Single chain Fv: A ligand in receptor-mediated gene delivery

We have used an anti-human polymeric immunoglobulin receptor (plgR) single chain Fv (scFv) to deliver reporter genes to epithelial cells in vitro. The scFv was constructed from a monoclonal antibody directed against plgR and a cysteine residue was added at the carboxyl end to facilitate its conjugation to polylysine (polyK) via the heterobifunctional cross-linker SPDP. ScFv-cys was expressed in Drosophila S2 cells and purified to homogeneity using conventional column chromatography. ScFv-polyK, and polyK as control, were condensed with a DNA expression plasmid containing the luciferase reporter gene driven by the CMV promoter into unimolecular (with respect to DNA) complexes under high salt conditions. Target cells were MDCK cells transfected with human plgR and repeatedly sorted for high-level receptor expression, with untransfected MDCK cells as control. Receptor-bearing MDCK cells were readily transfected by scFv-cys containing, plgR directed complexes, and expression could be blocked by addition of excess human secretory component (SC), the extracellular portion of plgR. In contrast, MDCK cells that did not express plgR were not transfected. Nontargeted complexes were not effective in transfecting MDCK cells with or without plgR. Targeted complexes also transfected human tracheal epithelial cells in primary culture, corroborating the plgR-mediated gene delivery. These data indicate that a scFv directed against human plgR can direct foreign genes specifically into receptor-bearing cells in vitro. We have expressed and purified a ligand that is efficient and specific in plgR-mediated gene delivery.