Hypoxia improves expansion potential of human cord blood–derived hematopoietic stem cells and marrow repopulation efficiency

Abstract

In bone marrow, hematopoietic stem cells (HSCs) reside in the most hypoxic endosteum niche, whereas the proliferating progenitors are located near the relatively oxygen-rich vascular region. High oxygen tension is potentially detrimental to HSCs. The objective of this investigation was to compare cellular, functional, and molecular responses of human umbilical cord blood (UCB)-derived hematopoietic stem and progenitor cells in culture under hypoxic and normoxic conditions. CD133-enriched UCB cells were cultured in growth factor containing serum-free and serum-supplemented medium under 5% O(2) (hypoxia) or 21% O(2) (normoxia) for 10 d. The phenotypes of expanded cells were analyzed by flow cytometry and the engraftability by SCID-repopulation assay. The expression of hypoxia-inducible factor (HIF)-1α and some of its target genes was analyzed by real-time RT-PCR. In hypoxic culture, CD34(+) CD38(-) cells were expanded about 27-fold, which was significantly (P < 0.01) higher than that obtained in normoxic culture. Serum-free culture did not support the growth of cells in the presence of 21% O(2) . Myeloid colony-forming potential of cells was significantly (P < 0.05) increased in 5% O(2) compared with 21% O(2) culture. SCID-repopulation efficiency seems to be better preserved in the cells cultured under hypoxic conditions. Hypoxia significantly (P < 0.05) induced the expression of HIF-1α, vascular endothelial growth factor (VEGF), and ABCG2 genes and also upregulated CXCR4 receptor expression. Low oxygen tension enhanced the proliferation of UCB-derived HSC/progenitor cells and maintenance of SCID-repopulating cells than normoxia. These expanded cells are expected to be beneficial in the patients who lack human leukocyte antigen (HLA)-matched donors.