Phage Display-Derived Ligand for Mucosal Transcytotic Receptor GP-2 Promotes Antigen Delivery to M Cells and Induces Antigen-Specific Immune Response.

Successful oral immunization depends on efficient delivery of antigens (Ags) to the mucosal immune induction site. Glycoprotein-2 (GP-2) is an integral membrane protein that is expressed specifically on M cells within follicle-associated epithelium (FAE) and serves as transcytotic receptor for luminal Ags. In this study, we selected peptide ligands against recombinant human GP-2 by screening a phage display library and evaluated their interaction with GP-2 in vitro and ex vivo. Selected peptides were conjugated to the C-terminal of enhanced green fluorescence protein (EGFP) and evaluated for their ability to induce an immune response in mice. One of our selected peptides, Gb-1, showed high binding affinity to GP-2 and, when fused to EGFP, significantly increased the uptake of EGFP by M cells compared to EGFP alone. After oral administration, the Gb1-EGFP fusion induced efficient mucosal and systemic immune responses in mice measured at the level of antigen-specific serum and fecal antibodies, cytokine secretion, and lymphocyte proliferation. Furthermore, the IgG subclasses and cytokine secretion showed that ligand Gb-1 induced a Th2-type immune response. Collectively, our findings suggest that the ligand we selected through phage library screening is capable of targeting Ags to GP-2 on M cells and can be used as an oral vaccine adjuvant.