Intratumoral three-cell-type clusters are a conserved feature of endogenous antitumor immunity.

Effective antitumor immunity ultimately depends on the priming and activation of tumor-specific cytotoxic CD8+ T cells; however, the role of intratumoral cell-cell immune interactions remains incompletely understood. Recent work has revealed that the temporospatial colocalization of dendritic cells (DCs), helper T cells (Th), and cytotoxic T lymphocytes (CTL) within the tumor immune microenvironment following immune checkpoint blockade correlates with clinical response. Herein, we report the integration of more than one million spatially resolved single-cell profiles across six spatial proteomic and transcriptomic assays, which demonstrated that DC:Th:CTL three-cell-type clusters were common even in immunotherapy-naïve and highly desmoplastic tumors, such as fibrolamellar carcinoma and pancreatic ductal adenocarcinoma (PDAC). We found that these immune triads were enriched for functionally important type 1 conventional DC, mature DCs enriched in immunoregulatory molecules (mregDC), CXCL13+ Th, and GZMK+ effector CTL phenotypes. Subsequent multiplex immunofluorescence imaging of more than 450 primary PDAC tumors showed that the density of antigen-presenting cell (APC):Th:CTL three-cell-type clusters was correlated with intratumoral T-cell clonal expansion and improved overall survival. These findings suggest that DC:Th:CTL triads are conserved across solid tumors and highlight the importance of intratumoral spatial niches in mediating endogenous antitumor immunity.