604. Comparison of Intra-Cisterna Magna and Lumbar Puncture Intrathecal Delivery of scAAV9 GeneTherapy for Giant Axonal Neuropathy

Abstract

Giant axonal neuropathy (GAN) is a rare pediatric neurodegenerative disorder characterized by progressive neuropathy that presents as early as 3 years of age and with ultimate mortality during the second or third decade of life. GAN is caused by autosomal recessive loss-of-function mutations in the GAN gene that encodes for the gigaxonin protein. Gigaxonin plays a role in the organization/degradation of intermediate filaments (IFs) and GAN patients are pathologically characterized by large axonal swellings filled with disorganized aggregates of IFs. While GAN is primarily described as a progressive peripheral neuropathy, diffuse pathology from disorganized IFs is apparent throughout the central nervous system, enteric nervous system and other organ systems. An NIH-sponsored Phase I study is underway to test the safety of intrathecal lumbar puncture (LP) administration of scAAV9/JeT-GAN to treat the most severe aspects of GAN, namely the motor and sensory neuropathy. Gigaxonin gene transfer through a single LP injection is the first proposed therapy for GAN. Intra-cisterna magna (ICM) delivery of AAV9 vectors shows high transduction of the brain and spinal cord of animals; however, this method of vector delivery has not yet been tested for the treatment of GAN. This study compared the efficacy of using ICM or LP delivery of the scAAV9/JeT-GAN vector to treat GAN KO mice. GAN KO mice were injected with scAAV9/JeT-GAN at 15 months of age using ICM or LP delivery and motor performance was tested monthly. In agreement with our previous studies, we found that GAN KO mice have impaired motor performance around 20 months of age and that this deficit is attenuated with LP delivery of scAAV9/JeT-GAN. In contrast, GAN KO mice receiving ICM-delivered scAAV9/JeT-GAN did not have significantly improved motor function as compared to vehicle treated GAN KO mice. Analyses of disease-relevant pathologies in the brain, spinal cord, and peripheral nerves of these mice are ongoing. To date, antibodies are not available to reliably detect gigaxonin protein expression via immunohistochemical (IHC) analysis, so to directly compare the transduction of the two intrathecal delivery methods, we injected wild-type mice with ~4 × 1011 vg scAAV9/GFP via an ICM or LP injection, which is a higher dose than has been reported in any publication. Mice were harvested 4-weeks post-injection and the biodistribution of scAAV9 was analyzed via semi-quantitative PCR and IHC analysis of GFP. Compared to LP-injected mice, GFP expression was notably higher and more wide-spread in the brains of ICM-injected mice, while higher amounts of GFP were detected in the sciatic nerves of LP-injected mice as compared to ICM-injected mice. IHC analysis is ongoing and we will present a detailed map of the transduction of ICM- and LP-delivered scAAV9/GFP across the central and peripheral nervous systems and different organ systems. In conclusion, we report here that ICM-delivery of scAAV9/JeT-GAN does not attenuate motor deficits in GAN KO mice. Furthermore, the vector spread varies between ICM and LP delivery, suggesting that the site of intrathecal injection may have a critical impact on the therapeutic benefit of gene vectors for a given disease.