Nanoparticle Vaccines Based on the Receptor Binding Domain (RBD) of Porcine deltacoronavirus (PDCoV) Elicit Robust Protective Immune Responses in mice

Abstract Background Porcine deltacoronavirus (PDCoV), a novel swine enteropathogenic coronavirus, that causes acute diarrhea, vomiting, dehydration and mortality in neonatal piglets, resulting in significant economic losses to the swine industry worldwide. At present, there are no effective prevention and control measures for PDCoV. Methods We expressed the dimer receptor binding domain of PDCoV spike protein (RBD-dimer) and ferritin (SC-Fe) through the prokaryotic expression system, and successfully constructed RBD-Fe nanoparticles by covalentially coupling PDCoV RBD-dimer and SC-Fe using the SpyTag/SpyCatcher system. The immunoprotection of RBD-Fe nanoparticles was evaluated in mice. Results The boosting effect on immune responses of the homologous prime-boost regime showed that RBD-Fe nanoparticles promptly and efficiently elicited specific humoral and cellular immune responses in mice. Notably, PDCoV spike (S)-specific IgG and neutralizing antibody (NA) responses from the RBD-Fe group were detected in immunized mice. The histopathological results showed that immunization with RBD-Fe nanoparticles significantly enhanced the resistance of mice to PDCoV infection. Conclusion This study successfully developed a candidate nanoparticle vaccine, providing protection against virulent PDCoV in mice.