Abstract 2570: Deciphering local immunosuppression in pancreatic cancer: targeting CAF-myeloid cell crosstalk to enhance immune response

Abstract Immunotherapy has revolutionized cancer treatment but remains largely ineffective in pancreatic ductal adenocarcinoma (PDAC). A hallmark of PDAC is local immunosuppression, driving cytotoxic T cell exclusion and deactivation, undermining immune-mediated tumor control. Better understanding of the cellular crosstalk in the tumor microenvironment (TME) and identifying stromal and immune populations shaping this immunosuppressive landscape is critically needed. Oncogenic KRAS activation in PDAC cells promotes recruitment and proliferation of tumor-supporting stromal cells while excluding cancer-targeted cytotoxic T cells. Local immunosuppression is driven by interactions between subtypes of cancer-associated fibroblasts (CAFs) and resident myeloid cells. Previous efforts to reverse immunosuppression by targeting individual stromal populations have largely failed, highlighting the complexity of stromal interactions in the TME. The stromal diversity of PDAC complicates investigating paracrine signaling involving multiple cell types. To address this, we use in vivo mouse models that recapitulate human disease, alongside a novel tumor explant system enabling short-term culture of intact human or murine PDAC tissue. These explants retain histopathological architecture and cellular diversity, providing a medium-throughput platform for testing drugs and mechanistic hypotheses in the native TME. Preliminary data show that Smoothened inhibition (SMOi) reduces myCAF proliferation and activity but drives CD11b-positive myeloid cell expansion in vivo. We hypothesize local immunosuppression in PDAC is sustained by a delicate balance between myCAFs and myeloid cells, collectively hindering T cell infiltration. Single-cell RNA sequencing of control vs. SMOi-treated murine PDAC identified stromal subpopulations maintaining immunosuppression and revealed specific myeloid subtypes emerging after SMOi. Strikingly, combining SMOi with anti-Gr1 or CCR1 inhibition (CCR1i) markedly increased cytotoxic T cell numbers—up to 20-fold—within the TME. We are now exploring whether these T cells’ activity can be further enhanced using additional immunomodulatory agents. Testing therapeutic combinations in the same TME allows us to identify synergistic effects that may inform future PDAC immunotherapy. Our work elucidates complex immunosuppressive mechanisms in PDAC, leveraging a novel tumor explant system and in vivo models. Our ultimate goal is to develop translatable regimens that neutralize local immunosuppression, enabling cytotoxic T cells to infiltrate, proliferate, and effectively attack cancer cells. Citation Format: Marie C. Hasselluhn, Lukas Vlahos, Yuanqing Xue, Dafydd Thomas, Quin T. Waterbury, Allison C. Hess, Tanner C. Dalton, Amanda R. Decker-Farrell, Alvaro Curiel Garcia, Stephen A. Sastra, Carmine F. Palermo, Timothy C. Wang, Andrea Califano, Kenneth P. Olive. Deciphering local immunosuppression in pancreatic cancer: targeting CAF-myeloid cell crosstalk to enhance immune response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2570.