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 co-localization of dendritic cells (DC), T helper (Th) cells, and cytotoxic T lymphocytes (CTL) within the tumor immune microenvironment following immune checkpoint blockade correlates with clinical response. In this study, we report the integration of more than 1 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. We found that these immune triads were enriched for functionally important type 1 conventional DC, mature DCs enriched in immunoregulatory molecules, CXCL13+ Th, and GZMK+ effector CTL phenotypes. Subsequent multiplex immunofluorescence imaging of more than 450 primary pancreatic ductal adenocarcinoma tumors showed that the density of antigen-presenting cell: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.