Th ese RNA viruses can transfect nondividing cells such as mature airway epithelial cells [25] . Th e virus stably but randomly integrates into the genome and expression is likely to last for the lifetime of the cell (~100 days). Th e transgene can be transmitted post mitosis, and there is also a risk of tumorigenesis if the transgene integrates near an oncogene. Th e development of leukemias in children following gene therapy for severe combined immunodefi ciency highlights this risk [26, 27] . While lentiviral vectors may be useful to correct a gene defi ciency associated with increased risk of ALI, the long-lived gene expression of lentiviral delivered genes may be more suitable for chronic diseases than for ALI/ARDS.