The potent antitumor effects of combined p16 gene and GM-CSF gene therapy through efficient induction of antitumor immunity

Abstract

Purpose: Tumor suppressor gene therapy and cytokine gene therapy have limited antitumor effects when used alone. Thus, in the present study, we investigated the antitumor potentials of the combined transfer of the p16 tumor suppressor gene and the murine granulocyte-macrophage colony-stimulating factor (GM-CSF) gene. Methods: The adenovirus-harboring p16 gene (Adp16) and adenovirus-harboring GM-CSF (AdGMCSF) gene were utilized for the treatment of established tumors in vivo. The mice were inoculated s.c. with Renca renal carcinoma cells and 3 days later received an intratumoral injection of Adp16 in combination with AdGMCSF. Results: The results demonstrated that tumor-bearing mice treated with Adp16 and AdGMCSF showed more potent inhibition of tumor growth and a prolonged survival period than mice treated with Adp16, AdGMCSF, adenovirus-expressing β-galactosidase or PBS (P < 0.01). Treatments of the mice with Adp16 alone or AdGMCSF alone also showed obvious antitumor effects as compared with those mice treated with PBS (P < 0.05). After combined p16 and AdGMCSF gene therapy, the expression of H-2K^d and Fas molecules on freshly isolated tumor cells increased markedly, and more CD₄ ⁺ T cells and CD₈ ⁺ T cells infiltrated in the tumor sites. The cytotoxicity of natural killer cells and specific cytotoxic T lymphocytes increased more significantly after the combined therapy. Conclusions: Our results demonstrated that combination p16 gene and GM-CSF gene therapy could inhibit the growth of established tumors in mice more significantly through efficient induction of antitumor immunity.