CFTR and cystic fibrosis: Phase I single-dose studies demonstrated the safety of the gene transfer agent, tgAAVCF, in human application and its successful delivery to the maxillary sinuses and lungs of patients with CF. Although vector-derived CFTR mRNA expression was beyond the detection limit, the sinus transepithelial potential was assessable on days 7 and 14 after infection, indicating the transient functional restoration (Wagner et al., 1998; Aitken et al., 2001; Flotte et al., 2003).