Cell-Selective Adeno-Associated Virus-Mediated Gene Regulation Therapy Rescues Mortality and Seizure Phenotypes in a Dravet Syndrome Mouse Model and Is Well Tolerated in Nonhuman Primates.

Dravet syndrome (DS) is a developmental and epileptic encephalopathy caused by monoallelic loss-of-function variants in the gene. encodes for the alpha subunit of the voltage-gated type I sodium channel (Na1.1), the primary voltage-gated sodium channel responsible for generation of action potentials in GABAergic inhibitory interneurons. In these studies, we tested the efficacy of an adeno-associated virus serotype 9 (AAV9) gene regulation therapy, AAV9-RE-eTF, designed to target transgene expression to GABAergic inhibitory neurons and reduce off-target expression within excitatory cells, in the mouse model of DS. Biodistribution and preliminary safety were evaluated in nonhuman primates (NHPs). AAV9-RE-eTF was engineered to upregulate expression levels within GABAergic inhibitory interneurons to correct the underlying haploinsufficiency and circuit dysfunction. A single bilateral intracerebroventricular (ICV) injection of AAV9-RE-eTF in postnatal day 1 mice led to increased mRNA transcripts, specifically within GABAergic inhibitory interneurons, and Na1.1 protein levels in the brain. This was associated with a significant decrease in the occurrence of spontaneous and hyperthermia-induced seizures, and prolonged survival for over a year. In NHPs, delivery of AAV9-RE-eTF by unilateral ICV injection led to widespread vector biodistribution and transgene expression throughout the brain, including key structures involved in epilepsy and cognitive behaviors, such as hippocampus and cortex. AAV9-RE-eTF was well tolerated, with no adverse events during administration, no detectable changes in clinical observations, no adverse findings in histopathology, and no dorsal root ganglion-related toxicity. Our results support the clinical development of AAV9-RE-eTF (ETX101) as an effective and targeted disease-modifying approach to SCN1A DS.