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This article summarizes pooled data from three Phase 3 trials demonstrating that mepolizumab reduces COPD exacerbations in patients with elevated blood eosinophil counts (BEC), regardless of whether these elevations are persistent or variable over time. Benefits were observed in exacerbation reduction including those requiring emergency care or hospitalization, while patients with persistently low BECs (<150 cells/µL) showed no therapeutic advantage. This finding challenges the notion that persistent eosinophilia is required for selecting eligible patients and supports a broader identification of treatable eosinophilic COPD phenotypes.
Study Background
Chronic obstructive pulmonary disease (COPD) is a progressive respiratory condition characterized by airflow limitation and chronic inflammation. Exacerbations contribute heavily to morbidity, mortality, and healthcare costs. Blood eosinophil count (BEC) has emerged as a biomarker for type 2 (T2) inflammation, which can predict responsiveness to eosinophil-targeted therapies like mepolizumab, an anti-IL-5 monoclonal antibody that reduces eosinophil activity. However, BEC can be variable within patients over time, raising questions about the most reliable criteria for identifying candidates for treatment. This study addresses the impact of BEC variability on the efficacy of mepolizumab in COPD, potentially refining biomarker-driven patient selection and therapeutic strategy.
Study Design
Data were pooled from three randomized, double-blind, placebo-controlled Phase 3 clinical trials: METREX (NCT02105948), METREO (NCT02105961), and MATINEE (NCT04133909). Participants included patients with COPD who received either 100 mg mepolizumab or placebo. Each patient’s historical BEC within 12 months prior to randomization was recorded alongside screening and baseline counts. The primary efficacy endpoint was annualized rate of moderate or severe COPD exacerbations. Secondary analyses included exacerbations leading to emergency department (ED) visits or hospitalizations. Subgroup analyses examined outcomes stratified by BEC thresholds at different timepoints, evaluating persistently elevated, intermittently elevated, and persistently low eosinophil profiles.
Key Findings
The pooled analysis demonstrated that mepolizumab significantly reduced annualized rates of moderate or severe COPD exacerbations in patients with elevated BEC (≥150 cells/µL) at any time within the 12 months pre-randomization, at screening, or baseline. Notably:
- Patients with any BEC elevation ≥300 cells/µL showed a 21% reduction in exacerbation rates versus placebo.
- Those with persistently elevated BECs experienced a 12% to 27% reduction in exacerbations depending on the subgroup definition.
- Patients with variable eosinophil counts—alternating between elevated and non-elevated states—demonstrated a 22% to 36% reduction in exacerbations with mepolizumab.
- Mepolizumab reduced exacerbations requiring ED visits and/or hospitalizations across subgroups with BEC ≥150 cells/µL, emphasizing clinical relevance.
- Conversely, patients with persistently low BEC (<150 cells/µL) throughout the observation period did not benefit.
The data support the hypothesis that a single measurement or historical elevated BEC can be sufficient for identifying patients likely to respond to mepolizumab, and that persistent eosinophil elevation is not mandatory.
Expert Commentary
These results provide compelling evidence to expand COPD patient eligibility criteria for mepolizumab treatment beyond persistent eosinophilia. The variability in BEC—long considered a limitation—may in fact represent a treatable phenotype. This aligns with evolving understanding that COPD is a heterogeneous disease, with eosinophilic inflammation as a dynamic component. Clinicians should consider historical and intermittent elevations in BEC when assessing patients, rather than relying solely on a single baseline measurement. Further research is warranted to optimize timing and frequency of BEC assessments to guide therapy.
However, the heterogeneity among the three trial populations and the varying BEC thresholds employed could affect generalizability. Additionally, longitudinal biomarker stability and factors influencing BEC fluctuations (e.g., corticosteroid use, infections) merit consideration.
Conclusion
Mepolizumab shows clinically meaningful reductions in COPD exacerbations in patients with type 2 inflammatory features, including those with variable blood eosinophil counts over time. Persistent eosinophilia is not a prerequisite for treatment responsiveness. These findings support more flexible biomarker-based approaches in identifying eosinophilic COPD phenotypes and tailoring personalized inhaled and biologic therapies.
Funding and Clinical Trials Registration
The analysis was supported by data from the METREX (NCT02105948), METREO (NCT02105961), and MATINEE (NCT04133909) Phase 3 clinical trials. Funding details were not specifically provided in the abstract.
References
1. Criner GJ, Watz H, Han MK, Martinez FJ, Gould S, Min J, Biswas A, Kolterer S, Singh D. Mepolizumab Efficacy in COPD: Insights from Longitudinal Patterns of Blood Eosinophil Counts and Their Variability Across Three Clinical Trials. American Journal of Respiratory and Critical Care Medicine. 2026 Jun 9. PMID: 42265988.
2. Pavord ID, Chanez P, Criner GJ, et al. Mepolizumab for eosinophilic chronic obstructive pulmonary disease. N Engl J Med. 2017;377(17):1613-1629.
3. Bafadhel M, McKenna S, Terry S, et al. Blood eosinophils to direct corticosteroid treatment of exacerbations of chronic obstructive pulmonary disease: a randomized placebo-controlled trial. Am J Respir Crit Care Med. 2012;186(1):48-55.
4. Singh D, Kampschulte J, Cromwell O, et al. Longitudinal blood eosinophil variability in COPD and impact on inhaled corticosteroid outcomes: a prospective cohort study. Eur Respir J. 2021;57(5):2002954.
