Fig. 1.

A: phase-contrast and fluorescent images of a cord blood-derived “late” endothelial progenitor cell (EPC) colony. Endothelial cells derived from the long-term culture of mononuclear cells (at least 2–4 wk) can form highly proliferative colonies derived from single circulating endothelial cells. Left: phase-contrast image of an EPC colony derived from umbilical cord blood mononuclear cells. Right: confocal microscopy image of an endothelial colony stained with the endothelial surface stain Ulex europaeus lectin (green = fluorescein isothiocyanate label), the nucleus stain 4′,6-diamidino-2-phenylindole (blue) as well as uptake of acetylated low density lipoprotein (red = DiI label). B and C: flow cytometry phenotyping of EPCs using the endothelial surface marker CD31 [platelet endothelial cell adhesion molecule (PECAM)] and the myeloid surface marker CD45. Late EPCs (or colony-forming EPCs) derived from the long-term culture (at least 3–4 wk) of circulating mononuclear cells from adult blood and umbilical cord blood are positive for the endothelial marker CD31 (PECAM) but not for the myeloid marker CD45 while “early” EPCs [or cultured carcinogenic cells (CACs)] derived from the short-term culture (4 days) of adult mononuclear cells also express the myeloid marker CD45. The negative isotype control antibody staining is shown in gray.