PGE 2 limits effector expansion of tumour-infiltrating stem-like CD8 + T cells.

Cancer-specific TCF1+ stem-like CD8+ T cells can drive protective anticancer immunity through expansion and effector cell differentiation1-4 ; however, this response is dysfunctional in tumours. Current cancer immunotherapies2,5-9 can promote anticancer responses through TCF1+ stem-like CD8+ T cells in some but not all patients. This variation points towards currently ill-defined mechanisms that limit TCF1+ CD8+ T cell-mediated anticancer immunity. Here we demonstrate that tumour-derived prostaglandin E2 (PGE2 ) restricts the proliferative expansion and effector differentiation of TCF1+ CD8+ T cells within tumours, which promotes cancer immune escape. PGE2 does not affect the priming of TCF1+ CD8+ T cells in draining lymph nodes. PGE2 acts through EP2 and EP4 (EP2 /EP4 ) receptor signalling in CD8+ T cells to limit the intratumoural generation of early and late effector T cell populations that originate from TCF1+ tumour-infiltrating CD8+ T lymphocytes (TILs). Ablation of EP2 /EP4 signalling in cancer-specific CD8+ T cells rescues their expansion and effector differentiation within tumours and leads to tumour elimination in multiple mouse cancer models. Mechanistically, suppression of the interleukin-2 (IL-2) signalling pathway underlies the PGE2 -mediated inhibition of TCF1+ TIL responses. Altogether, we uncover a key mechanism that restricts the IL-2 responsiveness of TCF1+ TILs and prevents anticancer T cell responses that originate from these cells. This study identifies the PGE2 -EP2 /EP4 axis as a molecular target to restore IL-2 responsiveness in anticancer TILs to achieve cancer immune control.