CD4+ T cell-mediated cytotoxicity eliminates primary tumor cells in metastatic melanoma through high MHC class II expression and can be enhanced by inhibitory receptor blockade

• Published in: Tumor biology Vol. 37; no. 12; pp. 15949 - 15958
• Main Authors: Yan, Hongxia, Hou, Xianglian, Li, Tianhang, Zhao, Li, Yuan, Xiaozhou, Fu, Hongjun, Zhu, Ruijie
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.12.2016; Springer Nature B.V
• Subjects: Biomedical and Life Sciences; Biomedicine; Cancer Research; Cytotoxicity; Immunotherapy; Melanoma; Metastasis; Original Article; MHC class II; CD4+ T cell; Melanoma
• ISSN: 1010-4283; 1423-0380
• DOI: 10.1007/s13277-016-5456-5

Metastatic melanoma is a rapidly progressing disease with high mortality rate and limited treatment options. Immunotherapy based on tumor-targeting cytotoxic T cell responses represents a promising strategy. To assist in its development, we examined the possibility and efficacy of using CD4 + cytotoxic T cells. The regulatory mechanisms controlling CD4 + T cell-mediated cytotoxicity were also investigated. We found that naturally occurring granzyme B and perforin-expressing CD4 + cytotoxic T cells can be recovered from metastatic melanoma patients at significantly elevated frequencies compared to those from healthy controls. These CD4 + cytotoxic T cells were also capable of killing autologous tumor cells harvested from metastatic melanoma, independent of CD8 + T cells or any other cell types. However, several restricting factors were observed. First, the cytolytic activity by CD4 + T cells required high MHC class II expression on melanoma cells, which was not satisfied in a subset of melanomas. Second, the granzyme B and perforin release by activated CD4 + cytotoxic T cells was reduced after coculturing with autologous melanoma cells, characterized by low LAMP-1 expression and low granzyme B and perforin secretion in the supernatant. This suggested that inhibitory mechanisms were present to suppress CD4 + cytotoxic T cells. Indeed, blockade of PD-1 and CTLA-4 had increased the cytolytic activity of CD4 + T cells but was only effective in MHC class II high but not MHC class II low melanomas. Together, our study showed that CD4 + T cell-mediated cytotoxicity could eliminate primary melanoma cells but the efficacy depended on MHC class II expression.