Synergistic antitumor interaction of human monocyte chemotactant protein-1 gene transfer and modulator for tumor-infiltrating macrophages

Purpose. In order to evaluate the possibility of synergistic antitumor gene therapy by the gene delivery of monocyte chemotactant protein-1 (MCP- 1/MCAF/IE), the effect of a biological response modulater for macrophages on tumor progression of gene transfected tumor cells was studied. Methods. Cachexia-inducing adenocarcinoma cells (cell line colon 26, clone 20) were transfected with either a control plasmid or MCP-1 cDNA. Results. The production of MCP-1 reached 70-80 ng/ml in vitro when transfectant cells were cultured at a cell density of 1 x 10⁵ cells/ml for 3 days. Transfection of MCP-1 cDNA did not affect the growth rate in vitro. Also, MCP-1-transfectants formed tumors after intra-footpad inoculation similar in size to the parental cells. The number of infiltrating macrophages in the primary tumor of the transfectant rapidly increased from the 3rd to 5th day after inoculation as revealed by immunohistochemical staining using an antibody against mouse macrophages. An earlier, greater, but no longer-lasting increase in tumor- infiltrating macrophages was induced in tumors by MCP-1 transfection was compared to that induced by the parent cells. On the 10th day after the inoculation, the tumor-infiltrating macrophages in mice inoculated MCP-1 transfectants were decreased to a level similar to that of the parent cells. Groups of mice were treated intraperitoneally with LPS at different times after the inoculation. Tumor cells producing high levels of MCP-1 were significantly lysed by macrophages treated with LPS, whereas parental or control transfected cells were not. Conclusions. Combination immunotherapy can provide a rationale for the application of MCP-1 treatment to increase immunological responses to cancer.