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Eosinophils in chronic obstructive pulmonary disease: are they just another biomarker?

PURPOSE OF REVIEW
Interest in blood eosinophils as a biomarker of responsiveness to therapy in chronic obstructive pulmonary disease (COPD) continues to grow, with recommendations regarding their adjunctive use incorporated into the GOLD 2019 treatment algorithm. The present review summarizes some key recent papers referencing differential treatment effects based on blood eosinophil counts.


RECENT FINDINGS
Post-hoc analyses of trials of inhaled corticosteroids in COPD have shown greater treatment responses in patients with higher blood eosinophil levels, with some exceptions. Eosinophil-directed treatment with oral corticosteroids showed equivalent benefits to noneosinophil-directed therapy, with reduced corticosteroid exposure. Prespecified analyses of recent prospective trials of therapies incorporating inhaled corticosteroids were generally supportive of previous findings, so evidence for the use of blood eosinophils as biomarkers is gathering. Nonetheless, the anti-interleukin (IL)-5 receptor antagonist benralizumab, which depletes blood eosinophils, showed no treatment benefit in patients with COPD selected for eosinophilic phenotype and treatment of COPD with the IL-5 antagonist, mepolizumab showed inconsistent results.


SUMMARY
The 2019 GOLD COPD Strategy document embraced the use of the blood eosinophil to guide ICS therapy in management of patients with stable COPD and frequent exacerbations. Although post-hoc and several prospective studies with prespecified subgroup analyses have supported this approach, questions still remain about how to incorporate this new assessment tool into real-life management of COPD and more research is required to validate its adoption into clinical practice. There is an absence of data to support the use of biologic therapy in patients with an eosinophilic COPD phenotype at this stage.