Multiple sclerosis (MS) is a chronic disabling disease of the central nervous system in which the body’s immune cells attack and destroy the myelin coating of nerve cells (demyelination). MS is believed to affect approximately 400,000 people in the United States, striking primarily between the ages of 20 and 50 years, and disproportionately affecting women. Patients with MS have characteristic lesions on imaging studies of the brain and spinal cord. These lesions are believed to result when leukocytes (white blood cells) cross the blood-brain barrier and initiate a series of events resulting in inflammation, demyelination, and plaque formation. The most common forms of MS are relapsing-remitting (RRMS) and primary progressive (PPMS). Usual care for MS includes drugs that interfere with the overactive immune response such as corticosteroids and other immunemodifying drugs, in particular, interferon beta-1a. However, B cells, immune cells that make antibodies, have now been implicated and, since B-cell depletion has shown benefit in autoimmune disorders like rheumatoid arthritis, it is being explored for MS.