Immunomodulatory gene therapy with interleukin 12 and 4-1BB ligand: Long-term remission of liver metastases in a mouse model

Background: The success of immunomodulatory cancer therapy is frequently ha mpered by the transient nature of the antitumor immune response. We have sh own previously in a mouse model that interleukin 12 (IL-12) generates a str ong natural killer (NK) cell-mediated antitumor response and reduces liver metastases induced by a colon carcinoma cell line, However, only a small pe rcentage of the treated animals developed the cytotoxic T-lymphocytic respo nse required for a long-term systemic antitumor immunity, 4-1BB is a co-sti mulatory molecule expressed on the surface of activated T cells. Interactio n of 4-1BB with its natural ligand (4-1BBL) has been shown to amplify T-cel l (especially CD8+)-mediated immunity, In this study, we investigated the e ffects of adenovirus-mediated gene therapy delivering both IL-12 and 4-1BBL genes on mice with hepatic metastases induced by colon cancer cells. Metho ds: Syngeneic BALB/c mice received intrahepatic injection of poorly immunog enic MCA26 colon cancer cells. Various combinations of replication-defectiv e adenoviruses expressing IL-12 and 4-1BBL genes were injected into the est ablished liver tumors. Changes in tumor size and animal survival were then monitored. All statistical tests were two-sided, Results: The long-term sur vival rate of mice treated with the combination of IL-12 and 4-1BBL was sig nificantly improved over that of animals in the control group (P = .0001). In vivo depletion of NK cells or CD8+ T cells completely abolished the long -term survival advantage of the IL-12 plus 4-1BBL-treated animals (P<.002). Moreover, the systemic immunity induced by this combination treatment prot ected these animals against a subcutaneous challenge with parental MCA26 ce lls, Conclusion: Adenovirus-mediated transfer of IL-12 and 4-1BBL genes dir ectly into liver tumors resulted in tumor regression that required both NK and CD8+ T cells and generated a potent, long-lasting antitumor immunity.