Mapping alveolar binding sites in vivo using phage peptide libraries.

Targeting lung tissue is nonselective due in part to the lack of specific cell-surface receptors identified on target lung cells. We used in vivo phage display to identify a panel of peptides that can bind selectively to lung epithelial cells with less binding to nonepithelial cells. By direct intratracheal instillation of phage libraries into the lung, we isolated and identified 143 individual phage clones. Three phage clones revealed enhanced binding to the lung in vitro and in vivo. These three identified peptides were synthesized and demonstrated selective binding to epithelial cells in lung tissue versus the control peptide. Further, the peptides specifically bound to freshly isolated type II alveolar epithelial cells compared with Hep2 cells. The results suggest that the airway phage display approach could be exploited for analyzing the molecular diversity in the lower respiratory tract.