The use of mesenchymal stem cells has been reported as a treatment for a number of disease processes in both humans and animals. The peer reviewed literature contains a substantial number of scientific studies performed in the laboratory, but there are few clinical reports showing improved outcomes following stem cell treatment, especially in horses.
What are stem cells and how do we get them?
To help better understand the field, we must define what we call a stem cell. In general terms, a stem cell can be defined as a master cell that is capable of reproducing itself and that has the potential to become one of the body’s more specific or differentiated cells, of which there are hundreds. It is important to note the adult stem cells differ from fetal or embryonic stem cells, the latter of which is often discussed in the press from an ethical standpoint. In equine medicine, the safety of fetal stem cells is just now being investigated and will need to undergo a more rigorous governmental approval process prior to commercialization. Adult stem cells can be isolated from many of the body’s various tissues, but most research has focused on bone derived cells, which will be the main focus of this article. Fat is also used as an origin of stem cells and was the source used by the first commercial veterinary laboratory. However, two published equine studies found fat derived cells to be inferior when looking at differentiation into musculoskeletal tissue such as cartilage and tendon. (Vidal et al. 2008; Kisiday et al. 2008). Further, researchers looking into equine stem cells are focusing on bone derived cells suggesting this cell source will be used the future.
Bone derived cells in horses are most often obtained from an aspirate of either the hip or sternum with apparent minimal discomfort. The procedure typically takes less than 15 minutes and can be done standing under light sedation. Historic reports suggested direct treatment with an unmodified bone marrow aspirate was considered “stem cell” therapy (Herthel 2001). This is no longer an accepted description given only 0.01% to 0.001% of the mononuclear cells collected this way are stem cells. Instead the term “stem cell treatment” is reserved for the process by which the stem cells are selected and then expanded by cell culture technique to provide adequate numbers. While the absolute number of stems cells required to improve clinical outcomes is not definitively known, compilation of published laboratory research suggests that 5 million or greater cells are necessary for significant outcomes. To date, obtaining such numbers can only be accomplished through culture expansion techniques. Therefore, the state of art today is to collect a low volume bone marrow aspirate and culture expand the stem cells prior to injection into the joint or tendon. This is different from umbilical derived cells from blood or cells from adipose tissue that are injected without culture expansion.
Results of clinical studies
Reports of long term clinical improvements following stem cell treatment have been published in the peer reviewed literature by two groups, notably both using bone derived cells. The first group, led by Roger Smith and others from the Royal Veterinary College (RVC), has focused on the treatment of superficial digital flexor tendon (SDF) injuries. This group has compelling evidence that treating injured SDF with stem cells decreases the re-injury rate by almost half, a significant step forward in tendon treatment (Godwin et al. 2012). A similar decrease in re-injury rate with SDF and ligamentous injuries, including chronic suspensory lesions, has also been observed by researchers at Colorado State (CSU). Furthermore, CSU researchers have obtained long term follow up on treating joint injury; especially involving the meniscus in the stifle. Specifically, they have shown a significant improvement in grade 3 meniscal tears after injection stem cells after surgery, (60% return to work, Ferris et al. 2011) compared to surgery alone (6% return to work, Walmsley et al. 2003). While much more work on dosage and timing of treatments is required, initial results following clinical cases in a CSU study suggest that treating once; at least 30 days post injury and with at least 5 million cells appears to provide good long term outcomes. Recently a randomized controlled study demonstrated waiting longer than 2 weeks post injury was “critical for long-term amelioration of tendinopathy and chondroid metaplasia” in a sheep model utilized to mimic rotor cuff injuries/tendon injury (Smith et al. 2012). Thus, early treatment with stem cells should be carefully reconsidered.
Also in the area of bone derived stem cell research, investigators at Cornell University found use of stem cells for the treatment of experimental created injuries and have some interesting results for both cartilage and tendon healing; the clinical applications of this work are hopefully forthcoming.
Commercial availability and ongoing research
Both groups (RVC and CSU) with long-term clinical outcomes have made their techniques available to veterinarians by creating commercial laboratories. (RVC: VetCell, and CSU: Advanced Regenerative Therapies (ART)). Both of these laboratories utilize bone marrow aspirate, culture expansion and a single treatment into the site of the injury. Recently three new commercial labs have come on-line (UC-Davis, Alamo Pintado and Rood and Riddle). Institutes such as the Marion duPont Scott Equine
Medical Center (EMC) are culturing their own bone marrow derived stem cells for clinical use and have initiated research studies. These groups offer culture-expanded bone marrow stem cells. The recommendations of these new labs are different than those of RVC, CSU and EMC. Specifically, they have been advocating multiple treatments, intravenous administrations, and larger volume (50ml) marrow draws, which in people is associated with pain and dilution of the stem cells. While some studies in laboratory animals have utilized such treatment protocols, this novel approach in the equine field will require safety and efficacy trials as well as critical evaluation of efficacy prior to this method becoming a standard treatment protocol. Furthermore, care must be taken to prevent the grouping of different approaches under a general stem cell category to ensure that the horse owner and veterinarian are aware of the pros or cons associated with each approach. The group at UC-Davis has changed their focus from cord blood to adult derived bone marrow stem cells and is researching some of these novel equine administration techniques, although it is too early to comment on the clinical applications (Sole et al. 2011).
In summary, culture expanded bone marrow derived stem cells appear to be the state of the art in equine medicine today. Horse owners are encouraged to have their veterinarians to look at the research and long-term clinical outcomes from each of the commercial groups prior to making decisions on both case and laboratory selection. Also equally important is to not to be too persuaded by “miracle” stories or marketing techniques touting the benefits in the field of stem cells.
The veterinary community needs your assistance to increase funding for research on use of mesenchymal stem cells as a treatment for a number of disease processes in equines.
Please contact the American Association of Equine Practitioners Foundation ( www.aaepfoundation.org ), the American Quarter Horse Foundation ( www.aqha.com/foundation ), Grayson Jockey-Club Research Foundation ( www.grayson-jockeyclub.org ), Morris Animal Foundation ( www.morrisanimalfoundation.org ) or your favorite veterinary school or research institution to make a contribution towards equine research.
By David D. Frisbie, DVM, PhD, Dipl. ACVS, Associate Professor, Orthopaedic Research Center, College of Veterinary Medicine and Biomedical Sciences, Colorado State University
This is just one of the many efforts that the AAEP Foundation is coordinating on behalf of the industry through the Equine Research Coordination Group (ERCG), which is comprised of researchers and organizations that support equine research. Formally organized in 2006, the ERCG has a mission of advancing the health and welfare of horses by promoting the discovery and sharing of new knowledge, enhancing awareness of the need for targeted research, educating the public, expanding fundraising opportunities and facilitating cooperation among funding agencies.
The ERCG is a group that comprises researchers and organizations that support equine research. Participants in the ERCG include equine foundations and multiple university research representatives. Current participants include: American Association of Equine Practitioners Foundation, American Horse Council, American Quarter Horse Foundation, Grayson-Jockey Club Research Foundation, Havemeyer Foundation, Morris Animal Foundation, Oaktree Charitable Foundation, United States Equestrian Federation Foundation and university researchers and representatives: Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM (Texas A & M University); Gregory Ferraro, DVM (University of California-Davis); C. Wayne McIlwraith, BVSc (DVM), PhD, FRCVS, DSc, Dipl. ACVS (Colorado State University); James Moore, DVM, PhD, Dipl. ACVS (University of Georgia); Rustin Moore, DVM, PhD, Dipl. ACVS (The Ohio State University); Corinne Sweeney, DVM, Dipl. ACVIM (University of Pennsylvania); Mats Troedsson, DVM, PhD, Dipl. ACT (University of Kentucky); and Nathaniel White II, DVM, MS, Dipl. ACVS (Virginia-Maryland Regional College of Veterinary Medicine).
Ferris DJ, Frisbie DD, McIlwraith CW, Kawcak CE. Current joint therapy usage in equine practice: a survey of veterinarians 2009. Equine Vet J 2011;43:530-535.
Godwin EE, Young NJ, Dudhia J, Beamish IC, Smith RKW. Implantation of bone marrow-derived mesenchymal stem cells demonstrates improved outcome in horses with overstrain injury of the superficial digital flexor tendon. Equine Vet J 2012;44:25-32.
Herthel DJ. Enhanced suspensory ligament healing in 100 horses by stem cell and other bone marrow components. Am Assoc Equine Pract 2001;47:319-321.
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Smith MM, Ravi V, Dart AJ, Young AA, Sonnabend DH, Little CB. The timing of bone-marrow-derived mesenchymal stem cell injection is critical for long-term benefit to infraspinatus tendon in a sheep model. Orthop Res Soc 2012;37:0161.
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