In vivo suicide gene therapy in solid tumor xenografts consisting of A549 cells. The nude mice bearing the subcutaneous tumors were infected with either SET or HRE–SET retroviruses, followed by daily intraperitoneal injection of 20 mg/kg ganciclovir (GCV) for 2 weeks, with exposure to 2 Gy radiation on days 2, 4 and 6. Tumor size was measured every 2 days. Control, A549 cells injection only; H + G, HRE–SET transfection and GCV; H + R, HRE–SET transfection and radiation; H + R + G, HRE–SET transfection, radiation and GCV; R, A549 injection and radiation; S + G, SET transfection and GCV; S + R, SET transfection and radiation; S + R + G, SET transfection, radiation and GCV.