Evaluating the Efficacy and Safety of Transitioning Patients From Natalizumab to Ocrelizumab

Inclusion Criteria: * Male or female with relapsing form of MS, age 18 to 65, inclusive, at the time of informed consent. * In the opinion of the investigator, able to understand the purpose and risk of the study and provide signed informed consent document. * Must have received a stable dose of NTZ for 12 or more consecutive months, and have had no evidence of on-NTZ disease activity (clinically or on MRI) for the 6 months prior to the screening visit. * Naïve to OCR. * No evidence, in the opinion of the investigators of significant cognitive limitation or psychiatric disorder that would interfere with the conduct of the study. * EDSS of ≤ 6.0 at screening. * Female patients of childbearing potential must practice effective contraception and continue contraception during the study. Exclusion Criteria: * History of primary or secondary progressive multiple sclerosis. * Evidence of active hepatitis B infection at screening. * Any mental condition of such that patient is unable to understand the nature, scope, and possible consequences of the study. * Patients with untreated hepatitis C or tuberculosis. Patients who have history of progressive multifocal leukoencephalopathy (PML) or known to be HIV positive, per standard care. * Any persistent or severe infection. * Pregnancy or lactation. * Significant or uncontrolled somatic disease or severe depression in the last year. * Inability to complete an MRI. * Previous treatment with B-cell targeted therapies. * Current use of immunosuppressive medication. * Patients who have had evidence of disease activity within the 6 months prior to screening. This includes MS relapse, or new or enlarging T2 lesions or Gd+ enhancing lesions, or disability progression. * Patients with any significant comorbidity that in the opinion of the investigator, would interfere with participation in the study.