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Therapeutic gene transfer into articular cartilage is a potential means to stimulate reparative activities in tissue lesions. We previously demonstrated that direct application of recombinant adeno-associated virus (rAAV) vectors to articular chondrocytes in their native matrix in situ as well as sites of tissue damage allowed for efficient and sustained reporter gene expression. Here we test the hypothesis that rAAV-mediated overexpression of fibroblast growth factor 2 (FGF-2), one candidate for enhancing the repair of cartilage lesions, would lead to the production of a biologically active factor that would facilitate the healing of articular cartilage defects. In vitro, FGF-2 production from an rAAV-delivered transgene was sufficient to stimulate chondrocyte proliferation over a prolonged period of time. In vivo, application of the therapeutic vector significantly improved the overall repair, filling, architecture, and cell morphology of osteochondral defects in rabbit knee joints. Differences in matrix synthesis were also observed, although not to the point of statistical significance. This process may further benefit from cosupplementation with other factors. These results provide a basis for rAAV application to sites of articular cartilage damage to deliver agents that promote tissue repair.

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 transplanted articular chondrocytes enhances the repair of fullthickness (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 constructed 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 demonstrate 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 transplanted genetically modified chondrocytes may be applicable to sites of focal articular cartilage damage.

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Successful gene transfer into articular cartilage is a prerequisite for gene therapy of articular joint disorders. In the present study we tested the hypothesis that recombinant adeno-associated virus (rAAV) vectors are capable of effecting gene transfer in isolated articular chondrocytes in vitro, articular cartilage tissue in vitro, and sites of articular damage in vivo. Using an rAAV vector carrying the Escherichia coli beta-galactosidase gene (lacZ) under the control of the cytomegalovirus (CMV) immediate-early promoter/enhancer (rAAV-lacZ), transduction efficiency exceeded 70% for isolated normal human adult articular chondrocytes, and osteoarthritic human articular chondrocytes. These were comparable to the transduction efficiency obtained with neonatal bovine articular chondrocytes. Transduction of explant cultures of articular cartilage resulted in reporter gene expression within the tissue of all three cartilage types to a depth exceeding 450 microm, which remained present until 150 days. When rAAV-lacZ vectors were applied to femoral chondral defects and osteochondral defects in vivo in a rat knee model, reporter gene expression was achieved for at least 10 days after transduction. These data suggest that AAV-based vectors can efficiently transduce and stably express foreign genes in articular chondrocytes, including chondrocytes of normal and osteoarthritic human articular cartilage. The data further suggest that the same rAAV vectors are capable of transducing chondrocytes in situ within their native matrix to a depth sufficient to be of potential clinical significance. Finally, the data demonstrate that these rAAV vectors are capable of effectively delivering recombinant genes to chondral and osteochondral defects in vivo.

Articular cartilage is routinely subjected to mechanical forces and to cell-regulatory molecules. Previous studies have shown that mechanical stimuli can influence articular chondrocyte metabolic activity, and biochemical studies have shown that growth factors and cytokines control many of the same cell functions. Little is known, however, of the relationships or interplay, if any, between these two key components of the articular environment. This study investigated the comparative and interactive effects of low amplitude, sinusoidal, dynamic compression and insulin-like growth factor-I (IGF-I), a polypeptide in synovial fluid that is anabolic for cartilage. In bovine patellofemoral cartilage explants, IGF-I increased protein and proteoglycan synthesis 90% and 120%, respectively while dynamic compression increased protein and proteoglycan synthesis 40Y1 and go%, respectively. Stimulation by IGF-I was significantly greater than by dynamic compression for both protein and proteoglycan synthesis. When applied together, the two stimuli enhanced protein and proteoglycan synthesis by 180% and 290%, respectively, a degree greater than that achieved by either stimulus alone. IGF-I augmented protein synthesis with a time constant of 12.2 h. Dynamic compression increased protein synthesis with a time constant of 2.9 h, a rate significantly faster than that of IGF-I, suggesting that these signals act via distinct cell activation pathways. When used together, dynamic compression and IGF-I acted with a time constant of 5.6 h. Thus, dynamic compression accelerated the biosynthetic response to IGF-I and increased transport of IGF-I into the articular cartilage matrix, suggesting that, in addition to independently stimulating articular chondrocytes, cyclic compression may improve the access of soluble growth factors to these relatively isolated cells.

We examined nonviral, lipid-mediated gene transfer methods as potential tools for efficient transfection of articular chondrocytes. Transfection conditions were determined for primary cultures of normal human articular, osteoarthritic human articular and normal bovine articular chondrocytes using a lacZ reporter gene construct with the commercially available cationic liposomes Cellfectin, DMRIE-C, LipofectAmine, Lipofectin, LipoTaxi, TransFast and the lipid-based reagent FuGENE 6. Optimized conditions were then evaluated in an ex vivo model of chondrocyte transplantation. FuGENE 6 transfection produced the maximum levels of transgene expression. Transfection efficiency was cell type specific and affected by DNA concentration, lipid/DNA ratio and the presence of hyaluronidase, a matrix-degrading

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