stem cell injection site reactions in horses

Horses are at risk of adverse effects anytime they receive injections. However, researchers recently determined that stem cell injection site reactions in horses were uncommon in the population they studied.

Veterinarians use bone-marrow-derived mesenchymal stem cells (BM-MSCs) to treat a variety of musculoskeletal injuries in horses. In a perfect world, and in some cases, veterinarians collect bone marrow from the injured horse to culture into stem cells for use in that individual. However, that’s not always a practical option. Stem cells take time and funds to produce, which many horses and owners simply don’t have.

Practitioners now have the option of using stem cells produced from another horse’s bone marrow. These MSCs can be just as or even more effective than using a horse’s own stem cells, but using tissues harvested from one animal for use in another has been a source of concern, said Tena Ursini, DVM, CERP, a large animal clinical sciences clinical instructor at the University of Tennessee College of Veterinary Medicine, in Knoxville.

“Previous concerns were based on the premise that tissues taken from one individual would be more reactive in another individual of the same species,” she said. “Any time you administer a biological substance to an animal, they could potentially create an immune response and create antibodies to that substance, even to their own cells.”

This could cause local injection site reactions or even render the cells less effective in treating the injury, she said.

However, in their recent study of 230 injections of stem cells proliferated from a single donor horse, only 10 (4.35%) were associated with adverse reactions in synovial, or joint, structures (three injections) and soft tissues (seven injections).

Additionally, administering multiple injections to the same horse didn’t appear to affect efficacy.

“While we were not able to assess clinical outcome, several horses in our recent study received up to 10 doses of stem cells in their lifetime for various injuries,” Ursini said. “None of these horses reacted, and the cells did not seem to be less effective at healing the tissue.”

A “universal donor” might help stem cell treatment go smoothly if a horse’s own tissue can’t be used, but finding that donor remains challenging. Ursini and colleagues outlined in their study a strict set of standards regarding donors’ cell characteristics.

“We wanted to limit variability (and) create a stable product that was the least inflammatory, most durable, with the most healing capacity,” she said.

The researchers were required to submit these cell characteristics to the U.S. Food and Drug Administration (FDA), Ursini added.

“The FDA classifies stem cells as a drug,” she said. “We needed set standards to get provisional approval in order to use our cells clinically as an ‘investigational new animal drug.’” Research regarding the cells is ongoing. Allogenic (from another horse) cells from our universal donor are available to any licensed veterinarian and are shipped overnight for clinical use.”

The study, “Retrospective analysis of local injection site adverse reactions associated with 230 allogenic administrations of marrow-derived mesenchymal stem cells in 164 horses,” was published in the Equine Veterinary Journal.