Improving brain delivery of adeno-associated viral gene therapy vectors for the treatment of MPS IIIC

MPS IIIC is caused by mutations in the HGSNAT gene. HGSNAT deficiency affects lysosomal catabolism of heparan sulfate (HS), resulting in widespread CNS pathology in infants and children, leading to behavioural problems, cognitive decline and, finally, dementia and death before adulthood. Currently there are no existing treatments for MPS IIIC and the development of treatments is difficult as the deficient enzyme cannot cross the blood brain barrier or diffuse between cells. We have developed an adeno-associated virus (AAV) based gene therapy for MPS IIIC which is efficacious in a MPS IIIC murine model via injection into the brain parenchyma. Although effective in a small murine brain, the architecture and volume is considerably different from a human brain, and the failure of previous clinical trials for AAV vectors using intraparenchymal injection, means that large animal experiments are essential in optimising widespread distribution needed for clinical efficacy. Due to the inability of HGSNAT to cross-correct cells, intracerebral delivery of vector needs to target the maximum number of cells, and with the use of convection enhanced delivery (CED) this can be achieved. CED has the potential to treat diseases with global pathology such as MPS IIIC as it overcomes the issues with current delivery methods and can be administered to multiple sites. We compared different conditions to determine optimal vector spread of an AAV9-GFP vector in the sheep brain, which is 130mL in volume, at clinically applicable volumes and titres whilst keeping volume identical throughout. We compared 4 intraparenchymal sites, against intraventricular injection, and compared different flow rates at 2 single intraparenchymal sites. We found a rate of 1μL/min into the corpus striatum produced the greatest vector distribution, whilst intraventricular outcomes were comparatively poor. However, further studies are currently ongoing to improve this further with the aim of determining the optimal delivery system for gene therapy of MPS IIIC.