THE BIOLOGY OF HEMATOPOIETIC STEM-CELLS

Hematopoietic stem cells (HSC) are the only cells in the blood-forming tissues that can give rise to all blood cell types and that can self- renew to produce more HSC. In mouse and human, HSC represent up to 0.0 5% of cells in the bone marrow. HSC are almost entirely responsible fo r the radioprotective and short- and long-term reconstituting effects observed after bone marrow transplantation. The subsets of HSC that gi ve rise to short-term vs long-term multilineage reconstitution can be separated by phenotype, demonstrating that the fates of HSC are intrin sically determined. Here we review the ontogeny and biology of HSC, th eir expression of fate-determining genes, and the clinical importance of HSC for transplantation and gene therapy.