Natalizumab Re-Initiation of Dosing

Study 101-MS-322 (NCT00306592) is conducted to evaluate the safety of natalizumab monotherapy following re-exposure to natalizumab of former clinical trial participants in Studies C-1801 (NCT00027300), C-1802 (NCT00030966), and C-1803 (NCT00097760). This study includes participants in North America. In parallel with the conduct of this study, a similar study, 101-MS-321 (NCT00297232) is initiated for participants in Europe and the rest of the world. The primary purpose and primary outcome for both studies are identical, therefore, the combined Week 48 data from both studies are presented. In addition, after 48 weeks, participants from 101-MS-322 (NCT00306592) can enter study 101-MS-321 (NCT 00297232), which is considered the Long-Term Treatment Period of 101-MS-322 (NCT00306592).