Translating stem and progenitor cell biology to the clinic: Barriers and opportunities

Stem cells are the natural units of embryonic generation, and also adult re generation, of a variety of tissues. Recently, the List of tissues that use the model of differentiation from stem to progenitor to mature cell has in creased from blood to include a variety of tissues, including both central and peripheral nervous systems and skeletal muscle; it is also possible tha t all organs and tissues are derived from, and still contain, stem cells. B ecause the number and activities of stem cells and their progeny are homeos tatically regulated, clinical stem cell transplantation could greatly add t o the physician's armamentarium against degenerative diseases.