Elexacaftor/tezacaftor/ivacaftor efficacy in intestinal organoids with rare CFTR variants in comparison to CFTR-F508del and CFTR-wild type controls.

Cystic fibrosis is a life-shortening genetic disease caused by pathological variants of the cystic fibrosis transmembrane conductance regulator gene. The CFTR modulator therapy elexacaftor, tezacaftor and ivacaftor (ETI) rescues CFTR protein function and has made a significant impact on the lives of many people with CF. In Europe, ETI is currently available for people with CF who have at least one F508del mutation whilst the effect of ETI on rare CFTR variants remains unknown, albeit that many of such variants may be restored through ETI. Italy has a high prevalence of rare CFTR variants compared to the rest of Europe, potentially leading to significant undertreatment of people with rare CFTR variants. In this study, we used patient-derived intestinal organoids to identify individuals harboring rare CFTR variants who might benefit from ETI modulator therapy. Two CFTR-dependent readouts (steady-state lumen area and forskolin-induced swelling) in intestinal organoids were characterized to assess CFTR function rescue upon ETI incubation. Functional restoration by CFTR modulators was compared to wild type CFTR function, ETI-treated organoids harboring genotypes currently eligible for ETI therapy (F508del/class I) and organoids harboring non-responsive genotypes. Our data showed in vitro response to ETI within or beyond the range of CFTR function associated with F508del-ETI in 19 out of 28 organoids. This suggest that a large percentage of people with rare CFTR variants without access to ETI may benefit from this treatment.