A Multicenter, Randomized, Double-blind, Placebo-controlled, Parallel Group Phase III Study to Evaluate Corticosteroid-reduction and -sparing effects of Mepolizumab 750 mg intravenously in Subjects with Hypereosinophilic Syndromes (HES) and to evaluate the Efficacy and Safety of Mepolizumab in controlling the Clinical Signs and Symptoms of HES over Nine Months
