NZ754959B2

NZ754959B2 - Anti-activin a antibodies and uses thereof

Info

Publication number: NZ754959B2
Application number: NZ754959A
Authority: NZ
Inventors: Jesper Gromada; Esther Latres; Lori C Morton; Andrew J Murphy; George D Yancopoulos
Original assignee: Regeneron Pharmaceuticals Inc
Priority date: 2013-07-30
Filing date: 2014-07-30
Publication date: 2022-06-28

Abstract

The present invention provides antibodies that bind to Activin A and methods of using the same. According to certain embodiments of the invention, the antibodies are fully human antibodies that bind to Activin A with high affinity. The antibodies of the invention are useful for the treatment of diseases and disorders characterized by decreased muscle mass or strength, such as sarcopenia, cachexia, muscle injury, muscle wasting/atrophy, cancer, fibrosis, and weight loss. The antibodies of the invention are also useful in combination with GDF8 binding proteins for the treatment of diseases and disorders characterized by decreased muscle mass or strength. The antibodies of the invention are also useful for the prevention, treatment, or amelioration of disorders and diseases caused by, promoted by, exacerbated by, and/or aggravated by Activin A, such as renal fibrosis. seases and disorders characterized by decreased muscle mass or strength, such as sarcopenia, cachexia, muscle injury, muscle wasting/atrophy, cancer, fibrosis, and weight loss. The antibodies of the invention are also useful in combination with GDF8 binding proteins for the treatment of diseases and disorders characterized by decreased muscle mass or strength. The antibodies of the invention are also useful for the prevention, treatment, or amelioration of disorders and diseases caused by, promoted by, exacerbated by, and/or aggravated by Activin A, such as renal fibrosis.

Description

ANTI-ACTIVIN A ANTIBODIES AND USES THEREOF This ation is a onal of New Zealand patent application 716854, which is the national phase entry in New Zealand of PCT international application (published FIELD OF THE INVENTION The present invention generally relates to antibodies, and antigen-binding fragments thereof, which are specific for Activin A, and s of use thereof, including methods of using antibodies specific for Activin A in conjunction with a tin inhibitor.

BACKGROUND Activins belong to the transforming growth factor-beta (TGF-β) superfamily and exert a broad range of biological effects on cell proliferation, differentiation, and apoptosis. Activins are homo- or heterodimers of InhibinβA, InhibinβB, nβC and InhibinβE, different combinations of which create the various members of the activin protein group. For example, Activin A is a homodimer of InhibinβA and Activin B is a homodimer of InhibinβB, whereas Activin AB is a heterodimer of InhibinβA and nβB and Activin AC is a heterodimer of InhibinβA and InhibinβC (Tsuchida, K. et al., Cell Commun Signal 7:15 (2009)).

Activin A binds to and activates or complexes on the surface of cells known as Activin Type II receptors (Type IIA and Type IIB, also known as ActRIIA and ActRIIB, respectively). The activation of these receptors leads to the phosphorylation of an Activin Type I or (e.g., Alk4 or 7), which in turn leads to the phosphorylation of SMAD 2 and 3 proteins, the formation of SMAD complexes (with SMAD4), and the translocation of the SMAD complex to the cell nucleus, where SMAD2 and SMAD3 function to regulate transcription of s genes (Sozzani, S. and Musso, T., Blood 117(19):5013-5015 (2011)).

Numerous other s bind to and activate ActRIIB, including GDF8 (myostatin), Activin B, n AB, Inhibin A, Inhibin B, GDF3, GDF11, Nodal, BMP2, BMP4, BMP7, BMP9, and BMP10. Blocking the interactions of ActRIIB with its s can lead to beneficial physiological effects. For example, GDF8 plays a central role in the pment and maintenance of skeletal muscle, acting as a negative regulator of muscle mass rron AC et al. (1997). Nature 387(6628):83-90). Administration of ActRIIB-Fc (i.e., the extracellular portion of the Type IIB receptor, ActRIIB, ized by fusion to an IgG Fc domain) leads to significant increases in skeletal muscle mass and improves muscle weight and measurements of muscle strength in mice (Lee SJ, et al. (2005) Proc Natl Acad Sci U S A 102(50):18117- 18122). The efficacy of ActRIIB-Fc is attenuated but not eliminated in Mstn (myostatin) null mice, demonstrating that other ActRIIB ligand(s) in addition to myostatin can function as negative regulators of muscle growth. Thus, a need exists for additional inhibitors of ActRIIB signaling that can provide clinical benefits. It is an object of the invention to go at least some way toward g this need; and/or to at least provide the public with a useful choice.

] In this ication where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a t for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

BRIEF SUMMARY OF THE INVENTION [0004B] In a first aspect, the invention provides an isolated antibody or antigen-binding fragment thereof that specifically binds Activin A with a binding dissociation equilibrium constant (KD) of less than about 5 pM as measured in a surface n resonance assay at 25ºC, wherein the antibody or antigen-binding fragment comprises three complementarity determining regions (CDRs) of a heavy chain le region (HCVR); and three CDRs of a light chain variable region (LCVR), wherein the HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3 domains se the amino acid ces of SEQ ID NOs: 687278-80, respectively. [0004C] In a second aspect, the invention provides a pharmaceutical composition sing the antibody or antigen-binding fragment according to the first aspect, and a pharmaceutically acceptable carrier or diluent. [0004D] In a third aspect, the invention relates to a method of increasing muscle mass or strength in a subject, sing stering the pharmaceutical composition according to the second aspect. [0004E] In a fourth aspect, the ion provides a pharmaceutical composition comprising the antibody or n-binding fragment ing to the first aspect, a GDF8 antagonist, and a pharmaceutically acceptable carrier or diluent. [0004F] In a fifth aspect, the invention relates to use of an anti-Activin A antibody or antigenbinding fragment thereof in the manufacture of a medicament for treating, preventing or ameliorating a disease or er characterized by decreased muscle mass or strength, wherein the anti-Activin A antibody or antigen-binding fragment thereof comprises three complementarity ining regions (CDRs) of a HCVR; and three CDRs of a LCVR, wherein the HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3 domains comprise the amino acid sequences of SEQ ID NOs: 687278-80, respectively. [0004G] In a sixth aspect, the invention s to use of an anti-Activin A antibody or antigenbinding fragment thereof and an anti-GDF8 antibody or antigen-binding fragment thereof in the manufacture of a medicament for treating, preventing or ameliorating a disease or disorder characterized by decreased muscle mass or strength, wherein the Activin A antibody or antigen-binding fragment thereof comprises three complementarity determining regions (CDRs) of a HCVR; and three CDRs of a LCVR, wherein the HCDR1-HCDR2-HCDR3-LCDR1-LCDR2- LCDR3 domains se the amino acid sequences of SEQ ID NOs: 687278-80, respectively. [0004H] In a seventh aspect, the ion relates to use of n-binding molecule that is a bispecific antibody comprising an Activin A-specific g domain and a GDF8-specific binding domain in the manufacture of a medicament for treating, preventing or ameliorating a disease or disorder characterized by decreased muscle mass or strength, wherein the Activin A-specific binding domain comprises: three complementarity determining regions (CDRs) of a HCVR; and three CDRs of a LCVR, wherein the HCDR2-HCDR3-LCDR1-LCDR2- LCDR3 s comprise the amino acid sequences of SEQ ID NOs: 687278-80, respectively.

BRIEF DESCRIPTION Described are antibodies that bind n βA and dimers containing inhibin βA, e.g., Activin A, Activin AB, etc.. The antibodies of the description are useful, inter alia, for inhibiting Activin ated signaling, ing beneficial clinical outcomes through the inhibition of Activin A-mediated signaling, e.g., for treating diseases and disorders caused by or related to Activin A activity and/or signaling. The antibodies of the description also have utility for use in conjunction with tors of other ligands of the ActRIIA and ActRIIB receptors, such as GDF8 inhibitors.

The antibodies of the description can be full-length (for e, an IgG1 or IgG4 antibody) or may comprise only an antigen-binding portion (for example, a Fab, F(ab’)2 or scFv fragment), and may be modified to affect functionality, e.g., to eliminate residual effector functions (Reddy et al., J Immunol 164:1925-1933 (2000)).

Described are isolated antibodies, or antigen-binding fragments thereof, that specifically bind Activin A with a g association equilibrium constant (Ka) of less than about 500 nM and a dissociation brium constant (KD) of less than about 5 pM as measured in a e plasmon resonance assay at 25ºC. In some embodiments of the description, the isolated antibodies, or antigen-binding fragments thereof, specifically bind Activin A with a KD of less than about 4 pM as ed in a e plasmon resonance assay at 25ºC. In some embodiments of the description, the isolated antibodies, or antigen-binding fragments thereof, specifically bind Activin A with a binding association equilibrium constant (Ka) of less than about 500 nM.

Described are isolated antibodies, or n-binding fragments thereof, that specifically bind Activin A and block binding of at least one Activin A receptor to Activin A. In some embodiments of the description, the isolated antibodies, or antigen-binding fragments thereof, block Activin A binding to an n A receptor with an IC50 value of less than about 80 pM as measured in an in vivo receptor/ligand binding ay at 25ºC. In some embodiments of the description, the isolated antibodies, or antigen-binding fragments thereof, block Activin A g to an Activin A receptor with an IC50 value of less than about 60 pM as measured in an in vivo receptor/ligand binding bioassay at 25ºC. Also described are, or antigen-binding fragments thereof, that specifically bind Activin A and block activation of at least one Activin A receptor by Activin A. In some embodiments of the description, the isolated antibodies, or antigen-binding fragments thereof, do not significantly block binding of n A to an Activin Type II receptor. In some embodiments of the description, the isolated antibodies, or antigenbinding fragments thereof, inhibit binding of Activin A to an Activin A or selected from the group consisting of Activin Type IIA receptor (ActRIIA), Activin Type IIB receptor (ActRIIB), and Activin Type I receptor. In some embodiments of the description, the isolated antibodies, or antigen-binding fragments thereof, inhibit Activin A-mediated activation of SMAD complex signaling. bed are antibodies, or antigen-binding fragments f comprising a heavy chain variable region (HCVR) having an amino acid sequence ed from the group consisting of SEQ ID NO: 2, 18, 34, 50, 66, 82, 98, 106, 114, 122, 130, 138, 154, 162, 170, 178, 186, 194, and 202, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

Also described is an antibody or antigen-binding fragment of an antibody comprising a light chain variable region (LCVR) having an amino acid sequence ed from the group consisting of SEQ ID NO: 10, 26, 42, 58, 74, 90, 146, and 210, or a substantially similar sequence f having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

Also described is an antibody or antigen-binding fragment f comprising a HCVR and LCVR (HCVR/LCVR) sequence pair selected from the group consisting of SEQ ID NO: 2/10, 18/26, 34/42, 50/58, 66/74, 82/90, 98/90, 106/90, 114/90, 122/90, 130/90, 138/146, 154/146, 162/146, 170/146, 6, 186/146, 194/146, and 202/210.

Also described is an dy or antigen-binding nt of an antibody comprising a heavy chain CDR3 (HCDR3) domain having an amino acid sequence selected from the group ting of SEQ ID NO: 8, 24, 40, 56, 72, 88, 104, 112, 120, 128, 136, 144, 160, 168, 176, 184, 192, 200, and 208, or a substantially similar ce thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; and a light chain CDR3 (LCDR3) domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 16, 32, 48, 64, 80, 96, 152, and 216, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

In certain embodiments, the antibody or antigen-binding portion of an antibody comprises a HCDR3/LCDR3 amino acid sequence pair ed from the group consisting of SEQ ID NO: 8/16, 24/32, 40/48, 56/64, 72/80, 88/96, 104/96, 112/96, 120/96, 128/96, 136/96, 144/152, 160/152, 168/152, 176/152, 184/152, 192/152, 200/152, and 208/216.

Also described is an antibody or fragment thereof further comprising a heavy chain CDR1 (HCDR1) domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 4, 20, 36, 52, 68, 84, 100, 108, 116, 124, 132, 140, 156, 164, 172, 180, 188, 196, and 204, or a substantially r sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% ce identity; a heavy chain CDR2 (HCDR2) domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 6, 22, 38, 54, 70, 86, 102, 110, 118, 126, 134, 142, 158, 166, 174, 182, 190, 198, and 206, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; a light chain CDR1 ) domain having an amino acid sequence selected from the group ting of SEQ ID NO: 12, 28, 44, 60, 76, 92, 148, and 212, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; and a light chain CDR2 (LCDR2) domain having an amino acid sequence ed from the group consisting of SEQ ID NO: 14, 30, 46, 62, 78, 94, 150, and 214, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity.

Certain non-limiting, ary antibodies and antigen-binding fragments of the description comprise HCDR1-HCDR2-HCDR3-LCDR1-LCDR2-LCDR3 domains, respectively, having the amino acid sequences selected from the group consisting of: SEQ ID NOs: 48 14-16 (e.g. H4H10423P); 202430-32 (e.g. H4H10424P); 364046-48 (e.g.

H4H10426P); 5662-64 (e.g. H4H10429P); 687278-80 (e.g. H4H10430P); 84- 869296 (e.g. H4H10432P2; 10010494-96 (e.g. 33P2); 108112- 9296 (e.g. H4H10436P2); 11612094-96 (e.g. H4H10437P2); 12412894- 96 (e.g. H4H10438P2); 13213694-96 (e.g. H4H10440P2); 140144150-152 (e.g. H4H10442P2); 156160150-152 (H4H10445P2); 164168150-152 (H4H10446P2); 172176150-152 (H4H10447P2); 180184150-152 (H4H10448P2); 188192150-152 (H4H10452P2); 196200150-152 468P2); and 204208214-216 (H2aM10965N).

In a related embodiment, the description includes an antibody or antigen-binding fragment of an antibody which ically binds Activin A, wherein the antibody or fragment comprises the heavy and light chain CDR domains contained within heavy and light chain variable region (HCVR/LCVR) sequences selected from the group ting of SEQ ID NO: 2/10, 18/26, 34/42, 50/58, 66/74, 82/90, 98/90, 106/90, 114/90, , 130/90, 138/146, 154/146, 162/146,170/146, 6, 186/146,194/146, and 202/210. Methods and techniques for identifying CDRs within HCVR and LCVR amino acid sequences are well known in the art and can be used to identify CDRs within the specified HCVR and/or LCVR amino acid sequences disclosed herein. ary conventions that can be used to identify the boundaries of CDRs include, e.g., the Kabat definition, the Chothia definition, and the AbM definition. In general terms, the Kabat tion is based on sequence variability, the Chothia definition is based on the location of the ural loop regions, and the AbM definition is a compromise between the Kabat and Chothia approaches. See, e.g., Kabat, "Sequences of Proteins of Immunological Interest," National Institutes of , Bethesda, Md. (1991); Al- Lazikani et al., J Mol Biol 7-948 (1997); and Martin et al., PNAS (USA) 86:9268-9272 . Public databases are also available for identifying CDR sequences within an antibody.

Also described are nucleic acid molecules encoding anti-Activin A antibodies or portions f. For example, described are nucleic acid molecules encoding any of the HCVR amino acid sequences listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide ce selected from any of the HCVR nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% ce identity thereto.

Described are nucleic acid molecules encoding any of the LCVR amino acid sequences listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide sequence selected from any of the LCVR nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity o.

Also described are nucleic acid molecules encoding any of the HCDR1 amino acid sequences listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide sequence selected from any of the HCDR1 nucleic acid sequences listed in Table 2, or a substantially r sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity o.

Also described are nucleic acid molecules encoding any of the HCDR2 amino acid sequences listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide sequence selected from any of the HCDR2 nucleic acid sequences listed in Table 2, or a substantially similar sequence f having at least 90%, at least 95%, at least 98% or at least 99% sequence identity thereto.

Also described are nucleic acid molecules encoding any of the HCDR3 amino acid sequences listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide sequence selected from any of the HCDR3 nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% ce identity thereto.

Also described are nucleic acid molecules encoding any of the LCDR1 amino acid sequences listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide ce ed from any of the LCDR1 nucleic acid sequences listed in Table 2, or a ntially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity thereto.

Also described are nucleic acid molecules encoding any of the LCDR2 amino acid sequences listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide sequence selected from any of the LCDR2 nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% ce identity thereto.

Also described are c acid molecules encoding any of the LCDR3 amino acid ces listed in Table 1; in certain embodiments the nucleic acid molecule comprises a polynucleotide sequence selected from any of the LCDR3 nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity thereto.

Also described are nucleic acid molecules encoding an HCVR, wherein the HCVR comprises a set of three CDRs (i.e., HCDR1-HCDR2-HCDR3), wherein the HCDR1-HCDR2- HCDR3 amino acid sequence set is as defined by any of the ary anti-Activin A antibodies listed in Table 1.

Also described are nucleic acid molecules encoding an LCVR, wherein the LCVR comprises a set of three CDRs (i.e., LCDR1-LCDR2-LCDR3), n the LCDR1-LCDR2- LCDR3 amino acid sequence set is as defined by any of the ary anti-Activin A antibodies listed in Table 1.

Also described are c acid molecules encoding both an HCVR and an LCVR, wherein the HCVR comprises an amino acid sequence of any of the HCVR amino acid sequences listed in Table 1, and wherein the LCVR comprises an amino acid sequence of any of the LCVR amino acid sequences listed in Table 1. In n embodiments, the nucleic acid molecule comprises a polynucleotide sequence selected from any of the HCVR c acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% ce identity thereto, and a polynucleotide sequence selected from any of the LCVR nucleic acid sequences listed in Table 2, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity thereto. In certain embodiments, the nucleic acid molecule encodes an HCVR and LCVR, wherein the HCVR and LCVR are both derived from the same ctivin A dy listed in Table 1.

Also described are recombinant expression s capable of expressing a polypeptide comprising a heavy or light chain variable region of an anti-Activin A antibody. For example, the description includes recombinant expression vectors comprising any of the c acid molecules mentioned above, i.e., nucleic acid les encoding any of the HCVR, LCVR, and/or CDR sequences as set forth in Table 1. Also included within the scope of the description are host cells into which such vectors have been introduced, as well as methods of producing the antibodies or portions thereof by culturing the host cells under conditions permitting production of the antibodies or antibody fragments, and recovering the antibodies and antibody fragments so produced.

The description es anti-Activin A dies having a modified carbohydrate content. In some applications, modification to remove undesirable ylation sites may be useful. In some applications, modification to alter glycosylation patterns may be useful, e.g., modifying an dy to lack a fucose moiety t on an oligosaccharide chain, for example, to increase antibody ent cellular cytotoxicity (ADCC) function (see Shield et al.

J Biol Chem 277:26733 (2002)). In other applications, cation of galactosylation can be made in order to modify complement dependent cytotoxicity (CDC). In some ations, antibodies may have modified glycosylation patterns in order to minimize effector function. For example, antibodies may be modified to obtain additionally ylated or sialylated antibodies.

In another ment, described is a pharmaceutical composition comprising a recombinant human antibody or fragment thereof which specifically binds Activin A and a pharmaceutically acceptable carrier. In a related embodiment, the description features a composition which is a combination of an anti-Activin A antibody and a second eutic agent. In one embodiment, the second therapeutic agent is any agent that is advantageously combined with an anti-Activin A antibody. Exemplary agents that may be advantageously combined with an anti-Activin A antibody include, without limitation, other agents that inhibit Activin A activity (including other antibodies or antigen-binding fragments thereof, peptide inhibitors, small molecule nists, etc.) and/or agents which do not directly bind Activin A but nonetheless interfere with, block or attenuate Activin A-mediated signaling. In one embodiment, the secondary therapeutic agent inhibits, interferes, blocks and/or attenuates the activity of another ligand of the ActRIIA and/or ActRIIB receptor (e.g., GDF8, Activin B, Activin AB, Inhibin A, Inhibin B, GDF3, GDF11, Nodal, BMP2, BMP4, and/or BMP7). In one ment, the secondary therapeutic agent is an anti-GDF8 nist (e.g., a human anti- GDF8 antibody or n-binding fragment thereof). Exemplary DF8 agents for use with the anti-Activin A antibodies of the description include a human anti-GDF8 antibody (e.g., an anti-GDF8 antibody comprising any of the HCVR/LCVR or CDR amino acid sequences as set forth in US 2011-0293630 A1 (e.g., H4H1657N2, which is an anti-GDF8 antibody with heavy chain complementarity determining regions (HCDRs) of a HCVR comprising SEQ ID NO:217 (e.g., the CDR1, CDR2, and CDR3 sequences set forth in SEQ ID , 219, and 220, respectively), and the light chain complementarity ining regions (LCDRs) of a LCVR comprising SEQ ID NO:221 (e.g., the CDR1, CDR2, and CDR3 sequences set forth in SEQ ID NO:222, 223, and 224)). Additional combination therapies and co-formulations involving the anti-Activin A antibodies of the description are disclosed elsewhere .

In an additional embodiment, described is an antigen-binding molecule comprising an Activin A-specific binding domain and a GDF8-specific binding domain. In one embodiment of this embodiment, the antigen-binding le is a bispecific antibody comprising a first variable domain that specifically binds Activin A and a second variable domain that specifically binds GDF8.

In yet another embodiment, described are eutic s for inhibiting n A activity using an anti-Activin A dy or antigen-binding portion of an antibody of the description, wherein the therapeutic methods comprise administering a therapeutically effective amount of a pharmaceutical composition comprising an dy or antigen-binding fragment of an antibody of the description. The disorder treated is any disease or condition which is improved, ameliorated, inhibited or prevented by removal, inhibition or reduction of Activin A activity or signaling. The anti-Activin A antibodies or antibody fragments of the ption may function to block the interaction between Activin A and an Activin Type II receptor (e.g., Activin Type IIA receptor and/or Activin Type IIB receptor); between Activin A and an Activin Type I receptor; between n A and both a Type II and a Type I receptor; or otherwise inhibit the signaling activity of Activin A.

The description also includes the use of an anti-Activin A antibody or antigen binding portion of an antibody of the description in the manufacture of a medicament for the treatment of a disease or disorder related to or caused by Activin A ty in a patient. Also described are methods for increasing muscle mass or strength in a subject by administering to the t an Activin A antibody or antigen-binding fragment thereof. Also described are methods for increasing muscle mass or strength in a subject by administering to the t an Activin A- specific binding protein and a GDF8-specific binding protein, or by administering to the subject an antigen-binding molecule comprising an Activin A-specific binding domain and a GDF8- specific binding domain.

The description also includes methods for treating, ting and/or ameliorating a disease or disorder characterized by decreased muscle mass or strength by administering to a t in need thereof an Activin A-specific binding protein (e.g., an anti-Activin A antibody). In a related embodiment, methods of the description include the treating, preventing and/or rating a e or disorder characterized by decreased muscle mass or th by administering to a subject in need thereof an Activin A-specific binding protein and a GDF8- specific g protein (e.g., an anti-Activin A antibody and an anti GDF8 antibody). Methods of the description also include treating, ting and/or ameliorating a disease or disorder characterized by decreased muscle mass or strength by administering to a subject in need thereof an antigen-binding le comprising an Activin A-specific binding domain and a GDF8-specific binding domain. Diseases or disorders characterized by decreased muscle mass or th that can be treated, prevented and/or ameliorated using methods of the description include sarcopenia, cachexia (e.g., idiopathic cachexia or cachexia secondary to another condition (e.g., cancer, chronic renal failure, or c obstructive pulmonary disease)), muscle injury, muscle wasting and/or atrophy (e.g., caused by or associated with disuse, lization, bed rest, injury, medical treatment, surgical ention (e.g., hip fracture, hip replacement, and knee replacement) and by necessity of mechanical ventilation), cancer, obesity, diabetes, arthritis, multiple sclerosis, muscular dystrophy, amyotrophic lateral sis, Parkinson's disease, osteoporosis, osteoarthritis, enia, and metabolic syndromes (e.g., one or more of diabetes, obesity, nutritional disorders, organ atrophy, chronic obstructive pulmonary disease, and anorexia).

The description also includes methods for treating, preventing and/or ameliorating diseases or disorders caused by, promoted by, exacerbated by, or aggravated by the activity of a molecule containing inhibin βA (e.g., dimers containing inhibin βA , e.g., n A, n AB, etc.) by administering to a subject in need thereof a binding protein specific for Activin A (i.e., inhibin βA dimer), e.g., an anti-Activin A antibody or antigen-binding fragment thereof. In one embodiment, methods of the description include methods of ng, ting, and/or ameliorating renal fibrosis by administering to a subject in need f an anti-Activin A antibody. In particular embodiments, methods of the description include methods of treating, preventing, and/or ameliorating renal fibrosis caused by chronic kidney disease (e.g., as a consequence of hypertension, diabetes, glomerulonephritis, inherited diseases (such as polycystic kidney disease), malformations of the kidney, autoimmune disease (e.g., lupus), or obstructions (e.g., kidney stones, tumors, enlarged prostate gland), or repeated urinary infections) by administering to a subject in need thereof an anti-Activin A antibody. Additional ments include methods of treating, preventing, and/or ameliorating sepsis, chronic heart failure, chronic obstructive pulmonary disease, benign or malignant pheochromocytoma, uterine ds/leiomyomata, preeclampsia, keloids, hypertrophic scars, or pulmonary artery hypertension by stering to a subject in need thereof an anti-Activin A antibody.

Additional embodiments include methods of treating, preventing, and/or ameliorating cachexia caused by, promoted by, exacerbated by,or aggravated by Activin A activity by administering to a subject in need thereof an anti-Activin A antibody. Additional embodiments include methods of treating, preventing, and/or ameliorating weight loss caused by, promoted by, exacerbated by,or aggravated by Activin A ty by administering to a subject in need thereof an anti- Activin A antibody.

Other ments will become apparent from a review of the ensuing detailed description.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a matrix showing the results of an dy cross-competition assay in which a first anti-Activin A antibody ("Antibody Sample") was applied to an anti-human FC- coated sensor tip, followed by emersion in a solution of a second ctivin A dy (1 µM) und to n A. Binding responses ical values 0.22 to 1.84) for each antibody combination tested are ed. Binding responses presented in white boxes with black type indicate no competition for g of Activin A, suggesting distinct binding regions.

Figure 2: Panel A shows the effects of 21 days of anti-GDF8 antibody treatment (H4H1657N2, 10mg/kg or 30 mg/kg) on average peak c force compared to isotype control antibody. Data analyzed using one- way analysis of variance (ANOVA) followed by Tukey’s test. *p<0.05 significance over isotype control (n=6, unpaired Student t test); n.s. = not tically significant compared to isotype 30mg/kg. Panel B shows the increase in tibialis anterior (TA) muscle peak tetanic force in H4H1657N2-treated mice (10mg/kg) versus mice d with isotype control antibodies for three weeks (n=6), when ated by electric current over a range of frequencies (40 to 100 Hz). Data are expressed as mean average peak force ± SEM.

Figure 3: Panel A shows the design of an experiment to evaluate the effects of H4H1657N2 during the recovery phase from hind limb suspension-induced muscle atrophy.

Panel B shows the percentage change in TA and Gastrocnemius (GA) muscle weights for H4H1657N2-treated and isotyple control antibody-treated mice post-recovery after 7 days of hind limb suspension (HLS+7Rec) versus mice without a ry period after 7 days of hind limb suspension (HLS) and control mice (non-HLS control). Values are expressed as the mean tage change over control non-HLS values ± SEM. Data analyzed using one- way analysis of variance (ANOVA) followed by Tukey’s test. * = p<0.05 significance over Non-HLS group. # = p<0.05 significance over HLS group.

Figure 4: Panel A shows the effects of the stration of the ctivin A antibody H4H10446P2 on body weight of mice overexpressing Activin A (versus isotype control). Data was analyzed using two-way analysis of variance (Repeated Measures ANOVA + Boneferroni Multiple Comparison Test) followed by Tukey’s test. *= p<0.05 vs Isotype l; #= p<0.05 vs n A + Isotype Control. Panel B shows the effects of ctivin A antibody H4H10446P2 on tibialis or (TA) and Gastrocnemius (GA) muscle weights in mice overexpressing Activin A (versus isotype control). Data analyzed using one- way analysis of variance (ANOVA) followed by Tukey’s test. *= p<0.05 over Vector + e Control; #= p<0.05 over Activin A + Isotype Control.

ED DESCRIPTION Before the present invention is described, it is to be understood that this invention is not limited to particular methods and experimental conditions bed, as such methods and conditions may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims. [0041A] Certain statements that appear herein are broader than what appears in the ents of the invention. These statements are provided in the interests of providing the reader with a better understanding of the invention and its practice. The reader is directed to the anying claim set which defines the scope of the invention.

Unless defined otherwise, all technical and scientific terms used herein have the same g as commonly understood by one of ordinary skill in the art to which this invention belongs. As used herein, the term "about," when used in reference to a particular recited numerical value, means that the value may vary from the recited value by no more than 1%.

For example, as used herein, the expression "about 100" includes 99 and 101 and all values in between (e.g., 99.1, 99.2, 99.3, 99.4, etc.).

] The term "comprising" as used in this specification and claims means sting at least in part of". When interpreting statements in this specification, and claims which include the term "comprising", it is to be understood that other es that are additional to the features prefaced by this term in each statement or claim may also be present. Related terms such as "comprise" and "comprised" are to be interpreted in similar manner.

Although any methods and materials r or equivalent to those described herein can be used in the practice or testing of the present ion, the preferred methods and materials are now described.

Antigen-Specific Binding Proteins The description relates to compositions sing antigen-specific g proteins.

More specifically, described is a composition comprising an Activin A-specific binding protein.

As used herein, the expression "antigen-specific binding protein" means a protein comprising at least one domain which specifically binds a particular antigen. Exemplary categories of antigen-specific binding proteins include antibodies, antigen-binding ns of antibodies, peptides that specifically interact with a particular n (e.g., peptibodies), receptor molecules that specifically interact with a particular antigen, and proteins comprising a ligand-binding portion of a receptor that specifically binds a ular antigen.

The descriptionincludes antigen-specific binding proteins that specifically bind Activin A, i.e., "Activin ific binding proteins". Activins are homo- and hetero-dimeric molecules comprising beta subunits, i.e., Inhibin βA, inhibin βB, inhibin βC, and/or inhibin βE. The βA subunit has the amino acid ce of SEQ ID NO:226 and the βB subunit has the amino acid sequence of SEQ ID . Activin A is a homodimer of two βA subunits; Activin B is a homodimer of two βB subunits; Activin AB is a heterodimer of one βA subunit and one βB subunit; and Activin AC is a heterodimer of one βA subunit and one βC subunit. An Activin A- ic binding protein may be an antigen-specific binding protein that specifically binds the βA subunit. Since the βA subunit is found in Activin A, n AB, and Activin AC molecules, an "Activin A-specific binding protein" can be an antigen-specific binding protein that specifically binds Activin A as well as n AB and Activin AC (by virtue of its interaction with the βA subunit). Therefore, according to one embodiment of the description, an Activin A-specific binding protein specifically binds Activin A; or Activin A and Activin AB; or Activin A and Activin AC; or Activin A, Activin AB and Activin AC, but does not bind other B ligands such as Activin B, GDF3, GDF8, BMP2, BMP4, BMP7, BMP9, BMP10, GDF11, Nodal, etc. Thus, in one embodiment of the description, an Activin A-specific binding protein specifically binds to Activin A but does not bind significantly to Activin B or Activin C. In another embodiment, an Activin A-specific binding protein may also bind to Activin B (by virtue of cross-reaction with the βB subunit, i.e., nβB). In another embodiment, an n A-specific binding n is a binding protein that binds specifically to Activin A but does not bind to any other ligand of ActRIIB. In another embodiment, an Activin A-specific binding protein is a g protein and binds specifically to Activin A and does not bind to any Bone genetic Protein (BMP) (e.g., BMP2, BMP4, BMP6, BMP9, BMP10). In another embodiment, an n A-specific binding protein is a binding protein that binds specifically to Activin A but does not bind to any other member of the transforming growth factor beta (TGFβ) superfamily.

The description also includes antigen-specific binding proteins that ically bind GDF8, i.e., "GDF8-specific g proteins". The term "GDF8" (also referred to as "growth and differentiation factor-8" and "myostatin") means the protein having the amino acid sequence of SEQ ID NO:225 (mature n). According to the description, GDF8-specific binding proteins specifically bind GDF8 but do not bind other ActRIIB s such as GDF3, BMP2, BMP4, BMP7, BMP9, BMP10, GDF11, Activin A, Activin B, Activin AB, Nodal, etc.

In the t of the description, molecules such as ActRIIB-Fc (e.g., "ACE-031"), which comprise the ligand-binding portion of the ActRIIB receptor, are not considered in A-specific binding proteins" or "GDF8-specific binding proteins" because such molecules bind multiple ligands besides GDF8, Activin A and Activin AB.

All nces to proteins, polypeptides and protein nts herein are intended to refer to the human version of the respective protein, polypeptide or protein fragment unless explicitly specified as being from a non-human species.

Antigen-Binding Molecules with Two Different Antigen-Specific Binding Domains The descriptionalso includes antigen-binding molecules comprising two different antigen-specific binding s. In particular, the descriptionincludes n-binding molecules comprising an Activin A-specific binding domain and a GDF8-specific g domain. The term "antigen-specific binding domain," as used herein, includes polypeptides comprising or consisting of: (i) an antigen-binding nt of an antibody molecule, (ii) a peptide that specifically interacts with a particular antigen (e.g., a peptibody), and/or (iii) a ligand-binding portion of a receptor that specifically binds a particular antigen. For example, the descriptionincludes bispecific antibodies with one arm comprising a first heavy chain variable region/light chain variable region (HCVR/LCVR) pair that specifically binds Activin A and another arm comprising a second HCVR/LCVR pair that specifically binds GDF8.

Specific Binding The term "specifically binds" or the like, as used herein, means that an antigen-specific binding protein, or an antigen-specific binding domain, forms a complex with a particular antigen characterized by a dissociation constant (KD) of 500 pM or less, and does not bind other unrelated antigens under ordinary test ions. ated ns" are proteins, peptides or polypeptides that have less than 95% amino acid identity to one another. s for determining whether two molecules ically bind one another are well known in the art and include, for example, equilibrium dialysis, surface plasmon resonance, and the like. For example, an antigen-specific binding protein or an antigen-specific binding domain, as used in the context of the description, es molecules that bind a particular antigen (e.g., Activin A and/or AB, or GDF8) or a portion thereof with a KD of less than about 500 pM, less than about 400 pM, less than about 300 pM, less than about 200 pM, less than about 100 pM, less than about 90 pM, less than about 80 pM, less than about 70 pM, less than about 60 pM, less than about 50 pM, less than about 40 pM, less than about 30 pM, less than about 20 pM, less than about 10 pM, less than about 5 pM, less than about 4 pM, less than about 2 pM, less than about 1 pM, less than about 0.5 pM, less than about 0.2 pM, less than about 0.1 pM, or less than about 0.05 pM, as measured in a surface plasmon resonance assay.

As used herein, an antigen-specific binding protein or antigen-specific binding domain "does not bind" to a specified molecule (e.g., "does not bind GDF11", "does not bind BMP9", "does not bind , etc.) if the protein or binding domain, when tested for binding to the molecule at 25ºC in a surface plasmon resonance assay, exhibits a KD of greater than 50.0 nM, or fails to exhibit any binding in such an assay or equivalent thereof.

The term "surface plasmon resonance", as used herein, refers to an optical phenomenon that allows for the analysis of real-time interactions by ion of alterations in protein concentrations within a biosensor matrix, for example using the BIAcore™ system (Biacore Life Sciences division of GE Healthcare, Piscataway, NJ).

The term "KD ", as used herein, means the equilibrium dissociation constant of a particular protein-protein interaction (e.g., antibody-antigen interaction). Unless indicated otherwise, the KD values disclosed herein refer to KD values determined by surface plasmon resonance assay at 25ºC.

Antibodies and Antigen-Binding nts of Antibodies As indicated above, an antigen-specific binding protein can comprise or consist of an antibody or antigen-binding fragment of an antibody. Furthermore, in the case of antigenbinding molecules sing two different antigen-specific binding domains, one or both of the antigen-specific g domains may comprise or consist of an antigen-binding fragment of an As used herein, "an antibody that binds Activin" or an "anti-Activin A antibody" includes antibodies, and n-binding nts thereof, that bind a soluble fragment of the Activin A protein and may also bind to an Activin βA subunit-containing Activin dimer.

The term "antibody", as used herein, means any antigen-binding le or molecular complex comprising at least one complementarity determining region (CDR) that specifically binds to or interacts with a particular antigen (e.g., Activin A). The term "antibody" includes immunoglobulin les comprising four ptide chains, two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds, as well as ers thereof (e.g., IgM). Each heavy chain comprises a heavy chain variable region (abbreviated herein as HCVR or VH) and a heavy chain constant region. The heavy chain nt region comprises three domains, CH1, CH2 and CH3. Each light chain comprises a light chain variable region (abbreviated herein as LCVR or VL) and a light chain constant region. The light chain constant region comprises one domain (CL1). The VH and VL regions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDRs), interspersed with regions that are more conserved, termed framework regions (FR). Each VH and VL is composed of three CDRs and four FRs, arranged from amino-terminus to carboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3, CDR3, FR4. In different embodiments of the description, the FRs of the anti-Activin A antibody (or n-binding portion thereof) may be identical to the human germline sequences, or may be naturally or artificially modified. An amino acid sus sequence may be defined based on a side-by-side analysis of two or more CDRs.

The term "antibody", as used herein, also es antigen-binding fragments of full antibody les. The terms "antigen-binding portion" of an antibody, "antigen-binding fragment" of an antibody, and the like, as used , include any naturally occurring, enzymatically obtainable, synthetic, or genetically engineered ptide or glycoprotein that specifically binds an antigen to form a complex. Antigen-binding fragments of an antibody may be derived, e.g., from full antibody molecules using any suitable standard techniques such as proteolytic digestion or recombinant genetic engineering techniques involving the manipulation and expression of DNA encoding antibody variable and optionally constant s. Such DNA is known and/or is readily available from, e.g., commercial sources, DNA libraries (including, e.g., phage-antibody libraries), or can be synthesized. The DNA may be sequenced and manipulated chemically or by using molecular y techniques, for example, to arrange one or more variable and/or constant s into a le configuration, or to introduce , create cysteine residues, modify, add or delete amino acids, etc.

Non-limiting es of n-binding fragments include: (i) Fab fragments; (ii) F(ab')2 fragments; (iii) Fd fragments; (iv) Fv fragments; (v) single-chain Fv (scFv) molecules; (vi) dAb fragments; and (vii) minimal recognition units consisting of the amino acid residues that mimic the hypervariable region of an antibody (e.g., an isolated complementarity determining region (CDR) such as a CDR3 peptide), or a constrained FR3-CDR3-FR4 peptide. Other engineered molecules, such as domain-specific antibodies, single domain antibodies, domaindeleted antibodies, chimeric antibodies, CDR-grafted antibodies, diabodies, triabodies, tetrabodies, minibodies, nanobodies (e.g. monovalent dies, bivalent nanobodies, etc.), small modular immunopharmaceuticals (SMIPs), and shark variable IgNAR domains, are also encompassed within the sion "antigen-binding fragment," as used herein.

An antigen-binding fragment of an antibody will typically comprise at least one variable domain. The variable domain may be of any size or amino acid composition and will generally comprise at least one CDR which is adjacent to or in frame with one or more framework sequences. In antigen-binding fragments having a VH domain associated with a VL domain, the VH and VL domains may be situated relative to one r in any suitable arrangement. For example, the variable region may be c and contain VH-VH, VH-VL or VL-VL dimers. atively, the antigen-binding fragment of an antibody may contain a monomeric VH or VL domain.

In certain embodiments, an antigen-binding fragment of an antibody may contain at least one variable domain covalently linked to at least one constant domain. Non-limiting, exemplary configurations of variable and nt domains that may be found within an antigen-binding nt of an antibody of the description include: (i) VH-CH1; (ii) VH-CH2; (iii) VH-CH3; (iv) VH-CH1-CH2; (v) VH-CH1-CH2-CH3; (vi) VH-CH2-CH3; (vii) VH-CL; (viii) VL-CH1; (ix) VLCH2 ; (x) VL-CH3; (xi) VL-CH1-CH2; (xii) VL-CH1-CH2-CH3; (xiii) VL-CH2-CH3; and (xiv) VL-CL. In any configuration of variable and constant domains, including any of the exemplary configurations listed above, the variable and constant domains may be either directly linked to one r or may be linked by a full or partial hinge or linker region. A hinge region may consist of at least 2 (e.g., 5, 10, 15, 20, 40, 60 or more) amino acids which result in a flexible or semi-flexible linkage between adjacent variable and/or constant domains in a single polypeptide molecule.

Moreover, an antigen-binding fragment of an antibody of the description may comprise a homodimer or hetero-dimer (or other er) of any of the variable and constant domain configurations listed above in non-covalent association with one another and/or with one or more monomeric VH or VL domain (e.g., by disulfide bond(s)).

As with full antibody molecules, antigen-binding nts may be monospecific or multispecific (e.g., bispecific). A multispecific antigen-binding fragment of an antibody will typically comprise at least two different variable domains, wherein each variable domain is capable of specifically g to a separate antigen or to a different epitope on the same n. Any multispecific antibody format, ing the exemplary ific antibody formats disclosed herein, may be adapted for use in the context of an antigen-binding nt of an antibody of the description using routine techniques available in the art.

The antibodies of the description may function through complement-dependent xicity (CDC) or antibody-dependent cell-mediated xicity (ADCC). "Complementdependent cytotoxicity" (CDC) refers to lysis of antigen-expressing cells by an antibody of the description in the presence of complement. "Antibody-dependent cell-mediated cytotoxicity" (ADCC) refers to a cell-mediated reaction in which nonspecific cytotoxic cells that express Fc ors (FcRs) (e.g., Natural Killer (NK) cells, neutrophils, and macrophages) recognize bound antibody on a target cell and thereby lead to lysis of the target cell. CDC and ADCC can be ed using assays that are well known and available in the art. (See, e.g., U.S. Patent Nos 5,500,362 and 337, and Clynes et al., PNAS USA -656 (1998)). The constant region of an antibody is important in the ability of an antibody to fix complement and mediate cell-dependent cytotoxicity. Thus, the isotype of an antibody may be selected on the basis of whether it is desirable for the antibody to mediate cytotoxicity.

In n embodiments of the description, the anti-Activin A antibodies of the description are human antibodies. The term "human dy", as used herein, is intended to include antibodies having variable and nt regions derived from human germline immunoglobulin sequences. The human antibodies of the description may include amino acid residues not encoded by human germline immunoglobulin sequences (e.g., mutations introduced by random or site-specific mutagenesis in vitro or by somatic mutation in vivo), for example in the CDRs and in particular CDR3. However, the term "human antibody", as used herein, is not intended to include antibodies in which CDR sequences derived from the germline of another ian species, such as a mouse, have been grafted onto human framework sequences.

The antibodies of the description may, in some ments, be recombinant human antibodies. The term "recombinant human antibody", as used herein, is intended to include all human antibodies that are prepared, expressed, created or isolated by recombinant means, such as antibodies expressed using a recombinant expression vector ected into a host cell (described further below), antibodies ed from a recombinant, combinatorial human antibody library (described further below), antibodies isolated from an animal (e.g., a mouse) that is transgenic for human immunoglobulin genes (see e.g., Taylor et al., Nucl Acids Res :6287-6295 (1992)) or antibodies prepared, expressed, created or ed by any other means that involves splicing of human immunoglobulin gene sequences to other DNA ces. Such recombinant human antibodies have variable and constant regions derived from human germline immunoglobulin sequences. In certain embodiments, r, such inant human antibodies are subjected to in vitro mutagenesis (or, when an animal transgenic for human Ig sequences is used, in vivo somatic mutagenesis) and thus the amino acid sequences of the VH and VL regions of the recombinant antibodies are sequences that, while derived from and related to human germline VH and VL sequences, may not naturally exist within the human antibody germline repertoire in vivo.

Human antibodies can exist in two forms that are associated with hinge heterogeneity.

In one form, an immunoglobulin molecule comprises a stable four chain construct of approximately 150-160 kDa in which the dimers are held together by an interchain heavy chain disulfide bond. In a second form, the dimers are not linked via inter-chain disulfide bonds and a molecule of about 75-80 kDa is formed composed of a covalently coupled light and heavy chain (half-antibody). These forms have been extremely difficult to separate, even after affinity purification.

The frequency of appearance of the second form in various intact IgG isotypes is due to, but not d to, structural differences associated with the hinge region isotype of the antibody. A single amino acid substitution in the hinge region of the human IgG4 hinge can significantly reduce the appearance of the second form (Angal et al. Molecular Immunology :105 1993)) to levels lly ed using a human IgG1 hinge. The instant description encompasses antibodies having one or more mutations in the hinge, CH2 or CH3 region which may be desirable, for example, in production, to improve the yield of the desired antibody form.

The antibodies of the ption may be isolated antibodies. An "isolated antibody," as used herein, means an dy that has been identified and ted and/or recovered from at least one component of its natural environment. For example, an antibody that has been separated or removed from at least one ent of an organism, or from a tissue or cell in which the antibody naturally exists or is naturally produced, is an "isolated antibody" for purposes of the description. An isolated antibody also includes an antibody in situ within a recombinant cell. Isolated antibodies are antibodies that have been subjected to at least one purification or isolation step. According to certain embodiments, an isolated dy may be substantially free of other cellular material and/or chemicals.

The descriptionincludes neutralizing and/or ng anti-Activin A antibodies. A "neutralizing" or "blocking" antibody, as used herein, is intended to refer to an antibody whose binding to Activin A: (i) interferes with the interaction between Activin A and an Activin A receptor (e.g., Activin Type IIA receptor, Activin Type IIB receptor, Activin Type I receptor, etc.); (ii) interferes with the formation of Activin-Activin receptor complexes; and/or (iii) results in inhibition of at least one ical function of Activin A. The inhibition caused by an Activin A neutralizing or blocking dy need not be complete so long as it is detectable using an appropriate assay. Exemplary assays for detecting Activin A inhibition are described in the working Examples herein.

The anti-Activin A antibodies disclosed herein may comprise one or more amino acid substitutions, insertions and/or deletions in the ork and/or CDR regions of the heavy and light chain variable domains as compared to the corresponding germline sequences from which the dies were derived. Such mutations can be readily ascertained by comparing the amino acid sequences disclosed herein to germline sequences available from, for example, public dy ce databases. The ptionincludes antibodies, and antigen-binding fragments thereof, which are derived from any of the amino acid sequences disclosed herein, n one or more amino acids within one or more ork and/or CDR regions are mutated to the corresponding residue(s) of the germline sequence from which the antibody was derived, or to the corresponding residue(s) of another human germline sequence, or to a conservative amino acid substitution of the corresponding germline residue(s) (such sequence changes are referred to herein collectively as "germline mutations"). A person of ordinary skill in the art, starting with the heavy and light chain variable region sequences disclosed herein, can easily produce numerous antibodies and antigen-binding fragments which comprise one or more individual germline ons or combinations thereof. In certain embodiments, all of the framework and/or CDR residues within the VH and/or VL domains are mutated back to the residues found in the original germline sequence from which the antibody was derived. In other embodiments, only certain residues are mutated back to the al ne sequence, e.g., only the mutated residues found within the first 8 amino acids of FR1 or within the last 8 amino acids of FR4, or only the d residues found within CDR1, CDR2 or CDR3. In other embodiments, one or more of the framework and/or CDR residue(s) are mutated to the corresponding residue(s) of a different ne sequence (i.e., a germline sequence that is different from the germline sequence from which the antibody was ally derived).

Furthermore, the antibodies of the descriptionmay n any ation of two or more germline mutations within the framework and/or CDR regions, e.g., wherein certain individual residues are mutated to the corresponding residue of a particular germline sequence while certain other residues that differ from the original germline sequence are ined or are mutated to the corresponding residue of a different germline sequence. Once obtained, antibodies and n-binding fragments that contain one or more germline mutations can be easily tested for one or more desired property such as, improved binding specificity, increased binding affinity, improved or enhanced antagonistic or agonistic biological properties (as the case may be), reduced immunogenicity, etc. Antibodies and antigen-binding fragments obtained in this general manner are encompassed within the description.

The ption also includes anti-Activin A antibodies sing variants of any of the HCVR, LCVR, and/or CDR amino acid sequences disclosed herein having one or more conservative substitutions. For example, the descriptionincludes ctivin A antibodies having HCVR, LCVR, and/or CDR amino acid sequences with, e.g., 10 or fewer, 8 or fewer, 6 or fewer, 4 or fewer, etc. conservative amino acid substitutions relative to any of the HCVR, LCVR, and/or CDR amino acid sequences disclosed herein.

The term "epitope" refers to an antigenic determinant that interacts with a specific antigen binding site in the variable region of an dy molecule known as a paratope. A single antigen may have more than one epitope. Thus, different antibodies may bind to different areas on an antigen and may have different biological effects. Epitopes may be either conformational or linear. A conformational epitope is produced by spatially juxtaposed amino acids from ent segments of the linear polypeptide chain. A linear epitope is one produced by adjacent amino acid residues in a polypeptide chain. In certain circumstance, an epitope may include moieties of saccharides, phosphoryl groups, or sulfonyl groups on the antigen.

The term "substantial identity" or "substantially identical," when referring to a nucleic acid or fragment thereof, indicates that, when lly aligned with riate tide insertions or deletions with another c acid (or its complementary strand), there is nucleotide sequence identity in at least about 95%, and more preferably at least about 96%, 97%, 98% or 99% of the nucleotide bases, as measured by any well-known algorithm of sequence identity, such as FASTA, BLAST or Gap, as discussed below. A nucleic acid le having substantial ty to a reference nucleic acid molecule may, in certain instances, encode a polypeptide having the same or substantially r amino acid sequence as the polypeptide encoded by the reference nucleic acid molecule.

As applied to polypeptides, the term "substantial similarity" or "substantially similar" means that two peptide sequences, when optimally aligned, such as by the programs GAP or BESTFIT using default gap weights, share at least 95% sequence identity, even more preferably at least 98% or 99% sequence identity. Preferably, residue positions which are not cal differ by conservative amino acid substitutions. A "conservative amino acid substitution" is one in which an amino acid residue is substituted by another amino acid residue having a side chain (R group) with similar chemical ties (e.g., charge or hydrophobicity).

In l, a vative amino acid substitution will not substantially change the functional properties of a n. In cases where two or more amino acid sequences differ from each other by conservative substitutions, the t ce identity or degree of similarity may be adjusted upwards to t for the conservative nature of the substitution. Means for making this ment are well-known to those of skill in the art. See, e.g., Pearson, W.R., Methods Mol Biol 24: 307-331 (1994). Examples of groups of amino acids that have side chains with r chemical properties include (1) aliphatic side chains: glycine, alanine, valine, leucine and isoleucine; (2) aliphatic-hydroxyl side chains: serine and threonine; (3) amide-containing side chains: asparagine and glutamine; (4) aromatic side chains: phenylalanine, tyrosine, and tryptophan; (5) basic side chains: lysine, ne, and histidine; (6) acidic side chains: aspartate and glutamate, and (7) -containing side chains are cysteine and methionine.

Preferred conservative amino acids substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, -arginine, alanine-valine, glutamate-aspartate, and asparagineglutamine.

Alternatively, a conservative replacement is any change having a positive value in the PAM250 log-likelihood matrix disclosed in Gonnet et al., Science 256: 1443-1445 (1992). A "moderately conservative" ement is any change having a nonnegative value in the PAM250 log-likelihood matrix.

Sequence similarity for polypeptides, which is also referred to as sequence identity, is typically measured using sequence analysis software. Protein analysis software matches similar sequences using measures of similarity assigned to various substitutions, ons and other cations, including conservative amino acid substitutions. For instance, GCG software contains programs such as Gap and Bestfit which can be used with default parameters to determine ce homology or sequence identity between closely related polypeptides, such as homologous polypeptides from different species of organisms or between a wild type protein and a mutein thereof. See, e.g., GCG Version 6.1. Polypeptide sequences also can be compared using FASTA using default or recommended parameters, a program in GCG Version 6.1. FASTA (e.g., FASTA2 and ) provides alignments and percent sequence identity of the regions of the best overlap n the query and search ces (see, e.g., Pearson, W.R., Methods Mol Biol 132: 185-219 (2000)). Another preferred algorithm when comparing a sequence of the description to a database containing a large number of sequences from different organisms is the computer program BLAST, especially BLASTP or TBLASTN, using default parameters. See, e.g., ul et al., J Mol Biol 215:403-410 (1990) and ul et al., Nucleic Acids Res 25:3389-402 (1997).

Biological Characteristics of the Antibodies The description includes anti-Activin A antibodies and antigen-binding fragments thereof that bind Activin A with high affinity. For example, the description includes antibodies and n-binding fragments of antibodies that bind Activin A (e.g., at 25ºC or 37ºC) with a KD of less than about 30 nM as measured by surface plasmon resonance, e.g., using the assay format as defined in Example 3 herein. In certain ments, the antibodies or antigenbinding fragments of the description bind n A with a KD of less than about 25 nM, less than about 20 nM, less than about 15 nM, less than about 10 nM, less than about 5 nM, less than about 2 nM, less than about 1 nM, less than about 500 pM, less than about 250 pM, less than about 240 pM, less than about 230 pM, less than about 220 pM, less than about 210 pM, less than about 200 pM, less than about 190 pM, less than about 180 pM, less than about 170 pM, less than about 160 pM, less than about 150 pM, less than about 140 pM, less than about 130 pM, less than about 120 pM, less than about 110 pM, less than about 100 pM, less than about 95 pM, less than about 90 pM, less than about 85 pM, less than about 80 pM, less than about 75 pM, less than about 70 pM, less than about 65 pM, less than about 60 pM, less than about 55 pM, less than about 50 pM, less than about 45 pM, less than about 40 pM, less than about pM, less than about 30 pM, less than about 25 pM, less than about 20 pM, less than about pM, less than about 10 pM, less than about 9 pM, less than about 8 pM, less than about 7 pM, less than about 6 pM, less than about 5 pM, less than about 4 pM, or less than about 3 pM, as measured by surface plasmon resonance, e.g., using the assay format as defined in Example 3 herein, or a substantially r assay.

The description also includes anti-Activin A antibodies and n-binding fragments thereof that inhibit n A-mediated cellular signaling. For example, the description includes anti-Activin A antibodies that inhibit the activation of the SMAD complex signal transduction pathway via the binding of Activin A to Activin Type I or II receptors with an IC50 value of less than about 4 nM, as measured in a cell-based blocking bioassay, e.g., using the assay format as defined in e 5 herein, or a substantially similar assay. In certain embodiments, the antibodies or antigen-binding fragments of the description inhibit the activation of the SMAD complex signal transduction pathway via the binding of Activin A to Activin Type I or II receptors with an IC50 value of less than about 3nM, less than about 2 nM, less than about 1 nm, less than about 500 pM, less than about 250 pM, less than about 240 pM, less than about 230 pM, less than about 220 pM, less than about 210 pM, less than about 200 pM, less than about 190 pM, less than about 180 pM, less than about 170 pM, less than about 160 pM, less than about 150 pM, less than about 140 pM, less than about 130 pM, less than about 120 pM, less than about 110 pM, less than about 100 pM, less than about 95 pM, less than about 90 pM, less than about 85 pM, less than about 80 pM, less than about 75 pM, less than 70 pM, less than about 65 pM, less than about 60 pM, less than about 55 pM, less than about 50 pM, less than about 49 pM, less than about 48 pM, less than about 47 pM, less than about 46 pM, less than about 45 pM, less than about 44 pM, less than about 43 pM, less than about 42 pM, less than about 41 pM, less than about 40 pM, or less than about 39 pM, as measured in a cell-based ng bioassay, e.g., using the assay format as defined in Example 5 herein, or a substantially similar assay. In certain ments, the antibodies or antigen-binding fragments of the description inhibit the signaling activing of Activin B by interfering with the binding of n B to Activin Type I or II receptors with an IC50 value of less than about 50 nM, less than about 20 nM, less than about 10 nm, less than about 5 nM, or less than about 1 nM, , as measured in a cell-based blocking bioassay, e.g., using the assay format as defined in e 5 herein, or a substantially similar assay. In certain embodiments, the antibodies or antigen-binding nts of the description inhibit the activation of the SMAD complex signal transduction pathway via the binding of Activin AB to Activin Type I or II receptors with an IC50 value of less than about 500 pM, less than about 450 pM, less than about 440 pM, less than about 430 pM, less than about 420 pM, less than about 410 pM, less than about 400 pM, less than about 390 pM, less than about 380 pM, less than about 370 pM, less than about 360 pM, less than about 350 pM, less than about 340 pM, less than about 320 pM, less than about 310 pM, less than about 300 pM, less than about 290 pM, less than about 280 pM, less than about 270 pM, less than about 260 pM, less than about 250 pM, less than about 240 pM, less than about 230 pM, less than about 220 pM, less than about 210 pM, less than about 200 pM, less than about 190 pM, less than about 180 pM, less than about 170 pM, less than about 160 pM, less than about 150 pM, or less than about 140 pM, as measured in a cell-based blocking bioassay, e.g., using the assay format as defined in e 5 herein, or a substantially similar assay. In certain embodiments, the antibodies or antigen-binding fragments of the description inhibit the tion of the SMAD complex signal transduction pathway via the g of Activin AC to Activin Type I or II receptors with an IC50 value of less than about 1 nM, less than about 900 pM, less than about 800 pM, less than about 750 pM, less than about 700 pM, less than about 650 pM, less than about 600 pM, or less than about 580 pM, as measured in a cellbased blocking bioassay, e.g., using the assay format as defined in Example 5 herein, or a substantially similar assay.

The antibodies of the description may possess one or more of the aforementioned biological characteristics, or any combinations thereof. Other biological characteristics of the antibodies of the descriptionwill be evident to a person of ordinary skill in the art from a review of the present disclosure including the working Examples herein.

Anti-Activin A Antibodies Comprising Fc Variants According to certain ments, anti-Activin A antibodies are described comprising an Fc domain comprising one or more mutations which enhance or diminish antibody binding to the FcRn receptor, e.g., at acidic pH as compared to neutral pH. For example, the description includes anti-Activin A antibodies comprising a on in the CH2 or a CH3 region of the Fc , wherein the mutation(s) increases the affinity of the Fc domain to FcRn in an acidic environment (e.g., in an endosome where pH ranges from about 5.5 to about 6.0). Such mutations may result in an se in serum half-life of the antibody when administered to an . Non-limiting examples of such Fc modifications include, e.g., a modification at position 250 (e.g., E or Q); 250 and 428 (e.g., L or F); 252 (e.g., L/Y/F/W or T), 254 (e.g., S or T), and 256 (e.g., S/R/Q/E/D or T); or a cation at position 428 and/or 433 (e.g., H/L/R/S/P/Q or K) and/or 434 (e.g., A, W, H, F or Y [N434A, N434W, N434H, N434F or N434Y]); or a modification at on 250 and/or 428; or a modification at position 307 or 308 (e.g., 308F, , and 434. In one ment, the modification comprises a 428L (e.g., M428L) and 434S (e.g., N434S) modification; a 428L, 259I (e.g., V259I), and 308F (e.g., V308F) modification; a 433K (e.g., H433K) and a 434 (e.g., 434Y) modification; a 252, 254, and 256 (e.g., 252Y, 254T, and 256E) modification; a 250Q and 428L modification (e.g., T250Q and M428L); and a 307 and/or 308 modification (e.g., 308F or 308P). In yet another embodiment, the modification comprises a 265A (e.g., D265A) and/or a 297A (e.g., N297A) modification.

For e, the description includes anti-Activin A dies comprising an Fc domain comprising one or more pairs or groups of mutations selected from the group consisting of: 250Q and 248L (e.g., T250Q and M248L); 252Y, 254T and 256E (e.g., M252Y, S254T and T256E); 428L and 434S (e.g., M428L and N434S); 257I and 311I (e.g., P257I and Q311I); 257I and 434H (e.g., P257I and N434H); 376V and 434H (e.g., D376V and N434H); 307A, 380A and 434A (e.g., T307A, E380A and N434A); and 433K and 434F (e.g., H433K and N434F). All possible combinations of the foregoing Fc domain mutations, and other ons within the antibody variable domains disclosed herein, are contemplated within the scope of the description.

The description also includes anti-Activin A antibodies comprising a chimeric heavy chain constant (CH) region, wherein the chimeric CH region comprises ts derived from the CH s of more than one immunoglobulin isotype. For example, the antibodies of the description may se a chimeric CH region comprising part or all of a CH2 domain derived from a human IgG1, human IgG2 or human IgG4 molecule, combined with part or all of a CH3 domain derived from a human IgG1, human IgG2 or human IgG4 molecule. According to certain embodiments, the antibodies of the description comprise a chimeric CH region having a chimeric hinge region. For example, a chimeric hinge may comprise an "upper hinge" amino acid sequence (amino acid residues from positions 216 to 227 according to EU numbering) derived from a human IgG1, a human IgG2 or a human IgG4 hinge region, combined with a "lower hinge" sequence (amino acid residues from positions 228 to 236 ing to EU numbering) derived from a human IgG1, a human IgG2 or a human IgG4 hinge region.

According to certain embodiments, the chimeric hinge region comprises amino acid residues derived from a human IgG1 or a human IgG4 upper hinge and amino acid residues derived from a human IgG2 lower hinge. An antibody comprising a chimeric CH region as described herein may, in certain embodiments, t modified Fc effector functions without adversely affecting the therapeutic or pharmacokinetic ties of the antibody. (See, e.g., U.S. ional Appl. No. ,578, filed February 1, 2013).

Epitope g and Related logies The description es anti-Activin A antibodies which interact with one or more amino acids found within Activin A (e.g., within the Activin Type II receptor binding site). The epitope to which the antibodies bind may consist of a single contiguous sequence of 3 or more (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more) amino acids located within the n βA subunit. Alternatively, the epitope may consist of a plurality of noncontiguous amino acids (or amino acid sequences) located within the Activin A dimer.

Various ques known to s of ordinary skill in the art can be used to determine whether an antibody "interacts with one or more amino acids" within a polypeptide or protein. Exemplary techniques include, e.g., routine cross-blocking assay such as that described Antibodies, Harlow and Lane (Cold Spring Harbor Press, Cold Spring Harb., NY), alanine ng mutational analysis, peptide blots analysis (Reineke, Methods Mol Biol 248:443-463 (2004)), and e cleavage analysis. In on, methods such as epitope excision, epitope extraction and chemical modification of antigens can be employed (Tomer, Protein Science 9:487-496 (2000)). Another method that can be used to identify the amino acids within a polypeptide with which an antibody interacts is hydrogen/deuterium exchange detected by mass spectrometry. In general terms, the hydrogen/deuterium exchange method involves deuterium-labeling the protein of interest, followed by binding the antibody to the deuterium-labeled protein. Next, the protein/antibody complex is transferred to water to allow hydrogen-deuterium exchange to occur at all residues except for the residues protected by the antibody (which remain deuterium-labeled). After dissociation of the antibody, the target protein is subjected to protease cleavage and mass spectrometry analysis, thereby revealing the deuterium-labeled residues which correspond to the specific amino acids with which the antibody interacts. See, e.g., Ehring, Analytical Biochemistry 267(2):252-259 (1999); Engen and Smith, Anal. Chem. A-265A (2001).

The ption further includes anti-Activin A antibodies that bind to the same epitope as any of the specific exemplary antibodies described herein (e.g., H4H10423P, H4H10424P, H4H10426P, H4H10429P, H4H10430P, 32P2, 33P2, H4H10436P2, H4H10437P2, H4H10438P2, H4H10440P2, H4H10442P2, H4H10445P2, H4H10446P2, H4H10447P2, H4H10448P2, H4H10452P2, H4H10468P2, H2aM10965N, etc.). Likewise, the description also includes anti-Activin A antibodies that compete for binding to Activin A with any of the specific ary dies described herein (e.g., 23P, H4H10424P, H4H10426P, H4H10429P, H4H10430P, H4H10432P2, H4H10433P2, H4H10436P2, H4H10437P2, H4H10438P2, H4H10440P2, H4H10442P2, H4H10445P2, H4H10446P2, H4H10447P2, H4H10448P2, H4H10452P2, H4H10468P2, H2aM10965N, etc.). For e, the ption includes anti-Activin A antibodies that cross-compete for g to Activin A with one or more antibodies of "Bin 1" as defined in Example 4 herein (e.g., H4H10423P, H4H10446P2, H4H10468P2 and H4H10442P2). The description also includes anti-Activin A antibodies that cross-compete for g to Activin A with one or more antibodies of "Bin 2" as defined in Example 4 herein (e.g., H4H10429, H4H1430P, H4H10432P2, H4H10436P2, and H4H10440P2).

One can easily determine whether an antibody binds to the same epitope as, or competes for binding with, a reference ctivin A antibody by using routine s known in the art and exemplified herein. For example, to ine if a test antibody binds to the same epitope as a reference anti-Activin A antibody of the description, the reference antibody is allowed to bind to Activin A (or a βA subunit-containing heterodimer). Next, the ability of a test antibody to bind to Activin A is assessed. If the test antibody is able to bind to Activin A following saturation binding with the reference ctivin A dy, it can be ded that the test antibody binds to a different epitope than the reference anti-Activin A antibody. On the other hand, if the test antibody is not able to bind to Activin A following saturation binding with the reference anti-Activin A antibody, then the test dy may bind to the same epitope as the epitope bound by the reference anti-Activin A antibody of the description. Additional routine mentation (e.g., peptide mutation and binding analyses) can then be carried out to confirm whether the observed lack of binding of the test antibody is in fact due to binding to the same epitope as the reference antibody or if steric blocking (or another phenomenon) is responsible for the lack of observed binding. Experiments of this sort can be performed using ELISA, RIA, Biacore, flow cytometry or any other quantitative or qualitative antibody-binding assay available in the art. In accordance with n ments of the description, two antibodies bind to the same (or overlapping) epitope if, e.g., a 1-, 5-, 10-, 20- or 100-fold excess of one antibody inhibits binding of the other by at least 50% but preferably 75%, 90% or even 99% as measured in a competitive binding assay (see, e.g., Junghans et al., Cancer Res. 50:1495-1502 (1990)). Alternatively, two antibodies are deemed to bind to the same epitope if essentially all amino acid mutations in the antigen that reduce or eliminate binding of one antibody reduce or ate binding of the other. Two antibodies are deemed to have "overlapping epitopes" if only a subset of the amino acid mutations that reduce or ate binding of one antibody reduce or eliminate binding of the other.

To determine if an antibody competes for binding (or cross-competes for binding) with a reference anti-Activin A antibody, the above-described binding methodology is performed in two orientations: In a first orientation, the reference dy is d to bind to Activin A protein (or a βA t-containing dimer) under saturating conditions followed by assessment of binding of the test antibody to the Activin A molecule. In a second orientation, the test antibody is allowed to bind to Activin A under saturating conditions followed by assessment of g of the reference dy to Activin A. If, in both orientations, only the first (saturating) antibody is capable of binding to Activin A, then it is concluded that the test antibody and the reference antibody compete for binding to Activin A (see, e.g., the assay format described in Example 4 herein, in which a test Activin A dy is captured onto sensor tips that are then submerged in a solution containing a reference Activin A antibody und with Activin A). As will be appreciated by a person of ordinary skill in the art, an antibody that competes for binding with a nce antibody may not necessarily bind to the same epitope as the reference antibody, but may sterically block binding of the reference antibody by binding an pping or adjacent epitope.

Anti-Activin A antibodies of the description may bind to an epitope on Activin A that is within or near the binding site for an Activin Type II receptor, directly block interaction between Activin A and an Activin Type II receptor, and indirectly block interaction between Activin A and an Activin Type I receptor. Anti-Activin A antibodies of the description may bind to an epitope on Activin A that is within or near the binding site for the Activin Type I receptor and directly block interaction between Activin A and an n Type I receptor. In one ment of the ption, an anti-Activin A dy of the description that binds to Activin A at or near the Activin Type I receptor binding site does not block interaction between Activin A and an Activin A Type II receptor.

Preparation of Human Antibodies Methods for generating monoclonal antibodies, including fully human monoclonal dies are known in the art. Any such known methods can be used in the context of the descriptionto make human antibodies that specifically bind to human Activin A.

Using VELOCIMMUNE™ technology, for example, or any other known method for generating fully human monoclonal antibodies, high affinity chimeric antibodies to human Activin A are initially isolated having a human variable region and a mouse constant region. As in the experimental section below, the antibodies are characterized and selected for ble characteristics, including affinity, selectivity, epitope, etc. If necessary, mouse constant regions are replaced with a d human constant region, for example wild-type or modified IgG1 or IgG4, to generate a fully human anti-Activin A antibody. While the constant region selected may vary according to specific use, high affinity antigen-binding and target specificity teristics reside in the variable region. In certain instances, fully human ctivin A antibodies are isolated directly from antigen-positive B cells.

Bioequivalents The anti-Activin A antibodies and antibody fragments of the description encompass proteins having amino acid ces that vary from those of the described dies but that retain the ability to bind human Activin A. Such variant antibodies and antibody fragments comprise one or more additions, deletions, or substitutions of amino acids when compared to parent sequence, but exhibit biological activity that is essentially equivalent to that of the described antibodies. Likewise, the anti-Activin A antibody-encoding DNA ces of the description encompass sequences that comprise one or more additions, deletions, or substitutions of nucleotides when compared to the disclosed sequence, but that encode an anti- n A antibody or antibody fragment that is ially bioequivalent to an anti-Activin A antibody or antibody fragment of the description. Examples of such variant amino acid and DNA sequences are discussed above.

Two antigen-binding proteins, or antibodies, are considered bioequivalent if, for example, they are ceutical equivalents or pharmaceutical alternatives whose rate and extent of absorption do not show a significant difference when administered at the same molar dose under similar experimental conditions, either single does or multiple dose. Some antibodies will be considered equivalents or pharmaceutical alternatives if they are equivalent in the extent of their absorption but not in their rate of absorption and yet may be considered bioequivalent because such differences in the rate of absorption are intentional and are reflected in the labeling, are not essential to the attainment of effective body drug concentrations on, e.g., chronic use, and are considered medically insignificant for the particular drug product studied.

In one embodiment, two antigen-binding ns are ivalent if there are no clinically meaningful differences in their , purity, and potency.

In one embodiment, two antigen-binding proteins are ivalent if a patient can be switched one or more times between the reference product and the biological product without an expected increase in the risk of adverse effects, including a clinically significant change in immunogenicity, or diminished iveness, as compared to continued therapy without such switching.

In one ment, two n-binding proteins are bioequivalent if they both act by a common mechanism or mechanisms of action for the condition or conditions of use, to the extent that such mechanisms are known.

Bioequivalence may be demonstrated by in vivo and in vitro methods. Bioequivalence measures include, e.g., (a) an in vivo test in humans or other s, in which the concentration of the dy or its metabolites is measured in blood, plasma, serum, or other biological fluid as a function of time; (b) an in vitro test that has been correlated with and is reasonably predictive of human in vivo bioavailability data; (c) an in vivo test in humans or other mammals in which the appropriate acute pharmacological effect of the antibody (or its target) is measured as a function of time; and (d) in a well-controlled clinical trial that establishes safety, efficacy, or bioavailability or bioequivalence of an antibody.

Bioequivalent variants of anti-Activin A antibodies of the description may be constructed by, for example, making various tutions of es or sequences or deleting terminal or internal residues or sequences not needed for biological activity. For example, cysteine residues not essential for biological activity can be deleted or replaced with other amino acids to prevent formation of unnecessary or incorrect olecular disulfide s upon ration. In other contexts, bioequivalent antibodies may include anti-Activin A dy variants comprising amino acid s which modify the glycosylation characteristics of the antibodies, e.g., mutations which eliminate or remove ylation.

Species Selectivity and Species Cross-Reactivity Described are anti-Activin A antibodies that bind to human Activin A but not to Activin A from other species. The description also includes anti-Activin A antibodies that bind to human Activin A and to Activin A from one or more non-human species. For example, the anti- Activin A antibodies of the description may bind to human Activin A and may bind or not bind, as the case may be, to one or more of mouse, rat, guinea pig, hamster, gerbil, pig, cat, dog, rabbit, goat, sheep, cow, horse, camel, cynomologous, marmoset, rhesus or chimpanzee Activin A. ing to certain exemplary embodiments, anti-Activin A dies are described which specifically bind human Activin A (e.g., Activin A or a βA subunit-containing heterodimer) and cynomolgus monkey (e.g., Macaca fascicularis) Activin A.

Immunoconjugates The description encompasses ctivin A monoclonal antibodies conjugated to a therapeutic moiety ("immunoconjugate"), such as a cytotoxin, a herapeutic drug, an immunosuppressant or a radioisotope. Cytotoxic agents include any agent that is detrimental to cells. Examples of suitable cytotoxic agents and chemotherapeutic agents for forming immunoconjugates are known in the art (see for example, WO 05/103081). pecific Antibodies The antibodies of the descriptionmay be monospecific, bi-specific, or multispecific.

Multispecific antibodies may be specific for different epitopes of one target polypeptide or may contain antigen-binding domains specific for more than one target polypeptide. See, e.g., Tutt et al., J Immunol 147:60-69 (1991); Kufer et al., Trends Biotechnol 22:238-244 (2004). The anti-Activin A antibodies of the descriptioncan be linked to or co-expressed with another functional molecule, e.g., another peptide or n. For example, an antibody or nt thereof can be functionally linked (e.g., by chemical coupling, genetic fusion, alent association or otherwise) to one or more other molecular entities, such as another antibody or dy fragment to produce a bi-specific or a multispecific antibody with a second binding specificity. For example, the descriptionincludes bi-specific antibodies wherein one arm of an globulin is specific for human Activin A or a fragment thereof, and the other arm of the immunoglobulin is specific for a second therapeutic target or is conjugated to a therapeutic moiety. One embodiment of the description includes bi-specific antibodies wherein one arm of an immunoglobulin is specific for human Activin A or a fragment thereof, and the other arm of the immunoglobulin is specific for GDF8.

] An exemplary bi-specific antibody format that can be used in the context of the description involves the use of a first immunoglobulin (Ig) CH3 domain and a second Ig CH3 , wherein the first and second Ig CH3 domains differ from one another by at least one amino acid, and wherein at least one amino acid ence reduces binding of the bispecific antibody to Protein A as compared to a bi-specific dy lacking the amino acid difference (see, e.g., US Patent No. 8,586,713). In one ment, the first Ig CH3 domain binds Protein A and the second Ig CH3 domain contains a mutation that reduces or abolishes Protein A binding such as an H95R modification (by IMGT exon numbering; H435R by EU numbering).

The second CH3 may further comprise a Y96F modification (by IMGT; Y436F by EU). Further modifications that may be found within the second CH3 include: D16E, L18M, N44S, K52N, V57M, and V82I (by IMGT; D356E, L358M, N384S, K392N, V397M, and V422I by EU) in the case of IgG1 antibodies; N44S, K52N, and V82I (IMGT; N384S, K392N, and V422I by EU) in the case of IgG2 antibodies; and Q15R, N44S, K52N, V57M, R69K, E79Q, V82I, and L105P (by IMGT; Q355R, N384S, K392N, V397M, R409K, E419Q, V422I, and L445P by EU) in the case of IgG4 antibodies. Variations on the bi-specific antibody format described above are contemplated within the scope of the description.

Other ary bispecific formats that can be used in the context of the description include, without limitation, e.g., ased or diabody bispecific s, IgG-scFv s, dual variable domain (DVD)-Ig, Quadroma, knobs-into-holes, common light chain (e.g., common light chain with knobs-into-holes, etc.), CrossMab, CrossFab, (SEED)body, leucine zipper, Duobody, IgG1/IgG2, dual acting Fab (DAF)-IgG, and Mab2 bispecific formats (see, e.g., Klein et al., mAbs 4:6, 1-11 (2012), and references cited therein, for a review of the foregoing formats). ific antibodies can also be constructed using peptide/nucleic acid conjugation, e.g., n unnatural amino acids with onal chemical reactivity are used to generate site-specific antibody-oligonucleotide conjugates which then self-assemble into multimeric complexes with defined composition, valency and geometry. (See, e.g., Kazane et al., J Am Chem Soc. 135(1):340–346 (2013)).

Therapeutic Formulation and Administration Described are pharmaceutical itions sing the anti-Activin A antibodies or antigen-binding fragments thereof of the description. The pharmaceutical compositions of the description are formulated with suitable carriers, excipients, and other agents that provide improved er, delivery, tolerance, and the like. A multitude of appropriate formulations can be found in the formulary known to all pharmaceutical chemists: Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, PA. These formulations include, for example, powders, pastes, ointments, jellies, waxes, oils, , lipid nic or anionic) containing vesicles (such as LIPOFECTIN™, Life Technologies, Carlsbad, CA), DNA ates, anhydrous absorption , -water and water-in-oil emulsions, emulsions carbowax (polyethylene glycols of various molecular weights), semi-solid gels, and semi-solid mixtures containing carbowax. See also Powell et al. "Compendium of excipients for parenteral formulations" PDA, J Pharm Sci Technol 52:238-311 (1998).

The dose of antibody administered to a patient may vary depending upon the age and the size of the patient, target disease, conditions, route of administration, and the like. The preferred dose is typically calculated according to body weight or body surface area. When an antibody of the descriptionis used for treating a condition or disease associated with Activin A activity in an adult patient, it may be advantageous to intravenously administer the antibody of the ptionnormally at a single dose of about 0.01 to about 20 mg/kg body weight, more preferably about 0.02 to about 7, about 0.03 to about 5, or about 0.05 to about 3 mg/kg body weight. ing on the severity of the condition, the frequency and the on of the treatment can be adjusted. Effective dosages and schedules for administering anti-Activin A antibodies may be determined empirically; for example, patient progress can be monitored by periodic assessment, and the dose adjusted accordingly. er, pecies scaling of dosages can be performed using well-known s in the art (e.g., Mordenti et al., Pharmaceut Res 8:1351 (1991)).

Various delivery systems are known and can be used to administer the pharmaceutical composition of the description, e.g., ulation in liposomes, articles, microcapsules, recombinant cells capable of expressing an antibody or other therapeutic n of the description, receptor mediated endocytosis (see, e.g., Wu et al., J Biol Chem 262:4429-4432 (1987)). The antibodies and other therapeutically active components of the ptionmay also be delivered by gene therapy techniques. Methods of uction include, but are not limited to, intradermal, intramuscular, intraperitoneal, intravenous, subcutaneous, intranasal, epidural, and oral routes. The composition may be administered by any convenient route, for example by infusion or bolus injection, by absorption through epithelial or mucocutaneous linings (e.g., oral mucosa, rectal and intestinal mucosa, etc.) and may be administered together with other biologically active agents. Administration can be systemic or local.

A pharmaceutical composition of the descriptioncan be delivered subcutaneously or intravenously with a standard needle and syringe. In addition, with respect to subcutaneous delivery, a pen delivery device readily has applications in delivering a pharmaceutical composition of the description. Such a pen delivery device can be reusable or disposable. A reusable pen delivery device lly utilizes a replaceable cartridge that contains a pharmaceutical composition. Once all of the pharmaceutical ition within the cartridge has been stered and the cartridge is empty, the empty cartridge can readily be discarded and replaced with a new cartridge that contains the pharmaceutical composition. The pen delivery device can then be reused. In a disposable pen delivery device, there is no replaceable cartridge. Rather, the disposable pen ry device comes prefilled with the pharmaceutical composition held in a reservoir within the device. Once the reservoir is emptied of the ceutical composition, the entire device is discarded.

Numerous le pen and autoinjector delivery devices have applications in the subcutaneous delivery of a pharmaceutical ition of the description. Examples include, but are not limited to AUTOPEN™ (Owen Mumford, Inc., Woodstock, UK), DISETRONIC™ pen (Disetronic Medical Systems, Bergdorf, Switzerland), HUMALOG MIX 75/25™ pen, HUMALOG™ pen, HUMALIN 70/30™ pen (Eli Lilly and Co., Indianapolis, IN), NOVOPEN™ I, II and III (Novo Nordisk, Copenhagen, k), NOVOPEN JUNIOR™ (Novo Nordisk, Copenhagen, Denmark), BD™ pen (Becton Dickinson, in Lakes, NJ), OPTIPEN™, OPTIPEN PRO™, OPTIPEN STARLET™, and OPTICLIK™ (sanofi-aventis, urt, Germany), to name only a few. Examples of disposable pen delivery devices having applications in subcutaneous delivery of a pharmaceutical composition of the description include, but are not limited to the SOLOSTAR™ pen i-aventis), the FLEXPEN™ (Novo k), and the N™ (Eli Lilly), the SURECLICKTM Autoinjector (Amgen, Thousand Oaks, CA), the PENLETTM (Haselmeier, Stuttgart, Germany), the EPIPEN (Dey, L.P.), and the HUMIRATM Pen (Abbott Labs, Abbott Park IL), to name only a few.

In certain situations, the pharmaceutical composition can be red in a controlled release system. In one embodiment, a pump may be used (see Langer, supra; Sefton, CRC Crit. Ref. Biomed. Eng. 14:201 (1987)). In another embodiment, polymeric materials can be used; see, Medical Applications of Controlled Release, Langer and Wise (eds.), 1974, CRC Pres., Boca Raton, Florida. In yet another embodiment, a lled release system can be placed in proximity of the composition’s , thus requiring only a fraction of the systemic dose (see, e.g., Goodson, 1984, in Medical Applications of Controlled Release, supra, vol. 2, pp. 115-138). Other controlled release systems are discussed in the review by Langer, e 249:1527-1533 (1990).

] The injectable preparations may include dosage forms for enous, subcutaneous, intracutaneous and intramuscular injections, drip infusions, etc. These injectable preparations may be prepared by methods publicly known. For example, the injectable preparations may be prepared, e.g., by dissolving, suspending or emulsifying the antibody or its salt described above in a sterile aqueous medium or an oily medium conventionally used for injections. As the aqueous medium for injections, there are, for e, physiological saline, an isotonic solution containing glucose and other auxiliary agents, etc., which may be used in combination with an appropriate solubilizing agent such as an alcohol (e.g., l), a polyalcohol (e.g., propylene glycol, polyethylene glycol), a nonionic surfactant [e.g., polysorbate 80, HCO-50 (polyoxyethylene (50 mol) adduct of enated castor oil)], etc. As the oily medium, there are employed, e.g., sesame oil, soybean oil, etc., which may be used in combination with a solubilizing agent such as benzyl benzoate, benzyl alcohol, etc. The injection thus prepared is preferably filled in an appropriate ampoule.

Advantageously, the pharmaceutical compositions for oral or parenteral use described above are prepared into dosage forms in a unit dose suited to fit a dose of the active ingredients. Such dosage forms in a unit dose include, for example, tablets, pills, capsules, ions (ampoules), suppositories, etc. The amount of the aforesaid antibody contained is generally about 5 to about 500 mg per dosage form in a unit dose; especially in the form of injection, it is preferred that the aforesaid antibody is contained in about 5 to about 100 mg and in about 10 to about 250 mg for the other dosage forms.

Therapeutic Uses of the Antibodies The antibodies of the description are useful, inter alia, for the treatment, prevention and/or amelioration of any disease or disorder associated with or mediated by n A expression, signaling, or activity, or treatable by blocking the interaction between Activin A and an Activin A receptor (e.g., ActRIIA, B, n Type I receptor, etc.) or otherwise inhibiting Activin A activity and/or signaling. For example, described are methods of treating ions or afflictions which can be cured, alleviated or improved by increasing muscle strength/power and/or muscle mass and/or muscle function in an dual, or by bly ng metabolism (carbohydrate, lipid and protein processing) by specifically binding Activin A and not binding other B ligands, or by specifically g Activin A and GDF8 and not binding other ActRIIB ligands. For example, the descriptionincludes methods for sing muscle strength/power and/or muscle mass and/or muscle on in a subject, or for treating a disease or disorder characterized by decreased muscle mass or strength in a subject, by administering to the subject an Activin A-specific binding protein. The descriptionalso includes methods for increasing muscle strength/power and/or muscle mass and/or muscle function in a subject, or for treating a e or disorder characterized by decreased muscle mass or strength in a subject, by administering to the subject an Activin A-specific binding protein and a GDF8-specific binding protein. Any of the n A-specific binding proteins and/or GDF8- specific binding proteins disclosed or referred to herein can be used in the context of these embodiments. For example, the therapeutic methods of the description include stering to a subject an anti-Activin A dy and/or an anti-GDF8 antibody.

Thus, in the t of the methods of treatment described herein, the anti-Activin A antibody may be administered as a monotherapy (i.e., as the only therapeutic agent) or in combination with one or more additional therapeutic agents (e.g., an anti-GDF8 antibody), further examples of which are described elsewhere herein.

In methods which comprise administering an Activin A-specific binding protein and a GDF8-specific g protein to a subject, the Activin A-specific binding protein and the GDF8- specific binding protein may be administered to the subject at the same or substantially the same time, e.g., in a single therapeutic dosage, or in two separate dosages which are administered simultaneously or within less than about 5 minutes of one another. Alternatively, the Activin A-specific binding protein and the GDF8-specific binding protein may be administered to the t sequentially, e.g., in separate therapeutic dosages separated in time from one another by more than about 5 minutes.

The description also es methods for increasing muscle strength/power and/or muscle mass and/or muscle function in a subject, or for treating a e or disorder characterized by decreased muscle mass or strength in a subject, by administering to the subject an antigen-binding molecule comprising an Activin A-specific binding domain and a GDF8-specific binding domain. Any of the antigen-binding molecules disclosed or referred to herein can be used in the context of this ment. For example, the therapeutic s of the description include administering to a subject a bispecific antibody comprising a first variable domain comprising a HCVR/LCVR pair that specifically binds Activin A and a second variable domain comprising a HCVR/LCVR pair that specifically binds GDF8.

The compositions of the description may be administered to a subject along with one or more additional therapeutic agents, including, e.g., growth factor tors, immunosuppressants, anti-inflammatory agents, metabolic inhibitors, enzyme inhibitors, and xic/cytostatic agents. The additional therapeutic agent(s) may be administered prior to, concurrent with, or after the administration of the Activin A- and GDF8-specific binding ns of the description.

Exemplary diseases, disorders and conditions that can be treated with the compositions of the descriptioninclude, but are not limited to, enia, cachexia r idiopathic or ary to other conditions, e.g., cancer, chronic renal failure, or chronic ctive pulmonary disease), muscle injury, muscle trauma, muscle wasting and muscle atrophy, e.g., muscle atrophy or wasting caused by or associated with disuse, e.g., muscular, immobilization, bed rest, injury, medical treatment or surgical intervention (e.g., hip fracture, hip replacement, knee replacement, and other joint, tendon, or ligament injuries such as tears in the anterior cruciate ligament (ACL) and/or the medial collateral ligament (MCL), etc.), muscular dystrophy (e.g., Myotonic, Duchenne, Becker, Limb-girdle, capulohumeral (FSHD, also known as Landouzy-Déjérine disease), Congenital, Oculopharyngeal, Distal, Emery-Dreifuss, etc.), orticoid-induced myopathy, stroke rehabilitation (e.g., rehabilitation for stroke hemiparesis) or by necessity of mechanical ventilation. The compositions of the description may also be used to treat, prevent or ameliorate diseases such as , obesity, diabetes, arthritis, multiple sis, muscular dystrophy, amyotrophic lateral sclerosis, Parkinson's e, osteoporosis, osteoarthritis, osteopenia, and metabolic syndromes (including, but not limited to diabetes, obesity, nutritional disorders, organ atrophy, chronic obstructive pulmonary disease, and ia). Additional es, disorders, and conditions that can be prevented, treated and/or ameliorated using compositions of the description include sepsis, c heart failure, benign and malignant pheochromocytoma, uterine fibroids/leiomyomata, preeclampsia, keloids and hypertrophic scars, and pulmonary artery hypertension.

Improved Specificity of Binding and ty The description includes methods for sing muscle strength/power and/or muscle mass and/or muscle function in a subject, or for treating a disease or disorder characterized by decreased muscle mass or strength in a subject, or for treating a disease or disorder caused by, ed by, or aggravated by Activin A activity, without causing adverse effects associated with the administration of molecules which bind multiple (e.g., 3 or more) ActRIIB ligands. In other words, methods using anti-Activin A antibodies or antigen binding proteins thereof (e.g., wherein the anti-Activin A antibody only significantly binds to n A) may treat a disease or disorder without causing unwanted or adverse effects seen with molecules which bind multiple ActRIIB ligands. For example, the clinical molecule referred to as ACE-031 (Acceleron Pharma, Inc., Cambridge, MA) is a multimer consisting of the extracellular portion of ActRIIB fused to an IgG Fc domain (this molecule is also referred to herein as "ActRIIB-Fc"). BFc binds Activin A as well as other B ligands such as, e.g., Activin B, GDF8, GDF11, BMP9, BMP10, and TGFβ, and is known to cause various adverse effects when administered to human patients. Significantly, the present inventors have unexpectedly discovered that specifically inhibiting n A and GDF8 (e.g., by administering an anti-Activin A antibody and an anti-GDF8 dy), while not inhibiting other ActRIIB ligands such as Activin B, GDF11, BMP9, BMP10, and TGFβ, results in an increase in muscle mass that is at least equivalent to that observed by administration of ActRIIB-Fc, t causing the adverse effects associated with binding agents such as ActRIIB-Fc.

Combination Therapies and Formulations The description includes compositions and therapeutic ations comprising any of the anti-Activin A antibodies described herein in combination with one or more additional therapeutically active components, and methods of ent comprising administering such ations to subjects in need thereof. The description also includes compositions and therapeutic formulations comprising any of the anti-Activin A antibodies described herein in combination with one or more additional eutically active ents, and methods of treatment comprising administering such combinations to subjects in need thereof. For example, the anti-Activin A antibodies of the description may also be administered and/or coformulated in combination with antivirals, antibiotics, analgesics, corticosteroids, steroids, oxygen, antioxidants, metal chelators, IFN-gamma, and/or NSAIDs. The anti-Activin A antibodies of the ption may also be stered as part of a treatment regimen that also es radiation treatment and/or conventional chemotherapy (e.g., in the context of methods of ng cancer or inhibiting tumor growth). Any of the aforementioned additional therapeutically active components may be administered in combination with any of the anti- Activin A antibodies of the ption for the treatment of any disease or disorder in which administration of an anti-Activin A antibody is cial, including, e.g., enia, cachexia, muscle injury, muscle wasting and muscle atrophy. Any of the aforementioned additional therapeutically active components may also be administered in combination with any of the anti-Activin A antibodies of the description along with a GDF8 inhibitor (e.g., an anti-GDF8 The additional eutically active ent(s) may be administered to a subject prior to administration of an anti-Activin A antibody of the description. For example, a first component may be deemed to be administered "prior to" a second component if the first component is administered 1 week , 72 hours before, 60 hours before, 48 hours before, 36 hours before, 24 hours before, 12 hours before, 6 hours before, 5 hours before, 4 hours before, 3 hours before, 2 hours before, 1 hour before, 30 s , 15 minutes , 10 minutes before, 5 minutes before, or less than 1 minute before administration of the second component. In other ments, the additional therapeutically active component(s) may be administered to a subject after administration of an anti-Activin A antibody of the description.

For example, a first component may be deemed to be administered " a second component if the first component is administered 1 minute after, 5 minutes after, 10 minutes after, 15 minutes after, 30 minutes after, 1 hour after, 2 hours after, 3 hours after, 4 hours after, 5 hours after, 6 hours after, 12 hours after, 24 hours after, 36 hours after, 48 hours after, 60 hours after, 72 hours after administration of the second component. In yet other embodiments, the additional therapeutically active ent(s) may be administered to a subject concurrent with administration of anti-Activin A antibody of the description. rrent" administration, for purposes of the description, includes, e.g., administration of an anti-Activin A antibody and an additional therapeutically active component to a subject in a single dosage form, or in separate dosage forms administered to the subject within about 30 minutes or less of each other. If administered in separate dosage forms, each dosage form may be administered via the same route (e.g., both the anti-Activin A antibody and the additional therapeutically active component may be administered intravenously, subcutaneously, intravitreally, etc.); alternatively, each dosage form may be administered via a different route (e.g., the anti-Activin A antibody may be administered locally (e.g., intravitreally) and the additional therapeutically active component may be stered systemically). In any event, administering the components in a single dosage from, in te dosage forms by the same route, or in separate dosage forms by different routes are all considered "concurrent administration," for purposes of the present disclosure. For purposes of the present disclosure, administration of an anti-Activin A antibody "prior to", "concurrent with," or "after" (as those terms are defined herein above) administration of an additional therapeutically active ent is considered administration of an anti-Activin A antibody "in combination with" an additional therapeutically active component).

The description includes pharmaceutical compositions in which an anti-Activin A dy of the description is co-formulated with one or more of the additional therapeutically active component(s) as described elsewhere herein.

Dosage The amount of active ingredient (e.g., anti-Activin A antibodies, anti-GDF8 antibodies given in combination with anti-Activin A dies, or bispecific antibodies that specifically bind Activin A and GDF8) that can be administered to a subject is, generally, a therapeutically effective amount. As used herein, the phrase "therapeutically effective amount" means a dose of antigen-specific binding ns and/or n-binding molecules that results in a detectable increase in one or more of the ing parameters: body weight, muscle mass (e.g., tibialis or [TA] muscle mass, gastrocnemius [GA] muscle mass, quadriceps [Quad] muscle mass, etc.), muscle strength/power, and/or muscle function. For example, a "therapeutically effective amount" of an n A-specific g protein and/or a GDF8-specific binding protein includes, e.g., an amount of Activin A-specific binding protein and/or GDF8-specific binding protein that, when administered to a test subject, causes an increase in TA or GA muscle mass of at least 2%, 5%, 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60% or more, compared to control treated subjects, e.g., as illustrated in Example 7, herein.

In the case of antibodies of the description (e.g., anti-Activin A dies, anti-GDF8 antibodies given in combination with anti-Activin A dies, or bispecific antibodies that specifically bind Activin A and GDF8), a therapeutically effective amount can be from about 0.05 mg to about 600 mg; e.g., about 0.05 mg, about 0.1 mg, about 1.0 mg, about 1.5 mg, about 2.0 mg, about 10 mg, about 20 mg, about 30 mg, about 40 mg, about 50 mg, about 60 mg, about 70 mg, about 80 mg, about 90 mg, about 100 mg, about 110 mg, about 120 mg, about 130 mg, about 140 mg, about 150 mg, about 160 mg, about 170 mg, about 180 mg, about 190 mg, about 200 mg, about 210 mg, about 220 mg, about 230 mg, about 240 mg, about 250 mg, about 260 mg, about 270 mg, about 280 mg, about 290 mg, about 300 mg, about 310 mg, about 320 mg, about 330 mg, about 340 mg, about 350 mg, about 360 mg, about 370 mg, about 380 mg, about 390 mg, about 400 mg, about 410 mg, about 420 mg, about 430 mg, about 440 mg, about 450 mg, about 460 mg, about 470 mg, about 480 mg, about 490 mg, about 500 mg, about 510 mg, about 520 mg, about 530 mg, about 540 mg, about 550 mg, about 560 mg, about 570 mg, about 580 mg, about 590 mg, about 600 mg, about 610 mg, about 620 mg, about 630 mg, about 640 mg, about 650 mg, about 660 mg, about 670 mg, about 680 mg, about 690 mg, about 700 mg, about 710 mg, about 720 mg, about 730 mg, about 740 mg, about 750 mg, about 760 mg, about 770 mg, about 780 mg, about 790 mg, about 800 mg, about 810 mg, about 820 mg, about 830 mg, about 840 mg, about 850 mg, about 860 mg, about 870 mg, about 880 mg, about 890 mg, about 900 mg, about 910 mg, about 920 mg, about 930 mg, about 940 mg, about 950 mg, about 960 mg, about 970 mg, about 980 mg, about 990 mg, or about 1000 mg, of the respective antibody.

The amount of antibody of the description (e.g., anti-Activin A antibodies, anti-GDF8 antibodies given in combination with anti-Activin A antibodies, or bispecific antibodies that ically bind Activin A and GDF8) contained within the individual doses may be sed in terms of milligrams of antibody per kilogram of patient body weight (i.e., mg/kg). For example, the anti-Activin A, anti-GDF8 and/or anti-Activin A/anti-GDF8 bispecific antibodies of the descriptionmay be administered to a patient at a dose of about 0.0001 to about 50 mg/kg of patient body weight (e.g. 0.1 mg/kg, 0.5 mg/kg, 1.0 mg/kg, 1.5 mg/kg, 2.0 mg/kg, 2.5 mg/kg, 3.0 mg/kg, 3.5 mg/kg, 4.0 mg/kg, 4.5 mg/kg, 5.0 mg/kg, 5.5 mg/kg, 6.0 mg/kg, 6.5 mg/kg, 7.0 mg/kg, 7.5 mg/kg, 8.0 mg/kg, 8.5 mg/kg, 9.0 mg/kg, 9.5 mg/kg, 10.0 mg/kg, 10.5 mg/kg, 11.0 mg/kg, 11.5 mg/kg, 12.0 mg/kg, 12.5 mg/kg, 13.0 mg/kg, 13.5 mg/kg, 14.0 mg/kg, 14.5 mg/kg, .0 mg/kg, 15.5 mg/kg, 16.0 mg/kg, 16.5 mg/kg, 17.0 mg/kg, 17.5 mg/kg, 18.0 mg/kg, 18.5 mg/kg, 19.0 mg/kg, 19.5 mg/kg, 20.0 mg/kg, etc.).

The compositions of the description may comprise equal amounts of n A-specific binding n and GDF8-specific binding protein. Alternatively, the amount of Activin A- specific binding protein in the composition may be less than or greater than the amount of GDF8-specific binding protein. A person of ordinary skill in the art, using routine experimentation, will be able to determine the riate amounts of the individual components in the compositions of the description necessary to produce a desired therapeutic effect.

Administration ns According to certain embodiments of the description, multiple doses of an active ingredient (e.g., an ctivin A antibody, an anti-GDF8 antibody administered in combination with an anti-Activin A dy, a pharmaceutical composition comprising a combination of anti- Activin A antibody and any of the additional therapeutically active agents mentioned herein, ing, e.g., an anti-GDF8 dy, or a bispecific antibody that specifically bind Activin A and GDF8) may be administered to a subject over a defined time course. The methods according to this embodiment comprise sequentially administering to a subject le doses of an active ingredient of the description. As used herein, "sequentially administering" means that each dose of an active ingredient is administered to the subject at a different point in time, e.g., on different days separated by a predetermined interval (e.g., hours, days, weeks or months).

The description includes methods which comprise sequentially administering to the patient a single initial dose of an active ingredient, followed by one or more secondary doses of the active ingredient, and optionally followed by one or more tertiary doses of the active ient.

The terms "initial dose," dary doses," and "tertiary " refer to the temporal sequence of administration of the active ingredient, e.g., ctivin A antibody of the description or of a combination therapy of the description, e.g., an anti-Activin A antibody and an anti-GDF8 antibody. Thus, the "initial dose" is the dose which is administered at the beginning of the treatment regimen (also referred to as the "baseline dose"); the "secondary doses" are the doses which are stered after the initial dose; and the "tertiary doses" are the doses which are stered after the secondary doses. The initial, ary, and ry doses may all contain the same amount of the active ingredient, e.g., anti-Activin A antibody, but generally may differ from one another in terms of frequency of administration. In certain embodiments, however, the amount of the active ingredient, e.g., anti- Activin A dy, contained in the initial, ary and/or tertiary doses varies from one another (e.g., adjusted up or down as appropriate) during the course of treatment. In certain embodiments, two or more (e.g., 2, 3, 4, or 5) doses are administered at the beginning of the treatment regimen as "loading doses" followed by subsequent doses that are administered on a less nt basis (e.g., enance doses").

In certain exemplary embodiments of the description, each secondary and/or tertiary dose is administered 1 to 26 (e.g., 1, 1½, 2, 2½, 3, 3½, 4, 4½, 5, 5½, 6, 6½, 7, 7½, 8, 8½, 9, 9½, 10, 10½, 11, 11½, 12, 12½, 13, 13½, 14, 14½, 15, 15½, 16, 16½, 17, 17½, 18, 18½, 19, 19½, 20, 20½, 21, 21½, 22, 22½, 23, 23½, 24, 24½, 25, 25½, 26, 26½, or more) weeks after the immediately preceding dose. The phrase "the immediately preceding dose," as used herein, means, in a sequence of multiple administrations, the dose of the active ingredient, e.g., an anti- Activin A dy, which is stered to a patient prior to the administration of the very next dose in the sequence with no intervening doses.

] The methods ing to this embodiment may comprise stering to a patient any number of secondary and/or tertiary doses of an active ingredient of the description, e.g., an anti- Activin A antibody. For example, in certain ments, only a single secondary dose is administered to the patient. In other embodiments, two or more (e.g., 2, 3, 4, 5, 6, 7, 8, or more) secondary doses are administered to the patient. Likewise, in certain ments, only a single tertiary dose is administered to the patient. In other embodiments, two or more (e.g., 2, 3, 4, 5, 6, 7, 8, or more) tertiary doses are administered to the patient.

In embodiments involving multiple secondary doses, each secondary dose may be administered at the same frequency as the other secondary doses. For example, each secondary dose may be administered to the patient 1 to 2 weeks or 1 to 2 months after the immediately preceding dose. Similarly, in embodiments involving multiple tertiary doses, each tertiary dose may be administered at the same frequency as the other tertiary doses. For example, each tertiary dose may be stered to the patient 2 to 12 weeks after the immediately preceding dose. In certain embodiments of the description, the frequency at which the secondary and/or tertiary doses are administered to a patient can vary over the course of the treatment regimen. The frequency of administration may also be adjusted during the course of treatment by a physician depending on the needs of the individual patient following clinical examination.

The description includes administration regimens in which 2 to 6 loading doses are administered to a t a first frequency (e.g., once a week, once every two weeks, once every three weeks, once a month, once every two months, etc.), followed by administration of two or more maintenance doses to the patient on a less frequent basis. For e, ing to this embodiment, if the loading doses are stered at a frequency of once a month, then the maintenance doses may be administered to the patient once every six weeks, once every two months, once every three months, etc.).

Diagnostic Uses of the Antibodies The ctivin A antibodies of the description may also be used to detect and/or measure Activin A, or Activin A-expressing cells in a sample, e.g., for diagnostic purposes. For example, an anti-Activin A antibody, or fragment f, may be used to diagnose a condition or disease characterized by nt expression (e.g., over-expression, under-expression, lack of expression, etc.) of n A. Exemplary diagnostic assays for Activin A may comprise, e.g., contacting a sample, obtained from a patient, with an anti-Activin A antibody of the description, wherein the anti-Activin A antibody is labeled with a detectable label or reporter molecule.

Alternatively, an led anti-Activin A antibody can be used in diagnostic applications in combination with a secondary antibody which is itself detectably labeled. The detectable label or reporter molecule can be a radioisotope, such as 3H, 14C, 32P, 35S, or 125I; a fluorescent or chemiluminescent moiety such as fluorescein isothiocyanate, or ine; or an enzyme such as alkaline phosphatase, alactosidase, horseradish peroxidase, or luciferase. Specific exemplary assays that can be used to detect or measure Activin A in a sample e enzymelinked immunosorbent assay (ELISA), radioimmunoassay (RIA), and fluorescence-activated cell sorting (FACS). s that can be used in Activin A diagnostic assays according to the description include any tissue or fluid sample obtainable from a patient which contains detectable quantities of Activin A protein, or fragments thereof, under normal or pathological conditions. Generally, levels of Activin A in a particular sample obtained from a healthy patient (e.g., a patient not afflicted with a disease or condition associated with abnormal Activin A levels or activity) will be measured to initially establish a baseline, or standard, level of Activin A. This baseline level of n A can then be ed against the levels of n A measured in samples obtained from individuals suspected of having an Activin A-related disease or condition.

EXAMPLES The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the methods and itions of the invention, and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers used (e.g., amounts, temperature, etc.) but some experimental errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, molecular weight is average molecular , temperature is in degrees Centigrade, and pressure is at or near atmospheric.

Example 1. Generation of Human Antibodies to Activin A An immunogen comprising the Activin A protein (inhibin-βA dimer) was administered directly, with an adjuvant to stimulate the immune response, to a VELOCIMMUNE® mouse comprising DNA encoding human Immunoglobulin heavy and kappa light chain variable regions. The antibody immune response was monitored by a Activin A-specific immunoassay.

When a desired immune response was achieved splenocytes were ted and fused with mouse myeloma cells to preserve their viability and form hybridoma cell lines. The oma cell lines were screened and selected to fy cell lines that produce Activin A-specific dies. Using this technique several anti-Activin A chimeric antibodies (i.e., antibodies possessing human variable domains and mouse constant domains) were obtained. An exemplary antibody obtained in this manner is H2aM10965N. The human variable domains from the chimeric antibodies were uently cloned onto human constant domains to make fully human ctivin A antibodies as described herein. ctivin A antibodies were also isolated directly from antigen-positive B cells without fusion to myeloma cells, as described in US 2007/0280945A1. Using this method, several fully human anti-Activin A antibodies (i.e., dies possessing human variable domains and human constant domains) were ed; exemplary antibodies ted in this manner were designated as follows: H4H10423P, H4H10429P, H4H10430P, H4H10432P2, H4H10440P2, H4H10442P2, 36P2, and H4H10446P2.

Certain biological properties of the exemplary anti-Activin A antibodies generated in accordance with the methods of this Example are described in detail in the Examples set forth below.

Example 2. Heavy and Light Chain Variable Region Amino Acid ces Table 1 sets forth the heavy and light chain variable region amino acid sequence pairs of ed anti-Activin A antibodies and their corresponding antibody identifiers. The corresponding nucleic acid sequence identifiers are set forth in Table 2.

Table 1: Amino Acid Sequence Identifiers SEQ ID NOs: Antibody Designation HCVR HCDR1 HCDR2 HCDR3 LCVR LCDR1 LCDR2 LCDR3 H4H10423P 2 4 6 8 10 12 14 16 H4H10424P 18 20 22 24 26 28 30 32 H4H10426P 34 36 38 40 42 44 46 48 H4H10429P 50 52 54 56 58 60 62 64 H4H10430P 66 68 70 72 74 76 78 80 H4H10432P2 82 84 86 88 90 92 94 96 33P2 98 100 102 104 90 92 94 96 H4H10436P2 106 108 110 112 90 92 94 96 H4H10437P2 114 116 118 120 90 92 94 96 H4H10438P2 122 124 126 128 90 92 94 96 H4H10440P2 130 132 134 136 90 92 94 96 H4H10442P2 138 140 142 144 146 148 150 152 H4H10445P2 154 156 158 160 146 148 150 152 H4H10446P2 162 164 166 168 146 148 150 152 H4H10447P2 170 172 174 176 146 148 150 152 H4H10448P2 178 180 182 184 146 148 150 152 H4H10452P2 186 188 190 192 146 148 150 152 H4H10468P2 194 196 198 200 146 148 150 152 H2aM10965N 202 204 206 208 210 212 214 216 Table 2: Nucleic Acid Sequence Identifiers SEQ ID NOs: Antibody Designation HCVR HCDR1 HCDR2 HCDR3 LCVR LCDR1 LCDR2 LCDR3 H4H10423P 1 3 5 7 9 11 13 15 H4H10424P 17 19 21 23 25 27 29 31 H4H10426P 33 35 37 39 41 43 45 47 H4H10429P 49 51 53 55 57 59 61 63 H4H10430P 65 67 69 71 73 75 77 79 H4H10432P2 81 83 85 87 89 91 93 95 H4H10433P2 97 99 101 103 89 91 93 95 H4H10436P2 105 107 109 111 89 91 93 95 H4H10437P2 113 115 117 119 89 91 93 95 H4H10438P2 121 123 125 127 89 91 93 95 H4H10440P2 129 131 133 135 89 91 93 95 H4H10442P2 137 139 141 143 145 147 149 151 H4H10445P2 153 155 157 159 145 147 149 151 46P2 161 163 165 167 145 147 149 151 H4H10447P2 169 171 173 175 145 147 149 151 H4H10448P2 177 179 181 183 145 147 149 151 H4H10452P2 185 187 189 191 145 147 149 151 H4H10468P2 193 195 197 199 145 147 149 151 H2aM10965N 201 203 205 207 209 211 213 215 ] Antibodies are typically referred to herein according to the ing nomenclature: Fc prefix (e.g. "H1M," "H2aM," "H4H"), ed by a numerical identifier (e.g. "10423," "10424," or "10426" as shown in Tables 1 and 2), followed by a "P," "P2" or "N" suffix. Thus, according to this lature, an antibody may be referred to herein as, e.g., " H4H10423P," " H4H10432P2," "H2aM10965N," etc. The H1M, H2M and H4H prefixes on the antibody designations used herein indicate the particular Fc region isotype of the antibody. For example, an "H2aM" antibody has a mouse IgG2a Fc, whereas an "H4H" antibody has a human IgG4 Fc.

As will be appreciated by a person of ordinary skill in the art, an antibody having a ular Fc isotype can be converted to an antibody with a different Fc isotype (e.g., an antibody with a mouse IgG2a Fc can be converted to an dy with a human IgG4, etc.), but in any event, the variable domains (including the CDRs) – which are indicated by the numerical identifiers shown in Table 1 – will remain the same, and the binding properties are expected to be identical or substantially similar regardless of the nature of the Fc domain.

Control Constructs Used in the Following Examples Anti-Activin A l molecules were included in the following Examples for comparative purposes. The l dy designated herein as Control 1 is a human anti- Activin A antibody with heavy and light chain variable domain sequences of "A1" as set forth in US 8,309,082. Control 2 is an anti-human Activin or Type II B antibody (anti-ActR2B mAb) disclosed as MOR8159 in U.S. Patent Application No. 2012/0237521 A1. l 3 is a murine anti-Activin A monoclonal antibody from R&D Systems, Minneapolis, MN (catalog number MAB3381). l 4 is an Activin Type IIB or-Fc fusion molecule (a soluble Activin RIIB receptor extracelullar domain ed with a C-terminal human IgG1 Fc fusion protein (E23-P133 of NP_001097 followed by a Gly-Ser linker followed by a C-terminal human IgG1 Fc fusion), the sequence of which is ed as SEQ ID .

Example 3. Antibody Binding to Human Activin A as Determined by Surface Plasmon Resonance Binding affinities and kinetic constants for antigen binding to selected purified anti- human Activin A monoclonal antibodies were determined using a real-time surface plasmon resonance biosensor (Biacore T200 or Biacore 4000, GE Healthcare Life Sciences, Piscataway, NJ) assay at 25°C and 37ºC. Antibodies, expressed as either mouse Fc (prefix H2aM) or human Fc (prefix H4H), were captured on their tive anti-Fc sensor surfaces (mAb capture format). Anti-Activin A antibodies were captured on either a goat anti-mouse IgG polyclonal antibody (GE Healthcare, #BR38) or a mouse anti-human IgG monoclonal antibody (GE Healthcare, #BR39) surface created through direct amine coupling to a Biacore CM5 sensor chip. Kinetic experiments were carried out using either HBS-EP (10mM HEPES, 150mM NaCl, 3mM EDTA, 0.05% Surfactant P20, at pH 7.4) or PBS-P (10mM Sodium Phosphate, 2.7mM KCl, 137mM NaCl, 0.02% NaN3, 0.05% Surfactant P20, pH 7.4), as both the running buffer and the sample buffer. Antigen-antibody association rates were ed by injecting various concentrations (4-fold dilutions ranging from 50 to 0.2 nM) of either Activin A (R&D s, # 338-AC-050/CF), Activin B (R&D Systems, # 659-AB-025/CF), Activin AB (R&D Systems, # 1006-AB-005), Activin AC (R&D Systems, # 4879-AC/CF), or n E (Novus icals, 3729-P01) over the captured antibody surface. Antibody-antigen association was red for 240 seconds while dissociation in buffer was monitored for 600 seconds. Kinetic ation and dissociation rate constants were determined by processing and g the data using Scrubber software version 2.0c. g equilibrium dissociation constants (KD) and dissociative half-lives (t1/2) were then calculated from the kinetic rate constants as: KD (M) = kd / ka and t½ (min) = [ln2/(60*kd)]. Kinetic binding parameters for different anti-Activin A monoclonal antibodies are shown in Tables 3 to 10. (NB = no binding observed under the conditions used; NT = not tested).

Table 3: Binding Characteristics of Anti-Activin A Antibodies to Activin A at 25ºC Amount of Activin mAb ACaptured Antibody (RU ± SE) (RU) ka (M-1s-1) kd (s-1) KD (Molar) t1/2 (min) H4H10423P 86.2 ± 0.7 19.4 3.33E+06 1.09E-04 3.26E-11 106.4 H4H10424P 337 82 3.14E+06 04 2.29E-10 16 H4H10426P 81 23 1.18E+07 7.00E-04 5.95E-11 16 H4H10429P 115.2 ± 1 24.9 7.82E+06 6.39E-05 8.17E-12 180.8 H4H10430P 90.3 ± 4.2 19.4 07 1.67E-04 3.52E-12 69 H4H10432P2 109.6 ± 1.2 20.7 1.57E+07 5.00E-05 ≤ 3.18E-12 ≥231 H4H10433P2 102 16 1.42E+07 5.77E-04 4.06E-11 20 H4H10436P2 113.6 ± 0.6 23.2 8.85E+06 1.68E-04 1.90E-11 68.7 H4H10437P2 167 30 1.58E+07 2.13E-03 10 5 H4H10438P2 124 25 1.20E+07 5.88E-04 4.92E-11 20 H4H10440P2 79.2 ± 0.7 12.9 3.76E+06 9.28E-05 2.47E-11 124.5 H4H10442P2 139.3 ± 1 31.3 1.10E+07 5.00E-05 ≤ 4.55E-12 ≥231 H4H10445P2 149 43 2.40E+06 5.00E-05 ≤ 2.08E-11 ≥231 H4H10446P2 104.6 ± 0.7 24.1 1.29E+07 5.00E-05 ≤ 12 ≥231 H4H10447P2 164 43 2.36E+06 5.00E-05 ≤ 2.12E-11 ≥231 H4H10448P2 244 64 4.76E+06 5.00E-05 ≤ 11 ≥231 H4H10452P2 191 55 4.69E+06 5.00E-05 ≤ 1.07E-11 ≥231 H4H10468P2 93 ± 0.1 21.7 7.86E+06 5.00E-05 ≤ 12 ≥231 H2aM10965N 393 76 1.48E+06 1.10E-03 7.45E-10 10 Control 1 84.7 ± 0.3 15.9 7.26E+06 9.92E-05 1.37E-11 116.4 For kd values that are italicized, no dissociation of the analyte was observed under these experimental conditions, and the value of kd was ore fixed at 5.0E-05 s-1 Table 4: Binding Characteristics of Anti-Activin A dies to to Activin A at 37ºC Amount of Activin mAb ACaptured 20nM t1/2 Antibody (RU ± SE) (RU) ka (M-1s-1) kd (s-1) KD (Molar) (min) H4H10423P 101 ± 1.4 25.2 3.95E+06 5.00E-05 -11 ≥231 H4H10424P 231 58 4.59E+06 3.64E-03 7.94E-10 3 H4H10426P 71 21 1.61E+07 1.98E-03 1.23E-10 6 H4H10429P 150.8 ± 5.3 31.4 07 5.00E-05 ≤3.75E-12 ≥231 H4H10430P 109.3 ± 1.3 25.0 07 1.51E-04 3.97E-12 76.5 H4H10432P2 141.8 ± 1.6 25.1 2.30E+07 5.00E-05 ≤2.18E-12 ≥231 H4H10433P2 85 12 2.00E+07 1.07E-03 5.37E-11 11 H4H10436P2 139.8 ± 1.4 29.4 1.49E+07 5.00E-05 -12 ≥231 H4H10437P2 115 20 2.04E+07 4.68E-03 2.29E-10 2 H4H10438P2 99 18 07 03 1.27E-10 5 H4H10440P2 98.6 ± 1.1 15.3 6.37E+06 3.28E-04 5.15E-11 35.2 H4H10442P2 181 ± 2.5 40.5 1.44E+07 5.00E-05 ≤3.48E-12 ≥231 H4H10445P2 120 36 4.33E+06 05 ≤ 1.15E-11 ≥231 H4H10446P2 137.2 ± 1.7 31.5 1.54E+07 5.00E-05 ≤ 3.25E-12 ≥231 H4H10447P2 126 36 4.69E+06 5.00E-05 ≤ 1.07E-11 ≥231 H4H10448P2 175 49 7.86E+06 5.00E-05 ≤ 6.36E-12 ≥231 H4H10452P2 146 43 7.94E+06 5.00E-05 ≤ 6.30E-12 ≥231 H4H10468P2 98.7 ± 0.7 24.5 07 5.00E-05 ≤ 12 ≥231 H2aM10965N 435 80 2.35E+06 4.15E-03 1.77E-09 3 Control 1 93.9 ± 0.7 18.0 8.99E+06 5.00E-05 ≤ 5.56E-12 ≥231 For kd values that are italicized, no dissociation of the analyte was observed under these mental conditions, and the value of kd was therefore fixed at 5.0E-05 s-1 Table 5: Binding Characteristics of Anti-Activin A Antibodies to Activin B at 25ºC Amount of 50nM mAb Ag Captured Bound Antibody (RU ± SE) (RU) ka (M-1s-1) kd (s-1) KD ) t1/2 (min) H4H10423P 83.1 ± 0.6 4.7 4.89E+05 3.02E-02 08 0.4 H4H10429P 112.3 ± 0.7 26.4 3.49E+06 1.31E-02 3.75E-09 0.9 H4H10432P2 104.4 ± 1.8 5.1 NB NB NB NB H4H10436P2 110.8 ± 3.9 32.8 9.52E+06 5.28E-04 5.54E-11 21.9 H4H10440P2 75.7 ± 0.8 18.8 1.06E+06 1.16E-03 1.09E-09 10.0 H4H10442P2 136 ± 0.7 3.4 NB NB NB NB H4H10430P 88 ± 0.5 3.9 NB NB NB NB H4H10446P2 101.5 ± 0.4 3.6 NB NB NB NB H4H10468P2 92.5 ± 0.2 6.2 NB NB NB NB Control 1 84.1 ± 0.3 6.4 NB NB NB NB Table 6: g Characteristics of Anti-Activin A Antibodies to Activin B at 37ºC Amount of 50nM mAb Ag Captured Bound Antibody (RU ± SE) (RU) ka (M-1s-1) kd (s-1) KD ) t1/2 (min) H4H10423P 96 ± 1.2 4.4 NB NB NB NB H4H10429P 142.8 ± 1.3 25.3 3.43E+06 3.43E-02 9.98E-09 0.3 H4H10432P2 134.1 ± 1.7 5.1 NB NB NB NB H4H10436P2 132 ± 1.4 38.1 9.78E+06 1.36E-03 1.39E-10 8.5 H4H10440P2 94 ± 4.5 20.9 1.28E+06 4.19E-03 3.29E-09 2.8 H4H10442P2 173.1 ± 1.4 4.4 NB NB NB NB H4H10430P 105.8 ± 1.3 3.6 NB NB NB NB H4H10446P2 131.4 ± 1.2 3.8 NB NB NB NB H4H10468P2 95.5 ± 1 3.4 NB NB NB NB l 1 90.2 ± 0.9 2.7 NB NB NB NB Table 7: Binding Characteristics of Anti-Activin A Antibodies to n AB at 25ºC Amount of 50nM mAb Ag ed Bound Antibody (RU ± SE) (RU) ka 1) kd (s-1) KD ) t1/2 (min) H4H10423P 81.3 ± 0.5 14.7 6.13E+05 2.03E-02 3.31E-08 0.6 H4H10429P 110.7 ± 0.5 40.0 4.53E+06 04 2.28E-11 111.7 H4H10432P2 101.2 ± 1.6 38.3 4.00E+06 2.27E-03 5.68E-10 5.1 H4H10436P2 107.5 ± 0.3 28.2 7.66E+06 2.61E-04 3.41E-11 44.2 H4H10440P2 73.7 ± 0.4 15.5 2.97E+06 5.26E-04 1.77E-10 22.0 42P2 133.3 ± 0.6 34.6 5.53E+06 1.77E-03 3.20E-10 6.5 H4H10430P 86.9 ± 0.5 33.0 1.17E+07 2.17E-04 1.85E-11 53.3 H4H10446P2 99.8 ± 0.4 31.9 4.99E+06 4.06E-03 8.15E-10 2.8 H4H10468P2 92.1 ± 0.2 34.7 3.76E+06 2.09E-03 5.56E-10 5.5 Control 1 83.5 ± 0.6 31.1 3.44E+06 2.83E-04 8.22E-11 40.9 Table 8: Binding Characteristics of Anti-Activin A dies to Activin AB at 37ºC Amount of 50nM mAb Ag Captured Bound Antibody (RU ± SE) (RU) ka (M-1s-1) kd (s-1) KD (Molar) t1/2 (min) H4H10423P 90.8 ± 1.2 21.7 8.80E+05 2.13E-02 08 0.5 H4H10429P 137.7 ± 1.2 50.0 6.47E+06 4.88E-04 7.55E-11 23.6 H4H10432P2 127.7 ± 1.3 44.4 5.40E+06 5.92E-03 1.10E-09 2.0 36P2 126.8 ± 0.8 33.9 1.03E+07 4.58E-04 4.43E-11 25.2 H4H10440P2 88.9 ± 1.7 17.7 5.20E+06 1.63E-03 3.14E-10 7.1 H4H10442P2 166.5 ± 1.7 45.9 9.17E+06 4.25E-03 4.64E-10 2.7 H4H10430P 101.6 ± 1.2 41.0 1.01E+07 5.41E-04 5.35E-11 21.3 46P2 126.6 ± 1.2 41.5 6.08E+06 8.17E-03 1.34E-09 1.4 H4H10468P2 92.2 ± 0.8 34.5 5.03E+06 4.43E-03 8.80E-10 2.6 Control 1 86.4 ± 0.6 29.3 06 7.38E-04 1.96E-10 15.7 Table 9: Binding Characteristics of Anti-Activin A Antibodies to Activin AC at 25ºC Amount of 50nM mAb Ag Captured Bound dy (RU ± SE) (RU) ka (M-1s-1) kd (s-1) KD (Molar) t1/2 (min) H4H10423P 79.9 ± 0.4 -0.8 NB NB NB NB H4H10429P 108.9 ± 0.5 28.0 9.13E+05 05 9.97E-11 126.9 H4H10432P2 101.6 ± 0.7 34.9 6.29E+05 1.87E-03 2.98E-09 6.2 H4H10436P2 106.7 ± 0.4 30.1 6.98E+05 1.56E-03 2.24E-09 7.4 H4H10440P2 73.5 ± 0.4 11.8 5.13E+05 2.27E-04 4.42E-10 50.8 H4H10442P2 132.5 ± 3.1 18.6 1.31E+06 2.05E-03 1.57E-09 5.6 30P 85.1 ± 0.3 23.6 1.23E+06 1.09E-02 8.86E-09 1.1 H4H10446P2 96.9 ± 0.5 12.6 1.04E+06 1.22E-02 1.18E-08 0.9 H4H10468P2 91.4 ± 0.3 17.2 7.98E+05 5.92E-03 7.41E-09 2.0 Control 1 82.5 ± 0.3 22.3 5.58E+05 2.25E-03 4.03E-09 5.1 Table 10: Binding Characteristics of Anti-Activin A Antibodies to Activin AC at 37ºC Amount of 50nM mAb Ag Captured Bound dy (RU ± SE) (RU) ka (M-1s-1) kd (s-1) KD (Molar) t1/2 (min) H4H10423P 85.9 ± 1.1 0.0 NB NB NB NB H4H10429P 132.6 ± 1.2 35.7 1.34E+06 6.20E-04 4.62E-10 18.6 H4H10432P2 123.8 ± 1.4 34.6 7.22E+05 9.02E-03 1.25E-08 1.3 H4H10436P2 122.9 ± 1.3 32.6 8.81E+05 3.31E-03 3.75E-09 3.5 H4H10440P2 86.6 ± 2.7 13.3 7.18E+05 04 1.05E-09 15.3 H4H10442P2 160.1 ± 1.5 21.4 1.46E+06 5.99E-03 4.10E-09 1.9 H4H10430P 96.8 ± 1 25.3 1.20E+06 2.00E-02 1.67E-08 0.6 46P2 120.3 ± 1 14.4 05 2.16E-02 2.25E-08 0.5 68P2 88.4 ± 0.8 10.7 7.19E+05 1.24E-02 1.73E-08 0.9 Control 1 83.2 ± 0.9 15.6 6.51E+05 6.52E-03 1.00E-08 1.8 As shown in Tables 3 and 4, anti-Activin A antibodies of the description bound to Activin A with KD values ranging from less than 3.18pM (i.e., ≤ 3.18E-12) to 745pM (i.e., 7.45E- ) at 25ºC and with KD values ranging from less than 2.18pM (i.e., ≤ 2.18E-12) to 1.77nM (1.77E-09) at 37ºC. As shown in Tables 5 and 6, several of the anti-Activin A antibodies (i.e., H4H10432P2, H4H10442P2, H4H10430P2, H4H10446P2, and H4H10468P2) demonstrated no measurable binding to Activin B at 25ºC or 37ºC. Some of the antibodies demonstrated able g to Activin AB with KD values ranging from approximately 18.5pM (i.e., 1.85E-11) to 33.1 nM (i.e., 08) at 25ºC (Table 7) and from approximately 44.3pM (i.e., 11) to 24.2nM (i.e., 2.42E-08) at 37ºC (Table 8). Some of the antibodies demonstrated measurable binding to Activin AC with KD values ranging from approximately 99.7pM (i.e., 9.97E-11) to 11.8 nM (i.e., 1.18E-08) at 25ºC (Table 9) and from approximately 462pM (i.e., 4.62E-10) to 22.5nM (i.e., 2.25E-08) at 37ºC (Table 10). Furthermore, none of the tested anti- n A antibodies of the description demonstrated measurable binding to Inhibin E (data not shown).

Example 4. Antibody Binding to ta family members as Determined by Surface Plasmon Resonance n A mAbs were tested for binding cross-reactivity to a panel of TGF-beta family members. For the binding experiment, a Biacore 4000 instrument was used. The antibodies H4H10429P, H4H10430P, H4H10436P2, H4H10442P2, H4H10446P2; Control 4 (the ActR2B soluble ecto domain protein produced with a C-terminal human IgG1 Fc tag (ActR2B-hFc; SEQ ID NO:227)); and an isotype control antibody were captured on a Biacore CM4 biosensor chip that was first derivatized by amine coupling with a monoclonal mouse anti-human Fc dy (GE, Catalog# BR39). All Biacore binding s were performed in HBS-T running buffer (0.01 M HEPES pH 7.4, 0.5 M NaCl, 3 mM EDTA, 0.5mg/ml bovine serum albumin, 0.05% v/v Surfactant P20). Human TGF-beta family member ligands were purchased from R&D systems (Activin A, #338-AC; Activin B, #659-AB; Activin AB, AB; Activin AC, AC; BPM2, #355-BM; hBMP4, #314-BP; hBMP6, #507-BP; hBMP7, #354-BP; hBMP9, #3209-BP; hBMP10, #2926-BP; hGDF8, #788-G8; hGDF11, #1958-GD). All binding measurements were performed at 37°C. e levels ranging from 60 - 200 resonance units (RUs) were obtained for each of the antibodies or the soluble receptor. Over the captured antibody surface was injected the TGF-beta family ligands through concentrations g from 3.1nM to 200nM. g values for the 200nM analyte injections are shown in Table 11.

Table 11: Binding of anti-Activin A monoclonal antibodies to human TGF-β family ligands at 37°C Binding response (resonance units) for 200nM of TGF-beta family ligand injected over captured antibody sensor surface TGF-beta tro l) family ligand tested H4H10429P H4H10430P H4H10436P2 H4H10442P2 H4H10446P2 H4H8925C Control 4 (ActR2B-hFc) sitive Co n (P o Isotype l mAb Activin A 56.8 69.1 56.5 63.9 53.2 67.6 70.9 -0.1 Activin B 51.5 0.4 60.1 -1.8 2.6 0.3 68.0 1.9 Activin AB 76.5 95.0 54.3 65.2 66.7 102.0 59.5 -0.1 Activin AC 43.1 34.8 55.6 14.2 15.2 32.5 59.4 -0.1 hBMP2 3.6 -1.7 14.9 -2.3 3.3 -4.0 36.9 -1.0 hBMP4 1.1 -0.6 19.3 -0.7 0.8 -0.5 26.4 0.4 hBMP6 4.6 5.7 4.0 1.1 5.3 4.8 86.3 5.1 hBMP7 9.2 6.4 13.6 1.5 5.7 4.5 64.2 4.3 hBMP9 33.4 -0.6 11.7 0.0 -0.3 -0.1 32.3 -1.0 hBMP10 32.4 0.3 22.5 -0.7 0.5 0.0 34.2 0.3 GDF8 -0.4 -0.1 -0.5 0.5 0.7 -0.1 25.8 0.5 GDF11 1.6 3.0 0.0 1.0 1.8 3.3 24.2 3.0 The observed binding responses of the captured n A antibodies to the injected TGF-beta family ligands at 200nM could be compared to the g responses of a negative control antibody (Isotype Control mAb), which provides a measure of background-level nonspecific binding, and to the binding responses of ActR2B-hFc, which was observed to bind to the entire panel of TGF-beta family members tested and therefore serves as a positive control ligand-binding protein (Table 11). From this ison, it was found that several of the antibodies (e.g., 30, H4H10442, H4H20446) bound to Activin A, Activin AB, n AC but not appreciably to Activin B or to the BMP or GDF ligands. It was also found that some of the antibodies bound with r cross-reactivity to additional TGF-beta family ligands. For example, 29P bound appreciably to Activin A, n B, Activin AB, Activin AC and also to BMP9 and BMP10. H4H10436P2 showed appreciable binding to Activin A, n B, Activin AB, Activin AC, BMP2, BMP4, BMP7, BMP9, and BMP10. From these data it is shown that antibodies with different binding specificities to TGF-beta family ligands can be obtained after immunizing mice with the Activin A ligand.

Example 5. Cross-Competition Analysis of anti-Activin A Antibodies A cross-competition assay was conducted to assess the ability of a panel of 9 antibodies (H4H10446P2, H4H10468P2, H4H10442P2, H4H10423P, H4H10430P, H4H10429P, H4H10432P2, H4H10436P2 and H4H10440P2) to compete with one r for g to human n A. Two isotype control antibodies and two control Activin A dies, Control 1 (a human anti-Activin A antibody with heavy and light chain variable domain sequences of "A1" as set forth in US 8,309,082) and Control 3 (MAB3381, available from R&D Systems, Inc., Minneapolis, MN) were also ed in the assays. All assays were performed at 25°C with a microtiter plate shaking rate of 1000 rpm in Octet HBST buffer (0.01 M HEPES pH7.4, 0.15M NaCl, 3 mM EDTA, 0.05% v/v tant P20, 0.1mg/mL BSA) according to manufacturer's instructions (ForteBio Corp., Menlo Park, CA). Briefly, an amount of anti-Activin A antibody giving a binding resopnse of approximately 1.8nm was captured onto anti-human Fc antibody coated Octet sensor tips (Fortebio, # 18-0015) by dipping the tips for 5 minutes in a 10µg/mL solutions of each anti-Activin A antibody. Any remaining Fc g sites on the tips were blocked by incubating the tips in a 50ug/mL solution of irrelevant antibody for 5 minutes. Sensor tips were then submerged into wells containing a solution of 50nM n A (R&D Systems, # 338-AC/CF) pre-bound with 1μM of a second anti-Activin A antibody. Binding of the second Activin A antibody / Activin A solution to the Activin A antibody coated sensor tip was monitored for 5 minutes at 1000 rpm. The response of the mAb/Activin A complex binding to the ctivin A coated sensor tip was compared and competitive/noncompetitive behavior of different anti-Activin A onal antibodies was determined. Results are illustrated in Figure 1.

In Figure 1, competitive binding responses are shown in black or light gray g and indicate that the ponding antibody pairs compete with one another for binding to n A. Light gray boxes with black font represent binding response for self-competition between the same antibodies. Black boxes with white font represent antibodies that compete for Activin A binding in both directions, independent of the order of binding. Dark grey boxes with black font represent readings for isotype control (i.e., non-binding) antibodies, indicating a lack of binding of isotype control antibodies to anti-Activin A antibody-Activin A complexes (when isotype control antibodies are bound to the Octet sensor tip) or the lack of binding of isotype control antibodies to Activin A (when isotype control dies are used as the second antibody in wells with Activin A). . White boxes with black font represent no competition between antibodies, which suggests the dies have distinct binding epitopes on Activin A.

Four antibodies, H4H10446P2, H4H10468P2, H4H10442P2, and H4H10423P, bi- ionally compete with each other for g to Activin A. Additionally, these four antibodies do not compete with Control 1 or Control 3 for binding. Three of these four Activin A antibodies, H4H10446P2, H4H10468P2, and H4H10442P2, do not cross compete with any other Activin A dies. One of the four antibodies (H4H10423P) also bidirectionally competes with H4H10430P for binding to Activin A. Five antibodies, H4H10430P, H4H10429, H4H10432P2, H4H10436P2, and H4H10440P2, bi-directionally compete with each other for binding to Activin A, as well as with Control 1 and Control 3. Four of these five antibodies (i.e., 29, H4H10432P2, H4H10436P2, and H4H10440P2) do not cross compete with any other Activin A antibodies, whereas H4H10423P also cross-competes with H4H10430P, as noted above.

The results of this Example indicate that the anti-Activin A antibodies of the description can be grouped into two distinct "bins" based on epitope binding characteristics: Bin 1 includes H4H10423P, H4H10446P2, H4H10468P2 and H4H10442P2. Bin 2 includes H4H10429, H4H1430P, 32P2, H4H10436P2, and H4H10440P2. Further, one antibody from each bin, i.e., H4H10423P and 0P, cross-compete with each other. The results of this Example suggest that the antibodies of Bin 1 bind to distinct regions on Activin A than the antibodies of Bin 2.

Example 6. Inhibition of Activin A-Mediated Receptor Activation and SMAD Complex Signaling with Anti-Activin A Antibodies To further characterize anti-Activin A antibodies of the description, a bioassay was developed to detect the activation of the activin Type IIA and IIB receptors (ActRIIA and ActRIIB, respectively) and the subsequent phosphorylation and activation of an Activin Type I receptor. The ction between ActRIIA and ActRIIB and activin leads to the induction of diverse cellular ses including growth regulation, metastatis of cancer cells and entiation of nic stem cells (Tsuchida, K. et al., Cell Commun Signal 7:15 (2009)).

Phosphorylation and activation of the Type I receptor leads to phosphorylation of SMAD 2 and 3 proteins which form activated SMAD complexes leading to transcriptional regulation of genes.

To detect the tion of the SMAD complex signal transduction pathway via activin binding to activin Type II receptors, a human A204 rhabdomyosarcoma cell line (ATCC, # HTB- 82) was transfected with a Smad 2/3-luciferase reporter plasmid (CAGAx12-Luc; Dennler, 1998) to create the A204/CAGAx12-Luc cell line. A204/CAGAx12-Luc cells were ined in McCoy’s 5A (Irvine ific, # 9090) supplemented with 10% fetal bovine serum (FBS), llin/streptomycin/glutamine and 250 µg/mL of G418. For the bioassay, A204/CAGAx12- Luc cells were seeded onto 96-well assay plates at 10,000 cells/well in low serum media, 0.5%FBS and OPTIMEM (Invitrogen, #31985-070), and incubated at 37°C and 5% CO2 overnight. To determine the ligand dose response, Activin A (R&D Systems, #338-AC), n B (R&D Systems, #659-AB), Activin AB (R&D Systems, #1066-AB) and Activin AC (R&D Systems, #4879-AC/CF) were ly diluted at 1:3 from 100 to M and added to cells starting along with a control containing no Activin. Activin A, Activin B, Activin AB, and Activin AC were observed to activate the A204/CAGAx12-Luc cell line with EC50 values of 99pM, 47pM, 19pM, and 4.4nM, respectively. To measure inhibition, dies were serially diluted at 1:3 starting from 100 to 0.002nM, 1000 to 0.02nM, or 300 to 0.005nM including control samples containing either an appropriate isotype control antibody or no antibody and added to cells with a constant concentration of 100pM Activin A, 50pM Activin B, 30pM Activin AB or 4nM Activin AC. Also used as a positive blocking control in this assay was Control 4 (ActRIIB-hFc; SEQ ID No:227). After 5.5 hours of incubation in 37°C and 5% CO2, OneGlo substrate (Promega, # E6051) was added and then luciferase activity was detected using a Victor X (Perkin Elmer) instrument. The results were analyzed using nonlinear regression ameter logistics) with Prism 5 software (GraphPad).

As shown in Table 12, anti-Activin A antibodies of the description d 100pM of Activin A with IC50 values ranging from 39pM to 3.5nM, while Control 1 blocked with an IC50 value of 83pM. A subset of the anti-Activin A antibodies of the description were tested for ng Activin B, AB, and AC. Four of the 9 dies tested blocked 50pM of Activin B with IC50 values ranging from 130pM to 100nM. Five antibodies of the description that were tested for Activin B blockade only blocked at high antibody concentrations, while l 1 did not show any measurable n B blockade. Eight antibodies of the description tested blocked 30pM of Activin AB with IC50 values ranging from 100pM to 8.2nM, while Control 4 blocked with an IC50 value of 540pM. One dy, H4H10423P, only demonstrated weak blockade of Activin AB. Seven of the 8 antibodies tested blocked 4nM of n AC with IC50 values ranging from 580pM to 6.5nM, while Control 4 blocked with an IC50 value of 1.1nM. One dy, H4H10423P, did not demonstrate any blockade of Activin AC. Both mouse IgG (mIgG isotype control) and human IgG (hIgG isotype control) negative controls did not block ligand activation of the receptors.

Table 12: Inhibition of Activin A, n B, n AB, and Activin AC by anti-Activin A antibodies (IC50 [M]) Constant: Activin A Activin B Activin AB Activin AC Antibody H4H10423P 2.0E-10 Weak Blocker Non-Blocker H4H10424P 7.6E-10 H4H10426P 2.3E-10 29P 1.6E-10 7.9E-08 2.9E-10 5.8E-10 H4H10430P 6.1E-11 Block at High Conc. 1.0E-10 9.3E-10 32P2 1.1E-10 Block at High Conc. 8.0E-10 9 H4H10433P2 1.5E-10 1.0E-07 H4H10436P2 0 1.3E-10 1.4E-10 1.3E-09 H4H10437P2 2.9E-10 Block at High Conc.

H4H10438P2 2.6E-10 H4H10440P2 2.8E-10 5.2E-09 4.3E-10 7.5E-10 H4H10442P2 5.6E-11 2.2E-09 6.5E-09 H4H10445P2 5.3E-11 H4H10446P2 4.7E-11 Block at High Conc. 8.2E-09 5.6E-09 H4H10447P2 7.8E-11 H4H10448P2 4.6E-11 H4H10452P2 1 H4H10468P2 3.9E-11 Block at High Conc. 2.3E-09 3.4E-09 H2aM10965N 3.5E-09 mIgG isotype Non-Blocker control hIgG isotype ocker Non-Blocker Non-Blocker Non-Blocker control Control 1 8.3E-11 Non-Blocker 5.4E-10 1.1E-09 . The bioassay using A204/CAGAx12-Luc cells could also be stimulated by GDF8 (R&D s, Cat # 788-G8/CF) and GDF11 (R&D Systems, Cat # 1958-GD-010/CF). To test for functional inhibition of these ligands with activin A antibodies, the assay was performed using conditions described above but substituting GDF8 or GDF11 for the activating ligand, which resulted in EC50 values of 188 pM and 84 pM, respectively. In this assay, activation by a nt tration of 0.50 nM GDF8 or 0.40 nM GDF11 was completely blocked by Control 4 with IC50 values of 298pM and 214pM, respectively. Using these same constant concentrations of s, no inhibition of either GDF8 or GDF11 was observed by the activin A antibodies, H4H10446P2 and H4H10430P, when tested at up to 100nM of the antibodies. On a separate day, the activin A antibodies H4H10429P and H4H10436P2 were tested for inhibition in this assay in the presence of constant concentrations of 250pM GDF8 or 250 pM GDF11, and no inhibition was observed after incubation of the cells with up to 150 nM of the tested n A antibodies; GDF8 and GDF11 alone in this assay exhibited EC50 values of 124pM and 166pM, respectively. These data demonstrate that the Activin A antibodies H4H10446P2, H4H10430P, H4H10429P and H4H10436P2 do not functionally t GDF8 or GDF11. e 7. Stimulation of Skeletal Muscle rophy using Activin A dies Skeletal muscle hypertrophy induced by administration of a myostatin-specific antagonist, the anti-GDF8 antibody H4H1657N2 (see US 2011-0293630 A1), or a combination of H4H1657N2 and different anti-Activin A antibodies, was evaluated in CB17 SCID mice. The extent of hypertrophy was measured ve to treatment with an e-matched control antibody. Also included in these studies was treatment with the extracellular domain of human ActRIIB, produced with a C-terminal human IgG1 Fc domain (Control 4, SEQ ID No: 227).

Control 4 has been previously shown to induce muscle hypertrophy in vivo and also to bind and block the ty of multiple TGF-beta family member ligands , TA et al. Mol Endocrinol 22:2689-702 (2008); Lee, SJ et al. Proc Natl Acad Sci U.S.A. 102(50):18117-22 (2005)).

A total of eight anti-Activin A antibodies of the description and Control 1 were tested in combination with H4H1657N2 or alone in eight studies, in comparison to isotype control, Control 4, H4H1657N2 alone, or Control 2 (an anti-Activin RIIB antibody having VH/VL of the antibody MOR08159 described in US 2010/0272734 A1) treatment groups. For the studies, male CB17 SCID mice ic, #CB17SC-M) of approximately 10 weeks of age were divided evenly according to body weight into 6 groups of 5 mice. Groups of mice were treated in each study as described in Table 13.

Table 13: Antibodies and controls tested in in vivo muscle hypertrophy s Study Dosing interval of Dosing interval of # Samples Tested Dosage 1 dosage 1 Dosage 2 dosage 2 Isotype Control 10mg/kg days 0, 3, and 7 8mg/kg day 14 H4H1657N2 10mg/kg days 0, 3, and 7 8mg/kg day 14 Control 4 10mg/kg days 0, 3, and 7 8mg/kg day 14 H4H10423P+H4H1657N2 10mg/kg+10mg/kg days 0, 3, and 7 8mg/kg+8mg/kg day 14 H4H10432P2+H4H1657N2 10mg/kg+10mg/kg days 0, 3, and 7 8mg/kg+8mg/kg day 14 H4H10442P2+H4H1657N2 10mg/kg+10mg/kg days 0, 3, and 7 8mg/kg+8mg/kg day 14 Isotype Control 10mg/kg days 0, 3, and 7 8mg/kg day 14 H4H1657N2 10mg/kg days 0, 3, and 7 8mg/kg day 14 Control 4 10mg/kg days 0, 3, and 7 8mg/kg day 14 H4H10429P+H4H1657N2 10mg/kg+10mg/kg days 0, 3, and 7 8mg/kg+8mg/kg day 14 H4H10436P2+H4H1657N2 10mg/kg+10mg/kg days 0, 3, and 7 8mg/kg+8mg/kg day 14 H4H10440P2+H4H1657N2 10mg/kg+10mg/kg days 0, 3, and 7 +8mg/kg day 14 Isotype Control 10mg/kg days 0, 3, 7, and 14 H4H1657N2 10mg/kg days 0, 3, 7, and 14 3 Control 4 g days 0, 3, 7, and 14 N/A H4H10446P2+H4H1657N2 10mg/kg+10mg/kg days 0, 3, 7, and 14 H4H10430P+H4H1657N2 10mg/kg+10mg/kg days 0, 3, 7, and 14 Isotype l 25mg/kg days 0, 3, 7, and 14 H4H1657N2 10mg/kg days 0, 3, 7, and 14 30P 10mg/kg days 0, 3, 7, and 14 4 N/A H4H10430P+H4H1657N2 2mg/kg+10mg/kg days 0, 3, 7, and 14 H4H10430P+H4H1657N2 10mg/kg+10mg/kg days 0, 3, 7, and 14 H4H10430P+H4H1657N2 25mg/kg+10mg/kg days 0, 3, 7, and 14 e Control 25mg/kg days 0, 3, 7, and 14 7N2 10mg/kg days 0, 3, 7, and 14 H4H10446P2 10mg/kg days 0, 3, 7, and 14 N/A H4H10446P2+H4H1657N2 +10mg/kg days 0, 3, 7, and 14 H4H10446P2+H4H1657N2 g+10mg/kg days 0, 3, 7, and 14 46P2+H4H1657N2 25mg/kg+10mg/kg days 0, 3, 7, and 14 days 0, 3, 7, 14, and N/A Isotype Control 10mg/kg 21 days 0, 3, 7, 14, and H4H1657N2 10mg/kg 21 days 0, 3, 7, 14, and Control 4 10mg/kg 21 days 0, 3, 7, 14, and Control 1 10mg/kg 21 days 0, 3, 7, 14, and Control 1+H4H1657N2 10mg/kg+10mg/kg 21 Isotype Control 10mg/kg days 0, 3, 7, and 14 Control 4 10mg/kg days 0, 3, 7, and 14 7 Control 2 25mg/kg days 0, 3, 7, and 14 N/A H4H10430P+H4H1657N2 10mg/kg+10mg/kg days 0, 3, 7, and 14 H4H10446P2+H4H1657N2 10mg/kg+10mg/kg days 0, 3, 7, and 14 Isotype Control 25mg/kg days 0, 3, 7, and 14 H4H1657N2 10mg/kg days 0, 3, 7, and 14 Control 4 g days 0, 3, 7, and 14 8 N/A Control 2 g days 0, 3, 7, and 14 H4H10423P+H4H1657N2 25mg/kg+10mg/kg days 0, 3, 7, and 14 H4H10430P+H4H1657N2 25mg/kg+10mg/kg days 0, 3, 7, and 14 For studies 1-5, 7, and 8, antibodies and Control 4 were administered subcutaneously at a dose of 10 mg/kg of each protein twice during the first week of the experiment (days 0 and 3) and once at a dose of 10 mg/kg of each protein during the second week (day 7). A final dose of antibody or Control 4 during the third week (day 14) was administered subcutaneously at 8mg/kg for studies #1 and #2 or at 10mg/kg for s #3 - #8 (Table 13). On day 21, mice were euthanized and total body weight for each mouse was measured. For study 6, antibodies were administered for previous studies 1-5 but the treatment was extended to day 28 with an additional injection at day 21. The tibialis anterior (TA) and gastrocnemius (GA) muscles from each mouse were dissected and weighed. Tissue weights were normalized to the starting body weight, and the mean percent change in weight over the mean weight of the isotype l antibody treatment group was calculated. Results summarized in Tables 14-21 are expressed as mean percent increase over isotype control ± standard error of the mean.

Table 14: Percent change in body and muscle weights compared to isotype control treatment, Study 1 H4H10423P H4H10432P2 Isotype H4H10442P2 + H4H1657N2 Control 4 + + Control H4H1657N2 H4H1657N2 7N2 mg/kg + 10 mg/kg + 10 mg/kg + Dose 10 mg/kg 10 mg/kg 10 mg/kg mg/kg 10 mg/kg 10 mg/kg Body Weight 0.00 + 0.91 10.99 + 0.48 18.45 + 0.89 13.36 + 1.10 12.84 + 0.98 12.09 + 0.78 TA Muscle 0.00 + 1.15 19.54 + 2.67 45.80 + 1.47 32.03 + 2.12 24.83 + 2.95 40.76 + 2.59 GA Muscle 0.00 + 0.89 26.46 + 3.63 31.91 + 1.40 27.58 + 1.61 26.39 + 1.87 30.62 + 2.32 As shown in Table 14, in the first study, Control 4 induced significant hypertrophy in all muscles examined, with increases of 45.80 ± 1.47% in TA, and 31.91 ± 1.4% in GA weights as compared to the isotype control treated mice. Treatment with H4H1657N2 alone also induced hypertrophy in TA (19.54 ± 2.67% increase) and GA (26.46 ± 3.63% increase) muscle s, but it was less efficacious than Control 4. The combination of H4H1657N2 + H4H10442P2 induced similar ses in e TA (40.76 ± 2.59%) and GA (30.62 ± 2.32%) muscle weights as compared to mice treated with l 4. The ation treatments H4H1657N2/H4H10423P and H4H1657N2/H4H10432P2 did not induce increases in e TA weights as great as those induced by the H4H16757N2/H4H10442P or the Control 4 treatments.

Table 15: Percent change in body and muscle weights compared to isotype control treatment, Study 2 H4H10440P2 Isotype H4H10429P + H4H10436P2+ H4H1657N2 Control 4 + Control H4H1657N2 H4H1657N2 H4H1657N2 mg/kg + 10 10 mg/kg + 10 mg/kg + Dose 10 mg/kg 10 mg/kg 10 mg/kg mg/kg 10 mg/kg 10 mg/kg Body Weight 0.00 + 2.53 4.12 + 2.19 11.22 + 1.71 7.17 + 1.57 7.89 + 0.37 1.89 + 1.39 TA Muscle 0.00 + 3.59 16.70 + 2.73 43.47 + 2.37 34.14 + 2.55 29.31 + 1.59 14.55 + 2.22 GA Muscle 0.00 + 3.54 18.54 + 3.48 29.24 + 2.22 26.24 + 3.11 26.55 + 2.41 15.65 + 2.66 As shown in Table 15, in the second study, Control 4 induced hypertrophy in all muscles ed, with increases of 43.47 ± 2.37% in average TA weight and 29.24 ± 2.22% in GA e muscle weight as compared with the isotype control treated mice. In this study, treatment with 7N2 alone also induced increases in TA and GA average muscle s (16.7 ±2.73% and 18.54 ± 3.48%, respectively) as compared with the isotype control treated mice, but these average increases were less than those observed for the Control 4 treatment group. The combination treatments H4H1657N2/H4H10429P and H4H1657N2/H4H10436P2 induced increases in average TA (34.14 ± 2.55% and 29.31 ± 1.59%, respectively) and average GA (26.24 ± 3.11% and 26.55 ± 2.41%, respectively), ses that were between the increases observed for either H4H1657N2 or Control 4 alone.

The combination H4H1657N2/H4H10440P2 did not induce increases in TA or GA average weights as great as those induced by the other two combinations in this study or by the Control 4 treatment.

Table 16: Percent change in body and muscle weights compared to isotype control treatment, Study 3 H4H10446P2 + H4H10430P + Isotype Control H4H1657N2 Control 4 H4H1657N2 H4H1657N2 Dose 10 mg/kg + 10 10 mg/kg + 10 mg/kg 10 mg/kg 10 mg/kg mg/kg mg/kg Body Weight 0.00 + 2.00 1.43 + 1.14 18.92 + 3.53 10.90 + 2.51 8.88 + 1.58 TA Muscle 0.00 + 2.13 14.19 + 3.19 39.90 + 3.58 40.01 + 3.67 28.30 + 3.27 GA Muscle 0.00 + 1.62 15.73 + 0.58 34.01 + 2.87 31.29 + 2.60 21.55 + 2.30 As shown in Table 16, in the third study, Control 4 induced hypertrophy in all muscles examined, with increases of 39.90 ± 3.58% in average TA muscle weight, and 34.01 ± 2.87% in average GA muscle weight as compared with the e l-treated mice. ent with H4H1657N2 alone also d increases in TA (14.19 ± 3.19%) and GA e muscle weight (15.73 ± 0.58%) as compared with the isotype control treated mice, but these average increases were less than those ed for the Control 4 treatment group. The combination treatment H4H1657N2/H4H10446P2 induced similar increases in TA (40.01 ± 3.67%) and GA (31.29 ± 2.60%) average muscle weights as for mice treated with Control 4. The combination treatment with H4H1657N2/H4H10430P induced increases in TA (28.30 ± 3.27%) and GA (21.55 ± 2.30%) average muscle s that were between those observed for 7N2 alone and the H4H1657N2/H4H10446P2 combination ent.

Table 17: Percent change in body and muscle weights compared to isotype control treatment, Study 4 H4H10430P 30P H4H10430P Isotype H4H1657N2 H4H10430P + + + Control H4H1657N2 H4H1657N2 H4H1657N2 Dose 2 mg/kg + 10 mg/kg + 25mg/kg + 10 mg/kg 10 mg/kg 10 mg/kg 10mg/kg 10 mg/kg mg/kg 0.00 ± 0.57 9.89 ± 0.98 4.20 ± 1.00 14.53 + 0.80 12.61 ± 1.81 13.78 ± 1.58 Weight TA Muscle 0.00 ± 3.04 21.05 ± 2.64 7.83 ± 2.74 39.02 ± 3.55 40.20 ± 2.48 44.92 ± 5.70 GA Muscle 0.00 ± 2.71 22.85 ± 2.28 8.86 ± 1.24 27.57 ± 1.26 22.46 ± 5.03 30.22 ± 2.97 As shown in Table 17, in the fourth study, H4H1657N2 induced hypertrophy in the muscles examined, with increase of 21.05 ± 2.64% in average TA muscle weight and 22.85 ± 2.28% in average GA muscle weight as compared with the isotype control treated mice. In this study, treatment with H4H10430P alone slightly increased muscle weights as compared to the isotype l d mice but the values were not statistically significant. The combination ent of H4H1657N2 and H4H10430P at 10mg/kg and 2mg/kg, respectively, induced increases in TA (39.02 ± 3.55%) and GA (27.57 ± 1.26%) e muscle weights that were greater in TA muscle than those observed for H4H1657N2 or H4H10430P alone. The combination treatment of H4H1657N2 and H4H10430P at 10mg/kg and 10mg/kg, respectively, induced increases in TA (40.20 ± 2.48%) and GA (22.46 ± 5.03%) average muscle weights that were greater in TA muscle than those observed for H4H1657N2 or 30P alone. The combination treatment of H4H1657N2 and H4H10430P at 10mg/kg and 25mg/kg, respectively, induced increases in TA (44.92 ± 5.70%) and GA (30.22 ± 2.97%) average muscle s that were greater in TA muscle than those observed for H4H1657N2 or H4H10430P alone.

Table 18: Percent change in body and muscle weights compared to isotype control treatment, Study 5 46P2 H4H10446P2 H4H10446P2 Isotype H4H1657N2 H4H10446P2 + + + Control H4H1657N2 H4H1657N2 H4H1657N2 Dose 2 mg/kg + 10 mg/kg + 10 25mg/kg + 10 mg/kg 10 mg/kg 10 mg/kg 10mg/kg mg/kg mg/kg 0.00 + .94 + 1.03 0.29 + 1.33 14.26 + 1.45 12.61 + 1.26 16.31 + 2.04 Weight 1.23 TA Muscle 0.00 + .40 + 1.35 3.70 + 1.67 51.29 + 4.20 49.64 + 4.08 49.79 + 5.46 GA Muscle 0.00 + 22.82 + 1.97 2.70 + 1.06 39.24 + 3.08 35.56 + 3.39 35.14 + 3.49 As shown in Table 18, in the fifth study, H4H1657N2 induced hypertrophy in the muscles examined, with increase of 25.4 ±1.35% in average TA muscle weight and 22.82 ±1.97% in average GA muscle weight as compared with the isotype control treated mice. In this study, treatment with H4H10446P2 alone induced a low level of muscle hypertrophy with increase of 3.70 ±1.67% in average TA muscle weight and 2.70 ±1.06% in average GA muscle weight as compared with the isotype control treated mice. The combination treatment of H4H1657N2 and 46P2 at g and 2mg/kg, respectively, induced increases in TA (51.29 ± 4.20%) and GA (39.24 ± 3.08%) average muscle s that were greater than those observed for H4H1657N2 or H4H10446P2 alone. The combination treatment of H4H1657N2 and H4H10446P2, each at a g dose, induced increases in TA (49.64 ± 4.08%) and GA (35.56 ± 3.39%) average muscle weights that were greater than those ed for H4H1657N2 or 46P2 alone. The combination treatment of 7N2 and H4H10446P2 at 10mg/kg and g, respectively, induced increases in TA (49.79 ± .46%) and GA (35.14 ± 3.49%) average muscle weights that were greater than those observed for H4H1657N2 or H4H10446P2 alone.

Table 19: Percent change in body and muscle weights compared to isotype control ent, Study 6 Isotype Control 1 1 + Control 4 H4H1657N2 Control 1 Control H4H1657N2 Dose 10 mg/kg 10 mg/kg 10 mg/kg 10 mg/kg 10 mg/kg + 10 mg/kg Body Weight 0.00 + 0.51 17.04 + 2.90 8.92 + 1.26 3.52 + 0.86 15.84 + 0.75 TA Muscle 0.00 + 2.15 47.34 + 2.63 17.21 + 2.97 4.54 + 2.25 30.06 + 5.51 GA Muscle 0.00 + 1.71 32.17 + 3.81 21.57 + 1.90 2.72 + 1.30 30.72 + 3.64 As shown in Table 19, in the sixth study, Control 4 induced hypertrophy in all muscles examined, with increases of 47.34 ± 2.63% in average TA weight and 32.17 ± 3.81% in GA average muscle weight as compared with the isotype control treated mice. In this study, treatment with H4H1657N2 alone also induced increases in TA and GA average muscle weights 17.21 ± 2.97% and 21.57 ± 1.90%, respectively, as compared with the e control treated mice, but these average increases were less than those observed for the Control 4 treatment group. In this study, treatment with Control 1 alone induced a low level of muscle hypertrophy with increase of 4.54 ±2.25% in average TA muscle weight and 2.72+1.30% in average GA muscle weight as compared with the isotype control treated mice. The combination treatment of H4H1657N2 and Control 1 at 10mg/kg and 10mg/kg, respectively, induced increases in TA (30.06 ± 5.51%) and GA (30.72 ± 3.64%) average muscle s that were greater than those observed for H4H1657N2 or Control 1 alone.

Table 20: Percent change in body and muscle weights compared to isotype control ent, Study 7 Isotype H4H10430P + H4H10446P2 + Control 4 Control2 Control 7N2 H4H1657N2 Dose 10 mg/kg + 10 mg/kg 10 mg/kg 25 mg/kg 10 mg/kg + 10 mg/kg mg/kg Body Weight 0.00 + 0.90 8.17 + 3.30 19.18 + 1.75 10.55 + 1.48 11.67 + 0.98 TA Muscle 0.00 + 2.30 34.43 + 5.92 36.75 + 3.88 33.13 + 2.02 41.28 + 2.76 GA Muscle 0.00 + 2.01 14.86 + 3.65 26.41 + 3.16 22.82 + 1.34 29.21 + 2.62 ] As shown in Table 20, in the seventh study, Control 4-induced hypertrophy in all muscles examined, with increases of 34.43 ± 5.92% in average TA weight and 14.86 ± 3.65% in GA average muscle weight as compared with the isotype control treated mice. In this study, treatment with l 2 alone induced hypertrophy in the muscles examined, with increases of 36.75 ± 3.88% in average TA weight and 26.41 ± 3.16% in GA average muscle weight as compared with the isotype control treated mice. The combination treatment H4H1657N2 and 30P at 10mg/kg and 10mg/kg, respectively, d increases in TA (33.13 ± 2.02%) and GA (22.82 ± 1.34%) average muscle s that were between increases observed for ActRIIB-Fc alone and Control 2 alone. The combination treatment H4H1657N2 and H4H10446P2 at 10mg/kg and 10mg/kg, respectively, d increases in TA (41.28 ± 2.76%) and GA (29.21 ± 2.62%) average muscle weights.

Table 21: Percent change in body and muscle weights compared to isotype control treatment, Study 8 23P H4H10430P Isotype l 4 7N2 Control 2 + + Control 7N2 H4H1657N2 Dose 25 mg/kg + 25 mg/kg + mg/kg 25 mg/kg 10 mg/kg 25 mg/kg mg/kg 10 mg/kg 0.00 + 0.64 19.81 + 0.90 8.64 + 1.30 21.56 + 1.29 10.45 + 1.40 15.45 + 1.18 Weight TA Muscle 0.00 + 2.72 53.74 + 5.31 18.44 + 2.30 39.90 + 1.69 36.33 + 3.67 43.83 + 1.56 GA Muscle 0.00 + 0.76 39.39 + 4.56 21.17 + 1.72 25.87 + 2.72 28.18 + 3.11 31.24 + 1.90 As shown in Table 21, in the eighth study, Control 4 induced hypertrophy in all muscles examined, with ses of 53.74 ± 5.31% in average TA weight and 39.39 ± 4.56% in GA average muscle weight as compared with the isotype control treated mice. In this study, treatment with H4H1657N2 alone also induced ses in TA and GA average muscle weights of 18.44 ± 2.30% and 21.17 ± 1.72%, respectively, as compared with the isotype l treated mice, but these average increases were less than those observed for the Control 4 treatment group. In this study, ent with Control 2 alone induced hypertrophy in the muscles examined, with increases of 39.90 ± 1.69% in average TA weight and 25.87 ± 2.72% in GA average muscle weight as compared with the isotype control treated mice. The combination treatment H4H1657N2 and H4H10423P at 10mg/kg and 25mg/kg, respectively, induced increases in TA (36.33 ±3.67%) and GA (28.18 ± 3.11%) average muscle s as compared with the isotype control treated mice. The combination treatment H4H1657N2 and H4H10430P at 10mg/kg and 25mg/kg, respectively, induced increases in TA (43.83 ± 1.56%) and GA (31.24 ± 1.90%) average muscle weights that were between increases observed for Control 4 alone and Control 2 alone.

These studies show that administration of ctivin A antibodies with a myostatin inhibitor can further se skeletal muscle hypertrophy to a significantly greater degree than treatment with a myostatin inhibitor alone at the doses and injection frequencies tested..

Example 8. Blocking of Activin A Binding using Activin A Antibodies ] The ability of selected anti-Activin A antibodies to block the interaction of Activin A with its receptors, ActRIIB and ActRIIA, as well as its endogenous antagonist, tatin, was determined using a Biacore 3000 instrument. For this experiment, Control 4 (human ActRIIB expressed with a C-terminal human Fc tag (SEQ )), human ActRIIA expressed with a C- terminal human Fc tag (hActRIIA-Fc; R&D Systems, # 340-R2-100), or Follistatin-288 (R&D Systems, #5836-FS-025) were amine-coupled to a Biacore CM5 sensor surface. Activin A (R&D Systems, #338-AC) at a fixed concentration of 5nM either alone or mixed with Activin A antibodies, hActRIIA-Fc, IB-Fc, or isotype l antibody at a final concentration of 60 nM (12-fold molar excess over Activin A) was incubated at room ature for 1 hour. The antibody-Activin A mixtures were then injected over the amine-coupled Control 4, hActRIIA-Fc, or Follistatin-288 surfaces at a flow rate of 20uL/min. The binding signal (RU) was measured at 150 seconds after the start of the injection, and this signal was subtracted by the ed RU value for a negative control reference surface to ine the specific binding signal. The percentage of free Activin A binding over the receptor or antagonist surfaces in the presence of each anti-Activin A antibody was calculated as the ratio of the observed specific binding signal divided by the specific binding signal from 5nM Activin A in the presence of no antibody.

Table 22: Blocking of Activin A Binding to Follistatin by anti-Activin A Antibodies Follistatin-288 surface (3000RU captured)-Normalized to Activin A (% bound RU w/ no inhibitor) (nM) concentration mAb/protein H4H10442P2 H4H10446P2 30P H4H10440P2 H4H10429P H4H10436P2 23P Control 1 Control 3 hActRIIA-hFc hFc) (hActRIIB- Control 4 control isotype (-) 0 100 100 100 100 100 100 100 100 100 100 100 100 0.94 73 77 79 76 97 78 120 83 172 156 169 100 1.88 46 54 59 57 80 61 122 68 170 148 163 102 3.75 6 7 15 17 20 16 103 27 145 138 151 97 7.5 3 3 1 4 1 1 97 0 33 116 120 102 3 3 1 2 1 1 96 1 5 60 43 102 3 3 1 1 2 2 94 1 7 11 1 104 60 3 3 1 0 3 2 93 2 9 13 1 103 As shown in Table 22, 6 of the 7 anti-Activin A antibodies of the ption tested and both Control 1 and Control 3 blocked the binding of Actin A to Follistatin-288 . One antibody of the description, H4H10423P, did not prevent binding of Activin A to Follistatin-288. l 4 and hActRIIA-Fc blocked the binding of Activin A to Follistatin-288 at higher concentrations.

Table 23: Blocking of Activin A Binding to hActRIIA-Fc by anti-Activin A dies g hActRIIA-hFc surface (8000RU captured)-Normalized to Activin A (% bound RU w/ no inhibitor) tration (nM) mAb/protein 42P2 H4H10446P2 H4H10430P H4H10440P2 H4H10429P H4H10436P2 H4H10423P Control 1 Control 3 hActRIIA-hFc hFc) Control 4 (hActRIIB- isotype (-) control 0.00 100 100 100 100 100 100 100 100 100 100 100 100 0.94 114 111 81 75 87 75 112 82 207 236 276 109 1.88 114 115 62 52 66 55 114 66 190 222 266 112 3.75 95 85 19 17 19 16 111 28 139 188 231 110 7.50 105 94 3 6 1 2 110 1 32 128 160 115 113 108 2 4 1 2 112 1 1 50 51 116 117 98 2 3 1 2 114 1 1 5 2 118 60 118 118 2 3 1 2 116 2 0 3 1 119 As shown in Table 23, 4 of the 7 anti-Activin A antibodies of the description tested and both Control 1 and Control 3 blocked the binding of hActRIIA-Fc to Activin A. Three antibodies of the description, H4H10442P2, H4H10446P2, and H4H10423P, did not prevent binding of Activin A to hActRIIA-Fc. Control 4 and hActRIIA-Fc blocked the binding of Activin A to hActRIIA-Fc.

Table 24: Blocking of Activin A g to hActRIIB-Fc by anti-Activin A Antibodies IB-hFc (Control 4) surface (4000RU captured)-Normalized to Activin A (% bound RU w/ no inhibitor) concentration (nM) mAb/protein H4H10442P2 H4H10446P2 H4H10430P H4H10440P2 H4H10429P H4H10436P2 H4H10423P Control 1 Control 3 hActRIIA-hFc hFc) Control 4 (hActRIIB- isotype (-) control 0.00 100 100 100 100 100 100 100 100 100 100 100 100 0.94 110 107 80 79 87 80 93 85 135 131 149 105 1.88 106 105 62 58 67 60 78 69 133 129 148 105 3.75 88 76 20 19 19 19 47 31 120 127 144 104 7.50 103 95 4 7 2 3 42 2 33 113 130 107 115 115 3 4 2 2 42 2 2 56 51 110 122 89 3 4 2 3 41 2 1 5 3 111 60 124 129 3 4 3 4 41 3 2 5 2 115 As shown in Table 24, 4 of the 7 anti-Activin A antibodies of the description tested and both Control 1 and Control 3 blocked the binding of n A to hActRIIB-Fc. Two antibodies of the description, H4H10442P2 and H4H10446P2, did not prevent binding of n A to hActRIIB-Fc. One antibody of the ption, H4H10423P, demonstrated the ability to partial block the binding of Activin A to hActRIIB-Fc at higher concentrations of antibody tested. Both IB-Fc and hActRIIA-Fc blocked the g of Activin A to hActRIIB-Fc.

Example 9. s of H4H1657N2 on Muscle Mass and Exercise mance The effects of the anti-GDF8 antibody H4H1657N2 on muscle mass and exercise performance was evaluated in aged male C57BL/6 mice (19 months old).

Mice were randomized into four groups /group), a sedentary or exercise group receiving subcutaneous doses of H4H1657N2 or an e l antibody (10mg/kg) twice weekly for 21 days (6 ions). Mice in the exercise group were placed on an exercise regimen involving one training session a day, consisting of 20 minutes on an Exer 6M treadmill (Columbus Instruments, Columbus, OH) at 10m/min with a 5° incline, five days a week for three utive weeks. At the end of three weeks of treatment, endurance was measured in all four groups using a treadmill tion test. The data were analyzed with two-way ANOVA followed by Tukey HSD test. Muscle weights were reported as ized weights (i.e., muscle weights were normalized to the body s measured at the start of the experiment). Results for quadriceps muscle are provided in Table 25 as average % change for each group (± standard error of the mean) compared to the isotype control antibody group.

Table 25: Quadracept Muscle Weight Change Isotype 7N2 Isotype Control + H4H1657N2 + Control (Sedentary) Exercise Exercise (Sedentary) 0.00 ± 2.72 15.77 ± 2.73 9.85 ± 3.57 17.66 ± 3.24 Weight % Change from isotype control. Means ± SEM are shown.

As seen in Table 25, H4H1657N2 treatment resulted in significant increases in the mass of quadriceps muscles (p<0.01 significance over isotype control for both H4H1657N2 groups). Increases in hindlimb muscle group weights (TA, GA,) were seen in exercised (17.4%, 12.5%, respectively) and sedentary (14.1%, 11.6%, respectively) aged mice, compared with an isotype l antibody. A slight increase in muscle weight was observed between exercised and sedentary aged mice that received isotype control antibody, but it was not statistically significant(Table 25).

The effects of H4H1657N2 treatment on exercise endurance was also examined in 19 month old male C57BL/6 mice (Table 26).

Table 26: Endurance Testing Isotype Control H4H1657N2 Isotype Control H4H1657N2 + (Sedentary) (Sedentary) + Exercise Exercise Time Ran until 27.94 ± 4.12 28.54 ± 6.10 50.26 ± 8.56 73.23 ± 4.68 Exhaustion (min) Distance Ran until tion 428.42 ± 71.91 535.99 ± 155.61 930.06 ± 179.78 1366.65 ± 95.91 In exercised aged mice, H4H1657N2 also induced significant increases in nce, as measured by treadmill running time (73.2 min versus 50.2 min) and distance (1.33 km versus 0.93 km), compared with the isotype control group (Table 26). However, in sedentary mice, H4H1657N2 did not icantly increase endurance compared with the isotype control group.

As in the muscle weight study, 7N2 induced significant increases in endurance, as measured by treadmill running time and distance, in the exercised mice only, but not in the sedentary mice. These results show that 7N2 increases al performance outcomes when ed with exercise training. e 10. Effects of H4H1657N2 on Skeletal Muscle Mass and Isometric Force in Mice The ability of 7N2 to induce skeletal muscle hypertrophy was assessed in vivo in 9 week old male 6 mice.

Repeated subcutaneous doses of H4H1657N2 or an isotype control dy, at either or 30 mg/kg, were administered twice weekly for 3 weeks (n=6). H4H1657N2 treatment for 21 days produced increases in body weight of 4.7 ± 2.3% (n.s.) and 7.1 ± 1.5% (n.s.), respectively, compared to mice receiving isotype control administered at equal doses.

Individual muscle weights were increased as follows ed to isotype control kg & 30mg/kg): Tibialis anterior (19.4 ± 4.9%** & 20.6± 1.5%**), Gastrocnemius: (14.9 ± 2.9%** & .3 ± 1.9%***), and Quadriceps (17.7 ± 3.6%* & 26.2 ± 3.8%**). (All stats by One Way ANOVA with Tukey’s post hoc test [* p<.05; ** p<.01; *** p<.001; n.s. = not statistically ent].) The increase in Tibialis or (TA) muscle mass was accompanied by an increase in ex vivo isometric force, indicating the ability to in both muscle function and mass. Mice previously treated with repeated subcutaneous doses of H4H1657N2 or isotype control dy (at 10 mg/kg administered twice weekly for 3 weeks, n= 6 per group) were individually anesthetized and maintained under Isoflurane gas while the TA muscle was excised placed in a oxygenated lactated ringers bath constantly maintained at 25ºC. The superior end of the TA was firmly tied to a submerged ion in the bath while the distal tendon was tied to 305C lever arm (Cambridge s). Optimal length was determined by slightly stretching the TA and then testing the force produced by a 1Hz stimulation at a minimal voltage. TA muscles were repeatedly stretched and ated until there was a decline in force and then relaxed to the previous position. Voltage was then entally increased in a series of 1HZ stimulations to achieve maximal force output. Once optimal length and voltage had been determined, TA muscles were stimulated for 400 milliseconds at increasing frequencies (40-100Hz) to determine maximum tetanic force. TA muscles were given 2 minute rest periods between each tetanic stimulation.

TA muscles from mice treated with an isotype control antibody at 10mg/kg and 30 mg/kg dose for 21 days generated an average peak c force of 892.6 ± 37 and 906.1 ± 37.8, respectively. TA muscles from mice treated with H4H1657N2 generated an average peak tetanic force of 1041.3 ± 31.7 and 1003.3 ± 35.7 mN, respectively. These force values represent se of 16.7%* (10mg/kg) and 10.7%n.s (30mg/kg) in average peak tetanic force compared to isotype control (Figure 2A). The overall drug effect of H4H1657N2 treatment on peak tetanic force was tically different from isotype control at both 10mg/kg and 30mg/kg doses (10mg/kg dose shown in Figure 2B). (Figure 2A: statistical analysis by One Way ANOVA with Tukey’s post hoc test [* p<.05; n.s. = not statistically different]. Figure 2B: statistical analysis by Two way ANOVA and Sidaks post hoc test [p>0.0001].) e 11. H4H1657N2 Improves the Recovery from Hind Limb sion (HLS)- induced y ] The effect of H4H1657N2 on skeletal muscle mass during the recovery phase from 7 days of hindlimb suspension (HLS) induced atrophy was assessed in one-year old C57BL/6 male mice.

At day 0, eighteen mice were ded by the tail so that both hind legs could not touch the ground for the duration of 7 days. Mice were housed in special cages with free access to food and water. Concurrently, one additional group of six mice was left in normal caging and served as a control (Non-HLS control). At day 7, the suspended mice were taken down and ized by percentage of body weight lost during HLS into three groups (n=6 each). At day 7, the muscle weights from the Non-HLS control group and one HLS group (HLS group) were taken to assess the percentage of atrophy in se to HLS. The two remaining HLS groups (n=6 each) were allowed to recover for 8 days (i.e., day 7 through day 15 of the experiment) in normal caging and treated subcutaneously with 10mg/kg doses of either 7N2 or an isotype control on days 7 and 10 (i.e., after zero days and 3 days of recovery) (HLS+7Rec+H4H1657N2 and HLS+7rec+Isotype Control, respectively). At day 15 (i.e., after 8 days of recovery), muscle weights were taken to assess the tage of recovery after HLS-induced atrophy.

As seen in Figure 3B, seven days of HLS resulted in significant loss of mass in both tibialis anterior (TA) and gastrocnemius (GA) (HLS group), as compared to the Non-HLS control group (-13.7%* and -14.8%* respectively). After 8 days of recovery, the HLS+7rec+Isotype Control group maintained losses in TA and GA muscle mass (-6.3% and -7.5%) as compared to the Non-HLS control group, whereas the HLS+7Rec+H4H1657N2 group showed gains in mass (4.7% and 5%) as compared to the Non-HLS group.

When comparing the two recovery groups (i.e., HLS+7Rec+H4H1657N2 versus ec+Isotype Control), the effects of H4H1657N2 on TA and GA mass were not statistically different from the effects seen with the isotype control antibody. However, while the HLS+7rec+Isotype Control group’s muscle mass was not statistically ent from the HLS group or the Non-HLS control group, the HLS+7Rec+H4H1657N2 group had statistically larger TA and GA mass when compared to the HLS group. (All stats by One Way ANOVA with Tukey’s post hoc test [* p<0.05 vs. No HLS; ## p<0.01 vs. HLS.) Example 12. tion of BMP receptor type I and II tion By Anti-Activin A Antibodies and ActRIIB-Fc Bone morphogenetic proteins (BMPs) belong to the TGF-β superfamily and are involved in regulation of many physiological processes by activating receptor complexes on the cell surface that are composed of BMP receptor types I and II. Activation of receptors leads to phosphorylation of SMAD proteins and transcriptional activation of ligand-responsive genes.

A bioassay was developed to detect the regulation of BMP ing in W17 cells, a mouse bone marrow stromal cell line previously shown to be responsive to BMP2. The cells were engineered to stably express a luciferase reporter (i.e., BMP-responsive element (BRE(2X)-luciferase-IRES-GFP)), and sorted for high sion of GFP. The resultant stable cell line is referred to as W17/BRE-luc and was maintained in 10% FBS, DMEM, Pen/Strep, and 200µg/ml G418. These cells were used to measure BMP activation and the inhibition of this activation by anti-Activin A antibodies and ActRIIB-hFc (Control 4, SEQ ID No:227).

The ability of four ctivin A antibodies and ActRIIB-hFc to inhibit BMP signaling was evaluated using the W17/BRE-luc cell line. For the bioassay, W17/BRE-luc cells are seeded onto 96-well assay plates at 10,000 cells/well and incubated at 37°C and 5% CO2 overnight. The next day, BMP2, BMP4, BMP6, BMP9 or BMP10 were ly diluted at 1:3 and added to cells from 100nM to 0.002nM (including no BMP control for dose responses). For inhibition of BMPs by anti-Activin A antibodies or ActRIIB-hFc, dies or ActRIIB-hFc were serially diluted at 1:3 from 1000nM to 0.02nM (including no antibody, control antibody, or ve control for ActRIIB-hFc (i.e., an irrelevant protein tagged with hFc, "Control Protein")) and added to cells along with 100pM BMP2, 100pM BMP4, 10nM BMP6, 800pM BMP9 or 4nM BMP10, as indicated. Luciferase activity was detected after 5.5 hrs of incubation in 37°C and % CO2 with Victor X (Perkin Elmer) and the results were analyzed using using nonlinear regression (4-parameter logistics) with Prism 5 software (GraphPad).

As shown in Table 27 below, H4H10446P2 and H4H10430P did not inhibit of any of the BMPs tested, whereas the other Activin A antibodies tested (H4H10429 and H4H10436P2) and ActRIIB-hFc all showed some inhibition of some of the BMPs. H4H10429P showed tion of BMP9 and BMP10 with IC50 values of 8.1nM and 3.5nM, respectively, but did not inhibit BMP2, BMP4 and BMP6. H4H10436P2 showed weak inhibition of BMP2 and BMP4 at highest concentrations of the antibody and tion of BMP10 with an IC50 value of >100nM, but did not show any inhibition of BMP6 and BMP9. ActRIIB-hFc showed inhibition of BMP9 and BMP10 with IC50 values of 2nM and 1nM but did not inhibit BMP2, BMP4, and BMP6.

Neither of the l les (i.e., an isotype control antibody (Control mAb) and irrelevant protein tagged with hFc (Control Protein)), were seen to inhibit any of the BMPs, whereas BMP2, BMP4, BMP6, BMP9, or BMP10 alone (i.e., t dies or hFc-tagged proteins) activated the W17/BRE-luc cells with EC50 values of 34pM, 63pM, 4.5nM, 260pM, and 2.5nM, respectively.

Table 27. Inhibition by anti-Activin A antibodies and ActRIIb-hFc of BMPs in W17/BRE-luc cells LIgands BMP2 BMP4 BMP6 BMP9 BMP10 EC50 [M] 3.4E-11 6.3E-11 4.5E-09 2.6E-10 2.5E-09 Constant BMP 100pM 100pM 10nM 800pM 4nM Antibodies IC50 [M] IC50 [M] IC50 [M] IC50 [M] IC50 [M] H4H10446P2 No Inhibition No Inhibition No Inhibition No Inhibition No Inhibition H4H10430P No Inhibition No Inhibition No Inhibition No Inhibition No Inhibition 29P No Inhibition No Inhibition No Inhibition 8.1E-09 3.5E-09 Weak (31% Weak (51% H4H10436P2 inhibition at inhibition at No tion No Inhibition > 1.0E-07 1uM) 1uM) ActRIIB-hFc No Inhibition No Inhibition No Inhibition 2.0E-09 1.0E-09 Control mAb No Inhibition No Inhibition No Inhibition No Inhibition No Inhibition Control Protein No Inhibition No tion No Inhibition No tion No Inhibition Example 13. Treatment with anti-Activin A Antibody H4H10446P2 reduces Renal Fibrosis in vivo ] The effect of a specific anti-activin A antibody of the description, H4H10446P2, on renal fibrosis was determined in an unilateral ureteral obstruction (UUO) mouse model of renal fibrosis. The UUO model was developed by complete on of the left ureter while keeping the right kidney function intact. Briefly, UUO was performed in mice under Ketamine/Xylazine esia, whereby the left ureter was accessed via flank incision, and two ligatures were placed on the proximal one-third of the ureter using 5-0 silk thread at 5mm apart. Sham surgeries were done in a similar fashion without placing any ligatures on the ureter. In this model, severe fibrosis develops in the kidney within 14 days following UUO, which has been assessed by measuring kidney collagen by directly measuring the amount of hydroxyproline in the sample, which is referred to as the hydroxyproline method. Hydroxyproline is a specific component of collagens, and represents approximately 14.4% of the amino acid composition of collagen in most mammalian tissues (Cochrane et al., J Am Soc Nephrol 16:3623-30 (2005)).

To measure collagen content via the hydroxyproline method, first frozen kidney samples were dried overnight using a vacuum chamber. Dried kidney tissue samples were then homogenized in an ice-cold NaCl/NaHCO3 solution and were then hydrolyzed using 6 M HCl. The samples were subsequently dried using a vacuum centrifuge, and then were rehydrated using 0.1 M HCl. The hydroxyproline in the rehydrated samples was oxidized with 300mM Chloramine T (Sigma, # 857319) and Ehrlich’s reagent [3.5M p-dimethylaminobenzaldehyde (FW: , Sigma, # 39070) in 60% perchloric acid , # 311413)] was then added to develop the color. Finally, using a ophotometer, ance of the samples was measured at 558 nm and this was ed to hydroxyproline rds (Sigma, # H5534) of known concentration, to determine the kidney hydroxyproline content. The ed yproline value was then multiplied by a factor of 6.94 to determine the collagen value. Fourteen days ing UUO, dry kidney weight decreases as a result of parenchymal damage. Sham (n = 10) or UUO (n = 20) surgeries were med on 16-week old male C57BL/6 mice (Taconic farms, Inc.). Mice, which ent UUO surgery, were then divided into two groups. Each UUO group received a subcutaneous injection of either H4H10446P2 (40 mg/kg, n = 10) or an isotype control antibody (40 mg/kg, n = 10), which does not bind to any known mouse protein, ng a day before the surgeries, and on 1, 3, 6, 8, 10, and 13 days after the surgery. The mice that underwent the sham surgery received e (sterile PBS) during this time using the same schedule as the UUO groups. All the mice were sacrificed on day 14 following surgery. The kidney weights were measured, and the kidneys were flash-frozen using liquid nitrogen, and kept at -80oC until the collagen content was measured. Kidney en content was measured using the yproline method, and then expressed as either total kidney collagen (μg) or kidney collagen normalized to kidney weight (μg/mg of dry weight). tical analysis was done using y ANOVA with Turkey’s multiple comparison test. The results including summarizes total kidney collagen, normalized kidney collagen, and dry kidney weights for each treatment group were expressed as mean ± SEM in Table 28 below.

Table 28. Total Kidney collagen, Normalized Kidney Collagen, and Dry Kidney Weight in each group (mean ± SEM) Treatment Group Total Kidney Normalized Kidney Collagen Dry Kidney Collagen (μg) (μg/mg of tissue dry weight) Weight (g) Sham + e 429.6 ± 25.93 8.16 ± 0.29 0.0524 ± 0.002 UUO + Isotype Control 980.7 ± 50.48 25.07 ± 0.86 0.0396 ± 0.0027 UUO + H4H10446P2 730.7 ± 48.02 17.48 ± 0.79 0.0422 ± 0.0029 As shown in Table 28, both total kidney en and kidney collagen normalized to kidney weight was significantly increased in UUO mice compared to sham-operated mice.

UUO mice treated with H4H10446P2 exhibited significant reduction in both total kidney collagen and kidney collagen normalized to kidney weight (approximately 45% reduction in fibrotic collagen) compared to isotype control antibody treated UUO mice, indicating the anti-activin A antibody lead to decreased is in the kidney. UUO mice treated with H4H10446P2 ted an increase in dry kidney weight compared to the isotype control antibody treated UUO mice, indicating preservation of parenchyma in the anti-activin A antibody treated mice.

Example 14. Effects of H4H10446P2 on Body Weight and Muscle Mass in mice overexpressing Activin A To assess the efficacy of H4H10446P2 in neutralizing elevated levels of Activin A in mice, Activin A was over-expressed in C57BL/6 mice (10 weeks-old) by ynamic ry (HDD) of a DNA construct encoding full-length n A. Mice were randomized into three groups (n=5-6/group); one was injected with a mixture of saline/2.5μg of a DNA construct control in presence of an isotype control antibody, and two groups were ed with a mixture of saline/2.5μg of a DNA construct containing Activin A in presence of an isotype control antibody or H4H10446P2. DNA constructs were injected on day 0, and antibodies were administered on days 0 and 4 at 2.5 mg/kg (2 injections) for 7 days. Muscle weights were reported as normalized weights (i.e., muscle weights were normalized to the body s measured at the start of the experiment). Results for body weights are shown as average change from starting body weights. Results for tibialis anterior (TA) and gastrocnemius (GA) muscles are shown in Figure 4 as average percent change for each group (± standard error of the mean) compared to the HDD delivery of a construct l + e control antibody group. The data were analyzed with one or two-way ANOVA followed by Tukey HSD test.

As seen in Figure 4, seven days after HDD, delivery of Activin A in mice treated with an isotype control antibody resulted in significant decreases in body weights 1 ± 2.46%) and the mass of tibialis and gastrocnemius muscles (of -13.96 ± 1.85% and of -10.34 ± 1.51%, respectively) (p<0.01 significance over isotype control). Delivery of Activin A in mice treated with H4H10446P2 resulted in a significant attenuation of body weights (-1.49 ± 1.98%) and the mass of tibialis and gastrocnemius muscles at the end of seven days of ent (of -2.57 ± 1.26% and of -1.77 ± 2.42%, respectively).

The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various cations of the invention in addition to those described herein will become nt to those skilled in the art from the foregoing ption and the accompanying figures. Such modifications are intended to fall within the scope of the appended claims.

Claims

What is d is:

1. An isolated antibody or antigen-binding fragment thereof that specifically binds Activin A with a binding dissociation equilibrium constant (KD) of less than about 5 pM as measured in a surface plasmon resonance assay at 25ºC, wherein the antibody or antigen-binding fragment comprises three mentarity determining s (CDRs) of a heavy chain variable region (HCVR); and three CDRs of a light chain variable region (LCVR), wherein the HCDR1-HCDR2- HCDR3-LCDR1-LCDR2-LCDR3 domains comprise the amino acid ces of SEQ ID NOs: 687278-80, respectively.

2. The isolated antibody or antigen-binding fragment thereof of claim 1, wherein the isolated antibody or antigen-binding fragment thereof specifically binds Activin A with a KD of less than about 4 pM as measured in a surface plasmon resonance assay at 25ºC.

3. The isolated antibody or n-binding fragment thereof of claim 1, wherein the isolated antibody or antigen-binding fragment thereof specifically binds Activin A with a binding association equilibrium constant (Ka) of less than about 500 nM.

4. The isolated antibody or antigen-binding fragment thereof of claim 1 or 2, wherein the antibody or antigen-binding fragment thereof blocks binding of at least one Activin A receptor to Activin A.

5. The isolated antibody or antigen-binding fragment thereof of claim 1 or 2, n the antibody or antigen-binding fragment thereof blocks tion of at least one Activin A receptor by Activin A.

6. The isolated antibody or antigen-binding fragment thereof of claim 4, wherein the antibody or antigen-binding fragment f blocks Activin A binding to an Activin A receptor with an IC50 value of less than about 80 pM as ed in an in vivo receptor/ligand binding bioassay at 25ºC.

7. The isolated antibody or antigen-binding fragment thereof of claim 6, wherein the antibody or antigen-binding fragment thereof blocks Activin A binding to an Activin A receptor with an IC50 value of less than about 60 pM as measured in an in vivo receptor/ligand binding ay at 25ºC.

8. The ed antibody or antigen-binding fragment thereof of any one of claims 1 to 7, wherein the antibody or antigen-binding fragment thereof ts binding of Activin A to an Activin A receptor selected from the group consisting of Activin Type IIA receptor (ActRIIA), Activin Type IIB or IB), and Activin Type I receptor.

9. The isolated antibody or antigen-binding fragment thereof of any one of claims 1 to 8, wherein the antibody or antigen-binding fragment thereof inhibits Activin A-mediated activation of SMAD complex signaling.

10. The isolated antibody or antigen-binding fragment thereof of any one of claims 1 to 8, n the antibody or antigen-binding fragment thereof competes for binding to Activin A with a reference antibody comprising a heavy chain variable region (HCVR)/light chain variable region (LCVR) sequence pair ed from the group consisting of SEQ ID NOs: