An Improved Adeno-Associated Virus Vector for Neurological Correction of the Mouse Model of Mucopolysaccharidosis IIIA.

Patients with the lysosomal storage disease mucopolysaccharidosis IIIA (MPSIIIA) lack the lysosomal enzyme N-sulfoglucosamine sulfohydrolase (SGSH), one of the many enzymes involved in degradation of heparan sulfate. Build-up of un-degraded heparan sulfate results in severe progressive neurodegeneration for which there is currently no treatment. Experimental gene therapies based on gene addition are currently being explored. Following preclinical evaluation in MPSIIIA mice, an adeno-associated virus vector of serotype rh10 designed to deliver SGSH and sulfatase modifying factor 1 (SAF301) was trialed in four MPSIIIA patients, showing good tolerance and absence of adverse events with some improvements in neurocognitive measures. This study aimed to improve SAF301 further by removing sulfatase modifying factor 1 (SUMF1) and assessing if expression of this gene is needed to increase the SGSH enzyme activity (SAF301b). Second, the murine phosphoglycerate kinase (PGK) promotor was exchanged with a chicken beta actin/CMV composite (CAG) promotor (SAF302) to see if SGSH expression levels could be boosted further. The three different vectors were administered to MPSIIIA mice via intracranial injection, and SGSH expression levels were compared 4 weeks post treatment. Removal of SUMF1 resulted in marginal reductions in enzyme activity. However, promotor exchange significantly increased the amount of SGSH expressed in the brain, leading to superior therapeutic correction with SAF302. Biodistribution of SAF302 was further assessed using green fluorescent protein (GFP), indicating that vector spread was limited to the area around the injection tract. Further modification of the injection strategy to a single depth with higher injection volume increased vector distribution, leading to more widespread GFP distribution and sustained expression, suggesting this approach should be adopted in future trials.

AAV9 intracerebroventricular gene therapy improves lifespan, locomotor function and pathology in a mouse model of Niemann-Pick type C1 disease.

Niemann-Pick type C disease (NP-C) is a fatal neurodegenerative lysosomal storage disorder. It is caused in 95% of cases by a mutation in the NPC1 gene that encodes NPC1, an integral transmembrane protein localized to the limiting membrane of the lysosome. There is no cure for NP-C but there is a disease-modifying drug (miglustat) that slows disease progression but with associated side effects. Here, we demonstrate in a well-characterized mouse model of NP-C that a single administration of AAV-mediated gene therapy to the brain can significantly extend lifespan, improve quality of life, prevent or ameliorate neurodegeneration, reduce biochemical pathology and normalize or improve various indices of motor function. Over-expression of human NPC1 does not cause adverse effects in the brain and correctly localizes to late endosomal/lysosomal compartments. Furthermore, we directly compare gene therapy to licensed miglustat. Even at a low dose, gene therapy has all the benefits of miglustat but without adverse effects. On the basis of these findings and on-going ascendency of the field, we propose intracerebroventricular gene therapy as a potential therapeutic option for clinical use in NP-C.

A novel adeno-associated virus capsid with enhanced neurotropism corrects a lysosomal transmembrane enzyme deficiency.

Recombinant adeno-associated viruses (AAVs) are popular in vivo gene transfer vehicles. However, vector doses needed to achieve therapeutic effect are high and some target tissues in the central nervous system remain difficult to transduce. Gene therapy trials using AAV for the treatment of neurological disorders have seldom led to demonstrated clinical efficacy. Important contributing factors are low transduction rates and inefficient distribution of the vector. To overcome these hurdles, a variety of capsid engineering methods have been utilized to generate capsids with improved transduction properties. Here we describe an alternative approach to capsid engineering, which draws on the natural evolution of the virus and aims to yield capsids that are better suited to infect human tissues. We generated an AAV capsid to include amino acids that are conserved among natural AAV2 isolates and tested its biodistribution properties in mice and rats. Intriguingly, this novel variant, AAV-TT, demonstrates strong neurotropism in rodents and displays significantly improved distribution throughout the central nervous system as compared to AAV2. Additionally, sub-retinal injections in mice revealed markedly enhanced transduction of photoreceptor cells when compared to AAV2. Importantly, AAV-TT exceeds the distribution abilities of benchmark neurotropic serotypes AAV9 and AAVrh10 in the central nervous system of mice, and is the only virus, when administered at low dose, that is able to correct the neurological phenotype in a mouse model of mucopolysaccharidosis IIIC, a transmembrane enzyme lysosomal storage disease, which requires delivery to every cell for biochemical correction. These data represent unprecedented correction of a lysosomal transmembrane enzyme deficiency in mice and suggest that AAV-TT-based gene therapies may be suitable for treatment of human neurological diseases such as mucopolysaccharidosis IIIC, which is characterized by global neuropathology.