Highly Efficient Ex Vivo Expansion of Human Hematopoietic Stem Cells Using Delta1-Fc Chimeric Protein.

[Background and purposes] Ex vivo expansion of hematopoietic stem cells (HSCs) has been explored in the fields of stem cell biology, gene therapy and clinical transplantation. The use of Notch ligands or soluble IL-6 receptor combined with IL-6 has been a major technique that revealed several fold expansion of human cord blood SCID repopulating cells (SRCs). These studies, however, have been conducted in an independent manner, which hampered direct comparison and evaluation of the effect of combination of these methods. Our purpose of this study is to clarify these issues in a chemically defined serum-free medium that allows us to develop clinical usage of the culture condition. We also compared the efficiencies of SRC isolation with magnetic beads targeting CD34 and CD133.