A marked heterogeneity is exhibited by asthma both clinically and at the 
molecular level with different phenotypes driven by diverse mechanistic pathways 
that require specifically targeted treatments. Biologics aimed at IL-4/13, IL-5 
or IgE are proven or potentially effective treatments for patients with 
difficult to treat eosinophilic asthma. Importantly, it is now widely accepted 
that biologic-based therapies give significant clinical improvements in those 
patient populations where asthma phenotypes are taken into account. Such asthma 
phenotypes have been identified by reproducible and straightforward 
discriminatory biomarkers. This short review discusses recent studies of the 
effectiveness of the anti-IL-5 reslizumab in relation to the use of simple 
reproducible biomarkers in eosinophilic asthma.