PV interneuron-targeted CRISPRa rescue of SCN1A haploinsufficiency in Dravet syndrome

Dravet syndrome is a severe epileptic encephalopathy caused by SCN1A haploinsufficiency, which leads to reduced NaV1.1 expression in parvalbumin (PV)-expressing interneurons and disrupted excitatory-inhibitory balance in the brain. We developed an AAV-based CRISPR activation system (AAV9-E2-dCas9-VP64) to selectively upregulate SCN1A from its endogenous locus in PV interneurons. An in vitro saturating guide RNA (gRNA) screen across the human SCN1A promoter identified a lead guide with robust and highly specific engagement of the SCN1A locus. This lead gRNA was validated in human Dravet syndrome model GABAergic neurons, where dose-dependent and specific SCN1A upregulation was observed. Intracerebroventricular (ICV) administration in a mouse model of Dravet syndrome produced dose-dependent improvement in survival as well as reduced susceptibility to hyperthermia-induced seizures and increased NaV1.1 protein expression, with maintained PV interneuron selectivity and minimal off-target expression. In a study in juvenile cynomolgus macaques, MRI-guided ICV administration of the vector was well tolerated, achieved broad cortical biodistribution, and maintained strong detargeting of peripheral tissues, with substantially lower peripheral dCas9 expression relative to the brain. These results support PV interneuron-selective SCN1A gene modulation via CRISPR activation as a promising therapeutic strategy for Dravet syndrome. AAV9-E2-dCas9-VP64 (RT101) is currently in preclinical development and is being advanced toward evaluation in the clinic.