Abstract A032: Cancer associated fibroblasts drive classical to basal change associated with increased T cell presence in pancreatic ductal adenocarcinoma

Abstract Introduction: A complex immunosuppressive tumor microenvironment (TME) is a distinctive feature of pancreatic ductal adenocarcinoma (PDAC). The TME consists of an admixture of cell types including epithelial, endothelial, immune cells of both myeloid and lymphoid origin, and cancer-associated fibroblasts (CAFs). The traditionally defined subtypes of PDAC tumor cells include classical, associated with the retention of epithelial markers and a better prognosis, and basal, which is characterized by a quasi-mesenchymal phenotype with poorer responses to chemotherapy and worse overall survival. Additionally, CAF subtypes are associated with specific roles within the TME. These include inflammatory (iCAF), with the capacity to secrete IL-6, myofibroblastic (myCAF), defined by high levels of alpha smooth muscle actin (αSMA) expression, and antigen presenting (apCAF), defined by expression of HLA-DR and antigen processing and presentation capacity. We hypothesized that interactions between CAFs and tumor cells altered tumor cell phenotype and could be delineated. Methods: Using multi-omics platforms, we evaluated the impact of CAF populations on tumor cell phenotype. Our approach integrated multiplex immunohistochemistry, imaging mass cytometry (IMC) and RNA-scope of patient tumor tissues with functional in vitro studies from matched patient-derived organoid (PDO) and CAF cocultures. The dynamic impact of CAFs on PDOs was examined using a combination of bulk RNA sequencing, multiparametric flow cytometry and secretome analysis, in addition to RT-qPCR and western blot comparing cocultures to matched PDO monocultures. Results: IMC of 15 patient tumors revealed distinct neighborhoods of CAFs and tumor cells. iCAFs were in close proximity to classical tumor cells, while myCAFs were in close proximity to basal tumor cells. Further, in our PDO-CAF co-cultures the PDOs underwent a shift from classical to basal subtype in 42% of co-cultures, a phenomenon also inferred in patient tissues by associating collagen content with classical or basal designation. We also captured a tumor cell population expressing both basal and classical markers that may represent a transition state. The shift from classical to basal tumor cell subtype was accompanied by enhanced epithelial-mesenchymal transition and a loss of IL-8 secretion. Interestingly, when we examined immune cell distribution within tumor tissues, T cells were both the most proximal and the most abundant immune cell type in relation to tumor cells. Moreover, the highest frequency of total and activated T cells was seen in close association with basal tumor cells. Conclusions: Our study underscores the importance of understanding the complex interplay between CAFs and tumor cells in PDAC. Further, we identify a relationship between T cells and tumor cell subtypes. By leveraging high-dimensional data and patient-derived models, we provide new insights into the spatial and functional dynamics of the PDAC TME, paving the way for novel therapeutic strategies to reprogram the TME and enhance patient survival. Citation Format: Jacquelyn W Zimmerman, Samantha Guinn, Mili Ramani, Brayan Perez, Joseph A Tandurella, Daniel J Zabransky, Jae W Lee, Emma Kartalia, Jignasha Patel, Sarah Shin, Alexei Hernandez, Courtney Cannon, Nicole Gross, Soren Charmsaz, Elana J Fertig, Richard A Burkhart, Won J Ho, Elizabeth M Jaffee. Cancer associated fibroblasts drive classical to basal change associated with increased T cell presence 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 A032.