Stem cell-based therapies, in which the body's own cells are stimulated to contribute to the repair process, are enormously promising in all areas of medicine, including articular cartilage regeneration. Yet our understanding of stem cells continues to evolve. Many thought, and some advertise, that stem cells alone are able to make new cartilage and cure arthritis. However, the scientist who popularized the theory that bone marrow stem cells are the precursors to all tissues, now points to a new understanding of how stem cells work.
Stem cells live on the walls of blood vessels. The more vessels, the more cells, so fat has the most. Bone marrow is also an excellent source. At the time of an injury to a joint or an insult to the body, such as an infection, the cells are called into action. They migrate to the site of injury, and release growth factors, antibiotics and other proteins necessary for repair.
The cells are so powerful that the drugs they release kill most invading bacteria long before the host feels a reaction. Examples of these antibiotic-like proteins are called “defensins” which live in your mouth, and protect you from all the nasty bugs that your hands contaminate your food with, and from your dog's unexpected mouth-to-mouth kiss.
When bones break, or ligaments tear, the stem cells release anabolic factors that kick off the healing response. They stay around or recruit their friends to release other factors sequentially in the healing process; one factor is specific to taking away the broken fragments and another at rebuilding the tissue. The stem cells are the general contractors, calling in the subs, the plumbers and painters at just the right time.
Which brings us to the headline: “Stem cells alone do not make cartilage.” Cartilage needs different expertise at different times. The contractor cells are called chondrocytes and fibrochondrocytes. These cells produce the collagen and matrices that surround the cells. So while stem cells are crucial to the repair of injured joints, it is only when they are applied in concert with a range of healing stimuli that they effectively solve problems.
In orthopedics, while injecting stem cells often helps, just injecting cells simply isn't enough to fix the problems. The field of biologic joint repair is evolving daily, now focusing on ways to combine the critical cells of each type of tissue with the stimulating activity of growth factors and stem cells. It is this coordination that is most likely to produce the cures for tissue injury and arthritis that we so urgently need.
Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco. He pioneers advanced orthopedic surgical and rehabilitation techniques to repair, regenerate and replace damaged cartilage and ligaments.