Abstract 5340: Impact of binding epitope and antigen size on the cytotoxic activity of MCSP-specific BiTE antibodies for treatment of melanoma

Abstract

Abstract Melanoma chondroitin sulphate proteoglycan (MCSP; also called CSPG4, HMW-MAA, MSK16, MCSPG, MEL-CSPG, NG2, or gp240) is a surface antigen frequently expressed on human melanoma cells, which is involved in cell adhesion, invasion and spreading, angiogenesis, complement inhibition, and signalling. MCSP has therefore been frequently selected as target antigen for development of antibody- and vaccine-based therapeutic approaches. We have here used a large panel of monoclonal antibodies against human MCSP for generation of single-chain MCSP/CD3-bispecific antibodies of the BiTE (for bispecific T cell engager) class. BiTE antibodies can transiently connect the T cell receptor subunit CD3 on T cells with a surface antigen on target cells leading to a highly efficient redirected lysis of target cells. This involves cytolytic synapse formation and delivery of perforin and granzymes. BiTE-engaged T cells are capable of serial target cell lysis, and are not affected by immune escape mechanisms interfering with peptide antigen processing and presentation, or clonal T cell differentiation. Despite similar binding affinity to MCSP, respective BiTE antibodies greatly differed in their potency of redirected lysis of CHO target cells stably transfected with full-length human MCSP, MCSP deletion mutants or fusion proteins. BiTE antibodies binding to the membrane proximal domain D3 of MCSP were more potent than those binding to more distal domains. This epitope distance effect was corroborated with EpCAM/CD3-bispecific BiTE antibody MT110 by using MCSP/EpCAM fusion proteins as surface target antigens. Generally, CHO cells expressing small surface antigens were better lysed than those with large antigens, indicating that antigen size is also an important factor for BiTE potency. This is in line with the observation that target cell lysis by membrane proximally-binding BiTE antibodies improved upon omission of more distal MCSP domains. The present study for the first time relates the size of surface antigens and positioning of binding domains to BiTE potency of target cell lysis via redirected cytotoxic T cells. In case of the MCSP antigen, this provides the basis for selection of a maximally potent BiTE antibody candidate for development of a novel melanoma therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5340.