Site-specific modifications to AAV8 capsid yields enhanced brain transduction in the neonatal MPS IIIB mouse.

Mucopolysaccharidosis type IIIB (MPS IIIB) is an autosomal recessive lysosomal disease caused by defective production of the enzyme α-N-acetylglucosaminidase. It is characterized by severe and complex central nervous system degeneration. Effective therapies will likely target early onset disease and overcome the blood-brain barrier. Modifications of adeno-associated viral (AAV) vector capsids that enhance transduction efficiency have been described in the retina. Herein, we describe for the first time, a transduction assessment of two intracranially administered adeno-associated virus serotype 8 variants, in which specific surface-exposed tyrosine (Y) and threonine (T) residues were substituted with phenylalanine (F) and valine (V) residues, respectively. A double-mutant (Y444 + 733F) and a triple-mutant (Y444 + 733F + T494V) AAV8 were evaluated for their efficacy for the potential treatment of MPS IIIB in a neonatal setting. We evaluated biodistribution and transduction profiles of both variants compared to the unmodified parental AAV8, and assessed whether the method of vector administration would modulate their utility. Vectors were administered through four intracranial routes: six sites (IC6), thalamic (T), intracerebroventricular, and ventral tegmental area into neonatal mice. Overall, we conclude that the IC6 method resulted in the widest biodistribution within the brain. Noteworthy, we demonstrate that GFP intensity was significantly more robust with AAV8 (double Y-F + T-V) compared to AAV8 (double Y-F). This provides proof of concept for the enhanced utility of IC6 administration of the capsid modified AAV8 (double Y-F + T-V) as a valid therapeutic approach for the treatment of MPS IIIB, with further implications for other monogenic diseases.

Mucopolysaccharidosis III (Sanfilippo Syndrome)- disease presentation and experimental therapies.

Sanfilippo Syndrome or Mucopolysaccharidosis Ill (MPS Ill) is a group of lysosomal storage diseases resulting from a deficiency of one of four lysosomal enzymes: Type A - heparan N-sulfatase (SGSH), Type B - a-N-acetylglucosaminidase (NAGLU), Type C - acetyl CoA a-glucosaminide acetyltransferase (HGSNAT) and Type D - N-acetylglucosamine-6-sulfatase (GNS). Each of these enzymes is necessary for degradation of heparan sulfate. Deficiency of any of these enzymes manifests as a neurodegenerative disorder with accompanying somatic manifestations. Typically this presents early in life with developmental delays followed by developmental regression and usually results in death sometime during the second decade of life, though several less severe cases have been described living into late adulthood (30's to 60's). Often there is a delay of several years from time of symptom onset to diagnosis. Currently treatment is limited to supportive care. We will briefly discuss the typical natural history and presumed pathophysiology of the disease. We will also discuss current experimental therapies being pursued for treatment of this devastating disease. These include enzyme replacement, gene therapy, stem cell therapy, and substrate reduction approaches.