Mode of action and clinical studies with alemtuzumab.

The lymphocyte depleting anti-CD52 monoclonal antibody alemtuzumab has been used in Cambridge, UK, as an experimental treatment of multiple sclerosis since 1991. One phase-2 trial (CAMMS-223) and two phase-3 studies (CARE-MS1 and CARE-MS2) have confirmed its efficacy in treatment-naive patients, and have established superiority over interferon beta-1a in patients who continue to relapse in spite of first-line therapy (Cohen et al., 2012; Coles et al., 2008; Coles et al., 2012a; Coles et al., 2012b). Despite causing a prolonged T cell lymphopenia, significant infections have not been an issue following treatment; rather alemtuzumab's primary safety concern is secondary autoimmunity, occurring up to five years after treatment and maximally at two years: 30% of patients develops thyroid autoimmunity, and 1% develops idiopathic thrombocytopenic purpura (ITP). In addition, 4 out of 1486 patients (<0.3%) treated on the commercially sponsored studies developed glomerulonephritis. Two of these patients developed anti-glomerular basement membrane disease, a condition which may result in renal failure unless treated aggressively. In September 2013, the European Medicine Agency (EMA) ruled that the benefit-to-risk balance for alemtuzumab was favourable, approving it as a first-line therapy for adults with active relapsing remitting multiple sclerosis (under the trade name Lemtrada). Lemtrada is now also approved as a treatment of multiple sclerosis in Canada, Australia, Switzerland, Israel, Mexico and Brazil. However, in December 2013, Lemtrada failed to gain approval from the U.S. Food and Drug Administration (FDA), with concerns over trial design and safety stated as the main reasons. In this review we describe our local experience and explain the rationale behind its initial use as a treatment of multiple sclerosis and behind the design of the commercially sponsored trials, summarising their key findings. We also sum up our understanding of its mechanism of action.