Background

Use of ivacaftor, the first clinically available CFTR (cystic fibrosis [CF] transmembrane conductance regulator) modulator, leads to sustained improvements in pulmonary function and structural lung disease measured by computed tomography (1, 2). A limited number of studies have sought to determine the effects of ivacaftor on airway inflammation, a key driver of CF lung disease, with conflicting results (3, 4). Neutrophilic airway inflammation in young children with CF is a known risk factor for future bronchiectasis (5). Hence, demonstration of the effects of modulator treatment on airway inflammation is a critical consideration for the potential of long-term disease modification. Understanding the level of residual disease activity in children on highly effective modulators will inform the need for nonmodulator treatments.