<em>In Vitro</em> Characterization of Circulating Endothelial Progenitor Cells Isolated from Patients with Acute Coronary Syndrome

<div><h3>Background</h3><p>The current understanding of the functional characteristics of circulating endothelial progenitor cells (EPC) is limited, especially in patients affected by cardiovascular diseases. In this study, we have analyzed the <em>in vitro</em> clonogenic capacity of circulating EPC, also known as endothelial colony-forming cells (ECFC), in patients with acute coronary syndrome (ACS), in comparison to the colony forming unit-endothelial-like cells (CFU-EC) of hematopoietic/monocytic origin.</p> <h3>Methodology/Principal Findings</h3><p>By culturing peripheral blood mononuclear cells (PBMC) of patients with ACS (n = 70), CFU-EC were frequently isolated (from 77% of ACS patients), while EPC/ECFC were obtained only in a small subset (13%) of PBMC samples, all harvested between 7–14 days after the acute cardiovascular event. Notably, <em>ex-vivo</em> generation of EPC/ECFC was correlated to a higher <em>in vitro</em> release of PDGF-AA by the corresponding ACS patient PBMC. By using specific endothelial culture media, EPC/ECFC displayed <em>in vitro</em> expansion capacity, allowing the phenotypic and functional characterization of the cells. Indeed, after expansion, EPC/ECFC exhibited a normal diploid chromosomal setting by FISH analysis and an immunophenotype characterized by: <em>i</em>) uniform positivity for the expression of CD105, CD31, CD146 and Factor VIII, <em>i</em>) variable expression of the CD34, CD106 and CD184 markers, and <em>iii</em>) negativity for CD45, CD90, CD117 and CD133. Of interest, in single-cell replanting assays EPC/ECFC exhibited clonogenic expansion capacity, forming secondary colonies characterized by variable proliferation capacities.</p> <h3>Conclusion/Significance</h3><p>Our data indicate that a careful characterization of true EPC is needed in order to design future studies in the clinical autologous setting of patients with ACS.</p>