Tendon and ligament injuries are frequent in sport horses and are prone to recurrence due to incomplete healing. Platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs) are increasingly used, but data controlled on the early effects of autologous MSCs remain limited. A prospective randomized, double-blind, placebo-controlled trial was conducted in horses with naturally occurring tendinopathies. After standardized PRP pretreatment, non-responders were randomized to receive intralesional autologous muscle-derived MSCs (mdMSCs, n = 17) or placebo (n = 6). Clinical and ultrasonographic parameters were evaluated at the recruitment period (T0) before the administration of the local treatment (T1), 4 (T2) and 8 weeks later (T3). Eighteen horses from both groups received at T2 a second intralesional injection of mdMSCs at the investigator’s discretion; this phase was not randomized. Horses treated with mdMSCs showed significant improvements from T1 to T2 across both clinical and ultrasonographic parameters, whereas no significant changes were observed in the placebo group. Between-group comparison at T2 confirmed the significant superiority of mdMSCs. Further improvements were observed between T2 and T3 in the 18 horses that received a second injection. No systemic adverse events were recorded, and local reactions were mild and transient. This randomized controlled trial demonstrates early clinical and ultrasonographic efficacy of autologous mdMSCs in equine tendinopathy, with additional benefit from a second injection. The autologous approach combines efficacy and safety while avoiding the immunological and logistical constraints of allogeneic strategies.

Mesenchymal stromal/stem cells (MSCs) are increasingly investigated as intra-articular therapies for equine osteoarthritis (OA), although most studies have focused on allogeneic or combination-based approaches. Evidence supporting the use of autologous MSCs as a stand-alone treatment remains limited. The present study evaluated the safety and clinical evolution following intra-articular administration of autologous muscle-derived MSCs (mdMSCs) in horses with naturally occurring chronic OA. Thirteen horses with confirmed clinical disease were included. Each affected joint received a single injection, with the administered cell dose adapted to joint size (1 × 10⁷ or 2 × 10⁷ cells). Clinical assessments were conducted at baseline and at 6 and 12 weeks post-treatment using the American Association of Equine Practitioners (AAEP) lameness scale, together with a joint inflammation score and a composite total clinical score (TCS). Clinical scores decreased over time, with statistically significant improvements observed at both follow-up time points. Seven of thirteen horses met the predefined responder criteria based on AAEP improvement, including complete resolution of lameness in several cases. The treatment was well tolerated, with only mild and transient local reactions that resolved without intervention. These results indicate that intra-articular administration of autologous mdMSCs is associated with clinically relevant improvement in horses with chronic OA.