Enhancing T cell persistence of CAR-redirected T cells in solid tumors

T cell persistence is likely to promote long-term anti-tumor effects after adoptive T cell transfer. We have recently shown that incorporation of the ICOS intracellular domain into chimeric antigen receptors (CARs) significantly increased Th17 cell persistence in vivo, compared to CARs with CD28 or 4-1BB intracellular domains [1]. Here, we hypothesized that CD4⁺ and CD8⁺ T cells require distinct cytokine and costimulation signals for optimal persistence. To test this hypothesis, we compared the in vivo antitumor effects and persistence of combined CD4⁺ T cells (bulk or Th17-polarized) and CD8⁺ T cells redirected with CARs containing CD28, 4-1BB or ICOS-based costimulatory domains. Using multiple mouse tumor models, we demonstrate that the ICOS intracellular domain significantly enhanced the in vivo persistence of CAR-expressing CD4⁺ T cells, and that both persistence and tumor infiltration were further enhanced by culturing these cells under Th17-polarizing conditions. Importantly, Th17-polarized CD4⁺ T cells expressing an ICOS-based CAR significantly increased the circulatory persistence of bulk CD8⁺ T cells expressing either CD28- or 4-1BB-based CARs. We further demonstrate that the antitumor effect of CAR-expressing CD8⁺ T cells was enhanced when co-injected with ICOS-redirected Th17 cells. Collectively, our data suggest that combining Th17 CD4⁺ T cells redirected with an ICOS-based CAR with CD8⁺ CAR-T cells will enhance their persistence and antitumor efficacy.