Summary

A significant number of hematopoietic stem/progenitor cells(HSPC) in human umbilical cord blood could serve as a reservoirfor the placental vasculature, yet, their morphological andfunctional features are not completely understood. Here, wedescribe the characterization of purified CD133⁺ progenitorcells from umbilical cord blood, a subset of CD34⁺ hematopoieticprogenitors that were grown in proliferation mediumcontaining Flt3-ligand, thrombopoietin and stem cell factor.Following isolation and enrichment of the CD133⁺ cells byimmunomagnetic cell sorting, they remained non-adherent forup to 40 days in culture and expressed different pluripotencymarkers including Sox-1, Sox-2, FGF-4, Rex-1 and Oct-4.Oct-4expression was confirmed by laser-assisted single cell pickingwith subsequent quantitative real-time RT-PCR.The expressionof Oct-4 indicates a pluripotent phenotype of CD133⁺ cells andappears to be of functional relevance: After three weeks inendothelial differentiation medium, suspended cells became adherent, developed an endothelial cell-like morphology, boundfluoresceine isothiocyanate-labeled Ulex europaeus agglutinin-1,took up acetylated Di-LDL, and expressed other endothelialmarkers such as PECAM-1 or VEGFR-2. Concomitantly, Oct-4expression was significantly reduced. Moreover, following treatmentwith retinoic acid, CD133⁺ cells exhibited neuralmorphology 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 recombinanthuman chorionic gonadotropin induced proliferation ofthe CD133⁺ cells in a dose-specific manner.Our results indicatethat CD133⁺ HSPC from umbilical cord blood may have agreater differentiation potential than previously recognized andgive rise to proliferative endothelial cells participating in placentalvasculogenesis.