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 0.05% of cells in the bone marrow. HSC are almost entirely responsible for the radioprotective and short- and long-term reconstituting effects observed after bone marrow transplantation. The subsets of HSC that give rise to short-term vs long-term multilineage reconstitution can be separated by phenotype, demonstrating that the fates of HSC are intrinsically determined. Here we review the ontogeny and biology of HSC, their expression of fate-determining genes, and the clinical importance of HSC for transplantation and gene therapy.