Natalizumab (NTZ) is a FDA approved treatment for relapsing-forms of multiple sclerosis (MS) with pivotal studies showing an annualized relapse-rate (ARR) reduction of 68%, a reduction of new gadolinium (Gd+) lesions by 92% and a reduction of disability of 42% compared to placebo.NTZ is highly effective in controlling MS but the risk of developing progressive multifocal leukoencephalopathy (PML) increases with the duration of the use of natalizumab. It can have a serious and life threatening complication in about 1 in 500 to 1 in 250 patients who have had more that 18 infusions due PML and who have a detected antibody (Ab) for the JC virus. The risk of PML is much greater in patients who have had prior immunosuppressive (IS) treatment. The combination of detected anti-JCV Ab , duration of NTZ treatment of greater than 24 months and prior IS increases the risk of development PML to an incidence of 11 per 1000 treated patients. So there is a need to have an alternative MS disease modifying treatment (DMT) to use for patients at risk to develop PML from NTZ treatment that might be sufficiently effective for MS so as not to have the patients' MS worsen while lowering or eliminating the risk of PML.