Mutations in the CFTR gene that lead to premature stop codons or splicing defects cause cystic fibrosis (CF) and are not amenable to treatment by small-molecule modulators. Here, we investigate the use of adenine base editor (ABE) ribonucleoproteins (RNPs) that convert A•T to G•C base pairs as a therapeutic strategy for three CF-causing mutations. Using ABE RNPs, we corrected in human airway epithelial cells premature stop codon mutations (R553X and W1282X) and a splice-site mutation (3849 + 10 kb C > T). Following ABE delivery, DNA sequencing revealed correction of these pathogenic mutations at efficiencies that reached 38–82% with minimal bystander edits or indels. This range of editing was sufficient to attain functional correction of CFTR-dependent anion channel activity in primary epithelial cells from CF patients and in a CF patient-derived cell line. These results demonstrate the utility of base editor RNPs to repair CFTR mutations that are not currently treatable with approved therapeutics.

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The airway‐surface liquid pH (pHASL) is slightly acidic relative to the plasma and becomes more acidic in airway diseases, leading to impaired host defense. CO 2 in the large airways decreases during inspiration (0.04% CO 2) and increases during expiration (5% CO 2). Thus, we hypothesized that pHASL would fluctuate during the respiratory cycle. We measured pHASL on cultures of airway epithelia while changing apical CO 2 concentrations. Changing apical CO 2 produced only very slow pHASL changes, occurring in minutes, inconsistent with respiratory phases that occur in a few seconds. We hypothesized that pH changes were slow because airway‐surface liquid has little carbonic anhydrase activity. To test this hypothesis, we applied the carbonic anhydrase inhibitor acetazolamide and found minimal effects on CO 2‐induced pHASL changes. In contrast, adding carbonic anhydrase significantly increased the rate of change in pHASL. Using pH‐dependent rates obtained from these experiments, we modeled the pHASL during respiration to further understand how pH changes with physiologic and pathophysiologic respiratory cycles. Modeled pHASL oscillations were small and affected by the respiration rate, but not the inspiratory:expiratory ratio. Modeled equilibrium pHASL was affected by the inspiratory:expiratory ratio, but not the respiration rate. The airway epithelium is the only tissue that is exposed to large and rapid CO 2 fluctuations. We speculate that the airways may have evolved minimal carbonic anhydrase activity to mitigate large changes in the pHASL during breathing that could potentially affect pH‐sensitive components of ASL.

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