Porcine deltacoronavirus (PDCoV), an emerging enteropathogenic coronavirus, causes diarrhea in piglets and possesses the potential to infect humans. However, there are no commercially available vaccines for PDCoV. In this study, the immune responses to the spike (S) protein and receptor-binding domain (RBD) trimer were examined in mice. Neutralization assays and flow cytometry analysis demonstrated that S protein elicited more robust neutralizing antibodies (NAbs) and cellular immune responses than the RBD trimer. Spike protein and inactivated vaccine were used in the assessment of immunogenicity in piglets and sows. Immunized piglets, sows, and suckling pig showed high NAb titers and S-specific sIgA in colostrum, milk, and serum. The piglets/suckling pig from the immunized group displayed significantly fewer microscopic lesions in the intestinal tissue, with only one or no piglet showing mild diarrhea. However, all piglets/suckling pig showed mild to watery diarrhea and exhibited a high level of viral shedding in the challenged control group. The feces from the piglets/suckling pig in the S protein and inactivated vaccine group exhibited reduced viral load. Of note, vaccine-elicited NAbs last for more than 4 months in immunized piglets. Together, our data demonstrate for the first time the protective efficacy of S-based subunit vaccine, which could be a candidate vaccine against PDCoV. IMPORTANCE As an emerging porcine enteropathogenic coronavirus that has the potential to infect humans, porcine deltacoronavirus (PDCoV) is receiving increasing attention. However, no effective commercially available vaccines against this virus are available. In this work, we designed a spike (S) protein and receptor-binding domain (RBD) trimer as a candidate PDCoV subunit vaccine. We demonstrated that S protein induced more robust humoral and cellular immune responses than the RBD trimer in mice. Furthermore, the protective efficacy of the S protein was compared with that of inactivated PDCoV vaccines in piglets and sows. Of note, the immunized piglets and suckling pig showed a high level of NAbs and were associated with reduced virus shedding and mild diarrhea, and the high level of NAbs was maintained for at least 4 months. Importantly, we demonstrated that S protein-based subunit vaccines conferred significant protection against PDCoV infection.

Currently licensed dengue vaccines do not induce long-term protection in children without prior dengue virus exposure. A better understanding of the mechanism by which the immune system prevents dengue virus infection is urgently needed to improve vaccine efficacy. In this study, the induction of protective antibody responses against dengue virus infection was tested in a non-human primate model using the heterologous prime-boost vaccination approach. Groups of cynomolgus macaques were immunized with a priming dose of attenuated dengue viruses and followed by two booster doses of virus-like particles in four monovalent arms, or in the tetravalent arm (prM + E)-expressing plasmids. At 1 month post-immunization, all macaques had elevated levels of neutralizing antibodies, and live viral challenges revealed an overall protective efficacy of 91% (40/44 macaques protected) against infection with clinical isolates. Breakthrough infections occurred in macaques with distinctive antibody profiles at the time of challenge: two macaques had the lowest neutralizing antibodies against the respective DENV-1 and -4 challenge strains among the respective groups, whereas two other DENV-4-infected macaques exhibited high levels of neutralizing and virus-binding antibodies. The ratio of antibodies recognizing a DENV-4-specific epitope and those that bound viral particles was at the lowest levels in the latter DENV-4-infected macaques, indicating an underrepresentation of antibodies targeting the serotype-specific epitope. Protection among macaques challenged with DENV-2 or -3 coincided with vigorous EDIII-binding antibody responses induced by booster immunization. A combination of attenuated viruses for priming and non-infectious particle-based antigens for boosting may be a more effective means of preventing dengue. IMPORTANCE Currently licensed dengue vaccines do not induce long-term protection in children without previous exposure to dengue viruses in nature. These vaccines are based on selected attenuated strains of the four dengue serotypes and employed in combination for two or three consecutive doses. In our search for a better dengue vaccine candidate, live attenuated strains were followed by non-infectious virus-like particles or the plasmids that generate these particles upon injection into the body. This heterologous prime-boost immunization induced elevated levels of virus-specific antibodies and helped to prevent dengue virus infection in a high proportion of vaccinated macaques. In macaques that remained susceptible to dengue virus, distinct mechanisms were found to account for the immunization failures, providing a better understanding of vaccine actions. Additional studies in humans in the future may help to establish whether this combination approach represents a more effective means of preventing dengue by vaccination.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), emerged in Wuhan, China, in December 2019. As of September 2023, there have been over 770 million confirmed cases of COVID-19, including over 6.9 million deaths. Epidemiologic studies have indicated that comorbidities of obesity and diabetes mellitus are associated with increased morbidity and mortality following SARS-CoV-2 infection. We determined how the comorbidities of obesity and diabetes affect morbidity and mortality following SARS-CoV-2 infection in unvaccinated and adjuvanted spike nanoparticle (NVX-CoV2373) vaccinated mice. We find that obese/diabetic mice infected with SARS-CoV-2 have increased morbidity and mortality compared to age-matched normal mice. Mice that were fed a high-fat diet (HFD) and then vaccinated with NVX-CoV2373 produce equivalent neutralizing antibody titers compared to those fed a normal diet (ND). However, the HFD mice have reduced viral clearance early in infection. Analysis of the inflammatory immune response in HFD mice demonstrates a recruitment of neutrophils that was correlated with increased mortality and reduced clearance of the virus. Depletion of neutrophils in diabetic/obese vaccinated mice reduced disease severity and protected mice from lethality. This model recapitulates the increased disease severity associated with obesity and diabetes in humans with COVID-19 and is an important comorbidity to study with increasing obesity and diabetes across the world. IMPORTANCE Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has caused a wide spectrum of diseases in the human population, from asymptomatic infections to death. It is important to study the host differences that may alter the pathogenesis of this virus. One clinical finding in coronavirus disease 2019 (COVID-19) patients is that people with obesity or diabetes are at increased risk of severe illness from SARS-CoV-2 infection. We used a high-fat diet model in mice to study the effects of obesity and type 2 diabetes on SARS-CoV-2 infection as well as how these comorbidities alter the response to vaccination. We find that diabetic/obese mice have increased disease after SARS-CoV-2 infection and they have slower clearance of the virus. We find that the lungs of these mice have increased neutrophils and that removing these neutrophils protects diabetic/obese mice from disease. This demonstrates why these diseases have increased risk of severe disease and suggests specific interventions upon infection.

ABSTRACT Ephrin-B2 (EFNB2) is a ligand for six Eph receptors in humans and functions as a cell entry receptor for several henipaviruses including the Nipah virus (NiV), a pathogenic zoonotic virus with pandemic potential. To understand the sequence basis of promiscuity for EFNB2 binding to the attachment glycoprotein of NiV (NiV-G) and Eph receptors, we performed deep mutagenesis on EFNB2 to identify mutations that enhance binding to NiV-G over EphB2, one of the highest affinity Eph receptors. The mutations highlight how different EFNB2 conformations are selected by NiV-G versus EphB2. Specificity mutations are enriched at the base of the G-H binding loop of EFNB2, especially surrounding a phenylalanine hinge upon which the G-H loop pivots, and at a phenylalanine hook that rotates away from the EFNB2 core to engage Eph receptors. One EFNB2 mutant, D62Q, possesses pan-specificity to the attachment glycoproteins of closely related henipaviruses and has markedly diminished binding to the six Eph receptors. However, EFNB2-D62Q has high residual binding to EphB3 and EphB4. A second deep mutational scan of EFNB2 identified combinatorial mutations to further enhance specificity to NiV-G. A triple mutant of soluble EFNB2, D62Q-Q130L-V167L, has minimal binding to Eph receptors but maintains binding, albeit reduced, to NiV-G. Soluble EFNB2 decoy receptors carrying the specificity mutations were potent neutralizers of chimeric henipaviruses. These findings demonstrate how specific residue changes at the shared binding interface of a promiscuous ligand (EFNB2) can influence selectivity for multiple receptors, and may also offer insight toward the development of henipavirus therapeutics and diagnostics. IMPORTANCE Ephrin-B2 (EFNB2) is a ligand for six Eph receptors in humans and regulates multiple cell developmental and signaling processes. It also functions as the cell entry receptor for Nipah virus and Hendra virus, zoonotic viruses that can cause respiratory and/or neurological symptoms in humans with high mortality. Here, we investigate the sequence basis of EFNB2 specificity for binding the Nipah virus attachment G glycoprotein over Eph receptors. We then use this information to engineer EFNB2 as a soluble decoy receptor that specifically binds the attachment glycoproteins of the Nipah virus and other related henipaviruses to neutralize infection. These findings further mechanistic understanding of protein selectivity and may facilitate the development of diagnostics or therapeutics against henipavirus infection.

Influenza A viruses (IAV) utilize sialic acid (Sia) containing cell surface glycoconjugates for host cell infection, and IAV strains from different host species show preferences for structurally distinct Sia at the termini of glycoconjugates. Various types of cell surface glycoconjugates (N-glycans, O-glycans, glycolipids) display significant diversity in both structure and carbohydrate composition. To define the types of sialylglycoconjugates that facilitate IAV infection, we utilized the CRISPR/Cas9 technique to truncate the three major types of glycoconjugates, either individually or in combination, by targeting glycosyltransferases essential to glycan biosynthesis in a human lung epithelial cell line. Our studies show that both human and avian IAV strains do not display strict preferences for a specific type of glycoconjugate. Interestingly, truncation of the three major types of glycoconjugates significantly decreased replication of human IAV strains, yet did not impact replication of avian IAV strains. Unlike human IAV strains, avian IAV strains were able to efficiently utilize other less prevalent shorter glycoconjugates such as sialyl Tn and sialyl T antigens. Taken together, our studies demonstrate that avian IAV strains utilize a broader repertoire of glycoconjugates for host cell infection as compared to human IAV strains. IMPORTANCE It is well known that influenza A viruses (IAV) initiate host cell infection by binding to sialic acid, a sugar molecule present at the ends of various sugar chains called glycoconjugates. These sugar chains can vary in chain length, structure, and composition. However, it remains unknown if IAV strains preferentially bind to sialic acid on specific glycoconjugate type(s) for host cell infection. Here, we utilized CRISPR gene editing to abolish sialic acid on different glycoconjugate types in human lung cells, and evaluated human versus avian IAV infections. Our studies show that both human and avian IAV strains can infect human lung cells by utilizing any of the three major sialic acid-containing glycoconjugate types, specifically N-glycans, O-glycans, and glycolipids. Interestingly, simultaneous elimination of sialic acid on all three major glycoconjugate types in human lung cells dramatically decreased human IAV infection, yet had little effect on avian IAV infection. These studies show that avian IAV strains effectively utilize other less prevalent glycoconjugates for infection, whereas human IAV strains rely on a limited repertoire of glycoconjugate types. The remarkable ability of avian IAV strains to utilize diverse glycoconjugate types may allow for easy transmission into new host species.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) recombinant protein vaccines have been widely used in the real world and shown good protective effects. A vaccine prepared from the ancestral SARS-CoV-2 receptor-binding domain (RBD) homodimer was previously made a candidate in view of its effectiveness in rodents and nonhuman primates. Here, we report that the RBD homodimers of ancestral SARS-CoV-2 as well as the variant RBD dimers from the Beta, Delta, Lambda, Omicron, and Omicron sublineages, which were rapidly prepared using our universal dimeric protein platform, elicit both strong immunogenicity and good protection in vivo. The ancestral RBD vaccine was verified to provide cross-protection against the SARS-CoV-2 Delta variant from lethal challenge. A heterogeneous booster with Omicron BA.1 dimeric RBD vaccine based on a two-dose ancestral vaccine prime reduced the viral loads in Omicron BA.1 virus-challenged animals. In addition, vaccines prepared from dimeric Omicron XBB.1.5 RBD completely protected the mice from lethal challenge by Omicron XBB.1.16 and reduced the viral infection in the respiratory tract of Syrian hamsters. Thus, RBD homodimer vaccines can confer good protection against SARS-CoV-2 and its variants when used in homogeneous or heterogeneous boosting schemes. IMPORTANCE Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants achieved immune escape and became less virulent and easily transmissible through rapid mutation in the spike protein, thus the efficacy of vaccines on the market or in development continues to be challenged. Updating the vaccine, exploring compromise vaccination strategies, and evaluating the efficacy of candidate vaccines for the emerging variants in a timely manner are important to combat complex and volatile SARS-CoV-2. This study reports that vaccines prepared from the dimeric receptor-binding domain (RBD) recombinant protein, which can be quickly produced using a mature and stable process platform, had both good immunogenicity and protection in vivo and could completely protect rodents from lethal challenge by SARS-CoV-2 and its variants, including the emerging Omicron XBB.1.16, highlighting the value of dimeric recombinant vaccines in the post-COVID-19 era.

The 2019 coronavirus disease (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) highlighted significant gaps in our mechanisms to prevent and control cross-species transmission of animal coronaviruses. Porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine delta coronavirus (PDCoV) are common porcine coronaviruses with similar clinical features. In the absence of effective drugs and methods of prevention and control, outbreaks of these viruses have led to significant economic losses in the global pig industry. Here, we report the effect of five fatty acids against porcine coronaviruses: sodium butyrate, lauric acid, palmitic acid, docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA). DHA and EPA reduced viral replication by attenuating the endoplasmic reticulum stress and inhibiting PEDV, TGEV, and PDCoV infections in vero cells, PK-15 cells, and LLC-PK1 cells in vitro, respectively. Additionally, DHA and EPA increased the host antioxidant levels and reduced inflammation. In conclusion, we report here for the first time the antiviral effects of DHA and EPA on porcine coronaviruses and provide a molecular basis for the development of new fatty acid-based therapies to control porcine coronavirus infection and transmission. IMPORTANCE Porcine epidemic diarrhea caused by porcine coronaviruses remains a major threat to the global swine industry. Fatty acids are extensively involved in the whole life of the virus. In this study, we found that docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) significantly reduced the viral load of porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), and porcine delta coronavirus (PDCoV) and acted on the replication of the viruses rather than attachment and entry. We further confirmed that DHA and EPA inhibited PEDV replication by alleviating the endoplasmic reticulum stress. Meanwhile, DHA and EPA alleviate PEDV-induced inflammation and reactive oxygen species (ROS) levels and enhance the cellular antioxidant capacity. These data indicate that DHA and EPA have antiviral effects on porcine coronaviruses and provide a molecular basis for the development of new fatty acid-based therapies to control porcine coronavirus infection and transmission.