Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference in their entirety.

Definitions

The terms “BMP6” and “Bone Morphogenetic Protein 6” refer, interchangeably, to a 57 kDa monomeric protein. BMP6 is a member of the transforming growth factor beta (TGF-beta) superfamily of regulatory molecules. The amino acid sequence of human BMP6 is shown in SEQ ID NO: 40. The amino acid sequence of mouse BMP6 is shown in SEQ ID NO: 42. Unless otherwise noted, reference to BMP6 refers to the human form.

The term “antibody”, as used herein, is intended to refer to immunoglobulin molecules comprised of four polypeptide chains, two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds (i.e., “full antibody molecules”), as well as multimers thereof (e.g. IgM) or antigen-binding fragments thereof. Each heavy chain is comprised of a heavy chain variable region (“HCVR” or “V_H”) and a heavy chain constant region (comprised of domains C_H1, C_H2 and C_H3). Each light chain is comprised of a light chain variable region (“LCVR or “V_L”) and a light chain constant region (C_L). The V_Hand V_Lregions can be further subdivided into regions of hypervariability, termed complementarity determining regions (CDR), interspersed with regions that are more conserved, termed framework regions (FR). Each V_Hand V_Lis 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 certain embodiments of the invention, the FRs of the antibody (or antigen binding fragment thereof) may be identical to the human 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.

Substitution of one or more CDR residues or omission of one or more CDRs is also possible. Antibodies have been described in the scientific literature in which one or two CDRs can be dispensed with for binding. Padlan et al. (FASEB J. 1995, 9:133-139) analyzed the contact regions between antibodies and their antigens, based on published crystal structures, and concluded that only about one fifth to one third of CDR residues actually contact the antigen. Padlan also found many antibodies in which one or two CDRs had no amino acids in contact with an antigen (see also, Vajdos et al. 2002 J Mol Biol 320:415-428).

CDR residues not contacting antigen can be identified based on previous studies by molecular modeling and/or empirically. If a CDR or residue(s) thereof is omitted, it is usually substituted with an amino acid occupying the corresponding position in another human antibody sequence or a consensus of such sequences. Positions for substitution within CDRs and amino acids to substitute can also be selected empirically. Empirical substitutions can be conservative or non-conservative substitutions.

The fully human BMP6 monoclonal antibodies disclosed herein may comprise one or more amino acid substitutions, insertions and/or deletions in the framework and/or CDR regions of the heavy and light chain variable domains as compared to the corresponding germline sequences. Such mutations can be readily ascertained by comparing the amino acid sequences disclosed herein to germline sequences available from, for example, public antibody sequence databases. The present invention includes antibodies, and antigen-binding fragments thereof, which are derived from any of the amino acid sequences disclosed herein, wherein one or more amino acids within one or more framework and/or CDR regions are mutated to the corresponding residue(s) of the germline sequence from which the antibody was derived, or to the corresponding residue(s) of another human germline sequence, or to a conservative amino acid substitution of the corresponding germline residue(s) (such sequence changes are referred to herein collectively as “germline mutations”). A person of ordinary skill in the art, starting with the heavy and light chain variable region sequences disclosed herein, can easily produce numerous antibodies and antigen-binding fragments that comprise one or more individual germline mutations or combinations thereof. In certain embodiments, all of the framework and/or CDR residues within the V_Hand/or V_Ldomains are mutated back to the residues found in the original germline sequence from which the antibody was derived. In other embodiments, only certain residues are mutated back to the original germline sequence, e.g., only the mutated residues found within the first 8 amino acids of FR1 or within the last 8 amino acids of FR4, or only the mutated residues found within CDR1, CDR2 or CDR3. In other embodiments, one or more of the framework and/or CDR residue(s) are mutated to the corresponding residue(s) of a different germline sequence (i.e., a germline sequence that is different from the germline sequence from which the antibody was originally derived). Furthermore, the antibodies of the present invention may contain any combination of two or more germline mutations within the framework and/or CDR regions, e.g., wherein certain individual residues are mutated to the corresponding residue of a particular germline sequence while certain other residues that differ from the original germline sequence are maintained or are mutated to the corresponding residue of a different germline sequence. Once obtained, antibodies and antigen-binding fragments that contain one or more germline mutations can be easily tested for one or more desired property such as, improved binding specificity, increased binding affinity, improved or enhanced antagonistic or agonistic biological properties (as the case may be), reduced immunogenicity, etc. Antibodies and antigen-binding fragments obtained in this general manner are encompassed within the present invention.

The present invention also includes fully human anti-BMP6 monoclonal antibodies comprising variants of any of the HCVR, LCVR, and/or CDR amino acid sequences disclosed herein having one or more conservative substitutions. For example, the present invention includes anti-BMP6 antibodies having HCVR, LCVR, and/or CDR amino acid sequences with, e.g., 10 or fewer, 8 or fewer, 6 or fewer, 4 or fewer, etc. conservative amino acid substitutions relative to any of the HCVR, LCVR, and/or CDR amino acid sequences disclosed herein.

The term “human antibody”, as used herein, is intended to include antibodies having variable and constant regions derived from human germline immunoglobulin sequences. The human mAbs of the invention may include amino acid residues not encoded by human germline immunoglobulin sequences (e.g., mutations introduced by random or site-specific mutagenesis in vitro or by somatic mutation in vivo), for example in the CDRs and in particular CDR3. However, the term “human antibody”, as used herein, is not intended to include mAbs in which CDR sequences derived from the germline of another mammalian species (e.g., mouse), have been grafted onto human FR sequences.

The term “specifically binds,” or “binds specifically to”, or the like, means that an antibody or antigen-binding fragment thereof forms a complex with an antigen that is relatively stable under physiologic conditions. Specific binding can be characterized by an equilibrium dissociation constant of at least about 1×10⁻⁶M or less (e.g., a smaller K_Ddenotes a tighter binding). Methods for determining whether two molecules specifically bind are well known in the art and include, for example, equilibrium dialysis, surface plasmon resonance, and the like. As described herein, antibodies that bind specifically to BMP6 have been identified by surface plasmon resonance, e.g., BIACORE™. Moreover, multi-specific antibodies that bind to one domain in BMP6 and one or more additional antigens or a bi-specific that binds to two different regions of BMP6 are nonetheless considered antibodies that “specifically bind”, as used herein.

The term “high affinity” antibody refers to those mAbs having a binding affinity to BMP6, expressed as K_D, of at least 10⁻⁷M; preferably 10⁻⁸M; more preferably 10⁻⁹M, even more preferably 10⁻¹⁰M, even more preferably 10⁻¹¹M, as measured by surface plasmon resonance, e.g., BIACORE™ or solution-affinity ELISA.

By the term “slow off rate”, “Koff” or “kd” is meant to describe an antibody that dissociates from BMP6 with a rate constant of 1×10⁻³s⁻¹or less, preferably 1×10⁻⁴s⁻¹or less, as determined by surface plasmon resonance, e.g., BIACORE™.

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. The terms “antigen-binding fragment” of an antibody, or “antibody fragment”, as used herein, refers to one or more fragments of an antibody that retain the ability to bind to BMP6.

In specific embodiments, antibody or antibody fragments of the invention may be conjugated to a therapeutic moiety (“immunoconjugate”), such as an antibiotic, a second anti-BMP6 antibody, or an antibody to a cytokine such as IL-1, IL-6, or TGF-β, or any other therapeutic moiety useful for treating an iron-deficiency anemia or an iron-deficiency related disorder.

An “isolated antibody”, as used herein, is intended to refer to an antibody that is substantially free of other antibodies (Abs) having different antigenic specificities (e.g., an isolated antibody that specifically binds BMP6, or a fragment thereof, is substantially free of Abs that specifically bind antigens other than BMP6).

The term “surface plasmon resonance”, as used herein, refers to an optical phenomenon that allows for the analysis of real-time biomolecular interactions by detection of alterations in protein concentrations within a biosensor matrix, for example using the BIACORE™ system (Pharmacia Biosensor AB, Uppsala, Sweden and Piscataway, N.J.).

The term “K_D”, as used herein, is intended to refer to the equilibrium dissociation constant of a particular antibody-antigen interaction.

The term “epitope” refers to an antigenic determinant that interacts with a specific antigen-binding site in the variable region of an antibody molecule known as a paratope. A single antigen may have more than one epitope. Thus, different antibodies may bind to different areas on an antigen and may have different biological effects. The term “epitope” also refers to a site on an antigen to which B and/or T cells respond. It also refers to a region of an antigen that is bound by an antibody. Epitopes may be defined as structural or functional. Functional epitopes are generally a subset of the structural epitopes and have those residues that directly contribute to the affinity of the interaction. Epitopes may also be conformational, that is, composed of non-linear amino acids. In certain embodiments, epitopes may include determinants that are chemically active surface groupings of molecules such as amino acids, sugar side chains, phosphoryl groups, or sulfonyl groups, and, in certain embodiments, may have specific three-dimensional structural characteristics, and/or specific charge characteristics.

The term “substantial identity” or “substantially identical,” when referring to a nucleic acid or fragment thereof, indicates that, when optimally aligned with appropriate nucleotide insertions or deletions with another nucleic acid (or its complementary strand), there is nucleotide sequence identity in at least about 90%, and more preferably at least about 95%, 96%, 97%, 98% or 99% of the nucleotide bases, as measured by any well-known algorithm of sequence identity, such as FASTA, BLAST or GAP, as discussed below. A nucleic acid molecule having substantial identity to a reference nucleic acid molecule may, in certain instances, encode a polypeptide having the same or substantially similar amino acid sequence as the polypeptide encoded by the reference nucleic acid molecule.

As applied to polypeptides, the term “substantial similarity” or “substantially similar” means that two peptide sequences, when optimally aligned, such as by the programs GAP or BESTFIT using default gap weights, share at least 90% sequence identity, even more preferably at least 95%, 98% or 99% sequence identity. Preferably, residue positions, which are not identical, differ by conservative amino acid substitutions. A “conservative amino acid substitution” is one in which an amino acid residue is substituted by another amino acid residue having a side chain (R group) with similar chemical properties (e.g., charge or hydrophobicity). In general, a conservative amino acid substitution will not substantially change the functional properties of a protein. In cases where two or more amino acid sequences differ from each other by conservative substitutions, the percent or degree of similarity may be adjusted upwards to correct for the conservative nature of the substitution. Means for making this adjustment are well known to those of skill in the art. See, e.g., Pearson (1994) Methods Mol. Biol. 24: 307-331, which is herein incorporated by reference. Examples of groups of amino acids that have side chains with similar chemical properties include 1) aliphatic side chains: glycine, alanine, valine, leucine and isoleucine; 2) aliphatic-hydroxyl side chains: serine and threonine; 3) amide-containing side chains: asparagine and glutamine; 4) aromatic side chains: phenylalanine, tyrosine, and tryptophan; 5) basic side chains: lysine, arginine, and histidine; 6) acidic side chains: aspartate and glutamate, and 7) sulfur-containing side chains: cysteine and methionine. Preferred conservative amino acids substitution groups are: valine-leucine-isoleucine, phenylalanine-tyrosine, lysine-arginine, alanine-valine, glutamate-aspartate, and asparagine-glutamine. Alternatively, a conservative replacement is any change having a positive value in the PAM250 log-likelihood matrix disclosed in Gonnet et al. (1992) Science 256: 1443 45, herein incorporated by reference. A “moderately conservative” replacement is any change having a nonnegative value in the PAM250 log-likelihood matrix.

Sequence similarity for polypeptides is typically measured using sequence analysis software. Protein analysis software matches similar sequences using measures of similarity assigned to various substitutions, deletions and other modifications, including conservative amino acid substitutions. For instance, GCG software contains programs such as GAP and BESTFIT which can be used with default parameters to determine sequence homology or sequence identity between closely related polypeptides, such as homologous polypeptides from different species of organisms or between a wild type protein and a mutein thereof. See, e.g., GCG Version 6.1. Polypeptide sequences also can be compared using FASTA with default or recommended parameters; a program in GCG Version 6.1. FASTA (e.g., FASTA2 and FASTA3) provides alignments and percent sequence identity of the regions of the best overlap between the query and search sequences (Pearson (2000) supra). Another preferred algorithm when comparing a sequence of the invention to a database containing a large number of sequences from different organisms is the computer program BLAST, especially BLASTP or TBLASTN, using default parameters. See, e.g., Altschul et al. (1990) J. Mol. Biol. 215: 403-410 and (1997) Nucleic Acids Res. 25: 3389-3402, each of which is herein incorporated by reference.

In specific embodiments, the antibody or antibody fragment for use in the method of the invention may be mono-specific, bi-specific, or multi-specific. Multi-specific antibodies may be specific for different epitopes of one target polypeptide or may contain antigen-binding domains specific for epitopes of more than one target polypeptide.

By the phrase “therapeutically effective amount” is meant an amount that produces the desired effect for which it is administered. The exact amount will depend on the purpose of the treatment, and will be ascertainable by one skilled in the art using known techniques (see, for example, Lloyd (1999) The Art, Science and Technology of Pharmaceutical Compounding).

General Description

Bone morphogenetic protein 6 (BMP6) is a 57 kDa protein which has been shown to be involved in a variety of physiological processes including regulating iron levels. BMP6 signaling leads to phosphorylation of SMAD1/5/8 and translocation of SMAD4 to the nucleus, where it promotes hepcidin (a negative regulator of serum iron) transcription upon binding to proximal and distal sites on its promoter. Hemojuvelin (HJV, HFE2) is a co-receptor for BMP6 which, enhances signaling. Reduced binding of BMP6 to HJV reduces hepcidin transcription, thereby promoting serum iron levels.

The antibodies described herein demonstrate specific binding to BMP6 and in some embodiments, may be useful for treating patients suffering from iron-deficiency anemia or an iron-deficiency related disorder. They may be used alone or as adjunct therapy with other therapeutic moieties or modalities known in the art for treating iron-deficiency anemia or an iron-deficiency related disorder, such as, but not limited to, iron supplementation through iron supplements, dietary changes to promote serum iron and/or intravenous delivery of iron, blood transfusion, and iron promoting medications. They may be used in conjunction with additional antibodies specific for antigens other than BMP6 or may combined with other types of treatments.

In some embodiments, the antibodies described herein may be useful in preventing, treating or managing an iron-deficiency anemia or an iron-deficiency related disorder.

In certain embodiments, the antibodies of the invention are obtained from mice immunized with a primary immunogen, such as a native, full length human BMP6 (SEQ ID NO: 40) or BMP6 fragments, followed by immunization with a secondary immunogen, or with an immunogenically active fragment of BMP6.

The immunogen may be an immunogenic fragment of BMP6 or DNA encoding the fragment thereof. The immunogen may be BMP6 coupled to a histidine tag and/or to a fragment of Fc region of an antibody.

The amino acid sequence of full length human BMP6 is shown as SEQ ID NO: 40. The full length amino acid sequence of mouse BMP6 is shown as SEQ ID NO: 42.

In certain embodiments, antibodies that bind specifically to BMP6 may be prepared using fragments of the above-noted regions, or peptides that extend beyond the designated regions by about 5 to about 20 amino acid residues from either, or both, the N or C terminal ends of the regions described herein. In certain embodiments, any combination of the above-noted regions or fragments thereof may be used in the preparation of BMP6-specific antibodies. In certain embodiments, any one or more of the above-noted regions of BMP6, or fragments thereof may be used for preparing monospecific, bispecific, or multi-specific antibodies.

Antigen-Binding Fragments of Antibodies

Unless specifically indicated otherwise, the term “antibody,” as used herein, shall be understood to encompass antibody molecules comprising two immunoglobulin heavy chains and two immunoglobulin light chains (i.e., “full antibody molecules”) as well as antigen-binding fragments thereof. 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. The terms “antigen-binding fragment” of an antibody, or “antibody fragment”, as used herein, refers to one or more fragments of an antibody that retain the ability to specifically bind to BMP6. An antibody fragment may include a Fab fragment, a F(ab′)₂fragment, a Fv fragment, a dAb fragment, a fragment containing a CDR, or an isolated CDR. 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.

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 (CODR) such as a ODR3 peptide), or a constrained FR3-CDR3-FR4 peptide. Other engineered molecules, such as domain-specific antibodies, single-domain antibodies, domain-deleted antibodies, chimeric antibodies, CODR-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.

An antigen-binding fragment of an antibody will typically comprise at least one variable domain. The variable domain may be of any size or amino acid composition and will generally comprise at least one CDR, which is adjacent to or in frame with one or more framework sequences. In antigen-binding fragments having a V_Hdomain associated with a V_Ldomain, the V_Hand V_Ldomains may be situated relative to one another in any suitable arrangement. For example, the variable region may be dimeric and contain V_H-V_H, V_H-V_Lor V_L-V_Ldimers. Alternatively, the antigen-binding fragment of an antibody may contain a monomeric V_Hor V_Ldomain.

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 antigen-binding fragment of an antibody of the present invention include: (i) V_H-C_H1; (ii) V_H-C_H2; (iii) V_H-C_H3; (iv) V_H-C_H1-C_H2; (v) V_H-C_H1-C_H2-C_H3; (vi) V_H-C_H2-C_H3; (vii) V_H-C_L; (viii) V_L-C_H1; (ix) V_L-C_H2; (x) V_L-C_H3; (Xi) V_L-C_H1-C_H2; (xii) V_L-C_H1-C_H2-C_H3; (xiii) V_L-C_H2-C_H3; and (Xiv) V_L-C_L. 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 V_Hor V_Ldomain (e.g., by disulfide bond(s)).

As with full antibody molecules, antigen-binding fragments may be mono-specific or multi-specific (e.g., bi-specific). A multi-specific antigen-binding fragment of an antibody will typically comprise at least two different variable domains, wherein each variable domain is capable of specifically binding to a separate antigen or to a different epitope on the same antigen. Any multi-specific antibody format, including the exemplary bi-specific antibody formats disclosed herein, may be adapted for use in the context of an antigen-binding fragment of an antibody of the present invention using routine techniques available in the art.

The present invention includes anti-BMP6 antibodies and antigen-binding fragments having immunoglobulin chains that include the amino acid sequences set forth herein as well as variants having cellular and/or in vitro post-translational modifications. For example, the present invention includes antibodies and antigen-binding fragments thereof that specifically bind to BMP6 comprising heavy and/or light chain amino acid sequences set forth herein (e.g., CDR-H1, CDR-H2, CDR-H3, CDR-L1, CDR-L2 and/or CDR-L3) as well as antibodies and fragments wherein one or more amino acid residues is glycosylated, one or more Asn residues is deamidated, one or more residues (e.g., Met, Trp and/or His) is oxidized, the N-terminal Gln is pyroglutamate (pyroE) and/or the C-terminal Lysine is missing.

The present invention includes recombinant methods for making anti-BMP6 antibodies or antigen-binding fragments thereof of the present invention, or an immunoglobulin chain thereof, comprising (i) introducing one or more polynucleotides encoding a light and/or a heavy immunoglobulin chain of said antibody or antigen-binding fragment (e.g., a heavy chain or V_Hthereof or immunoglobulin comprising the HCDR1, HCDR2 and HCDR3 thereof and/or a light chain or V_Lthereof or immunoglobulin comprising the LCDR1, LCDR2 and LCDR3 thereof), for example, wherein the polynucleotide is in a vector and/or is operably linked to a promoter; (ii) culturing the host cell (e.g., Chinese hamster ovary (CHO) cell or Pichia cell or Pichia pastoris cell) under condition favorable to expression of the polynucleotide(s) and, (iii) optionally, isolating the antibody or fragment or chain from the host cell and/or medium in which the host cell is grown. When making an antibody or antigen-binding fragment comprising more than one immunoglobulin chain, e.g., an antibody that comprises two heavy immunoglobulin chains and two light immunoglobulin chains, co-expression of the chains in a single host cell leads to association of the chains, e.g., in the cell or on the cell surface or outside the cell if such chains are secreted, so as to form the antibody or antigen-binding fragment molecule. The methods include those wherein only a heavy immunoglobulin chain or only a light immunoglobulin chain (e.g., any of those discussed herein including mature fragments and/or variable domains thereof) is expressed. Such chains are useful, for example, as intermediates in the expression of an antibody or antigen-binding fragment that includes such a chain. The present invention includes the products of such expression methods (e.g., antibodies, antigen-binding fragments, V_Hs, or V_Ls).

Preparation of Human Antibodies

Methods for generating human antibodies in transgenic mice are known in the art. Any such known methods can be used in the context of the present invention to make human antibodies that specifically bind to BMP6.

Using VELOCIMMUNE® technology (see, for example, U.S. Pat. No. 6,596,541, Regeneron Pharmaceuticals, VELOCIMMUNE®) or any other known method for generating monoclonal antibodies, high affinity chimeric antibodies to BMP6 are initially isolated having a human variable region and a mouse constant region. The VELOCIMMUNE® technology involves generation of a transgenic mouse having a genome comprising human heavy and light chain variable regions operably linked to endogenous mouse constant region loci such that the mouse produces an antibody comprising a human variable region and a mouse constant region in response to antigenic stimulation. The DNA encoding the variable regions of the heavy and light chains of the antibody are isolated and operably linked to DNA encoding the human heavy and light chain constant regions. The DNA is then expressed in a cell capable of expressing the fully human antibody.

Generally, a VELOCIMMUNE® mouse is challenged with the antigen of interest, and lymphatic cells (such as B-cells) are recovered from the mice that express antibodies. The lymphatic cells may be fused with a myeloma cell line to prepare immortal hybridoma cell lines, and such hybridoma cell lines are screened and selected to identify hybridoma cell lines that produce antibodies specific to the antigen of interest. DNA encoding the variable regions of the heavy chain and light chain may be isolated and linked to desirable isotypic constant regions of the heavy chain and light chain. Such an antibody protein may be produced in a cell, such as a CHO cell. Alternatively, DNA encoding the antigen-specific chimeric antibodies or the variable domains of the light and heavy chains may be isolated directly from antigen-specific lymphocytes.

Initially, high-affinity chimeric antibodies are isolated having a human variable region and a mouse constant region. The antibodies are characterized and selected for desirable characteristics, including affinity, selectivity, epitope, etc. The mouse constant regions are replaced with a desired human constant region to generate the fully human antibody of the invention, for example wild type or modified IgG1 or IgG4. While the constant region selected may vary according to specific use, high affinity antigen-binding and target specificity characteristics reside in the variable region.

In general, the antibodies of the instant invention possess very high affinities, typically possessing K_Dof from about 10⁻¹²through about 10⁻⁷M, when measured by binding to antigen either immobilized on solid phase or in solution phase. The mouse constant regions are replaced with desired human constant regions to generate the fully human antibodies of the invention. While the constant region selected may vary according to specific use, high affinity antigen-binding and target specificity characteristics reside in the variable region.

Bioequivalents

The anti-BMP6 antibodies and antibody fragments of the present invention encompass proteins having amino acid sequences that vary from those of the described antibodies, but that retain the ability to bind BMP6. Such variant antibodies and antibody fragments comprise one or more additions, deletions, or substitutions of amino acids when compared to parent sequence, but exhibit biological activity that is essentially equivalent to that of the described antibodies. Likewise, the antibody-encoding DNA sequences of the present invention encompass sequences that comprise one or more additions, deletions, or substitutions of nucleotides when compared to the disclosed sequence, but that encode an antibody or antibody fragment that is essentially bioequivalent to an antibody or antibody fragment of the invention.

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

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

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

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

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

Bioequivalent variants of the antibodies of the invention may be constructed by, for example, making various substitutions of residues or sequences or deleting terminal or internal residues or sequences not needed for biological activity. For example, cysteine residues not essential for biological activity can be deleted or replaced with other amino acids to prevent formation of unnecessary or incorrect intramolecular disulfide bridges upon renaturation. In other contexts, bioequivalent antibodies may include antibody variants comprising amino acid changes, which modify the glycosylation characteristics of the antibodies, e.g., mutations that eliminate or remove glycosylation.

Anti-BMP6 Antibodies Comprising Fc Variants

According to certain embodiments of the present invention, anti-BMP6 antibodies are provided comprising an Fc domain comprising one or more mutations which enhance or diminish antibody binding to the FcRn receptor, e.g., at acidic pH as compared to neutral pH. For example, the present invention includes anti-BMP6 antibodies comprising a mutation in the C_H2 or a C_H3 region of the Fc domain, wherein the mutation(s) increases the affinity of the Fc domain to FcRn in an acidic environment (e.g., in an endosome where pH ranges from about 5.5 to about 6.0). Such mutations may result in an increase in serum half-life of the antibody when administered to an animal. Non-limiting examples of such Fc modifications include, e.g., a modification at position 250 (e.g., E or Q); 250 and 428 (e.g., L or F); 252 (e.g., L/Y/F/W or T), 254 (e.g., S or T), and 256 (e.g., S/R/Q/E/D or T); or a modification at position 428 and/or 433 (e.g., H/L/R/S/P/Q or K) and/or 434 (e.g., A, W, H, F or Y [N434A, N434W, N434H, N434F or N434Y]); or a modification at position 250 and/or 428; or a modification at position 307 or 308 (e.g., 308F, V308F), and 434. In one embodiment, the modification comprises a 428L (e.g., M428L) and 434S (e.g., N434S) modification; a 428L, 259I (e.g., V259I), and 308F (e.g., V308F) modification; a 433K (e.g., H433K) and a 434 (e.g., 434Y) modification; a 252, 254, and 256 (e.g., 252Y, 254T, and 256E) modification; a 2500 and 428L modification (e.g., T250Q and M428L); and a 307 and/or 308 modification(s) (e.g., 308F and/or 308P). In yet another embodiment, the modification comprises a 265A (e.g., D265A) and/or a 297A (e.g., N297A) modification.

For example, the present invention includes anti-BMP6 antibodies comprising an Fc domain comprising one or more pairs or groups of mutations selected from the group consisting of: 2500 and 248L (e.g., T250Q and M248L); 252Y, 254T and 256E (e.g., M252Y, S254T and T256E); 428L and 434S (e.g., M428L and N434S); 257I and 311I (e.g., P257I and Q311I); 257I and 434H (e.g., P257I and N434H); 376V and 434H (e.g., D376V and N434H); 307A, 380A and 434A (e.g., T307A, E380A and N434A); and 433K and 434F (e.g., H433K and N434F). All possible combinations of the foregoing Fc domain mutations, and other mutations within the antibody variable domains disclosed herein, are contemplated within the scope of the present invention.

The present invention also includes anti-BMP6 antibodies comprising a chimeric heavy chain constant (C_H) region, wherein the chimeric C_Hregion comprises segments derived from the C_Hregions of more than one immunoglobulin isotype. For example, the antibodies of the invention may comprise a chimeric C_Hregion comprising part or all of a C_H2 domain derived from a human IgG1, human IgG2 or human IgG4 molecule, combined with part or all of a C_H3 domain derived from a human IgG1, human IgG2 or human IgG4 molecule. According to certain embodiments, the antibodies of the invention comprise a chimeric C_Hregion having a chimeric hinge region. For example, a chimeric hinge may comprise an “upper hinge” amino acid sequence (amino acid residues from positions 216 to 227 according to EU numbering) derived from a human IgG1, a human IgG2 or a human IgG4 hinge region, combined with a “lower hinge” sequence (amino acid residues from positions 228 to 236 according to EU numbering) derived from a human IgG1, a human IgG2 or a human IgG4 hinge region. According to certain embodiments, the chimeric hinge region comprises amino acid residues derived from a human IgG1 or a human IgG4 upper hinge and amino acid residues derived from a human IgG2 lower hinge. An antibody comprising a chimeric C_Hregion as described herein may, in certain embodiments, exhibit modified Fc effector functions without adversely affecting the therapeutic or pharmacokinetic properties of the antibody. (See, e.g., U.S. Provisional Appl. No. 61/759,578, filed Feb. 1, 2013, the disclosure of which is hereby incorporated by reference in its entirety).

Biological Characteristics of the Antibodies

In general, the antibodies of the present invention may function by binding to BMP6. In some embodiments, the antibodies of the present invention may bind to another antigen (cross-reactive antibodies).

In certain embodiments, the antibodies of the present invention may be bi-specific antibodies. The bi-specific antibodies of the invention may bind one epitope in one domain and may also bind one epitope in a second domain of BMP6. In certain embodiments, the bi-specific antibodies of the invention may bind two different epitopes in the same domain.

In one embodiment, the invention provides a fully human monoclonal antibody or antigen-binding fragment thereof that binds to BMP6, wherein the antibody or fragment thereof exhibits one or more of the following characteristics: (i) comprises a HCVR having an amino acid sequence selected from the group consisting of SEQ ID NO: 1 and 3, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; (ii) comprises a LCVR having an amino acid sequence selected from the group consisting of SEQ ID NO: 2 and 4, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; (iii) comprises a HCDR3 domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 7 and 13, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; and a LCDR3 domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 10 and 16, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; (iv) comprises a HCDR1 domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 5 and 11, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; a HCDR2 domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 6 and 12, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; a LCDR1 domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 8 and 14, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; and a LCDR2 domain having an amino acid sequence selected from the group consisting of SEQ ID NO: 9 and 15, or a substantially similar sequence thereof having at least 90%, at least 95%, at least 98% or at least 99% sequence identity; and (v) binds to BMP6 with a K_Dequal to or less than 10⁻⁷.

Certain anti-BMP6 antibodies of the present invention are able to bind to and neutralize the activity of BMP6, as determined by in vitro or in vivo assays. The ability of the antibodies of the invention to bind to and neutralize the activity of BMP6 may be measured using any standard method known to those skilled in the art, including binding assays, or activity assays, as described herein.

The peptides may be modified to include addition or substitution of certain residues for tagging or for purposes of conjugation to carrier molecules, such as, KLH. For example, a cysteine may be added at either the N-terminal or C-terminal end of a peptide, or a linker sequence may be added to prepare the peptide for conjugation to, for example, KLH for immunization.

The antibodies specific for BMP6 may contain no additional labels or moieties, or they may contain an N-terminal or C-terminal label or moiety. In one embodiment, the label or moiety is biotin. In a binding assay, the location of a label (if any) may determine the orientation of the peptide relative to the surface upon which the peptide is bound. For example, if a surface is coated with avidin, a peptide containing an N-terminal biotin will be oriented such that the C-terminal portion of the peptide will be distal to the surface. In one embodiment, the label may be a radionuclide, a fluorescent dye or a MRI-detectable label. In certain embodiments, such labeled antibodies may be used in diagnostic assays including imaging assays.

Epitope Mapping and Related Technologies

The present invention includes anti-BMP6 antibodies which interact with one or more amino acids found within one or more regions of BMP6. The epitope to which the antibodies bind may consist of a single contiguous sequence of 3 or more (e.g., 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or more) amino acids located within any of the aforementioned regions of the BMP6 molecule (e.g. a linear epitope in a domain). Alternatively, the epitope may consist of a plurality of non-contiguous amino acids (or amino acid sequences) located within either or both of the aforementioned regions of the BMP6 molecule (e.g. a conformational epitope).

Various techniques known to persons of ordinary skill in the art can be used to determine whether an antibody “interacts with one or more amino acids” within a polypeptide or protein. Exemplary techniques include, for example, routine cross-blocking assays, such as that described in Antibodies, Harlow and Lane (Cold Spring Harbor Press, Cold Spring Harbor, NY). Other methods include alanine scanning mutational analysis, peptide blot analysis (Reineke (2004) Methods Mol Biol 248:443-63), peptide cleavage analysis, crystallographic studies and NMR analysis. In addition, methods such as epitope excision, epitope extraction and chemical modification of antigens can be employed (Tomer (2000) Protein Science 9: 487-496). Another method that can be used to identify the amino acids within a polypeptide with which an antibody interacts is hydrogen/deuterium exchange detected by mass spectrometry. In general terms, the hydrogen/deuterium exchange method involves deuterium-labeling the protein of interest, followed by binding the antibody to the deuterium-labeled protein. Next, the protein/antibody complex is transferred to water and exchangeable protons within amino acids that are protected by the antibody complex undergo deuterium-to-hydrogen back-exchange at a slower rate than exchangeable protons within amino acids that are not part of the interface. As a result, amino acids that form part of the protein/antibody interface may retain deuterium and therefore exhibit relatively higher mass compared to amino acids not included in the interface. After dissociation of the antibody, the target protein is subjected to protease cleavage and mass spectrometry analysis, thereby revealing the peptides containing the deuterium-labeled residues that contain specific amino acids with which the antibody interacts. See, e.g., Ehring (1999) Analytical Biochemistry 267(2):252-259; Engen and Smith (2001) Anal. Chem. 73: 256A-265A.

The term “epitope” refers to a site on an antigen to which B and/or T cells respond. B-cell epitopes can be formed both from contiguous amino acids or noncontiguous amino acids juxtaposed by tertiary folding of a protein. Epitopes formed from contiguous amino acids are typically retained on exposure to denaturing solvents, whereas epitopes formed by tertiary folding are typically lost on treatment with denaturing solvents. An epitope typically includes at least 3, and more usually, at least 5 or 8-10 amino acids in a unique spatial conformation.

Modification-Assisted Profiling (MAP), also known as Antigen Structure-based Antibody Profiling (ASAP) is a method that categorizes large numbers of monoclonal antibodies (mAbs) directed against the same antigen according to the similarities of the binding profile of each antibody to chemically or enzymatically modified antigen surfaces (see US 2004/0101920, herein specifically incorporated by reference in its entirety). Each category may reflect a unique epitope either distinctly different from or partially overlapping with epitope represented by another category. This technology allows rapid filtering of genetically identical antibodies, such that characterization can be focused on genetically distinct antibodies. When applied to hybridoma screening, MAP may facilitate identification of rare hybridoma clones that produce mAbs having the desired characteristics. MAP may be used to sort the antibodies of the invention into groups of antibodies binding different epitopes.

In certain embodiments, the anti-BMP6 antibodies or antigen-binding fragments thereof bind an epitope within any one or more of the regions exemplified in human BMP6, as exemplified in SEQ ID NO: 40, or to a fragment thereof.

The present invention includes human anti-BMP6 antibodies that bind to the same epitope, or a portion of the epitope, as any of the specific exemplary antibodies described herein, or an antibody having the CDR sequences of any of the exemplary antibodies described herein. Likewise, the present invention also includes anti-BMP6 antibodies that compete for binding to BMP6 or a BMP6 fragment with any of the specific exemplary antibodies described herein, or an antibody having the CDR sequences of any of the exemplary antibodies described herein.

One can easily determine whether an antibody binds to the same epitope as, or competes for binding with, a reference anti-BMP6 antibody by using routine methods known in the art. For example, to determine if a test antibody binds to the same epitope as a reference anti-BMP6 antibody of the invention, the reference antibody is allowed to bind to a BMP6 protein or peptide under saturating conditions. Next, the ability of a test antibody to bind to the BMP6 molecule is assessed. If the test antibody is able to bind to BMP6 following saturation binding with the reference anti-BMP6 antibody, it can be concluded that the test antibody binds to a different epitope than the reference anti-BMP6 antibody. On the other hand, if the test antibody is not able to bind to the BMP6 protein following saturation binding with the reference anti-BMP6 antibody, then the test antibody may bind to the same epitope as the epitope bound by the reference anti-BMP6 antibody of the invention.

To determine if an antibody competes for binding with a reference anti-BMP6 antibody, the above-described binding methodology is performed in two orientations: In a first orientation, the reference antibody is allowed to bind to a BMP6 protein under saturating conditions followed by assessment of binding of the test antibody to the BMP6 molecule. In a second orientation, the test antibody is allowed to bind to a BMP6 molecule under saturating conditions followed by assessment of binding of the reference antibody to the BMP6 molecule. If, in both orientations, only the first (saturating) antibody is capable of binding to the BMP6 molecule, then it is concluded that the test antibody and the reference antibody compete for binding to BMP6. As will be appreciated by a person of ordinary skill in the art, an antibody that competes for binding with a reference antibody may not necessarily bind to the identical epitope as the reference antibody, but may sterically block binding of the reference antibody by binding an overlapping or adjacent epitope.

Two antibodies bind to the same or overlapping epitope if each competitively inhibits (blocks) binding of the other to the antigen. That is, a 1-, 5-, 10-, 20- or 100-fold excess of one antibody inhibits binding of the other by at least 50% but preferably 75%, 90% or even 99% as measured in a competitive binding assay (see, e.g., Junghans et al., Cancer Res. 1990 50:1495-1502). Alternatively, two antibodies have the same epitope if essentially all amino acid mutations in the antigen that reduce or eliminate binding of one antibody reduce or eliminate binding of the other. Two antibodies have overlapping epitopes if some amino acid mutations that reduce or eliminate binding of one antibody reduce or eliminate binding of the other.

Additional routine experimentation (e.g., peptide mutation and binding analyses) can then be carried out to confirm whether the observed lack of binding of the test antibody is in fact due to binding to the same epitope as the reference antibody or if steric blocking (or another phenomenon) is responsible for the lack of observed binding. Experiments of this sort can be performed using ELISA, RIA, surface plasmon resonance, flow cytometry or any other quantitative or qualitative antibody-binding assay available in the art.

Immunoconjugates

The invention encompasses a human anti-BMP6 monoclonal antibody conjugated to a therapeutic moiety (“immunoconjugate”), such as an agent that is capable of reducing the severity of an iron-deficiency anemia or an iron-deficiency related disorder, or to ameliorate at least one symptom associated with an iron-deficiency anemia or an iron-deficiency related disorder. As used herein, the term “immunoconjugate” refers to an antibody that is chemically or biologically linked to a radioactive agent, a cytokine, an interferon, a target or reporter moiety, an enzyme, a toxin, or a therapeutic agent. The antibody may be linked to the radioactive agent, cytokine, interferon, target or reporter moiety, enzyme, toxin, or therapeutic agent at any location along the molecule so long as it is able to bind its target. An example of immunoconjugate is an antibody drug conjugate. In some embodiments, the agent may be a second different antibody to BMP6, or to a cytokine such as IL-1, IL-6, or a chemokine such as TGF-β. The type of therapeutic moiety that may be conjugated to the anti-BMP6 antibody will take into account the condition to be treated and the desired therapeutic effect to be achieved. Examples of suitable agents for forming immunoconjugates are known in the art; see for example, WO 05/103081. The preparation of immunoconjugates and immunotoxins is generally well known in the art (see, e.g., U.S. Pat. No. 4,340,535). Immunoconjugates are described in detail, for example, in U.S. Pat. Nos. 7,250,492, 7,420,040 and 7,411,046, each of which is incorporated herein in their entirety.

Multi-Specific Antibodies

The antibodies of the present invention may be mono-specific, bi-specific, or multi-specific. Multi-specific antibodies may be specific for different epitopes of one target polypeptide or may contain antigen-binding domains specific for more than one target polypeptide. See, e.g., Tutt et al., 1991, J. Immunol. 147:60-69; Kufer et al., 2004, Trends Biotechnol. 22:238-244. The antibodies of the present invention can be linked to or co-expressed with another functional molecule, e.g., another peptide or protein. For example, an antibody or fragment thereof can be functionally linked (e.g., by chemical coupling, genetic fusion, noncovalent association or otherwise) to one or more other molecular entities, such as another antibody or antibody fragment to produce a bi-specific or a multi-specific antibody with a second binding specificity. For example, the present invention includes bi-specific antibodies wherein one arm of an immunoglobulin is specific for the N-terminal region of BMP6, or a fragment thereof, and the other arm of the immunoglobulin is specific for the C-terminal region of BMP6, or a second therapeutic target, or is conjugated to a therapeutic moiety. An exemplary bi-specific antibody format that can be used in the context of the present invention involves the use of a first immunoglobulin (Ig) C_H3 domain and a second Ig C_H3 domain, wherein the first and second Ig C_H3 domains differ from one another by at least one amino acid, and wherein at least one amino acid difference reduces binding of the bi-specific antibody to BMP6 as compared to a bi-specific antibody lacking the amino acid difference. In one embodiment, the first Ig C_H3 domain binds BMP6 and the second Ig C_H3 domain contains a mutation that reduces or abolishes BMP6 binding such as an H95R modification (by IMGT exon numbering; H435R by EU numbering). The second C_H3 may further comprise a Y96F modification (by IMGT; Y436F by EU). Further modifications that may be found within the second C_H3 include: D16E, L18M, N44S, K52N, V57M, and V82I (by IMGT; D356E, L358M, N384S, K392N, V397M, and V422I by EU) in the case of IgG1 antibodies; N44S, K52N, and V82I (IMGT; N384S, K392N, and V422I by EU) in the case of IgG2 antibodies; and Q15R, N44S, K52N, V57M, R69K, E79Q, and V82I (by IMGT; Q355R, N384S, K392N, V397M, R409K, E419Q, and V422I by EU) in the case of IgG4 antibodies. Variations on the bi-specific antibody format described above are contemplated within the scope of the present invention.

Other exemplary bispecific formats that can be used in the context of the present invention include, without limitation, e.g., scFv-based or diabody bispecific formats, IgG-scFv fusions, dual variable domain (DVD)-Ig, Quadroma, knobs-into-holes, common light chain (e.g., common light chain with knobs-into-holes, etc.), CrossMab, CrossFab, (SEED)body, leucine zipper, Duobody, IgG1/IgG2, dual acting Fab (DAF)-IgG, and Mab²bispecific formats (see, e.g., Klein et al. 2012, mAbs 4:6, 1-11, and references cited therein, for a review of the foregoing formats). Bispecific antibodies can also be constructed using peptide/nucleic acid conjugation, e.g., wherein unnatural amino acids with orthogonal chemical reactivity are used to generate site-specific antibody-oligonucleotide conjugates which then self-assemble into multimeric complexes with defined composition, valency and geometry. (See, e.g., Kazane et al., J. Am. Chem. Soc. [Epub: Dec. 4, 2012]).

Therapeutic Administration and Formulations

The invention provides therapeutic compositions comprising the anti-BMP6 antibodies or antigen-binding fragments thereof as discussed herein. The therapeutic compositions in accordance with the invention can be administered with suitable carriers, excipients, and other agents that are incorporated into formulations to provide improved transfer, delivery, tolerance, and the like. A multitude of appropriate formulations can be found in the formulary known to all pharmaceutical chemists: Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, PA These formulations include, for example, powders, pastes, ointments, jellies, waxes, oils, lipids, lipid (cationic or anionic) containing vesicles (such as LIPOFECTIN®), DNA conjugates, anhydrous absorption pastes, oil-in-water and water-in-oil emulsions, emulsions carbowax (polyethylene glycols of various molecular weights), semi-solid gels, and semi-solid mixtures containing carbowax. See also Powell et al. “Compendium of excipients for parenteral formulations” PDA (1998) J Pharm Sci Technol 52:238-311.

The dose of antibody may vary depending upon the age and the size of a subject to be administered, target disease, conditions, route of administration, and the like. When the antibody of the present invention is used for preventing or treating an iron-deficiency anemia or an iron-deficiency related disorder, it is advantageous to intravenously administer the antibody of the present invention normally at a single dose of about 0.1 to about 100 mg/kg body weight, more preferably about 5 to about 100, about 10 to about 90, or about 20 to about 70 mg/kg body weight. Depending on the severity of the condition, the frequency and the duration of the treatment can be adjusted. In certain embodiments, the antibody or antigen-binding fragment thereof of the invention can be administered as an initial dose of at least about 0.1 mg to about 800 mg, about 1 to about 500 mg, about 5 to about 300 mg, or about 10 to about 200 mg, to about 100 mg, or to about 50 mg. In certain embodiments, the initial dose may be followed by administration of a second or a plurality of subsequent doses of the antibody or antigen-binding fragment thereof in an amount that can be approximately the same or less than that of the initial dose, wherein the subsequent doses are separated by at least 1 day to 3 days; at least one week, at least 2 weeks; at least 3 weeks; at least 4 weeks; at least 5 weeks; at least 6 weeks; at least 7 weeks; at least 8 weeks; at least 9 weeks; at least 10 weeks; at least 12 weeks; or at least 14 weeks.

Various delivery systems are known and can be used to administer the pharmaceutical composition of the invention, e.g., encapsulation in liposomes, microparticles, microcapsules, recombinant cells capable of expressing the mutant viruses, receptor mediated endocytosis (see, e.g., Wu et al. (1987) J. Biol. Chem. 262:4429-4432). Methods of introduction include, but are not limited to, intradermal, transdermal, intramuscular, intraperitoneal, intravenous, subcutaneous, intranasal, epidural and oral routes. The composition may be administered by any convenient route, for example by infusion or bolus injection, by absorption through epithelial or mucocutaneous linings (e.g., oral mucosa, rectal and intestinal mucosa, etc.) and may be administered together with other biologically active agents. Administration can be systemic or local. The pharmaceutical composition can be also delivered in a vesicle, in particular a liposome (see, for example, Langer (1990) Science 249:1527-1533).

The use of nanoparticles to deliver the antibodies of the present invention is also contemplated herein. Antibody-conjugated nanoparticles may be used both for therapeutic and diagnostic applications. Antibody-conjugated nanoparticles and methods of preparation and use are described in detail by Arruebo, M., et al. 2009 (“Antibody-conjugated nanoparticles for biomedical applications” in J. Nanomat. Volume 2009, Article ID 439389, 24 pages, doi: 10.1155/2009/439389), incorporated herein by reference. Nanoparticles for drug delivery have also been described in, for example, U.S. Pat. Nos. 8,277,812, 8,258,256, 8,257,740, 8,246,995, 8,236,330, each incorporated herein in its entirety.

In certain situations, the pharmaceutical composition can be delivered in a controlled release system. In one embodiment, a pump may be used. In another embodiment, polymeric materials can be used. In yet another embodiment, a controlled release system can be placed in proximity of the composition's target, thus requiring only a fraction of the systemic dose.

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

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

Numerous reusable pen and autoinjector delivery devices have applications in the subcutaneous delivery of a pharmaceutical composition of the present invention. Examples include, but certainly are not limited to AUTOPEN® (Owen Mumford, Inc., Woodstock, UK), DISETRONIC™ pen (Disetronic Medical Systems, Burghdorf, Switzerland), HUMALOG MIX 75/25™ pen, HUMALOG® pen, HUMALIN 70/30™ pen (Eli Lilly and Co., Indianapolis, IN), NOVOPEN® I, II and III (Novo Nordisk, Copenhagen, Denmark), NOVOPEN JUNIOR™ (Novo Nordisk, Copenhagen, Denmark), BD pen (Becton Dickinson, Franklin Lakes, NJ), OPTIPEN®, OPTIPEN® PRO, OPTIPEN® STARLET, and OPTICLIK™ (Sanofi-aventis, Frankfurt, Germany), to name only a few. Examples of disposable pen delivery devices having applications in subcutaneous delivery of a pharmaceutical composition of the present invention include, but certainly are not limited to the SOLOSTAR® pen (Sanofi-aventis), the FLEXPEN® (Novo Nordisk), and the KWIKPEN® (HUMALOG®), the SURECLICK® Autoinjector (, the PENLET (Haselmeier, Stuttgart, Germany), the EPIPEN® (Mylan® and the HUMIRA® Pen (Abbott Labs, Abbott Park, IL), to name only a few.

Advantageously, the pharmaceutical compositions for oral or parenteral use described above are prepared into dosage forms in a unit dose suited to fit a dose of the active ingredients. Such dosage forms in a unit dose include, for example, tablets, pills, capsules, injections (ampoules), suppositories, etc. The amount of the aforesaid antibody contained is generally about 5 to about 500 mg per dosage form in a unit dose; especially in the form of injection, it is preferred that the aforesaid antibody is contained in about 5 to about 100 mg and in about 10 to about 250 mg for the other dosage forms. The present invention includes an injection device (e.g., a pre-filled syringe or pre-filled autoinjector) or a vial (e.g., a glass or plastic vial) comprising an antibody or antigen-binding fragment of the present invention or pharmaceutical composition thereof which includes a pharmaceutically acceptable carrier.

Therapeutic Uses of the Antibodies

In certain embodiments of the invention, the present antibodies are useful for treating an iron-deficiency anemia or an iron-deficiency related disorder, or at least one symptom associated with an iron-deficiency anemia or an iron-deficiency related disorder. The antibodies of the invention are also contemplated for prophylactic use in patients at risk for developing an iron-deficiency anemia or an iron-deficiency related disorder. These patients include the elderly, or patients immunocompromised due to illness or treatment with immunosuppressive therapeutics. It is contemplated that the antibodies of the invention may be used alone, or in conjunction with a second agent, or third agent for treating an iron-deficiency anemia or an iron-deficiency related disorder, or for alleviating at least one symptom or complication associated with an iron-deficiency anemia or an iron-deficiency related disorder. The second or third agents may be delivered concurrently with the antibodies of the invention, or they may be administered separately, either before or after the antibodies of the invention. A patient that may receive an antibody or antigen-binding fragment of the invention or a pharmaceutical composition thereof includes, for example, an animal such as a mammal such as a human (e.g., an elderly human, for example, 65 years of age or older), rabbit, mouse, rat, cow, pig, dog, primate, horse or sheep.

In a further embodiment of the invention the present antibodies are used for the preparation of a pharmaceutical composition for treating patients suffering from an iron-deficiency anemia or an iron-deficiency related disorder.

Combination Therapies

Combination therapies may include an anti-BMP6 antibody of the invention and any additional therapeutic agent(s) that may be advantageously combined with an antibody of the invention, or with a biologically active fragment of an antibody of the invention.

The antibodies may be used in conjunction with other therapies, such as moieties or modalities known in the art for treating iron-deficiency anemia or an iron-deficiency related disorder, such as, but not limited to, iron supplementation through iron supplements, dietary changes to promote serum iron and/or intravenous delivery of iron, blood transfusion, and iron promoting medications.

The additional therapeutically active component(s) may be administered prior to, concurrent with, or after the administration of the anti-BMP6 antibody of the present invention. For purposes of the present disclosure, such administration regimens are considered the administration of an anti-BMP6 antibody “in combination with” one or more additional therapeutically active component(s).

Diagnostic Uses of the Antibodies

The anti-BMP6 antibodies of the present invention may also be used to detect and/or measure BMP6 in a sample, e.g., for diagnostic purposes. Exemplary diagnostic assays for BMP6 may comprise, e.g., contacting a sample, obtained from a patient, with an anti-BMP6 antibody of the invention, wherein the anti-BMP6 antibody is labeled with a detectable label or reporter molecule or used as a capture ligand to selectively isolate BMP6 from patient samples. Alternatively, an unlabeled anti-BMP6 antibody can be used in diagnostic applications in combination with a secondary antibody which is itself detectably labeled. The detectable label or reporter molecule can be a radioisotope, such as ³H, ¹⁴C, ³²P, ³⁵S, or ¹²⁵I; a fluorescent or chemiluminescent moiety such as fluorescein isothiocyanate, or rhodamine; or an enzyme such as alkaline phosphatase, β-galactosidase, horseradish peroxidase, or luciferase. Specific exemplary assays that can be used to detect or measure BMP6 in a sample include enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA), and fluorescence-activated cell sorting (FACS).

Samples that can be used in BMP6 diagnostic assays according to the present invention include any tissue or fluid sample obtainable from a patient, which contains detectable quantities of either BMP6, or fragments thereof, under normal or pathological conditions. Generally, levels of BMP6 in a particular sample obtained from a healthy patient (e.g., a patient not afflicted with an iron-deficiency anemia or an iron-deficiency related disorder) will be measured to initially establish a baseline, or standard, level of BMP6. This baseline level of BMP6 can then be compared against the levels of BMP6 measured in samples obtained from individuals suspected of having an iron-deficiency anemia or an iron-deficiency related disorder related condition, or symptoms associated with such condition.

The antibodies specific for BMP6 may contain no additional labels or moieties, or they may contain an N-terminal or C-terminal label or moiety. In one embodiment, the label or moiety is biotin. In a binding assay, the location of a label (if any) may determine the orientation of the peptide relative to the surface upon which the peptide is bound. For example, if a surface is coated with avidin, a peptide containing an N-terminal biotin will be oriented such that the C-terminal portion of the peptide will be distal to the surface. In some embodiments, the label may be detectable label such as a radionuclide, a fluorescent dye or a MRI-detectable label. Detectable labels may be linked to the antibodies wherein such antibodies may be used in imaging assays.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the methods and compositions of the invention, and are not intended to limit the scope of what the inventors regard as their invention. Unless indicated otherwise, parts are parts by weight, molecular weight is average molecular weight, temperature is in degrees Celsius, and pressure is at or near atmospheric.

Example 1. Generation of Human Antibodies to BMP6

Human antibodies to BMP6 were generated in a VELOCIMMUNE® mouse comprising DNA encoding human Immunoglobulin heavy and kappa light chain variable regions. The mice were immunized with a stabilized full-length BMP6 protein.

The antibody immune response was monitored by a BMP6-specific immunoassay. When a desired immune response was achieved, splenocytes were harvested and fused with mouse myeloma cells to preserve their viability and form hybridoma cell lines. The hybridoma cell lines were screened and selected to identify cell lines that produce BMP6-specific antibodies. The cell lines were used to obtain several anti-BMP6 chimeric antibodies (i.e., antibodies possessing human variable domains and mouse constant domains).

Exemplary antibodies generated as disclosed above were designated as H4H17855P and H4H17871P. The biological properties of the exemplary antibodies generated in accordance with the methods of this Example are further described in the Examples below.

Example 2. Heavy and Light Chain Variable Region Amino Acid Sequences

Table 1 sets forth the heavy and light chain variable region amino acid sequence pairs of selected antibodies specific for BMP6 and their corresponding antibody identifiers. Antibodies are typically referred to herein according to the following nomenclature: Fc prefix (e.g. “H4H”), followed by a numerical identifier (e.g., “7855” as shown in Table 1), followed by a “P” suffix. Thus, according to this nomenclature, an antibody may be referred to as, e.g., “H4H17855P”. The H4H prefix on the antibody designations used herein indicates the particular Fc region of the antibody. For example, an “H4H” antibody has a human IgG4 Fc.

TABLE 1

Antibody
SEQ ID NOs:

Designation
HCVR
HCDR1
HCDR2
HCDR3
LCVR
LCDR1
LCDR2
LCDR3

H4H17855P
1
5
6
7
2
8
9
10

H4H17871P
3
11
12
13
4
14
15
16

Example 3. Binding Kinetics of Human Monoclonal Antibodies to BMP6

Equilibrium dissociation constants (K_Dvalues) for human and mouse BMP6 binding to purified anti-BMP6 monoclonal antibodies of this invention were determined using a real-time surface plasmon resonance (SPR) biosensor instrument, MASS-1. All binding studies were performed in 10 mM HEPES, 150 mM NaCl, 3 mM EDTA, 1 μg/mL Heparin, and 0.05% v/v Surfactant Tween-20, pH 7.4 (HBS-EHT) running buffer at 25° C. and 37° C. The HCA sensor surface was first derivatized by amine coupling the monoclonal mouse anti-human Fc antibody (GE, #BR100839) and anti-BMP6 monoclonal antibodies were individually captured. Different concentrations of human BMP6 reagents (hBMP6; R&D Systems, Cat #507-BP; 60 nM-0.94 nM; 4-fold serial dilution) or mouse BMP6 (mBMP6; R&D Systems, Cat #6325-BM; 60 nM and 15 nM) prepared in HBS-EHT running buffer were injected over the captured anti-BMP6 monoclonal antibody for 4 minutes at a flow rate of 30 μL/minute, while the dissociation of BMP6 reagent bound to captured anti-BMP6 monoclonal antibody was monitored for 10 minutes in HBS-EHT running buffer. Kinetic association (k_a) and dissociation (k_d) rate constants were determined by fitting the real-time binding sensorgrams to a 1:1 binding model with mass transport limitation using Scrubber 2.0c software. Binding dissociation equilibrium constant (K_D) and dissociative half-life (t½) for different anti-BMP6 monoclonal antibodies were calculated from the kinetic rate constants as:

K
D

⁡

(
M
)

=

kd
ka

,

and
⁢

⁢
t
⁢

⁢
1
⁢

/

⁢
2
⁢

⁢

(
min
)

=

ln
⁡

(
2
)

60
*
kd

Binding kinetic parameters for hBMP6 or mBMP6 binding to different anti-BMP6 monoclonal antibodies of this invention at 25° C. and 37° C. are shown in Tables 2 through 5.

As shown in Table 2, at 25° C., both antibodies of the invention bound human BMP6 with K_Dvalues of 195 pM and 355 pM. As shown in Table 3, at 37° C., both antibodies of the invention bound human BMP6 with K_Dvalues of 240 pM and 1.34 nM. As shown in Table 4, at 25° C., both antibodies of the invention bound mouse BMP6 with K_Dvalues of 3.39 nM and 3.55 nM. As shown in Table 5, at 37° C., both antibodies of the invention bound mouse BMP6 with K_Dvalues of 4.0 nM and 6.46 nM.

TABLE 2

Binding kinetics parameters of hBMP6 binding

to anti-BMP6 monoclonal antibodies at 25° C.

60 nM

mAb
hBMP6

mAb
Capture
Bound
k_a
k_d
K_D
t1/2

Captured
Level (RU)
(RU)
(1/Ms)
(1/s)
(M)
(min)

H4H17855P
282 ± 2.4
72
1.78E+05
6.30E−05
3.55E−10
183

H4H17871P
243 ± 1.8
52
2.83E+05
4.14E−05
1.95E−10
279

Isotype
345 ± 1.8
2
NB
NB
NB
NB

Control mAb

NB; no binding was observed under the current experimental conditions.

TABLE 3

Binding kinetics parameters of hBMP6 binding

to anti-BMP6 monoclonal antibodies at 37° C.

60 nM

mAb
hBMP6

mAb
Capture
Bound
k_a
k_d
K_D
t1/2

Captured
Level (RU)
(RU)
(1/Ms)
(1/s)
(M)
(min)

H4H17855P
319 ± 9.3
83
6.11E+04
8.17E−05
1.34E−09
141

H4H17871P
286 ± 7.7
43
4.16E+04
1.00E−05 ^#
2.40E−10
1155

Isotype
407 ± 3.4
2
NB
NB
NB
NB

Control mAb

NB; no binding was observed under the current experimental conditions.

^# under the current experimental conditions, no dissociation of hBMP6 was observed from the captured anti-BMP6 monoclonal antibody and k_dvalue was manually fixed at 1.00E−05 when fitting the real time binding sensorgrams.

TABLE 4

Binding kinetics parameters of mBMP6 binding

to anti-BMP6 monoclonal antibodies at 25° C.

60 nM

mAb
mBMP6

mAb
Capture
Bound
k_a
k_d
K_D
t1/2

Captured
Level (RU)
(RU)
(1/Ms)
(1/s)
(M)
(min)

H4H17855P
274 ± 4.8
41
3.66E+04
1.30E−04
3.55E−09
89

H4H17871P
237 ± 2.8
25
3.74E+04
1.27E−04
3.39E−09
91

Isotype
346 ± 1.1
3
NB
NB
NB
NB

Control mAb

NB: no binding was observed under the current experimental conditions.

TABLE 5

Binding kinetics parameters of mBMP6 binding

to anti-BMP6 monoclonal antibodies at 37° C.

60 nM

mAb
mBMP6

mAb
Capture
Bound
k_a
k_d
K_D
t1/2

Captured
Level (RU)
(RU)
(1/Ms)
(1/s)
(M)
(min)

H4H17855P
295 ± 3.7
46
2.38E+04
1.54E−04
6.46E−09
75

H4H17871P
288 ± 2.5
19
2.35E+04
9.43E−05
4.00E−09
123

Isotype
408 ± 6.2
3
NB
NB
NB
NB

Control mAb

*NB indicates that no binding was observed under the current experimental conditions.

Example 4. Blocking of BMP6 Receptor Binding by Anti-BMP6 Monoclonal Antibodies

Blocking of BMP6 from binding to its receptors, Hemojuvelin, ActR2A or ActR2B by anti-BMP6 monoclonal antibodies (mAbs) was determined using a real-time surface plasmon resonance (SPR) biosensor instrument, Biacore 3000. All binding studies were performed in 10 mM HEPES, 150 mM NaCl, 3 mM EDTA, 1 μg/mL Heparin, and 0.05% v/v Surfactant Tween-20, pH 7.4 (HBS-EHT) buffer at 25° C.

Approximately 10500, 5000 and 5000 RU of human Hemojuvelin expressed with a human Fc tag (hHJV-hFc; SEQ ID: 37), human ActR2A extracellular domain expressed with a C-terminal human Fc tag (hActR2A-hFc; SEQ ID: 38), human ActR2B extracellular domain expressed with a C-terminal human Fc tag (hActR2B-hFc; SEQ ID: 39), respectively were individually immobilized on different flow cells of CM4 sensor surface using the EDC/NHS surface chemistry; while the activated/deactivated surface was used as reference control surface. A concentration of 10 nM human BMP-6 was pre-mixed with 400 nM anti-BMP-6 mAbs for at least 2 hours before the start of the experiment. The mixture of BMP6 and anti-BMP6 mAbs was injected over different immobilized sensor surfaces for 10 minutes at a flow rate of 5 μL/min. The binding of 27 nM BMP6 to immobilized surfaces was used to assess percent blocking while the non-specific binding of anti-BMP6 mAbs without BMP6 was also tested.

As shown in Table 6, the anti-BMP6 antibodies of the invention demonstrated partial blocking of BMP6 binding to hHJV-hFc. The anti-BMP6 antibodies of the invention demonstrated enhanced binding of BMP6 to the hActR2A-hFc and hActR2B-hFc surfaces.

TABLE 6

Blocking of BMP6 from binding to its receptors, Hemojuvelin,

ActR2A or ActR2B by anti-BMP6 monoclonal antibodies.

Isotype

H4H17855P
H4H17871P
Control mAb

hHJV-hFc
400 nM mAb
39
27
14

Surface
Binding (RU)

400 nM mAb +
266
111
299

10 nM hBMP-6

Binding (RU)

% Blocking
61
84
41

hActR2A-
400 nM mAb
34
30
17

hFc Surface
Binding (RU)

400 nM mAb +
2490
659
246

10 nM hBMP-6

Binding (RU)

% Blocking
−400
−46
43

hActR2B-
400 nM mAb
37
28
15

hFc Surface
Binding (RU)

400 nM mAb +
2486
711
187

10 nM hBMP-6

Binding (RU)

% Blocking
−563
−94
25

Example 5. Anti-BMP6 Antibodies Blocking BMP6 Binding to Hemojuvelin and ActivinR2A

The ability of anti-BMP6 monoclonal antibodies to block binding of human BMP6 to two natural binding partners, the co-receptor Hemojuvelin (HJV), and a type II binding receptor, Activin Receptor 2a (ActR2a), was measured using two competition sandwich ELISAs.

The human BMP6 protein used in the experiments was purchased from R&D systems (hBMP6; Cat ##507-BP/CF) and was biotinylated for detection purposes (biot-hBMP6) and the molecular weight of 30 kDa was used for calculations as BMP6 protein is naturally a dimer. The HJV protein used in the experiments was comprised of a portion of the human HJV extracellular domain (aa Gln36-Ser399) expressed with a linker sequence and the Fc portion of the human IgG1 at the C-terminus (hHJV-hFc; SEQ ID: 37) The Activin R2a protein was purchased from R&D Systems (hActR2a-hFc; R&D systems, Cat #340-RC2). An isotype antibody control, was included, along with a commercially available goat-anti-hBMP6 positive blocking control antibody (R&D Systems, Cat #AF507).

Experiments were carried out using the following procedure. Receptors were coated in Hank's Balanced Salt Solution (HBSS) separately at a concentration of 5 μg/mL for hHJV-hFc and 2.5 g/mL for hActR2a-hFc on a 96-well microtiter plate overnight at 4° C. Nonspecific binding sites were subsequently blocked using a 1.0% (w/v) solution of BSA in HBSS. In other microtiter plates, a constant amount of 2.5 nM of biot-BMP6 (for HJV capture) or 1.5 nM biot-BMP6 (for ActR2a capture) protein was titrated with anti-BMP6 antibodies or isotype control antibodies ranging from 5.1 pM to 300 nM in serial dilution in HBSS with 1.0% BSA and 3.33 g/mL heparin. These antibody-protein complexes, after a one-hour incubation, were transferred to the microtiter plate coated with hHJV-hFc or hActR2a-hFc. After two hours of incubation at room temperature, the wells were washed, and plate-bound biot-BMP6 was detected with neutravidin conjugated with horseradish peroxidase (HRP) (Thermo Scientific, Cat #31030). The plates were then developed using TMB substrate solution (BD Biosciences, Cat #555214) according to manufacturer's recommendation and absorbance at 450 nm was measured on a Victor X5 plate reader.

Data analysis was performed using a sigmoidal dose-response model within Prism™ software (GraphPad). The calculated IC₅₀value, defined as the concentration of antibody required to reduce 50% of biot-BMP6 binding to hHJV-hFc or hActR2a-hFc, was used as an indicator of blocking potency. Percent blockade at indicated concentration of the antibody tested was calculated as an indicator of the ability of the antibodies to block the binding of 2.5 nM or 1.5 nM of biot-BMP6 to hHJV-hFc or hActR2a-hFc on the plate, respectively. In the calculation, binding signal of the sample of the constant biot-BMP6 without the presence of the antibody for each assay was referenced as 100% binding or 0% blocking; and the baseline signal of the sample of buffer only without the presence of biot-BMP6 was referenced as 0% binding or 100% blocking.

The blockade of each antibody at the maximum concentration of 300 nM antibody was calculated and compared. In addition, for the blocking of BMP6 binding to ActR2a, the blockade of each antibody at 11.1 nM was calculated and reported to reflect the enhanced binding signal of biot-BMP6 in the presence of some antibodies in this assay.

The blocking results of the two assays are summarized in Table 7. The two antibodies of the invention blocked >90% of 2.5 nM biot-BMP6 protein binding to hHJV-hFc with 300 nM of antibody. The blocking potency (IC₅₀value) of H4H17855P was calculated at 0.522 nM, which was below the lower limit of quantitation for the assay of 1.25 nM. The IC₅₀value of H4H17871P blocking BMP6 protein binding to hHJV-hFc was 1.61 nM. The potency of the positive control anti-BMP6 commercial Ab was 2.32 nM with 93% blocking at 300 nM antibody. The Comparator Ab blocked with an IC₅₀value of 2.99 nM with maximal blocking of 88%. The isotype control antibody blocked <30% at concentrations up to 300 nM antibody, as expected.

The two test antibodies, H4H17855P and H4H17871P, enhanced biot-BMP6 protein binding to hActR2a-hFc 29.8% and 15.5%, respectively at 11.1 nM, while blocking 19.5% and 37.3% at 300 nM antibody. The positive control anti-BMP6 commercial Ab blocked 92.8% with an IC₅₀of 11.8 nM. The Comparator Ab blocked >30% at 300 nM, but did not have a sigmoidal curve so no IC₅₀value was reported. The isotype control antibody blocked <30%, as expected.

TABLE 7

Effect of anti-BMP6 antibodies in Blocking ELISA

300 nM Ab

300 nM Ab
11.1 nM Ab

Blocking of
Blocking of
Blocking of
Blocking of
Blocking of

2.5 nM Biot-
2.5 nM Biot-
1.5 nM Biot-
1.5 nM Biot-
1.5 nM Biot-

hBMP6
hBMP6
hBMP6
hBMP6
hBMP6

Binding to
Binding to
Binding to
Binding to
Binding to

HJV-hFc
HJV-hFc
ActR2a-hFc
ActR2a-hFc
ActR2a-hFc

Antibody
IC50 (M)
(%)
IC50 (M)
(%)
(%)

H4H17855P
5.22E−10*
97.0
Enhancer
19.5
−29.8

H4H17871P
1.61E−09
94.9
Enhancer/Blocker
37.3
−15.5

Controls

Comparator Ab
2.99E−09
88.2
IC
47.7
−1.6

ant-BMP6
2.32E−09
93.0
1.18E−08
92.8
53.7

commercial Ab

Isotype control
NB
26.3
NB
19.9
25.7

Ab

IC indicates inconclusive IC₅₀value due to non-sigmoidal blocking curve

NB indicated non-blocking (<30%)

*indicates value below the lower limit of quantitation of 1.25E−09M for the BMP6 blocking HJV assay

Example 6. Binding Cross-Reactivity of Anti-BMP6 Monoclonal Antibodies

Binding cross-reactivity of anti-BMP6 monoclonal antibodies to BMP6 family members, (Human: BMP6, BMP5, BMP7, BMP8A, BMP9, BMP10, BMP12, BMP14, BMP3b, Activin A, and GDF3 and mouse: BMP6 and GDF6) was determined using a real-time Bio-Layer Interferometry (BLI) biosensor using Octet HTX instrument. All binding studies were performed in 10 mM HEPES, 150 mM NaCl, 3 mM EDTA, 1 mg/mL BSA, 50 μg/mL Heparin, and 0.05% v/v Surfactant Tween-20, pH 7.4 (HBS-EBHT) buffer at 25° C. with the plate shaking at a speed of 1000 rpm. To assess binding cross-reactivity, Protein A coated Octet biosensor (Pall ForteBio Corp., #18-5010) was first dipped in wells containing 20 μg/mL of anti-BMP6 monoclonal antibodies for 4 minutes followed by submerging in wells containing 100 nM of different BMP6 family members for 4 minutes. The biosensors were washed in HBS-EBHT buffer in between every step of the experiment. At the end of each cycle, the Protein A biosensor was regenerated using three alternate 5 second dips in 10 mM Glycine pH 2.0 and 10 second dip HBS-EBHT buffer. The real-time binding response was monitored during the course of the experiment and the binding response at the end of every step was recorded and tabulated as shown in Tables 8A and 8B.

TABLE 8A

Binding cross-reactivity of anti-BMP6 monoclonal antibodies.

mAb
mAb Capture
Human
Mouse
Human
Human
Human
Human

Captured
Level (nm)
BMP6
BMP6
BMP7
BMP8A
BMP9
BMP10

H4H17855P
4.76 ± 0.19
0.29
0.09
0.05
−0.02
0.00
−0.01

H4H17871P
4.31 ± 0.14
0.21
0.09
0.00
0.00
0.01
0.01

Isotype control
4.12 ± 0.06
−0.05
−0.06
−0.05
−0.05
−0.03
−0.04

mAb

TABLE 8B

Binding cross-reactivity of anti-BMP6 monoclonal antibodies.

Human
Human

mAb
BMP12/
BMP14/
Human
Human
Human
Mouse
Human

Captured
GDF7
GDF5
BMP5
Activin A
GDF3
GDF6
BMP3b

H4H17855P
0.03
−0.02
0.01
−0.02
0.03
−0.02
0.27

H4H17871P
0.01
−0.01
−0.01
−0.01
0.03
−0.02
0.19