Particle-Mediated Gene Transfer of Granulocyte-Macrophage Colony-Stimulating Factor cDNA to Tumor Cells: Implications for a Clinically Relevant Tumor Vaccine

The necessity for prolonged tissue culture manipulations limits the clinical application of many forms of gene therapy in patients with malignancies. We hypothesized that granulocyte-macrophage colony-stimulating factor (GM-CSF) cDNA in a plasmid expression vector could be effectively introduced into resting tumor cells, without the need for tissue culture propagation prior to or following transfection, and that efficient expression of transgenic GM-CSF by the transfected tumor cells would confer an effective immune response against tumors. GM-CSF cDNA in expression vectors was coated onto gold particles and accelerated with a gene gun device into mouse and human tumor cells. Human tumor tissue transfected within 4 hr of surgery produced significant levels of transgenic human GM-CSF protein in vitro. Human GM-CSF was readily detectable in serum and at the injection site following subcutaneous implantation of these transfected tumor cells into nude mice. Transfected and irradiated murine B16 melanoma cells produced ≥100 ng/ml murine GM-CSF/10⁶ cells per 24 hr in vitro for at least 10 days. The antitumor efficacy of this nonviral approach was tested using irradiated B16 tumor cells that were transfected with mGM-CSF cDNA and injected into mice as a tumor “vaccine.” Subsequent challenge of these mice with nonirradiated, nontransfected B16 tumor cells showed that 58% of the animals were protected from the tumor by the prior vaccine treatment. In contrast, only 2% of control animals were protected by prior treatment with irradiated B16 cells transfected with the vector containing the luciferase gene. These results suggest that particle-mediated transfection of fresh tumor explants with cytokine cDNA is an effective and clinically attractive approach for cancer therapy.

Overview summary

Granulocyte-macrophage colony-stimulating factor (GM-CSF) cDNA in a nonviral expression vector was introduced into both murine tumor cells in tissue culture and fresh human tumor explants. The GM-CSF vector construct was transferred to tumor cells by attaching the DNA to gold particles and then accelerating these particles into the tumor cells ex vivo with a gene gun. Expression of the GM-CSF protein product was detected in vitro after gene transfer in both human and murine tumors. When the transfected murine tumor was used as a vaccine, mice were protected from subsequent challenge with wild-type tumor. These results suggest that particle-mediated transfection of fresh tumor explants with GM-CSF cDNA is an effective and clinically attractive approach for cancer therapy.