Mepolizumab is an anti-IL-5 humanized IgG1κ antibody that is FDA-approved for the treatment of severe eosinophilic asthma, hypereosinophilic syndrome, and eosinophilic granulomatosis with polyangiitis (EGPA) (24). Here, IL5 is linked to eosinophilic granulomatosis with polyangiitis.