IntroductionThe objective of this study was to evaluate the tolerability and efficacy at 3 months of intravenous (IV) allogeneic uterine-derived mesenchymal stromal cells (UMSCs) for osteoarthritis (OA) in client-owned cats.MethodsThis was a randomized, masked, placebo-controlled pilot study conducted across six veterinary clinics. Thirty-five client-owned cats with naturally occurring OA were randomly assigned to receive two intravenous injections, given 14 days apart, of one of three treatments: 5 million (5M) UMSCs, 20 million (20M) UMSCs, or saline placebo. Client-Specific Outcome Measures (CSOM), Owner Overall Assessment (OOA), Veterinarian Overall Assessment (VOA) and Veterinarian Pain Assessment (VPA) were recorded at day 0, 14, 30, 60 and 90.ResultsAt day 90, predefined treatment success was achieved in: CSOM and OOA for 7/9(78%) 5M UMSC and 10/12(83%) 20M UMSC treated cats compared to 4/11(36.4%) placebo-treated cats for both outcomes; VOA for 4/8(50%) 5M UMSC and 8/12(67%) 20M UMSC treated cats compared to 2/10(20%) placebo-treated cats; and VPA for 6/8(75%) 5M UMSC and 10/12(83%) 20M UMSC treated cats compared to 5/11(45%) placebo-treated cats. Treatment-related adverse events were observed in 1/10 (10%) 5M UMSC treated cats, 5/13 (38%) 20M UMSC treated cats, and 2/12 (16.7%) saline treated cats. The most common treatment related events reported in the first 24 hours were transient vomiting or nausea, weakness, lethargy, hypersalivation, tachypnea and malodorous breath.DiscussionThis study demonstrated that IV administration of allogeneic UMSCs was well tolerated and showed improvement in owner and veterinarian outcomes at both 5M UMSC and 20M UMSC dosing to at least 3 months in cats with naturally occurring OA. Intravenous MSC therapy shows promise for cats with OA and warrants further exploration.