Just the FACS or Stalking the Elusive Circulating Endothelial Progenitor Cell

In 1997, Asahara, Isner, and colleagues startled the vascular biology community by reporting that progenitor cells capable of differentiating into vascular endothelium are present in the circulation of adults and that these cells may contribute to the formation of new blood vessels at sites of injury.1 These findings challenged the then-established view that although endothelial progenitor cells (EPCs or angioblasts) contribute to de novo vessel formation (vasculogenesis) in the embryo, new blood vessels in the adult can only arise by outgrowth of mature endothelial cells from existing blood vessels (angiogenesis). In this new paradigm, it was proposed that EPCs develop and reside in the bone marrow until various forms of tissue injury or stress lead to their release into the circulation (where they could be isolated and enumerated) and then recruitment into sites of repair.2 A veritable cottage industry ensued correlating the frequency of circulating EPCs with the activity of different diseases. PubMed lists over 1800 publications describing circulating EPCs in the 15 years since the initial Asahara et al report and over 500 of these use flow cytometry (often referred to as FACS or fluorescence activated cell sorting …