Effects of combined granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-2, and interleukin-12 based immunotherapy against intracranial glioma in the rat

Cytokines play a major role in the regulation of the immune system. Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to be useful for immunotherapy against glioma because it can stimulate dendritic cells to present tumor antigen. Interleukin-2 (IL-2) is involved in T-cell expansion, and interleukin-12 (IL-12) drives the T-helper cell type I response. Previous studies have shown that each of these cytokines alone can induce the regression of tumor cells. In the present study we postulated that peripheral infusion of GM-CSF along with either IL-2 or IL-12 and irradiated tumor cells can lead to increased survival from 9L brain tumors. 9L gliosarcoma cells (10⁶) were implanted in the brains of syngeneic Fischer 344 rats. Osmotic minipumps were utilized for subcutaneous, continuous delivery of GM-CSF, either alone or with IL-2 or IL-12. Irradiated 9L cells were injected subcutaneously at various time points during treatment. Delayed-type hypersensitivity (DTH) and immunohistological analysis were used to further characterize the anti-tumor response. Treatment with GM-CSF and irradiated tumor cells led to an increase in survival rate in rats with intracranial 9L tumors when compared to untreated animals. The addition of IL-2 or IL-12 to the GM-CSF/tumor cell therapy further increased the survival rate up to 90%. The anti-tumor response was associated with vigorous DTH against 9L cells and increased infiltration of CD4+ and CD8+ lymphocytes into the tumor. These results suggest that the combined infusion of GM-CSF and other cytokines may be effective adjuvants in treating brain tumors.