Therapeutic monoclonal antibodies kill target cells by multiple mechanisms including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent phagocytosis (ADP), complement-dependent cytotoxicity (CDC), and direct induction of apoptosis. Antibody binding to FcgRIIIA (CD16), which is expressed on NK cells, macrophages, and CD8+ cells, is essential for ADCC. MDX-1401 is a fully human monoclonal antibody of IgG1 (kappa) isotype that binds to human CD30. This second generation anti-CD30 antibody was derived from parental antibody MDX-060 but differs in that the oligosaccharides of the IgG1 lack fucose, a property that conveys increased antibody affinity for Fc receptor CD16 (FcgRIIIa) and thus stimulates both more potent and efficacious ADCC than a fucosylated IgG1. The KD of the parental antibody for CD30 expressed on L540 Hodgkin’s lymphoma cells is approximately 1.4 nM while the KD of MDX-1401 is 1.9 nM, demonstrating that binding affinity for antigen are nearly identical. However, the EC50 for MDX-1401 binding to CD16-transfected cells is approximately 3 nM compared to barely detectable binding by parental antibody, confirming that the absence of fucose conveys increased affinity for FcgRIIIa. Data is presented that demonstrates MDX-1401 has significantly improved potency and efficacy in an ADCC assay as evidenced by a decrease in EC50 as well as an increase in maximum specific lysis. Importantly, the enhanced ADCC activity is observed among a large panel of cell lines with varying numbers of CD30 receptors per cell, including one cell line with low antigen expression in which parental antibody failed to induce ADCC. MDX-1401 enhances ADCC activity with all polymorphic variants including lower affinity FcgRIIIa Phe/Phe158 and FcgRIIIa Phe/Val158 effector cells. Furthermore, MDX-1401 is efficacious in inhibiting growth of CD30+ tumor xenografts in mice. The low doses of antibody required for ADCC activity irrespective of donor genotype, the capacity to mediate ADCC of target cells expressing low levels of CD30, and increased in vivo efficacy support the development of MDX-1401 for treatment of malignant lymphoma. Phase 1 studies in subjects with Hodgkin’s lymphoma are currently underway.

Disclosures: Cardarelli:Medarex: Employment. Preston:Medarex: Employment, Equity Ownership. Black:Medarex: Employment. Passmore:Medarex: Employment. Chen:Medarex Inc.: Employment. Chen:Medarex Inc.: Employment. Liu:Medarex, Inc.: Employment. Kuhne:Medarex Inc.: Employment. Srinivasan:MEDAREX, INC.: Employment, Equity Ownership. Assad:Medarex: Employment. Witte:Medarex: Employment, Equity Ownership. Coccia:Medarex: Employment. Graziano:Medarex: Employment. King:Medarex: Employment.

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