Monocyte chemoattractant protein-1 (MCP-1) gene transduction: an effective tumor vaccine strategy for non-intracranial tumors.
Recently, there has been renewed interest in the concept of tumor vaccines using genetically engineered tumor cells expressing a variety of cytokines to increase their immunogenicity. Human MCP-1 (JE) is a potent chemoattractant and activator of monocytes and T lymphocytes and thus a good candidate gene for a tumor vaccine. We therefore evaluated the efficacy of vaccines consisting of irradiated tumor cells transduced with the murine MCP-1 gene in the syngeneic 9L gliosarcoma brain tumor model. 9L cell lines stably expressing murine MCP-1 (9L-JE) and control cell lines expressing neomycin 3' phosphotransferase (9L-Neo) were generated by infection with a Moloney murine leukemia retroviral vector. Fisher 344 rats were immunized with intradermal injections of 5 x 10(5) or 2 x 10(6) irradiated (5000 cGy) 9L-JE, 9L-Neo, and wild-type 9L (9L-WT) cells. Two weeks later immunized and non-immunized animals were challenged with various doses of intradermal (5 x 10(6)-5 x 10(7) or intracerebral (2 x 10(4)-5 x 10(5) 9L-WT cells. Intradermal tumors grew in all non-immunized animals. No tumors grew in animals immunized with irradiated 9L-JE or 9L-Neo cells and challenged with inocula of fewer than 5 x 10(5) 9L-WT cells. With higher inocula up to 10(7) cells, tumors appeared in all the animals, but subsequently regressed in the immunized animals. Tumors in animals immunized with 9L-JE were always smaller than tumors in the other groups. In addition, only the 9L-JE vaccine protected against tumor inocula of 5 x 10(7) cells. Thus vaccination with MCP-1-expressing cells was able to protect animals against at least a 100-fold larger number of challenge tumor cells than vaccination with control cells. In contrast to studies with intradermal tumors, immunization with 9L-JE and 9L-Neo produced only minimal protection against intracerebral tumors. There was no significant difference between the 9L-JE and 9L-Neo vaccines in intracerebral challenge. This study suggests that tumor vaccines expressing cytokine genes such as MCP-1 can increase the antitumor response. However, the protective effect of these vaccines appears to be largely limited to intradermal tumors rather than intracerebral tumors.