Surface Expression of CD63 and HLA-DR in circulating eosinophils correlates with Improved Clinical Control After Treatment Optimization in asthma

Background Eosinophils are key effectors in asthma, especially within the T2-high phenotype. Conventional biomarkers such as blood eosinophils, FeNO, and IgE incompletely reflect disease activity. Surface markers like CD63 and HLA-DR might provide additional insight into eosinophil activation and treatment response. Objective To evaluate whether CD63 and HLA-DR expression on circulating eosinophils correlates with clinical improvement after therapy optimization in severe asthma. Methods In this pre-randomization analysis of 105 adults enrolled in an anti-IL5 trial (NCT05001529), patients underwent a 3-month run-in with optimized therapy per GINA guidelines. Clinical data, lung function, FeNO, IgE, and eosinophil counts were collected. Flow cytometry assessed CD63 and HLA-DR expression. Associations with clinical improvement, defined by ACT score and exacerbation frequency, were analysed. Results ACT scores improved from 21 to 24 and uncontrolled asthma prevalence dropped from 50% to 16%. HLA-DR expression declined significantly and correlated with improved asthma control (β = 0.03, p = 0.05). CD63 expression did not change overall but remained elevated in patients with persistent symptoms. Neither marker correlated with eosinophil count, FeNO, or IgE. Conclusions HLA-DR and CD63 may serve as functional biomarkers of asthma activity. Eosinophil immunophenotyping could complement traditional biomarkers and guide personalized therapy.