Stem cells have varying degrees of differentiation potential. The fertilized oocyte or zygote has the ability to form all tissues, both the embryo itself and placental tissue. Embryonic stem cells are considered pluripotent because they can differentiate into almost any type of cell from any of the 3 germ layers. Another few steps down the developmental hierarchy are stromal cells, which are multipotent. These cells are found throughout the body in various tissues, including bone marrow, adipose tissue, muscle, liver, brain, umbilical cord blood, peripheral blood, and pancreas. They are capable of differentiating into various tissues such as cartilage, muscle, and neuronal cells. Stromal cells have immune privilege and thus have many potential applications for tissue engineering and regenerative medicine. Adult stromal cells are currently being investigated for treatment of tendon and ligament injuries in several animal models as well as osteoarthritis in dogs. Stromal cell technology has significant potential for future impact on how tissue is repaired or restored following injury or disease. Regenerative medicine—which centers on the use of stem cells to repair, replace, or regenerate cells, tissues, and organs—is a rapidly growing science. Many current treatments may be augmented or supplanted by regenerative medicine.

Commentary: This timely review article outlines the true state of the art of stem cell research and its potential application to a variety of medical conditions. It also outlines the studies required to establish efficacy for this potentially exciting new avenue of treatment. Stem cell research may be an example of marketing getting ahead of science. This article helps to refocus us on where we currently stand in the evolution of this promising technology.—David F. Senior, BVSc, Diplomate ACVIM & ECVIM

Mesenchymal stromal cells: Past, present, and future. Spencer ND, Gimble JM, Lopez MJ. VET SURG 40:129-139, 2011.