CCR2 and neoplasm: Hence, the current study uses an adoptive transfer system in which BM CX3CR1+ cells (cx3cr1gfp) from CCR2+ mice harboring a targeted replacement of the CX3CR1gene by an enhanced green fluorescent protein (EGFP) reporter gene together with the CD45.1 are transferred into control CCR2−/− mice, to show that these cells, which are approximately 7% of BM CD11b+ cells, are not only essential for direct support of the tumor, but also obligatory for the recruitment of other BMD CD11b+ cells to support tumor development and angiogenesis.