There’s no place like home, but where is home for a stem cell, exactly? Although stem cell research has advanced at a phenomenal rate (equine veterinarians can now isolate, process/culture, and inject stem cells into horses to treat a growing number of conditions), what those cells actually do once injected into the horse’s body and whether they stay put remain a mystery.

At the 2011 North American Veterinary Regenerative Medicine Association Conference, held June 2-4, in Lexington, Ky., several researchers presented their data on stem cell "homing," and the results aren’t quite what any of the groups expected.

Alan Nixon, BVSc, MS, Dipl. ACVS, and Ashlee Watts, DVM, Dipl. ACVS, both surgeons at Cornell University’s College of Veterinary Medicine, discussed a recent study in which they hypothesized the stem cells would "engraft" to damaged cartilage in arthritic joints, but not the healthy cartilage in normal joints.

After tracking injected stem cells labeled with fluorescent nanoparticles that they injected into 29 joints–17 healthy and 12 osteoarthritic fetlock or stifle joints–from 10 horses, the team found the stem cells didn’t engraft to the cartilage in any of the horses. Instead of engrafting to cartilage, the cells were found in the lining of the joint, called the synovial membrane