What goes up must come down: biomarkers and novel biologicals in severe asthma

Asthma is a heterogeneous airway disease characterized by typical symptoms in combination with variable airway obstruction. Most patients with asthma have well controlled symptoms and a low risk of asthma attacks with inhaled corticosteroid (ICS) treatment. However, a clinically important subgroup (~ 10%) remains symptomatic and/or at risk of asthma attacks despite maximum inhaled therapy. Patients with severe asthma are responsible for a significant proportion of healthcare costs attributable to asthma and have a large unmet need for better treatments. An important advance in recent years has been the recognition that severe asthma is heterogeneous with respect to clinical problems and the pattern of lower airway inflammation. Identification of eosinophilic inflammation in the airways has become an important priority as novel biologicals that target Th2 cytokines, such as anti-IL5, anti-IL-13 and combined anti-IL-4/13 are showing considerable promise as treatments for this subgroup. It has also become clear that anti-IgE (Omalizumab), the first monoclonal antibody registered for treatment of severe asthma, is only active in patients with active eosinophilic airway inflammation. The future will be identification of potentially responsive patients on the basis of raised biomarkers and, as suggested by the title of this review, targeted treatment with specific cytokine blockade that has a direct effect on the biomarkers. In this review, we outline an approach to the clinical assessment of patients potentially suitable for biological treatment and describe in detail the likely clinical impact of established and new biological treatments.