BACKGROUND: Treatments for Churg-Strauss syndrome (CSS), a rare eosinophilic 
vasculitis characterized by asthma, sinusitis, peripheral eosinophilia, 
pulmonary infiltrates, and tissue infiltration, are limited by toxicity or poor 
efficacy. Levels of IL-5, a cytokine regulating eosinophils, can be increased in 
patients with CSS. Mepolizumab, a humanized monoclonal anti-IL-5 antibody, 
decreases steroid requirements in patients with non-CSS hypereosinophilic 
syndromes.
OBJECTIVE: The purpose of this study was to assess whether mepolizumab would 
safely allow corticosteroid tapering in patients with steroid-dependent CSS 
while decreasing serum markers of disease activity.
METHODS: This open-label pilot study treated 7 patients with 4 monthly doses of 
mepolizumab to assess whether it safely decreased CSS disease activity and 
permitted tapering of systemic corticosteroids.
RESULTS: Mepolizumab was safe and well tolerated in patients with CSS. 
Mepolizumab reduced eosinophil counts and allowed for safe corticosteroid 
reduction in all 7 subjects. On cessation of mepolizumab, CSS manifestations 
recurred, necessitating corticosteroid bursts.
CONCLUSION: Mepolizumab is a safe and well-tolerated therapy in patients with 
CSS, offering clinical benefit by enabling corticosteroid tapering while 
maintaining clinical stability.