D96-07 Correlation Between Segmental Bronchial Wall Thickness and Bronchoalveolar Lavage Markers of Inflammation and Mucus Before and After Elexacaftor-Tezacaftor-Ivacaftor Therapy

Background Cystic fibrosis(CF) lung disease is characterized by bronchial dilatation, wall thickening, and mucus plugs(MPs). In CF patients treated with elexacaftor/tezacaftor/ivacaftor(ETI), chest CT metrics have shown persistent bronchial wall thickening despite improvements in other disease markers. This study investigates the relationship between bronchial wall thickening, MPs, and inflammation in CF patients before and after 1.5 years of ETI therapy. Aim To explore the contributions of infection, inflammation and MPs, to bronchial wall thickening in CF patients, with the hypothesis that inflammation and mucus both contribute to bronchial wall thickening, and that ETI treatment influences these factors over time. Methods Nine adult CF patients (mean age 35 years, 2 males, 7 females), all chronically infected with Pseudomonas aeruginosa(Pa), underwent bronchoalveolar lavage(BAL) of five lung segments and a chest CT scan at two time-points: before and 1.5 years after initiating ETI therapy (Durfey et al, Cell Host &Microbe 2025). CT scans were analyzed using LungQ software, which measures: at the segmental level bronchial and arterial (BA) dimensions to calculate bronchial wall area/bronchial outer area (Bwa/Boa) and BA-ratios; mucus plug number and volume; and ventilation abnormalities. In BAL fluid inflammatory markers (neutrophilic elastase(NE), IL-8, IL-1β) were assessed, sialic acid as a mucus marker and Pa colony forming units(CFU). Relationships between Bwa/Boa and biomarkers were analyzed using Spearman correlations and linear regression. Results ETI therapy significantly reduced bronchial wall thickening (Bwa/Boa), inflammatory markers, MPs, and Pa CFU across most lung segments. Prior to ETI treatment, Bwa/Boa was significantly correlated with NE and IL-1β (r = 0.488, p < 0.001 and r = 0.361, p = 0.026, respectively. Furthermore, Bwa/Boa correlated with sialic acid. On ETI Bwa/Boa remained correlated with all inflammatory markers (though the correlation with NE weakened), and MPs. Segmental analysis revealed marked heterogeneity, with many segments showing incomplete recovery of Bwa/Boa despite reduced inflammation and mucus burden. Linear regression identified NE as the strongest pre-treatment correlate of bronchial Bwa/Boa. After 1.5 years of ETI treatment the combination NE and sialic acid explained the most variance in Bwa/Boa. Conclusion ETI therapy in CF patients significantly reduces: inflammatory markers; bronchial wall thickening; and MPs. NE was the primary predictor of bronchial wall thickening before ETI treatment, and the combination of NE and sialic acid post-therapy. These findings highlight the complex relationship between bronchial wall thickening and inflammation, mucus, and infection. ETI therapy improves disease activity but bronchial wall thickening persist as does inflammation and infection in some patients. This abstract is funded by: Sophia Foundation & Thirona