Correction of Mucopolysaccharidosis type 1: Targeting safe harbor loci using genome editing
BACKGROUND: Mucopolysaccharidosis type I (MPSI) is a lysosomal storage disease (LSD) whose manifestations start in early infancy and include relentless neurologic decline, progressive skeletal deformities, and respiratory compromise for which current treatments have limited effectiveness.
GAP: Current interventions for LSDs including MPSI are hematopoietic stem cell transplantation (HSCT), which has high morbidity and mortality due to transplant-related complications, and enzyme replacement therapy (ERT), where the blood-brain barrier limits the usefulness to cases without neurological involvement.
HYPOTHESIS: We hypothesize that the treatment of LSDs, beginning with MPSI, can be improved by modifying the patient’s own blood stem cells using genome editing to insert the enzymes into well-characterized locations known as “safe harbors.” We predict that human hematopoietic stem cells can be effectively and safely modified without losing their stem cell properties and that the modified human cells should correct a humanized model of the disease.
METHODS: The fundamental approach uses CRISPR/Cas9 and AAV6 to introduce functional enzyme into a well-characterized genomic locus into human CD34+ hematopoietic cells isolated from cord blood or mobilized peripheral blood from donors. We use in vitro and in vivo studies to demonstrate the safety and efficacy of the modification.
RESULTS: Human blood stem cells modified with CRISPR/Cas9 secrete supra-endogenous enzyme levels, maintain long-term repopulation and multi-lineage differentiation potential, and can correct biochemical and phenotypic abnormalities in an immunocompromised mouse model of Mucopolysaccharidosis type I. These pre-clinical studies provide proof-of-concept evidence of the safety and efficacy of using genome-edited human hematopoietic stem cells modified to express a lysosomal enzyme to correct the biochemical, structural, and behavioral phenotype of a mouse model of MPSI, a canonical lysosomal storage disease. Moreover, this work provides specific evidence of safety and efficacy to support the optimization and development of this strategy into a clinical protocol to treat patients with MPSI and a platform approach to potentially treat other lysosomal storage disorders.
IMPACT: If successful the approach would constitute a treatment platform for MPSI and other LSDs.