Phenotypic and functional characterisation of ovine mesenchymal stem cells: application to a cartilage defect model

Background: Multipotent mesenchymal stromal cells (MSC) are of particular interest for their potential clinical use in cartilage engineering, but a consistent model is missing in large animals.
Objective: In the absence of any detailed study reporting a complete characterisation of the mesenchymal cells isolated from sheep bone marrow, we fully characterised adherent stromal cells and developed a pre-clinical model of cartilage engineering by implantation of autologous MSC in the Merinos sheep.
Methods: Ovine MSC (oMSC) were isolated from bone marrow, expanded and further characterised according to the recently proposed definition of the MSC. The experimental model consists of partial-thickness lesions created in the inner part of the patellae of the posterior legs. Lesions were filled with oMSC with or without chitosan, with or without transforming growth factor (TGF)b-3, in a fibrin clot.
Results: oMSC were shown to display the three main characteristics of MSC: adherence to plastic, phenotypic profile (positive for CD44, CD105, vimentin and negative for CD34 and CD45), and trilineage differentiation potential. We also report two other important functional characteristics of MSC: support of long-term haemato- poiesis and immunosuppressive capacity. In vivo, 2 months after implantation the histological analysis revealed chondrocyte-like cells surrounded by a hyaline- like cartilaginous matrix that was integrated to the host cartilage when oMSC were combined with chitosan and TGFb-3.
Conclusions: This study provides for the first time a strong characterisation of oMSC and establishes the basis for a model of cartilage engineering in a large animal.