An oncolytic virus–delivered TGFβ inhibitor overcomes the immunosuppressive tumor microenvironment

Oncolytic viruses (OV) are promising forms of immunotherapy that have demonstrated clinical benefit in difficult-to-treat cancers such as metastatic melanoma. However, their adoption in other malignancies has been limited, in part, due to poorly understood mechansims of therapeutic resistance. Here, bulk RNA-seq was performed on oncolytic vaccinia virus-sensitive and -resistant murine head and neck squamous cell carcinomas (MEERvvS and MEERvvR, respectively) to explore potential means of OV resistance. These results corroborated a potential role for TGF-beta mediated stabilization of immunosuppressive regulatory T cells in the tumor microenvironment of OV-resistant MEERvvR-bearing mice. Subsequently, treatment with oncolytic vaccinia virus engineered to expess a dominant negative TGF-β signaling inhibitor (VVtgfbi) restored sensitivity to OV-mediated cell death among MEERvvR tumors. Single-cell RNA seq performed on CD45+ immune cells isolated from tumors suggests TGF-β inhibition may also reduce the presence and activity of myeloid-derived suppressor cell populations within the tumor microenvironment. Intradermal MEERvvS and MEERvvR tumor grafts were extracted, cultured ex-vivo in triplicate and subjected to bulk RNA sequencing.