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

Background The aim of this study was to identify circulating endothelial-progenitor cells (EPC) with colony-forming capacity and compare them with the monocytic-macrophage lineage. Methods Forty-two healthy donor 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. Results The number of EPC colonies was higher in BM than in mobilized or steady-state PB. Using EPC medium, monoeytic 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 v WE Colonies were CD4(+), CD13(+dim), CD14(+), CD 15(++), CD 16(-/-+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 ofpre-cultured and cultured monocytes was similar to that describedfor EPC. Discussion Our results suggest that the so-called 'EPC' obtained at 7 days of culture belong to the monocyte-macropbage lineage, as they share immunophenotypic and molecular features.