Magnetic Resonance Imaging as a Readout of CLN5 Gene Therapy Efficacy in Sheep.

Purpose: Neuronal ceroid lipofuscinoses (NCL; Batten disease) are a group of rare inherited neurodegenerative disorders caused by mutations in one of 13 ceroid lipofuscinosis neuronal (CLN) genes. The diseases share a common set of symptoms, including motor and cognitive dysfunction, progressive loss of vision, and seizure activity. A naturally occurring model of CLN5 NCL exists in New Zealand Borderdale sheep, which exhibit similar clinical disease and post-mortem pathology to the human disease. Recent trials of concurrent intracerebroventricular and intravitreal gene therapy in sheep with CLN5 disease confirmed the therapeutic efficacy of this approach. Given the documented natural history of brain volume changes, detected by MRI, in sheep with CLN5 disease, the current study sought to utilize MRI as both a longitudinal readout and cross-sectional measure of therapeutic efficacy in treated sheep.

Method: Sheep treated at a pre-symptomatic timepoint underwent five T1-weighted structural MRI scans between 5 and 18 months of age. Sheep treated at early and advanced symptomatic disease stages underwent a single MRI at 18 months of age. All scans from treated sheep were compared to historical healthy control and affected untreated sheep at each age.

Finding: Pre-symptomatic treated sheep showed growth in intracranial volume at a comparable rate to healthy control sheep over the course of the study. Whilst grey matter volume decreased and cerebrospinal fluid volume increased in treated sheep, this was to a much smaller degree than in untreated affected sheep. The majority of the cortical regions assessed showed stable volumes over the course of the study, with the notable exception of the cerebellum. Both early and advanced symptomatic treated sheep showed intracranial volumes comparable to untreated affected sheep at 18 months of age. However, when individual tissue types were assessed, grey and white matter were significantly larger, and cerebrospinal fluid was significantly smaller in early symptomatic sheep compared to untreated affected sheep, while the same volumes in advanced symptomatic treated sheep were comparable to untreated affected sheep. Cortical regions assessed showed an age-at-treatment and dose effect.

Conclusion: This study has demonstrated that MRI, a clinically relevant outcome measure, can be successfully utilized to assess therapeutic efficacy in a large animal model of CLN5 NCL, both in a longitudinal study and a cross-sectional study when robust natural history data is available for comparison.