Understanding internalization of rotavirus VP6 nanotubes by cells: towards a recombinant vaccine

Development of a novel bivalent vaccine candidate against hepatitis A virus and rotavirus using reverse vaccinology and immunoinformatics

The hepatitis A virus (HAV) and rotavirus are mainly transmitted through fecal-oral and person-to-person contact, and cause severe gastrointestinal complications and liver disease. This work used reverse vaccinology and immunoinformatic methods to create a novel bivalent vaccine against rotavirus and HAV. The amino acid sequences of HAV-rotavirus proteins (VP1 and VP8∗) were retrieved from the GenBank database. Various computational approaches were employed to predict highly conserved regions and the most immunogenic B-cell and T-cell epitopes of VP8 and VP1 of rotavirus and HAV proteins in both humans and BALB/c. Moreover, the predicted fusion protein was analyzed regarding primary and secondary structures and homology validation. In this study, we used two highly conserved peptide sequences of VP8 and VP1 of rotavirus and HAV that induce T and B cell immunogenicity. According to T-cell epitope prediction, this area comprises 2713 antigenic peptides for HLA class II and 30 HLA class I antigenic peptides, both of which are virtually entirely conserved in the Iranian population. In this study, validation as well as analysis of the secondary and three-dimensional structure of the VP8∗-rotavirus + AAY + HAV-VP1 fusion protein, with the aim of designing a multi-epitope vaccine with different receptors. TLR 3, 4 high immunogenic binding ability with immunological properties and interaction between multi-epitope target and TLR were predicted, and it is expected that the target fusion protein has stable antigenic potency and compatible half-life. The above is suggested as a universal vaccination program.

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.

Fusion Protein of Rotavirus VP6 and SARS-CoV-2 Receptor Binding Domain Induces T Cell Responses

Vaccines based on mRNA and viral vectors are currently used in the frontline to combat the ongoing pandemic caused by the novel Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). However, there is still an urgent need for alternative vaccine technologies inducing/boosting long-lasting and cross-reactive immunity in different populations. As a possible vaccine candidate, we employed the rotavirus VP6-protein platform to construct a fusion protein (FP) displaying receptor-binding domain (RBD) of SARS-CoV-2 spike protein (S) at the N-terminus of VP6. The recombinant baculovirus-insect cell produced VP6-RBD FP was proven antigenic in vitro and bound to the human angiotensin-converting enzyme 2 (hACE2) receptor. The FP was used to immunize BALB/c mice, and humoral- and T cell-mediated immune responses were investigated. SARS-CoV-2 RBD-specific T cells were induced at a high quantity; however, no RBD or S-specific antibodies were detected. The results suggest that conformational B cell epitopes might be buried inside the VP6, while RBD-specific T cell epitopes are available for T cell recognition after the processing and presentation of FP by the antigen-presenting cells. Further immunogenicity studies are needed to confirm these findings and to assess whether, under different experimental conditions, the VP6 platform may present SARS-CoV-2 antigens to B cells as well.

Rotavirus Inner Capsid VP6 Acts as an Adjuvant in Formulations with Particulate Antigens Only

Novel adjuvants present a concern for adverse effects, generating a need for alternatives. Rotavirus inner capsid VP6 protein could be considered a potential candidate, due to its ability to self-assemble into highly immunogenic nanospheres and nanotubes. These nanostructures exhibit immunostimulatory properties, which resemble those of traditional adjuvants, promoting the uptake and immunogenicity of the co-administered antigens. We have previously elucidated an adjuvant effect of VP6 on co-delivered norovirus and coxsackievirus B1 virus-like particles, increasing humoral and cellular responses and sparing the dose of co-delivered antigens. This study explored an immunostimulatory effect of VP6 nanospheres on smaller antigens, P particles formed by protruding domain of a norovirus capsid protein and a short peptide, extracellular matrix protein (M2e) of influenza A virus. VP6 exhibited a notable improving impact on immune responses induced by P particles in immunized mice, including systemic and mucosal antibody and T cell responses. The adjuvant effect of VP6 nanospheres was comparable to the effect of alum, except for induction of superior mucosal and T cell responses when P particles were co-administered with VP6. However, unlike alum, VP6 did not influence M2e-specific immune responses, suggesting that the adjuvant effect of VP6 is dependent on the particulate nature of the co-administered antigen.

Rotavirus VP6 Adjuvant Effect on Norovirus GII.4 Virus-Like Particle Uptake and Presentation by Bone Marrow-Derived Dendritic Cells In Vitro and In Vivo

We have previously shown that rotavirus (RV) inner capsid protein VP6 has an adjuvant effect on norovirus (NoV) virus-like particle- (VLP-) induced immune responses and studied the adjuvant mechanism in immortalized cell lines used as antigen-presenting cells (APCs). Here, we investigated the uptake and presentation of RV VP6 and NoV GII.4 VLPs by primary bone marrow-derived dendritic cells (BMDCs). The adjuvant effect of VP6 on GII.4 VLP presentation and NoV-specific immune response induction by BMDC in vivo was also studied. Intracellular staining demonstrated that BMDCs internalized both antigens, but VP6 more efficiently than NoV VLPs. Both antigens were processed and presented to antigen-primed T cells, which responded by robust interferon γ secretion. When GII.4 VLPs and VP6 were mixed in the same pulsing reaction, a subpopulation of the cells had uptaken both antigens. Furthermore, VP6 copulsing increased GII.4 VLP uptake by 37% and activated BMDCs to secrete 2-5-fold increased levels of interleukin 6 and tumor necrosis factor α compared to VLP pulsing alone. When in vitro-pulsed BMDCs were transferred to syngeneic BALB/c mice, VP6 improved NoV-specific antibody responses. The results of this study support the earlier findings of VP6 adjuvant effect in vitro and in vivo.

Rotavirus vaccines: why continued investment in research is necessary

PURPOSE OF REVIEW

Rotavirus vaccines were first introduced more than a decade ago and have had a tremendous impact on reducing the number of hospitalizations and deaths due to rotavirus-associated diarrhea. This review will discuss current rotavirus vaccines, post-licensure surveillance, progress in non-replicating vaccine development, and why continued research is important for understanding a virus that remains a globally leading cause of death due to diarrhea.

RECENT FINDINGS

Research advances have enhanced our understanding of how vaccines induce protection against subsequent severe disease, how the virus replicates and spreads in the face of the host immune system, and basic mechanisms governing the viral life cycle.

SUMMARY

Much remains to be learned about how to improve vaccine success, what are the molecular determinants of host range and virulence, and what are the interactions of the virus with the host that drive its replicative success, among many other important questions.

Rotavirus capsid VP6 protein acts as an adjuvant in vivo for norovirus virus-like particles in a combination vaccine

Rotavirus (RV) and norovirus (NoV) are the 2 leading causes of acute viral gastroenteritis worldwide. We have developed a non-live NoV and RV vaccine candidate consisting of NoV virus-like particles (VLPs) and recombinant polymeric RV VP6 protein produced in baculovirus-insect cell expression system. Both components have been shown to induce strong potentially protective immune responses. As VP6 nanotubes are highly immunogenic, we investigated here a possible adjuvant effect of these structures on NoV-specific immune responses in vivo. BALB/c mice were immunized intramuscularly with a suboptimal dose (0.3 μg) of GII.4 or GI.3 VLPs either alone or in a combination with 10 μg dose of VP6 and induction of NoV-specific antibodies in sera of experimental animals were measured. Blocking assay using human saliva or synthetic histo-blood group antigens was employed to test NoV blocking antibodies. Suboptimal doses of the VLPs alone did not induce substantial anti-NoV antibodies. When co-administered with the VP6, considerable titers of not only type-specific but also cross-reactive IgG antibodies against NoV VLP genotypes not included in the vaccine composition were induced. Most importantly, NoV-specific blocking antibodies, a surrogate for neutralizing antibodies, were generated. Our results show that RV VP6 protein has an in vivo adjuvant effect on NoV-specific antibody responses and support the use of VP6 protein as a part of the NoV-RV combination vaccine, especially when addition of external adjuvants is not desirable.

Rotavirus capsid VP6 tubular and spherical nanostructures act as local adjuvants when co-delivered with norovirus VLPs

A subunit protein vaccine candidate based on norovirus (NoV) virus‐like particles (VLPs) and rotavirus (RV) VP6 protein against acute childhood gastroenteritis has been proposed recently. RV VP6 forms different oligomeric nanostructures, including tubes and spheres when expressed in vitro, which are highly immunogenic in different animal models. We have shown recently that recombinant VP6 nanotubes have an adjuvant effect on immunogenicity of NoV VLPs in mice. In this study, we investigated if the adjuvant effect is dependent upon a VP6 dose or different VP6 structural assemblies. In addition, local and systemic adjuvant effects as well as requirements for antigen co‐delivery and co‐localization were studied. The magnitude and functionality of NoV GII.4‐specific antibodies and T cell responses were tested in mice immunized with GII.4 VLPs alone or different combinations of VLPs and VP6. A VP6 dose‐dependent adjuvant effect on GII.4‐specific antibody responses was observed. The adjuvant effect was found to be strictly dependent upon co‐administration of NoV GII.4 VLPs and VP6 at the same anatomic site and at the same time. However, the adjuvant effect was not dependent on the types of oligomers used, as both nanotubes and nanospheres exerted adjuvant effect on GII.4‐specific antibody generation and, for the first time, T cell immunity. These findings elucidate the mechanisms of VP6 adjuvant effect in vivo and support its use as an adjuvant in a combination NoV and RV vaccine.

Rotavirus Recombinant VP6 Nanotubes Act as an Immunomodulator and Delivery Vehicle for Norovirus Virus-Like Particles

We have recently shown that tubular form of rotavirus (RV) recombinant VP6 protein has an in vivo adjuvant effect on the immunogenicity of norovirus (NoV) virus-like particle (VLP) vaccine candidate. In here, we investigated in vitro effect of VP6 on antigen presenting cell (APC) activation and maturation and whether VP6 facilitates NoV VLP uptake by these APCs. Mouse macrophage cell line RAW 264.7 and dendritic cell line JAWSII were used as model APCs. Internalization of VP6, cell surface expression of CD40, CD80, CD86, and major histocompatibility class II molecules, and cytokine and chemokine production were analyzed. VP6 nanotubes were efficiently internalized by APCs. VP6 upregulated the expression of cell surface activation and maturation molecules and induced secretion of several proinflammatory cytokines and chemokines. The mechanism of VP6 action was shown to be partially dependent on lipid raft-mediated endocytic pathway as shown by methyl-β-cyclodextrin inhibition on tumor necrosis factor α secretion. These findings add to the understanding of mechanism by which VP6 exerts its immunostimulatory and immunomodulatory actions and further support its use as a part of nonlive RV-NoV combination vaccine.

Rotavirus VP6 preparations as a non-replicating vaccine candidates

Rotavirus (RV) structural proteins VP4 and VP7, located on the surface of viral particles, elicit neutralizing antibodies (Abs) and are therefore considered to be important components of RV vaccines. However, despite inducing neutralizing Abs, limits of cross-neutralizing activity and lack of full correlation with protection limit the usefulness of these proteins as protective agents against RV disease. VP6 protein, which forms the middle layer of RV particles, is discussed as an alternative vaccine candidate since it can induce cross-protective immune responses against different RV strains although the Ab raised is not neutralizing. This report reviews different functions of VP6 that can lead to considering it as an alternative vaccine against RV disease.

Effect of metal catalyzed oxidation in recombinant viral protein assemblies

Background

Protein assemblies, such as virus-like particles, have increasing importance as vaccines, delivery vehicles and nanomaterials. However, their use requires stable assemblies. An important cause of loss of stability in proteins is oxidation, which can occur during their production, purification and storage. Despite its importance, very few studies have investigated the effect of oxidation in protein assemblies and their structural units. In this work, we investigated the role of in vitro oxidation in the assembly and stability of rotavirus VP6, a polymorphic protein.

Results

The susceptibility to oxidation of VP6 assembled into nanotubes (VP6_NT) and unassembled VP6 (VP6_U) was determined and compared to bovine serum albumin (BSA) as control. VP6 was more resistant to oxidation than BSA, as determined by measuring protein degradation and carbonyl content. It was found that assembly protected VP6 from in vitro metal-catalyzed oxidation. Oxidation provoked protein aggregation and VP6_NT fragmentation, as evidenced by dynamic light scattering and transmission electron microscopy. Oxidative damage of VP6 correlated with a decrease of its center of fluorescence spectral mass. The in vitro assembly efficiency of VP6_U into VP6_NT decreased as the oxidant concentration increased.

Conclusions

Oxidation caused carbonylation, quenching, and destruction of aromatic amino acids and aggregation of VP6 in its assembled and unassembled forms. Such modifications affected protein functionality, including its ability to assemble. That assembly protected VP6 from oxidation shows that exposure of susceptible amino acids to the solvent increases their damage, and therefore the protein surface area that is exposed to the solvent is determinant of its susceptibility to oxidation. The inability of oxidized VP6 to assemble into nanotubes highlights the importance of avoiding this modification during the production of proteins that self-assemble. This is the first time that the role of oxidation in protein assembly is studied, evidencing that oxidation should be minimized during the production process if VP6 nanotubes are required.