Evidence for antigen production in muscles by dengue and Japanese encephalitis DNA vaccines and a relation to their immunogenicity in mice

Enhanced immunogenicity and protective efficacy in mice following a Zika DNA vaccine designed by modulation of membrane-anchoring regions and its association to adjuvants

Zika virus (ZIKV) is a re-emerging pathogen with high morbidity associated to congenital infection. Despite the scientific advances since the last outbreak in the Americas, there are no approved specific treatment or vaccines. As the development of an effective prophylactic approach remains unaddressed, DNA vaccines surge as a powerful and attractive candidate due to the efficacy of sequence optimization in achieving strong immune response. In this study, we developed four DNA vaccine constructs encoding the ZIKV prM/M (pre-membrane/membrane) and E (envelope) proteins in conjunction with molecular adjuvants. The DNA vaccine candidate (called ZK_ΔSTP), where the entire membrane-anchoring regions were completely removed, was far more immunogenic compared to their counterparts. Furthermore, inclusion of the tPA-SP leader sequence led to high expression and secretion of the target vaccine antigens, therefore contributing to adequate B cell stimulation. The ZK_ΔSTP vaccine induced high cellular and humoral response in C57BL/6 adult mice, which included high neutralizing antibody titers and the generation of germinal center B cells. Administration of ZK-ΔSTP incorporating aluminum hydroxide (Alum) adjuvant led to sustained neutralizing response. In consistency with the high and long-term protective response, ZK_ΔSTP+Alum protected adult mice upon viral challenge. Collectively, the ZK_ΔSTP+Alum vaccine formulation advances the understanding of the requirements for a successful and protective vaccine against flaviviruses and is worthy of further translational studies.

Antibody-dependent enhancement representing in vitro infective progeny virus titer correlates with the viremia level in dengue patients

Dengue virus (DENV) causes dengue fever (DF) and dengue hemorrhagic fever in humans. Some DF patients suddenly develop severe symptoms around the defervescent period. Although the pathogenic mechanism of the severe symptoms has not been fully elucidated, the viremia level in the early phase has been shown to correlate with the disease severity. One of the hypotheses is that a phenomenon called antibody-dependent enhancement (ADE) of infection leads to high level of viremia. To examine the plausibility of this hypothesis, we examined the relationship between in vitro ADE activity and in vivo viral load quantity in six patients with dengue diseases. Blood samples were collected at multiple time points between the acute and defervescent phases, and the balance between neutralizing and enhancing activities against the autologous and prototype viruses was examined. As the antibody levels against DENV were rapidly increased, ADE activity was decreased over time or partially maintained against some viruses at low serum dilution. In addition, positive correlations were observed between ADE activity representing in vitro progeny virus production and viremia levels in patient plasma samples. The measurement of ADE activity in dengue-seropositive samples may help to predict the level of viral load in the subsequent DENV infection.

DENV-3 precursor membrane (prM) glycoprotein enhances E protein immunogenicity and confers protection against DENV-2 infections in a murine model

To improve a DNA vaccine containing the truncated dengue virus serotype 2 (DENV-2) envelope (E) protein and evaluate the influence of precursor membrane (prM) glycoprotein polymorphism on E protein immunogenicity, two vaccine candidates have been constructed by upstream insertion of the DENV-2 and DENV-3 prM genes into the DENV-2 E gene, named pCID2EtD2prM and pCID2EtD3prM, respectively. Both constructs were able to induce antibody production, which were neutralizing against DENV-2 in a murine model. Splenocytes of immunized groups, when challenged with virus, demonstrated Th1 cytokine pattern and proliferation, in addition to the increase of specific T cells. Vaccine candidates pCID2EtD2prM and pCID2EtD3prM confer 70% and 90% protection against DENV-2, respectively. The pCID2EtD3prM plasmid conferred only 40% protection in the lethal challenge with DENV-2. The results demonstrate that DENV-3 prM has a greater influence on the immunogenicity of the E protein and, probably due to its role as a chaperone, these results may be related to the correct folding and, consequently, an increase in the presentation efficiency of produced transcripts.

Title: Gene transfer by pyro-drive jet injector is a novel therapeutic approach for muscle diseases

The angiogenic gene therapy is an attractive approach for the treatment of ischemic muscle diseases, including peripheral arterial disease and ischemic heart diseases. Although a variety of gene transfer methods have been developed, the efficiency of gene transfer is still limited. We have been developing the needleless high-energy bioinjector device, Pyro-drive Jet Injector (PJI), based on pyrotechnics using a combination of ignition powder and gunpowder, however, the utility of PJI in gene transfer into muscle tissues remains unclear. pcDNA3.1 plasmid containing Flag was injected to the thigh muscles of C57BL/6J mice using PJI or needle, as a control. Histological analysis demonstrated that the protein expression of Flag was observed in a wider range in PJI group than in needle group. To assess the validity of PJI for gene therapy, pcDNA3.1-human fibroblast growth factor 2 (FGF2), which has angiogenic activity and tissue protective properties, was injected into the ischemic thigh muscles with PJI or needle. ELISA assay revealed that the protein expression of FGF2 was increased in the thigh muscle tissues by PJI-mediated gene delivery. Significantly, histological analyses revealed that muscle fiber cross-sectional area and the number of endothelial marker CD31 (+) cells was increased in ischemic hind-limb tissues of the PJI-FGF2 group but not in those of needle-FGF2 group. To expand the applicability of the PJI-mediated gene transfer, pcDNA3.1-venus plasmid was injected into murine hearts with PJI or needle. PJI method was successful in gene transfer into murine hearts, especially into cardiomyocytes, with high efficiency when compared to needle method. Collectively, the non-needle, non-liposomal and non-viral gene transfer by PJI could be a novel therapeutic approach for muscle diseases.

Dengue Virus and Vaccines: How Can DNA Immunization Contribute to This Challenge?

Dengue infections still have a tremendous impact on public health systems in most countries in tropical and subtropical regions. The disease is systemic and dynamic with broad range of manifestations, varying from mild symptoms to severe dengue (Dengue Hemorrhagic Fever and Dengue Shock Syndrome). The only licensed tetravalent dengue vaccine, Dengvaxia, is a chimeric yellow fever virus with prM and E genes from the different dengue serotypes. However, recent results indicated that seronegative individuals became more susceptible to develop severe dengue when infected after vaccination, and now WHO recommends vaccination only to dengue seropositive people. One possibility to explain these data is the lack of robust T-cell responses and antibody-dependent enhancement of virus replication in vaccinated people. On the other hand, DNA vaccines are excellent inducers of T-cell responses in experimental animals and it can also elicit antibody production. Clinical trials with DNA vaccines have improved and shown promising results regarding the use of this approach for human vaccination. Therefore, in this paper we review preclinical and clinical tests with DNA vaccines against the dengue virus. Most of the studies are based on the E protein since this antigen is the main target for neutralizing antibody production. Yet, there are other reports with DNA vaccines based on non-structural dengue proteins with protective results, as well. Combining structural and non-structural genes may be a solution for inducing immune responses aging in different infection moments. Furthermore, DNA immunizations are also a very good approach in combining strategies for vaccines against dengue, in heterologous prime/boost regimen or even administering different vaccines at the same time, in order to induce efficient humoral and cellular immune responses.

Key Amino Acid Substitution for Infection-Enhancing Activity-Free Designer Dengue Vaccines

Dengue is a globally important disease caused by four serotypes of dengue virus. Dengue vaccine development has been hampered by antigenic cross-reactivity among serotypes, which potentially causes antibody-dependent enhancement of infection and disease severity. Here we found that a single amino acid substitution in the envelope protein at position 87 from aspartic acid to asparagine or at position 107 from leucine to phenylalanine is critical for suppressing the induction of infection-enhancing antibody in a mouse model. The site and type of amino acid substitution were determined via neutralization escape using an enhancing-activity-only monoclonal antibody that was engineered to reveal neutralizing activity. Mutated dengue type 1 DNA vaccines containing either or both amino acid substitutions induced neutralizing antibodies devoid of enhancing activity against all serotypes. The effect of substitution was further demonstrated using other serotypes and a tetravalent formulation. This finding may contribute to the development of infection-enhancing-activity-free dengue vaccines.

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Amino acids at E87 or E107 are critical for dengue-enhancing antibody induction

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Neutralization escape is useful for identifying the key types or sites of amino acids

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Each substitution can be applied to antigens of all four dengue serotypes

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A modified tetravalent DNA vaccine suppresses enhancing antibody induction in mice

A DNA vaccine against yellow fever virus: development and evaluation

Attenuated yellow fever (YF) virus 17D/17DD vaccines are the only available protection from YF infection, which remains a significant source of morbidity and mortality in the tropical areas of the world. The attenuated YF virus vaccine, which is used worldwide, generates both long-lasting neutralizing antibodies and strong T-cell responses. However, on rare occasions, this vaccine has toxic side effects that can be fatal. This study presents the design of two non-viral DNA-based antigen formulations and the characterization of their expression and immunological properties. The two antigen formulations consist of DNA encoding the full-length envelope protein (p/YFE) or the full-length envelope protein fused to the lysosomal-associated membrane protein signal, LAMP-1 (pL/YFE), aimed at diverting antigen processing/presentation through the major histocompatibility complex II precursor compartments. The immune responses triggered by these formulations were evaluated in H2b and H2d backgrounds, corresponding to the C57Bl/6 and BALB/c mice strains, respectively. Both DNA constructs were able to induce very strong T-cell responses of similar magnitude against almost all epitopes that are also generated by the YF 17DD vaccine. The pL/YFE formulation performed best overall. In addition to the T-cell response, it was also able to stimulate high titers of anti-YF neutralizing antibodies comparable to the levels elicited by the 17DD vaccine. More importantly, the pL/YFE vaccine conferred 100% protection against the YF virus in intracerebrally challenged mice. These results indicate that pL/YFE DNA is an excellent vaccine candidate and should be considered for further developmental studies.

Dengue virus vaccine development

Dengue virus (DENV) is a significant cause of morbidity and mortality in tropical and subtropical regions, causing hundreds of millions of infections each year. Infections range from asymptomatic to a self-limited febrile illness, dengue fever (DF), to the life-threatening dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). The expanding of the habitat of DENV-transmitting mosquitoes has resulted in dramatic increases in the number of cases over the past 50 years, and recent outbreaks have occurred in the United States. Developing a dengue vaccine is a global health priority. DENV vaccine development is challenging due to the existence of four serotypes of the virus (DENV1-4), which a vaccine must protect against. Additionally, the adaptive immune response to DENV may be both protective and pathogenic upon subsequent infection, and the precise features of protective versus pathogenic immune responses to DENV are unknown, complicating vaccine development. Numerous vaccine candidates, including live attenuated, inactivated, recombinant subunit, DNA, and viral vectored vaccines, are in various stages of clinical development, from preclinical to phase 3. This review will discuss the adaptive immune response to DENV, dengue vaccine challenges, animal models used to test dengue vaccine candidates, and historical and current dengue vaccine approaches.

Origin and distribution of divergent dengue virus: novel database construction and phylogenetic analyses

Dengue virus (DENV), a mosquito-borne agent that exists as four serotypes (DENV-1–4), induces dengue illness. DENV has a positive-sense, ssRNA genome of approximately 11 kb that encodes a capsid protein, a premembrane protein and an envelope glycoprotein, in addition to seven nonstructural proteins. These individual genes show sequence variations that can be analyzed phylogenetically to yield several genotypes within each serotype. Here, the sequences of individual DENV genes were collected and used to construct a novel DENV database. This database was then used to characterize the evolution of individual genotypes in several countries. Interestingly, the database provided evidence for recombination between two or three different genotypes to yield new genotypes. This novel database will be available on the internet and is expected to be highly useful for dengue genetic studies, including phylogenetic analyses.

A mouse monoclonal antibody against dengue virus type 1 Mochizuki strain targeting envelope protein domain II and displaying strongly neutralizing but not enhancing activity

Dengue fever and its more severe form, dengue hemorrhagic fever, are major global concerns. Infection-enhancing antibodies are major factors hypothetically contributing to increased disease severity. In this study, we generated 26 monoclonal antibodies (MAbs) against the dengue virus type 1 Mochizuki strain. We selected this strain because a relatively large number of unique and rare amino acids were found on its envelope protein. Although most MAbs showing neutralizing activities exhibited enhancing activities at subneutralizing doses, one MAb (D1-IV-7F4 [7F4]) displayed neutralizing activities without showing enhancing activities at lower concentrations. In contrast, another MAb (D1-V-3H12 [3H12]) exhibited only enhancing activities, which were suppressed by pretreatment of cells with anti-FcγRIIa. Although antibody engineering revealed that antibody subclass significantly affected 7F4 (IgG3) and 3H12 (IgG1) activities, neutralizing/enhancing activities were also dependent on the epitope targeted by the antibody. 7F4 recognized an epitope on the envelope protein containing E118 (domain II) and had a neutralizing activity 10- to 1,000-fold stronger than the neutralizing activity of previously reported human or humanized neutralizing MAbs targeting domain I and/or domain II. An epitope-blocking enzyme-linked immunosorbent assay (ELISA) indicated that a dengue virus-immune population possessed antibodies sharing an epitope with 7F4. Our results demonstrating induction of these antibody species (7F4 and 3H12) in Mochizuki-immunized mice may have implications for dengue vaccine strategies designed to minimize induction of enhancing antibodies in vaccinated humans.

Needle-free jet injection of small doses of Japanese encephalitis DNA and inactivated vaccine mixture induces neutralizing antibodies in miniature pigs and protects against fetal death and mummification in pregnant sows

Japanese encephalitis (JE) virus causes abortion and stillbirth in swine, and encephalitis in humans and horses. We have previously reported that immunogenicity of a DNA vaccine against JE was synergistically enhanced in mice by co-immunization with a commercial inactivated JE vaccine (JEVAX) under a needle-free injection system. Here, we found that this immunization strategy was also effective in miniature pigs. Because of the synergism, miniature pigs immunized twice with a mixture of 10 μg of DNA and a 1/100 dose of JEVAX developed a high neutralizing antibody titer (1:190 at 90% plaque reduction assay). Even using 1 μg of DNA, 3 of 4 pigs developed neutralizing antibodies. Following challenge, all miniature pigs with detectable neutralizing antibodies were protected against viremia. Pregnant sows inoculated with 10 or 1 μg of DNA mixed with JEVAX (1/100 dose) developed antibody titers of 1:40-1:320. Following challenge, fetal death and mummification were protected against in DNA/JEVAX-immunized sows.

Evaluation of extracellular subviral particles of dengue virus type 2 and Japanese encephalitis virus produced by Spodoptera frugiperda cells for use as vaccine and diagnostic antigens

New or improved vaccines against dengue virus types 1 to 4 (DENV1 to DENV4) and Japanese encephalitis virus (JEV), the causative agents of dengue fever and Japanese encephalitis (JE), respectively, are urgently required. The use of noninfectious subviral extracellular particles (EPs) is an inexpensive and safe strategy for the production of protein-based flavivirus vaccines. Although coexpression of premembrane (prM) and envelope (E) proteins has been demonstrated to produce EPs in mammalian cells, low yields have hindered their commercial application. Therefore, we used an insect cell expression system with Spodoptera frugiperda-derived Sf9 cells to investigate high-level production of DENV2 and JEV EPs. Sf9 cells transfected with the prM and E genes of DENV2 or JEV secreted corresponding viral antigens in a particulate form that were biochemically and biophysically equivalent to the authentic antigens obtained from infected C6/36 mosquito cells. Additionally, equivalent neutralizing antibody titers were induced in mice immunized either with EPs produced by transfected Sf9 cells or with EPs produced by transfected mammalian cells, in the context of coimmunization with a DNA vaccine that expresses EPs. Furthermore, the results of an enzyme-linked immunosorbent assay (ELISA) using an EP antigen derived from Sf9 cells correlated significantly with the results obtained by a neutralization test and an ELISA using an EP antigen derived from mammalian cells. Finally, Sf9 cells could produce 10- to 100-fold larger amounts of E antigen than mammalian cells. These results indicate the potential of Sf9 cells for high-level production of flavivirus protein vaccines and diagnostic antigens.

Adenovirus-based vaccines generate cytotoxic T lymphocytes to epitopes of NS1 from dengue virus that are present in all major serotypes

Dengue virus (DENV) infection is an expanding global threat to public health. Effective vaccine and treatment approaches remain elusive. B cell-directed vaccines may be complicated by an antibody-dependent enhancement (ADE) phenomenon based on cross-serotype, nonneutralizing antibodies. We hypothesized that a CD8(+) T cell-directed genetic vaccine that targets a DENV nonstructural protein, NS1, could be a potential strategy to overcome the ADE barrier and accomplish cross-serotype protection. We selected an adenovirus-based vector as the dengue vaccine carrier. To bypass preexisting immunity to human adenoviruses and to improve vaccine efficacy, we created vaccine vectors, based on simian adenoviruses SAdV22 and SAdV25 as well as human adenovirus serotype 5, expressing the NS1 antigen of the Hainan strain, DENV serotype 2. An NS1 peptide library was screened to identify the immunodominant and functional epitope within the NS1 protein for H-2(d)-restricted CD8(+) T cells in BALB/c mice, using interferon-gamma enzyme-linked immunospot and intracellular cytokine-staining assays. Our study identified the 9-mer AGPWHLGKL (NS1(265273)) as the H-2(d)-restricted T cell epitope whose sequence is highly conserved among 26 strains of DENV serotypes 1, 2, 3, and 4, suggesting potential cross-serotype protection of NS1-directed genetic vaccines in the BALB/c model of DENV infection. Importantly, we characterized the cytokine profile of CD8(+) NS1-specific T cells in BALB/c mice vaccinated with HAdV-5-NS1, SAdV-22-NS1, and SAdV-25 NS1 and demonstrated the effective in vivo cytolytic killing capacity of CD8(+) T cells from SAdV-25-NS1-vaccinated mice.

Co-immunization with West Nile DNA and inactivated vaccines provides synergistic increases in their immunogenicities in mice

West Nile virus is now distributed throughout many temperate, subtropical and tropical areas: vaccines need to be developed that are affordable for developed and developing countries. Here, we constructed and evaluated a DNA vaccine expressing the premembrane and envelope proteins of West Nile virus (pcWNME). Mice immunized twice with 100 or 10 microg of pcWNME developed high or moderate levels of neutralizing antibodies, respectively. These mice were protected from viremia and death after lethal challenge. Mice immunized with a mixture of 1 microg of pcWNME and a small amount (1/10 dose) of a commercial inactivated vaccine developed moderate levels of neutralizing antibodies, whereas immunization with pcWNME or the inactivated vaccine alone induced only low or undetectable levels: co-immunization with the DNA and protein vaccines synergistically increased their own immunogenicities. The synergism reduced the amount of DNA sufficient to induce neutralizing antibodies: a single immunization with doses as low as 0.1 microg induced a titer of 1:40 at a 90% plaque reduction 6 or 9 weeks after immunization. Both IgG1 and IgG2a antibodies were induced in mice by co-immunization with the DNA and protein vaccines.

Dengue tetravalent DNA vaccine increases its immunogenicity in mice when mixed with a dengue type 2 subunit vaccine or an inactivated Japanese encephalitis vaccine

We previously developed a dengue tetravalent DNA vaccine that can induce neutralizing antibodies against four dengue viruses in mice. Here, we demonstrated that immunogenicity of our tetravalent vaccine is synergistically increased in mice by co-immunization with dengue type 2 virus (DENV2) subviral extracellular particles (D2EPs) or inactivated Japanese encephalitis vaccine (JEVAX). A single immunization with a mixture of 100 microg of the tetravalent vaccine and 150 ng of D2EPs or a 1/10 dose of JEVAX induced moderate levels of neutralizing antibodies in a 90% plaque reduction assay. Immunized mice were protected from "artificial" viremia created by intravenous injection with DENV2.

Dengue tetravalent DNA vaccine inducing neutralizing antibody and anamnestic responses to four serotypes in mice

We developed a dengue tetravalent DNA vaccine consisting of plasmids expressing premembrane and envelope genes of each of four serotypes of dengue viruses. BALB/c mice immunized twice with the tetravalent vaccine at a dose of 100 microg (25 microg for each serotype) using a needle-free jet injector developed neutralizing antibodies against all serotypes. There was no interference among the four components included in this combination vaccine. Tetravalent vaccine-immunized mice showed anamnestic neutralizing antibody responses following challenge with each dengue serotype: responses to challenges from serotypes different to those used for neutralization tests were also induced.

Needle-free jet injection of a mixture of Japanese encephalitis DNA and protein vaccines: a strategy to effectively enhance immunogenicity of the DNA vaccine in a murine model

Combined immunization with gene-based and protein-based vaccines can increase vaccine effectiveness. We previously demonstrated, using a murine model for Japanese encephalitis (JE), that simultaneous immunization with a DNA vaccine (pcJEME) by the intramuscular route and a protein vaccine consisting of subviral extracellular particles (EPs) by the subcutaneous route provided a synergistic increase in immunogenicities of these vaccines. Here, we investigated a novel immunization protocol consisting of a single inoculation with a mixture of DNA and protein vaccines using a needle-free jet injector. Immunization of ddY mice with 1 microg of pcJEME mixed with 1 microg of EPs or a 1/100 dose of commercial inactivated JE vaccine (JEVAX) induced neutralizing antibody titers of 1:40 to 1:80 (90% plaque reduction) 6 weeks after immunization, whereas immunization with DNA or protein alone only induced low titers (< or =1:10). Co-immunization with pcDNA3, a CpGcontaining vector of the vaccine plasmid, increased immunogenicity of JEVAX to some extent. IgG1/IgG2a isotype profiles supported increased production of EPs in pcJEME-inoculated mice by needle-free injection and an adjuvant effect of the vector on immunogenicity of JEVAX.

Histidine 39 in the dengue virus type 2 M protein has an important role in virus assembly

The mature flavivirus particle comprises a nucleocapsid core surrounded by a lipid bilayer containing the membrane (M) (derived from the precursor prM) and envelope (E) proteins. The formation of intracellular prM/E heterodimers occurs rapidly after translation and is believed to be important for the assembly and secretion of immature virus particles. In this study, the role of the His residue at position 39 in the M protein (M39) of dengue virus type 2 (DENV-2) in the virus life cycle was investigated. Mutations encoding basic (Arg), non-polar (Leu and Pro) and uncharged polar (Asn, Gln and Tyr) amino acids at M39 were introduced into a DENV-2 genomic-length cDNA clone and their effects on virus replication were examined. Substitution of the His residue with non-polar amino acids abolished virus replication, whereas substitution with basic or uncharged polar amino acids decreased virus replication moderately ( approximately 2 log(10) p.f.u. ml(-1) decrease in viral titre for Arg and Asn) or severely (>3.5 log(10) p.f.u. ml(-1) decrease in viral titre for Gln and Tyr). Selected mutations were introduced into a prM-E gene cassette and expressed transiently in COS cells to investigate whether the mutations impaired prM/E association or secretion. None of the mutations was found to disrupt the formation of intracellular prM/E heterodimers. However, the mutations that abolished virus replication prevented secretion of prM/E complexes. The results of this study pinpoint a critical residue in the M protein that potentially plays a role in viral morphogenesis, secretion and entry.