ABSTRACT
Cells capable of both differentiation and perpetual self-renewal are termed stem cells. Some adult tissues have relatively rapid tissue turnover that mandates a dynamic stem cell compartment. Circulating blood cells have a limited half-life and are continually regenerated from pleuripotent hematopoietic stem cells (HSCs). While the exact phenotype of HSCs is unknown, subpopulations expressing the surface membrane antigen CD34 are pleuripotent stem cells capable of reconstituting life-long hematopoiesis following marrow ablative lethal irradiation.[1]
Although HSCs are primarily located in the axial bone marrow, low numbers of HSCs are found in the peripheral vascular circulation during steady state. The numbers of HSCs in the circulation can be increased after recovery from moderate-intensity chemotherapy or with the administration of hematopoietic growth factors (HGFs) such as granulocytecolony stimulating factor (G-CSF). These mobilized HSCs and partially committed progenitor cells may be easily collected from the circulation by apheresis and cryopreserved for later use. Hundreds of millions of CD34+ cells may be easily and repetitively collected from a patient. Currently, so other adult stem cells (e.g. neural stem cells) are so readily accessible and available in such large numbers.
