Differentiation of cord blood–derived CD34⁺ cells into endothelial cells. (A) Phase contrast photomicrograph of cord blood CD34⁺ cells at 7 and 21 days of culture. At 7 days, the formation of small colonies of adherent cells (arrow) is observed, and by 21 days a confluent endothelial-like monolayer has formed. (B) Western blotting of cell lysates (5 μg total protein/lane) from cord blood CD34⁺ cells at 7 and 21 days of culture probed with anti–PECAM-1, VE-cadherin, Tie-1, Tie-2, VWF antibodies, and the appropriate control species IgGs.