Targeting transgene expression to airway epithelia and submucosal glands, prominent sites of human CFTR expression

Targeting therapeutic gene expression to disease-affected tissues is an essential component of effective and safe gene therapy. After birth, CFTR gene expression in human lungs is localized predominantly in the epithelial cells lining the upper airways, especially in the ducts and serous tubules of the submucosal glands. We have developed a K18 expression cassette, based on the DNA control elements of the human cytokeratin 18 gene. Temporal and spatial analyses of transgenic mice demonstrated that this expression cassette targets transgene expression to almost all cell types in which CFTR is expressed. Airway epithelium expression started as early as 11.5 days of gestational age and continued into the adulthood of the transgenic mice. In these adult mice, the pattern of the reporter expression strikingly matched that of the human cytokeratin 18 and human CFTR genes. The transgene expression was epithelium-specific and undetectable in connective tissue, muscle, bone, cartilage, blood, and endothelial cells. Significantly, high levels of expression were detected in tracheal submucosal glands. Together, these results suggest that our K18 expression cassette has a high potential for clinical application in gene therapy for patients with cystic fibrosis.