SummaryA significant number of hematopoietic stem/progenitor cells (HSPC) in human umbilical cord blood could serve as a reservoir for the placental vasculature, yet, their morphological and functional features are not completely understood. Here, we describe the characterization of purified CD133+ progenitor cells from umbilical cord blood, a subset of CD34+ hematopoietic progenitors that were grown in proliferation medium containing Flt3-ligand, thrombopoietin and stem cell factor. Following isolation and enrichment of the CD133+ cells by immunomagnetic cell sorting, they remained non-adherent for up to 40 days in culture and expressed different pluripotency markers including Sox-1, Sox-2, FGF-4, Rex-1 and Oct-4. Oct-4 expression was confirmed by laser-assisted single cell picking with subsequent quantitative real-time RT-PCR.The expression of Oct-4 indicates a pluripotent phenotype of CD133+ cells and appears to be of functional relevance: After three weeks in endothelial differentiation medium, suspended cells became adherent, developed an endothelial cell-like morphology, bound fluoresceine isothiocyanate-labeled Ulex europaeus agglutinin-1, took up acetylated Di-LDL, and expressed other endothelial markers such as PECAM-1 or VEGFR-2. Concomitantly, Oct-4 expression was significantly reduced. Moreover, following treatment with retinoic acid, CD133+ cells exhibited neural morphology associated with the expression of β-III-tubulin. CD133+ cells were found to express the luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor, detected by RT-PCR and immunocytochemistry. The recombinant human chorionic gonadotropin induced proliferation of the CD133+ cells in a dose-specific manner. Our results indicate that CD133+ HSPC from umbilical cord blood may have a greater differentiation potential than previously recognized and give rise to proliferative endothelial cells participating in placental vasculogenesis.