Multiple sclerosis 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). Patients with multiple sclerosis 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. Multiple sclerosis affects 400,000 people in the United States and over 2.5 million worldwide. Relapsing remitting multiple sclerosis, in which symptom-free periods alternate with phases of active disease affects 85% of patients. Usual care for multiple sclerosis includes drugs that interfere with the overactive immune response such as corticosteroids and other immune-modifying drugs, in particular, interferon beta-1a.