Objective: To investigate the synergistic anti-tumor effects of murine IL-12 gene and HSV-TK gene therapy in mice bearing liver cancer. Methods: Mouse liver cancer MM45T. Li (H-2d) cells were transfected with retroviral vector containing IL-12 gene or HSV-TK gene insert. Gene-modified liver cancer cells, MM45T. Li/IL-12 and MM45T. Li/TK, with stable expression of IL-12 and TK were obtained. Balb/c mice were inoculated subcutaneously with 2′105 MM45T. Li cells. When the tumor reached a size of 0.5-1.0 cm, a mixture of MM45T.Li/TK cells and 60Co-irradiated MM45T. Li/IL-12 cell were injected intratumoraly. Ganciclovir (GCV) was injected ip (40 mg.kg-1.d-1) for 10 days. Intratumoral injection of 60Co-irradiated MM45T. Li/IL-12 cells was repeated twice in one week apart. Mice with distant tumors were treated according to the same protocol. CTL activity of spleen cells was measured by 51Cr-release assay and phenotype of tumor infiltrating lymphocytes by immunohistochemical staining. Results: In mice treated with MM45T. Li/IL-12 or MM45T. Li/TK+GCV individually led to moderate reduction in tumor growth, but neither could eradicate the tumor completely, while in 60% of mice treated with a mixture of MM45T. Li/IL-12 and MM45T. Li/TK cells plus GCV, complete tumor regression was observed, with no tumor recurrence for two months. The growth of distant tumor was also inhibited significantly in mice similarly treated. Most of the mice received combined gene therapy plus GCV had abundant CD4+, CD8+T lymphocyte infiltration. Their CTL activity was significantly higher than in mice received single gene therapy. Conclusion Combination therapy with IL-12 gene and HSV-TK gene plus GCV is effective for mouse liver cancer.
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