Combination immunotherapy including OncoVEX^mGMCSF creates a favorable tumor immune micro-environment in transgenic BRAF murine melanoma

Talimogene Laherparepvec (OncoVEX^mGMCSF), an oncolytic virus, immune checkpoint inhibitor anti-programmed cell death protein 1 (anti-PD1), and BRAF inhibition (BRAFi), are all clinically approved for treatment of melanoma patients and are effective through diverse mechanisms of action. Individually, these therapies also have an effect on the tumor immune microenvironment (TIME). Evaluating the combination effect of these three therapies on the TIME can help determine when combination therapy is most appropriate for further study. In this study, we use a transgenic murine melanoma model (Tyr::CreER; BRAF^CA/+; PTEN^flox/flox), to evaluate the TIME in response to combinations of BRAFi, anti-PD1, and OncoVEX^mGMCSF. We find that mice treated with the triple combination BRAFi + anti-PD1 + OncoVEX^mGMCSF have decreased tumor growth compared to BRAFi alone and prolonged survival compared to control. Flow cytometry shows an increase in percent CD8 + /CD3 + cytotoxic T Lymphocytes (CTLs) and a decrease in percent FOXP3 + /CD4 + T regulatory cells (Tregs) in tumors treated with OncoVEX^mGMCSF compared to mice not treated with OncoVEX^mGMCSF. Immunogenomic analysis at 30d post-treatment shows an increase in Th1 and interferon-related genes in mice receiving OncoVEX^mGMCSF + BRAFi. In summary, treatment with combination BRAFi + anti-PD1 + OncoVEX^mGMCSF is more effective than any single treatment in controlling tumor growth, and groups receiving OncoVEX^mGMCSF had more tumoral infiltration of CTLs and less intratumoral Tregs in the TIME. This study provides rational basis to combine targeted agents, oncolytic viral therapy, and checkpoint inhibitors in the treatment of melanoma.