Versatile stem cells, young and old. A review

Both embryonic and somatic stem cells have been studied in recent years wit h particular regard to their differentiation potential. In vitro studies al low a considerable amplification of such cells in culture as well as the in duction of commitment in different directions under proper stimulating fact ors. Moreover, a surprising versatility has been discovered, which makes po ssible a `reprogramming' of stem cells into a lineage pathway which may be completely different from the expected direction: for instance, a productio n of brain cells from blood progenitors has been obtained. It is thus possi ble to envisage methods of producing in culture sufficient amounts of stem cells, committed to a certain pathway, which can be transplanted in vivo to replace damaged tissues and organs.