1. Introduction
re-injuries, tendinopathies, lameness, multipotent mesenchymal stromal
INFLAMMATION, DISEASE, RECRUITMENT, PATHOPHYSIOLOGY
These authors contributed equally to this work.The treatment of tendinopathies with multipotent mesenchymal stromal cells (MSCs) is a promising option in equine and human medicine. However, conclusive clinical evidence is lacking. The purpose of this study was to gain insight into clinical treatment efficacy and to identify suitable outcome measures for larger clinical studies. Fifteen horses with early naturally occurring tendon disease were assigned to intralesional treatment with allogeneic adipose-derived MSCs suspended in serum or with serum alone through block randomization (dosage adapted to lesion size). Clinicians and horse owners remained blinded to the treatment during 12 months (seven horses per group) and 18 months (seven MSC-group and five control-group horses) of follow-up including clinical examinations and diagnostic imaging. Clinical inflammation, lameness, and ultrasonography scores improved more over time in the MSC group. The lameness score difference significantly improved in the MSC group compared with the control group after 6 months. In the MSC group, five out of the seven horses were free of re-injuries and back to training until 12 and 18 months. In the control group, three out of the seven horses were free of re-injuries until 12 months. These results suggest that MSCs are effective for the treatment of early-phase tendon disease and provide a basis for a larger controlled study.The multipotent mesenchymal stromal cell (MSC) treatment of tendon injuries in horses was first described in a report dating almost 20 years back by now [The conflicting outcomes of experimental studies could be due to different models for tendon lesion induction used (collagenase injection vs. mechanical disruption), while no model can actually reflect the complex naturally occurring pathophysiology [The lack of a comprehensive clinical study on horses is due to the anticipated difficulties in the recruitment of suitable equine patients and compliant horse owners who agree to the blinded treatment and cope with the efforts associated with the follow-up [