An SDF-1 trap for myeloid cells stimulates angiogenesis.

In this issue of Cell, Grunewald et al. (2005) examine the role of hematopoietic cells in the formation of new blood vessels. They show that organ-specific expression of vascular endothelial growth factor (VEGF) is sufficient to mobilize and recruit hematopoietic cells from the bone marrow to the blood, but retention of the proangiogenic subpopulation of hematopoietic cells in peripheral organs requires an additional factor, stromal-derived factor 1 (SDF-1).