Dendritic cell redundancy enables priming of anti-tumor CD4+ T cells in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is resistant to current immunotherapies and lacks effective anti-tumor CD8+ T cells, which is potentially due to insufficient cross-presentation by cDC1s. Here, we combine a STING agonist with anti-CTLA-4 and anti-PD-1 to achieve durable remissions and immunologic memory in multiple mouse models of poorly immunogenic PDAC. We find that tumor control does not depend on CD8+ T cells or tumor cell MHC expression but instead requires IFNγ-producing CD4+ T cells (Th1s) that are primed by dendritic cells in lymph nodes. The triple combination immunotherapy induces an accumulation of activated cDC2s carrying tumor antigen into tumor-draining lymph nodes; cDC2s are required for orthotopic tumor clearance. Intratumoral CD4+ T cells and cDC2s remain present in treatment-naive and chemotherapy-exposed human PDAC. In chemotherapy-exposed patients' blood, cDC2s outnumber cDC1s by 10-fold. Therefore, therapeutic targeting of the cDC2-CD4+ T cell-IFNγ axis could be efficacious in PDAC.