Stem cell therapy is another exciting regenerative therapy available at Atlantic Equine Services. Research into stem cell therapy is currently on-going and will guide our application of this technology in equine sports medicine over time.
A stem cell is an early progenitor cell that retains its ability to differentiate into multiple different cell types as it replicates and divides. Embryonic stem cells are the most primitive types of stem cells. They can divide into any type of cell in the body as the organism grows from a single-celled zygote into a fully developed living being. Adult humans and animals also have stem cells in their body. Adult stem cells are more committed towards their final lineage than embryonic stem cells. They are further classified by the lineage for which they are destined — either as hematopoietic stem cells, destined to become a blood cell, or as mesenchymal stem cells, destined to become one of the connective tissues of the body such as bone, muscle, tendon, nerve, etc.
Adult mesenchymal stem cells receive their signal to differentiate into a more specific tissue type through chemical signals known as cytokines. These cytokines are released by other cell types in response to injury or tissue damage, or as part of the normal turnover of tissue in the body. Platelets are especially important for this process as they contain high concentrations of many important growth factor cytokines, which serve to attract stem cells from the body to sites of injury. Once stem cells are recruited to an area of injury by cytokines, they interact with other cells and cytokines in the area to differentiate into the specific tissue types needed for the repair.
Stem cells do not speed up the rate of healing of an injury, but they are thought to improve the quality of the repair and reduce scar tissue formation. This is particularly important in injuries of equine tendons and ligaments. Healing, from an evolutionary perspective, is designed to return an organism to a level of function required for basic survival — it is not designed to repair the injury back to top physiologic condition. Much of the healing of an acute injury occurs through the recruitment of fibroblasts that manufacture scar tissue. This scar tissue will quickly fill in any defects left by the injury and wall off the injured area from infection. As healing progresses, the temporary scar tissue is slowly replaced by a more permanent repair. It is theorized that by increasing the number of stem cells and growth factors at the site of repair, we can encourage the body to rebuild more normal tissue rather than rely on fibroblasts to make a permanent scar. Research is still ongoing, but studies across a variety of species, including horses and humans, have shown improved quality of tissue repair associated with stem cell use in tendon healing.
STEM CELL HARVESTING PROTOCOL
There are many ways to isolate stem cells from the adult horse today. Bone marrow aspirates from the sternum of the horse are relatively easily performed and can be obtained at the farm. Once the bone marrow aspirate has been performed, the cells are shipped to a laboratory where the mesenchymal stem cells are isolated and expanded in tissue culture until sufficient numbers are reached for treatment. This process can take from 3-4 weeks to reach the optimized dose of 10-25 million stem cells per treatment. The stem cells are then typically injected into the site of injury under ultrasound guidance.
Mesenchymal stem cells can also be isolated from fatty tissue in the horse. For this procedure, a surgical incision is made near the tail head of the horse and a section of fatty tissue is removed and sent to a laboratory for cell retrieval. Typically these cells are returned for injection within 48 hours of harvesting. Since these cells are not cultured and expanded, the total dose of mesenchymal stem cells is lower than with bone marrow derived stem cell therapy.
Research is still ongoing to determine the best timing of injection and quantity of stem cells needed to optimize healing in the horse. In addition to ultrasound guided stem cell therapy, stem cells have also been administered systemically through intravenous injection, intra-articularly in joints with cartilage damage, or through distal limb perfusions for tendon injuries deep in the foot where ultrasound guidance is not possible. Stem cell therapy is often used in conjunction with platelet-rich plasma therapy and/or shockwave therapy, as the various therapies work synergistically to optimize healing.