Abstract C037: KMT2D loss in pancreatic cancer cells leads to an immunosuppressive tumor microenvironment by upregulating the interferon and inflammatory response pathways

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDAC) is highly resistant to chemoradiation and immune therapies, which is at least in part driven by its immunosuppressive tumor microenvironment (TME) consisting of dense cancer-associated fibroblasts (CAF) and highly suppressed immune cells. Lysine methyltransferase 2D (KMT2D), also known as MLL4 in mice, has been identified as one of the most frequently altered epigenetic regulators in PDAC. Most importantly, KMT2D mutation was found in more than 80% of neoadjuvant-treated PDAC, suggesting that KMT2D loss may be associated with treatment resistance. In human PDAC, low KMT2D protein level is correlated with worse survival. However, it is unknown whether KMT2D loss in PDAC cells modulates the TME. This project aimed to elucidate the role of KMT2D in remodeling the immune and stromal environment in PDAC. We first screened for changes in the immune cell population by performing immunohistochemistry (IHC) stains with human PDAC samples. We found that primary human tumors with low KMT2D expression had increased immunosuppressive tumor-associated neutrophils. xCell digital dissection analysis with The Cancer Genome Atlas (TCGA) data revealed that KMT2D-low PDAC had decreased effector T cell signature and enriched immunosuppressive Treg cell signature. Single-cell RNA sequencing analysis showed that KMT2D-low PDAC had increased suppressive myeloid cells and decreased CD8 T cells. We then generated Ptf1a-Cre; LSL-KrasG12D; Mll4+/+ (KCM+/+) and Ptf1a-Cre; LSL-KrasG12D; Mll4f/f (KCMf/f) mice to model pancreas-specific loss of Mll4 in the background of Kras mutation, a classic PDAC genetic mouse model. All KCM+/+ mice younger than 12 weeks had normal pancreas or low-grade pancreatic intraepithelial neoplasia (PanIN). In contrast, 66% of KCMf/f mice developed high-grade PanIN lesions or PDAC by 12 weeks. Immunohistochemistry staining showed that infiltration of immunosuppressive myeloid cells (tumor-associated macrophages and neutrophils) increased, whereas the presence of CD8+ T cells decreased in Mll4-deficient pancreata. Additionally, myofibroblastic CAFs, defined as PDPN+aSMA+ CAFs, decreased in KCMf/f mice pancreata compared to KCM+/+ pancreata. Mechanistically, we found that KMT2D loss in PDAC cells upregulates the interferon and inflammatory response pathways, including many cytokines and chemokines. These results suggest that KMT2D is a critical tumor suppressor, partly by promoting an immunogenic and tumor-suppressive TME. Cytokines in the interferon and inflammatory response pathways may serve as potential therapeutic targets, especially for treatment-resistant PDACs and KMT2D-deficient PDACs. Citation Format: Hong S. Kim, Jing Yang, Shuang Lu, Marina Pasca di Magliano, Kai Ge, Jiaqi Shi. KMT2D loss in pancreatic cancer cells leads to an immunosuppressive tumor microenvironment by upregulating the interferon and inflammatory response pathways [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr C037.