Multicenter Study of Hyperpolarized Xenon Magnetic Resonance Imaging in Children with Cystic Fibrosis Following Initiation of Cystic Fibrosis Transmembrane Regulator Modulator Therapy (HyPOINT)

<b>Rationale:</b> Elexacaftor/tezacaftor/ivacaftor (ETI) has significantly improved lung function in people with cystic fibrosis (CF), prompting the need for outcome measures that can detect mild disease. In this new era of CFTR (CF transmembrane regulator) modulator therapy, more sensitive endpoints are required to evaluate the progression of early lung disease and to determine the efficacy of new CF therapies. Before the availability of highly effective therapies, xenon-129 magnetic resonance imaging (MRI) was shown to be more sensitive to regional ventilation changes compared with spirometry. <b>Objectives:</b> To evaluate the longitudinal changes in pulmonary function and Xe MRI outcomes after treatment with ETI in children and young people with CF. <b>Methods:</b> Lung function was assessed longitudinally at baseline and 1, 6, and 12 months after ETI treatment initiation in children and young people with CF between the ages of 6 and 18 years at four study sites. Ventilation defect percentage (VDP), reader defect percentage (RDP), lung clearance index (LCI) and forced expiratory volume in 1 second (FEV₁) were reported. <b>Results:</b> A total of 28 participants were enrolled; 25 completed at least baseline and one-month measurements. All four measures (RDP, VDP, LCI, and FEV₁) improved at one month after ETI initiation, with mean (standard deviation) absolute changes of -1.2 (1.7) in LCI, 6.9 (12.3) in FEV₁ % predicted, -4.3 (4.8) in VDP, and -7.8 (9.6) in RDP. Xe MRI outcomes (RDP and VDP) showed the largest relative treatment effects, with mean relative improvements of 43% and 72%, respectively. One-third of participants (8 of 25) had improvements in VDP and RDP but did not show improvements in FEV₁. <b>Conclusions:</b> Xe MRI captures sustained ventilation improvements after ETI initiation. Xe MRI metrics may provide a suitable endpoint for future interventional trials, particularly for people with CF with mild lung disease.