The efficacy of off-label IL-5-modulating treatment in rare eosinophil-mediated diseases

Dear Editor, Interleukin (IL)-5 is a pivotal factor in eosinophilic inflammation. It promotes eosinophil hematopoiesis, chemotaxis, and activation. The role of IL-5 in the pathogenesis of eosinophilic asthma has been extensively studied and demonstrated in human subjects, as well in murine models. Humanized monoclonal antibodies against IL-5 (mepolizumab and reslizumab) and IL-5 receptor α-subunit (IL-5Rα; benralizumab) have recently been introduced for the treatment of severe eosinophilic asthma. A number of clinical trials have also evaluated the efficacy of IL-5-modulating agents in eosinophilic granulomatosis with polyangiitis (EGPA). Consequently, subcutaneous administration of mepolizumab is currently approved for use in severe asthma, as well as for EGPA. Likewise, benralizumab is indicated for severe and refractory eosinophilic asthma in adults, albeit not yet for EGPA. Eosinophilic disorders, other than asthma, that have also been evaluated for IL-5-modulating therapy include chronic eosinophilic pneumonia and hyper-eosinophilic syndrome.