Gene therapy in musculoskeletal repair.

Local and regional gene therapy has improved healing in preclinical trials of articular and other muculoskeletal conditions. Combinations of cell supplementation and cells overexpressing growth factor genes have shown promising results for improving cartilage repair, enhancing delayed union of fractures, and driving organized tendon repair. Proof of concept has been developed using viral vectors, predominantly adenovirus, to deliver growth factor genes, such as BMP-2, TGF-beta1, and IGF-I. Integrating vectors, such as retrovirus and lentivirus, have improved the duration of gene-induced repair, however, increased risk factors have limited broad application. Cartilage repair can be improved using chondrocyte or stem cell transplantation with cells expressing IGF-I, BMP-2, or FGF-2. In cartilage injury and secondary osteoarthritis models, a combination of IL-1 knockdown and growth factor supplementation has restored cartilage matrix and stabilized the osteoarthritic process. Ultimately, nonviral vectors may provide similar control of catabolic activity in cartilage and synovial structures, which may further improve outcome after chondrocyte or mesenchymal stem cell (MSC) implantation. MSCs derived from bone marrow, fat, or other connective tissues provide a multipotent cell source that may be privileged vectors for skeletal gene therapy. MSCs expressing BMP-2, TGF-beta1, LMP-1, IGF-I, or GDF-5 have enhanced cartilage, bone, and tendon repair. Overall, the field of orthopedic gene therapy for enhanced tissue repair has made significant preclinical advances. Combining existing cell transplant technology to deliver differentiated cells in a minimally invasive way, with genes that improve matrix formation, provides a manageable protocol for a persisting anabolic impact.