Phase 2 Efficacy, Safety, and Tolerability Study of Natalizumab in Focal Epilepsy

Key Inclusion Criteria: * Must have focal epilepsy diagnosed on clinical grounds and as applicable supported by electroencephalogram findings \[Scheffer 2017\] and brain imaging. Participants with multifocal epilepsy may be included if all other entry criteria are met. * Must have a drug-resistant epilepsy defined as failure of adequate trials of 2 (or more) tolerated and appropriately chosen and used AEDs (whether as monotherapies or in combination) \[Kwan 2010\]. * Experiences 6 or more seizures during the 6-week prospective baseline period and is not seizure free for more than 21 consecutive days during the prospective baseline period Key Exclusion Criteria: * Focal aware seizures without motor signs are the only seizure type. * Diagnosis of generalized, combined generalized and focal, or unknown epilepsy * Known progressive structural CNS lesion. * History of seizures occurring in predominantly clustered patterns, as determined by the Investigator, over the 12 months prior to the Screening Visit (Week -6) or during the 6-week prospective baseline period, where individual seizures cannot be counted. * History of status epilepticus within the previous 6 months. * Known history or presence of non-epileptic seizures. NOTE; Other protocol defined Inclusion/Exclusion criteria may apply