Expansion, Differentiation and Transplantation of Human Endothelial Progenitor Cells Derived from Umbilical Cord Blood CD34+ Cells

Transplantation of endothelial progenitor cells (EPCs)/endothelial cells (ECs) has been developed as a cell therapy for ischemic diseases and hemophilia A, due to the capacities of these cells to repair vascular damage and produce factor VIII. The strategies and the mechanisms of this type of cell therapy have been extensively investigated in the past decades. However, given the problems associated with host immune responses to grafts in allotransplantation, the difficulties in obtaining adequate numbers of suitable cells for transplantation represent additional obstacles for a successful cell therapy. In the present study, human umbilical cord blood CD34+ mesenchymal cells (MCs), which generate low immune response, have been adopted as the source of endothelial progenitors. Our major goal is to establish a highly efficient approach to stimulate the expansion and subsequent differentiation of human endothelial progenitor cells (EPCs), in order to obtain sufficient quantities of healthy cells for therapeutic use. The CD34+ cells isolated from human umbilical cord blood were cultured for 6 days in a customized basal medium supplemented with a modified cytokine cocktail, including SCF, Flt-3L, TPO, IL-3, and GM-CSF. At the end of proliferation stage, cell number was calculated with Flow Cytometry, and cell morphology was characterized as well. The numbers of CD34+ cells and CD34+/CD133+/VEGFR-2+ early EPCs cells were found to be increased by approximately 108-fold and 41.9-fold, respectively, on day 6. In the differentiation stage, the attached cells were transferred to EGM-2 basal medium supplemented with FBS and additional nutrients, including VEGF, IGF, EGF, and FGF, for another 15 days. Following this two-step culture, the generated adherent cells were found to have proliferated more than 1200 folds over the initial EPCs, and they were identified as mature endothelial cells expressing CD31, vWF and FVIII. Furthermore, we developed a nonobese diabetic, severe combined immunodeficient (NOD/SCID) mouse model with portal sinusoidal endothelium injury. The NOD/SCID mice were treated with the produced EPCs/ECs through hepatic portal vein injection at the dose of 6x10^6 cells. Tissue examination demonstrated that GFP-labeled transplanted cells migrated and integrated into liver structure, where they expressed specific endothelial cell markers. Therefore, through our unique approach, we can provide an excellent source of healthy endothelial progenitors for cell therapy.