Can we distinguish circulating endothelial progenitor cells?

by Alexey Bersenev on June 1, 2012 · 0 comments

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Endothelial progenitor cells (EPCs) is a promising therapeutic cell population and disease prognostic marker. Detection of true EPCs in the blood is not easy task. There are serious controversies in the field, based on difference in EPCs identification by flow cytometry and functional assays:

A recent review of the controversies in EPC definition determined that some of the clinical trials published in 2010 claiming to quantify EPCs actually quantified hematopoietic stem cells. In addition to the lack of clear flow cytometric definition, the necessary functional assays to verify a cell type’s true identity are often lacking, but they are imperative for full characterization and mechanistic determination of how these cells function in vessel formation in vivo.

A new study can solve some mystery surrounding circulating EPCs. From the editorial:

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…

Applying an improved polychromatic flow cytometry technique and functional colony assay, Mund et al. were able to distinguish circulating true EPCs from mature endothelial cells:

As expected, EPCs are found to express CD34 as well as the endothelial cell markers CD105, CD145, and CD146 but lack CD45 (found on leukocytes) and AC133 (found on hematopoietic progenitor cells and often in the past used to [mis]identify EPCs). Disappointingly, this “final” population contains both the EPCs as well as mature circulating endothelial cells (CECs).

What prior studies were detecting as CD133+ actually extracellular microvesicles:

Mund and coworkers show that some cell populations that contain EPCs by positive markers are contaminated by erythrocytes and monocytes as well as by anucleated, subcellular microparticles derived from endothelial cells or platelets. One must actively gate out these false signals by positive staining for erythrocyte or monocyte markers instead of relying on light scattering as well as by using positive nDNA staining with DAPI, a feature lacking in microparticles.

Editorial commentary concludes:

… it will be necessary to re-examine past conclusions about EPC frequencies in the circulation in different patient populations as almost all of the literature in the past 15 years has misidentified the cells that have been enumerated. (The same may be true for CECs.)

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