Modulation of the biologic activity of the rabbit intervertebral disc by gene therapy: An in vivo study of adenovirus-mediated transfer of the human transforming growth factor β1 encoding gene

Study Design. In vivo studies using a rabbit model to determine the biologic effects of direct, adenovirus-mediated transfer of a therapeutic gene to the intervertebral disc. Objectives. 1) To deliver an exogenous therapeutic gene to rabbit lumbar intervertebral discs in vivo, 2) to quantify the resulting amount of gene expression, and 3) to determine the effect on the biologic activity of the discs. Summary of Background Data. Although growth factors such as transforming growth factor β1 appear to have promising therapeutic properties, there currently is no practical method for sustained delivery of exogenous growth factors to the disc for the management of certain chronic types of disease (e.g., disc degeneration). A possible solution is to modify the disc cells genetically through gene transfer such that the cells manufacture the desired growth factors endogenously on a continuous basis. Methods. Saline, with or without virus, was injected directly into lumbar discs of 22 skeletally mature female New Zealand white rabbits. Group 1 (n = 11) received the adenovirus construct Ad/CMV-hTGFβ1 containing the therapeutic human transforming growth factor β1-encoding gene. Group 2 (n = 6) received adenovirus containing the luciferase marker gene. Group 3 (n = 5) received saline only. The rabbits were killed 1 week after injection. Immunohistochemical staining for human transforming growth factor β1 was performed on the disc tissues of one rabbit from Group 1. Nucleus pulposus tissues from the remaining rabbits were cultured in serumless medium. Bioassays were performed to determine human transforming growth factor β1 production and proteoglycan synthesis. Results. Discs injected with Ad/CMV-hTGFβ1 exhibited extensive and intense positive immunostaining for transforming growth factorβ1. The nucleus pulposus tissues from the discs injected with Ad/CMV-hTGFβ1 exhibited a 30-fold increase in active transforming growth factorβ1 production, and a 5-fold increase in total (active + latent) transforming growth factor β1 production over that from intact control discs (P < 0.05). Furthermore, these tissues exhibited a 100% increase in proteoglycan synthesis compared with intact control tissue, which was statistically significant (P < 0.05). Conclusions. The results of this study suggest that the intervertebral disc is an appropriate site for adenovirus-mediated transfer of exogenous genes and subsequent production of therapeutic growth factors. Gene therapy therefore may have useful applications for study of the basic science of the intervertebral disc and for clinical management of degenerative disc disease.