Personalized therapy with CFTR modulators: Response of p.Ile148Asn variant.

Background: Elucidating the molecular and cellular effects caused by CFTR variants is crucial to understand Cystic Fibrosis (CF) disease pathophysiology, but also to predict disease severity, to provide genetic counselling, and to determine the most adequate therapeutic strategy for people with CF (pwCF). While the current CFTR modulator drugs (CFTRm) are approved mainly for pwCF with the most prevalent variant, p.Phe508del, pwCF carrying rare and/or uncharacterized CFTR variants are not eligible. However, previous studies have shown that such rare variants can be rescued by the approved CFTRm, suggesting clinical benefit for those pwCF. Here, we characterized the rare and non-eligible p.Ile148Asn CFTR variant found in Portuguese pwCF, regarding CFTR processing, traffic and function, and response to existing CFTRm.

Methods: We used the forskolin-induced swelling (FIS) assay in intestinal organoids (IOs) from 2 CF individuals carrying p.Ile148Asn in heterozygosity with p.Phe508del and p.Gly542Ter, respectively. Additionally, a Cystic Fibrosis Bronchial Epithelial (CFBE) cell line expressing p.Ile148Asn-CFTR was generated to study the molecular defect of this variant individually.

Results: Our results show that p.Ile148Asn is a CF-causing variant, impairing both CFTR plasma membrane (PM) traffic and function, albeit partially. Moreover, p.Ile148Asn-CFTR can be rescued by approved CFTRm in CFBE cells and IOs, suggesting potential clinical benefit for these individuals.

Conclusion: The work emphasizes the importance of testing CFTRm for rare variants not included in the drug label. It also shows that the 'theranostic' approach using IOs from pwCF, which captures the genetic background of each individual, complements theratyping in cell lines that focuses only on CFTR variants.