Expression of VEGFR-2 on CD34⁺ cells from different hematopoietic sources identifies a small subpopulation of circulating endothelial cells.

Viable CD34⁺ cells, as shown by the typical fluorscence in forward and side scatter (A), were isolated from cytokine-mobilized PB (C), CB (D), and FL (E). Subsequently, the number of CD34⁺VEGFR-2⁺ cells was analyzed by 2-color flow cytometry using a combination of FITC-labeled MoAbs to the extracellular domain of VEGFR-2 (clones 4.13 and 6.64) and PE-labeled MoAb directed to CD34. X-axis represents log fluorescence intensity. Percentage of positive cells was compared to isotype control (B).