Overview of endothelial cell hierarchy. High proliferative potential- endothelial colony forming cells (HPP-ECFC) give rise to all other subsequent endothelial progenitor cells, can achieve greater than 100 population doublings and can form secondary and tertiary colonies upon replating. Low proliferative potential –endothelial colony forming cells (LPP-ECFC) can give rise to colonies containing more than 50 cells, whilst endothelial cell clusters give rise to colonies with fewer than 50 cells. Neither LPP-ECFC or endothelial clusters can give rise to secondary or tertiary colonies. Mature endothelial cells are terminally differentiated and have a limited proliferative potential .