Vectors for airway gene delivery

Delivery of genes to the airway epithelium for therapeutic purposes seemed easy at first, because the epithelial cells interface with the environment and are therefore accessible. However, problems encountered were more substantial than were originally expected. Nonviral systems may be preferred for long-term gene expression, for they can be dosed repeatedly. Two nonviral gene transfer systems have been in clinical trials, lipid-mediated gene transfer and DNA nanoparticles. Both have sufficient efficiency to be candidates for correction of the cystic fibrosis defect, and both can be dosed repeatedly. However, lipid-mediated gene transfer in the first generation provokes significant inflammatory toxicity, which may be engineered out by adjustments of the lipids, the plasmid CpG content, or both. Both lipid-mediated gene transfer and DNA nanoparticles in the first generation have short duration of expression, but reengineering of the plasmid DNA to contain mostly eukaryotic sequences may address this problem. Considerable advances in the understanding of the cellular uptake and expression of these agents and in their practical utility have occurred in the last few years; these advances are reviewed here.