Immunization of Mice by Rotavirus NSP4-VP6 Fusion Protein Elicited Stronger Responses Compared to VP6 Alone

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.

Unravelling aggregation propensity of rotavirus A VP6 expressed as E. coli inclusion bodies through in silico prediction

The inner capsid protein of rotavirus, VP6, emerges as a promising candidate for next-generation vaccines against rotaviruses owing to its abundance in virion particles and high conservation. However, the formation of inclusion bodies during prokaryotic VP6 expression poses a significant hurdle to rotavirus research and applications. Here, we employed experimental and computational approaches to investigate inclusion body formation and aggregation-prone regions (APRs). Heterologous recombinant VP6 expression in Escherichia coli BL21(DE3) cells resulted in inclusion body formation, confirmed by transmission electron microscopy revealing amorphous aggregates. Thioflavin T assay demonstrated incubation temperature-dependent aggregation of VP6 inclusion bodies. Computational predictions of APRs in rotavirus A VP6 protein were performed using sequence-based tools (TANGO, AGGRESCAN, Zyggregator, Waltz, FoldAmyloid, ANuPP, Camsol intrinsic) and structure-based tools (SolubiS, CamSol structurally corrected, Aggrescan3D). A total of 24 consensus APRs were identified, with 21 of them being surface-exposed in VP6. All identified APRs display a predominance of hydrophobic amino acids, ranging from 33 to 100%. Computational identification of these APRs corroborates our experimental observation of VP6 inclusion body or aggregate formation. Characterization of VP6's aggregation propensity facilitates understanding of its behaviour during prokaryotic expression and opens avenues for protein engineering of soluble variants, advancing research on rotavirus VP6 in pathology, therapy, and diagnostics.

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.

The synergy of recombinant NSP4 and VP4 from porcine rotavirus elicited a strong mucosal response

Porcine rotavirus (PoRV) is one of the main pathogens causing diarrhea in piglets, and multiple genotypes coexist. However, an effective vaccine is currently lacking. Here, the potential adjuvant of nonstructural protein 4 (NSP4) and highly immunogenic structural protein VP4 prompted us to construct recombinant NSP486-175aa (NSP4*) and VP426-476aa (VP4*) proteins, combine them as immunogens to evaluate their efficacy. Results indicated that NSP4* enhanced systemic and local mucosal responses induced by VP4*. The VP4*-IgG, VP4*-IgA in feces and IgA-secreting cells in intestines induced by the co-immunization were significantly higher than those induced by VP4* alone. Co-immunization of NSP4* and VP4* also induced strong cellular immunity with significantly increased IFN-λ than the single VP4*. Summarily, the NSP4* as a synergistical antigen exerted limited effects on the PoRV NAbs elevation, but conferred strong VP4*-specific mucosal and cellular efficacy, which lays the foundation for the development of a more effective porcine rotavirus subunit vaccine.

Correlates of immune protection against human rotaviruses: natural infection and vaccination

Species A rotaviruses are the leading viral cause of acute gastroenteritis in children under 5 years of age worldwide. Despite progress in the characterization of the pathogenesis and immunology of rotavirus-induced gastroenteritis, correlates of protection (CoPs) in the course of either natural infection or vaccine-induced immunity are not fully understood. There are numerous factors such as serological responses (IgA and IgG), the presence of maternal antibodies (Abs) in breast milk, changes in the intestinal microbiome, and rotavirus structural and non-structural proteins that contribute to the outcome of the CoP. Indeed, while an intestinal IgA response and its surrogate, the serum IgA level, are suggested as the principal CoPs for oral rotavirus vaccines, the IgG level is more likely to be a CoP for parenteral non-replicating rotavirus vaccines. Integrating clinical and immunological data will be instrumental in improving rotavirus vaccine efficacy, especially in low- and middle-income countries, where vaccine efficacy is significantly lower than in high-income countries. Further knowledge on CoPs against rotavirus disease will be helpful for next-generation vaccine development. Herein, available data and literature on interacting components and proposed CoPs against human rotavirus disease are reviewed, and limitations and gaps in our knowledge in this area are discussed.

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.

Rotavirus VP6: involvement in immunogenicity, adjuvant activity, and use as a vector for heterologous peptides, drug delivery, and production of nano-biomaterials

The first-generation, live attenuated rotavirus (RV) vaccines, such as RotaTeq and Rotarix, were successful in reducing the number of RV-induced acute gastroenteritis (AGE) and child deaths globally. However, the low efficacy of these first-generation oral vaccines, coupled with safety concerns, required development of improved RV vaccines. The highly conserved structural protein VP6 is highly immunogenic, and it can generate self-assembled nano-sized structures, including tubes and spheres (virus-like particles; VLPs). Amongst the RV proteins, only VP6 shows these features. Interestingly, VP6-assembled structures, in addition to being highly immunogenic, have several other useful characteristics that could allow them to be used as adjuvants, immunological carriers, and drug-delivery vehicles as well as acting a scaffold for production of valuable nano-biomaterials. This review provides an overview of the self-assembled nano-sized structures of VP6-tubes/VLPs and their various functions.

Co-administration of rotavirus nanospheres VP6 and NSP4 proteins enhanced the anti-NSP4 humoral responses in immunized mice

Inconveniences associated with the efficacy and safety of the World Health Organization (WHO) approved/prequalified live attenuated rotavirus (RV) vaccines, sounded for finding alternative non-replicating modals and proper RV antigens (Ags). Herein, we report the development of a RV candidate vaccine based on the combination of RV VP6 nanospheres (S) and NSP4_112-175 proteins (VP6S + NSP4). Self-assembled VP6S protein was produced in insect cells. Analyses by western blotting and transmission electron microscopy (TEM) indicated expression of VP6 trimer structures with sizes of ≥140 kDa and presence of VP6S. Four group of mice were immunized (2-dose formulation) intra-peritoneally (IP) by either¨VP6S + NSP4¨ or each protein alone (VP6S or NSP4_112-175) emulsified in aluminium hydroxide or control. Results indicated that VP6S + NSP4 formulation induced significant anti-VP6 IgG (P < 0.001) and IgA (P < 0.05) as well as anti-NSP4 IgG (P < 0.001) and enhancement of protective immunity. Analyses of anti-VP6S and anti-NSP4 IgG subclass (IgG1 and IgG2a) showed IgG1/IgG2a ≥6 and IgG1/IgG2a ≥3 ratios, respectively indicating Th2 polarization of immune responses. The combination of VP6S + NSP4 proteins emulsified in aluminum hydroxide adjuvant might present a dual universal, efficient and cost-effective candidate vaccine against RV infection.

Combined use of lactic-acid-producing bacteria as probiotics and rotavirus vaccine candidates expressing virus-specific proteins

Due to the lower efficacy of currently approved live attenuated rotavirus (RV) vaccines in developing countries, a new approach to the development of safe mucosally administered live bacterial vectors is being considered, using probiotic bacteria as an efficient delivery platform for heterologous RV antigens. Lactic acid bacteria (LAB), which are considered food-grade bacteria and normal microbiota, have been utilized throughout history as probiotics and developed since the 1990s as a delivery system for recombinant heterologous proteins. Over the last decade, LAB have frequently been used as a platform for the delivery of various RV antigens to the mucosa. Given the appropriate safety profile for neonates and providing the benefits of probiotics, recombinant LAB-based vaccines could potentially address the need for a subunit RV vaccine. The present review focuses mainly on different recombinant LAB vaccine constructs for RV and their potential as an alternative recombinant vaccine against RV disease.

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.