Activated sputum eosinophils associated with exacerbations in children on mepolizumab

Background MUPPITS-2 was a randomized, placebo-controlled clinical trial that demonstrated mepolizumab (anti-interleukin-5) reduced exacerbations and blood and airway eosinophils in urban children with severe eosinophilic asthma. Despite this reduction in eosinophilia, exacerbation risk persisted in certain patients treated with mepolizumab. This raises the possibility that subpopulations of airway eosinophils exist that contribute to breakthrough exacerbations. Objective Determine the effect of mepolizumab on airway eosinophils in childhood asthma. Methods Sputum samples were obtained from 53 MUPPITS-2 participants. Airway eosinophils were characterized using mass cytometry and grouped into subpopulations using unsupervised clustering analyses of 38 surface and intracellular markers. Differences in frequency and immunophenotype of sputum eosinophil subpopulations were assessed based on treatment arm and frequency of exacerbations. Results Median sputum eosinophils were significantly lower among mepolizumab treated participants compared to placebo (58% lower, 0.35% [95% CI 0.01-0.74], p=0.04). Clustering analysis identified three subpopulations of sputum eosinophils with varied expression of CD62L. CD62Lint and CD62Lhi eosinophils exhibited significantly elevated activation marker and eosinophil peroxidase expression, respectively. In mepolizumab-treated participants, CD62Lint and CD62Lhi eosinophils were more abundant in participants who experienced exacerbations than in those who did not (100% higher for CD62Lint, 0.04% [95% CI 0.0-0.13], p=0.04; 93% higher for CD62Lhi, 0.21% [95% CI 0.0-0.77], p=0.04). Conclusion Children with eosinophilic asthma treated with mepolizumab had significantly lower sputum eosinophils. However, CD62Lint and CD62Lhi eosinophils were significantly elevated in participants that had exacerbations on mepolizumab, suggesting that eosinophil subpopulations exist that contribute to exacerbations despite anti-IL-5 treatment.