Evaluation of nonbiomedical and biomedical grade alginates for the transplantation of genetically modified articular chondrocytes to cartilage defects in a large animal model in vivo

Abstract

Genetically modified chondrocytes embedded in alginate improve cartilage repair in experimental models, and alginates are clinically used for articular chondrocyte transplantation. In the present study, we tested the hypothesis that the alginate system allows for sustained transgene expression in cartilage defects in a preclinical large animal model in vivo. Primary cultures of ovine articular chondrocytes were transfected with the Photinus pyralis luc or the Escherichia coli lacZ genes in monolayer culture in vitro using eight different nonviral compounds. Optimally transfected chondrocytes were encapsulated in spheres composed of nonbiomedical or biomedical grade alginates for evaluation of luciferase expression, cell numbers and viabilities in vitro. Transfected chondrocytes encapsulated in spheres comprised of the different alginates were then implanted into osteochondral defects in the knee joints of sheep to examine the profiles of transgene expression in vivo. Ovine articular chondrocytes were efficiently transfected with FuGENE 6. Transgene expression was detectable after encapsulation in the alginates over 21 days in vitro. Transplantation of genetically modified chondrocytes to cartilage defects in vivo resulted in maximal transgene expression on day 1 after transfection, with a decrease by day 21, the longest time point evaluated. Remarkably, the reduction in luciferase activity was less pronounced when biomedical grade alginates were employed, compared to nonbiomedical grade alginates, suggesting that such alginates might be better suited to support elevated transgene expression after transplantation of genetically modified chondrocytes. This approach may be of value to study the effects of potential therapeutic genes upon cartilage repair in a clinically relevant setting.