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 over the 3 month Retrospective Period.
* On a stable type and dose regimen of up to a maximum of 4 approved Anti Seizure Drugs for at least 1 month prior to the Retrospective Period.
* 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 to general anesthesia, surgery, or intra-operative magnetic resonance imaging (MRI).
* 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.
* Bilateral or multifocal epilepsy; or inability to confidently lateralize seizure onset.
* 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.
* MRI evidence of epileptogenic, extra-temporal lesions, or dual temporal lobe pathology.
* Status epilepticus within the year prior to Screening.