Research in context
Evidence before this study
Eosinophils are inflammatory cells associated with airway inflammation in asthma, and represent an important biomarker for identification of patients with eosinophilic asthma. We searched PubMed on Nov 26, 2015, for English-language articles with the terms “asthma”, “anti-interleukin-5”, and “eosinophil” in the title or abstract. Our search yielded 26 results, which included a meta-analysis of randomised placebo-controlled trials of mepolizumab in patients with asthma. On the basis of our systematic review of the literature, mepolizumab appears to be the only interleukin-5 monoclonal antibody using a blood eosinophil threshold of at least 150 cells per μL at baseline in asthma clinical trials.
Added value of this study
To our knowledge, this is the first analysis to systematically assess the clinical effects of mepolizumab in patients with different thresholds of blood eosinophil counts at baseline. This approach used counts obtained at baseline from more than 1000 patients participating in two large-scale, randomised placebo-controlled trials of mepolizumab. Our analysis provides further evidence that blood eosinophils are a robust marker for selecting patients that would benefit from specific treatments and are also associated with the response to anti-interleukin-5 therapies such as mepolizumab.
Implications of all the available evidence
Clinical trials of other interleukin-5 inhibitors in development (ie, reslizumab and benralizumab) have used different blood eosinophil thresholds at baseline when investigating the effect of interleukin-5 inhibition on clinical outcomes, and confusion has arisen about the best cutoff point. We provide evidence from a large patient population with severe eosinophilic asthma that supports the value of blood eosinophil counts as a biomarker to guide therapy, and to provide guidance on the probable effect of that therapy in patients with severe asthma.