TKT and neoplasm: To explore the potential application of ERE73s-ARF (−13) constructs in cancer cell-specific gene therapy, we next examined the anti-tumor effects of Ad-ERE73 (1 + 2)-ARF (−13)-TK and Ad-ERE73 (3 + 4)-ARF (−13)-TK in a xenograft mouse model (Figure 4A).