Abstract B122: Genetically engineered Vaccinia Virus expressing MHC-I as a precision medicine cancer vaccine

Abstract Immunotherapy is a promising treatment strategy for many forms of cancer; however, patient response rates vary with only a subset of patients responding favorably within a cohort. Recently, progress has been made in the development of oncolytic viral therapy (OV), which uses viruses to selectively target and kill cancer cells while inducing anti-tumor immunity. Producing a strong anti-cancer immune response is challenging, and strategies to direct immune responses toward the tumor are key to developing novel therapeutics. Current oncolytics struggle to stimulate potent anti-tumor responses and though the immune system offers an immense resource that can be used to treat cancers, these cells must be instructed to recognize cancer cells as foreign. T cell recognition and killing of cells requires the expression of the major histocompatibility complex (MHC) that can present peptides from cancer cells and stimulate T cell responses. The ability to target this response toward a cancer specific peptide is critical for the directed activity of T cells. Vaccinia virus (VACV) is a promising oncolytic due to its safety profile, manipulatable genome, and its induction of potent immune responses. Here, we investigated the use of modified VACV expressing MHC-I with a defined peptide and ß2-microglobulin as a single chain trimer (SCT), and the T cell co-stimulatory molecule CD80 (VACV4x-SCT). We began by determining if OV treatment of murine EMT6 breast cancer can lead to tumor regression in vivo. A previously described EMT6 tumor specific antigen, E22, was expressed by the SCT. Following intratumoral virus treatment, ∼70% of mice cleared the tumor, and E22 specific CD8+ T cells were observed to infiltrate tumors. Further, all mice that cleared primary tumor rejected secondary tumor challenge. The use of combination therapy was then evaluated, where tumor bearing mice were treated with VACV4x -SCTE22 and anti-PDL-1, which further enhanced animal survival, surpassing 75%. The ability to clear tumor and stimulate tumor specific T cells using VACV treatment led us to explore the use of OV therapy in a metastatic model. Here, we implanted tumors bilaterally and treated only one tumor. This led to the clearance of both tumors in ∼25% of mice, and the clearance of primary tumor but disease progression of secondary tumor in 13% of mice. With the ability to induce tumor clearance at a non-OV treated site, we investigated the efficacy of percutaneous administration on tumor clearance and immune stimulation. VACV4x-SCTE22 administered as a single percutaneous dose led to an extension in survival, however percutaneous immunization was not as effective as intratumoral treatment. Though modest tumor clearance was observed, E22 specific CD8+ T cells were detected in mice that did not clear the tumor. These data highlight the potential to generate a VACV stimulated immune response by delivery of a defined peptide-MHC-I complex. Bolstering a T cell response using virus is an important step for the advancement of immunotherapies and the use of VACV as a vaccine platform. Citation Format: Shae J Komant, Jun Li Wang, Nicole Favis, David H Evans, Ryan S Noyce, Troy A Baldwin. Genetically engineered Vaccinia Virus expressing MHC-I as a precision medicine cancer vaccine [abstract]. In: Proceedings of the AACR IO Conference: Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2025 Feb 23-26; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2025;13(2 Suppl):Abstract nr B122.