Systemic and local paracrine cytokine therapies using transduced tumor cells are synergistic in treating intracranial tumors

Development of an effective immunotherapeutic approach for treatment of CNS tumors must take into account the unique anatomic and immunologic features of the brain. We explored the antitumor immune response in the brain elicited by nonreplicating melanoma cells genetically engineered to produce either granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-2 (IL-2) in a paracrine fashion. Using a new model of intracranial melanoma in C57BL/6 mice, the cytokine-producing cells were given either as a subcutaneous vaccine to induce systemic antitumor immunity or as a direct injection into the brain as local immunotherapy. We found that GM-CSF-transduced cells, as a subcutaneous vaccine but not as an intracranial injection, afforded some protection from intracranial challenge with the wildtype tumor. In contrast, direct intracranial injection of tumor cells secreting IL-2 was protective whereas flank vaccination with IL-2 transductants was not. Combination therapy with both the subcutaneous GM-CSF-transductants as a vaccine and local administration of IL-2-transductants in the brain achieved a synergistic response. These findings provide a basis for the application of paracrine cytokine delivery to brain cancer therapy both as a systemic vaccine and via local administration. The demonstration of synergy between paracrine cytokine therapies holds promise as a novel therapy for brain tumors.