Adenovirus-mediated IL-12 gene therapy in combination with radiotherapy for murine liver cancer

Objective: To investigate the synergistic antitumor effects of adenovirus-mediated IL-12 gene therapy in combination with radiotherapy in mice bearing liver cancer. Methods: Balb/c mice bearing liver cancer received the treatment at day 1 with tumor local irradiation (TLI) of 20 Gy or mask irradiation when tumor size reached 0.6-1.0 cm. Within 1 hour after irradiation, adenovirus containing IL-12 gene or PBS was intra-tumor injected once a week. Forty-eight hours after the second injection, IFN-γ levels in sera and the supernatant of cultured spleen cells were assayed by ELISA, CTL activity of spleen cells was measured by 3H-TdR release assay, and phenotypes of tumor-infiltrating lymphocytes were analysed by immunohistochemical staining. Results: The growth of tumors in animals treated with a combination of IL-12 gene therapy and TLI was inhibited more significantly than those with either single treatment (P < 0.01). Tumors of about 50% mice with the combined treatment were eradicated and there was no tumor developed after rechallenged with subcutaneous injection of MM45T. Li cells. immunohistochemical staining showed that combined treatment of IL-12 gene therapy and TLI could induce abundant CD4+ and CD8+ lymphocyte infiltration and tumor-specific cytolytic activities, and the levels of IFN-γ in sera were higher in IL-12 gene therapy and IL-12 gene therapy combined with TLI groups. Conclusion: These results suggest that IL-12 gene therapy combined with radiotherapy is more effective than both single treatment modalities and can induce specific antitumor immuno-response greatly