Cytotoxic T-lymphocyte-associated protein 4 expressed by melanoma cells does not affect melanoma-specific cytotoxic T lymphocytes in the effector phase

Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) is one of the important molecules that regulate the anti-melanoma T-cell response. Currently, there are some reports showing that CTLA-4 is expressed not only by T cells but also by various kinds of tumor cells, including melanoma cells. However, there is no report that shows the role of CTLA-4 expressed by melanoma cells in melanoma-specific cytotoxic T-lymphocyte (CTL) response. In this report, we confirmed substantial CTLA-4 expression and the localization of CTLA-4 in melanoma cell lines and tissues. Also, we examined its impact on melanoma-specific CTL in vitro, and found that CTLA-4 expressed by melanoma cells does not affect melanoma-specific CTL in the effector phase. Our findings suggest the importance of elucidating the role of CTLA-4 expressed by melanoma cells, particularly in anti-CTLA-4 antibody therapy.