601. Gene Therapy for Cockayne Syndrome

Abstract

Cockayne Syndrome (CS) is a rare autosomal recessive genetic disorder. The majority of CS cases involve mutations in either the CSA (25%) or CSB (75%) gene, leading to defective transcription-coupled nucleotide excision repair and RNA polymerase II mediated transcription. Clinically this presents as progressive degeneration of the central nervous system, retina, cardiovascular system, and cochlea, causing mental retardation, post-natal growth defects, pigmented retinopathy, cataracts, dermal UV sensitivity, organ dysfunction and shortened life expectancy.CSA and CSB single mutant mice display retinal degeneration with age and ocular sensitivity to ionizing radiation. Because limited publications on these mouse models exist we began by characterizing the retinal dysfunction through histology and electroretinography (ERG). We found that the retinal degeneration in CSA and CSB mutant mice (C57Bl6 background) was occurring over a slower time course (over 1 year) than previously reported. Therefore we aimed to increase the rate of retinal degeneration in these animals using UV light exposure, whole body radiation, or high intensity light exposure. Our goal was to increase the speed of retinal degeneration to a timeframe that is more readily studied for the purposes of gene therapy correction. Preliminary data indicates that we can cause a decrease in the scotopic ERG (b-wave) 2 weeks after high-dose ultraviolet light exposure (100000J/m^2), a change not seen in C57Bl6 mice at the same UV dose. There was also a decrease in b-wave amplitude following radiation exposure (2-3 gray) in the CSB mouse model that was not seen in C57Bl6 mice. Histology on these mice is currently pending. Improving the rate of photoreceptor loss will allow us to perform rAAV based gene therapy to deliver the CSB gene back to the retina and ascertain whether UV and radiation resistance can be restored.While single mutant CSA and CSB mice do not have significant neurological deficits, when crossed with XPA deficient mice they develop clinical signs similar to severely affected human patients. Signs in these mice include neurologic deficits, poor weight gain and death around postnatal day 21. These mice could be ideal candidates to show that correction of both the central nervous system disease as well as the retinal degeneration is possible in a single model. To determine if both the brain and retina could be targeted in the same animal (and therefore model what may be necessary in the human patients) we have looked at targeting both organs simultaneously using either a single IV injection in neonatal mice or a combined intra-cerebral ventricular (ICV) injection and IV injection in the same animal. We found that delivery of the rAAV vector (regardless of serotype tested) into the retro-orbital sinus at postnatal day 1-3 leads to widespread transduction of the retina. Temporal vein delivery postnatal day 1-3 only resulted in transduction of the inner layer of the retina, not the photoreceptors. When ICV and IV injections were combined in neonates widespread brain and retinal transduction was achieved.These preliminary data indicate that a murine model for retinal gene therapy of CS is feasible and that potentially both the retina and brain could be targeted in a single model.