The importance of being not significant: blood eosinophils and clinical responses do not correlate in severe asthma patients treated with Mepolizumab in real life.

Introduction. Mepolizumab (MEP) was commercialized for the treatment of severe eosinophilic asthma since at least 2 years in Italy. Its efficacy was well confirmed in the real-life setting, but a predictive biomarker for efficacy still lacks. It was hypothesized that the magnitude of the response could be positively related to the baseline eosinophil count. Thus, we tested this hypothesis on our available population. Methods. The analysis was performed on 138 patients, with severe asthma and who had received MEP for at least 1 year. The baseline eosinophil count was correlated to the change (12 months vs baseline) in some relevant parameters: oral corticosteroids intake, forced expiratory volume in 1 second, asthma control test score, number of exacerbations per year, fractional exhaled nitric oxide . Results. Data were available for 138 patients (78 females, 60 males, mean age 58±10 years) who completed at least 1 year of MEP treatment. By using the Spearman and Pearson tests, no significant correlation could be found between the baseline eosinophil count and the percentage change in the considered parameters (r between -0.091 and 0.093; p= NS). Conclusion. There is no detectable correlation between the baseline eosinophil count and the magnitude of the effects of MEP after 1 year of therapy, although the overall efficacy remains confirmed. Under the present conditions, the eosinophil count alone seems not to be a reliable predictive marker of the efficacy of MEP.