The first clinical evidence of the successful use of mepolizumab—a monoclonal antibody that prevents the binding of IL-5 to its receptor—was described in 2010 in two distinct studies of patients with EGPA treated with mepolizumab infusions at a dose of 750 mg monthly (195, 196). This evidence concerns the gene IL5 and eosinophilic granulomatosis with polyangiitis.