Human Cord Blood-Derived AC133+ Progenitor Cells Preserve Endothelial Progenitor Characteristics after Long Term In Vitro Expansion

Abstract

BackgroundStem cells/progenitors are central to the development of cell therapy approaches for vascular ischemic diseases. The crucial step in rescuing tissues from ischemia is improvement of vascularization that can be achieved by promoting neovascularization. Endothelial progenitor cells (EPCs) are the best candidates for developing such an approach due to their ability to self-renew, circulate and differentiate into mature endothelial cells (ECs). Studies showed that intravenously administered progenitors isolated from bone marrow, peripheral or cord blood home to ischemic sites. However, the successful clinical application of such transplantation therapy is limited by low quantities of EPCs that can be generated from patients. Hence, the ability to amplify the numbers of autologous EPCs by long term in vitro expansion while preserving their angiogenic potential is critically important for developing EPC based therapies. Therefore, the objective of this study was to evaluate the capacity of cord blood (CB)-derived AC133+ cells to differentiate, in vitro, towards functional, mature endothelial cells (ECs) after long term in vitro expansion.MethodologyWe systematically characterized the properties of CB AC133+ cells over the 30 days of in vitro expansion. During 30 days of culturing, CB AC133+ cells exhibited significant growth potential that was manifested as 148-fold increase in cell numbers. Flow cytometry and immunocytochemistry demonstrated that CB AC133+ cells' expression of endothelial progenitor markers was not affected by long term in vitro culturing. After culturing under EC differentiation conditions, cells exhibited high expression of mature ECs markers, such as CD31, VEGFR-2 and von Willebrand factor, as well as the morphological changes indicative of differentiation towards mature ECs. In addition, throughout the 30 day culture cells preserved their functional capacity that was demonstrated by high uptake of DiI fluorescently conjugated-acetylated-low density lipoprotein (DiI-Ac-LDL), in vitro and in vivo migration towards chemotactic stimuli and in vitro tube formation.ConclusionsThese studies demonstrate that primary CB AC133+ culture contained mainly EPCs and that long term in vitro conditions facilitated the maintenance of these cells in the state of commitment towards endothelial lineage.

Development of Serum-Free Quality and Quantity Control Culture of Colony-Forming Endothelial Progenitor Cell for Vasculogenesis

“…These reports suggest that poor responses to cellular therapy are due to quantitative and/or qualitative impairment of the EPC fraction. To further augment the efficacy of EPC transplantation, several methodological approaches to enhance EPC bioactivities are currently being developed [5,[23][24][25][26][27][28].…”

“…In this regard, the several culture systems of suspended EPC phenotype have been developed and demonstrated the significance of EPC expansions ex vivo and the efficiency of cultured CD34 ϩ or CD133 ϩ cell transplant for neovascularization in ischemic animal models [5,[23][24][25][26][27][28].…”

Regulation of EPCs: The Gateway to Blood Vessel Formation

“…Finally, more primitive nonadherent EPC populations have also been described [12,35]. A detailed description of these cells is provided below.…”

“…We and others have isolated a nonadherent EPC population from the CD133 + MNC population of UCB and PB [12,35]. We have described a population of nonadherent EPCs termed nonadherent endothelial forming cells (naEFCs [12]).…”

“…+ MNCs in serum-free defined nonadherent culture conditions and then transferred the progenitors into endothelial culture conditions [35,51]. These naEFCs and CD133 + EPCs express CD31 and VEGFR2 in addition to being able to take up Ac-LDL and bind UEA-1 lectin and contribute to in vitro tube formation with ECs [12,35].…”