Abstract
Oncolytic herpes simplex virus-1 (oHSV) is novel FDA-approved immunotherapy for advanced melanoma patients in US. Also, oHSV is recently approved for the treatment of recurrent GBM in Japan. We have shown that oHSV treatment of GBM cells induces NICD cleavage and NOTCH activation in adjacent uninfected glioma cells via HSV-1 microRNA-H16 (Otani Y and Yoo JY, Clin Cancer Res, 2020), however, the consequences of NOTCH on immunotherapy in GBM is unknow. Here we have investigated the impact of oHSV-induced NOTCH signaling on the tumor microenvironment (TME). Analysis of TCGA GBM data and experimental murine models revealed NOTCH induced immunosuppressive myeloid cell recruitment and limited anti-tumor immunity. In oHSV treated tissue, viral infection educated tumor associated macrophages to secrete CCL2 which recruited monocytic myeloid derived suppressor cell (MDSC) that attenuated anti-tumor immunity. Consistent with this, CCL2 induction was also observed in serum of recurrent GBM patients treated with oHSV (NCT03152318). Importantly, blockade of NOTCH signaling reduced the oHSV induced immunosuppressive environment and activated a CD8 dependent anti-tumor memory response. These findings present the opportunities for combination therapies that can help improve therapeutic benefit and anti-tumor immunity in GBM.