Gene Therapy for Metastatic Brain Tumors by Vaccination with Granulocyte-Macrophage Colony-Stimulating Factor-Transduced Tumor Cells

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Abstract
We have developed an ex vivo gene therapy paradigm for the treatment of brain tumors using granulocyte-macrophage colony-stimulating factor (GM-CSF). Murine B16 melanoma cells were infected with MFG recombinant retrovirus containing the mouse GM-CSF cDNA. Subcutaneous vaccination of syngeneic mice with irradiated GM-CSF-secreting B16 melanoma cells was capable of completely protecting animals against subsequent intracranial B16 tumor inoculation, with up to 5 × 103 cells. Histologic evaluation revealed the presence of neutrophils, eosinophils, and lymphocytes, including CD4+, CD8+, and CD45R+ cells, in the intracerebral inoculation site, peaking 4 days after intracranial inoculation. In contrast, nonvaccinated animals or animals vaccinated with irradiated, nontransduced B16 cells succumbed to intracranial tumor within 3 weeks after inoculation. Treatment of established intracranial B16 melanoma tumors with subcutaneous injection of irradiated GM-CSF-secreting B16 cells significantly delayed death, as compared to injection of irradiated nontransduced B16 cells or no treatment. In addition, treatment of established intracerebral GL261 gliomas by vaccination with irradiated GM-CSF-secreting B16 cells mixed with irradiated, transduced, or nontransduced GL261 cells also extended survival. These B16/GL261 co-vaccinations also improved outcome and, in some cases, induced immunological memory that protected survivors from subsequent intracranial challenge with GL261 tumor cells. These findings indicate that peripheral vaccination with irradiated tumor cells in the presence of GM-CSF-producing cells can initiate a potent antitumor immune response against intracranial neoplasms. To develop a protocol for tumor vaccination against experimental brain tumors, granulocyte-macrophage colony-stimulating factor (GM-CSF) was expressed and secreted in murine B16 melanoma and GL261 glioma cell lines. Subcutaneous vaccination with irradiated GM-CSF-secreting B16 melanoma cells protected animals from subsequent intracranial B16 tumor inoculation. Treatment of established intracranial B16 tumors with B16-GM-CSF vaccination also prolonged survival. Vaccination with GM-CSF-secreting cells correlated with tumor infiltration of cytotoxic T cells, B cells, neutrophils and eosinophils. Furthermore, treatment with B16-GM-CSF cells did not protect from intracranial GL261 tumor, but B16-GM-CSF cells mixed with GL261 cells was protective. These findings indicate that vaccination against intracranial neoplasms does not arise from nonspecific systemic GM-CSF secretion, but rather from GM-CSF secretion from the autologous tumor vaccine or from a nearby donor cell.