Pancreatic tumor microenvironment reprogramming via alloantigen-expressing virotherapy elicits tumor rejection and improves immunotherapy response

Abstract Pancreatic ductal adenocarcinoma (PDAC), the most common malignant type of pancreatic cancer, is characterized by a dense desmoplastic stroma, low neoantigen burden, and a highly immunosuppressive tumor microenvironment (TME), which severely limit cytotoxic T-cell infiltration and the efficacy of immune therapies. Here, we present a novel strategy harnessing acute transplant rejection mechanisms by employing a recombinant oncolytic rVMG vector engineered to express the murine H-2Kk MHC class I alloantigen (rVMG-H-2Kk), thereby inducing tumor-specific antigenic mismatch responses. In vitro , rVMG-H-2Kk exhibited strong replication and cytolytic activity while inducing cell surface expression of both H-2Kk and endogenous H-2Kb, in addition to upregulation of antigen presentation genes (β2-microglobulin, Tap1, and Tapbp). In two independent immunocompetent PDAC models, intratumoral and systemic delivery of rVMG-H-2Kk delayed tumor progression and prolonged survival. Multiplex immunohistochemistry and immunophenotyping revealed substantial TME remodeling, marked by increased effector T-cell infiltration, regulatory T-cell depletion, and reduced fibrosis. Spatial transcriptomics further showed compartment-specific immune activation and epithelial metabolic reprogramming, corroborating with enhanced tumor immunogenicity. Despite these effects, rVMG-H-2Kk also induced compensatory immunosuppressive pathways, including upregulation of antiviral response genes and immune checkpoint receptors such as PDL-2. Importantly, combination therapy with rVMG-H-2Kk and murine checkpoint blockade (anti-PD-1 and anti-CTLA-4) drastically improved survival than checkpoint blockade alone. Strikingly, surviving mice resisted tumor rechallenge, indicating the establishment of durable antitumor memory. Collectively, these findings establish rVMG-H-2Kk as a novel immunotherapeutic platform capable of converting immune-cold tumors into immune-hot, sensitizing tumors to immune checkpoint inhibitors, and establishing durable antitumor immunity in PDAC. One Sentence Summary Oncolytic virus-based delivery of an alloantigen improves antitumor immunity and synergizes with immune checkpoint inhibitors in pancreatic cancer. Significance statement Delivery of murine alloantigens via an engineered oncolytic vesiculovirus, combined with immune checkpoint blockade, overcomes immunosuppressive barriers and establishes durable antitumor immunity in PDAC.