The first clinically approved OV, Talimogenelaherparepvec (TVEC), is a genetically modified type I herpes simplex virus (HSV)that expresses granulocyte-macrophage colony-stimulating factor(GM-CSF)16 and is now incorporated in the treatmentprotocols of a select group of patients with melanoma. The gene discussed is CSF2; the disease is melanoma.