Development of a vaccine based on mRNA assembly of PEDV virus-like particle

ABSTRACT

Porcine epidemic diarrhea virus (PEDV) represents a highly contagious enteropathogenic coronavirus affecting swine. This virus elicits acute diarrhea in neonatal nursing piglets, with mortality approaching 100%, and, thus, imposes enormous economic burdens on the worldwide pork industry. Therefore, developing safe and effective vaccines remains a top priority for controlling PEDV. Here, we constructed a lipid-nanoparticle (LNP)-encapsulated messenger RNA (mRNA) vaccine. This vaccine encodes the four major structural proteins of PEDV: spike (S), membrane (M), envelope (E), and nucleocapsid (N), which self-assemble into virus-like particle (VLP). Compared with a PEDV S-only mRNA vaccine and a commercial PEDV/transmissible gastroenteritis virus (TGEV) bivalent inactivated vaccine in a mouse model, this VLP mRNA vaccine induced significantly higher levels of IgG, mucosal IgA, and neutralizing antibodies. It also enhanced the lymphocyte proliferation index and expanded the populations of T and B cells. Subsequent evaluations in sows showed that the VLP mRNA vaccine elicited robust PEDV-specific immune responses in vivo

. Furthermore, piglets that suckled colostrum from these vaccinated sows gained protection against challenge with a virulent PEDV strain. These protected piglets exhibited lower diarrhea scores, reduced viral shedding, less severe intestinal lesions, and decreased mortality. Collectively, these findings demonstrate that the developed PEDV VLP mRNA platform constitutes a highly promising strategy for preventing PEDV infections.

IMPORTANCE

PEDV-induced watery diarrhea in neonatal piglets remains a major threat to the global swine industry, while current commercial vaccines are predominantly inactivated formulations or S-only subunit vaccines, whose efficacy and broad-spectrum protection continue to be limited. We, therefore, incorporated the four PEDV structural proteins (S-M-E-N) into a LNP mRNA vaccine that self-assembles into VLPs in vivo

. In mice, the mRNA-VLP platform elicited significantly higher systemic IgG, mucosal IgA, and neutralizing antibody titers than an S-only mRNA control or a commercial PEDV/TGEV inactivated vaccine, while expanding both T- and B-cell populations. Maternal immunization of pregnant sows converted these responses into potent systemic immunity that protected suckling piglets against virulent challenge, as evidenced by markedly reduced diarrhea scores, intestinal lesions, viral shedding, and mortality. Collectively, the developed PEDV mRNA-VLP platform offers a highly promising strategy for preventing PEDV infection.

Background:

Porcine epidemic diarrhea virus (PEDV) represents a highly contagious enteropathogenic coronavirus affecting swine. This virus elicits acute diarrhea in neonatal nursing piglets, with mortality approaching 100%, and, thus, imposes enormous economic burdens on the worldwide pork industry. Therefore, developing safe and effective vaccines remains a top priority for controlling PEDV.

PEDV is classified within the Alphacoronavirus genus of the family Coronaviridae. It is an enveloped virus with a positive-sense single-stranded RNA genome. The PEDV genome is about 28 kb in length and contains seven open reading frames (ORFs). These ORFs encode a set of viral proteins, including the replicase polyproteins 1a and 1ab, spike (S) protein, ORF3, envelope (E) protein, membrane (M) protein, and nucleocapsid (N) protein. The coronavirus spike protein is a multifunctional protein responsible for mediating viral entry into host cells. The coronavirus E protein is a small integral membrane protein that serves a critical function in the process of viral assembly. The M protein plays a central role in virion morphogenesis. Coronavirus N proteins bind to genomic RNA to form ribonucleoprotein complexes. PEDV was first identified in Europe during the early 1970s. After 2010, highly pathogenic variant strains of PEDV have spread widely among pig herds, resulting in considerable economic losses on a global scale. Vaccine immunization is still an effective method to control the epidemic of PEDV. Currently, a variety of PEDV single vaccines or multiple vaccines containing PEDV are available, but conventional inactivated or attenuated vaccines are the main ones. The immune efficacy of inactivated vaccines is often weak, while attenuated vaccines require long development periods and carry the risk of re-intensification of virulence and recombination with circulating strains. It is crucial to develop new and efficient PEDV vaccines.

Methods:

Here, we constructed a lipid-nanoparticle (LNP)-encapsulated messenger RNA (mRNA) vaccine. This vaccine encodes the four major structural proteins of PEDV: spike (S), membrane (M), envelope (E), and nucleocapsid (N), which self-assemble into virus-like particle (VLP). Compared with a PEDV S-only mRNA vaccine and a commercial PEDV/transmissible gastroenteritis virus (TGEV) bivalent inactivated vaccine in a mouse model, this VLP mRNA vaccine was evaluated. Subsequent evaluations in sows showed that the VLP mRNA vaccine elicited robust PEDV-specific immune responses in vivo. Furthermore, piglets that suckled colostrum from these vaccinated sows gained protection against challenge with a virulent PEDV strain.

Results:

The VLP mRNA vaccine induced significantly higher levels of IgG, mucosal IgA, and neutralizing antibodies compared with a PEDV S-only mRNA vaccine and a commercial PEDV/TGEV bivalent inactivated vaccine in a mouse model. It also enhanced the lymphocyte proliferation index and expanded the populations of T and B cells.

In sows, the VLP mRNA vaccine elicited robust PEDV-specific immune responses in vivo. Piglets that suckled colostrum from these vaccinated sows gained protection against challenge with a virulent PEDV strain. These protected piglets exhibited lower diarrhea scores, reduced viral shedding, less severe intestinal lesions, and decreased mortality.

Data Summary:

The VLP mRNA vaccine induced significantly higher levels of IgG, mucosal IgA, and neutralizing antibodies compared with the S-only mRNA control and the commercial inactivated vaccine. It also enhanced the lymphocyte proliferation index and expanded T- and B-cell populations. In the challenge study, piglets from vaccinated sows exhibited lower diarrhea scores, reduced viral shedding, less severe intestinal lesions, and decreased mortality.

Conclusions:

Collectively, these findings demonstrate that the developed PEDV VLP mRNA platform constitutes a highly promising strategy for preventing PEDV infections. The developed PEDV mRNA-VLP platform offers a highly promising strategy for preventing PEDV infection.

Practical Significance:

PEDV-induced watery diarrhea in neonatal piglets remains a major threat to the global swine industry, while current commercial vaccines are predominantly inactivated formulations or S-only subunit vaccines, whose efficacy and broad-spectrum protection continue to be limited. The developed PEDV mRNA-VLP platform offers a highly promising strategy for preventing PEDV infection, thereby potentially reducing the economic burden on the worldwide pork industry.