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Allogeneic hematopoietic cell transplantation (HCT) benefits children with Hurler syndrome (MPS-IH). However, survivors remain burdened by substantial MPS-IH related residual disease. We studied the feasibility, safety and biochemical impact of augmentative recombinant intravenous enzyme replacement therapy (IV-ERT) post transplantation. Ten children with MPS-IH and ≥2 years from successful HCT underwent IV-ERT for 2 years’ duration. Patients were monitored for anti-drug antibody (ADA) development, including inhibitory capacity and changes in urinary excretion of glycosaminoglycans (uGAG). Three patients demonstrated low-level ADA at baseline, though all children tolerated IV-ERT well. Eight patients developed ADA over the 2-year study, with 3 (38%) meeting criteria for an inhibitory ADA response. The aggregate cohort experienced a reduction in uGAG from baseline to study end, which was enhanced in children with low or no ADA response. Conversely, children with inhibitory ADA showed increase in uGAG over time. IV-ERT in previously transplanted children with MPS-IH appears safe and can reduce uGAG, although this is reversed by the presence of inhibitory ADA. These data show a biochemical change after initiation of post-HCT IV-ERT, but the occurrence of ADA and inhibitory antibodies are a concern and should be monitored in future efficacy trials. This trial was registered at www.clinicaltrials.gov, NCT01173016, 07/30/2010.

Tordo et al. present a novel AAV gene therapy vector, AAV-TT, which exceeds the current benchmark neurotropic serotypes AAV9 and AAVrh10 and enables unprecedented correction of a lysosomal transmembrane enzyme deficiency. AAV-TT based gene therapies may thus be suitable for the treatment of human neurological diseases characterised by global neuropathology., 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.

Development of a human mitochondrial gene delivery vector is a critical step in the ability to treat diseases arising from mutations in mitochondrial DNA. Although we have previously cloned the mouse mitochondrial genome in its entirety and developed it as a mitochondrial gene therapy vector, the human mitochondrial genome has been dubbed unclonable in E. coli, due to regions of instability in the D-loop and tRNA(Thr) gene.We tested multi- and single-copy vector systems for cloning human mitochondrial DNA in E. coli and Saccharomyces cerevisiae, including transformation-associated recombination.Human mitochondrial DNA is unclonable in E. coli and cannot be retained in multi- or single-copy vectors under any conditions. It was, however, possible to clone and stably maintain the entire human mitochondrial genome in yeast as long as a single-copy centromeric plasmid was used. D-loop and tRNA(Thr) were both stable and unmutated.This is the first report of cloning the entire human mitochondrial genome and the first step in developing a gene delivery vehicle for human mitochondrial gene therapy.