Adenovirus-interleukin-12-mediated tumor regression in a murine hepatocellular carcinoma model is not dependent on CD1-restricted natural killer T cells

The cytokine interleukin-12 (IL-12) has shown potent antitumor activity in several tumor models. Recently, natural killer (NR)T cells have been propos ed to mediate the antitumor effects of IL-12, In this study, the antitumor response of IL-12 was investigated in a gene therapeutic model against s.c. growing mouse hepatocellular carcinomas using an adenoviral vector express ing murine IL-12 (AdVmIL-12), An adenoviral-based system was chosen because of the ability of adenoviruses to transduce dividing and nondividing cells and because of their high transduction efficiencies. Our goals were to exa mine the efficacy of AdVmIL-12 in a hepatocellular carcinoma model and to i nvestigate the mechanism of the AdVmIL-12-mediated antitumor response with specific interest in the role of NK T cells. Our studies demonstrate that i ntratumoral AdVmIL-12mediated regression of s.c. hepatocellular tumors is a ssociated with rapid antitumor responses. AdVmIL-12 treatment was associate d with an immune cellular infiltrate consisting of CD4 and CD8 T lymphocyte s, macrophages, NK cells, and NK T cells. Antibody ablation of CD4 and CD8 T cells and use of NK cell-defective beige mice failed to abrogate the resp onse to AdVmIL-12, Studies in T-cell- and B-cell-deficient severe combined immunodeficient and recombinase activating gene-2-deficient mice and T-cell -, B-cell-, and NK cell-defective severe combined immunadeficient/beige mic e also failed to abrogate this response. AdVmIL-12 retained potent antitumo r activity in mice with specific genetic defects in immune cellular cytotox icity (perforin knockout mice) and costimulation (CD28 knockout mice). Use of mice with specific NK T cell deficiencies, V(alpha)14 T-cell receptor an d CD1 knockout mice, also failed to abrogate the response to AdVmIL-12, His tological and immunohistochemical studies of AdVmIL-12-treated tumors showe d extensive inhibition of neovascularization and a marked decrease in facto r VIII-stained endothelial cells. Our studies indicate that the antitumor r esponse of AdVmIL-12 is independent of direct cytotoxic cellular immunity ( specifically, the function of NK T cells) and suggest that the initial mech anisms of AdVmIL-12-mediated tumor regression involve inhibition of angioge nesis.