The anti-IL-5 monoclonal antibody mepolizumab is approved for the treatment of eosinophil-driven diseases including EGPA in multiple regions worldwide [47–49]; however, anti-IL-5 therapies are not currently approved by the National Institute for Health and Care Excellence in the UK for the treatment of EGPA. The gene discussed is IL5; the disease is eosinophilic granulomatosis with polyangiitis.