Murine sarcoma MC12 cells were transfected with the gene coding for murine granulocyte-macrophage colony-stimulating factor (GM-CSF). Tumorigenicity of a variety of cell clones with different expression of the inserted gene was assessed. All of the genetically manipulated MC12 cell clones examined were found to be less tumorigenic than the parental MC12 cell population. No correlation was observed between the production of GM-CSF by the clones and their tumorigenicity. It has been found that irradiation of the GM-CSF-producing cells with the dose of 150 Gy did not significantly inhibit the GM-CSF production during the period of 5 days after irradiation. These findings provided us with the rationale for using the irradiated GM-CSF-producing MC12 sarcoma vaccine for therapy. It has further been found than immunosensitivity of the genetically manipulated, GM-CSF-producing tumour targets to the IL-2-activated killer (LAK) cell-mediated cytolysis was significantly increased, as compared to the parental target cell population. Irradiated, GM-CSF-producing tumour vaccines were used for therapy of 3-day-old MC12 sarcoma transplants in syngeneic mice and for therapy of surgically induced minimal residual tumour disease. Neither small tumour transplants, nor tumour residua after surgery were significantly sensitive to the therapy with GM-CSF-producing tumour vaccines.

Institute of Molecular Genetics Academy of Sciences of the Czech Republic Prague

DNA-vaccination via tattooing induces stronger humoral and cellular immune responses than intramuscular delivery supported by molecular adjuvants