Recruited by macrophage chemo-attractants (i.e, CCL2, MCP1, CSF-1), tumor-associated macrophages represent up to 50% of tumor-infiltrating cells, as seen in melanoma, renal cancer, and colonic carcinoma (145, 146), suggesting they may be able to efficiently infiltrate into solid tumors upon adoptive transfer. The gene discussed is CCL2; the disease is renal carcinoma.