Here, we demonstrate a significant ex vivo expansion of human hematopoietic stem cells capable of repopulating in NOD/SCID mice. Using a combination of stem cell factor (SCF), Flk2/Flt3 ligand (FL), thrombopoietin (TPO), and a complex of IL-6 and soluble IL-6 receptor (IL-6/sIL-6R), we cultured cord blood CD34+ cells for 7 days and transplanted these cells into NOD/SCID mice. Bone marrow engraftment was judged successful when recipient animals contained measurable numbers of human CD45+ cells 10–12 weeks after transplantation. When cells were cultured with SCF+FL+TPO+IL-6/sIL-6R, 13 of 16 recipients were successfully engrafted, and CD45+ cells represented 11.5% of bone marrow cells in engrafted recipients. Cells cultured with a subset of these factors were less efficiently engrafted, both as measured by frequency of successful transplantations and prevalence of CD45+ cells. In animals receiving cells cultured with all 4 factors, human CD45+ cells represented various lineages, including a large number of CD34+ cells. The proportion of CD45+ cells in recipient marrow was 10 times higher in animals receiving these cultured cells than in those receiving comparable numbers of fresh CD34+ cells, and the expansion rate was estimated at 4.2-fold by a limiting dilution method. Addition of IL-3 to the cytokine combination abrogated the repopulating ability of the expanded cells. The present study may provide a novel culture method for the expansion of human transplantable hematopoietic stem cells suitable for clinical applications.
Takahiro Ueda, Kohichiro Tsuji, Hiroshi Yoshino, Yasuhiro Ebihara, Hiroshi Yagasaki, Hiroaki Hisakawa, Tetsuo Mitsui, Atsushi Manabe, Ryuhei Tanaka, Kimio Kobayashi, Mamoru Ito, Kiyoshi Yasukawa, Tatsutoshi Nakahata