Th9 cells are subjected to PD-1/PD-L1-mediated inhibition and are capable of promoting CD8 T cell expansion through IL-9R in colorectal cancer

Abstract Th9 cells are named after their expression of IL-9. Studies in recent years demonstrated that Th9 cells could contribute to antitumor immunity by enhancing the recruitment and activation of mast cells, natural killer cells, CD8 T cells, and dendritic cells in the tumor microenvironment. To determine whether Th9 cells participate in colorectal cancer (CRC), we collected resected tumor samples from 20 CRC patients. In the tumor-infiltrating lymphocytes (TILs), IL-9+IL-4− CD4+ T cells could be observed and were present at higher frequencies than the IL-9+IL-4+ and the IL-9−IL-4+ cells, suggesting that the majority of IL-9-producing TILs were bona fide Th9 cells. IL-9-secreting TILs presented particularly high PD-1 expression directly ex vivo. The expression of IL-9 was significantly reduced with PD-L1-mediated inhibition, which in turn was suppressed by anti-PD-1 blocking. Interestingly, the circulating CD4+ T cell compartment in CRC patients also presented Th9 enrichment, characterized by higher IL-9+IL-4− and IL-9+IL-4+ cell frequencies in the CXCR3−CCR6− compartment as compared to that in non-cancer controls. Using exogenous TGF-β and IL-4, we were capable of enriching Th9 cells without concurrent enrichment of Th2 cells. Th9-enriched CD4+ T cells, but not Th9-non-enriched cells, significantly increased the expansion of activated CD8+ T cells, in a manner that was dependent on the expression of IL-9R. In addition, the frequencies of Th9 cells in the tumor were positively correlated with the frequencies of CD8+ TILs. Together, we demonstrated that Th9 cells infiltrated CRC tumor, could be regulated via the PD-1/PD-L1 pathway, and could contribute the CD8+ T cell expansion.