Our recent experience with mepolizumab demonstrated that specifically targeting eosinophils in patient with severe asthma had a prednisone-sparing effect (11) and decrease exacerbations (11,12). In this study it also improved their lung function including in those patients with associated COPD. This is not surprising given that persistent airway eosinophilia can contribute to airway remodeling (13). Indeed, the improvement in FEV1 was associated with a decrease in sputum hyaluron (14) over the six month treatment period. Changes in lung function and symptoms have not been consistently observed in previous mepolizumab trials (12,15). This is clearly related to how precise the patients where phenotyped in terms of sputum eosinophilia. In studies that recruited patients who had persistent sputum eosinophilia, decrease in exacerbations were associated with improvements in FEV1 (16).