Abstract PO-063: Regulatory T cells regulate fibroblast differentiation during pancreatic carcinogenesis

Pancreatic ductal adenocarcinoma (PDA) is characterized by an extensive fibrotic stroma, which includes vascular elements, infiltrating immune cells, extracellular matrix and a large number of fibroblasts. The tumor microenvironment as a whole has been believed to be immunosuppressive. However, how different cell populations within the stroma contribute to the establishment of the immunosuppression is not fully understood. We sought to investigate the crosstalk between cancer cells, fibroblasts and immune cells within pancreatic cancer with the goal to identify novel targets for PDA treatment. Targeting regulatory T cell (Treg), which acts to suppress immune responses, is considered as one potential approach to relieve the immunosuppression of pancreatic cancer. However, we previously showed that Treg depletion in a genetically engineered mouse model of pancreatic cancer (KC;Foxp3DTR) failed to relieve immunosuppression and led to accelerated tumor progression. We discovered that Treg depletion reprogramed the fibroblast population, with loss of tumor-restraining, smooth muscle actin-expressing fibroblasts. Conversely, Treg depletion resulted in differentiation of inflammatory fibroblast subsets with an increase in chemokines Ccl3, Ccl6, and Ccl8. To fully understand the contribution of Tregs to pancreatic carcinogenesis, we performed single-cell RNA-sequencing (scRNA-seq) with Pancreatic intraepithelial neoplasia (PanIN) from KC mouse and Treg depleted PanIN lesions from KC;Foxp3DTR mouse. scRNA-seq allows us to address cell type identification and heterogeneity of cell responses by unsupervised clustering, which uncovered dramatic differences in several stromal cell populations including fibroblast, CD4 T cell and macrophage subsets between the KC and KC;Foxp3DTR pancreata. We have expanded list of genes that are regulated in tumor associated fibroblasts upon Treg depletion through scRNA-seq. For example, Il33 was one of down-regulated genes in fibroblasts upon Treg depletion. We also obtained potential ligands/receptors interactions between tumor cells, fibroblasts and immune cells through interactome analysis. Our data describe an unexpected crosstalk between Tregs and fibroblasts and point to new mechanisms regulating fibroblast differentiation in pancreatic cancer. Citation Format: Yaqing Zhang, Katelyn L. Donahue, Wei Yan, Zeribe C. Nwosu, Kristee L. Brown, Sion Yang, Howard C. Crawford, Costas A. Lyssiotis, Timothy L. Frankel, Filip Bednar, Marina Pasca di Magliano. Regulatory T cells regulate fibroblast differentiation during pancreatic carcinogenesis [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-063.