In vitro transport of active alpha(1)-antitrypsin to the apical surface ofepithelia by targeting the polymeric immunoglobulin receptor

In cystic fibrosis (CF), the intense host inflammatory response to chronic infection largely accounts for the progressive pulmonary disease, and ultim ately death. Neutrophils are the prominent inflammatory cells in the lungs of patients with CF, and large amounts of neutrophil elastase (NE) are rele ased during phagocytosis. Resides having direct effects on structural elast in, NE stimulates the release of proinflammatory mediators from the respira tory epithelium and is a potent secretogogue. Therapeutic use of elastase i nhibitors in CF has been complicated by difficulties in delivery to the cri tical site in the airway-the surface of the epithelium. We describe a uniqu e strategy to protect the respiratory epithelial cell surface directly by c apitalizing on the nondegradative transcytotic pathway of the polymeric imm unoglobulin receptor (pIgR). A recombinant fusion protein was constructed c onsisting of an antihuman pIgR single-chain Fv (scFv) antibody linked to hu man a:l-antitrypsin (A1AT), an inhibitor of NE. The recombinant scFv-A1AT f usion protein bound specifically to the pIgR on the basolateral surface of an epithelial cell monolayer, and was transported and released into the api cal medium where the A1AT domain was capable of forming an inactivation com plex with NE. Thus, A1AT linked to an antihuman pIgR scFv was delivered in receptor-specific fashion from the basolateral to apical surface and was re leased as an active antiprotease, indicating that it is feasible to deliver therapeutic proteins to the apical surface of epithelia by targeting the p IgR.