Abstract A066: <i>Wilm’s Tumor 1</i>-Expressing Stromal Cells Promote Pancreatic Cancer Growth

Abstract Cancer associated fibroblasts (CAFs) are a prevalent cell population in the microenvironment of pancreatic cancer. The contribution of cell of origin to CAF heterogeneity is still incompletely understood. Expression of the transcription factor Wilm’s Tumor 1 (Wt1) marks mesothelial cells, as well as a transcriptionally distinct population of fibroblasts in the normal pancreas. WT1/Wt1 expression also defines a population of CAFs in both human and mouse pancreatic cancer. We employed a previously described tamoxifen-inducible model of lineage tracing wherein cells expressing Wt1 and their progeny are labelled with tdTomato. To determine the functional role of these cells, we generated a diphtheria-toxin inducible model to deplete Wt1-expressing cells in orthotopic tumors. By lineage tracing, we found that Wt1 + cells expand in pancreatic cancer, where they give rise to a population of inflammatory pSTAT3+ CAFs. Depletion of Wt1 +stromal cells resulted in smaller tumors with decreased pSTAT3+ cells. Contrary to our expectations, these tumors also had increased immunosuppressive macrophage activation and reduced infiltration of CD8+ and FOXP3+ T cells. Notably, the reduction in tumor weights observed with Wt1 + cell depletion was independent of CD8+ and CD4+ T cells. Instead,Wt1 + cancer-associated fibroblasts expressed high levels of known tumor-promoting ligands that likely interact directly with the tumor epithelium to drive progression. Accordingly, Wt1-expressing cell-depleted tumors had reduced epithelial MAPK activation. In vitro analyses also demonstrated the ability of fibroblast-conditioned media to augment epithelial, KRAS-dependent MAPK activation. Together, our data show that Wt1 + stromal cells represent a tumor-promoting CAF population; while this population might constitute a potential therapeutic target, caution will be needed to avoid exacerbating immune suppression. Citation Format: Allison C. Bischoff, Kristee Brown, Emily L. Lasse-Opsahl, Hannah R. Watkoske, Carlos E. Espinoza, Jude Ogechukwu. Okoye, Alberto C. Olivei, Leah M. Green, Ridesh Rai, Stephanie The, Wei Yan, Aaron D. denDekker, Eileen S. Carpenter, Jiaqi Shi, Filip Bednar, Timothy L. Frankel, Yaqing Zhang, Marina Pasca di Magliano. Wilm’s Tumor 1-Expressing Stromal Cells Promote Pancreatic Cancer Growth [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3):Abstract nr A066.