Recombinant nucleocapsid-like particles from dengue-2 induce functional serotype-specific cell-mediated immunity in mice

Protective Immunity to Dengue Virus Induced by DNA Vaccines Encoding Nonstructural Proteins in a Lethal Challenge Immunocompetent Mouse Model

Dengue virus represents the main arbovirus affecting humans, but there are no effective drugs or available worldwide licensed vaccine formulations capable of conferring full protection against the infection. Experimental studies and results generated after the release of the licensed anti-DENV vaccine demonstrated that induction of high-titer neutralizing antibodies does not represent the sole protection correlate and that, indeed, T cell-based immune responses plays a relevant role in the establishment of an immune protective state. In this context, this study aimed to further demonstrate protective features of immune responses elicited in immunocompetent C57BL/6 mice immunized with three plasmids encoding DENV2 nonstructural proteins (NS1, NS3, and NS5), which were subsequently challenged with a DENV2 strain naturally capable of inducing lethal encephalitis in immunocompetent mouse strains. The animals were immunized intramuscularly with the DNA vaccine mix and complete protection was observed among vaccinated mice. Vaccine induced protection correlated with the cytokine profiles expressed by spleen cells and brain-infiltrating mononuclear cells. The results confirm the pivotal role of cellular immune responses targeting nonstructural DENV proteins and validate the experimental model based on a DENV2 strain capable of infecting and killing immunocompetent mice as a tool for the evaluation of protective immunity induced by anti-DENV vaccines.

Formation of Virus-Like Particles of the Dengue Virus Serotype 2 Expressed in Silkworm Larvae

To explore virus-like particles formation of dengue virus serotype type 2 (DENV-2) structural proteins of, C, prM, E were expressed in silkworm larvae using recombinant Bombyx mori nucleopolyhedroviruses (BmNPV). Each recombinant BmNPV bacmid coding the 2C-prM-E polypeptide and E protein fused with the signal peptide of bombyxin from B. mori was injected into silkworm larvae. The expressed proteins were collected from hemolymph and fat body, and purified using affinity chromatography. E protein was observed at 55 kDa. The DENV virus-like particles (DENV-LPs) with a diameter approximately 35 nm was observed using transmission electron microscopy (TEM) and immunogold-labelling TEM analysis. The binding of each partially purified proteins to heparin, one of receptors for DENV was confirmed. DENV-LPs were secreted in silkworm larval hemolymph even still low amount, but the E protein and heparin binding function were confirmed.

The Development of Peptide-based Antimicrobial Agents against Dengue Virus

Dengue fever has become an imminent threat to international public health because of global warming and climate change. The World Health Organization proclaimed that more than 50% of the world’s population is at risk of dengue virus (DENV) infection. Therefore, developing a clinically ap-proved vaccine and effective therapeutic remedy for treating dengue fever is imperative. Peptide drug de-velopment has become a novel pharmaceutical research field. This article reviews various peptides-based antimicrobial agents targeting three pathways involved in the DENV lifecycle. Specifically, they are peptide vaccines from immunomodulation, peptide drugs that inhibit virus entry, and peptide drugs that interfere with viral replication. Many antiviral peptide studies against DENV have been conducted in animal model trials, and progression to clinical trials for these promising peptide drugs is anticipated.

Production and Biomedical Application of Flavivirus-like Particles

Many viruses belonging to the Flaviviridae family are transmitted by invertebrate vectors. Among those transmitted by mosquitos, there are many human pathogens of great medical importance, such as Japanese encephalitis virus, West Nile virus, dengue virus, Zika virus, or yellow fever virus. Millions of people contract mosquito-borne diseases each year, leading to thousands of deaths. Co-circulation of genetically similar flaviviruses in the same areas result in the generation of crossreactive antibodies, which is of serious concern for the development of effective vaccines and diagnostic tests. This review provides comprehensive insight into the potential use of virus-like particles as safe and effective antigens in both diagnostics tests, as well as in the development of vaccines against several mosquito-borne flaviviruses.

Aiming at the heart: the capsid protein of dengue virus as a vaccine candidate

INTRODUCTION

Dengue fever remains as a health problem worldwide. Although Dengvaxia®, was registered in several countries, the results after the immunization of people suggest an increase of risk in non-immune persons and children younger than 9 years old. No other vaccine is registered so far, thus the development of a safe and effective vaccine continues to be a priority for the WHO and the scientific community.

AREAS COVERED

This work reviews the structural and antigenic properties of the capsid protein of Dengue virus, along with results of studies performed to assess the immunogenicity and protective capacity in animals of vaccine candidates based on this protein.

EXPERT OPINION

The generation of a memory cellular immune response alone, after vaccination against Dengue virus, could be advantageous, as there would not be risk of increasing viral infectivity through sub-neutralizing antibodies. However, it is improbable to achieving sterilizing immunity. In this scenario, an infection could stablished but without the appearance of the severe disease. The cell-mediated immunity should keep the virus at bay. The capsid protein induces a protective immune response in animals without the induction of virus-binding antibodies. Vaccine candidates based on this protein could be an attractive strategy to induce protection against the severe Dengue disease.

Molecular engineering and plant expression of an immunoglobulin heavy chain scaffold for delivery of a dengue vaccine candidate

In order to enhance vaccine uptake by the immune cells in vivo, molecular engineering approach was employed to construct a polymeric immunoglobulin G scaffold (PIGS) that incorporates multiple copies of an antigen and targets the Fc gamma receptors on antigen-presenting cells. These self-adjuvanting immunogens were tested in the context of dengue infection, for which there is currently no globally licensed vaccine yet. Thus, the consensus domain III sequence (cEDIII) of dengue glycoprotein E was incorporated into PIGS and expressed in both tobacco plants and Chinese Ovary Hamster cells. Purified mouse and human cEDIII-PIGS were fractionated by HPLC into low and high molecular weight forms, corresponding to monomers, dimers and polymers. cEDIII-PIGS were shown to retain important Fc receptor functions associated with immunoglobulins, including binding to C1q component of the complement and the low affinity Fcγ receptor II, as well as to macrophage cells in vitro. These molecules were shown to be immunogenic in mice, with or without an adjuvant, inducing a high level IgG antibody response which showed a neutralizing potential against the dengue virus serotype 2. The cEDIII-PIGS also induced a significant cellular immune response, IFN-γ production and polyfunctional T cells in both the CD4+ and CD8+ compartments. This proof-of-principle study shows that the potent antibody Fc-mediated cellular functions can be harnessed to improve vaccine design, underscoring the potential of this technology to induce and modulate a broad-ranging immune response.

The tetravalent formulation of domain III-capsid proteins recalls memory B- and T-cell responses induced in monkeys by an experimental dengue virus infection

Tetra DIIIC is a vaccine candidate against dengue virus (DENV) composed by four chimeric proteins that fuse the domain III of the envelope protein of each virus to the corresponding capsid protein. Containing B- and T-cell epitopes, these proteins form aggregates after the incubation with an immunostimulatory oligodeoxynucleotide, and their tetravalent formulation induces neutralizing antibodies and cellular immune response in mice and monkeys. Also, Tetra DIIIC protects mice after challenge with each DENV, and the monovalent formulation obtained from DENV-2 protects monkeys upon homologous viral challenge. However, in the last years, new evidences have arisen regarding domain III of DENV envelope protein as irrelevant target for neutralizing antibodies in humans. Nevertheless, vaccination with domain III induces a neutralizing antibody response that confers protection against re-infection. In addition, it has been demonstrated that the induction of a cellular immune response is essential to protect during the infection. This response can also avoid severe manifestations of dengue disease, associated to the antibody-dependent enhancement of the infection. In this study, we observed that Tetra DIIIC was able to boost the antiviral and neutralizing antibody responses previously generated in monkeys during an experimental DENV infection, demonstrating that domain III is targeted by B cells during the viral infection. Additionally, Tetra DIIIC successfully boosted the cellular immune response generated by the viruses, probably against T-cells epitopes in the capsid proteins. These results highlight the functionality of Tetra DIIIC as a vaccine candidate against DENV.

A Tetravalent Formulation Based on Recombinant Nucleocapsid-like Particles from Dengue Viruses Induces a Functional Immune Response in Mice and Monkeys

Despite the considerable effort that has been invested in elucidating the mechanisms of protection and immunopathogenesis associated with dengue virus infections, a reliable correlate of protection against the disease remains to be found. Neutralizing Abs, long considered the prime component of a protective response, can exacerbate disease severity when present at subprotective levels, and a growing body of data is challenging the notion that their titers are positively correlated with disease protection. Consequently, the protective role of cell-mediated immunity in the control of dengue infections has begun to be studied. Although earlier research implicated cellular immunity in dengue immunopathogenesis, a wealth of newer data demonstrated that multifunctional CD8⁺ T cell responses are instrumental for avoiding the more severe manifestations of dengue disease. In this article, we describe a new tetravalent vaccine candidate based on recombinant dengue virus capsid proteins, efficiently produced in Escherichia coli and purified using a single ion-exchange chromatography step. After aggregation to form nucleocapsid-like particles upon incubation with an oligodeoxynucleotide containing immunostimulatory CpG motifs, these Ags induce, in mice and monkeys, an IFN-γ-secreting cell response that significantly reduces viral load after challenge without the contribution of antiviral Abs. Therefore, this new vaccine candidate may not carry the risk for disease enhancement associated with Ab-based formulations.

Dengue encephalitis-associated immunopathology in the mouse model: Implications for vaccine developers and antigens inducer of cellular immune response

Despite the many efforts made by the scientific community in the development of vaccine candidates against dengue virus (DENV), no vaccine has been licensed up to date. Although the immunopathogenesis associated to the disease is a key factor to take into account by vaccine developers, the lack of animal models that reproduce the clinical signs of the disease has hampered the vaccine progress. Non-human primates support viral replication, but they are very expensive and do not show signs of disease. Immunocompromised mice develop viremia and some signs of the disease; however, they are not valuable for vaccine testing. Nowadays, immunocompetent mice are the most used model to evaluate the immunogenicity of vaccine candidates. These animals are resistant to DENV infection; therefore, the intracranial inoculation with neuroadapted virus, which provokes viral encephalitis, represents an alternative to evaluate the protective capacity of vaccine candidates. Previous results have demonstrated the crucial role of cellular immune response in the protection induced by the virus and vaccine candidates in this mouse encephalitis model. However, in the present work we are proposing that the magnitude of the cell-mediated immunity and the inflammatory response generated by the vaccine can modulate the survival rate after viral challenge. We observed that the intracranial challenge of naïve mice with DENV-2 induces the recruitment of immune cells that contribute to the reduction of viral load, but does not increase the survival rate. On the contrary, animals treated with cyclophosphamide, an immunosuppressive drug that affects proliferating lymphocytes, had a higher viral load but a better survival rate than untreated animals. These results suggest that the immune system is playing an immunopathogenic role in this model and the survival rate may not be a suitable endpoint in the evaluation of vaccine candidates based on antigens that induce a strong cellular immune response.

Key concepts, strategies, and challenges in dengue vaccine development: an opportunity for sub-unit candidates?

Despite 70 years of research that has intensified in the past decade, a safe and efficacious dengue vaccine has yet to be available. In addition to the expected challenges such as identifying immune correlates of protection, the dengue vaccine field has faced additional hurdles including the necessity to design a tetravalent formulation and the risk of antibody-mediated disease enhancement. Nevertheless, tetravalent live attenuated vaccine candidates have reached efficacy trials and demonstrated some benefit, despite imbalanced immunogenicity and incomplete protection against the four serotypes. Meanwhile, the development of sub-unit dengue vaccines has gained momentum. As the target of most of the neutralizing antibodies so far reported, the virus envelope E protein has been the focus of much effort and represents the leading dengue sub-unit vaccine candidate. However, its notorious poor immunogenicity has prompted the development of innovative approaches to make E-derived constructs part of the second generation dengue vaccines portfolio.

Analysis of cell-mediated immune responses in support of dengue vaccine development efforts

Dengue vaccine development has made significant strides, but a better understanding of how vaccine-induced immune responses correlate with vaccine efficacy can greatly accelerate development, testing, and deployment as well as ameliorate potential risks and safety concerns. Advances in basic immunology knowledge and techniques have already improved our understanding of cell-mediated immunity of natural dengue virus infection and vaccination. We conclude that the evidence base is adequate to argue for inclusion of assessments of cell-mediated immunity as part of clinical trials of dengue vaccines, although further research to identify useful correlates of protective immunity is needed.

A novel tetravalent formulation combining the four aggregated domain III-capsid proteins from dengue viruses induces a functional immune response in mice and monkeys

Our group developed a subunit vaccine candidate against dengue virus based on two different viral regions: the domain III of the envelope protein and the capsid protein. The novel chimeric protein from dengue-2 virus [domain III-capsid (DIIIC-2)], when presented as aggregated incorporating oligodeoxynucleotides, induced anti-viral and neutralizing antibodies, a cellular immune response and conferred significant protection to mice and monkeys. The remaining constructs were already obtained and properly characterized. Based on this evidence, this work was aimed at assessing the immune response in mice of the chimeric proteins DIIIC of each serotype, as monovalent and tetravalent formulations. Here, we demonstrated the immunogenicity of each protein in terms of humoral and cell-mediated immunity, without antigen competition on the mixture forming the formulation tetra DIIIC. Accordingly, significant protection was afforded as measured by the limited viral load in the mouse encephalitis model. The assessment of the tetravalent formulation in non-human primates was also conducted. In this animal model, it was demonstrated that the formulation induced neutralizing antibodies and memory cell-mediated immune response with IFN-γ-secreting and cytotoxic capacity, regardless the route of immunization used. Taken together, we can assert that the tetravalent formulation of DIIIC proteins constitutes a promising vaccine candidate against dengue virus, and propose it for further efficacy experiments in monkeys or in the dengue human infection model, as it has been recently proposed.

Tetravalent dengue DIIIC protein together with alum and ODN elicits a Th1 response and neutralizing antibodies in mice

Dengue disease is a global challenge for healthcare systems particularly during outbreaks, and millions of dollars are spent every year for vector control. An efficient and safe vaccine that is cost-effective could resolve the burden that dengue virus imposes on affected countries. We describe here the immunogenicity of a tetravalent formulation of a recombinant fusion protein consisting of E domain III and the capsid protein of dengue serotypes 1-4 (Tetra DIIIC). E domain III is an epitope for efficient neutralizing antibodies while the capsid protein contains T cell epitopes. Besides combining B and T cell epitopes, Tetra DIIIC is highly immunogenic due to its aggregate form and a two-component adjuvant. Following previous studies assessing the monovalent DIIIC formulations, we addressed here the quality and breadth of the T cell- and antibody response of Tetra DIIIC in mice. Tetra DIIIC induced a Th1-type response against all four DENV serotypes and dengue-specific antibodies were predominantly IgG1 and IgG2a and neutralizing, while the induction of neutralizing antibodies was dependent on IFN signaling. Importantly, the Th1 and IgG1/IgG2a profile of the DIIIC vaccine approach is similar to an efficient natural anti-dengue response.

The protein DIIIC-2, aggregated with a specific oligodeoxynucleotide and adjuvanted in alum, protects mice and monkeys against DENV-2

Previously, we reported the ability of the chimeric protein DIIIC-2 (domain III of the dengue envelope protein fused to the capsid protein of dengue-2 virus), to induce immunity and protection in mice, when it is highly aggregated with a non-defined oligodeoxynucleotide (ODN) and adjuvanted in alum. In this work, three different defined ODNs were studied as aggregating agents. Our results suggest that the nature of the ODN influences the capacity of protein DIIIC-2 to activate cell-mediated immunity in mice. Consequently, the ODN 39M was selected to perform further experiments in mice and nonhuman primates. Mice receiving the preparation 39M-DIIIC-2 were solidly protected against dengue virus (DENV) challenge. Moreover, monkeys immunized with the same preparation developed neutralizing antibodies, as measured by four different neutralization tests varying the virus strains and the cell lines used. Two of the immunized monkeys were completely protected against challenge, whereas the third animal had a single day of low-titer viremia. This is the first work describing the induction of short-term protection in monkeys by a formulation that is suitable for human use combining a recombinant protein from DENV with alum.

Recombinant dengue 2 virus NS3 protein conserves structural antigenic and immunological properties relevant for dengue vaccine design

The NS3 protein is a multifunctional non-structural protein of flaviviruses implicated in the polyprotein processing. The predominance of cytotoxic T cell lymphocytes epitopes on the NS3 protein suggests a protective role of this protein in limiting virus replication. In this work, we studied the antigenicity and immunogenicity of a recombinant NS3 protein of the Dengue virus 2. The full-length NS3 gene was cloned and expressed as a His-tagged fusion protein in Escherichia coli. The pNS3 protein was purified by two chromatography steps. The recombinant NS3 protein was recognized by anti-protease NS3 polyclonal antibody and anti-DENV2 HMAF by Western Blot. This purified protein was able to stimulate the secretion of high levels of gamma interferon and low levels of interleukin-10 and tumor necrosis factor-α in mice splenocytes, suggesting a predominantly Th-1-type T cell response. Immunized BALB/c mice with the purified NS3 protein showed a strong induction of anti-NS3 IgG antibodies, essentially IgG2b, as determined by ELISA. Immunized mice sera with recombinant NS3 protein showed specific recognition of native dengue protein by Western blotting and immunofluorescence techniques. The successfully purified recombinant protein was able to preserv the structural and antigenic determinants of the native dengue protein. The antigenicity shown by the recombinant NS3 protein suggests its possible inclusion into future DENV vaccine preparations.

A tetravalent dengue vaccine containing a mix of domain III-P64k and domain III-capsid proteins induces a protective response in mice

Recombinant fusion proteins containing domain III of the dengue virus envelope protein fused to the P64k protein from Neisseria meningitidis and domain III of dengue virus type 2 (D2) fused to the capsid protein of this serotype were immunogenic and conferred protection in mice against lethal challenge, as reported previously. Combining the domain III-P64k recombinant proteins of dengue virus types 1, 3 and 4 (D1, D3, and D4) with the domain III-capsid protein from D2, we obtained a novel tetravalent formulation containing different antigens. Here, the IgG and neutralizing antibody response, the cellular immune response, and the protective capacity against lethal challenge in mice immunized with this tetravalent formulation were evaluated. The neutralizing antibody response obtained against D1, D2 and D3, together with the high levels of IFNγ secretion induced after stimulation with the four dengue serotypes, supports the strategy of using a new tetravalent formulation containing domain III of the envelope protein fused to the capsid protein of each dengue virus serotype.

Understanding the dengue viruses and progress towards their control

Traditionally, the four dengue virus serotypes have been associated with fever, rash, and the more severe forms, haemorrhagic fever and shock syndrome. As our knowledge as well as understanding of these viruses increases, we now recognise not only that they are causing increasing numbers of human infections but also that they may cause neurological and other clinical complications, with sequelae or fatal consequences. In this review we attempt to highlight some of these features in the context of dengue virus pathogenesis. We also examine some of the efforts currently underway to control this "scourge" of the tropical and subtropical world.

Total chemical synthesis of dengue 2 virus capsid protein via native chemical ligation: role of the conserved salt-bridge

The dengue capsid protein C is a highly basic alpha-helical protein of ~100 amino acid residues that forms an emphipathic homodimer to encapsidate the viral genome and to interact with viral membranes. The solution structure of dengue 2 capsid protein C (DEN2C) has been determined by NMR spectroscopy, revealing a large dimer interface formed almost exclusively by hydrophobic residues. The only acidic residue (Glu87) conserved in the capsid proteins of all four serotypes of dengue virus forms a salt bridge with the side chains of Lys45 and Arg55'. To understand the structural and functional significance of this conserved salt bridge, we chemically synthesized an N-terminally truncated form of DEN2C ((WT)DEN2C) and its salt bridge-void analog (E87A)DEN2C using the native chemical ligation technique developed by Kent and colleagues. Comparative biochemical and biophysical studies of these two synthetic proteins using circular dichroism spectroscopy, fluorescence polarization, protein thermal denaturation, and proteolytic susceptibility assay demonstrated that the conserved salt bridge contributed to DEN2C dimerization and stability as well as its resistance to proteolytic degradation. Our work provided insight into the role of a fully conserved structural element of the dengue capsid protein C and paved the way for additional functional studies of this important viral protein.

A vaccine formulation consisting of nucleocapsid-like particles from Dengue-2 and the fusion protein P64k-domain III from Dengue-1 induces a protective immune response against the homologous serotypes in mice

In previous studies we reported the cloning, expression and purification of the capsid protein from Dengue-2 virus. Subsequently, we described an in vitro-assembly process for the capsid protein, which resulted in nucleocapsid-like particles (recNLPs) that induced functional cell-mediated immunity and protection in mice. Moreover, our group reported the evaluation in non-human primates of the fusion protein P64k-domain III from Dengue-1 (PD10). This protein proved to be immunogenic and protective when Freund's adjuvant, but not alum, was used. Based on the previously demonstrated capacity of recNLPs to potentiate the immunogenicity of heterologous proteins, in this study we assess the immune response elicited by the formulation PD10-recNLPs-alum and its protective capacity against Dengue-1 and Dengue-2 virus. As expected, the humoral immune response was mainly directed against Dengue-1, while high levels of IFN-γ secretion were detected after stimulation with Dengue-1 and Dengue-2. Consistently, animals immunized with the bivalent formulation were significantly protected against challenge with either Dengue serotype. In conclusion, this report describes a novel formulation based on recombinant proteins and alum, which is protective against Dengue-1 and Dengue-2 in mice.

Purified and highly aggregated chimeric protein DIIIC-2 induces a functional immune response in mice against dengue 2 virus

It was previously reported that DIIIC-2 (a fusion protein composed of domain III of the envelope protein and the capsid protein from dengue 2 virus), as an aggregate antigen from a partially purified preparation, induced a functional protective immune response against dengue 2 virus in the mouse encephalitis model. In the present work, a purification procedure was developed for DIIIC-2, and soluble and aggregated fractions of the purified protein were characterized and evaluated in mice. The purification process rendered a protein preparation of 91 % purity, and the remaining 9 % consisted of fragments and aggregates of the same recombinant protein. After the in vitro aggregation process, upon addition of oligodeoxynucleotides, 80 % of the protein formed aggregates, whereas 20 % remained as soluble protein. An immunological evaluation revealed the proper immunogenicity of the aggregated purified protein in terms of induction of antiviral and neutralizing antibodies, cell-mediated immunity and protection upon dengue 2 virus challenge in the mouse encephalitis model. Based on these results, we can assert that the purified protein DIIIC-2 is functional and could be used for further scalable steps and preclinical studies in non-human primates.