An early-stage clinical trial reported that experimental gene therapy using chemogenetics nearly eliminated seizures in three adults with drug-resistant epilepsy tied to hippocampal sclerosis. In each participant, seizures fell by more than 90% per month after receiving gene-laden viral vectors infused directly into the seizure source region. The approach uses engineered viruses to deliver a gene that makes neurons responsive to a system-compatible drug, allowing clinicians to adjust treatment potency with pharmacologic control. The investigators reported no serious side effects in the small cohort. Independent neurologists cautioned that the study remains small and raised questions about long-term exposure to the post-treatment drug, which has known safety considerations at higher doses.