Figure 1: Stem cell developmental potential. Stem cells (SCs) are typically classified according to developmental potential, with pluripotent embryonic SCs (ESCs) possessing the greatest capacity for differentiation. Multipotent tissuecommitted SCs are restricted to producing cell types of the tissue from which the SCs are derived. A long-held belief of the process of SC commitment is that it proceeds unidirectionally from left to right, with decreasing potential and increasing lineage commitment. More recently, the extent of lineage commitment of tissue SCs has been challenged by findings of transdifferentiation of cells from one lineage to a different lineage under certain circumstances, giving rise to the concept of adult SC plasticity. BM, bone marrow.