For example, talimogene laherparepvec (T-VEC) [10,11], which is a herpes simplex virus strain that was engineered to encode the immune adjuvant granulocyte-macrophage colony-stimulating factor (GM-CSF), was approved as a first-in-class OV in U.S.A. in 2015 to treat metastatic melanoma. The gene discussed is CSF2; the disease is metastatic melanoma.