Severe hypereosinophilic syndrome successfully treated with a monoclonal antibody against interleukin 5 receptor α - benralizumab.

Hypereosinophilic syndrome (HES) is a group of a rare diseases characterized by marked eosinophilia in blood or tissue and eosinophil-related clinical manifestations. Benralizumab is a humanized, monoclonal antibody against interleukin 5 (IL-5) receptor α, which is expressed on human eosinophils. Here, we present the case of a patient with severe HES in whom treatment with benralizumab, an anti-IL-5 receptor monoclonal antibody, was initiated 6 months ago. Prior to benralizumab administration, the patient was treated with glucocorticoids (GS) and mepolizumab. However, instead of the applied treatment and normal level of peripheral eosinophils the patient presented with fluctuating lower respiratory tract symptoms and recurrent exacerbations of HES. Treatment with benralizumab (30 mg s.c. every 4-6 weeks) was started, resulting in significant improvement of respiratory signs and symptoms, normalization of eosinophil count and significant reduction of the methylprednisolone dose (after 5 doses of benralizumab administration). No substantial side effects have been noted during treatment and 6-month follow-up. We argue that in the severe and relapsing course of HES, rescue treatment with benralizumab should be taken into account, particularly in cases of relative inefficacy of GS and mepolizumab.