CSF2 and neoplasm: OVs are also engineered to express immunomodulatory payloads [e.g. GM-CSF, IL-12, or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)], incorporate tumor-specific promoters or delete oncogenes (e.g., E1B in AdV, ICP34.5 in HSV-1), to improve safety and selectivity (12–14).