RESEARCH ARTICLE Enhanced repair of articular cartilage defects in vivo by transplanted chondrocytes overexpressing insulin-like growth factor I (IGF-I) H Madry 1 , G Kaul 1 , M Cucchiarini 1 , U Stein 2 , D Zurakowski 3 , K Remberger 2 , MD Menger 4 , D Kohn 1 and SB Trippel 5 1 Laboratory for Experimental Orthopaedics, Department of Orthopaedic Surgery, Saarland University, Homburg, Germany; 2 Department of Pathology, Saarland University, Homburg, Germany; 3 Harvard University, Boston, Massachusetts, USA; 4 Department of Surgery, Saarland University, Homburg, Germany; and 5 Indiana University, Indianapolis, Indiana, USA Traumatic articular cartilage lesions have a limited capacity to heal. We tested the hypothesis that overexpression of a human insulin-like growth factor I (IGF-I) cDNA by trans- planted articular chondrocytes enhances the repair of full- thickness (osteochondral) cartilage defects in vivo. Lapine articular chondrocytes were transfected with expression plasmid vectors containing the cDNA for the Escherichia coli lacZ gene or the human IGF-I gene and were encapsulated in alginate. The expression patterns of the transgenes in these implants were monitored in vitro for 36 days. Transfected allogeneic chondrocytes in alginate were transplanted into osteochondral defects in the trochlear groove of rabbits. At three and 14 weeks, the quality of articular cartilage repair was evaluated qualitatively and quantitatively. In vitro, IGF-I secretion by implants con- structed from IGF-I-transfected chondrocytes and alginate was 123.2722.3 ng/10 7 cells/24 h at day 4 post transfection and remained elevated at day 36, the longest time point evaluated. In vivo, transplantation of IGF-I implants improved articular cartilage repair and accelerated the formation of the subchondral bone at both time points compared to lacZ implants. The data indicate that allogeneic chondrocytes, transfected by a nonviral method and cultured in alginate, are able to secrete biologically relevant amounts of IGF-I over a prolonged period of time in vitro. The data further demon- strate that implantation of these composites into deep articular cartilage defects is sufficient to augment cartilage defect repair in vivo. These results suggest that therapeutic growth factor gene delivery using encapsulated and trans- planted genetically modified chondrocytes may be applicable to sites of focal articular cartilage damage. Gene Therapy (2005) 12, 1171–1179. doi:10.1038/ sj.gt.3302515; published online 7 April 2005 Keywords: cartilage defects; IGF-I; gene transfer; chondrocytes; alginate; cell transplantation Introduction Traumatic articular cartilage defects do not heal sponta- neously. Efforts to achieve repair of these lesions have been limited by the challenge of stimulating the resident cells to form new cartilage. When cell-based therapy is employed, there arises the additional challenge of retaining the transplanted cells in the defect. 1 The initial healing response to an osteochondral articular cartilage defect is mediated, in part, by cell signaling polypeptides that act on cells derived either from the joint cavity 2 or the bone marrow. 3 Such polypeptides influence the rate of articular cartilage repair. 3–6 Insulin-like growth factor-I (IGF-I) is a 7.6 kDa polypeptide growth factor that stimulates both matrix synthesis and cell proliferation of chondrocytes. In particular, it increases chondrocyte production of proteoglycan and type-II collagen, two principal constituents of cartilage. 7–9 The exogenous administration of human IGF-I has been reported to enhance the cell-based repair of articular cartilage defects. 3,6 Delivery of recombinant human IGF-I protein to articular cartilage has been achieved by intra-articular injection, 10 by supplementing a fibrin clot with IGF-I 3 and by combining composites of chondrocytes and polymerized fibrin with IGF-I. 6 The development of IGF-I as a therapeutic agent for articular cartilage disorders has been restrained by its short intra-articular residence time and the intrinsic paucity of articular chondrocytes to serve as target cells. Genetically engineered chondrocytes could be used to both secrete a therapeutic growth factor and to supply a cell population capable of responding to an exogenous repair stimulus. We previously reported that overexpres- sion of a human IGF-I cDNA promotes new tissue formation in an ex vivo model of articular chondrocyte transplantation 11 and enhances tissue engineering of cartilage. 12 When luciferase-transfected chondrocytes embedded in alginate were implanted into articular cartilage defects in vivo, reporter gene expression Received 25 April 2004; accepted 29 January 2005; published online 7 April 2005 Part of this work was presented at the 49th Annual Meeting of the Orthopaedic Research Society, February 2–5, 2003, New Orleans, Louisiana, USA Correspondence: Dr H Madry, Laboratory for Experimental Orthopaedics, Department of Orthopaedic Surgery, Saarland University Medical Center, 66421 Homburg/Saar, Germany Gene Therapy (2005) 12, 1171–1179 & 2005 Nature Publishing Group All rights reserved 0969-7128/05 $30.00 www.nature.com/gt