Mepolizumab was the first registered (in 2004) anti–IL-5 biologic for the treatment of severe eosinophilic asthma (SEA), before validation in other conditions including CRSwNP, hypereosinophilic syndrome (HES), and eosinophilic granulomatosis with polyangiitis (EGPA). Here, IL5 is linked to chronic rhinosinusitis with nasal polyps.