The development of isolation and culture techniques for mesenchymal progenitor cells from various tissues has promoted interest in the use of these cells for repair and regeneration of musculoskeletal tissues. The chondrogenic differentiation of these pluripotential cells seems to be mediated by numerous cytokines most of which belong to the transforming growth factor-beta superfamily. Strategies to repair articular cartilage have focused on delivery of these cytokines or progenitor cells to the area of damage. More recently, with the development of gene transfer techniques, these cells have become the target of in vivo gene therapy, which involves direct injection of viral and nonviral vectors carrying transgenes. Furthermore, they are viewed as potential carriers of the transgenes for ex vivo gene therapy, in which the gene transfer is done in vitro with culture-expanded cells that then are implanted or injected. In vitro data suggest that the chondrogenic potential of these cells is maintained with virally mediated ex vivo gene transfer. By transducing these cells with chondroinductive factors, the bioactive factors and the target cells are delivered to the repair site.

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