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The last decade has seen the approval of several new biologics for the treatment of severe asthma-targeting specific endotypes and phenotypes. This review will examine how evidence generated from the mepolizumab clinical development program showed that blood eosinophil counts, rather than sputum or tissue eosinophil counts, evolved as a pharmacodynamic and predictive biomarker for the efficacy of treatment with mepolizumab in patients with severe eosinophilic asthma. Based on the available evidence and combined with clinical judgement, a baseline blood eosinophil threshold of 150 cells/μL or greater or a historical blood eosinophil threshold of 300 cells/μL or greater will allow selection of patients with severe eosinophilic asthma who are most likely to achieve clinically significant reductions in the rate of exacerbations with mepolizumab treatment.

Original publication




Journal article


The Journal of allergy and clinical immunology

Publication Date





1509 - 1518


Respiratory Therapeutic Area, GlaxoSmithKline, Research Triangle Park, NC. Electronic address:


Blood Cells, Eosinophils, Sputum, Animals, Humans, Asthma, Pulmonary Eosinophilia, Disease Progression, Anti-Asthmatic Agents, Interleukin-5, Leukocyte Count, Severity of Illness Index, Predictive Value of Tests, Biomarkers, Pharmacological, Antibodies, Monoclonal, Humanized