Regulable Transgene Expression in Dorsal Root Ganglia of a Replication-Defective Herpes Simplex Virus Type 1 Vector by Means of Sciatic Nerve Injection

Background: Targeted and controllable gene delivery to neurons is essential to efforts to facilitate peripheral nerve regeneration. The authors investigated both the in vitro and in vivo expression profiles of a tetracycline-controlled, replication-defective, herpes simplex virus type 1–based vector. Methods: Mouse primary dorsal root ganglia cells were infected with QR9TO-LacZ in the absence or presence of tetracycline. LacZ gene expression was examined. It was also injected into sciatic nerves in CD-1 mice fed with and without tetracycline. LacZ expression in the upstream dorsal root ganglia was examined. Results: Following inoculation with QR9TO-LacZ, approximately 40 percent of the cultured primary dorsal root ganglia cells exhibited strong LacZ activity in the presence of tetracycline at 48 and 72 hours, whereas little was detected in those in the absence of tetracycline. Quantitative analysis revealed that the β-galactosidase activity within cells exposed to tetracycline increased 181-fold at 48 hours (p < 0.001) and 47-fold at 72 hours after infection (p < 0.05) compared with those without tetracycline. However, this LacZ transgene activity in the presence of tetracycline tapered off to less than sevenfold over baseline 168 hours after infection (p < 0.05). Furthermore, successful uptake of this replication-defective viral vector was evident in upstream dorsal root ganglia after sciatic nerve injection in mice. In addition, its expression profile was similar to that in vitro, as strong β-galactosidase activity was evident only in mice fed with a doxycycline-containing diet, and it tapered off by 168 hours. Conclusion: The replication-defective herpes simplex virus type 1–based vector, which provides tightly regulated transgene expression in dorsal root ganglia by means of peripheral nerve injection, represents an appealing approach to improve peripheral nerve regeneration.