Abstract 1970: Inhibition of BRAF-V600E increases melanocyte antigen expression and antigen-specific recognition in melanoma without altering T cell function

Abstract

Abstract Given the high prevalence of BRAFV600E mutations in melanoma, targeted therapy against BRAF, or its mutated form, is a promising new therapeutic approach for patients with melanoma. Preliminary evidence suggests that BRAFV600E contributes to immune escape, and that blocking its activity via MAPK pathway inhibition leads to increased expression of melanocyte differentiation antigens, supporting the potential use of combination targeted therapy and immunotherapy. However, indiscriminate MAPK pathway inhibition may have deleterious effects on the immune system and lead to T cell dysfunction. The purpose of these studies was to explore the role of oncogenic BRAF in immune evasion by melanoma cells through its suppression of melanocyte differentiation antigens (MDAs). Furthermore, we sought to evaluate the effect of MAPK pathway inhibition on T lymphocyte function as a basis for combined targeted therapy and immunotherapy. Melanoma cell lines were cultured with MEK inhibitors (U0126, PD0325901) or a specific inhibitor of BRAFV600E (PLX4720) and expression of MDAs was assayed at the mRNA and protein level. The level of micro-opthalmia transcription factor (MITF), a transcriptional regulator of MDAs, was also assayed. Untreated and treated melanoma cell lines were co-cultured with antigen-specific T lymphocytes (generated by transduction of lymphocytes with MART-1- and gp100-specific T cell receptors) and reactivity was measured via interferon gamma release. The effect of MAPK pathway inhibition on T lymphocyte function was analyzed by assaying fold-expansion after OKT-3 & IL-2 stimulation as well as antigen-specific interferon gamma release. Inhibition of MAPK pathway in melanoma cell lines resulted in increased levels of MDAs which was associated with improved antigen-specific recognition by MART-1- and gp100-specific T lymphocytes. This was associated with higher intracellular levels of MITF. Treatment with MEK inhibitors resulted in impaired T lymphocyte function, as assayed by T cell expansion and antigen-specific interferon gamma release, whereas T cell function was preserved after treatment with a specific inhibitor of BRAFV600E. These findings suggest that oncogenic BRAF contributes to immune evasion by transcriptional repression of melanocyte antigen expression through MITF, which may be reversed by targeted MAPK pathway inhibition. Selective inhibition of BRAFV600E enhances MDA expression while preserving T cell function, whereas MEK inhibition has deleterious effects on T cell function. These data have important implications for the design of clinical trials using combined targeted therapy and immunotherapy for melanoma as well as other cancers. 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 1970.