Highly successful therapeutic vaccinations combining dendritic cells and tumor cells secreting granulocyte macrophage colony-stimulating factor.

In an attempt to induce potent immune antitumor activities, we investigated, within the rat 9L gliosarcoma model, distal therapeutic vaccinations associating three therapies: dendritic cell vaccination, intratumoral granulocyte macrophage colony-stimulating factor (GM-CSF) gene transfer, and tumor apoptosis induction. Vaccines of dendritic cells coinjected with processed GM-CSF secreting 9L cells induced systemic responses, resulting in the complete regression of distant preimplanted 9L tumor masses in, with the best strategy, 94% of male rats. All of the cured rats developed a long-term resistance to a rechallenge with parental cells. The curative responses were correlated with the detection of elevated specific cytotoxic activities and a CD4+, CD8+ T cell-, and natural killer (NK) cell-mediated IFN-gamma production. The survival rate of the rat seemed more directly linked to the amount of GM-CSF secreted by the transduced tumor cells, which in turn depended on the toxicity of the apoptosis-inducing treatment, than to the level of apoptosis induced. Unexpectedly, alive GM-CSF secreting 9L cells became apoptotic when injected in vivo. Thus we documented the positive role of apoptosis in the induction of therapeutic antitumor responses by comparing, at equal GM-CSF exogenous supply, the effects of dendritic cells coinjected with apoptotic or necrotic 9L cells. The data showed the superior therapeutic efficiency of combined vaccines containing apoptotic tumor cells. In conclusion, vaccinations with dendritic cells associated with apoptotic tumor cells secreting GM-CSF show a very high therapeutic potency that should show promise for the treatment of human cancer.

Granulocyte macrophage-colony stimulating factor gene transfer to induce a protective anti-tumoral immune response against the 9L rat gliosarcoma model.

The injection of irradiated tumor cells genetically engineered to express the granolocyte macrophage-colony stimulating factor (GM-CSF) is reported as stimulating antitumoral immunity in several animal models. We used the 9L gliosarcoma rat model to investigate the potency of this strategy in relation to the central nervous system. After in vitro transduction experiments to generate 9L murine cells producing GM-CSF (9LmGM-CSF cells), we found that with the exception of one rat subcutaneously (s.c.) grafted with 108 9LmGM-CSF cells, syngenic rats s.c. injected (dorsal route) with 106-108 viable 9LmGM-CSF cells did not develop s.c. 9L gliosarcomas, while rats s.c. grafted with the same number of naive 9L cells died between 25 and 45 days postgraft. Intracerebral stereotactic injections of 4.104 naive 9L (without s.c. 9LmGM-CSF treatment) killed all the rats within 18-24 days, while s.c. grafting with 108 9LmGM-CSF cells wholly prevented the development of 9L brain gliosarcomas. These results outline the feasibility of the GM-CSF gene transfer approach in glioma (or at least gliosarcoma) gene therapy and could therefore serve as a basis for the development of an adjuvant treatment of glioblastomas using GM-CSF-producing tumor cell vaccines.