Gene transfer can prevent stereotypical disease development in ovine CLN5 and CLN6 models of NCL

Abstract

Gene therapy represents a promising treatment strategy for the NCLs. Sheep with naturally occurring NCLs are ideal translational subjects for gene therapy studies as they have large complex human-like gyrencephalic brains and recapitulate the key molecular, pathological and clinical features of the human diseases. Indications of the successful treatment of six CLN5-/- sheep via combinatorial intracerebroventricular and intraparenchymal injections of lentiviral or AAV9 vectors expressing ovine CLN5 were reported in Cordoba 20141. Both vector platforms afforded sustained protection from stereotypical disease onset and progression. Consequently in vivo monitoring was extended beyond the intended endpoint to 27 months. Cognitive and neurological function was reserved, whilst longitudinal structural neuroimaging by CT and MRI scanning revealed normalisation of intracranial volumes and brain integrity. Quality of life was profoundly improved for the treated sheep and one AAV9 treated sheep is still grazing peacefully at 37 months. The onset of visual deficits was delayed, from 11 months in untreated CLN5 -/- sheep to 21-24 months in the treated cohorts. Supporting neuropathological data detailing CLN5 transgene expression and the impact upon the lysosomal storage pathology, glial activation and neuronal loss will be presented. One of six similarly AAV9-CLN6 injected CLN6 -/- sheep also maintained phenotypic correction. This sheep retained vision and was clinically indistinguishable from age-matched control animals at 26 months of age. Post mortem neuropathological studies revealed a significant diminution in disease-associated lysosomal storage, gliosis, atrophy and neurodegeneration after AAV9-mediated CLN6 transfer. Second-generation vector studies, using self-complementary AAV9 cassettes and direct intracerebroventricular injections, are underway. Sheep with established disease have been injected and updated in vivo monitoring results will be presented. Collectively the in vivo assessments and neuropathological results indicate a very good prognoses for translation to human CLN5 and CLN6 gene therapy.