A human epithelium-specific vector optimized in rat pneumocytes for lung gene therapy

Gene therapy vectors based on mammalian promoters offer the potential for i ncreased cell specificity and may be less susceptible than viral promoters to transcription attenuation by host cytokines. The human cytokeratin 18 (K 18) gene is naturally expressed in the lung epithelia, a target site for ge ne therapies to treat certain genetic pediatric lung diseases. Our original vector based on the promoter and 5' control elements of K18 offered excell ent epithelial cell specificity but relatively low expression levels compar ed with viral promoters. In the present study, we found that adding a stron ger SV40 poly(A) signal boosted primary rat lung epithelial cell expression but greatly reduced cell specificity. Addition of a 3' portion of the K18 gene to our vector as a 3' untranslated region (UTR) improved epithelial ce ll-specific expression by reducing expression in lung fibroblasts. The effe ct of the 3' UTR was not related to gross differences in cell-specific spli cing. A deletion variant of this UTR further increased lung epithelial cell expression while retaining some cell specificity. These data illustrate th e possibilities for using 3' UTR to regulate cell-specific transgene expres sion. Our improved K18 vector should prove useful for pediatric lung gene t herapy applications.