The main goals of this clinical study are to learn if AMT-260 is safe and tolerable and works to reduce the frequency of seizures in adults with unilateral mesial temporal lobe epilepsy (MTLE).

In this first clinical study of AMT-260, two dose levels will be studied to find the best dose of AMT-260. All eligible participants will receive AMT-260 at one of the two dose levels (i.e., there is no placebo in this study).

AMT-260 is intended for a one-time administration, without the need to remove or destroy any part of the brain. Participation in this study would not prevent later pursuit of other treatment options.

Participants will be monitored through study site visits, telephone calls, blood tests, and questionnaires about how their seizures affect daily life. Participants will record seizures using an electronic seizure diary.

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.