A preliminary study of synovial fluid-derived mesenchymal stromal cell therapy for canine osteoarthritis

Dogs with osteoarthritis (OA) may benefit from stromal cell therapies, but there is a lack of such established therapies. Accordingly, we investigated the feasibility and safety of synovial fluid (SF)-derived mesenchymal stromal cell (MSC) transplantation for canine OA. MSCs were isolated from SF (n = 15) or by joint lavage (JLF; n = 12) from the knee joints of dogs undergoing orthopedic surgery (n = 25), and then cultured on a dish (passage 1) and a polyethylene terephthalate (PET) nonwoven fabric scaffold (passage 2). We obtained 2166 ± 1177 (SF) or 1640 ± 1064 (JLF) × 10⁴ primary cells and 18,673 ± 8500 (SF) or 16,870 ± 3348 (JLF) × 10⁴ passaged cells, surpassing the target number. Passaged cells were morphologically uniform, self-proliferating, CD29, CD44, CD90, and CD105-positive, and CD31-negative cells, with the ability to differentiate into osteoblasts, chondrocytes, and adipocytes. Healthy dogs (n = 3) then received a 1-mL allogenic MSC suspension (at 1×, 5×, and 10 × 10⁷ cells), harvested and prepared with the same method, by intraarticular injection (with contralateral knees as negative controls), and were evaluated for adverse clinical signs, hematologic and biochemical parameters periodically, and joint images and pathology at day 90. No abnormal findings were found in any dogs, confirming the safety of allogeneic MSC transplantation.