Abstract PR009: CD4+ T cells instruct cancer-associated fibroblasts to promote immune control of pancreatic cancer

Abstract

Cancer-associated fibroblasts (CAFs) are key regulators of tumor progression and therapeutic response in pancreatic ductal adenocarcinoma (PDAC). While CAF-mediated immune modulation has been extensively studied, it remains poorly understood whether adaptive immune cells reciprocally shape CAF heterogeneity and function within the tumor microenvironment. Here, we investigated immune-stromal crosstalk using murine orthotopic models of PDAC representing immunologically “hot” (6421c2) and “cold” (FC1245) tumors. Flow cytometry and immunofluorescence analyses revealed distinct fibroblast states associated with divergent immune microenvironments. Hot tumors were enriched for MHC-II+ CAFs and Ly6C+ inflammatory CAFs (iCAFs), whereas cold tumors were dominated by αSMA+ myofibroblasts (myCAFs). In Rag2-/- mice, MHC-II+ CAFs were significantly reduced in hot tumors, demonstrating that adaptive immunity is required for the induction or maintenance of MHC-II+ subsets. To identify the responsible immune populations, we examined CAF composition following regulatory T cell (Treg) ablation in Foxp3DTR mice. Treg ablation significantly increased MHC-II+ CAFs in both hot and cold PDAC models. Mechanistically, induction of MHC-II+ CAFs was independent of CD8+ T cells but required IFNγ-producing CD4+ conventional T cells (T-bet+ Th1s). Consistently, IFNγ blockade abrogated both MHC-II+ CAF accumulation and anti-tumor control following Treg depletion. To examine whether stromal MHC-II expression functionally contributes to tumor suppression, we generated bone marrow chimeras with selective MHC-II deficiency in non-hematopoietic stromal compartments while preserving antigen presentation in immune cells. Stromal MHC-II deficiency resulted in increased metastatic burden relative to MHC-II-sufficient controls. Fibroblast-specific deletion of MHC-II similarly impaired tumor control following Treg ablation, supporting a functional role for CAF-intrinsic MHC-II expression in restraining PDAC progression. Together, these findings demonstrate that CD4+ T cells actively instruct CAF states in PDAC and identify a novel immune-stromal regulatory axis in which Tregs promote disease progression by suppressing IFNγ-driven induction of MHC-II+ CAFs.