390. Impact of rAAV9-ABCD1 Upon Behavioral Outcome in a Mouse Model of X-ALD

Abstract

X-linked adrenoleukodystrophy(X-ALD) is a devastating neurological disorder caused by mutations in the ABCD1 gene that encodes a peroxisomal ATP-binding cassette (ABC) transporter. We previously reported successful transduction of central nervous system cells in vitro and in vivo using recombinant adeno-associated virus serotype 9 (rAAV9) vector for delivery of the human ABCD1 gene (ABCD1). Here we report first results of long term experiments to evaluate the therapeutic effect of AAV9-ABCD1 in a mouse model of X-ALD that develops motor and sensory symptoms around 18 months of age.rAAV9 encoding ABCD1 (rAAV9-ABCD1) was delivered to Abcd1-/- mouse CNS by stereotactic intraventricular (ICV) injection at young (4 months) and old (12 months) age, while intravenous (IV) injection was tested at only old age (12 months). Mouse body weight was monitored every month, while mouse behavior including hind limb reflex extension (scoring system 0-4, paralysis to normal), mechanical sensitivity (von Frey testing) and motor function (rotarod testing) were recorded starting from 15 months of age. No changes in body weight occurred regardless of delivery route or age injected, suggesting no obvious toxicity of the rAAV9-ABCD1 vector. ICV injection at both young and old age showed significant improvement upon mouse hind limb reflex extension after 15 months of age. Scores of hind limb reflex extension in untreated Abcd1-/- mice dropped to 1.75 at 18 months of age (wild type mice: 3.5), whereas Abcd1–/– mice treated via ICV at an old age retained scores around 3.25 (p<0.05). ABCD1-/- mice treated via ICV at a young age had an average score of 3.5 at 15 months (compared to untreated Abcd1-/- mice: 2.4; p<0.05). IV injection at old age showed mild but not significant improvement. Mechanical sensitivity also improved after both ICV injection at young age and IV injection at old age but not ICV injection in old Abcd1-/- mice. Analysis of rotarod data is pending.We conclude that rAAV9-mediated ABCD1 gene transfer is safe and efficacious at improving behavior of a known X-ALD mouse model including mouse hind limb reflex extension and mechanical sensitivity. However timing and delivery route are crucial determinants of efficacy and need to be independently assessed.