Mucopolysaccharidosis type IIIB syndrome (Sanfilippo disease) is a rare autosomic recessif disorder caused by mutations in the α-N-
acetylglucosaminidase (
NAGLU) gene coding for a lysosomal
enzyme, leading to neurodegeneration and progressive deterioration of cognitive abilities in affected children. To supply the missing
enzyme, several recent human gene therapy trials relied on the deposit of adeno-associated virus (AAV) vectors directly into the brain. We reported safety and efficacy of an intracerebral
therapy in a phase 1/2 clinical trial (https://clinicaltrials.gov/ct2/show/NCT03300453), with a recombinant AAV serotype 2/5 (rAAV2/5) coding human
NAGLU in four children with
MPS IIIB syndrome receiving immunosuppression. It was reported that AAV-mediated gene
therapies might elicit a strong host immune response resulting in decreased transgene expression. To address this issue, we performed a comprehensive analysis of cellular immunity and
cytokine patterns generated against the therapeutic
enzyme in the four treated children over 5.5 years of follow-up. We report the emergence of memory and polyfunctional CD4+ and CD8+ T lymphocytes sensitized to the transgene soon after the start of
therapy, and appearing in peripheral blood in waves throughout the follow-up. However, this response had no apparent impact on CNS transgene expression, which remained stable 66 months after surgery, possibly a consequence of the long-term immunosuppressive treatment. We also report that gene therapy did not trigger
neuroinflammation, evaluated through the expression of
cytokines and
chemokines in patients' CSF. Milder
disease progression in the youngest patient was found associated with low level and less differentiated circulating
NAGLU-specific T cells, together with the lack of proinflammatory
cytokines in the CSF. Findings in this study support a systematic and comprehensive immunomonitoring approach for understanding the impact immune reactions might have on treatment safety and efficacy of gene
therapies.