BACKGROUND: Alemtuzumab, a humanized monoclonal antibody that targets CD52 on 
lymphocytes and monocytes, may be an effective treatment for early multiple 
sclerosis.
METHODS: In this phase 2, randomized, blinded trial involving previously 
untreated, early, relapsing-remitting multiple sclerosis, we assigned 334 
patients with scores of 3.0 or less on the Expanded Disability Status Scale and 
a disease duration of 3 years or less to receive either subcutaneous interferon 
beta-1a (at a dose of 44 microg) three times per week or annual intravenous 
cycles of alemtuzumab (at a dose of either 12 mg or 24 mg per day) for 36 
months. In September 2005, alemtuzumab therapy was suspended after immune 
thrombocytopenic purpura developed in three patients, one of whom died. 
Treatment with interferon beta-1a continued throughout the study.
RESULTS: Alemtuzumab significantly reduced the rate of sustained accumulation of 
disability, as compared with interferon beta-1a (9.0% vs. 26.2%; hazard ratio, 
0.29; 95% confidence interval [CI], 0.16 to 0.54; P<0.001) and the annualized 
rate of relapse (0.10 vs. 0.36; hazard ratio, 0.26; 95% CI, 0.16 to 0.41; 
P<0.001). The mean disability score on a 10-point scale improved by 0.39 point 
in the alemtuzumab group and worsened by 0.38 point in the interferon beta-1a 
group (P<0.001). In the alemtuzumab group, the lesion burden (as seen on 
T(2)-weighted magnetic resonance imaging) was reduced, as compared with that in 
the interferon beta-1a group (P=0.005). From month 12 to month 36, brain volume 
(as seen on T(1)-weighted magnetic resonance imaging) increased in the 
alemtuzumab group but decreased in the interferon beta-1a group (P=0.02). 
Adverse events in the alemtuzumab group, as compared with the interferon beta-1a 
group, included autoimmunity (thyroid disorders [23% vs. 3%] and immune 
thrombocytopenic purpura [3% vs. 1%]) and infections (66% vs. 47%). There were 
no significant differences in outcomes between the 12-mg dose and the 24-mg dose 
of alemtuzumab.
CONCLUSIONS: In patients with early, relapsing-remitting multiple sclerosis, 
alemtuzumab was more effective than interferon beta-1a but was associated with 
autoimmunity, most seriously manifesting as immune thrombocytopenic purpura. The 
study was not powered to identify uncommon adverse events. (ClinicalTrials.gov 
number, NCT00050778.)