Sequential Immunotherapy by Vaccination with GM-CSF Expressing Glioma Cells and CTLA-4 Blockade Effectively Treats Established Murine Intracranial Tumors

Abstract

Malignant glioma is an incurable disease with a relatively short median survival. Several clinical trials have demonstrated that immunotherapy with vaccination is a safe and possibly effective way of prolonging survival. Antibody-based blockade of CTLA-4 ligation on T lymphocytes is associated with enhanced antitumor immunity in animal models of cancer and in patients with advanced melanoma. We hypothesized that sequential therapy with GM-CSF - expressing whole glioma cell vaccination and CTLA-4 blockade is an effective strategy for treating established intracranial gliomas. GL261 glioma cells were injected into the right frontal lobes of syngeneic C57/BL6 mice. At days 3, 6, and 9 after tumor implantation, mice were treated with subcutaneous injection of irradiated GMCSF-expressing GL261 cells. Mice were also treated with intraperitoneal injection of anti-CTLA-4 monoclonal antibodies (mAbs), either at days 3, 6, and 9 or days 12, 15, and 18. Animals were followed for survival. Splenocytes were harvested at day 22 for use in ELISPOT assays. Early treatment of established intracranial gliomas with high-dose CTLA-4 blockade was associated with increased survival in GL261-bearing mice. Later treatment with anti-CTLA-4 mAbs did not significantly improve survival compared to control-treated mice. Early vaccination followed by subsequent CTLA-4 blockade was associated with significantly improved survival versus either treatment alone and intensified tumor-specific immunity as measured by interferon-gamma ELISPOT. Sequential immunotherapy with GM-CSF-expressing irradiated glioma cells and CTLA-4 blockade synergistically prolongs survival in mice bearing established intracranial gliomas.