CFTR and cystic fibrosis: Gene transfer studies using an adenoviral delivery vector that transduced only 20% of CF HBECs fully rescued ion transport with a WT CFTR transgene (Excoffon et al., 2009), and a similar study using a human parainfluenza viral vector demonstrated normal CFTR activity with 25% of the epithelium transduced (Zhang L et al., 2009).