TKT and neoplasm: In HSV lacking the TK gene, replication relies heavily on actively dividing cells to provide the necessary TK. HSV with a deletion in the γ34.5 gene and a mutation in UL39 uses enzymes from actively dividing tumor cells for replication. Additionally, HSV expressing IL-12 exhibits anti-tumor effects in vivo by combining oncolysis with the stimulation of T cell-mediated immune responses.