Document resource
Introduction Severe asthma is characterised by inflammation and structural remodelling of the airways, typically resistant to standard therapies. Mepolizumab, an anti-IL-5 biologic, reduces eosinophil levels and improves asthma control. Limited evidence exists investigating the effect of mepolizumab on airway remodelling and bronchial epithelium. We aimed to characterise the bronchial epithelial cell response to mepolizumab treatment at a single cell level with a focus on its potential role in modulating remodelling.Methods Twenty patients with severe asthma (blood eosinophils ≥300 cells/uL at baseline) were recruited ( NCT05144087). Good quality paired airway samples were obtained from 12 patients through bronchoscopy before and after 6 months of mepolizumab treatment. We performed single-cell RNA sequencing (scRNA-seq) on bronchial brushes using 3’ chemistry. Data processing was done using Cell Ranger, seurat DESeq2 paired analysis and CellChat. Pathway enrichment analyses were performed using gene set enrichment analysis (GSEA).Results The IL5-Ra (alpha subunit of the IL5 receptor) gene was highly expressed in ciliated epithelial cells. After mepolizumab treatment, distinct transcriptional changes were seen in ciliated cells, basal cells, and ionocytes, with the highest number of differentially expressed genes (DEGs) in ciliated cells (325 DEGs). We found significantly decreased SMAD2 mRNA levels and suppression of 28 SMAD2-dependent genes as well as changes in the expression of genes related to cell-cell junction (5 genes) and remodelling (20 genes). Overall, we observed a positive induction of pathways related to epithelial integrity and barrier function after mepolizumab treatment. Inferred cell-cell communication networks revealed a reduction in structural and remodelling pathway intercellular activity, showing reduced markers of epithelial damage and subepithelial fibrosis.Conclusion In addition to targeting eosinophils, mepolizumab treatment also modifies the transcriptional profile of specific bronchial epithelial cell populations. Our data indicate that mepolizumab suppresses remodelling signals and restores epithelial barrier integrity and homeostasis, potentially via reducing the expression of SMAD2, a key transcription factor in TGF-beta signaling. Overall, our findings support a role for IL-5 in modulating airway structural cells and reveal previously unrecognised mechanisms by which anti-IL5 therapy may confer clinical benefit in severe asthma.