Differing effects of mepolizumab across the life course

The history of asthma treatment is full of near misses. Inhaled and oral corticosteroids would not be in the therapeutic armamentarium if not for the late, great Harry Morrow-Brown's demonstration in 1958, using his medical school microscope, that these treatments worked well, but only in those with sputum eosinophilia. This early realisation of the importance of personalised medicine was rapidly forgotten in the excitement of new and powerful steroid-based treatments. Therefore, when the humanised anti-interleukin 5 (IL-5) monoclonal mepolizumab was first tested in adult asthma, it was nearly rejected as inactive until it was trialled in the right subgroup, namely patients with eosinophilic, attack-prone asthma.