Early Versus Delayed Start of Ocrevus Zunovo for Relapsing Multiple Sclerosis

Participants With Relapsing Multiple Sclerosis (Rapid-Start and Delayed-Start Cohorts) Inclusion Criteria: * Age 18 years or older. * Diagnosis of relapsing-remitting multiple sclerosis according to the 2017 McDonald criteria. * At least one gadolinium-enhancing lesion on an MRI of the brain, cervical spine, or thoracic spine within 4 weeks of relapse or hospitalization. Exclusion Criteria: * Diagnosis of primary progressive multiple sclerosis. * Active hepatitis B. * Current pregnancy. * Allergy to gadolinium contrast or known allergy to ocrelizumab. * Unable to complete an MRI. * Contraindication to or intolerance of oral or intravenous corticosteroids. * Another known neurological disorder, including a history of progressive multifocal leukoencephalopathy. * Active bacterial, viral, fungal, or mycobacterial infection, or a history of recurrent aspiration pneumonia requiring antibiotic treatment. * A condition that may require chronic systemic corticosteroids or immunosuppressants during the study. * Treatment with an anti-CD20 or other B-cell-depleting therapy within 6 months before enrollment. * Active cancer or malignancy. * Prisoner status. * Limited English-speaking capacity. * Unable to provide informed consent. Healthy Control Participants Inclusion Criteria: * Age 18 years or older. * Able and willing to provide written informed consent and undergo study blood draws. * No diagnosis or history of multiple sclerosis, clinically isolated syndrome, or another inflammatory or demyelinating disorder of the central nervous system. * In generally good health, as determined by medical history and investigator review. Exclusion Criteria: * Multiple sclerosis, clinically isolated syndrome, myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), neuromyelitis optica spectrum disorder (NMOSD), or another neurological disorder that may affect study results. * An autoimmune, inflammatory, hematologic, or immunodeficiency disorder that may affect B- or T-cell measurements. * Active bacterial, viral, fungal, or mycobacterial infection at enrollment or blood collection. * Current use of a disease-modifying therapy, B-cell-depleting therapy, systemic immunosuppressant, immunomodulatory therapy, or chronic systemic corticosteroids. * Active cancer or malignancy, except adequately treated localized skin cancer if permitted by the investigator. * Current pregnancy. * A medical condition that, in the investigator's judgment, could increase risk, interfere with participation, or affect interpretation of immune cell or biomarker results. * Unable or unwilling to undergo blood collection. * Prisoner status. * Limited English-speaking capacity. * Unable to provide informed consent.