Unité de Thérapie cellulaire et Inserm U362, Institut Gustave‐Roussy, Villejuif, France.
During the recent years, experimental data obtained in the murin system led to a drastic change in our classical concepts of adult stem cells. Until recently, these cells, in addition to their classical self‐renewal and differentiation abilities, were supposed to exhibit tissue‐specificity. This concept has been challenged by bone marrow transplantation experiments in demonstrating that not marrow cells could generate not only hematopoietic cells but also muscle cells, hepatic cells or neuronal cells in lethally irradiated recipients. Conversely, muscle cells or brain cells could generate hematopoietic cells upon transplantation. The term "plasticity" has been coined to explain this phenomenon which could be due to the persistence in adult tissues, of stem cells with multi‐differentiation ability or to the "transdifferentiation" ability of some adult cells committed to differentiation, under the influence of some environmental cues, a phenomenon which is known to occur
in vitro. The phenotype of cells at the origin of « plasticity » is currently the subject of investigations and controversies in many laboratories. If the functional nature of several types of cells generated after bone