Norovirus P particle, a novel platform for vaccine development and antibody production

Structural insight of cell surface sugars in viral infection and human milk glycans as natural antiviral substance

Viral infections are caused by the adhesion of viruses to host cell receptors, including sialylated glycans, glycosaminoglycans, and human blood group antigens (HBGAs). Atomic-level structural information on the interactions between viral particles or proteins with glycans can be determined to provide precise targets for designing antiviral drugs. Milk glycans, existing as free oligosaccharides or glycoconjugates, have attracted increasing attention; milk glycans protect infants against infectious diseases, particularly poorly manageable viral infections. Furthermore, several glycans containing structurally distinct sialic acid/fucose/sulfate modifications in human milk acting as a "receptor decoy" and serving as the natural antiviral library, could interrupt virus-receptor interaction in the first line of defense for viral infection. This review highlights the basis of virus-glycan interactions, presents specific glycan receptor binding by gastroenterovirus viruses, including norovirus, enteroviruses, and the breakthroughs in the studies on the antiviral properties of human milk glycans, and also elucidates the role of glycans in respiratory viruses infection. In addition, recent advances in methods for performing virus/viral protein-glycan interactions were reported. Finally, we discuss the prospects and challenges of the studies on the clinical application of human milk glycan for viral interventions.

Effects of Rotavirus NSP4 on the Immune Response and Protection of Rotavirus-Norovirus Recombinant Subunit Vaccines in Different Immune Pathways

Diarrheal disease continues to be a major cause of global morbidity and mortality among children under 5 years of age. To address the current issues associated with oral attenuated rotavirus vaccines, the study of parenteral rotavirus vaccines has promising prospects. In our previous study, we reported that rotavirus nonstructural protein 4 (NSP4) did not increase the IgG antibody titer of co-immune antigen but did have a protective effect against diarrhea via the intramuscular injection method. Here, we explored whether NSP4 can exert adjuvant effects on mucosal immune pathways. In this study, we immunized mice via muscle and nasal routes, gavaged them with the rotavirus Wa strain or the rotavirus SA11 strain, and then tested the protective effects of immune sera against both viruses. The results revealed that the serum-specific VP8* IgG antibody titers of the mice immunized via the nasal route were much lower than those of the mice immunized by intramuscular injection, and the specific IgA antibodies were almost undetectable in the bronchoalveolar lavage fluid (BALF). NSP4 did not increase the titer of specific VP8* antibodies in either immune pathway. Therefore, in the two vaccines (PP-NSP4-VP8* and PP-VP8*+NSP4) used in this study, NSP4 was unable to perform its potential adjuvant role through the mucosal immune pathway. Instead, NSP4 was used as a co-immunized antigen to stimulate the mice to produce specific binding antibodies that play a protective role against diarrhea.

GII.6 norovirus major capsid protein VP1 derived from distinct clusters induce cross-blocking effects

Unlike pandemic GII.4 norovirus, GII.6 norovirus shows limited sequence variation in its major capsid protein VP1. In this study, we investigated the VP1 expression profiles, binding abilities, and cross-blocking effects of three GII.6 norovirus strains derived from three distinct variants. Norovirus VP1 was expressed using a recombinant baculovirus expression system and characterized by transmission electron microscopy, mass spectrometry, salivary histo-blood group antigen (HBGA)-virus like particles (VLPs) binding and binding blockade assays. Mass spectrometry revealed the expected molecular weight (MW) of full-length proteins and degraded or cleaved fragments of all three VP1 proteins. Peptide mapping showed loss of 2 and 3 amino acids from the N- and C-terminus, respectively. Further, the co-expression of VP1 and VP2 proteins did not lead to extra fragmentation during mass spectrometry. Salivary HBGA-VLP binding assay revealed similar binding patterns of the three GII.6 VP1 proteins. Salivary HBGA-VLP binding blockade assay induced cross-blocking effects. Our results demonstrate similar binding abilities against salivary HBGAs and specific cross-blocking effects for GII.6 norovirus strains derived from distinct variants, suggesting that fewer GII.6 strains from different evolutionary variants are needed for the development of norovirus vaccines.

A Pseudovirus Nanoparticle Displaying the Vaccinia Virus L1 Protein Elicited High Neutralizing Antibody Titers and Provided Complete Protection to Mice against Mortality Caused by a Vaccinia Virus Challenge

The recent worldwide incidence of mpox infection and concerns about future emerging variants of mpox viruses highlight the need for the development of a new generation of mpox vaccines. To achieve this goal, we utilized our norovirus S nanoparticle vaccine platform to produce and evaluate two pseudovirus nanoparticles (PVNPs), S-L1 and S-J1. These PVNPs displayed the L1 neutralizing antigen target of the vaccinia virus and a yet-untested J1 antigen of the mpox virus, respectively, with the aim of creating an effective nanoparticle-based mpox vaccine. Each self-assembled PVNP consists of an inner shell resembling the interior layer of the norovirus capsid and multiple L1 or J1 antigens on the surface. The PVNPs improved the antibody responses toward the displayed L1 or J1 antigens in mice, resulting in significantly greater L1/J1-specific IgG and IgA titers than those elicited by the corresponding free L1 or J1 antigens. After immunization with the S-L1 PVNPs, the mouse sera exhibited high neutralizing antibody titers against the vaccinia virus, and the S-L1 PVNPs provided mice with 100% protection against mortality caused by vaccinia virus challenge. In contrast, the S-J1 PVNPs induced low neutralizing antibody titers and conferred mice weak protective immunity. These data confirm that the L1 protein is an excellent vaccine target and that the readily available S-L1 PVNPs are a promising mpox vaccine candidate worthy of further development.

A Viral Protein 4-Based Trivalent Nanoparticle Vaccine Elicited High and Broad Immune Responses and Protective Immunity against the Predominant Rotaviruses

The current live rotavirus (RV) vaccines show reduced effectiveness in developing countries, calling for vaccine strategies with improved efficacy and safety. We generated pseudovirus nanoparticles (PVNPs) that display multiple ectodomains of RV viral protein 4 (VP4), named S-VP4e, as a nonreplicating RV vaccine candidate. The RV spike protein VP4s that bind host receptors and facilitate viral entry are excellent targets for vaccination. In this study, we developed scalable methods to produce three S-VP4e PVNPs, each displaying the VP4e antigens from one of the three predominant P[8], P[4], and P[6] human RVs (HRVs). These PVNPs were recognized by selected neutralizing VP4-specific monoclonal antibodies, bound glycan receptors, attached to permissive HT-29 cells, and underwent cleavage by trypsin between VP8* and VP5*. 3D PVNP models were constructed to understand their structural features. A trivalent PVNP vaccine containing the three S-VP4e PVNPs elicited high and well-balanced VP4e-specific antibody titers in mice directed against the three predominant HRV P types. The resulting antisera neutralized the three HRV prototypes at high titers; greater than 4-fold higher than the neutralizing responses induced by a trivalent vaccine consisting of the S60-VP8* PVNPs. Finally, the trivalent S-VP4e PVNP vaccine provided 90-100% protection against diarrhea caused by HRV challenge. Our data supports the trivalent S-VP4e PVNPs as a promising nonreplicating HRV vaccine candidate for parenteral delivery to circumvent the suboptimal immunization issues of all present live HRV vaccines. The established PVNP-permissive cell and PVNP-glycan binding assays will be instrumental for further investigating HRV-host cell interactions and neutralizing effects of VP4-specific antibodies and antivirals.

An experimental universal swine influenza a virus (IAV) vaccine candidate based on the M2 ectodomain (M2e) peptide does not provide protection against H1N1 IAV challenge in pigs

Swine flu is a common disease problem in North American pig populations and swine influenza A viruses (IAV) are extremely diverse and the lack of cross protection between heterologous strains is impacting vaccine efficacy in the field. The objective of this study was to design and test a novel swine flu vaccine targeting the M2 ectodomain (M2e) of IAV, a highly conserved region within the IAV proteome. In brief, an M2e peptide was designed to match the predominant swine IAV M2 sequence based on global analysis of sequences from pigs and humans. The resulting sequence was used to synthesize the M2e peptide coupled to a carrier protein. The final vaccine concentration was 200 µg per dose, and a commercial, microemulsion-based aqueous adjuvant was added. Nine 3-week-old IAV negative piglets were randomly assigned to three groups and rooms including non-vaccinated pigs (NEG-CONTROLs) and vaccinated pigs using the intramuscular (M2e-IM) or the intranasal route (M2e-IN). Vaccinations were done at weaning and again at 2 weeks later. An in-house enzyme-linked immunosorbent assay (ELISA) was developed and validated to study the M2e IgG antibody response and demonstrated M2e-IM pigs had a higher systemic antibody response compared to M2e-IN pigs. Subsequently, an IAV challenge study was conducted. The results indicated that M2e-IM vaccinated pigs were not protected from H1N1 (US pandemic clade, global clade 1A.3.3.2) challenge despite having a strong humoral anti-M2e immune response. In conclusion, while the experimental IAV vaccine was able to induce anti-M2e antibodies, when challenged with H1N1, the vaccinated pigs were not protected, perhaps indicating that reactivity to the M2e antigen alone is not sufficient to reduce clinical signs, lesions or shedding associated with experimental IAV challenge.

Identification of a GII.6 norovirus blockade antibody epitope

Noroviruses (NoVs) are the leading agent that causes acute viral gastroenteritis worldwide. Sporadic cases of GII.6 NoV have been reported primarily in addition to occasional outbreaks. Using the major capsid protein VP1 of GII.6 NoV derived from three distinct clusters, we demonstrated three blockade monoclonal antibodies (mAbs, 1F7, 1F11, and 2B6) generated previously exhibited cluster-specific binding effects. Combining sequence alignment and blocking immune epitopes, we sequentially designed a total of 18 mutant proteins containing one, two, or three mutations, or swapped regions. Indirect enzyme-linked immunosorbent assay (ELISA) demonstrated that the three blocking mAbs lost or showed significantly reduced binding for H383Y, D387N, V390D, and T391D mutant proteins. Combining data from mutant proteins with swapping regions and point mutations, the binding region of the three mAbs was mapped to residues 380-395. Sequence alignment of this region showed within-cluster conservation and between-cluster variations, further strengthening the idea of blockade epitope-mediated evolution of NoV.

Development of Chimeric Hepatitis B (HBV) - Norovirus (NoV) P particle as candidate vaccine against Hepatitis B and norovirus infection

Introduction

Hepatitis B remains a global problem with no effective treatment. Here, a mucosal vaccine candidate was developed with HBsAg and HBcAg, to provide both prophylactic and therapeutic protection against hepatitis B. The antigens were presented using the P particle of human norovirus (HuNov). As a result, the chimeric HBV - HuNoV P particle can act as a dual vaccine for hepatitis B and HuNoV.

Methods

The vaccine candidate was expressed and purified from Escherichia coli BL21 (DE3) cells. HBV-HuNoV chimeric P particles were successfully expressed and isolated, with sizes of approximately 25.64 nm. Then, the HBV-HuNoV chimeric P particles were evaluated for safety and immunogenicity in mice and gnotobiotic (Gn) pigs. After three doses (5 µg/dose in mice and 200 µg/dose in Gn pigs) of intranasal immunization, humoral and cellular immune responses, as well as toxicity, were evaluated.

Results

The vaccine candidate induced strong HBV-HuNoV specific IFN-γ producing T-cell responses in the ileum, spleen, and blood of Gn pigs. Serum IgG and IgA antibodies against HBV-HuNoV chimeric P particles also increased significantly in Gn pigs. Increased HBsAg- and HuNoV-specific serum IgG responses were observed in mice and Gn pigs, although not statistically significant. The vaccine candidate did not show any toxicity in mice.

Conclusions

In summary, the chimeric HBV-HuNoV P particle vaccine given intranasally was safe and induced strong cellular and humoral immune responses in Gn pig. Modifications to the vaccine structure and dosage need to be evaluated in future studies to further enhance immunogenicity and induce more balanced humoral and cellular responses.

The αTSR Domain of Plasmodium Circumsporozoite Protein Bound Heparan Sulfates and Elicited High Titers of Sporozoite Binding Antibody After Displayed by Nanoparticles

Introduction

Malaria is a devastating infectious illness caused by protozoan Plasmodium parasites. The circumsporozoite protein (CSP) on Plasmodium sporozoites binds heparan sulfate proteoglycan (HSPG) receptors for liver invasion, a critical step for prophylactic and therapeutic interventions.

Methods

In this study, we characterized the αTSR domain that covers region III and the thrombospondin type-I repeat (TSR) of the CSP using various biochemical, glycobiological, bioengineering, and immunological approaches.

Results

We found for the first time that the αTSR bound heparan sulfate (HS) glycans through support by a fused protein, indicating that the αTSR is a key functional domain and thus a vaccine target. When the αTSR was fused to the S domain of norovirus VP1, the fusion protein self-assembled into uniform S₆₀-αTSR nanoparticles. Three-dimensional structure reconstruction revealed that each nanoparticle consists of an S₆₀ nanoparticle core and 60 surface displayed αTSR antigens. The nanoparticle displayed αTSRs retained the binding function to HS glycans, indicating that they maintained authentic conformations. Both tagged and tag-free S₆₀-αTSR nanoparticles were produced via the Escherichia coli system at high yield by scalable approaches. They are highly immunogenic in mice, eliciting high titers of αTSR-specific antibody that bound specifically to the CSPs of Plasmodium falciparum sporozoites at high titer.

Discussion and Conclusion

Our data demonstrated that the αTSR is an important functional domain of the CSP. The S₆₀-αTSR nanoparticle displaying multiple αTSR antigens is a promising vaccine candidate potentially against attachment and infection of Plasmodium parasites.

Combinations but Not a Single PlpE Epitope Induces Host Protective Immunity against Pasteurella multocida

Pasteurella multocida is the causative agent of a wide range of diseases (pasteurellosis) and a zoonotic pathogen in humans. Recombinant subunit vaccines are hot spots in recent pasteurellosis vaccine development. A chimeric vaccine is also constructed for rabbit hemorrhagic disease virus (RHDV) protective antigen VP60 chimeric with fragments of Pasteurella multocida protective antigen PlpE. The protective efficacy of the chimeric vaccine against P. multocida is not as high as that of PlpE, and the reason is not well known. In this study, we analyzed the linear B-cell epitopes of PlpE and then assessed the protective efficacy of these epitopes and their combinations. It was found that the immunodominant region of PlpE was mainly located in the region between the 21st to the 185th amino acids from the N terminus. Overlapping peptide scanning results demonstrated that this region contained six nonoverlapping epitopes, and epitope E was the predominant epitope. Chimeric protein antigens were constructed of single nonoverlapping PlpE epitopes or their combinations chimeric with the RHDV VP60 P domain. Immunization with recombinant antigen chimeric with a single PlpE epitope exhibited poor immunoprotection, whereas immunization with recombinant antigen chimeric with PlpE epitope combinations (epitopes A and E; epitopes C and E; epitopes A, C, and E; and epitopes B, D, and F) exhibited significant immunoprotection. In a word, P. multocida protective antigen PlpE contained six nonoverlapping linear B-cell epitopes, and combinations but not a single epitope induced host protective immunity. Our work will give help for future chimeric vaccine design.

Self-assembled multiepitope nanovaccine based on NoV P particles induces effective and lasting protection against H3N2 influenza virus

Current seasonal influenza vaccines confer only limited coverage of virus strains due to the frequent genetic and antigenic variability of influenza virus (IV). Epitope vaccines that accurately target conserved domains provide a promising approach to increase the breadth of protection; however, poor immunogenicity greatly hinders their application. The protruding (P) domain of the norovirus (NoV), which can self-assemble into a 24-mer particle called the NoV P particle, offers an ideal antigen presentation platform. In this study, a multiepitope nanovaccine displaying influenza epitopes (HMN-PP) was constructed based on the NoV P particle nanoplatform. Large amounts of HMN-PP were easily expressed in Escherichia coli in soluble form. Animal experiments showed that the adjuvanted HMN-PP nanovaccine induced epitope-specific antibodies and haemagglutinin (HA)-specific neutralizing antibodies, and the antibodies could persist for at least three months after the last immunization. Furthermore, HMN-PP induced matrix protein 2 extracellular domain (M2e)-specific antibody-dependent cell-mediated cytotoxicity, CD4+ and CD8+ T-cell responses, and a nucleoprotein (NP)-specific cytotoxic T lymphocyte (CTL) response. These results indicated that the combination of a multiepitope vaccine and self-assembled NoV P particles may be an ideal and effective vaccine strategy for highly variable viruses such as IV and SARS-CoV-2.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at 10.1007/s12274-023-5395-6.

Virus Infections in Older People

Older people are more prone to viral infections, and often have worse outcomes. This was well demonstrated during the COVID-19 pandemic, where a disproportionate number of deaths occurred in the oldest and frailest people. The assessment of the older person with a viral infection is complicated by the high prevalence of multiple comorbidities and sensory or cognitive impairment. They often present with common geriatric syndromes such as falls or delirium, rather than the more typical features of a viral illness in younger people. Comprehensive geriatric assessment by a specialist multidisciplinary team is the gold standard of management, as viral illness is unlikely to present in isolation of other healthcare needs. We discuss the presentation, diagnosis, prevention, and management of common viral infections-respiratory syncytial virus, coronavirus, norovirus, influenza, hepatitis, herpes, and dengue viruses-with special consideration of infections in the older patient.

Characterization of surface-exposed structural loops as insertion sites for foreign antigen delivery in calicivirus-derived VLP platform

Chimeric virus-like particles (cVLPs) show great potential in improving public health as they are safe and effective vaccine candidates. The capsid protein of caliciviruses has been described previously as a self-assembling, highly immunogenic delivery platform. The ability to significantly induce cellular and humoral immunity can be used to boost the immune response to low immunogenic foreign antigens displayed on the surface of VLPs. Capsid proteins of caliciviruses despite sequence differences share similar architecture with structural loops that can be genetically modified to present foreign epitopes on the surface of cVLPs. Here, based on the VP1 protein of norovirus (NoV), we investigated the impact of the localization of the epitope in different structural loops of the P domain on the immunogenicity of the presented epitope. In this study, three distinct loops of NoV VP1 protein were genetically modified to present a multivalent influenza virus epitope consisting of a tandem repeat of M2/NP epitopes. cVLPs presenting influenza virus-conserved epitopes in different localizations were produced in the insect cells and used to immunize BALB/c mice. Specific reaction to influenza epitopes was compared in sera from vaccinated mice to determine whether the localization of the foreign epitope has an impact on the immunogenicity.

Cross-reactive neutralizing human monoclonal antibodies mapping to variable antigenic sites on the norovirus major capsid protein

Human noroviruses are the major viral cause of acute gastroenteritis around the world. Although norovirus symptoms are in most cases mild and self-limited, severe and prolonged symptoms can occur in the elderly and in immunocompromised individuals. Thus, there is a great need for the development of specific therapeutics that can help mitigate infection. In this study, we sought to characterize a panel of human monoclonal antibodies (mAbs; NORO-123, -115, -273A, -263, -315B, and -250B) that showed carbohydrate blocking activity against the current pandemic variant, GII.4 Sydney 2012. All antibodies tested showed potent neutralization against GII.4 Sydney virus in human intestinal enteroid culture. While all mAbs recognized only GII.4 viruses, they exhibited differential binding patterns against a panel of virus-like particles (VLPs) representing major and minor GII.4 variants spanning twenty-five years. Using mutant VLPs, we mapped five of the mAbs to variable antigenic sites A (NORO-123, -263, -315B, and -250B) or C (NORO-115) on the major capsid protein. Those mapping to the antigenic site A showed blocking activity against multiple variants dating back to 1987, with one mAb (NORO-123) showing reactivity to all variants tested. NORO-115, which maps to antigenic site C, showed reactivity against multiple variants due to the low susceptibility for mutations presented by naturally-occurring variants at the proposed binding site. Notably, we show that cross-blocking and neutralizing antibodies can be elicited against variable antigenic sites. These data provide new insights into norovirus immunity and suggest potential for the development of cross-protective vaccines and therapeutics.

A Pseudovirus Nanoparticle-Based Trivalent Rotavirus Vaccine Candidate Elicits High and Cross P Type Immune Response

Rotavirus infection continues to cause significant morbidity and mortality globally. In this study, we further developed the S60-VP8* pseudovirus nanoparticles (PVNPs) displaying the glycan receptor binding VP8* domains of rotavirus spike proteins as a parenteral vaccine candidate. First, we established a scalable method for the large production of tag-free S60-VP8* PVNPs representing four rotavirus P types, P[8], P[4], P[6], and P[11]. The approach consists of two major steps: selective precipitation of the S-VP8* proteins from bacterial lysates using ammonium sulfate, followed by anion exchange chromatography to further purify the target proteins to a high purity. The purified soluble proteins self-assembled into S60-VP8* PVNPs. Importantly, after intramuscular injections, the trivalent vaccine consisting of three PVNPs covering VP8* antigens of P[8], P[4], and P[6] rotaviruses elicited high and broad immunogenicity in mice toward the three predominant P-type rotaviruses. Specifically, the trivalent vaccine-immunized mouse sera showed (1) high and balanced IgG and IgA antibody titers toward all three VP8* types, (2) high blocking titer against the VP8*-glycan receptor interaction, and (3) high and broad neutralizing titers against replications of all P[8], P[4], and P[6] rotaviruses. Therefore, trivalent S60-VP8* PVNPs are a promising non-replicating, parenteral vaccine candidate against the most prevalent rotaviruses worldwide.

Norovirus-VLPs expressing pre-erythrocytic malaria antigens induce functional immunity against sporozoite infection

Despite the development of prophylactic anti-malarial drugs and practices to prevent infection, malaria remains a health concern. Preclinical testing of novel malaria vaccine strategies achieved through rational antigen selection and novel particle-based delivery platforms is yielding encouraging results. One such platform, self-assembling virus-like particles (VLP) is safer than attenuated live viruses, and has been approved as a vaccination tool by the FDA. We explore the use of Norovirus sub-viral particles lacking the natural shell (S) domain forming the interior shell but that retain the protruding (P) structures of the native virus as a vaccine vector. Epitope selection and their surface display has the potential to focus antigen specific immune responses to crucial epitopes. Recombinant P-particles displaying epitopes from two malaria antigens, Plasmodium falciparum (Pf) CelTOS and Plasmodium falciparum (Pf) CSP, were evaluated for immunogenicity and their ability to confer protection in a murine challenge model. Immune responses induced in mice resulted either in sterile protection (displaying PfCelTOS epitopes) or in antibodies with functional activity against sporozoites (displaying PfCSP epitopes) in an in vitro liver-stage development assay (ILSDA). These results are encouraging and support further evaluation of this platform as a vaccine delivery system.

Using Species a Rotavirus Reverse Genetics to Engineer Chimeric Viruses Expressing SARS-CoV-2 Spike Epitopes

Species A rotavirus (RVA) vaccines based on live attenuated viruses are used worldwide in humans. The recent establishment of a reverse genetics system for rotoviruses (RVs) has opened the possibility of engineering chimeric viruses expressing heterologous peptides from other viral or microbial species in order to develop polyvalent vaccines. We tested the feasibility of this concept by two approaches. First, we inserted short SARS-CoV-2 spike peptides into the hypervariable region of the simian RV SA11 strain viral protein (VP) 4. Second, we fused the receptor binding domain (RBD) of the SARS-CoV-2 spike protein, or the shorter receptor binding motif (RBM) nested within the RBD, to the C terminus of nonstructural protein (NSP) 3 of the bovine RV RF strain, with or without an intervening Thosea asigna virus 2A (T2A) peptide. Mutating the hypervariable region of SA11 VP4 impeded viral replication, and for these mutants, no cross-reactivity with spike antibodies was detected. To rescue NSP3 mutants, we established a plasmid-based reverse genetics system for the bovine RV RF strain. Except for the RBD mutant that demonstrated a rescue defect, all NSP3 mutants delivered endpoint infectivity titers and exhibited replication kinetics comparable to that of the wild-type virus. In ELISAs, cell lysates of an NSP3 mutant expressing the RBD peptide showed cross-reactivity with a SARS-CoV-2 RBD antibody. 3D bovine gut enteroids were susceptible to infection by all NSP3 mutants, but cross-reactivity with SARS-CoV-2 RBD antibody was only detected for the RBM mutant. The tolerance of large SARS-CoV-2 peptide insertions at the C terminus of NSP3 in the presence of T2A element highlights the potential of this approach for the development of vaccine vectors targeting multiple enteric pathogens simultaneously. IMPORTANCE We explored the use of rotaviruses (RVs) to express heterologous peptides, using SARS-CoV-2 as an example. Small SARS-CoV-2 peptide insertions (<34 amino acids) into the hypervariable region of the viral protein 4 (VP4) of RV SA11 strain resulted in reduced viral titer and replication, demonstrating a limited tolerance for peptide insertions at this site. To test the RV RF strain for its tolerance for peptide insertions, we constructed a reverse genetics system. NSP3 was C-terminally tagged with SARS-CoV-2 spike peptides of up to 193 amino acids in length. With a T2A-separated 193 amino acid tag on NSP3, there was no significant effect on the viral rescue efficiency, endpoint titer, and replication kinetics. Tagged NSP3 elicited cross-reactivity with SARS-CoV-2 spike antibodies in ELISA. We highlight the potential for development of RV vaccine vectors targeting multiple enteric pathogens simultaneously.

Evaluation of a bivalent recombinant vaccine candidate targeting norovirus and rotavirus: Antibodies to rotavirus NSP4 exert antidiarrheal effects without virus neutralization

We previously found that when tandemly expressed with S_R69A -VP8*, nonstructural protein 4 (NSP4) of the rotavirus Wa strain exerts a minor effect on elevating the antibody responses targeting the rotavirus antigen VP8* of the 60-valent nanoparticle S_R69A -VP8* but could fully protect mice from diarrhea induced by the rotavirus strain Wa. In this study, we chose comparably less immunogenic norovirus 24-valent P particles with homogenous (i.e., VP8* from rotavirus) and heterogeneous (i.e., protruding domain of norovirus) antigens and in more challenging rotavirus SA11 strain-induced diarrhea mouse models to evaluate its main role in recombinant gastroenteritis virus-specific vaccines. The results showed that although as an adjuvant NSP4 exerted limited effects on the elevation of norovirus-specific or VP8*-specific neutralizing antibody production, as an antigen it could confer potent protection, particularly when synergized with VP8*, in rotavirus SA11 strain-induced diarrhea mouse models, possibly blocking the invasion of the intestinal wall by enterotoxin. NSP4 may be unnecessary for other recombinant vaccines as adjuvants, and its display mode should be evaluated specifically to avoid blocking coexpressed antigens in the norovirus P particles. This article is protected by copyright. All rights reserved.

Development and characterization of recombinant ASFV CD2v protein nanoparticle-induced monoclonal antibody

African swine fever (ASF) caused by African swine fever virus (ASFV) is becoming a serious threat to the swine industry worldwide. CD2v is a key pathogenic factor of ASFV and the protective antigen with low immunogenicity, whereas viral protein-based nanoparticles have advantages of precise assembly and high immunogenicity. In this study, the CD2v protein fused with Norovirus (NoV) P particle assembled into nanoparticle for improved immunogenicity. Then, CD2v protein nanoparticle and monomer CD2v protein were expressed in HEK293F cells. The former induced higher levels of antibodies, and thus highly potent monoclonal antibodies (mAbs) were generated and characterized. The highest antibody titration of mAb 10A3 reached 1:2048000, and mAb 2E9 had the highest inhibition percent of 84% when competed with ASFV positive serum. Meanwhile, all mAbs reacted specifically with the denatured CD2v protein, and the linear epitope with the location of amino acids 28th to 51st of CD2v extracellular domain sequence was identified. In summary, this study produced a highly immunogenic CD2v protein and generated high-titer mAbs, the precise location of linear epitope on the CD2v was further determined. These findings may provide a powerful help for etiology and serological detection of ASFV.

Bioengineered pseudovirus nanoparticles displaying the HA1 antigens of influenza viruses for enhanced immunogenicity

Even with implementation of current influenza vaccines, influenza still claims up to 500,000 lives worldwide annually, indicating a need for a better vaccine strategy. We have developed a technology to generate unique S60-HA1 pseudovirus nanoparticles (PVNPs) that display the receptor-binding HA1 domains of influenza viruses. Each self-assembled S60-HA1 PVNP consists of a T = 1 icosahedral S60 nanoparticle that resembles the inner shell of norovirus capsid and 60 surface-displayed HA1 antigens that are excellent vaccine targets. Soluble S60-HA1 PVNPs presenting HA1 antigens of H7N9 influenza virus subtypes have been produced efficiently in large amount. Their three-dimensional (3D) structures have been solved by cryogenic electron microscopy. The PVNP-displayed HA1 antigens react with HA-specific antibody, and retain authentic sialic acid binding specificity and hemagglutinate human erythrocytes. The PVNPs are highly immunogenic, eliciting high titers of HA1-specific antibodies in mice and the mouse sera strongly inhibited hemagglutinations of homologous and heterologous influenza virus HA proteins. Therefore, the S60-HA1 PVNPs may provide useful reagents to study influenza viruses and offer a potential new vaccine tactic to fight the deadly influenza disease.

Antigenicity and immunogenicity of HA2 and M2e influenza virus antigens conjugated to norovirus-like, VP1 capsid-based particles by the SpyTag/SpyCatcher technology

Virus-like particles (VLPs) modified through different molecular technologies are employed as delivery vehicles or platforms for heterologous antigen display. We have recently created a norovirus (NoV) VLP platform, where two influenza antigens, the extracellular domain of matrix protein M2 (M2e) or the stem domain of the major envelope glycoprotein hemagglutinin (HA2) are displayed on the surface of the NoV VLPs by SpyTag/SpyCatcher conjugation. To demonstrate the feasibility of the platform to deliver foreign antigens, this study examined potential interference of the conjugation with induction of antibodies against conjugated M2e peptide, HA2, and NoV VLP carrier. High antibody response was induced by HA2 but not M2e decorated VLPs. Furthermore, HA2-elicited antibodies did not neutralize the homologous influenza virus in vitro. Conjugated NoV VLPs retained intact receptor binding capacity and self-immunogenicity. The results demonstrate that NoV VLPs could be simultaneously used as a platform to deliver foreign antigens and a NoV vaccine.

Rotavirus spike protein ΔVP8* as a novel carrier protein for conjugate vaccine platform with demonstrated antigenic potential for use as bivalent vaccine

Conjugate vaccine platform is a promising strategy to overcome the poor immunogenicity of bacterial polysaccharide antigens in infants and children. A carrier protein in conjugate vaccines works not only as an immune stimulator to polysaccharide, but also as an immunogen; with the latter generally not considered as a measured outcome in real world. Here, we probed the potential of a conjugate vaccine platform to induce enhanced immunogenicity of a truncated rotavirus spike protein ΔVP8*. ΔVP8* was covalently conjugated to Vi capsular polysaccharide (Vi) of Salmonella Typhi to develop a bivalent vaccine, termed Vi-ΔVP8*. Our results demonstrated that the Vi-ΔVP8* vaccine can induce specific immune responses against both antigens in immunized mice. The conjugate vaccine elicits high antibody titers and functional antibodies against S. Typhi and Rotavirus (RV) when compared to immunization with a single antigen. Together, these results indicate that Vi-ΔVP8* is a potent and immunogenic vaccine candidate, thus strengthening the potential of conjugate vaccine platform with enhanced immune responses to carrier protein, including ΔVP8*.

Development of a bivalent conjugate vaccine candidate against rotaviral diarrhea and tuberculosis using polysaccharide from Mycobacterium tuberculosis conjugated to ΔVP8* protein from rotavirus

Conjugation of carbohydrate antigens with a carrier protein is a clinically proven strategy to overcome the poor immunogenicity of bacterial polysaccharide. In addition to its primary role, which is to help generate a T cell-mediate long-lasting immune response directed against the carbohydrate antigen, the carrier protein in a glycoconjugate vaccine can also play an important role as a protective antigen. Among carrier proteins currently used in licensed conjugate vaccines, non-typeable Haemophilus influenzae protein D has been used as an antigenically active carrier protein. Our previous studies also indicate that some carrier proteins provide B cell epitopes, along with T cell helper epitopes. Herein we investigated the dual role of truncated rotavirus spike protein ΔVP8* as a carrier and a protective antigen. Capsular polysaccharide lipoarabinomannan (LAM), purified from Mycobacterium tuberculosis (M.tb), was chemically conjugated with ΔVP8*. Mouse immunization experiments showed that the resultant conjugates elicited strong and specific immune responses against the polysaccharide antigen, and the responses were comparable to those induced by Diphtheria toxoid (DT)-based conjugates. The conjugate vaccine induced enhanced antibody titers and functional antibodies against ΔVP8* when compared to immunization with the unconjugated ΔVP8*. Thus, these results indicate that ΔVP8* can be a relevant carrier protein for glycoconjugate vaccine and the glycoconjugates consisting of ΔVP8* with LAM are effective bivalent vaccine candidates against rotavirus and tuberculosis.

Parenteral, non-live rotavirus vaccine: recent history and future perspective

Since the widespread introduction of oral and live attenuated rotavirus vaccines around the world in 2009, the impacts of disease burden and the effects of disease reduction in developing countries have been proven. However, in low and middle-income countries, the vaccine efficacy is somewhat lower than in developed countries due to differences in nutritional conditions, microbial environments of individuals, and other factors. In addition, as oral, live vaccines have been found to be associated with rare but serious side effects, the development of a next-generation vaccine with safety, improved effectiveness, and ease of storage is currently underway. New vaccine strain developed by the Centers for Disease Control and Prevention in the United States are undergoing preclinical testing of efficacy, antigen dose, and administration route in the form of a heat-treated inactive vaccine, and a recombinant protein-based trivalent subunit vaccine developed by the Program for Appropriate Technology in Health is undergoing clinical trial in phase III. Several research groups are also developing non-replicating protein-based rotavirus vaccines using virus-like particles and nanoparticles. This review provides a brief overview of the development status and technology of parenteral, non-live rotavirus vaccines worldwide.

Immunization with Leishmania tarentolae-derived norovirus virus-like particles elicits high humoral response and stimulates the production of neutralizing antibodies

BACKGROUND

Noroviruses are a major cause of epidemic and sporadic acute non-bacterial gastroenteritis worldwide. Unfortunately, the development of an effective norovirus vaccine has proven difficult and no prophylactic vaccine is currently available. Further research on norovirus vaccine development should be considered an absolute priority and novel vaccine candidates are needed. One of the recent approaches in safe vaccine development is the use of virus-like particles (VLPs). VLP-based vaccines show great immunogenic potential as they mimic the morphology and structure of viral particles without the presence of the virus genome.

RESULTS

This study is the first report showing successful production of norovirus VLPs in the protozoan Leishmania tarentolae (L. tarentolae) expression system. Protozoan derived vaccine candidate is highly immunogenic and able to not only induce a strong immune response (antibody titer reached 10⁴) but also stimulate the production of neutralizing antibodies confirmed by receptor blocking assay. Antibody titers able to reduce VLP binding to the receptor by > 50% (BT₅₀) were observed for 1:5-1:320 serum dilutions.

CONCLUSIONS

Norovirus VLPs produced in L. tarentolae could be relevant for the development of the norovirus vaccine.

Development and Application of a Novel Rapid and Throughput Method for Broad-Spectrum Anti-Foodborne Norovirus Antibody Testing

Foodbone norovirus (NoV) is the leading cause of acute gastroenteritis worldwide. Candidate vaccines are being developed, however, no licensed vaccines are currently available for managing NoV infections. Screening for stimulated antibodies with broad-spectrum binding activities can be performed for the development of NoV polyvalent vaccines. In this study, we aimed to develop an indirect enzyme-linked immunosorbent assay (ELISA) for testing the broad spectrum of anti-NoV antibodies. Capsid P proteins from 28 representative NoV strains (GI.1–GI.9 and GII.1–GII.22 except GII.11, GII.18, and GII.19) were selected, prepared, and used as coating antigens on one microplate. Combined with incubation and the horseradish peroxidase chromogenic reaction, the entire process for testing the spectrum of unknown antibodies required 2 h for completion. The intra-assay and inter-assay coefficients of variation were less than 10%. The new method was successfully performed with monoclonal antibodies and polyclonal antibodies induced by multiple antigens. In conclusion, the indirect ELISA assay developed in this study had a good performance of reliability, convenience, and high-throughput screening for broad-spectrum antibodies.

[Viruses and bats: interdisciplinary issues]

The virologists' attention to bats (Сhiroptera) changed in the late 20th century as the concept of emerging infections grew in popularity. Since the beginning of the COVID-19 pandemic, the number of publications on bat viruses has increased profoundly.History of the problem; biodiversity of Chiroptera and related viruses; medical and veterinary significance of some viral genera and subgenera (Lyssavirus, Henipavirus, Marburgvirus, Ebolavirus, Sarbecovirus, Merbecovirus), as well as problems of bat protection, are addressed in a concise form. Literature search was carried out in electronic databases, mainly for the period of 2000-2021. Publications in Russian that are poorly represented in English-language reviews are also included. The purpose of the review is to substantiate the importance of an interdisciplinary approach in the context of increased interest in the study of viral infections in bats. This review was written for researchers who have not previously dealt with this problem.Since the beginning of this century, the number of known virus species associated with bats has increased by an order of magnitude (&gt;200). The families Rhabdoviridae, Coronaviridae, Paramyxoviridae are in the first ranks according to the number of findings, and the highest diversity of viruses has been established for the families Vespertilionidae, Pteropodidae, Molossidae. Interdisciplinary cooperation positively influences the efficiency, biological safety and practical significance of the ongoing research. The best results were achieved by multidisciplinary teams with good cross-training in several specialties. Many papers emphasize the need to balance health and conservation interests.The analysis of scientific publications indicates a change in research approaches in this area: from collecting individual facts within the framework of narrow specialties to a comprehensive assessment of new knowledge from ecological, evolutionary and socio-economic positions. Results of the research emphasize the need to maintain complex approaches addressing public health needs and environmental protection. The importance of bat-borne viral infections determines the necessity for correction and interdepartmental coordination of scientific research and surveillance of wildlife zoonoses in the Russian Federation.

Epidemiology and evolution of Norovirus in China

Norovirus (NoV) has been recognized as a leading cause of gastroenteritis worldwide. This review estimates the prevalence and genotype distribution of NoV in China to provide a sound reference for vaccine development. Studies were searched up to October 2020 from CNKI database and inclusion criteria were study duration of at least one calendar year and population size of >100. The mean overall NoV prevalence in individuals with sporadic diarrhea/gastroenteritis was 16.68% (20796/124649, 95% CI 16.63-16.72), and the detection rate of NoV was the highest among children. Non-GII.4 strains have replaced GII.4 as the predominant caused multiple outbreaks since 2014. Especially the recombinant GII.P16-GII.2 increased sharply, and virologic data show that the polymerase GII.P16 rather than VP1 triggers pandemic. Due to genetic diversity and rapid evolution, predominant genotypes might change unexpectedly, which has become major obstacle for the development of effective NoV vaccines.

Simvastatin Reduces Protection and Intestinal T Cell Responses Induced by a Norovirus P Particle Vaccine in Gnotobiotic Pigs

Noroviruses (NoVs) are a leading cause of acute gastroenteritis worldwide. P particles are a potential vaccine candidate against NoV. Simvastatin is a cholesterol-reducing drug that is known to increase NoV infectivity. In this study, we examined simvastatin’s effects on P particle-induced protective efficacy and T-cell immunogenicity using the gnotobiotic pig model of human NoV infection and diarrhea. Pigs were intranasally inoculated with three doses (100 µg/dose) of GII.4/VA387-derived P particles together with monophosphoryl lipid A and chitosan adjuvants. Simvastatin-fed pigs received 8 mg/day orally for 11 days prior to challenge. A subset of pigs was orally challenged with 10 ID₅₀ of a NoV GII.4/2006b variant at post-inoculation day (PID) 28 and monitored for 7 days post-challenge. Intestinal and systemic T cell responses were determined pre- and postchallenge. Simvastatin abolished the P particle’s protection and significantly increased diarrhea severity after NoV infection. Simvastatin decreased proliferation of virus-specific and non-specific CD8 T cells in duodenum and virus-specific CD4 and CD8 T cells in spleen and significantly reduced numbers of intestinal mononuclear cells in vaccinated pigs. Furthermore, simvastatin significantly decreased numbers of duodenal CD4+IFN-γ+, CD8+IFN-γ+ and regulatory T cells and total duodenal activated CD4+ and CD8+ T cells in vaccinated pigs pre-challenge at PID 28. Following challenge, simvastatin prevented the IFN-γ+ T cell response in spleen of vaccinated pigs. These results indicate that simvastatin abolished P particle vaccine-induced partial protection through, at least in part, impairing T cell immunity. The findings have specific implications for the development of preventive and therapeutic strategies against NoV gastroenteritis, especially for the elderly population who takes statin-type drugs.

Glycan-Induced Protein Dynamics in Human Norovirus P Dimers Depend on Virus Strain and Deamidation Status

Noroviruses are the major cause of viral gastroenteritis and re-emerge worldwide every year, with GII.4 currently being the most frequent human genotype. The norovirus capsid protein VP1 is essential for host immune response. The P domain mediates cell attachment via histo blood-group antigens (HBGAs) in a strain-dependent manner but how these glycan-interactions actually relate to cell entry remains unclear. Here, hydrogen/deuterium exchange mass spectrometry (HDX-MS) is used to investigate glycan-induced protein dynamics in P dimers of different strains, which exhibit high structural similarity but different prevalence in humans. While the almost identical strains GII.4 Saga and GII.4 MI001 share glycan-induced dynamics, the dynamics differ in the emerging GII.17 Kawasaki 308 and rare GII.10 Vietnam 026 strain. The structural aspects of glycan binding to fully deamidated GII.4 P dimers have been investigated before. However, considering the high specificity and half-life of N373D under physiological conditions, large fractions of partially deamidated virions with potentially altered dynamics in their P domains are likely to occur. Therefore, we also examined glycan binding to partially deamidated GII.4 Saga and GII.4 MI001 P dimers. Such mixed species exhibit increased exposure to solvent in the P dimer upon glycan binding as opposed to pure wildtype. Furthermore, deamidated P dimers display increased flexibility and a monomeric subpopulation. Our results indicate that glycan binding induces strain-dependent structural dynamics, which are further altered by N373 deamidation, and hence hint at a complex role of deamidation in modulating glycan-mediated cell attachment in GII.4 strains.

Linear B-Cell Epitopes in Human Norovirus GII.4 Capsid Protein Elicit Blockade Antibodies

Human norovirus (HuNoV) is the leading cause of nonbacterial gastroenteritis worldwide with the GII.4 genotype accounting for over 80% of infections. The major capsid protein of GII.4 variants is evolving rapidly, resulting in new epidemic variants with altered antigenic potentials that must be considered for the development of an effective vaccine. In this study, we identify and characterize linear blockade B-cell epitopes in HuNoV GII.4. Five unique linear B-cell epitopes, namely P2A, P2B, P2C, P2D, and P2E, were predicted on the surface-exposed regions of the capsid protein. Evolving of the surface-exposed epitopes over time was found to correlate with the emergence of new GII.4 outbreak variants. Molecular dynamic simulation (MD) analysis and molecular docking revealed that amino acid substitutions in the putative epitopes P2B, P2C, and P2D could be associated with immune escape and the appearance of new GII.4 variants by affecting solvent accessibility and flexibility of the antigenic sites and histo-blood group antigens (HBAG) binding. Testing the synthetic peptides in wild-type mice, epitopes P2B (336-355), P2C (367-384), and P2D (390-400) were recognized as GII.4-specific linear blockade epitopes with the blocking rate of 68, 55 and 28%, respectively. Blocking rate was found to increase to 80% using the pooled serum of epitopes P2B and P2C. These data provide a strategy for expanding the broad blockade potential of vaccines for prevention of NoV infection.

Effects of rotavirus NSP4 protein on the immune response and protection of the SR69A-VP8* nanoparticle rotavirus vaccine

Rotavirus causes severe diarrhea and dehydration in young children. Even with the implementation of the current live vaccines, rotavirus infections still cause significant mortality and morbidity, indicating a need for new rotavirus vaccines with improved efficacy. To this end, we have developed an SR69A-VP8*/S60-VP8* nanoparticle rotavirus vaccine candidate that will be delivered parenterally with Alum adjuvant. In this study, as parts of our further development of this nanoparticle vaccine, we evaluated 1) roles of rotavirus nonstructural protein 4 (NSP4) that is the rotavirus enterotoxin, a possible vaccine target, and an immune stimulator, and 2) effects of CpG adjuvant that is a toll-like receptor 9 (TLR9) ligand and agonist on the immune response and protection of our SR69A-VP8*/S60-VP8* nanoparticle vaccine. The resulted vaccine candidates were examined for their IgG responses in mice. In addition, the resulted mouse sera were assessed for i) blocking titers against interactions of rotavirus VP8* proteins with their glycan ligands, ii) neutralization titers against rotavirus replication in cell culture, and iii) passive protection against rotavirus challenge with diarrhea in suckling mice. Our data showed that the Alum adjuvant appeared to work better with the SR69A-VP8*/S60-VP8* nanoparticles than the CpG adjuvant, while an addition of the NSP4 antigen to the SR69A-VP8*/S60-VP8* vaccine may not help to further increase the immune response and protection of the resulted vaccine.

A Nanoparticle-Based Trivalent Vaccine Targeting the Glycan Binding VP8* Domains of Rotaviruses

Rotavirus causes severe gastroenteritis in children. Although vaccines are implemented, rotavirus-related diarrhea still claims ~200,000 lives annually worldwide, mainly in low-income settings, pointing to a need for improved vaccine tactics. To meet such a public health need, a P24-VP8* nanoparticle displaying the glycan-binding VP8* domains, the major neutralizing antigens of rotavirus, was generated as a new type of rotavirus vaccine. We reported here our development of a P24-VP8* nanoparticle-based trivalent vaccine. First, we established a method to produce tag-free P24-VP8* nanoparticles presenting the VP8*s of P[8], P[4], and P[6] rotaviruses, respectively, which are the three predominantly circulating rotavirus P types globally. This approach consists of a chemical-based protein precipitation and an ion exchange purification, which may be scaled up for large vaccine production. All three P24-VP8* nanoparticle types self-assembled efficiently with authentic VP8*-glycan receptor binding function. After they were mixed as a trivalent vaccine, we showed that intramuscular immunization of the vaccine elicited high IgG titers specific to the three homologous VP8* types in mice. The resulted mouse sera strongly neutralized replication of all three rotavirus P types in cell culture. Thus, the trivalent P24-VP8* nanoparticles are a promising vaccine candidate for parenteral use against multiple P types of predominant rotaviruses.

Update on rotavirus vaccine underperformance in low- to middle-income countries and next-generation vaccines

In the decade since oral rotavirus vaccines (ORV) were recommended by the World Health Organization for universal inclusion in all national immunization programs, significant yet incomplete progress has been made toward reducing the burden of rotavirus in low- to middle-income countries (LMIC). ORVs continue to demonstrate effectiveness and impact in LMIC, yet numerous factors hinder optimal performance and evaluation of these vaccines. This review will provide an update on ORV performance in LMIC, the increasing body of literature regarding factors that affect ORV response, and the status of newer and next-generation rotavirus vaccines as of early 2020. Fully closing the gap in rotavirus prevention between LMIC and high-income countries will likely require a multifaceted approach accounting for biological and methodological challenges and evaluation and roll-out of newer and next-generation vaccines.

Establishment of a two-step purification scheme for tag-free recombinant Taiwan native norovirus P and VP1 proteins

The protruding (P) domain of the major capsid protein VP1 of norovirus (NoV) is the crucial element for immune recognition and host receptor binding. The heterologous P protein expressed by Pichia pastoris self-assembles into P particles. However, tag-free NoV protein purification schemes have rarely been reported due to the low isoelectric point of NoV proteins, which leads to highly competitive binding between the target protein and yeast host cell proteins at alkaline pH. In this study, a two-step purification scheme based on surface histidines and the charge on the NoV GII.4 strain P protein was developed. Using HisTrap and ion exchange chromatography, the P protein was directly purified, with a recovery of 28.1% and purity of 82.1%. Similarly, the NoV capsid protein VP1 was also purified using HisTrap and gel filtration chromatography based on native surface histidines and self-assembly ability, with 20% recovery and over 90% purity. Dynamic light scattering and transmission electron microscopy analyses of the purified NoV P revealed that most of these small P particles were triangle-, square- and ring-shaped, with a diameter of approximately 14 nm, and that the purified NoV VP1 self-assembles into particles with a diameter of approximately 47 nm. Both the purified NoV P and VP1 particles retained human histo-blood group antigen-binding ability, as evidenced by a saliva-binding assay.

Differences in Illness Severity among Circulating Norovirus Genotypes in a Large Pediatric Cohort with Acute Gastroenteritis

Norovirus is a major pathogen identified in children with acute gastroenteritis (AGE), little is known about the strain's diversity and their clinical severity. Stool and/or rectal swabs were collected from children ≤18 years of age recruited at emergency departments (ED), and a provincial nursing advice phone line due to AGE symptoms in the province of Alberta, Canada between December 2014 and August 2018. Specimens were tested using a reverse transcription real time PCR and genotyped by Sanger sequencing. The Modified Vesikari Scale score (MVS) was used to evaluate the disease severity. The objectives are to identify the Genogroup and Genotype distribution and to compare illness severity between the GI and GII genogroups and to complete further analyses comparing the GII genotypes identified. GII.4 was the genotype most commonly identified. Children with GII.4 had higher MVS scores (12.0 (10.0, 14.0; p = 0.002)) and more prolonged diarrheal (5 days (3.0, 7.8)) and vomiting (3.2 days (1.7, 5.3; p < 0.001)) durations compared to other non GII.4 strains. The predominant strain varied by year with GII.4 Sydney[P31] predominant in 2014/15, GII.4 Sydney[P16] in 2015/16 and 2017/18, and GII.3[P12] in 2016/17. Genogroup II norovirus strains predominated in children with AGE with variance between years; clinical severity associated with different strains varied with episodes being most severe among GII.4 infected children.

SARS-CoV-2 S1 is superior to the RBD as a COVID-19 subunit vaccine antigen

Since its emergence in December 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has developed into a global pandemic within a matter of months. While subunit vaccines are one of the prominent options for combating coronavirus disease 2019 (COVID-19), the immunogenicity of spike protein-based antigens remains unknown. When immunized in mice, the S1 domain induced much higher IgG and IgA antibody levels than the receptor-binding domain (RBD) and more efficiently neutralized SARS-CoV-2 when adjuvanted with alum. It is inferred that a large proportion of these neutralization epitopes are located in the S1 domain but outside the RBD and that some of these are spatial epitopes. This finding indicates that expression systems with posttranslational modification abilities are important to maintain the natural configurations of recombinant spike protein antigens and are critical for effective COVID-19 vaccines. Further, adjuvants prone to a Th1 response should be considered for S1-based subunit COVID-19 vaccines to reduce the potential risk of antibody-dependent enhancement of infection.

Application of a multiplex salivary immunoassay to detect sporadic incident norovirus infections

Norovirus is one of the most common causes of gastroenteritis. Following infection, anti-norovirus salivary immunoglobulin G (IgG) rises steeply within 2 weeks and remains elevated for several months; this immunoconversion can serve as an indicator of infection. We used a multiplex salivary immunoassay to study norovirus infections among 483 visitors to a Lake Michigan beach in 2015. Saliva was collected on the day of the beach visit (S1); after 10–14 days (S2); and after 30–40 days (S3). Luminex microspheres were coupled to recombinant antigens of genogroup I (GI) and II (GII) noroviruses and incubated with saliva. Immunoconversion was defined as at least 4-fold increase in anti-norovirus IgG antibody response from S1 to S2 and a 3-fold increase from S1 to S3. Ten (2.1%) immunoconverted to either GI (2) or GII (8) norovirus. Among those who immunoconverted, 40% reported at least one gastrointestinal symptom and 33% reported diarrhea, compared to 15% (p = 0.06) and 8% (p = 0.04) among those who did not immunoconvert, respectively. The two participants who immunoconverted to GI norovirus both swallowed water during swimming (p = 0.08). This study demonstrated the utility of a non-invasive salivary immunoassay to detect norovirus infections and an efficient approach to study infectious agents in large cohorts.

Parenterally Administered P24-VP8* Nanoparticle Vaccine Conferred Strong Protection against Rotavirus Diarrhea and Virus Shedding in Gnotobiotic Pigs

Current live rotavirus vaccines are costly with increased risk of intussusception due to vaccine replication in the gut of vaccinated children. New vaccines with improved safety and cost-effectiveness are needed. In this study, we assessed the immunogenicity and protective efficacy of a novel P24-VP8* nanoparticle vaccine using the gnotobiotic (Gn) pig model of human rotavirus infection and disease. Three doses of P24-VP8* (200 μg/dose) intramuscular vaccine with Al(OH)₃ adjuvant (600 μg) conferred significant protection against infection and diarrhea after challenge with virulent Wa strain rotavirus. This was indicated by the significant reduction in the mean duration of diarrhea, virus shedding in feces, and significantly lower fecal cumulative consistency scores in post-challenge day (PCD) 1-7 among vaccinated pigs compared to the mock immunized controls. The P24-VP8* vaccine was highly immunogenic in Gn pigs. It induced strong VP8*-specific serum IgG and Wa-specific virus-neutralizing antibody responses from post-inoculation day 21 to PCD 7, but did not induce serum or intestinal IgA antibody responses or a strong effector T cell response, which are consistent with the immunization route, the adjuvant used, and the nature of the non-replicating vaccine. The findings are highly translatable and thus will facilitate clinical trials of the P24-VP8* nanoparticle vaccine.

Norovirus Capsid Protein-Derived Nanoparticles and Polymers as Versatile Platforms for Antigen Presentation and Vaccine Development

Major viral structural proteins interact homotypically and/or heterotypically, self-assembling into polyvalent viral capsids that usually elicit strong host immune responses. By taking advantage of such intrinsic features of norovirus capsids, two subviral nanoparticles, 60-valent S₆₀ and 24-valent P₂₄ nanoparticles, as well as various polymers, have been generated through bioengineering norovirus capsid shell (S) and protruding (P) domains, respectively. These nanoparticles and polymers are easily produced, highly stable, and extremely immunogenic, making them ideal vaccine candidates against noroviruses. In addition, they serve as multifunctional platforms to display foreign antigens, self-assembling into chimeric nanoparticles or polymers as vaccines against different pathogens and illnesses. Several chimeric S₆₀ and P₂₄ nanoparticles, as well as P domain-derived polymers, carrying different foreign antigens, have been created and demonstrated to be promising vaccine candidates against corresponding pathogens in preclinical animal studies, warranting their further development into useful vaccines.

Protective immunity against influenza virus challenge by norovirus P particle-M2e and HA2-AtCYN vaccines in chickens

Development of a broadly reactive influenza vaccine that can provide protection against emerging type A influenza viruses is a big challenge. We previously demonstrated that a vaccine displaying the extracellular domain of the matrix protein 2 (M2e) on the surface loops of norovirus P-particle (M2eP) can partially protect chickens against several subtypes of avian influenza viruses. In the current study, a chimeric vaccine containing a conserved peptide from the subunit 2 of hemagglutinin (HA) glycoprotein (HA2) and Arabidopsis thaliana cyanase protein (AtCYN) (HA2-AtCYN vaccine) was evaluated in 2-weeks-old chickens. Depending on the route of administration, the HA2-AtCYN vaccine was shown to induce various levels of HA2-specific IgA in tears as well as serum IgG, which were associated with partial protection of chickens against tracheal shedding of a low pathogenicity H5N2 challenge virus. Furthermore, intranasal administration with a combination of HA2-AtCYN and M2eP vaccines resulted in enhanced protection compared to each vaccine alone. Simultaneous intranasal administration of the vaccines did not interfere with secretory IgA induction by each vaccine. Additionally, significantly higher M2eP-specific proliferative responses were observed in peripheral blood mononuclear cells of all M2eP-vaccinated groups when compared with the mock-vaccinated group. Although tripling the number of M2e copies did not enhance the protective efficacy of the chimeric vaccine, it significantly reduced immunodominance of P-particle epitopes without affecting the robustness of M2e-specific immune responses. Taken together, our data suggests that mucosal immunization of chickens with combinations of mechanistically different cross-subtype-conserved vaccines has the potential to enhance the protective efficacy against influenza virus challenge.

Immune response and protective efficacy of the S particle presented rotavirus VP8* vaccine in mice

Rotaviruses cause severe diarrhea in infants and young children, leading to significant morbidity and mortality. Despite implementation of current rotavirus vaccines, severe diarrhea caused by rotaviruses still claims ∼200,000 lives of children with great economic loss worldwide each year. Thus, new prevention strategies with high efficacy are highly demanded. Recently, we have developed a polyvalent protein nanoparticle derived from norovirus VP1, the S particle, and applied it to display rotavirus neutralizing antigen VP8* as a vaccine candidate (S-VP8*) against rotavirus, which showed promise as a vaccine based on mouse immunization and in vitro neutralization studies. Here we further evaluated this S-VP8* nanoparticle vaccine in a mouse rotavirus challenge model. S-VP8* vaccines containing the murine rotavirus (EDIM strain) VP8* antigens (S-mVP8*) were constructed and immunized mice, resulting in high titers of anti-EDIM VP8* IgG. The S-mVP8* nanoparticle vaccine protected immunized mice against challenge of the homologous murine EDIM rotavirus at a high efficacy of 97% based on virus shedding reduction in stools compared with unimmunized controls. Our study further supports the polyvalent S-VP8* nanoparticles as a promising vaccine candidate against rotavirus and warrants further development.

A Secreted Viral Nonstructural Protein Determines Intestinal Norovirus Pathogenesis

Murine norovirus (MNoV) infects a low percentage of enteric tuft cells and can persist in these cells for months following acute infection. Both tuft-cell tropism and resistance to interferon-λ (IFN-λ)-mediated clearance during persistent infection requires the viral nonstructural protein 1/2 (NS1/2). We show that processing of NS1/2 yields NS1, an unconventionally secreted viral protein that is central for IFN-λ resistance. MNoV infection globally suppresses intestinal IFN-λ responses, which is attributable to secreted NS1. MNoV NS1 secretion is triggered by caspase-3 cleavage of NS1/2, and a secreted form of human NoV NS1 is also observed. NS1 secretion is essential for intestinal infection and resistance to IFN-λ in vivo. NS1 vaccination alone protects against MNoV challenge, despite the lack of induction of neutralizing anti-capsid antibodies previously shown to confer protection. Thus, despite infecting a low number of tuft cells, NS1 secretion allows MNoV to globally suppress IFN responses and promote persistence.

Active immunization with norovirus P particle-based amyloid-β chimeric protein vaccine induces high titers of anti-Aβ antibodies in mice

BACKGROUND

Active immunotherapy targeting amyloid-β (Aβ) is a promising treatment for Alzheimer's disease (AD). Numerous preclinical studies and clinical trials demonstrated that a safe and effective AD vaccine should induce high titers of anti-Aβ antibodies while avoiding the activation of T cells specific to Aβ.

RESULTS

An untagged Aβ1-6 chimeric protein vaccine against AD based on norovirus (NoV) P particle was expressed in Escherichia coli and obtained by sequential chromatography. Analysis of protein characteristics showed that the untagged Aβ1-6 chimeric protein expressed in soluble form exhibited the highest particle homogeneity, with highest purity and minimal host cell protein (HCP) and residual DNA content. Importantly, the untagged Aβ1-6 chimeric soluble protein could induce the strongest Aβ-specific humoral immune responses without activation of harmful Aβ-specific T cells in mice.

CONCLUSIONS

The untagged Aβ1-6 chimeric protein vaccine is safe and highly immunogenic. Further research will determine the efficacy in cognitive improvement and disease progression delay.

Structural Adaptations of Norovirus GII.17/13/21 Lineage through Two Distinct Evolutionary Paths

Human noroviruses (huNoVs), which cause epidemic acute gastroenteritis, recognize histo-blood group antigens (HBGAs) as host attachment factors affecting host susceptibility. HuNoVs are genetically diverse, containing at least 31 genotypes in the two major genogroups (genogroup I [GI] and GII). Three GII genotypes, GII genotype 17 (GII.17), GII.13, and GII.21, form a unique genetic lineage, in which the GII.17 genotype retains the conventional GII HBGA binding site (HBS), while the GII.13/21 genotypes acquire a completely new HBS. To understand the molecular bases behind these evolutionary changes, we solved the crystal structures of the HBGA binding protruding domains of (i) an early GII.17 variant (the 1978 variant) that does not bind or binds weakly to HBGAs, (ii) the new GII.17 variant (the 2014/15 variant) that binds A/B/H antigens strongly via an optimized GII HBS, and (iii) a GII.13 variant (the 2010 variant) that binds the Lewis a (Lea) antigen via the new HBS. These serial, high-resolution structural data enable a comprehensive structural comparison to understand the evolutionary changes of the GII.17/13/21 lineage, including the emergence of the new HBS of the GII.13/21 sublineage and the possible HBS optimization of the recent GII.17 variant for an enhanced HBGA binding ability. Our study elucidates the structural adaptations of the GII.17/13/21 lineage through distinct evolutionary paths, which may allow a theory explaining huNoV adaptations and evolutions to be put forward.IMPORTANCE Our understanding of the molecular bases behind the interplays between human noroviruses and their host glycan ligands, as well as their evolutionary changes over time with alterations in their host ligand binding capability and host susceptibility, remains limited. By solving the crystal structures of the glycan ligand binding protruding (P) domains with or without glycan ligands of three representative noroviruses of the GII.17/13/21 genetic lineage, we elucidated the molecular bases of the human norovirus-glycan interactions of this special genetic lineage. We present solid evidence on how noroviruses of this genetic lineage evolved via different evolutionary paths to (i) optimize their glycan binding site for higher glycan binding function and (ii) acquire a completely new glycan binding site for new ligands. Our data shed light on the mechanism of the structural adaptations of human noroviruses through different evolutionary paths, facilitating our understanding of human norovirus adaptations, evolutions, and epidemiology.

Human Monoclonal Antibodies That Neutralize Pandemic GII.4 Noroviruses

BACKGROUND & AIMS

Human noroviruses are responsible for approximately 200,000 deaths worldwide each year. In 2012, the GII.4 Sydney strain emerged and became the major circulating norovirus strain associated with human disease. Our understanding of the human norovirus-specific antibody response is limited because few human monoclonal antibodies (mAbs) to noroviruses have been described, and there are no functional assays to measure virus neutralization. We studied the antibody-mediated response to the genogroup (G) II.4 strain by isolating mAbs to GII.4 from infected patients and developing virus neutralization assays.

METHODS

We used a robust human hybridoma technique to isolate mAbs from patients previously infected with norovirus and identified mAbs that blocked virus binding to cell receptors, using virus-like particles to test blockade ability. We tested the ability of select mAbs to neutralize live human noroviruses using stem cell-derived human enteroids.

RESULTS

We isolated a panel of 25 IgG or IgA human mAbs that recognized norovirus GII.4 Sydney 2012 and determined their potential to block virus binding to cell receptors. In competition binding studies, most antibodies recognized 3 major antigenic sites on the GII.4 Sydney 2012 protruding (P) domain.

CONCLUSIONS

We isolated and characterized human mAbs that neutralize live human norovirus GII.4 Sydney 2012-the predominant strain responsible for recent outbreaks. Analyses of these antibodies identified neutralizing epitopes; further studies will provide insight into the human immune response to this deadly virus.

Bioengineered Norovirus S60 Nanoparticles as a Multifunctional Vaccine Platform

Homotypic interactions of viral capsid proteins are common, driving viral capsid self-formation. By taking advantage of such interactions of the norovirus shell (S) domain that naturally builds the interior shells of norovirus capsids, we have developed a technology to produce 60-valent, icosahedral S₆₀ nanoparticles through the E. coli system. This has been achieved by several modifications to the S domain, including an R₆₉A mutation to destruct an exposed proteinase cleavage site and triple cysteine mutations (V₅₇C/Q₅₈C/S₁₃₆C) to establish inter-S domain disulfide bonds for enhanced inter-S domain interactions. The polyvalent S₆₀ nanoparticle with 60 exposed S domain C-termini offers an ideal platform for antigen presentation, leading to enhanced immunogenicity to the surface-displayed antigens for vaccine development. This was proven by constructing a chimeric S₆₀ nanoparticle displaying 60 rotavirus (RV) VP8* proteins, the major RV-neutralizing antigen. These S₆₀-VP8* particles are easily produced and elicited high IgG response in mice toward the displayed VP8* antigens. The mouse antisera after immunization with the S₆₀-VP8* particles exhibited high blockades against RV VP8* binding to its glycan ligands and high neutralizing activities against RV infection in culture cells. The three-dimensional structures of the S₆₀ and S₆₀-VP8* particles were studied. Furthermore, the S₆₀ nanoparticle can display other antigens, supporting the notion that the S₆₀ nanoparticle is a multifunctional vaccine platform. Finally, the intermolecular disulfide bond approach may be used to stabilize other viral-like particles to display foreign antigens for vaccine development.

Therapeutics and Immunoprophylaxis Against Noroviruses and Rotaviruses: The Past, Present, and Future

Background:

Noroviruses and rotaviruses are important viral etiologies of severe gastroenteritis. Noroviruses are the primary cause of nonbacterial diarrheal outbreaks in humans, whilst rotaviruses are a major cause of childhood diarrhea. Although both enteric pathogens substantially impact human health and economies, there are no approved drugs against noroviruses and rotaviruses so far. On the other hand, whilst the currently licensed rotavirus vaccines have been successfully implemented in over 100 countries, the most advanced norovirus vaccine has recently completed phase-I and II trials.

Methods:

We performed a structured search of bibliographic databases for peer-reviewed research litera-ture on advances in the fields of norovirus and rotavirus therapeutics and immunoprophylaxis.

Results:

Technological advances coupled with a proper understanding of viral morphology and replication over the past decade has facilitated pioneering research on therapeutics and immunoprophylaxis against noroviruses and rotaviruses, with promising outcomes in human clinical trials of some of the drugs and vaccines. This review focuses on the various developments in the fields of norovirus and rotavirus thera-peutics and immunoprophylaxis, such as potential antiviral drug molecules, passive immunotherapies (oral human immunoglobulins, egg yolk and bovine colostral antibodies, llama-derived nanobodies, and anti-bodies expressed in probiotics, plants, rice grains and insect larvae), immune system modulators, probiot-ics, phytochemicals and other biological substances such as bovine milk proteins, therapeutic nanoparti-cles, hydrogels and viscogens, conventional viral vaccines (live and inactivated whole virus vaccines), and genetically engineered viral vaccines (reassortant viral particles, virus-like particles (VLPs) and other sub-unit recombinant vaccines including multi-valent viral vaccines, edible plant vaccines, and encapsulated viral particles).

Conclusions:

This review provides important insights into the various approaches to therapeutics and im-munoprophylaxis against noroviruses and rotaviruses..

Application of a salivary immunoassay in a prospective community study of waterborne infections

Quantifying sporadic waterborne infections in community settings can be challenging. Salivary antibody immunoassays are a promising non-invasive tool that can be used in prospective studies of common infections, especially those involving children. This study was conducted in a Massachusetts city, which uses a microbiologically contaminated river as its water source, during summer-early winter periods before and after construction of a new drinking water treatment plant. Monthly saliva samples (7480 samples from 1170 children and 816 adults) were analyzed for immunoglobulin G (IgG) responses to recombinant proteins of Cryptosporidium, one genogroup I (GI) and two GII noroviruses. Immunoconversion was defined as at least four-fold increase in specific antibody responses between two monthly samples with a post-conversion response above a flexible age-dependent cut-off. Episodes of gastroenteritis (diarrhea or vomiting or cramps) were associated with 3.2 (95% confidence limits 1.1; 9.5) adjusted odds ratio (aOR) of immunoconversion to Cryptosporidium; episodes of combined diarrhea and vomiting symptoms were associated with 3.5 (0.8; 15.0) and 4.6 (1.7; 12.6) aORs of an immunoconversion to GI and GII noroviruses, respectively. Swimming in natural water bodies or chlorinated pools was associated with 2.3 (0.4; 15.4) and 4.9 (1.6; 15.5) aORs of immunoconversion to Cryptosporidium, respectively. In a subset of study participants who did not use home water filters, consumption of at least some amount of non-boiled tap water reported in a monthly recall survey was associated with 11.1 (1.2; 100.0) and 0.6 (0.1; 2.5) aORs of immunoconversion to Cryptosporidium before and after the new water treatment plant construction, respectively. Among individuals who used home water filters, associations between non-boiled tap water consumption and Cryptosporidium immunoconversion were not significant before and after new plant construction with aORs of 0.8 (0.2; 3.3) and 0.3 (0.1; 1.6), respectively. The interaction effect of study phase and non-boiled tap water consumption on Cryptosporidium immunoconversions was statistically significant in the entire study population with aOR of 5.4 (1.1; 25.6). This was the first study that has used a salivary antibody immunoassay to demonstrate significant associations between gastrointestinal symptoms and Cryptosporidium and norovirus infections, and between water-related exposures and Cryptosporidium infections.