Ferritin Complex Vaccine against Porcine Epidemic Diarrhea Virus (PEDV) Using Screened Immunogenic Sequences from Fv-Antibody Library

Abstract

A ferritin complex vaccine against porcine epidemic diarrhea virus (PEDV) was developed using an autodisplayed Fv-antibody library. The Fv-antibody represented the variable region of the heavy chain of IgG (VHH) and the Fv-antibody library was prepared by randomizing the complementarity determining region 3 (CDR3) of VHH. As the first step, four Fv-antibodies with a binding affinity to the receptor binding domain (RBD) of PEDV spike protein (SP) were screened from the Fv-antibody library. Then, the binding site of the Fv-antibody (antigenic site) on the PEDV RBD was analyzed using docking simulation; each binding sequence of the screened Fv-antibodies was found to be distributed far apart. In order to express the immunogenic sequence of PEDV vaccine, the gaps between the binding sites on PEDV RBD were filled with the nonimmunogenic sequence modules, and the immunogenic sequences for vaccine could be prepared as single proteins. The immunogenic sequence was expressed together with the ferritin molecule, and the ferritin complex vaccine was prepared in the spherical-shaped nanoparticle through a self-assembly of 24 ferritin molecules. Each immunogenic sequence was expressed on the outer surface of the ferritin complex vaccine, which was injected into mice. The injected ferritin complexes vaccine activated the vaccine-related immune responses by analyzing the IgG subtyping, secretion of vaccine-related cytokines, and CD4+/CD8+ T-cell profiles. Finally, the neutralizing activity of antisera to prevent the infection of PEDV was analyzed using cell-based infection assay. The neutralizing activity was evaluated according to the official directive for the neutralizing activity of PEDV vaccines. The four kinds of ferritin complexes showed a neutralizing activity in between positive and negative controls, and ferritin complex 2 showed a neutralizing activity as high as the positive control.