Abstract 5574: Role of KMT2C and KMT2D in modulating tumor immune microenvironment of endometrial cancer

Abstract BACKGROUND: Recent molecular classifications of Endometrial Cancer (EC) have enhanced prognostic accuracy and helped guide targeted therapies. Among frequently mutated factors are epigenetic regulators like lysine methyltransferases KMT2C and KMT2D which monomethylate H3K4 at enhancer sites and their loss of function (LOF) mutation is associated with genomic instability, altered chromatin accessibility and increased immune evasion. Although increased CD8+ T cells infiltration and high PDL1 expression in postmenopausal EC patients is linked to poor prognosis, the impact of epigenetic mutation on immune signaling remains poorly understood. Pan-cancer analysis by Cao et al suggests that low KMT2C expression may reduce immunosuppressive and better immunotherapy responses, with similar patterns seen in other cancers suggesting a potential role in modulating immune response. METHODS: CRISPR technology was used to generated KMT2C and KMT2D knockouts in 12Z and HEC1a cells and whole cell lysates of these cells were used for immunoblotting analysis. Next, Immunohistochemistry on KMT2D KO mouse tissues were performed to look at specific immune markers. Finally, flow cytometry analysis was done to understand the makeup of the tumor microenvironment and explore the differences in the role of various immune cells. RESULTS: TCGA database showed upregulation of immune factors like IFN-G and CTLA-4 when KMT2C is altered. Immunoblotting analysis of the CRISPR knockout cells showed upregulation of PDL1 expression in KMT2C knockout cells. Further, Immunohistochemistry of KMT2D KO mouse tissues showed decreased CD8+ expression. Following this, flow cytometry analysis of KMT2D KO mouse tissues showed increased myeloid derived suppressor cells and decreased CD8+ and CD4+ cells which indicates an immunosuppressive environment. CONLCUSION: Overall, these findings highlight the role of KMT2C and KMT2D mutations on the tumor immune microenvironment and support their potential as predictive biomarker for ICI responsiveness in endometrial cancer. The mixed clinical efficacy of immunotherapies, it is critical to understand the intricacies of the tumor microenvironment. Future studies will focus on replicating the results in KMT2C KO mice and further understand the potential of KMT2C and KMT2D alteration in shaping the immune microenvironment. Citation Format: Sanjeev Ganesh, Swornalata Pukhrambam, Juveria Ali, Savannah Hughes, Heather Marie Gibson, Michael Wilson. Role of KMT2C and KMT2D in modulating tumor immune microenvironment of endometrial cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 5574.