Natalizumab (Tysabri®) within 6 months prior to Screening OR 1 month prior to screening if subject has a positive Nabs (neutralizing antibodies) to Tysabri® Treatment within the past 5 years or current treatment with any of the following agents: cyclosporine, cladribine, agents that are immunosuppressive (e.g., entanercept), murine protein, T-cell vaccination), or stem cell transplantation prior to Screening.