Chronic obstructive pulmonary disease's eosinophilic phenotype: Clinical characteristics, biomarkers and biotherapy.

COPD is a chronic, heterogeneous inflammatory disorder of the airways with persistent and poorly reversible airflow limitation, causing symptoms such as cough, shortness of breath, and sputum production. Despite optimal treatment, some patients remain symptomatic due to the disease's heterogeneity, manifesting in various phenotypes. One notable phenotype involves eosinophilic inflammation, with a variable prevalence. Identifying eosinophilic phenotypes is crucial for tailored therapeutic strategies, as they respond favorably to corticosteroids and potentially biologics. Recent advances in both clinical trials and spontaneous research have helped understand the biological and clinical characteristics of this phenotype, although no universal consensus has been reached yet on the definition of the cut-off values of the eosinophil peripheral blood count. Moreover, there is evidence of novel emerging biomarkers which might go beyond the sole eosinophil count, while significant advancements in terms of pharmacological treatment have been made, with dupilumab being the first biological drug being licensed for COPD patients with elevated circulating eosinophils in the stable phase. In light of the above, although several papers have been written on the relationship between eosinophils and COPD, in the present work we endeavored to summarize and discuss the pivotal literature findings regarding the eosinophilic COPD in order to help define the biological and clinical features of this peculiar phenotype, with particular attention to the use of established and emerging biomarkers, as well as current and future therapeutic perspectives.