Ex Vivo Expansion of Human Hematopoietic Stem Cells
Recent progress of embryology has provided significant insight into hematopoietic stem cell biology. There has been great interest in the ex vivo expansion of human hemopoietic stem/progenitor cells for a variety of clinical applications. I present a novel approach using soluble interleukin-6 receptor (sIL-6R) for ex vivo expansion of human hemopoietic stem/progenitor cells. Our FACS analysis revealed that most immature progenitor cells such as CFU-Mix and LTCIC were included in the CD34+gp130+IL-6R− population, suggesting that sIL-6R/IL-6 but not IL-6 may be potent for the ex vivo expansion of immature human progenitor cells. sIL-6R/IL-6 dramatically stimulated expansion of various progenitors including CFU-GEMM and CFU-Blast as well as CD34+ cells in the presence of stem cell factor (SCF) or flt3/flk-2 ligand (FL). A combination of sIL-6R/IL-6 and SCF expanded CFU-Mix approximately 68 fold in serum-free culture by day 14. More than 100-fold expansion of total and multipotential progenitors was obtained from CD34+IL-6R− cells but not from CD34+IL-6R+ cells in culture with sIL-6/IL6/SCF. Addition of thrombopoietin (TPO) to culture with sIL-6R/IL-6/SCF or sIL-6/IL-6/FL significantly enhanced the expansion of immature progenitor cells. These findings suggest that gp130 in combination with Kit or flk-2/flt3 signalings may be potent for ex vivo expansion of human hematopoietic stem/progenitor cells.