Interleukin-12 enhances the antitumor activity of cytotoxic T lymphocytes against lung adenocarcinoma engrafted in severe combined immunodeficient mice

Background. Through a number of biologic activities, interleukin 12 (IL-12) has proven to be a potential antitumor cytokine in mice bearing a variety of malignancies. However, in clinical trials in humans, the eradication of solid tumors remains difficult. Methods. A lung cancer cell line (PC-9)-specific cytotoxic T lymphocytes (CTL) were generated by multiple stimulations, with irradiated PC-9 cells, of regional lymph node lymphocytes obtained from patients with lung cancer whose cells expressed the same HLA-A locus haplotype as PC-9 (HLA-A24). Severe combined immunodeficient (SCID) mice bearing a subcutaneous graft of PC-9 were then intravenously injected with anti-PC-9-specific CTLs. Under these conditions, the in-vivo effect of recombinant human (rh) IL-2 and rh IL-12 was evaluated, based on tumor growth. Results. Mice that received either rh IL-2 or rh IL-12 exhibited no inhibitory effect on tumor growth. However, mice that received adoptive immunotherapy (AIT) alone exhibited a significant inhibition of tumor growth in the PC-9 graft in comparison to untreated mice. When mice were treated with AIT combined with rh IL-2 + rh IL-12 administration, tumor growth was significantly suppressed. A significant difference was observed in the growth of the PC-9 graft between AIT + IL-2 + IL-12 treatment and AIT + IL-2 treatment. Four of eight mice in the AIT + IL-2 + IL-12-treated group showed complete tumor regression. Conclusion. IL-12 showed a synergistic effect with adoptive immunotherapy, using CTL in a tumor-engrafted SCID model. These results are therefore considered to provide a sufficient rationale for IL-2 + IL-12-based immunotherapy using CTL transfer for patients with lung cancer.