Novel Cystic Fibrosis Ferret Model Enables Visualization of CFTR Expression Cells and Genetic CFTR Reactivation

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). While gene therapy holds promise as a cure, the cell-type-specific heterogeneity of CFTR expression in the lung presents significant challenges. Current CF ferret models closely replicate the human disease phenotype but have limitations in studying functional complementation through cell-type-specific CFTR restoration. To address this, we developed a new transgenic ferret line, CFTR^{int1-eGFP(lsl)}, in which a Cre-recombinase (Cre)-excisable enhanced fluorescent protein (eGFP) reporter cassette is knocked in (KI) to intron 1 of the CFTR locus. Breeding this reporter line with CFTR^G551D CF ferret resulted in a novel CF model, CFTR^{int1-eGFP(lsl)/G551D}, with disease onset manageable via the administration of CFTR modulator VX770. In this study, we confirmed two key properties of the CFTR^{int1-eGFP(lsl)/G551D} CF ferrets: (1) cell-type-specific expression of the CFTR(N-24)-eGFP fusion protein, driven by the intrinsic CFTR promoter, in polarized epithelial cultures and selected tissues, and (2) functional reversion of the KI allele via Cre-mediated excision of the reporter cassette. This model provides a valuable tool for studying the effects of targeted CFTR reactivation in a cell-type-specific manner, which is crucial for enhancing our understanding of CFTR's roles in modulating airway clearance and innate immunity, and for identifying relevant cellular targets for CF gene therapy.