Brain transplantation of genetically corrected Sanfilippo type B neural stem cells induces partial cross-correction of the disease

Sanfilippo syndrome type B (mucopolysaccharidosis type IIIB) is a recessive genetic disorder that severely affects the brain due to a deficiency in the enzyme a-N-acetylglucosaminidase (NAGLU), leading to intra-lysosomal accumulation of partially degraded heparan sulfate. There are no effective treatments for this disorder. In this project, we carried out an ex vivo correc-tion of neural stem cells derived from Naglu-'- mice (iNSCs) induced pluripotent stem cells (iPSC) using a modified enzyme in which human NAGLU is fused to an insulin-like growth fac-tor II receptor binding peptide in order to improve enzyme up-take. After brain transplantation of corrected iNSCs into Naglu-'-mice and long-term evaluation of their impact, we successfully detected NAGLU-IGFII activity in all transplanted animals. We found decreased lysosomal accumulation and reduced astrocytosis and microglial activation throughout transplanted brains. We also identified a novel neuropatholog-ical phenotype in untreated Naglu-'- brains with decreased levels of the neuronal marker Map2 and accumulation of synaptophysin-positive aggregates. Upon transplantation, we restored levels of Map2 expression and significantly reduced formation of synaptophysin-positive aggregates. Our findings suggest that genetically engineered iNSCs can be used to effec-tively deliver the missing enzyme to the brain and treat Sanfi- lippo type B-associated neuropathology.