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 beta 1 encoding gene

Study Design. In vivo studies using a rabbit model to determine the biologi c 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 in tervertebral discs in vivo, 2) to quantify the resulting amount of gene exp ression, and 3) to determine the effect on the biologic activity of the dis cs. Summary of Background Data. Although growth factors such as transforming gr owth factor beta 1 appear to have promising therapeutic properties, there c urrently 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 desir ed growth factors endogenously on a continuous basis. Methods. Saline, with or without virus, was injected directly into lumbar d iscs of 22 skeletally mature female New Zealand white rabbits. Group 1 (n = 11) received the adenovirus construct Ad/CMV-hTGF beta 1 containing the th erapeutic human transforming growth factor beta 1-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 beta 1 w as performed on the disc tissues of one rabbit from Group 1. Nucleus pulpos us tissues from the remaining rabbits were cultured in serumless medium. Bi oassays were performed to determine human transforming growth factor beta 1 production and proteoglycan synthesis. Results. Discs injected with Ad/CMV-hTGF beta 1 exhibited extensive and int ense positive immunostaining for transforming growth factor beta 1. The nuc leus pulposus tissues from the discs injected with Ad/CMV-hTGF beta 1 exhib ited a 30-fold increase in active transforming growth factor beta 1 product ion, and a 5-fold increase in total (active + latent) transforming growth f actor beta 1 production over that from intact control discs (P < 0.05). Fur thermore, 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 ther efore may have useful applications for study of the basic science of the in tervertebral disc and for clinical management of degenerative disc disease.