Endothelial progenitor cells - hype or hope?

The discovery of endothelial progenitor cells (EPC) radically altered our views of adult tissue angiogenesis, indicating the contribution of circulating bone marrow-derived cells to new blood vessel formation, rather than migration and replication of local endothelial cells. This opened up the prospect of new ways to repair damaged tissues, using EPC to encourage neoangiogenesis or the re-endothelialization of larger vessels. Within less than 5 years from the description of EPC and the inception of experimental studies, human studies were started with the aim of using autologous bone marrow-derived EPC to enhance tissue function after ischemic vascular injury, particularly after myocardial infarction (MI). However, the clinical studies have shown at best modestly encouraging results. Moreover, subsequent investigation has made it clear that these EPC are not true endothelial progenitors, although they are likely to play a role in angiogenesis by virtue of the release of paracrine angiogenic factors. This review summarizes knowledge of EPC and our current understanding of their function, together with what is known of the properties of genuine endothelial progenitor cells and how they will be used in the future to design more effective means of therapeutic angiogenesis.