Abrogating Regulatory T Cells Overcomes Tumor-Specific T cell Exhaustion and Prevents Metastatic Pancreatic Cancer

Abstract Pancreatic ductal adenocarcinoma (PDA) has a dismal 5-year survival rate of 10%. Lethality is attributed to late diagnosis, early metastasis, and therapeutic resistance. We identified pancreatic tumor cells derived from mice which resist immunotherapy (e.g., escape variants, EV) rapidly metastasize upon re-implantation into the pancreas of syngeneic and immunocompetent mice. EVs retain the dominant tumor antigen, and despite a defect in IFNg-inducible MHC class I upregulation, EVs remain sensitive to tumor antigen specific T cell-mediated lysis in vitro, suggesting EVs may confer unique qualities in vivo to resist T cell killing. Using a peptide:MHC tetramer based approach, we identified that tumor-specific CD8 T cells in EV tumors have increased Granzyme B production and a reduction in prototypical exhaustion markers Pd1, Lag3, and Tox. Further, restoring MHC class I upregulation reversed this phenotype. Notably, primary tumors from EVs were significantly enriched with Foxp3+ Tregs compared to parental tumors. Using a genetic model, we identified that Treg depletion resulted in a drastic reduction in tumor burden and metastasis and improved tumor-specific T cell function in EV tumors, expanding a putative anti-metastatic CD8 T cells subset. Investigation of tumor-cell intrinsic changes identified elevated expression of the receptor tyrosine kinase Ddr2in multiple EVs compared to immunotherapy naïve cells. Our data supports the novel hypothesis that Ddr2 overexpression drives intratumoral Treg accumulation and promotes metastasis. In summary, Tregs are key drivers of T cell exhaustion and immunosuppression in pancreatic cancer and may prove a valuable clinical target for tumors that evade immune checkpoint blockade. Supported by NIH T32 grant – AG029796 – Functional Proteomics of Aging Training Program