Treatment of spinal injury muscle spasticity by spinal subpial AAV9-GAD65/VGAT delivery: An efficacy and safety study in rat, pig, and NHP.

The loss in segmental inhibitory GABAergic tone plays the key role in the development of spinal injury-induced muscle spasticity. We use a subpial segment-targeted delivery of adeno-associated virus vector(s) expressing GAD65 (glutamic acid decarboxylase-65) and VGAT (vesicular GABA transporter) transgenes in rats with spinal transection-induced spasticity. In treated animals, a significant suppression in spasticity was seen at 5-8 weeks after treatment. Naive rats, pigs, and non-human primates (NHPs) injected with human equivalent dose of treatment vectors and surviving for 3 weeks to 4.5 years showed normal motor function and pinch-evoked response. A significant increase in the number of VGLUT2 terminals co-expressing GAD65 and VGAT protein in vector-injected segment was seen. This corresponded with the presence of transgene-specific rat Gad2 or human GAD2 and rat Slc32a1 or human SLC32A1 mRNA signal. No spinal toxicity was noted in NHPs at 4.5 years post vector delivery. Analysis of peripheral organs (liver, spleen, and skeletal muscle) showed minimal or no detectable transgenes in pigs and NHPs. These data demonstrate that a single-time-point spinal-segment-targeted subpial delivery of GAD65/VGAT transgenes is effective in suppressing spinal injury-induced spasticity and has a favorable long-term safety profile as defined by normal neurological function and histopathology in naive pigs and NHPs.