Ortega et al tried to address the second of these questions by performing a post hoc analysis of data from two randomized double-blind, placebo-controlled studies of mepolizumab. The doses of mepolizumab differed in these studies. In the Mepolizumab for severe eosinophilic asthma (DREAM) trial, IV mepolizumab 75 mg, 250 mg, or 750 mg was evaluated, whereas in the Mepolizumab as Adjunctive Therapy in Patients With Severe Asthma (MENSA) trial, 75 mg IV or 100 mg subcutaneously was studied. In addition to standard care (high-dose inhaled corticosteroids plus ≥ one additional controller with or without daily oral corticosteroids), these doses were given to patients with a history of at least two severe asthma exacerbations in the previous year and raised peripheral blood eosinophil counts. In the DREAM trial, sputum eosinophils were enumerated in 14% of patients. The study by Ortega et al examined the effect of treatment (all doses combined) on the annualized rate of exacerbations in patients stratified by baseline eosinophil counts (≥ 150 cells/μL, ≥ 300 cells/μL, ≥ 400 cells/μL, and ≥ 500 cells/μL) and baseline blood eosinophil ranges (< 150 cells/μL, ≥ 150 cells/μL to < 300 cells/μL, ≥ 300 cells/μL to < 500 cells/μL, and ≥ 500 cells/μL). The main observation was that the asthma exacerbation rate reduction with mepolizumab increased progressively from 52% in patients with a baseline blood eosinophil count of at least 150 cells/μL to 70% in patients with a baseline count of at least 500 cells/μL. A similar gradation in exacerbation reduction was observed with baseline eosinophil count ranges (26% for < 150 cells/μL to 70% for ≥ 500 cells/μL). Thus, it is clear from this analysis that when exacerbation rates are modeled as a function of blood eosinophils and measured on a continuous scale, the higher the level of blood eosinophil count, the greater the treatment response to anti-IL5 therapy. A similar relationship between blood eosinophil counts and treatment response has been reported with reslizumab and benralizumab. The data that are currently available to us do not allow us to derive any inferences as to whether a particular cutoff value of blood eosinophil count (eg, > 150 cells/μL or, historically, > 300 cells/μL for mepolizumab, > 300 cells/μL for benralizumab or > 400 cells/μL for reslizumab) is specific to the treatment responses of all of these monoclonal antibodies.