Protective efficacy of a plasmid DNA encoding Japanese encephalitis virus envelope protein fused to tissue plasminogen activator signal sequences: studies in a murine intracerebral virus challenge model

NS1: a promising novel target antigen with strong immunogenicity and protective efficacy for avian flavivirus vaccine development

Tembusu virus (TMUV), an avian pathogenic flavivirus, has emerged as a significant threat to the duck industry in Southeast Asia, causing substantial economic losses. Due to the antibody-dependent enhancement (ADE) effect of TMUV subneutralizing antibodies, there is a pressing need to further develop new TMUV vaccine target antigens that ensure both safety and efficacy. Here, the TMUV non-structural protein 1 (NS1) as a target for development of effective anti-TMUV vaccines was unveiled. The amino acid sequences of TMUV NS1 exhibit a high degree of conservation across different strains (92.63-100%). To investigate the potential of TMUV NS1 as a vaccine target, the TMUV NS1-based plasmids were constructed and identified the C-terminal 30 amino acids residues of TMUV E (EC30) as an effective signal peptide for promoting NS1 expression and secretion. Subsequently, the plasmid pVAX1-EC30-NS1 was employed to immunize ducks, resulting in specific anti-NS1 IgG responses being stimulated, while without inducing anti-TMUV neutralizing antibodies. Furthermore, the cellular immune responses triggered by the TMUV NS1 were evaluated, observing a notable increase in lymphocyte proliferation at 4 wk and 6 wk postinjection with the pVAX1-EC30-NS1. Additionally, there was a significant up-regulation of NS1-specific Il-4 and Ifnγ levels at these time points. Following this, ducks from different groups were challenged with TMUV, and remarkably, those immunized with the NS1 vaccine displayed significantly lower viral copies both at 3 d postinfection (dpi) and 7 dpi (P < 0.05) compared to ducks immunized with the control vector. Notably, the NS1 demonstrated remarkable protection against TMUV challenge without causing severe gross lesions. Collectively, these findings highlighted the impressive immunogenicity and protectivity of the TMUV NS1. Consequently, NS1 holds great promise as a novel antigen target for the development of efficient and safe TMUV vaccines.

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.

Characterization of thermostable Newcastle disease virus recombinants expressing the hemagglutinin of H5N1 avian influenza virus as bivalent vaccine candidates

Newcastle disease virus (NDV) has been used as a vector in the development of vaccines and gene delivery. In the present study, we generated the thermostable recombinant NDV (rNDV) expressing the different forms of hemagglutinin (HA) of highly pathogenic avian influenza virus (HPAIV) H5N1 based on the full-length cDNA clone of thermostable TS09-C strain. The recombinant thermostable Newcastle disease viruses, rTS-HA, rTS-HA1 and rTS-tPAs/HA1, expressed the HA, HA1 or modified HA1 protein with the tissue plasminogen activator signal sequence (tPAs), respectively. The rNDVs displayed similar thermostability, growth kinetics and pathogenicity compared with the parental TS09-C virus. The tPAs facilitated the expression and secretion of HA1 protein in cells infected with rNDV. Animal studies demonstrated that immunization with rNDVs elicited effective H5N1- and NDV-specific antibody responses and conferred immune protection against lethal H5N1 and NDV challenges in chickens and mice. Importantly, vaccination of rTS-tPAs/HA1 resulted in enhanced protective immunity in chickens and mice. Our study thus provides a novel thermostable NDV-vectored vaccine candidate expressing a soluble form of a heterologous viral protein, which will greatly aid the poultry industry in developing countries.

Soluble PD-1-based vaccine targeting MUC1 VNTR and survivin improves anti-tumor effect

Soluble PD-1 (sPD1) can bind with ligands PD-L1/PD-L2 on the surface of dendritic cells (DCs). Therefore, a sPD1 vaccine fused with an immunogen can increase T cell activation against cancer. Here, we constructed a MUC1 and survivin (MS) combination gene tumor vaccine expressing MS fused with soluble PD-1 (sPD1/MS). To investigate whether the sPD1/MS fusion vaccine could enhance tumor-specific immune responses, its immunogenicity and anti-tumor activity were examined after intramuscular immunization in mice. Compared with the MS DNA vaccine, the specific cytolysis rate of the sPD1/MS fusion DNA vaccine was increased from 21.64% to 34.77%. Moreover, the sPD1/MS vaccine increased the tumor suppression rate from 17.18% to 30.96% and prolonged survival from 6.96% to 19.44% in a murine colorectal cancer model. Combining the sPD1/MS vaccine with oxaliplatin improved the tumor suppression rate to 74.71% in the murine colorectal cancer model. The sPD1/MS vaccine could also exert a good anti-tumor effect, increasing the tumor infiltrated CD8⁺ T cells by 6.5-fold (from 0.10% to 0.65%) in the murine lung cancer model. In conclusion, the sPD1/MS vaccine showed good immunogenicity and anti-tumor effect by activating lymphocytes effectively.

Human IgG Fc promotes expression, secretion and immunogenicity of enterovirus 71 VP1 protein

Enterovirus (EV71) can cause severe neurological diseases, but the underlying pathogenesis remains unclear. The capsid protein, viral protein 1 (VP1), plays a critical role in the pathogenicity of EV71. High level expression and secretion of VP1 protein are necessary for structure, function and immunogenicity in its natural conformation. In our previous studies, 5 codon-optimized VP1 DNA vaccines, including wt-VP1, tPA-VP1, VP1-d, VP1-hFc and VP1-mFc, were constructed and analyzed. They expressed VP1 protein, but the levels of secretion and immunogenicity of these VP1 constructs were significantly different (P<0.05). In this study, we further investigated the protein levels of these constructs and determined that all of these constructs expressed VP1 protein. The secretion level was increased by including a tPA leader sequence, which was further increased by fusing human IgG Fc (hFc) to VP1. VP1-hFc demonstrated the most potent immunogenicity in mice. Furthermore, hFc domain could be used to purify VP1-hFc protein for additional studies.

Tailoring a Combination Preerythrocytic Malaria Vaccine

The leading malaria vaccine candidate, RTS,S, based on the Plasmodium falciparum circumsporozoite protein (CSP), will likely be the first publicly adopted malaria vaccine. However, this and other subunit vaccines, such as virus-vectored thrombospondin-related adhesive protein (TRAP), provide only intermediate to low levels of protection. In this study, the Plasmodium berghei homologues of antigens CSP and TRAP are combined. TRAP is delivered using adenovirus- and vaccinia virus-based vectors in a prime-boost regime. Initially, CSP is also delivered using these viral vectors; however, a reduction of anti-CSP antibodies is seen when combined with virus-vectored TRAP, and the combination is no more protective than either subunit vaccine alone. Using an adenovirus-CSP prime, protein-CSP boost regime, however, increases anti-CSP antibody titers by an order of magnitude, which is maintained when combined with virus-vectored TRAP. This combination regime using protein CSP provided 100% protection in C57BL/6 mice compared to no protection using virus-vectored TRAP alone and 40% protection using adenovirus-CSP prime and protein-CSP boost alone. This suggests that a combination of CSP and TRAP subunit vaccines could enhance protection against malaria.

Nonstructural protein NS1 immunodominant epitope detected specifically in dengue virus infected material by a SELDI-TOF/MS based assay

Dengue virus (DV) infection is the most common mosquito-born viral disease of public health significance. Though most patients only suffer from flu-like symptoms, a small group of patients experiences more severe forms of the disease. The viral nonstructural protein 1 (NS1), a secreted protein correlating with viremia, is a key element used for dengue diagnosis with potential implications in severe dengue prognosis. Capture-ELISAs for the early detection of the NS1 protein in the sera during the acute febrile stage are commonly used in routine by diagnostic laboratories. In this study, the detection of NS1 protein in DV-infected material was assessed by an alternative method combining a single NS1-directed monoclonal antibody and the SELDI-TOF/MS technology. According to the epitope mapping, the antibodies used are mainly directed against an immuno-dominant peptide located on the C-terminal part of the protein. The NS1 SELDI-TOF assay is specific, has a sensitivity level close to capture-ELISAs and is potentially useful for a coupled serotyping/detection assay or for the detection of subtle post-translational modifications on the protein.

Scaling-up recombinant plasmid DNA for clinical trial: current concern, solution and status

Gene therapy and vaccines are rapidly developing field in which recombinant nucleic acids are introduced in mammalian cells for enhancement, restoration, initiation or silencing biochemical function. Beside simplicity in manipulation and rapid manufacture process, plasmid DNA-based vaccines have inherent features that make them promising vaccine candidates in a variety of diseases. This present review focuses on the safety concern of the genetic elements of plasmid such as propagation and expression units as well as their host genome for the production of recombinant plasmid DNA. The highlighted issues will be beneficial in characterizing and manufacturing plasmid DNA for save clinical use. Manipulation of regulatory units of plasmid will have impact towards addressing the safety concerns raised in human vaccine applications. The gene revolution with plasmid DNA by alteration of their plasmid and production host genetics will be promising for safe delivery and obtaining efficient outcomes.

Electroporation-mediated genetic vaccination for antigen mapping: application to Plasmodium falciparum VAR2CSA protein

Genetic vaccination, consisting in delivering a genetically engineered plasmid DNA by a non-viral vector or technique into a tissue, is currently of great interest. New delivery technique including DNA transfer by electroporation recently greatly improved the potency of this concept. Because it avoids the step of producing a recombinant protein, it is particularly of use in studying the immunogenic properties of large proteins. Here we describe the use of electroporation mediated DNA immunization to identify important protective epitopes from the large VAR2CSA protein from Plasmodium falciparum implicated in the pathology of placental malaria. Immunizing mice and rabbit with DNA plasmids encoding different fragments of VAR2CSA leads to high titer antisera. Moreover an N-terminal region of the protein was found to induce protective functional antibodies.

Genetic immunization with plasmid DNA mediated by electrotransfer

The concept of DNA immunization was first advanced in the early 1990s, but was not developed because of an initial lack of efficiency. Recent technical advances in plasmid design and gene delivery techniques have allowed renewed interest in the idea. Particularly, a better understanding of genetic immunization has led to construction of optimized plasmids and the use of efficient molecular adjuvants. The field also took great advantage of new delivery techniques such as electrotransfer. This is a simple physical technique consisting of injecting plasmid DNA into a target tissue and applying an electric field, allowing up to a thousandfold more expression of the transgene than naked DNA. DNA immunization mediated by electrotransfer is now effective in a variety of preclinical models against infectious or acquired diseases such as cancer or autoimmune diseases, and is making its way through the clinics in several ongoing phase I human clinical trials. This review will briefly describe genetic immunization mediated by electrotransfer and the main fields of application.

Comparison of immune response generated against Japanese encephalitis virus envelope protein expressed by DNA vaccines under macrophage associated versus ubiquitous expression promoters

Background

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis, with ~50,000 cases reported annually worldwide. Vaccination is the only measure for prevention. Recombinant vaccines are an efficient and safe alternative for formalin inactivated or live attenuated vaccines. Nowadays, incorporation of molecular adjuvants has been the main strategy for melioration of vaccines. Our attempt of immunomodulation is based on targeting antigen presenting cells (APC) "majorly macrophages" by using macrosialin promoter. We have compared the immune response of the constructed plasmids expressing JEV envelope (E) protein under the control of aforesaid promoter and cytomegalovirus (CMV) immediate early promoter in mouse model. Protection of immunized mice from lethal challenge with JEV was also studied.

Results

The E protein was successfully expressed in the macrophage cell line and was detected using immunofluorescence assay (IFA) and Western blotting. APC expressing promoter showed comparable expression to CMV promoter. Immunization of mice with either of the plasmids exhibited induction of variable JEV neutralizing antibody titres and provided protection from challenge with a lethal dose of JEV. Immune splenocytes showed proliferative response after stimulation with the JEV antigen (Ag), however, it was higher for CMV promoter. The magnitude of immunity provided by APC dominant promoter was non-significantly lower in comparison to CMV promoter. More importantly, immune response directed by APC promoter was skewed towards Th1 type in comparison to CMV promoter, this was evaluated by cytokine secretion profile of immune splenocytes stimulated with JEV Ag.

Conclusions

Thus, our APC-expressing DNA vaccination approach induces comparable immunity in comparison to ubiquitous promoter construct. The predominant Th1 type immune responses provide opportunities to further test its potency suitable for response in antiviral or anticancer vaccines.

DNA vaccines against dengue virus type 2 based on truncate envelope protein or its domain III

Two DNA vaccines were constructed encoding the ectodomain (domains I, II and III) of the DENV2 envelope protein (pE1D2) or only its domain III (pE2D2), fused to the human tissue plasminogen activator signal peptide (t-PA). The expression and secretion of recombinant proteins was confirmed in vitro in BHK cells transfected with the two plasmids, detected by immunofluorescence or immunoprecipitation of metabolically labeled gene products, using polyclonal and monoclonal antibodies against DENV2. Besides, results reveal that the ectodomain of the E protein can be efficiently expressed in vivo, in a mammalian system, without the prM protein that is hypothesized to act as a chaperonin during dengue infection. Balb/c mice were immunized with the DNA vaccines and challenged with a lethal dose of DENV2. All pE1D2-vaccinated mice survived challenge, while 45% of animals immunized with the pE2D2 died after infection. Furthermore, only 10% of pE1D2-immunized mice presented some clinical signs of infection after challenge, whereas most of animals inoculated with the pE2D2 showed effects of the disease with high morbidity degrees. Levels of neutralizing antibodies were significantly higher in pE1D2-vaccinated mice than in pE2D2-immunized animals, also suggesting that the pE1D2 vaccine was more protective than the pE2D2.

Transgene optimization, immunogenicity and in vitro efficacy of viral vectored vaccines expressing two alleles of Plasmodium falciparum AMA1

BACKGROUND

Apical membrane antigen 1 (AMA1) is a leading candidate vaccine antigen against blood-stage malaria, although to date numerous clinical trials using mainly protein-in-adjuvant vaccines have shown limited success. Here we describe the pre-clinical development and optimization of recombinant human and simian adenoviral (AdHu5 and ChAd63) and orthopoxviral (MVA) vectors encoding transgene inserts for Plasmodium falciparum AMA1 (PfAMA1).

METHODOLOGY/PRINCIPAL FINDINGS

AdHu5-MVA prime-boost vaccination in mice and rabbits using these vectors encoding the 3D7 allele of PfAMA1 induced cellular immune responses as well as high-titer antibodies that showed growth inhibitory activity (GIA) against the homologous but not heterologous parasite strains. In an effort to overcome the issues of PfAMA1 antigenic polymorphism and pre-existing immunity to AdHu5, a simian adenoviral (ChAd63) vector and MVA encoding two alleles of PfAMA1 were developed. This antigen, composed of the 3D7 and FVO alleles of PfAMA1 fused in tandem and with expression driven by a single promoter, was optimized for antigen secretion and transmembrane expression. These bi-allelic PfAMA1 vaccines, when administered to mice and rabbits, demonstrated comparable immunogenicity to the mono-allelic vaccines and purified serum IgG now showed GIA against the two divergent strains of P. falciparum encoded in the vaccine. CD8(+) and CD4(+) T cell responses against epitopes that were both common and unique to the two alleles of PfAMA1 were also measured in mice.

CONCLUSIONS/SIGNIFICANCE

Optimized transgene inserts encoding two divergent alleles of the same antigen can be successfully inserted into adeno- and pox-viral vaccine vectors. Adenovirus-MVA immunization leads to the induction of T cell responses common to both alleles, as well as functional antibody responses that are effective against both of the encoded strains of P. falciparum in vitro. These data support the further clinical development of these vaccine candidates in Phase I/IIa clinical trials.

Bioinformatics in new generation flavivirus vaccines

Flavivirus infections are the most prevalent arthropod-borne infections world wide, often causing severe disease especially among children, the elderly, and the immunocompromised. In the absence of effective antiviral treatment, prevention through vaccination would greatly reduce morbidity and mortality associated with flavivirus infections. Despite the success of the empirically developed vaccines against yellow fever virus, Japanese encephalitis virus and tick-borne encephalitis virus, there is an increasing need for a more rational design and development of safe and effective vaccines. Several bioinformatic tools are available to support such rational vaccine design. In doing so, several parameters have to be taken into account, such as safety for the target population, overall immunogenicity of the candidate vaccine, and efficacy and longevity of the immune responses triggered. Examples of how bio-informatics is applied to assist in the rational design and improvements of vaccines, particularly flavivirus vaccines, are presented and discussed.

Japanese encephalitis-a pathological and clinical perspective

Japanese encephalitis (JE) is the leading form of viral encephalitis in Asia. It is caused by the JE virus (JEV), which belongs to the family Flaviviridae. JEV is endemic to many parts of Asia, where periodic outbreaks take hundreds of lives. Despite the catastrophes it causes, JE has remained a tropical disease uncommon in the West. With rapid globalization and climatic shift, JEV has started to emerge in areas where the threat was previously unknown. Scientific evidence predicts that JEV will soon become a global pathogen and cause of worldwide pandemics. Although some research documents JEV pathogenesis and drug discovery, worldwide awareness of the need for extensive research to deal with JE is still lacking. This review focuses on the exigency of developing a worldwide effort to acknowledge the prime importance of performing an extensive study of this thus far neglected tropical viral disease. This review also outlines the pathogenesis, the scientific efforts channeled into develop a therapy, and the outlook for a possible future breakthrough addressing this killer disease.

Generation of high-titer neutralizing antibodies against botulinum toxins A, B, and E by DNA electrotransfer

Botulinum neurotoxins are known to be among the most toxic known substances. They produce severe paralysis by preventing the release of acetylcholine at the neuromuscular junction. Thus, new strategies for efficient production of safe and effective anti-botulinum neurotoxin antisera have been a high priority. Here we describe the use of DNA electrotransfer into the skeletal muscle to enhance antiserum titers against botulinum toxin serotypes A, B, and E in mice. We treated animals with codon-optimized plasmid DNA encoding the nontoxic but highly immunogenic C-terminal heavy chain fragment of the toxin. By employing both codon optimization and the electrotransfer procedure, the immune response and corresponding neutralizing antiserum titers were markedly increased. The cellular localization of the antigen and the immunization regimens were also shown to increase neutralizing titers to >100 IU/ml. This study demonstrates that DNA electrotransfer is an effective procedure for raising neutralizing antiserum titers to remarkably high levels.

Enhancement of humoral and cellular immunity in mice against Japanese encephalitis virus using a DNA prime-protein boost vaccine strategy

A synthetic multi-epitope gene containing critical epitopes of the Japanese encephalitis virus (JEV) envelope gene was cloned into both prokaryotic and eukaryotic expression vectors. The recombinant plasmid and purified recombinant protein (heterologously expressed in Escherichia coli) were used as immunogens in a mouse model. The results indicate that both the recombinant protein and the DNA vaccine induce humoral and cellular immune responses. Neutralising antibody titres in mice in the pcDNA-TEP plus rEP group increased considerably relative to mice immunised using either pcDNA-TEP or rEP alone (P<0.05). Furthermore, the highest levels of interleukin (IL)-2, interferon-gamma and IL-4 were induced following priming with the DNA vaccine and boosting with the recombinant protein. Together these findings demonstrate that a DNA-recombinant protein prime-boost vaccination strategy can produce high levels of antibody and trigger significant T cell responses in mice, highlighting the potential value of such an approach in the prevention of JEV infection.

Immunization with plasmid DNA encoding influenza A virus nucleoprotein fused to a tissue plasminogen activator signal sequence elicits strong immune responses and protection against H5N1 challenge in mice

DNA vaccination is an effective means of eliciting both humoral and cellular immunity. Most of influenza vaccines targeted at hemagglutinin (HA) show efficient immunogenicity for protecting subjects against influenza virus infection. However, major antigenic variations of HA may facilitate the virus in developing resistance against such vaccines. DNA vaccines encoding conserved antigens protect animals against diverse viral subtypes, but their potency requires further improvement. In the present study, a DNA vaccine encoding the conserved nucleoprotein (NP) with a tissue plasminogen activator (tPA) signal sequence (ptPAs/NP) was generated, and immune responses were examined in vaccinated mice. A higher level of NP expression and secretion was observed in lysates and supernatants of the cells transfected with ptPAs/NP when compared to a plasmid encoding the wild-type full-length NP (pflNP). Immunofluorescence studies showed the cytoplasmic localization of the NP protein expressed from ptPAs/NP, but not from pflNP. In mice, the ptPAs/NP vaccine elicited higher levels of the NP-specific IgG and CD8(+) T cell-stimulating responses than that of pflNP. Vaccination with ptPAs/NP efficiently cleared the homologous H5N1 influenza virus in the infected lungs and induced partial cross-protection against heterologous, highly pathogenic H5N1 strains in mice. Our results may contribute to the development of protective immunity against diverse, highly pathogenic H5N1 virus subtypes.

Targeting the vaccinia virus L1 protein to the cell surface enhances production of neutralizing antibodies

The current live-orthopoxvirus vaccine is associated with minor to serious adverse affects, and is contraindicated for use in a significant portion of the population. As an alternative vaccine, we have previously shown that a DNA subunit vaccine (4pox) based on four orthopoxvirus immunogens (L1R, B5R, A27L and A33R) can produce protective immunity against lethal orthopoxvirus challenges in mice and nonhuman primates. Because antibodies are critical for protection against secondary orthopoxvirus infections, we are now interested in strategies that will enhance the humoral immune response against vaccine targets. Here, we tested the immunogenicity of an L1R construct to which a tissue plasminogen activator signal sequence was placed in frame with the full-length L1R gene. The tPA-L1R construct produced a more robust neutralizing antibody response in vaccinated mice when the DNA vaccine was administered by gene-gun as a prime/single boost. When the tPA-L1R construct was substituted for the unmodified L1R gene in the 4pox vaccine, given as a prime and single boost, animals were better protected from lethal challenge with vaccinia virus (VACV). These findings indicate that adding a tPA-leader sequence can enhance the immunogenicity of the L1R gene when given as a DNA vaccine. Furthermore, our results demonstrate that a DNA-based vaccine is capable of establishing protection from lethal orthopoxvirus challenges when administered as a prime and single boost without requiring adjuvant.

Current use and development of vaccines for Japanese encephalitis

BACKGROUND

Japanese encephalitis (JE) is a significant cause of human morbidity and mortality throughout Asia. Vaccines for JE have been available for many years and their use has been effective in reducing the incidence of JE disease in several countries but, as disease incidence has decreased, concerns regarding adverse events following immunisation have increased.

OBJECTIVE

To review existing JE vaccines and new candidates in advanced preclinical or clinical evaluation.

METHODS

The review primarily covers published and some unpublished literature from the past decade describing current use of approved JE vaccines in various parts of the world, and advanced development and clinical testing of alternative vaccine candidates.

RESULTS/CONCLUSION

There is a clear need for additional licensing of existing or new JE vaccines. Several promising candidates are currently in use or completing clinical trials.

Smallpox DNA vaccine delivered by novel skin electroporation device protects mice against intranasal poxvirus challenge

Previously, we demonstrated that an experimental smallpox DNA vaccine comprised of four vaccinia virus genes (4pox) administered by gene gun elicited protective immunity in mice challenged with vaccinia virus, and in nonhuman primates challenged with monkeypox virus (Hooper JW, et al. Smallpox DNA vaccine protects nonhuman primates against lethal monkeypox. J Virol 2004;78:4433-43). Here, we report that this 4pox DNA vaccine can be efficiently delivered by a novel method involving skin electroporation using plasmid DNA-coated microneedle arrays. Mice vaccinated with the 4pox DNA vaccine mounted robust antibody responses against the four immunogens-of-interest, including neutralizing antibody titers that were greater than those elicited by the traditional live virus vaccine administered by scarification. Moreover, vaccinated mice were completely protected against a lethal (>10LD(50)) intranasal challenge with vaccinia virus strain IHD-J. To our knowledge, this is the first demonstration of a protective immune response being elicited by microneedle-mediated skin electroporation.

From sequence to antibody: genetic immunisation is suitable to generate antibodies against a rare plant membrane protein, the KAT 1 channel

Monoclonal antibodies against the K(+) channel KAT1 of Arabidopsis thaliana, a low abundance, plant plasma membrane protein, were generated by genetic immunisation to avoid the time and labour consuming purification of native or recombinant proteins and peptides usually necessary for conventional immunisation techniques. The resulting polyclonal and monoclonal antibody sera recognised a single protein band in a microsomal fraction of wild-type A. thaliana leaves and in membrane fractions of transgenic yeast cells and tobacco plants expressing the KAT1 protein. Therefore, genetic immunisation is suitable for generating monoclonal antibodies against plant proteins and particularly, against plant membrane proteins of low abundance.

DNA vaccines against dengue virus based on the ns1 gene: The influence of different signal sequences on the protein expression and its correlation to the immune response elicited in mice

We analyzed four DNA vaccines based on DENV-2 NS1: pcENS1, encoding the C-terminal from E protein plus the NS1 region; pcENS1ANC, similar to pcENS1 plus the N-terminal sequence from NS2a (ANC); pcTPANS1, coding the t-PA signal sequence fused to NS1; and pcTPANS1ANC, similar to pcTPANS1 plus the ANC sequence. The NS1 was detected in lysates and culture supernatants from pcTPANS1-, pcENS1- and pcENS1ANC-transfected cells and not in cells with pcTPANS1ANC. Only the pcENS1ANC leads the expression of NS1 in plasma membrane, confirming the importance of ANC sequence for targeting NS1 to cell surface. High levels of antibodies recognizing conformational epitopes of NS1 were induced in mice immunized with pcTPANS1 and pcENS1, while only few pcENS1ANC-inoculated animals presented detectable anti-NS1 IgG. Protection against DENV-2 was verified in pcTPANS1- and pcENS1-immunized mice, although the plasmid pcTPANS1 induced slight higher protective immunity. These plasmids seem to activate distinct patterns of the immune system.

Ensuring safety of DNA vaccines

In 1990 a new approach for vaccination was invented involving injection of plasmid DNA in vivo, which elicits an immune response to the encoded protein. DNA vaccination can overcome most disadvantages of conventional vaccine strategies and has potential for vaccines of the future. However, today 15 years on, a commercial product still has not reached the market. One possible explanation could be the technique's failure to induce an efficient immune response in humans, but safety may also be a fundamental issue. This review focuses on the safety of the genetic elements of DNA vaccines and on the safety of the microbial host for the production of plasmid DNA. We also propose candidates for the vaccine's genetic elements and for its microbial production host that can heighten the vaccine's safety and facilitate its entry to the market.

Protection against dengue type 2 virus induced in mice immunized with a DNA plasmid encoding the non-structural 1 (NS1) gene fused to the tissue plasminogen activator signal sequence

Dengue is one of the most important arboviral diseases in humans, and although efforts over the last decades have dealt with the development of a vaccine, this vaccine is not available yet. In order to evaluate the potential of a DNA vaccine based on the non-structural 1 (NS1) protein against dengue virus (DENV), we constructed the pcTPANS1 plasmid which contains the secretory signal sequence derived from human tissue plasminogen activator (t-PA) fused to the full length of the DENV-2 NS1 gene. Results indicate that pcTPANS1 promotes correct expression of NS1 in eukaryotic cells and drives secretion of the recombinant protein to the surrounding medium in a dimeric form. Balb/c mice, intramuscularly inoculated with this plasmid, presented high levels of antibodies, recognizing mainly surface-exposed conformational epitopes present in the NS1 protein expressed by insect cells. Long-term antibody response was observed in animals 56 weeks after the first plasmid inoculation, and a rapid, efficient secondary response was observed after a DNA boost. Vaccinated animals were challenged against DENV-2 in two murine models, based on intracerebral (i.c.) and intraperitoneal (i.p.) virus inoculations, and in both cases, pcTPANS1-immunized mice were protected. Overall, these results provide further support for the use of such a plasmid in a possible approach for the development of a vaccine against DENV.

Immunization with plasmid DNA encoding a truncated, secreted form of the bovine viral diarrhea virus E2 protein elicits strong humoral and cellular immune responses

The major protective antigen of bovine viral diarrhea virus (BVDV), the E2 protein, is cell-associated and not expressed on the cell surface. In this study we evaluated a DNA vaccine encoding various secreted versions of E2. In vitro analysis demonstrated that deletion of the transmembrane anchor and addition of the signal sequence of bovine herpesvirus-1 (BHV-1) (gDsDeltaE2) resulted in efficient secretion of E2 into the culture medium. In contrast, full-length E2, either without or with gDs (gDsE2), as well as truncated E2 without gDs (DeltaE2), remained entirely cell-associated. Mice immunized with plasmid encoding gDsDeltaE2 developed significantly higher IgG and virus neutralizing antibody titres compared to animals vaccinated with plasmid encoding E2, DeltaE2 or gDsE2. To optimize secretion of E2, the efficiency of gDs was compared with that of the tissue plasminogen activator signal (tPAs) sequence. In addition, the effect of the plasmid backbone was assessed by comparing two vectors. Four plasmids, pMASIA-gDsDeltaE2, pMASIA-tPAsDeltaE2, pSLKIA-gDsDeltaE2 and pSLKIA-tPAsDeltaE2, were constructed and administered intradermally to mice. The mice immunized with pMASIA-tPAsDeltaE2 developed the strongest and most balanced immune responses. Vaccination of cattle confirmed that pMASIA-tPAsDeltaE2 elicited both strong humoral and cellular immune responses and thus could be a candidate DNA vaccine against BVDV.

Protection against Atlantic halibut nodavirus in turbot is induced by recombinant capsid protein vaccination but not following DNA vaccination

Fish nodaviruses (betanodaviruses) are small, non-enveloped icosahedral single-stranded positive-sense RNA viruses that can cause viral encephalopathy and retinopathy (VER) in a number of cultured marine teleost species, including Atlantic halibut (Hippoglossus hippoglossus). A recombinant protein vaccine and a DNA vaccine were produced, based on the same capsid-encoding region of the Atlantic halibut nodavirus (AHNV) genome, and tested for protection in juvenile turbot (Scophthalmus maximus). Vaccine efficacy was demonstrated in the fish vaccinated with recombinant capsid protein but not in the DNA-vaccinated fish, despite the fact that in vivo expression of the DNA vaccine-encoded antigen was confirmed by RNA in situ hybridisation and immunohistochemistry. Combined DNA and recombinant vaccine administration did not improve the effect of the latter. Surprisingly, fish vaccinated with 50 microg recombinant protein demonstrated a threefold lower survival rate than the two groups that received 10 microg recombinant protein. Neither the recombinant protein vaccine nor the DNA vaccine induced anti-viral antibodies 9 weeks after immunisation, while antibodies reactive with the recombinant protein were detectable mainly in fish vaccinated with 50 microg recombinant protein. The study also demonstrates evidence of viral replication inside the myocytes of intramuscularly challenged fish.

Common host genes are activated in mouse brain by Japanese encephalitis and rabies viruses

This study identified nine genes whose expression is upregulated in the central nervous system (CNS) of mice during Japanese encephalitis virus (JEV) infection. These include: cathepsin S, oligoadenylate synthetase (OAS), GARG49/IRG2, lymphocyte antigen-6A (Ly-6A), macrophage activation gene-2 (Mpa2), early growth response gene1 (Egr1), pyrimidine 5'-nucleotidase (P5N), apolipoprotein D (ApoD) and STAT1. Activation of all nine genes during JEV infection was confirmed by Northern blot analysis. JEV replication was inhibited in the majority of mice immunized with Biken JEV vaccine, and these mice also exhibited reduced expression of JEV-inducible CNS genes. Thus, there is a good correlation between virus load and upregulation of host CNS genes. It was also demonstrated that all the CNS genes activated by JEV are also upregulated during rabies virus infection. In addition, GARG49, STAT1, cathepsin S and ApoD are known to be upregulated in the CNS by Sindbis virus, an alphavirus, and this supports the proposal that common host cell pathways are activated in the CNS by different neurotropic viruses.

Japanese encephalitis vaccines: moving away from the mouse brain

Japanese encephalitis (JE) is a severe disease that is widespread throughout Asia and is spreading beyond its traditional boundaries. Three vaccines are currently in use against JE but only one is available internationally, a mouse-brain-derived inactivated vaccine first used in the 1930s. Although this vaccine has been effective in reducing the incidence of JE, it is relatively expensive and has been linked to severe allergic and neurological reactions. Cell-culture-derived inactivated and attenuated vaccines have been developed but are only used in the People's Republic of China. Other vaccines currently in various stages of development are DNA vaccines, a chimeric yellow fever-JE viral vaccine, virus-like particle vaccines and poxvirus-based vaccines. Poxvirus-based vaccines and the chimeric yellow fever-JE vaccine have been tested in Phase I clinical trials. These new vaccines have the potential to significantly reduce the impact of JE in Asia, particularly if used in an oral vaccine delivery strategy.