Neoantigen-specific stem cell memory-like CD4+ T cells mediate immunotherapy of solid tumors

The expansion of neoantigen (NeoAg)-specific T cells often accompanies clinical responses to immunotherapies, highlighting the importance of these cells for antitumor immunity. While NeoAg-specific CD8+ T cells have been broadly studied, the role of NeoAg-specific CD4+ T cells is less well understood. To study the antitumor mechanisms of NeoAg-specific CD4+ T cells, we sorted single CD4+ T cells specific for an epitope derived from a mutated clathrin heavy chain gene (CLTCH129>Q) expressed by the murine squamous cell carcinoma VII (SCC VII) tumor. T cell receptor (TCR) sequencing analysis revealed the presence of four distinct TCR clonotypes and expression of these TCRs in primary cells was sufficient to confer preferential recognition of CLTCH129>Q as compared to the corresponding wildtype CLTC epitope. Despite differences in TCR avidity, both moderate and high avidity CD4+ T cells were capable of proliferating to similar levels in response to tumor antigen in vivo and enhancing primary tumor immunity in a CD8+ T cell- and CD40L-dependent manner. Finally, we demonstrate that adoptive cellular therapy (ACT) with T stem cell memory (TSCM)-like CLTCH129>Q-specific CD4+ T cells differentiated ex vivo in culture with IL-7 and IL-15 promotes therapeutic tumor immunity associated with enhanced T cell persistence, maintenance of adoptively transferred TSCM-like cells in the tumor-draining lymph node (tdLN), and activation of CD8+ T cells in the tdLN. Overall, these findings illuminate the mechanistic role of NeoAg-specific CD4+ T cells in tumor immunity, provide insights into the impact of TCR avidity on the helper functions of CD4+ T cells, and highlight the therapeutic potential of ACT with TCR-engineered CD4+ T cells. Neoantigen-specific TCR engineered CD4+ T cells cultured in either IL-7 and IL-15 or IL-2 were adoptively transferred into SCC VII tumor-bearing mice one day following cyclophosphamide preconditioning. 9 days following adoptive transfer, tumors and lymph nodes from 2 replicate animals per condition were collected, single cell suspensions were made, and adoptively transferred CD90.1+ CD4+ T cells were sorted from each for RNA-sequencing