The transplantation of unmanipulated cord blood (CB) cells has two major disadvantages: (a) the low number of hematopoietic stem and progenitor cells (colony-forming cells [CFCs]) in each harvest limits its application to children, and (b) there is a long period (30 days) of post-transplantation cytopenia [1]. Simultaneous ex vivo amplification of the CFCs and primitive stem cells could resolve both problems. Extensive ex-pansion of nonobese diabetic/severe combined immuno-deficiency (NOD/SCID) mice-repopulating cells (SRCs) in long-term (4-to 12-week) cultures [2] is not suitable for clinical application for several reasons. On the other hand, short-term (7-to 10-day) ex vivo amplification of CFCs usually leads to loss of primitive stem cells that impairs the long-term engraftment capacity of expanded cells in animals and humans [3][4][5][6] AbstractIn the present work, we tested the hypothesis that liquid cultures (LCs) of cord blood CD34 + cells at an appropriate low O 2 concentration could simultaneously allow colony-forming cell (CFC) expansion and nonobese diabetic/severe combined immunodeficiency mice-repopulating cell (SRC) maintenance. We first found that 3% was the minimal O 2 concentration, still allowing the same rate of CFC expansion as at 20% O 2 . We report here that 7-day LCs of cord blood CD34 + cells at 3% O 2 maintain SRC better than at 20% O 2 and allow a similar amplification of CFCs (35-to 50-fold) without modifying the CD34 + cell proliferation. Their phenotypic profile (antigens: HLA-DR, CD117, CD33, CD13, CD11b, CD14, CD15, and CD38) was not modified, with exception of CD133, whose expression was lower at 3% O 2 . These results suggest that low O 2 concentrations similar to those found in bone marrow participates in the regulation of hematopoiesis by favoring stem cell-renewing divisions. This expansion method that avoids stem cell exhaustion could be of paramount interest in hematopoietic transplantation by allowing the use of small-size grafts in adults. Stem Cells 2004;22:716-724

STEM CELLS 2006;24: 65-73

Maco Biotech HP 01 medium is suitable for clinical-scale expansion of CD 34+ cells with the SCF, G-CSF, and MGDF cytokine cocktail, permitting an intensive amplification of CFCs and maintenance of SRCs.