Severe asthma, a part of difficult-to-treat asthma, represents a poorly controlled asthma despite maximally optimized treatment and its adherence. Uncontrolled asthma is judged by poor symptom control, frequent exacerbations requiring oral corticosteroids (OCS), or severe exacerbations requiring hospitalization. It is considered to be 5 percent or less of all asthmatics (GINA 2019).
In the treatment of severe asthma, in parallel with progress in the elucidation of the it pathogenesis at the end of the 20th century, biologics targeting particular molecular pathways (such as IgE, IL-5,) have become key players over the past two decades, and our humanized anti IL-5 monoclonal antibody, mepolizumab, has also become a part of it.
It was already evident by the end of the 20th century that eosinophils have a key role in asthma pathologies, partly based on mouse models.
Attempts to show efficacy of humanized anti IL-5 monoclonal antibodies in asthma were initially unsuccessful in mild asthma, but a proof-of-Concept study targeting moderate-to- severe asthma in Phase IIa, and other POC studies for severe eosinophilic asthma to show efficacy in exacerbation reduction and reducing OCS have led to the identification of populations that respond to this asset.
In addition, now efficacy (exacerbation, OCS-reduction, QOL) and safety data including relatively longer period one are shown with phase IIb-III studies including DREAM, MENSA, SIRIUS, MUSCA, COSMOS, COSMEX, COLUMBA, and now available in a clinical setting in Japan.
Overseas, REALITI-A studies have been reported on effectiveness and safety as a real-world data. In the meantime, evidence generation mainly based on database-based studies have been currently conducted and published to show effectiveness also in Japan.