Pre-clinical Safety and Efficacy of Lentiviral Vector-Mediated Ex Vivo Stem Cell Gene Therapy for the Treatment of Mucopolysaccharidosis IIIA

Hematopoietic stem cell gene therapy is a promising therapeutic strategy for the treatment of neurological disorders, since transplanted gene-corrected cells can traffic to the brain, bypassing the blood-brain barrier, to deliver therapeutic protein to the CNS. We have developed this approach for the treatment of Mucopolysaccharidosis type IIIA (MPSIIIA), a devastating lysosomal storage disease that causes progressive cognitive decline, leading to death in early adulthood. In a previous pre-clinical proof-of-concept study, we demonstrated neurological correction of MPSIIIA utilizing hematopoietic stem cell gene therapy via a lentiviral vector encoding the SGSH gene. Prior to moving to clinical trial, we have undertaken further studies to evaluate the efficiency of gene transfer into human cells and also safety studies of biodistribution and genotoxicity. Here, we have optimized hCD34+ cell transduction with clinical grade SGSH vector to provide improved pharmacodynamics and cell viability and validated effective scale-up and cryopreservation to generate an investigational medicinal product. Utilizing a humanized NSG mouse model, we demonstrate effective engraftment and biodistribution, with no vector shedding or transmission to germline cells. SGSH vector genotoxicity assessment demonstrated low transformation potential, comparable to other lentiviral vectors in the clinic. This data establishes pre-clinical safety and efficacy of HSCGT for MPSIIIA

An improved AAV 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 sulphate. Build-up of undegraded heparan sulphate results in severe progressive neurodegeneration for which there is currently no treatment. Experimental gene therapies based on gene addition are currently being explored. Following pre-clinical evaluation in MPSIIIA mice, an AAVrh10 vector designed to deliver SGSH and sulfatase modifying factor 1 (SAF301) was trialled in four MPSIIIA patients showing good tolerance and absence of adverse events with some improvements in neurocognitive measures. Here we aimed to further improve SAF301 by removing sulfatase modifying factor 1 (SUMF1) and assess if expression of this gene is needed to increase the SGSH enzyme activity (SAF301b). Secondly, we exchanged the murine phosphoglycerate kinase (PGK) promotor with a chicken beta actin/CMV composite (CAG) promotor (SAF302) to see if we could further boost SGSH expression levels. 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 GFP (SAF302GFP), 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