Low signal strength enhances the antitumor activity of human CAR Th17 cells

Abstract

Abstract We reported the antitumor activity of human Th17 cells (engineered to express a chimeric antigen receptor (CAR) that recognizes mesothelin) regresses large human mesothelioma tumors when infused into mice, but it remains unknown what type and what level of co-signal strength impacts their functional fate and antitumor activity. To address this question, human Th17 cells were activated with a high (3 beads: 1 T cell), medium (1:10) or low (1:100) signal via CD3-beads coated with either CD28 or ICOS agonists. We discovered Th17 cells activated with low ICOS signal were highly multifunctional (IL-17A, IFN-γ, IL-2 and IL-22) and possessed a less differentiated phenotype (high CD62L and CD45RA expression) than cells activated with a high ICOS signal. In comparison to low ICOS signal strength, Th17 cells activated with low CD28 signal strength were poorly functional and terminally differentiated. Of clinical significance, in two distinct tumor models (human mesothelioma and murine melanoma), we found that Th17 cells regressed large tumors to a better extent when primed with a low or medium ICOS signal strength compared to if they were activated with a high ICOS signal strength, or with any level of CD28 signal strength. Our data is compelling given that most ACT clinical trials use high CD3/CD28 activation to expand patients’ cells. Specifically, our work suggests the use of a low bead to T cell ratio will result in a more simple and clinically feasible method to expand highly therapeutic T cells for the clinic.