A Safety and Efficacy study of AAV2-hAADC for AADC deficiency

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The goal of this proposal is to further evaluate the safety and feasibility of gene transfer to provide aromatic L- amino acid decarboxylase (AADC) enzyme into the midbrain of patients with AADC deficiency and continue Biologics License Application (BLA)-enabling studies as per FDA recommendations. AADC deficiency is a devastating genetic neurometabolic disorder which causes hypotonia, dystonia, intense and long-lasting oculogyric crises (OGC), developmental delay and chronic and severe neurological dysfunction. A gene therapy based on delivering of a recombinant adeno-associated virus carrying the DDC human gene (AAV2-AADC) to the brain structures that physiologically AADC enzyme (midbrain) could be a most needed disease-modifying treatment for AADC deficiency. Eight (8) AADC deficient patients have been treated (160 µL) in our initial NIH- funded trial in the US under BB-IND-16127 and an additional 15 subjects under an ethics committee-approved compassionate use program (CUP) in Poland. The latter received a larger infusion volume (≤300 μL) and a shorter surgical procedure. Both approaches were safe and well-tolerated regardless of dose or volume of infusion. OGCs stopped a few weeks after the surgery and subjects’ sleep, mood and irritability improved. Most subjects are gaining head control and muscular tone, developing purposeful movements and some are even sitting up and starting to walk without support, regardless of their age. Encouraged by the safety and positive biomarker and clinical outcomes observed in those groups, we propose an extension of the BB-IND-16127 study to (i) determine the long-term (up to 5 years) safety and tolerability of the surgical infusion of already treated subjects (n=8) (ii) determine the safety and tolerability of a larger volume of Cohort 2 vector concentration into the SN/VTA administered via a surgical procedure optimized to increase safety by reducing surgical and anesthesia times (single-cannula insertion per hemisphere) in AADC deficient patients >4 years, and (iii) demonstrate effective restoration of AADC function by measuring CSF neurotransmitter metabolites and changes in brain FDOPA uptake on PET imaging. This will be a multi-center study with subjects to be treated at The Ohio State University and at the University of California San Francisco. As per our discussions with FDA, the study design includes a 12-month lead-in period that will serve as a natural history control group to explore potential efficacy of this novel treatment. Cohorts 3 (4-13 years, n≤12) and 4 (>13 years, n≤12) will then receive a larger infusion volume of AAV2-AADC at the same titer Cohort 2 received (2.6 x 1012 vg/mL; up to 300 μL/hemisphere). Renewal of funding for this trial will enable assessment of the safety and tolerability of an optimized dose and delivery procedure to enhance distribution of AADC expression within the midbrain, which we hypothesize may lead to further clinical improvement. Completion of this exploratory clinical trial will pave the way to registration of this disease-modifying AAV2-hAADC gene therapy for AADC deficiency and future gene therapies for other neurological disorders.