Abstract B071: Antigen-presenting cancer-associated fibroblasts are required for ICI-sensitivity in pancreatic ductal adenocarcinoma

Abstract Cancer-associated fibroblasts (CAFs) are a hallmark of many cancers and are particularly prevalent in pancreatic ductal adenocarcinoma (PDAC). This highly fibrotic environment is thought to play a role in resistance to therapy; however, attempts to target CAFs have been unsuccessful in clinical trials. Deeper insights into CAF biology have revealed that these cells are heterogeneous in origin, gene expression, and function. RNA sequencing studies have identified a subset of CAFs, antigen-presenting CAFs (apCAFs), which are defined by MHC-II and interact with CD4 T cells. Given the importance of CD4 T cells in the antitumor response in PDAC, understanding apCAF biology could demonstrate ways to promote their differentiation and enhance T cell activity. Methods: Two clones differing in sensitivity to ICIs, sKPC (sensitive) and rKPC (resistant), derived from the autochthonous KPC murine PDAC model, were implanted orthotopically into the pancreas of syngeneic C57BL/6 mice. Mice were untreated, treated with dual checkpoint inhibition, or immunized with a KRAS peptide vaccine. Tumors were harvested for TME characterization, functional assays, single-cell RNA sequencing (scRNAseq), and imaging mass cytometry (IMC). apCAFs, CD11c+, and CD4+ T cells were isolated for functional assays. Peptide-pulsed apCAFs and CD11c+ cells were cultured with naïve OT-II CD4+ T cells or sKPC tumor infiltrating CD4+ T cells. apCAF KO mice were generated by crossing PDGFRαCre and MHC-IIflx mice. Results: Immunosensitive sKPC tumors are characterized by higher immune cell and apCAF infiltration than rKPC tumors. These apCAFs activate tumor-infiltrating CD4 T cells and induce regulatory T cell (Treg) differentiation, but not production of immunosuppressive cytokines. IMC analysis shows greater proximity of apCAFs to CD4 T cells in sKPC tumors compared with rKPC tumors. Remarkably, apCAF KO mice implanted with sKPC tumors lose sensitivity to ICI. scRNAseq has uncovered a unique transcriptome of apCAFs depending on tumor of origin and time following tumor implantation, revealing potential targets by which to quantitatively and qualitatively modulate apCAFs and enhance the antitumor response. Furthermore, scRNAseq of CD4 T cells cocultured with apCAFs has shown a unique pattern of CD4 T cell gene upregulation depending on the TME from which apCAFs were isolated, which could yield strategies to modulate not only apCAFs but also CD4 T cell activity. Conclusions: apCAFs are more abundant and more proximal to CD4 T cells in immunosensitive tumors, and apCAF KO sKPC tumor-bearing mice lose sensitivity to ICI. Together these data implicate apCAFs as essential mediators of the antitumor immune response. The unique transcriptome of apCAFs and cocultured CD4 T cells depending on tumor of origin suggests multiple strategies to modulate their interactions. Although a small proportion of the TME, modulating apCAF number or function could provide a solution to the currently unmet need of new and more effective treatments for PDAC patients. Citation Format: Saumya Maru, Meredith Wetzel, Jacob T Mitchell, Nicole Gross, Lalitya Andaloori, Kathryn Howe, Emma Kartalia, Guanglan Mo, James Leatherman, Won Jin Ho, Luciane Kagohara, Elana Fertig, Edward J Pearce, Elizabeth M Jaffee. Antigen-presenting cancer-associated fibroblasts are required for ICI-sensitivity in pancreatic ductal adenocarcinoma abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84 (17 Suppl₂): Abstract nr B071.