Tandem truncated rotavirus VP8* subunit protein with T cell epitope as non-replicating parenteral vaccine is highly immunogenic

Insights into recent advancements in human and animal rotavirus vaccines: Exploring new frontiers

Rotavirus infections cause severe gastroenteritis and dehydration in young children and animals worldwide, leading to high rates of morbidity and mortality, predominantly in low- and middle-income countries. In the past decade, substantial progress has been made in the development and implementation of rotavirus vaccines, which have been essential in alleviating the global burden of this disease, not only in human being but also in livestock species like calves and piglets, where these infections can cause significant economic losses. By synthesizing the latest research and real-world evidence, this review article is designated to provide deep insights into the current state of rotavirus vaccine technology and its global implementation as well as the application of rotavirus vaccines in veterinary settings and their importance in controlling zoonotic transmission and maintaining food security.

Evaluating the Compatibility of Three Aluminum Salt-Adjuvanted Recombinant Protein Antigens (Trivalent NRRV) Combined with a Mock Trivalent Sabin-IPV Vaccine: Analytical and Formulation Challenges

In this work, we describe compatibility assessments of a recombinant, trivalent non-replicating rotavirus vaccine (t-NRRV) candidate with a mock trivalent Sabin inactivated polio vaccine (t-sIPV). Both t-sIPV and t-NRRV are incompatible with thimerosal (TH), a preservative commonly used in pediatric pentavalent combination vaccines (DTwP-Hib-HepB) distributed in low- and middle-income countries (LMICs), preventing the development of a heptavalent combination. The compatibility of t-NRRV with a mock DTwP-Hib-HepB formulation is described in a companion paper. This case study highlights the analytical and formulation challenges encountered when combining a mock t-sIPV vaccine (unadjuvanted) with Alhydrogel® (AH) adjuvanted t-NRRV. Selective and stability-indicating competition ELISAs were implemented to monitor antibody binding to each of the six antigens (±AH). Simple mixing caused the undesired desorption of t-NRRV from AH with the concomitant binding of t-sIPV to AH. Although the former effect was mitigated by dialyzing sIPV bulks, decreased sIPV storage stability was observed at accelerated temperatures in the bivalent combination with a rank-ordering of P[8] > P[6] > P[4] and sIPV3 > sIPV2 > sIPV1. The compatibility of AH-adsorbed t-sIPV with alternative preservatives was evaluated, and parabens (methyl, propyl) were identified for potential use in this multi-dose bivalent formulation. Along with a companion paper, the lessons learned are discussed to facilitate the future formulation development of pediatric combination vaccines with new antigens.

Evaluating the Compatibility of New Recombinant Protein Antigens (Trivalent NRRV) with a Mock Pentavalent Combination Vaccine Containing Whole-Cell Pertussis: Analytical and Formulation Challenges

Introducing new recombinant protein antigens to existing pediatric combination vaccines is important in improving coverage and affordability, especially in low- and middle-income countries (LMICs). This case-study highlights the analytical and formulation challenges encountered with three recombinant non-replicating rotavirus vaccine (NRRV) antigens (t-NRRV formulated with Alhydrogel® adjuvant, AH) combined with a mock multidose formulation of a pediatric pentavalent vaccine used in LMICs. This complex formulation contained (1) vaccine antigens (i.e., whole-cell pertussis (wP), diphtheria (D), tetanus (T), Haemophilus influenza (Hib), and hepatitis B (HepB), (2) a mixture of aluminum-salt adjuvants (AH and Adju-Phos®, AP), and (3) a preservative (thimerosal, TH). Selective, stability-indicating competitive immunoassays were developed to monitor binding of specific mAbs to each antigen, except wP which required the setup of a mouse immunogenicity assay. Simple mixing led to the desorption of t-NRRV antigens from AH and increased degradation during storage. These deleterious effects were caused by specific antigens, AP, and TH. An AH-only pentavalent formulation mitigated t-NRRV antigen desorption; however, the Hib antigen displayed previously reported AH-induced instability. The same rank-ordering of t-NRRV antigen stability (P[8] > P[4] > P[6]) was observed in mock pentavalent formulations and with various preservatives. The lessons learned are discussed to enable future multidose, combination vaccine formulation development with new vaccine candidates.

Characterization and immunogenicity of a novel chimeric hepatitis B core-virus like particles (cVLPs) carrying rotavirus VP8*protein in mice model

Given the efficacy and safety issues of the WHO for approved/prequalified live attenuated rotavirus (RV) vaccines, studies on alternative non-replicating modals and proper RV antigens are actively undertaken. Herein, we report the novel chimeric hepatitis B core-virus like particles (VLPs) carrying RV VP8*26-231 protein of a P [8] strain (cVLPVP8*), as a parenteral VLP RV vaccine candidate. SDS-PAGE and Western blotting analyses indicated the expected size of the E. coli-derived HBc-VP8* protein that self-assembled to cVLPVP8* particles. Immunization in mice indicated development of higher levels of IgG and IgA as well as higher IgG1/IgG2a ratios by cVLPVP8* vaccination compared to the VP8* alone. Assessment of neutralizing antibodies (nAbs) indicated development of heterotypic nAbs with cross-reactivity to a heterotypic RV strain by cVLPVP8* immunization compared to VP8* alone. The observed anti-VP8* cross-reactivity might indicate the possibility of developing a Pan-genomic RVA vaccine based on the cVLPVP8* formulation that deserves further challenge studies.

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.

Experimental Methods to Study the Pathogenesis of Human Enteric RNA Viruses

Every year, millions of children are infected with viruses that target the gastrointestinal tract, causing acute gastroenteritis and diarrheal illness. Indeed, approximately 700 million episodes of diarrhea occur in children under five annually, with RNA viruses norovirus, rotavirus, and astrovirus serving as major causative pathogens. Numerous methodological advancements in recent years, including the establishment of novel cultivation systems using enteroids as well as the development of murine and other animal models of infection, have helped provide insight into many features of viral pathogenesis. However, many aspects of enteric viral infections remain elusive, demanding further study. Here, we describe the different in vitro and in vivo tools available to explore different pathophysiological attributes of human enteric RNA viruses, highlighting their advantages and limitations depending upon the question being explored. In addition, we discuss key areas and opportunities that would benefit from further methodological progress.

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.

Formulation and preclinical studies with a trivalent rotavirus P2-VP8 subunit vaccine

More effective rotavirus vaccines are essential for preventing extensive diarrheal morbidity and mortality in children under five years of age in low-resource regions. Nonreplicating rotavirus vaccines (NRRV) administered parenterally provide an alternate vaccination method to the current licensed oral vaccine. Live attenuated vaccines and may generate increased efficacy in low-resource settings because the parenteral administration route bypasses some of the challenges associated with oral administration, including differences in intestinal environments. Work described here supports development of a trivalent NRRV vaccine for parenteral administration to avoid complications of the gastrointestinal route. Recombinant VP8* subunit proteins representing some of the most prevalent strains of rotavirus infecting humans - DS-1 (P[4]), 1076 (P[6]), and Wa (P[8]) - were combined with an aluminum adjuvant and the P2 epitope of tetanus toxoid to enhance the immune response to this NRRV antigen. Vaccine formulation development included selection of aluminum hydroxide (Alhydrogel®) as an appropriate adjuvant as well as an optimal buffer to maintain antigen stability and optimize antigen binding to the adjuvant. Characterization assays were used to select the lead vaccine formulation and monitor formulation stability. The NRRV liquid formulation was stable for one year at 2°C to 8°C and four weeks at 37°C. Immunogenicity of the NRRV formulation was evaluated using a guinea pig model, where we demonstrated that the adjuvant provided a 20-fold increase in neutralization titer against a homologous antigen and that the P2-fusion also enhanced the serum neutralizing antibody responses. This vaccine candidate is currently being evaluated in human clinical trials.

Enhanced GII.4 human norovirus infection in gnotobiotic pigs transplanted with a human gut microbiota

The role of commensal microbiota in enteric viral infections has been explored extensively, but the interaction between human gut microbiota (HGM) and human norovirus (HuNoV) is poorly understood. In this study, we established an HGM-Transplanted gnotobiotic (Gn) pig model of HuNoV infection and disease, using an infant stool as HGM transplant and a HuNoV GII.4/2006b strain for virus inoculation. Compared to germ-free Gn pigs, HuNoV inoculation in HGMT Gn pigs resulted in increased HuNoV shedding, characterized by significantly higher shedding titres on post inoculation day (PID) 3, 4, 6, 8 and 9, and significantly longer mean duration of virus shedding. In addition, virus titres were significantly higher in duodenum and distal ileum of HGMT Gn pigs on PID10, while comparable and transient HuNoV viremia was detected in both groups. 16S rRNA gene sequencing demonstrated that HuNoV infection dramatically altered intestinal microbiota in HGMT Gn pigs at the phylum (Proteobacteria, Firmicutes and Bacteroidetes) and genus (Enterococcus, Bifidobacterium, Clostridium, Ruminococcus, Anaerococcus, Bacteroides and Lactobacillus) levels. In summary, enhanced GII.4 HuNoV infection was observed in the presence of HGM, and host microbiota was susceptible to disruption upon HuNoV infection.

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.

Evolution of P[8], P[4], and P[6] VP8* genes of human rotaviruses globally reported during 1974 and 2017: possible implications for rotavirus vaccines in development

Non-replicating parenteral rotavirus (RV) vaccine candidates are in development in an attempt to overcome the lower efficacy and effectiveness of oral RV vaccines in low-income countries. One of the leading candidates is a truncated recombinant VP8* protein, expressed in Escherichia coli from original sequences of the prototype RV genotypes P[8], P[4], or P[6] isolated before 1983. Since VP8* is highly variable, it was considered useful to examine the evolutionary changes of RV strains reported worldwide over time in relation to the three P2-VP8 vaccine strains. Here, we retrieved from the GenBank 6,366 RV VP8* gene sequences of P[8], P[4], or P[6] strains isolated between 1974 and 2017, in 77 countries, and compared them with those of the three P2-VP8 vaccine strains: Wa (USA, 1974, G1P[8]), DS-1 (USA, 1976, G2P[4]), and 1076 (Sweden, 1983, G2P[6]). Phylogenetic analysis showed that 94.9% (4,328/4,560), 99.8% (1,141/1,143), and 100% (663/663) of the P[8], P[4], and P[6] strains, respectively, reported globally between 1974 and 2018 belong to non-vaccine lineages. These P[8], P[4], and P[6] RV strains have a mean of 9%, 5%, and 6% amino acid difference from the corresponding vaccine strains. Additionally, in the USA, the mean percentage difference between all the P[8] RV strains and the original Wa strain increased over time: 4% (during 1974-1980), 5% (1988-1991), and 9% (2005-2013). Our analysis substantiated high evolutionary changes in VP8* of the P[8], P[4], and P[6] major RV strains and their increasing variations from the candidate subunit vaccine strains over time. These findings may have implications for the development of new RV vaccines.

Antibody responses to chimeric peptides derived from parasite antigens in mice and other animal species

Peptide vaccines constitute an interesting alternative to classical vaccines due to the possibility of selecting specific epitopes, easy of production and safety. However, an inadequate design may render these peptides poorly immunogenic or lead to undesirable outcomes (e.g., formation of B neoepitopes). As an approach to vaccine development, we evaluated the antibody response to chimeras composed of two or three known B epitopes from Trichinella and Fasciola, and several linkers (GSGSG, GPGPG and KK) in species as different as mice, sheep and turbot. All these species could mount an effective immune response to the short chimeric peptides. Nevertheless, this response depended on several factors including a favorable orientation of B-cell epitopes, adequateness of linkers and/or probability of formation of T neoepitopes. We also observed that, at least in mice, the inclusion of a decoy epitope may have favorable consequences on the antibody response to other epitopes in the chimera.

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.

Rotavirus epidemiology and vaccine demand: considering Bangladesh chapter through the book of global disease burden

BACKGROUND

Rotavirus is the major cause of gastroenteritis in children throughout the world. Every year, a large number of children aged < 5 years die from rotavirus-related diarrhoeal diseases. Though these infections are vaccine-preventable, the vast majority of children in low-income countries suffer from the infection. The situation leads to severe economic loss and constitutes a major public health problem.

METHODS

We searched electronic databases including PubMed and Google scholar using the following words: "features of rotavirus," "epidemiology of rotavirus," "rotavirus serotypes," "rotavirus in Bangladesh," "disease burden of rotavirus," "rotavirus vaccine," "low efficacy of rotavirus vaccine," "inactivated rotavirus vaccine". Publications until July 2017 have been considered for this work.

RESULTS AND CONCLUSION

Currently, two live attenuated vaccines are available throughout the world. Many countries have included rotavirus vaccines in national immunization program to reduce the disease burden. However, due to low efficacy of the available vaccines, satisfactory outcome has not yet been achieved in developing countries such as Bangladesh. Poor economic, public health, treatment, and sanitation status of the low-income countries necessitate the need for the most effective rotavirus vaccines. Therefore, the present scenario demands the development of a highly effective rotavirus vaccine. In this regard, inactivated rotavirus vaccine concept holds much promise for reducing the current disease burden. Recent advancements in developing an inactivated rotavirus vaccine indicate a significant progress towards disease prophylaxis and control.

Decreased performance of live attenuated, oral rotavirus vaccines in low-income settings: causes and contributing factors

INTRODUCTION

Numerous studies have shown that the oral rotavirus vaccines are less effective in infants born in low income countries compared to those born in developed countries. Identifying the specific factors in developing countries that decrease and/or compromise the protection that rotavirus vaccines offer, could lead to a path for designing new strategies for the vaccines' improvement.

AREAS COVERED

We accessed PubMed to identify rotavirus vaccine performance studies (i.e., efficacy, effectiveness and immunogenicity) and correlated performance with several risk factors. Here, we review the factors that might contribute to the low vaccine efficacy, including passive transfer of maternal rotavirus antibodies, rotavirus seasonality, oral polio vaccine (OPV) administered concurrently, microbiome composition and concomitant enteric pathogens, malnutrition, environmental enteropathy, HIV, and histo blood group antigens.

EXPERT COMMENTARY

We highlight two major factors that compromise rotavirus vaccines' efficacy: the passive transfer of rotavirus IgG antibodies to infants and the  co-administration of rotavirus vaccines with OPV. We also identify other potential risk factors that require further research because the data about their interference with the efficacy of rotavirus vaccines are inconclusive and at times conflicting.

The rotavirus vaccine development pipeline

Rotavirus disease is a leading global cause of mortality and morbidity in children under 5 years of age. The effectiveness of the two globally used oral rotavirus vaccines quickly became apparent when introduced into both developed and developing countries, with significant reductions in rotavirus-associated mortality and hospitalizations. However, the effectiveness and impact of the vaccines is reduced in developing country settings, where the burden and mortality is highest.

New rotavirus vaccines, including live oral rotavirus candidates and non-replicating approaches continue to be developed, with the major aim to improve the global supply of rotavirus vaccines and for local implementation, and to improve vaccine effectiveness in developing settings. This review provides an overview of the new rotavirus vaccines in development by developing country manufacturers and provides a rationale why newer candidates continue to be explored. It describes the new live oral rotavirus vaccine candidates as well as the non-replicating rotavirus vaccines that are furthest along in development.

Contribution of Maternal Immunity to Decreased Rotavirus Vaccine Performance in Low- and Middle-Income Countries

The role of maternal immunity, received by infants either transplacentally or orally from breast milk, in rotavirus vaccine (RV) performance is evaluated here. Breastfeeding withholding has no effect on vaccine responses, but higher levels of transplacental rotavirus-specific IgG antibody contribute to reduced vaccine seroconversion. The gaps in knowledge on the factors associated with low RV efficacy in low- and middle-income countries (LMIC) remain, and further research is needed to shed more light on these issues.