Growth and differentiation factor 8 is a protein that is classified with the transforming growth factor-β (“TGF-β”) superfamily. Generally, the proteins of the TGF-β superfamily are initially expressed as precursor (a/k/a prohormone) that undergoes proteolytic cleavage at a cluster of basic residues about 110-140 amino acids from the precursor protein C-terminus. In each case, the active, or mature, TGF-β species is believed to be a disulfide-linked dimer of the cleaved precursor protein C-terminal regions.
Growth and differentiation factor 8, hereinafter GDF8, is also art-known as myostatin. The genes encoding the precursor of GDF8 (hereinafter “precursor GDF8”) have been cloned from a wide range of organisms. These include the human and murine precursor GDF8 (Nestor et al., 1998, Proc. Natl. Acad. Sci. 95:14938-43; U.S. Pat. No. 5,827,733, incorporated by reference herein). It has also been reported that GDF8 immunoreactivity is detectable in human skeletal muscle in both type 1 and type 2 fibers. Antibodies and assays for detecting GDF8 are described, e.g., by U.S. Pat. No. 6,096,506.
It has further been reported that GDF8 plays a role in down-regulating or inhibiting the growth and development of skeletal muscle, as confirmed by GDF8 knock-out mice (McPherron et al., 1997, Nature 387:83-90). For this reason, there have been previous attempts, particularly in the field of animal husbandry, to modulate GDF8 activity in animals by several means, with the goal of down-regulating GDF8 activity in order to enhance the growth, and/or relative muscle mass, of various food animals.
For example, U.S. Pat. No. 6,399,312 describes a precursor GDF8 gene promoter and an assay, with the proposal that the assay be used to identify a theoretical inhibitor of that promotor. U.S. Pat. No. 6,656,475 describes a method of inhibiting the effect of GDF8 on a cell by contacting the cell with a GDF8 prodomain that competes for a GDF8 receptor, and reports that the C-terminus of mature GDF8 may vary. U.S. Pat. No. 6,004,937 describes the use of follistatin as a possible antagonist of GDF8. None of these methods has resulted in any practical applications in the fields of animal husbandry or clinical applications (either human or veterinary).
The art has also attempted to employ antibody and vaccine technology for downregulating GDF8 function. For instance, U.S. Pat. No. 6,369,201, incorporated by reference herein, describes peptides, i.e., fragments of GDF8 protein, and a vaccine for eliciting anti-GDF8 antibodies. That patent also reported an unspecified degree of growth or weight gain, relative to controls, in rodents immunized with several of the reported GDF8 peptide fragments.
Other physiological roles for GDF8 have also been described. For example, U.S. Pat. No. 6,368,597, incorporated by reference herein, has suggested that inhibiting GDF8 function is useful for treating Type II diabetes, e.g., by administering an anti-GDF8 antibody or anti-GDF8 vaccine to a patient having this condition.
Recently, U.S. Pat. No. 6,730,306, the contents of which are incorporated by reference herein, has described recombinant plant viruses that express chimeric proteins. These chimeric proteins are formed by the fusion of a plant viral (or virus) coat protein (VCP), and a peptide or polypeptide of interest. According to U.S. Pat. No. 6,730,306, by infecting plant cells with such recombinant plant viruses, relatively large quantities of the desired fusion proteins are produced. When a VCP protein is fused with a polypeptide antigen of interest, the location of the fused polypeptide antigen must be carefully selected to be exposed to an immune system, binding antibody, and the like. With appropriate protein engineering, the fusion VCP may be used as an immunogen or antigen to induce an antibody response and/or protective immunity against the polypeptide of interest, or as a reagent for developing and conducting immunoassays useful in detecting such a polypeptide of interest.
There remains a longstanding need in the art for improved antigens and immunogens for eliciting an anti-GDF8 immune response, as well as for improved GDF8 antibodies capable of highly specific binding to GDF8.
The citation of any reference herein should not be construed as an admission that such reference is available as “Prior Art” to the instant application.
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