Intratumoral injection of GM-CSF gene encoded recombinant vaccinia virus elicits potent antitumor response in a mixture melanoma model.

A recombinant vaccinia virus containing and expressing the gene for murine granulocyte-macrophage colony-stimulating factor (VVGM-CSF) was constructed and tested for its antitumor activity. A murine tumor model was established by injecting 10(5) B16F10 melanoma cells into the right rear leg of C57BL/6 mice. Three days after B16F10 inoculation, VVGM-CSF or a thymidine kinase gene-deficient vaccinia virus (VVTK) were injected intratumorly twice weekly for 3 weeks. The results showed that VVGM-CSF treatment significantly inhibited the growth of subcutaneous tumor and delayed the survival period of tumor-bearing mice. Splenic lymphokine-activated killer cell, natural killer cell, and cytotoxic T lymphocyte activities were not found to be altered after VVGM-CSF or VVTK therapy. Cytotoxic and phagocytic activity of peritoneal macrophages were found to be greatly elevated in mice treated with VVGM-CSF. Nitric oxide released from the macrophages was also increased. Considering these data, we may speculate that continuous secretion of GM-CSF and activation of macrophages may contribute to the antitumor effects of VVGM-CSF injected intratumorally.