CSF2 and cancer: Engineered oncolytic HSV-1 virotherapy (oHSV) has shown great promise in targeting difficult-to-treat adult cancers as demonstrated by the recent FDA approval of the first oncolytic virus, talimogene laherparapvec (T-VEC), an oHSV that contains deletions in the neurovirulence gene γ134.5 and that produces granulocyte macrophage colony-stimulating factor (GM-CSF) during replication.