Identification of Endothelial Cells and Their Progenitors.

Blood vessel formation is a key feature in physiologic and pathologic processes. Once considered a homogeneous cell population that functions as a passive physical barrier between blood and tissue, endothelial cells (ECs) are now recognized to be quite "heterogeneous." While numerous attempts to enhance endothelial repair and replacement have been attempted using so called "endothelial progenitor cells" it is now clear that a better understanding of the origin, location, and activation of stem and progenitor cells of the resident vascular endothelium is required before attempting exogenous cell therapy approaches. This chapter provides an overview for performance of single-cell clonogenic studies of human umbilical cord blood circulating endothelial colony-forming cells (ECFC) that represent distinct precursors for the endothelial lineage with vessel forming potential.