Abstract 1344: myCAFs and iCAFs have similar lineage

Abstract Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense stroma primarily composed of cancer associated fibroblasts (CAFs). These fibroblasts are a diverse population of cells; some groups of fibroblasts have been shown to play tumor supporting roles while others have been shown to be tumor suppressing. Two prolific and well-characterized CAF subtypes—myofibroblasts (myCAFs) and inflammatory CAFs (iCAFs)—could potentially have different regulatory effects on tumor growth. Understanding the tissue origin of these two groups of CAFs could assist in understanding the complex and heterogeneous roles they might play in PDAC development. Previous studies in our group showed that the splanchnic mesenchyme, a layer of mesenchyme adjacent to the fetal pancreatic epithelium, gives rise to the majority of the total CAF population. Here, I aim to test the hypothesis that both iCAFs and myCAFs originate from the splanchnic mesenchyme. myCAFs have been previously observed to be proximal to tumor cells and express αSMA at a higher level, while iCAFs have been observed to be distal to tumor cells and express αSMA at a lower level. Here, we used a genetically engineered mouse PDAC model carrying KrasG12D/+;p53Frt/+;Pdx1FlpO/+;Isl1cre/+;R26Tomato/+ alleles. In this model, epithelial specific FlpO expression leads to Kras activation and p53 deletion, causing tumorigenesis. Simultaneously, splanchnic specific Cre expression leads to permanent tomato expression in the splanchnic descendants. The pancreata of these mice were harvested, fixed, and mounted onto slides. Co-immunostaining with αSMA and tomato was then done. The stained slides were scanned, and the Inform software was used to segment and phenotype the cells. More than 95% of αSMA high cells were tomato positive, and more than 95% of αSMA low cells were also tomato positive. We thus conclude that both myCAFs and iCAFs originate from the splanchnic mesenchyme. Consistent with previous in vitro studies, this lineage tracing study suggests that different CAF subtypes are likely due to patterning influenced by different factors within the tumor microenvironment. Citation Format: Thomas S. Walter, Lu Han, Michael Ostrowski. myCAFs and iCAFs have similar lineage [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1344.