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 ess ential component of effective and safe gene therapy. After birth, CFTR gene expression in human lungs is localized predominantly in the epithelial cel ls lining the upper airways, especially in the ducts and serous tubules of the submucosal glands. We have developed a K18 expression cassette, based o n the DNA control elements of the human cytokeratin 18 gene. Temporal and s patial analyses of transgenic mice demonstrated that this expression casset te targets transgene expression to almost all cell types in which CFTR is e xpressed. Airway epithelium expression started as early as 11.5 days of ges tational age and continued into the adulthood of the transgenic mice. In th ese adult mice, the pattern of the reporter expression strikingly matched t hat of the human cytokeratin 18 and human CFTR genes. The transgene express ion was epithelium-specific and undetectable in connective tissue, muscle, bone, cartilage, blood, and endothelial cells. Significantly, high levels o f expression were detected in tracheal submucosal glands. Together, these r esults suggest that our K18 expression cassette has a high potential for cl inical application in gene therapy for patients with cystic fibrosis.