NZ567242A

NZ567242A - Use of an IL-21/IL-21R agonist for modulating interleukin-21 receptor activity and treating cancer

Info

Publication number: NZ567242A
Application number: NZ56724202A
Authority: NZ
Inventors: Beatriz Carreno; Laura Carter; Matthew J Whitters; Mary Collins; Deborah A Young; Glenn Larsen; Debra D Donaldson; Leslie D Lowe; Kyri Dunussi; Margery Ma; Joann S Witek; Marion T Kasaian; Michelle Ungar
Original assignee: Genetics Inst Llc
Priority date: 2001-10-04
Filing date: 2002-10-04
Publication date: 2009-11-27

Abstract

Use of a therapeutically effective amount of an IL-21/IL-21R agonist for the manufacture of a medicament for treating, preventing or ameliorating a cancer.

Description

<div class="application article clearfix" id="description"> *10055442798* 5 6 7 2 42 PATENTS FORM NO. 5 Our ref: FIP228724NZPR Divisional Application out of NZ 532021 NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION Use of an IL-21/IL-21R agonist for modulating interleukin-21 receptor activity We, Genetics Institute, LLC of 87 Cambridge Park Drive, Cambridge, Massachusetts, 02140, United States of America hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: " iiOTU-GOTUAL PROP^.IT " cn ;ic™ OF N.Z. ~ & APR 2008 ncoriv^n (followed by page 1 a) 101147012_1.DOC:FIP:qwgtn RECEIVED at IPONZ on 05 November 2009 la USE OF AN IL-21/IL-21R AGONIST FOR MODULATING INTERLEUKIN-21 RECEPTOR ACTIVITY Field of the Invention The present invention and the invention of New Zealand Patent Application No. 532021, from which the present application was divided, and the invention of NZ 580885, which was divided from the present application, relate in general to compositions and their use for modulating interleukin-21 (IL-21 )/IL-21 receptor (MU-1) activity using IL-21 receptor agonists and antagonists. The compositions disclosed herein are useful as immunotherapeutical agents. Background of the Invention Human IL-21 is cytokine about a 131-amino acids in length that shows sequence homology to IL-2, IL-4 and IL-15 (Parrish-Novak et al. (2000) Nature 408:57-63). Despite low sequence homology among interleukin cytokines, cytokines share a common fold into a "four-helix-bundle" structure that is representative of the family. Most cytokines bind either the class I or the class II cytokine receptors. Class II cytokine receptors include the receptors for IL-10 and the interferons, whereas class I cytokine receptors include the receptors for IL2-IL7, IL-9, IL-11-13, and IL-15, as well as hematopoietic growth factors, leptin and growth hormone (Cosman, D. (1993) Cytokine 5:95-106). Human IL-21R is a class I cytokine receptor that is expressed in lymphoid tissues, in particular by NK, B and T cells (Parrish-Novak et al. (2000) supra). The nucleotide and amino acid sequences encoding human interleukin-21 (IL-21) and its receptor (IL-21R) are described in WO 00/53761; WO 01/85792; Parrish-Novak et al. (2000) supra; Ozaki et al. (2000) Proc. Natl. Acad. Sci. USA 97:11439-114444. IL-21Rhas the highest sequence homology to IL-2 receptor P chain and IL-4 receptor a chain (Ozaki et al. (2000) supra). Upon ligand binding, IL-21R associates with the common gamma cytokine receptor chain (yc) that is shared by receptors for IL-2, IL-3, IL-4, IL-7, IL-9, IL-13 and IL-15 (Ozaki et al. (2000) supra; Asao et al. (2001) J. Immunol. 167:1-5). The widespread lymphoid distribution of IL-21 R suggests that IL-21 may play a role in immune regulation. Indeed, in vitro studies have shown that IL-21 significantly modulates the function of B cells, CD4+ and CD8+ T cells, and NK cells (Parrish-Novak et al. (2000) supra; Kasaian, M.T. et al. (2002) (followed by page 2) 2 Immunity. 16:559-569). Nevertheless, evidence supporting a regulatory effect of IL-21 in vivo is limited. Summary of the Invention Compositions and their use for modulating the activity of, and/or an interaction between, an interleukin-21 (EL-21) and an IL-21 receptor (also referred to herein as "IL-21R" or "MU-1") using agonists or antagonists of IL-21 or IL-21R (also referred to herein as an "IL-21/IL-21R agonist" or "agonist," and "IL-21/IL-21R antagonist" or "antagonist," respectively) are disclosed in the present specification and the specification of NZ 532021, which is directed to the use of an EL-21/IL-21R antagonist comprising the amino acid sequence of SEQ ID NO:29 (Figures 10A-10C), or a sequence at least 90% or more identical thereto, in an amount sufficient to inhibit or reduce immune cell activity, for the manufacture of a medicament for treating, preventing or ameliorating an arthritic disorder. NZ 532021 is also directed to the use of an IL-21/IL-21R antagonist comprising the amino acid sequence of SEQ ID NO:25 (Figures 8A-8C), or a sequence at least 90% or more identical thereto, in an amount sufficient to inhibit or reduce immune cell activity in the subject, for the manufacture of a medicament for treating, preventing or ameliorating an arthritic disorder. The invention of NZ 532021 is also directed to fusion proteins and compositions comprising the amino acid sequence of SEQ ID NO:29 or SEQ ID NO:25 or of a sequence at least 90% or more identical thereto. The descriptions of the inventions of both the present application and NZ 532021 are retained herein for clarity and completeness. In one embodiment of NZ 532021, Applicants have shown that reducing IL-21R activity by using an IL-21 antagonist, e.g., a fusion protein that includes the extracellular domain of the IL-21R fused to an Fc immunoglobulin region, ameliorates inflammatory symptoms in collagen-induced arthritis (CIA) animal models (Example 7). Expression of IL-21R mRNA is upregulated in the paws of CIA mice (Example 8). Accordingly, antagonists of IL-21/IL-21R activity can be used to induce immune suppression in vivo, e.g., for treating or preventing immune cell-associated pathologies (e.g., pathologies associated with aberrant activity of one or more of mature T cells (mature CD8+, mature CD4+ T cells), mature NK cells, B cells, macrophages and megakaryocytes, including transplant rejection and autoimmune disorders, e.g., arthritis (including rheumatoid arthritis). Accordingly, in one aspect, the invention of NZ 532021 features use of an IL-21/IL-21R antagonist for the manufacture of a medicament for treating (e.g., curing, suppressing, (followed by page 2a) 2a ameliorating, delaying or preventing the onset of, or preventing recurrence or relapse of) or preventing an immune cell-associated disease, e.g., rheumatoid arthritis, in a subject, the medicament comprises: an IL-21/IL-21R antagonist, in an amount sufficient to inhibit or reduce immune cell activity and/or cell number. The medicament comprising the IL-21/IL-21R antagonist can be adapted for administration alone or in combination with other therapeutic modalities as described herein. Preferably, the subject is a mammal, e.g., a human suffering from an immune cell-associated pathology (e.g., pathology associated with aberrant activity of one or more of mature T cells (mature CD8+, mature CD4+ T cells), mature NK cells, B cells, macrophages and megakaryocytes, including transplant rejection and autoimmune disorders. For example, the medicament can be used to treat or prevent, in a subject, an immune cell-associated (followed by page 3) WO 03/028630 3 PCT/USfl 2/29839 disorders, e.g., a disorder chosen from one or more of: transplant rejection or an autoimmune disorder (e.g., including, for example, diabetes mellitus (type I), arthritis (including rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis, psoriatic arthritis, and ankylosing spondylitis), multiple sclerosis, myasthenia gravis, vasculitis, 5 systemic lupus eiythematosis, autoimmune thyroiditis, dermatitis (including atopic dermatitis and eczematous dermatitis), psoriasis, scleroderma, asthma, allergy, 1BD or Crohn's disease). Treatment of an arthritic disorder, e.g., a disorder chosen from one or more of rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis, psoriatic arthritis, or ankylosing spondylitis (preferably, rheumatoid arthritis) using the IL-21- or 10 IL-21R antagonists of the present invention is preferred. In one embodiment, the IL-21/IL-21R antagonist interacts with, e.g., binds to, IL-21 or IL-21R. preferably, mammalian, e.g., human IL-21 or IL-21R (referred to herein as an "3L-21 antagonist" and "IL-21R antagonist," respectively), and reduces or inhibits one or more IL-21 and/or IL-21R activities. Preferred antagonists bind to IL-21 or IL-21R 15 with high affinity, e.g., with an affinity constant of at least about 107 M~l, preferably about 10s M"i, and more preferably, about lO^M-l to jolO M"1 or stronger. For example, an IL-21/IL-21R antagonist can reduce and/or inhibit EL-21R activity by neutralizing IL-21. In one embodiment, the antagonist can be a fusion protein that includes a fragment of an IL-21R fused to a non-IL21R fragment, e.g., an 20 immunoglobulin Fc region. In other embodiments, the antagonist is an anti-IL21R or anti-IL2 l antibody or an antigen-binding fragment thereof, a soluble form of the IL-21 receptor, a peptide or a small molecule inhibitor. In one embodiment, the EL-21/TL-21R antagonist is an anti-IL21R or anti-IL2l antibody, or an antigen-binding fragment thereof. E.g., the antibody is a monoclonal or 25 single specificity antibody, that binds to IL-21, e.g., human IL-21, or an IL-21 receptor, e.g., human IL-21 receptor polypeptide, or an antigen-binding fragment thereof (e.g., an Fab, F(abr)2, Fv or a single chain Fv fragment). Preferably, the antibody is a human, humanized, chimeric, or in \ntro generated antibody to human IL-21 or human IL-21 receptor polypeptide. Preferably, the antibody is a neutralizing antibody. 30 In other embodiments, the IL-2 l/EL-21R antagonist includes full length, or a fragment of an IL-21 polypeptide, e.g., an IL-21 receptor-binding domain of an IL-21 polypeptide, e.g., a human IL-21 polypeptide (e.g., a human IL-21 polypeptide as WO 03/028(130 4 PCT/US02/29839 described herein having an amino acid sequence shown as SEQ ID NO: 19) or a sequence at least 85%, 90%, 95%, 98% or more identical thereto; or encoded by a corresponding nucleotide sequence shown as SEQ ID NO: 18 or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. Alternatively, the antagonist includes full length (e.g., 5 from about amino acids 1-538 or 20-538 of SEQ ID NO:2; or from about amino acids 1 -529 or 20-529 of SEQ ID NO: 10), or a fragment of an IL-21 receptor polypeptide, e.g., an IL-21-binding domain of an 3L-21 receptor polypeptide, e.g., a soluble fragment of an IL-21R (e.g., a fragment of an IL-21R comprising the extracellular domain of murine or human EL-21R; e.g., from about amino acids 1-235,1-236,20-235,20-236 of SEQ ID 10 NO:2 (human), or from about amino acids 1-236,20-236 of SEQ ED NO: 10 (murine), or encoded by the corresponding nucleotides of SEQ ID NO: 1 or 9, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. In one embodiment the antagonist is a fusion protein comprising the aforesaid IL-21 or H-21 receptor polypeptides or fragments thereof and, e.g., fused to, a second 15 moiety, e.g., a polypeptide (e.g., an immunoglobulin chain, a GST, Lex-A or MBP polypeptide sequence). In a preferred embodiment, the fusion protein includes at least a fragment of an IL-21R polypeptide, which is capable of binding IL-21, e.g., a soluble fragment of an IL-2IR (e.g., a fragment of an IL-21R comprising the extracellular domain of murine or human IL-21R; e.g., from about amino acids acids 1-235, 1-236, 20-20 235,20-236 of SEQ ID NO:2 (human), or from about amino acids 1-236,20-236 of SEQ ID N0:10 (murine), or encoded by the corresponding nucleotides of SEQ ID NO:l or 9, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto) and, e.g., fused to, a second moiety, e.g., a polypeptide (e.g., an immunoglobulin chain, an Fc fragment, a heavy chain constant regions of the various isotypes, including: IgGl, IgG2, IgG3, IgG4, 25 IgM, IgAl, IgA2, IgD, and IgE). For example, the fusion protein can include the extracellular domain of human IL-21R, e.g., from about amino acids 1-235,1-236,20-235,20-236 of SEQ ID NO:2, and, e.g., fused to, a human immunoglobulin Fc chain (e.g., human IgG, e.g., human IgGl or a mutated form of human IgGl). In one embodiment, the human Fc sequence has been mutated at one or more amino acids, e.g., 30 mutated at residues 254 and 257 of SEQ ID NO:28, from the wild type sequence to reduce Fc receptor binding. In other embodiments, the fusion protein can include the extracellular domain of murine IL-21R, e.g., from about amino acids 1-236,20-235 of WO 03/028630 PCT/USO2/29839 SBQ ID NO: 10 (murine), and, e.g., fused to, a marine immunoglobulin Fc chain (e.g., murine IgG, e.g., murine IgG2a or a mutated form of murine IgG2a). The fusion proteins may additionally include a linker sequence joining the first moiety, e.g., an IL-21R fragment, to the second moiety, e.g., the immunoglobulin 5 fragment In other embodiments, additional amino acid sequences can be added to the N-or C-terminus of the fusion protein to facilitate expression, steric flexibility, detection and/or isolation or purification. Examples of antagonistic fusion proteins that can be used in the methods of the invention are shown in Figures 7-15. ]n one embodiment, the fusion protein includes an 10 amino acid sequence chosen from, e.g., SEQ ID NO:23, SEQ ID NO:25, SEQ ID NO:27. SEQ ID NO-.29, SEQ ID NO:31, SEQ ID NO:33, SEQ ID NO:35, SEQ ID NO-.37, or SEQ ID NO:39, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. In other embodiments, the fusion protein includes an amino acid sequence encoded by a nucleotide sequence chosen from, e.g., SEQ ED NO:22, SEQ ID NO:24, SEQ ID NO:26, 15 SEQ ID NO:28, SEQ 3D N0:30, SEQ ID NO:32, SEQ ID NO:34, SEQ ID NO:36, or SEQ ID NO:38, or a sequence at least 85%. 90%, 95%, 98% or more identical thereto. Preferred fusion proteins have the amino acid sequence shown as SEQ ID NO:25 or SEQ ID NO:29 (Figures 8A-SC- and 10A-10C, respectively), or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. In other embodiments, the fusion protein includes 20 an amino acid sequence encoded by a nucleotide sequence chosen from, e.g., SEQ ID NO:24 or SEQ ID NO:28 (Figures 8A-8C and 10A-10C, respectively), or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. Most preferably, the fusion protein has the amino acid sequence shown as SEQ ID NO:29, or has an amino acid sequence encoded by a nucleotide sequence shown as SEQ ID NO:28 (Figure 10A-10C). 25 The IL-21/IL-21R antagonists described herein, e.g., the fusion protein described herein, can be derivatized or linked to another functional molecule, e.g., another peptide or protein (e.g., an Fab' fragment). For example, the fusion protein or an antibody, or antigen-binding portion, can be functionally linked (e.g., by chemical coupling, genetic fusion, non-covalent association or otherwise) to one or more other molecular entities, 30 such as an antibody (e.g., a bispecific or a multispecific antibody), toxins, radioisotopes, cytotoxic or cytostatic agents, among others. WO 03/028630 PCT/US02/29839 6 In one embodiment, the IL-21/1L-21R antagonists described herein, e.g., the pharmaceutical compositions thereof are administered in combination therapy, i.e., combined with other agents, e.g., therapeutic agents, which are useful for treating immune cell-associated pathological disorders, e.g., a disorder chosen from one or more 5 of: arthritis (including rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis, psoriatic arthritis, or ankylosing spondylitis), or scleroderma, systemic lupus erythematosis, or vasculitis; preferably, rheumatoid arthritis). For example, the combination therapy can include one or more JL-21/EL-21R antagonists, e.g., an anti-EL-21- or anti-IL-21R antibody or an antigen-binding fragment thereof; an IL-21R fusion 10 protein; a soluble IL-21R receptor; a peptide inhibitor or a small molecule inhibitor) co-formulated with, and/or co-administered with, one or more additional therapeutic agents, e.g., one or more cytokine and growth factor inhibitors, immunosuppressants, antiinflammatory agents, metabolic inhibitors, enzyme inhibitors, and/or cytotoxic or cytostatic agents, as described in more herein. 15 Examples of preferred additional therapeutic agents that can be co-administered and/or co-formulated with one or more IL-21/IL-21R antagonists, include, but are not limited to, one or more of: TNF antagonists (e.g., chimeric, humanized, human or in vitro generated antibodies, or antigen-binding fragments thereof, that bind to TNF; soluble fragments of a TNF receptor, e.g., p55 or p75 human TNF receptor or derivatives 20 thereof, e.g., 75 kdTNFR-IgG (75 kD TNF receptor-IgG fusion protein, Enbrel™-1, p55 kD TNF receptor-IgG fusion protein; TNF enzyme antagonists, e.g., TNFa converting enzyme (TACE) inhibitors); antagonists of IL-12, IL-15, IL-I7, IL-1S, IL-22; T cell and B cell depleting agents (e.g., anti-CD4 or anti-CD22 antibodies); small molecule inhibitors, e.g., methotrexate and leflunomide; sirolimus (rapamycin) and analogs 25 thereof, e.g., CCI-779; Cox-2 and cPLA2 inhibitors; NSAIDs; p38 inhibitors, TPL-2, Mk-2 and NFkb inhibitors; RAGE or soluble RAGE; P-selectin or PSGL-1 inhibitors (e.g., small molecule inhibitors, antibodies thereto, e.g., antibodies to P-selectin); estrogen receptor beta (ERB) agonists or ERB-NFkb antagonists. Most preferred additional therapeutic agents that can be co-administered and/or co-formulated with one 30 or more IL-21/IL-21R antagonists include one or more of: a soluble fragment of a TNF receptor, e.g., p55 or p75 human TNF receptor or derivatives thereof e.g., 75 kdTNFR- 7 IgG (75 kD TNF receptor-IgG fusion protein, Enbrel™^ methotrexate, leflunomide, or a sirolimus (rapamycin) or an analog thereof, e.g., CCI-779. Applicants have further shown that an IL-21 /IL-21R agonist, e.g., an IL-21 polypeptide, stimulates immunity in vivo against immunogenic and non-immunogenic tumor cells (Example 9). The increased immunity is due in part by the IL-21-mediated potentiation of mature CD8+ T cell effector function. IL-21/IL-21R agonists can be used by themselves or in combination with an antigen, e.g., as an adjuvant (e.g., a vaccine adjuvant), to up-regulate an immune response in vivo, e.g., for example, for use in treating cancer or an infectious disorder in a subject. Accordingly, the present invention provides use of a therapeutically effective amount of an IL-21 /IL-21R agonist for the manufacture of a medicament for treating (e.g., curing, suppressing, ameliorating, delaying or preventing the onset of, or preventing recurrence or relapse of) or preventing a cancer, in a subject, the medicament comprises: an IL-21/IL-21R agonist, e.g., an agent that increases or potentiates IL-21/IL-21R activity, in an amount sufficient to increase immune cell (e.g., CD8+ cell) activity (e.g., effector cell activity) and/or cell number. Exemplary cancer disorders include, but are not limited to, a solid tumor, a soft tissue tumor (e.g., a lymphoma or a leukemia), and a metastatic lesion. Also disclosed is the use of an effective adjuvanting amount of an IL-21/IL-21R agonist (e.g., a IL-21 polypeptide or a biologically active fragment thereof, or a nucleic acid encoding the same) for the manufacture of a composition for increasing the ability of a vaccine composition containing an antigen, e.g., an antigen from a pathogen, e.g., a bacterial, viral and parasitic pathogen, or a tumor cell, to elicit a protective immune response in a subject against the antigen wherein the composition is adapted for simultaneous or sequential administration with the vaccine composition. In one embodiment, the pathogen against which the vaccine is directed is an intracellular pathogen, e.g., a virus, bacterium, or protozoan. The pathogen may also be an extracellular parasite, e.g., a helminth or bacterium. The antigen may be a whole cell, a protein, a protein subunit or fragment. 1 -2 NOV 2009 iRFCEIVtD 8 Preferred IL-21/IL-21R agonists bind to IL-21 or IL-21R with high affinity, e.g., with an affinity constant of at least about 10? M~l, preferably about 10^ M"l, and more preferably, about 10^ M"^t0 10^ or stronger. In one embodiment of the present invention, the IL-21/IL-21R agonist is an IL-21 polypeptide, e.g., a human IL-21 polypeptide, or an active fragment thereof (e.g., a human IL-21 polypeptide comprising the amino acid sequence shown as SEQ ID NO: 19, or encoded by a nucleotide sequence shown as SEQ ID NO:l 8, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto). In other embodiments, the IL-21/IL-21R agonist is a fusion protein comprising ail IL-21 polypeptide, e.g., human IL-21 polypeptide, or a fragment thereof and, e.g., fused to, a second moiety, e.g., a polypeptide (e.g., an immunoglobulin chain, an Fc fragment, a heavy chain constant regions of the various isotypes, including: IgGl, IgG2, IgG3, IgG4, IgM, IgAl, IgA2, IgD, and IgE); an agonist antibody or antigen-binding fragment thereof, to the IL-21 receptor; or a small molecule or peptide agonist. In other embodiments, the IL-21/IL-21 R agonist is an agent that increases the activity or levels of IL-21 by, e.g., increasing expression, processing and/or secretion of functional IL-21. Nucleic acids encoding the aforesaid IL-21/IL-21R agonists and/or antigen can also be administered to the subject. The IL-21/IL-21R agonists described herein can be used, alone or in combination, with other therapeutic modalities. If desired, the IL-21/IL-21R agonist can be administered in conjunction with one or more additional agents that increase an immune response, e.g., an agent that enhances an immune response to a cancer or infectious disease, in the subject (e.g., an antigen, an antigenic peptide, alone or in combination with an antigen-presenting cell, e.g., a dendritic cell). For example, the IL-21/IL-21R agonist(s) can be administered by themselves, or in combination with an antigen, e.g., as an adjuvant (e.g., a vaccine adjuvant) and/or in combination with other cytokines (e.g., IL-2, GM-CSF and/or IL-15). The combination therapy can be carried out in any order, e.g., IL-15 and antigen can be coadministered to a subject, followed by boosting the immune response by administering IL-21 and the antigen. Preferably, the subject is a mammal, e.g., a human suffering a cancer or an infectious disorder. The IL-21/EL-21R agonist is preferably designed to increase the immune response 9 to a cancer or infectious disease. The infectious disease can be caused by, e.g., bacterial, parasitic or viral agents. A change in immune cell activity includes any variation(s), e.g., increase/decrease, in one or more of: proliferation, cytokine secretion and/or production, survival, differentiation, cell responsiveness (e.g., desensitization), cytolytic activity, effector cell activity, gene expression, among others, of the immune cell contacted with an IL-21/IL-21R agonist or antagonist compared to a reference, e.g., an untreated immune cell. For example, contacting an immune cell with an IL-21/IL-21R agonist, e.g., an IL-21 polypeptide, can induce one or more of: proliferation, cytolytic activity, effector cell function, or cytokine secretion of one or more of: antigen- or anti-CD3 antibody stimulated thymocytes; lymph node T cells, mature CD4+ T cells, mature CD8+ T cells, or macrophages. Responsiveness of immune cells, e.g., T cells, to stimulatory signals can also be modulated using an agonist or antagonist as described herein. For example, proliferation of T cells to alloantigens can be increased in the presence of an IL-21-polypeptide. IL-21 may also enhance proliferation and/or differentiation of mature CD8+ T cells. For example, priming of CD8+ T cells in the presence of IL-21 can generate effector cells with enhanced lytic (CTL) activity and/or increased ability to secrete cytokines, e.g., IFNy. In other embodiments, IL-21/IL-21R agonist can be used to induce the proliferation and/or cytokine secretion of macrophages. In another aspect, the invention of NZ 532021 features a fusion protein that includes at least a fragment of an IL-21R polypeptide, which is capable of binding an IL-21 polypeptide, e.g., a soluble fragment of an IL-21R (e.g., a fragment of an IL-21R comprising the extracellular domain of murine or human IL-21R; e.g., from about amino acids 1-235,1-236,20-235,20-236 of SEQ ID NO:2 (human), or from about amino acids 1-236,20-236 of SEQ ID NO: 10 (murine), or encoded by the corresponding nucleotides of SEQ ID NO:l or 9, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto) and, e.g., fused to, a second moiety, e.g., a polypeptide (e.g., an immunoglobulin chain, an Fc fragment, a heavy chain constant regions of the various isotypes, including: IgGl, IgG2, IgG3, IgG4, IgM, IgAl, IgA2, IgD, and IgE). For example, the fusion protein can include the extracellular domain of human IL-21R, e.g., from about amino acids 1-235, 1-236, 20-235, 20-236 of SEQ ID NO:2, and, e.g., fused to, a human immunoglobulin Fc chain (e.g., human IgG, e.g., 10 human IgGl or a mutated form of human IgGl). In one embodiment, the human Fc sequence has been mutated at one or more amino acids, e.g., mutated at residues 254 and 257 of SEQ ED NO:28, from the wild type sequence to reduce Fc receptor binding. In other embodiments, the fusion protein can include the extracellular domain of murine IL-21R, e.g., from about amino acids 1-236,20-236 of SEQ ID NO: 10 (murine), and, e.g., fused to, a murine immunoglobulin Fc chain (e.g., murine IgG, e.g., murine IgG2a or a mutated form of murine IgG2a). The fusion proteins may additionally include a linker sequence joining the IL-21R fragment to the second moiety. In other embodiments, additional amino acid sequences can be added to the N- or C-tenninus of the fusion protein to facilitate expression, detection and/or isolation or purification. The fusion protein described herein, can be derivatized or linked to another functional molecule, e.g., another peptide or protein (e.g., an Fab1 fragment). For example, the fusion protein can be functionally linked (e.g., by chemical coupling, genetic fusion, non-covalent association or otherwise) to one or more other molecular entities, such as an antibody (e.g., a bispecific or a multispecific antibody), toxins, radioisotopes, cytotoxic or cytostatic agents, among others. Examples of antagonistic fusion proteins that can be used in the methods of the invention are shown in Figures 7-15. In one embodiment, the fusion protein includes an amino acid sequence chosen from, e.g., SEQ ID NO:23, SEQ ID NO:25, SEQ ID NO:27, SEQ ID NO:29, SEQ ID NO:31, SEQ ID NO:33, SEQ CD NO:35, SEQ ID NO:37, or SEQ ID NO:39, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. In other embodiments, the fusion protein includes an amino acid sequence encoded by a nucleotide sequence chosen from, e.g., SEQ ID NO:22, SEQ ID NO:24, SEQ ID NO:26, SEQ ID NO:28, SEQ ID N0:30, SEQ ID NO:32, SEQ ID NO:34, SEQ ID NO:36, or SEQ ID NO:38, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. Preferred fusion proteins have the amino acid sequence shown as SEQ ID NO:25 or SEQ ID NO:29 (Figures 8A-8C and 10A-10C, respectively), or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. In other embodiments, the fusion protein includes an amino acid sequence encoded by a nucleotide sequence chosen from, e.g., SEQ ID NO:24 or SEQ ID NO:28 (Figures 8A-8C and 10A-10C, respectively), or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. Most preferably, the fusion protein has the amino acid sequence 11 showa as SEQ ID NO:29, or has an amino acid sequence encoded by a nucleotide sequence shown as SEQ ED NO:28 (Figure 10A-10C). The invention of NZ 532021 also features nucleic acid sequences that encode the fusion proteins described herein. In another aspect, the invention of NZ 532021 provides, compositions, e.g., pharmaceutical compositions, which include a pharmaceuticaily acceptable carrier and at least one of IL-21/IL-21 R agonist or an antagonist as described herein (e.g., a fusion protein described herein). In one embodiment, the compositions, e.g., pharmaceutical compositions, comprise a combination of two or more one of the aforesaid IL-21/IL-21R agonists or antagonists. Combinations of the IL-21/IL-21R agonists or antagonists and a drug, e.g., a therapeutic agent (e.g., one or more cytokine and growth factor inhibitors, immunosuppressants, anti-inflammatory agents, metabolic inhibitors, enzyme inhibitors, and/or cytotoxic or cytostatic agents, as described in more herein) or an antigen, e.g., an antigenic peptide and/or an antigen-presenting cell, are also within the scope of the invention. In one embodiment of the invention of NZ 532021, the pharmaceutical composition includes an IL-21/IL-21R antagonist agonist and at least one additional therapeutic agent, in a pharmaceutically-acceptable carrier. Examples of preferred additional therapeutic agents that can be co-formulated in a composition, e.g., a pharmaceutical composition, with one or more IL-21/IL-21R antagonists, include, but are not limited to, one or more of: TNF antagonists (e.g., chimeric, humanized, human or in vitro generated antibodies, or antigen-binding fragments thereof, that bind to TNF; soluble fragments of a TNF receptor, e.g., p55 or p75 human TNF receptor or derivatives thereof, e.g., 75 kdTNFR-IgG (75 kD TNF receptor-IgG fusion protein, Enbrel™^ p55 kD TNF receptor-IgG fusion protein; TNF enzyme antagonists, e.g., TNFa converting enzyme (TACE) inhibitors); antagonists of IL-12, IL-15, IL-17, IL-18, IL-22; T cell and B cell depleting agents (e.g., anti-CD4 or anti-CD22 antibodies); small molecule inhibitors, e.g., methotrexate and leflunomide; sirolimus (rapamycin) and analogs thereof, e.g., CCI-779; Cox-2 and cPLA2 inhibitors; NSAIDs; p38 inhibitors, TPL-2, Mk-2 and NFkb inhibitors; RAGE or soluble RAGE; P-selectin or PSGL-1 inhibitors (e.g., small molecule inhibitors, antibodies thereto, e.g., antibodies to P-selectin): estrogen receptor beta (ERB) agonists or ERB-NFkb antagonists. Most preferred additional therapeutic agents that 12 can be co-administered and/or co-formulated with one or more IL-21/IL-21R antagonists include one or more of: a soluble fragment of a TNF receptor, e.g., p55 or p75 human TNF receptor or derivatives thereof, e.g., 75 kdTNFR-IgG (75 kD TNF receptor-IgG fusion protein, Enbrel™1; methotrexate, leflunomide, or a sirolimus (rapamycin) or an analog thereof, e.g., CCI-779. In another embodiment of the invention of NZ 532021, a pharmaceutical composition useful as a vaccine comprising an antigen from a pathogenic microorganism, e.g., a viral, bacterial or parasitic microorganism, and an effective adjuvanting amount of an IL-21/IL-21R agonist, in a pharmaceuticallt acceptable carrier, is provided. In one embodiment, the resulting composition is capable of eliciting the vaccinated subject's immunity for a protective response to the pathogen. The IL-21/IL-21R agonist and antigen used in the composition may be a polypeptide or biologically active fragment thereof, or in a composition comprising nucleic acids encoding the same. These nucleic acids, together with the appropriate promoter sequences, may be employed directly as an antigen administered with, or close in time to, the IL-21/IL-21R agonist adjuvant. Alternatively, these nucleic acids sequences may be transduced in alternate vaccine strains of the pathogenic microorganism, and upon expression in vivo may provide the antigen of the vaccine. In other embodiments, the invention provides a composition, e.g., a pharmaceutical composition, for the treatment or amelioration of a cancer, and a method for adjuvanting a cancer "vaccine," in a phaimaceutically acceptable carrier. A cancer vaccine may comprise an antigen expressed on the surface of a cancer or a tumor cell. This antigen may be naturally present on the cancer cell. Alternatively, the cancer cell may be manipulated ex vivo and transfected with a selected antigen, which it then expresses when introduced into the patient. An exemplary pharmaceutical composition described herein can contain a cancer- or a tumor cell-antigen (either alone as a protein, biologically active fragment thereof, or nucleic acid encoding same), or a cell, e.g., a cancer cell, transfected with the cancer or tumor cell antigen, in combination with an IL-21/IL-21R agonist (e.g., an agonist as described herein, a fragment thereof, or a nucleic acid encoding the same). In one embodiment, the co-administration of IL-21/IL-21R agonist with the tumor cell antigen enhances the CD8+ T-cell effector cell activity of the tumor cell antigen. 13 Methods of producing the aforesaid compositions, e.g., vaccine compositions, are also encompassed by the present invention. The following terms are used interchangeably herein: "MU-1" and "IL-21R," and peptides, polypeptides and proteins. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In the case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. Other features and advantages of the invention will be apparent from the following detailed description and claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A depicts the full-length cDNA sequence of murine IL-21R/MU-1. The nucleotide sequence corresponds to nucleotides 1-2628 of SEQ ID NO:9. Figures 2A-2B depict the amino acid sequences of murine and human IL-21R/MU-1. Figure 2A depicts the amino acid sequence of murine IL-21R/MU-1 (corresponding to the amino acids 1-529 of SEQ ID NO: 10). There is a predicted leader sequence at amino acids 1-19, which was predicted by SPScan with score of 10.1 (bold- face type). There is a predicted transmembrane domain at amino acids 237-253 of SEQ ID NO: 10 (underlined). Predicted signaling motifs include the following regions: Box 1: amino acids 265-274 and Box 2: amino acids 311 -324 (bold and underlined); six tyrosine's are located at amino acid positions 281, 319, 361,369, 397, and 510, of SEQ ID NO: 10. The WSXWS motif (SEQ ID intellectual property OFFICP N.7 -2 NOV 2009 14 N0:8) is located at amino acid residue 214 to amino acid residue 218 (in large, bold-face type). Potential STAT docking sites include, amino acids 393-398 and amino acids 510-513 of SEQ ID NO: 10. Figure 2B depicts the amino acid sequence of human MU-1 (corresponding to SEQ ID NO:2). The location of the predicted signal sequence (about amino acids 1-19 of SEQ ID NO:2); WSXWS motif (about amino acids 214-218 of SEQ ID NO:2); and transmembrane domain (about amino acids 236-252,236-253,236-254, of SEQ ID NO:2 (underlined)). Potential JAK binding sites, signaling motifs and STAT docking sites are also indicated. The approximate location of these sites is boxed. Figure 3 depicts the GAP comparison of human and murine MU-1 cDNA sequences (corresponding to nucleic acids 1-1909, 1960-2050, and 2151-2665 of SEQ ID NO:l for the purposes of the alignment and nucleic acids 151 -2628 of SEQ ID NO:9, respectively). HuMU-1 = human MU-1, murMU-1 = murine MU- 1. Gap Parameters: Gap Weight = 50, Average Match = 10.000, Length Weight = 3, Average Mismatch = 0.000. Percent Identity = 66.116. Figure 4 depicts a GAP comparison of the human MU-1 protein (corresponding to amino acids 1-538 of SEQ ID NO:2) and the murine MU-1 protein (corresponding to amino acids 1-529 of SEQ ID NO: 10). BLOSUM62 amino acid substitution matrix. (Henikoff, S. and Henikoff, J. G. (1992)). Amino acid substitution matrices from protein blocks (Proc, Natl. Acad. Sci. USA 89: 10915-10919). Gap parameters = Gap Weight: 8, Average Match = 2.9-12, Length Weight = 2, Average Mismatch =-2.003. Percent Identity = 65.267. Figure 5 depicts a multiple sequence alignment of the amino acids of human MU-1 (corresponding to SEQ ID NO:2), murine MU-1 (corresponding to SEQ ID N0:10), and human IL2beta chain (GENbank Accession No. M26062). Leader and transmembrane domains are underlined. Conserved cytokine receptor module motifs are indicated by boldface type. Potential signaling regions are indicated by underlining and bold-face type. intellectual property OFFICE OF N.2 -2 NOV 2009 np^cniCH 15 Figwe 6 depicts signaling through MU-1. MU-1 phosphoiylates STAT 5 in Clone E7 EPO-MU-1 chimera. Under the conditions specified in Example 3, signaling through MU-1 results in the phosphorylation of STAT 5 at all time-points tested. Treatment of controls or the chimeric BAF-3 cells with IL-3 resulted in phosphorylation of STAT 3, but not STAT 1 or 5. Figures 7A-7B depict an alignment of the nucleotide and amino acid sequences of "human IL-21R monomer (corresponding to amino acids 20-235 of SEQ ID NO:2) fused at the amino terminal to honey bee leader sequence and His6 tags (amino acids 1-44 of SEQ ID NO:23). The nucleotide and amino acid sequences are shown as SEQ ID NO:22 and SEQ ID NO:23, respectively. Figures 8A-8C depict an alignment of the nucleotide and amino acid sequences of human IL-21R extracellular domain (corresponding to amino acids 1-235 of SEQ ID NO:2) fused at the C-terminus via a linker (corresponding to amino acids 236-243 of SEQ ID NO:25) to human immunoglobulin G1 (IgGl) Fc sequence (corresponding to amino acids 244-467 of SEQ ID NO:25). The nucleotide and amino acid sequences are shown as SEQ ID NO:24 and SEQ ID NO:25, respectively. Figures 9A-9C depict an alignment of the nucleotide and amino acid sequences of human IL-21R extracellular domain (corresponding to amino acids 1-235 of SEQ ID NO:2) fused at the C-terminus via a linker (corresponding to amino acids 236-243 of SEQ ID NCh27) to hitman immunoglobulin G1 (IgGl) Fc sequence (corresponding to amino acids 244-467 of SEQ ID NO:27), and His6 sequence tag (corresponding to amino acids 468-492 of SEQ ID NO:27). The nucleotide and amino acid sequences are shown as SEQ ID NO:26 and SEQ ED NO:27, respectively. Figures 1 OA-IOC depicts an alignment of the nucleotide and amino acid sequences of human IL-21R extracellular domain (corresponding to amino acids 1-235 of SEQ ED NO:2) fused at the C-terminus via a linker (corresponding to amino acids 236-243 of SEQ ID NO:29) to human immunoglobulin G1 (IgGl) Fc sequence (corresponding to amino acids 244-467 of SEQ ID NO:29)to human immunoglobulin G1 (IgGl) Fc mutated sequence. The 16 human Fc sequence has been mutated at residues 254 and 257 from the wild type sequence to reduce Fc receptor binding. The nucleotide and amino acid sequences are shown as SEQ ID NO:28 and SEQ ID NO:29, respectively. Figures 11A-11B depict an alignment of the nucleotide and amino acid sequences of human EL-21R extracellular domain (corresponding to amino acids 1-235 of SEQ ID NO:2) fused at the C-terminus to a rhodopsin sequence tag. The nucleotide and amino acid sequences are shown as SEQ ID N0:30 and SEQ ID NO:31, respectively. Figures 12A-12C depict an alignment of the nucleotide and amino acid sequences of human IL-21R extracellular domain (corresponding to amino acids 1-235 of SEQ 3D NO:2) fused at the C-terminus to an EK cleavage site and mutated IgGl Fc region (corresponding to amino acids 236-470 of SEQ ED NO:33). Hie nucleotide and amino acid sequences are shown as SEQ ED NO:32 and SEQ 3D NO:33, respectively. Figures I3A-13B depict an alignment of the nucleotide and amino acid sequences of murine IL-21R extracellular domain fused at the C-tenninus to mouse immunoglobulin G2a (IgG2a). The nucleotide (genomic) and amino acid sequences are shown as SEQ ED NO:34 and SEQ ID NO:35, respectively. Figures 14A-14B depict an alignment of the nucleotide and amino acid sequences of murine EL-21R extracellular domain fiised at the C-terminus to Flag and His6 sequence tags. The nucleotide (genomic) and amino acid sequences are shown as SEQ ID NO:36 and SEQ ID NO:37, respectively. Figures 15A-15B depict an alignment of the nucleotide and amino acid sequences of (honey bee leader) murine IL-21R extracellular domain fused at the C-terminus to Flag and His6 sequence tags. The nucleotide (genomic) and amino acid sequences are shown as SEQ ID NO:38 and SEQ ED NO:39, respectively. Figure 16 is a timetable summarizing the prophylactic, therapeutic and semi-therapeutic treatment schedules for the experiments using collagen-induced arthritis (CIA) mouse models. 17 Figure 2 7 is a graph depicting the effects of muIL21RPc (200 ug/mouse 3x/week) on a semi-therapeutic CIA mouse as a function, of days post treatment Mouse Ig (200 fig/mouse 3 x/week) was used as a control. Figure 18 is a graph depicting the effects of murine IL-21 on mean CIA score as a function of days post collagen boost Mice were injected with 1 p-g of murine IL21 intraperitoneally when presenting a total body score of 2-4. Figure 19, panels A-B, are photographs showing increased expression of IL-21 R mRNA in arthritic paws of mice with CIA (panel A) compared to negative controls (panel B). Figures 20A-20C are bar graphs depicting the level and biological activity of IL-21 secreted by IL-21 - transduced B16F1 and MethA cells. Figure 20A shows the level of EL-21 secretion by transduced tumor cells. Figures 20(B, C) are bar graphs depicting the biological activity of IL-21 secreted by transduced tumor cells. Naive splenocytes from either C57BL/6 (B) or Balb/C (C) mice were stimulated for 72 hours with the indicated concentrations of irradiated syngeneic tumor cells. The cultures were supplemented with sub-optimal amount of anti-CD3 and anti-CD28 mAb in 96-weIl plates. 3H thymidine was added during the last 6 hours of culture. Figures 21A-21C are graphs depicting the in vitro growth characteristics of transduced tumor cells and evaluation of EL-21R expression. Figures 21A and 21B depict the number of B16F1-IL-21 and B16F1-GFP or MethA-IL-21 and MethA-GFP tumor cells, respectively, with respect to time in culture. Figure 21C is a bar graph depicting expression of IL-21RmRNA in the transfected cells was normalized to cyclophilin values and expressed as relative unite (RU.). Figures 22A-22B are linear graphs depicting the in vivo growth characteristics of transduced tumor cells. IL-21 or GFP expressing tumor cells were injected in syngeneic naive mice as indicated. Tumor size was scored by multiplying perpendicular diameters and 18 was averaged for all mice in each group. (A) Tumor growth ill C57BL/6 mice that were injected with 105 of B16F1-IL-21 or GFP cells. (B) Tumor growth in Balb/C mice that were injected with either lxl 06 or 2x106 of MethA-IL-21 or MethA-GFP cells. Figures 23A-23B are linear graphs depicting the changes in B16F1-IL-21 tumor growth in scid and nude mice with respect to number of days after injection of B16F1-IL-21 cells. B16F1-IL-21 and B16F1-GFP tumor cells (105/mouse) were injected into C57BL/6 scid (A) or C57BL/6 nude (B) mice. Tumor size was monitored twice weekly. Figures 24A-24B are linear graphs depicting the growth of B16F1-IL-21 cells in vivo in CD4+, CD8+ T or NK cell depleted mice. A) C57BL/6 were depleted of CD4+ or CD8+ T cells by three consecutive injections of anti-CD4 or anti-CD8 mAb on days -3, -2 and -1 before tumor cell injection and every other day post 105 B16F1-IL-21 and B16F1-GFP tumor cell injection, (rat IgG was used as isotype control). B) C57BL/6 were depleted of NK cells by one injection of anti-asialo GM1 Ab on day -1 before tumor cell injection and twice per week post 105 B16F1-EL-21 and B16F1-GFP tumor cell injection, (rat IgG or rabbit IgG were used as isotype controls for T and NK cell depletion respectively). Tumor size was monitored twice per week as described in Figure 23. Figures 25A-25C are graphs showing TRP-2 specific T cell responses in B16F1 -IL-21 injected mice. (A) Equal numbers of splenocytes (2-4x105) from mice injected with either B16F1-EL-21 or B16F1-GFP were stimulated with 5|ig/ml of TRP-2 peptide in the presence of 20 U of IL-2 in an ELISPOT plate pre-coated with anti-IFNy Ab. After 24 hours, the plate was developed and spot forming units were counted. Results are expressed as number of spot forming units/million of splenocytes (SPU/million splenocytes). (B) Cytolytic activity of splenocytes from B16F1-IL-21 or (C) control B16F1-GFP injected mice were tested against RMA-S cells pulsed with TRP-2 or OVA peptide (control). Cytolytic activity was measured by standard 4-hr Cr51 Release Assay Figures 26A-26B are linear graphs depicting the in vivo growth of B16F1-IL-21 cells in EFNy and IL-10"'" mice. (A) IFNy';" mice or (B) IL-10"7" mice were injected with 105 of 19 either B16F1 -IL-21 or B16F1-GFP tumor cells and the tumor growth was monitored twice weekly. Figures 27A-27B are bar graphs depicting IL-21R and IL-21 expression by naive CD8+ T cells. CD8+/CD62L+ T cells were sorted from LN of 2C TCR Tg mice and stimulated with anti-CD3 (2.5ug/ml plate-bound), IL-21 (12.5ng/ml) or anti-CD28 (7.5ug/ml plate-bound). At the indicated times, cells were harvested, RNA prepared and RPA analysis performed. Samples were quantitated by phosphoimager analysis relative to an internal control. (A) Quantitation of RPA pixels for IL-21R bands. (B) Quantitation of RPA pixels for IL-21 bands. Figures 28A-28D are linear graphs depicting the effects of EL-21 on proliferation of CD8+ T cells. (A) IL-21 enhances antigen stimulation of CD8+ T cells. Purified 2C CD8+ T cells were stimulated for 72hrs with irradiated Balb/c splenocytes at 5:1 APC:T ratio with the indicated amount of IL-21 or equivalent dilution of mock-transfected supernatant (representative experiment, n=5). (B) Effect of IL-21 vs IL-2, IL-12, IL-15 on antigen stimulation. 2C T cells were stimulated with 3:1 T-depleted APC:T ratio and the indicated concentration of cytokine (n=3). (C) IL-21 acts directly on CD8+ T cells to specifically enhance proliferation. 2C CD8+ T cells were stimulated on anti-CD3-coated plates (2.5ug/ml) with the indicated titer of IL-21 +/- mIL-21R.Fc (20ug/ml) (n=3). (D) Effect of IL-21 vs IL-2, IL-12, EL-15 on anti-CD3 mAb stimulation (5ug/ml plate-bound). Figures 29A-29C are graphs showing the effects of IL-21 on development of CD8+ T cell effector functions. (A) IL-21 enhances CTL generation. 2C T cells were stimulated with irradiated APCs (APC:T) and IL-2 (lOU/ml), IL-21 (titer) or the equivalent dilution of mock supernatant for 4 days then washed, counted and set up in a 4hr CTL assays using 51 -Cr-labeled P815 as specific targets (representative experiment, n=3). (B) IL-21 is comparable to IL-12, EL-15 for inducing lytic activity from CD8+ T cells. 2C CD8+ T cells were stimulated and assayed for CTL activity as in (A) using IL-2 (5ng/ml), IL-15 (50ng/ml), IL-12 (5ng/ml), IL-21 (25ng/ml). (C) IL-21 during priming results in increased ability to produce EFNg. 2C T cells were stimulated as indicated in (B) for 5 days then washed and restimulated for on anti-CD3-coated plates (lug/ml). EFNg ELISAs were done on 40hr supematants. 20 DETAILED DESCRIPTION OF THE INVENTION Methods and compositions for modulating interleukin-21 (TL-21)/IL-21 receptor (MU-1) activity using agonists or antagonists of IL-21 or IL-21 receptor ("IL-21R" or "MU-1"), are disclosed. IL-21/IL-21R antagonists can be used to induce immune suppression in vivo, e.g., for treating or preventing immune cell-associated pathologies (e.g., pathologies associated with aberrant activity of one or more of mature T cells (mature CD8+, mature CD4+ T cells), mature NK cells, B cells, macrophages and megakaryocytes, including transplant rejection and autoimmune disorders). IL-21/IL-21R agonists can be used by themselves or in combination with an antigen, e.g., as an adjuvant (e.g., a vaccine adjuvant), to up-regulate an immune response in vivo, e.g., for example, for use in treating cancer and infectious disorders. (followed by page 21) WO 03/028630 21 PCT/US02/29839 In one embodiment, Applicants have shown that a reduction of IL-21R activity by using a neutralizing fusion protein that includes the extracellular domain of the IL-21R fused to an Fc immunoglobulin region ameliorates inflammatory symptoms in mouse collagen-induced arthritis (CIA) animal models (Example 7). Expression of IL-21R 5 rnRNA is upregulated in the paws of CIA mice (Example 8). Accordingly, IL-21R binding agents that antagonize IL-21/EL-21R activity can be used to induce immune suppression in vivo, e.g., for treating or preventing immune cell-associated pathologies (e.g., pathologies associated with aberrant activity of one or more of T cells (CD8+, CD4+ T cells), NK cells, B cells, macrophages and megakaryocytes, including transplant 10 rejection and autoimmune disorders). In other embodiments, Applicants have shown that agonistic IL-21R binding agent stimulate, primarily via stimulation of CD8+T cells, innate and adaptive immunity in yz'vo against immunogenic and non-immunogenic tumor cells (Example 9). Accordingly, binding agents that stimulate the EL-21/JL-21R pathway can be used by 15 themselves or in combination with an antigen, e.g., as an adjuvant (e.g., a vaccine adjuvant), to up-regulate an immune response in vivo, e.g., for example, for use in treating cancer and infectious disorders. 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. 20 The term "MU-1," "MU-1 protein," "interleukin-21 receptor" or "IL-21R," as used herein, refers to a class I cytokine family receptor, also known as N1LR (WO 01/85792; Parrish-Novak et al. (2000) Nature 408:57-63; Ozaki et al. (2000) Proc. Natl Acad. Sci. USA 97:11439-114444). MU-1 is homologous to the shared p chain of the IL-2 and IL-15 receptors, and IL-4oc (Ozaki et al. (2000) supra). Upon ligand binding, 25 3L-21R/MU-1 is capable of interacting with a common y cytokine receptor chain (yc) (Asao et al. (2001) J. Immunol. 167:1-5), and inducing the phosphorylation of STAT1 and STAT3 (Asao et al. (2001) or STATS (Ozaki et al. (2000). MU-1 shows widespread lymphoid tissue distribution. The term "MU-1" refers to a receptor (preferably of mammalian, e.g., murine or human origin) which is capable of interacting with, e.g., ' 30 binding to, IL-21 (preferably of mammalian, e.g., murine or human IL-21) and having one of the following features: (i) an amino acid sequence of a naturally occurring mammalian MU-1 polypeptide H-21R/MU-1 or a fragment thereof, e.g., an amino acid 22 sequence shown as SEQ ID NO:2 (human) or SEQ ID N0:10 (murine) or a fragment thereof; (ii) an amino acid sequence substantially homologous to, e.g., at least 85%, 90%, 95%, 98%, 99% homologous to, an amino acid sequence shown as SEQ ID NO:2 (human) or SEQ ID NO: 10 (murine) or a fragment thereof; (iii) an amino acid sequence which is encoded by a naturally occurring mammalian IL-21R/MU-1 nucleotide sequence or a fragment thereof (e.g., SEQ ID NO:l (human) or SEQ ID NO:9 (murine) or a fragment thereof); (iv) an amino acid sequence encoded by a nucleotide sequence which is substantially homologous to, e.g., at least 85%, 90%, 95%, 98%, 99% homologous to, a nucleotide sequence shown as SEQ ID NO:l (human) or SEQ ID NO:9 (murine) or a fragment thereof; (v) an amino acid sequence encoded by a nucleotide sequence degenerate to a naturally occurring IL-21R/MU-1 nucleotide sequence or a fragment thereof, e.g., SEQ ID NO:l (human) or SEQ ID NO:9 (murine) or a fragment thereof; or (vi) a nucleotide sequence that hybridizes to one of the foregoing nucleotide sequence sequences under stringent conditions, e.g., highly stringent conditions. The IL-21R/MU-1 is of mammalian, preferably, human origin. The nucleotide sequence and the predicted amino acid sequence of human IL-21R/MU-1 are shown in SEQ ID NO:l and SEQ ID NO:2, respectively. Analysis of the human IL-21R/MU-1 amino acid sequence (SEQ ID NO:2; Figure 2B) revealed the following structural features: a leader sequence (about amino acids 1-19 of SEQ ID NO:2 (Figure 2B)); WSXWS motif (about amino acids 214-218 of SEQ ID NO:2); transmembrane domain (about amino acids 236-252 of SEQ ID NO:2 (Figure 2B)); an extracellular domain (about amino acids 1-235 of SEQ ID NO:2); and an intracellular domain (about 253-538 of SEQ ID NO:2). The mature human IL-21 R/MU-1 is believed to have the sequence of amino acids 20-538 of SEQ ID NO:2. The IL-21R/MU-1 cDNA was deposited with the American Type Culture Collection on Mar. 10, 1998, as accession number ATCC 98687. Any form of IL-21 R/MU-1 proteins of less than full length can be used in the methods and compositions of the present invention, provided that it retains the ability to bind to an IL-21 polypeptide. IL-21R/MU-1 proteins of less than full length, e.g., soluble IL-21R, can be produced by expressing a corresponding fragment of the polynucleotide encoding the full-length MU-1 protein in a host cell. These corresponding polynucleotide fragments are also part of the present invention. Modified intellectual property OFFICF OP N.7 -2 NOV 2009 Rtc ElvtO WO «3/«28630 23 PCT/US02/29839 polynucleotides as described above may be made by standard molecular biology techniques, including construction of appropriate desired deletion mutants, site-directed mutagenesis methods or by the polymerase chain reaction using appropriate oligonucleotide primers. 5 As used herein, a "soluble IL-21R/MU-1 polypeptide" is a EL-21R/MU-1 polypeptide incapable of anchoring itself in a membrane. Such soluble polypeptides include, for example, MU-1 or IL-21R polypeptides that lack a sufficient portion of their membrane spanning domain to anchor the polypeptide or are modified such that the membrane spanning domain is non-functional. E.g., a soluble fragment of an IL-21R 10 (e.g., a fragment of an IL-21R comprising the extracellular domain of murine or human 3L-21R includes an amino acid sequence from about amino acids 1-235, 1-236, 20-235, 20-236 of SEQ ID NO:2 (human), or from about amino acids 1-236,20-236 of SEQ ED NO: 10 (murine). A soluble IL-21R/MU-1 polypeptide can additionally include, e.g., be fused to, a second moiety, e.g., a polypeptide (e.g., an immunoglobulin chain, a GST, 15 Lex-A or MBP polypeptide sequence). For example, a fusion protein can includes at least a fragment of an 3L-21R polypeptide, which is capable of binding IL-21, e.g., a soluble fragment of an IL-21R (e.g., a fragment of an IL-21R comprising the extracellular domain of mvirine or human IL-21R; e.g., from about amino acids acids 1-235,1-236, 20-235,20-236 of SEQ ID NO:2 (human), or from about amino acids 1-236,20-236 of SEQ 20 ID NO.IO (murine), fused to a second moiety, e.g., a polypeptide (e.g., an immunoglobulin chain, an Fc fragment, a heavy chain constant regions of the various isotypes, including: IgGl, IgG2, IgG3, IgG4, IgM, IgAl, IgA2, IgD, and IgE). The term "interleukin-21" or "11.-21" refers to a cytokine showing sequence homology to IL-2, IL-4 and IL-15 (Parrish-Novak et al. (2000) Nature 408:57-63). 25 Despite low sequence homology among interleukin cytokines, cytokines share a common fold into a "four-helix-bundle" structure that is representative of the family. It is expressed primarily in activated CD4+ T cells, and has been reported to have effects on NK, B and T cells (Parrish-Novak et al (2000) supra; Kasaian, M.T. et al. (2002) supra). H-21 binds to IL-21R (also referred to herein as MU-1 and NILR). Upon IL-21 binding, 30 activation of IL-21R leads to stat5 or stat3 signaling (Ozaki et al. (2000) supra). The term "IL-21" or "IL-21 polypeptide" refers to a protein (preferably of mammalian, e.g., murine or human origin) which is capable of interacting with, e.g., binding to, IL-21R WO 03/(128630 24 PCT/US02/29839 e.g., murine or human IL-21) and having one of the following features: (i) an amino acid sequence of a naturally occurring mammalian IL-21 or a fragment thereof, e.g., an amino acid sequence shown as SEQ ID NO: 19 (human) or a fragment thereof; (ii) an amino acid sequence substantially homologous to, e.g., at least 5 85%, 90%, 95%, 98%, 99% homologous to, an amino acid sequence shown as SEQ ID NO: 19 (human) or a fragment thereof; (iii) an amino acid sequence which is encoded by a naturally occurring mammalian IL-21 nucleotide sequence or a fragment thereof (e.g., SEQ ID NO: 18 (human) or a fragment thereof); (iv) an amino acid sequence encoded by a nucleotide sequence which is substantially homologous to, e.g., at least 85%, 90%, 10 95%, 98%, 99% homologous to, a nucleotide sequence shown as SEQ ID NO:18 (human) or a fragment thereof; (v) an amino acid sequence encoded by a nucleotide sequence degenerate to a naturally occurring IL-21 nucleotide sequence or a fragment thereof, e.g., SEQ ID NO: 19 (human) or a fragment thereof; or (vi) a nucleotide sequence that hybridizes to one of the foregoing nucleotide sequence sequences under stringent 15 conditions, e.g., highly stringent conditions. The phrase "a biological activity of a MU-1 or IL-21R polypeptide refers to one or more of the biological activities of the corresponding mature MU-1 protein, including, but not limited to, (1) interacting with, e.g., binding to, an IL-21 polypeptide; (2) associating with signal transduction molecules, e.g., yc, jakl; (3) stimulating 20 phosphorylation and/or activation of stat proteins, e.g., stat 5 and/or stat3; and/or (4) modulating, e.g., stimulating or decreasing, proliferation, differentiation, effector cell function, cytolytic activity, cytokine secretion, and/or survival of immune cells, e.g., T cells (CD8+, CD4+ T cells), NK cells, B cells, macrophages and megakaryocytes). As used herein, a "IL-21/IL-21R agonist", that is useful in the method of the 25 invention, refers to an agent which potentiates, induces or otherwise enhances one or biological activities of an IL-21R/MU-1 polypeptide. Preferably, the agonist interacts ■with, e.g., binds to, an IL-21RMU-1 polypeptide. As used herein, a 'TL-21/IL-21R antagonist", that is useful in the method of the invention, refers to an agent which reduces, inhibits or otherwise diminishes one or 30 biological activities of an IL-21R/MU-1 polypeptide. Preferably, the antagonist interacts with, e.g., binds to, an IL-21R/MU-1 polypeptide. Antagonism using an IL-21/IL-21R WO 03/028630 PCT/US02/29839 25 antagonist does not necessarily indicate a total elimination of the 1L-21R/MU-1 polypeptide biological activity. As used herein, a "therapeutically effective amount" of an IL-21/TL-21R agonist or antagonist refers to an amount of an agent which is effective, upon single or multiple 5 dose administration to a subject, e.g., a human patient, at curing, reducing the severity of, ameliorating one or more symptoms of a disorder, or in prolonging the survival of the subject beyond that expected in the absence of such treatment. As used herein, "a prophylactically effective amount" of an IL-2LTL-21R agonist or antagonist refers to an amount of an EL-21/1L-2LR agonist or antagonist which is 10 effective, upon single- or multiple-dose administration to a subject, e.g., a human patient, in preventing or delaying the occurrence of the onset or recurrence of a disorder, e.g., a disorder as described herein. The term "induce", "inhibit", "potentiate", "elevate", "increase", "decrease" or the like, e.g., which denote quantitative differences between two states, refer to at least 15 statistically significant differences between die two states. The term "in combination" in this context means that the agents are given substantially contemporaneously, either simultaneously or sequentially. If given sequentially, at the onset of administration of the second compound, the first of the two compounds is preferably still detectable at effective concentrations at the site of 20 treatment. As used herein, a "fusion protein" refers to a protein containing two or more operably associated, e.g., linked, moieties, e.g., protein moieties. Preferably, the moieties are covalently associated. The moieties can be directly associate, or connected via a spacer or linker. 25 As used herein, the term "antibody" refers to a protein comprising at least one, and preferably two, heavy (H) chain variable regions (abbreviated herein as VH), and at least one and preferably two light (L) chain variable regions (abbreviated herein as VL). The VH and VL regions can be farther subdivided into regions of hypervariability, termed "complementarity determining regions" ("CDR"), interspersed with regions that 30 are more conserved, termed "framework regions" (FR). The extent of the framework region and CDR's has been precisely defined (see, Kabat, E.A., et al (1991) Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human WO 03/(128630 PCT/US02/29839 26 Services, NIH Publication No. 91-3242, and Chothia. C. et aL (1987) J. MoL Biol. 196:901-917, which are incorporated herein by reference). Each VH and VL is composed of three CDR's and fourFRs, arranged from amino-tenmniis to carboxy-terminus in the following order: FR1, CDR1, ER2, CDR2, FR3, CDR3, FR4. 5 The antibody can further include a heavy and light chain constant region, to thereby form a heavy and light immunoglobulin chain, respectively, ia one embodiment, the antibody is a tetramer of two heavy immunoglobulin chains and two light immunoglobulin chains, wherein the heavy and light immunoglobulin chains are interconnected by, e.g., disulfide bonds. The heavy chain constant region is comprised of 10 three domains, CHI, CH2 and CH3. The light chain constant region is comprised of one domain, CL. The variable region of the heavy and light chains contains a binding domain that interacts with an antigen. The constant regions of the antibodies typically mediate the binding of the antibody to host tissues or factors, including various cells of the immune system (e.g., effector cells) and the first component (Clq) of the classical 15 complement system. As used herein, the term "immunoglobulin'1 refers to a protein consisting of one or more polypeptides substantially encoded by immunoglobulin genes. The recognized human immunoglobulin genes include the kappa, lambda, alpha (IgAl and IgA2), gamma (IgGl, IgG2, IgG3, IgG4). delta, epsilon and mu constant region genes, as well as 20 the myriad immunoglobulin variable region genes. Full-length immunoglobulin "light chains" (about 25 Kd or 214 amino acids) are encoded by a variable region gene at the NH2-terminus (about 110 amino acids) and a kappa or lambda constant region gene at the COOH—terminus. Full-length immunoglobulin "heavy chains" (about 50 Kd or 446 amino acids), are similarly encoded by a variable region gene (about 116 amino acids) 25 and one of the other aforementioned constant region genes, e.g., gamma (encoding about 330 amino acids). As used herein, "isotype" refers to the antibody class (e.g., IgM or IgGl) that is encoded by heavy chain constant region genes. The term "antigen-binding fragment" of an antibody (or simply "antibody 30 portion," or "fragment"), as used herein, refers to one or more fragments of a full-length antibody that retain the ability to specifically bind to an antigen (e.g., CD3). Examples of binding fragments encompassed within the term "antigen-binding fragment" of an WO 03/028630 27 PCT/US02/29839 antibody include (i) a Fab fragment, a monovalent fragment consisting of the VL, VH, C-L 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 5 a single arm of an antibody, (v) a dAb fragment (Ward et al, (1989) Nature 341:544-546), which consists of a 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 10 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. Natl. Acad. Sci. USA 85-5879-5883). Such single chain antibodies are also intended to be encompassed within the term "antigen-binding fragment" of an antibody. These antibody fragments are obtained using conventional techniques known to those with skill in the 15 art, and the fragments are screened for utility in the same manner as are intact antibodies. Sequences similar or homologous (e.g., at least about 85% sequence identity) to the sequences disclosed herein are also part of this application. In some embodiment, the sequence identity can be about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or higher. Alternatively, substantial identity exists when the nucleic acid segments will 20 hybridize under selective hybridization conditions (e.g. > highly stringent hybridization conditions), to the complement of the strand. The nucleic acids may be present in whole cells, in a cell lysate, or in a partially purified or substantially pure form. Calculations of "homology" or "sequence identity" between two sequences (Hie terms are used interchangeably herein) are performed as follows. The sequences are 25 aligned for optimal comparison purposes (e.g., gaps can be introduced in one or both of a first and a second amino acid or nucleic acid sequence for optimal alignment and nonhomologous sequences can be disregarded for comparison purposes). In a preferred embodiment, the length of a reference sequence aligned for comparison purposes is at least 30%, preferably at least 40%, more preferably at least 50%, even more preferably at 30 least 60%, and even more preferably at least 70%, 80%, 90%, 100% of the length of the reference sequence. The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. "When a position in the first WO 03/028630 28 PCT/US02/29839 sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position (as used herein amino acid or nucleic acid "identity" is equivalent to amino acid or nucleic acid "homology"). The percent identity between the two sequences is a function of the 5 number of identical positions shared by the sequences, 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. In a preferred 10 embodiment, the percent identity between two amino acid sequences is determined using the Needleman and Wunsch ((1970) J. Mol. Biol. 48:444-453 ) algorithm which has been incorporated into the GAP program in the GCG software package (available at http://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. In yet 15 another preferred embodiment, the percent identity between two nucleotide sequences is determined using the GAP program in the GCG software package (available at http://www.gcg.com), using a NWSgapdna_CMP matrix and a gap weight of40,50,60, 70, or 80 and a length weight of 1, 2,3, 4, 5, or 6. A particularly preferred set of parameters (and the one that should be used if the practitioner is uncertain about what 20 parameters should be applied to determine if a molecule is within a sequence identity or homology limitation of the invention) are a Blossum 62 scoring matrix with a gap penalty of 12, a gap extend penalty of 4, and a frameshift gap penalty of 5. The percent identity between two amino acid or nucleotide sequences can also be determined using the algorithm of E. Meyers and W. Miller ((1989) CABIOS, 4:11-17) which has been 25 incorporated into the ALIGN program (version 2.0), using a P AM12Q weight residue table, a gap length penalty of 12 and a gap penalty of 4. As used herein, the term "hybridizes under stringent conditions" describes conditions for hybridization and washing. Stringent conditions are known to those skilled in the art and can be found in Current Protocols in Molecular Biology, John 30 Wiley & Sons, N.Y. (1989), 6.3.1-6.3.6. Aqueous and nonaqueous methods are described in that reference and either can be used. A preferred, example of stringent hybridization conditions are hybridization in 6X sodium chloride/sodium citrate (SSC) at WO 03/028630 29 PCT/US02/29839 about 45°C, followed by one or more washes in 0.2X SSC, 0.1% SDS at S0°C. Another example of stringent hybridization conditions are hybridization in 6X SSC at about 45°C, followed by one or more washes in 0.2X SSC, 0.1% SDS at 55DC. A further example of stringent hybridization conditions are hybridization in 6X SSC at about 45 °C, followed 5 by one or more washes in 0.2X SSC, 0.1% SDS at60°C. Preferably, stringent hybridization conditions are hybridization in 6X SSC at about 45DC, followed by one or more washes in 0.2X SSC, 0.1% SDS at 65°C. Particularly preferred highly stringent conditions (and the conditions that should be used if the practitioner is uncertain about what conditions should be applied to determine if a molecule is within a hybridization 10 limitation of the invention) are 0.5M sodium phosphate, 7% SDS at 65 °C, followed by one or more washes at 0.2X SSC, 1% SDS at 65°C. It is understood that the IL-21/IL-21R agonists and antagonists of the present invention may have additional conservative or non-essential amino acid substitutions, which do not have a substantial effect on their functions. 15 A "conservative amino acid substitution" is one 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 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, 20 asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine). The term "recombinant host cell" (or simply "host cell"), as used herein, is 25 intended to refer to a cell into which a recombinant expression vector has been introduced. It should be understood that such terms are intended to refer not only to the particular subject cell, but to the progeny of such a cell. Because certain modifications may occur in succeeding generations due to either mutation or environmental influences, such progeny may not, in fact, be identical to the parent cell, but are still included within 30 the scope of the term "host cell" as used herein. WO 03/028630 30 FCT/US02/29839 IL-21/EL-21R Agonists and Antagonists Li one embodiment, an IL-21 R/MU-1 polypeptide or active fragments thereof ma)' be fiised to a second moiety, e.g., an immunoglobulin or a fragment thereof (e.g., an Fc binding fragment thereof). For example, soluble forms of the IL-21R/MU-1 may be 5 fused through "linker" sequences to the Fc portion of an immunoglobulin. Other fusions proteins, such as those with GST, Lex-A or MBP, may also be used. The fusion proteins may additionally include a linker sequence joining the IL-21 or IL-21R fragment to the second moiety. For example, the fusion protein can include a peptide linker, e.g., a peptide linker of about 4 to 20, more preferably, 5 to 10, amino 10 acids in length; the peptide linker is 8 amino acids in length. Each of the amino acids in the peptide linker is selected from the group consisting of Gly, Ser, Asn, Thr and Ala; the peptide linker includes a Gly-Ser element. In other embodiments, the fusion protein includes a peptide linker and the peptide linker includes a sequence having the formula (Ser-Gly-GIy-Gly- GIv)y wherein y is 1,2, 3,4, 5,6, 7, or 8. 15 In other embodiments, additional amino acid sequences can be added to the N- or C-terminus of the fusion protein to facilitate expression, detection and/or isolation or purification. For example, IL-21/IL-21R fusion protein may be linked to one or more additional moieties, e.g., GST, His6 tag, FLAG tag. For example, the fusion protein may additionally be linked to a GST fusion protein in which the fusion protein sequences are 20 fused to the C-terminus of the GST (:. e., glutathione S-transferase) sequences. Such fusion proteins can facilitate the purification of the MU-1 fusion protein. In another embodiment, the fusion protein is includes a heterologous signal sequence (i.e., a pofypeptide sequence that is not present in a polypeptide encoded by a Mu-1 nucleic acid) at its N-terminus. For example, the native Mu-1 sigrial sequence can 25 be removed and replaced with a signal sequence from another protein. In certain host cells (e.g., mammalian host cells), expression and/or secretion of Mu-1 can be increased through use of a heterologous signal sequence. A chimeric or fusion protein of the invention can be produced by standard recombinant DNA techniques. For example, DNA fragments coding for the different 30 polypeptide sequences are ligated together in-frame in accordance with conventional techniques, e.g., by employing blunt-ended or stagger-ended termini for ligation, restriction enzyme digestion to provide for appropriate termini, filling-in of cohesive WO 03/028630 31 PCT/US02/29839 ends as appropriate, alkaline phosphatase treatment to avoid undesirable joining, and enzymatic ligation. In another embodiment, the fusion gene can be synthesized b}' conventional techniques including automated DNA synthesizers. Alternatively, PCR. amplification of gene fragments can be carried out using anchor primers that give rise to 5 complementary overhangs between two consecutive gene fragments that can subsequently be annealed and reamplified to generate a chimeric gene sequence (see, for example, Ausubel et al. (eds.) CURRENT PROTOCOLS IN MOLECULAR BIOLOGY, John Wiley & Sons, 1992). Moreover, many expression vectors are commercially available that encode a fusion moiety (e.g., an Fc region of an immunoglobulin heavy chain). A 10 Mu-1 encoding nucleic acid can be cloned into such an expression vector such that the fusion moiety is linked in-frame to the immunoglobulin protein. In some embodiments, MU-1 fusion polypeptides exist as oligomers, such as dinners or trimers. The first polypeptide, and/or nucleic acids encoding the first polypeptide, can be 15 constructed using methods known in the art. In some embodiments, the Mu-1 polypeptide moiety is provided as a variant Mu-1 polypeptide having a mutation in the naturally-occurring Mu-1 sequence (wild type) that results in higher affinity (relative to the non-mutated sequence) binding of the Mu-1 polypeptide to a IL-21. 20 In some embodiments, the Mu-1 polypeptide moiety is provided as a variant Mu- 1 polypeptide having mutations in the naturally-occurring Mu-1 sequence (wild type) that results in a Mu-1 sequence more resistant to proteolysis (relative to the non-mutated sequence). In some embodiments, the first polypeptide includes full-length Mu-1 25 polypeptide. Alternatively, the first polypeptide comprise less than full-length Mu-1 polypeptide. A signal peptide that can be included in the fusion protein is MPLLLLLLLLPSPLHP (SEQ ID NO:21). If desired, one or more amino acids can additionally be inserted between the first polypeptide moiety comprising the Mu-1 30 moiety and the second polypeptide moiety. The second polypeptide is preferably soluble. In some embodiments, the second polypeptide enhances the half-life, (e.g., the serum half-life) of the linked polypeptide. In WO 03/028630 32 PCT/US02/29839 some embodiments, the second polypeptide includes a sequence that facilitates association of the fusion polypeptide with a second Mu-1 polypeptide. In preferred embodiments, the second polypeptide includes at least a region of an immunoglobulin polypeptide. Immunoglobulin fusion polypeptide are known in the art and are described 5 in e.g., US Patent Nos. 5,516,964; 5,225,538; 5,428,130; 5,514,582; 5,714,147; and 5,455,165. In some embodiments, the second polypeptide comprises a full-length immunoglobulin polypeptide. Alternatively, the second polypeptide comprise less than full-length immxmoglobulin polypeptide, e.g., a heavy chain, light chain, Fab, Fab2, Fv, 10 or Fc. Preferably, the second polypeptide includes the heavy chain of an immunoglobulin polypeptide. More preferably, the second polypeptide includes the Fc region of an immunoglobulin polypeptide. In another aspect of the invention the second polypeptide has less effector function that the effector function of a Fc region of a wild-type immunoglobulin heavy 15 chain. Fc effector function includes for example, Fc receptor binding, complement fixation and T cell depleting activity (see for example, US Patent No. 6,136,310). Methods for assaying T cell depleting activity, Fc effector function, and antibody stability are known in the art. In one embodiment the second polypeptide has low or no affinity for the Fc receptor. Id an alternative embodiment, the second polypeptide has low or no 20 affinity for complement protein C1 q. A preferred second polypeptide sequence includes the amino acid sequence of SEQ ID NO: 17. This sequence includes a Fc region. Underlined amino acids are those that differ from the amino acid found in the corresponding position of the wild-type immunoglobulin sequence: 25 HTCP PCPAPEALGAPSVFLFP PKPKDTLMISRTPEVTCWVDVSHEDPEVKFNWYVDGVEVHN. K TKPREEQYNSTYRWSVLTVLHQDWLNGKEYKCKVSNFALPVPIEKTISKAKGQPREPQVYTL P 30 SREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSR1 Q QGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO:17) Examples of antagonistic fusion proteins that can be used in the methods of the 35 invention are shown in Figures 7-15. In one embodiment, the fusion protein includes an amino acid sequence chosen from, e.g., SEQ ID NO:23, SEQ ID NO:25, SEQ ID NO:27, WO 03/028630 33 PCT/USW2/29839 SEQ 3D NO:29, SEQ ID N0:31, SEQ ID N0.33, SEQ ID NO:35, SEQ ID NO:37, or SEQ ID NO:39, or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. In other embodiments, the fusion protein includes an amino acid sequence encoded by a nucleotide sequence chosen from, e.g., SEQ ID NO:22, SEQ ID NO:24, SEQ ID NO:26, 5 SEQ ID NO:28, SEQ ID N0:30, SEQ ID NO:32, SEQ ID NO:34, SEQ ID NO:36, or SEQ ID NO:3S, or a sequence ai least 85%, 90%, 95%, 98% or more identical thereto. Preferred fusion proteins have the amino acid sequence shown as SEQ IDNO;25 or SEQ ID NO:29 (Figures SA-8C and 10A-10C, respectively), or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. In other embodiments, the fusion protein includes 10 an amino acid sequence encoded by a nucleotide sequence chosen from, e.g., SEQ ID NO:24 or SEQ ID NO:28 (Figures 8A-8C and 1 OA-10C, respectively), or a sequence at least 85%, 90%, 95%, 98% or more identical thereto. Most preferably, the fusion protein has the amino acid sequence shown as SEQ ED NO:29, or has an amino acid sequence encoded by a nucleotide sequence shown as SEQ ID NO:28 (Figure 1 OA-10C). 15 In other embodiments, the IL-21/IL-21R agonists or antagonists are antibodies, or antigen-binding fragments thereof, that bind to IL-21 or IL-21R, preferably, mammalian (e.g., human or murine) 2L-21 orIL-21R. MU-1 proteins of the invention may also be used to immunize animals to obtain polyclonal and monoclonal antibodies which specifically react with the MU-1 protein 20 and which may inhibit binding of ligands to the receptor. Such antibodies may be obtained using the entire MU-1 as an immunogen, or by using fragments of MU-1. Smaller fragments of the MU-1 may also be used to immunize animals. The peptide immunogens additionally may contain a cysteine residue at the carboxyl terminus, and are conjugated to a hapten such as keyhole limpet heinocyanin (KLH). Additional peptide 25 immunogens may be generated by replacing tyrosine residues with sulfated tyrosine residues. Methods for synthesizing such peptides are known in the art, for example, as in R. P. Merrifield, J.Amer.Chem.Soc. 85,2149-2154 (1963); J. L. Krstenansky, et al., FEBS Lett. 211,10 (1987). Neutralizing or non-neutralizing antibodies (preferably monoclonal antibodies) 30 binding to MU-1 protein may also be useful in the treatment of conditions described above. These neutralizing monoclonal antibodies may be capable of blocking ligand binding to the MU-1 receptor chain. WO 03/028630 34 PCT/U S02/29839 The present invention further provides for compositions comprising an antibody that specifically reacts with an IL-21 or an IL-21R. Human monoclonal antibodies (mAbs) directed against IL-21 or IL-21R can be generated using transgenic mice carrying the human immunoglobulin genes rather than 5 the mouse system. Splenocytes from these transgenic mice immunized with the antigen of interest are used to produce hybridomas that secrete human mAbs with specific affinities for epitopes from a human protein (see, e.g., Wood et al. International Application WO 91/00906, Kucherlapati et al. PCT publication WO 91/10741; Lonberg et al. International Application WO 92/03918; Kay et al. International Application 10 92/03917; Lonberg, N. et al. 1994 Nature 368:856-859; Green, L.L. et al. 1994 Nature Genet. 7:13-21; Morrison, S.L. et al. 1994 Proc. Natl Acad. Sci. USA 81:6851-6855; Bruggeman et aL 1993 Year Immunol 7:33-40; Tuaillon et al. 1993 PNAS 90:3720-3724; Bruggeman et al. 1991 Eur J Immunol 21:1323-1326). Monoclonal antibodies can also be generated by other methods known to those skilled in 15 the art of recombinant DNA technology. An alternative method, referred to as the "combinatorial antibody display" method, has been developed to identify and isolate antibody fragments having a particular antigen specificity, and can be utilized to produce monoclonal antibodies (for descriptions of combinatorial antibody display see e.g., Sastry et al. 1989 PNAS 86:5728; Huse et al. 1989 Science 246:1275; and Orlandi et al. 1989 20 PNAS 86:3833). After immunizing an animal with an immunogen as described above, the antibody repertoire of the resulting B-cell pool is cloned. Methods are generally known for obtaining the DNA sequence of the variable regions of a diverse population of immunoglobulin molecules by using a mixture of oligomer primers and PCR. For instance, mixed oligonucleotide primers corresponding to the 5* leader (signal peptide) 25 sequences and/or framework 1 (FR1) sequences, as well as primer to a conserved 3' constant region primer can be used for PCR amplification of the heavy and light chain variable regions from a number of murine antibodies (Larrick et al.,1991, Biotechniques 11:152-156). A similar strategy can also been used to amplify human heavy and light chain variable regions from human antibodies (Larrick et al., 1991, Methods: Companion 30 to Methods in Enz)>mology 2:106-110). Chimeric antibodies, including chimeric immunoglobulin chains, can be produced by recombinant DNA techniques known in the art. For example, a gene WO 03/028630 PCT/US02/29839 35 encoding the Fc constant region of a murine (or other species) monoclonal antibody molecule is digested with restriction enzymes to remove the region encoding the murine Fc; and the equivalent portion of a gene encoding a human Fc constant region is substituted (see Robinson et al., International Patent Publication PCT/US86/02269; 5 Akira, et al., European Patent Application 184,187; Taniguchi. M., European Patent Application 171.496; Morrison et al., European Patent Application 173,494; Neuberger et al., International Application WO 86/01533; Cabiily et al. U.S. Patent No. 4,816,567; Cabilly et al., European Patent Application 125,023; Better et al. (1988 Science 240:1041-1043); liu et al. (1987) PNAS 84:3439-3443; liu et al., 1987, J. Immunol. 10 139:3521-3526; Sun et al. (1987) PNAS 84:214-218; Nishimura et al., 1987, Cane. Res. 47:999-1005; Wood et al. (1985) Nature 314:446-449; and Shaw et al., 1988, J. Natl Cancer hist. 80:1553-1559). An antibody or an immunoglobulin chain can be humanized by methods known in the art. Humanized antibodies, including humanized immunoglobulin chains, can be 15 generated by replacing sequences of the Fv variable region which are not directly involved in antigen binding with equivalent sequences from human Fv variable regions. General methods for generating humanized antibodies are provided by Morrison, S. L., 1985, Science 229:1202-1207, by Oi et al., 1986, BioTechniques 4:214, and by Queen et al. US 5,585,089, US 5,693,761 and US 5,693,762, the contents of all of which are 20 hereby incorporated by reference. Those methods include isolating, manipulating, and expressing the nucleic acid sequences that encode all or part of immunoglobulin Fv variable regions from at least one of a heavy or light chain. Sources of such nucleic acid are well known to those skilled in the art and, for example, may be obtained from a hybridoma producing an antibody against a predetermined target. The recombinant DNA 25 encoding the humanized antibody, or fragment thereof, can then be cloned into an appropriate expression vector. Humanized or CDR-grafted antibody molecules or immunoglobulins can be produced by CDR-graftmg or CDR substitution, wherein one, two, or all CDR's of an immunoglobulin chain can be replaced. See e.g., U.S. Patent 5,225,539; Jones et al. 30 1986 Nature 321:552-525; Verhoeyan et al. 1988 Science 239:1534; Beidler et al. 1988 J. Immunol 141:4053-4060; Winter US 5,225,539, the contents of all of which are hereby expressly incorporated by reference. Winter describes a CDR-grafting method WO 03/028630 36 PCT/US02/29839 which maybe used to prepare the humanized antibodies of the present invention (UK Patent Application GB 2188638A filed on March 26, 1987; Winter US 5,225,539), the contents of which is expressly incorporated by reference. All of the CDR's of a particular human antibody may be replaced with at least a portion of a non-human CDR or only 5 some of the CDR's may be replaced with non-human CDR's. It is only necessary to replace the number of CDR's required for binding of the humanized antibody to a predetermined antigen. Monoclonal, chimeric and humanized antibodies, which have been modified by, e.g., deleting, adding, or substituting other portions of the antibody, e.g., the constant 10 region, are also within the scope of the invention. For example, an antibody can be modified as follows: (i) by deleting the constant region; (ii) by replacing the constant region with another constant region, e.g., a constant region meant to increase half-life, stability or afBnity of the antibody, or a constant region from another species or antibody class; or (iii) by modifying one or more amino acids in the constant region to alter, for 15 example, the number of glycosylation sites, effector cell function, Fc receptor (FcR) binding, complement fixation, among others. Methods for altering an antibody constant region are known in the art. Antibodies with altered function, e.g. altered affinity for an effector ligand, such as FcR on a cell, or the CI component of complement can be produced by replacing at least one 2C amino acid residue in the constant portion of the antibody with a different residue (see e.g., EP 3S8,151 Al, US 5,624,821 and US 5,648,260, the contents of all of which are hereby incorporated by reference). Similar type of alterations could be described which if applied to the murine, or other species immunoglobulin would reduce or eliminate these functions. 25 For example, it is possible to alter the affinity of an Fc region of an antibody (e.g., an IgG, such as a human IgG) for an FcR (e.g., Fc gamma Rl), or for Clq binding by replacing the specified residue(s) with a residue(s) having an appropriate functionality on its side chain, or by introducing a charged functional group, such as glutamate or aspartate, or perhaps an aromatic non-polar residue such as phenylalanine, tyrosine, 30 tryptophan or alanine (see e.g., US 5,624,821). Amino acid sequences of IL-21 polypeptides are publicly known. For example, the nucleotide sequence and amino acid sequence of a human IL-21 is available at WO «3/02fM*»30 37 PCT/11S02/29839 Genbank Acc. No. X_011082. The disclosed human IL-21 nucleotide sequence is presented below: 1 grctgaagtga aaacgagacc aaggtctagc tctactgttg gtacttatga gatccagtcc 5 €1 tggcaacatg gagaggattg tcatctgtct gatggtcatc ttcttgggga cactggtcca 121 caaatcaagc tcceaaggtc aagatcgcca catgattaga atgcgtcaac ttatagatat 181 tgttgatcag ctgaaaaatt atgtgaatga cttggtccct gaatttctgc 10 cagctccaga 241 agatgtagag acaaactgtg agtggtcagc tttttcctgc tttcagaagg cccaactaaa 301 gtcagcaaat acaggaaaca atgaaaggat aatcaatgta tcaattaaaa agctgaagag 15 361 gaaaccacct tccacaaat-g cagggagaag acagaaacac agactaacat gcccttcatg 4 21 tgattcttat gagaaaaaac cacccaaaga attcctagaa agattcaaat cacttctcca 4 81 aaagatgatt catcagcatc tgtcctctag aacacacgga agtgaagatt 20 cctgaggatc 541 taacttgcag ttggacacta tgttacatac tctaatatag tagtgaaagt catttctttg 601 tattccaagt ggaggag (SEQ ID NO:18) 25 The amino acid sequence of the disclosed human IL-21 polypeptide is presented below: MRSSPGNMERIVICLMVIFLGTLVHKSSSQGQDRHMIRMRQLIDIVDQLKNYVNDLVPE FLPAPEDVETNCEWSAFSCFQKAQLKSANTGNNERIINVSIKKLKRKPPSTNAGRRQKH RLTCPSCDSYEKKPPKEFLERFKSLLQKMIHQHLSSRTHGSEDS (SEQ ID NO:19) 30 The invention also encompasses nucleic acids that hybridize to the nucleotide sequence set forth in SEQ ID NO:l, SEQ ID NO:22, SEQ ID NO:24, SEQ ED NO:26, SEQ ID NO:28, SEQ ID N0:30, SEQ ID NO:32, SEQ ID NO:34, SEQ ID NO:36, or SEQ ID NO:38, under highly stringent conditions (for example, 0.1X SSC at 650 C.). 3 5 Isolated polynucleotides which encode MU-1 proteins or fusion proteins, but which differ from the nucleotide sequence set forth in SEQ ID NOT, SEQ ID NO:22, SEQ ID NO:24, SEQ ID NO:26, SEQ ID NO:28, SEQ ID N0:30, SEQ ID NO:32, SEQ ID NO:34, SEQ ID NO:36, or SEQ ID NO:38s by virtue of the degeneracy of the genetic code are also encompassed by the present invention. Variations in the nucleotide 40 sequence as set forth in SEQ ID NO: 1, SEQ ID NO:22, SEQ ID NO:24, SEQ ID NO:26, SEQ ID NO:28, SEQ ID N0:30, SBQ ID NO:32, SEQ ID NO:34, SEQ ID NO:36, or SEQ ID NO:38, which are caused by point mutations or by induced modifications are also included in the invention. WO 03/028630 38 PCT/VS02/29839 The isolated polynucleotides of the invention may be operably linked to an expression control sequence such as the pMT2 or pED expression vectors disclosed in Kaufinan et a!., Nucleic Acids Res. 19,4485-4490 (1991), in order to produce the MU-1 protein recombinant]}'. Many suitable expression control sequences are known in the art 5 General methods of expressing recombinant proteins are also know and axe exemplified in R. Kaufinan, Methods in Enzymology 185, 537-566 (1990). As defined herein "operably linked" means enzymatically or chemically ligated to form a covalent bond between the isolated polynucleotide of the invention and the expression control sequence, in such a way that the MU-1 protein is expressed by a host cell which has been 10 transformed (transfected) with the ligated polynucleoiide/expression control sequence. The term "vector", as used herein, is intended to refer to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a "plasmid", which refers to a circular double stranded DNA loop into which additional DNA segments may be ligated. Another type of vector is a viral vector, 15 wherein additional DNA segments may be ligated into the viral genome. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) can be integrated into the genome of a host cell upon introduction into the host cell, and thereby are replicated 20 along with the host genome. Moreover, certain vectors are capable of directing the expression of genes to which they are operatively linked. Such vectors are referred to herein as "recombinant expression vectors" (or simply, "expression vectors"). In general, expression vectors of utility in recombinant DNA techniques are often in the form of plasmids. In the present specification, "plasmid" and "vector" may be used 25 interchangeably as the plasmid is the most commonly used form of vector. However, the invention is intended to include such other forms of expression vectors, such as viral vectors (e.g., replication defective retroviruses, adenoviruses and adeno-associated viruses), which serve equivalent functions. The term "regulatory sequence" is intended to includes promoters, enhancers and 30 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, inGoeddel; Gene Expression TecJinology: Methods in WO 03/028630 39 PCT/VS02/29839 Enzymology 185, 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 5 sequences for mammalian host cell expression include viral elements that direct high leve2s of protein expression in mammalian cells, such as promoters and/or enhancers derived from FF-la promoter and BGH poly A cytomegalovirus (CMV) (such as the CMV promoter/enhancer), Simian Virus 40 (SV40) (such as the SV40 promoter/enhancer), adenovirus, (e.g., the adenovirus major late promoter (AdMLP)) and 10 polyoma. For further description of viral regulatory elements, and sequences thereof, see e.g., U.S. Patent No. 5,168,062 by Stinski, U.S. Patent No. 4,510,245 by Bell et al. and U.S. Patent No. 4,968,615 by Schaffner et al. Hie recombinant expression vectors of the invention may carry additional sequences, such as sequences that regulate replication of the vector in host cells (e.g., 15 origins of replication) and selectable marker genes. The selectable marker gene facilitates selection of host cells into which the vector has been introduced (see e.g., U.S. Patents 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. 20 Preferred selectable marker genes include the dihydrofolate reductase (DHFR) gene (for use in dhfr" host cells with methotrexate selection/amplification) and the neo gene (for G418 selection). A number of types of cells may act as suitable host cells for expression of the MU-1 protein or fusion protein thereof. Any cell type capable of expressing functional 25 MU-1 protein may be used. Suitable mammalian host cells include, for example, monkey COS cells, Chinese Hamster Ovary (CHO) cells, human kidney 293 cells, human epidermal A431 cells, human Colo205 cells, 3T3 cells, CV-1 cells, other transformed primate cell lines, normal diploid cells, cell strains derived from in vitro culture of primary tissue, primary explants, HeLa cells, mouse L cells, BHK, HL-60, U937, HaK, 30 Rat2, BaF3, 32D, FDCP-1, PC 12, Mix or C2C12 cells. The MU-1 protein or fusion protein thereof may also be produced by operably linking the isolated polynucleotide of the invention to suitable control sequences in one WO 03/028630 40 PCT/US02/29839 or more insect expression vectors, and employing an insect expression system. Materials and methods for baculovirus/insect cell expression systems are commercially available in kit form from, e.g., Invitrogen, San Diego, Calif. U.S.A. (the MaxBac® kit), and such methods are well known in the art, as described in Summers and Smith, Texas 5 Agricultural Experiment Station Bulletin No. 1555 (1987), incorporated herein by reference. Soluble forms of the MU-1 protein may also be produced in insect cells using appropriate isolated polynucleotides as described above. Alternatively, the MU-1 protein or fusion protein thereof may be produced in lower eukaryotes such as yeast or in prokaryotes such as bacteria. Suitable yeast strains 10 include Saccharomyces cerevisiae, Schizosaccharomyces ponibe, Kluyveromyces strains, Candida, or any yeast strain capable of expressing heterologous proteins. Suitable bacterial strains include Escherichia coli, Bacillus subtilis, Salmonella typhimurium, or any bacterial strain capable of expressing heterologous proteins. Expression in bacteria may result in formation of inclusion bodies incorporating 15 the recombinant protein. Thus, refolding of the recombinant protein may be required in order to produce active or more active material. Several methods for obtaining correctly folded heterologous proteins from bacterial inclusion bodies are known in the art. These methods generally involve solubilizing the protein from the inclusion bodies, then denaturing the protein completely using a chaotropic agent When cysteine residues are 20 present in the primary amino acid sequence of the protein, it is often necessary to accomplish the refolding in an environment which allows correct formation of disulfide bonds (a redox system). General methods of refolding are disclosed in Kohno, Meth. Enzym., 185:187-195 (1990). EP 0433225 and copending application U.S. Ser. No. 08/163,877 describe other appropriate methods. 25 The MU-1 protein or fusion protein thereof may also be expressed as a product of transgenic animals, e.g., as a component of the milk of transgenic cows, goats, pigs, or sheep which are characterized by somatic or germ cells containing a polynucleotide sequence encoding the MU-1 protein or fusion protein thereof. The MU-1 protein or fusion protein thereof may be prepared by growing a culture 30 transformed host cells under culture conditions necessary to express the desired protein. The resulting expressed protein may then be purified from the culture medium or cell extracts. Soluble forms of the MU-1 protein or fusion protein thereof can be purified WO 03/028630 41 PCT/US02/29839 from conditioned media Membrane-bound forms of MU-1 protein of the invention can be purified by preparing a total membrane fraction from the expressing cell and extracting the membranes with a non-ionic detergent such as Triton X-100. The MU-1 protein or fusion protein can be purified using methods known to 5 those skilled in the art. For example, the MU-1 protein of the invention can be concentrated using a commercially available protein concentration filter, for example, an Amicon or MUlipore PeUicon ultrafiltration unit. Following the concentration step, the concentrate can be applied to a purification matrix such as a gel filtration medium. Alternatively, an anion exchange resin can be employed, for example, a matrix or 10 substrate having pendant diethylaminoethyl (DEAE) or polyetheyleneiraine (PEI) groups. The matrices can be acrylaxnide, agarose, dextran, cellulose or other types commonly employed in protein purification. Alternatively, a cation exchange step can be employed. Suitable cation exchangers include various insoluble matrices comprising sulfopropyl or caiboxymethyl groups. Sulfopropyl groups are preferred (e.g., S-Sephaxose ® columns). 15 The purification of the MU-1 protein or fusion protein from culture supernatant may also include one or more column steps over such afBnity resins as concanavalin A-agarose, heparin-toyopearl® or Cibacrom blue 3GA Sepharose®; or by hydrophobic interaction chromatography using such resins as phenyl ether, butyl ether, or propyl ether; or by immunoaffinity chromatography. Finally, one or more reverse-phase high performance 20 liquid chromatography (RP-HPLC) steps employing hydrophobic RP-HPLC media, e.g., silica gel having pendant methyl or other aliphatic groups, can be employed to further purify the MU-1 protein. Affinity columns including antibodies to the MU-1 protein can also be used in purification in accordance with known methods. Some or all of the foregoing purification steps, in various combinations or with other known methods, can 25 also be employed to provide a substantially purified isolated recombinant protein. Preferably, the isolated MU-1 protein is purified so that it is substantially free of other mammalian proteins. MU-1 proteins or fusion proteins of the invention may also be used to screen for agents which are capable of binding to MU-1. Binding assays using a desired binding 30 protein, immobilized or not, are well known in the art and may be used for this purpose using the MU-1 protein of the invention. Purified cell based ox protein based (cell free) screening assays may be used to identify such agents. For example, MU-1 protein may WO 03/028630 42 PCT/USO2/29839 be immobilized in purified form on a carrier and binding or potential ligands to purified MU-1 protein maybe measured Pharmaceutical Compositions IL-21 /TL-21 R-agomsts or antagonists may be used as a pharmaceutical 5 composition when combined with apharmaceutically acceptable carrier. Such a composition may contain, in addition to the IL-2 l/IL-2 I R-agonists or antagonists and carrier, various diluents, fillers, salts, buffers, stabilizers, solubilizers, and other materials well known in the art. The term "pharmaceuticaDy acceptable" means a non-toxic material that does not interfere with the effectiveness of the biological activity of the 10 active ingredient(s). The characteristics of the carrier will depend on the route of administration. The pharmaceutical composition of the invention may also contain cytokines, lymphokines, or other hematopoietic factors such as M-CSF, GM-CSF, IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, ILr7, IL-8, EL-9, IL-10, IL-11, IL-12, IL-14, IL-15, G-CSF, stem cell 15 factor, and erythropoietin. The pharmaceutical composition may also include anti- cytokine antibodies as described in more detail below. The pharmaceutical composition may contain thrombolytic or anti-thrombotic factors such as plasminogen activator and Factor VUX The pharmaceutical composition may further contain other anti-mflammatnry agents as described in more detail below. Such additional factors and/or 20 agents may be included in the pharmaceutical composition to produce a synergistic effect with an IL-2 i/IL-2IR-agonists or antagonists, or to minimize side effects caused by the IL-2 l/IL-2 lR-agomsts or antagonists. Conversely IL-2 l/IL-2 IR-agonists or antagonists may be included in formulations of the particular cytokine, lymphokine, other hematopoietic factor, thrombolytic or anti-thrombotic factor, or anti-inflammatory agent 25 to minimize side effects of the cytokine, lymphokine, other hematopoietic factor, thrombolytic or anti-thrombotic factor, or anti-inflammatory agent. The pharmaceutical composition of the invention may be in the form of a liposome in which IL-21/IL-2lR-agomsts or antagonists is combined, in addition to other phaimaceutically acceptable carriers, with amphipathic agents such as lipids which exist 30 in aggregated form as micelles, insoluble monolayers, liquid crystals, or lamellar layers which in aqueous solution. Suitable lipids for liposomal formulation include, without limitation, monoglycerides, diglycerides, sulfatides, lysolecithin, phospholipids, saponin, WO 03/(128630 43 PCT/US02/29839 bile acids, and the lilce. Preparation of such liposomal formulations is within the level of skill in the art, as disclosed, for example, in U.S. Pat. No. 4,235,871; U.S. Pat No. 4,501,728; U.S. Pat. No. 4,837,028; and U.S. Pat No. 4,737,323, all of which are incorporated herein by reference. 5 As used herein, the term "therapeutically effective amount" means the total amount of each active component of the pharmaceutical composition or method that is sufficient to show a meaningful patient benefit, e.g., amelioration of symptoms of, healing of, or increase in rate of healing of such conditions. When applied to an individual active ingredient, administered alone, the term refers to that ingredient alone. 10 When applied to a combination, the term refers to combined amounts of the active ingredients that result in the therapeutic effect, whether administered in combination, serially or simultaneously. In practicing the method of treatment or use of the present invention, a therapeutically effective amount of an IL-21 /IL-2 lR-agonist or antagonist is administered 15 to a subject, e.g., mamma] (e.g., a human). An IL-2 l/IL-2 IR-agonists or antagonists may be administered in accordance with the method of the invention either alone or in combination with other therapies such as treatments employing cytokines, lymphokines or other hematopoietic factors, or anti-inflammatory agents. When co-administered with one or more agents, an IL-21- and/or IL-21R-binding agent may be administered either 20 simultaneously with the second agent, or sequentially. If administered sequentially, the attending physician will decide on the appropriate sequence of administering an IL-21 /TL-2 IR-agonist or antagonist in combination with other agents. Administration of an IL-21/IL-2 lR-agonist or antagonist used in the pharmaceutical composition or to practice the method of the present invention can be 25 carried out in a variety of conventional ways, such as oral ingestion, inhalation, or cutaneous, subcutaneous, or intravenous injection. Intravenous administration to the patient is preferred. "When a therapeutically effective amount of an IL-2 l/TL-2 IR-agonist or antagonist is administered orally, the binding agent will be in the form of a tablet, capsule, powder, 30 solution or elixir. When administered in tablet form, the pharmaceutical composition of the invention may additionally contain a solid carrier such as a gelatin or an adjuvant. The tablet, capsule, and powder contain from about 5 to 95% binding agent, and WO 03/028630 44 PCT/US02/29839 preferably from about 25 to 90% binding agent. When administered in liquid form, a liquid carrier such as water, petroleum, oils of animal or plant origin such as peanut oil, mineral oil, soybean oil, or sesame oil, or synthetic oils maybe added. The liquid form of the pharmaceutical composition may further contain physiological saline solution, 5 dextrose or other saccharide solution, or glycols such as ethylene glycol, propylene glycol or polyethylene glycol. When administered in liquid form, the pharmaceutical composition contains from about 0.5 to 90% by weight of the binding agent, and preferably from about 1 to 50% the binding agent When a therapeutically effective amount of an IL-21 /IL-21 R-agonist or antagonist 10 is administered by intravenous, cutaneous or subcutaneous injection, binding agent will be in the form of a pyrogen-free, parenterally acceptable aqueous solution. The preparation of such parenterally acceptable protein solutions, having due regard to pH, isotonicity, stability, and the like, is within the skill in the art. A preferred pharmaceutical composition for intravenous, cutaneous, or subcutaneous injection should 15 contain, in addition to binding agent an isotonic vehicle such as Sodium Chloride Injection, Ringefs Injection, Dextrose Injection, Dextrose and Sodium Chloride Injection, Lactated Ringer's Injection, or other vehicle as known in the art The pharmaceutical composition of the present invention may also contain stabilizers, preservatives, buffers, antioxidants, or other additive known to those of skill in the art. 20 The amount of an JL~2 l/HL-2IR-agonist or antagonist in the pharmaceutical composition o f the present invention will depend upon the nature and severity of the condition being treated, and on the nature of prior treatments that the patient has undergone. Ultimately, the attending physician will decide the amount of binding agent with which to treat each individual patient. Initially, the attending physician will 25 administer low doses of binding agent and observe the patient's response. Larger doses of binding agent may be administered until the optimal therapeutic effect is obtained for the patient, and at that point the dosage is not generally increased further. It is contemplated that the various pharmaceutical compositions used to practice the method of the present invention should contain about 0.1 p.g to about 100 mg IL-21/IL-21R-30 agonist or antagonist per kg body weight. The duration of intravenous therapy using the pharmaceutical composition of the present invention will vary, depending on the severity of the disease being treated and the WO 03/028630 45 FCT/US02/29839 condition and potential idiosyncratic response of each individual patient It is contemplated that the duration of each application of the IL-2 l/IL-21 R-agonist or antagonist will be in the range of 12 to 24 hours of continuous intravenous administration. Ultimately the attending physician will decide on the appropriate 5 duration of intravenous therapy using the pharmaceutical composition of the present invention. The polynucleotide and proteins of the present invention are expected to exhibit one or more of the uses or biological activities (including those associated with assays cited herein) identified below. Uses or activities described for proteins of the present 10 invention may be provided by administration or use of such proteins or by administration or use of polynucleotides encoding such proteins (such as, for example, in gene therapies or vectors suitable for introduction of DNA). Uses of IL-2 l/IL-21R-Agonists to Enhance an Tmrrmne Response hi one aspect, the present invention provides methods for increasing immune cell, 15 e.g., T-cell (e.g., CD8+ T cell) proliferation by contacting an immune cell or a population of immune cells with an IL-21 or IL-21R binding agent which potentiates or enhances the activity of an IL-21 polypeptide. These methods are based, at least in part, on the finding that an agonist IL-21R binding agent stimulated, primarily via stimulation of CD8+T cells, innate and adaptive immunity in vivo against immunogenic and non-immunogenic 20 tumor cells (Example 9). The methods are also based, in part, on the finding that IL-21 induces proliferation of antigen- or anti-CD3 antibody stimulated thymocytes, lymph node T cells, CD4+ T cells, or CDS+ T cells. Applicants also show that proliferation of T cells to alloantigeris can be increased in the presence of IL-21. hi addition, IL-21 may also enhance proliferation and/or differentiation of CD8+ T cells (Example 10). For 25 example, priming of CD8+ T cells in the presence of IL-21 can generate effector cells with enhanced lytic (CTL) activity and/or increased ability to secrete cytokines, e.g., IFNy. IL-21 - or an IL-21R binding agent that stimulates IL-21 /IL-21R activity can be used to induce the proliferation and/or cytokine secretion of macrophages. 11-21 also has effects on memory T cells and antigen presenting cells (APCs). IL-21 has also been 30 found to be produced by activated CD4+ cells. Accordingly, binding agents that stimulate the IL-21/IL-21R pathway can be used by themselves or in combination with an antigen, WO 03/028630 46 PCT/US02/29839 e.g., as an adjuvant (e.g., a vaccine adjuvant), to up-regulate an immune response in vivo, e.g., for example, for use in treating cancer and infectious disorders. In one embodiment, agonistic IL-2i/IL~21R agonists may be useful in the treatment of various immune deficiencies and disorders (including severe combined 5 immunodeficiency (SCID)), e.g., in regulating (up or down) growth and proliferation of T anchor B lymphocytes, as well as effecting the cytolytic activity of NK cells and other cell populations. These immune deficiencies may be genetic or be caused by viral (e.g., HfV) as well as bacterial or fungal infections, or may result from autoimmune disorders. More specifically, infectious diseases causes by viral, bacterial, fungal or other infection 10 may be treatable using a protein of the present invention, including infections by HIV, hepatitis viruses, herpesviruses, mycobacteria, Leishmania spp., malaria spp. and various fungal infections such as candidiasis. Of course, in this regard, a protein of the present invention may also be useful where a boost to the immune system generally may be desirable, i.e., in the treatment of cancer. 15 Upregulation of an antigen function (preferably a B lymphocyte antigen function), as a means of up regulating immune responses, may also be useful in therapy. Upregulation of immune responses may be in the form of enhancing an existing immure response or eliciting an initial immune response. For example, enhancing an immune response through stimulating B lymphocyte antigen function may be useful in cases of 20 viral infection. In addition, systemic viral diseases such as influenza, the common cold, and encephalitis might be alleviated by the administration of stimulatory forms of B lymphocyte antigens systemically. Alternatively, anti-viral immune responses may be enhanced in an infected patient by removing T cells from the patient, costimulating the T cells in vitro with viral 25 antigen-pulsed APCs either expressing a peptide of the present invention or together with a stimulatory form of a soluble peptide of the present invention and reintroducing the in vitro activated T cells into the patient Another method of enhancing anti-viral immune responses would be to isolate infected cells from a patient, transfect them with a nucleic acid encoding a protein of the present invention as described herein such that the cells 30 express all or a portion of the protein on their surface, and reintroduce the transfected cells into the patient. The infected cells would now be capable of delivering a costimulatory signal to, and thereby activate, T cells in vivo. WO 03/02863© 47 PCT/US02/29839 En another application, up regulation or enhancement of antigen function may be useful in the induction of tumor immunity. Tumor cells (e.g., sarcoma, melanoma, lymphoma, leukemia, neuroblastoma, carcinoma) transfected with a nucleic acid encoding at least one peptide of the present invention can be administered to a subject to 5 overcome tumor-specific tolerance in the subject If desired, the tumor cell can be transfected to express a combination of peptides. For example, tumor cells obtained from a patient can be transfected ex vivo with an expression vector directing the expression of an IL-2 l/IL-21R agonist, alone or in combination with, a peptide having B7-2-lIke activity alone, or in conjunction with a peptide having B7-l-like activity and/or 10 B7-3-like activity. The transfected tumor cells are returned to the patient to result in expression of the peptides on the surface of the transfected cell. Alternatively, gene therapy techniques can be used to target a tumor cell for transfection in vh>o. The presence of an IL-21/IL-21R agonist, in combination with a peptide having the activity of a B lymphocyte antigen(s) on the surface of the tumor cell provides the 15 necessary costimulation signal to T cells to induce a T cell mediated immune response against the transfected tumor cells, in addition, tumor cells which lack MHC class I or MHC class II molecules, or which fail to reexpress sufficient amounts of MHC class I or MHC class II molecules, can be transfected with nucleic acid encoding all or a portion of (e.g., a cytoplasmic-domain truncated portion) of an MHC class .alpha, a chain protein 20 and microglobulin protein or an MHC class II a chain protein and an MHC class H J3 chain protein to thereby express MHC class I or MHC class E proteins on the cell surface. Expression of the appropriate class I or class H MHC in conjunction with an IL-21/TL-21R agonist and/or a peptide having the activity of a B lymphocyte antigen (e.g., B7-1, B7-2, B7-3) induces a T cell mediated immune response against the transfected 25 tumor cell. Optionally, a gene encoding an antisense construct which blocks expression of an MHC class II associated protein, such as the invariant chain, can also be cotransfected with a DNA encoding an IL-21/IL-21R agonist and/or a peptide having the activity of a B lymphocyte antigen to promote presentation of tumor associated antigens and induce tumor specific immunity. Thus, the induction of a T cell mediated immune 30 response in a human subject may be sufficient to overcome tumor-specific tolerance in the subject. WO 03/(128630 48 PCT/US02/29839 In other embodiments, the IL-2 l/IL-21R agonists can be used as vaccine adjuvants. Adjuvants are immune modulating compounds that have the ability to enhance and/or steer the development and profile of immune responses against various antigens that are themselves poorly immunogenic. Cytokines and/or lymphokines can be 5 used as adjuvants. The appropriate selection of adjuvants can induce good humoral and cellular immune responses that would not develop in the absence of adjuvant. In particular, adjuvants have significant effects in enhancing the immune response to subunit and peptide antigens in vaccines. Their stimulatory activity is also beneficial to the development of antigen-specific immune responses directed against protein antigens. 10 For a variety of antigens that require strong mucosal responses, high serum titers, induction of CTL and vigorous cellular responses, adjuvant and cytokine/lymphokine combinations provide stimuli that are not provided by most antigen preparations. As used herein, the phrase "vaccine adjuvant" or "vaccine therapy" is intended to mean the use of an IL-2 l/IL-21R agonist, e.g., an IL-21 polypeptide or polynucleotide 15 encoding the same, in combination with an antigen (e.g., viral, parasitic and bacterial polypeptides, proteins or peptides), or other antigens (e.g., tumor or cancer cell polypeptides, proteins or peptides) or polynucleotides encoding the antigen to enhance, suppress or otherwise modulate an immune response to the antigen. For the purpose of this definition, "combination" shall mean use in conjunction with, simultaneous with 20 (combined or uncombined) or sequentially with an antigen. The term "vaccine adjuvant composition" refers to a vaccine adjuvant that additionally includes immunologically acceptable diluents or carriers in a conventional manner to prepare injectable liquid solutions or suspensions. The vaccine adjuvant composition may additionally include agents that further enhance an immune response 25 elicited by IL-21. For example, the vaccine adjuvant composition may additionally include 3-O-deacylated monophosphoryl lipid A (MPL™) or monophosphoiyl lipid A and derivatives and analogs thereof. MPL™ can be used in a range of l-100^g/dose. The antigens used for vaccine therapy include proteins, peptides or polypeptides derived from immunogenic and non-immunogenic proteins, as well as any of the 30 following: saccharides, proteins, poly- or oligonucleotides, or other macromolecular components, or fragments thereof. As used in this section, a "peptide" comprises a series of at least six amino acids and contains at least one antigenic determinant, while a WO 03/(128630 49 PCT/US02/29839 "polypeptide" is a longer molecule than a peptide, but does not constitute a full-length protein. As used herein, a "fragment" comprises a portion, but less than all of a saccharide, protein, poly- or oligonucleotide, or other macromolecular components. As used herein, the term "effective adjuvanting amount" means a dose of the 5 combination of adjuvants described herein, which is suitable to elicit an increased immune response in a vertebrate host. The particular dosage will depend in part upon the age, weight and medical condition of the host, as well as on the method of administration and the antigen. The vaccine adjuvant composition of the invention can be administered to a 10 human or non-human vertebrate by a variety of routes, including, but not limited to, intranasal, oral, vaginal, rectal, parenteral, intradermal, transdermal (see, e.g., International application WO 98/20734 (44), which is hereby incorporated by reference), intramuscular, intraperitoneal, subcutaneous, intravenous and intraarterial. The amount of the antigen component or components of the antigenic composition will vary 15 depending in part upon the identity of the antigen, as well as upon the age, weight and medical condition of the host, as well as on die method of administration. Again, suitable doses are readily determined by persons skilled in the art. It is preferable, although, not required, that the antigen and the combination of adjuvants be administered at the same time. The number of doses and the dosage regimen for the antigenic 20 composition are also readily determined by persons skilled in the art. In some instances, the adjuvant properties of the combination of adjuvants may reduce the number of doses needed or the time course of the dosage regimen. The combinations of adjuvants of this invention are suitable for use in combination with wide variety of antigens from a wide variety of pathogenic 25 microorganisms, including but not limited to those from viruses, bacteria, fungi or parasitic microorganisms that infect humans and non-human vertebrates, or from a cancer cell or tumor cell (e.g., sarcoma, melanoma, lymphoma, leukemia, neuroblastoma, carcinoma). The antigen may comprise peptides or polypeptides derived from proteins, as well as fragments of any of the following: saccharides, proteins, poly- or 30 oligonucleotides, cancer or tumor cells, allergens, amyloid peptide protein, or other macromolecular components, hi some instances, more than one antigen is included in the antigenic composition. WO 03/028630 56 PCT/US02/29839 Desirable viral vaccines containing the adjuvant combinations of this invention include those directed to the prevention and/or treatment of disease caused by, without limitation, Human immunodeficiency virus, Simian immunodeficiency virus, Respiratory syncytial virus, Parainfluenza virus types 1-3, Influenza virus, Herpes simple* virus, Human cytomegalovirus, Hepatitis A virus, Hepatitis B virus, Hepatitis C virus, Human papillomavirus, poliovirus, rotavirus, calici viruses, Measles virus, Mumps virus, Rubella virus, adenovirus, rabies virus, canine distemper virus, rinderpest virus, coronavirus, parvovirus, infectious fhinotracheitis viruses, feline leukemia virus, feline infectious peritonitis virus, avian infectious bursal disease virus, Newcastle disease virus, Marek's disease virus, porcine respiratory and reproductive syndrome virus, equine arteritis virus and various Encephalitis viruses, in one embodiment, the IL-21/IL-21R agonists is administered in combination with a TNF antagonist, e.g., a TNF antagonist as described herein, to treat a Hepatitis C virus infection. Desirable bacterial vaccines containing the adjuvant combinations of this invention include those directed to the prevention and/or treatment of disease caused by, without limitation, Haemophilus influenzae (both typable and nontypable), Haemophilus somius, Moraxella catarrhalis, Streptococcus pneumoniae, Streptococcus pyogen es, Streptococcus agalactiae, Streptococcus faecalis, Helicobacter pylori, Neisseria meningitidis, Neisseria gonorrhoeae, Chlamydia trachomatis, Chlamydia pneumoniae, Chlamydia psittaci, Bordetella pertussis^ Salmonella typhi, Salmonella typhimurium, Salmonella choleraesuis, Escherichia coli, Shigella,, Vibrio cholerae, Corynebacteriwn diphtheriae, Mycobacterium tuberculosis, Mycobacterium avium- Mycobacterium intracellular complex, Proteus mirabilis, Proteus vulgaris, Staphylococcus aureus, Clostridium tetani, Leptospira interrogans, Borrelia burgdorferi, Pasteurella haemolytica, Pasteurella multocida, Actinobacillus pleuropneumonias and Mycoplasma gafosepticum. Desirable vaccines against fungal pathogens containing the adjuvant combinations of this invention include those directed to the prevention and/or treatment of disease caused by, without limitation, Aspergillis, Blastomyces, Candida, Coccidiodes, Cryptococcus and Histoplasma. Desirable vaccines against parasites containing the adjuvant combinations of this invention include those directed to the prevention and/or treatment of disease caused by, WO 03/028630 51 PCT/US02/29839 without limitation, Leishmania major, Ascaris, Trichuris, Giardia, Schistosoma, Cryptosporidium, Trichomonas, Toxoplasma gondii and Pneumocystis carinii. Desirable vaccines for eliciting a therapeutic or prophylactic anti-cancer effect in a vertebrate host, which contain the adjuvant combinations of this invention, include 5 those utilizing a cancer antigen or tumor-associated antigen including, without limitation, prostate specific antigen (PSA), prostate-specific membrane antigen (PSMA), carcino-embiyonic antigen (CEA), MUC-1, Her2, CA-125, MAGE-3, EGFR, HELP, GCC, CD66-c, prostasin, TMPRSS3, TADG 12 and TADG 15. Desirable vaccines for moderating responses to allergens in a vertebrate host 10 which contain the adjuvant combinations of this invention, include those containing an allergen or fragment thereof. Examples of such allergens are described in United States Patent Number 5,830,877 (45) and published International Patent Application Number WO 99/51259 (46), which are hereby incorporated by reference, and include pollen, insect venoms, animal dander, fungal spores and drugs (such as penicillin). The vaccines 15 interfere with the production of IgE antibodies, a known cause of allergic reactions. Desirable vaccines for preventing or treating disease characterized by amyloid deposition in a vertebrate host, which contain the adjuvant combinations of this invention, include those containing portions of amyloid peptide protein (APP). This disease is referred to variously as Alzheimer's disease, amyloidosis or amyloidogenie 20 disease. Thus, the vaccines of this invention include the adjuvant combinations of this invention plus Af3 peptide, as well as fragments of Aj3 peptide and antibodies to A{i peptide or fragments thereof. In the case of HIV and STV, the antigenic compositions comprise at least one protein, polypeptide, peptide or fragment derived from said protein. In some instances, 25 multiple HIV or SIV proteins, polypeptides, peptides and/or fragments are included in the antigenic composition. The adjuvant combination formulations of this invention are also suitable for inclusion as an adjuvant in polynucleotide vaccines (also known as DNA vaccines). Such vaccines may farther include facilitating agents such as bupivicaine (see U.S. 30 Patent Number 5,593,972 (49), which is hereby incorporated by reference). Uses of IL-21/IL-21R. Antagonists to Decrease Immune Cell Activity WO 03/CI28630 PCT/US02/29839 52 In yet another aspect, the invention features a method for inhibiting the activity of an immune cell, e.g., mature T cells {mature CD8+T cells, mature CD4+ T cells), mature NK cells, B cells, macrophages and megakaryocytes, or a population thereof, by contacting a population of T cells with an IL-2 l/IL-21R antagonist in an amount 5 sufficient to inhibit the activity of the immune cell or population. Antagonists of IL-21 and/or IL-21R (e.g., a fusion protein or a neutralizing antibody, as described herein) can also be administered to subjects for which inhibition of an immune response is desired. These conditions include, e.g., autoimmune disorders (e.g., arthritic disorders), or organ transplantation. 10 Applicants have shown that a reduction of IL-21R activity by using a neutralizing fusion protein that includes the extracellular domain of the IL-21R fused to an Fc immunoglobulin region ameliorates inflammatory symptoms in mouse collagen-induced arthritis (CIA) animal models (Example 7). Expression of IL-21R mRNA is upregulated in the paws of CIA mice (Example 8). Accordingly, IL-21R binding agents that 15 antagonize EL-21/EL-21R activity can be used to induce immune suppression in vivo, e.g., for treating or preventing immune cell-associated pathologies, including transplant rejection and autoimmune disorders. The IL-21R DNA also maps to the chromosomal locus for Crohn's disease. As a result, binding agents of the present invention may be used to treat Crohn's disease and 20 other inflammatory bowel diseases. The subject method can also be used to modulate (e.g., inhibit) the activity, e.g., proliferation, differentiation, survival) of an immune or hematopoietic ceil (e.g., a cell of myeloid, lymphoid, eiythroid lineages, or precursor cells thereof), and, thus, can be used to treat or prevent a variety of immune disorders. Non-limiting examples of the disorders 25 that can be treated or prevented include, but are not limited to, transplant rejection, autoimmune diseases (including, for example, diabetes mellitus, arthritis (including rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis, psoriatic arthritis), multiple sclerosis, encephalomyelitis, myasthenia gravis, systemic lupus erythematosis, autoimmune thyroiditis, dermatitis (including atopic dermatitis and eczematous 30 dermatitis), psoriasis, Sjogren's Syndrome, Crohn's disease, aphthous ulcer, iritis, conjunctivitis, keratoconjunctivitis, ulcerative colitis, spondyoarthropathy, ankylosing spondylitis, intrinsic asthma, allergic asthma, cutaneous lupus erythematosus, WO <13/028630 53 PCT/U SO 2/29839 scleroderma, vaginitis, proctitis, drug eruptions, leprosy reversal reactions, erythema nodosum leprosum, autoimmune uveitis, allergic encephalomyelitis, acute necrotizing hemorrhagic encephalopathy, idiopathic bilateral progressive sensorineural hearing loss, aplastic anemia, pure red cell anemia, idiopathic thrombocytopenia, polychondritis, 5 Wegener's granulomatosis, chronic active hepatitis, Stevens-Johnson syndrome, idiopathic sprue, lichen planus, Graves' disease, sarcoidosis, primary biliary cirrhosis, uveitis posterior, and interstitial lung fibrosis), graft-versus-host disease, and allergy such as, atopic allergy. Preferred disorders that can be treated using the binding agents of the invention include arthritic disorders (e.g., rheumatoid arthritis, juvenile rheumatoid 10 arthritis, osteoarthritis, psoriatic arthritis, and ankylosing spondylitis (preferably, rheumatoid arthritis)), multiple sclerosis, type I diabetes, lupus (SLE), IBD, Crohn's disease, asthma, vasculitis, allergy, scleroderma and psoriasis. In another embodiment, IL-2 l/IL-21R antagonists, alone or in combination with, other therapeutic agents as described herein (e.g., TNF antagonists) can be used to treat 15 multiple myeloma and related B Ijmphocytic malignancies (Brenne, A. et al. (2002) Blood Vol. 99(10):3756-3762). Using the IL-21/IL-21R antagonists, it is possible to modulate immune responses, in a number of ways. Down regulation may be in the form of inhibiting or blocking an immune response already in progress or may involve preventing the induction of an 20 immune response. The functions of activated T cells may be inhibited by suppressing T cell responses or by inducing specific tolerance in T cells, or both. Immunosuppression of T cell responses is generally an active, non-antigen-specific, process that requires continuous exposure of the T cells to the suppressive agent. Tolerance, which involves inducing non-responsiveness or anergy in T cells, is distinguishable from 25 immunosuppression in that it is generally antigen-specific and persists after exposure to the tolerizing agent has ceased. Operationally, tolerance can be demonstrated by the lack of a T cell response upon reexposure to specific antigen in the absence of the tolerizing agent Down regulating or preventing one or more antigen functions (including without 30 limitation B lymphocyte antigen functions, e.g., preventing high level lymphokine synthesis by activated T cells, will be useful in situations of tissue, skin and organ transplantation and in graft-versus-host disease (GVHD). For example, blockage of T cell WO 03/028630 54 PCT/US02/29839 function should result in reduced tissue destruction in tissue transplantation. Typically, in tissue transplants, rejection of the transplant is initiated through its recognition as foreign by T cells, followed by an immune reaction that destroys the transplant The administration of an JL-21/IL^21R antagonist, in combination with a molecule which 5 inhibits or blocks interaction of a B7 lymphocyte antigen with its natural ligand(s) on immune cells (such as a soluble, monomelic form of a peptide having B7-2 activity alone or in conjunction with a monomelic form of a peptide having an activity of another B lymphocyte antigen (e.g., B7-1, B7-3) or blocking antibody), prior to transplantation can lead to the binding of the molecule to the natural ligand(s) on the immune cells without 10 transmitting the corresponding costimulatory signal. Blocking B lymphocyte antigen function in this matter prevents cytokine synthesis by immune cells, such as T cells, and thus acts as an immunosuppressant. Moreover, the lack of costirmilation may also be sufficient to anergize the T cells, thereby inducing tolerance in a subject. Induction of long-term tolerance by B lymphocyte antigen-blocking reagents may avoid the necessity 15 of repeated administration of these blocking reagents. To achieve sufficient immunosuppression ot tolerance in a subject it may also be necessary to block the function of a combination of B lymphocyte antigens. The efficacy of particular blocking reagents in preventing organ transplant rejection or GVHD can be assessed using animal models that are predictive of efficacy in 20 humans. Examples of appropriate systems which can be used include allogeneic cardiac grafts in rats and xenogeneic pancreatic islet cell grafts in mice, both of which have been used to examine the immunosuppressive effects of CTLA4Ig fusion proteins in vivo as described in Lenschow et al., Science 257:789-792 (1992) and Turka et al., Proc. Natl. Acad. Sci U.S.A., 89:11102-11105 (1992). In addition, murine models of GVHD (see 25 Paul ed., Fundamental Immunology, Raven Press, New York, 1989, pp. 846-847) can be used to determine the effect of blocking B lymphocyte antigen function in vivo on the development of that disease. Blocking antigen function may also be therapeutically useful for treating autoimmune diseases. Many autoimmune disorders are the result of inappropriate 30 activation of T cells that are reactive against self tissue and which promote the production of cytokines and autoantibodies involved in the pathology of the diseases. Preventing the activation of autoreactive T cells may reduce or eliminate disease WO 03/028630 PCT/US02/29839 55 symptoms. Administration of IL-2 l/IL-21R antagonists in combination with reagents which block costimulation of T cells by disrupting receptorrligand interactions of B lymphocyte antigens can be used to inhibit T cell activation and prevent production of autoantibodies or T cell-derived cytokines which maybe involved in the disease process. 5 Additionally, IL-21 /EL-21R antagonists in combination with blocking reagents may induce antigen-specific tolerance of autoreactive T cells which could lead to long-term relief from the disease. The efficacy of these agents in preventing or alleviating autoimmune disorders can be determined using a number of well-characterized animal models of human autoimmune diseases. Examples include murine experimental 10 autoimmune encephalitis, systemic lupus erythmatosis in MRL/lpr/lpr mice or NZB hybrid mice, murine autoimmune collagen arthritis, diabetes mellitus in NOD mice and BB rats, and murine experimental myasthenia gravis (see Paul ed., Fundamental Immunology, Raven Press, New York, 1989, pp. 840-856). In one embodiment, the IL-2 l/IL-21R antagonists, e.g., pharmaceutical 15 compositions thereof, are administered in combination therapy, i.e.s combined with other agents, e.g., therapeutic agents, that are useful for treating pathological conditions or disorders, such as immune and inflammatory disorders. The term "in combination" in this context means that the agents are given substantially contemporaneously, either simultaneously or sequentially. If given sequentially, at the onset of administration of the 20 second compound, the first of the two compounds is preferably still detectable at effective concentrati ons at the site of treatment. For example, the combination therapy can include one or more IL-21/IL-21R antagonists, e.g., an antibody or an antigen-binding fragment thereof (e.g., a chimeric, humanized, human, or in vitro generated antibody or antigen-binding fragment thereof) 25 against IL-21 or IL-21 receptor, an IL-21 fusion protein, a soluble IL-21 receptor, peptide inhibitor or a small molecule inhibitor) co-formulated with, and/or co-administered with, one or more additional therapeutic agents, e.g., one or more cytokine and growth factor inhibitors, immunosuppressants, anti-inflammatory agents, metabolic inhibitors, enzyme inhibitors, and/or cytotoxic or cytostatic agents, as described in more detail below, 30 Furthermore, one or more 3L-21/IL-21R antagonists described herein may be used in combination with two or more of the therapeutic agents described herein. Such combination therapies may advantageously utilize lower dosages of the administered WO 03/028630 PCT/US02/29839 56 therapeutic agents, thus avoiding possible toxicities or complications associated with the various monotherapies. Moreover, the therapeutic agents disclosed herein act on pathways that differ from the IL-2 l/IL-21R receptor pathway, and thus are expected to enhance and/or synergize with the effects of the 3L-21/IL-21R antagonists. 5 Preferred therapeutic agents used in combination wife an IL-2 l/EL-21R antagonist are those agents that interfere at different stages in the autoimmune and subsequent inflammatory response. In one embodiment, one or more IL-2 l/EL-21R antagonist described herein may be co-formulated with, and/or co-administered with, one or more additional agents such as other cytokine or growth factor antagonists (e.g., soluble 10 receptors, peptide inhibitors, small molecules, ligand fusions); or antibodies or antigen-binding fragments thereof that bind to other targets (e.g., antibodies that bind to other cytokines or growth factors, their receptors, or other cell surface molecules); and antiinflammatory cytokines or agonists thereof. Non-limiting examples of the agents that can be used in combination with the IL-21/IL-21R antagonists described herein, include, 15 but are not limited to, antagonists of one or more interleukins (ILs) or their receptors, e.g., antagonists of EL-1, IL-2, EL-6, IL-7, IL-S, IL-12, IL-13, IL-15, IL-16, IL-18, and IL-22; antagonists of cytokines or growth factors or their receptors, such as tumor necrosis factor (TNF), LT, EMAP-IL GM-CSF, FGF and PDGF. IL-21/IL-21R antagonists can also be combined with inhibitors of, e.g., antibodies to, cell surface molecules such as 20 CD2, CD3, CD4, CDS, CD25, CD2S, CD30, CD40, CD45, CD69, CD80 (B7.1), CDS6 (B7.2), CD90, or their ligands, including CD154 (gp39 or CD40L), or LFA-l/ICAM-1 and VLA-4/VCAM-1 (Yusuf-Makagiansar H. etal, (2002) Med Res Rev 22(2): 146-67). Preferred antagonists that can be used in combination with IL-21/IL-21R antagonists described herein include antagonists of IL-1, IL-12, TNFa, IL-15, IL-17, IL-18, and IL-25 22. Examples of those agents include IL-12 antagonists, such as chimeric, humanized, human or in vitro generated antibodies (or antigen-binding fragments thereof) that bind to IL-12 (preferably human IL-12), e.g., the antibody disclosed in WO 00/56772, Genetics Institute/BASF); IL-12 receptor inhibitors, e.g., antibodies to human 30 IL-12 receptor, and soluble fragments of the IL-12 receptor, e.g., human IL-12 receptor. Examples of IL-15 antagonists include antibodies (or antigen-binding fragments thereof) against IL-15 or its receptor, e.g., chimeric, humanized, human or in vitro generated WO 03/028630 57 antibodies to human IL-15 or its receptor, soluble fragments of the EL-15 receptor, and IL-15-binding proteins. Examples of IL-18 antagonists include antibodies, e.g., chimeric, humanized, human or in vitro generated antibodies (or antigen-binding fragments thereof), to human IL-18, soluble fragments of the EL-18 receptor, and IL-18 binding 5 proteins (IL-18BP, Mallet et al. (2001) C-irc. Res. 28). Examples of IL-1 antagonists include Interleukin-l-converting enzyme (ICE) inhibitors, such as Vx740, IL-1 antagonists, e.g., IL-1RA (ANKINRA, AMGEN), sILlRJI (Immunex), and anti-IL-1 receptor antibodies (or antigen-binding fragments thereof). Examples of TNF antagonists include chimeric, humanized, human or in vitro 10 generated antibodies (or antigen-binding fragments thereof) to TNF (e.g., human TNF a), such as D2E7, (human TNFa antibody, U.S. 6,258,562; BASF), CDP-571/CDP-870/BAY-l0-3356 (humanized anti-TNFa antibody; Celltech/Pharmacia), cA2 (chimeric anti-TNFa antibody; RemicadeTM, Centocor); anti-TNF antibody fragments (e.g., CPDS70); soluble fragments of the TNF receptors, e.g., p55 or p75 human TNF receptors 15 or derivatives thereof, e.g., 75 kdTNFR-IgG (75 kD TNF receptor-IgG fusion protein, EnbrelTM; Immunex; see e.g., Arthritis & Rheumatism (1994) Vol. 37, S295; J. Invest. Med. (1996) Vol. 44,235A), p55 kdTNFR-IgG (55 kD TNF receptor-IgG fusion protein (Lenercept)); enzyme antagonists, e.g., TNFa converting en2yme (TACE) inhibitors (e.g., an alpha-sulfonyl hydroxamic acid derivative, WO 01/55112, and N-hydroxyformamide 20 TACE inhibitor GW 3333, -005, or -022); and TNF-bp/s-TNFR (soluble TNF binding protein; see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S284; Amer. J. Physiol. - Heart and Circulator)' Physiology (1995) Vol. 268, pp. 37-42). Preferred TNF antagonists are soluble fragments of the TNF receptors, e.g., p55 or p75 human TNF receptors or derivatives thereof, e.g., 75 kdTNFR-IgG, and TNFa converting 25 enzyme (TACE) inhibitors. In other embodiments, the IL-21-/IL21R binding agents described herein can be administered in combination with one or more of the following: IL-13 antagonists, e.g., soluble IL-13 receptors (sIL-13) and/or antibodies against IL-13; EL-2 antagonists, e.g., DAB 486-IL-2 and/or DAB 389-IL-2 (IL-2 fusion proteins; Seragen; see e.g., Arthritis & 30 Rheumatism (1993) Vol. 36,1223), and/or antibodies to IL-2R, e.g., anti-Tac (humanized anti-IL-2R; Protein Design Labs, Cancer Res. 1990 Mar 1;50(5): 1495-502). Yet another combination includes IL-21 antagonists in combination with non-depleting PCT7US02/29839 WO 03/028630 58 PCT/US02/29839 anti-CD4 inhibitors (IDEC-CE9.1/SB 210396 (non-depleting primatiz.edanti-CD4 antibody; IDEC/SmithKlme). Yet other preferred combinations include antagonists of the co-stimulatoiy pathway CD80 (B7.1) or CD86 (B7.2) including antibodies, soluble receptors or antagonistic ligands; as well as p-selectin glycoprotein ligand (PSGL), anti-5 inflammatory cytokines, e.g., IL-4 (DN AX/Schering); IL-10 (SCH 52000; recombinant IL-10 DNAX/Schering); IL- 13 and TGFD, and agonists thereof (e.g., agonist antibodies). In other embodiments, one or more IL-21-/IL21R binding agents can be co-formulated with, and/or co-administered with, one or more anti-inflammatory drugs, 10 immunosuppressants, or metabolic or enzymatic inhibitors. Non-limiting examples of the drugs or inhibitors that can be used in combination with the IL-21 antagonists described herein, include, but are not limited to, one or more of: non-steroidal antiinflammatory drug(s) (NSAIDs), e.g., ibuprofen, Tenidap (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S280)), Naproxen (see e.g., Neuro 15 Report (1996) Vol. 7, pp. 1209-1213), Meloxicam, Piroxicam, Diclofenac, and Indomethacin; Sulfasalazine (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S281); corticosteroids such as prednisolone; cytokine suppressive antiinflammatory drug(s) (CSAIDs); inhibitors of nucleotide biosynthesis, e.g., inhibitors of purine biosynthesis, folate antagonists (e.g., methotrexate (N-[4~[[(2,4-diamino-6-20 pteridhyl)methyl]methylamiao]benzoyl]-L-glutamic acid); and inhibitors of pyrimidine biosynthesis, e.g., dihydroorotate dehydrogenase (DHODH) inhibitors (e.g., leflunomide (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), SI31; Inflammation Research (1996) Vol. 45, pp. 103-107). Preferred therapeutic agents for use in combination with IL-2 l/IL-21R antagonists include NSAIDs, CSAIDs, (DHODH) 25 inhibitors (e.g., leflunomide), and folate antagonists (e.g., methotrexate). Examples of additional inhibitors include one or more of: corticosteroids (oral, inhaled and local injection); immunosuppresants, e.g., cyclosporin, tacrolimus (FKL-506); and mTOR inhibitors, e.g., sirolimus (rapamycin) or rapamycin derivatives, e.g., soluble rapamycin derivatives (e.g., ester rapamycin derivatives, e.g., CCI-779 (Elit L. (2002) 30 Current Opinion Investig. Drugs 3(8): 1249-53; Huang, S. et al.. (2002) Current Opinion Investig. Drugs 3(2):295-304); agents which interfere with signaling by proinflammatory cytokines such as TNFa or IL-1 (e.g. IRAK, NIK, IKK, p3S or MAP kinase inhibitors); WO 03/028<>30 59 PCT/US02/29839 COX2 inhibitors, e.g., celecoxib and variants thereof, MK-966, see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S81); phosphodiesterase inhibitors, e.g., R973401 (phosphodiesterase Type IV inhibitor; see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S282)); phospholipase inhibitors, e.g., inhibitors of 5 cytosolic phospholipase 2 (cPIA2) (e.g., trifluoromethyl ketone analogs (U.S. 6,350,892)); inhibitors of vascular endothelial cell growth factor or growth factor receptor, e.g., VEGF inhibitor and/or VEGF-R inhibitor; and inhibitors of angiogenesis. Preferred therapeutic agents for use in combination with IL-21 /IL-21R antagonists immunosuppresants, e.g., cyclosporin, tacrolimus (FK-506); and mTOR inhibitors, e.g., 10 sirolitnus (rapamycin) or rapamycin derivatives, e.g., soluble rapamycin derivatives (e.g., ester rapamycin derivatives, e.g., CCI-779; COX2 inhibitors, e.g., celecoxib and variants thereof; and phospholipase inhibitors, e.g., inhibitors of cytosolic- phospholipase 2 (cPLA2) (e.g., trifluoromethyl ketone analogs) Additional examples of therapeutic agents that can be combined with an EL-15 2 l/IL-21R antagonist include one or more of: 6-mercaptopurines (6-MP); azathioprine sulphasalazine; mesalazine; olsalazine chloroquinine/hy&roxychloroquine; pencillamine; aurothiomalate (intramuscular and oral); azathioprine; cochicine; beta-2 adrenoreceptor agonists (salbutamol, terbutaline, salmeteral); xanthines (theophj'Iline, aminophylline); cromoglycate; nedocromil; ketotifen; ipratropium and oxitropium; mycophenolate 20 mofetil; adenosine agonists; antithrombotic agents; complement inhibitors; and adrenergic agents. The use of the IL-21-/EL21R binding agents disclosed herein in combination with other therapeutic agents to treat or prevent specific immune disorders is discussed in further detail below. 25 Non-limiting examples of agents for treating or preventing arthritic disorders (e.g., rheumatoid arthritis, inflammatory arthritis, rheumatoid arthritis, juvenile rheumatoid arthritis, osteoarthritis and psoriatic arthritis), with which an IL-21-/IL21R binding agent can be combined include one or more of the following: IL-12 antagonists as described herein, NSAIDs; CSAIDs; TNF's, e.g., TNFa, antagonists as described 30 herein; non-depleting anti-CD4 antibodies as described herein; IL-2 antagonists as described herein; anti-inflammatory cytokines, e.g., IL-4, IL-10, IL- 13 and TGFa, or agonists thereof; JL-1 or IL-1 receptor antagonists as described herein); WO 03/028630 m PCT/US02/29839 phosphodiesterase inhibitors as described herein; COX-2 inhibitors as described herein; Hoprost (see e.g., Arthritis & Rheumatism (1996) Vol 39, Ho. 9 (supplement), S82); methotrexate; thalidomide (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S282) and thalidomide-related drugs (e.g., Celgen); leflunomide; inhibitor 5 of plasminogen activation, e.g., tranexamic acid; see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S2S4); cytokine inhibitor, e.g., T-614; see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S282); prostaglandin El (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S282); azathioprine (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S2S1); an inhibitor of 10 interleukin-1 converting enzyme (ICE); zap-70 and/or lck inhibitor (inhibitor of the tyrosine kinase zap-70 or lck); an inhibitor of vascular endothelial cell growth factor or vascular endothelial cell growth factor receptor as described herein; an inhibitor of angiogenesis as described herein; corticosteroid anti-inflammatory drugs (e.g.s SB2O35S0); TNF-convertase inhibitors; interleukin-11 (see e.g., Arthritis & Rheumatism 15 (1996) Vol. 39, No. 9 (supplement), S296); interleukin-13 (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S308); interleukin-17 inhibitors (see e.g., Arthritis & Rheumatism (1996) Vol. 39, No. 9 (supplement), S120); gold; penicillamine; chloroquine; hydroxychloroquine; chlorambucil; cyclophosphamide; cyclosporine; total lymphoid irradiation; anfi-thymocyte globulin; CD5-toxins; oraily-20 administered peptides and collagen; lobenzarit disodium; Cytokine Regulating Agents (CRAs) HP228 and HP466 (Houghten Pharmaceuticals, Inc.); ICAM-1 antisense phosphorothioate oligodeoxynucleotides (ISIS 2302; Isis Pharmaceuticals, Inc.); soluble complement receptor 1 (TP10; T Cell Sciences, Inc.); prednisone; orgotein; glycosaminoglycan polysulphate; minocycline; anti-IL2R antibodies; marine and 25 botanical lipids (fish and plant seed fatty acids; see e.g., DeLuca et al. (1995) Rheum. Dis. Clin. North Am. 21:759-777); auranofin; phenylbutazone; meclofenamic acid; flufenamic acid; intravenous immune globulin; zileuton; mycophenolic acid (RS-61443); tacrolimus (FK-506); sirolimus (rapamycin); amiprilose (therafectin); cladribine (2-chlorodeoxyadenosine); and azaribine. Preferred combinations include one or more IL-30 21 antagonists in combination with methotrexate or leflunomide, and in moderate or severe rheumatoid arthritis cases, cyclosporine. WO 03/(128630 PCT/US02/29839 61 Preferred examples of inhibitors to use ia combination with UL-21/IL-21R. to treat arthritic disorders include TNF antagonists (e.g., chimeric, humanized, human or in vitro generated antibodies, or antigen-binding fragments thereof, that bind to TNF; soluble fragments of a TNF receptor, e.g., p55 or p75 human TNF receptor or derivatives 5 thereof, e.g., 75 kdTNFR-IgG (75 kD TNF receptor-IgG fusion protein, Enbrel™-1, p55 kD TNF receptor-IgG fusion protein; TNF enzyme antagonists, e.g., TNFa converting enzyme (TACE) inhibitors); antagonists of IL-12, IL-15, IL-17, IL-18, IL-22; T cell and B cell depleting agents (e.g., anti-CD4 or anti-CD22 antibodies); small molecule inhibitors, e.g., methotrexate and leflunomide; sirolimus (rapamycin) and analogs 10 thereof; e.g., CCI-779; Cox-2 and cPLA2 inhibitors; NSAIDs; p38 inhibitors, TPL-2, Mk-2 and NFkb inhibitors; RAGE or soluble RAGE; P-selectin or PSGL-I inhibitors (e.g., small molecule inhibitors, antibodies thereto, e.g., antibodies to P-selectin); estrogen receptor beta (ERB) agonists or ERB-NFkb antagonists. Most preferred additional therapeutic agents that can be co-administered and/or co-formulated with one 15 or more IL-21/IL-21R antagonists include one or more of: a soluble fragment of a TNF receptor, e.g.. p55 or p75 human TNF receptor or derivatives thereof, e.g., 75 kdTNFR-IgG (75 kD TNF receptor-IgG fusion protein, EnbrelTM); methotrexate, leflunomide, or a sirolimus (rapamycin) or an analog thereof, e.g., CCI-779. Non-limiting examples of agents for treating or preventing multiple sclerosis with 20 which an IL-21-HL21R binding agent can be combined include the following: interferons, e.g., interferon-alphala (e.g., Avonex™; Biogen) and interferon-lb (Betaseron™; Chiron/Berlex); Copolymer 1 (Cop-1; Copaxone™; leva Pharmaceutical Industries, Inc.); hyperbaric oxygen; intravenous immunoglobulin; clabribine; TNF antagonists as described herein; corticosteroids; prednisolone; methylprednisolone; 25 azathioprine; cyclophosphamide; cyclosporine; methotrexate; 4-aminopyridine; and tizanidine. Additional antagonists that can be used in combination with IL-21 include antibodies to or antagonists of other human cytokines or growth factors, for example, TNF, LT, IL- 1, IL-2, IL-6, JL-7, IL-8, IL-12 IL-15, IL- 16, IL- IS, EMAP-11, GM- CSF, FGF, and PDGF. IL-21 antagonists as described herein can be combined with antibodies 30 to cell surface molecules such as CD2, CD3, CD4, CDS, CD25, CD28, CD30, CD40, CD45, CD69, CD SO, CD86, CD90 or their ligands. The IL-21 antagonists may also be combined with agents, such as methotrexate, cyclosporine, FK506, rapamycin, WO 03/028630 62 PCT/US02/29839 mycophenolate mofetil, leflunomide, NSAIDs, for example, ibuprofen, corticosteroids such as prednisolone, phosphodiesterase inhibitors, adenosine agonists, antithrombotic agents, complement inhibitors, adrenergic agents, agents which interfere with signaling by proinflammatory cytokines as described herein, IL- lb converting enzyme inhibitors 5 (e.g., Vx740), anti-P7s. PSGL, TACE inhibitors, T-cell signaling inhibitors such as kinase inhibitors, metal loproteinase inhibitors, sulfasalazine, azathioprine, 6-mercaptopurines. angiotensin converting enzyme inhibitors, soluble cytokine receptors and derivatives thereof, as described herein, and anti-inflammatory cytokines (e.g. IL-4, H- 10, IL-13 and TGF). 10 Preferred examples of therapeutic agents for multiple sclerosis with which the IL- 21 antagonists can be combined include interferon-b, for example, IFNb-la and IFNb-lb; Copaxone, corticosteroids, IL-1 inhibitors, TNF inhibitors, antibodies to CD40 ligand and CD80, IL-12 antagonists. Non-limiting examples of agents for treating or preventing inflammatory bowel 15 disease or Crohn's disease with which an IL-2 l/IL-21R antagonist can be combined include the following: budenoside; epidermal growth factor; corticosteroids; cyclosporin, sulfasalazine; aminosalicylates; 6-mereaptopurine; azathioprine; metronidazole; lipoxygenase inhibitors; mesalamine; olsalazine; balsalazide; antioxidants; thromboxane inhibitors; IL-1 receptor antagonists; anti-IL-1 monoclonal 20 antibodies; anti-IL-6 monoclonal antibodies; growth factors; elastase inhibitors; pyridinyl-imidazole compounds; TNF antagonists as described herein; IL-4, IL-10, IL-13 and/or TGFb cytokines or agonists thereof (e.g., agonist antibodies); interleukin-11; glucuronide- or dextran-conj ugated prodrugs of prednisolone, dexamethasone or budesonide; ICAM-1 antisense phosphorothioate oligodeoxynucleotides (ISIS 2302; Isis 25 Pharmaceuticals, Inc.); soluble complement receptor 1 (TP10; T Cell Sciences, Inc.); slow-release mesalazine; methotrexate; antagonists of Platelet Activating Factor (PAF); ciprofloxacin; and lignocaine. In one embodiment, an IL-21/IL21R antagonists can be used in combination with one or more antibodies directed at other targets involved in regulating lmmnns responses, 30 e.g., transplant rejection or graft-v-host disease. Non-limiting examples of agents for treating or preventing immune responses with which an IL-21/IL21R antagonist of the invention can be combined include the following; antibodies against cell surface WO 03/028630 63 PCT/US02/29839 molecules, including but not limited to CD25 (interleukin-2 receptor-a.), CDlla (LFA-1), CD54 (ICAM-1), CD4, CD45, CD28/CTLA4, CD80 (B7-1) and/or CD86 (B7-2). In yet another embodiment, an IL-21/IL21R antagonist is used in combination with one or more general immunosuppressive agents, such as cyclosporin A or FK506. 5 Another aspect of the present invention accordingly relates to kits for carrying out the combined administration of the IL-21/IL21R antagonists with other therapeutic compounds. In one embodiment, the kit comprises one or more binding agents formulated in a pharmaceutical carrier, and at least one agent, e.g., therapeutic agent, formulated as appropriate, in one or more separate pharmaceutical preparations. 10 Assays for Measuring the Activity of IL-21/IL21R Agonists as Immune Activators The activity of IL-21/IL21R agonists as activators of an immune system can, among other means, be measured by the following methods: Suitable assays for thymocyte or splenocyte cytotoxicity include, without limitation, those described in: Current Protocols in Immunology, Ed by J. E. Coligan, A. 15 M. Kruisbeek, D. H. Margulies, E. M. Shevach, W Strober, Pub. Greene Publishing Associates and Wiley-Interscience (Chapter 3, In Vitro assays for Mouse Lymphocyte Function 3.1-3.19; Chapter 7, Immunologic studies in Humans); Herrmann et al., Proc. Natl. Acad. Sci. U.S A. 78:2488-2492,1981; Herrmann et al., J. Immunol 128:1968-1974, 1982; Handa et al., J. Immunol. 135:1564-1572,1985; Takai et al., J. Immunol. 20 137:3494-3500,1986; Takai et al., J. Immunol. 140:508-512,1988; Herrmann et al., Proc. Natl. Acad. Sci. U.S.A. 78:2488-2492,1981; Herrmann et al., J. Immunol. 128:1968-1974, 1982; Handa et al., J. Immunol. 135:1564-1572, 1985; Takai et al., J. Immunol. 137:3494-3500,1986; Bowmanet al., J. Virology 61:1992-1998; Talcai et al., J. Immunol. 140:508-512,1988; Bertagnolli et al., Cellular Immunology 133:327-341, 25 1991; Brown et al., J. Immunol. 153:3079-3092,1994. Assays for T-cell-dependent immunoglobulin responses and isotype switching (which will identify, among others, proteins that modulate T-cell dependent antibody responses and that affect Thl/Th2 profiles) include, without limitation, those described in: Maliszewski, J. Immunol. 144:3028-3033,1990; and Assays for B cell function: In 30 vitro antibody production, Mond, J, J. and Brunswick, M. In Current Protocols in Immunology. J. E.e.a. Coligan eds. Vol 1 pp. 3.8.1-3.S.16, John Wiley and Sons, Toronto. 1994. WO (13/0286 30 64 PCT/US02/29S39 Mixed lymphocyte reaction (MLR) assays (which will identify, among others, proteins that generate predominantly Thl and CTL responses) include, without limitation, those described in: Current Protocols in Immunology, Ed by J. E. Coligan, A. M. Kruisbeelc, D. H. Margulies, E. M. Shevach, W Strober, Pub. Greene Publishing 5 Associates and Wiley-Interscience (Chapter 3, in Vitro assays for Mouse Lymphocyte Function 3.1-3.19; Chapter 7, Immunologic studies in Humans); Takai et al., J. Immunol. 137:3494-3500,1986; Takai et al., J. Immunol. 140:508-512,1988; Bertagnolli et al., J. Immunol. 149:3778-3783, 1992. Dendritic cell-dependent assays (which will identify, among others, proteins 10 expressed by dendritic cells that activate naive T-cells) include, without limitation, those described in: Guery et al., J. Immunol. 134:536-544,1995; Inaba et al., Journal of Experimental Medicine 173:549-559,1991; Macatonia et al., Journal of Immunology 154:5071-5079,1995; Porgador et al., Journal of Experimental Medicine 182:255-260, 1995; Nair et al., Journal of Virology 67:4062-4069,1993; Huang et al., Science 15 264:961-965, 1994; Macatonia et al., Journal of Experimental Medicine 169:1255-1264, 1989; Bhardwaj et al., Journal of Clinical Investigation 94:797-807, 1994; and Inaba et al., Journal of Experimental Medicine 172:631-640, 1990. Assays for lymphocyte survival/apoptosis (which will identify, among others, proteins that prevent apoptosis after superantigen induction and proteins that regulate 20 lymphocyte homeostasis) include, without limitation, those described in: Darzynkiewicz et al., Cytometry 13:795-808,1992; Gorczyca et al., Leukemia 7:659-670,1993; Gorczyca et al., Cancer Research 53:1945-1951,1993; Itoh et al., Cell 66:233-243,1991; Zacharchulc, Journal of Immunology 145:4037-4045,1990; Zamai et al., Cytometry 14:891-897,1993; Gorczyca et al., International Journal of Oncology 1:639-648, 1992. 25 Assays for proteins that influence early steps of T-cell commitment and development include, without limitation, those described in: Antica et al., Blood 84:111-117,1994; Fine et al., Cellular Immunology 155:111-122,1994; Galy et al., Blood 85:2770-2778,1995; Toki et al., Proc. Nat Acad Sci. U.S.A. 88:7548-7551,1991. Assays for Measuring the Activity of IL-21/IL21R Agonists or Antagonists as 30 Modulators of Cytokine Production and Cell Proliferation/Differentiation The activity of IL-21/IL21R agonists or antagonists as modulator of cytokine production and cell proliferation/differentiation can be tested using any one of a number WO 03/028630 65 PCT/US® 2/29839 of routine factor dependent cell proliferation assays for cell lines including, without limitation, 32D, DA2, DAlG, T10, B9, B9/11, BaF3, MC9/G, M+(preB M+), 2B8, RB5, DAI, 123, TI165, HT2, CTLL2, TF-1, Mo7e and CMK Assays for T-cell or thymocyte proliferation include without limitation those 5 described in; Current Protocols in Immunology, Ed by J. E. Coligan, A. M. Kruisbeek, D. H. Margulies, E. M. Shevach, W Strober, Pub. Greene Publishing Associates and Wiley-Interscience (Chapter 3, In Vitro assays for Mouse Lymphocyte Function 3.1-3.19; Chapter 7, immunologic studies in Humans); Takai et aL, J. Immunol. 137:3494-3500, 1986; Bertagnolli et al., J. Immunol. 145:1706-1712, 1990; Bertagnolli et al., Cellular 10 Immunology 133:327-341, 1991; Bertagnolli, et al, J. Immunol. 149:3778-3783, 1992; Bowman et al., J. Immunol. 152: 1756-1761, 1994. Assays for cytokine production and/or proliferation of spleen cells, lymph node cells or thymocytes include, without limitation, those described in: Polyclonal T cell stimulation, Kruisbeek, A. M. and Shevach, E. M. In Current Protocols in Immunology. J. E.e.a. 15 Coligan eds. Vol 1 pp. 3.12.1-3.12.14, John Wiley and Sons, Toronto. 1994; and Measurement of mouse and human Interferon .gamma., Schreiber, R.D. In Current Protocols in Immunology. J. E.e.a. Coligan eds. Vol 1 pp. 6.S.1-6.8.S, John Wiley and Sons, Toronto. 1994. Assays for proliferation and differentiation of hematopoietic and lymphopoietic 20 cells include, without limitation, those described in: Measurement of Human and Murine Ihterleukin 2 and Interleukin 4, Bottomly, K., Davis, L. S. and Lipsky, P. E. In Current Protocols in Immunology. J. E.e.a. Coligan eds. Vol 1 pp. 6.3.1-6.3.12, John Wiley and Sons, Toronto. 1991; deVries et al., J. Exp. Med. 173:1205-1211, 1991; Moreau et al., Nature 336:690-692,1988; Greenberger et al, Proc. Natl. Acad. Sci. U.S.A. 80:2931-25 2938.1983; Measurement of mouse and human interleukin 6-Nordan, R, In Current Protocols in Immunology. J. E.e.a. Coligan eds. Vol 1 pp. 6.6.1-6.6.5, John Wiley and Sons, Toronto. 1991; Smith et al., Proc. Natl. Acad. Sci. U.S.A 83:1857-1861, 1986; Measurement of human Interleukin 11 -Bennett, F., Giannotti, J., Clark, S. C. and Turner, K. J. Ia Current Protocols in Immunology. J. E.e.a. Coligan eds. Vol 1 pp. 6.15.1 30 John Wiley and Sons, Toronto. 1991; Measurement of mouse and human Interleukin 9— Ciarletta, A., Giannotti, J., Clark, S. C. and Turner, K. J. In Current Protocols in WO 03/1128630 PCT/US02/29839 66 Immunology. J. E.e.a. Coligan eds. Vol 1 pp. 6.13.1, John Wiley and Sons, Toronto. 1991. Assays for T-cell clone responses to antigens (which will identify, among others, proteins that affect APC-T cell interactions as well as direct T-cell effects by measuring 5 proliferation and cytokine production) include, without limitation, those described in: Current Protocols in Immunology, Ed by J. E. Coligan, A. M. Kruisbeek, D. H. Margulies, E. M. Shevach, W Strober, Pub. Greene Publishing Associates and Wiley-Interscience (Chapter 3, In Vitro assays for Mouse Lymphocyte Function; Chapter 6, Cytokines and their cellular receptors; Chapter 7, Immunologic studies in Humans); 10 Weinberger et al., Proc. Natl. Acad. Sci. U.S A. 77:6091-6095,1980; Weinberger et al., Eur. J. immun. 11:405-411,1981; Takai etal., J. Immunol. 137:3494-3500,19S6; Talcai et al., J. Immunol. 140:508-512, 1988. Assays for Measuring the Activity of IL-21/EL21R Agonists or Antagonists as Regulators of Hematopoiesis 15 IL-21/IL21R agonists or antagonists may be useful in regulation of hematopoiesis and, consequently, in the treatment of myeloid or lymphoid cell deficiencies. Even marginal biological activity in support of colony forming cells or of factor-dependent cell lines indicates involvement in regulating hematopoiesis, e.g. in supporting the growth and proliferation of erythroid progenitor cells alone or in combination with other 20 cytokines, thereby indicating utility, for example, in treating various anemias or for use in conjunction with irradiation/chemotherapy to stimulate the production of erythroid precursors and/or erythroid cells; in supporting the growth and proliferation of myeloid cells such as granulocytes and monocytes/macrophages (i.e., traditional CSF activity) useful, for example, in conjunction with chemotherapy to prevent or heat consequent 25 myelo-suppression; in supporting the growth and proliferation of megakaryocytes and consequently of platelets thereby allowing prevention or treatment of various platelet disorders such as thrombocytopenia, and generally for use in place of or complimentary to platelet transfusions; and/or in supporting the growth and proliferation of hematopoietic stem cells which are capable of maturing to any and all of the above-30 mentioned hematopoietic cells and therefore find therapeutic utility in various stem cell disorders (such as those usually treated with transplantation, including, without limitation, aplastic anemia and paroxysmal nocturnal hemoglobinuria), as well as in WO 03/028630 61 PCT/US02/29839 repopulating the stem cell compartment post irradiation/chemotherapy, either in-vivo or ex-vivo in conjunction with bone marrow transplantation or with peripheral progenitor cell transplantation (homologous or heterologous)) as normal cells or genetically manipulated for gene therapy. 5 The activity of the IL-21- or IL-21R binding agents may, among other means, be measured by the following methods: Suitable assays for proliferation and differentiation of various hematopoietic lines are cited above. Assays for embryonic stem cell differentiation (which will identify, among others, 10 proteins that influence embryonic differentiation hematopoiesis) include, without limitation, those described in: Johansson et al. Cellular Biology 15:143-151, 1995: Keller et al, Molecular and Cellular Biology 13:473-486,1993; McClanahan et al., Blood 81:2903-2915, 1993. Assays for stem cell survival and differentiation (which will identify, among 15 others, proteins that regulate lympho-hematopoiesis) include, without limitation, those described in: Msthylcellulose colony forming assays, Freshney, M.G. In Culture of Hematopoietic Cells. R. I. Freshney, et al. eds. Vol pp. 265-268, Wiley-Liss, Inc., New York, N.Y. 1994; Hirayama et al., Proc. Natl. Acad. Sci. U.S.A. 89:5907-5911,1992; Primitive hematopoietic colony forming cells with high proliferative potential, McNiece, 20 I. K. and Biiddell, R. A. In Culture of Hematopoietic Cells. R. I Freshney, et al. eds. Vol pp. 23-39, Wiley-Liss, Inc., New York, N.Y. 1994; Neben et al., Experimental Hematology 22:353-359,1994; Cobblestone area forming cell assay, Ploemacher, R. E. In Culture of Hematopoietic Cells. R. I. Freshney, et al. eds. Vol pp. 1-21, Wiley-Liss, Inc., New York, N.Y. 1994; Long teim bone marrow cultures in the presence of stromal 25 cells, Spooncer, E., Dexter, M. and Allen, T. In Culture of Hematopoietic Cells. R. I. Freshney, et al. eds. Vol pp. 163-179, Wiley-Liss, Inc., New York, N.Y. 1994; Long term culture initiating cell assay, Sutherland, H. J. In Culture of Hematopoietic Cells. R. I. Freshney, et al. eds. Vol pp. 139-162, Wiley-Liss, Inc., New York, N.Y. 1994. The invention will be further illustrated in the following non-limiting examples. 68 Example 1: Isolation and Characterization of Murine MU-1 cDNAs: A partial fragment of the murine homolog of the Mu-1 receptor was isolated by PCR using oligonucleotides derived from the human sequences. cDNA was prepared from RNA isolated from 17 day old murine thymus and from the murine 2D6 T cell line. A DNA fragment of approximately 300 nucleotides was amplified from the cDNA by PCR with the following oligonucleotides, corresponding to regions 584-603 and 876- 896, respectively, of the human cDNA sequence in FIG. 1 (corresponding to SEQ ID NO: 1): AGCATCAAG CCGGCTCCCCC (5p) (SEQ ID NO: 11) CTCCATTCAC TCCAGGTCCC (3p) (SEQ ID NO: 12) Amplification was carried out using Taq polymerase in IX Taq buffer containing 1.5 mM of magnesium chloride for 30 cycles at 94° C for one minute, 50° C for 1 minute, and 72° C for one minute. The DNA sequence of this fragment was determined, and two oligonucleotides were derived from an internal portion of this fragment with the following sequences: TTGAACGTGACTGRGGCCTT (5P) (SEQ ID NO: 13) TGAATGAAGTGCCTGGCTGA (3P) (SEQ ID NO: 14) The oligonucleotides were used to amplify an internal 262 nucleotide fragment of the original PCR product (corresponding to nucleotides 781-1043 of the murine cDNA sequence of Figure 1, and SEQ ID NO: 9) to use as a hybridization probe to screen a cDNA library isolated from the 2D6T T cell line. Filters were hybridized at 65° C using standard 5X SSC hybridization conditions and washed into SSC at 65° C. Twenty clones were isolated that hybridized to the probe in a screen of 426,000 clones. DNA sequence was determined from two independent clones. Full length sequence of clone #6 confirmed that it was the full-length murine homolog of human MU-1 (SEQ ID NO:9). The fiill-length nucleotide sequence of murine MU-1 is shown in Figure 1 (corresponding to SEQ ID NO:9). The nucleotide sequence has a predicted leader sequence at nucleotides 407-463, coding sequence at nucleotides 407-1993, and a termination codon at nucleotides 1994-1996. Nucleotides 1-406 correspond to the 5' untranslated region and nucleotides 1997-2628 correspond to the 3' untranslated region. intellectual property OFFICE ' -2 NOV 2009 RPHEI V tOl 69 The predicted protein sequence of murine MU-1 is shown in Figure 2 (corresponding to SEQ ID NO: 10). This murine MU-1 protein contains a predicted leader sequence determined by SPScan (score= 10.1) (corresponding to amino acids 1-19 of SEQ ID NO: 10), and a predicted transmembrane domain (corresponding to amino acids 237-253 of SEQ ID NO: 10). Predicted signaling motifs include the following regions: Box 1: amino acids 265-274 of SEQ ID NO: 10, Box 2: amino acids 311-324 of SEQ ID NO: 10, six tyrosine residues at positions 281,319, 361, 369, 397, and 510 of SEQ ID NO: 10. Potential STAT docking sites include: STAT5, EDDGYPA (SEQ ID N0:20), STAT3, YLQR. intellectual property OFFICE OF N.2 -2 NOV 2083 RECEIVED WO 03/028630 PCT/USU2/29839 70 Example 2: Comparison of Human and Marine MU-1: The GAP algorithm was used to compare the human and murine MU-1 amino acids. A comparison of the murine and human predicted protein sequences is shown in 5 figure 4. The amino acids were 65.267% identical using the GAP algorithm. The alignment was generated by BLOSUM62 amino acid substitution matrix (Henikoff S. and Henikoff, J. G. (1992)). Amino acid substitution matrices from protein blocks (Proc. Natl. Acad. Sci. USA 89: 10915-10919). Gap parameters= Gap Weight: 8, Average Malcb= 2.9 12, Length Weight= 2. Average Mismatch^ -2.003. Percent Similarity= 10 69.466. A comparison of the human andmurine cDNA nucleotide sequences is shown in figure 3. The DNA sequences are 66.116% identical when aligned using the GAP algorithm. Gap Parameters: Gap Weights 50. Average Match 10.000, Length Weight^ 3, Average Mismatch= 0.000. Percent Similarity^ 66.198. 15 Both human and mouse MU-1 proteins are members of the Type 1 cytokine receptor superfamily. Evaluation of the sequence of both murine and human MU-1 reveals the presence of potential Box-i and Box-2 signaling motifs. Six tyrosine residues are present in the cytoplasmic domain, and could also be important in signaling functions of MU-1. Comparison of the sequences of MU-1 with other members of the family 20 suggested the presence of potential docking sites for STAT 5 and STAT 3. Example 3: Determination of STAT signaling pathways used bv Human MU-1: BAF-3 cells were engineered to express a chimeric cytokine receptor consisting of the extracellular domain of the human EPO receptor and the intracellular domain of 25 the MU-1 receptor. BAF-3 cells that expressed huEPORJMU-l(cyto) chimeric receptors proliferated in response to human soluble EPO. These cfells were analyzed to determine which STAT molecules were phosphoiylated in response to EPO signaling. Briefly, control unmodified parental BAF-3 cells and EPOR/MU chimeric BAF-3 cells were rested from 3L-3 containing growth medium, and restimulated with either IL-3 or EPO 30 for 0,15, 30 and 60 minutes. The cells were pelleted and resuspended in ice cold lysis buffer containing oithovanadate, to preserve phosphoryiated tyrosines. Equal amounts of cell lysate were electrophoresed by SDS-PAGE and blotted onto nitrocellulose WO 03/02863(1 71 PCT/US02/29839 membranes for western analysis. Duplicate blots were stained for phosphorylated and nonphosphoraled forms of STAT 1, 3, 5, and 6 by using antibodies specific for each form of the STAT molecule. HELA cells, non-activated and activated with alpha-interferon were used as positive controls. 5 These results indicated that under these specific conditions, signaling through MU-1 results in the phosphorylation of STAT 5 at all time-points tested (1=0, T=15', T=30', 1=60'). Treatment of controls or the chimeric BAF-3 cells with IL-3 resulted in phosphorylation of STAT 3, but not STAT 1 or 5. 10 F vamnle 4: Tissue Expression of Murine and Human MU-1 Northern Analysis Northern blots of polyA+ RNA from various tissues (Clonetech, Palo Alto, CA) were performed as recommended by the manufacturer. For the murine blots, a 262 nucleotide fragment corresponding to nucleotides 781-1043 of Fig. 1 and SEQ ID NO:9 15 was used for hybridization. A single transcript of murine MU-1 was detected in adult murine spleen, lung, and heart tissues. The larger transcript observed in human tissues was not observed in mouse tissues. Two transcripts of human MU-1 were detected in adult human lymphoid tissues, 20 PBLs, thymus, spleen and lymph node, and in fetal lung. In Situ Hybridization In situ hybridization studies were performed by Phylogency Inc. of Columbus, OH (according to the method of Lyons et al., 1990, J. Cell. Biol: 111:2427-2436.) Briefly, serial 5-7 micron paraffin sections were deparaffinized, fixed, digested with 25 proteinase K, treated with tri-ethanolamine and dehydrated. cKNAs were prepared from linearized cDNA templates to generate antisense and sense probes. The cRNA transcripts were synthesized according to manufacturer's conditions (Ambion) and labeled with 35S-UTP. Sections were hybridized overnight, stringently washed and treated with RNAase A and dipped in nuclear track emulsion and exposed for 2-3 weeks. Control 30 sections were hybridized with sense probes to indicate the background level of the procedure. The murine probe consisted of a n 186bp fragment corresponding to WO 03/028630 72 PCTYUS02/29839 nucleotides 860-1064 (SEQ ID NO;9). The human probe was a 23 bp PCR product generated from human MU-1 DNA. Murine MU-1 expression was observed in the lymph nodes of the adult small intestine at germinal centers and muscular is external. Specialized lymph nodes and Peyers patches also exhibited murine MU-1 expression. Human MU-1 expression was detected at germinal centers of the lymph nodules in the cortex. The medulla, which contains macrophages, was negative for human MU-1. In human spleen, human MU-1 expression was detected in the regions of white pulp but not red pulp. Example 5: Expression of Human MU-1 in cells and cell lines: RNAse protection analysis was performed on resting and activated human T cells and the B cell lines, Raji and RPMI8866. and the I cell line Jurkat. Human T cells were activated with anti-CD 3 and anti-CD28. The cell lines were activated by Phorbol ester and ionomycin. MU-1 riboprobe-producing plasmid was constructed by inserting a 23 bp PCR product (PCR was performed by using 5' primer CACAAAGCTTCAGTATGAGCTGCAGTACAGGAACCGGGGA (SEQ ID NO: 15) and 3' primer CACAGGATCCCTTTAACTCCTCTGACTGGGTCTGAAAGAT (SEQ ID NO: 16)) into the BamH I and HindTIT sites of pGEM3zf(-) (Promega, Madison, Wl) vector. To make the riboprobe, the riboprobe-producing plasmid was linearized with HinriTTT The resulting DNA was phenol/chlorofonn extracted and precipitated with ethanol. T7 RNA polymerase was used to make the riboprobe according to the protocol suggested by the vendor (PharMingen, San Diego, CA). The RNAse protection assay was performed by using PharMingen's RiboQuant Multi-Probe Ribonuclease Protection Assay system. 2.0ug of total RNA were included in each RPA reaction, after RNAse digestion, the protected riboprobes were run on a QuickPoint rapid nucleic acid separation system (Novex, San Diego, CA). Gels were dried and exposed according to the suggestion of the vendor. Human MU-1 RNA is upregulated in anti-CD3 +anti-CD28 stimulated human purified CD3+ cells when compared with unstimulated populations. MU-1 is also upregulated upon restimulation in Thl and Th2-skewed T cell populations. The B cell WO 03/028630 73 PCT/U SO2/29839 lines, RPMI 8866 and Raji, constitutivBly express MU-1 while the Jurkat T cell line does not. Example 6: Binding of Hnman MU-1 to Known Cytokines 5 Both human and murine Ig fusion proteins were constructed and immobilized on Biacore chips in an effort to identify the ligand for MU-1. A variety of cell culture conditioned media as well as a panel of known cytokines were evaluated for binding to MU-1. Some cj'tokines were also tested in combination with other receptor chains in the family to consider the possibility that MU-1 may require a second receptor chain for 10 ligand binding. The following cytokines were tested and found to be negative for MU-1 binding: mIL-2, hIL-2, hIL-i5, mIL-7, TSLP, TSLP+IL7, TSLP+IL7R, TSLP+IL7g, TSLP+ IL-2, TSLP + 1L2 + IL2Rbeta, IL2Rbeta, lL2Rgamma, IL7R, lL2+2Rbeta, lL2+2Rgamma, IL15+IL2Rbeta, lL15+2Rgamma, lL7+2Rgamma, IL2+IL7R, IL1 5+IL7R, IL7-fTL7R. Known receptors have been immobilized as well and tested for 15 MUFc binding with negative results. IL-IS will bind to IL2Rb but not IL2Rg or MUFc. Example 7: Effect of Modalation of IL-21/IL-21R Pathway on the Severity of Symptoms in Collagen-Induced Arthritis fCIA) Mice This example shows that IL-21R antagonists, e.g., IL-21R-Ig fusion proteins 20 (murine IL21RFc protein or "mulL21RFc") or anti-IL21R antibodies, ameliorate symptoms in a collagen-induce arthritis (CIA) murine model. In contrast, administration of IL-21 exacerbates the arthritic symptoms in CIA mice. Male DBA/1 (Jackson Laboratories, Bar Harbor, Maine) mice were used for all experiments. Arthritis was induced with the use of bovine collagen type II (Chondrex, 25 Redmond, WA). Bovine collagen type H (Chondrex, Redmond, WA) was dissolved in 0.1 M acetic acid and emulsified in an equal volume of CFA (Sigma) containing lmg/ml Mycobacterium tuberculosis (strain H37RA). 100 pg of bovine collagen was injected subcutaneously in the base of the tail on day 0. On day 21, mice were inj ected subcutaneously, in the base of the tail, with a solution containing 100 ug of bovine 30 collagen in 0.1M acetic acid that had been mixed with an equal volume of Incomplete Freund's adjuvant (Sigma). Naive animals received the same sets of injections, minus collagen. The dosing protocol is shown schematically in Figure 16. MuIL21RFc was WO 03/028630 74 PCT/USO2/29839 administered prophylactically or therapeutically to DBA mice. In the therapeutic regimen, treatment was initiated if disease was observed for two consecutive days in a mouse. Mice were monitored at least three times a week for disease progression. 5 Individual limbs were assigned a clinical score based on the index: 0 = normal, no swelling; 1 = visible erythema accompanied by 1-2 swollen digit, or mild swelling in ankle; 2 = pronounced erythema, characterized by mild to moderate paw swelling and/or two swollen digits; 3 = extensive swelling of the entire paw, i.e., extending into ankle or wrist joint; 4 = resolution of swelling, ankylosis of the paw; difficulty in use of limb or 10 joint rigidity. Thus, the sum of all limb scores for any given mouse yielded a maximum total body score of 16. At various stages of disease, animals were euthanized, tissues were harvested and paws were fixed in 10% formalin for histology or 4% paraformaldeyde, pH 7.47, decalcified in 20% EDTA (pH 8.0) and embedded in paraffin for in situ hybridization. 15 Using light microscopy the paws were scored on a 5-grade scoring method (0-4) to characterize the intensity and extent of arthritis. Inflammatory infiltrates were used for scoring in addition to other changes related to the inflammation, such as pannus formation, fibrous of the synovial membrane, articular cartilage erosin and/or subchondral bone destruction. Hisotology grades were determined using readings of 20 individual paws: NAD=0 or nothing abnormal discovered; l=Slight to moderate; 2: Mild to moderate; 3: Marked and 4:Massive. A reduction in the severity of the symptoms was observed after prophylactic treatment of CIA mice using muIL2 lRFc (100 jag or 200 pig) administered intraperitoneally (ip) every other day starting one day before the collagen boost (data not 25 shown). The effects of muIL21RFc (200 jag/mouse 3x/week) on a semi-therapeutic CIA mouse as a function of day post treatment are shown in Figure 17. Mouse Ig (200 p.g/mouse 3x/week) was used as a control. A reduction in the severity score is shown starting from day 7 post treatment. 30 Administration of IL-21 exacerbates the arthritic symptoms in CIA mice. Figure 18 is a graph depicting the mean CIA score as a function of days post collagen boost. WO 03/<!28630 PCT/US02/29839 75 Mice administered with 1 mg of murine IL-21 intraperitoneally (ip) showed higher CIA scores that control PBS-treated mice. These experiments demonstrate that administration of an IL-21R antagonist, e.g., IL-21R-Fc fusion proteins, to CIA mice either prophylactically or semi-therapeutically 5 significantly ameliorated arthritic symptoms. In contrast, administration of IL-21 exacerbates the symptoms. Example 8: In situ hybridization of IL-21R transcripts The expression of IL-21R mRNA in arthritic paws of mice with CIA was 10 determined. Anti-sense murine IL-21R riboprobes were used (Figure 19, panel A); sense probes were used as negative controls (Figure 19, panel B). Digoxygenin labeled probes were prepared with the use of a DIG RNA labeling mix (Roche Diagnostics, Mannheim,Germany), as described by the manufacturer. Expression of IL-21 receptor mRNA was detected in macrophages, neutrophils, 15 fibroblasts, a subpopulation of lymphocytes, synoviocytes and epidermis (Figure 19, panel A). Decreased staining was seen in the control paws or with sense probes (Figure 19, panel B). mIL-21R mRNA positive cells were: neutrophils (NT), and macrophages (M). In sitit hybridization shows enhanced expression of IL-21R in the paws of arthritic mice. 20 Example 9: In vivo Activation of IL-21 Receptor Generates Potent Anti-Tnmor Responses This example shows that administration of IL-21-expressing tumor cells enhances anti-tumor responses in vivo in both immunogenic and non-immunogenic tumor models. 25 CD8+ T cells and NK cells are necessary for tumor destruction and subsequent development of tumor antigen specific T cells. IL-21 present at the tumor microenvironment potentiates both innate and adaptive immunity in vivo anti-tumor responses. 30 Experimental Procedures Mice. Female C57BL/6, Balb/C, IFNy"A and IL-IO^ mice in C57BL/6 background were purchased from Jackson Laboratories (Bar Harbor, ME.). C57BL/6 scid and nude mice WO 03/028630 76 PCT/US02/29839 were purchased from Taconic (Germantowri, NY). EL-21R"/" mice were generated at Wyeth Research, MA. and maintained at Charles Rivers Laboratories (Andover, MA) (Kasaian, M.T. et al. (2002) Immunity. 16:559-569). Mice were maintained and treated in accordance with National Institutes of Health and American Association of Laboratory 5 Animal Care regulations. Tumor cell lines and reagents. Two tumor cells lines, B16F1 melanoma and MethA fibrosarcoma, were used in the experiments described herein. B16F1 melanoma and MethA fibrosarcoma cells have been extensively used in tumor vaccination models to 10 study the in vivo anti-tumor effect of various cytokines. B16F1 tumor cells are poorly immunogenic, in that previous vaccination with irradiated wild-type tumor cells only protects 20% of vaccinated mice against subsequent live B16F1 challenge (Dranoff, G. et al. (1993) PNAS 90:3539-3543). In contrast, MethA, a methycholantheren induced fibrosarcoma, are highly immunogenic (i.e., vaccination with irradiated MethA cells 15 leads to almost 100% protection against subsequent live MethA challenge). B16F1 melanoma cells were maintained in culture in DMEM medium supplemented with 10% heat in-activated fetal bovine serum, 2% glutamine, and 1% penicillin-streptomycin. MethA fibrosarcoma cells were maintained by intraperitoneal passage in Balb/C mice. B16F1 melanoma specific TRP-2 (SVYDFFVWL, SEQ ID 20 NO: ) (van Elsas, A. et al. (2001) Journal of Experimental Medicine 194:481 -489; Sutmuller, R.P. et al. (2001) Journal of Experimental Medicine. 194:823-832) and control peptide OVA 2.57-254 (SIINFEKX, SEQ ED NO: ) were synthesized at the Wyeth Research, MA. Monoclonal Abs anti-CD3, anti-CD28 and rat IgG2a, and IL-2 cytokine used in this paper were all purchased from PharMingen (San Diego, CA). 25 Generation of IL-21 and. greeji fluorescent protein (GFP) expressing tumor cells. B16F1 and MethA tumor cells were engineered to express IL-21 and GFP, or only GFP. Retroviral vectors encoding mlL21 -IRES-GFP or 3RES-GEP were constructed using GFP-RV vector (Ranganath, S. et al. (1998) Journal of Immunology 161:3822-3826). 30 High titer retrovirus was obtained by transfecting 293-VSVg eootropic packaging cell line(Ory, D.S. et al. (1996) 93:11400-11406). Spin infections were performed at 1SOO rpm for 40 minutes at room temperature. Cells were infected 3 times. Tumor cells WO (13/028630 77 PCT/USO2/29839 expressing GFP were enriched by flow sorting and the purity of GFP expressing cells was greater than 90%. In vivo tumor studies. C57BL/6 mice were shaved on the back and injected i.d. with 105 5 B16F1-IL-21 or control B16F1-GFP. Balb/C mice were injected with either 106 or 2x10* MethA-IL-21 or control MethA-GFP cells. Tumor growth was monitored by measuring perpendicular diameters with a caliper. Mice were sacrificed when the tumors displayed severe ulceration or reached a size of200mm2. In general, 10 mice per group were used in each experiment and representative results are shown from experiments repeated two 10 or more times with similar results. In vivo depletion studies. CD4+ or CDS+ T cell depletion was accomplished by i.p.injectmg 400 Dg per mouse of either anti-CD4 (GK1.5), anti-CDB (53-6.7) mAbs or rat IgG isotype control for three consecutive days before tumor cell injection. Ab 15 injections were continued eveiy other day post tumor cell injection for 12 days. For NK cell depletion, 50 jxl of rabbit anti-mouse/rat asialo GM1 polyclonal ab (Cedarlane, Ontario, CA) was injected i.p. one day before tumor cell injection. Mice similarly injected with normal rabbit serum were used for control. After tumor cell inoculation, antibody injections were continued twice per week for two weeks. T- and NK cell-20 depletion was confirmed in lymph nodes and spleens one day before tumor challenge (for T cells) or on the same day of tumor cell challenge (for NK cells) by flow cytometry using relevant antibodies. FACS analysis showed that greater than 99% of the relevant population of T cells or NK cells were depleted in mice treated with anti-CD4, anti-CDS, aiiti asialo GM1. In contrast, mice treated with isotype controls displayed T lymphocyte 25 profiles similar to the profiles of untreated mice. IL-21 enzyme-linked immunosorbent assay (ELISA). Overnight supematants from 106 B16F1-IL-21, B16F1-GFP, MethA-IL-21 and MethA-GFP tumor cells were assayed for IL-21 levels by ELISA as detailed in Dunussi-Joarmopoulos, K et al. (1998) Blood 30 91:222-230. In brief, mMul-mutmIgG2a(WyethResearch(MA.) was used as coating antibody and anti-mouse EL-21 (R&D systems, Minneapolis, MN.) was used as capture WO 03/028630 78 PCT/US02/29839 Ab. Purified rnTL-21 (Wyeth Research, MA) (ECasaian, M.T. et al. (2002) supra) was used as control. IL-21R mRNA expression detected by Taqman. RNA was isolated from different tumor 5 cell lines according to the manufacturer's instructions (Promega, Madison, WI). mRNA extracted from splenocytes that had been activated with plate bound anti-CD3 (1 fig/ml) and anti-CD2S (1 }ig/ml) mAbs (BD PharMingen) for 24 hours was used for positive control. Purified RNA was treated with DNase (Ambion Inc, Austin, Tx) and adjusted to a concentration of 50 ng/jxl before mRNA analysis by quantitative TaqMan polymerase 10 chain reaction (PCR) analysis. IL-21R and cyclophyiin-specific primer pairs and probes were designed using PrimerExpress software and were prepared by Wyeth Research (primers: 5'-GCCTTCTCAGGACGCTATGAT-3' (SEQ ID N0:40) and 5'-CCCTACAGCACGTAGTTGGA-3' (SEQ ID NO:41) and probe TCCTGGGACTCAGCTTATGACGAACC) (SEQ ID NO:42). Standard curves for each 15 gene were generated with RNA from known IL-21R expressing cells. mRNA expression in control and transduced cell lines was normalized based on cyclophilia expression in each cell line and the results are presented as relative units (R.U.) of mRNA. Proliferation Assay. Splenocytes (2x105 cells/well) from either C57BL/6 or Balb/C 20 mice were stimulated with various concentrations of syngeneic irradiated tumor cells that expressed either GFP or IL-21 in 96-well plates. 3H thymidine at 1 p.Ci/well (PerkinElmer Life Sciences, Boston, MA) was added during the last 6 hours of culture. After harvesting the supernatant onto glass fiber filter mats, 3H-thymindine incorporation was determined by liquid scintillation counting. 25 Elispot Assay. TRP-2 specific T cell responses were determined by IFN-y Elispot kit (R&D systems) following manufacturers instructions. In brief, 2xl05 to 4x10s of splenocytes (from tumor injected mice) in 200 pi complete medium containing 5 |i.g/ml of specific TRP-2 peptides (van Elsas, A. (2001) J Exp. Med. 194:481-489) or non-30 specific OVA peptides and 20U/ml murine IL-2 (PharMmgen) were placed into each well. Hie plate was incubated for 24 hr at 37°C in a CO2 incubator. Plates were then incubated overnight at 4°C with detection Ab, followed by 2-hr incubation with WO 03/028630 79 PCT/US02/29839 Streptavi din-alkaline phosphatase conjugate. Spots were visualized with 5-bromo4 chloro-3' Indolylphosphaie p-Toluidixie Salt/Nitro Bluetetrazolium Chloride (BCIP/HBT) alkaline phosphotase substrate (R&D systems). Plates were washed with tap water and air-dried, and spots were counted with a stereomicroscope and re-5 calculated to per 106 cells with background spots subtracted. Generally, less than 10 spots/well were detected when OVA peptide was used as antigen. In vitro restimuLation of splenocytes from tumor cell-inoculated mice. Tumor peptide specific T cell lines were generated as described in Bloom, M.B. et al. (1997) J. Exp. 10 Med. 185:453-459. In brief, mice were inoculated with either B16F1-GFP orB16Fl-EL-21 cells. After 8-11 daj's, splenocytes were harvested and cultured with 5 ug/ml of TRP-2 peptide (van Elsas, A et al. (2001) supra), On the third day of culture, 20 U/ml of IL-2 (BD PharMingen) was added to each culture. After 5 days, cells were used for 51 Cr release assay. 15 CTL Assay. Cytotoxicity against targets was quantified using a 4-h 31 Cr release assay. Briefly, RMA-S cells were pulsed with TRP-2 peptide at 10 [xg/ml and labeled with Na251Cr04 (PerkihElmer Life Sciences) for 1 hr at 37°C. After washing,51 Cr labeled target cells were incubated with T cell lines generated from C57BL/6 mice injected with 20 tumor cells described earlier a.t different E:T ratios in 96-round bottom plates. After 4-hour incubation at 37°C, supemataats were collected and radioactivity was detected in a scintillation counter (Wallac, Turku, Finland). Percentage specific lysis was calculated as 100 x [(release by CTL-spontaneous release) / (maximal release-spontaneous release)]. Maximal release was determined by the addition of 1 % Triton X-100. Spontaneous 25 release in the absence of CTL was generally less than 15% of maximal release. IL-21 transduced B16F1 and MethA. cells secrete biolosicallv functional IL-21 B16F1 and MethA tumor cells were transduced to express GEP plus IL-21 (B16Fl/MethA-IL21) or GFP (Bl6Fl/MethA-GFP)?respectively. Overnight 30 supematants from 106 of B16F1-IL-21, B16F1-GFP, MethA-IL-21 or MethA-GFP tumor cells were assayed by ELISA as described in Experimental Protocols, above. As shown inFig. 20A, B16F1-IL-21 and MethA-IL-21 cells, but notB16F1-GFP or MethA-GFP WO 03/(528630 PCT/US02/29839 80 tumor ceils, secreted substantial amount of IL-21 in overnight cultures. To determine whether the IL-21 cytokine secreted by the transduced cells was biological functional, irradiated IL-21 or GFP expressing tumor cells were used to stimulate naive syngenic splenocytes from C56BL/6 or Balb/C mice in the presence of sub-optimal amount of anti-CD3 (500 ng/znl) and anti-CD28 (10 |xg/ml). As shown in Fig. 20B and 20C, B16F1-IL-21 and MethA-IL-21 cells enhanced nai've splenocyte proliferation when compared with control GFP expressing cells at all concentrations tested. These results suggest that EL-21 secreted by transduced tumor cells is biologically functional. IL-21 does not affect tumor cell growth in vitro The effect of IL-21 on the in \itro growth characteristics of transduced B16F1 and MethA cells was examined. B16F1-IL-21 and B16F1-GFP or MethA-IL-21 and MethA-GFP tumor cells were cultured at a concentration of 105/ 1.5ml culture media in 12-well plates. Cell numbers were monitored daily by trypan blue exclusion assay. The results are presented as means of duplicates. RNA from anti-CD3 and anti-CD28 mAb activated C57BL/6 splenocytes was used as positive control. Equal numbers of tumor cells were cultured in 12-well plates, and viable cell numbers were determined at various time points. As shown in Fig. 21A and 21B, the growth kinetics of IL-21 producing tumor cells was very similar to that of the GFP expressing control tumor cells in a period of 5 days. This indicates that IL-21 did not have any apparent effect on the in vitro growth characteristics of transduced tumor cells. The unresponsiveness of tumor cells to IL-21 was further confirmed with the lack of the IL-21R expression by tumor cells in quantitative Taqman PCR analysis. Figure 21C is a bar graph depicting quantitation of cyclophilin and IL-21R mRNA extracted from transduced tumor cells, determined by Taqman PCR. Expression of IL-21R mRNA in the transfected cells was normalized to cyclophilin values and expressed as relative unite (R.U.). RNA from anti-CD3 and anti-CD28 mAb activated C57BL/6 splenocytes was used as positive control. t IL-21 inhibits tumor growth in vivo To assess the in vivo effects of EL-21 on tumor growth, B16F1-IL-21 or MethA-IL-21 tumor cells were inoculated i.d. into the flank of syngenic mice. As shown in Fig. 22A, no tumor formation was detected in any of the C57BL/6 mice inoculated with WO 03/02X63(1 PCT/US02/29839 8J B16F1 -IL-21 tumor cells for more than 27 weeks post tumor injection. On the contrary, all C57BL/6 mice bearing B16F1-GEP cells grew tumors starting as early as day 9. Control tumors increased rapidly in size and these mice had to be sacrificed two to three weeks after tumor cell inoculation due to heavy tumor burden. In the MethA model, 5 small but palpable tumor masses were detected one week post tumor inoculation with either MethA-IL-21 or MethA-GFP cells in Balb/C mice (Fig. 22B). However, MethA-IL-21 tumors gradually reduced in size starting from week two (day 31) and eventually regressed completely in 100% of mice, whereas 80% of control MethA-GFP tumors continued to grow in size until the mice were sacrificed. These results show that the 10 presence of IL-21 at the tumor microenvironment triggers potent immune responses that lead to rejection of both immunogenic and non-immunogeuic tumors. IL-21 cannot prevent tumor growth in scid and nude mice In order to determine the relative roles of the cellular and humoral immune 15 responses in the rejection of IL-2I-transduced tumor cells, equal numbers (105) of B16F1-IL-21 or control B16F1-GEP cells were injected into T and B cell deficient (scid) mice. Both B16F1-IL-21 and B16F1-GFP cells showed similar growth kinetics in scid mice (Fig. 23 A), indicating that lymphocytes (B and/or T cells) are required for the IL-21 / mediated tumor rejection. The role of T cells was also confirmed in experiments with 20 C57BL/6 nude/nude mice. As shown in Fig. 23B, all nude mice inoculated with B16F1-IL-21 cells developed tumors, albeit with slower growth kinetics, Taken together, these results indicate that IL-21 mediated anti-tumor responses require the participation of the adaptive immunity. 25 CD8~ T, but not CD4+ T cells are required for IL-21 mediated tumor refection To further dissect which T cell subset(s) is (are) important for the IL-21 induced effect, in vivo depletion of lymphocyte subpopulations b}' administering anti-CD4 or anti-CD S mAbs was performed. As shown in Fig. 25A B16F1-TL-21 tumors did not grow in CD4+ T cell depleted mice and in control rat IgG treated mice. However, palpable 30 tumors grew out in seven out of ten CD8+ T cell depleted mice suggesting that CD8+ but not CD4+ T cells are necessaiy for the IL-21 induced anti-tumor response. Of interest, the growth of B16F1-EL-21 in CD8+ T cell depleted mice was significantly delayed WO 03/0286JO 82 PCT/US02/29839 suggesting that cells other than CD8+ T cells may be responsible for the suppression of early phase tumor growth. NK cells are required for the IL-21 induced anti-tumor response 5 Accumulated experimental evidence supports the role of NK cells as first line of defense in promoting anti-tumor immunity (Smyth, MJ. et al. (2001) International Immunology 13:459-463; Smyth, MJ. etal. (2002) Curr. Opin.Imm.unol. 14:165-171; Smyth, MJ. etal. (2002) Blood. 99:1259-1266). This possibility was examined by injecting equal numbers of B16F1-IL-21 tumor cells into NK. cell depleted mice or 10 control C57BL/6 mice. No detectable tumor formation was observed in control C57BL/6 mice, whereas, all oftheNK cell depleted mice grew out tumors two weeks post B16F1-EL-21 tumor cell inoculation. This result shows that NK cells, in addition to CD8+ T ceils, are necessary for IL-21 induced anti-tumor response. 15 IL-21 supports the generation ofIFNrsecretin? tumor antigen specific T cells and enhances tumor antigen specific CTL activity It has been recently demonstrated that a nonameric peptide consisting of residues 180-188 of normal melanocyte differentiation antigen tyrosinase-related protein 2 (TPR-2), is one of the tumor rejection antigens for the B16 melanoma that is recognized by B16 20 melanoma-reactive cytotoxic T lymphocytes (van Elsas, A. et al. (2001) supra; Sutmuller, R.P. (2001) J. Exp. Med. 194:823-832). TPR-2 peptide was used to evaluate the in vivo effect of IL-21 on T cell responses. Splenocytes from mice injected with either IL-21 or GFP expressing B16F1 cells were stimulated in vitro with TPR-2 peptide in an IFNy ELISPOT assay. As shown in Fig. 26A, the number of IFNy producing cells 25 inB16Fl-IL-21 injected mice was 3-fold higher than that of B16F1-GFP injected mice. To further characterize IL-21 mediated anti-tumor T cell responses, splenocytes from either IL-21 or GFP expressing tumor-injected mice were first stimulated in vitro with TRP-2 peptide as described herein and then used for in vitro CTL assays. B16F1 cell line used in the experiments described herein expresses low level of MHC class I 30 molecules, as determined with flow cytometry (van Elsas, A et al. (2001) supra; Sutmuller. R.P. (2001) supra.; Lim, Y.S. et al. (1998) Molecules & Cells 8:629-636). Therefore, RMA-S cells were used as antigen presenting cells in our CTL assays. As WO 03/028630 83 PCT/US02/29839 shown in Fig. 26B, splenocytes from B16FI-1L-21 injected mice had enhanced cytolytic activity towards TRP-2 peptide pulsed RMA-S cells compared to GFP expressing tumor (Fig. 26C) at all E;T ratios, despite some cross-reactivity observed towards OVA peptide. These results indicate that IL-21-mediated tumor rejection supports the development of 5 tumor antigen-specific cytolytic T cell responses. TRP-2 is one of the antigens that is shared between B16F1 tumor cells and normal malenocytes, thus CTLs detected here are actually autoreactive T cells. Indeed, 10-20% of C57BL/6 mice developed local hair and skin depigmentation at the site of B16F1-IL-21 tumor cell but not control cell injection (data not shown). 10 IL-21 induced anti-tumor response is independent oflFN-randIL-10 IFNy and IL-10 have been reported previously to be important for tumor rejection (Gerard, C.M. et al. (1996) Human Gene Therapy, 7:23-31; Lim, Y.S. et al (1998) Molecules & Cells 8:629-636). ELISOP results suggest that IL-21 enhanced tumor-specific cells producing IFNy but not IL-10. To test the involvement of IFNy and IL-10 15 in IL-21-mediated anti-tumor effect, equal numbers ofB16Fl-IL-21 orB16Fl-GFP tumor cells were injected into either IFNy"7' or IL-10"7" mice. As shown in Figs. 27A-27B, none of the aforementioned cytokine deficient mice formed tumors post BI6F1-IL-21 cell injection. However, B16F1-GFP control cells grew out tumors in all of the IFNy"7' and IL-10"''" mice. These data show that IL-21 mediated anti-tumor effect does not 20 require active participation of IFNy or IL-10. Cytokine gene-therapy was used to study the in vivo immunoregulatory potential of IL-21. This example shows that IL-21, when secreted at the tumor site by genetically modified B16F1 melanoma or MethA fibrosarcoma cells, fuels efficacious antitumor immune responses that require the presence of the cognate IL-21R (Fig. 23). CD8+ T 25 cells and NK cells are necessary for tumor destruction and subsequent development of tumor antigen specific T cells (Fig. 24A and 24B). Major Thl and Th2 cytokines, IFNy and IL-10 respectively, do not appear to be essential for the IL-21 mediated anti-tumor responses (Fig. 26A and 26B). The rapid and definitive elimination of IL-21-transduced B16 melanoma tumor 30 cells described herein is in contrast with data obtained in other cytokine gene vaccination models. Mice immunized with TL-4-, JL-5-, TL-6-, IL-12-, IFNy-, TNFa- or GM-CSF-transduced B16 vaccines displayed moderate delay m tumor formation, albeit eventually WO 03/(128630 84 PCT/US02/29S39 all mice succumbed to lethal tumors (Dranoff, G. et al. (1993) PNAS 90:3539-3543; Nagai, H. et al. (2000)J. Invest. Dermat. 115:1059-1064). Furthermore, GM-CSF, IL-5, IL-6, and TNF-a expressing cells caused significant side effects, ranging from hepatosplenomegaly, wasting and shivering, to death. To date, only IL-2 and IL-10 have 5 been reported in the literature to induce complete regression of transduced B16 tmnors in vivo (Dranoff G. et al. (1993) supra; Gerard, CM. (1996) Human Gene Therap)> 7:23-31). In the studies described herein, syngeneic mice injected with live B16F1 -IL-21 or MethA-IL-21 transduced tumor cells did not develop clinically overt tumor for a period of more than 27 weeks post tumor inoculation. Furthermore, flow cytometry analysis of 10 lymphoid cells from spleens and lymph nodes removed from immunized mice did not show any major changes in cell population (data not shown), suggesting that the paracrine secretion of IL-21 at the tumor microenvironment orchestrates efficacious antitumor responses without causing detectable systemic side effects. B16F1-3L-21 tumor grew out in IL-21R"/" mice but not in C57BL/6 (control) 15 mice. This strongly indicates that IL-21 and IL-21R interaction is critical for the IL-21-mediated effect despite of the apparent redundancy in IL-21R signaling pathway with other cytokine receptors (Parrish-Novak et al. (2000) supra; Ozaki et al. (2000) supra; Asao et al. (2001) supra). The outgrowth of B16F1-1L-21 tumors in IL-21R"/~ mice, however, should not be attributed to an intrinsic defect in T and NK cell development, as 20 IL-21 R"a mice have normal NK and T cells which respond to cytokines other than IL-21 (Kasaian, M.T. et al. (2002) supra). Innate and the adaptive immune system may participate in the immune responses against tumors. IL-21 can enhance both NK and T cell activation in vitro. The in vi\>o depletion experiment described herein showed that both NK cells and CDS+ T cells are 25 required for complete IL21 -B16F1 tumor rej ection. Involvement of NK cells in tumor surveillance is confirmed by the NK depletion experiment described herein (Fig. 24B). Given that B16F1-IL-21 cells express very low level of MHC class I molecules (data not shown), inoculation of live B16F1-IL-21 cells may generate an initial local inflammatory response. NEC cells can act as a first line of defense against tamor cells (Trinchieri, G. 30 (1994) J. Exp. Med. 180:417-421; Levitsky, HI et al. (1994) J. Exp. Med. 179:1215-1224; Wu, T.C. (1995) J. Exp. Med. 182:1415-1421). This early phase of tumor killing generates a plethora of tumor derived antigens, which in turn can be taken up by WO 03/028630 85 PCT/US02/29839 professional APCs and presented to MHC-restricted cytotoxic T cells. The contribution of NK cells to the early surveillance of B16F1 -IL-21 cells before adaptive immune responses being generated is farther reflected by the significantly delayed B16F1-IL-21 tumor growth in CDS4 T cell depleted mice (Fig. 24A). 5 Evidence of the involvement of T cells in IL-21 induced tumor regression is provided by the restoration of tumor growth in nude mice (Fig. 23B). Both CD4+ and CD8+ T cells have been described in various tumor cell-based vaccine strategies to be important for the induction of tumor regression and the development of protective immunity (Colombo, M.P., and G. Forni (1994) Immunology Today 15:48-51; Hock, H. 10 etal. (1993) PNAS 90:2774-2778; Hung, K. et al. (1998) J Exp. Med 188:2357-2368; Segal, B.M. et al. (2002) J. Immunol. 168:1-4). Studies have shown that CD4+ T helper cells are required for the activation of naive CD8+ T cells (Clarke, S.R. (2000) Journal of Leukocyte Biology. 67:607-614). In contrast, the findings described above demonstrate that CD8+ but not CD4+ T cells are required for the anti-tumor response of IL-21. The 15 findings disclosed herein appear to be consistent with recent studies that have demonstrated that eliminating CD4+ T cells may actually enhance the anti-tumor effect of cytokine gene therapy in vivo (Sutmuller, R.P. et al. (2001) Journal of Experimental Medicine. 194:823-832; Nagai, H. et al. (2000) Journal of Investigative Dermatology 115:1059-1064), IL-21 may also enhance the activation of naive CD8+ T cells by 20 lowering the threshold of co-stimulation necessary for T cell activation, and/or augmenting antigen presentation of the IL-21R bearing APCs (Schoenberger, S.P. et al. (1998) Natwe. 393:480-483; Bennett, S.R. et al. (1998) Nature 393:478-480). Mice injected with B16FI-IL-21 tumor cells developed hair and skin depigmentation around the injection sites. It is likely that autoimmunity against normal 25 mouse melanocyte was induced through a common epitope shared with B16 tumor cells in the close proximity of tumor injection sites. Using cytokine gene transduced B16 melanoma cells in conjunction with anti-CD4 depletion or CTLA-4 blockade, other investigators have also reported similar observation. However, the skin de-pigmentation is vitiligo-like, suggesting a more systemic involvement of the putative autoimmune cells 30 against melanocytes (Sutmuller, R.P. et al. (2001) Journal of Experimental Medicine. 194:823-832; Nagai, H. (2000) Journal of Investigative Dermatology. 115:1059-1064; van Elsas, A. et al (1999) Journal of Experimental Medicine. 190:355-366). TRP-2 is WO 03/028630 86 PCT/US02/29839 one of such shared epitopes between B16F1 tumor cells and normal melanocytes. As T cells with high af&nity to self-antigens are deleted in the thymus, TRP-2 specific T cells escaping thymic deletion must be of low avidity. Nevertheless, B16F1-3L-21 tumor injected mice have more than three fold of TRP-2 specific T cells than B16F1-GFP 5 (control) tumor injected mice, suggesting that IL-21 lowers the threshold for naive T cell activation in B16F1-IL-21 injected mice. The anti-tumor activity of IL-21 also correlates with enhanced CD8+ T cell functions, as demonstrated by both increased antigen specific IFNy production, and by augmented tumor specific CTL activities. Although IFNy and IL-10 have both been 10 described to play an essential role in tumor rejection, our experiments with IFNy and IL-10 deficient mice indicate that their presence is not required for IL-21 mediated tumor rejection. In summary, the results presented herein suggest that at least three mutually nonexclusive mechanisms underlie the IL-21-mediated anti-tumor response: (I) 15 paracrine secretion of IL-21 in the tumor microenvironment triggers and supports the initial innate tumor surveillance mediated by NK cells; (2) IL-21 activates APCs and facilitates uptake of tumor debris and subsequent tumor antigen presentation to nai've T cells, hence the adaptive immune response by CD 8+ T cells; (3) IL-21 lowers the threshold for nave T cell activation, thereby allowing the recruitment and activation of 20 low-affinity autoreactive T cells that escaped central tolerance. Example 10:IL-21 Enhances Antigen-Specific CDS- T Cetl Responses This Example shows that an analysis of IL-21 and IL-21R mRNA expression, and the effects of IL-21 on the responses of, murine CD8+ T cells. Naive CD8+ T cells 25 express IL-21R and expression is upregulated upon stimulation. CD8+ T cells only express detectable IL-21 mRNA when stimulated in the presence of exogenous EL-21. IL-21 specifically enhances proliferation of antigen- or anti-CD3 mAb-stimulated CDS+ T cells although it is not as potent as IL-2 at limiting levels of stimulation. However, compared to IL-2, the presence of IL-21 during in vitro priming of CD8+ T cells results 30 in the development of effector cells with increased ability to lyse target cells and produce IFNy. These findings support a role for IL-21 in the generation of CD8+- T cell responses. WO 03/028630 PCT/US02/29839 87 Experimental Protocols Reagents. Murine IL-21 was produced by transfection of COS cells and concentration of the supernatant; activity was referenced to rxnIL-21 (R&D Systems, Minneapolis, MN) 5 by bioassay. Equivalent volumes of concentrated mock transfectant supernatant were used as a control. 2L-21R.Fc was constructed linking the predicted extracellular domain of human IL-21R to murine IgG2a carboxy tail with mutations to minimize Fc binding and complement fixation. rHL-2 (R&D Systems, Minneapolis, MN), rmIL-12 (Wyeth, Cambridge, MA), rmTL-15 (R&D Systems), rmIL-21 (R&D Systems) were used as 10 indicated. Mice. 2C TCR Temice whose TCR is specific for the Ld allo-antigen were bred and maintained at Charles River Laboratories (Wilmington, MA). RPAs 15 T cell assays. T cells were purified from 2C TCR Tg lymph nodes using negative selection columns (R&D Systems) or sorted based on CDS and CD62L expression. Purified T cells (2x105/ml) were stimulated with plate-bound anti-CD3 mAb (2C11; Wyeth, Cambridge, MA) or irradiated Balb/c splenocytes (2000R; l-5x!06/ml) and 20 cytokines as indicated. Proliferation was determined by 3H-thymidine incorporation (1 uCi/well). For priming, cultures were set as above with the indicated cytokines for 4-6 days. Cells were harvested, washed, counted and used in 4hr CTL assays with 5x103 51 Cr-labeled P815 (specific) or EL4 (non-specific) targets at the effectontarget ratios noted or restimulated on anti-CD3 mAb coated plates (lug/ml) for 40hrs. 25 IL-21R and IL-21 expression by CD 8+ T cells. Previous reports have shown lymphoid-restricted expression of IL-21R and IL-21 expression by activated human CD4+ T cells. Using RNAse protection assays we have analyzed the expression of IL-21R and IL-21 mRNA by naive murine CD8+ T cells. CD8+CD62L+ 2C TCR+ cells were sorted and stimulated with anti-CD3 mAb in the presence of mock- or IL-21-30 transfected COS supernatant or anti-CD28 mAb and RNA was prepared for IL-21R or IL-21 RNAse protection assays (Figure 27A). WO <13/0 286 30 PCT/US02/29839 Freshly isolated CD8+ T cells expressed IL-21R mRNA implying that these cells are capable of responding to IL-21. Quantitation of signal intensity relative to an internal standard showed that TCR-mediated activation resulted in ~2-fold increase in 3L-21R mRNA levels (Figure 27A). TCR-activation with CD28 costimuiation resulted in ~4-5 fold increase of IL-21R mRNA suggesting that physiologic, 2-signal activation of CD8+ T cells would result in up-regulation of IL-21R expression and increased sensitivity to IL-21, Interestingly, the presence of IL-21 during stimulation also induced a ~4-fold increase in IL-21R expression, providing evidence for a mechanism for IL-21 to amplify IL-21 -responsiveness during CD8+ T cell activation. The expression of IL-21R by naive 10 CD8+ T cells distinguishes it from receptors of other cytokines which also act on CD 8+ T cells such as those for IL-2, IL-12 or IL-15 which require activation for expression. Nearly identical results were observed in non-transgenic CD8+ T cells (data not shown). IL-21 mRNA expression was analyzed from the same purified murine CD8+ T cells. Naive, anti-CD3, or anti-CD3/anti-CD28 mAb-activated murine CD8+ T cells 15 were found not express significant IL-21 mRNA (Figure 28B). This is in agreement with results using human CD 8+ T cells and contrasts with observations in CD4+ T cells where activation has been shown to up-regulate IL-21 mRNA expression. Interestingly, stimulation with anti-CD3 mAb and exogenous IL-21 resulted in strong upregulation of IL-21 mRNA expression (2-fold after 36 hours and 8-fold after 60 hours of stimulation) 20 showing that CD8+ T cells are capable of producing this cytokine. Thus, CD8+ T ceils express IL-21R mRNA, and in the presence of exogenous IL-21 up-regulate further IL-21R expression as well as de novo IL-21 expression. Activated CD4+ T cells are the likely source of the initial IL-21 driving these events. In this way, IL-21 is similar to IL-2 which is also produced predominantly by CD4+ T cells and 25 utilized by CDS+ T cells. Our results suggest a mechanism exists for maintaining IL-21 responsiveness during CD8+ T cell activation independent of CD4+ T cell-derived IL-21. IL-21 enhances proliferation of CD8+ T cells. IL-21 has been shown to augment the proliferation of human B cells stimulated with anti-CD40 and human and murine T cells stimulated with immobihzed anti-CD3 30 roAb [1,2]. Here, we analyzed the effect of IL-21 on antigen-stimulation of purified CD8+ murine T cells and found that proliferation of 2C CD8+ T cells was enhanced by WO 03/028630 89 PCT/US02/29839 IL-21 in a dose-dependent maimer (Figure 29A). IL-21 exhibited similar potency to IL-15, but was not as potent as IL-2 or IL-12 (Figure 29B). Because IL-21 can affect B cell function [1], the next experiment assesses whether IL-21 was augmenting 2C CD 8+ T cell proliferation by acting directly on T cells 5 or indirectly via effects on the APCs in this system. Purified 2C CD8+ T cells were stimulated with immobilized anti-CD3 mAb in the presence of increasing amounts of IL-21 (Figure 28C). As with antigen responses, IL-21 enhanced CD8+ T cell proliferation to anti-CD3 stimulation in a dose-dependent manner. While this does not rale out a possible effect of IL-21 on APCs, it does support that this cytokine can act directly on T 10 cells to modulate their function. Comparison of cytokine effects using anti-CD3 stimulation of CD8+ T cells revealed that IL-21 and IL-15 induce similar levels of proliferation, however IL-2 and IL-12 are more potent than IL-21 at inducing proliferation (Figure 28D). Because the IL-21 used in the majority of these studies was supernatant 15 concentrated from COS transfectants, an IL-21R.Fc fusion protein was used to specifically neutralize IL-21 responses. ELlSAs were done to show that mIL-21R.Fc bound to mIL-21, and that it was capable of neutralizing binding of EL-21 to its receptor (data not shown). 2C CD 8+ T cells were stimulated with immobilized anti-CD3 mAb and increasing amounts of IL-21 in the presence or absence of IL-21R.Fc (Figure 28C). 20 IL-21-induced responsiveness was inhibited by the addition of soluble IL-21R.Fc showing that the enhanced proliferation observed in the presence of IL-21 -transfectant supernatant was specifically due to IL-21. IL-21R.Fc had no effect on IL-2 or IL-15-mediated proliferation (data not shown). IL-21 specifically enhanced antigen-induced proliferation of murine CD8+ T 25 cells, on average resulting in 3-fold and 6-fold increased proliferation with antigen or anti-CD3 stimulation, respectively (n=5). This may be the result of comparatively lower levels of IL-21R expression, competition for gammac in the case of IL-2 and IL-15, or the biological effect of this cytokine. The data shown here extends our previous results showing IL-21 enhanced proliferation of allo-antigen stimulation of unseparated T cells 30 and underscores the potential importance of IL-21 in physiologic responses mediated by CD8+ T cells. In contrast to its ability to potentiate CD8+ T cell proliferation, IL-21 does not support the growth of murine NK cells and inhibits IL-15-mediated NK cell WO 03/028630 90 PCT/US02/29839 growth. These results suggest that IL-21 may activate distinct signaling programs in different cell types. In agreement with results using unseparated T cells, it was found that IL-21 was most effective at augmenting the proliferation of purified CDS+ T cells at suboptimal levels of anti-CD3 or antigen stimulation (data not shown). This suggests 5 that IL-21 serves as an accessory signal enhancing the sensitivity of cells responding to limiting antigen. Like IL-2, IL-21 is made by activated CD4+ T cells and acts on CD 8+ T cells to enhance their proliferation and may contribute to the T-helper activity attributed to CD4+ T cells. Thus, although IL-21 does enhance CD 8+ T cell proliferation it is not as potent as T-cell-derived IL-2 or macrophage-derived IL-12 suggesting non-10 redundant roles for these cytokines. IL-21 enhances lytic activity of CD8+ effector T cells. Having demonstrated that IL-21 enhances CD8+ T cell proliferation, we next examined the effects of IL-21 on CD8+ T cell differentiation. 2C TCR Tg CD8+ T cells were primed in vitro in the presence of the indicated cytokine(s) then harvested and equal 15 numbers of cells were assayed for CTL activity (Figure 29 A). The presence of IL-21 during priming resulted in the generation of CD 8+ effector T cells with higher lytic activity on a per cell basis than cells primed in the absence of IL-21. This increased lytic activity was even more pronounced when IL-2 was also present during priming (Figure 29B). None of these priming conditions resulted in the ability to kill non-specific target 20 cells (data not shown). Thus, IL-21 potently enhances the development of antigen-specific CD8+ T cell effector function. Other cytokines such as IL-12 and IL-15 have also been shown to enhance CTL differentiation. IL-21 was compared to these cytokines and was comparable in its ability to induce potent CTLs (Figure 29B). Previously, we have shown that IL-21 can augment IL-15-induced development 25 of allo-antigen specific CTL and IL-15-induced NK lytic activity. The data presented here, using defined antigen-specific priming and target cells, extends this result by showing that IL-21 alone or in combination with IL-2 can enhance CTL development from naive CD8+ T cells. Several mechanisms could account for this including increased sensitivity to antigen levels, increased expression of adhesion molecules or 30 increased expression of granule enzymes. Studies are underway to examine these possibilities, preliminary data suggests that EL-21 induced higher granzyme A mRNA expression. Importantly, although IL-2 was much more potent than IL-21 in stimulating WO 03/028630 91 PCT/US02/29839 CD8+ T cell proliferation, priming in the presence of IL-21 generated significantly more lytic activity. Despite the fact they share homology, a receptor chain and are both made by CD4+ T cells, the findings presented here underscore fee unique roles of IL-2 and IL-21 and suggest an important role for IL-21 in the generation of CD8+ T cell responses. 5 TT.-7.1 C.D8+ T cellIFNgamma for IFNg) vroduction. Iq addition to CTL activity, differentiated CD8+ effector T ceils secrete high levels of IFNO when restimulated with antigen. Therefore, we analyzed whether IL-21 present during priming modulated the ability of CD8+ T cells to produce IFNg and compared this to other cytokines known to affect CD8+ T cell responses. 2C TCR Tg T 10 cells were primed with antigen/APCs, IL-2 and the indicated cytokine for 5 days then equal numbers of cells were restimulated with anti-CD3 mAb (Figure 29C). IL-21 treatment during CDS+ T cell priming resulted in the generation of cells producing higher titers of IFNg than cells primed in die absence of IL-21 (13-fold increase). Using cytokine doses that generated equivalent CTL activity, CD8+ T cells primed in the 15 presence of IL-12 or IL-21 produced similar titers of IFNg IL-15 was most effective at inducing IFNg producing CD8+ T cells. As both IL-15 and IL-21 similarly enhanced the development of CDS+ T cell lytic activity (Figure 29B), this differential ability to induce IFNgamma production suggests non-redundant roles for these related cytokines. These results are particularly interesting as IL-21 has recently been shown to antagonize IL-12-20 induced IFNgamma production by CD4+ T cells. Thus, IL-21 plays opposing roles in the differentiation of CD4+ and CD8+ T cells into IFNg-producing cells. This is consistent with the ability of CD8+ T cells to produce IFNg in an IL-12/Stat4 independent manner. In conclusion, exposure to IL-21 results in increased ability to secrete IFNg consistent with, its role as differentiation factor for CD8+ T cells. 25 The experiments described herein show that IL-21 is a potent growth and differentiation factor for CD8+ T cells responding to antigen. IL-21R-deficient animals have functional CD8+ T cells. This finding, coupled with the data presented herein, implies that IL-21 responses are not required for CD8+ T cell development/maintenance but rather that IL-21 augments the generation of effector function. Like EL-2, IL-21 is 30 made by activated CD4+ T cells and our results comparing the actions of these two cytokines suggest that although IL-2 potently drives the proliferation of CD8+ T cells, IL-21 is much more effective at promoting CDS+ T effector differentiation. Recen%, WO <13/028630 92 PCT/US02/29839 IL-21 has been shown to be produced primarily by Th2 cells, suggesting a mechanism for the development IFNg-producing CTLs during Th2 responses. IL-15 is similar to IL-21 in its ability to induce nave cell proliferation and CTL development but is much more effective at eliciting IENg production. Like IL-2, IL-12 also induces strong CD8+ T cell 5 proliferation and like IL-21 it induces potent CTL activity and IFNg production. Thus IL-2, IL-12, IL-15 and IL-21 are effective at enhancing different aspects of nai've CD8+ T cell responses. In addition, these cytokines are made by different cell types: IL-2 and IL-21 are secreted by activated CD4+ T cells while IL-12 is made by activated macrophages and IL-15 is produced by stromal cells, endothelial cells as well as macrophages. Taken 10 together, this suggests that IL-2, IL-12, IL-15 and IL-21 act at distinct phases and sites of immune responses are not redundant. We have previously proposed that IL-21 may be a mediator of the transition between innate and adaptive immune responses, the data presented here showing enhancement of CDS+ T cell responses support this hypothesis. Given its potent effects on CD8+ T cells, it will be interesting to analyze the role of IL-15 21 in CD8+ responses to tumors and viral infections in vivo. f,vample ll:Primary Macrophages Express IL-21R and Respond to IL-21 by Proliferating and Secreting Increased Levels of Cytokines and Chemokioes This Example describes the finding that IL-21 acts as a proliferation factor for 20 hematopoietic cells specifically promoting the growth of macrophages and bone marrow progenitor cells. The effect of IL-21 alone and in combination with other factors in modulating hematopoeitic cell growth was examined. It was found that IL-21 acts as a proliferation factor for mouse and human hematopoietic cells specifically promoting the growth of 25 macrophage colonies in methylcellulose from lineage negative murine bone marrow progenitors. IL-21 also acts to enhance proliferation of human CD34+ cells and results in increased expression of the macrophage specific marker CD 14. Utilizing CD14+ cells sorted from human bone marrow, it has been shown by RNAse Protection Analysis (RPA) that the IL-21R is expressed on macrophages, and is upregulated by TNF and IL-1 30 following growth in GMCSF. Thus, suggesting a role of other inflammatory cytokines in regulating IL-21 responsiveness. Expression of IL-21R protein on mouse and human macrophages has been detected using FACS analysis. IL-21 acts directly on these cells WO 03/(12863(1 93 PCT/USO2/29839 resulting in activation, growth and increased secretion of chemokines and cytokines. Taken together, these results show that the EL-2 l/IL-21R complex is important in regulating macrophage growth and function, and in influencing macrophage responses at inflammatory sites. The contents of all references, pending patent applications and published patents, cited throughout this application are hereby expressly incorporated by reference. Equivalents Those skilled in Hie art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents of fee specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims. 94 </div>

Claims

<div class="application article clearfix printTableText" id="claims"> What is claimed is:

1. Use of a therapeutically effective amount of an IL-2 l/IL-21R agonist for the manufacture of a medicament for treating, preventing or ameliorating a cancer.

2. The use of claim 1, wherein the use of an IL-21/IL-21R agonist increases immune cell activity.

3. The use of claim 2, wherein the immune cell is a CD8+ cell, and the activity is increased effector cell activity.

4. The use of claim 1, wherein the cancer is selected from the group consisting of a solid tumor, a soft tissue tumor, and a metastatic lesion.

5. The use of claim 1, wherein the medicament comprising the IL-21/IL-21R agonist is adapted for administration alone.

6. The use of claim 1, wherein the medicament comprising the IL-21/IL-21R agonist is adapted for administration in combination with an antigen from a cancer or tumor cell.

7. The use of any one of claims 1-6, wherein the medicament comprising the IL-21/IL-21R agonist is adapted for administration in combination with one or more cytokines chosen from IL-2, GM-CSF or IL-15.

8. The use of any one of claims 1-6, wherein the subject is a mammal.

9. The use of claim 8, wherein the subject is a human.

10. The use of any one of claims 1-9, wherein the IL-21/IL-21R agonist is selected from a group consisting of an IL-21 polypeptide, an active fragment of an IL-21 polypeptide, a fusion protein comprising an IL-21 polypeptide, an agonistic IL-21R antibody, an antigen-binding fragment of an agonistic IL-21R antibody, an agonistic small molecule and a peptide agonist. intellectual property OFFICF Op N.Z -2 NOV 2009 RECEIVED 95

11. The use of any one of claims 1-9, wherein the IL-21/IL-21R agonist is a human IL-21 polypeptide comprising the amino acid sequence shown as SEQ ID NO: 19, or a sequence at least 90% or more identical thereto.

12. The use of claim 1, substantially as herein described with reference to any one of the Examples and/or Figures thereof.

13. The use of any one of claims 1 to 11, substantially as herein described. -2 NOV 2009 received </div>