CFTR and cystic fibrosis: In particular, CF rabbits exhibit robust readouts of CFTR function for immediate testing of pharmacotherapy/genetic therapy, including: (a) the classic NPD measurement and spontaneous development of upper airway pathology; (b) abnormal GI bioelectric properties coupled to weight loss and mortality; (c) a CFTR protein responsive to human CFTR modulators, including VX770; and (d) lower airway bronchiolar CFTR expression and abnormal bioelectric properties.