An Open-Label, Multicenter, Extension Study to Evaluate the Safety and Tolerability of Natalizumab Following Re-Initiation of Dosing in Multiple Sclerosis Subjects Who Have Completed Study C-1801, C-1802, C-1803, or C-1808 and a Dosing Suspension Safety Evaluation

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.