Large nontransplanted hepatocellular carcinoma in woodchucks: Treatment with adenovirus-mediated delivery of interleukin 12/B7.1 genes

Background: Cytokine-based gene therapy strategies efficiently stimulate im mune responses against many established transplanted tumors, leading to rej ection of the tumor. In this study, we investigated the therapeutic potenti al of cancer immunotherapy in a clinically more relevant model, woodchucks with primary hepatocellular carcinomas induced by woodchuck hepatitis virus . Methods: Large (2-5 cm), established intrahepatic tumors were given an in jection once with 1 X 10(9) plaque-forming units of AdIL-12/B7.1, an adenov irus vector carrying genes for murine interleukin 12 and B7.1, or of AdEGFP , the control virus, and regression of the tumors was then monitored. Five animals were used in total. Results: In four tumor-bearing animals, the ant itumor response was assessed by autopsy and histologic analysis within 1-2 weeks after treatment. Tn all animals treated with AdIL-12/B7.1 therapy ver sus AdEGFP therapy, we observed substantial tumor regression (P = .006; two -sided unpaired Student's t test) accompanied by a massive infiltration of T lymphocytes. These tumors also contained increased levels of CD4(+) and C D8(+) T cells and interferon gamma (IFN gamma). In continuously growing tum or nodules given an injection of the control virus or in nontumoral liver, no such effects (i.e., tumor regression and increased levels of CD4(+) and CD8(+) T cells and IFN gamma) were detected. In the fifth animal, monitored for long-term antitumor efficacy by magnetic resonance imaging (MRI) after intratumoral vector administration by MRI guidance, the tumor was almost c ompletely eliminated (greater than or equal to 95%) 7 weeks after treatment . Conclusion: Adenovirus vector-based immunotherapy appears to be an effect ive treatment of large nontransplanted (orthotopic) tumors that acquire mal ignant characteristics in a stepwise process, reflecting the real-world sce nario of hepatocellular carcinoma in humans.