Abstract: Osteoarthritis (OA) is a chronic degenerative joint disease that causes locomotor dysfunction in horses.In recent years,intra-articular injection of mesenchymal stromal cells (MSCs) and their derivatives have become a potential treatment for equine OA.MSC-derived cell-free therapies use bioactive substances secreted by isolated MSCs as formulations instead of the MSCs themselves.The main formulations currently include mesenchymal stromal cell-conditioned medium (MSC-CM) and extracellular vesicles (EVs),which theoretically have lower immunogenicity and carcinogenic risks,showing great potential for application.Since factors such as tissue source,isolation procedures,culture conditions,and storage conditions during the preparation process can affect the secretome composition and therapeutic effects,it is necessary to further optimize the production protocol to develop a more reliable method specifically for the treatment of OA.The proposed mechanisms of MSC-derived cell-free therapy for treating OA involve various bioactive factors secreted by MSCs.These factors activate or inhibit cellular pathways,leading to immunomodulatory effects,inhibition of chondrocyte apoptosis,promotion of cartilage and matrix repair and synthesis,and reduction of matrix catabolism.The recent research advancements in MSC-derived cell-free therapy for treating equine OA primarily consist of in vitro cell-level studies.These studies demonstrate that MSC-derived cell-free therapy has anti-inflammatory and growth-promoting effects on chondrocytes,indicating its potential application in treating equine OA.The authors reviewed the preparation,therapeutic mechanism,and potential applications of MSC cell-free therapy in order to provide reference for its future research and clinical applications.

Key words: mesenchymal stromal cells; cell-free therapy; equine osteoarthritis; extracellular vesicles; mesenchymal stromal cell-conditioned medium