Survival of bone marrow mesenchymal stem cells labelled with red fluorescent protein in an ovine model of collagenase-induced tendinitis.

Objective: The aim of this study was to track the survival and efficacy of allogeneic bone marrow mesenchymal stem cells (BM-MSC) marked with red fluorescent protein (BM-MSCRFP) in an ovine model of collagenaseinduced tendinopathy. Methods: Bone marrow was harvested from one donor sheep and BM-MSC were isolated, cultivated and transfected with red fluorescent protein (BM-MSCRFP). Collagenase was injected into both Achilles tendons in the remaining nine sheep. After two weeks the left tendon was injected with a solution of 6 × 106 BM-MSCRFP and fibrin glue, while only fibrin glue was administered to the contralateral tendon in each sheep. After three, four and six weeks the tendons were harvested and evaluated for morphology, collagen I deposition, presence of CD34+ cells, and fluorescent labelled BM-MSC. Results: We demonstrated that delivery of BM-MSC into tendon lesions had positive effects on the injured tendons. The BM-MSCRFP survived at three, four and six weeks after treatment, leading to better quality healing of tendons as compared to the controls, where no labelled cells were detected. Interestingly, we demonstrated high expression of CD34+ cells in tendons that had been treated with BM-MSCRFP. Clinical relevance: Mesenchymal stem cell allografts have a positive effect on tendon healing and local injection of BM-MSC directly into the tendon allows the homing of BM-MSC for good efficiency of engraftment.