Cystic Fibrosis (CF) is a life threatening genetic disorder resulting from mutations found in the gene known as the cystic fibrosis transmembrane conductance regulator (CFTR). Defects in this gene prevent correct chloride and bicarbonate transport in and out of cells. It has become increasingly important to develop new in vitro model systems capable of predicting in vivo clinical effectiveness of modulator therapy among patients with CF. This objective represents a significant and unmet need for advancing personalized therapeutics in the disease. The current trial is intended to show for the first time that primary iPS cells differentiated to an airway epithelial phenotype can be used to predict in vivo clinical response for rare CF patient populations, with the long-term goal of facilitating drug access for individuals with unusual (or even private) CF variants.

Trikafta is currently approved for patients with CF carrying at least one copy of the common F508del variant and over 170 other CFTR abnormalities. Because approximately 90% of CF patients in the United States meet these criteria, pharmacotherapies (Trikafta in particular) are now available to a sizable majority of those with the disease. However, thousands of patients harboring relatively common variants will remain without effective drug therapy. Others with ultra-rare or private CFTR mutations have forms of the disease that are very likely to benefit from available drugs, but do not have access to these therapies. It has been estimated that over 1,000 CFTR mutations are represented by less than 5 patients each. Establishing processes so that individuals with very rare and/or poorly characterized alleles can gain access to effective modulator treatment remains one of the predominant challenges in the field.

This clinical study will enroll 42 participants without the F508del mutation, carrying partial function or N1303K mutations not approved for Trikafta, and who are not expected to be approved for CFTR modulator treatment in the immediate future. Substudy 1 will comprise an open-label, two center trial of orally administered elexacaftor, tezacaftor and ivacaftor (Trikafta) that will enroll 22 patients with rare/orphan genotypes. Substudy 2 will enroll 20 participants who encode the N1303K variant as emblematic of a mutation not approved for Trikafta, but are likely to respond to the treatment.

Each participant will have clinical and/or preclinical evidence that Trikafta should offer benefit, and each will be given Trikafta for approximately four weeks. The researchers will monitor clinical endpoints that include FEV1, sweat chloride, quality of life, and weight. The study will differentiate iPS cells from each subject to generate airway epithelial monolayers that can be tested for response to Trikafta. In this way, this study will evaluate an emerging and readily accessible in vitro surrogate endpoint as a predictor of clinical response. This trial will also serve as a pilot/test case for other clinical protocols relevant to patients with rare CFTR variants and evidence of residual function who do not have an approved modulator therapy, due to rarity of their mutation. It is hypothesized that a robust correlation will be established between in vitro Trikafta responsiveness of iPS cells and in vivo benefit (FEV1) in patients, and provide a powerful tool for utilizing iPS cells to identify rare CF patient populations most suitable for cystic fibrosis modulator therapy.