TKT and ovarian cancer: Because several preclinical studies have demonstrated that genotoxic potential is not identical among all retroviral vector systems [20], and IRES could enable two different gene expressed simultaneously [21], we constructed pLXSN/tk-MCP-1 which co-expresses tk and MCP-1, and assessed the antitumor effect of pLXSN/tk-MCP-1 on ovarian cancer.