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.