Background:In Parkinson disease (PD), the benefit of levodopa therapy becomes less marked over

Widespread distribution of gene products at clinically relevant levels throughout the CNS has been challenging. Adeno-associated virus type 9 (AAV9) vector has been reported as a good candidate for intravascular gene delivery, but low levels of preexisting antibody titers against AAV in the blood abrogate cellular transduction within the CNS. In the present study we compared the effectiveness of vascular delivery and cerebrospinal fluid (CSF) delivery of AAV9 in transducing CNS tissue in nonhuman primates. Both delivery routes generated similar distribution patterns, although we observed a more robust level of transduction after CSF delivery. Consistent with previous reports administering AAV9, we found greater astrocytic than neuronal tropism via both routes, although we did find a greater magnitude of CNS transduction after CSF delivery compared with intravascular delivery. Last, we have demonstrated that delivery of AAV9 into the CSF does not shield against AAV antibodies. This has obvious implications when developing and/or implementing any clinical trial studies.

Thus far, this gene therapy approach has been well tolerated and shows PET evidence of sustained gene expression. These initial findings demonstrate the safety of the therapy; higher doses of adeno-associated viral vector containing the human aromatic l-amino acid decarboxylase gene in the next cohort of patients may further increase dopamine production in the putamen and provide more profound clinical benefit.

We investigated the movement of interstitially infused macromolecules within the central nervous system (CNS) in rats with high and low blood pressure (BP)/heart rate and in rats euthanized immediately before infusion (no heart action). Adeno-associated virus 2 (AAV2), fluorescent liposomes, or bovine serum albumin was infused into rat striatum (six hemispheres per group) by convection-enhanced delivery (CED). After infusion, distribution volumes were evaluated. The rats with high BP/heart rate displayed a significantly larger distribution of the infused molecules within the injected site and more extensive transport of those molecules to the globus pallidus. This difference was particularly apparent for AAV2, for which a 16.5-fold greater distribution of viral capsids was observed in the rats with high BP/heart rate than in the rats with no heartbeat. Similar results were observed for liposomes, despite their larger diameter. The distribution of all infused molecules in all rats that had low or no blood flow was confined to the space around brain blood vessels. These findings show that fluid circulation within the CNS through the perivascular space is the primary mechanism by which viral particles and other therapeutic agents administered by CED are spread within the brain and that cardiac contractions power this process.

Adeno-associated viral (AAV) vectors are a rapidly emerging gene therapy platform for the treatment of neurological diseases. In preclinical studies, transgenes encoding therapeutic proteins, microRNAs, antibodies or gene-editing machinery have been successfully delivered to the central nervous system with natural or engineered viral capsids via various routes of administration. Importantly, initial clinical studies have demonstrated encouraging safety and efficacy in diseases such as Parkinson disease and spinal muscular atrophy, as well as durability of transgene expression. Here, we discuss key considerations and challenges in the future design and development of therapeutic AAV vectors, highlighting the most promising targets and recent clinical advances.

We report the results of a long-term follow-up of subjects in a phase 1 study of AAV2-hAADC (adeno-associated virus type 2-human aromatic L-amino acid decarboxylase) gene therapy for the treatment of Parkinson's disease (PD). Ten patients with moderately advanced PD received bilateral putaminal infusions of either a low or a high dose of AAV2-hAADC vector. An annual positron emission tomography (PET) imaging with [(18)F]fluoro-L-m-tyrosine tracer was used for evaluation of AADC expression, and a standard clinical rating scale [Unified Parkinson's Disease Rating Scale (UPDRS)] was used to assess effect. Our previous analysis of the 6-month data suggested that this treatment was acutely safe and well tolerated. We found that the elevated PET signal observed in the first 12 months persisted over 4 years in both dose groups. A significantly increased PET value compared with the presurgery baseline was maintained over the 4-year monitoring period. The UPDRS in all patients off medication for 12 hr improved in the first 12 months, but displayed a slow deterioration in subsequent years. This analysis demonstrates that apparent efficacy continues through later years with an acceptable safety profile. These data indicate stable transgene expression over 4 years after vector delivery and continued safety, but emphasize the need for a controlled efficacy trial and the use of a higher vector dose.

Dopamine, the major neurotransmitter depleted in Parkinson disease, can be synthesized and regulated in vivo with a combination of intrastriatal AAV-hAADC gene therapy and administration of the dopamine precursor l-Dopa. When tested in MPTP-lesioned monkeys, this approach resulted in long-term improvement in clinical rating scores, significantly lowered l-Dopa requirements, and a reduction in l-Dopa-induced side effects. Positron emission tomography with [(18)F]FMT confirmed persistent AADC activity, demonstrating for the first time that infusion of AAV vector into primate brain results in at least 6 years of transgene expression. AAV-hAADC restores the ability of the striatum to convert l-Dopa into dopamine efficiently. Introduction of this therapy into the clinic holds promise for Parkinson patients experiencing the motor complications that result from escalating l-Dopa requirements against a background of disease progression.

Objective To understand the safety, putaminal coverage, and enzyme expression of adeno‐associated viral vector serotype‐2 encoding the complementary DNA for the enzyme, aromatic L‐amino acid decarboxylase (VY‐AADC01), delivered using novel intraoperative monitoring to optimize delivery. Methods Fifteen subjects (three cohorts of 5) with moderately advanced Parkinson's disease and medically refractory motor fluctuations received VY‐AADC01 bilaterally coadministered with gadoteridol to the putamen using intraoperative magnetic resonance imaging (MRI) guidance to visualize the anatomic spread of the infusate and calculate coverage. Cohort 1 received 8.3 × 10 11 vg/ml and ≤450 μl per putamen (total dose, ≤7.5 × 10 11 vg); cohort 2 received the same concentration (8.3 × 10 11 vg/ml) and ≤900 μl per putamen (total dose, ≤1.5 × 10 12 vg); and cohort 3 received 2.6 × 10 12 vg/ml and ≤900 μl per putamen (total dose, ≤4.7 × 10 12 vg). (18)F‐fluoro‐L‐dihydroxyphenylalanine positron emission tomography (PET) at baseline and 6 months postprocedure assessed enzyme activity; standard assessments measured clinical outcomes. Results MRI‐guided administration of ascending VY‐AADC01 doses resulted in putaminal coverage of 21% (cohort 1), 34% (cohort 2), and 42% (cohort 3). Cohorts 1, 2, and 3 showed corresponding increases in enzyme activity assessed by PET of 13%, 56%, and 79%, and reductions in antiparkinsonian medication of –15%, –33%, and –42%, respectively, at 6 months. At 12 months, there were dose‐related improvements in clinical outcomes, including increases in patient‐reported ON‐time without troublesome dyskinesia (1.6, 3.3, and 1.5 hours, respectively) and quality of life. Interpretation Novel intraoperative monitoring of administration facilitated targeted delivery of VY‐AADC01 in this phase 1 study, which was well tolerated. Increases in enzyme expression and clinical improvements were dose dependent. ClinicalTrials.gov Identifier: NCT01973543 Ann Neurol 2019;85:704–714