Effect of lumacaftor-ivacaftor on mucociliary clearance and clinical outcomes in cystic fibrosis: Results from the PROSPECT MCC sub-study

•The effect of lumacaftor-ivacaftor (L-I) on mucociliary clearance and clinical endpoints was tested.•L-I did not improve whole lung mucociliary clearance in F508del homozygotes.•Only cough-assisted clearance improved without apparent effects on other MCC outcomes.•Sweat chloride, but no other clinical endpoints (e.g. FEV1, LCI), improved.•Lack of MCC improvement after L-I differs from that measured after highly effective modulators.