Alemtuzumab is a humanized monoclonal antibody directed against CD52. A single cycle of alemtuzumab, administered over 5 days, depletes lymphocytes. Reconstitution causes prolonged alterations in the lymphocyte repertoire, with relatively increased regulatory T-cell numbers and reduced naïve T cells. It is currently approved for the treatment of B-cell chronic lymphocytic leukemia and is being considered for licensing for multiple sclerosis (MS).When first used, alemtuzumab successfully reduced relapses and new lesion formation based on magnetic resonance imaging in people with progressive MS, but this cohort continued to accumulate disability, associated with progressive cerebral atrophy, presumably due to axonal degeneration. From this experience, we advocated that immunotherapies should be given early in the course of the disease. Since then, one phase II and two phase III trials have shown that alemtuzumab reduces the relapse rate, compared with the active comparator interferon beta-1a (IFNβ-1a), in treatment-naïve and treatment-experienced MS up to 10 years from disease onset. Furthermore, in two of these trials, alemtuzumab reduced the risk of accumulating disability compared with IFNβ-1a; indeed alemtuzumab treatment led to an improvement in disability and reduction in cerebral atrophy. Safety issues are infusion-associated reactions, mainly controlled by methyl-prednisolone, antihistamines, and antipyretics; mild to moderate infections; and autoimmunity. After 5 years, 30 to 40% of alemtuzumab patients have developed autoimmunity, largely against the thyroid gland, but rarely (2%) against platelets in immune thrombocytopenia, and in a few cases, Goodpasture's renal syndrome.Alemtuzumab is an effective therapy for early relapsing-remitting multiple sclerosis, offering disability improvement at least to 5 years after treatment. Its use requires careful monitoring so that potentially serious side effects can be treated early and effectively.
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