Abstract 5560: KRASG12Dinhibition stimulates antigen presentation and potentiates mRNA-based immunotherapy in pancreatic cancer

Abstract Inhibition of constitutively-active KRASG12D, a powerful oncogenic driver in pancreatic ductal adenocarcinoma (PDAC), has been shown to sensitize tumors to T-cell-mediated immunotherapy in preclinical models. However, the influence of KRASG12D inhibition on tumor cell antigen presentation remains unclear. Therefore, we employed a multi-omic profiling workflow to investigate alterations in the proteome and peptide MHC-I ligandome (immunopeptidome) following the treatment of HPAC human cancer cells with a RAS(ON) G12D-selective inhibitor RMC-9945 (representative of investigational agent zoldonrasib), and/or IFNɣ in vitro. KRASG12D inhibition induced a unique IFN response signature and potentiated the expression of proteins involved in antigen processing and presentation. Immunopeptidomic analysis revealed a two-fold increase in both ligand abundance and diversity, reflecting the differential expression of proteins induced by KRASG12D inhibition. We hypothesized that KRASG12D signaling inhibition in preclinical models could augment immune responses initiated by immunization targeting tumor antigens in vivo via the following mechanism: the release of antigens from KRASG12D-induced cell death, coupled with increased MHC-I expression on remaining tumor cells, would enhance interactions with T cells activated by immunization. To test this, we orthotopically inoculated C57Bl/6 mice with a murine PDAC-KRASG12D cell line engineered to express the model self/tumor-associated antigen gp100. Mice were then immunized with either empty ionizable lipid nanoparticles (e-iLNPs) or iLNPs packaged with mRNA encoding full-length gp100 (gp100-iLNP). Prior to and during subsequent vaccine boost doses, mice were treated continuously with either KRASG12D inhibitor RMC-9945 or vehicle. Mice treated with both gp100 mRNA-iLNP immunization and KRASG12D inhibition exhibited significant tumor regression that was sustained over time compared to either treatment modality alone. This anti-tumor response was associated with a superior antigen-specific T cell response to subsequent immunizations, the retention of functional tumor antigen-specific cytotoxic T lymphocytes in both the tumor microenvironment and local secondary lymphoid organs, and sustained MHC-I and MHC-II surface expression on tumor cells. These preclinical findings underscore the dynamic nature by which PDAC antigen presentation can be modulated by KRAS signaling inhibition and IFNɣ. Combining allele-specific KRAS inhibition with tumor antigen immunization resulted in sustained tumor regression in vivo and was associated with the retention and function of tumor antigen-specific T cells. This rationalizes the combination of both approaches for enhanced anti-tumor activity, offering a strategy that is worth exploring clinically for improving outcomes in pancreatic cancer treatment. Citation Format: Amanda Creech, Hailey Lee, Khalid Rashid, Tony Luu, Emma Lieberman, Michael Srienc, Alykhan Premji, Ahmad Kassem, Luyi Li, James Wohlschlegel, Timothy Donahue, Norbert Pardi, Caius Radu. KRASG12Dinhibition stimulates antigen presentation and potentiates mRNA-based immunotherapy in pancreatic 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 5560.