Rescue by elexacaftor-tezacaftor-ivacaftor of the G1244E cystic fibrosis mutation's stability and gating defects are dependent on cell background

Cystic fibrosis is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, and nearly 90% of patients have at least one copy of the Phe508del CFTR mutation. In a phase 2 trial involving patients who were heterozygous for the Phe508del CFTR mutation and a minimal-function mutation (Phe508del-minimal function genotype), the next-generation CFTR corrector elexacaftor, in combination with tezacaftor and ivacaftor, improved Phe508del CFTR function and clinical outcomes.

Cystic fibrosis transmembrane conductance regulator (CFTR) modulators correct the basic defect caused by CFTR mutations. Improvements in health outcomes have been achieved using the combination of a CFTR corrector and potentiator in people with CF (pwCF) homozygous for F508del . The addition of elexacaftor (ELX; VX-445), a next-generation CFTR corrector, to tezacaftor/ivacaftor (TEZ/IVA) further improved F508del-CFTR function and clinical outcomes in a phase 2 study in pwCF homozygous for F508del . A phase 3, multi-centre, randomised, double-blind, active-controlled trial of ELX in triple combination with TEZ/IVA (ELX/TEZ/IVA) in pwCF homozygous for F508del was conducted. Eligible participants were aged ≥12 years with stable disease and percent predicted forced expiratory volume in 1 second (ppFEV 1 ) of 40 to 90, inclusive. After a four-week TEZ/IVA run-in, participants were randomised 1:1 to four weeks of ELX/TEZ/IVA versus TEZ/IVA alone. The primary endpoint was absolute change from baseline (measured at the end of the TEZ/IVA run-in) in ppFEV 1 at week 4. Key secondary endpoints were absolute change in sweat chloride and CF Questionnaire–Revised respiratory domain (CFQ-R RD) score. ClinicalTrials.gov , number NCT03525548 . Between August and December 2018, 113 participants were enrolled. Following the run-in, 107 participants were randomised and completed the 4-week treatment period. The ELX/TEZ/IVA group had improvements in ppFEV 1 (10·0 percentage points, 95% CI 7·4 to 12·6, p<0·0001), sweat chloride concentration (−45·1 mmol/L, 95% CI −50·1 to −40·1, p<0·0001), and CFQ-R RD score (17·4 points, 95% CI 11·8 to 23·0, p<0·0001) compared with the TEZ/IVA group. ELX/TEZ/IVA was well tolerated, with no discontinuations. Most adverse events were mild or moderate; serious adverse events occurred in 4% (n=2) of participants receiving ELX/TEZ/IVA and 2% (n=1) receiving TEZ/IVA. ELX/TEZ/IVA provided clinically robust benefit vs TEZ/IVA alone with a favourable safety profile and demonstrates the potential to lead to transformative improvements in the lives of pwCF homozygous for F508del .

The availability of the human genome sequence and tools for interrogating individual genomes provide an unprecedented opportunity to apply genetics to medicine. Mendelian conditions, which are caused by dysfunction of a single gene, offer powerful examples that illustrate how genetics can provide insights into disease. Cystic fibrosis, one of the more common lethal autosomal recessive Mendelian disorders, is presented here as an example. Recent progress in elucidating disease mechanism and causes of phenotypic variation, as well as in the development of treatments, demonstrates that genetics continues to play an important part in cystic fibrosis research 25 years after the discovery of the disease-causing gene.