STRATA

Treatment tested

• Natalizumab

  Integrin alpha-4/beta-1 inhibitor|Integrin alpha-4/beta-7 inhibitor

Key Inclusion Criteria * MS subjects who completed Study C-1801 (NCT00027300), C-1802 (NCT00030966), or C-1803 (NCT00097760) and a Dosing Suspension Safety Evaluation (neurological examination or a magnetic resonance imaging scan) or participated in the IMA 04001 (STARS) Study * Subjects who are considered by the Investigator to be free of signs and symptoms suggestive of progressive multifocal leukoencephalopathy and willing to discontinue and remain free from concomitant immunosuppressive or immunomodulatory treatment (including IFN-beta and glatiramer acetate) while being treated with natalizumab during the study. * In addition, subjects who completed 48 weeks of treatment in Study 101-MS-322 (NCT00306592) in Canada will be allowed to enter this study at the start of the long-term treatment period (Week 52 - 480). Key Exclusion Criteria * Considered by the Investigator to be immunocompromised * History of persistent anti-natalizumab antibodies, based upon testing from prior natalizumab studies * History of any major disease or malignancy * Discontinued natalizumab in a previous study due to allergic reaction NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.

The primary objectives for the initial treatment period of this study are to further evaluate the safety of natalizumab monotherapy by evaluating the risk of hypersensitivity reactions and immunogenicity following re-exposure to natalizumab and confirming the safety of switching from interferon (IFN), glatiramer acetate, or other multiple sclerosis (MS) therapies to natalizumab. The primary objective for the long-term treatment period of this study is to evaluate the long-term impact of natalizumab monotherapy on the progression of disability measured by Expanded Disability Status Scale (EDSS) changes over time.