Blood eosinophil count group shifts and kinetics in severe eosinophilic asthma

Abstract

Background: Blood eosinophil count (BEC) measurements are a noninvasive, relatively reliable surrogate marker for eosinophilic airway inflammation. Single measurements of peripheral BEC greater than or equal to 150 cells/μL predict the response to anti-eosinophil therapies for patients with characteristics of severe eosinophilic asthma.

Objective: To describe how BECs shift over time for patients with severe, uncontrolled asthma receiving placebo in 2 large, randomized, placebo-controlled clinical trials of benralizumab (SIROCCO and CALIMA).

Methods: Our analysis included all adult patients who were randomized to placebo in the SIROCCO and CALIMA phase III benralizumab studies. Patients were categorized into baseline BEC groups of less than 150 cells/μL, greater than or equal to 150 cells/μL but less than 300 cells/μL, and greater than or equal to 300 cells/μL. The timing of the initial shift from baseline to a different group was evaluated at weeks 4, 8, 24, and 40 and at the end of treatment. Baseline characteristics, including oral corticosteroid use, were described based on the presence or absence of a BEC group shift.

Results: Of the 734 evaluable patients, 65% (n = 474) shifted BEC groups during the study, and most patients (86% [n = 410]) shifted by week 24. Patients who started in the less than 150 cells/μL group tended to shift groups earlier, with 59% shifting by week 4 compared with 38% to 55% for other groups in the same time frame. Patients who shifted BEC groups vs those who did not tend to have lower BECs, more oral corticosteroid use, and less incidence of nasal polyps or past polypectomy.

Conclusion: A single BEC measurement, particularly when low, may be inadequate to help establish a phenotype of severe eosinophilic asthma.

Trial registration: ClinicalTrials.gov Identifiers NCT01928771 (SIROCCO trial) and NCT01914757 (CALIMA trial).