A population of spindle shaped plastic-adherent cells, with multiple differentiation into a number of different mesodermal tissues in vitro were first described by Friedenstein in 1966, and were named mesenchymal stem cells (MSCs) by Caplan in 1991. Although it becomes the most global usage description, it still remains debate whether MSCs are truly stem cells due to the progress achieved on the biology of MSCs.The present data show that the therapeutic effects of MSCs were as sporting cells secreting bioactive factors, which stimulate patient's own tissue-specific resident stem cells to regenerate new tissues rather than as stem cells differentiation to new tissues in vivo. Unfortunately,the stem ness of MSCs was much exaggerated by some researchers, which caused the patients with unrealistic expectations that exogenously supplied MSCs would differentiate into regenerating tissue-producing cells. So some researchers argued that the MSC should be renamed to Mesenchymal stromal cells or medicinal signaling cells. In this article, we will summarize the developmental definition and origin of MSCs, and discuss how to use the term MSCs more correctively.

Mesenchymal stem cells; Mesenchymal stromal cells; Medicinal signal cells; Pericytes