Hypoxia Impairs CD8⁺ T Cell Fitness and Is Associated with a Dysfunctional CD8⁺ T Cell State in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense stromal microenvironment and profound hypoxia, which contribute to therapeutic resistance. Using an in vitro system incorporating pancreatic cancer cells and cancer-associated fibroblasts (CAFs), we show that hypoxia suppresses CD8⁺ T cell accumulation and, in combination with cancer cell- and CAF-derived factors, further impairs T cell fitness by increasing cell death and reducing proliferation. Although the combination of hypoxia and cancer cell/CAF-derived factors enhances IFNγ and granzyme B expression in CD8⁺ T cells on a per-cell basis, the overall number of functional effector T cells is markedly reduced. Analysis of human PDAC single-cell RNA sequencing data corroborates these findings, revealing that CD8⁺ T cells enriched for hypoxia signatures exhibit elevated apoptosis and stress-response pathways. Furthermore, hypoxia is associated with downregulation of stemness-related genes and upregulation of terminal differentiation markers. Together, these data suggest that the integration of intrinsic hypoxic responses and extrinsic cues from tumor cells and CAFs impairs CD8⁺ T cell fitness and correlates with a terminally differentiated, dysfunctional T cell state.