Effect of in vitro expansion of EPCs on in vivo vasculogenesis. Matrigel implants containing cbEPCs and HSVSMCs (4:1 ratio) were evaluated after one week. (A-C) H&E staining of Matrigel implants (× 400) containing cbEPCs at passages 3 (A), 6 (B), and 12 (C). HDMECs implants (with HSVSMCs; 4:1 ratio) were used as control for mature ECs (D; × 400). All images are representative of implants harvested from 4 different animals (scale bar represents 50 μm). (E) Microvessel density in Matrigel implants was quantified by counting lumenal structures containing red blood cells. Each bar represents the mean microvessel density value determined from 4 separated implants and animals ± SD. *P < .05 compared with HDMEC. †P < .05 compared with cbEPC-P3. ‡P < .05 compared with cbEPC-P6.