Whether it’s an intravenous medication, a corticosteroid shot, or a vaccination, injections are commonplace in equine medicine. Stem cells, the key component in a popular new type of regenerative therapy, are also administered via injection. But where do the cells go once they’ve left the syringe and entered the horse’s body? And do they stay where they need to stay, or go where they need to go?

Mathieu Spriet, DVM, MS, Dipl. ACVR, ECVDI, assistant professor in the Department of Surgical and Radiological Sciences at the University of California (UC), Davis, School of Veterinary Medicine, and a team of researchers recently set out to find an easy, noninvasive method of tracking stem cells injected into a horse’s lower leg, and to see if different methods of administration had a different effect on where the cells travel once administered. He presented the findings at the North American Veterinary Regenerative Medicine Conference, held June 2-4 in Lexington, Ky.

"Basically, we wanted to know where the cells are going, whether they stay (where they were injected), and how many of them stay there; Ideally we want the cells to … where the lesion is and stay there," Spriet explained.

Stem cells have been tracked using a material called green fluorescent protein; however, this technique requires a terminal study (i.e., the test horses are euthanized during the process of the study) to observe the results. Spriet et al. wanted to see if using a different material and method–a radioactive mixture of  the tracing compounds hexamethylpropyleneamine oxime (HMPAO) and Technetium-99m (TcHMPAO) introduced within the stem cells and tracked using a gamma camera (scintigraphic imaging)–would allow for in vivo (in the live horse) stem cell tracking. The TcHMPAO material and aforementioned method had previously been proven effective in rodents, but had never been tested in horses. If successful, "the technique is a noninvasive approach and allows multiple assessments over time for up to 24 hours after cell injections," Spriet noted