Tesfay, Mulu Z.

Background 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). Methods We present a novel strategy harnessing acute transplant rejection mechanisms by employing a recombinant oncolytic rVMG vector engineered to express murine alloantigens H-2Kb (rVMG-H-2Kb) or H-2Kk (rVMG-H-2Kk), thereby inducing tumor-specific antigenic mismatch responses. Results In vitro, rVMG-H-2Kb and 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 immunocompetent PDAC models, intratumoral and systemic delivery of rVMG-H-2Kb and rVMG-H-2Kk delayed tumor progression, with rVMG-H-2Kk conferring a survival advantage. 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 programmed death-ligand-2. Importantly, combination therapy with rVMG-H-2Kk and murine checkpoint blockade (anti-programmed cell death protein-1 and anti-cytotoxic T-lymphocyte-associated protein 4) drastically improved survival compared to checkpoint blockade alone. Strikingly, surviving mice resisted tumor rechallenge, indicating the establishment of durable antitumor memory. Conclusion These findings establish rVMG-mediated alloantigen delivery 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.

Abstract Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, thus, there is an urgent need to develop more effective therapeutic options for this dismal condition. Tumor-infiltrating lymphocytes (TILs) are associated with improved response to immune checkpoint blockade in HCC, but their low abundance in most cases limits their therapeutic efficacy. Here, we demonstrate, in mice, that low-dose intratumoral immunovirotherapy with the trivalent measles, mumps, and rubella vaccine (MMR) induces superior tumor-growth delay and extended host survival compared to individually administered vaccines for measles, mumps, or rubella viruses. Further, our results show that MMR therapy synergizes with PD-1 and CTLA-4 blockade to reprogram the tumor microenvironment, resulting in increased CD8+ TIL infiltration and reduced PD-1 expression on TILs, among other effects. These changes in the immunological landscape translated into greater survival and more durable tumor-specific and memory immune responses for hosts. Comprehensive toxicology analysis revealed no evidence of MMR-induced liver or kidney toxicity after intrahepatic administration. This work reinforces an unrecognized role of MMR plus ICB in reprogramming the immune landscape in HCC through multimodal immune activation, providing a strong rationale for further development of MMR-based therapies for HCC. Citation Format: Mulu Z. Tesfay, Aleksandra Cios, Khandoker Usran Ferdous, Randal S. Shelton, Isabelle Miousse, Camila C. Simoes, Alexei Basnakian, Rangaswamy Govindarajan, Martin Cannon, Mitesh J. Borad, Bolni M Nagalo. Live attenuated MMR vaccines modulate tumor immune cell infiltration and synergize with standard of care to prolong survival in preclinical HCC models [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 4378.

The global burden of hepatocellular carcinoma (HCC) continues to rise, driven by increasing metabolic risk factors such as nonalcoholic fatty liver disease, obesity, and type II diabetes. Patients with advanced HCC have limited therapeutic options and a dismal prognosis. While recent advancements in combination therapies—including immune checkpoint blockade (ICB) with anti-PD-1/PD-L1 and anti-CTLA-4 agents and anti-angiogenics—have improved survival for some, up to 80% of patients fail to respond, underscoring an unmet need for new strategies. Emerging data indicate a strong association between increased tumor-infiltrating lymphocytes (TILs) and better responses in ICB-treated HCC, suggesting TIL enhancement as a promising approach. However, HCC’s inherent low immunogenicity and immunosuppressive tumor microenvironment (TME) limit the efficacy of current TIL-promoting strategies. Here, we demonstrate that low-dose intratumoral immunotherapy using the trivalent MMR vaccine—composed of live attenuated measles, mumps, and rubella viruses—modulates TME immune infiltration, increases cytotoxic T cell frequency, and delays tumor growth in multiple murine HCC models. Importantly, intratumoral or systemic MMR administration in combination with dual ICB (anti-mPD-1/anti-mCTLA-4) significantly prolongs survival, promoting tumor-specific and memory immune responses in both subcutaneous and orthotopic HCC models. These findings reveal a unique mechanism of vaccine-induced anti-tumor activity, highlighting MMR as a viable, globally accessible option for enhancing immune responses in advanced HCC therapy. Citation Format: Mulu Z. Tesfay,Aleksandra Cios,Khandoker U. Randal S. Shelton,Bahaa Mustafa,Camila C. Simoes,Steven Post,Thomas Kelly,Moaven Moaven,Lewis R. Roberts,Mitesh J. Borad,Martin J. Cannon,Alexei Basnakian,Nagalo Bolni. Live attenuated MMR vaccines modulate tumor immune cell infiltration and synergize with standard of care to prolong survival in preclinical HCC models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 945.

ABSTRACT Because of its very low human seroprevalence, vesicular stomatitis virus (VSV) has promise as a systemic oncolytic agent for human cancer therapy. However, as demonstrated in this report, the VSV infectious titer drops by 4 log units during the first hour of exposure to nonimmune human serum. This neutralization occurs relatively slowly and is mediated by the concerted actions of natural IgM and complement. Maraba virus, whose G protein is about 80% homologous to that of VSV, is relatively resistant to the neutralizing activity of nonimmune human serum. We therefore constructed and rescued a recombinant VSV whose G gene was replaced by the corresponding gene from Maraba virus. Comparison of the parental VSV and VSV with Maraba G substituted revealed nearly identical host range properties and replication kinetics on a panel of tumor cell lines. Moreover, in contrast to the parental VSV, the VSV with Maraba G substituted was resistant to nonimmune human serum. Overall, our data suggest that VSV with Maraba G substituted should be further investigated as a candidate for human systemic oncolytic virotherapy applications. IMPORTANCE Oncolytic virotherapy is a promising approach for the treatment of disseminated cancers, but antibody neutralization of circulating oncolytic virus particles remains a formidable barrier. In this work, we developed a pseudotyped vesicular stomatitis virus (VSV) with a glycoprotein of Maraba virus, a closely related but serologically distinct member of the family Rhabdoviridae , which demonstrated greatly diminished susceptibility to both nonimmune and VSV-immune serum neutralization. VSV with Maraba G substituted or lentiviral vectors should therefore be further investigated as candidates for human systemic oncolytic virotherapy and gene therapy applications.

ABSTRACT We are developing oncolytic vesicular stomatitis viruses (VSVs) for systemic treatment of multiple myeloma, an incurable malignancy of antibody-secreting plasma cells that are specifically localized in the bone marrow. One of the presumed advantages for using VSV as an oncolytic virus is that human infections are rare and preexisting anti-VSV immunity is typically lacking in cancer patients, which is very important for clinical success. However, our studies show that nonimmune human and mouse serum can neutralize clinical-grade VSV, reducing the titer by up to 4 log units in 60 min. In addition, we show that neutralizing anti-VSV antibodies negate the antitumor efficacy of VSV, a concern for repeat VSV administration. We have investigated the potential use of covalent modification of VSV with polyethylene glycol (PEG) or a function-spacer-lipid (FSL)–PEG construct to inhibit serum neutralization and to limit hepatosplenic sequestration of systemically delivered VSV. We report that in mice passively immunized with neutralizing anti-VSV antibodies, PEGylation of VSV improved the persistence of VSV in the blood circulation, maintaining a more than 1-log-unit increase in VSV genome copies for up to 1 h compared to the genome copy numbers for the non-PEGylated virus, which was mostly cleared within 10 min after intravenous injection. We are currently investigating if this increase in PEGylated VSV circulating half-life can translate to increased virus delivery and better efficacy in mouse models of multiple myeloma.