Human VP8* mAbs neutralize rotavirus selectively in human intestinal epithelial cells

Human norovirus cultivation systems and their use in antiviral research

Human norovirus (HuNoV) is a major cause of acute gastroenteritis and foodborne diseases, affecting all age groups. Despite its clinical needs, no approved antiviral therapies are available. Since the discovery of HuNoV in 1972, studies on anti-norovirals, mechanism of HuNoV infection, viral inactivation, etc., have been hampered by the lack of a robust laboratory-based cultivation system for HuNoV. A recent breakthrough in the development of HuNoV cultivation systems has opened opportunities for researchers to investigate HuNoV biology in the context of de novo HuNoV infections. A tissue stem cell-derived human intestinal organoid/enteroid (HIO) culture system is one of those that supports HuNoV replication reproducibly and, to our knowledge, is most widely distributed to laboratories worldwide to study HuNoV and develop therapeutic strategies. This review summarizes recently developed HuNoV cultivation systems, including HIO, and their use in antiviral studies.

Infant Non-Secretor Histoblood Group Antigen Phenotype Reduces Susceptibility to Both Symptomatic and Asymptomatic Rotavirus Infection

The infant non-secretor histoblood group antigen phenotype is associated with reduced risk of symptomatic rotavirus diarrhea, one of the leading global causes of severe pediatric diarrheal disease and mortality. However, little is known regarding the role of secretor status in asymptomatic rotavirus infections. Therefore, we performed a nested case-control study within a birth cohort study previously conducted in Dhaka, Bangladesh, to determine the association between infant secretor phenotype and the odds of asymptomatic rotavirus infection, in addition to the risk of rotavirus diarrhea, in unvaccinated infants. In the parent cohort, infants were enrolled in the first week of life and followed through the first two years of life with multiple clinic visits and active surveillance for diarrheal illness. Secretor phenotyping was performed on saliva. Eleven surveillance stools collected over the first year of life were tested for rotavirus by real-time RT-PCR, followed by conventional PCR and amplicon sequencing to identify the infecting P-type of positive specimens. Similar to findings for symptomatic diarrhea, infant non-secretors experienced significantly fewer primary episodes of asymptomatic rotavirus infection through the first year of life in a likely rotavirus P-genotype-dependent manner. These data suggest that non-secretors experienced reduced risk from rotavirus due to decreased susceptibility to infection rather than reduced infection severity.

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.

Human intestinal organoids as models to study enteric bacteria and viruses

Laboratory studies of host-microbe interactions have historically been carried out using transformed cell lines and animal models. Although much has been learned from these models, recent advances in the development of multicellular, physiologically active, human intestinal organoid (HIO) cultures are allowing unprecedented discoveries of host-microbe interactions. Here, we review recent literature using HIOs as models to investigate the pathogenesis of clinically important enteric bacteria and viruses and study commensal intestinal microbes. We also discuss limitations of current HIO culture systems and how technical advances and innovative engineering approaches are providing new directions to improve the model. The studies discussed here highlight the potential of HIOs for studying microbial pathogenesis, host-microbe interactions, and for preclinical development of therapeutics and vaccines.

Analysis between ABO blood group and clinical outcomes in COVID-19 patients and the potential mediating role of ACE2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become the most common coronavirus that causes large-scale infections worldwide. Currently, several studies have shown that the ABO blood group is associated with coronavirus disease 2019 (COVID-19) infection and some studies have also suggested that the infection of COVID-19 may be closely related to the interaction between angiotensin-converting enzyme 2 (ACE2) and blood group antigens. However, the relationship between blood type to clinical outcome in critically ill patients and the mechanism of action is still unclear. The current study aimed to examine the correlation between blood type distribution and SARS-CoV-2 infection, progression, and prognosis in patients with COVID-19 and the potential mediating role of ACE2. With 234 patients from 5 medical centers and two established cohorts, 137 for the mild cohort and 97 for the critically ill cohort, we found that the blood type A population was more sensitive to SARS-CoV-2, while the blood type distribution was not relevant to acute respiratory distress syndrome (ARDS), acute kidney injury (AKI), and mortality in COVID-19 patients. Further study showed that the serum ACE2 protein level of healthy people with type A was significantly higher than that of other blood groups, and type O was the lowest. The experimental results of spike protein binding to red blood cells also showed that the binding rate of people with type A was the highest, and that of people with type O was the lowest. Our finding indicated that blood type A may be the biological marker for susceptibility to SARS-CoV-2 infection and may be associated with potential mediating of ACE2, but irrelevant to the clinical outcomes including ARDS, AKI, and death. These findings can provide new ideas for clinical diagnosis, treatment, and prevention of COVID-19.

Combined Live Oral Priming and Intramuscular Boosting Regimen with Rotarix® and a Nanoparticle-Based Trivalent Rotavirus Vaccine Evaluated in Gnotobiotic Pig Models of G4P[6] and G1P[8] Human Rotavirus Infection

Human rotavirus (HRV) is the causative agent of severe dehydrating diarrhea in children under the age of five, resulting in up to 215,000 deaths each year. These deaths almost exclusively occur in low- and middle-income countries where vaccine efficacy is the lowest due to chronic malnutrition, gut dysbiosis, and concurrent enteric viral infection. Parenteral vaccines for HRV are particularly attractive as they avoid many of the concerns associated with currently used live oral vaccines. In this study, a two-dose intramuscular (IM) regimen of the trivalent, nanoparticle-based, nonreplicating HRV vaccine (trivalent S60-VP8*), utilizing the shell (S) domain of the capsid of norovirus as an HRV VP8* antigen display platform, was evaluated for immunogenicity and protective efficacy against P[6] and P[8] HRV using gnotobiotic pig models. A prime-boost strategy using one dose of the oral Rotarix® vaccine, followed by one dose of the IM trivalent nanoparticle vaccine was also evaluated. Both regimens were highly immunogenic in inducing serum virus neutralizing, IgG, and IgA antibodies. The two vaccine regimens failed to confer significant protection against diarrhea; however, the prime-boost regimen significantly shortened the duration of virus shedding in pigs challenged orally with the virulent Wa (G1P[8]) HRV and significantly shortened the mean duration of virus shedding, mean peak titer, and area under the curve of virus shedding after challenge with Arg (G4P[6]) HRV. Prime-boost-vaccinated pigs challenged with P[8] HRV had significantly higher P[8]-specific IgG antibody-secreting cells (ASCs) in the spleen post-challenge. Prime-boost-vaccinated pigs challenged with P[6] HRV had significantly higher numbers of P[6]- and P[8]-specific IgG ASCs in the ileum, as well as significantly higher numbers of P[8]-specific IgA ASCs in the spleen post-challenge. These results suggest the promise of and warrant further investigation into the oral priming and parenteral boosting strategy for future HRV vaccines.

Isolation, Propagation and Genotyping of Human Rotaviruses Circulating among Children with Gastroenteritis in Two Egyptian University Hospitals

Simple Summary

Group A rotaviruses are the most common cause of acute gastroenteritis affecting Egyptian children under the age of five, with symptoms ranging from asymptomatic infection to severe dehydration or death. In the present work, diarrheal samples from Egyptian children admitted to gastrointestinal pediatric wards of two main governmental hospitals were collected and molecularly analyzed for Group A rotavirus. Our findings revealed that rotaviruses accounted for more than one-sixth of all cases under study, peaking in the winter. G1P[8] was the most prevalent rotavirus genotype in this study. The two cell lines used in our work coherently isolated and propagated rotavirus strains. Continuous rotavirus detection and genome sequencing of the successfully isolated strains will be recommended in the future in order to support the control of such viruses, and tackle the problem in Egypt.

Abstract

The most prevalent cause of infectious neonatal diarrhea is Group A rotavirus (RVA). Unfortunately, there is a dearth of data on the incidence of rotavirus-associated infections among Egyptian children. The present study aimed to isolate, propagate, and genotype human rotaviruses circulating among Egyptian children with acute gastroenteritis admitted to two main university pediatric hospitals, Abo El-Reesh and El-Demerdash, over two consecutive winters, 2018–2020. Diarrheal samples (n = 230) were screened for Group A rotavirus RNA using RT-PCR assay. In positive samples (n = 34), multiplex semi-nested PCR was utilized to determine G and P genotypes. Thirty-four (14.8%) of the collected samples tested positive. The genotype distribution revealed that G1P[8] was the predominant rotavirus genotype throughout the current study. All rotavirus-positive fecal samples were passaged twice on human colorectal adenocarcinoma cell line (Caco-2) and rhesus monkey kidney epithelial cell line (MA104). Both cell lines could successfully isolate 14.7% (n = 5 out of 34) of the identified strains; however, Caco-2 cell line was shown to be more efficient than MA104 in promoting the propagation of human rotaviruses identified in Egyptian children’s feces.

Rotavirus Infection in Swine: Genotypic Diversity, Immune Responses, and Role of Gut Microbiome in Rotavirus Immunity

Rotaviruses (RVs) are endemic in swine populations, and all swine herds certainly have a history of RV infection and circulation. Rotavirus A (RVA) and C (RVC) are the most common among all RV species reported in swine. RVA was considered most prevalent and pathogenic in swine; however, RVC has been emerging as a significant cause of enteritis in newborn piglets. RV eradication from swine herds is not practically achievable, hence producers’ mainly focus on minimizing the production impact of RV infections by reducing mortality and diarrhea. Since no intra-uterine passage of immunoglobulins occur in swine during gestation, newborn piglets are highly susceptible to RV infection at birth. Boosting lactogenic immunity in gilts by using vaccines and natural planned exposure (NPE) is currently the only way to prevent RV infections in piglets. RVs are highly diverse and multiple RV species have been reported from swine, which also contributes to the difficulties in preventing RV diarrhea in swine herds. Human RV-gut microbiome studies support a link between microbiome composition and oral RV immunogenicity. Such information is completely lacking for RVs in swine. It is not known how RV infection affects the functionality or structure of gut microbiome in swine. In this review, we provide a detailed overview of genotypic diversity of swine RVs, host-ranges, innate and adaptive immune responses to RVs, homotypic and heterotypic immunity to RVs, current methods used for RV management in swine herds, role of maternal immunity in piglet protection, and prospects of investigating swine gut microbiota in providing immunity against rotaviruses.

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.

Plasma VP8∗-Binding Antibodies in Rotavirus Infection and Oral Vaccination in Young Bangladeshi Children

BACKGROUND

Despite the availability and success of live-attenuated oral vaccines, rotavirus (RV) remains the leading cause of pediatric gastroenteritis worldwide. Next-generation vaccines targeting RV VP8∗ are under evaluation, but the role of VP8∗-specific antibodies in human immunity to RV and their potential as immune correlates of protection remains underexplored.

METHODS

We measured plasma RV VP8∗-binding antibodies in 2 cohorts of young children in Dhaka, Bangladesh. Plasma from a cohort study of 137 unvaccinated children aged 6-24 months old hospitalized with acute gastroenteritis was assessed for VP8∗ antibody seropositivity. VP8∗ antibodies were compared with the current standard for RV immunity, total RV-specific IgA (RV-IgA). Additionally, VP8∗ antibody responses were measured as part of an immunogenicity trial of a monovalent, oral, live-attenuated RV vaccine (Rotarix).

RESULTS

Fewer children with acute RV gastroenteritis were seropositive for VP8∗-binding IgA or IgG antibodies at hospital admission compared with RV-IgA, suggesting that the absence of VP8∗-binding antibodies more accurately predicts susceptibility to RV gastroenteritis than RV-IgA in unvaccinated children. However, when present, these antibodies appeared insufficient to protect fully from disease and no threshold antibody level for protection was apparent. In vaccinated children, these antibodies were very poorly induced by Rotarix vaccine, suggesting that VP8∗-specific antibodies alone are not necessary for clinical protection following oral vaccination.

CONCLUSIONS

This work suggests that VP8∗-binding antibodies may not be sufficient or necessary for protection from RV gastroenteritis following prior RV infection or oral vaccination; the role of VP8∗ antibodies induced by parenteral vaccination with non-replicating vaccines remains to be determined.

Mechanisms of Cell Entry by dsRNA Viruses: Insights for Efficient Delivery of dsRNA and Tools for Improved RNAi-Based Pest Control

While RNAi is often heralded as a promising new strategy for insect pest control, a major obstacle that still remains is the efficient delivery of dsRNA molecules within the cells of the targeted insects. However, it seems overlooked that dsRNA viruses already have developed efficient strategies for transport of dsRNA molecules across tissue barriers and cellular membranes. Besides protecting their dsRNA genomes in a protective shell, dsRNA viruses also display outer capsid layers that incorporate sophisticated mechanisms to disrupt the plasma membrane layer and to translocate core particles (with linear dsRNA genome fragments) within the cytoplasm. Because of the perceived efficiency of the translocation mechanism, it is well worth analyzing in detail the molecular processes that are used to achieve this feat. In this review, the mechanism of cell entry by dsRNA viruses belonging to the Reoviridae family is discussed in detail. Because of the large amount of progress in mammalian versus insect models, the mechanism of infections of reoviruses in mammals (orthoreoviruses, rotaviruses, orbiviruses) will be treated as a point of reference against which infections of reoviruses in insects (orbiviruses in midges, plant viruses in hemipterans, insect-specific cypoviruses in lepidopterans) will be compared. The goal of this discussion is to uncover the basic principles by which dsRNA viruses cross tissue barriers and translocate their cargo to the cellular cytoplasm; such knowledge subsequently can be incorporated into the design of dsRNA virus-based viral-like particles for optimal delivery of RNAi triggers in targeted insect pests.

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*.

Rotavirus research: 2014-2020

Rotaviruses are major causes of acute gastroenteritis in infants and young children worldwide and also cause disease in the young of many other mammalian and of avian species. During the recent 5-6 years rotavirus research has benefitted in a major way from the establishment of plasmid only-based reverse genetics systems, the creation of human and other mammalian intestinal enteroids, and from the wide application of structural biology (cryo-electron microscopy, cryo-EM tomography) and complementary biophysical approaches. All of these have permitted to gain new insights into structure-function relationships of rotaviruses and their interactions with the host. This review follows different stages of the viral replication cycle and summarizes highlights of structure-function studies of rotavirus-encoded proteins (both structural and non-structural), molecular mechanisms of viral replication including involvement of cellular proteins and lipids, the spectrum of viral genomic and antigenic diversity, progress in understanding of innate and acquired immune responses, and further developments of prevention of rotavirus-associated disease.

Monoreassortant rotaviruses of multiple G types are differentially neutralized by sera from infants vaccinated with ROTARIX® and RotaTeq®

Rotavirus is a leading cause of pediatric diarrheal mortality. The rotavirus outer capsid consists of VP7 and VP4 proteins, which respectively determine viral G and P type and are primary targets of neutralizing antibodies. To elucidate VP7-specific neutralizing antibody responses, we engineered monoreassortant rotaviruses each containing a human VP7 segment from a sequenced clinical specimen or a vaccine strain in an identical genetic background. We quantified replication and neutralization of engineered viruses using sera from infants vaccinated with monovalent ROTARIX® or multivalent RotaTeq® vaccines. Immunization with RotaTeq® induced broader neutralizing antibody responses than ROTARIX®. Inclusion of a single dose of RotaTeq® in the schedule enhanced G-type neutralization breadth of vaccinated infant sera. Cell type-specific differences in infectivity, replication, and neutralization were detected for some monoreassortant viruses. These findings suggest that rotavirus VP7, independent of VP4, can contribute to cell tropism and the breadth of vaccine-elicited neutralizing antibody responses.

Novel antigen panel for modern broad-spectrum recombinant rotavirus A vaccine

Purpose

Recombinant rotavirus A vaccines are being developed as an alternative to existing live oral attenuated vaccines. One of the main problems in the production of such vaccines is the genetic diversity of the strains that are in circulation. The goal of this study was to create an antigen panel for modern broad-spectrum recombinant rotavirus A vaccine.

Materials and Methods

The antigens of rotavirus were cloned and expressed in Escherichia coli. Antigenic specificity was investigated by Western blot analysis, which was performed using commercial polyclonal antisera to several RVA strains. Phylogenetic analysis was based on the amino acid sequences of the VP8^* protein fragment of human RVA isolates representing genotypes P[4], P[6], and P[8].

Results

A universal panel of antigens was established, including consensus and conserved sequences of structural proteins VP8^*, VP5^*, and VP7, which are the main targets of neutralizing antibodies. For the first time, a consensus approach was used in the design of extended antigens based on VP8^* (genotypes P[4], P[6], and P[8]) and VP5^* (genotype P[8]) proteins' fragments. In addition, a gene coding the protein (ep-875) containing several copies of conserved short neutralizing epitopes of VP8^*, VP7, and VP5^* was created. Western blot analysis demonstrated that three synthetic VP8^*-based antigens were not recognized by commercial antiserum against rotavirus strains isolated more than 35 years ago, but the specific activity of the VP5^* and ep-875 antigens was confirmed. The problems of serological mismatch of vaccine strains and antigens with currently circulating strains are discussed.

Conclusion

Five antigens representing sequences of structural proteins belonging to different genotypes can be used in various combinations (from mono- to pentavalent mixtures) for the development of an effective broad-spectrum rotavirus vaccine.

Organoids to Dissect Gastrointestinal Virus-Host Interactions: What Have We Learned?

Historically, knowledge of human host-enteric pathogen interactions has been elucidated from studies using cancer cells, animal models, clinical data, and occasionally, controlled human infection models. Although much has been learned from these studies, an understanding of the complex interactions between human viruses and the human intestinal epithelium was initially limited by the lack of nontransformed culture systems, which recapitulate the relevant heterogenous cell types that comprise the intestinal villus epithelium. New investigations using multicellular, physiologically active, organotypic cultures produced from intestinal stem cells isolated from biopsies or surgical specimens provide an exciting new avenue for understanding human specific pathogens and revealing previously unknown host-microbe interactions that affect replication and outcomes of human infections. Here, we summarize recent biologic discoveries using human intestinal organoids and human enteric viral pathogens.

The Rotavirus Vaccine Landscape, an Update

Rotavirus is the leading cause of severe acute childhood gastroenteritis, responsible for more than 128,500 deaths per year, mainly in low-income countries. Although the mortality rate has dropped significantly since the introduction of the first vaccines around 2006, an estimated 83,158 deaths are still preventable. The two main vaccines currently deployed, Rotarix and RotaTeq, both live oral vaccines, have been shown to be less effective in developing countries. In addition, they have been associated with a slight risk of intussusception, and the need for cold chain maintenance limits the accessibility of these vaccines to certain areas, leaving 65% of children worldwide unvaccinated and therefore unprotected. Against this backdrop, here we review the main vaccines under development and the state of the art on potential alternatives.

Rotavirus cell entry: not so simple after all

Rotaviruses are important agents of severe gastroenteritis in young children, and show a very selective cell and tissue tropism, as well as significant age and host restriction. In the last few years, these properties have been associated with the initial interaction of the virus with histo-blood group antigens on the cell surface, although post-attachment interactions have also been found to define the susceptibility to infection of human enteroids. These initial interactions seem also to determine the virus entry pathway, as well as the induction of signaling cascades that influence the virus intracellular vesicular traffic and escape from endosomes. Here we review the current knowledge of the different stages of the virus entry journey.

Rescue of Infectious Rotavirus Reassortants by a Reverse Genetics System Is Restricted by the Receptor-Binding Region of VP4

The rotavirus species A (RVA) capsid contains the spike protein VP4, which interacts with VP6 and VP7 and is involved in cellular receptor binding. The capsid encloses the genome consisting of eleven dsRNA segments. Reassortment events can result in novel strains with changed properties. Using a plasmid-based reverse genetics system based on simian RVA strain SA11, we previously showed that the rescue of viable reassortants containing a heterologous VP4-encoding genome segment was strain-dependent. In order to unravel the reasons for the reassortment restrictions, we designed here a series of plasmids encoding chimeric VP4s. Exchange of the VP4 domains interacting with VP6 and VP7 was not sufficient for rescue of viable viruses. In contrast, the exchange of fragments encoding the receptor-binding region of VP4 resulted in virus rescue. All parent strains and the rescued reassortants replicated efficiently in MA-104 cells used for virus propagation. In contrast, replication in BSR T7/5 cells used for plasmid transfection was only efficient for the SA11 strain, whereas the rescued reassortants replicated slowly, and the parent strains failing to produce reassortants did not replicate. While future research in this area is necessary, replication in BSR T7/5 cells may be one factor that affects the rescue of RVAs.

Prospecting Human Milk Oligosaccharides as a Defense Against Viral Infections

In addition to providing maximal nutritional value for neonatal growth and development, human milk functions as an early defense mechanism against invading pathogens. Human milk oligosaccharides (HMOs), which are abundant in human milk, are a diverse group of heterogeneous carbohydrates with wide ranging protective effects. In addition to promoting the colonization of beneficial intestinal flora, HMOs serve as decoy receptors, effectively blocking the attachment of pathogenic bacteria. HMOs also function as bacteriostatic agents, inhibiting the growth of gram-positive bacteria. Based on this precedence, an emerging area in the field has focused on characterizing the antiviral properties of HMOs. Indeed, HMOs have been evaluated as antiviral agents, with many possessing activity against life-threatening infections. This targeted review provides insight into the known glycan-binding interactions between select HMOs and influenza, rotavirus, respiratory syncytial virus, human immunodeficiency virus, and norovirus. Additionally, we review the role of HMOs in preventing necrotizing enterocolitis, an intestinal disease linked to viral infections. We close with a discussion of what is known broadly regarding human milk oligosaccharides and their interactions with coronaviruses.

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.

Reverse Genetics Approach for Developing Rotavirus Vaccine Candidates Carrying VP4 and VP7 Genes Cloned from Clinical Isolates of Human Rotavirus

Species A rotaviruses (RVs) are a leading cause of severe acute gastroenteritis in infants and children younger than 5 years. Currently available RV vaccines were adapted from wild-type RV strains by serial passage of cultured cells or by reassortment between human and animal RV strains. These traditional methods require large-scale screening and genotyping to obtain vaccine candidates. Reverse genetics is a tractable, rapid, and reproducible approach to generating recombinant RV vaccine candidates carrying any VP4 and VP7 genes that provide selected antigenicity. Here, we developed a vaccine platform by generating recombinant RVs carrying VP4 (P[4] and P[8]), VP7 (G1, G2, G3, G8, and G9), and/or VP6 genes cloned from human RV clinical samples using the simian RV SA11 strain (G3P[2]) as a backbone. Neutralization assays using monoclonal antibodies and murine antisera revealed that recombinant VP4 and VP7 monoreassortant viruses exhibited altered antigenicity. However, replication of VP4 monoreassortant viruses was severely impaired. Generation of recombinant RVs harboring a chimeric VP4 protein for SA11 and human RV gene components revealed that the VP8* fragment was responsible for efficient infectivity of recombinant RVs. Although this system must be improved because the yield of vaccine viruses directly affects vaccine manufacturing costs, reverse genetics requires less time than traditional methods and enables rapid production of safe and effective vaccine candidates.IMPORTANCE Although vaccines have reduced global RV-associated hospitalization and mortality over the past decade, the multisegmented genome of RVs allows reassortment of VP4 and VP7 genes from different RV species and strains. The evolutionary dynamics of novel RV genotypes and their constellations have led to great genomic and antigenic diversity. The reverse genetics system is a powerful tool for manipulating RV genes, thereby controlling viral antigenicity, growth capacity, and pathogenicity. Here, we generated recombinant simian RVs (strain SA11) carrying heterologous VP4 and VP7 genes cloned from clinical isolates and showed that VP4- or VP7-substituted chimeric viruses can be used for antigenic characterization of RV outer capsid proteins and as improved seed viruses for vaccine production.

Next-generation rotavirus vaccine developers meeting: Summary of a meeting sponsored by PATH and the bill & melinda gates foundation (19-20 June 2019, Geneva)

Despite the contribution of currently licensed live, oral rotavirus vaccines (LORVs) to alleviating the burden of severe disease and death from rotavirus gastroenteritis, those vaccines have proven less efficacious in resource-limited settings than in high- and middle-income countries. It has been proposed that the residual burden of rotavirus disease might be overcome with parenterally administered vaccines, or next-generation rotavirus vaccines (NGRV). To better define the progress of development of these vaccines, a meeting of vaccine developers and manufacturers engaged in NGRV research and development was convened in Geneva in June 2019. Several NRGVs are in various stages of preclinical development, and two have already entered clinical testing. The vaccine platforms include subunit protein, inactivated whole virus, virus-like particle and RNA-based vaccines. Meeting participants included groups involved in NGRV development, scientists investigating correlates of protection of rotavirus vaccines, and representatives of international organizations with insight into considerations for vaccine introduction. This report summarizes the presentations shared at the meeting.

Isolation and characteristics of the human rotavirus isolate CY2017

Our study aimed to determine whether a virus from fecal samples is human rotavirus (HRV), the main pathogen that causes autumn diarrhea. Specimens were obtained from the feces from children with autumn diarrhea treated at Chuiyangliu Hospital and used to infect MA104 cells, subcultured and observed by electron microscopy. RNA was extracted, cDNA was synthesized by reverse transcription, and plaque formation and hemagglutination were assessed. The cytopathic effect (CPE) were associated with the fourth passage in subculture. CPE extracts were examined by electron microscopy, which allowed us to observe the shape of HRV particles. Amplification of the VP4 gene from HRV was used to identify the viruses as group A rotavirus. The virus causes red blood cell aggregation. The virus isolate was designated as HRV CY2017.

Is SARS-CoV-2 Also an Enteric Pathogen With Potential Fecal-Oral Transmission? A COVID-19 Virological and Clinical Review

In as few as 3 months, coronavirus disease 2019 (COVID-19) has spread and ravaged the world at an unprecedented speed in modern history, rivaling the 1918 flu pandemic. Severe acute respiratory syndrome coronavirus-2, the culprit virus, is highly contagious and stable in the environment and transmits predominantly among humans via the respiratory route. Accumulating evidence suggest that this virus, like many of its related viruses, may also be an enteric virus that can spread via the fecal-oral route. Such a hypothesis would also contribute to the rapidity and proliferation of this pandemic. Here we briefly summarize what is known about this family of viruses and literature basis of the hypothesis that severe acute respiratory syndrome coronavirus-2 is capable of infecting the gastrointestinal tract and shedding in the environment for potential human-to-human transmission.

TMPRSS2 and TMPRSS4 promote SARS-CoV-2 infection of human small intestinal enterocytes

Gastrointestinal symptoms and fecal shedding of SARS-CoV-2 RNA are frequently observed in COVID-19 patients. However, it is unclear whether SARS-CoV-2 replicates in the human intestine and contributes to possible fecal-oral transmission. Here, we report productive infection of SARS-CoV-2 in ACE2⁺ mature enterocytes in human small intestinal enteroids. Expression of two mucosa-specific serine proteases, TMPRSS2 and TMPRSS4, facilitated SARS-CoV-2 spike fusogenic activity and promoted virus entry into host cells. We also demonstrate that viruses released into the intestinal lumen were inactivated by simulated human colonic fluid, and infectious virus was not recovered from the stool specimens of COVID-19 patients. Our results highlight the intestine as a potential site of SARS-CoV-2 replication, which may contribute to local and systemic illness and overall disease progression.

TMPRSS2 and TMPRSS4 promote SARS-CoV-2 infection of human small intestinal enterocytes

Gastrointestinal symptoms and fecal shedding of SARS-CoV-2 RNA are frequently observed in COVID-19 patients. However, it is unclear whether SARS-CoV-2 replicates in the human intestine and contributes to possible fecal-oral transmission. Here, we report productive infection of SARS-CoV-2 in ACE2+ mature enterocytes in human small intestinal enteroids. Expression of two mucosa-specific serine proteases, TMPRSS2 and TMPRSS4, facilitated SARS-CoV-2 spike fusogenic activity and promoted virus entry into host cells. We also demonstrate that viruses released into the intestinal lumen were inactivated by simulated human colonic fluid, and infectious virus was not recovered from the stool specimens of COVID-19 patients. Our results highlight the intestine as a potential site of SARS-CoV-2 replication, which may contribute to local and systemic illness and overall disease progression.

Sero-epidemiological study of the rotavirus VP8* protein from different P genotypes in Valencia, Spain

The aims of the present work were to determine the prevalence and titer of serum antibodies against several rotavirus VP8* proteins from different P genotypes in children and adults in Valencia, Spain; and to determine the role of the secretor status (FUT2_G428A polymorphism) in the antibody response. The VP8* protein from the P[4], P[6], P[8], P[9], P[11], P[14] and P[25] genotypes were produced in E. coli. These proteins were tested with 88 serum samples from children (n = 41, 3.5 years old in average) and from adults (n = 47, 58 years old in average) by ELISA. A subset of 55 samples were genotyped for the FUT2_G428A polymorphism and the antibody titers compared. The same subset of samples was also analysed by ELISA using whole rotavirus Wa particles (G1P[8]) as antigen. Ninety-three per cent of the samples were positive for at least one of the VP8* antigens. Differences in the IgG seroprevalence were found between children and adults for the P[4], P[8] and P[11] genotypes. Similarly, significant differences were found between adults and children in their antibody titers against the P[4], P[8], and P[11] VP8* genotypes, having the children higher antibody titers than adults. Interestingly, positive samples against rare genotypes such as P[11] (only in children), P[14] and P[25] were found. While no statistical differences in the antibody titers between secretors and non-secretors were found for any of the tested P genotypes studied, a higher statistic significant prevalence for the P[25] genotype was found in secretors compared to non-secretors. Significant differences in the antibody titers between secretors and non-secretors were found when the whole viral particles from the Wa rotavirus strain (G1P[8]) were used as the antigen.

Generation of Simian Rotavirus Reassortants with VP4- and VP7-Encoding Genome Segments from Human Strains Circulating in Africa Using Reverse Genetics

Human rotavirus A (RVA) causes acute gastroenteritis in infants and young children. The broad use of two vaccines, which are based on RVA strains from Europe and North America, significantly reduced rotavirus disease burden worldwide. However, a lower vaccine effectiveness is recorded in some regions of the world, such as sub-Saharan Africa, where diverse RVA strains are circulating. Here, a plasmid-based reverse genetics system was used to generate simian RVA reassortants with VP4 and VP7 proteins derived from African human RVA strains not previously adapted to cell culture. We were able to rescue 1/3 VP4 mono-reassortants, 3/3 VP7 mono-reassortants, but no VP4/VP7 double reassortant. Electron microscopy showed typical triple-layered virus particles for the rescued reassortants. All reassortants stably replicated in MA-104 cells; however, the VP4 reassortant showed significantly slower growth compared to the simian RVA or the VP7 reassortants. The results indicate that, at least in cell culture, human VP7 has a high reassortment potential, while reassortment of human VP4 from unadapted human RVA strains with simian RVA seems to be limited. The characterized reassortants may be useful for future studies investigating replication and reassortment requirements of rotaviruses as well as for the development of next generation rotavirus vaccines.

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.