Differentiation of CD34⁺ hematopoietic cells to endothelial cells. (a) Adherent endothelial colonies formed after 15 to 20 days in culture incubation with VEGF/IGF/bFGF (original magnification × 400). (b) Formation of endothelial monolayer after continuous incubation with VEGF (original magnification × 600). (c) Endothelial monolayers incorporating acetylated LDL (original magnification × 600). (d) CD34⁺ differentiated cells that stained positively for vWF antigen (original magnification × 600). (e) CD34-selected cells expressing Flk-1 mRNA. BMEC, bone marrow endothelial cells; BM, bone marrow; CB, cord blood; PB, peripheral blood; FL, fetal liver; HUVEC, human umbilical vein endothelial cells.