To determine the biodistribution and toxicity of intra-striatal administration of a recombinant adeno-associated virus serotype 5, huntingtin microRNA (rAAV5-miHTT) gene therapy construct during a 26-week observation period in non-human primates (NHPs).

NHP data on pharmacodynamics, pharmacokinetics, viral immunogenicity/shedding, and local/systemic toxicity are critical in predicting the safety of AAV gene therapy in humans.

Four equal groups of male and female NHPs (n=24) were administered 4x100 microliters to the striatum by real-time, MRI-guided convection-enhanced delivery of either vehicle alone, or AAV5-miHTT. Blood, CSF, urine, saliva, semen, feces, and nasal secretions were collected at pre-dose, 1, 3, 5, and 6 months. Post-mortem brain and peripheral organ biopsies were collected for neuropathological and molecular analyses.

AAV5 DNA (vector) was expressed widely throughout the brain, with the highest levels in the striatum with spread to both deep and superficial gray matter structures.  Outside the central nervous system, low vector DNA (at least 100-fold less than striatum) levels were found in the optic nerve, liver and spinal cord with extremely low levels in other organs. Total miHTT RNA in the brain, and miHTT in CSF extracellular vesicles, were persistent over a 6-month observation period. Vector levels were undetectable in urine, saliva, semen, and nasal secretions by 3 months; and in the CSF and plasma by 3 to 6 months depending on the dose administered. Serum AAV5 neutralizing antibodies were present at 6 months without an elevation in cytokines.  Routine clinical chemistry tests, and macroscopic or microscopic tissue examinations did not show evidence of significant systemic toxic effects.

Bilateral intra-striatal administration of rAAV5-miHTT is safe and well-tolerated in NHPs. The widespread distribution and expression of the miHTT transgene in brain tissues and CSF demonstrate the ability of rAAV5-miHTT to transduce the neuroanatomical areas involved in the pathology of HD.