CCL2 and colon carcinoma: 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.