348. Correction of CNS and Somatic Pathology by Intra-Cerebrospinal Fluid Gene Therapy for Mucopolysaccharidosis Type II

Abstract

Mucopolysaccharidosis type II (MPSII), or Hunter Syndrome, is a X-linked recessive Lysosomal Storage Disease (LSD) caused by deficiency in Iduronate-2-sulfatase (IDS), an enzyme involved in the stepwise degradation of the glycosaminoglycans (GAGs) heparan sulfate (HS) and dermatan sulfate (DS). GAG storage builds up in the CNS and peripheral tissues causing severe neurologic and multisystemic somatic disease. Patients usually die during the second decade of life. Periodic intravenous enzyme replacement therapy (ERT) currently constitutes the only approved therapeutic option for MPSII. However, the inability of recombinant IDS to efficiently cross the blood-brain barrier limits the efficacy of the approach in treating neurological symptoms. Alternatively, the periodic infusion of ERT to the cerebrospinal fluid is under clinical testing, but serious adverse events associated with the use of intrathecal drug delivery devices have been reported. Here we report a gene therapy approach directly addressing the CNS pathology of MPSII. Through a minimally invasive procedure we delivered adeno-associated virus vectors of serotype 9 encoding IDS (AAV9-Ids) to the CSF of MPSII mice with already established disease. Four months after vector administration, treated mice showed a significant increase in IDS activity throughout the encephalon, with full resolution of lysosomal storage lesions, reversal of lysosomal dysfunction, normalization of the brain transcriptomic signature and disappearance of neuroinflammation. Moreover, our approach not only resulted in widespread distribution of vector in the CNS but also in liver transduction, providing a peripheral source of therapeutic protein that corrected the storage disease in visceral organs, with evidence of cross-correction of non-transduced organs by circulating enzyme. Importantly, MPSII mice treated with AAV9-Ids also showed normalization of behavioural deficits. These results provide a strong proof of concept for the clinical translation of our approach for the treatment of Hunter patients with cognitive impairment.