Short-term endothelial progenitor cell colonies are composed of monocytes and do not acquire endothelial markers

BackgroundThe aim of this study was to identify circulating endothelial progenitor cells (EPC) with colony-forming capacity and compare them with the monocytic–macrophage lineage.MethodsForty-two healthy donors were analyzed. EPC were cultured with VEGF and b-FGF. Sequential studies were performed on days +7 (colonies) +21 and +35. Monocytic cells were cultured using the same conditions as EPC until day +21 or alternatively by adding IGF.ResultsThe number of EPC colonies was higher in BM than in mobilized or steady-state PB. Using EPC medium, monocytic cells formed cord-like structures but no colonies. However, colonies grew when IGF was added to the medium. By immunocytochemistry, colonies showed CD45, CD31 and lysozyme but no vWF. Colonies were CD4+, CD13+dim, CD14+, CD15++, CD16-/+dim, CD31+dim, CD33+dim, CD45+, CD105-/+dim, lysozyme+ and VE-cadherin+, and constantly negative for CD34, CD133 and KDR, when flow cytometry was used. The immunophenotype of pre-cultured and cultured monocytes was similar to that described for EPC.DiscussionOur results suggest that the so-called ‘EPC’ obtained at 7 days of culture belong to the monocyte–macrophage lineage, as they share immunophenotypic and molecular features.