CD34⁺FGFR⁺ cells give rise to endothelial cells in culture.

CD34⁺FGFR⁺ cells grow in small groups (A), beadlike strings (B), or clusters (C) of small round cells, similar in size to freshly isolated cells (D). Cultured cells treated with rabbit antihuman VWF IgG and secondary goat antirabbit FITC IgG show expression of VWF (E), whereas those treated with control IgG in place of antibodies to VWF do not stain (F). To ensure the specificity of VWF staining, HUVECs and K562 cells were used as positive and negative controls, respectively. HUVECs display positive staining with VWF IgG (G) and no staining with control IgG (H), whereas no expression of VWF (I) is observed in K562 cells (J). Cultured CD34⁺FGFR⁺ cells that express VWF (K) also incorporate DiI-ac-LDL (L). Freshly isolated CD34⁺FGFR⁺ cells neither express VWF (M, shaded histogram) nor incorporate ac-LDL (N, shaded histogram). Open histograms represent control histograms, ie, cells incubated in the absence of antibodies to VWF (M) or in the absence of DiI-ac-LDL (N). CD34⁺FGFR⁺ (O,P) and CD34⁺FGFR⁻ (Q,R) cells were cultured on OP9 feeder layers in the presence of FGF-2 and VEGF. Wells seeded with CD34⁺FGFR⁺ cells contained substantial numbers of adherent VE-cadherin–expressing cells (P), whereas cells in wells containing CD34⁺FGFR⁻ cells lacked expression of VE-cadherin (R). Phase contrast microscopy of the same fields is shown in O and Q. Scale bars = 20 μm for panels A-L and O-R.