Monocyte chemoattractant protein-1 stimulates tumor necrosis and recruitment of macrophages into tumors in tumor-bearing nude mice: increased granulocyte and macrophage progenitors in murine bone marrow.

Monocyte chemoattractant protein-1 (MCP-1) belongs to the newly recognized "chemokine" superfamily of activation-inducible cytokines. We report here that MCP-1 gene-transferred mouse myeloma cells modulate tumor necrosis in myeloma-bearing nude mice. We established an MCP-1-producing myeloma cell line (X63-MCP-1) by transfection with human MCP-1 cDNA as well as interleukin-8-producing X63 cells (X63 IL-8). Each cell line showed the same growth characteristics in vitro, and 1 x 10(7) cells per mouse were injected into the peritoneal cavity resulting in the formation of tumors. Hematologic studies, including peripheral white blood cell counts and differentiation, showed no differences among the groups. They formed tumors in the same manner, which we observed from weeks 2.5 to 9. MCP-1 mice showed more tumor necrosis and infiltration of the macrophages into the tissue surrounding the tumor. In situ hybridization, using a partial cDNA as a probe, showed that macrophages contained MCP-1 mRNA. Bone marrow cell colony-forming assay showed a greater number of both granulocyte and macrophage colonies in MCP-1 mouse femur than in those of controls or interleukin-8 mice. MCP-1 has no direct stimulatory activity on stem cells, but longer exposure to MCP-1 in vivo might stimulate both granulocyte and macrophage progenitors and recruitment of macrophages into tumors, and it might explain the antitumor activity of macrophages in tumor-bearing nude mice.