Exploratory Study of the Safety, Tolerability and Efficacy of Multiple Regimens of Natalizumab in Adult Participants With Relapsing Multiple Sclerosis (MS)

Key Inclusion Criteria: * Ability to provide written informed consent * Subjects of childbearing potential must practice effective contraception during the study * A documented diagnosis of Relapsing Remitting Multiple Sclerosis (RRMS) * Free of MS relapse for 12 months prior to randomization * Treatment with natalizumab for a minimum of 12 months immediately prior to randomization. * In the 12 months prior to commencing natalizumab, subject must have experienced a minimal level of disease activity as defined by 2 or more documented clinical relapses OR 1 relapse and documented MRI activity, defined by the presence of at least 1 Gd enhancing lesion on MRI, unrelated to the relapse. Key Exclusion Criteria: * Known history of Human Immunodeficiency Virus (HIV), hepatitis C and/or hepatitis B virus * Positive for anti-natalizumab antibodies at screening * MRI positive for Gd-enhancing lesions at study entry * Subjects for whom MRI is contraindicated * History of any clinically significant cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic (including diabetes), urologic, pulmonary, neurologic (except for RRMS), dermatologic, psychiatric, renal, or other major disease * History of malignant disease, including solid tumors and hematologic malignancies (with the exception of cured basal cell and squamous cell carcinomas of the skin) * History of transplantation or any anti-rejection therapy * History of severe allergic or anaphylactic reactions or known hypersensitivity to any drug * A clinically significant infectious illness within 30 days prior to screening or progressive multifocal leukoencephalopathy (PML) or other opportunistic infections at any time * Signs or symptoms suggestive of any serious infection, based on medical history, physical examination or laboratory testing NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.