chain bispecific molecule comprising two binding determinants. Bispecific molecules may comprise at least two single chain - molecules. Methods for preparing bispecific molecules are described for example in U.S. Patent Number 5,260,203; U.S. Patent Number 5,455,030; U.S. Patent Number 4,881,175; U.S. Patent Number 5,132,405; U.S. Patent Number 5,091,513; U.S. Patent Number 5,476,786; U.S. Patent Number 5,013,653; U.S. Patent Number 5,258,498; and U.S. Patent Number 5,482,858. 51 Binding of the bispecific molecules to their specific targets can be confirmed by, for example, enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), FACS analysis, bioassay (e.g., growth inhibition), or Western Blot assay. Each of these assays generally detects the presence of protein-antibody complexes of particular interest by S employing a labeled reagent (e.g., an antibody) specific for the complex of interest. For example, the FcR-antibody complexes can be detected using e.g., an enzyme-linked antibody or antibody fragment which recognizes and specifically binds to the antibody-FcR complexes. Alternatively, the complexes can be detected using any of a variety of other immunoassays. For example, the antibody can be radioactively labeled and used in a radioimmunoassay (RIA) ko (see, for example, Weintraub, B., Principles of Radioimmunoassays, Seventh Training Course on Radioligand Assay Techniques, The Endocrine Society, March, 1986, which is incorporated by reference herein). The radioactive isotope can be detected by such means as the use of a y counter or a scintillation counter or by autoradiography. Pharmaceutical Compositions is In another aspect, the present invention provides a composition, e.g., a pharmaceutical composition, containing one or a combination of monoclonal antibodies, or antigen-binding portion(s) thereof, of the present invention, formulated together with a pharmaceutically acceptable carrier. Such compositions may include one or a combination of (e.g., two or more different) antibodies, or immunoconjugates or bispecific molecules of the invention. 20 For example, a pharmaceutical composition of the invention can comprise a combination of antibodies (or immunoconjugates or bispecifics) that bind to different epitopes on the target antigen or that have complementary activities. Pharmaceutical compositions of the invention also can be administered in combination therapy, i.e., combined with other agents. For example, the combination therapy can include 2S an anti-PD-I antibody of the present invention combined with at least one other anti-* inflammatory or immunosuppressant agent. Examples of therapeutic agents that can be used in combination therapy are described in greater detail below in the section on uses of the antibodies of the invention. As used herein, "pharmaceutically acceptable carrier" includes any and all solvents, '1 dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like that are physiologically compatible. Preferably, the carrier is suitable for intravenous, intramuscular, subcutaneous, parenteral, spinal or epidermal administration (e.g., by injection or infusion). Depending on the route of administration, the active compound, i.e., antibody, immunoconjuage, or bispecific molecule, may be coated in a 35 material to protect the compound from the action of acids and other natural conditions that may inactivate the compound. The pharmaceutical compounds of the invention may include one or more pharmaceutically acceptable salts. A "pharmaceutically acceptable salt" refers to a salt that retains the desired biological activity of the parent compound and does not impart any 52 undesired toxicological effects (see e.g., Berge, S.M., et al. (1977)J Pharm. Sci. 6:1-19). Examples of such salts include acid addition salts and base addition salts. Acid addition salts include those derived from nontoxic inorganic acids, such as hydrochloric, nitric, phosphoric, sulfuric, hydrobromic, hydroiodic, phosphorous and the like, as well as from nontoxic organic 5 acids such as aliphatic mono- and dicarboxylic acids, phenyl-substituted alkanoic acids, hydroxy alkanoic acids, aromatic acids, aliphatic and aromatic sulfonic acids and the like. Base addition salts include those derived from alkaline earth metals, such as sodium, potassium, magnesium, calcium and the like, as well as from nontoxic organic amines, such as N, N-dibenzylethylenediamine, N-methylglucamine, chloroprocaine, choline, diethanolamine, i o ethylenediamine, procaine and the like. A pharmaceutical composition of the invention also may include a pharmaceutically acceptable anti-oxidant. Examples of pharmaceutically acceptable antioxidants include: (1) water soluble antioxidants, such as ascorbic acid, cysteine hydrochloride, sodium bisulfate, sodium metabisulfite, sodium sulfite and the like; (2) oil-soluble antioxidants, such as ascorbyl \5 palmitate, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), lecithin, propyl gallate, alpha-tocopherol, and the like; and (3) metal chelating agents, such as citric acid, ethylenediamine tetraacetic acid (EDTA), sorbitol, tartaric acid, phosphoric acid, and the like. Examples of suitable aqueous and nonaqueous carriers that may be employed in the pharmaceutical compositions of the invention include water, ethanol, polyols (such as glycerol, 20 propylene glycol, polyethylene glycol, and the like), and suitable mixtures thereof, vegetable oils, such as olive oil, and injectable organic esters, such as ethyl oleate. Proper fluidity can be maintained, for example, by the use of coating materials, such as lecithin, by the maintenance of the required particle size in the case of dispersions, and by the use of surfactants. 2 5 These compositions may also contain adjuvants such as preservatives, wetting agents, emulsifying agents and dispersing agents. Prevention of presence of microorganisms may be ensured both by sterilization procedures, supra, and by the inclusion of various antibacterial and antifungal agents, for example, paraben, chlorobutanol, phenol sorbic acid, and the like. It may also be desirable to include isotonic agents, such as sugars, sodium chloride, and the 30 like into the compositions. In addition, prolonged absorption of the injectable pharmaceutical form may be brought about by the inclusion of agents which delay absorption such as aluminum monostearate and gelatin. Pharmaceutically acceptable carriers include sterile aqueous solutions or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or 'S dispersion. The use of such media and agents for pharmaceutically active substances is known in the art. Except insofar as any conventional media or agent is incompatible with the active compound, use thereof in the pharmaceutical compositions of the invention is contemplated. Supplementary active compounds can also be incorporated into the compositions. 53 Therapeutic compositions typically must be sterile and stable under the conditions of manufacture and storage. The composition can be formulated as a solution, microemulsion, liposome, or other ordered structure suitable to high drug concentration. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, polyol (for example, 5 glycerol, propylene glycol, and liquid polyethylene glycol, and the like), and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. In many cases, it will be preferable to include isotonic agents, for example, sugars, polyalcohols such as mannitol, sorbitol, or sodium chloride in the composition. ~O Prolonged absorption of the injectable compositions can be brought about by including in the composition an agent that delays absorption, for example, monostearate salts and gelatin. Sterile injectable solutions can be prepared by incorporating the active compound in the required amount in an appropriate solvent with one or a combination of ingredients enumerated above, as required, followed by sterilization microfiltration. Generally, 15 dispersions are prepared by incorporating the active compound into a sterile vehicle that contains a basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and freeze-drying lyophilizationn) that yield a powder of the active ingredient plus any additional desired ingredient from a 2o previously sterile-filtered solution thereof The amount of active ingredient which can be combined with a carrier material to produce a single dosage form will vary depending upon the subject being treated, and the particular mode of administration. The amount of active ingredient which can be combined with a carrier material to produce a single dosage form will generally be that amount of the C5 composition which produces a therapeutic effect. Generally, out of one hundred per cent, this amount will range from about 0.01 per cent to about ninety-nine percent of active ingredient, preferably from about 0.1 per cent to about 70 per cent, most preferably from about 1 per cent to about 30 per cent of active ingredient in combination with a pharmaceutically acceptable carrier. 3 0 Dosage regimens are adjusted to provide the optimum desired response (e.g., a therapeutic response). For example, a single bolus may be administered, several divided doses may be administered over time or the dose may be proportionally reduced or increased as indicated by the exigencies of the therapeutic situation. It is especially advantageous to formulate parenteral compositions in dosage unit form for ease of administration and 35 uniformity of dosage. Dosage unit form as used herein refers to physically discrete units suited as unitary dosages for the subjects to be treated; each unit contains a predetermined quantity of active compound calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. The specification for the dosage unit forms of the invention are dictated by and directly dependent on (a) the unique characteristics of the active 54 compound and the particular therapeutic effect to be achieved, and (b) the limitations inherent in the art of compounding such an active compound for the treatment of sensitivity in individuals. For administration of the antibody, the dosage ranges from about 0.0001 to 100 mg/kg, and more usually 0.01 to 5 mg/kg, of the host body weight. For example dosages can be 0.3 mg/kg body weight, 1 mg/kg body weight, 3 mg/kg body weight, 5 mg/kg body weight or 10 mg/kg body weight or within the range of 1-10 mg/kg. An exemplary treatment regime entails administration once per week, once every two weeks, once every three weeks, once every four weeks, once a month, once every 3 months or once every three to 6 months. tO Preferred dosage regimens for an anti-PD-I antibody of the invention include 1 mg/kg body weight or 3 mg/kg body weight via intravenous administration, with the antibody being given using one of the following dosing schedules: (i) every four weeks for six dosages, then every three months; (ii) every three weeks; (iii) 3 mg/kg body weight once followed by 1 mg/kg body weight every three weeks. S In some methods, two or more monoclonal antibodies with different binding specificities are administered simultaneously, in which case the dosage of each antibody administered falls within the ranges indicated. Antibody is usually administered on multiple occasions. Intervals between single dosages can be, for example, weekly, monthly, every three months or yearly. Intervals can also be irregular as indicated by measuring blood levels 20 of antibody to the target antigen in the patient. In some methods, dosage is adjusted to achieve a plasma antibody concentration of about 1-1000 pg /ml and in some methods about 25-300 g /ml. Alternatively, antibody can be administered as a sustained release formulation, in which case less frequent administration is required. Dosage and frequency vary depending is on the half-life of the antibody in the patient. In general, human antibodies show the longest half life, followed by humanized antibodies, chimeric antibodies, and nonhuman antibodies. The dosage and frequency of administration can vary depending on whether the treatment is prophylactic or therapeutic. In prophylactic applications, a relatively low dosage is administered at relatively infrequent intervals over a long period of time. Some patients 3) continue to receive treatment for the rest of their lives. In therapeutic applications, a relatively high dosage at relatively short intervals is sometimes required until progression of the disease is reduced or terminated, and preferably until the patient shows partial or complete amelioration of symptoms of disease. Thereafter, the patient can be administered a prophylactic regime. Actual dosage levels of the active ingredients in the pharmaceutical compositions of the present invention may be varied so as to obtain an amount of the active ingredient which is effective to achieve the desired therapeutic response for a particular patient, composition, and mode of administration, without being toxic to the patient. The selected dosage level will depend upon a variety of pharmacoldnetic factors including the activity of the particular 55 compositions of the present invention employed, or the ester, salt or aide thereof, the route of administration, the time of administration, the rate of excretion of the particular compound being employed, the duration of the treatment, other drugs, compounds and/or materials used in combination with the particular compositions employed, the age, sex, weight, condition, s general health and prior medical history of the patient being treated, and like factors well known in the medical arts. A "therapeutically effective dosage" of an anti-PD-1 antibody of the invention preferably results in a decrease in severity of disease symptoms, an increase in frequency and duration of disease symptom-free periods, or a prevention of impairment or disability due to to the disease affliction. For example, for the treatment of tumors, a "therapeutically effective dosage" preferably inhibits cell growth or tumor growth by at least about 20%, more preferably by at least about 40%, even more preferably by at least about 60%, and still more preferably by at least about 80% relative to untreated subjects. The ability of a compound to inhibit tumor growth can be evaluated in an animal model system predictive of efficacy in 1s human tumors. Alternatively, this property of a composition can be evaluated by examining the ability of the compound to inhibit, such inhibition in vitro by assays known to the skilled practitioner. A therapeutically effective amount of a therapeutic compound can decrease tumor size, or otherwise ameliorate symptoms in a subject. One of ordinary skill in the art would be able to determine such amounts based on such factors as the subject's size, 20 the severity of the subject's symptoms, and the particular composition or route of administration selected. In another aspect, the instant disclosure provides a pharmaceutical kit of parts comprising an anti-PD-1 antibody and an anti-CTLA-4 antibody, as described herein. The kit may also fiuther comprise instructions for use in the treatment of a hyperproliferative 'LS disease (such as cancer as described herein). In another embodiment, the anti-PD-1 and anti-CTLA-4 antibodies may be co-packaged in unit dosage form. In certain embodiments, two or more monoclonal antibodies with different binding specificities (e.g., anti-PD-1 and anti-CTLA-4) are administered simultaneously, in which case the dosage of each antibody administered falls within the ranges indicated. Antibody can be 30 administered as a single dose or more commonly can be administered on multiple occasions. Intervals between single dosages can be, for example, weekly, monthly, every three months or yearly. Intervals can also be irregular as indicated by measuring blood levels of antibody to the target antigen in the patient. In some methods, dosage is adjusted to achieve a plasma antibody concentration of about 1-1000 pg /ml and in some methods about 25-300 pg/ml. 3S A composition of the present invention can be administered via one or more routes of administration using one or more of a variety of methods known in the art. As will be appreciated by the skilled artisan, the route and/or mode of administration will vary depending upon the desired results. Preferred routes of administration for antibodies of the invention include intravenous, intramuscular, intradermal, intraperitoneal, subcutaneous, spinal or other 56 parenteral routes of administration, for example by injection or infusion. The phrase "parenteral administration" as used herein means modes of administration other than enteral and topical administration, usually by injection, and includes, without limitation, intravenous, intramuscular, intraarterial, intrathecal, intracapsular, intraorbital, intracardiac, intradermal, s intraperitoneal, transtracheal, subcutaneous, subcuticular, intraarticular, subcapsular, subarachnoid, intraspinal, epidural and intrasternal injection and infusion. Alternatively, an antibody of the invention can be administered via a non-parenteral route, such as a topical, epidermal or mucosal route of administration, for example, intranasally, orally, vaginally, rectally, sublingually or topically. 10 The active compounds can be prepared with carriers that will protect the compound against rapid release, such as a controlled release formulation, including implants, transdermal patches, and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Many methods for the preparation of such formulations S are patented or generally known to those skilled in the art. See, e.g., Sustained and Controlled Release Drug Delivery Systems, J.R. Robinson, ed., Marcel Dekker, Inc., New York, 1978. Therapeutic compositions can be administered with medical devices known in the art. For example, in a preferred embodiment, a therapeutic composition of the invention can be ?o administered with a needleless hypodermic injection device, such as the devices disclosed in U.S. Patent Nos. 5,399,163; 5,383,851; 5,312,335; 5,064,413; 4,941,880; 4,790,824; or 4,596,556. Examples of well-known implants and modules useful in the present invention include: U.S. Patent No. 4,487,603, which discloses an implantable micro-infusion pump for dispensing medication at a controlled rate; U.S. Patent No. 4,486,194, which discloses a 25 therapeutic device for administering medicants through the skin; U.S. Patent No. 4,447,233, which discloses a medication infusion pump for delivering medication at a precise infusion rate; U.S. Patent No. 4,447,224, which discloses a variable flow implantable infusion apparatus for continuous drug delivery; U.S. Patent No. 4,439,196, which discloses an osmotic drug delivery system having multi-chamber compartments; and U.S. Patent No. 4,475,196, 320 which discloses an osmotic drug delivery system. These patents are incorporated herein by reference. Many other such implants, delivery systems, and modules are known to those skilled in the art. In certain embodiments, the human monoclonal antibodies of the invention can be formulated to ensure proper distribution in vivo. For example, the blood-brain barrier (BBB) 3S excludes many highly hydrophilic compounds. To ensure that the therapeutic compounds of the invention cross the BBB (if desired), they can be formulated, for example, in liposomes. For methods of manufacturing liposomes, see, e.g., U.S. Patents 4,522,811; 5,374,548; and 5,399,331. The liposomes may comprise one or more moieties which are selectively transported into specific cells or organs, thus enhance targeted drug delivery (see, e.g., V.V. 57 Ranade (1989) J Clin. Pharmacol. 22:685). Exemplary targeting moieties include folate or biotin (see, e.g., U.S. Patent 5,416,016 to Low et al.); mannosides (Umezawa et al., (1988) Biochem. Biophys. Res. Commun. 15_3:1038); antibodies (P.G. Bloeman et al. (1995) FEBS Lett. 357:140; M. Owais etal. (1995) Antimicrob. Agents Chemother. 3_2:180); surfactant 5 protein A receptor (Briscoe et al. (1995) Am. J. Physiol. 1233:134); p 12 0 (Schreier et al. (1994) J Biol. Chem. 269:9090); see also K. Keinanen; M.L. Laukkanen (1994) FEBSLett. 346:123; J.J. Killion; I.J. Fidler (1994) Immunomethods 4:273. Uses and Methods of the Invention The antibodies, antibody compositions and methods of the present invention have I o numerous in vitro and in vivo utilities involving, for example, detection of PD-I or enhancement of immune response by blockade of PD-1. In a preferred embodiment, the antibodies of the present invention are human antibodies. For example, these molecules can be administered to cells in culture, in vitro or ex vivo, or to human subjects, e.g., in vivo, to enhance immunity in a variety of situations. Accordingly, in one aspect, the invention ts provides a method of modifying an immune response in a subject comprising administering to the subject the antibody, or antigen-binding portion thereof, of the invention such that the immune response in the subject is modified. Preferably, the response is enhanced, stimulated or up-regulated. As used herein, the term "subject" is intended to include human and non-human 20 animals. Non-human animals includes all vertebrates, e.g., mammals and non-mammals, such as non-human primates, sheep, dogs, cats, cows, horses, chickens, amphibians, and reptiles, although mammals are preferred, such as non-human primates, sheep, dogs, cats, cows and horses. Preferred subjects include human patients in need of enhancement of an immune response. The methods are particularly suitable for treating human patients having a 2 disorder that can be treated by augmenting the T-cell mediated immune response. In a particular embodiment, the methods are particularly suitable for treatment of cancer cells in vivo. To achieve antigen-specific enhancement of immunity, the anti-PD-1 antibodies can be administered together with an antigen of interest. When antibodies to PD-i are administered together with another agent, the two can be administered in either order or simultaneously. The invention further provides methods for detecting the presence of human PD-I antigen in a sample, or measuring the amount of human PD-1 antigen, comprising contacting the sample, and a control sample, with a human monoclonal antibody, or an antigen-binding portion thereof, which specifically binds to human PD-1, under conditions that allow for formation of a complex between the antibody or portion thereof and human PD-1. The &s formation of a complex is then detected, wherein a difference complex formation between the sample compared to the control sample is indicative the presence of human PD-I antigen in the sample. Given the specific binding of the antibodies of the invention for PD-1, compared to CD28, ICOS and CTLA-4, the antibodies of the invention can be used to specifically detect 58 PD-I expression on the surface of cells and, moreover, can be used to purify PD-I via immunoaffinity purification. Cancer Blockade of PD-1 by antibodies can enhance the immune response to cancerous cells S in the patient. The ligand for PD-1, PD-Li, is not expressed in normal human cells, but is abundant in a variety of human cancers (Dong et al. (2002) Nat Med 8:787-9). The interaction between PD-I and PD-LI results in a decrease in tumor infiltrating lymphocytes, a decrease in T-cell receptor mediated proliferation, and immune evasion by the cancerous cells (Dong et al. (2003) JMolMed 8i:281-7; Blank et al. (2005) Cancer Immunol. Immunother. to 54:307-314; Konishi et al. (2004) Clin. Cancer Res. 10:5094-100). Immune suppression can be reversed by inhibiting the local interaction of PD-1 to PD-L1 and the effect is additive when the interaction of PD-1 to PD-L2 is blocked as well (Iwai et al. (2002) PNAS 29:12293 7; Brown'et al. (2003) J. Immunol. 170:1257-66). While previous studies have shown that T cell proliferation can be restored by inhibiting the interaction of PD-I to PD-Li, there have '5 been no reports of a direct effect on cancer tumor growth in vivo by blocking the PD-1I/PD-LI interaction. In one aspect, the present invention relates to treatment of a subject in vivo using an anti-PD-1 antibody such that growth of cancerous tumors is inhibited. An anti-PD-1 antibody may be used alone to inhibit the growth of cancerous tumors. Alternatively, an anti PD-I antibody may be used in conjunction with other immunogenic agents, standard cancer ZO treatments, or other antibodies, as described below. Accordingly, in one embodiment, the invention provides a method of inhibiting growth of tumor cells in a subject, comprising administering to the subject a therapeutically effective amount of an anti-PD-1 antibody, or antigen-binding portion thereof. Preferably, the antibody is a human anti-PD-I antibody (such as any of the human anti-human PD-I 25 antibodies described herein). Additionally or alternatively, the antibody may be a chimeric or humanized anti-PD-I antibody. Preferred cancers whose growth may be inhibited using the antibodies of the invention include cancers typically responsive to immunotherapy. Non-limiting examples of preferred cancers for treatment include melanoma (e.g., metastatic malignant melanoma), renal cancer 30 (e.g. clear cell carcinoma), prostate cancer (e.g. hormone refractory prostate adenocarcinoma), breast cancer, colon cancer and lung cancer (e.g. non-small cell lung cancer). Additionally, the invention includes refractory or recurrent malignancies whose growth may be inhibited using the antibodies of the invention. Examples of other cancers that may be treated using the methods of the invention 35 include bone cancer, pancreatic cancer, skin cancer, cancer of the head or neck, cutaneous or intraocular malignant melanoma, uterine cancer, ovarian cancer, rectal cancer, cancer of the anal region, stomach cancer, testicular cancer, uterine cancer, carcinoma of the fallopian tubes, carcinoma of the endometrium, carcinoma of the cervix, carcinoma of the vagina, carcinoma of the vulva, Hodgkin's Disease, non-Hodgkin's lymphoma, cancer of the esophagus, cancer of 59 the small intestine, cancer of the endocrine system, cancer of the thyroid gland, cancer of the parathyroid gland, cancer of the adrenal gland, sarcoma of soft tissue, cancer of the urethra, cancer of the penis, chronic or acute leukemias including acute myeloid leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, solid tumors 5 of childhood, lymphocytic lymphoma, cancer of the bladder, cancer of the kidney or ureter, carcinoma of the renal pelvis, neoplasm of the central nervous system (CNS), primary CNS lymphoma, tumor angiogenesis, spinal axis tumor, brain stem glioma, pituitary adenoma, Kaposi's sarcoma, epidermoid cancer, squamous cell cancer, T-cell lymphoma, environmentally induced cancers including those induced by asbestos, and combinations of k said cancers. The present invention is also useful for treatment of metastatic cancers, especially metastatic cancers that express PD-Li (Iwai et al. (2005) Int. Immunol. 17:133-144). Optionally, antibodies to PD-1 can be combined with an immunogenic agent, such as cancerous cells, purified tumor antigens (including recombinant proteins, peptides, and carbohydrate molecules), cells, and cells transfected with genes encoding immune stimulating S cytokines (He et al (2004) J. Immunol. 173:4919-28). Non-limiting examples of tumor vaccines that can be used include peptides -of melanoma antigens, such as peptides of gp100, MAGE antigens, Trp-2, MART 1 and/or tyrosinase, or tumor cells transfected to express the cytokine GM-CSF (discussed further below). In humans, some tumors have been shown to be immunogenic such as melanomas. It is 2 0 anticipated that by raising the threshold of T cell activation by PD-i blockade, we may expect to activate tumor responses in the host. PD-I blockade is likely to be most effective when combined with a vaccination protocol. Many experimental strategies for vaccination against tumors have been devised (see Rosenberg, S., 2000, Development of Cancer Vaccines, ASCO Educational Book Spring: 60 25 62; Logothetis, C., 2000, ASCO Educational Book Spring: 300-302; Khayat, D. 2000, ASCO Educational Book Spring: 414-428; Foon, K. 2000, ASCO Educational Book Spring: 730-738; see also Restifo, N. and Sznol, M., Cancer Vaccines, Ch. 61, pp. 3023-3043 in DeVita, V. et aL (eds.), 1997, Cancer: Principles and Practice of Oncology. Fifth Edition). In one of these strategies, a vaccine is prepared using autologous or allogeneic tumor cells. These cellular 30 Yaccines have been shown to be most effective when the tumor cells are transduced to express GM-CSF. GM-CSF has been shown to be a potent activator of antigen presentation for tumor vaccination (Dranoff et al. (1993) Proc. Natl. Acad Sci USA. 90: 3539-43). The study of gene expression and large scale gene expression patterns in various tumors has led to the definition of so called tumor specific antigens (Rosenberg, SA (1999) ?8 Immunity 10: 281-7). In many cases, these tumor specific antigens are differentiation antigens expressed in the tumors and in the cell from which the tumor arose, for example melanocyte antigens gp100, MAGE antigens, and Trp-2. More importantly, many of these antigens can be shown to be the targets of tumor specific T cells found in the host. PD-1 blockade may be used in conjunction with a collection of recombinant proteins and/or peptides 60 expressed in a tumor in order to generate an immune response to these proteins. These proteins are normally viewed by the immune system as self antigens and are therefore tolerant to them. The tumor antigen may also include the protein telomerase, which is required for the synthesis of telomeres of chromosomes and which is expressed in more than 85% of human cancers and in only a limited number of somatic tissues (Kim, N et al. (1994) Science 266: 2011-2013). (These somatic tissues may be protected from immune attack by various means). Tumor antigen may also be "neo-antigens" expressed in cancer cells because of somatic mutations that alter protein sequence or create fusion proteins between two unrelated sequences (ie. bcr-abl in the Philadelphia chromosome), or idiotype from B cell tumors. (0 Other tumor vaccines may include the proteins from viruses implicated in human cancers such a Human Papilloma Viruses (HiPV), Hepatitis Viruses (HBV and HCV) and Kaposi's Herpes Sarcoma Virus (KHSV). Another form of tumor specific antigen which may be used in conjunction with PD-I blockade is purified heat shock proteins (HSP) isolated from the tumor tissue itself. These heat shock proteins contain fragments of proteins from the 5 tumor cells and these HSPs are highly efficient at delivery to antigen presenting cells for eliciting tumor immunity (Suot, R & Srivastava, P (1995) Science 269:1585-1588; Tamura, Y. et al. (1997) Science 278:117-120). Dendritic cells (DC) are potent antigen presenting cells that can be used to prime antigen-specific responses. DC's can be produced ex vivo and loaded with various protein 20 and peptide antigens as well as tumor cell extracts (Nestle, F. et al. (1998) Nature Medicine 4: 328-332). DCs may also be transduced by genetic means to express these tumor antigens as well. DCs have also been fused directly to tumor cells for the purposes of immunization (Kugler, A. et al. (2000) Nature Medicine 6:332-336). As a method of vaccination, DC immunization may be effectively combined with PD-1 blockade to activate more potent anti S tumor responses. PD-1 blockade may also be combined with standard cancer treatments. PD-1 blockade may be effectively combined with chemotherapeutic regimes. In these instances, it may be possible to reduce the dose of chemotherapeutic reagent administered (Mokyr, M. et al. (1998) Cancer Research 58: 5301-5304). An example of such a combination is an anti-PD-1 antibody in combination with decarbazine for the treatment of melanoma. Another example of such a combination is an anti-PD-1 antibody in combination with interleukin-2 (IL-2) for the treatment of melanoma. The scientific rationale behind the combined use of PD-1 blockade and chemotherapy is that cell death, that is a consequence of the cytotoxic action of most chemotherapeutic compounds, should result in increased levels of tumor antigen in the 35 antigen presentation pathway. Other combination therapies that may result in synergy with PD-1 blockade through cell death are radiation, surgery, and hormone deprivation. Each of these protocols creates a source of tumor antigen in the host. Angiogenesis inhibitors may also be combined with PD-1 blockade. Inhibition of angiogenesis leads to tumor cell death which may feed tumor antigen into host antigen presentation pathways. 61 PD-1 blocking antibodies can also be used in combination with bispecific antibodies that target Fc alpha or Fc gamma receptor-expressing effectors cells to tumor cells (see, e.g., U.S. Pat. Nos. 5,922,845 and 5,837,243). Bispecific antibodies can be used to target two separate antigens. For example anti-Fc receptor/anti tumor antigen (e.g., Her-2/neu) S bispecific antibodies have been used to target macrophages to sites of tumor. This targeting may more effectively activate tumor specific responses. The T cell arm of these responses would by augmented by the use of PD-I blockade. Alternatively, antigen may be delivered directly to DCs by the use of bispecific antibodies which bind to tumor antigen and a dendritic cell specific cell surface marker. 1Co Tumors evade host immune surveillance by a large variety of mechanisms. Many of these mechanisms may be overcome by the inactivation of proteins which are expressed by the tumors and which are immunosuppressive. These include among others TGF-beta (Kehrl, J. et al. (1986)J. Exp. Med. 163: 1037-1050), IL-10 (Howard, M. & O'Garra, A. (1992) Immunology Today 13: 198-200), and Fas ligand (Hahne, M. et al. (1996) Science 274: 1363 is 1365). Antibodies to each of these entities may be used in combination with anti-PD-1 to counteract the effects of the immunosuppressive agent and favor tumor immune responses by the host. Other antibodies which may be used to activate host immune responsiveness can be used in combination with anti-PD-1. These include molecules on the surface of dendritic 20 cells which activate DC function and antigen presentation. Anti-CD40 antibodies are able to substitute effectively for T cell helper activity (Ridge, J. et al. (1998) Nature 393: 474-478) and can be used in conjuction with PD-I antibodies (Ito, N. et al. (2000) Immunobiology 201 (5) 527-40). Activating antibodies to T cell costimulatory molecules such as CTLA-4 (e.g., US Patent No. 5,811,097), OX-40 (Weinberg, A. et al. (2000) Immunol 16A: 2160-2169), 4 25 IBB (Melero, I. et al. (1997) Nature Medicine 3: 682-685 (1997), and ICOS (Hutloff, A. et al. (1999) Nature 397: 262-266) may also provide for increased levels of T cell activation. Bone marrow transplantation is currently being used to treat a variety of tumors of hematopoietic origin. While graft versus host disease is a consequence of this treatment, therapeutic benefit may be obtained from graft vs. tumor responses. PD-1 blockade can be 30o used to increase the effectiveness of the donor engrafted tumor specific T cells. There are also several experimental treatment protocols that involve ex vivo activation and expansion of antigen specific T cells and adoptive transfer of these cells into recipients in order to antigen-specific T cells against tumor (Greenberg, R. & Riddell, S. (1999) Science 285: 546-51). These methods may also be used to activate T cell responses to infectious is agents such as CMV. Ex vivo activation in the presence of anti-PD-1 antibodies may be expected to increase the frequency and activity of the adoptively transferred T cells. Infectious Diseases Other methods of the invention are used to treat patients that have been exposed to particular toxins or pathogens. Accordingly, another aspect of the invention provides a 62 method of treating an infectious disease in a subject comprising administering to the subject an anti-PD-1 antibody, or antigen-binding portion thereof; such that the subject is treated for the infectious disease. Preferably, the antibody is a human anti-human PD-I antibody (such as any of the human anti-PD-I antibodies described herein). Additionally or alternatively, the 5 antibody can be a chimeric or humanized antibody. Similar to its application to tumors as discussed above, antibody mediated PD-1 blockade can be used alone, or as an adjuvant, in combination with vaccines, to stimulate the immune response to pathogens, toxins, and self-antigens. Examples of pathogens for which this therapeutic approach may be particularly useful, include pathogens for which there is I C currently no effective vaccine, or pathogens for which conventional vaccines are less than completely effective. These include, but are not limited to HIV, Hepatitis (A, B, & C), Influenza, Herpes, Giardia, Malaria, Leishmania, Staphylococcus aureus, Pseudomonas Aeruginosa. PD-1 blockade is particularly useful against established infections by agents such as HIV that present altered antigens over the course of the infections. These novel epitopes s are recognized as foreign at the time of anti-human PD-I administration, thus provoking a strong T cell response that is not dampened by negative signals through PD-1. Some examples of pathogenic viruses causing infections treatable by methods of the invention include HIV, hepatitis (A, B, or C), herpes virus (e.g., VZV, HSV-1, HAV-6, HSV II, and CMV, Epstein Barr virus), adenovirus, influenza virus, flaviviruses, echovirus, rhinovirus, coxsackie virus, cornovirus, respiratory syncytial virus, mumps virus, rotavirus, measles virus, rubella virus, parvovirus, vaccinia virus, HTLV virus, dengue virus, papillomavirus, molluscum virus, poliovirus, rabies virus, JC virus and arboviral encephalitis virus. Some examples of pathogenic bacteria causing infections treatable by methods of the 2 5 invention include chlamydia, rickettsial bacteria, mycobacteria, staphylococci, streptococci, pneumonococci, meningococci and conococci, klebsiella, proteus, serratia, pseudomonas, legionella, diphtheria, salmonella, bacilli, cholera, tetanus, botulism, anthrax, plague, leptospirosis, and Lymes disease bacteria. Some examples of pathogenic fungi causing infections treatable by methods of the 3o invention include Candida (albicans, krusei, glabrata, tropicalis, etc.), Cryptococcus neoformans, Aspergillus fumigatuss, niger, etc.), Genus Mucorales (mucor, absidia, rhizophus), Sporothrix schenkii, Blastomyces dermatitidis, Paracoccidioides brasiliensis, Coccidioides immitis and Histoplasma capsulatum. Some examples of pathogenic parasites causing infections treatable by methods of the invention include Entamoeba histolytica, Balantidium col, Naegleriafowleri, Acanthamoeba sp., Giardia lambia, Cryptosporidium sp., Pneumocystis carinii, Plasmodium vivax, Babesia microti, Trypanosoma brucei, Trypanosoma cruzi, Leishmania donovani, Toxoplasma gondi, and Nippostrongylus brasiliensis. 63 In all of the above methods, PD-I blockade can be combined with other forms of immunotherapy such as cytokine treatment (e.g., interferons, GM-CSF, G-CSF, IL-2), or bispecific antibody therapy, which provides for enhanced presentation of tumor antigens (see, e.g., Holliger (1993) Proc. Natl. Acad Sci. USA 90:6444-6448; PoIjak (1994) Structure S 2:1121-1123). Autoimmune reactions Anti-PD-i antibodies may provoke and amplify autoimmune responses. Indeed, induction of anti-tumor responses using tumor cell and peptide vaccines reveals that many anti-tumor responses involve anti-self reactivities (depigmentation observed in anti-CTLA-4 + 00 GM-CSF-modified B16 melanoma in van Elsas et al. supra; depigmentation in Trp-2 vaccinated mice (Overwijk, W. et al. (1999) Proc. Natl. Acad Sci. U.S.A. 96: 2982-2987); autoimmune prostatitis evoked by TRAMP tumor cell vaccines (Hurwitz, A. (2000) supra), melanoma peptide antigen vaccination and vitilago observed in human clinical trials (Rosenberg, SA and White, DE (1996) J Immunother Emphasis Tumor Immunol 19 (1): 81-4). s . Therefore, it is possible to consider using anti-PD-1 blockade in conjunction with various self proteins in order to devise vaccination protocols to efficiently generate immune responses against these self proteins for disease treatment. For example, Alzheimers disease involves inappropriate accumulation of As3 peptide in amyloid deposits in the brain; antibody responses against amyloid are able to clear these amyloid deposits (Schenk et al., (1999) 2O Nature 400: 173-177). Other self proteins may also be used as targets such as IgE for the treatment of allergy and asthma, and TNFa for rhematoid arthritis. Finally, antibody responses to various hormones may be induced by the use of anti-PD-I antibody. Neutralizing antibody responses to reproductive hormones may be used for contraception. Neutralizing antibody response to 25 hormones and other soluble factors that are required for the growth of particular tumors may also be considered as possible vaccination targets. Analogous methods as described above for the use of anti-PD-1 antibody can be used for induction of therapeutic autoimmune responses to treat patients having an inappropriate accumulation of other self-antigens, such as amyloid deposits, including As in Alzheimer's 3, disease, cytokines such as TNFoc, and IgE. Vaccines Anti-PD-1 antibodies may be used to stimulate antigen-specific immune responses by coadministration of an anti-PD-1 antibody with an antigen of interest (e.g., a vaccine). Accordingly, in another aspect the invention provides a method of enhancing an immune 30 response to an antigen in a subject, comprising administering to the subject: (i) the antigen; and (ii) an anti-PD-I antibody, or antigen-binding portion thereof, such that an immune response to the antigen in the subject is enhanced. Preferably, the antibody is a human anti human PD-I antibody (such as any of the human anti-PD-I antibodies described herein). Additionally or alternatively, the antibody can be a chimeric or humanized antibody. The 64 antigen can be, for example, a tumor antigen, a viral antigen, a bacterial antigen or an antigen from a pathogen. Non-limiting examples of such antigens include those discussed in the sections above, such as the tumor antigens (or tumor vaccines) discussed above, or antigens from the viruses, bacteria or other pathogens described above. Suitable routes of administering the antibody compositions (e.g., human monoclonal antibodies, multispecific and bispecific molecules and immunoconjugates ) of the invention in vivo and in vitro are well known in the art and can be selected by those of ordinary skill. For example, the antibody compositions can be administered by injection (e.g., intravenous or subcutaneous). Suitable dosages of the molecules used will depend on the age and weight of the subject and the concentration and/or formulation of the antibody composition. As previously described, human anti-PD-1 antibodies of the invention can be co administered with one or other more therapeutic agents, e.g., a cytotoxic agent, a radiotoxic agent or an immunosuppressive agent. The antibody can be linked to the agent (as an immunocomplex) or.can be administered separate from the agent. In the latter case (separate &5 administration), the antibody can be administered before, after or concurrently with the agent or can be co-administered with other known therapies, e.g., an anti-cancer therapy, e.g., radiation. Such therapeutic agents include, among others, anti-neoplastic agents such as doxorubicin (adriamycin), cisplatin bleomycin sulfate, carmustine, chlorambucil, decarbazine and cyclophosphamide hydroxyurea which, by themselves, are only effective at levels which 2,0 are toxic or subtoxic to a patient. Cisplatin is intravenously administered as a 100 mg/dose once every four weeks and adriamycin is intravenously administered as a 60-75 mg/ml dose once every 21 days. Co-administration of the human anti-PD-I antibodies, or antigen binding fragments thereof, of the present invention with chemotherapeutic agents provides two anti-cancer agents which operate via different mechanisms which yield a cytotoxic effect to 2 5 human tumor cells. Such co-administration can solve problems due to development of resistance to drugs or a change in the antigenicity of the tumor cells which would render them unreactive with the antibody. Also within the scope of the present invention are kits comprising the antibody compositions of the invention (e.g., human antibodies, bispecific or multispecific molecules, 30 or immunoconjugates) and instructions for use. The kit can further contain a least one additional reagent, or one or more additional human antibodies of the invention (e.g., a human antibody having a -complementary activity which binds to an epitope in PD-I antigen distinct from the first human antibody). Kits typically include a label indicating the intended use of the contents of the kit. The term label includes any writing, or recorded material supplied on or 'S with the kit, or which otherwise accompanies the kit. Combination therapy The present invention is based, in part, on the following experimental data. Mouse tumor models (MC38 colon cancer and SA1/N fibrosarcoma) were used to examine the in vivo effect of treating a tumor by combining immunostimulatory therapeutic antibodies 65 anti-CTLA-4 and anti-PD-1. The immunotherapeutic combination was provided either simultaneous with the implant of tumor cells (Examples 14 and 17) or after the tumor cells were implanted for a time sufficient to become an established tumor (Examples 15, 16 and 18). Regardless of the timing of antibody treatment, it was found that anti-CTLA-4 antibody S treatment alone and anti-PD-I antibody (chimeric antibody in which a rat anti-mouse PD-I was modified with a mouse immunoglobulin Fc region, see Example 1) treatment alone had a modest effect on reducing tumor growth in the MC38 tumor model (see, e.g., Figures 21, 24 and 27). The anti-CTLA-4 antibody alone was quite effective in the SAl/N tumor model (see Figure 30D), which required a lower anti-CTLA-4 antibody dose for the combination 1 o studies in this model. Nonetheless, the combination treatment of anti-CTLA-4 antibody and anti-PD-1 antibody showed an unexpected, significantly greater effect on reducing tumor growth as compared to treatment with either antibody alone (see, e.g., Figures 21D, 24D, 30F and 33H-J). In addition, the results of Examples 14, 16 and 18 show that the combination treatment of anti-CTLA-4 antibody and anti-PD-1 antibody had a significant (synergistic) IS effect on tumor growth even at sub-optimal therapeutic doses as compared to treatment with either antibody alone (i.e., the combination therapy was surprisingly more effective at subtherapeutic doses than either monotherapy). Without wishing to be bound by theory, it is possible that by raising the threshold of T cell activation by PD-1 and CTLA-4 blockade, anti tumor responses may be activated in a host. 20 In one embodiment, the present invention provides a method for treating a hyperproliferative disease, comprising administering a PD-I antibody and a CTLA-4 antibody to a subject. In further embodiments, the anti-PD-1 antibody is administered at a subtherapeutic dose, the anti-CTLA-4 antibody is administered at a subtherapeutic dose, or both are administered at a subtherapeutic dose. In another embodiment, the present invention ?5 provides a method for altering an adverse event associated with treatment of a hyperproliferative disease with an immunostimulatory agent, comprising administering an anti-PD-1 antibody and a subtherapeutic dose of anti-CTLA-4 antibody to a subject. In certain embodiments, the subject is human. In certain embodiments, the anti-CTLA-4 antibody is human sequence monoclonal antibody 10DI and the anti-PD-1 antibody is human 30 sequence monoclonal antibody, such as 17D8, 2D3, 4H1, 5C4 and 4AI 1. Human sequence monoclonal antibodies 17D8, 2D3, 4Hi, 5C4 and 4A1 1 havebeen isolated and structurally characterized, as described in U.S. Provisional Patent No. 60/679,466. The anti-CTLA-4 antibody and anti-PD-1 monoclonal antibodies (mAbs) and the human sequence antibodies of the invention can be produced. by a variety of techniques, 3Ss including conventional monoclonal antibody methodology, e.g., the standard somatic cell hybridization technique of Kohler and Milstein (1975)Nature 256:495. Any technique for producing monoclonal antibody can be employed, e.g., viral or oncogenic transformation of B lymphocytes. One animal system for preparing hybridomas is the murine system. Hybridoma production in the mouse is a very well-established procedure. Immunization 66 protocols and techniques for isolation of immunized splenocytes for fusion are known in the art. Fusion partners (e.g., murine myeloma cells) and fusion procedures are also known (see, e.g., Harlow and Lane (1988) Antibodies, A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor New York). s Anti-CTLA-4 antibodies of the instant invention can bind to an epitope on human CTLA-4 so as to inhibit CTLA-4 from interacting with a human B7 counterreceptor. Because interaction of human CTLA-4 with human B7 transduces a signal leading to inactivation of T-cells bearing the human CTLA-4 receptor, antagonism of the interaction effectively induces, augments or prolongs the activation of T cells bearing the human CTLA-4 t C receptor, thereby prolonging or augmenting an immune response. Anti-CTLA-4 antibodies are described in U.S. Patent Nos. 5,811,097; 5,855,887; 6,051,227; in PCT Application Publication Nos. WO 01/14424 and WO 00/37504; and in U.S. Patent Publication No. 2002/0039581. Each of these references is specifically incorporated herein by reference for purposes of description of anti-CTLA-4 antibodies. An exemplary clinical anti-CTLA-4 1s antibody is human monoclonal antibody 10DI as disclosed in WO 01/14424 and U.S. Patent Application No. 09/644,668. Antibody 10DI has been administered in single and multiple doses, alone or in combination with a vaccine, chemotherapy, or interleukin-2 to more than 500 patients diagnosed with metastatic melanoma, prostate cancer, lymphoma, renal cell cancer, breast cancer, ovarian cancer, and HIV. Other anti-CTLA-4 antibodies encompassed t0 by the methods of the present invention include, for example, those disclosed in: WO 98/42752; WO 00/37504; U.S. Patent No. 6,207,156; Hurwitz et al. (1998) Proc. Nat. Acad Sci. USA 95(17):10067-10071; Camacho et al. (2004) J. Clin. Oncology 22(145): Abstract No. 2505 (antibody CP-675206); and Mokyr et al. (1998) Cancer Res. 58:5301-5304. In certain embodiments, the methods of the instant invention comprise use of an anti-CTLA-4 antibody -S that is a human sequence antibody, preferably a monoclonal antibody and in another embodiment is monoclonal antibody 1ODI. In certain embodiments, the anti-CTLA-4 antibody binds to human CTLA-4 with a KD of 5 x 10~8 M or less, binds to human CTLA-4 with a KD of 1 x 10-8 M or less, binds to human CTLA-4 with a KD of 5 x 10-9 M or less, or binds to human CTLA-4 with a KD of between 1 x 30 10-'M and 1 x 10* M or less. The combination of antibodies is useful for enhancement of an immune response against a hyperproliferative disease by blockade of PD-i and CTLA-4. In a preferred embodiment, the antibodies of the present invention are human antibodies. For example, these molecules can be administered to cells in culture, in vtro or ex vivo, or to human SS subjects, e.g., in vivo, to enhance immunity in a variety of situations. Accordingly, in one aspect, the invention provides a method of modifying an immune response in a subject comprising administering to the subject an antibody combination, or a combination of antigen binding portions thereof, of the invention such that the immune response in the subject is modified. Preferably, the response is enhanced, stimulated or up-regulated. In another 67 embodiment, the instant disclosure provides a method of altering adverse events associated with treatment of a hyperproliferative disease with an immunostimulatory therapeutic agent, comprising administering an anti-PD-1 antibody and a subtherapeutic dose of ariti-CTLA-4 antibody to a subject. Blockade of PD-1 and CTLA-4 by antibodies can enhance the immune response to cancerous cells in the patient. Cancers whose growth may be inhibited using the antibodies of the instant disclosure include cancers typically responsive to immunotherapy. Representative examples of cancers for treatment with the combination therapy of the instant disclosure include melanoma (e.g., metastatic malignant melanoma), renal cancer, prostate o cancer, breast cancer, colon cancer and lung cancer. Examples of other cancers that may be treated using the methods of the instant disclosure include bone cancer, pancreatic cancer, skin cancer, cancer of the head or neck, cutaneous or intraocular malignant melanoma, uterine cancer, ovarian cancer, rectal cancer, cancer of the anal region, stomach cancer, testicular cancer, uterine cancer, carcinoma of the fallopian tubes, carcinoma of the endometrium, t carcinoma of the cervix, carcinoma of the vagina, carcinoma of the vulva, Hodgkin's Disease, non-Hodgkin's lymphoma, cancer of the esophagus, cancer of the small intestine, cancer of the endocrine system, cancer of the thyroid gland, cancer of the parathyroid gland, cancer of the adrenal gland, sarcoma of soft tissue, cancer of the urethra, cancer of the penis, chronic or acute leukemias including acute myeloid leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, solid tumors of childhood, lymphocytic lymphoma, cancer of the bladder, cancer of the kidney or ureter, carcinoma of the renal pelvis, neoplasm of the central nervous system (CNS), primary CNS lymphoma, tumor angiogenesis, spinal axis tumor, brain stem glioma, pituitary adenoma, Kaposi's sarcoma, epidermoid cancer, squamous cell cancer, T-cell lymphoma, environmentally induced cancers 2-S including those induced by asbestos, and combinations of said cancers. The present invention is also useful for treatment of metastatic cancers. In certain embodiments, the combination of therapeutic antibodies discussed herein may be administered concurrently as a single composition in a pharmaceutically acceptable carrier, or concurrently as separate compositions with each antibody in a pharmaceutically 30 acceptable carrier. In another embodiment, the combination of therapeutic antibodies can be administered sequentially. For example, an anti-CTLA-4 antibody and an anti-PD-1 antibody can be administered sequentially, such as anti-CTLA-4 being administered first and anti-PD-1 second, or anti-PD-1 being administered first and anti-CTLA-4 second. Furthermore, if more than one dose of the combination therapy is administered sequentially, . 5 the order of the sequential administration can be reversed or kept in the same order at each time point of administration, sequential administrations may be combined with concurrent administrations, or any combination thereof. For example, the first administration of a combination anti-CTLA-4 antibody and anti-PD-1 antibody may be concurrent, the second administration may be sequential with anti-CTLA-4 first and anti-PD-1 second, and the third 68 administration may be sequential with anti-PD-i first and anti-CTLA-4 second, etc. Another representative dosing scheme may involve a first administration that is sequential with anti PD-1 first and anti-CTLA-4 second, and subsequent administrations may be concurrent. Optionally, the combination of anti-PD-1 and anti-CTLA-4 antibodies can be further S combined with an immunogenic agent, such as cancerous cells, purified tumor antigens (including recombinant proteins, peptides, and carbohydrate molecules), cells, and cells transfected with genes encoding immune stimulating cytokines (He et al. (2004) J. Immunol. 173:4919-28). Non-limiting examples of tumor vaccines that can be used include peptides of melanoma antigens, such as peptides of gp100, MAGE antigens, Trp-2, MARTI and/or o tyrosinase, or tumor cells transfected to express the cytokine GM-CSF (discussed further below). A combined PD-1 and CTLA-4 blockade can be further combined with a vaccination protocol. Many experimental strategies for vaccination against tumors have been devised (see Rosenberg, S. (2000) Development of Cancer Vaccines, ASCO Educational Book Spring: IS 60-62; Logothetis, C., 2000, ASCO Educational Book Spring: 300-302; Khayat, D. (2000) ASCO Educational Book Spring: 414-428; Foon, K. (2000) ASCO Educational Book Spring: 730-738; see also Restifo and Sznol, Cancer Vaccines, Ch. 61, pp. 3023-3043 in DeVita et al. (eds.), 1997, Cancer: Principles and Practice of Oncology. Fifth Edition). In one of these strategies, a vaccine is prepared using autologous or allogeneic tumor cells. These cellular 2C vaccines have been shown to be most effective when the tumor cells are transduced to express GM-CSF. GM-CSF has been shown to be a potent activator of antigen presentation for tumor vaccination (Dranoff et al. (1993) Proc. Natl. Acad Sci US.A. 9Q: 3539-43). The study of gene expression and large scale gene expression patterns in various tumors has led to the definition of so called tumor specific antigens (Rosenberg (1999) 25 Immunity 10:281-7). In many cases, these tumor specific antigens are differentiation antigens expressed in the tumors and in the cell from which the tumor arose, for example melanocyte antigens gp100, MAGE antigens, and Trp-2. More importantly, many of these antigens can be shown to be the targets of tumor specific T cells found in the host. In certain embodiments, a combined PD-1 and CTLA-4 blockade using the antibody compositions 30 described herein may be used in conjunction with a collection of recombinant proteins and/or peptides expressed in a tumor in order to generate an immune response to these proteins. These proteins are normally viewed by the immune system as self-antigens and are, therefore, tolerant to them. The tumor antigen may also include the protein telomerase, which is required for the synthesis of telomeres of chromosomes and which is expressed in more than S 85% of human cancers and in only a limited number of somatic tissues (Kim et al. (1994) Science 266: 2011-2013). (These somatic tissues may be protected from immune attack by various means). Tumor antigen may also be "neo-antigens" expressed in cancer cells because of somatic mutations that alter protein sequence or create fusion proteins between two 69 unrelated sequences (i.e., bcr-abl in the Philadelphia chromosome), or idiotype from B cell tumors. Other tumor vaccines may include the proteins from viruses implicated in human cancers such a Human Papilloma Viruses (HPV), Hepatitis Viruses (HBV and HCV) and S Kaposi's Herpes Sarcoma Virus (KHSV). Another form of tumor specific antigen which may be used in conjunction with PD-I blockade is purified heat shock proteins (HSP) isolated from the tumor tissue itself These heat shock proteins contain fragments of proteins from the tumor cells and these HSPs are highly efficient at delivery to antigen presenting cells for eliciting tumor immunity (Suot & Srivastava (1995) Science 262:1585-1588; Tamura et al. '4 (1997) Science 278:117-120). Dendritic cells (DC) are potent antigen presenting cells that can be used to prime antigen-specific responses. DC's can be produced ex vivo and loaded with various protein and peptide antigens as well as tumor cell extracts (Nestle et al. (1998) Nature Medicine 4: 328-332). DCs may also be transduced by genetic means to express these tumor antigens as (5 well. DCs have also been fused directly to tumor cells for the purposes of immunization (Kugler et al. (2000) Nature Medicine 6:332-336). As a method of vaccination, DC immunization may be effectively further combined with a combined PD-I and CTLA-4 blockade to activate more potent anti-tumor responses. A combined PD-I and CTLA-4 blockade may also be further combined with standard 10 cancer treatments. For example, a combined PD-1 and CTLA-4 blockade may be effectively combined with chemotherapeutic regimes. In these instances, as is observed with the combination of anti-PD-1 and anti-CTLA-4 antibodies, it may be possible to reduce the dose of other chemotherapeutic reagent administered with the combination of the instant disclosure (Mokyr et al. (1998) Cancer Research 58: 5301-5304). An example of such a combination is 25 a combination of anti-PD-1 and anti-CTLA-4 antibodies further in combination with decarbazine for the treatment of melanoma. Another example is a combination of anti-PD-1 and anti-CTLA-4 antibodies further in combination with interleukin-2 (IL-2) for the treatment of melanoma. The scientific rationale behind the combined use ofPD-1 and CTLA-4 blockade with chemotherapy is that cell death, which is a consequence of the cytotoxic action ?> of most chemotherapeutic compounds, should result in increased levels of tumor antigen in the antigen presentation pathway. Other combination therapies that may result in synergy with a combined PD-1 and CTLA-4 blockade through cell death include radiation, surgery, or hormone deprivation. Each of these protocols creates a source of tumor antigen in the host. Angiogenesis inhibitors may also be combined with a combined PD-1 and CTLA-4 blockade. 5 Inhibition of angiogenesis leads to tumor cell death, which may also be a source of tumor antigen to be fed into host antigen presentation pathways. A combination of PD-1 and CTLA-4 blocking antibodies can also be used in combination with bispecific antibodies that target Fca or Fcy receptor-expressing effector cells to tumor cells (see, e.g., U.S. Pat. Nos. 5,922,845 and 5,837,243). Bispecific antibodies can 70 be used to target two separate antigens. For example anti-Fc receptor/anti tumor antigen (e.g., Her-2/neu) bispecific antibodies have been used to target macrophages to sites of tumor. This targeting may more effectively activate tumor specific responses. The T cell arm of these responses would by augmented by the use of a combined PD-1 and CTLA-4 blockade. 5 Alternatively, antigen may be delivered directly to DCs by the use of bispecific antibodies which bind to tumor antigen and a dendritic cell specific cell surface marker. In another example, a combination of anti-PD-I and anti-CTLA-4 antibodies can be used in conjunction with anti-neoplastic antibodies, such as Rituxan* (rituximab), Herceptin* (trastuzumab), Bexxar* (tositumomab), Zevalin* (ibritumomab), Campath* (alemtuzumab), 0 Lymphocide* (eprtuzumab), Avastin* (bevacizumab), and Tarceva* (erlotinib), and the like. By way of example and not wishing to be bound by theory, treatment with an anti-cancer antibody or an anti-cancer antibody conjugated to a toxin can lead to cancer cell death (e.g., tumor cells) which would potentiate an immune response mediated by CTLA-4 or PD-1. In an exemplary embodiment, a treatment of a hyperproliferative disease (e.g., a cancer tumor) 15 may include an anti-cancer antibody in combination with anti-PD-1 and anti-CTLA-4 antibodies, concurrently or sequentially or any combination thereof, which may potentiate an anti-tumor immune responses by the host. Tumors evade host immune surveillance by a large variety of mechanisms. Many of these mechanisms may be overcome by the inactivation of proteins, which are expressed by 20 the tumors and which are immunosuppressive. These include, among others, TGF-p (Kehrl, J. et al. (1986) J Exp. Med. 163: 1037-1050), IL-10 (Howard, M. & O'Garra, A. (1992) Immunology Today 13: 198-200), and Fas ligand (Hahne, M. et al. (1996) Science 274: 1363 1365). In another example, antibodies to each of these entities may be further combined with an anti-PD-1 and anti-CTLA-4 combination to counteract the effects of immunosuppressive 25 agents and favor anti-tumor immune responses by the host. Other antibodies that may be used to activate host immune responsiveness can be further used in combinationwith an anti-PD-1 and anti-CTLA-4 combination. These include molecules on the surface of dendritic cells that activate DC function and antigen presentation. Anti-CD40 antibodies are able to substitute effectively for T cell helper activity (Ridge, J. et al. 3o (1998) Nature 393: 474-478) and can be used in conjunction with an anti-PD-1 and anti-CTLA-4 combination (Ito, N. et al. (2000) Immunobiology 201 (5) 527-40). Activating antibodies to T cell costimulatory molecules, such as OX-40 (Weinberg, A. et al. (2000) Immunol 164: 2160-2169), 4-1BB (Melero, I. et al. (1997) Nature Medicine 3: 682-685 (1997), and ICOS (Hutlof, A. et al. (1999) Nature 392: 262-266) may also provide for increased 35 levels of T cell activation. Bone marrow transplantation is currently being used to treat a variety of tumors of hematopoietic origin. While graft versus host disease is a consequence of this treatment, therapeutic benefit may be obtained from graft vs. tumor responses. A combined PD-1 and 71 CTLA-4 blockade can be used to increase the effectiveness of the donor engrafted tumor specific T cells. There are also several experimental treatment Orotocols that involve ex vivo activation and expansion of antigen specific T cells and adoptive transfer of these cells into recipients in 5 order to antigen-specific T cells against tumor (Greenberg, R. & Riddell, S. (1999) Science 285: 546-51). These methods may also be used to activate T cell responses to infectious agents such as CMV. Ex vivo activation in the presence of anti-PD-1 and anti-CTLA-4 antibodies may be expected to increase the frequency and activity of the adoptively transferred T cells. iO As set forth herein, organs can exhibit immune-related adverse events following immunostimulatory therapeutic antibody therapy, such as the GI tract (diarrhea and colitis) and the skin (rash and pruritis) after treatment with anti-CTLA-4 antibody. For example, non-colonic gastrointestinal immune-related adverse events have also been observed in the esophagus (esophagitis), duodenum (duodenitis), and ileum (ileitis) after anti-CTLA-4 s antibody treatment. In certain embodiments, the present invention provides a method for altering an adverse event associated with treatment of a hyperproliferative disease with an immunostimulatory agent, comprising administering a anti-PD-1 antibody and a subtherapeutic dose of anti-CTLA-4 antibody to a subject. For example, the methods of the 2C present invention provide for a method of reducing the incidence of immunostimulatory therapeutic antibody-induced colitis or diarrhea by administering a non-absorbable steroid to the patient. Because any patient who will receive an immunostimulatory therapeutic antibody is at risk for developing colitis or diarrhea induced by such an antibody, this entire patient population is suitable for therapy according to the methods of the present invention. 25 Although steroids have been administered to treat inflammatory bowel disease (IBD) and prevent exacerbations of IBD, they have not been used to prevent (decrease the incidence of) IBD in patients who have not been diagnosed with IBD. The significant side effects associated with steroids, even non-absorbable steroids, have discouraged prophylactic use. In further embodiments, a combination PD-1 and CTLA-4 blockade (i.e., '1 immunostimulatory therapeutic antibodies anti-PD-1 and anti-CTLA-4) can be further combined with the use of any non-absorbable steroid. As used herein, a "non-absorbable steroid" is a glucocorticoid that exhibits extensive first pass metabolism such that, following metabolism in the liver, the bioavailability of the steroid is low, i.e., less than about 20%. In one embodiment of the invention, the non-absorbable steroid is budesonide. Budesonide is a T3 locally-acting glucocorticosteroid, which is extensively metabolized, primarily by the liver, following oral administration. ENTOCORT EC* (Astra-Zeneca) is a pH- and time dependent oral formulation of budesonide developed to optimize drug delivery to the ileum and throughout the colon. ENTOCORT EC* is approved in the U.S. for the treatment of mild to moderate Crohn's disease involving the ileum and/or ascending colon. The usual oral 72 dosage of ENTOCORT EC* for the treatment of Crohn's disease is 6 to 9 mg/day. ENTOCORT EC* is released in the intestines before being absorbed and retained in the gut mucosa. Once it passes through the gut mucosa target tissue, ENTOCORT EC* is extensively metabolized by the cytochrome P450 system in the liver to metabolites with S negligible glucocorticoid activity. Therefore, the bioavailability is low (about 10%). The low bioavailability of budesonide results in an improved therapeutic ratio compared to other glucocorticoids with less extensive first-pass metabolism. Budesonide results in fewer adverse effects, including less hypothalamic-pituitary suppression, than systemically-acting corticosteroids. However, chronic administration of ENTOCORT EC* can result in systemic 0 glucocorticoid effects such as hypercorticism and adrenal suppression. See PDR 58P ed. 2004; 608-610. In still further embodiments, a combination PD-1 and CTLA-4 blockade (i.e., imnimunostimulatory therapeutic antibodies anti-PD-I and anti-CTLA-4) in conjunction with a non-absorbable steroid can be further combined with a salicylate. Salicylates include 5-ASA 'S agents such as, for example: sulfasalazine (AZULFIDINE*, Pharmacia & UpJohn); olsalazine (DIPENTUM*, Pharmacia & UpJohn); balsalazide (COLAZAL*, Salix Pharmaceuticals, Inc.); and mesalamine (ASACOL*, Procter & Gamble Pharmaceuticals; PENTASA*, Shire US; CANASA*, Axcan Scandipharm, Inc.; ROWASA*, Solvay). In accordance with the methods of the present invention, a salicylate administered in ,o combination with anti-PD-1 and anti-CTLA-4 antibodies and a non-absorbable steroid can .includes any overlapping or sequential administration of the salicylate and the non-absorbable steroid for the purpose of decreasing the incidence of colitis induced by the immunostimulatory antibodies. Thus, for example, methods for reducing the incidence of colitis induced by the immunostimulatory antibodies according to the present invention ? s encompass administering a salicylate and a non-absorbable concurrently or sequentially (e.g., a salicylate is administered 6 hours after a non-absorbable steroid), or any combination thereof. Further, according to the present invention, a salicylate and a non-absorbable steroid can be administered by the same route (e.g., both are administered orally) or by different routes (e.g., a salicylate is administered orally and a non-absorbable steroid is administered rectally), which t'o may differ from the route(s) used to administer the anti-PD-1 and anti-CTLA-4 antibodies. The present invention is further illustrated by the following examples which should not be construed as further limiting. The contents of all figures and all references, patents and published patent applications cited throughout this application are expressly incorporated herein by reference. 73 Examples Example 1: Generation of Human Monoclonal Antibodies Against PD-i Antigen Immunization protocols utilized as antigen both (i) a recombinant fusion protein S comprising the extracellular portion of PD-1 and (ii) membrane bound full-length PD-1. Both antigens were generated by recombinant transfection methods in a CHO cell line. Transgenic HuMab and KM miceTm Fully human monoclonal antibodies to PD-1 were prepared using the HCo7 strain of HuMab transgenic mice and the KM strain of transgenic transchromosomic mice, each of 10 which express human antibody genes. In each of these mouse strains, the endogenous mouse kappa light chain gene has been homozygously disrupted as described in Chen et al. (1993) EABO J. 12:811-820 and the endogenous mouse heavy chain gene has been homozygously disrupted as described in Example 1 of PCT Publication WO 01/09187. Each of these mouse strains carries a human kappa light chain transgene, KCo5, as described in Fishwild et al. 1S (1996) Nature Biotechnology 14:845-851. The HCo7 strain carries the HCo7 human heavy chain transgene as described in U.S. Patent Nos. 5,545,806; 5,625,825; and 5,545,807. The KM strain contains the SC20 transchromosome as described in PCT Publication WO 02/43478. HuMab and KM Immunizations: To generate fully human monoclonal antibodies to PD-1, HuMab mice and KM 10 micem were immunized with purified recombinant PD-1 fusion protein and PD-1-transfected CHO cells as antigen. General immunization schemes for HuMab mice are described in Lonberg, N. et al(1994) Nature 368(6474): 856-859; Fishwild, D. et al. (1996) Nature Biotechnology 14: 845-851 and PCT Publication WO 98/24884. The mice were 6-16 weeks. of age upon the first infusion of antigen. A purified recombinant preparation (5-50 Rg) of 25 PD-1 fusion protein antigen and 5 -10x10 6 cells were used to immunize the HuMab mice and KM mice" intraperitonealy, subcutaneously (Sc) or via footpad injection. Transgenic mice were immunized twice with antigen in complete Freund's adjuvant or Ribi adjuvant IP, followed by 3-21 days IP (up to a total of 11 immunizations) with the antigen in incomplete Freund's or Ribi adjuvant. The immune response was monitored by S retroorbital bleeds. The plasma was screened by ELISA (as described below), and mice with sufficient titers of anti-PD-I human immunogolobulin were used for fusions. Mice were boosted intravenously with antigen 3 days before sacrifice and removal of the spleen. Typically, 10-35 fusions for each antigen were performed. Several dozen mice were immunized for each antigen. '%s Selection of HuMab or KM MiceTh Producing Anti-PD-1 Antibodies: To select HuMab or KM mice" producing antibodies that bound PD-1, sera from immunized mice were tested by ELISA as described by Fishwild, D. etal. (1996). Briefly, microtiter plates were coated with purified recombinant PD-i fusion protein from transfected CHO cells at 1-2 pg /ml in PBS, 100 pl/wells incubated 4 *C overnight then blocked with 200 74 gl/well of 5% fetal bovine serum in PBS/Tween (0.05%). Dilutions of sera from PD-1 immunized mice were added to each well and incubated for 1-2 hours at ambient temperature. The plates were washed with PBS/Tween and then incubated with a goat-anti-human IgG polyclonal antibody conjugated with horseradish peroxidase (HRP) for 1 hour at room S temperature. After washing, the plates were developed with ABTS substrate (Sigma, A-1888, 0.22 mg/ml) and analyzed by spectrophotometer at OD 415-495. Mice that developed the highest titers of anti-PD-1 antibodies were used for fusions. Fusions were performed as described below and hybridoma supernatants were tested for anti-PD-1 activity by ELISA. Generation of Hybridomas Producing Human Monoclonal Antibodies to PD-: 0 The mouse splenocytes, isolated from the HuMab or KM mice, were fused to a mouse myeloma cell line either using PEG based upon standard protocols or electric field based electrofusion using a Cyto Pulse large chamber cell fusion electroporator (Cyto Pulse Sciences, Inc., Glen Burnie, MD). The resulting hybridomas were then screened for the production of antigen-specific antibodies. Single cell suspensions of splenocytes from immunized mice 's were fused to one-fourth the number of SP2/0 nonsecreting mouse myeloma cells (ATCC, CRL 1581) with 50% PEG (Sigma). Cells were plated at approximately 1x1O 5 /well in flat bottom microtiter plate, followed by about two week incubation in selective medium containing 10% fetal bovine serum, 10% P388D1 (ATCC, CRL TIB-63) conditioned medium, 3-5% origen (IGEN) in DMEM (Mediatech, CRL 10013, with high glucose, L-glutamine and 20 sodium pyruvate) plus 5 mM HEPES, 0.055 mM 2-mercaptoethanol, 50 mg/ml gentamycin and 1x HAT (Sigma, CRL P-7185). After 1-2 weeks, cells were cultured in medium in which the HAT was replaced with HT. Individual wells were then screened by ELISA (described above) for human anti-PD-1 monoclonal IgG antibodies. Once extensive hybridoma growth occurred, medium was monitored usually after 10-14 days. The antibody-secreting hybridomas were replated, screened again and, if still positive for human IgG, anti-PD-1 monoclonal antibodies were subcloned at least twice by limiting dilution. The stable subclones were then cultured in vitro to generate small amounts of antibody in tissue culture medium for further characterization. Hybridoma clones 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 were selected for further C) analysis. Example 2: Structural Characterization of Human Monoclonal Antibodies 17D8, 2D3, 4H1, 5C4, 4A11, 7D3 and 5F4 The cDNA sequences encoding the heavy and light chain variable regions of the 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 monoclonal antibodies were obtained from the 17D8, 3 S 2D3, 4H1, 5C4, 4A11, 7D3 and 5F4 hybridomas, respectively, using standard PCR techniques and were sequenced using standard DNA sequencing techniques. The nucleotide and amino acid sequences of the heavy chain variable region of 17D8 are shown in Figure 1A and in SEQ ID NO: 57 and 1, respectively. 75 The nucleotide and amino acid sequences of the light chain variable region of 17D8 are shown in Figure 1B and in SEQ ID NO: 64 and 8, respectively. Comparison of the 17D8 heavy chain immunoglobulin sequence to the known human germline immunoglobulin heavy chain sequences demonstrated that the 17D8 heavy chain 5 utilizes a VH segment from human germline VH 3-33, an undetermined D segment, and a JH segment from human germline JH 4b. The alignment of the 17D8 VH sequence to the germline VH 3-33 sequence is shown in Figure 8. Further analysis of the 17D8 VH sequence using the Kabat system of CDR region determination led to the delineation of the heavy chain CDR1, CDR2 and CD3 regions as shown in Figures 1A and 8, and in SEQ ID NOs: 15, 22 and I0 29, respectively. Comparison of the 17D8 light chain immunoglobulin sequence to the known human germline immunoglobulin light chain sequences demonstrated that the 17D8 light chain utilizes a VL segment from human germline VK L6 and a JK segment from human germline JK 4. The alignment of the 17D8 VL sequence to the germline VK L6 sequence is shown in 15 Figure 9. Further analysis of the 17D8 VL sequence using the Kabat system of CDR region determination led to the delineation of the light chain CDR1, CDR2 and CD3 regions as shown in Figures 1B and 9, and in SEQ ID NOs: 36, 43 and 50, respectively. The nucleotide and amino acid sequences of the heavy chain variable region of 2D3 are shown in Figure 2A and in SEQ ID NO: 58 and 2, respectively. The nucleotide and amino acid sequences of the light chain variable region of 2D3 are shown in Figure 2B and in SEQ ID NO: 65 and 9, respectively. Comparison of the 2D3 heavy chain immunoglobulin sequence to the known human germline immunoglobulin heavy chain sequences demonstrated that the 2D3 heavy chain utilizes a VH segment from human germline VH 3-3 3, a D segment from human germline 7 13 27, and a JH segment from human germline JH 4b. The alignment of the 2D3 VH sequence to the germline VH 3-33 sequence is shown in Figure 8. Further analysis of the 2D3 VH sequence using the Kabat system of CDR region determination led to the delineation of the heavy chain CDR1, CDR2 and CD3 regions as shown in Figures 2A and 8, and in SEQ ID NOs: 16, 23 and 30, respectively. 30 Comparison of the 2D3 light chain immunoglobulin sequence to the known human germline immunoglobulin light chain sequences demonstrated that the 2D3 light chain utilizes a VL segment from human germline VK L6 and a JK segment from human germline JK 4. The alignment of the 2D3 VL sequence to the germline VK L6 sequence is shown in Figure 9. Further analysis of the 2D3 VL sequence using the Kabat system of CDR region determination led to the delineation of the light chain CDRI, CDR2 and CD3 regions as shown in Figures 2B and 9, and in SEQ ID NOs: 37, 44 and 51, respectively. The nucleotide and amino acid sequences of the heavy chain variable region of 4H1 are shown in Figure 3A and in SEQ ID NO: 59 and 3, respectively. 76 The nucleotide and amino acid sequences of the light chain variable region of 4H1 are shown in Figure 3B and in SEQ ID NO: 66 and 10, respectively. Comparison of the 4H1 heavy chain immunoglobulin sequence to the known human germline immunoglobulin heavy chain sequences demonstrated that the 4H1 heavy chain 5 utilizes a VH segment from human germline VH 3-33, an undetermined D segment, and a JH segment from human germline JH 4b. The alignment of the 4H1 VH sequence to the germline VH 3-33 sequence is shown in Figure 8. Further analysis of the 4H1 VH sequence using the Kabat system of CDR region determination led to the delineation of the heavy chain CDR1, CDR2 and CD3 regions as shown in Figures 3A and 8, and in SEQ ID NOs: 17, 24 and 10 31, respectively. Comparison of the 4H1 light chain immunoglobulin sequence to the known human germline immunoglobulin light chain sequences demonstrated that the 4H1 light chain utilizes a VL segment from human germline VK L6 and a JK segment from human germline JK 1. The alignment of the 4H1 VL sequence to the germline VK L6 sequence is shown in Figure 10. 5. Further analysis of the 4H1 VL sequence using the Kabat system of CDR region determination led to the delineation of the light chain CDR1, CDR2 and CD3 regions as shown in Figures 3B and 10, and in SEQ ID NOs: 38, 45 and 52, respectively. The nucleotide and amino acid sequences of the heavy chain variable region of 5C4 are shown in Figure 4A and in SEQ ID NO: 60 and 4, respectively. Zo The nucleotide and amino acid sequences of the light chain variable region of 5C4 are. shown in Figure 4B and in SEQ ID NO: 67 and 11, respectively. Comparison of the 5C4 heavy chain immunoglobulin sequence to the known human germline immunoglobulin heavy chain sequences demonstrated that the 5C4 heavy chain utilizes a VH segment from human germline VH 3-33, an undetermined D segment, and a JH S5 segment from human germline JH 4b. The alignment of the 5C4 VH sequence to the germline VH 3-33 sequence is shown in Figure 8. Further analysis of the 5C4 VH sequence using the Kabat system of CDR region determination led to the delineation of the heavy chain CDR1, CDR2 and CD3 regions as shown in Figures 4A and 8, and in SEQ ID NOs: 18, 25 and 32, respectively. Comparison of the 5C4 light chain immunoglobulin sequence to the known human germline immunoglobulin light chain sequences demonstrated that the 5C4 light chain utilizes a VL segment from human germline VK L6 and a JK segment from human germline JK 1. The alignment of the 5C4 VL sequence to the germline VK L6 sequence is shown in Figure 10. Further analysis of the 5C4 VL sequence using the Kabat system of CDR region determination - led to the delineation of the light chain CDR1, CDR2 and CD3 regions as shown in Figures 4B and 10, and in SEQ ID NOs: 39, 46 and 53, respectively. The nucleotide and amino acid sequences of the heavy chain variable region of 4A1 1 are shown in Figure 5A and in SEQ ID NO: 61 and 5, respectively. 77 The nucleotide and amino acid sequences of the light chain variable region of 4A1 1 are shown in Figure 5B and in SEQ'ID NO: 68 and 12, respectively. Comparison of the 4A1 1 heavy chain immunoglobulin sequence to the known human germline immunoglobulin heavy chain sequences demonstrated that the 4A1 1 heavy chain 5 utilizes a VH segment from human germline VH 4-39, a D segment from human germline 3-9, and a JH segment from human germline JH 4b. The alignment of the 4A1 1 VH sequence to the germline VH 4-39 sequence is shown in Figure 11. Further analysis of the 4A11 VH sequence using the Kabat system of CDR region determination led to the delineation of the heavy chain CDR1, CDR2 and CD3 regions as shown in Figures 5A and 11, and in SEQ ID 0 NOs: 19, 26 and 33, respectively. Comparison of the 4A1 1 light chain immunoglobulin sequence to the known human germline immunoglobulin light chain sequences demonstrated that the 4A1 1 light chain utilizes a VL segment from human germline VK L15 and a JK segment from human germline JK 1. The alignment of the 4A1 1 VL sequence to the germline VK L6 sequence is shown in '5 Figure 12. Further analysis of the 4A11 VL sequence using the Kabat system of CDR region determination led to the delineation of the light chain CDR1, CDR2 and CD3 regions as shown in Figures 5B and 12, and in SEQ ID NOs: 40, 47 and 54, respectively. The nucleotide and amino acid sequences of the heavy chain variable region of 7D3 are shown in Figure 7A and in SEQ ID NO: 62 and 6, respectively. 90 The nucleotide and amino acid sequences of the light chain variable region of 7D3 are shown in Figure 7B and in SEQ ID NO: 69 and 13, respectively. Comparison of the 7D3 heavy chain immunoglobulin sequence to the known human germline immunoglobulin heavy chain sequences demonstrated that the 7D3 heavy chain utilizes a VH segment from human germline VH 3-33, a human germline 7-27 D segment, and IS a JH segment from human germline JH 4b. The alignment of the 7D3 VH sequence to the germline VH 3-33 sequence is shown in Figure 8. Further analysis of the 7D3 VH sequence using the Kabat system of CDR region determination led to the delineation of the heavy chain CDRI, CDR2 and CD3 regions as shown in Figures 6A and 8, and in SEQ ID NOs: 20, 27 and 34, respectively. 3so Comparison of the 7D3 light chain immunoglobulin sequence to the known human germline immunoglobulin light chain sequences demonstrated that the 7D3 light chain utilizes a VL segment from human germline VK L6 and a JK segment from human germline JK 4. The alignment of the 7D3 VL sequence to the germline VK L6 sequence is shown in Figure 9. Further analysis of the 7D3 VL sequence using the Kabat system of CDR region determination 3s led to the delineation of the light chain CDR1, CDR2 and CD3 regions as shown in Figures 6B and 9, and in SEQ ID NOs: 41, 48 and 55, respectively. The nucleotide and amino acid sequences of the heavy chain variable region of 5F4 are shown in Figure 7A and in SEQ ID NO: 63 and 7, respectively. 78 The nucleotide and amino acid sequences of the light chain variable region of 5F4 are shown in Figure 7B and in SEQ ID NO: 70 and 14, respectively. Comparison of the 5F4 heavy chain immunoglobulin sequence to the known human germline immunoglobulin heavy chain sequences demonstrated that the 5F4 heavy chain S utilizes a VH segment from human germline VH 4-39, a D segment from human germline 3-9, and a JH segment from human germline JH 4b. The alignment of the 5F4 VH sequence to the germline VH 4-39 sequence is shown in Figure 11. Further analysis of the 5F4 VH sequence using the Kabat system of CDR region determination led to the delineation of the heavy chain CDRl, CDR2 and CD3 regions as shown in Figures 7A and 11, and in SEQ ID (o NOs: 21, 28 and 35, respectively. Comparison of the 5F4 light chain immunoglobulin sequence to the known human germline immunoglobulin light chain sequences demonstrated that the 5F4 light chain utilizes a VL segment from human germline VK L15 and a JK segment from human germline JK 1. The alignment of the 5F4 VL sequence to the germline VK L6 sequence is shown in Figure 12. '6 Further analysis of the 5F4 VL sequence using the Kabat system of CDR region determination led to the delineation of the light chain CDR1, CDR2 and CD3 regions as shown in Figures 7B and 12, and in SEQ ID NOs: 42, 49 and 56, respectively. Example 3: Characterization of Binding Specificity and Binding Kinetics of Anti-PD-i Human Monoclonal Antibodies 20 In this example, binding affmity and binding kinetics of anti-PD-I antibodies were examined by Biacore analysis. Binding specificity; and cross-competition were examined by flow cytometry. Binding affinity and kinetics Anti-PD-i antibodies were characterized for affinities and binding kinetics by Biacore ' - analysis (Biacore AB, Uppsala, Sweden). Purified recombinant human PD-i fusion protein was covalently linked to a CM5 chip (carboxy methyl dextran coated chip) via primary amines, using standard amine coupling chemistry and kit provided by Biacore. Binding was measured by flowing the antibodies in HBS EP buffer (provided by Biacore AB) at a concentration of 267 nM at a flow rate of 50 pl/min. The antigen-antibody association 3 C kinetics was followed for 3 minutes and the dissociation kinetics was followed for 7 minutes. The association and dissociation curves were fit to a 1:1 Langmuir binding model using BlAevaluation software (Biacore AB). To minimize the effects of avidity in the estimation of the binding constants, only the initial segment of data corresponding to association and dissociation phases were used for fitting. The KD, k 0 , and kog values that were determined 3,5 are shown in Table 2. 79 Table 2. Biacore binding data for PD-1 human monoclonal antibodies. Affinity KD X On rate k. x Off rate kff x Sample # Sample ID 14.9 M 10, (1/Ms) 10- 1/s 1 17D8 0.16 2.56 0.45 2 2D3 1.20 3.77 4.52 3 4H1 5.46 3.15 1.72 4 5C4 0.73 4.32 3.15 5 4A11 0.13 0.76 0.099 6 7D3 2.49 18.2 4.54 7 5F4 2.91 8.74 2.54 Binding specificity by flow cytometry Chinese hamster ovary (CHO) cell lines that express recombinant human PD-I at the cell surface were developed and used to determine the specificity of PD-I human monoclonal 5 antibodies by flow cytometry. CHO cells were transfected with expression plasmids containing full length cDNA encoding transmembrane forms of PD-1. Binding of the 5C4 and 4H1 anti-PD-1 human monoclonal antibodies was assessed by incubating the transfected cells with the anti-PD-1 human monoclonal antibodies at a concentration of 20 ptg/ml. The cells were washed and binding was detected with a FITC-labeled anti-human IgG Ab. Flow a cytometric analyses were performed using a FACScan flow cytometry (Becton Dickinson, San Jose, CA). The results are depicted in Figures 13A (5C4) and 13B (4H1). The anti-PD-i human monoclonal antibodies bound to the CHO cells transfected with PD-1 but not to CHO cells that were not transfected with human PD-1. These data demonstrate the specificity of anti-PD-1 human monoclonal antibodies for PD-1.* 'S Binding specificity by ELISA against other CD28 family members A comparison of the binding of anti-PD-1 antibodies to CD28 family members was performed by standard ELISA using four different CD28 family members to examine the specificity of binding for PD-1. Fusion proteins of CD28 family members, ICOS, CTLA-4 and CD28 (R&D 20 Biosystems) were tested for binding against the anti-PD-1 human monoclonal antibodies 17D8, 2D3, 4H1, 5C4, and 4A11. Standard ELISA procedures were performed. The anti-PD-1 human monoclonal antibodies were added at a concentration of 20 pg/ml. Goat-anti-human IgG (kappa chain-specific) polyclonal antibody conjugated with horseradish peroxidase (HRP) was used as secondary antibody. The results are shown in Figure 14. Each of the anti-PD-1 2$ human monoclonal antibodies 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 and 5F4 bound with high specificity to PD-1, but not to the other CD28 family members. Example 4: Characterization of anti-PD-1 antibody binding to PD-1 expressed on the surface of human and monkey cells Anti-PD-I antibodies were tested for binding to cells expressing PD-I on their cell 3 a surface by flow cytometry. 80 Activated human T-cells, monkey peripheral blood mononuclear cells (PBMC), and CHO cells transfected with PD-1 were each tested for antibody binding. Human T cells and cynomolgous PBMC were activated by anti-CD3 antibody to induce PD-1 expression on T cells prior to binding with a human anti-PD-1 monoclonal antibody. Binding of the 5C4 and 5 4H1 anti-PD-I human monoclonal antibodies was assessed by incubating the transfected cells with either IgGi or IgG4 forms of the anti-PD-1 human monoclonal antibodies at different concentrations. The cells were washed and binding was detected with a FITC-labeled anti human IgG Ab. Flow cytometric analyses were performed using a FACScan flow cytometry (Becton Dickinson, San Jose, CA). The results are shown in Figures 15A (activated human T to cells), 15B (cynomolgous monkey PBMC) and I5C (PD-1-transfected CHO cells). The anti PD-1 monoclonal antibodies 5C4 and 4111 bound to activated human T cells, activated monkey PBMCs, and CHO cells transfected with human PD-1, as measured by the mean fluorescent intensity (MFI) of staining. These data demonstrate that the anti-PD-1 HuMAbs bind to both human and cynomolgous monkey cell surface PD-1. I s Example 5: Effect of human anti-PD-1 antibodies on cell proliferation and cytokine production in a Mixed Lymphocyte Reaction A mixed lymphocyte reaction was employed to demonstrate the effect of blocking the PD-I pathway to lymphocyte effector cells. T cells in the assay were tested for proliferation, IFN-gamma secretion and IL-2 secretion in the presence or absence of an anti-PD-1 HuMAb 20 antibody. Human T-cells were purified from PBMC using a human CD4+ T cell enrichment column (R&D systems). Each culture contained 105 purified T-cells and 104 allogeneic dendritic cells in a total volume of 200 pl. Anti-PD-1 monoclonal antibody 5C4, 4Hi, 17D8, 2D3 or a Fab fragment portion of 5C4 was added to each culture at different antibody 25 concentrations. Either no antibody or an isotype control antibody was used as a negative control. The cells were cultured for 5 days at 37*C. After day 5, 100 pl of medium was taken from each culture for cytokine measurement. The levels of IFN-gamma and other cytokines were measured using OptEIA ELISA kits (BD Biosciences). The cells were labeled with 3 H-thymidine, cultured for another 18 hours, and analyzed for cell proliferation. 0 The results are shown in Figures 16A (T cell proliferation), 16B (IFN-y secretion) and 16C (IL-2 secretion). The anti-PD-1 human monoclonal antibodies promoted T-cell proliferation, IFN-gamma secretion and IL-2 secretion in a concentration dependent manner. The 5C4-Fab fragment also promoted T-cell proliferation, IFN-gamma secretion and IL-2 secretion in a concentration dependent manner. In contrast, cultures containing the isotype control 35 antibody did not show an increase in T cell proliferation, IFN-gamma or IL-2 secretion. 81 Example 6: Blocking of ligand binding to PD-i by human anti-PD-1 antibodies Anti-PD-1 HuMAbs were tested for the ability to block binding of the ligands PD-Li and PD-L2 to PD-I expressed on transfected CHO cells by using a flow cytometry assay. PD-1 expressing CHO cells were suspended in FACS buffer (PBS with 4% fetal calf serum). Various concentrations of the anti-PD-1 HuMAbs 5C4 and 4Hi were added to the cell suspension and incubated at 4*C for 30 minutes. Unbound antibody was washed off and either FITC-labeled PD-Li fusion protein or FITC-labeled PD-L2 fusion protein was added into the tubes and incubated at 4*C for 30 minutes. Flow cytometric analyses were performed using a FACScan flowcytometer (Becton Dickinson, San Jose, CA). The results io are depicted in Figures 17A (blocking of PD-Li) and 17B (blocking of PD-L2). The anti PD-1 monoclonal antibodies 5C4 and 4H1 blocked binding of PD-Li and PD-L2 to CHO cells transfected with human PD-1, as measured by the mean fluorescent intensity (MFI) of staining. These data demonstrate that the anti-PD-1 HuMAbs block binding of ligand (both PD-LI and PD-L2) to cell surface PD-1. '5 Example 7: Effect of human anti-PD-1 antibodies on the release of cytokines in human blood The anti-PD-I HuMAbs were mixed with fresh human whole blood in order to determine whether the anti-PD-1 HuMAbs alone stimulated the release of certain cytokines from human blood cells. 500 pl of heparinized-fresh human whole blood, was added into each well. Either 10 pg or 100 pg of an anti-PD-1 HuMAb (4HI or 5C4,the latter either as an IgG1 or IgG4 isotype) was added to each well. Some wells were incubated with anti-CD3 antibody as a positive control, or a human IgG1 or human IgG4 antibody as isotype-matched negative controls. The cells were incubated at 37 *C for either 6 or 24 hours. The cells were spun 25 down and the plasma was collected for measurement of the cytokines IFN-gamma, TNF-alpha, IL-2, IL-4, IL-6, IL-10 and IL-12 using a cytokine cytometric bead array assay (BD Biosciences). The concentration of each cytokine (pg/ml) is shown in Tables 3a, with a 6 hour incubation, and 3b, with a 24 hour incubation, below. The results show that treatment with the human anti-PD-1 antibodies 5C4 and 4H1 alone did not stimulate human blood cells 30 to release any of the cytokines IFN-gamma, TNF-alpha, IL-2, IL-4, I-6, IL-10 and IL-12. 82 Table 3a. Cvtoine Production following hour incubation Ab IFN-gamma TNF-alpha IL-1O IL-6 II-4 IL-2 (pg/ml) _ (pg/ml pgl) (pg/ml) . (pg/ml) (pg/mil) No Ab 12.3 2 3 5 3.6 1.9 10 mg/ml 5000 530 82.6 510.4 37.2 467.9 anti-CD3 100 mg/ml 5000 571 91.3 530 43.9 551.5 anti-CD3 10 mg/mi 7 1.8 2.8 4.4 2.6 1.5 hIgGI 100 mg/ml 0 2.2 2.7 6 2.6 1.4 bIgGI 10 mg/ml 5.4 1.4 2.5 4.5 2.1 1.3 hIgG4 100 mg/ml 6.4 2.3 3 32.6 2.9 1.4 hIgG4 10 mg/ml 6.2 1.8 2.4 4.1 2.8 1.6 4H1 100 mg/ml 11.8 2 2.6 3.5 2.6 1.7 4H1 10 mg/ml 4.2 1.6 2.3 3.9 2.5 1.3 5C4 IgGI 100 mg/ml 0 1.4 2.2 3.6 2.1 1.2 5C4 IgGI 10 mg/ml 8.3 2.5 1.9 4.8 1.6 1.5 5C4IgG4 I 100 mg/ml 3.6 . 1.7 2.4 3.9 2.3 1.5 5C4 IgG4 83 Table 3b. Cytokine production following 4 hour incubation Ab IFN-gamma TNF-alpha IL-10 IL-6 IL-4 IL-2 (pg/ml) (pgl (p ) (pg/ml) (pg/ml) (pg/mL No Ab 11.2 2 6.1 5.9 2.6 1.7 10 mg/ml 5000 565.9 432 5000 64.5 1265.3 anti-CD3 100 mg/ml 5000 535 461 5000 73.8 1334.9 anti-CD3 10 mg/ml 0 0 0 0 0 0 hIgGI 100 mg/ml 11.5 1.7 7.9 60.8 2.9 1.5 hIgGI 10 mg/ml 24.6 3.1 8.3 63.4 3.1 2.3 hIgG4 100 mg/ml 11.2 1.8 8 27.7 3.1 2.4 hIgG4 10 mg/ml 27.3 2.9 8 13.9 5.3 2.6 4H1 100 mg/mI 17.5 2.5 4.4 7 4 2.1 4H1 10 mg/ml 9.1 2 7.6 68.5 3.5 1.8 5C4IgG1 100 mg/ml 12.9 1.9 6.1 25.3 2.9 1.7 5C4 IgG1 10 mg/ml 14 1.9 4.4 3.3 2.6 1.9 5C4 IgG4 100 mg/ml 0 0 0 0 0 0 5C4 IgG4 Example 8: Effect of anti-PD-1 antibodies on the apoptosis of T-cells The effect of anti-PD-I antibodies on the induction of apoptosis of T-cells was measured using an annexin V staining test. T cells were cultured in a mixed lymphocyte reaction, as described above in Example 5. The anti-PD-1 antibody 5C4 was added to the tube at a concentration of 25 pg/ml. A non specific antibody was used as a control. Annexin V and propidium iodide were added according to standard protocol (BD Biosciences). The mixture was incubated for 15 minutes in the dark at room temperature and then analyzed using a FACScan flowcytometer (Becton I Dickinson, San Jose, CA). The results are shown in Figure 18. The anti-PD-i antibody 5C4 did not have an effect on T-cell apoptosis. 84 Example 9: Effect of anti-PD-1 antibodies on cytokine secretion by viral-stimulated PBMC cells from a virus positive donor In this example, peripheral blood mononuclear cells (PBMC) from a donor positive for CMV were isolated and exposed to a CMV lysate in the presence or absence of anti-PD-1 B antibodies to examine the effect of the antibodies on cytokine secretion simulated by antigen. 2x10 5 human PMBCs from a CMV positive donor were cultured in a total volume of 200 pl and added into each well along with a lysate of CMV-infected cells. The anti-PD-1 HuMAb 5C4 was added to each well in various concentrations for 4 days. After day 4, 100 pl of medium was taken from each culture for cytokine measurement. The level of IFN I0 gamma was measured using OptEIA ELISA kits (BD Biosciences). The cells were labeled with 3 H-thymidine, cultured for another 18 hours, and analyzed for cell proliferation. The cell proliferation was analyzed using the Cell Titer-Glo reagent (Promega). The results are shown in Figure 19. The anti-PD-1 HuMab 5C4 increased IFN gamma secretion in a concentration dependent manner. These results shows that anti-PD-I HuMAbs can stimulate IS IFN-gamma release in a memory T cell response from PBMC cells previously stimulated against an antigen. Example 10: Effect of anti-PD-1 antibody on secondary antibody response to antigen Mice were immunized and rechallenged with a TI -antigen (DNP-Ficoll) and also treated with a rat anti-mouse-PD-I antibody, or a control antibody to examine the effect of the 20 anti-PD-I antibody on antibody titers. Female C57)3L6 mice were divided into two groups, with 6 mice/group. One group was treated with a control rat IgG and the other with a rat anti-mouse PD-I antibody. The mice were immunized with 5pg of DNP-Ficoll (a Ti-antigen) in 50pl CFA by i.p. at day 0. Either the control rat IgG antibody or the rat-mPD-1 antibody (200pg/mouse) was given by i.p. 2S at days -1, 0 and 2. Four weeks later, mice were rechallenged with 5pg of DNP-Ficoll in 50pl IFA by i.p. at day 0. Rat anti-mPD-1 antibody or control antibody (200ig/mouse) was given by i.p. at days 0 and 1. Antibody titers were measured by standard ELISA assay at day 7 following the boost. The results are shown in Table 4 below. In the mice treated with the anti-mPD-1 antibody, both IgM and IgG3 isotypes showed the greatest increase in titer 10 following challenge with the Ti-antigen, as compared to mice treated with a control antibody. These results demonstrate that anti-PD-1 treatment can increase antibody titers in response to Ti-antigen. 85 Table 4. Murine secondary response following treatment with anti-PD-1 antibody Antibody Control group Rat anti-mouse PD- P value Isotype 1 antibody IgM 606 1200 0.026 IgG 9 15.55 0.18 IgG1 1.2 1.1 0.83 IgG2b 5.05 9.26 0.18 IgG3 21.9 81.2 0.03 * Results shown are average concentration of antibody isotype (sg/ml) Example 11: Treatment of in vivo tumor model using anti-PD-1 antibodies Mice implanted with a cancerous tumor were treated in vivo with anti-PD-I antibodies 5 to examine the in vivo effect of the antibodies on tumor growth. As a positive control, an anti-CTLA-4 antibody was used, since such antibodies have been shown to inhibit tumor growth in vivo. In this experiment, the anti-PD-1 antibody used was a chimeric rat anti-mouse-PD-1 antibody generated using well known laboratory techniques. To generate the rat anti-mouse 00 PD-I antibody, rats were immunized with mouse cells transfected to express a recombinant mouse PD-I fusion protein (R&D Systems Catalog No. 1021-PD) and monoclonal antibodies were screened for binding to mouse PD-i antigen by ELISA assay. The rat anti-PD-1 antibody V regions were then recombinantly linked to a murine IgG1 constant region using standard molecular biology techniques and rescreened for binding to mouse PD-1 by ELISA s and FACS. The chimeric rat anti-mouse-PD-I antibody used herein is referred to as 4H2. For the tumor studies, female AJ mice between 6-8 weeks of age (Harlan Laboratories) were randomized by weight into 6 groups. The mice were implanted subcutaneously in the right flank with 2 x 106 SA1/N fibrosarcoma cells dissolved in 200 pl of DMEM media on day 0. The mice were treated with PBS vehicle, or antibodies at 10 mg/kg. 20 The animals were dosed by intraperitoneal injection with approximately 200 pL of PBS containing antibody or vehicle on days 1, 4, 8 and 11. Each group contained 10 animals and the groups consisted of: (i) a vehicle group, (ii) control mouse IgG, (iii) control hamster IgG, (iv) hamster anti-mouse CTLA-4 antibody and (v) the chimeric anti-PD-I antibody 4H2. The mice were monitored twice weekly for tumor growth for approximately 6 weeks. Using 't5 an electronic caliper, the tumors were measured three dimensionally (height x width X length) and tumor volume was calculated. Mice were euthanized when the tumors reached tumor end point (1500 mm 3 ) or show greater than 15% weight loss. The results are shown in Figure 20. The anti-PD-1 antibody extended the mean time to reaching the tumor end point volume (1500 mm 3 ) from -25 days in the control groups to -40 days. Thus, treatment with 30 an anti-PD-1 antibody has a direct in vivo inhibitory effect on tumor growth. 86 Example 12: Generation of Chimeric (Rat-Mouse) anti-PD-1 Antibody 4H2 Rat monoclonal antibody against mouse PD-1 antibodies (rat anti-mPD-1) were generated from rats immunized with mPD-1-hFc fusion protein using standard hybridoma production methods (see Kohler and Milstein (1975) Nature 256:495; and Harlow and Lane 5 (1988) Antibodies, A Laboratory Manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor New York). Eight hybridomas were subcloned, and antibodies were isolated and screened for their ability to block mouse PD-L2 (mPD-L2) binding to mPD-1. Several anti-mPD-1 antibodies capable of blocking mPD-L2 binding to mPD-1 were identified (see, e.g., activity of 4H2, Figure 41) and the binding affinity of several of these antibodies to mPD 10 1-Fc fusion protein was determined by ELISA (Figure 42). Antibody 4H2.B3 was further characterized, which is referred to interchangeably herein as "4H2." CHO cells expressing mouse PD-1 were constructed and incubated with 4112 anti-mPD-1 antibody at a concentration ranging from 200 g/ml to 0.012 pg/ml to determine the binding affmity of 4H2 to PD-1. Binding of anti-mPD-1 antibody to the PD-1 ts expressing CHO cells was detected by incubating with donkey-anti-rat IgG, FITC conjugated and measured by FACS. The anti-mPD-1 antibody had an EC5 0 (50% effective concentration) of about 0.38 ig (Figure 43) and aKD of 4.7 x 10-9 M. To examine the inhibition of PD-Li binding to PD-1, the same assay was performed except that the cells were also incubated with 0.16 jg mPD-LI-hFc fusion protein, then binding of PD-Li to the PD-1 2o expressing CHO cells was detected by incubating with goat-anti-human IgG (Fc specific), FITC conjugated and measuring binding signal by FACS (MFI, mean fluorescence intensity). The anti-mPD-1 antibody had an EC5 0 of about 0.72 pg (Figure 44). For use in the mouse tumor models, the 4H2 rat anti-mPD-1 needed to be modified so the mouse immune system would not neutralize the immunotherapeutic antibody (i.e., so the ?s antibody would have better pharmacokinetics) and to avoid antibody-dependent cellular cytotoxicity (ADCC) by reducing Fc receptor interactions (i.e., so blockade by anti-PD-I could be evaluated with being compromised by ADCC effects). The original rat anti-mPD-1 antibody, 4H2, was determined to be a rat IgG2a isotype. Hence, the Fc-portion of the 4H2 antibody was replaced with an Fc-portion from a mouse IgG1 isotype. Using the assay 3c described above,the binding affinity of the rat-mouse chimeric 4H2 to mPD-1 was found to be comparable to the rat 4H2.B3 anti-mPD-1 antibody (Figure 45). Similarly, inhibition of PD Li binding to PD-1 was comparable for both antibodies (Figure 46). Thus, the rat-mouse chimeric 4H2 anti-mPD-I antibody was used to examine the therapeutic efficacy of anti-PD-1 in combination with anti-CTLA-4. s Example 13: In Vivo Efficacy of Combination Therapy (anti-CTLA-4 and anti-PD-1 Antibodies) on Tumor Establishment and Growth MC38 colorectal cancer cells (PD-Li) (available from Dr. N. Restifo, National Cancer Institute, Bethesda, MD; or Jeffrey Schlom, National Institutes of Health, Bethesda, MD) were 87 implanted in C57BL/6 mice (2 x 106 cells/mouse). On day 0 (i.e., the day the MC38 cells were implanted in the mice), each of four groups of 10 mice each was injected intraperitoneally (IP) with one of the following: (1) mouse IgG (control), (2) anti-CTLA-4 monoclonal antibody 9D9 (mouse anti-mouse CTLA-4, obtained from J. Allison, Memorial S Sloan-Kettering Cancer Center, New York, NY), (3) anti-PD-1 monoclonal antibody 4H2 (chimeric antibody in which a rat anti-mouse PD-i was modified with a mouse Fc region, as described in Example 6), or (4) anti-CTLA-4 antibody 9D9 and anti-PD-1 antibody 4H2. Antibody injections were then further administered on days 3, 6 and 10. The single antibody treatments were dosed at 10 mg/kg, and the combination of anti-CTLA-4 antibody and 0 anti-PD-I antibody was dosed at 5 mg/kg of each antibody (i.e., 10 mg/kg of total antibody). Using an electronic caliper, the tumors were measured three dimensionally (height x width x length) and tumor volume was calculated. Mice were euthanized when the tumors reached a designated tumor end-point. The results are shown in Table 5 and Figure 21. Table 5. Percentage of Tumor-Free Mice Following Anti-PD-1 and/or Anti-CTLA 4 Treatment Treatment Total mice studied Tumor-free mice (%) mIgG1 10 0 anti-CTLA-4 10 1 (10) anti-PD-1 10 3 (30) anti-CTLA-4 + anti-PD-i 10 6 (60) Eight mice in the IgG group reached the tumor end-point by about day 30 and two mice (86066 and 87260) in the IgG group had ulcerated tumors (Figure 21A). In the anti CTLA-4 antibody alone group, seven mice reached the tumor end-point by about day 60, one mouse had an ulcerated tumor (84952), one mouse had a tumor with a volume of less than 20 1500 mm 3 (85246), and one mouse was tumor-free (86057) (Figure 21B). In the anti-PD-1 antibody alone group, six mice reached the tumor end-point by about day 60, one mouse had an ulcerated tumor (86055), and three mice were tumor-free (84955, 85239 and 86750) (Figure 21C). In the anti-CTLA-4 antibody and anti-PD-I antibody combination group, four mice reached the tumor end-point by about Day 40, and six mice were tumor-free (84596, 2S 85240, 86056, 86071, 86082 and 86761) (Figure 21D). Figure 22 shows that the mean tumor volume measured at day 21 was about 2955 mm 3 for the IgG control group; about 655 mn 3 for the CTLA-4 antibody alone group, about 510 mm 3 for the PD-I antibody alone group, and about 280 mm 3 for the anti-CTLA-4 antibody and anti-PD-1 antibody combination group. Figure 23 shows that the median tumor volume 30 measured at day 21 was about 2715 mm 3 for the IgG group; about 625 mnm for the CTLA-4 antibody alone group; about 525 mm 3 for the PD-I antibody alone group; and about 10 mm 3 88 for the CTLA-4 antibody and PD-I antibody combination group (and down to 0 mm 3 by day 32). This study indicates that, in a murine tumor model, CTLA-4 antibody treatment alone and PD-1 antibody treatment alone have a modest effect on tumor growth, and that the s combination treatment of CTLA-4 antibody and PD-I antibody has a significantly greater effect on tumor growth. It is interesting to note that the combination treatment with CTLA-4 antibody and PD-i antibody had a more significant effect on tumor growth at a dose of 5 mg/kg of each antibody as compared to the effect of either antibody alone when each is administered at a higher dose of 10 mg/kg. O Example 14: In Vivo Efficacy of Combination Therapy (anti-CTLA-4 and anti-PD-1 Antibodies) on Established Tumor Growth MC38 colorectal cancer cells (PD-L1~) were implanted in C57BL/6 mice (2 x 106 cells/mouse) for a time sufficient (about 6 to 7 days) to permit the formation of tumors. On day 6 post-implantation (day -1), tumor measurements were taken and mice were randomized Is based on mean tumor volume (about 250 mm 3 ) into 11 groups for subsequent antibody therapy. At day 0 (i.e., one week after the MC38 cells were implanted), mice were injected IP with (1) mouse IgG (control), (2) anti-CTLA-4 monoclonal antibody 9D9, (3) anti-PD-1 monoclonal antibody 4H2, or (4) anti-CTLA-4 monoclonal antibody 9D9 and anti-PD-1 antibody monoclonal antibody 4H2, at a concentration of 10 mg/kg per mouse. Antibody injections 20 were also administered on days 3, 6 and 10. The monoclonal antibody compositions used had low levels of endotoxin and did not significantly aggregate. Using an electronic caliper, the tumors were measured three dimensionally (height x width x length) and tumor volume was calculated. Tumor measurements were taken on day 0 (tumors at the beginning of treatment had a volume of about 125 mm 3 ), and on days 3, 6, 10, 13, 17 and 20 post-antibody Z5 injection. Mice were euthanized when the tumors reached a designated tumor end-point (a particular tumor volume such as 1500 mm 3 and/or when the mice showed greater than about 15% weight loss). All eleven mice in the IgG group reached the tumor end-point by about day 17 (Figure 24A). In the anti-CTLA-4 antibody alone group, seven of eleven mice reached the tumor 30 end-point by about day 12 (Figure 24B). In the anti-PD-1 antibody alone group, four mice reached the tumor end-point by about day 13 and two mice were tumor-free (Figure 24C). In the anti-CTLA-4 antibody and anti-PD-I antibody combination group, one mouse reached the tumor end-point by about day 17, one mouse reached the tumor end-point by about day 45 and nine mice were tumor-free on day 45 (Figure 24D). Figure 25 shows that the mean tumor volume measured at day 10 was about 1485 mm 3 for the IgG control group; about 1010 mm 3 for the CTLA-4 antibody alone group; about 695 mm 3 for the PD-i antibody alone group; and about 80 mm 3 for the anti-CTLA-4 antibody and anti-PD-1 antibody combination group. Figure 26 shows that the median tumor volume 89 measured at day 10 was about 1365 mm 3 for the IgG group; about 1060 mm for the anti CTLA-4 antibody alone group; about 480 mm 3 for the anti-PD-1 antibody alone group; and about 15 mm 3 for the anti-CTLA-4 antibody and anti-PD-I antibody combination group (which was down to 0 mm 3 by day 17). 5 This study indicates that, in a murine tumor model, treatment with the combination of CTLA-4 antibody and PD-i antibody has a significantly greater effect on tumor growth than either antibody alone, even when a tumor is already well established. Example 15: Dose Titration of Combination Therapy (anti-CTLA-4 and anti-PD-1 Antibodies) on Established Tumor Growth 10 MC38 colorectal cancer cells (PD-L1-) were implanted in C57BL/6 mice (2 x 106 cells/mouse) for a time sufficient (about 6 to 7 days) to permit the formation of tumors as described in Example 3. Groups of 10 mice were injected IP at days 0, 3, 6 and 10 as follows: Group (A) mouse IgG (control, 20 mg/kg), Group (B) anti-PD-1 monoclonal antibody 4H2 (10 mg/kg) and mouse IgG (10 mg/kg), Group (C) anti-CTLA-4 monoclonal antibody (5 9D9 (10 mg/kg) and mouse IgG (10 mg/kg), Group (D) anti-CTLA-4 monoclonal antibody 9D9 (10 mg/kg) and anti-PD-1 antibody monoclonal antibody 4H2 (10 mg/kg), Group (E) anti-CTLA-4 monoclonal antibody 9D9 (3 mg/kg) and anti-PD-I antibody monoclonal antibody 4H2 (3 mg/kg), or Group (F) anti-CTLA-4 monoclonal antibody 9D9 (1 mg/kg) and anti-PD-1 antibody monoclonal antibody 4H2 (1 mg/kg). Using an electronic caliper, the 2 o tumors were measured three dimensionally (height x width x length) and tumor volume was calculated. -Tumor measurements were taken at the beginning of treatment (i.e., on day 0 tumors had an average volume of about 90 mm 3 ), and on days 3, 6, 10, 13, 17 and 20 post-antibody treatment. Mice were euthanized when the tumors reached a designated tumor end-point (a particular tumor-volume such as 1500 mm 3 and/or when the mice showed greater 25 than about 15% weight loss). Figure 27A shows that all 10 control mice had reached a tumor end-point. Figure 27B shows that the group treated with 10 mg/kg anti-PD-1 antibody (Group B) had 6 mice that reached the tumor end-point and 4 mice with tumors having a volume of about 750 mm 3 or less. Figure 27C shows that the group treated with 10 mg/kg anti-CTLA-4 antibody (Group 30 C) had 3 mice that reached the tumor end-point and 7 mice with tumors having a volume of about 1000 mm 3 or less. Figure 27D shows that the group treated with a combination of 10 mg/kg anti-PD-1 antibody with 10 mg/kg anti-CTLA-4 antibody (Group D) had 2 mice with tumors having a volume of about 1000 mm 3 or less, and 8 mice that were tumor free. Figure 27E shows that the group treated with a combination of 3 mg/kg anti-PD-1 antibody with 3 Is mg/kg anti-CTLA-4 antibody (Group E) had one mouse that had reached the tumor end-point, 7 mice with tumors having a volume of about 500 mm 3 or less, and 2 mice that were tumor free. Figure 27F shows that the group treated with a combination of 1 mg/kg anti-PD-1 antibody with 1 mg/kg anti-CTLA-4 antibody (Group F) had 4 mice that had reached the 90 tumor end-point, 5 mice with tumors having a volume of about 1100 mm 3 or less, and one mouse that was tumor free. Figures 27G and 27H show the tumor volumes in mice treated sequentially with anti PD-1 antibody first and anti-CTLA-4 antibody second, and vice versa. The mice of Figure S 27G first received 10 mg/kg anti-CTLA-4 on each of days 0 and 3, and then received 10 mg/kg anti-PD-1 antibody on each of days 6 and 10. The mice of Figure 27H first received 10 mg/kg anti-PD-I antibody on each of days 0 and 3, and then received 10 mg/kg anti-CTLA-4 antibody on each of days 6 and 10. For group G at day 27, 8 mice reached the tumor end-point, one mouse had a very small tumor (which, after a significant delay, Io eventually grew out) and one mouse was tumor free. For group H at day 27, 8 mice reached the tumor end-point and 2 were tumor free. Figure 28 shows that the mean tumor volume measured at day 10 was about 1250 mm 3 for the IgG control group; about 470 mm 3 for the PD-I antibody with the IgG control; about 290 mm 3 for the CTLA-4 antibody with the IgG control (measured at day 6); about 40 mm 3 1S for the anti-CTLA-4 antibody (10 mg/kg) and anti-PD-I antibody (10 mg/kg) combination group; about 165 mm 3 for the anti-CTLA-4 antibody (3 mg/kg) and anti-PD-1 antibody (3 mg/kg) combination group; and about 400 mm 3 for the anti-CTLA-4 antibody (1 mg/kg) and anti-PD-1 antibody (1 mg/kg) combination group. Figure 29 shows that the median tumor volume measured at day 13 was about 1680 mm 3 for the IgG control group; about 400 mm 3 Z~-0 for the PD-i antibody with the IgG control; about 660 mm 3 for the CTLA-4 antibody with the IgG control; 0 mm 3 for the anti-CTLA-4 antibody (10 mg/kg) and anti-PD-I antibody (10 mg/kg) combination group; about 90 mm 3 for the anti-CTLA-4 antibody (3 mg/kg) and anti PD-I antibody (3 mg/kg) combination group; and about 650 mm 3 for the anti-CTLA-4 antibody (1 mg/kg) and anti-PD-1 antibody (1 mg/kg) combination group. For the 25 combination treatment of the anti-PD-1 antibody with the anti-CTLA-4 antibody, the number of mice per group that were tumor free at day 27 of the study was 8/10 (10 mg/kg), 2/10 (3 mg/kg) and 1/10 (1 mg/kg) (data not shown). This study indicates that, in a murine tumor model, treatment with the combination of CTLA-4 antibody and PD-i antibody functions in a dose dependent manner and has a o significantly greater effect on tumor growth than both antibodies alone, even at a lower dose and even when a tumor is already well established. Moreover, the antibodies may be administered sequentially (anti-CTLA-4 antibody first and anti-PD-1 antibody second, or vice versa) and the combination is still superior to the antibody monotherapies. Example 16: In Vivo Efficacy of Combination Therapy (anti-CTLA-4 and anti-PD-1 A s Antibodies) on Fibrosarcoma Establishment and Growth SAl/N fibrosarcoma cells (PD-L1r) (Leach et al. (1996) Science 271:1734-1736) were implanted subcutaneously in AIJ mice (2 x 106 cells/mouse) on day 0. On days 1, 4, 7 and 11 post-implantation, mice were injected IP as follows: Group (A) PBS alone (referred to as the 91 "vehicle"); Group (B) mouse IgG (control, 10 mg/kg per mouse), Group (C) anti-PD-1 monoclonal antibody 4H2 (10 mg/kg per mouse), Group (D) anti-CTLA-4 monoclonal antibody 9D9 (10 mg/kg or 0.2 mg/kg per mouse), and Group (E) anti-PD-1 monoclonal antibody 412 (10 mg/kg per mouse) in combination with anti-CTLA-4 monoclonal antibody 5 9D9 (0.2 mg/kg per mouse). The study lasted 41 days and tumor measurements were taken on various days throughout the course of the study (see Figure 29). Tumor volume was calculated by measuring tumors in three dimensions (height x width x length) using an electronic caliper. Mice were euthanized when the tumors reached a designated tumor end point-a volume of 1500 mm 3 and/or an ulcerated tumor. 0 Figures 30A and 30B show that 19 out of the 20 control (9/10 in Group A and 10/10 in Group B) mice had either reached a tumor end-point or had developed ulcerated tumors. Figure 30C shows that the group treated with 10 mg/kg anti-PD-I antibody (Group C) had 6 mice that reached a. tumor end-point (2 with a volume greater than 1500 mm 3 and 4 with an ulcerated tumor) and 4 mice that were tumor free. Figure 30D shows that the group treated iS with 10 mg/kg anti-CTLA-4 antibody (Group D) had 5 mice that reached a tumor end-point (2 with a volume greater than 1500 mm 3 and 3 with an ulcerated tumor), one mouse with a small tumor (volume of about 70 mm 3 ) and 4 mice that were tumor free. Figure 30E shows that the group treated with 0.2 mg/kg anti-CTLA-4 antibody (Group E) had 10 mice that reached a tumor end-point (6 with a volume greater than 1500 mm 3 and 4 with an ulcerated tumor). 20 Figure 30F shows that the group treated with a combination of 10 mg/kg anti-PD-1 antibody with 0.2 mg/kg anti-CTLA-4 antibody (Group F) had 2 mice that reached a tumor end-point (one with a volume greater than 1500 mm 3 and onewith an ulcerated tumor) and 8 mice that were tumor free. Figures 31 and 32 show the mean and median tumor volume, respectively, that 2-5 developed in treated and untreated mice over the course of this study. The tumor growth inhibition in mice treated with these antibodies, as compared to mice treated with the control antibody mouse IgG, is summarized in Table 6. 92 Table 6. Tumor Growth Inhibition and Tumor Free Mice Following Anti-PD-I and/or Anti-CTLA-4 Treatment Median Tumor TGI* (%) Median Tumor TGI (%) No. of Tumor Groupt Volume - mm 3 (Day 15) Volume - mm 3 (Day 19) Free Mice (Day (Day 15) (Day 19) 41) A 985 - 1140 - 0/10 B 635 - 1060 - 0/10 C 465 27 310 71 4/10 D 235 63 90 91 4/10 E 600 6 805 24 0/10 F 330 48 90 92 8/10 * TGI= tumor growth inhibition; the median could be calculated only when fewer than 50% of the mice reached the tumor end point. t Groups are as defined in Figure 30. A = vehicle (PBS); B = mouse IgG; C= anti-PD-1, 10 mg/kg; D = anti-CTLA-4, 10 mg/kg; E = anti-CTLA-4, 0.2 mg/kg; and F = anti-PD-1, 10 mg/kg with anti-CTLA-4, 0.2 mg/kg. These data further indicate that the combination therapy comprising anti:PD-1 and anti-CTLA-4 antibodies is substantially more effective than treatment with either antibody alone. Indeed, the combination is still more effective than single antibody treatments even when the combination therapy contains a subtherapeutic dose of anti-CTLA-4 antibody. These data also indicate that surprisingly the presence or absence of PD-Li on the tumor may have no effect on the efficacy of treatment with this antibody combination, although the presence of PD-Li may influence the effect of the antibody monotherapies in that expression of PD-Li on the tumor may also lead to inhibition of anti-tumor T cell responses (see Figure 40). Example 17: In Vivo Efficacy and Dose Titration of Combination Therapy (anti-CTLA-4 and anti-PD-1 Antibodies) on PD-L1~ Fibrosarcoma Growth SA1/N fibrosarcoma cells (PD-L1~) were implanted subcutaneously in A/J mice (2 x Lo 106 cells/mouse) on day 0 for a time sufficient (about 7 days) to permit the establishment of a tumor. On days 7, 10, 13 and 16 post-implantation, ten groups of 8 mice having an average tumor volume of 110 mm 3 were injected IP as follows: Group (A) PBS alone (referred to as the "vehicle"); Group (B) mouse IgG (control, 10 mg/kg per mouse); Group (C) anti-CTLA-4 monoclonal antibody 9D9 (0.25 mg/kg); Group (D) anti-CTLA-4 monoclonal antibody 9D9 25 (0.5 mg/kg per mouse); Group (E) anti-CTLA-4 monoclonal antibody 9D9 (5 mg/kg); Group (F) anti-PD-I monoclonal antibody 412 (3 mg/kg per mouse); Group (G) anti-PD-I monoclonal antibody 4H2 (10 mg/kg per mouse); Group (H) anti-PD-I monoclonal antibody 4H2 (10 mg/kg per mouse) in combination with anti-CTLA-4 monoclonal antibody 9D9 (0.25 mg/kg per mouse); Group (1) anti-PD-I monoclonal antibody 4H2 (10 mg/kg per mouse) in 3o combination with anti-CTLA-4 monoclonal antibody 9D9 (0.5 mg/kg per mouse); and Group 93 (J) anti-PD-1 monoclonal antibody 4H2 (3 mg/kg per mouse) in combination with anti-CTLA 4 monoclonal antibody 9D9 (0.5 mg/kg per mouse). On days 10, 13, 16 and 19 post-implantation, two groups of 6 mice having an average tumor volume of 255 mm 3 were injected IP as follows: Group (K) mouse IgG (control, 10 S mg/kg per mouse); and Group (L) anti-PD-I monoclonal antibody 4H2 (10 mg/kg per mouse) in combination with anti-CTLA-4 monoclonal antibody 9D9 (1 mg/kg per mouse). The study lasted 51 days and tumor measurements were taken on various days throughout the course of the study (see Figures 33-38). Tumor volume was calculated by measuring tumors in three dimensions (height x width x length) using an electronic caliper. Mice were t 0 euthanized when the tumors reached a designated tumor end-point-a volume of 1500 mm 3 and/or an ulcerated tumor. Figure 33 shows the response to immunostimulatory antibody treatment in mice with tumors having an initial volume of about 110 mm 3 (i.e., at the time of the first antibody treatment. Figures 33A and 33B show that all 16 control mice (Groups A and B) reached a is tumor end-point (15 with a tumor volume greater than 1500 mm 3 and 1 with an ulcerated tumor). Figures 33C-33E show that tumor bearing mice respond to treatment with anti-CTLA-4 antibody in a dose-dependent manner (e.g., Group C receiving 0.25 mg/kg had 7/8 mice reach the tumor end-point and one mouse with a tumor volume less than 200 mm 3 , whereas Group E receiving 5 mg/kg had 6/8 mice reach the tumor end-point and two mice zo were tumor free). Figures 33F and 33G show that mice responded about the same regardless of the anti-PD-1 antibody dose (Group F received 3. mg/kg and Group G received 10 mg/kg). In contrast, the mice receiving a combination treatment of 10 or 3 mg/kg anti-PD-1 antibody with 0.25 or 0.5 mg/kg anti-CTLA-4 antibody (Groups H, I and J) showed a significant reduction in tumor growth. For example, Figure 33J shows that the group treated with a 1s combination of 3 mg/kg anti-PD-1 antibody with 0.5 mg/kg anti-CTLA-4 antibody (Group J) had 2 mice that had ulcerated tumors, 2 mice with a tumor volume less than 500 mm 3 , and 4 mice that were tumor free. The unexpected synergistic effect of an anti-PD-1 antibody combined with an anti-CTLA-4 antibody, along with the surprising effectiveness of subtherapeutic levels of anti-CTLA-4 antibody in the combination, are shown in Figures 34 13 (mean tumor volume) and 35 (median tumor volume). Figure 36 shows the response to immunostimulatory antibody treatment in mice with larger tumors, those having an initial volume of about 250 mmn (i.e., at the time of the first antibody treatment). Figure 36A shows that all 6 control mice (Group K) reached a tumor end-point (4 with a tumor volume greater than 1500 mm 3 and 2 with an ulcerated tumor). 35 Figure 36B shows that the group treated with a combination of 10 mg/kg anti-PD-1 antibody with 1 mg/kg anti-CTLA-4 antibody (Group L) had one mouse with an ulcerated tumor, 4 mice with a tumor volume greater than 1500 mm 3 , and one mouse that was tumor free. The mean and median tumor volumes are shown in Figures 37 and 38. 94 The tumor growth inhibition in mice treated with these antibodies, as compared to mice treated with the control antibody mouse IgG, is summarized in Table 7 and Figure 39. Table 7. Tumor Growth Inhibition Fo lowing Anti-PD-1 and/or Anti-CTLA-4 Treatment Mean Tumor TGI* Median Tumor TGI Tumor No. Mice Group Volume - mm 3 (Mean) Volume - mm3 (Median) Free Mice at Tumor (Day 23) (Day 23) (Day 51) End Point A 700 -_1,380 B 1,710 - 1,360 - -_ C 1,050 39% 925 32 _ D 770 55% 505 63 - E 155 91% 100 93 2/8 6/8 F 1,050 39% 675 50 - 7/8 G . 1,070 37% 1,145 16 - 6/8 H 85 95% 25 98 4/8 3/8 I 75 96% 60 95 4/8 1/8 J 80 95% 5 99 4/8 0/8 K 1,900 - 2,125 - L 1,115 41 1,090 49 1/6 * TGI= tumor growth inhibition; the median could only be calculated when fewer than 50% of the mice reached the tumor end point. t Groups are as defined in Figures 33 and 36. For smaller initial tumor: A = vehicle (PBS); B = mouse IgG, 10 mg/kg; C = anti-CTLA-4, 0.25 mg/kg; D = anti-CTLA-4, 0.5 mg/kg; E = anti-CTLA-4, 5 mg/kg; F = anti-PD-1, 3 mg/kg; G= anti-PD-1, 10 mg/kg; H = anti-PD-1, 10 mg/kg with anti-CTLA-4, 0.25 mg/kg; I = anti-PD-1, 10 mg/kg with anti-CTLA-4, 0.5 mg/kg; D and J= anti-PD-1, 3 mg/kg with anti-CTLA-4, 0.5 mg/kg. For larger initial tumor: K = mouse IgG, 10 mg/kg; and L = anti-PD-1, 10 mg/kg with anti-CTLA-4, 0.25 mg/kg. Together these data indicate that the combination therapy comprising anti-PD-I and anti-CTLA-4 antibodies is substantially more effective than treatment with either antibody alone. In addition, surprisingly the dose of each antibody can be reduced without affecting is the synergistic efficacy of this combination of immunostimulatory therapeutic antibodies. The combination therapy still seems to be effective even when the tumor mass is more mature (i.e., larger). Example 18: Tumor Immunity in Mice Following anti-PD-1 Antibody Treatment and Re-Challenge with PD-L1 Fibrosarcoma Cells 2C0 Mice that survived tumor-free from a challenge with tumor cells and treatment with anti-PD-1 antibody (i.e., treatment similar to the efficacy studies described in Examples 5 and 6) were then re-challenged with tumor cells to investigate immunity to tumor formation after such a treatment. Briefly, in the initial challenge, SA1/N fibrosarcoma cells (PD-L1) were implanted subcutaneously in A/J mice (1 x 106 cells/mouse) on day 0. On days 1, 4, 7, 10, 14, 2 .17 and 20 post-implantation, groups of mice were injected IP with either mouse IgG (control, 10 mg/kg per mouse) or with one of various doses of anti-PD-1 monoclonal antibody 4H2 (30, 95 10, 3, 1 and 0.3 mg/kg per mouse). Tumor formation and volume was monitored with a precision electronic caliper twice a week until the study was complete. A group of 8 mice were tumor-free after the anti-PD1 antibody treatment (4 that were treated with 30 mg/kg, 2 with 3 mg/kg, one with 1 mg/kg, and one with 0.3 mg/kg). The eight treated, tumor-free A/J mice were re-challenged by subcutaneously implanting 1 x 106 SA1/N fibrosarcoma cells/mouse. As'a control, nine naive mice were subcutaneously implanted with 1 x 106 SA1/N fibrosarcoma cells/mouse. Tumor formation and volume was monitored with a precision electronic caliper twice a week until day 62 post implantation. All nine naive (control) mice reached the tumor end-point by day 22 post to implantation of the fibrosarcoma cells. In contrast, the eight tumor-free mice re-challenged with fibrosarcoma cells did not develop tumors up to 62 days post-implantation. Figure 47 shows the mean tumor volume for the naive and re-challenged mice. These results demonstrate that treatment with an immunostimulatory antibody, such as anti-PD-1, provides the treated subject with immunity to further tumor formation, even in the presence of cells I $ capable of forming a tumor. Example 19: Tumor Immunity in Mice Following Single Antibody Therapy (anti-PD-1) or Combination Antibody Therapy (anti-CTLA-4 and anti-PD-1 Re-Challenged with PD-L1~ Colorectal Cancer Cells Mice that survived tumor-free from a challenge with tumor cells and treatment with C either anti-PD-I antibody alone or anti-PD-1 antibody combined with anti-CTLA-4 antibody (i.e., treatment similar to the efficacy studies described in Examples 2-4) were then re-challenged with tumor cells to investigate immunity to tumor formation after such treatments. Briefly, in the initial challenge, MC38 colorectal cancer cells (PD-L1-) were implanted in C57BL/6 mice (2 x 106 cells/mouse) on day 0. On days 0, 3, 6 and 10 post .-5 implantation, groups of mice were injected IP with one of the following treatments: (1) mouse IgG (control, 10 mg/kg per mouse), anti-PD-1 monoclonal antibody 4H2, or (3) anti PD-I monoclonal antibody 4H2 in combination with anti-CTLA-4 monoclonal antibody 9D9. Tumor growth was monitored with a precision electronic caliper as described in Example 15. A group of 11 mice were tumor-free after the anti-PD 1 antibody treatment (2 total) or the 30 combination anti-PD-1/anti-CTLA-4 antibody treatment (9 total). The 11 treated, tumor-free C57BL/6 mice were re-challenged by implantation of 2 x 107 MC38 colorectal cancer cells/mouse (i.e., a dose of cells 10 x greater than the initial challenge). As a control, seven naive mice were implanted. with 2 x 10' MC38 colorectal cancer cells/mouse. Tumor formation and volume was monitored with a precision electronic S5 caliper for the duration of the re-challenge experiment (at least 20 days). Figure 48 shows that all seven naive (control) mice developed a tumor and reached the tumor end-point by day 18 post-implantation of the colorectal cancer cells. In contrast, all 11 tumor-free mice re challenged with colorectal cancer cells did not develop tumors up to 18 days post-implantation. 96 Figure 49 shows the mean tumor volume for the naive and re-challenged mice. These data indicate that, similar to the antibody monotherapy, the combination antibody therapy resulting in PD-i and CTLA-4 blockade produces a persistent immunity to tumor relapse. Example 20: In Vivo Efficacy of Combination Therapy (anti-CTLA-4 and anti-PD-1 5 Antibodies) on Established Tumor Growth CT26 colorectal cancer cells were implanted in BALB/Cmice (2 x 106 cells/mouse) for a time sufficient (about 10 days) to permit the formation of tumors. On day 10 post implantation, tumor measurements were taken and mice were randomized based on mean tumor volume (about 250 mm 3 ) into 5 groups for subsequent antibody therapy. At day 0 (i.e., I0 10 days after the CT26 cells were implanted), mice were injected IP with (1) mouse IgG (control), (2) anti-CTLA-4 monoclonal antibody 9D9, (3) anti-PD-1 monoclonal antibody 4H2, or (4) anti-CTLA-4 monoclonal antibody 9D9 and anti-PD-I antibody monoclonal antibody 4H2, at a concentration of 10 mg/kg per mouse. Antibody injections were also administered on days 3, 6 and 10. The monoclonal antibody compositions used had low levels of 5 S endotoxin and did not significantly aggregate. Using an electronic caliper, the tumors were measured three dimensionally (height x width x length) and tumor volume was calculated. Tumor measurements were taken on day 0 (tumors at the beginning of treatment had a volume of about 125 mm 3 ), and on days 3, 6, 10, 13, 17 and 20 post-antibody injection. Mice were euthanized when the tumors reached a designated tumor end-point (a particular tumor volume 20 such as 1500 mm 3 and/or when the mice showed greater than about 15% weight loss). The results are shown in Figure 50. This study indicates that, in a murine tumor model, treatment with the combination of CTLA-4 antibody and PD-1 antibody has a significantly greater effect on tumor growth than either antibody alone, even when a tumor is already well established. Example 21: Effect of human anti-PD-1 antibody on function of T regulatory cells 25 T regulatory cells are lymphocytes that suppress the immune response. In this example, T regulatory cells were tested for its inhibitory function on proliferation and IFN-gamma secretion of CD4+CD25- T cells in the presence or absence of an anti-PD-I human monoclonal antibody. T regulatory cells were purified from PBMC using a CD4+CD25+ regulatory T cell 30 isolation kit (Miltenyi Biotec). T regulatory cells were added into a mixed lymphocyte reaction (see above) containing purified CD4+CD25- T cells and allogeneic dendritic cells in a 2:1 ratio of CD4+CD25- to T regulatory cells. Anti-PD-i.monoclonal antibody 5C4 was added at a concentration of 10 Rg/ml. Either no antibody or an isotype control antibody was used as a negative control. Culture supernatants were harvested on Day 5 for cytokine M measurement using a Beadlyte cytokine detection system (Upstate). The cells were labeled with 3 H-thymidine, cultured for another 18 hours, and analyzed for cell proliferation. The results are shown in Figures SIA (T cell proliferation) and 51B (IFN-gamma secretion). The 97 addition of anti-PD-1 human monoclonal antibody 5C4 partially released inhibition imposed by Treg cells on proliferation and IFN-gamma secretion of CD4+CD25- T cells, indicating that anti-PD-1 antibodies have an effect on T regulatory cells. Example 22: Effect of human anti-PD-1 antibody on T cell activation In this example, effect of blockade of PD-1 pathway by anti-PD-1 antibody 5C4 on T cell activation was examined. Purified human CD4+ T cells (Dynal CD4 T cell purification kit) were activated with 1p g/ml soluble anti-CD3 antibody (BD) in the presence of autologous monocytes or monocyte-derived dendritic cells (DCs). Monocytes were purified using Miltenyi CD14 monocyte purification kit, and DCs was generated in vitro after culture of IC monocytes with GM-CSF and IL-4 (PeproTech) for 7 days. After three days of activation in the presence or absence of titrated anti-PD-I antibody or irrelevant isotype control mAb, culture supernatants were harvested for ELISA analysis of IFNy secretion while tritiated thymidine was added during the final 18 hours of the assay in order to measure T cell proliferation. The results shown in Figures 52A and 52B demonstrate that PD-1 blockade by '5 anti-PD-1 antibody resulted in enhanced T cell proliferation and IFN-y secretion. Synergic effect by anti-PD-1 antibody and anti-CTLA-4 antibody on T cell activation (specifically on IFN-y secretion) in the presence of monocytes was also observed. Example 23: Assessment of ADCC activity of anti-PD-1 antibody In this example, an antibody-dependent cellular cytotoxicity (ADCC) assay was 2o performed to evaluate whether anti-PD-I antibody could induce ADCC to target cells. Two versions of 5C4, one with an Fc region of human IgG1 (5C4-IgG1) and the other with an Fc region of human IgG4 (5C4-IgG4), were tested in the assay. The Delfia.Cell Cytotoxicity Kit from Perkin Elmer was used for the assay. Briefly, purified human CD4 T cells (Dynal CD4 T cell purification kit) were activated by plate-bound anti-CD3 antibody (BD) to induce 2s PD-i expression. Target activated CD4 T cells were then labeled with BATDA reagent. Labeled CD4 T cells were added to a V-bottom 96-well plate, followed by the addition of human PBMC (an effector to target (E/T) cell ratio of 50:1) and designed antibody. After incubation for 1 hour at 37*C, the plate was spun down. Supernatant was transferred into a flat bottom 96-well plate and the plate was read using a RubyStar plate reader. Results showed that Ic 5C4-IgG4 did not mediate ADCC on activated CD4 T cells, while 5C4-IgG1 did mediate ADCC on activated CD4 T cells (Figure 53), indicating that ADCC activity is related to its Fc region of the anti-PD-1 antibody. Example 24: Assessment of Complement-dependent Cytotoxicity of anti-PD-1 antibody In this -example, complement dependant cytotoxicity (CDC) of anti-PD-I antibody was examined. Two versions of 5C4, one with Fc region of human IgGI (5C4-IgG1) and the other with Fc region of human IgG4 (5C4-IgG4), were tested in the assay. Briefly, purified human 98 CD4 T cells (Dynal CD4 T cell purification kit) were activated by plate-bound anti-CD3 antibody (BD) to induce PD-1 expression. Serial dilutions of anti-PD-1 antibody (5C4) and control antibodies from 50 pg/mL to 640 pg/mL were tested for CDC in the presence of human complement (Quidel-Al 13). Alamar blue (Biosource International) was used to S measure cytotoxicity. The plate was read on a fluorescent plate reader (EX530 EM590). Viable cell counts are proportional to fluorescence units. Results showed that neither 5C4 IgG1 or 5C4-IgG4 mediated CDC on activated CD4 T cells, while the positive control antibody (anti-HLA-ABC antibody) did (Figure 54). Example 25: Assessment of PD-1 expression on human T cells I oIn this example, human PBMCs from different donors were examined for PD-I expression on various cell subsets by FACS. Biotinylated anti-PD-1 antibody, which has displayed a much higher sensitivity than commercially available anti-PD-I antibody on detection of PD-1 molecules on cell surface, was used in the assay. Bound antibody was detected using an PE-conjugated streptavidin. Flow cytometric analyses were performed using S a FACScan flow cytometry (Becton Dickinson) and Flowjo software (Tree Star). PD-I expression was detected on some peripheral human T cells, but not on B cells or monocytes. Further examination of T cell subsets indicates that PD-1 is expressed on CD4 and CD8 memory and effector T cells, but absent on naive CD4 or CD8 T cells. The present invention is not to be limited in scope by the specific embodiments - described herein. Indeed, various modifications of the invention, in addition to those described herein, will become apparent to those skilled in the art from the foregoing description and the accompanying figures. Such modifications are intended to fall within the scope of the appended claims. The invention is, therefore, to be limited only by the terms of the appended claims along with the full scope of equivalents to which the claims are entitled. 99

Claims (78)

1. An isolated monoclonal antibody, or antigen-binding portion thereof, wherein the antibody is selected from the group consisting of: a) an antibody comprising a heavy chain variable region CDR1 comprising amino acids having the S sequence set forth in SEQ ID NO: 15; a heavy chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 22; a heavy chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 29; 'o a light chain variable region CDRI comprising amino acids having the sequence set forth in SEQ ID NO: 36; a light chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 43; and a light chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 50; b) an antibody comprising a heavy chain variable region CDR1 comprising amino acids having the sequence set forth in SEQ ID NO: 16; a heavy chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 23; a heavy chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO:30; a light chain variable region CDR1 comprising amino acids having the sequence set forth in SEQ ID NO: 37; a light chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 44; and a light chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 51; c) an antibody comprising a heavy chain variable region CDRI comprising amino acids having the sequence set forth in SEQ ID NO: 17; a heavy chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 24; a heavy chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 31; a light chain variable region CDR] comprising amino acids having the sequence set forth in SEQ ID NO: 38; a light chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 45; and a light chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 52; d) an antibody comprising a heavy chain variable region CDRI comprising amino acids having the sequence set forth in SEQ ID NO: 19; 100 a heavy chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 26; a heavy chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 33; 5 a light chain variable region CDRI comprising amino acids having the sequence set forth in SEQ ID NO: 40; a light chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 47; and a light chain variable region CDR3 comprising amino acids having the 1o sequence set forth in SEQ ID NO: 54 e)an antibody comprising a heavy chain variable region CDR1 comprising amino acids having the sequence set forth in SEQ ID NO: 20; a heavy chain variable region CDR2 comprising amino acids having the 15 sequence set forth in SEQ ID NO: 27; a heavy chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 34; a light chain variable region CDRI comprising amino acids having the sequence set forth in SEQ ID NO: 41; 2D a light chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 48; and a light chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 55; and f) an antibody comprising 2s a heavy chain variable region CDR1 comprising amino acids having the sequence set forth in SEQ ID NO: 21; a heavy chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 28; a heavy chain variable region CDR3 comprising amino acids having the so sequence set forth in SEQ ID NO: 35; a light chain variable region CDRl comprising amino acids having the sequence set forth in SEQ ID NO: 42; a light chain variable region CDR2 comprising amino acids having the sequence set forth in SEQ ID NO: 49; and a light chain variable region CDR3 comprising amino acids having the sequence set forth in SEQ ID NO: 56, wherein the antibody specifically binds to PD-1.

2. The isolated monoclonal antibody, or antigen-binding portion thereof of claim 1, wherein the antibody is selected from the group consisting of: 40 a) an antibody comprising a heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 1; and a light chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 8; b) an antibody comprising a heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 2; and a light chain variable 5 region comprising amino acids having the sequence set forth in SEQ ID NO: 9; 101 c) an antibody comprising a heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 3; and a light chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 10; d) an antibody comprising a heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 5; and a light chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 12; e) an antibody comprising a heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 6; and a light chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 13; and f) an antibody comprising a heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 7; and a light chain variable s region comprising amino acids having the sequence set forth in SEQ ID NO:

14. 3. The isolated monoclonal antibody, or antigen-binding portion thereof, of any one of claims I to 2, wherein the antibody is a human antibody. 4. The isolated monoclonal antibody, or antigen-binding portion thereof, of claim 3, to wherein the antibody is IgG4 isotype. 5. A composition comprising the antibody, or antigen-binding portion thereof, of any one of claims I to 4, and a pharmaceutically acceptable carrier, 6. An immunoconjugate comprising the antibody, or antigen-binding portion thereof, of any one of claims I to 4, linked to a therapeutic agent. Ts 7. A bispecific molecule comprising the antibody, or antigen-binding portion thereof, of claim of any one of claims 1 to 4, linked to a second functional moiety having a different binding specificity than said antibody, or antigen-binding portion thereof. 8. An isolated nucleic acid molecule encoding the antibody, or antigen-binding portion thereof, of any one of claims 1 to 4. 30 9. An expression vector comprising the nucleic acid molecule of claim 8. 10. A host cell comprising the expression vector of claim 9. 11. A transgenic mouse comprising human immunoglobulin heavy and light chain transgenes, wherein the mouse expresses the antibody of any one of claims I to 4. 12. A hybridoma prepared from the transgenic mouse of claim 11, wherein the 35 hybridoma produces the antibody of any one of claims 1 to 4. 13. A method of modulating an immune response in a subject comprising administering 102 to the subject the antibody, or antigen-binding portion thereof, of any one of claims I to 4 such that the immune response in the subject is modulated. 14. A method of inhibiting growth of tumor cells in a subject, comprising administering to a subject the antibody, or antigen-binding portion thereof, of any one of claims I to 4 S in an amount effective to inhibit growth of the tumor cells.

15. The method of claim 14, wherein the tumor cells are of a cancer selected from the group consisting of melanoma, renal cancer, prostate cancer, breast cancer, colon cancer and lung cancer.

16. The method of claim 14, wherein the tumor cells are of a cancer selected from the %o group consisting of bone cancer, pancreatic cancer, skin cancer, cancer of the head or neck, cutaneous or intraocular malignant melanoma, uterine cancer, ovarian cancer, rectal cancer, cancer of the anal region, stomach cancer, testicular cancer, uterine cancer, carcinoma of the fallopian tubes, carcinoma of the endometrium, carcinoma of the cervix, carcinoma of the vagina, carcinoma of the vulva, Hodgkin's Disease, IS non-Hodgkin's lymphoma, cancer of the esophagus, cancer of the small intestine, cancer of the endocrine system, cancer of the thyroid gland, cancer of the parathyroid gland, cancer of the adrenal gland, sarcoma of soft tissue, cancer of the urethra, cancer of the penis, chronic or acute leukemias including acute myeloid leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, solid tumors of 20 childhood, lymphocytic lymphoma, cancer of the bladder, cancer of the kidney or ureter, carcinoma of the renal pelvis, neoplasm of the central nervous system (CNS), primary CNS lymphoma, tumor angiogenesis, spinal axis tumor, brain stem glioma, pituitary adenoma, Kaposi's sarcoma, epidermoid cancer, squamous cell cancer, T-cell lymphoma, environmentally induced cancers including those induced by asbestos, and combinations 26 of said cancers.

17. A method of treating an infectious disease in a subject comprising administering to the subject the antibody, or antigen-binding portion thereof, of any one of claims 1 to 4 such that the subject is treated for the infectious disease.

18. The method of claim 17, wherein the infectious disease is caused by a virus selected 30 from the group consisting of HIV, Hepatitis (A, B, & C), herpes virus (VZV, HSV-1, HAV-6, HSV-II, and CMV, Epstein Barr virus), adenovirus and influenza virus.

19. A method of enhancing an immune response to an antigen in a subject, comprising administering to the subject: (i) the antigen; and (ii) the antibody, or antigen-binding portion thereof, of any one of claims I to 4 such that an immune response to the antigen Is in the subject is enhanced.

20. The method of claim 19, wherein the antigen is a tumor antigen, a viral antigen, a bacterial antigen or an antigen from a pathogen.

21. A method for treating a hyperproliferative disease or altering an adverse event associated with treatment of a byperproliferative disease, which the method comprises: 103 (a) administering the anti-PD-1 antibody of any one of claims 1 to 4 to a subject, and (b) administering an anti-CTLA-4 antibody to the subject.

22. The method of claim 21, wherein the anti-PD-1 antibody is administered at a S subtherapeutic dose.

23. The method of claim 21, wherein the anti-CTLA-4 antibody is administered at a subtherapeutic dose.

24. The method of claim 21, wherein the anti-PD-1 antibody and the anti-CTLA-4 antibody are each administered at a subtherapeutic dose. oc 25. The method of claim 21, wherein the hyperproliferative disease is cancer.

26. The method of claim 21, wherein the cancer is a cancer selected from the group consisting of melanoma, renal cancer, prostate cancer, breast cancer, colon cancer and lung cancer.

27. An isolated human monoclonal antibody, or an antigen-binding portion thereof, wherein the antibody or antigen-binding portion thereof cross-competes for binding to PD-1 with a reference antibody or reference antigen-binding portion thereof comprising: a) a human heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: I and a human light chain variable o0 region comprising amino acids having the sequence set forth in SEQ ID NO: 8; b) a human heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 2 and a human light chain variable region comprising amino acids having the sequence set forth in SEQ ID 25 NO: 9; c) a human heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 3 and a human light chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 10; 30 d) a human heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 5 and a human light chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 12; e) a human heavy chain variable region comprising amino acids having Is the sequence set forth in SEQ ID NO: 6 and a human light chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 13; or f) a human heavy chain variable region comprising amino acids having the sequence set forth in SEQ ID NO: 7 and a human light chain variable 40 region comprising amino acids having the sequence set forth in SEQ ID NO: 14. 104 1. An isolated human monoclonal antibody, or an antigen-binding portion thereof, wherein the antibody binds to PD-i and wherein the antibody exhibits at least one of the following properties: a) binds to human PD-I with a KD of 1 x 10 7 M or less; 5 b) does not substantially bind to human CD28, CTLA-4 or ICOS; c) increases T-cell proliferation in an Mixed Lymphocyte Reaction (MLR) assay; d) increases interferon-gamma production in an MLR assay; or e) increases interleukin-2 (IL-2) secretion in an MLR assay. 2. The antibody of claim 1 which is full-length antibody of an IgGI or IgG4 isotype. .3. The antibody of claim 1 which is an antibody fragment or a single chain antibody. 4. The antibody of claim 1, wherein the antibody binds to human PD-I with a KD of 5 x 10~8 M or less. 5. The antibody of claim 1, wherein the antibody binds to human PD-i with a KD of 1 x 10~ M or less. 6. The antibody of claim 1, wherein the antibody binds to human PD-i with a KD of 5 x 10-9 M or less. 7. The antibody of claim 1, wherein the antibody binds to human PD-I with a KD Of between 1 x 10'sM and I x 10'0 M. 8. An isolated human monoclonal antibody, or an antigen-binding portion thereof, wherein 20 the antibody cross-competes for binding to PD-i with a reference antibody comprising: a) a human heavy chain variable region comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7; and b) a human light chain variable region comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14. 2 S 9. The antibody of claim 8, wherein the human heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 1 and the human light chain variable region comprises the amino acid sequence of SEQ ID NO: 8. 105 10. The antibody of claim 8, wherein the human heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 2 and the human light chain variable region comprises the amino acid sequence of SEQ ID NO: 9 11. The antibody of claim 8, wherein the human heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 3 and the human light chain variable region comprises the amino acid sequence of SEQ ID NO: 10. 12. The antibody of claim 8, wherein the human heavy chain. variable region comprises the amino acid sequence of SEQ ID NO: 4 and the human light chain variable region comprises the amino acid sequence of SEQ ID NO: 11. I 13. The antibody of claim 8, wherein the human heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 5 and the human light chain variable region comprises the amino acid sequence of SEQ ID NO: 12. 14. The antibody of claim 8, wherein the human heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 6 and the human light chain variable region comprises the amino acid sequence of SEQ ID NO: 13. 15. The antibody of claim 8, wherein-the human heavy chain variable region comprises the amino acid sequence of SEQ ID NO: 7 and the human light chain variable region comprises the amino acid sequence of SEQ ID NO: 14. 16. An isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a 20 heavy chain variable region that is the product of or derived from a human VH 3-33 gene, wherein the antibody specifically binds to PD-1. 17. An isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a heavy chain variable region that is the product of or derived from a human VH 4-39 gene, wherein the antibody specifically binds to PD-1. 2S 18. An isolated monoclonal antibody, or an antigen-binding portion thereof, comprising a light chain variable region that is the product of or derived from a human VK L6 gene, wherein the antibody specifically binds to PD-1. 19. An isolated monoclonal antibody, or an antigen-binding portion thereof comprising a light chain variable region that is the product of or derived from a human Vk L15 gene, wherein the antibody specifically binds to PD-1. 106 20. An isolated monoclonal antibody, or an antigen-binding portion thereof, comprising: a) a heavy chain variable region of a human VH 3-33 gene; and b) a light chain variable region of a human Vk L6 gene; wherein the antibody specifically binds to PD-1. 5 21. An isolated monoclonal antibody, or an antigen-binding portion thereof, comprising: a) a heavy chain variable region of a human VH 4-39 gene; and b) a light chain variable region of a human Vk L15 gene; wherein the antibody specifically binds to PD-1. 22. An isolated monoclonal antibody, or antigen-binding portion thereof, comprising a heavy to chain variable region that comprises CDR1, CDR2, and CDR3 sequences; and a light chain variable region that comprises CDR1, CDR2, and CDR3 sequences, wherein: a) the heavy chain variable region CDR3 sequence comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 29, 30, 31; 32, 33, 34 and 35, and conservative modifications thereof, b) the light chain variable region CDR3 sequence comprises an amino acid sequence selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56, and conservative modifications thereof, and c) the antibody specifically binds to PD-1. 23. The antibody of claim 22, wherein the heavy chain variable region CDR2 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28, and conservative modifications thereof, and the light chain variable region CDR2 sequence comprises an amino acid sequence selected-from the group consisting of amino acid sequences of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, and conservative modifications thereof 25 24. The antibody of claim 23, wherein the heavy chain variable region CDR1 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, and conservative modifications thereof, and the light chain variable region CDR1 sequence comprises an amino acid sequence selected from the group consisting of amino acid sequences of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, and conservative modifications thereof. 25. An isolated monoclonal antibody, or antigen-binding portion thereof, comprising a heavy chain variable region and a light chain variable region, wherein: 107 a) the heavy chain variable region comprises an amino acid sequence that is at least 80% homologous to an amino acid sequence selected from the group consisting of SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7; b) the light chain variable region comprises an amino acid sequence that is at least 80% 5 homologous to an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14; c) the antibody binds to human PD-i with a KD of 1 x 10-7M or less; and d) the antibody does not substantially bind to human CD28, CTLA-4 or ICOS. 26. The antibody of claim 25, wherein the antibody further comprises at least one of the 0 following properties: a) the antibody increases T-cell proliferation in an Mixed Lymphocyte Reaction (MLR) assay; b) the antibody increases interferon-gamma production in an MLR assay; or c) the antibody increases interleukin-2 (IL-2) secretion in an MLR assay. s 27. An isolated monoclonal antibody, or antigen-binding portion thereof, comprising: a) a heavy chain variable region CDRI comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21; b) a heavy chain variable region CDR2 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28; 2 c) a heavy chain variable region CDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35; d) a light chain variable region CDR1 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42; e) a light chain variable region CDR2 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49; and f) a light chain variable region CDR3 comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56; wherein the antibody specifically binds PD-1.

28. The antibody of claim 27, which comprises: o a) a heavy chain variable region CDRI comprising SEQ ID NO: 15; b) a heavy chain variable region CDR2 comprising SFQ ID NO: 22; c) a heavy chain variable region CDR3 comprising SEQ ID NO: 29; d) a light chain variable region CDR1 comprising SEQ ID NO: 36; e) a light chain variable region CDR2 comprising SEQ ID NO: 43; and 2 S . f) a light chain variable region CDR3 comprising SEQ ID NO: 50. 108

29. The antibody of claim 27, which comprises: a) a heavy chain variable region CDR1 comprising SEQ ID NO: 16; b) a heavy chain variable region CDR2 comprising SEQ ID NO: 23; c) a heavy chain variable region CDR3 comprising SEQ ID NO:30; d) a light chain variable region CDR1 comprising SEQ ID NO: 37; e) a light chain variable region CDR2 comprising SEQ ID NO: 44; and f) a light chain variable region CDR3 comprising SEQ ID NO: 51.

30. The antibody of claim 27, which comprises: a) a heavy chain variable region CDR1 comprising SEQ ID NO: 17; 1o b) a heavy chain variable region CDR2 comprising SEQ ID NO: 24; c) a heavy chain variable region CDR3 comprising SEQ ID NO: 31; d) a light chain variable region CDR1 comprising SEQ ID NO: 38; e) a light chain variable region CDR2 comprising SEQ ID NO: 45; and f) a light chain variable region CDR3 comprising SEQ ID NO: 52. 1 5 31. The antibody of claim 27, which comprises: a) a heavy chain variable region CDR1 comprising SEQ ID NO: 18; b) a heavy chain variable region CDR2 comprising SEQ ID NO: 25; c) a heavy chain variable region CDR3 comprising SEQ ID NO: 32; d) a light chain variable region CDR1 comprising SEQ ID NO: 39; ,Lo e) a light chain variable region CDR2 comprising SEQ ID NO: 46; and f) a light chain variable region CDR3 comprising SEQ ID NO: 53.

32. The antibody of claim 27, which comprises: a) a heavy chain variable region CDRI comprising SEQ ID NO: 19; b) a heavy chain variable region CDR2 comprising SEQ ID NO: 26; 25 c) a heavy chain variable region CDR3 comprising SEQ ID NO: 33; d) a light chain variable region CDR1 comprising SEQ ID NO: 40; e) a light chain variable region CDR2 comprising SEQ ID NO: 47; and f) a light chain variable region CDR3 comprising SEQ ID NO: 54.

33. The antibo of claim 27, which comprises: 30 a) a heavy chain variable region CDR1 comprising SEQ ID NO: 20; b) a heavy chain variable region CDR2 comprising SEQ ID NO: 27; c) a heavy chain variable region CDR3 comprising SEQ ID NO: 34; d) a light chain variable region CDR1 comprising SEQ ID NO: 41; e) a light chain variable region CDR2 comprising SEQ ID NO: 48; and . f) a light chain variable region CDR3 comprising SEQ ID NO: 55. 109

34. The antibody of claim 27, which comprises: a) a heavy chain variable region CDR1 comprising SEQ ID NO: 21; b) a heavy chain variable region CDR2 comprising SEQ ID NO: 28; c) a heavy chain variable region CDR3 comprising SEQ ID NO: 35; 5 d) a light chain variable region CDR1 comprising SEQ ID NO: 42; e) a light chain variable region CDR2 comprising SEQ ID NO: 49; and f) a light chain variable region CDR3 comprising SEQ ID NO: 56.

35. An isolated monoclonal antibody, or antigen-binding portion thereof comprising: a) a heavy chain variable region comprising an amino acid sequence selected from the o . group consisting of SEQ ID NOs: 1, 2, 3, 4, 5, 6 and 7; and b) a light chain variable region comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 8, 9, 10, 11, 12, 13 and 14; wherein the antibody specifically binds PD-1.

36. The antibody of claim 35, which comprises: is a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 1; and b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 8.

37. The antibody of claim 35, which comprises: a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 2; to and b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 9.

38. The antibody of claim 35, which comprises: a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 3; and b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 10.

39. The antibody of claim 35, which comprises: a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 4; and b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 11. So 40. The antibody of claim 35, which comprises: a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 5; and 110 b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 12.

41. The antibody of claim 35, which comprises: a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 6; and -5 b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 13.

42. The antibody of claim 35, which comprises: a) a heavy chain variable region comprising the amino acid sequence of SEQ ID NO: 7; and b) a light chain variable region comprising the amino acid sequence of SEQ ID NO: 14. a 43. A composition comprising the antibody, or antigen-binding portion thereof, of any one of claims 1-36, and a pharmaceutically acceptable carrier.

44. An immunoconjugate comprising the antibody, or antigen-binding portion thereof, of any one of claims 1-36, linked to a therapeutic agent.

45. A composition comprising the immunoconjugate of claim 44 and a pharmaceutically 5 acceptable carrier.

46. The immunoconjugate of claim 44, wherein the therapeutic agent is a cytotoxin.

47. A composition comprising the immunoconjugate of claim 46 and a pharmaceutically acceptable carrier.

48. The immunoconjugate of claim 44, wherein the therapeutic agent is a radioactive isotope. 0o 49. A composition comprising the immunoconjugate of claim 48 and a pharmaceutically acceptable carrier.

50. A bispecific molecule comprising the antibody, or antigen-binding portion thereof, of any one of claims 1-36, linked to a second functional moiety having a different binding specificity than said antibody, or antigen-binding portion thereof. 215 51. A composition comprising the bispecific molecule of claim 50, and a pharmaceutically acceptable carrier. 111

52. An isolated nucleic acid molecule encoding the antibody, or antigen-binding portion thereof, of any one of claims 1-36.

53. An expression vector comprising the nucleic acid molecule of claim 52.

54. A host cell comprising the expression vector of claim 53. s 55. A transgenic mouse comprising human immunoglobulin heavy and light chain transgenes, wherein the mouse expresses the antibody of any one of claims 1-36.

56. A hybridoma prepared from the mouse of claim 55, wherein the hybridoma produces said antibody.

57. A method of modulating an immune response in a subject comprising administering to (o the subject the antibody, or antigen-binding portion thereof; of any one of claims 1-36 such that the immune response in the subject is modulated.

58. A method of inhibiting growth of tumor cells in a subject, comprising administering to the subject a therapeutically effective amount of an anti-PD-I antibody, or antigen binding portion thereof S 59. The method of claim 58, wherein the antibody is a chimeric antibody.

60. The method of claim 58, wherein the antibody is a humanized antibody.

61. The method of claim 58, wherein the antibody is a fully human antibody.

62. The method of claim 58, wherein the tumor cells are of a cancer selected from the group consisting of melanoma, renal cancer, prostate cancer, breast cancer, colon cancer and 20 lung cancer.

63. The method of claim 58, wherein the tumor cells are of a cancer selected from the list consisting of bone cancer, pancreatic cancer, skin cancer, cancer of the head or neck, cutaneous or intraocular malignant melanoma, uterine cancer, ovarian cancer, rectal cancer, cancer of the anal region, stomach cancer, testicular cancer, uterine cancer, 25 carcinoma of the fallopian tubes, carcinoma of the endometrium, carcinoma of the cervix, carcinoma of the vagina, carcinoma of the vulva, Hodgkin's Disease, non-Hodgkin's lymphoma, cancer of the esophagus, cancer of the small intestine, cancer of the endocrine system, cancer of the thyroid gland, cancer of the parathyroid gland, cancer of 112 the adrenal gland, sarcoma of soft tissue, cancer of the urethra, cancer of the penis, chronic or acute leukemias including acute myeloid leukemia, chronic myeloid leukemia, acute lymphoblastic leukemia, chronic lymphocytic leukemia, solid tumors of childhood, lymphocytic lymphoma, cancer of the bladder, cancer of the kidney or ureter, carcinoma S of the renal pelvis, neoplasm of the central nervous system (CNS), primary CNS lymphoma, tumor angiogenesis, spinal axis tumor, brain stem glioma, pituitary adenoma, Kaposi's sarcoma, epidermoid cancer, squamous cell cancer, T-cell lymphoma, environmentally induced cancers including those induced by asbestos, and combinations of said cancers. 0 64. A method of inhibiting growth of tumor cells in a subject, comprising administering to a subject the antibody, or antigen-binding portion thereof, of any one of claims 1-36 in an amount effective to inhibit growth of the tumor cells.

65. A method of treating an infectious disease in a subject comprising administering to the subject the antibody, or antigen-binding portion thereof, of any one of claims 1-36 such that the subject is treated for the infectious disease.

66. The method of claim 65, wherein the infectious disease is selected from the list consisting of: HIV, Influenza, Herpes, Giardia, Malaria, Leishmania, the pathogenic infection by the virus Hepatitis (A, B, & C), herpes virus (e.g., VZV, HSV-1, HAV-6, HSV-II, and CMV, Epstein Barr virus), adenovirus, influenza virus, flaviviruses, 20 echovirus, rhinovirus, coxsackie virus, cornovirus, respiratory syncytial virus, mumps virus, rotavirus, measles virus, rubella virus, parvovirus, vaccinia virus, HTLV virus, dengue virus, papillomavirus, molluscum virus, poliovirus, rabies virus, JC virus and arboviral encephalitis virus, pathogenic infection by the bacteria chlamydia, rickettsial bacteria, mycobacteria, staphylococci, streptococci, pneumonococci, meningococci and 25 conococci, klebsiella, proteus, serratia, pseudomonas, legionella, diphtheria, salmonella, bacilli, cholera, tetanus, botulism, anthrax, plague, leptospirosis, and Lymes disease bacteria, pathogenic infection by the fungi Candida (albicans, krusei, glabrata, tropicalis, etc.), Cryptococcus neoformans, Aspergillus fumigatuss, niger, etc.), Genus Mucorales (mucor, absidia, rhizophus), Sporothrix schenkii, Blastomyces dermatitidis, 30 Paracoccidioides brasiliensis, Coccidioides immitis and Histoplasma capsulatum, and pathogenic infection by the parasites Entamoeba histolytica, Balantidium coli, Naegleriafowleri, Acanthamoeba sp., Giardia lambia, Cryptosporidium sp., Pneumocystis carinii, Plasmodium vivax, Babesia microti, Trypanosoma brucei, Trypanosoma cruzi, Leishmania donovani, Toxoplasma gondi, and Nippostrongylus 3S . brasiliensis. 113

67. A method of enhancing an immune response to an antigen in a subject, comprising administering to the subject: (i) the antigen; and (ii) the antibody, or antigen-binding portion thereof, of any one of claims 1-36 such that an immune response to the antigen in the subject is enhanced. S 68. The method of claim 67, wherein the antigen is a tumor antigen, a viral antigen, a bacterial antigen or an antigen from a pathogen.

69. A method for treating a hyperproliferative disease, which method comprises: (a) administering a anti-PD-1 antibody to a subject, and (b) administering a anti-CTLA-4 antibody to the subject.

70. The method of claim 69, wherein the anti-PD-1 antibody is administered at a subtherapeutic dose.

71. The method of claim 69, wherein the anti-CTLA-4 antibody is administered at a subtherapeutic dose.

72. The method of claim 69, wherein the anti-PD-1 antibody and the anti-CTLA-4 antibody S are each administered at a subtherapeutic dose.

73. The method according to claim 69 wherein the anti-PD-I antibody and the anti-CTLA-4 antibody are administered sequentially.

74. The method according to claim 73 wherein the anti-PD-I antibody is administered before the anti-CTLA-4 antibody. 2 75. The method according to claim 73 wherein the anti-CTLA-4 antibody is administered before the anti-PD-1 antibody.

76. The method according to claim 73 wherein the anti-PD-1 antibody and the anti-CTLA-4 antibody are administered concurrently.

77. The method according to claim 73 wherein the anti-PD-1 antibody and the anti-CTLA-4 2s antibody are admixed as a single composition and administered concurrently.

78. The method according to claim 73 comprising administering to a subject (a) a composition comprising the anti-PD-1 antibody and a pharmaceutically acceptable 114 carrier and (b) a composition comprising the anti-CTLA-4 antibody and a pharmaceutically acceptable carrier.

79. The method of any one of claims 69 to 78 wherein the hyperproliferative disease is cancer. s 80. The method of claim 79 wherein the cancer is colon cancer.

81. The method of any one of claims 68 to 79 wherein the subject is a human.

82. The method of any one of claims 68 to 79 wherein the anti-PD-1 antibody is a human sequence antibody.

83. The method of claim 82 wherein the anti-PD-1 human sequence antibody is a monoclonal antibody.

84. The method of claim 83 wherein the anti-PD-I human sequence monoclonal antibody is 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 or 5F4.

85. The method of any one of claims 68 to 79 wherein the anti-CTLA-4 antibody is a human sequence antibody. is 86. The method of claim 85 wherein the anti-CTLA-4 human sequence antibody is a monoclonal antibody.

87. The method of claim 86 wherein the anti-CTLA-4 human sequence monoclonal antibody is 1ODI (MDX-010).

88. A method for altering an adverse event associated with treatment of a hyperproliferative 2 0 disease with an immunostimulatory agent, which method comprises: (a) administering an anti-PD-i antibody to a subject, and (b) administering a subtherapeutic dose of anti-CTLA-4 antibody to the subject.

89. The method of claim 86 wherein the anti-PD-1 antibody is administered in a subtherapeutic dose. 2S 90. The method according to claim 88 wherein the anti-PD-I antibody and the anti-CTLA-4 antibody are administered sequentially. 115

91. The method according to claim 90 wherein the anti-PD-i antibody is administered before the anti-CTLA-4 antibody.

92. The method according to claim 90 wherein the anti-CTLA-4 antibody is administered before the anti-PD-1 antibody. S 93. The method according to claim 88 wherein the anti-PD-1 antibody and the anti-CTLA-4 antibody are administered concurrently.

94. The method according to claim 88 wherein the anti-PD-i antibody and the anti-CTLA-4 antibody are admixed as a single composition and administered concurrently.

95. The method according to claim 88 comprising administering to a subject (a) a 0 o composition comprising the anti-PD-i antibody and a pharmaceutically acceptable carrier and (b) a composition comprising the anti-CTLA-4 antibody and a pharmaceutically acceptable carrier.

96. The method of any one of claims 88 to 95 wherein the hyperproliferative disease is cancer.

97. The method of claim 96 wherein the cancer is colon cancer.

98. The method of any one of claims 88 to 95 wherein the subject is a human.

99. The method of any one of claims 88 to 95 wherein the anti-PD-I antibody is a human sequence antibody.

100. The method of claim 99 wherein the anti-PD-I human sequence antibody is a 20 monoclonal antibody.

101. The method of claim 100 wherein the anti-PD-i human sequence monoclonal antibody is 17D8, 2D3, 4H1, 5C4, 4A1 1, 7D3 or 5F4.

102. The method of any one of claims 88 to 95 wherein the anti-CTLA-4 antibody is a human sequence antibody. -2S 103. The method of claim 102 wherein the anti-CTLA-4 human sequence antibody is a monoclonal antibody. 116

104. The method of claim 103 wherein the anti-CTLA-4 human sequence monoclonal antibody is 1ODI (MDX-0 10).

105. A method for preparing an anti-PD-1 antibody comprising: (a) providing: (i) a heavy chain variable region antibody sequence comprising a CDR1 s sequence that is selected from the group consisting of SEQ ID NOs: 15, 16, 17, 18, 19, 20 and 21, a CDR2 sequence that is selected from the group consisting of SEQ ID NOs: 22, 23, 24, 25, 26, 27 and 28; and a CDR3 sequence that is selected from the group consisting of SEQ ID NOs: 29, 30, 31, 32, 33, 34 and 35; or (ii) a light chain variable region antibody sequence comprising a CDR1 sequence that is selected from the group consisting of SEQ ID NOs: 36, 37, 38, 39, 40, 41 and 42, a CDR2 sequence that is selected from the group consisting of SEQ ID NOs: 43, 44, 45, 46, 47, 48 and 49, and a CDR3 sequence that is selected from the group consisting of SEQ ID NOs: 50, 51, 52, 53, 54, 55 and 56; (b) altering at least one amino acid residue within at least one variable region antibody sequence, said sequence being selected from the heavy chain variable region antibody sequence and the light chain variable region antibody sequence, to create at least one altered antibody sequence; and (c) expressing the altered antibody sequence as a protein. Dated 27 June, 2011 Ono Pharmaceutical Co., Ltd. and Medarex, Inc. Patent Attorneys for the Applicant/Nominated Person' SPRUSON & FERGUSON 117