<b>Background:</b> The anti-IL-5 monoclonal antibody, mepolizumab, has shown clinical efficacy and safety for the treatment of severe eosinophilic asthma (SEA), chronic rhinosinusitis with nasal polyps (CRwNP) and eosinophilic granulomatosis with polyangiitis (EGPA). The gene discussed is IL5; the disease is eosinophilic granulomatosis with polyangiitis.