The fusion site of envelope fragments from each serotype of Dengue virus in the P64k protein, influence some parameters of the resulting chimeric constructs

Anti-Flavivirus Vaccines: Review of the Present Situation and Perspectives of Subunit Vaccines Produced in Escherichia coli

This article aims to review the present status of anti-flavivirus subunit vaccines, both those at the experimental stage and those already available for clinical use. Aspects regarding development of vaccines to Yellow Fever virus, (YFV), Dengue virus (DENV), West Nile virus (WNV), Zika virus (ZIKV), and Japanese encephalitis virus (JEV) are highlighted, with particular emphasis on purified recombinant proteins generated in bacterial cells. Currently licensed anti-flavivirus vaccines are based on inactivated, attenuated, or virus-vector vaccines. However, technological advances in the generation of recombinant antigens with preserved structural and immunological determinants reveal new possibilities for the development of recombinant protein-based vaccine formulations for clinical testing. Furthermore, novel proposals for multi-epitope vaccines and the discovery of new adjuvants and delivery systems that enhance and/or modulate immune responses can pave the way for the development of successful subunit vaccines. Nonetheless, advances in this field require high investments that will probably not raise interest from private pharmaceutical companies and, therefore, will require support by international philanthropic organizations and governments of the countries more severely stricken by these viruses.

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.

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.

The two component adjuvant IC31® potentiates the protective immunity induced by a dengue 2 recombinant fusion protein in mice

Here we evaluated the suitability of the synthetic adjuvant IC31® to potentiate the protective capacity of PD5 protein (domain III of the envelope protein of dengue 2 virus fused to the carrier protein P64k). Unlike Alum, PD5 mixed with IC31® induced complete protection against virus challenge in mice and increased IFN-γ secretion after in vitro re-stimulation. The induced antibody response was highly specific to the homologous serotype and showed both IgG1 and IgG2a subtypes. IC31® is a promising adjuvant for PD5 recombinant protein based vaccination against dengue. Future work should address the suitability of PD5/IC31® formulations in non-human primate models.

A tetravalent recombinant dengue domain III protein vaccine stimulates neutralizing and enhancing antibodies in mice

Dengue viruses co-circulate as four serologically distinct viruses (DENV1-4) that commonly infect individuals sequentially. Current DENV candidate vaccines incorporate the entire virion envelope E protein (E) ectodomain thereby stimulating both DENV serotype-specific and cross-reactive antibodies. Because the latter may enhance naturally acquired infection, such vaccine formulations must be tetravalent. We evaluated the neutralizing and enhancing antibody response to E domain III (dIII) proteins, in which serotype-specific neutralizing determinants are concentrated. Mice immunized with insect cell-secreted recombinant DENV-dIII proteins individually, and in tetravalent combination, produced serotype-specific IgG1 neutralizing antibodies that nevertheless exhibited measurable DENV enhancing activity in FcγR-bearing cells. Vaccine strategies directed to DENV-dIII-targeted neutralizing antibody production remain attractive but will likely require further modifications to induce safe, protective immunity.

Nucleocapsid-like particles of dengue-2 virus enhance the immune response against a recombinant protein of dengue-4 virus

In this study, we evaluate in mice a novel formulation containing nucleocapsid-like particles of dengue-2 virus (recNLP) co-immunized with a chimeric protein composed of the dengue-4 envelope domain III fused twice within the meningococcal P64k protein of Neisseria meningitidis (PD24). The animals receiving the PD24-recNLP mixture showed the highest levels of antiviral antibodies. Similar results were obtained for IFNγ secretion levels, indicating a functional Th1 cellular response. Consistently, the percentage of mice surviving after viral challenge was significantly higher for those immunized with the mixture than for those inoculated with PD24 protein alone. In addition, in vivo depletion experiments demonstrated the decisive role of CD4(+) and CD8(+) cells in the protection conferred by immunization with PD24-recNLP. In conclusion, this report demonstrates for the first time the adjuvant capacity of dengue-2 virus recNLP. Additionally, the evidence presented highlights the potential of these particles for enhancing the immune response against heterologous recombinant proteins.

Domain III of the envelope protein as a dengue vaccine target

A dengue vaccine should induce long-lasting, simultaneous protection to the four dengue viruses while avoiding the immune enhancement of viral infection. Domain III of the dengue envelope protein has been implicated in receptor binding, and is also the target of specific neutralizing antibodies. Domain III has emerged as a promising region for a subunit vaccine candidate. Here, we review the current state of knowledge on vaccine candidates based on domain III. Due to the results obtained concerning the immune response and protection in mice and monkeys, particular attention is paid to the chimeric protein domain III fused to p64k of Neisseria meningitidis.

Antibodies induced by dengue virus type 1 and 2 envelope domain III recombinant proteins in monkeys neutralize strains with different genotypes

In the present work, we evaluated the neutralizing capacity of the antibodies induced by dengue virus type 1 and 2 envelope domain III recombinant proteins in monkeys against strains of different dengue virus type 1 and 2 genotypes. Here we demonstrated that dengue virus type 1 and 2 recombinant proteins induced high titers of neutralizing antibodies against different genotype strains.

Characterization of the interaction of domain III of the envelope protein of dengue virus with putative receptors from CHO cells

Domain III (DIII) of the envelope protein of dengue virus (DENV) contains structural determinants for the interaction with cellular receptors. In the present study a solid phase assay and recombinant fusion proteins containing DENV-DIII of serotypes 1 and 2 were used to study structural features of the interaction of the envelope protein with putative receptors present in the microsomal fraction of CHO cells. Recombinant fusion proteins showed specific interaction with proteins present in the microsomal fraction. Binding of the fusion proteins across the pH range of 5.5-8.0 resembled that of virus particles, peaking at pH 6.0. This suggests that the interaction of DIII with cell receptor(s) is strengthened at endosomal pH. The effect of reduction and carbamidomethylation of cysteine residues on the binding to the microsomal fraction and in their recognition by antibodies suggests that the region of DIII that is interacting with putative receptor(s) overlaps only partially with a dominant epitope of the antibody response. The analysis of the residue conservation profile indicates that the surface of DIII is composed typically of specific sub-complex residues with an increased representation of specific type/subtype residues found at the surface that closely correlates with the dominant neutralizing epitope.

Anamnestic antibody response after viral challenge in monkeys immunized with dengue 2 recombinant fusion proteins

The suitability of dengue 2 envelope domain III recombinant fusion proteins [(fusion (PD5) and insertion (PD3) variants)] for inducing functional antibodies and a protective immune response in nonhuman primates has been reported. However, the evaluation of the antibody response after immunization did not correlate with the protection data as measured by viremia detection. Here, we characterized the anamnestic immune response after viral challenge in monkeys immunized with the dengue 2 recombinant proteins in an attempt to define correlates of protection useful for vaccine studies. Monkeys immunized with PD5 (most protected group) exhibited an earlier increase in the anti-DENV-2 IgM response after challenge compared to control animals. Hemagglutination-inhibiting (HAI) antibodies were increased significantly earlier in PD5-immunized animals compared to those immunized with PD3. The fully protected monkeys showed the earliest HAI antibody response. These results underline the usefulness of the anamnestic antibody response for supporting protection data. The induction of an early HAI and IgM antibody response after challenge suggest a protective role against dengue virus (DENV) infection in monkeys, supporting their use as correlates of protection in vaccine studies.

Expression in Pichia pastoris and immunological evaluation of a truncated Dengue envelope protein

Among the Dengue virus structural proteins, the Envelope glycoprotein is the most important because of its antigenic characteristics. In this work, the E protein from Dengue-2 virus truncated at the C-terminus region was successfully expressed in Pichia pastoris. The E2trunc gene was cloned under the AOX1 promoter from P. pastoris and the signal peptide of the sucrose invertase gene from Saccharomyces cerevisiae. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of expression revealed the presence of a protein with the expected size, which was completely associated to the insoluble fraction after cellular disruption. The recombinant N-glycosylated protein reacted with two conformational antibodies against Dengue-2, indicating a proper folding of it. In addition, it was able to induce antiviral antibodies after mice immunization.

Amino acid changes in the recombinant Dengue 3 Envelope domain III determine its antigenicity and immunogenicity in mice

The immunogenicity of the Envelope fragment from amino acid 284 to 426 of Dengue viruses, obtained as fusion proteins with P64k in Escherichia coli, has been previously tested by our group. Here, we studied two fusion proteins with P64k carrying the Envelope fragment from two strains of Dengue 3: H87 prototype strain (PD9) and an isolate from the Nicaragua 1994 outbreak (PD18). Sequence comparison of the Dengue Envelope fragments showed four amino acid differences. Only PD18 reacted with human antisera and induced a higher functional immune response in mice than PD9. Moreover, mice immunized with PD18 were less susceptible to Dengue 3 administered intracerebrally than those immunized with PD9. The results reveal that not all sequences of the Dengue Envelope fragment, at least in the context of P64k, are antigenic and generate a functional immune response against the native virus. This finding has direct implications for the design of vaccines based on fragments of the Envelope protein.

Cysteine mediated multimerization of a recombinant dengue E fragment fused to the P64k protein following immobilized metal ion affinity chromatography

A fragment of the Envelope protein of Dengue 2 virus encoding the amino acid (aa) 286-426 was fused to the P64k protein from Neisseria meningitidis. The hybrid gene (PD5) was expressed in Escherichia coli. The influence of using immobilized metal ion affinity chromatography (IMAC) in the purification process of PD5 was examined. After the elution, PD5 protein formed aggregates of high molecular weight depending on disulfide-bonds. The study of different conditions affecting the redox potential in the system revealed the influence of the copper ions on the multimerization of the protein, whereas metals with minor redox potential-for instance, zinc or nickel ions-did not cause this effect. It was also demonstrated that cysteines involved in this process belonged to the P64k protein. Finally, a PD5 purification process was established reaching a 85% of purity using the Zn(2+) as metal ion in the IMAC. This is a very useful finding due to the wide use of P64k as a carrier protein and the advantages of the IMAC as a chromatographic process.