MSCs: The need to rethink

Abstract

It has long been known that within bone marrow, a non-hematopoietic stem cell, capable of reforming a complete skeletal segment exists. Originally termed a bone marrow stromal stem cell and later renamed a "mesenchymal" stem cell ("MSC"), this cell has the capability to form cartilage, bone, hematopoiesis- supportive stroma, and marrow adipocytes. Furthermore, this cell also organizes marrow vasculature and is a component of the HSC niche, properties that make this cell inherently unique. Based on its cell surface properties (that solely represent connective tissue cells) and the use of less than stringent in vitro differentiation assays, "MSCs" have been reported to be found in virtually any connective tissue, with extensive differentiation capacities. Yet by rigorous criteria, MSCs from different tissues are not the same, are not ubiquitous, and they are not pluripotent. Considering the current interest in the use of MSCs from all types of tissues for not only tissue engineering but also in regenerative medicine (using the cells as a drug), there is an urgent need to get specific about the biology of MSCs from different tissues: What they are, where they came from, and what they can really do.