Adenovirus-vectored PDCoV vaccines induce potent humoral and cellular immune responses in mice

Design of multi-epitope chimeric phage nanocarrier vaccines for porcine deltacoronavirus

Porcine delta coronavirus (PDCoV) poses a significant threat to the swine industry. Thus, the development of innovative vaccine candidates is critical for PDCoV prevention. This study details the creation of a PDCoV nanoparticle vaccine utilizing bacteriophage (phage) T4 as a delivery platform. B cell and T cell epitopes of the PDCoV spike (S) protein were identified through bioinformatics and assembled into a tandem construct (termed Pep) using a linker. In silico molecular docking revealed stable interactions between Pep and TLR3. Immune stimulation predictions indicated that Pep could trigger a robust immune response. The prokaryotic Pep protein was conjugated with T4 phage to generate the recombinant T4-Pep phage. Experimental data demonstrated that a single T4 phage displayed at least 830 copies of Pep. In a mouse immunoprotection assay, T4-Pep induced significantly higher levels of specific IgG antibodies and superior neutralizing antibody titers against PDCoV compared to the Pep naked peptide antigen. Moreover, T4 phage exhibited potent immunostimulatory effects, with immunized mice showing protection against PDCoV infection. Histological analysis revealed enhanced intestinal mucosal integrity post-immunization. These findings suggest that bacteriophages are promising vectors for the efficient delivery of viral epitopes, offering a potential platform for developing vaccines against porcine enteric coronaviruses.

Isolation, phylogenetics, and characterization of a new PDCoV strain that affects cellular gene expression in human cells

Introduction

Porcine deltacoronavirus (PDCoV) is an enteropathogenic coronavirus that causes acute diarrhea, vomiting, dehydration, and even death in piglets, resulting in serious economic losses to the pork industry worldwide. PDCoV has received much attention owing to its broad host range, including humans, posing a potential threat to public health. However, the prevalence, characteristics, and host cellular gene expression of PDCoV remain poorly understood.

Methods

In this study, a new PDCoV strain (CHN/SX-Y/2023, GenBank number PQ373831) was successfully isolated, identified, and subjected to phylogenetic tree and transcriptome analysis in human hepatoma (Huh7) cells following PDCoV infection.

Results

The results showed that the CHN/SX-Y/2023 strain belongs to the Chinese lineage and causes cytopathic effects in canonical cell lines (LLC-PK1 and ST cells) and other cell lines (Huh7 and LMH cells). However, HEK-293T, EEC, MDBK, and Vero-CCL81 cells were not found to be susceptible in this study. Based on transcriptome analysis, 1,799 differentially expressed genes (DEGs) were upregulated and 771 were downregulated during PDCoV infection.

Discussion

Among the upregulated genes, FCGR1A, VSIG1, TNFRSF9, and PLCXD3 are associated with immunity, inflammation, and lipid catabolism. Moreover, Kyoto Encyclopedia of Genes and Genomes analysis revealed that the upregulated DEGs were significantly enriched in the MAPK, TNF, and NF-κB signaling pathways and viral protein interactions with cytokines and cytokine receptors. Protein-protein interaction networks showed that the upregulated genes CXCL8, DUSP1, PTGS2, and IL15 were associated with inflammation and immunity. In addition, the protein levels of p-IRF3, LC3-II, and ACSL4 increased, suggesting that PDCoV infection in Huh7 cells induces an intrinsic immune response, cellular autophagy, and ferroptosis. Collectively, our findings provide new insights into the characteristics and mechanisms of PDCoV infection.

An inactivated PDCoV vaccine induces robust neutralizing antibodies and immune protection in pigs lasting for three months

Porcine deltacoronavirus (PDCoV), a novel enteropathogenic coronavirus, causes diarrhea mainly in suckling piglets and has the potential to infect humans. Whereas, there is no commercially available vaccine which can effectively prevent this disease. In this study, to ascertain the duration of immune protection of inactivated PDCoV vaccine, suckling piglets were injected subcutaneously with inactivated PDCoV vaccine using a prime/boost strategy at 3 and 17-day-old. Neutralizing antibody assay showed that the level of the inactivated PDCoV group was still ≥1:64 at three months after prime vaccination. The three-month-old pigs were orally challenged with PDCoV strain CZ2020. Two pigs in challenge control group showed mild to severe diarrhea at 10-11 day-post-challenge (DPC), while the inactivated PDCoV group had no diarrhea. High levels of viral shedding, substantial intestinal villus atrophy, and positive straining of viral antigens in ileum were detected in challenge control group, while the pigs in inactivated PDCoV group exhibited significantly reduced viral load, minor intestinal villi damage and negative straining of viral antigens. These results demonstrated that PDCoV was pathogenic against three-month-old pigs and inactivated PDCoV vaccine can provide effective protection in pigs lasting for three months.

Prevention and Control of Swine Enteric Coronaviruses in China: A Review of Vaccine Development and Application

Swine enteric coronaviruses (SECs) cause significant economic losses to the pig industry in China. Although many commercialized vaccines against transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) are available, viruses are still widespread. The recent emergence of porcine deltacoronavirus (PDCoV) and swine acute diarrhea syndrome coronavirus (SADS-CoV), for which no vaccines are available, increases the disease burden. In this review, we first introduced the genomic organization and epidemiology of SECs in China. Then, we discussed the current vaccine development and application in China, aiming to provide suggestions for better prevention and control of SECs in China and other countries.