EPC colonies derived from human UCB. (A) Cobblestone-like clusters start to appear around 1 week after plating the mononuclear cells in a flask. Cell morphology was photographed on days 9, 11, 13, and 15 after seeding. (B-C) Adherent colonies were analyzed for the incorporation of PE-conjugated DiI-Ac-LDL (B, bright field; C, dark field). Note the strong incorporation of DiI-Ac-LDL into cells that were possibly macrophages based on their morphology (arrowheads). (D) Adherent cells were examined for the expression of CD31 and the incorporation of DiI-Ac-LDL by FACS. (E-F) CD45⁻/CD31⁺/DiI-Ac-LDL–positive cells were sorted and expanded for further experiments and these cells formed capillary tube–like structures on Matrigel. Bar indicates 50 μm.