ERVW-1 and neoplasm: Beyond the core design elements of T-VEC, RP1 additionally includes engineered up-regulation of US11 via placing under control of a strong constitutively active promoter leading to enhanced tumor-specific replication, and transgenic expression of GALV-GP R-, which is a truncated envelope glycoprotein from gibbon ape leukemia virus that enhances cell-to-cell fusion, promoting direct lysis of tumor cells and enhancing the spread of the virus within tumors.