Human Intervertebral Disc Cells Are Genetically Modifiable by Adenovirus-Mediated Gene Transfer

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Abstract
Study Design. Human intervertebral disc cells were cultured in monolayer and treated with adenovirus-containing marker genes to determine the susceptibility of the cells to adenovirus-mediated gene transfer. Objectives. To test the efficacy of the adenovirus-mediated gene transfer technique for transferring exogenous genes to human intervertebral disc cells in vitro. Summary of Background Data. Upregulated proteoglycan synthesis after direct in vivo adenovirus-mediated transfer of growth factor genes to the rabbit intervertebral disc has previously been reported. Before contemplating extending this approach to the treatment of human disc disease, it is necessary to demonstrate that human intervertebral disc cells are indeed susceptible to adenovirus-mediated gene transduction. Methods. Human intervertebral disc cells were isolated from disc tissue obtained from 15 patients during surgical disc procedures. The cells were cultured in monolayer and treated with saline containing five different doses of adenovirus carrying the lacZ gene (Ad/CMV-lacZ), saline containing adenovirus carrying the luciferase gene (Ad/CMV-luciferase), or saline alone. Transgene expression was analyzed by 5-bromo-4-chloro-3-indolyl-β-galactosidase (X-Gal) staining and luciferase assay. Results. Adenovirus efficiently transferred lacZ and luciferase marker genes to cells from degenerated discs as well as to cells from nondegenerated discs. A minimum dose of 150 MOI Ad/CMV-lacZ was found to be sufficient to achieve transduction of approximately 100% of disc cells—regardless of patient age, sex, surgical indication, disc level, and degeneration grade. No statistically significant difference in the luciferase activities could be detected in disc cell cultures from degenerated and nondegenerated discs treated with Ad/CMV-luciferase. Conclusions. In vitro transducibility of human intervertebral disc cells by adenovirus is relatively insensitive to disc degeneration grade. Because the rate-limiting step for successful gene therapy is the ability to transfer genesefficiently to the target tissue, the achievement of efficient gene transfer to human intervertebral disc cells(using a direct, adenovirus-mediated approach) is an important and necessary step in the development of gene therapy strategies for the management of human intervertebral disc disorders.