AMT-260 Gene Therapy Study in Adults With Unilateral Refractory Mesial Temporal Lobe Epilepsy

Inclusion Criteria: * Diagnosis of unilateral refractory MTLE * History of seizures with an average of ≥ 2 documented focal impaired awareness seizures or focal to bilateral tonic-clonic seizures per 30-day period in the 3 months prior to screening. * On a stable type and dose regimen of up to a maximum of 4 approved Anti Seizure Drugs for at least 6 months prior to screening. * Confirmed unilateral hippocampal pathology and concordant unilateral seizure focus * No evidence of focal neurocognitive dysfunction, inconsistent with disease pathology- related MRI and/or (18F)FDG-PET findings. * Women of childbearing potential (WOCBP) and fertile male subjects must be willing and able to use highly effective methods of birth control consistently and correctly throughout the study. * For WOCBP only: Negative pregnancy test. Exclusion Criteria: * Implanted devices that would contraindicate MRI; MRI-compatible devices must be implanted ≥3 months prior to Screening (vagus nerve stimulation devices will be up to discretion of the Investigator). * Any other contraindications for generalized anesthesia or surgery. * Medications that could confound clinical (e.g., antipsychotic medication and anti-viral therapy) and laboratory evaluations or could affect a participant's safety or their ability to undergo the neurosurgical procedure or comply with the procedures and study visit schedule. * Any seizures with contralateral or extra-temporal icta onset captured on EEG. * Dementia or other progressive neurological disorders and progressive brain lesions. * Previous major disease-unrelated neurosurgical intervention due to intracranial tumor, trauma, or bleeding and/or history of previous intracranial surgery for treatment of epileptic seizures, not including diagnostic stereo-EEG. * Magnetic resonance imaging evidence of epileptogenic, extra-temporal lesions, or dual temporal lobe pathology. * Inadequate vaccination status (including flu shots and other relevant immunizations such as COVID-19 per local guidelines and regulations).