Cancer cells (HeLa) or normal cells (NHDF) were infected with LC16m8-B5RmO, in which the B5R gene of LC16m8 was reverted to the sequence of the parent strain (LC16mO), and its modified viruses under serum-free culture conditions, and the cytotoxicity of these viruses was compared. The gene discussed is CYB5R3; the disease is cancer.