TKT and cancer: To understand the impact of the transgenes of WOTS-418 on cancer cell cytotoxicity in vitro, WR VV (wild type VV-tk+), WR-GFP (VV-tk− GFP+), and WOTS-418 (VV-tk−, HSV-tk418m+ and Fluc+) were each used to infect three human and three murine cancer cell lines.