Death receptor-independent activation-induced cell death in human melanoma antigen-specific MHC class I-restricted TCR-engineered CD4 T cells.

Engaging CD4 T cells in antitumor immunity has been quite challenging, especially in an Ag-specific manner, because most human solid tumors usually do not express MHC class II molecules. We have recently shown that human CD4 T cells engineered to express a human melanoma-associated antigenic epitope, MART-127-35, specific MHC class I-restricted transgenic TCR function as polyfunctional effectors that can exhibit a helper as well as cytolytic effector function, in an epitope-specific and MHC class I-restricted manner (Chhabra et al. 2008. J. Immunol. 181: 1063-1070; Ray et al. 2010. Clin. Immunol. 136: 338-347). TCR-engineered (TCReng) CD4 T cells therefore have translational potential, and clinical trials with MHC class I TCReng CD4 T cells are under way. In this study, we show that although TCReng CD4 T cells could be useful in cancer immunotherapy, they are also susceptible to epitope-specific activation-induced cell death (AICD). We also show that the AICD in TCReng CD4 T cells is a death receptor-independent process and that JNK and p53 play critical roles in this process as pharmacological inhibitors targeting JNK activation and p-53-mediated transcription-independent mitochondria-centric death cascade rescued a significant fraction of TCReng CD4 T cells from undergoing AICD without affecting their effector function. Our data offer novel insights toward AICD in TCReng CD4 T cells and identify several potential targets to interfere with this process.