Radiation combined with oncolytic vaccinia virus provides pronounced antitumor efficacy and induces immune protection in an aggressive glioblastoma model

Glioblastoma (GB) is a malignant and immune-suppressed brain cancer that remains incurable despite the current standard of care. Radiotherapy is a mainstay of GB treatment, however invasive cancer cells outside the irradiated field and radioresistance preclude complete eradication of GB cells. Oncolytic virus therapy harnesses tumor-selective viruses to spread through and destroy tumors while stimulating antitumor immune responses, and thus has potential for use following radiotherapy. We demonstrate that oncolytic ΔF4LΔJ2R vaccinia virus (VACV) replicates in and induces cytotoxicity of irradiated brain tumor initiating cells in vitro. Importantly, a single 10 Gy dose of radiation combined with ΔF4LΔJ2R VACV produced considerably superior anticancer effects relative to either monotherapy when treating immune-competent orthotopic CT2A-luc mouse models-significantly extending survival and curing the majority of mice. Mice cured by the combination displayed significantly increased survival relative to naïve age-matched controls following intracranial tumor challenge, with some complete rejections. Further, the combination therapy was associated with an increased ratio of CD8+ effector T cells to regulatory T cells compared to either monotherapy. This study validates the use of radiation with an oncolytic ΔF4LΔJ2R VACV to improve treatment of this malignant brain cancer.