Our ongoing efforts to improve pulmonary gene transfer for the treatment of lung diseases such as cystic fibrosis (CF) have led to the assessment of a lentiviral vector (simian immunodeficiency virus (SIV)) pseudotyped with the Sendai virus (SeV) envelope proteins F and HN (rSIV.F/HN).1 The latter contribute significantly to the high transduction efficiency of SeV-based vectors in the airway epithelium.2 Here, ERVW-1 is linked to cystic fibrosis.