Mesenchymal stem cells: Revisiting history, concepts, and assays

The concept of mesenchymal stem cells has gained wide popularity. Despite the rapid growth of the field, uncertainties remain with respect to the defining characteristics of these cells, including their potency and self-renewal. These uncertainties are reflected in a growing tendency to question the very use of the term. This commentary revisits the experimental origin of the concept of the population(s) referred to as mesenchymal stem cells and the experimental framework required to assess their sternness and function.