Acceleration of cartilage repair by genetically modified chondrocytes over expressing bone morphogenetic protein-7

Background: Cartilage has a limited capacity to heal. Although chondrocyte transplantation is a useful therapeutic strategy, the repair process can be lengthy. Previously we have shown that over expression of bone morphogenetic protein-7 (BMP-7) in chondrocytes by adenovirus-mediated gene transfer leads to increased matrix synthesis and cartilage-like tissue formation in vitro. In this context we hypothesized that implantation of genetically modified chondrocytes expressing BMP-7 would accelerate the formation of hyaline-like repair tissue in an equine model of cartilage defect repair. Methods: Chondrocytes treated with adenovirus vector encoding BMP-7 (AdBMP-7) or as control, an adenovirus vector encoding an irrelevant gene ( Escherichia coli cytosine deaminase, AdCD) were implanted into extensive (15 mm diameter) articular cartilage defects in the patellofemoral joints of 10 horses. Biopsies were performed to evaluate early healing at 4 weeks. At the terminal time point of 8 months, repairs were assessed for morphology, MRI appearance, compressive strength, biochemical composition and persistence of implanted cells. Results: Four weeks after surgery AdBMP-7-treated repairs showed an increased level of BMP-7 expression and accelerated healing, with markedly more hyaline-like morphology than control. Quantitative real-time polymerase chain reaction (PCR) analysis of the repair tissue 8 months after surgery showed that few implanted cells persisted. By this time, the controls had healed similarly to the AdBMP-7-treated defects, and no difference was detected in the morphologic, biochemical or biomechanical properties of the repair tissues from the two treatment groups. Conclusions: Implantation of genetically modified chondrocytes expressing BMP-7 accelerates the appearance of hyaline-like repair tissue in experimental cartilage defects. Clinical relevance: Rehabilitation after cell-based cartilage repair can be prolonged, leading to decreased patient productivity and quality of life. This study shows the feasibility of using genetically modified chondrocytes to accelerate cartilage healing.