Virus-derived tubular structure displaying foreign sequences on the surface elicit CD4+ Th cell and protective humoral responses

Nanoparticle- and Microparticle-Based Vaccines against Orbiviruses of Veterinary Importance

Bluetongue virus (BTV) and African horse sickness virus (AHSV) are widespread arboviruses that cause important economic losses in the livestock and equine industries, respectively. In addition to these, another arthropod-transmitted orbivirus known as epizootic hemorrhagic disease virus (EHDV) entails a major threat as there is a conducive landscape that nurtures its emergence in non-endemic countries. To date, only vaccinations with live attenuated or inactivated vaccines permit the control of these three viral diseases, although important drawbacks, e.g., low safety profile and effectiveness, and lack of DIVA (differentiation of infected from vaccinated animals) properties, constrain their usage as prophylactic measures. Moreover, a substantial number of serotypes of BTV, AHSV and EHDV have been described, with poor induction of cross-protective immune responses among serotypes. In the context of next-generation vaccine development, antigen delivery systems based on nano- or microparticles have gathered significant attention during the last few decades. A diversity of technologies, such as virus-like particles or self-assembled protein complexes, have been implemented for vaccine design against these viruses. In this work, we offer a comprehensive review of the nano- and microparticulated vaccine candidates against these three relevant orbiviruses. Additionally, we also review an innovative technology for antigen delivery based on the avian reovirus nonstructural protein muNS and we explore the prospective functionality of the nonstructural protein NS1 nanotubules as a BTV-based delivery platform.

Atomic structure of the translation regulatory protein NS1 of bluetongue virus

Bluetongue virus (BTV) non-structural protein 1 (NS1) regulates viral protein synthesis and exists as tubular and non-tubular forms in infected cells, but how tubules assemble and how protein synthesis is regulated are unknown. Here, we report near-atomic resolution structures of two NS1 tubular forms determined by cryo-electron microscopy. The two tubular forms are different helical assemblies of the same NS1 monomer, consisting of an amino-terminal foot, a head and body domains connected to an extended carboxy-terminal arm, which wraps atop the head domain of another NS1 subunit through hydrophobic interactions. Deletion of the C terminus prevents tubule formation but not viral replication, suggesting an active non-tubular form. Two zinc-finger-like motifs are present in each NS1 monomer, and tubules are disrupted by divalent cation chelation and restored by cation addition, including Zn2+, suggesting a regulatory role of divalent cations in tubule formation. In vitro luciferase assays show that the NS1 non-tubular form upregulates BTV mRNA translation, whereas zinc-finger disruption decreases viral mRNA translation, tubule formation and virus replication, confirming a functional role for the zinc-fingers. Thus, the non-tubular form of NS1 is sufficient for viral protein synthesis and infectious virus replication, and the regulatory mechanism involved operates through divalent cation-dependent conversion between the non-tubular and tubular forms.

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.

Live baculovirus acts as a strong B and T cell adjuvant for monomeric and oligomeric protein antigens

Recombinant proteins produced by baculovirus (BV) expression systems contain residual BV after crude purification. We studied adjuvant effect of BV on antibody and T cell responses against two model antigens, monomeric ovalbumin (OVA) protein and oligomeric norovirus (NoV) virus-like particles (VLPs). BALB/c mice were immunized intradermally with OVA alone or OVA formulated with live or inactivated BV, and VLP formulations comprised of chromatographically purified NoV GII.4 VLPs alone or mixed with BV, or of crude purified VLPs containing BV impurities from expression system. Live BV improved immunogenicity of NoV VLPs, sparing VLP dose up to 10-fold. Moreover, soluble OVA protein induced IgG2a antibodies and T cell response only when co-administered with live BV. BV adjuvant effect was completely abrogated by removal or inactivation of BV. These findings support the usage of crude purified proteins containing residual BV as vaccine antigens.

Defeating Bluetongue virus: new approaches in the development of multiserotype vaccines

Bluetongue virus (BTV) is a global threat to domestic and wild ruminants, causing massive economic losses throughout the world. New serotypes of the virus are rapidly emerging in different continents, unfortunately there is little cross-protection between BTV serotypes. The eradication of the virus from a region is particularly complicated in areas where multiple serotypes circulate for a long time. The present review summarizes the actual concerns about the spread of the virus and relevant approaches to develop efficient vaccines against BTV, in particular those focused on a multiserotype design.

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.

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

Rotavirus VP6 nanotubes are an attractive option for a recombinant vaccine against rotavirus disease. Protection against rotavirus infection and an adjuvant effect have been observed upon immunization with VP6 nanotubes. However, little information exists on how VP6 nanotubes interact with cells and trigger an immune response. In this work, the interaction between VP6 nanotubes and different cell lines was characterized. VP6 nanotubes were not cytotoxic to any of the animal or human cell lines tested. Uptake of nanotubes into cells was cell-line-dependent, as only THP1 and J774 macrophage cells internalized them. Moreover, the size and spatial arrangement of VP6 assembled into nanotubes allowed their uptake by macrophages, as double-layered rotavirus-like particles also displaying VP6 in their surface were not taken up. The internalization of VP6 nanotubes was inhibited by methyl-β-cyclodextrin, but not by genistein, indicating that nanotube entry is specific, depends on the presence of cholesterol in the plasma membrane, and does not require the activity of tyrosine kinases. The information generated here expands our understanding of the interaction of protein nanotubes with cells, which is useful for the application of VP6 nanotubes as a vaccine.

Synthesis and characterization of different immunogenic viral nanoconstructs from rotavirus VP6 inner capsid protein

In order to deliver low-cost viral capsomeres from a large amount of soluble viral VP6 protein from human rotavirus, we developed and optimized a biotechnological platform in Escherichia coli. Specifically, three different expression protocols were compared, differing in their genetic constructs, ie, a simple native histidine-tagged VP6 sequence, VP6 fused to thioredoxin, and VP6 obtained with the newly described small ubiquitin-like modifier (SUMO) fusion system. Our results demonstrate that the histidine-tagged protein does not escape the accumulation in the inclusion bodies, and that SUMO is largely superior to the thioredoxin-fusion tag in enhancing the expression and solubility of VP6 protein. Moreover, the VP6 protein produced according to the SUMO fusion tag displays well-known assembly properties, as observed in both transmission electron microscopy and atomic force microscopy images, giving rise to either VP6 trimers, 60 nm spherical virus-like particles, or nanotubes a few microns long. This different quaternary organization of VP6 shows a higher level of immunogenicity for the elongated structures with respect to the spheres or the protein trimers. Therefore, the expression and purification strategy presented here – providing a large amount of the viral capsid protein in the native form with relatively simple, rapid, and economical procedures – opens a new route toward large-scale production of a more efficient antigenic compound to be used as a vaccination tool or as an adjuvant, and also represents a top-quality biomaterial to be further modified for biotechnological purposes.

Obesity vaccines

Obesity is one of the largest and fastest growing public health problems in the world. Last century social changes have set an obesogenic milieu that calls for micro and macro environment interventions for disease prevention, while treatment is mandatory for individuals already obese. The cornerstone of overweight and obesity treatment is diet and physical exercise. However, many patients find lifestyle modifications difficult to comply and prone to failure in the long-term; therefore many patients consider anti-obesity drugs an important adjuvant if not a better alternative to behavioral approach or obesity surgery. Since the pharmacological options for obesity treatment remain quite limited, this is an exciting research area, with new treatment targets and strategies on the horizon. This review discusses the development of innovative therapeutic agents, focusing in energy homeostasis regulation and the use of molecular vaccines, targeting hormones such as somatostatin, GIP and ghrelin, to reduce body weight.

Immunization against active ghrelin using virus-like particles for obesity treatment

Ghrelin is a gut hormone that stimulates food intake. In physiological conditions, ghrelin plasma levels rise with fasting and decrease after meals. Obese individuals have low fasting ghrelin levels that rise after food restriction, which is pointed out as a reason for the difficulty in maintaining weight loss. Some bariatric surgery procedures prevent rise in ghrelin levels with weight loss and this has been hypothesised to contribute to the long-term success of the treatment. The main goal of this study was to develop a safe and effective anti-ghrelin vaccine for obesity, through the chemical conjugation of ghrelin with a virus like particle, namely NS1 protein tubules from the Bluetongue Virus (BTV) using a hetero-bifunctional cross linker. Male adult C57BL/6 mice, with a normal weight and with diet-induced obesity (DIO), were randomized into six weight matched groups (n=6/group) and each group of mice received three intra-peritoneal injections with two weeks intervals, containing either 75 μg of ghrelin- NS1 immunoconjugate, 75 μg of NS1 or PBS. Our data show that immunized animals present increasing titres of anti-ghrelin antibodies, while their cumulative food intake significantly decreased and energy expenditure was significantly enhanced, although there were no significative changes in body weight.Vaccinated DIO mice also displayed significant decrease of NPY gene expression in the basal hypothalamus reflecting a decrease in central orexigenic signals. This study suggests that this anti-ghrelin vaccine has a positive impact on energy homeostasis and may be an additional therapeutical tool to be used with diet and exercise for obesity treatment.

Electron tomography of the supramolecular structure of virus-infected cells

Visualizing the viral life cycle in the host challenges us to extend our understanding of the viral infection mechanism. Three-dimensional images obtained by advanced electron tomographic imaging techniques, if resolved to molecular resolution, are helpful for bridging the atomic structural information of proteins to cellular events. Characteristic large structures appear in virus-infected host cells through the life cycle of various viruses. These structures are likely to provide clues to understanding viral infection mechanisms, such as how viruses move in host cells, how they are assembled, how they egress and how they spread cell-to-cell. Here we review recent advances in the studies of the molecular architecture of virus machinery involved in the mechanism of virus infection using comprehensive electron tomographic imaging techniques.

Virus-like particles as a vaccine delivery system: myths and facts

Vaccines against viral disease have traditionally relied on attenuated virus strains or inactivation of infectious virus. Subunit vaccines based on viral proteins expressed in heterologous systems have been effective for some pathogens, but have often suffered from poor immunogenicity due to incorrect protein folding or modification. In this chapter we focus on a specific class of viral subunit vaccine that mimics the overall structure of virus particles and thus preserves the native antigenic conformation of the immunogenic proteins. These virus-like particles (VLPs) have been produced for a wide range of taxonomically and structurally distinct viruses, and have unique advantages in terms of safety and immunogenicity over previous approaches. With new VLP vaccines for papillomavirus beginning to reach the market place we argue that this technology has now ‘come-of-age’ and must be considered a viable vaccine strategy.

Manipulation of the bluetongue virus tubules for immunogen delivery

A multidisplay vaccine delivery system has been developed that is nonreplicating and has a protein-based particulate structure. The structure is composed of helical tubules comprising multiple copies of a single nonstructural (NS) protein 1 of bluetongue virus. The helical assemblies present the C terminus of the protein on the surface of the tubules, thereby displaying appended residues in regular and repeating arrays. The NS1 protein has been manipulated to carry chosen immunogens at this C terminus, such that many thousands of copies of the foreign immunogen are displayed on the surface of the tubules. The display system can accommodate more than 500 amino acid residues in length without perturbing the basic tubular structure. Many immunogens have been displayed and tested for immunogenicity and have been shown to stimulate both humoral and cellular responses. NS1 tubules represent a safe vaccine-delivery system with great potential in the vaccine arena.

Induction of human immunodeficiency virus type 1-specific T cells by a bluetongue virus tubule-vectored vaccine prime-recombinant modified virus Ankara boost regimen

In the absence of strategies for reliable induction of antibodies broadly neutralizing human immunodeficiency virus type 1 (HIV-1), vaccine efforts have shifted toward the induction of cell-mediated immunity. Here we describe the construction and immunogenicity of novel T-cell vaccine NS1.HIVA, which delivers the HIV-1 clade A consensus-derived immunogen HIVA on the surface of tubular structures spontaneously formed by protein NS1 of bluetongue virus. We demonstrated that NS1 tubules can accommodate a protein as large as 527 amino acids without losing their self-assembly capability. When injected into BALB/c mice by several routes, chimeric NS1.HIVA tubules induced HIV-1-specific major histocompatibility complex class I-restricted T cells. These could be boosted by modified virus Ankara expressing the same immunogen and generate a memory capable of gamma interferon (IFN-gamma) production, proliferation, and lysis of sensitized target cells. Induced memory T cells readily produced IFN-gamma 230 days postimmunization, and upon a surrogate virus challenge, NS1.HIVA vaccine alone decreased the vaccinia virus vv.HIVA load in ovaries by 2 orders of magnitude 280 days after immunization. Thus, because of its T-cell immunogenicity and antigenic simplicity, the NS1 delivery system could serve as a priming agent for heterologous prime-boost vaccination regimens. Its usefulness in primates, including humans, remains to be determined.

Virus-like particles: models for assembly studies and foreign epitope carriers

Virus‐like particles (VLPs), formed by the structural elements of viruses, have received considerable attention over the past two decades. The number of reports on newly obtained VLPs has grown proportionally with the systems developed for the expression of these particles. The chapter outlines the recent achievements in two important fields of research brought about by the availability of VLPs produced in a foreign host. These are: (1) The requirements for VLP assembly and (2) the use of VLPs as carriers for foreign epitopes. VLP technology is a rapidly advancing domain of molecular and structural biology. Extensive progress in VLP studies was achieved as the insect cell based protein production system was developed. This baculovirus expression system has many advantages for the synthesis of viral structural proteins resulting in the formation of VLPs. It allows production of large amounts of correctly folded proteins while also providing cell membranes that can serve as structural elements for enveloped viruses. These features give us the opportunity to gain insights into the interactions and requirements accompanying VLP formation that are similar to the assembly events occurring in mammalian cells. Other encouraging elements are the ability to easily scale up the system and the simplicity of purification of the assembled VLPs. The growing number of VLPs carrying foreign protein fragments on their surface and studies on the successful assembly of these chimeric molecules is a promising avenue towards the development of a new technology, in which the newly designed VLPs will be directed to particular mammalian cell types by exposing specific binding domains. The progress made in modeling the surface of VLPs makes them to date the best candidates for the design of delivery systems that can efficiently reach their targets.

Role of an arbovirus nonstructural protein in cellular pathogenesis and virus release

The insect-borne Bluetongue virus (BTV) is considered the prototypic Orbivirus, a member of the Reovirus family. One of the hallmarks of Orbivirus infection is the production of large numbers of intracellular tubular structures of unknown function. For BTV these structures are formed as the polymerization product of a single 64-kDa nonstructural protein, NS1, encoded by the viral double-stranded RNA genome segment 6. Although the NS1 protein is the most abundant viral protein synthesized in infected cells, its function has yet to be determined. One possibility is that NS1 tubules may be involved in the translocation of newly formed viral particles to the plasma membrane, and NS1-specific monoclonal antibodies have been shown to react with viral particles leaving infected cells. In the present study we generated a mammalian cell line that expresses a recombinant single-chain antibody fragment (scFv) derived from an NS1-specific monoclonal antibody (10B1) and analyzed the effect that this intracellular antibody has on BTV replication. Normally, BTV infection of mammalian cells in culture results in a severe cytopathic effect within 24 to 48 h postinfection manifested by cell rounding, apoptosis, and lytic release of virions into the culture medium. However, infection of scFv-expressing cells results in a marked reduction in the stability of NS1 and formation of NS1 tubules, a decrease in cytopathic effect, an increased release of infectious virus into the culture medium, and budding of virions from the plasma membrane. These results suggest that NS1 tubules play a direct role in the cellular pathogenesis and morphogenesis of BTV.

A Japanese encephalitis virus peptide present on Johnson grass mosaic virus-like particles induces virus-neutralizing antibodies and protects mice against lethal challenge

Protection against Japanese encephalitis virus (JEV) is antibody dependent, and neutralizing antibodies alone are sufficient to impart protection. Thus, we are aiming to develop a peptide-based vaccine against JEV by identifying JEV peptide sequences that could induce virus-neutralizing antibodies. Previously, we have synthesized large amounts of Johnson grass mosaic virus (JGMV) coat protein (CP) in Escherichia coli and have shown that it autoassembled to form virus-like particles (VLPs). The envelope (E) protein of JEV contains the virus-neutralization epitopes. Four peptides from different locations within JEV E protein were chosen, and these were fused to JGMV CP by recombinant DNA methods. The fusion protein autoassembled to form VLPs that could be purified by sucrose gradient centrifugation. Immunization of mice with the recombinant VLPs containing JEV peptide sequences induced anti-peptide and anti-JEV antibodies. A 27-amino-acid peptide containing amino acids 373 to 399 from JEV E protein, present on JGMV VLPs, induced virus-neutralizing antibodies. Importantly, these antibodies were obtained without the use of an adjuvant. The immunized mice showed significant protection against a lethal JEV challenge.