Induction of antitumor immunity by direct intratumoral injection of a recombinant adenovirus vector expressing interleukin-12

Direct intratumoral (i.t.) injection of adenoviruses (Ads) expressing specific immunostimulatory cytokines represents an attractive strategy for the clinical implementation of cytokine gene therapy of cancer. Interleukin-12 (IL-12) is a heterodimeric cytokine produced by antigen-presenting cells and promotes a T helper 1-like immune response. We have constructed an Ad vector (AdCMV-mIL-12) containing both chains of the murine IL-12 (mIL-12) gene linked by an internal ribosomal entry site sequence under the transcriptional control of the cytomegalovirus immediate-early gene promoter, which is able to mediate the transient expression of very high levels of biologically active mIL-12 both in vitro and in vivo. An i.t. injection of 4 × 108 plaque-forming units of AdCMV-mIL-12 resulted in a complete regression of day 7 established subcutaneous MC38 murine adenocarcinomas and MCA205 murine fibrosarcomas. Treated animals rejected a subsequent rechallenge with MC38 and MCA205, respectively, demonstrating the induction of long-lasting antitumor immunity. Specific antitumor cytotoxic T lymphocyte reactivity was detected in splenocytes harvested from treated animals. A significant increase in the numbers of both CD4+ and CD8+ T cells in the AdCMV-mIL-12-infected tumors was observed. Ad-mediated IL-12 gene therapy was also associated with measurable serum levels of mIL-12 and profound changes in the composition of splenic lymphocytes. Taken together, these results demonstrate the feasibility and efficacy of delivering IL-12 directly i.t. using a recombinant adenoviral vector.