Adeno-associated viral gene transfer of transforming growth factor-β1 to human mesenchymal stem cells improves cartilage repair

Bone marrow cells are routinely accessed clinically for cartilage repair. This study was performed to determine whether adeno-associated virus (AAV) effectively transduces human bone marrow-derived mesenchymal stem cells (hMSC) in vitro , whether AAV infection interferes with hMSC chondrogenesis and whether AAV-transforming growth factor-beta-1 (TGF- β 1)-transduced hMSC can improve cartilage repair in vivo. Adult hMSC were transduced with AAV-green fluorescent protein (GFP) or AAV-transforming growth factor β 1 (TGF β 1) and studied in pellet cultures. For in vivo studies, AAV–GFP and AAV–TGF- β 1-transduced hMSCs were implanted into osteochondral defects of 21 athymic rats. GFP was detected using fluorescent microscopy. Cartilage repair was assessed using gross and histological analysis at 4, 8 and 12 weeks. In pellet culture, GFP expression was visualized in situ through 21 days in vitro . In vivo GFP transgene expression was observed by in situ fluorescent surface imaging in 100% of GFP implanted defects at 2 , 67% at 8 and 17% at 12 weeks. Improved cartilage repair was observed in osteochondral defects implanted with AAV–TGF- β 1-transduced hMSC at 12 weeks ( P =0.0047). These results show that AAV is a suitable vector for gene delivery to improve the cartilage repair potential of human mesenchymal stem cells.