Manipulation of MAP3K Signaling to Improve CAR-T Cell Therapy

Adoptive cell therapy using chimeric antigen receptor (CAR)-T cells represents a promising approach for human cancer immunotherapy. In this study, we examine the role of a MAP3K in mediating CAR-T cell function by generating CAR-T cells expressing a stable form of MAP3K lacking its N-terminal region (MAP3KK Delta N). We hypothesize that MAP3K Delta N expression will promote CAR-T cell activation and metabolic fitness in the tumor microenvironment. Using molecular cloning, a retroviral vector encoding a human CD19(hCD19)-specific CAR and mouse MAP3KK Delta N was constructed and confirmed by DNA sequencing. CD8+ T cells were isolated from C57BL/6 mice, activated in vitro, and then transduced with the hCD19-CAR-MAP3K Delta N vector. For functional analysis, B16-hCD19 tumor-bearing mice were injected with CAR-T cells expressing either wildtype MAP3K (MAP3K-WT) or MAP3KK Delta N, and tumor growth was monitored. Expression of MAP3K-WT improved the tumor-suppression function of hCD19-CAR-T cells. Surprisingly, CAR-T cells expressing MAP3KK Delta N displayed a lower antitumor efficacy than those expressing MAP3K-WT. Furthermore, these results were correlated in vitro, where MAP3KK Delta N showed a response similar to control CAR and reduced tumor inhibition in comparison with MAP3K-WT. Expression of MAP3K-WT, but not MAP3KK Delta N, profoundly improves the antitumor function of CAR-T cells. It is possible that MAP3KK Delta N expression results in T cell overactivation, thereby promoting T cell exhaustion and activation-induced cell death. These results suggest that optimal, rather than excessive, T cell activation is critical for potential therapeutic applications using MAP3K expression. However, it is also possible that deletion of the N-terminal portion of MAP3K impairs its facilitation of T cell metabolic functions.