In this large (616 patients), double-blind, placebo-controlled, dose-ranging 
study of mepolizumab (a monoclonal antibody that blocks IL-5 binding to its 
receptor), patients were given placebo, 75-, 250- or 750-mg mepolizumab by 
intravenous infusion every 4 weeks for 1 year. Exacerbation rates at all doses 
were 50% less than those in the placebo group. There were no changes in any 
other asthma measures (symptoms, quality of life or lung function). This may be 
a useful advance for a subgroup of severe asthma with frequent exacerbations and 
persistent eosinophilia, which may be about half of severe asthmatics. More 
information on patient selection and cost-benefit will be required.