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.