Adenoviral gene transfer to spinal-cord neurons: intrathecal vs. intraparenchymal administration

The spinal cord is the site of many chronic, debilitating, neurological disorders that may be amenable to gene therapy. The present study, using quantitative and anatomical methods, examines the ability of replication deficient adenovirus to transfer a transcription cassette composed of the cytomegalovirus promoter driving the expression of the LacZ reporter gene (AdCMVbetagal) to spinal-cord neurons. Rats were microinjected with AdCMVbetagal into the spinal-cord parenchyma or subarachnoid space and sacrificed between 1 and 60 days post-infusion. The spinal cord was assayed for beta-galactosidase (beta-gal) activity fluorometrically (MUG). Intraparenchymal injection resulted in significant beta-gal activity at day 1, which peaked at day 7, and decreased at day 14 (21-, 57- and 9.8-fold of control respectively). The spatial distribution of beta-gal activity on day 7 was confined to the 1-cm section containing the injection site but was detected 2 cm caudal to this section by day 14. Histochemical staining and immunocytochemistry revealed a prominent reaction product in neurons, particularly motor neurons, and glia within the ventral grey matter bilaterally. Intrathecal viral injections showed comparatively modest, yet significant increases in beta-gal activity throughout the spinal cord with the greatest activity (170% control) closest to the catheter tip. This study demonstrates that AdCMVbetagal injected into the ventral spinal cord results in extensive in vivo neuronal gene transfer with beta-gal activity reaching a peak by day 7 and remaining detectable at 60 days. Intrathecal viral injections result in greater spatial distribution but a comparatively lower level of expression.