Tumor-derived prostaglandin E2 programs cDC1 dysfunction to impair intratumoral orchestration of anti-cancer T cell responses.

Type 1 conventional dendritic cells (cDC1s) are critical for anti-cancer immunity. Protective anti-cancer immunity is thought to require cDC1s to sustain T cell responses within tumors, but it is poorly understood how this function is regulated and whether its subversion contributes to immune evasion. Here, we show that tumor-derived prostaglandin E2 (PGE) programmed a dysfunctional state in intratumoral cDC1s, disabling their ability to locally orchestrate anti-cancer CD8 T cell responses. Mechanistically, cAMP signaling downstream of the PGE-receptors EP2 and EP4 was responsible for the programming of cDC1 dysfunction, which depended on the loss of the transcription factor IRF8. Blockade of the PGE-EP2/EP4-cDC1 axis prevented cDC1 dysfunction in tumors, locally reinvigorated anti-cancer CD8 T cell responses, and achieved cancer immune control. In human cDC1s, PGE-induced dysfunction is conserved and associated with poor cancer patient prognosis. Our findings reveal a cDC1-dependent intratumoral checkpoint for anti-cancer immunity that is targeted by PGE for immune evasion.