The effect of mepolizumab on blood eosinophil subtype granule protein gene expression in severe eosinophilic asthma

<bold>Purpose:</bold> Treatment with mepolizumab reduces blood eosinophil count and shifts distribution from inflammatory eosinophils (iEOS) to resident eosinophils (rEOS) in patients with severe eosinophilic asthma (SEA) (M. Fricker, et al. 2024, doi:10.1111/all.16267). However, data on changes in cytotoxic granule protein gene expression of residual blood eosinophil subtypes after treatment with an anti-IL-5 drug are lacking. <bold>Aim:</bold> to evaluate the expression of blood iEOS and rEOS granule protein <italic>CLC</italic>, <italic>EDN</italic>, <italic>EPX</italic>, <italic>ECP</italic>, and <italic>MBP</italic> genes following up to 24 weeks of mepolizumab treatment in SEA patients. <bold>Patients and Methods:</bold> 10 free of oral steroids SEA patients and 9 healthy control subjects (HS) were included. Patients were treated with mepolizumab 100 mg subcutaneous/4 weeks, and investigation tests were performed at 0, 4, 12, and 24 weeks. Blood eosinophils were isolated by Ficoll centrifugation and magnetic separation, then subtyped using magnetic separation against CD62L. Gene expression investigation was done using qRT-PCR analysis. <bold>Results:</bold> At baseline, granule proteins gene expression of both blood eosinophil subtypes was increased in SEA patients compared to the HS, <italic>p</italic><0.05, and iEOS-like cells had higher <italic>EPX</italic>, <italic>MBP</italic>, and <italic>CLC</italic> gene expression than rEOS-like cells, <italic>p</italic><0.05. In SEA patients, the gene expression of residual iEOS-like cells <italic>CLC</italic>, <italic>EPX</italic>, <italic>ECP</italic>, <italic>MBP</italic>, and residual rEOS-like cells <italic>CLC</italic>, <italic>MBP</italic>, and <italic>EDN</italic> decreased to the level of the HS group after 4, 12, and 24 weeks of mepolizumab treatment. <bold>Conclusion:</bold> The anti-IL-5 drug mepolizumab consistently reduced gene expression of most granule proteins in both subtypes of residual blood eosinophil to levels similar to those of healthy subjects.