SBIR-STTR Award

Passive and active humoral immune responses are mediated by the interaction of immunoglobulins and the low affinity Fc receptors, FcRIIB and FcRIIIA, present on the surface of effector cells. Recent proof-of-principle experiments in xenograft and syngenic tumor models indicate that the interaction between the Fc and the activation receptor, FcRIIIA, triggers a cytotoxic response in the presence of an anti-tumor antibody and that the inhibiting receptor, FcRIlB, restricts the cytotoxic response. Thus novel Fc domains that have increased affinity for FcRIIIA and a reduced affinity for FcRIIB have the potential to improve the efficacy of monoclonal therapeutic antibodies. We propose to identify high affinity Fc alleles by directed protein evolution of the human Fc using yeast surface display. Yeast display provides a unique platform that expresses and displays eukaryotic peptides efficiently and allows screening >107 independent Fc mutants. Successful identification of Fc alleles with a high affinity for FcRIIIA and a low affinity for FcRIIB will be pursued.

Thesaurus Terms:
allele, antibody receptor, directed evolution, immunogenetics, immunologic substance development /preparation CD antigen, immunoglobulin G, immunotherapy, receptor expression biotechnology, enzyme linked immunosorbent assay, site directed mutagenesis, tissue /cell culture, yeast

Tumor specific therapeutic antibodies direct the immune system to eliminate or prevent growth of tumor cells. Passive and active humoral immune responses are mediated via interactions between the IgG Fc domain and specific Fc receptors (FcR) present on the surfaces of effector cells. Proof of principal experiments show that it is the interaction between tumor specific antibodies and the FcR activating receptors on the surface of immune system effector cells that mediate tumor cell depletion. Modulation of the binding activity of the Fc domain to satisfy specific Fc receptor binding parameters will enable genetically engineered antibodies to act as efficient antitumor drugs. Novel Fc mutations that enhance the affinity of the Fc domain to FcgammaR3A and decrease the affinity to FcgammaR2B may play an important role in development of new therapeutics. These novel scaffolds could be ligated to Fabs that target tumor specific antigens and ultimately used as therapeutics to mount a successful cytotoxic response against tumor cells. Recent advances in proteomics and cDNA microarray technologies have aided in the identification of a number of tumor specific antigens. These peptides have been used for the development of antibodies that target specific cancer cells. To enhance the immune response against tumor cells we have developed a novel genetic screen to identify Fc mutants that preferentially bind to the activation receptor FcR3A. Further research and development of these Fc mutants should lead to therapeutic antibodies with increased capacity to trigger antibody dependent cytotoxic reactions against tumor cells. This proposal describes an experimental paradigm to identify Fc mutations, characterize the mutations in functional assays, and ultimately test therapeutic antibodies harboring the best Fc mutations in animal model studies.

Thesaurus Terms:
antibody, antibody receptor, immunogenetics, immunoglobulin structure, immunologic substance development /preparation, immunoregulation immunoglobulin G, immunotherapy, mutant, receptor expression biotechnology, clinical research, enzyme linked immunosorbent assay, human tissue, laboratory mouse, site directed mutagenesis, tissue /cell culture, yeast