Key Inclusion Criteria:  Male or Female, age ≥18 to 55 Focal seizures, clinically defined as TLE Has failed to achieve seizure control despite adequate trials of at least 2 ASDs at appropriate doses Currently on stable doses (at least 1 month) of approved ASDs Single seizure focus confirmed as within one temporal lobe For subjects entering Stage 1, seizure focus is in the non-dominant hemisphere. Seizure frequency averages ≥2 per 28-day period over the 6 months prior to screening.  Key Exclusion Criteria:  Epilepsy due to other and/or progressive neurologic disease Significant other medical condition which would impair safe participation Primary or secondary immunodeficiency Suicide attempt in the past year Severe psychiatric disorders Chronic indwelling intracranial device MRI indicating potential malignant lesion Pregnancy, or currently breastfeeding