The alleged plasticity of adult stem cells. Hemopoietic stem cells (HSCs), which are well known for their ability to give rise to all blood cells, have now been reported to give rise to cells derived from the 3 embryonic germ layers. The question mark relates to the opposing reports related to this issue. Whereas mesenchymal stem cells (MSCs) were first shown to give rise to mesodermal derivatives only, one subtype of these adult stem cells—multipotential adult progenitor cells (MAPCs)—apparently differentiate into a wide range of cell types of all germ layers.