An attractive vaccine candidate based on AP205 VLPs fusing with an RBM domain of a new porcine deltacoronavirus strain in China

Swine coronaviruses (SeCoV) have become a major concern in pig farming and have caused enormous economic losses all over the world. Porcine deltacoronavirus (PDCoV) is a newly emerged SeCoV, which was able to infect avians as well as humans. Therefore, developing efficient vaccines against PDCoV is not only important to pork production, but also contributes to public healthcare. In this study, we identified a new PDCoV strain, CHN/GD/2023, which was isolated from a diarrheal piglet colon. After a thorough sequence analysis of the Spike gene, CHN/GD/2023 was found to be closely related with other PDCoV viruses that have recently been isolated in China. Next, a VLP-based vaccine candidate, AP205-RBD, was produced by genetically fusing the receptor-binding domain (RBD) of CHN/GD/2023 to the C-terminus of the AP205 gene. The purified AP205-RBD successfully displayed RBD on the surface and exhibited a spherical particle structure with a diameter of 51 nm. The agarose gel image demonstrated that ssRNA from E. coli was packaged inside the AP205-RBD particle. In addition, AP205-RBD demonstrated potent immunogenicity in mice, as highly RBD-specific IgG titers were detected. Importantly, these antibodies were able to neutralize CHN/GD/2023 PDCoV in vitro, suggesting that the AP205-RBD vaccine is capable of protecting against viruses. Moreover, we surprisingly found that AP205-RBD elicited antibodies that could neutralize another strain of PDCoV that was previously isolated in China, implying that AP205-RBD could potentially protect animals from different PDCoV strains. In summary, a new PDCoV strain was isolated and identified in this study, and an effective vaccine candidate, AP205-RBD, was reported, which could induce broad antibody protection responses in mice.