Abstract 3572: Oncolytic virotherapy with the HSV-1 (VC2) vaccine strain induces anti-tumor T-cell responses in the murine 4T1 breast cancer model

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Abstract The tumor microenvironment (TME) plays important roles in suppression of anti-tumor immune responses. Immune suppression is achieved by multiple mechanisms including interfering with antigen presentation and inhibition of effector T-cell tissue infiltration. Altering specific TME properties can reduce immune-suppression and improve anti-tumor immunity with abscopal effects. Oncolytic Virotherapy (OV) is a promising approach for cancer treatment. We evaluated the efficacy of the HSV-1 (VC2) vaccine strain for the treatment of breast cancer using the murine stage-4 (4T1) syngeneic and immunocompetent breast cancer mouse model. Following Intratumoral (IT) injection of VC2 in mice bearing implanted 4T1 tumors, treatment efficacy was evaluated by monitoring tumor weight, immune infiltration, and metastasis in the lung. Animals treated with VC2 via the IT route exhibited significantly reduced metastasis and improved intra-tumoral T-cell infiltration. Improved T-cell infiltration was not due to viral replication since improved parameters were observed during late times post VC2 treatment when no viral replication was detectable. The total area of metastasis in the lung was significantly reduced compared to control groups. VC2 treated animals via the IT route had significantly higher cytotoxic splenocytes, evident by the in-vitro killing of 4T1 cells, compared to the control group. This improved cytotoxic activity, intratumoral T-cell infiltration, and reduced metastasis in the lung suggest that IT administration of VC2 altered TME in a way that induced better antigen recognition, processing, and presentation resulting in improved anti-tumor immune responses with an abscopal effect in the lung. Further understanding of the mechanisms involved in the observed improved anti-tumor immune responses will help improve treatment efficacy and provide new approaches for the treatment of solid tumors. Citation Format: Rafiq Nabi, Farhana Musarrat, Vladimir Chouljenko, Konstantin Kousoulas. Oncolytic virotherapy with the HSV-1 (VC2) vaccine strain induces anti-tumor T-cell responses in the murine 4T1 breast cancer model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3572.