Intracerebral Gene Therapy in Four Children with Sanfilippo B Syndrome: 5.5-Year Follow-Up Results

We report the safety (primary endpoint) and efficacy (secondary endpoint) of a novel intracerebral gene therapy at 5.5 years of follow-up in children with Sanfilippo B. An uncontrolled, phase 1/2 clinical trial was performed in four patients aged 20, 26, 30, and 53 months. Treatment consisted of 16 intracerebral and cerebellar deposits of a recombinant adeno-associated viral vector encoding human α-N-acetylglucosaminidase (rAAV2/5-hNAGLU) plus immunosuppression. An intermediate report at 30 months was previously published. Thirty treatment-emergent adverse events were reported between 30 and 66 months after surgery, including three classified as severe with no serious drug reactions. At 5.5 years, NAGLU activity was persistently detected in the lumbar cerebrospinal fluid (18% of unaffected control level). Circulating T cells reacting against NAGLU peptides were present, indicating a lack of acquired tolerance. Patients 2, 3, and 4 showed progressive brain atrophy and neurocognitive evolution that did not differ from untreated Sanfilippo A/B children. Patient 1, enrolled at 20 months of age, had a milder disease with normal brain imaging and a significantly better cognitive outcome than the three other patients and untreated patients, although not equivalent to normal children. After 5.5 years, the primary endpoint of this study was achieved with a good safety profile of the proposed treatment. We have also observed sustained enzyme production in the brain and absence of immunological tolerance. Cognitive benefit was not confirmed in the three oldest patients. Milder disease in the youngest patient supports further investigations of adeno-associated vector-mediated intracerebral gene therapy in Sanfilippo B.