Anti-actrii antibodies and uses thereof

Abstract

The invention provides novel antibodies that bind to activin type IIB receptor (ActRITB), or activin type IIA receptor (ActRIIa) or both. The antibodies block ligand binding to the receptors and modulate downstream signaling. The invention also provides novel compositions and methods for treating a metabolic disorder, improving glycemic control, promoting increased muscle mass, and reducing adipose tissue and treating osteoarthritis. The methods and compositions are used to treat type 2 diabetes.

Description

ANTI-ACTRII ANTIBODIES AND USES THEREOFRELATED APPLICATIONS AND INCORPORATION BY REFERENCE

[0001] This application claims priority to U.S. Provisional Application Serial No. 63 / 651,541, filed May 24, 2024, and U.S. Provisional Application Serial No. 63 / 692,313, filed September 9, 2024, each incorporated by reference herein in its entirety.

[0002] The foregoing applications, and all documents cited therein or during their prosecution (“appln cited documents”) and all documents cited or referenced in the appln cited documents, and all documents cited or referenced herein (“herein cited documents”), and all documents cited or referenced in herein cited documents, together with any manufacturer’s instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention. More specifically, all referenced documents are incorporated by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference.SEQUENCE LISTING

[0003] The instant application contains a Sequence Listing which has been submitted via Patent Center and is hereby incorporated by reference in its entirety. Said .xml copy, created on May 23, 2025, is named Y9432-99008.xml, and is 391,877 bytes in size.FIELD OF THE INVENTION

[0004] The invention provides novel antibodies that bind to activin type IIA receptor (ActRIIA), activin type IIB receptor (ActRIIB), or ActRIIB and ActRIIB. The antibodies block ligand binding and modulate downstream signaling. The invention also provides novel compositions and methods for treating a metabolic disorder, improving glycemic control, promoting increased muscle mass, and reducing adipose tissue. The methods and compositions are used to treat type 2 diabetes.BACKGROUND OF THE INVENTION

[0005] The TGF-0 superfamily includes multiple ligands and receptors that are widely expressed in disparate cell types. For example, myostatin, the activins (Act A, Act B, and Act AB) and growth / differentiating factor 11 (GDF11) signal through the ActRII receptors, ActRIIA and ActRIIB. Complexity arises from there being multiple ligands competing for receptor bindingsites, some interactions being inhibitory while others are activating, and there being functional redundancy.

[0006] Metabolic syndrome is a complex disorder, manifesting as obesity, hyperglycemia, hypertension and hyperlipidemia. Activin receptor type IIB (ActRIIB) binds several TGF-P superfamily ligands. ActRIIB has been implicated in regulation of muscle growth by myostatin, and signaling blockade with a soluble ActRIIB decoy receptor increased muscle mass and reduced adiposity. Signaling from ActRIIB has been implicated in arthritis pathogenesis (leon J. et al. 2023. Adv. Sci. 10:2205161).

[0007] Binding proteins are needed that bind to ActRIIA, that bind to ActRIIB, or bind to both ActRIIA and ActRIIB and modulate or block activity of one or both of the receptor proteins.

[0008] Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.SUMMARY OF THE INVENTION

[0009] There is a need for novel pharmaceutical compositions and methods for treatment of metabolic disorders, including metabolic syndrome, obesity, insulin resistance, and type 2 diabetes mellitus and osteoarthritis.

[0010] The invention provides novel anti-ActRII binding proteins for treatment or amelioriation of ActRIIB and / or ActRIIA mediated disorders. Binding proteins of the invention may be particularly adapted for use in dogs and cat but are not limited thereby. The invention provides antigen binding proteins designed or adapted to bind ActRIIB, ActRIIA, or ActRIIB and ActRIIA, in the manner of an antibody, i.e. by one or more complementarity determining regions (CDRs). In certain embodiments, the antigen binding protein binds to ActRIIB, to ActRIIA, or to ActRIIB and ActRIIA, and modulates or blocks activity of one or both of the receptor proteins. In certain embodiments, the antigen binding protein binds to ActRIIB, to ActRIIA, or to ActRIIB and ActRIIA and blocks ligand binding.

[0011] In certain embodiments, the invention provides a caninized or felinized antibody that binds to ActRIIB and ActRIIA, which comprises: (a) a heavy chain complementarity determining region 1 (HCDR1) comprising GYX28X29X30SX32YX34X35 (SEQ ID NO:296), wherein X28 comprises N, Q, S or T, X29 comprises F, I, L, M, or V, X30 comprises D, F, H, N, S, T, or W, X32 comprises S, or T, X 4 comprises I, L, or V, X35 comprises N, Q, P, or T; (b) a heavy chain complementarity determining region 2 (HCDR2) comprisingX50X51NPX54X55GX57X58X59X60X61X62X63X64 (SEQ ID NO:297), wherein X50 comprises A, G,H, M, N, Q, R, S, T, V, W, or Y, X51 comprises I, L, M, or W; X54comprises A, N, S, V, or Y, X55 comprises G, I, L, S, T, or W, X57 comprises S or T, Xss comprises T or V, X59 comprises L, Q, or S, Xeo comprises L, M, V, or Y, Xei comprises A or D, X62 comprises A, D, E, H, K, P, Q, R, S, or T, X63 comprises A, F, G, I, L, N, P, Q, S, V, or Y; Xe4 comprises A or V; (c) a heavy chain complementarity determining region 3 (HCDR3) comprising X99GWX102DX104 (SEQ ID NO:298), wherein X99 comprises D, G, S, or T; X102 comprises F or M; X104 comprises A, G, H,I, L, M, N, Q, R, S, T, V, or Y; (d) a light chain complementarity determining region 1 (LCDR1) comprising X23GX25X26X27X28X29X30X31X32X33YX35X36 (SEQ ID NO:299), wherein X23 comprises D, Q, or T, X25 comprises Q or S; X26 comprises A, E, F, G, H, K, L, M, P, Q, R, S, T, or V; X27 comprises A, E, G, K, L, N, P, R, or S; X28 comprises A or D; X29 comprises F, I, P, V, or Y; X30 comprises G or N; X31 comprises A, G, K, L, N, P, Q, R, S, or T; X32 comprises H, P, W, V, or Y; X33 comprises A, H, L, N, P, Q, or R; X35 comprises I, P, or V; X36 comprises A or N; (e) a light chain complementarity determining region 2 (LCDR2) comprising X52X53X54X55RX57X58 (SEQ ID NO:300), wherein X52 comprises G, H, N, or S; X53 comprises A, D, E, F, H, I, K, N, P, Q, R, S, T, or V; X54 comprises D, E, G, S, or T; X55 comprises K or R; X57 comprises D, E, G, H, I, K, L, M, N, P, Q, R, S, T, or V; X58comprises A, E, G, H, K, N, P, R, S, or Y; and (f) a light chain complementarity determining region 3 (LCDR3) comprising X92FX94GGX97YX99GX101 (SEQ ID NO:301), wherein X92 comprises L or T; X94 comprises A or S; X97 comprises A, R, S, or Y; X99 comprises D, E, F, G, H, I, K, L, M, N, Q, T, V, or Y; X101 comprises A, G, D, F, H, I, K, L, M, N, Q, R, S, T, V, or Y.

[0012] In certain embodiments, in HCDR1, 32 comprises S or T; X35 comprises N or Q; and no more than two of X28, X29, X30, and X34 differ from the corresponding positions of SEQ ID NO:17; in HCDR2, X50 comprises G, N, T, or V; X59 comprises L or S; Xeo comprises L, M, or Y; X62 comprises D, E, or P; X63 comprises A, S, or Q; and no more than two of X51, X54, X55, X57, X58, Xei, and X64 differ from the corresponding positions of SEQ ID NO: 17; in HCDR3, X99 comprises D, G, or S; X102 comprises F or M, X104 comprises V or Y; in LCDR1, X23 comprises D, Q or T; X26 comprises A, K, Q, or S; X31 comprises R or S; and no more than two of X25, X27, X28, X29, X30, X32, X33, X35, and X36 differ from the corresponding positions of SEQ ID NO: 16, in LCDR2, X55 comprises K or R; and no more than two of X52, X53, X54, X57, and X58 differ fromthe corresponding positions of SEQ ID NO: 16; and in LCDR3, X92 comprises L or T; X99 comprises D, K, L, T, or Y; X101 comprises G, M, S, or V.

[0013] In certain embodiments, in HCDR1, X32 comprises S or T; X35 comprises N or Q; and no more than one of X28, X29, X30, and X34 differ from the corresponding positions of SEQ ID NO:17; in HCDR2, X50 comprises G, N, T or V; X59 comprises L or S; Xeo comprises L, M, or Y; X62 comprises D, E, or P; X63 comprises A, S or Q; and no more than one of X51, X54, X55, X57, X58, Xei, and X64 differ from the corresponding positions of SEQ ID NO: 17; in HCDR3, X99 comprises D, G or S; X102 comprises F or M, X104 comprises V, or Y; in LCDR1, X23 comprises D, Q, or T; X26 comprises A, K, Q, or S; X31 comprises R or S; and no more than one of X25, X27, X28, X29, X30, X32, X33, X35, and X36 differ from the corresponding positions of SEQ ID NO : 16, in LCDR2, X55 comprises K or R; and no more than one of X52, X53, X54, X57, and X58 differ from the corresponding positions of SEQ ID NO: 16; and in LCDR3, X92 comprises L or T, X99 comprises D, K, L, T, or Y; X101 comprises G, M, or S; and no more than one of X94 and X97 differ from the corresponding positions of SEQ ID NO: 16.

[0014] In certain embodiments, HCDR1 comprises GYSFTSX32YIX35 (SEQ ID NO:302), wherein X32 comprises S or T; and X35 comprises N or Q; HCDR2 comprises X50INPVSGSTX59X60AX62X63VK (SEQ ID NO:303), wherein X50 comprises G, N, T or V; X59 comprises L or S; Xeo comprises L, M, or Y; X62 comprises D, E, or P; X63 comprises A, S or Q; HCDR3 comprises X99GWX102DX104 (SEQ ID NO:298), wherein X99 comprises D, G, S, or T; X102 comprises F or M; X104 comprises V, or Y; LCDR1 comprises X23GSX26SDVGX31YNYVN (SEQ ID NO:304), wherein X23 comprises D, Q, or T; X26 comprises A, K, Q, or S; X31 comprises R or S; LCDR2 comprises GVSX55RPS (SEQ ID NO:305), wherein X55 comprises K or R; and LCDR3 comprises X92FAGGSYX99GX101 (SEQ ID NO:306), wherein X92 comprises L or T; X99 comprises D, K, L, T, or Y; X101 comprises G, M, S, or V.

[0015] In certain embodiments, each of the CDRs comprises no more than one or two amino acid differences as compared to particular antibody heavy and light chains described herein, for example, CDRs of the heavy and light chains whose sequences are set forth in FIG. 1 or FIG. 2, which are of similar sequence and bind to ActRIIB with high affinity.

[0016] In certain embodiments, a binding protein of the invention comprises no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:68 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:97; or no more than two (2) substitutionsper VH-CDR as compared to SEQ ID NO:70 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:97; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:70 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:64; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:74 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO: 16; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:83 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO: 16; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:72 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:64; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO: 17 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:16.

[0017] In certain embodiments, a binding protein of the invention comprises no more than one (1) substitution per VH-CDR as compared to SEQ ID NO: 68 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 97; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:70 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:97; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:70 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:64; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:74 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 16; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:83 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 16; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO: 72 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 64; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO: 17 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 16.

[0018] In certain embodiments, one, two, or all three of HCDR1, HCDR2, and HCDR3 are independently selected from a corresponding CDR of SEQ ID NOV, SEQ ID NOV, SEQ ID NOVO, SEQ ID NOV 1, SEQ ID NO: 12, SEQ ID NO:13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NOVO, SEQ ID NO:22, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQ ID NO:26, SEQ ID NO:28, SEQ ID NOVO, SEQ ID NOV 1, SEQ ID NOV2, SEQ ID NOV3, SEQ ID NOV4, SEQ ID NOV5, SEQ IDNOV6, SEQ ID NOV7, SEQ ID NOV8, SEQ IDNOV9, SEQ ID NOVO, SEQ ID NO:41, SEQ IDNO:42, SEQ ID NO:43, SEQ ID NO:68, SEQ ID NO:69,SEQ ID NO:70, SEQ ID NO:71, SEQ IDNO:72, SEQ ID NO:73, SEQ ID NO:74, SEQ ID NO:75,SEQ ID NO:76, SEQ ID NO:77, SEQ ID NO 78, SEQ ID NO:79, SEQ ID NO:80, SEQ ID N0:81 ,SEQ ID NO:82, SEQ ID NO:83, SEQ IDNO:84, SEQ ID NO:85, SEQ ID NO:86, SEQ IDNO:87,SEQ ID NO:88, SEQ ID NO:89, SEQ ID NO:90, SEQ ID N0:91, SEQ ID NO:92, SEQ ID NO:93, SEQ ID NO:94, SEQ ID NO:95, or SEQ ID NO:96.

[0019] In certain embodiments, one, two, or all three of LCDR1, LCDR2, and LCDR3 are independently selected from a corresponding CDR of SEQ ID NO:8, SEQ ID NO: 16, SEQ ID NO:21, SEQ ID NO:27, SEQ ID NO:52, SEQ ID NO:53, SEQ ID NO:54, SEQ ID NO:55, SEQID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO:60, SEQ ID NO:61, SEQ ID NO:62, SEQ ID NO:63, SEQ ID NO:64, or SEQ ID NO:97.

[0020] In some embodiments, that antigen binding protein comprises the VH-CDRs and VL- CDRs of AHF39788, AHF39695, AHF39883, AHF39700, AHF39717, AHF39900, AHF39693, AHF39694, AHF39697, AHF39698, AHF39699, AHF39703, AHF39705, AHF39707,AHF39708, AHF39709, AHF39712, AHF39713, AHF39714, AHF39715, AHF39716,AHF39718, AHF39721, AHF39722, AHF39725, AHF39726, AHF39727, AHF39728,AHF39729, AHF39731, AHF39732, AHF39733, AHF39737, AHF39739, AHF39749,AHF39750, AHF39775, AHF39802, AHF39815, AHF39855, AHF39882, AHF39885, or AHF39891 as set out in Table 12.

[0021] In some embodiments, the antigen binding protein is felinized and comprises a heavy chain framework (FR1H+FR2H+FR3H+FR4H) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical, or at least 97% identical, or at least 98% identical, or at least 99% identical, or identical to the heavy chain framework of SEQ ID NO:7 or SEQ ID NO: 15 and a light chain framework (FR1L+FR2L+FR3L+FR4L) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical, or at least 97% identical, or at least 98% identical, or at least 99% identical, or identical to the light chain framework of SEQ ID NO: 8 or SEQ ID NO: 16.

[0022] In some embodiments, the antigen binding protein comprises the VH and VL domains of AHF39788, AHF39695, AHF39883, AHF39700, AHF39717, AHF39900, AHF39693, AHF39694, AHF39697, AHF39698, AHF39699, AHF39703, AHF39705, AHF39707,AHF39708, AHF39709, AHF39712, AHF39713, AHF39714, AHF39715, AHF39716,AHF39718, AHF39721, AHF39722, AHF39725, AHF39726, AHF39727, AHF39728,AHF39729, AHF39731, AHF39732, AHF39733, AHF39737, AHF39739, AHF39749, AHF39750, AHF39775, AHF39802, AHF39815, AHF39855, AHF39882, AHF39885, or AHF39891.

[0023] In certain embodiments, a binding protein of the invention comprises no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:294; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:289 and no more than two (2) substitutions per VL- CDR as compared to SEQ ID NO:27; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:294; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:291 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:295; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:295; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:293; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:292 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:293; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:28 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO: 17 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO: 16.

[0024] In certain embodiments, a binding protein of the invention comprises no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:294; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:289 and no more than one (1) substitutions per VL- CDR as compared to SEQ ID NO:27; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than one (1) substitutions per VH-CDR as compared to SEQ IDNO:290 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:294; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:291 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:295; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:295; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:293; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:292 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:293; or no more than one (1) substitutions per VH-CDR as compared to SEQ ID NO:28 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO:27.

[0025] In certain embodiments, the antigen binding protein comprises: the VH-CDRs of SEQ ID NO:288 and the VL-CDRs of SEQ ID NO:294; or the VH-CDRs of SEQ ID NO:289 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:294; or the VH- CDRs of SEQ ID NO:288 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:295; or the VH-CDRs of SEQ ID NO:288 and the VL- CDRs of SEQ ID NO: 293; or the VH-CDRs of SEQ ID NO: 292 and the VL-CDRs of SEQ ID NO:294; or the VH-CDRs of SEQ ID NO:28 and the VL-CDRs of SEQ ID NO:27.

[0026] In certain embodiments, the antigen binding protein comprises SEQ ID NO:288 and SEQ ID NO:293; or SEQ ID NO:288 and SEQ ID NO:294; or SEQ ID NO:289 and SEQ ID NO:27; or SEQ ID NO:290 and SEQ ID NO:27; or SEQ ID NO:290 and SEQ ID NO:294; or SEQ ID NO:288 and SEQ ID NO:27; or SEQ ID NO:290 and SEQ ID NO:295; or SEQ ID NO:292 and SEQ ID NO:294; or SEQ ID NO 28 and SEQ ID NO:27.

[0027] In certain embodiments, the antigen binding protein is caninized and comprises a heavy chain framework (FR1H+FR2H+FR3H+FR4H) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical, or at least 97% identical, or at least 98% identical, or at least 99% identical, or identical to SEQ ID NO:20, or SEQ ID NO:26 and a light chain framework (FR1L+FR2L+FR3L+FR4L) at least 75%, or at least 80%, or at least 85%, or atleast 90%, or at least 93%, or at least 95% identical, or at least 97% identical, or at least 98% identical, or at least 99% identical, or identical to SEQ ID NO:21, or SEQ ID NO:27.

[0028] In certain embodiments of the invention, the antigen binding protein is not bimagrumab or other antigen binding protein described in WO 2010 / 125003. In certain embodiments, the antigen binding protein comprises at least one (i.e., one, two, three, four, five, or six) complementarity determining region (CDR) as defined herein that is different from the corresponding CDR of bimagrumab. In certain embodiments, the antigen binding protein comprises at least one framework (FW) (i.e. FW1, FW2, FW3, FW4) as defined herein that is different from the corresponding FW of bimagrumab. In certain embodiments, the antigen binding protein comprises at least one (i.e., one, two, three, four, five, or six) IMGT complementarity determining region (CDR) that is different from the corresponding IMGT CDR of bimagrumab. In certain embodiments, the antigen binding protein comprises at least one IMGT framework (FW) i.e. or FW1, FW2, FW3, FW4 that is different from the corresponding IMGT FW of bimagrumab.

[0029] The invention provides nucleic acids encoding the aforementioned antigen binding proteins, vectors comprising the encoding nucleic acids, and host cells for propagating, manipulating, and / or expressing the encoding nucleic acids.

[0030] The invention provides a method of making the aforementioned antibodies and antigen binding fragments, which comprises expressing the encoding nucleic acids and collecting the expression products.

[0031] The invention provides a method of treatment comprising administering a pharmaceutically effective amount of an anti-ActRIIB / anti-ActRIIA binding protein to a subject. In certain embodiments, the anti-ActRIIB binding protein is used to treat a metabolic disorder, such as, without limitation, type 2 diabetes, metabolic syndrome, lipodystrophy, impaired glucose tolerance, elevated plasma insulin concentrations, insulin resistance, dyslipidemia, hyperglycemia, hyperlipidemia, hypertension, cardiovascular disease or obesity, including anti-psychotic drug- associated obesity, glucocorticoid-induced obesity, hypothalamic obesity. In certain embodiments, the metabolic disorder is in a companion animal. In certain embodiments, the metabolic disorder is associated with a known syndrome or genetic abnormality, not limited to Bardet-Biedl syndrome or Prader-Willi syndrome.

[0032] In certain embodiments, the anti-ActRIIB / anti-ActRIIA binding protein is used to treat an obesity related disorder, including but not limited to glucose intolerance, prediabetes,insulin resistance, high triglycerides, overweight associated physical impairment, osteoporosis, renal disease, cardiometabolic disease, non-alcoholic fatty liver disease, obstructive sleep apnea, sexual hormones impairment, endocrine reproductive disorders, osteoarthritis, gastrointestinal cancers, dyslipidemia, hypertension, heart failure, coronary heart disease, stroke, and / or gallstones.

[0033] In certain embodiments, the anti-ActRIIB / anti-ActRIIA binding protein is used to treat a subject suffering from a muscle disorder, such as but not limited to a muscle atrophy obesity- associated sarcopenia, sarcopenia, or diabetes-associated muscle atrophy.

[0034] In certain embodiments the ActRII antibody treatment reduces body weight in the subject. In certain embodiments the ActRII antibody treatment reduces fat mass in the subject. In certain embodiments the ActRII antibody treatment increases lean mass in the subject. In certain embodiments the ActRII antibody treatment reduces fat mass and increases lean mass in the subject. In certain embodiments the ActRII antibody treatment reduces fat mass and maintains lean mass in the subject. In certain embodiments the ActRII antibody treatment reduces waist circumference in the subject. In certain embodiments the ActRII antibody treatment reduces liver and / or non-liver fat mass in the subject. In certain embodiments the ActRII antibody treatment improves glycemic control in the subject.

[0035] Without limitation, in certain embodiments, the subject comprises a canine. In certain embodiments the subject comprises a feline. The subject can be a companion animal or a farm animal. In certain embodiments, the subject comprises a human.

[0036] In certain embodiments the efficacy of the ActRII antibody treatment is measured by at least one of the following: body weight; bioelectrical impedance analysis (BIA); dual X-ray absorptiometry (DXA); magnetic resonance imaging (MRI); waist circumference; decreased BMI; waist to hip ratio; wait to height ratio; blood lipids profile; leptin, adiponectin, and adipsin levels; urine biomarkers; hemoglobin Ale (HgbAlc) levels; hand dynamometry demonstrating muscle strength; glucose levels; insulin levels; short physical performance battery (SPPB); Impact of Weight on Quality of Life (IWQoL-Lite for CT) assessment; Short Form (36) Health Survey (SF- 36) assessment; homeostasis model assessment 2 (H0MA2); physical activity monitoring via actigraphy; and Monosodium lodoacetate (MIA) model of Osteoarthritis.

[0037] Accordingly, it is an object of the invention not to encompass within the invention any previously known product, process of making the product, or method of using the product such that Applicants reserve the right and hereby disclose a disclaimer of any previously known product,process, or method. It is further noted that the invention does not intend to encompass within the scope of the invention any product, process, or making of the product or method of using the product, which does not meet the written description and enablement requirements of the USPTO (35 U.S.C. §112, first paragraph) or the EPO (Article 83 of the EPC), such that Applicants reserve the right and hereby disclose a disclaimer of any previously described product, process of making the product, or method of using the product. It may be advantageous in the practice of the invention to be in compliance with Art. 53(c) EPC and Rule 28(b) and (c) EPC. All rights to explicitly disclaim any embodiments that are the subject of any granted patent(s) of applicant in the lineage of this application or in any other lineage or in any prior filed application of any third party is explicitly reserved. Nothing herein is to be construed as a promise.

[0038] It is noted that in this disclosure and particularly in the claims and / or paragraphs, terms such as "comprises," "comprised," "comprising," and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean "includes," "included," "including," and the like; and that terms such as "consisting essentially of' and "consists essentially of' have the meaning ascribed to them in U. S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.

[0039] These and other embodiments are disclosed or are obvious from and encompassed by, the following Detailed Description.BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1A-1B shows an alignment of amino acid sequences of exemplary VH heavy chain (Fig. 1A) (SEQ ID NOs: 17, and 30-43) and VL light chain (Fig. IB) (SEQ ID NOs: 16, and 52- 64) variable domains of Example 3. Mutated amino acids of the VH and VL chains are underlined in the sequence of the U111-WT starting sequence.

[0041] FIG. 2A-2B shows an alignment of amino acid sequences of exemplary VH heavy chain (Fig. 2A) (SEQ ID NOs: 17, 68-96) and VL light chain (Fig. 2B) (SEQ ID NOs: 16, 64 and 97) variable domains from the combinatorial library of Example 4.

[0042] FIG. 3A-3B shows alignments of amino acid sequences of exemplary caninized VH heavy chain (Fig. 3A) (SEQ ID NOs: 17, 28, 288-292 and 379, 375, 316, 376-377, 378, 326, 317, 380-383, 320, 384-385) and VL light chain (Fig. 3B) (SEQ ID NOs: 16, 27, 293-295, 386-387,321, 325-327, 305, 388-390, 312, 391-392) variable domains of Example 6. CDRs are shown according to Kabat.DETAILED DESCRIPTION OF THE INVENTION

[0043] The invention provides binding proteins that specifically bind to ActRIIB or to ActRIIA or to ActRIIB and to ActRIIA. In certain embodiments, the binding proteins are optimized for administration to a canine. In certain embodiments, the binding proteins are optimized for administration to a feline. In certain embodiments, the binding proteins are optimized for binding to ActRIIA. In certain embodiments, the binding proteins are optimized for binding to ActRIIB. In certain embodiments, the binding proteins are optimized for binding to ActRIIA and to ActRIIB. The invention identifies amino acid positions at which mutations may confer substantial changes in binding affinity of the binding proteins for their target, as well as amino acid postions that may be varied with little change in binding affinity.

[0044] In an aspect, the invention provides a binding protein that specifically binds to activin type IIB receptor (ActRIIB), which comprises: (a) a heavy chain complementarity determining region 1 (HCDR1) comprising GYX28X29X30SX32YX34X35 (SEQ ID NO:296), wherein X28 comprises N, Q, S or T; X29 comprises F, I, L, M, or V, X30 comprises D, F, H, N, S, T, or W, X32 comprises S, or T, X34 comprises I, L, or V; X35 comprises N, Q, P, or T; (b) a heavy chain complementarity determining region 2 (HCDR2) comprising X50X51NPX54X55GX57X58X59X60X61X62X63X64 (SEQ ID NO:297), wherein X50 comprises A, G,H, M, N, Q, R, S, T, V, W, or Y; X51 comprises I, L, M, or W; X54 comprises A, N, S, V, or Y; X55 comprises G, I, L, S, T, or W; X57 comprises S or T; X58 comprises T or V; X59 comprises L,Q, or S; Xeo comprises L, M, V, or Y; Xei comprises A or D; X62 comprises A, D, E, H, K, P, Q,R, S, or T; X63 comprises A, F, G, I, L, N, P, Q, S, V, or Y; XM comprises A or V; (c) a heavy chain complementarity determining region 3 (HCDR3) comprising X99GWX102DX104 (SEQ ID NO:298), wherein X99 comprises D, G, S, or T; X102 comprises F or M; X104 comprises A, G, H,I, L, M, N, Q, R, S, T, V, or Y; (d) a light chain complementarity determining region 1 (LCDR1) comprising X23GX25X26X27X28X29X30X31X32X33YX35X36 (SEQ ID NO:299), wherein X23 comprises D, Q or T, X25 comprises Q or S; X26 comprises A, E, F, G, H, K, L, M, P, Q, R, S, T, or V; X27 comprises A, E, G, K, L, N, P, R, or S; X28 comprises A or D; X29 comprises F, I, P, V, or Y; X30 comprises G or N; X31 comprises A, G, K, L, N, P, Q, R, S, or T; X32 comprises H, P,W, V, or Y; X33 comprises A, H, L, N, P, Q, or R; X35 comprises I, P, or V; X36 comprises A or N; (e) a light chain complementarity determining region 2 (LCDR2) comprising X52X53X54X55RX57X58 (SEQ ID NO:300), wherein X52 comprises G, H, N, or S; X53 comprises A, D, E, F, H, I, K, N, P, Q, R, S, T, or V; X54 comprises D, E, G, S, or T; X55 comprises K or R; X57 comprises D, E, G, H, I, K, L, M, N, P, Q, R, S, T, or V; X58 comprises A, E, G, H, K, N, P, R, S, or Y; and (f) a light chain complementarity determining region 3 (LCDR3) comprising X92FX94GGX97YX99GX101 (SEQ ID NO:301), wherein X92 comprises L or T; X94 comprises A or S; X97 comprises A, R, S, or Y; X99 comprises D, E, F, G, H, I, K, L, M, N, Q, T, V, or Y; X101 comprises A, G, D, F, H, I, K, L, M, N, Q, R, S, T, V, or Y.

[0045] In certain embodiments, in HCDR1, X32 comprises S or T; X35 comprises N or Q; and no more than two of X28, X29, X30, and X34 differ from the corresponding positions of SEQ ID NO: 17; in HCDR2, X50 comprises G, N, T or V; X59 comprises S, or L; Xeo comprises L, M, or Y; X62 comprises D, E, or P; X63 comprises A, S or Q; and no more than two of X51, X54, X55, X57, X58, Xei, and X64 differ from the corresponding positions of SEQ ID NO: 17; in HCDR3, X99 comprises D, G or S; X102 comprises F or M, X104 comprises V, or Y; in LCDR1, X23 comprises Q or T; X26 comprises A, K, Q, or S; X31 comprises R or S; and no more than two of X25, X27, X28, X29, X30, X32, X33, X35, and X36 differ from the corresponding positions of SEQ ID NO: 16, in LCDR2, X55 comprises K or R; and no more than two of X52, X53, X54, X57, and X58 differ from the corresponding positions of SEQ ID NO: 16; and in LCDR3, X99 comprises D, K, L, T, or Y; X101 comprises G, M, or S; and no more than two of X92, X94, and X97 differ from the corresponding positions of SEQ ID NO: 16.

[0046] In certain embodiments, in HCDR1, X32 comprises S or T; X35 comprises N or Q; and no more than one of X28, X29, X30, and X34 differ from the corresponding positions of SEQ ID NO: 17; in HCDR2, X50 comprises G, N, T or V; X59 comprises S, or L; Xeo comprises L, M, or Y; X62 comprises D, E, or P; X63 comprises A, S or Q; and no more than one of X51, X54, X55, X57, X58, Xei, and X64 differ from the corresponding positions of SEQ ID NO: 17; in HCDR3, X99 comprises D, G or S; X102 comprises F or M, X104 comprises V, or Y; in LCDR1, X23 comprises D, Q or T; X26 comprises A, K, Q, or S; X31 comprises R or S; and no more than one of X25, X27, X28, X29, X30, X32, X33, X35, and X36 differ from the corresponding positions of SEQ ID NO: 16, in LCDR2, X55 comprises K or R; and no more than one of X52, X53, X54, X57, and Xss differ from the corresponding positions of SEQ ID NO:16; and in LCDR3, X99 comprises D, K, L, T, or Y;Xioi comprises G, M, or S; and no more than one of X92, X94, and X97 differ from the corresponding positions of SEQ ID NO: 16.

[0047] In certain embodiments, HCDR1 comprises GYSFTSX32YIX35 (SEQ ID NO:302), wherein X32 comprises S or T; and X35 comprises N or Q; HCDR2 comprises X50INPVSGSTX59X60AX62X63VK (SEQ ID NO:303), wherein X50 comprises G, N, T or V; X59 comprises S, or L; Xeo comprises L, M, or Y; X62 comprises D, E, or P; X63 comprises A, S or Q; HCDR3 comprises X99GWX102DX104 (SEQ ID NO:298), wherein X99 comprises D, G, S, or T; X102 comprises F or M; X104 comprises V, or Y; LCDR1 comprises X23GSX26SDVGX31YNYVN (SEQ ID NO:304), wherein X23 comprises D, Q or T; X26 comprises A, K, Q, or S; X31 comprises R or S; LCDR2 comprises GVSX55RPS (SEQ ID NO:305), wherein X55 comprises K or R; and LCDR3 comprises LFAGGSYX99GX101 (SEQ ID NO:307), wherein X99 comprises D, K, L, T, or Y; X101 comprises G, M, or S.

[0048] In certain embodiments, one, two, or all three of HCDR1, HCDR2, and HCDR3 are independently selected from a corresponding CDR of SEQ ID NOY, SEQ ID NO:9, SEQ ID NOTO, SEQIDNO:11, SEQIDNO:12, SEQIDNO:13, SEQIDNO:14, SEQIDNO:15, SEQ ID NO: 17, SEQ ID NO:20, SEQ ID NO:22, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQIDNO:26, SEQIDNO:28, SEQIDNO:30, SEQIDNO:31, SEQIDNO:32, SEQIDNO:33, SEQIDNO:34, SEQIDNO:35, SEQ IDNO:36, SEQIDNO:37, SEQIDNO:38, SEQ IDNO:39, SEQIDNO:40, SEQIDNO:41, SEQ IDNO:42, SEQIDNO:43, SEQIDNO:68, SEQIDNO:69, SEQIDNO:70, SEQIDNO:71, SEQ IDNO:72, SEQIDNO:73, SEQIDNO:74, SEQIDNO:75, SEQIDNO:76, SEQIDNO:77, SEQ IDNO:78, SEQIDNO:79, SEQIDNO:80, SEQ IDNO:81, SEQIDNO:82, SEQIDNO:83, SEQIDNO:84, SEQIDNO:85, SEQIDNO:86, SEQIDNO:87, SEQIDNO:88, SEQIDNO:89, SEQ IDNO:90, SEQIDNO:91, SEQIDNO:92, SEQ IDNO:93, SEQ ID NO:94, SEQ ID NO:95, or SEQ ID NO:96.

[0049] In certain embodiments, one, two, or all three of LCDR1, LCDR2, and LCDR3 are independently selected from a corresponding CDR of SEQ ID NO:8, SEQ ID NO: 16, SEQ ID NO:21, SEQ ID NO:27, SEQ ID NO:52, SEQ ID NO:53, SEQ ID NO:54, SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO:60, SEQ ID NO:61, SEQ ID NO:62, SEQ ID NO:63, SEQ ID NO:64, or SEQ ID NO:97.

[0050] In certain embodiments, the antigen binding protein comprises VH-CDRs and VL-CDRs of a clone from Table 12.

[0051] In certain embodiments, the antigen binding protein comprises the VH-CDRs and VL- CDRs of AHF39693, AHF39694, AHF39695, AHF39697, AHF39698, AHF39699, AHF39700, AHF39703, AHF39705, AHF39707, AHF39708, AHF39709, AHF39712, AHF39713,AHF39714, AHF39715, AHF39716, AHF39717, AHF39718, AHF39721, AHF39722,AHF39725, AHF39726, AHF39727, AHF39728, AHF39729, AHF39731, AHF39732,AHF39733, AHF39737, AHF39739, AHF39749, AHF39750, AHF39775, AHF39788,AHF39802, AHF39815, AHF39855, AHF39882, AHF39883, AHF39885, AHF39891, or AHF39900.

[0052] In certain embodiments, the antigen binding protein comprises the VH-CDRs of SEQ ID NO:288 and the VL-CDRs of SEQ ID NO:294; or the VH-CDRs of SEQ ID NO:289 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:294; or the VH- CDRs of SEQ ID NO:288 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:295; or the VH-CDRs of SEQ ID NO:288 and the VL- CDRs of SEQ ID NO: 293; or the VH-CDRs of SEQ ID NO: 292 and the VL-CDRs of SEQ ID NO:294; or the VH-CDRs of SEQ ID NO:28 and the VL-CDRs of SEQ ID NO:27; or the VH- CDRs of SEQ ID NO: 17 and the VL-CDRs of SEQ ID NO: 16.

[0053] In certain embodiments, the invention provides a caninized or felinized antibody that binds to ActRIIB, which comprises: (a) a heavy chain complementarity determining region 1 (HCDR1) comprising GYX28FTSSY (SEQ ID NO:308), wherein X28 comprises S or T; (b) a heavy chain complementarity determining region 2 (HCDR2) comprising X50INX53X54X55GX57X58X59YAX62X63X64X65 (SEQ ID NO:309), wherein X50 comprises G, M, N, Q, or T; X53 comprises A or P; X54 comprises A, P, or V; X55 comprises A, I, S, or T; X57 comprises G, H, I, M, N, S, or T; Xsx comprises A or T; X59 comprises D, L, R, S, or Y; X62 comprises D or Q, X63 comprises A, K, or S, X64 comprises F or V, and Xes comprises K or Q; (c) a heavy chain complementarity determining region 3 (HCDR3) comprising ARGGWFDY (SEQ ID NO:310); (d) a light chain complementarity determining region 1 (LCDR1) comprising SSDVGSY (SEQ ID NO:311); (e) a light chain complementarity determining region 2 (LCDR2) comprising GXeoXei, wherein Xeo comprises I or V; Xei comprises I, P, or S; and (f) a light chain complementarity determining region 3 (LCDR3) comprising GTFAGGSYYGV (SEQ ID NO:312). In certain embodiments, HCDR1 comprises GYX28FTSSY (SEQ ID NO:308), whereinX28 comprises S or T; and HCDR2 comprises INPVSGSTSYAX62X63X64X55 (SEQ ID NO:313), wherein X62 comprises D or Q; X63 comprises A, K, or S; X64 comprises F or V; and Xes comprises K or Q.

[0054] In certain embodiments, in VH, X28 comprises S; X62 comprises D; X63 comprises K; X64 comprises F; and Xes comprises Q. In certain embodiments, X28 comprises S, Xe2 comprises Q; X63 comprises A; Xe4 comprises F; and Xes comprises Q. In certain embodiments, X28 comprises S, Xe2 comprises Q; Xe3 comprises K; Xe4 comprises V; and Xes comprises Q. In certain embodiements, X28 comprises S, Xe2 comprises Q; Xe3 comprises K; Xe4 comprises F; and Xes comprises K.

[0055] In certain embodiments, the antibody comprises a heavy chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO:7 and a light chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO:8. In certain embodiments, the antibody comprises a heavy chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO: 15 and a light chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO: 16.

[0056] In certain embodiments, the antibody comprises a heavy chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO:20 and a light chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO:21. In certain embodiments, the antibody comprises a heavy chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO:26 and a light chain variable domain at least 80%, at least 85%, at least 90%, at least 95%, or 100% identical to SEQ ID NO: 27.

[0057] In certain embodiments, the antibody comprises SEQ ID NO: 14 and SEQ ID NO: 8, or comprises SEQ ID NO: 17 and SEQ ID NO:8, or comprises SEQ ID NO:24 and SEQ ID NO:21, or comprises SEQ ID NO:25 and SEQ ID NO:21, or comprises SEQ ID NO:28 and SEQ ID NO:27.

[0058] In certain embodiments, the antigen binding protein comprises canine or caninized frameworks. In certain embodiments, the antigen binding protein comprises human or humanized frameworks. In certain embodiments, the antigen binding protein comprises feline or felinized frameworks.

[0059] In certain embodiments, the antigen binding protein comprises a heavy chain framework (FR1H+FR2H+FR3H+FR4H) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical to SEQ ID NO: 13. In certain embodiments, the binding protein comprises a light chain framework (FR1L+FR2L+FR3L+FR4L) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical to SEQ ID NO: 14. In certain embodiments, the antigen binding protein comprises a VH domain at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical to SEQ ID NO: 13, and a VL domain at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical to SEQ ID NO: 14.

[0060] According to certain exemplary embodiments of the present invention, the ActRIIB binding protein is an anti-ActRIIB antibody or antigen-binding fragment thereof. The term “antibody,” as used herein, includes immunoglobulin molecules comprising four polypeptide chains, two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds, as well as multimers thereof (e.g., IgM). In a typical antibody, each heavy chain comprises a heavy chain variable region (abbreviated herein as HCVR or VH) and a heavy chain constant region. The heavy chain constant region comprises three domains, CHI, 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 (CL). 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 invention, the FRs of the anti-ActRIIB antibody (or antigen-binding portion thereof) may be identical to the canine or feline germline sequences, or may be naturally or artificially modified. An amino acid consensus sequence may be defined based on a side-by-side analysis of two or more CDRs.

[0061] Antibody residues that have a substantial impact on affinity and specificity of binding to target antigen are primarily located in CDRs. Kabat et al. compiled and aligned immunoglobulin heavy and light chain sequences and were the first to propose a standardized numbering scheme for the variable regions of immunoglobulins identifying conserved and hypervariable regions and residues. (Kabat EA et al., 1979, Sequences of Immunoglobulin Chains: Tabulation and Analysisof Amino Acid Sequences of Precursors, V-regions, C-regions, J-Chain and BP-Microglobulins, Department of Health, Education, and Welfare, Public Health Service, National Institutes of Health). While the Kabat system is a widely adopted standard for numbering antibody residues, the hypervariable regions defined by Kabat do not exactly match with the structural aspects of antigen-binding loops. Chothia and Lesk developed a structure-based numbering scheme by aligning crystal structures of antibody variable regions and classified CDR loops in a small number of “canonical” classes (Chothia C, et al., 1987, Canonical structures for the hypervariable regions of immunoglobulins. J. Mol. Biol. 196:901-17. doi: 10.1016 / 0022-2836(87)90412-8). An advantage of the Chothia numbering scheme is that topologically aligned residues from different antibodies are localized at the same position number and the Chothia CDR definition corresponds in most antibody sequences to the structural antigen-binding loop. Lefranc introduced a new system based on germ-line sequences intended to standardize numbering for all proteins of the immunoglobulin superfamily, including T cell receptor chains. (Giudicelli V et al., 1997, IMGT, the international ImMunoGeneTics database. Nucleic Acids Res. 25:206-11), which was then extended to entire variable domains (Lefranc M-P et al., 2003, IMGT unique numbering for immunoglobulin and T cell receptor variable domains and Ig superfamily V-like domains. Dev Comp Immunol. 27:55-77. doi: 10.1016 / S0145-305X(02)00039-3). Additional numbering systems have been proposed to align unconventional frameworks (Abhinandan KR et al., 2008, Analysis and improvements to Kabat and structurally correct numbering of antibody variable domains. Mol Immunol. 45:3832-9. doi: 10.1016 / j.molimm.2008.05.022) and to subdivide variable chain sequences into multiple fragments including structurally invariant “cores” (Gelfand et al., 1998, Algorithmic determination of core positions in the VL and VH domains of immunoglobulin molecules. J Comput Biol. (1998) 5:467-77). In certain embodiments of the invention, CDR residues are identified according to such a standard system as set forth above. In certain embodiments, antibodies of the invention are identified by all or a subset of Kabat CDR residues of the antibody sequences set forth herein. In certain embodiments, antibodies of the invention are identified by all or a subset of Chothia CDR residues of the antibody sequences set forth herein. In certain embodiments, antibodies of the invention can be identified by all or a subset of IMGT CDR residues of the antibody sequences set forth herein. In certain embodiments, antibodies of the invention can be identified by CDR residues defined by two or more systems, comprising e.g., but not limited to, all or a subset of amino acids of VH-CDR1 according to firstsystem, e.g. Kabat, all or a subset of residues of VH-CDR2 according to a second system e g. Chothia, all or a subset of residues of VH-CDR3 according to Kabat, all or a subset of residues of VL-CDR1 according to Kabat, all or a subset of residues of VL-CDR2 according to IMGT, and all or a subset of residues of VL-CDR3 according to Chothia. In certain embodiements, CDRs may be most conveniently or most accurately described to include amino acids selected by the Applicant. According to the invention, CDRs can be described or identified based on amino acids observed to strongly determine ntigen biding and amino acids observed not to particpte in antigen binding.

[0062] The following non-limiting table shows VH and VL variable domain amino acid positions of interest at or adjacent to CDRs and a range of useful amino acids at each position. Numbering from the N terminal corresponds to VH clone 044 T28S (SEQ ID NO:28) and VL Clone 044 VL (SEQ ID NO:27). The table is based on experimental results which include large numbers of antibodies produced, screened, and tested, as well as and structural information (e.g., without limitation 3D structural information) and information known in the art regarding antibody structure / function both independent of antigen-specific binding, and taking into account antibodies that bind to ActRIIA, to ActRIIB, or to both ActRIIA and ActRIIB.The table is based on experimental results which include large numbers of antibodies produced, screened, and tested, as well as and structural information (e.g., without limitation 3D structural information) and information known in the art regarding antibody structure / function, both independent of antigen-specific binding, and taking into account antibodies that bind to ActRIIA, to ActRIIB, or to both ActRIIA and ActRIIB and can be referred to in conjunction with antibody sequence and binding information described herein. Morvan describes structures related to antibodies of the invention and interactions that affect binding to ActRIIA and ActRIIB and modulate ligand binding. (Morvan, F. et al., 2017, Proc Natl Acad Sci U S A 114: 12448-12453)Non-limiting exemplary coordinates of binding complexes can be found in PDB ID: 5nhw (doi . org / 10.2210 / pdb 5nhw / pdb) .

[0063] In certain embodiments, an amino acid residue is mutated into one that allows the properties of the amino acid side-chain to be conserved. Examples of the properties of amino acid side chains comprise: hydrophobic amino acids (A, I, L, M, F, P, W, Y, V), hydrophilic amino acids (R, D, N, C, E, Q, G, H, K, S, T), and amino acids comprising the following side chains: aliphatic side-chains (G, A, V, L, I, P); hydroxyl group-containing side-chains (S, T, Y); sulfur atom-containing side-chains (C, M); carboxylic acid- and amide-containing side-chains (D, N, E, Q); base-containing side-chains (R, K, H); and aromatic-containing side-chains (H, F, Y, W). The letters within parenthesis indicate the one-letter amino acid codes. Amino acid substitutions within each group are called conservative substitutions. It is well known that a polypeptide comprising a modified amino acid sequence in which one or more amino acid residues is deleted, added, and / or substituted can retain the original biological activity (Mark D. F. et al., Proc. Natl. Acad. Sci. U.S.A. 81 :5662-5666 (1984); Zoller M. J. and Smith M., Nucleic Acids Res. 10: 6487-6500 (1982); Wang A. et al., Science 224: 1431-1433; Dalbadie-McFarland G. et al., Proc. Natl. Acad. Sci. U.S.A. 79: 6409-6413 (1982)). The number of mutated amino acids is not limited, but in general, the number falls within 40% of amino acids of each CDR, and preferably within 35%, and still more preferably within 30% (e.g., within 25%). The identity of amino acid sequences can be determined as described herein.

[0064] The invention provides recombinant antibodies designed or modified to minimize antigenicity when administered to a subject, for example, without limitation, chimerization, caninization, felinization, or humanization. In certain embodiments, the antibodies are modified to remove T cell epitopes. Without limitation, the subject can be a canine or feline. The subject can be a human or a non-human primate. The subject can be a farm animal.

[0065] As used herein, the term “canine” includes all domestic dogs, Canis lupus familiaris or Canis familiaris, unless otherwise indicated.

[0066] As used herein, the term “feline” refers to any member of the Felidae family. Domestic cats, pure-bred and / or mongrel companion cats, and wild or feral cats are all felines.

[0067] As used herein the term “canine framework” or “feline framework” refers to the amino acid sequence of the heavy chain and light chain of a canine antibody other than the hypervariable region residues defined herein as CDR residues. With regard to a caninized antibody, in certainembodiments, canine CDRs are identified in canine antibody heavy and light chains variable domain sequences that closely match CDRs of ActRTIB-binding antibodies originating in other species. In certain embodiments, native canine CDRs are replaced with the corresponding foreign CDRs (e.g ., those from a rat or a mouse antibody) in both chains. With regard to a felinized antibody, in certain embodiments, feline CDRs are identified in feline antibody heavy and light chains variable domain sequences that closely match CDRs of ActRIIB-binding antibodies originating in other species. In certain embodiments, native feline CDRs are replaced with the corresponding foreign CDRs (e.g ., those from a rat or a mouse antibody) in both chains. Optionally the heavy and / or light chains of the caninized or felinized antibody may contain some mutated or foreign non-CDR residues, e.g., framework amino acid residues that vary among germline antibody sequence or mutations that preserve the conformation of the foreign CDRs within the antibody.

[0068] Five major isotypes (IgA, IgG, IgM, IgD, IgE) and two forms of light chain (K and 1) are present in dogs. In the dog, there are four subtypes for IgG, which are IgGA, IgGB, IgGC, and IgGD (Bergeron etal al, 2014, Comparative functional characterization of canine IgG subclasses. Veterinary Immunology and Immunopathology. 157:31-41). For the cat, there are three subtypes of IgG which are lgGla, IgGlb, and IgG2 (Streitzel et al. 2014, In vitro functional characterization of feline IgGs. Vet Immunol Immunopathol 158, 214-223, doi.org / 10.1016 / j.vetimm.2014.01.012).

[0069] The invention provides caninized and felinized antibodies engineered to modulate one or more effector functions or circulation half-life. Hinge and constant domains of an antibody engage host receptors or complement protein to mediate effector functions and regulate antibody circulation. In certain embodiments, one or more effector function is enhanced. In certain embodiments, one or more effector function is reduced or eliminated. In certain embodiments, antibodies of the invention comprise modifications to modulate antibody-dependent cytotoxicity (ADCC) and / or complement-dependent cytotoxicity (CDC). A non-limiting example involves engineering of canine IgGB constant region residues Met242 and / or Leu243 (EU numbering) to reduce effector function (see, e.g., Lund et al., Human Fc gamma RI and Fc gamma RII interact with distinct but overlapping sites on human IgG. J Immunol., 1991, 147:2657-62). In certain embodiments, a IgGB constant region of the invention comprises M242A and L243A substitution. In certain embodiments, the second constant domain (CH2) and / or the third constant domain(CH3) comprises mutations and combinations of mutations from wild-type designed to modulate binding to FcRn (neonatal Fc) receptor. In canine constant regions, such mutations include, without limitation substitutions of Ala426, for example A426Y or A426H, substitutions of Thr286, for example T286L or T286Y, substitutions of Tyr436, for example Y436H, and combinations of such mutations including but not limited to A426Y + T286L, A426Y + Y436H, A426H + T286L, and A426H + T286Y. In certain embodiments a chimeric or caninized antibody of the invention comprises a substitution at amino acid Asn434, such as but not limited to N434H. In feline constant regions, such mutations include, without limitation substitutions of Ser428, including but not limited to S428Y or S428L, substitutions of Gln311, including but not limited to Q311V, substitutions of Leu309, including but not limited to L309V, substitutions of Thr286, including but not limited to T286E, substitutions of Glu380, including but not limited to E380T, and combinations of such mutations including but not limited to S428Y + Q311V, S428Y + L309V, S428Y + Q311 V + T286E, S428Y + Q311 V + E380T, and S428Y +L309V + E380T. In certain embodiments a chimeric or felinized antibody of the invention comprises a substitution at amino acid Ser428 and / or Ser434 including but not limited to S428L and / or S434H.

[0070] The term “antibody,” as used herein, includes antigen-binding fragments of full antibody molecules. The terms “antigen-binding portion” of an antibody, “antigen-binding fragment” of an antibody, and the like, as used herein, include any naturally occurring, enzymatically obtainable, synthetic, or genetically engineered polypeptide or glycoprotein that specifically binds an antigen to form a complex. As used herein, the term “specifically binds” or “binds specifically” means that an ActRIIB binding protein of the invention reacts or associates more frequently, more rapidly, with greater duration and / or with greater affinity with ActRIIB than it does with alternative antigens. For example, an ActRIIB binding protein binds to ActRIIB with materially greater affinity (e.g., at least 2-fold or 5-fold or 10-fold or 20-fold or 50-fold or 100- fold or 500-fold or 1000-fold or 10,000-fold or greater) than it does to other proteins or peptides. In certain embodiments, the ActRIIB-binding protein binds to ActRIIB with an equilibrium dissociation constant KD for the epitope or target to which it binds of, e.g., 10'4M or smaller, e.g., IO'5M, IO’6M, IO’7M, IO’8M, IO’9M, IO'10M, 10'11M, or IO’12M. The term “high affinity” for an IgG antibody refers to an antibody having a KD of 1.0* 10'6M or less, or 3.0* 10‘7M or less, or 1.0x 1 O'7M or less, or 3.0x 10'8M or less, or l.Ox 10'8M or less, or 3.0x1 O'9M or less, or 1.0x1 O'9M or less, or from l.Ox 1 O'6M to 3.0x 1 O'7M, or from 3.0x 10'7M to 1.0x 10'7M, or from 1.0x 1 O’7M to 3.0* 1 O’8M, or from 3.0* 1 O'8M to 1.0* 1 O'8M, or from 1.0* 1 O'8M to 3.0* 1 O'9M, or from 3.0* 1 O’9M to 1 .0* 1 O’9M for a target antigen. The term “very high affinity” for an IgG antibody refers to an antibody having a Ko of 3.0* 1 O'10M or less, or 1.0*1 O'10M or less, or 3.0* 10'11M or less, or l.OxlO11M or less, or 3.0* 1012M or less or 1.0* 1012M or less, or from 1.O* 1O10M to 3.0* 1 O'10M, or from 3.0* 1 O'10M or to 1.0*1 O'10M or from 1.0* 1 O'10M to 3.0* 10'11M, or from 3.0X 10’11M or to l.Ox lO’11M, or from l.Ox lO’11M to 3.0* 10’12M, or from 3.0* 10’12M to 1.0* 1 O’12M. It will be recognized by one of skill that an antibody that specifically binds to a target (e.g., ActRIIB) from one species may also specifically bind to orthologs of ActRIIB. In certain embodiments, an ActRIIB binding protein of the invention also binds to ActRIIA. In certain embodiments an ActRIIB binding protein of the invention has an affinity for ActRIIB that is greater than 50 fold, or greater than 20-fold, or greater than 10-fold, or greater than 5-fold of its affinity for ActRIIA.

[0071] 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 domains. 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 biology techniques, for example, to arrange one or more variable and / or constant domains into a suitable configuration, or to introduce codons, create cysteine residues, modify, add or delete amino acids, etc.

[0072] Non-limiting examples of antigen-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, domain- deleted antibodies, chimeric antibodies, CDR-grafted antibodies, diabodies, triabodies, tetrabodies, minibodies, nanobodies (e.g. monovalent nanobodies, bivalent nanobodies, etc.), small modular immunopharmaceuticals (SMIPs), and shark variable IgNAR domains, are also encompassed within the expression "antigen-binding fragment," as used herein.

[0073] In certain embodiments, an antigen-binding fragment of an antibody comprises 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 another in any suitable arrangement. For example, the variable region may be dimeric and contain VH-VH, VH-VL or VL-VL dimers. Alternatively, the antigen-binding fragment of an antibody may contain a monomeric VH or VL domain.

[0074] 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 constant domains that may be found within an antigenbinding fragment of an antibody of the present invention 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) VL-CH2, (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 another 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 present invention may comprise a homo-dimer or hetero-dimer (or other multimer) 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)).

[0075] The term "diabody (Db)" refers to a bivalent antibody fragment constructed by gene fusion (for example, P. Holliger et al., Proc. Natl. Acad. Sci. USA 90: 6444-6448 (1993), EP 404,097, WO 93 / 11161). In general, a diabody is a dimer of two polypeptide chains. In the each of the polypeptide chains, a light chain variable region (VL) and a heavy chain variable region (VH) in an identical chain are connected via a short linker, for example, a linker of about five residues, so that they cannot bind together. Because the linker between the two is too short, the VL and VH in the same polypeptide chain cannot form a single chain V region fragment, but instead form a dimer. Thus, a diabody has two antigen-binding domains. When the VL and VH regions against the two types of antigens (a and b) are combined to form VLa-Vnb and VLb-Vua via a linker of aboutfive residues, and then co-expressed, they are secreted as bispecific Dbs. The antibodies of the present invention may be such Dbs.

[0076] A single-chain antibody (also referred to as "scFv") can be prepared by linking a heavy chain V region and a light chain V region of an antibody (for a review of scFv see Pluckthun "The Pharmacology of Monoclonal Antibodies" Vol. 113, eds. Rosenburg and Moore, Springer Verlag, N.Y., pp. 269-315 (1994)). Methods for preparing single-chain antibodies are known in the art (see, for example, U.S. Pat. Nos. 4,946,778; 5,260,203; 5,091,513; and 5,455,030). In such scFvs, the heavy chain V region and the light chain V region are linked together via a linker, preferably, a polypeptide linker (Huston, J. S. et al., Proc. Natl. Acad. Sci. U.S.A, 1988, 85, 5879-5883). The heavy chain V region and the light chain V region in a scFv may be derived from the same antibody, or from different antibodies. The peptide linker used to ligate the V regions may be any single-chain peptide consisting of 12 to 19 residues. A DNA encoding a scFv can be amplified by PCR using, as a template, either the entire DNA, or a partial DNA encoding a desired amino acid sequence, selected from a DNA encoding the heavy chain or the V region of the heavy chain of the above antibody, and a DNA encoding the light chain or the V region of the light chain of the above antibody; and using a primer pair that defines the two ends. Further amplification can be subsequently conducted using a combination of the DNA encoding the peptide linker portion, and the primer pair that defines both ends of the DNA to be ligated to the heavy and light chain respectively. After constructing DNAs encoding scFvs, conventional methods can be used to obtain expression vectors comprising these DNAs, and hosts transformed by these expression vectors. Furthermore, scFvs can be obtained according to conventional methods using the resulting hosts. These antibody fragments can be produced in hosts by obtaining genes that encode the antibody fragments and expressing these as outlined above. Antibodies bound to various types of molecules, such as polyethylene glycols (PEGs), may be used as modified antibodies. Methods for modifying antibodies are already established in the art. The term "antibody" in the present invention also encompasses the above-described antibodies.

[0077] The term "Kd" as used herein, refers to the dissociation constant of an antibody-antigen interaction. The dissociation constant, Kd, and the association constant, Ka, are quantitative measures of affinity. At equilibrium, free antigen (Ag) and free antibody (Ab) are in equilibrium with antigen-antibody complex (Ag-Ab), and the rate constants, ka and kd, quantitate the rates of the individual reactions. At equilibrium, ka [Ab][Ag]=kd [Ag-Ab], The dissociation constant, Kd,is given by: Kd=kd / ka=[Ag][Ab] / [Ag-Ab], Kd has units of concentration, most typically M, mM, nM, pM, etc. When comparing antibody affinities expressed as Kd, having greater affinity for ActRIIB is indicated by a lower value. The association constant, Ka, is given by: Ka=ka / kd=[Ag- Ab] / [Ag][Ab], Ka has units of inverse concentration, most typically M1, mM1, nM1, pM1, etc. As used herein, the term "avidity" refers to the strength of the antigen-antibody binding taking valency into account.

[0078] The antibodies obtained can be purified to homogeneity. The antibodies can be isolated and purified by a method routinely used to isolate and purify proteins. The antibodies can be isolated and purified by the combined use of one or more methods appropriately selected from column chromatography, filtration, ultrafiltration, salting out, dialysis, preparative polyacrylamide gel electrophoresis, and isoelectro-focusing, for example (Strategies for Protein Purification and Characterization: A Laboratory Course Manual, Daniel R. Marshak et al. eds., Cold Spring Harbor Laboratory Press (1996); Antibodies: A Laboratory Manual. Ed Harlow and David Lane, Cold Spring Harbor Laboratory, 1988). Such methods are not limited to those listed above. Chromatographic methods include affinity chromatography, ion exchange chromatography, hydrophobic chromatography, gel filtration, reverse-phase chromatography, and adsorption chromatography. These chromatographic methods can be practiced using liquid phase chromatography, such as HPLC and FPLC. Columns to be used in affinity chromatography include protein A columns and protein G columns. For example, protein A columns include Hyper D, POROS, and Sepharose F. F. (Pharmacia). Antibodies can also be purified by utilizing antigen binding, using carriers on which antigens have been immobilized.

[0079] Exemplary and non-limiting amino acid sequences of certain binding proteins, antigens and ligands described herein are provided in Table 1.

[0080] Unless explicitly referred to otherwise, the extent of each CDR sequence is as set forth in the claims of this application. Nevertheless, in certain embodiments, amino acids encompassed by CDR regions of the anti-ActRII antibodies herein may be explicitly identified according to IMGT, Kabat, or Chothia. In certain embodiments, CDR regions may be identified according to experimental methods and results, for example by selection of amino acids “grafted” from one variable domain to another in Example 1, as shown in Table 2. In certain embodiments, CDR regions may be identified according to ranges of amino acids selected to be mutated. To avoid confusion, CDR regions may be identified by amino acid numbering beginning at the N terminal of a VH or VL variable domain, as shown for clone 044 T28S in Table 2. In embodiments of the invention, framework amino acids comprise the variable domain amino acids not defined to beCDR amino acids. Unless explictly defined otherwise, CDRs herein are defined by the claims.

[0081] As used herein, the term “therapeutic agent” refers to any agent or material that has a beneficial effect on the mammalian recipient. Thus, “therapeutic agent” embraces both therapeutic and prophylactic molecules having nucleic acid or protein components.

[0082] “Treating” as used herein refers to ameliorating at least one symptom of, curing and / or preventing the development of a given disease or condition.

[0083] The anti-ActRII proteins described herein, including antibodies or fragments thereof, are useful for ameliorating, or reducing the symptoms of, or treating, or preventing, diseases and disorders associated with ActRII and ligands of ActRII, such as but not limited to activin and myostatin. The anti-ActRII proteins or fragments, as well as combinations with other agents, are to be administered in a therapeutically effective amount to subjects in need of treatment of diseases and disorders associated with ActRII and its ligands in the form of a pharmaceutical composition as described herein.

[0084] The compositions of the present invention and the disclosed antibodies have therapeutic utilities, because they have an impact on brown adipose tissue and / or average plasma glucose homeostasis without negatively impacting hematological parameters in an individual. For example, the disclosed compositions or molecules can be administered to a subject, to treat or prevent a variety of metabolic disorders. Therefore, the present invention contemplates using ActRIIB antibodies for treating or preventing diseases or conditions that are impacted by the presence of or related to the activities of brown adipose tissue, plasma glucose homeostasis / concentration and / or plasma insulin concentrations. Thus the compositions of the invention and the disclosed antibodies may be used in the treatment of metabolic disorders that are impacted or caused by or related to the activities of thermogenic adipocytes, plasma glucose concentration, glucose homeostasis and / or plasma insulin concentrations, prophylaxis and for delaying the onset of said disorders or symptoms thereof. The term "subject" or "individual" as used herein is intended to include human and non-human animals. Non-human animals include all vertebrates, e.g. mammals and non-mammals, such as non-human primates, sheep, dogs, cats, cows, horses, chickens, amphibians, and reptiles.

[0085] Hence, the invention also relates to methods of treatment in which compositions of the invention or the disclosed anti-ActRIIB antibodies inhibit, i.e. antagonize, function of ActRIIB and thereby induce metabolic effects, for example, resulting in the alleviation of a metabolic disorder. The invention provides a method of treating a patient suffering from a metabolic disorder comprising administering a therapeutically effective amount of an anti-ActRIIB antibody or the disclosed compositions to the patient.

[0086] In certain embodiments the invention relates to a method of treating a metabolic disorder in a subject, comprising administering to said subject an antibody binding to ActRIIB leading to increase in brown adipose tissue (BAT) while not increasing red blood cell levels in said subject. Examples of ActRIIB antibodies that can be used in the disclosed methods of treatment are those disclosed or described in detail above. In certain embodiments, the ActRIIB antibodies are comprised in the herein disclosed inventive compositions. In certain aspects, the mentioned metabolic disorder is a result of or caused by an increased average plasma glucose concentration, non normal glucose homeostasis and / or plasma insulin concentrations. In another embodiment, the metabolic disorder is selected from the group of obesity, Type 2 Diabetes, Metabolic Syndrome, lipodystrophy, impaired glucose tolerance, elevated plasma insulinconcentrations, insulin resistance, dyslipidemia, hyperglycemia, hyperlipidemia, hypertension, cardiovascular disease and respiratory conditions or problems.

[0087] In yet another aspect of the invention, the invention provides a method for increasing BAT in a subject while not increasing red blood cell levels, comprising administering to said subject an antibody binding to ActRIIB.

[0088] Furthermore, the invention provides a method for decreasing the average plasma glucose concentration, or controlling glucose homeostasis or insulin sensitivity in a subject while not increasing red blood cell levels, comprising administering to said subject an antibody binding to ActRIIB. In certain aspects, the average plasma glucose concentration is detected by measuring the glycated hemoglobin (glycosylated hemoglobin) levels.

[0089] The invention also relates to the use of an anti-ActRIIB antibody in the manufacture of a medicament for the treatment of a metabolic disorder, particularly obesity, Type 2 Diabetes, Metabolic Syndrome, lipodystrophy, impaired glucose tolerance, elevated plasma insulin concentrations, insulin resistance, dyslipidemia, hyperglycemia, hyperlipidemia, hypertension, cardiovascular disease or respiratory problems or for decreasing the average plasma glucose concentration, controlling the glucose homeostasis or the insulin sensitivity.

[0090] The methods are particularly suitable for treating, preventing or ameliorating metabolic disorders.

[0091] The invention also relates to the methods of treating a subject suffering from a metabolic disorder and a musculoskeletal diseases or disorders, such as muscle atrophy. Muscle atrophy can be obesity-associated sarcopenia, sarcopenia, or diabetes-associated muscle atrophy.

[0092] There are many causes of muscle atrophy, including as a result of treatment with a glucocorticoid such as cortisol, dexamethasone, betamethasone, prednisone, methylprednisolone, or prednisolone. The muscle atrophy can also be a result of denervation due to nerve trauma or a result of degenerative, metabolic, or inflammatory neuropathy (e.g., Guillian-Barre syndrome, peripheral neuropathy, or exposure to environmental toxins or drugs). In addition, the muscle atrophy can be a result of myopathy, such as myotonia; a congential myopathy, including nemalene myopathy, multi / minicore myopathy and myotubular (centronuclear) myopathy; mitochondrial myopathy; familial periodic paralysis; inflammatory myopathy; metabolic myopathy, such as caused by a glycogen or lipid storage disease; dermatomy ositi sis; polymyositis; inclusion body myositis; myositis ossificans; rhabdomyolysis and myoglobinurias. Other conditions leading tomusculoskeletal diseases or muscle atrophy are described in detail above. The treatment results may be complete, e.g., the total absence of a metabolic disorder. The results may also be partial, such that the peculiarity of the metabolic disorder in a subject is statistically significantly less pronounced than had the subject not received a composition of the present invention. Partial treatment results may be a decrease in severity of disease symptoms, an increase in frequency and duration of disease symptom-free periods, or a prevention of impairment or disability due to the disease affliction. An age-related condition as referred to herein may begin at the age of 50 years or older (i.e. 60, 70, 80 or older).

[0093] In certain embodiments the antibody compositions and methods are used for ameliorating, or reducing the symptoms of, or treating, or preventing pain of osteoarthritis (OA). OA is a slowly progressive degenerative joint disease characterized by whole-joint structural changes including articular cartilage, synovium, subchondral bone and periarticular components, leading to pain and loss of joint function. Chronic pain and OA are common in dogs and cats. 20- 30% of dogs are affected clinically and have signs of OA. Up to 40% of all cats being affected clinically, with 90% of all cats over 12 years of age have signs of OA.

[0094] In dogs the most common site of OA is the hip, followed by stifle (knee), shoulder and carpus. In cats hip, stifle, carpus or spine are most commonly affected.

[0095] In one embodiment, a patient may be pre-treated with an anti-ActRIIB antibody or composition of the invention prior to an anticipated period of enforced rest / inactivity. Such a period may occur when a patient is admitted to hospital, for example for surgery to the hip or leg. The inactivity may be localized, such as by casting of a broken limb or joint, or by administration of a paralytic agent.

[0096] In a further embodiment, the patient may be one who has not responded to previous treatments. For example, the patient may not have responded to treatment with IGF-1, IGF-2 or variants of IGF-1 or IGF-2, an anti-myostatin antibody, a myostatin propeptide, a myostatin decoy protein that binds ActRIIB but does not activate it, a beta 2 agonist, a Ghrelin agonist, a SARM, GH agonists / mimetics or follistatin. A simple way of measuring a patient's response to treatment may be timing how long it takes for a patient to climb a known height of stairs and comparing the results both before and after treatment.

[0097] The ActRIIB antibodies may be administered as the sole active agent or in conjunction with, e.g. as an adjuvant to or in combination to, other drugs e.g. IGF-1, IGF-2 or variants of IGF-1or IGF-2, an anti -myostatin antibody, a myostatin propeptide, a myostatin decoy protein that binds ActRIIB but does not activate it, a beta 2 agonist, a Ghrelin agonist, a SARM, GH agonists / mimetics or follistatin. For example, the antibodies of the invention may be used in combination with an IGF-1 mimetic as disclosed in WO2007 / 146689. In accordance with the foregoing the present invention provides in a yet further aspect: A method or use as defined above comprising co-administration, e.g. concomitantly or in sequence, of a therapeutically effective amount of an ActRIIB antibody , and at least one second drug substance, said second drug substance being IGF-1, IGF-2 or variants of IGF-1 or IGF-2, an anti-myostatin antibody, a myostatin propeptide, a myostatin decoy protein that binds ActRIIB but does not activate it, a beta 2 agonist, a Ghrelin agonist, a SARM, GH agonists / mimetics or follistatin.

[0098] Formulations and Methods of Administration

[0099] For in vivo use, a therapeutic agent as described herein is generally incorporated into a pharmaceutical composition prior to administration. Within such compositions, one or more therapeutic compounds as described herein are present as active ingredient(s) (i.e., are present at levels sufficient to provide a statistically significant effect on the symptoms of cystic fibrosis, as measured using a representative assay). A pharmaceutical composition comprises one or more such compounds in combination with any pharmaceutically acceptable carrier(s) known to those skilled in the art to be suitable for the particular mode of administration. In addition, other pharmaceutically active ingredients (including other therapeutic agents) may, but need not, be present within the composition.

[0100] The antibodies of the present invention can be formulated according to standard methods (see, for example, Remington's Pharmaceutical Science, latest edition, Mark Publishing Company, Easton, U.S.A), and may comprise pharmaceutically acceptable carriers and / or additives. The present invention relates to compositions (including reagents and pharmaceuticals) comprising the antibodies of the invention, and pharmaceutically acceptable carriers and / or additives. Exemplary carriers include surfactants (for example, PEG and Tween), excipients, antioxidants (for example, ascorbic acid), coloring agents, flavoring agents, preservatives, stabilizers, buffering agents (for example, phosphoric acid, citric acid, and other organic acids), chelating agents (for example, EDTA), suspending agents, isotonizing agents, binders, disintegrators, lubricants, fluidity promoters, and corrigents. However, the carriers that may be employed in the present invention are not limited to this list. In fact, other commonly used carrierscan be appropriately employed: light anhydrous silicic acid, lactose, crystalline cellulose, mannitol, starch, carmelose calcium, carmelose sodium, hydroxypropylcellulose, hydroxypropylmethyl cellulose, polyvinylacetaldiethylaminoacetate, polyvinylpyrrolidone, gelatin, medium chain fatty acid triglyceride, polyoxyethylene hydrogenated castor oil 60, sucrose, carboxymethylcellulose, corn starch, inorganic salt, and so on. The composition may also comprise other low-molecular-weight polypeptides, proteins such as serum albumin, gelatin, and immunoglobulin, and amino acids such as glycine, glutamine, asparagine, arginine, and lysine. When the composition is prepared as an aqueous solution for injection, it can comprise an isotonic solution comprising, for example, physiological saline, dextrose, and other adjuvants, including, for example, D-sorbitol, D-mannose, D-mannitol, and sodium chloride, which can also contain an appropriate solubilizing agent, for example, alcohol (for example, ethanol), polyalcohol (for example, propylene glycol and PEG), and non-ionic detergent (polysorbate 80 and HCO-50).

[0101] If necessary, antibodies of the present invention may be encapsulated in microcapsules (microcapsules made of hydroxycellulose, gelatin, polymethylmethacrylate, and the like), and made into components of colloidal drug delivery systems (liposomes, albumin microspheres, microemulsions, nano-particles, and nano-capsules) (for example, see "Remington's Pharmaceutical Science 16th edition", Oslo Ed. (1980)). Moreover, methods for making sustained- release drugs are known, and these can be applied for the antibodies of the present invention (Langer et al., J. Biomed. Mater. Res. 15: 167-277 (1981); Langer, Chem. Tech. 12: 98-105 (1982); U.S. Pat. No. 3,773,919; EP Patent Application No. 58,481; Sidman et al., Biopolymers 22: 547- 556 (1983); EP: 133,988).

[0102] A preferred route of administration in both canines and felines is by subcutaneous injection usually into the skin at the base of the neck. In certain embodiments, the anti-ActRIIB protein is packaged in an integrated delivery system such as a pen or prefilled syringe for subcutaneous administration. Ghil et al. describes administration of an anti-NGF antibody SB5, via prefilled syringe (PFS) and autoinjector (Al) pen based on injection site pain, patient preference, and safety in rheumatoid arthritis (RA) (See Ghil et al., Usability and safety of SB5 (an adalimumab biosimilar) prefilled syringe and autoinjector in patients with rheumatoid arthritis. Curr Med Res Opin 2019 Mar;35(3):497-502.) Compositions of the invention are similarly administered to canines, felines, and other mammals.

[0103] The term “therapeutically effective amount,” in reference to treating a disease state / condition, refers to an amount of a compound either alone or as contained in a pharmaceutical composition that is capable of having any detectable, positive effect on any symptom, aspect, or characteristics of a disease state / condition when administered as a single dose or in multiple doses. Such effect need not be absolute to be beneficial.

[0104] The terms “treat,” “treating” and “treatment” as used herein include administering a compound prior to the onset of clinical symptoms of a disease state / condition so as to prevent any symptom, as well as administering a compound after the onset of clinical symptoms of a disease state / condition so as to reduce or eliminate any symptom, aspect or characteristic of the disease state / condition. Such treating need not be absolute to be useful.

[0105] In certain embodiments, the present therapeutic agent may be systemically administered, e.g., orally, in combination with a pharmaceutically acceptable vehicle such as an inert diluent or an assimilable edible carrier. They may be enclosed in hard or soft shell gelatin capsules, may be compressed into tablets, or may be incorporated directly with the food of the patient's diet. For oral therapeutic administration, the active compound may be combined with one or more excipients and used in the form of ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, wafers, and the like. Such compositions and preparations should contain at least 0.1% of active compound. The percentage of the compositions and preparations may, of course, be varied and may conveniently be between about 2 to about 60% of the weight of a given unit dosage form. The amount of active compound in such therapeutically useful compositions is such that an effective dosage level will be obtained.

[0106] The tablets, troches, pills, capsules, and the like may also contain the following: binders such as gum tragacanth, acacia, com starch or gelatin; excipients such as dicalcium phosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearate; and a sweetening agent such as sucrose, fructose, lactose or aspartame or a flavoring agent such as peppermint, oil of Wintergreen, or cherry flavoring may be added. When the unit dosage form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier, such as a vegetable oil or a polyethylene glycol. Various other materials may be present as coatings or to otherwise modify the physical form of the solid unit dosage form. For instance, tablets, pills, or capsules may be coated with gelatin, wax, shellac or sugar and the like. A syrup or elixir may contain the active compound, sucrose or fructose as a sweetening agent, methyl andpropylparabens as preservatives, a dye and flavoring such as cherry or orange flavor. Of course, any material used in preparing any unit dosage form should be pharmaceutically acceptable and substantially non-toxic in the amounts employed. In addition, the active compound may be incorporated into sustained-release preparations and devices.

[0107] The active compound may also be administered intravenously or intraperitoneally by infusion or injection. Solutions of the active compound or its salts may be prepared in water, optionally mixed with a nontoxic surfactant. Dispersions can also be prepared in glycerol, liquid polyethylene glycols, triacetin, and mixtures thereof and in oils. Under ordinary conditions of storage and use, these preparations contain a preservative to prevent the growth of microorganisms.

[0108] The pharmaceutical dosage forms suitable for injection or infusion can include sterile aqueous solutions or dispersions or sterile powders comprising the active ingredient that are adapted for the extemporaneous preparation of sterile injectable or infusible solutions or dispersions, optionally encapsulated in liposomes. In all cases, the ultimate dosage form should be sterile, fluid and stable under the conditions of manufacture and storage. The liquid carrier or vehicle can be a solvent or liquid dispersion medium comprising, for example, water, ethanol, a polyol (for example, glycerol, propylene glycol, liquid polyethylene glycols, and the like), vegetable oils, nontoxic glyceryl esters, and suitable mixtures thereof. The proper fluidity can be maintained, for example, by the formation of liposomes, by the maintenance of the required particle size in the case of dispersions or by the use of surfactants. The prevention of the action of microorganisms can be brought about by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, sorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, buffers or sodium chloride. Prolonged absorption of the injectable compositions can be brought about by the use in the compositions of agents delaying absorption, for example, aluminum monostearate and gelatin.

[0109] Sterile injectable solutions are prepared by incorporating the active compound in the required amount in the appropriate solvent with various of the other ingredients enumerated above, as required, followed by filter sterilization. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and the freeze drying techniques, which yield a powder of the active ingredient plus any additional desired ingredient present in the previously sterile-filtered solutions.

[0110] Useful dosages of the compounds of the present invention can be determined by comparing their in vitro activity, and in vivo activity in animal models. In certain embodiments, a useful dose is from about 0.1 mg / kg to about 5 mg / kg or from about 0.5 mg / kg to about 2 mg / kg. Methods for the extrapolation of effective dosages in humans and animals of different sizes are known to the art; for example, see U.S. Pat. No. 4,938,949.

[0111] The amount of the compound, or an active salt or derivative thereof, required for use in treatment will vary not only with the particular salt selected but also with the route of administration, the nature of the condition being treated and the age and condition of the patient and will be ultimately at the discretion of the attendant physician or clinician.

[0112] In general, however, a suitable dose will be in the range of from about 0.5 to about 100 mg / kg, e.g., from about 10 to about 75 mg / kg of body weight per day, such as 3 to about 50 mg per kilogram body weight of the recipient per day, preferably in the range of 6 to 90 mg / kg / day, most preferably in the range of 15 to 60 mg / kg / day.

[0113] The compound is conveniently administered in unit dosage form; for example, containing 5 to 1000 mg, conveniently 10 to 750 mg, most conveniently, 50 to 500 mg of active ingredient per unit dosage form.

[0114] Ideally, the active ingredient should be administered to achieve peak plasma concentrations of the active compound of from about 0.5 to about 75 pM, preferably, about 1 to 50 pM, most preferably, about 2 to about 30 pM. This may be achieved, for example, by the intravenous injection of a 0.05 to 5% solution of the active ingredient, optionally in saline, or orally administered as a bolus containing about 1-100 mg of the active ingredient. Desirable blood levels may be maintained by continuous infusion to provide about 0.01-5.0 mg / kg / hr or by intermittent infusions containing about 0.4-15 mg / kg of the active ingredient(s).

[0115] The desired dose may conveniently be presented in a single dose or as divided doses administered at appropriate intervals, for example, as two, three, four or more sub-doses per day. The sub-dose itself may be further divided, e.g., into a number of discrete loosely spaced administrations

[0116] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined in the appended claims.

[0117] The present invention will be further illustrated in the following Examples which are given for illustration purposes only and are not intended to limit the invention in any way.ExamplesExample 1 - Felinization of Bimagrumab

[0118] The antibody bimagrumab (SEQ ID NO: 1, SEQ ID NO:2, Lach-Trifdieff et al., 2014, Mol Cell Biol, 34:606-618) was felinized by replacing the human frameworks with feline frameworks. Using a proprietary informatics approach, eight feline heavy chain frameworks were selected along with six light chain frameworks for felinizing bimagrumab. The heavy and light CDRs, as shown in Table 2, are a combination of the IMGT and Kabat definitions and were used for grafting into the selected feline heavy and light chain frameworks. The DNA for these felinized variable domains were synthesized with the feline IgGla constant (GenBank: BAA32229.1) and feline lambda constant domains (GenBank: XP 044897826.1). In addition, the DNA of the feline constant domains were synthesized with the bimagrumab heavy and light variable domains to create a feline chimeric construct (SEQ ID NO:3, SEQ ID NO:4). The constructs were cloned into a proprietary mammalian expression vector. Each of the different heavy and light chains for felinization were paired and co-transfected into HEK 293 cells, and the IgGs in the conditioned medium were purified with Mab Select SuRe protein A resin. The antibodies were buffered exchanged into 20 mM acetate, 136 mM NaCl, pH 5.5. An SPR assay was initially completed on the felinized antibodies using the Carterra instrument. The antigen for this analysis was feline activin receptor I1B (ActRIIB, SEQ ID NO:5) and was generated by expressing the extracellular domain of the feline activin receptor (Serl9-Thrl34, Genbank number XP 023116499.1) fused to the AviTag (Gly-Leu-Asn-Asp-Ile-Phe-Glu-Ala-Gln-Lys-Ile-Glu-Trp-His-Glu) (SEQ ID NO:331) and His-tag (His-His-His-His-His-His-His-His) (SEQ ID NO:332) at the C-terminus and a mouse IgG signal peptide at the N-terminus. This construct was subcloned into pcDNA3.4 (ThermoFisher) and transfected into HD CHO-SE cells (GenScript). The recombinant feline activin RIIB was purified from conditioned medium using HisTrap FF chromatography followed by the polishing step with HiLoad26 / 600 Superdex200pg chromatography. The binding kinetics for felinized clones with the highest affinity to ActRIIB were Clone 005 (SEQ ID NO:7, SEQ ID NO:8) and Clone 034 (SEQ ID NO:15, SEQ ID NO: 16). The frameworks for Clone 005 wereIGHV3-1*O1 and IGLV1-56*O1, and the frameworks for Clone 034 were IGHV35-l*01 and IGLV1 -32*01.

[0119] These two clones were further modified by evaluating the bimagrumab - ActivinRIIA (PDB 5nh3) structure. By matching the interacting regions, amino acid substitutions in the CDRs were identified that could potentially be used to increase affinity to Activin RIIA. The series of variants for Clone 005 that were generated included T28S (SEQ ID NO:9), Q62D (SEQ ID NO: 10), K63S (SEQ ID NO: 11), F64V (SEQ ID NO: 12), Q65K (SEQ ID NO: 13) and T28S / Q62D (SEQ ID NO: 14). For clone 034, the T28S heavy chain variant (SEQ ID NO: 17) was generated.

[0120] These variants along with the parental Clone 005 and Clone 034 sequences were subcloned into pcDNA 3.4 (ThermoFisher). An equal ratio of heavy chain and light chain plasmids for each were co-transfected into mammalian cells. Seven days following the transient transfection, the IgG in the conditioned medium was purified using MabSelect SuRe chromatography. The antibodies were buffer exchanged into 20 mM sodium acetate, 136 mM sodium chloride, pH 5.5.

[0121] The affinity of feline chimeric bimagrumab, the parental clones, and the variants were determined using a Biacore T200 instrument. Goat anti-feline IgG- Fc fragment specific (Jackson ImmunoResearch; 102-005-008) at 30 pg / ml in 10 mM acetate, pH 5.0 was immobilized onto CM5 sensor chip (Cytiva; 29104988) with NHS coupling at 10 pL / min for 420 seconds and then remaining sites blocked with ethanolamine at 10 pL / min for 420 seconds. The anti-feline ActRII antibodies were captured at 1-1.5 p.g / ml onto the coupled chip for 60 sec at 10 pl / min. Feline ActRIIB, binding was then assessed at multiple concentrations starting at 100 nM using PBSP+ running buffer (Cytiva) with a flow rate of 30 uL / min. The length of the association time was 120s and the dissociation time was run for 600s. The chip surface was regenerated with 10 mM glycine. Double reference-subtracted sensorgrams were fitted to a 1 :1 binding model using Biacore T200 Evaluation software. The kinetics of the feline Activin RUB binding to the antibodies is shown below in Table 3.

[0122] Variant were chosen from Clone 005 and Clone 034 and further characterized including affinity to feline activin receptor IIA (ActRIIA) which was generated by expressing the extracellular domain (Arg24-Phel02) of the feline activin receptor IIA (Genbank number XP 019693638.1) fused to the AviTag (Gly-Leu-Asn-Asp-Ile-Phe-Glu-Ala-Gln-Lys-Ue-Glu-Trp- His-Glu) (SEQ ID NO:331) and His-tag (His-His-His-His-His-His-His-His) (SEQ ID NO:332) at the C-terminus and a mouse IgG signal peptide at the N-terminus (SEQ ID NO:6). The Biacore method was identical to that described for ActivinRIIB with just the change in the antigen used in the analyte.

[0123] Additionally, the ability of the antibody to block binding of the putative ligands (Activin A and myostatin) to ActivinRIIB was assessed by SPR. The receptor blocking assays were completed by capturing 100 nM of biotinylated receptor ActivinRIIB on a Series S CAP chip with Biotin CAPture reagent (Cytiva). Antibodies were titrated in running buffer (1 X PBSP+, Cytiva) to 25, 50, and 100 nM and flowed over the receptor to bind. Next, either human Activin A at 50 nM (R&D Systems, 338-AC, Gly311-Ser426) or mouse myostatin at 100 nM (R&D Systems, 788-G8, Asp268-Ser376) was flowed over the chip. Both feline Activin A and feline myostatin have 100% sequence identity to human Activin A or mouse myostatin in the regions expressed in the commercial proteins (NCBI Ref Seq NP_001009856.1 and XP_003991021.1). The relative response units (RU) at the binding report point were used to calculate the inhibitionpercent by dividing the relative binding response of the cycles with antibody samples by an average of the Activin A-only or myostatin-only relative binding response (with no antibody present) that were collected throughout the assay. The ability of each antibody to block binding of Activin A to Activin Receptor IIB are described below in Table 5. The ability of each antibody to block binding of Activin Receptor IIB and myostatin are described below in Table 6.

[0124] The results demonstrate that Clone 005 variant T28S / Q62D and Clone 034 variant T28S potently block Activin A and myostatin binding to Activin RUB at all concentrations.Example 2 - Caninization of Bimagnimab

[0125] The antibody bimagrumab (SEQ ID NO: 1, SEQ ID NO:2) was also caninized by replacing the human frameworks with canine frameworks. Using a proprietary informatics approach, eight canine heavy chain frameworks were selected along with six canine light chain frameworks for caninizing bimagrumab. The heavy and light CDRs, as defined in Table 2, are a combination of the IMGT and Kabat definitions and were used for grafting into the selected canine heavy and light chain frameworks. The DNA for these caninized variable domains were synthesized with the canine IgGB constant and canine lambda constant domains (Bergeron et al, 2014, Vet Immunol Immunopathol, 157:31). In addition, the DNA of the canine constant domains were synthesized with the bimagrumab heavy and light variable domains to create canine chimeric construct (SEQ ID NO: 18, SEQ ID NO: 19). The constructs were cloned into a proprietary mammalian expression vector. Each of the different heavy and light chains were paired and cotransfected into HEK 293 cells, and the IgGs in the conditioned medium were purified withMabSelect SuRe protein A resin. The antibodies were buffered exchanged into PBS, pH 7.2. An SPR assay was initially completed on the caninized antibodies using the Carterra instrument. The antigen for this analysis was the same feline activin receptor IIB (ActRIIB) which has 100% identity to the canine receptor sequence in the extracellular domain used for expression (Ser30- Thrl45) of the canine activin receptor (Genbank number XP_038287841) fused to the AviTag (Gly-Leu-Asn-Asp-Ile-Phe-Glu-Ala-Gln-Lys-Ile-Glu-Trp-His-Glu) (SEQ ID NO:331) and His- tag (His-His-His-His-His-His-His-His) (SEQ ID NO:332) at the C-terminus and a mouse IgG signal peptide at the N-terminus (SEQ ID NO:5). This construct was subcloned into pcDNA3.4 (ThermoFisher) and transfected into HD CHO-SE cells (GenScript). The recombinant activin RIIB was purified from conditioned medium using HisTrap FF chromatography followed by HiLoad26 / 600 Superdex200pg. The binding kinetics for caninized clones with the highest affinity to ActRIIB were Clone 006 (SEQ ID NO:20, SEQ ID NO:21) and Clone 044 (SEQ ID NO:26, SEQ ID NO:27). The canine frameworks for Clone 006 were IGHV1-30 and IGLV1-157, and the canine frameworks for Clone 044 were IGHV3-41 and IGLV2-31.

[0126] Clones 006 and 044 were further modified by evaluating the bimagrumab - ActivinRIIA (PDB 5nh3) structure. By matching the interacting regions, we identified amino acid substitutions that could potentially be used to increase affinity to ActRIIA. The series of variants for Clone 006 that were generated included T28S / Q62D (SEQ ID NO:22), T28S / K63A (SEQ ID NO:23), T28S / F64V (SEQ ID NO:24), and T28S / Q65K (SEQ ID NO:25). For clone 044, the T28S heavy chain variant (SEQ ID NO:28) was generated.

[0127] These variants along with the parental Clone 006 and Clone 044 sequences were subcloned into pcDNA 3.4 (ThermoFisher). An equal ratio of heavy chain and light chain plasmids for each were co-transfected into CHO cells and the IgG in the conditioned medium was purified using MabSelect SuRe chromatography. The antibodies were buffer exchanged into PBS, pH 7.2.

[0128] The affinity for canine ActRIIB of canine chimeric bimagrumab, Clone 006, Clone variants of 006, Clone 044 and the Clone variant of 044 were determined using a Biacore T200 instrument. The antibodies were captured using a CM5 Series S chip amine coupled with an antidog Fc antibody (Jackson Immunoresearch, 304-005-008). Antigen, canine ActRIIB, binding was then assessed at multiple concentrations starting at 100 nM using PBSP+ running buffer (Cytiva) with a flow rate of 30 uL / min. The length of the association time was 120s and the dissociation time was run for 600s. The chip surface was regenerated with 10 mM glycine. Double reference-subtracted sensorgrams were fitted to a 1 : 1 binding model using Biacore T200 Evaluation software.[001291 The best two variants were chosen from clone 006 and best variant from 044 and further characterized including affinity to activin receptor IIA (ActRIIA). The antigen for this analysis was the same feline activin receptor IIA (ActRIIA) which has 100% identity to the canine receptor sequence in the extracellular domain used for expression (Arg24-Phel02) of the canine activin receptor (Genbank number XP_038282146.1) fused to the AviTag (Gly-Leu-Asn-Asp-Ile-Phe- Glu-Ala-Gln-Lys-Ile-Glu-Trp-His-Glu) (SEQ ID NO 331) and His-tag (His-His-His-His-His-His- His-His) (SEQ ID NO:332) at the C-terminus and a mouse IgG signal peptide at the N-terminus (SEQ ID NO:6). The Biacore method was identical to the ActivinRIIB with just the change in the antigen.

[0130] Additionally, the ability of the antibody to block binding of the putative ligands (Activin A and myostatin) to ActivinRIIB was assessed by SPR. The receptor blocking assays were completed by capturing 100 nM of biotinylated receptor ActivinRIIB on a Series S CAP chip with Biotin CAPture reagent (Cytiva). Antibodies were titrated in running buffer (1 X PBSP+,Cytiva) to 25, 50, and 100 nM and flowed over the receptor to bind. Next, either human Activin A at 50 nM (R&D Systems, 338-AC, Gly311-Ser426) or mouse myostatin at 100 nM (R&D Systems, 788-G8, Asp268-Ser376) was flowed over the chip. Canine Activin A has 97% sequence identity to human Activin A in the regions expressed in the commercial proteins (GenBank number XP_038279632.1). Canine myostatin has 100% sequence identity to mouse myostatin in the regions expressed in the commercial proteins (NCBI Ref Seq NP_001002959.1). The relative response units (RU) at the binding report point were used to calculate the inhibition percent by dividing the relative binding response of the cycles with antibody samples by an average of the Activin A-only or myostatin-only relative binding response (with no antibody present) that were collected throughout the assay. The ability of each antibody to block binding of Activin A to Activin Receptor IIB are described below in Table 9. The ability of each antibody to block binding of Activin Receptor IIB and Myostatin are described below in Table 10

[0131] The results demonstrate that Clone 006 variants T28S / F64V and T28S / Q65K along with Clone 044 variant T28S can potently block Activin A and myostatin binding to Activin RUB at all concentrations.Example 3 - Affinity Maturation of Felinized Clone 034 T28S

[0132] Felinized clone 034 T28S was subject to affinity maturation for Activin Receptor IIA and Activin Receptor IIB. The heavy variable domain of felinized clone 034 T28S (SEQ IDNO: 17) and the CHI domain was subcloned into the GenScript FASEBA plasmid. At the C- terminus of the heavy chain (VH-CH1) is the SASA (single-domain antibody against serum albumin) tag (SEQ ID NO:29) (see, SEQ ID NO:2 in US 2013 / 0129727A1) which has low pM affinity for albumin. The light chain of felinized clone 034 (SEQ ID NO: 16) was subcloned into a proprietary E. coli expression vector. Both the heavy chain and light chain had the PelB (pectate lyase B) signal peptide at the N-terminus to facilitate secretion of the Fab when expressed in TGI E. coli. The expression of the variable domains was regulated by the Lac promoter.

[0133] A variant library was generated for each CDR position in the heavy and light chains using the GenScript proprietary Precision Mutant Library (PML) which utilizes semiconductorbased oligonucleotide synthesis technology. The CDRs were defined using a combination of Kabat and IMGT criteria and the mutated residues selected for each CDR are shown below in Table 11. The residue numbers for the CDRs are shown in parentheses.

[0134] Forty -six PML clones were selected from each library for expression in E. coli in 96 deep-well plates by inoculating into 2YT medium and inducing with 0.2 mM IPTG overnight at room temperature. The Fab secreted in the medium was analyzed for binding activity by completing an ELISA for binding to activin receptor IIB (SEQ ID NO: 5) and activin receptor IIA (SEQ ID NO:6). For the relative binding affinity to activin receptor IIA, plates were coated with 5 pg / ml of BSA overnight at 4°C, washed 3X with 0.05% tween 20 in PBS, pH 7.4 (PBST), blocked non-specific interactions with 3% non-fat dry milk in PBS (phosphate-buffered saline, pH 7.4) at 37°C for 1 hour, washed 3X with PBST, added crude Fab supernatant (diluted 1 : 1 with PBST) incubated at 37°C for 1 hour, washed 3X with PBST, added 2.5 pg / ml of activin receptor IIA incubated at 37°C for 1 hour, washed 3X with PBST, added horseradish peroxidase (HRP) conjugated anti-His tag antibody (His tag present on activin receptor IIA) incubated at roomtemperature for 45 minutes, washed 3X with PBST and detected the HRP conjugate by incubating with TMB substrate for 10 minutes at room temperature and measured absorbance at 450 nm. The ELISA for the relative binding affinity to activin receptor IIB uses the same method except plates were coated with 0.312 [ig / ml of BSA and activin receptor IIB was added at 0.625 [ig / ml.

[0135] The top 38 clones with an apparent increase in affinity as measured by the ELISAs were sequenced to detect the variants in the VH (Fig. 1 A) or VL (Fig. IB) CDRs. 27 unique clones were confirmed by an off-rate screening assay in an SPR assay performed on a Biacore 8K (ActivinRIIA: Table 12; ActivinRIIB: Table 13). For the SPR analyses, bovine serum albumin (BSA) was immobilized to CM5 sensor chip. The sensor chip surface was activated with 50 mmol / L H-Hydroxysuccinimide and 200 mmol / L l-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride for 420 s. Afterwards, BSA diluted in 10 mM sodium acetate, pH 4.5 was injected. After the amine coupling reaction, the remaining active coupling sites on the chip surface were blocked with 1 mM ethanolamine hydrochloride. The selected Fab-SASA variants in conditioned medium were captured on the BSA-coated chips. The running buffer was HBS-EP (10 mM HEPES 500 mM NaCl, 3 mM EDTA, 0.05% Tween 20, pH 7.4). After equilibration, either feline activin receptor IIA or feline activin receptor IIB was injected for 120 seconds (association phase) followed by the injection of running buffer for 360 sec (dissociation phase). The off-rates (kd [Is]) of the Fab-SASA clones were determined using the Biacore evaluation software. The on- rates (ka [IZMs]) and affinities (KD [M]) are estimates since the concentration of the Fabs used in the analyses is unknown.

[0136] The “wild type” (WT) sequence consists of SEQ ID NO: 17 (VnO34-T28S) for the VH variable domain and SEQ ID NO: 16 (VL034) for the VL variable domain. Clones AHF32259- AHF32280 differ from WT by a single amino acid in the VH variable domain. Clones AHF32281- AHF32295 differ from WT by a single amino acid in the VL variable domain.

[0137] Exemplary non-limiting mutations observed to improve binding to ActRIIA and ActRIIB include S32T, N35Q, T50V, T50N, S59L, and G99S in VH and S26K, K55R Y99L, Y99D, Y99K, Y99T, V101M, V101G, and V101S in VL.Example 4 - Combinatorial Library Construction and Screening

[0138] The Fab variants S32T, N35Q, S59L, S63Q, S63A, G99S, K55R, and V101M shown in Table 14 were selected for combinatorial library construction. The S63Q, and S63A variants also tested the effect of amino acid changes to remove a site of potential post-translational modification.

[0139] The combinatorial library was constructed in the same Fab-SASA construct described above. The size of the constructed library is 2.2 x 107colony forming units. The library in-frame rate and diversity was obtained by DNA sequencing of 48 clones. The summary of the results is shown in Table 15.

[0140] The frequency of the VH variants and the VL variants are shown in Table 16 and Table17.

[0141] From the combinatorial library, 276 clones were randomly selected and their binding to activin receptor IIA and activin receptor IIB were evaluated using the ELISAs previously described. Clones that had increased binding to either activin receptor IIA or activin receptor IIB or both were sequenced. A total of 271 clones were sequenced and there were 91 unique clones. Unique clones which had an increase binding in the ELISA of >1.3-fold for binding to activin receptor IIB were selected for SPR binding to the two receptors. The 44 clones that met these criteria were analyzed in the SPR assay to accurately determine the off-rates and these data are shown Table 18 for ActivinRIIA and Table 19 ActivinRIIB. The “Sequence Code” lettersrepresent the amino acids at: VL position 55, VL position 101, VH position 32, VH position 35, VH position 59, VH position 63, and VH position 99. The on-rates (ka [1 / Ms]) and affinities (KD [M]) are estimates since the concentration of the Fabs used in the analyses is unknown. VH and VL sequences of the clones are indicated in Table 20 and Fig. 2A and Fig. 2B.Example 5 - Mutations to maintain or modulate binding and crossreactivity with ActRIIA and ActRIIB

[0142] The range of mutations compatible with binding to ActRIIA and / or ActRIIB was investigated. Table 21 and Table 22 show binding information for 394 mutants over 21 positions in the VH domain and 22 positions in the VL domain that bind to ActRIIA and ActRIIB as measured by ELISA assay. Variation of amino acids at the positions as shown maintained or modulated but did not disrupt binding to either or both of the ActRIIA and ActRIIB targets. The mutants represent several classes of which the following are non-limiting: mutants that have increased bindingactivity with ActRIIB and decreased binding with ActRIIA; mutants that have increased binding activity with ActRIIA and decreased binging with ActRIIB; mutants that have substantially unchanged binding activity with ActRIIA and substantially unchanged binding activity with ActRIIB. The binding data can be used to compare or guide combinations with mutants selected for binding activity with ActRIIA and / or ActRIIB. Three dimensional models of antibodies, including but not limited to anti-ActRIIA antibodies, anti-ActRIIB antibodies, anti-ActRIIA antibody-antigen complexes, and anti-ActRIIB antibody-antigen complexes can also be used in the analysis.Example 6 - Improving binding and cross-reactivity ofActRHA and ActRIIB with caninized Clone 044 variant T28S

[0143] Guided by affinity maturation of felinized clone 034 T28S, the caninized Clone 044 T28S (VH: SEQ ID NO:28; VL: SEQ ID NO:27) was engineered to improve the binding to activin receptor IIA (SEQ ID NO:6) while retaining binding to activin receptor IIB (SEQ ID NO:5). Five variable heavy chains (Table 23, SEQ ID NO:288, 289, 290, 291, 292) and 3 variable light chains(SEQ ID NO:293, 294, 295) were synthesized with changes in the CDR residues that showed favorable binding attributes in the felinized clones.

[0144] These variants were subcloned into pcDNA 3.4 (ThermoFisher). An equal ratio of heavy chain and light chain plasmids for each were co-transfected into CHO cells and the IgG in the conditioned medium was purified using MabSelect SuRe chromatography. The antibodies were buffer exchanged into PBS, pH 7.2.

[0145] The affinity for canine ActRIIA of canine affinity matured variants was determined using a Biacore T200 instrument. The antibodies were captured using a CM5 Series S chip amine coupled with an anti-dog Fc antibody (Jackson Immunoresearch, 304-005-008). Antigen, canine ActRIIA, binding was then assessed at multiple concentrations starting at 100 nM using PBSP+ running buffer (Cytiva) with a flow rate of 30 uL / min. The length of the association time was 120sand the dissociation time was run for 600s. The chip surface was regenerated with 10 mM glycine. Double reference-subtracted sensorgrams were fitted to a 1 :1 binding model using Biacore T200 Evaluation software. All caninized engineered variants showed improved affinity to ActRIIA compared to the parental 044 T28S variant (Table 24).

[0146] The affinity for canine ActRIIB was also assessed by SPR. The Biacore method was identical to the ActivinRIIA with just the change in the antigen. Improvement in affinity to activin receptor IIB was observed for all canine engineered variants compared to parental 044 T28S(Table 25)

[0147] Based on affinity results and sequence A044-695, A044-788, and A044-883 were chosen for further characterization. The ability of the antibodies to block binding of the putative ligands (Activin A and myostatin) to ActivinRIIB was assessed by SPR as previously described. The ability of each antibody to block binding of Activin A and myostatin to Activin Receptor IIB are shown below in Table 26.

[0148] The results demonstrate that all the canine engineered variants can potently block Activin A and myostatin binding to Activin RUB at all concentrations.* * *

[0149] Having thus described in detail preferred embodiments of the present invention, it is to be understood that the invention defined by the above paragraphs is not to be limited to particular details set forth in the above description as many apparent variations thereof are possible without departing from the spirit or scope of the present invention.

Claims

WHAT IS CLAIMED IS:1 . A caninized or felinized antigen binding protein that specifically binds to activin type II receptor (ActRII), which comprises:(a) a heavy chain complementarity determining region 1 (HCDR1) comprising GYX28X29X30SX32YX34X35 (SEQ ID NO:296), wherein X28 comprises N, Q, S or T; X29 comprises F, I, L, M, or V, X30 comprises D, F, H, N, S, T, or W, X32 comprises S, or T, X34 comprises I, L, or V; X35 comprises N, Q, P, or T;(b) a heavy chain complementarity determining region 2 (HCDR2) comprising X50X51NPX54X55GX57X58X59X60X61X62X63X64 (SEQ ID NO:297), wherein X50 comprises A, G, H, M, N, Q, R, S, T, V, W, or Y; X51 comprises I, L, M, or W; X54 comprises A, N, S, V, or Y; X55 comprises G, I, L, S, T, or W; X57 comprises S or T; X58 comprises T or V; X59 comprises L, Q, or S; Xeo comprises L, M, V, or Y; Xei comprises A or D; X62 comprises A, D, E, H, K, P, Q, R, S, or T; X63 comprises A, F, G, I, L, N, P, Q, S, V, or Y; X64 comprises A or V;(c) a heavy chain complementarity determining region 3 (HCDR3) comprising X99GWX102DX104 (SEQ ID NO:298), wherein X99 comprises D, G, S, or T; X102 comprises F or M; X104 comprises A, G, H, I, L, M, N, Q, R, S, T, V, or Y;(d) a light chain complementarity determining region 1 (LCDR1) comprising X23GX25X26X27X28X29X30X31X32X33YX35X36 (SEQ ID NO:299), wherein X23 comprises D, Q, or T, X25 comprises Q or S; X26 comprises A, E, F, G, H, K, L, M, P, Q, R, S, T, or V; X27 comprises A, E, G, K, L, N, P, R, or S; X28 comprises A or D; X29 comprises F, I, P, V, or Y; X30 comprises G or N; X31 comprises A, G, K, L, N, P, Q, R, S, or T; X32 comprises H, P, W, V, or Y; X33 comprises A, H, L, N, P, Q, or R; X35 comprises I, P, or V; X36 comprises A or N;(e) a light chain complementarity determining region 2 (LCDR2) comprising X52X53X54X55RX57X58 (SEQ ID NO:300), wherein X52 comprises G, H, N, or S; X53 comprises A, D, E, F, H, I, K, N, P, Q, R, S, T, or V; X54 comprises D, E, G, S, or T; X55 comprises K or R; X57 comprises D, E, G, H, I, K, L, M, N, P, Q, R, S, T, or V; X58 comprises A, E, G, H, K, N, P, R, S, or Y;(f) a light chain complementarity determining region 3 (LCDR3) comprising X92FX94GGX97YX99GX101 (SEQ ID NO:301), wherein X92 comprises L or T; X94 comprises A or S; X97 comprises A, R, S, or Y; X99 comprises D, E, F, G, H, I, K, L, M, N, Q, T, V, or Y; X101 comprises A, G, D, F, H, I, K, L, M, N, Q, R, S, T, V, or Y.

2. The antigen binding protein of any one of claims 1 or 2, wherein:HCDR1 comprises GYSFTSX32YIX35 (SEQ ID NO:302), wherein X32 comprises S or T; and X35 comprises N or Q;HCDR2 comprises X50INPVSGSTX59X60AX62X63VK (SEQ ID NO:303), wherein X50 comprises G, N, T or V; X59 comprises L or S; Xeo comprises L, M, or Y; X62 comprises D, E, or P; X63 comprises A, S or Q;HCDR3 comprises X99GWX102DX104 (SEQ ID NO:298), wherein X99 comprises D, G, S, or T; X102 comprises F or M; X104 comprises V, or Y;LCDR1 comprises X23GSX26SDVGX31YNYVN (SEQ ID NO:304), wherein X23 comprises D, Q, or T; X26 comprises A, K, Q, or S; X31 comprises R or S;LCDR2 comprises GVSX55RPS (SEQ ID NO:305), wherein X55 comprises K or R; and LCDR3 comprises X92FAGGSYX99GX101 (SEQ ID NO:306), wherein X92 comprises L or T, X99 comprises D, K, L, T, or Y; and X101 comprises G, M, S, or V.

3. The antigen binding protein of any one of claims 1 or 2, which comprises: no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:68 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:97; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:70 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:97; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:70 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:64; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:74 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO: 16; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:83 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO: 16; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:72 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:64; orno more than two (2) substitutions per VH-CDR as compared to SEQ ID NO: 17 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO: 16.

4. The antigen binding protein of any one of claims 1 or 2, which comprises: no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:68 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:97; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:70 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:97; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:70 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:64; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:74 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 16; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:83 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 16; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:72 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:64; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO: 17 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO: 16.

5. The antigen binding protein of any one of claims 1 to 4, wherein one, two, or all of HCDR1, HCDR2, and HCDR3 is independently selected from a corresponding CDR of SEQ ID NOT, SEQ ID NOT, SEQ ID NOTO, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 17, SEQ ID NO:20, SEQ ID NO:22, SEQ ID NO:23, SEQ ID NO:24, SEQ ID NO:25, SEQ ID NO:26, SEQ ID NO:28, SEQ ID NOTO, SEQ ID NO:31, SEQIDNO:32, SEQIDNO:33, SEQIDNO:34, SEQIDNO:35, SEQIDNO:36, SEQIDNO:37, SEQIDNO:38, SEQIDNO:39, SEQ ID NOTO, SEQIDNO:41, SEQIDNO:42, SEQ IDNO:43, SEQIDNO:68, SEQIDNO:69, SEQ ID NOTO, SEQIDNO:71, SEQIDNO:72, SEQIDNO:73, SEQIDNOT4, SEQIDNO:75, SEQIDNO:76, SEQIDNO:77, SEQIDNO:78, SEQIDNO:79, SEQIDNO:80, SEQIDNO:81, SEQ IDNO:82, SEQIDNO:83, SEQIDNO:84, SEQ IDNO:85, SEQIDNO:86, SEQIDNO:87, SEQ IDNO:88, SEQIDNO:89, SEQIDNO:90, SEQIDNO:91, SEQ ID NO:92, SEQ ID NO:93, SEQ ID NO:94, SEQ ID NO:95, SEQ ID NO:96, SEQ ID NO:288, SEQ ID NO:289, SEQ ID NO:290, SEQ ID NO:291, or SEQ ID NO:292.

6. The antigen binding protein of any one of claims 1 to 4, wherein one, two, or all ofLCDR1 , LCDR2, and LCDR3 is independently selected from a corresponding CDR of SEQ ID NO:8, SEQ ID NO: 16, SEQ ID NO:21, SEQ ID NO:27, SEQ ID NO:52, SEQ ID NO:53, SEQ ID NO:54, SEQ ID NO:55, SEQ ID NO:56, SEQ ID NO:57, SEQ ID NO:58, SEQ ID NO:59, SEQ ID NO: 60, SEQ ID NO:61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 97, SEQ ID NO:293, SEQ ID NO:294, or SEQ ID NO:295.

7. The antigen binding protein of any one of claims 1 to 4, which comprises the VH- CDRs and VL-CDRs of AHF39788, AHF39695, AHF39883, AHF39700, AHF39717, AHF39900, AHF39693, AHF39694, AHF39697, AHF39698, AHF39699, AHF39703,AHF39705, AHF39707, AHF39708, AHF39709, AHF39712, AHF39713, AHF39714,AHF39715, AHF39716, AHF39718, AHF39721, AHF39722, AHF39725, AHF39726,AHF39727, AHF39728, AHF39729, AHF39731, AHF39732, AHF39733, AHF39737,AHF39739, AHF39749, AHF39750, AHF39775, AHF39802, AHF39815, AHF39855,AHF39882, AHF39885, or AHF39891.

8. The antigen binding protein of any one of claims 1 to 7, which is felinized and comprises a heavy chain framework (FR1H+FR2H+FR3H+FR4H) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical, or identical to the heavy chain framework of SEQ ID NO: 7 or SEQ ID NO: 15 and a light chain framework (FR1L+FR2L+FR3L+FR4L) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical, or identical to the light chain framework of SEQ ID NO: 8 or SEQ ID NO: 16.

9. The antigen binding protein of any one of claims 1 to 7, which comprises the VH and VL domains of AHF39788, AHF39695, AHF39883, AHF39700, AHF39717, AHF39900, AHF39693, AHF39694, AHF39697, AHF39698, AHF39699, AHF39703, AHF39705,AHF39707, AHF39708, AHF39709, AHF39712, AHF39713, AHF39714, AHF39715,AHF39716, AHF39718, AHF39721, AHF39722, AHF39725, AHF39726, AHF39727,AHF39728, AHF39729, AHF39731, AHF39732, AHF39733, AHF39737, AHF39739,AHF39749, AHF39750, AHF39775, AHF39802, AHF39815, AHF39855, AHF39882,AHF39885, or AHF3989110. The antigen binding protein of any one of claims 1 or 2, which comprises: no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:293; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:294; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:289 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:294; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:291 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:295; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:288 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:27; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:290 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:295; or no more than two (2) substitutions per VH-CDR as compared to SEQ ID NO:292 and no more than two (2) substitutions per VL-CDR as compared to SEQ ID NO:293.

11. The antigen binding protein of any one of claims 1 or 2, which comprises: no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:288 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:293; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:288 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:294; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:289 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:27; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:290 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:27; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:290 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:294; orno more than one (1) substitution per VH-CDR as compared to SEQ ID NO:291 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:295; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:288 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:27; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:290 and no more than one (1) substitution per VL-CDR as compared to SEQ ID NO:295; or no more than one (1) substitution per VH-CDR as compared to SEQ ID NO:292 and no more than one (1) substitutions per VL-CDR as compared to SEQ ID NO: 293.

12. The antigen binding protein of claim 10, which comprises: the VH-CDRs of SEQ ID NO:288 and the VL-CDRs of SEQ ID NO:294; or the VH-CDRs of SEQ ID NO:289 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO: 290 and the VL-CDRs of SEQ ID NO: 294; or the VH-CDRs of SEQ ID NO:288 and the VL-CDRs of SEQ ID NO:27; or the VH-CDRs of SEQ ID NO:290 and the VL-CDRs of SEQ ID NO:295; or the VH-CDRs of SEQ ID NO:288 and the VL-CDRs of SEQ ID NO:293; or the VH-CDRs of SEQ ID NO: 292 and the VL-CDRs of SEQ ID NO: 294; or the VH-CDRs of SEQ ID NO:28 and the VL-CDRs of SEQ ID NO:27.

13. The caninized antigen binding protein of any one of claims 1 to 2 or 10 to 12, which comprises a heavy chain framework (FR1H+FR2H+FR3H+FR4H) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical, or identical to the heavy chain framework of SEQ ID NO:20 or SEQ ID NO:26 and a light chain framework (FR1L+FR2L+FR3L+FR4L) at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 93%, or at least 95% identical, or identical to the light chain framework of SEQ ID NO:21 or SEQ ID NO: 27.

14. The caninized antigen binding protein of any one of claims 1 to 2 or 10 to 13, which comprises SEQ ID NO:288 and SEQ ID NO:293; or SEQ ID NO:288 and SEQ ID NO:294; or SEQ ID NO:289 and SEQ ID NO:27; or SEQ ID NO:290 and SEQ ID NO:27; or SEQ ID NO:290 and SEQ ID NO:294; or SEQ ID NO:288 and SEQ ID NO:27; or SEQ ID NO:290 and SEQ IDNO:295; or SEQ ID NO:292 and SEQ ID NO:294; or SEQ ID NO 28 and SEQ ID NO 27; or SEQ ID NO: 17 and SEQ ID NO: 1615. An isolated nucleic acid sequence encoding an anti-ActRII antibody or antibody fragment of any one of claims 1 to 14.

16. A vector that comprises the nucleic acid of claim 15.

17. A recombinant cell which comprises the nucleic acid of any one of claims 15 or 16.

18. A cell that expresses the antigen binding protein of any one of claims 1 to 14 or the nucleic acid of claim 15.

19. A method of producing the antigen binding protein of any one of claims 1 to 14, which comprises culturing the cell of claim 18 under conditions that result in production of the antigen binding protein.

20. A pharmaceutical composition comprising a therapeutically effective amount of the antigen binding protein of any one of claims 1 to 14.

21. A method of blocking ligand binding to ActRIIB or ActRIIA which comprises contacting the ActRIIB or ActRIIA with an antigen binding protein of any one of claims 1 to 14.

22. A method of reducing adiposity in a subject which comprises administering to the subject a therapeutically effective amount of the antigen binding protein of any one of claims 1 to 14.

23. A method of increasing muscle mass in a subject which comprises administering to the subject a therapeutically effective amount of the antigen binding protein of any one of claims 1 to 14.

24. A method of treating osteoarthritis in a subject which comprises administering to the subject a therapeutically effective amount of the antigen binding protein of any one of claims 1 to 14.

25. A method of treating diabetes, insulin resistance, or improving glycemic control in a subject, which comprises administering to the subject a therapeutically effective amount of the antigen binding protein of any one of claims 1 to 14.

26. The method of any one of claims 22 - 25, wherein the subject comprises a canine.

27. The method of any one of claims 22 - 25, wherein the subject comprises a feline.

28. The method of any one of claims 22 - 25, wherein the subject comprises a human.

29. The antigen binding protein of any one of claims 1 to 15 for use in treatment.

30. The use of claim 29 to block ligand binding to ActRIIB or ActRIIA in a subject.

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