Lung mucus burden and treatment response assessed by MRI in the post-modulator era

Mucus is believed to be central to the progressive nature of cystic fibrosis lung disease. Poor clearance leads to plugging, inflammation, and infection, driving a cycle that eventually results in irreversible lung damage. We hypothesized that patients with higher mucus burden would demonstrate greater improvement in spirometry and ventilation when treated with modulator therapy.

We retrospectively analyzed data collected in 29 participants prior to and following initiation of elexacaftor/tezacaftor/ivacaftor (ETI) therapy. Participants performed ¹H and ¹²⁹Xe MRI, multiple breath washout tests, and spirometry. Structural abnormalities were quantified using a modified Brody scoring system. ¹²⁹Xe MRI abnormalities were measured by ventilation defect percent (VDP).

Participants with greater mucus burden (the top half, modified Brody score >2.5) showed improved FEV₁ (ΔFEV₁=10%_pred, p=.003), VDP (ΔVDP=-5.6%, p=.004), and lung clearance index (ΔLCI=-1.6, p=.008). Baseline mucus correlated with VDP (ρ=0.48, p = 4e-3), bronchial wall thickening (ρ=0.47, p=.03), and bronchiectasis (ρ=0.80, p = 4e-8). Baseline mucus scores (AUC=0.66) and VDP (AUC=0.75) were associated with lung function improvement (ΔFEV₁≥5%_pred) following modulator therapy.

Functional lung improvement following therapy was related to baseline mucus burden, indicating improved mucus clearance potentially drives better lung function in people receiving ETI therapy. MRI lung mucus scores and regional ventilation were both sensitive biomarkers and likely valuable secondary treatment outcomes in future gene therapies or clinical trials.