MSCs have many fascinating properties, including strong immunomodulatory effects, the ability to repair damaged tissues, and the capacity in vitro to differentiate into other cells types. These traits, combined with their easy availability from different sources, has prompted researchers to look at MSCs as promising raw materials for use in cell therapy, gene therapy, and tissue engineering, the three pillars of regenerative medicine. The cumulative efforts of scientists, researchers and life science companies have resulted in the development of 10 MSC-based approved therapeutics and 19 MSC-based approved bone matrices.
A new and exciting era is expected for MSCs as they get integrated into regenerative medicine technologies. In particular, there is the potential for the clinical translation of emerging technologies (such as the bioengineering of MSCs to perform specific functions), using MSC-derived exosomes instead of whole MSCs, and expanding the use of MSCs by utilizing them in large numbers within nascent industries, such as the clean meat industry.
MSCs were identified for the first time by Alexander Friedenstein as colony forming unit fibroblasts (CFU-F) and osteogenic stem cells. Since then, a number of names have been coined to denote mesenchymal stem cells (MSCs), including “stromal stem cells,” which was proposed in 1988 by Maureen Owen, Ph.D. In 1991, Arnold Caplan, Ph.D. coined the term “mesenchymal stem cells” to emphasize the self-renewal property and differentiation potential of the cells.
Later, this name was challenged by James Dennis, Ph.D. and colleagues who suggested that the cells behave like progenitors rather than stem cells. They proposed the term “mesenchymal progenitor cells.” In 2000, Paolo Bianco, M.D. and Pamela Gehron Robey, Ph.D. proposed the name “skeletal stem cell” to emphasize the fact that the cells give rise to components of the skeletal system.
Later, the term “multipotent adult progenitor cells” was coined by Yuehua Jiang, M.D. and colleagues. In 2010, Arnold Caplan, Ph.D. modified his earlier stand and suggested that the acronym MSC stand for “medicinal signaling cells.” Over time, the scientific community has come to a relatively uniform agreement that the term “MSC” is an acceptable way to name these cells. This acronym satisfies the strong and vocal community that has emerged to advocate against the use of term “stem cell” to identify MSCs, when they do not behave as such.
MSCs can be isolated from a diverse range of tissues. Originally, Friedenstein, et al. isolated MSCs from the bone marrow (BM) and stroma of the spleen and thymus. MSCs have since been derived from tissues as varied as the brain, spleen, liver, kidney, lung, bone marrow, muscle, thymus, and pancreas. However, bone marrow aspirates are still considered to be the most convenient and enriched source of MSCs.
Fetal tissue also contains MSCs, with common sources including umbilical cord blood and fetal placenta. These sources may represent ontogenetically younger MSCs. Evidence exists that MSCs from fetal sources can undergo more cell divisions before they reach senescence than MSCs from adult tissue. Variations at the genetic level have also been well documented for MSCs from different sources, as have differences in the types of chemokines and cytokines the cells produce.