Abstract 5621: MCSP/CD3-bispecific single-chain antibody construct engages CD4+ and CD8+ T cells for lysis of MCSP-expressing human uveal melanoma cells

Abstract

Abstract Uveal melanoma is the most common cancer of the eye and metastasizes in approximately 50% of patients. None of the current therapies prevents the development of metastases or extends the survival time of these patients. Bi-specific T cell engager (BiTE) are based on recombinant single-chain antibody constructs. These molecules can transiently connect T cells to tumor cells, leading to concomitant T cell activation and serial lysis of tumor cells. Recently, a BiTE antibody bi-specific for CD19 and CD3 (blinatumomab) has shown very high response rates in patients with refractory non-Hodgkin's B cell lymphoma (100%) and B-precursor acute lymphocytic leukemia (80%). These findings suggest that the mode of BiTE antibody action may also be useful for treatment of solid tumors. Human melanoma-associated chondroitin sulfate proteoglycan (MCSP, also known as HMW-MAA, gp240, or CSPG4), is expressed on the surface of >90% of human cutaneous melanoma lesions and cell lines, with restricted distribution in normal tissues. MCSP expression has also been detected in uveal melanoma tumor-tissue sections and could serve as a target antigen for immunotherapeutic approaches. Here we report that primary and metastatic uveal melanoma cell lines express MCSP and that CD4+ and CD8+ T cells are activated to lyse MCSP-expressing uveal melanoma cells by a novel BiTE antibody, which is bispecific for MCSP and CD3 (MCSP-BiTE). The surface of uveal melanoma cells was stained by anti-MCSP monoclonal antibodies when analyzed by flow cytometry. Seven out of 9 primary and 1 out of 3 metastatic uveal melanoma cell lines expressed MCSP at various expression levels. For functional analysis, CD4+ and CD8+ T cells were isolated from peripheral blood mononuclear cells (PBMC) of healthy donors using magnetic bead sorting. Both PBMC and unstimulated CD8+ T cells specifically lysed MCSP+ uveal melanoma cells in the presence of MCSP-BiTE as determined by 51Cr-release assays. As detected by ELISA, unstimulated CD4+ T cells produced IFNγ in response to MCSP-expressing uveal melanoma cells in the presence of MCSP-BiTE, and redirected lysis was evident by microscopy. In contrast, co-culture of T cells with MCSP-expressing uveal melanoma cells alone, or in the presence of a control BiTE, did not result in cytolytic activity or IFNγ release. Furthermore, naïve CD4+ and CD8+ T cells upregulated expression of T cell activation markers CD25 and CD137 solely in response to MCSP-expressing uveal melanoma cells decorated with MCSP-BiTE. BiTE-induced T cell activation required the expression of MCSP, as co-culture of T cells with MCSP-negative uveal melanoma cells in combination with MCSP-BiTE did not result in T cell activation. In conclusion, MCSP-BiTE can induce CD4+ and CD8+ T cells against MCSP-expressing uveal melanoma cells and should therefore be tested as a novel immunotherapy for uveal melanoma patients. 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 5621.