Characterization of spatial distribution of tumor-infiltrating CD8+ T cells refines their prognostic utility for pancreatic cancer survival

The abundance of cytotoxic T-cell infiltrates has important implications for patient outcome and therapeutic design for pancreatic ductal adenocarcinoma. However, intratumoral heterogeneity remains a challenge to understanding the complex immune microenvironment. We hypothesized that characterizing CD8+ cell distribution within pancreatic adenocarcinoma tissues might refine the prognostic value of tumor-infiltrating CD8+ lymphocytes. Using multiplex immunohistochemistry-based image analysis on whole-tissue sections of 214 pancreatic ductal adenocarcinomas, we measured CD8+ cell densities in the tumor center, the tumor margin, and the whole tumor, along with the proximity of CD8+ cells to carcinoma cells. Multivariable Cox regression analysis was performed to assess the associations of CD8+ cell densities with pancreatic cancer-specific survival, adjusting for clinicopathologic and immune-related features, including tumor expressions of TP53, SMAD4, and the programmed cell death 1 ligand 1 (CD274, PD-L1) and the extent of tertiary lymphoid structures. There was substantial heterogeneity in CD8+ cell density, with the mean density in the tumor center less than half that in the tumor margin. Tumor CD274 expression and extensive tertiary lymphoid structures were appeared to be associated with higher CD8+ cell density in the tumor margin (P = 0.037 and P = 0.005, respectively), but not with that in the tumor center (P > 0.50). The association of higher CD8+ cell density with prolonged survival was significant for the whole tumor (Ptrend = 0.009); however, the association was stronger for the tumor center (Ptrend = 0.002) and insignificant for the tumor margin (Ptrend = 0.07). Tumor cell–CD8+ cell distance correlated strongly with CD8+ cell density, whereas the density of CD8+ cells proximate to cancer cells exhibited no prognostic association. In conclusion, spatial computational analysis on pancreatic ductal adenocarcinoma reveals the prognostic validity of CD8+ cell density in the tumor center, where CD8+ cell infiltration is ununiformly restricted, likely suggesting pro-tumorigenic roles of the immunosuppressive tumor microenvironment of pancreatic cancer.