The Effect of Mepolizumab on Blood Eosinophil Subtype Distribution and Granule Protein Gene Expression in Severe Eosinophilic Asthma.

Purpose: Mepolizumab, which causes a decrease in the number of blood eosinophils, is used to treat patients with severe eosinophilic asthma (SEA). However, there is a relative lack of data on dynamic changes in blood eosinophil subtype distribution and their granule protein expression following anti-interleukin (IL)-5 treatment. Our objective was to evaluate blood inflammatory-like (iEOS-like) and resident-like (rEOS-like) eosinophil subtype distribution and CLC, EDN, EPX, ECP, and MBP gene expression following up to 24 weeks of treatment with mepolizumab in SEA patients.

Patients and methods: Ten free of oral steroids SEA patients and 9 healthy control subjects (HS) were included. Patients were treated with mepolizumab 100 mg subcutaneously/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 quantitative real time-polymerase chain reaction analysis.

Results: Approximately three-quarters of isolated blood eosinophils were iEOS-like cells before mepolizumab treatment, p<0.01. Blood eosinophil granule protein gene expression was increased in SEA patients compared to the HS, p<0.05, and iEOS-like cells EPX, MBP, and CLC gene expressions were higher than rEOS-like cells, p<0.05. Following 4, 12, and 24 weeks of treatment with mepolizumab, residual blood eosinophils shifted towards rEOS-like cells, p<0.05, and CLC, EPX, ECP, and MBP gene expression of both eosinophil subtypes decreased to HS levels.

Conclusion: Treating SEA patients with mepolizumab shifts blood eosinophil subtype distribution towards rEOS-like cells and reduces granule protein gene expression levels to those of healthy individuals.