alpha 1-Antitrypsin (alpha AT) deficiency, a hereditary cause of progressive emphysema, can potentially be treated by transfer of a functional human alpha 1AT gene to the respiratory epithelium. For such an approach to be successful, alpha 1AT must be provided to both the interstitium and the epithelial surface--that is, the alpha 1AT directed by the transferred gene must be secreted to both the apical and basolateral surfaces of the epithelial cells. To evaluate this concept, a recombinant, replication-deficient adenoviral vector (Ad-alpha 1AT) containing a human alpha 1AT cDNA driven by an adenovirus major late promoter was used to infect Bet-1A human respiratory epithelial cells. The infected cells expressed Ad-alpha 1AT-directed mRNA transcripts and synthesized and secreted functional human alpha 1AT as shown by [35S]methionine labeling and immunoprecipitation of a 52-kD glycosylated human alpha 1AT molecule capable of interacting with neutrophil elastase, its natural substrate. Bet-1A cells grown on microporous polycarbonate membranes formed tight junctions (resistance > 150 omega x cm2). After infection with Ad-alpha 1AT, [35S]methionine labeling and enzyme-linked immunoassay demonstrated that alpha 1AT was secreted into both the apical and basolateral compartments, with an average apical to basolateral ratio of 1.9 +/- 0.2. Thus, human respiratory epithelial cells infected with a recombinant adenoviral vector containing a human alpha 1AT cDNA secrete alpha 1AT across both the apical and basolateral cell membranes, suggesting that the respiratory epithelium could serve as a target for in vivo gene therapy of alpha 1AT deficiency.