Japanese encephalitis virus-specific proliferative responses of human peripheral blood T lymphocytes

Japanese encephalitis vaccines: Immunogenicity, protective efficacy, effectiveness, and impact on the burden of disease

Japanese encephalitis (JE) is a serious public health concern in most of Asia. The disease is caused by JE virus (JEV), a flavivirus transmitted by Culex mosquitoes. Several vaccines have been developed to control JE in endemic areas as well as to protect travelers and military personnel who visit or are commissioned from non-endemic to endemic areas. The vaccines include inactivated vaccines produced in mouse brain or cell cultures, live attenuated vaccines, and a chimeric vaccine based on the live attenuated yellow fever virus 17D vaccine strain. All the marketed vaccines belong to the JEV genotype III, but have been shown to be efficacious against other genotypes and strains, with varying degrees of cross-neutralization, albeit at levels deemed to be protective. The protective responses have been shown to last three or more years, depending on the type of vaccine and the number of doses. This review presents a brief account of the different JE vaccines, their immunogenicity and protective ability, and the impact of JE vaccines in reducing the burden of disease in endemic countries.

Human T cell responses to Japanese encephalitis virus in health and disease

Japanese encephalitis (JE) virus (JEV) is an important cause of encephalitis in children of South and Southeast Asia. However, the majority of individuals exposed to JEV only develop mild symptoms associated with long-lasting adaptive immunity. The related flavivirus dengue virus (DENV) cocirculates in many JEV-endemic areas, and clinical data suggest cross-protection between DENV and JEV. To address the role of T cell responses in protection against JEV, we conducted the first full-breadth analysis of the human memory T cell response using a synthetic peptide library. Ex vivo interferon-γ (IFN-γ) responses to JEV in healthy JEV-exposed donors were mostly CD8(+) and targeted nonstructural (NS) proteins, whereas IFN-γ responses in recovered JE patients were mostly CD4(+) and targeted structural proteins and the secreted protein NS1. Among patients, a high quality, polyfunctional CD4(+) T cell response was associated with complete recovery from JE. T cell responses from healthy donors showed a high degree of cross-reactivity to DENV that was less apparent in recovered JE patients despite equal exposure. These data reveal divergent functional CD4(+) and CD8(+) T cell responses linked to different clinical outcomes of JEV infection, associated with distinct targeting and broad flavivirus cross-reactivity including epitopes from DENV, West Nile, and Zika virus.

A comprehensive analysis of predicted HLA binding peptides of JE viral proteins specific to north Indian isolates

Japanese encephalitis (JE), a viral disease has significantly increased worldwide especially, in the developing region due to challenges in immunization, vector control and lack of appropriate treatment methods. An effective, yet an expensive heat-killed vaccine is available for the disease. Therefore, the design and development of short peptide vaccine candidate is promising. We used immune-informatics methods to perform a comprehensive analysis of the entire JEV proteome of north Indian isolate to identify the conserved peptides binding known specific HLA alleles among the documented JEV genotypes 1, 2, 3, 4 and 5. The prediction analysis identified 102 class I (using propred I) and 118 class II (using propred) binding peptides at 4% threshold value. These predicted HLA allele binding peptides were further analyzed for potential conserved region using IEDB (an immune epitope database and analysis resource). This analysis shows that 78.81% of class II (in genotype 2) and 76.47% of HLA I (in genotype 3) bound peptides are conserved. The peptides IPIVSVASL, KGAQRLAAL, LAVFLICVL and FRTLFGGMS, VFLICVLTV, are top ranking with potential super antigenic property by binding to all HLA allele members of B7 and DR4 super-types, respectively. This data finds application in the design and development of short peptide vaccine candidates and diagnostic agents for JE following adequate validation and verification.

Japanese encephalitis: the virus and vaccines

Japanese encephalitis (JE) is an infectious disease of the central nervous system caused by Japanese encephalitis virus (JEV), a zoonotic mosquito-borne flavivirus. JEV is prevalent in much of Asia and the Western Pacific, with over 4 billion people living at risk of infection. In the absence of antiviral intervention, vaccination is the only strategy to develop long-term sustainable protection against JEV infection. Over the past half-century, a mouse brain-derived inactivated vaccine has been used internationally for active immunization. To date, however, JEV is still a clinically important, emerging, and re-emerging human pathogen of global significance. In recent years, production of the mouse brain-derived vaccine has been discontinued, but 3 new cell culture-derived vaccines are available in various parts of the world. Here we review current aspects of JEV biology, summarize the 4 types of JEV vaccine, and discuss the potential of an infectious JEV cDNA technology for future vaccine development.

Japanese Encephalitis Virus Generated Neurovirulence, Antigenicity, and Host Immune Responses

In response to a JE virus attack, infected body cells start secretion of different cytokines and activate innate immune response. Virus starts neuronal invasion by entering into nerve cells and inflecting the central nervous system. It avoids exposure of body’s natural immunity and generates neurotrophic effects. Virus causes acute susceptibility to CNS and establishes encephalitis syndrome that results in very high fatality in children. In survivors, JEV inhibits the growth and proliferation of NCPs and imposes permanent neuronal disorders like cognitive, motor, and behavioral impairments. However, body cells start TCR mediated interactions, to recognize viral antigens with class I MHC complex on specific target cells, and operate mass killing of virus infected cells by increased CTL activity. Thus, both cell mediated and antibody interactions plays a central role in protection against JEV. In the present review article virus generated neurovirulence, antigenicity, and host immune responses are described in detail. More emphasis is given on diagnosis, clinical care, and active immunization with well-designed potential antiflavivirus vaccines. Further, for achieving an elite success against JEV, global eradication strategies are to be needed for making vaccination program more responsible and effective in endemic areas.

Detection by ELISA of antibodies to Japanese encephalitis virus nonstructural 1 protein induced in subclinically infected humans

Japanese encephalitis (JE) is a fatal mosquito-borne disease that is vaccine-preventable. The natural infection rate is a critical factor for evaluations of the necessity for vaccination. Detection of antibodies to virus nonstructural (NS) proteins is a theoretical strategy to survey natural infections among populations vaccinated with an inactivated JE vaccine consisting of only structural proteins. Here, we present our development of an enzyme-linked immunosorbent assay (ELISA) to detect low levels of NS1 antibodies induced in humans with subclinical infections. We used a casein-based ELISA diluent to minimize nonspecific reactions. A tentative cut-off value (0.185) was statistically calculated from NS1 antibody levels obtained with healthy American individuals negative for antibodies to JE virus. Comparison with our previously developed immunostaining method provided a significant correlation coefficient (0.764; P<0.001) and high qualitative agreement (82.5%). The presence of NS1 antibodies in sera was confirmed by Western blotting analysis. Using serially collected sera, we estimated the duration of NS1 antibodies between seroconversion and seroreversion to be 4.2 years.

Japanese encephalitis virus produces a CD4+ Th2 response and associated immunoprotection in an adoptive-transfer murine model

Japanese encephalitis is an acute infection of the central nervous system caused by Japanese encephalitis virus (JEV). The importance of an effective humoral response in preventing JEV infection has already been established, although the contribution of cellular immunity remains unclear. This study used an experimental murine model to understand the protective effects of cell-mediated immunity in JEV infection. Fourteen-day-old mice adoptively transferred with JEV-immune splenocytes were found to be protected from peripheral JEV challenge. The survival rate was reduced when transferred cells were depleted of their CD4+ T-cell population. Correspondingly, increased protection was observed when JEV-primed isolated CD4+ T cells were transferred compared with isolated CD8+ T cells. Mice protected from JEV infection by the adoptive transfer of JEV-immune splenocytes had higher levels of immunomodulatory cytokines and decreased expression of pro-inflammatory cytokines. Concurrent with the increase in Th2 cytokines, JEV-specific IgM and IgG1 antibody titres were found to be elevated in protected mice. Taken together, these data indicate a definite role for CD4+ T cells in protection from lethal JEV infection in naïve 14-day-old mice. Induction of a Th2 cytokine response and IgG1 antibody probably achieves an immunomodulatory effect that results in the enhanced survival of these animals.

Some observations on the tropism of Japanese encephalitis virus in rat brain

The clinical picture of viral encephalitis is determined by the affinity and persistence of the virus to different brain regions. Therefore, the present study was aimed to investigate the neuropathological changes following Japanese encephalitis virus (JEV) infection in rat at different time points. Twelve days old Wistar rats were infected by intracerebral inoculation of JEV. Presence of JEV antigen was detected in thalamus, striatum, cortex and mid brain on 3, 6, 10 and 20 days post inoculation (d.p.i.). Histopathological changes were also studied in different brain regions at different time points. The highest expression of JEV antigen was found on 6 dpi in all the brain regions studied. JEV antigen was maximum in thalamus on 6 d.p.i. and mid brain on 10 d.p.i. JEV antigen, however, was almost undetectable on 20 d.p.i. in all the regions. The classical pathological changes such as cellular infiltration, perivascular cuffing, meningeal disruption, neuronal damage, neuronal shrinkage, and plaque formation were observed up to 10 d.p.i. The present study reveals high affinity of JEV to thalamus, brainstem and striatum. Rat model of JEV infection may serve as a useful model for studying mechanism of cell injury and recovery in JE.

Conserved amino acids 193–324 of non-structural protein 3 are a dominant source of peptide determinants for CD4+ and CD8+ T cells in a healthy Japanese encephalitis virus-endemic cohort

Our earlier identification of the non-structural protein 3 (NS3) of Japanese encephalitis virus (JEV) as a dominant CD4+ as well as CD8+ T cell-eliciting antigen in a healthy JEV-endemic cohort with a wide HLA distribution implied the presence of several epitopes dispersed over the length of the protein. Use of various truncated versions of NS3 in lymphocyte stimulation and interferon (IFN)-γ secretion assays revealed that amino acids (aa) 193–324 of NS3 were comparable with, if not superior to, the full-length protein in evoking Th1 responses. The potential of this 14·4 kDa stretch to stimulate IFN-γ production from both subtypes of T cells in a manner qualitatively and quantitatively similar to the 68 kDa parent protein suggested the presence within it of both class I and II epitopes and demonstrated that the entire immunogenicity of NS3 was focused on aa 193–324. Interestingly, this segment contained five of the eight helicase motifs of NS3. Analysis of variability of the NS3 protein sequence across 16 JEV isolates revealed complete identity of aa 219–318, which is contained within the above segment, suggesting that NS3-specific epitopes tend to cluster in relatively conserved regions that harbour functionally critical domains of the protein.

Cell-mediated immune responses in healthy children with a history of subclinical infection with Japanese encephalitis virus: analysis of CD4+ and CD8+ T cell target specificities by intracellular delivery of viral proteins using the human immunodeficiency virus Tat protein transduction domain

Japanese encephalitis virus (JEV), a single-stranded positive-sense RNA virus of the family Flaviviridae, is the major cause of paediatric encephalitis in Asia. The high incidence of subclinical infections in Japanese encephalitis-endemic areas and subsequent evasion of encephalitis points to the development of immune responses against JEV. Humoral responses play a central role in protection against JEV; however, cell-mediated immune responses contributing to this end are not fully understood. The structural envelope (E) protein, the major inducer of neutralizing antibodies, is a poor target for T cells in natural JEV infections. The extent to which JEV non-structural proteins are targeted by T cells in subclinically infected healthy children would help to elucidate the role of cell-mediated immunity in protection against JEV as well as other flaviviral infections. The property of the Tat peptide of Human immunodeficiency virus to transduce proteins across cell membranes, facilitating intracellular protein delivery following exogenous addition to cultured cells, prompted us to express the four largest proteins of JEV, comprising 71 % of the JEV genome coding sequence, as Tat fusions for enumerating the frequencies of virus-specific CD4+ and CD8+ T cells in JEV-immune donors. At least two epitopes recognized by distinct HLA alleles were found on each of the non-structural proteins, with dominant antiviral Th1 T cell responses to the NS3 protein in nearly 96 % of the cohort. The data presented here show that non-structural proteins are frequently targeted by T cells in natural JEV infections and may be efficacious supplements for the predominantly antibody-eliciting E-based JEV vaccines.

Neurovirulence and host factors in flavivirus encephalitis--evidence from clinical epidemiology

Japanese encephalitis virus (JEV) and West Nile virus (WNV) provide some of the most important examples of emerging zoonotic viral encephalitides. For these flaviviruses, only a small proportion of those infected develop clinical features, and these may range from a non-specific flu-like illness to a severe fatal meningoencephalitis, often with Parkinsonian features, or a poliomyelitis-like flaccid paralysis. The factors governing the clinical presentations, and outcome of flavivirus infections are poorly understood, but studies have looked at viral virulence determinants and the host immune response. Previous studies on JEV have suggested that the distribution of the four genotypes across Asia may relate to the differing clinical epidemiology (epidemic disease in the north, endemic disease in the south). However, new data based on the complete nucleotide sequence of a virus representing one of the oldest lineages, and phylogenetic analyses of all JEV strains for which genetic data are available, suggest that the distribution is best explained in terms of the virus' origin in the Indonesia-Malaysia region (where all genotypes have been found), and the spread of the more recent genotypes to new geographical areas. Clinical studies have shown that innate immunity, as manifested by interferon alpha levels, is important in JEV and other flaviviruses, but treatment with interferon alpha did not improve the outcome. A failure of the humoral immune response, is associated with death from encephalitis caused by JEV and WNV. Cellular immunity has been less well characterized, but CD8+ and CD4+ T cells are thought to be important.

Characterization of Tick-Borne Encephalitis Virus–Specific Human T Lymphocyte Responses by Stimulation with Structural TBEV Proteins Expressed in a Recombinant Baculovirus

Very little information is available on human T cell responses following exposure to tick-borne encephalitis virus (TBEV) proteins, largely because the virus is a dangerous pathogen and relatively large amounts of purified antigen would be required for the functional characterization of cellular immune responses. We have produced recombinant TBEV proteins using the baculovirus expression system and tested them for their capacity to stimulate T cells in vitro. T lymphocytes from TBEV vaccinated individuals were characterized. The recombinant E and C proteins triggered CD4+ but not CD8+ cells to proliferate and to produce IFN-gamma and IL-5. T cell responses against recombinant NS3 protein were not detected. T cell lines with specificity for the E protein were also established. These lines were CD4+ and had a TH0 cytokine production pattern. Our results demonstrate the utility of recombinant viral proteins to study the generation and characterization of TBEV specific T cell responses.

Recent advances in Japanese encephalitis

Japanese encephalitis (JE), the most important cause of epidemic encephalitis worldwide, is confined to Asia, but its geographical area is spreading. West Nile virus, and other closely related flaviviruses, cause similar disease elsewhere. Recent cryoelectron microscopic studies have characterized the flavivirus envelope protein as a new class of viral fusion protein (class II), and examined its arrangement on the virion surface. Changes in the envelope protein's hinge region, or its putative receptor-binding domain, are associated with changes in neurovirulence in animal models of JE. Clinically, JE causes a wide range of presentations, including a poliolike flaccid paralysis. Seizures and raised intracranial pressure are associated with a poor outcome, and may be potentially treatable. A safe efficacious formalin-inactivated vaccine against JE has been available for many years, but is too expensive for use in most Asian countries. A newer live attenuated vaccine has been used in China, but its use elsewhere has been restricted by regulatory concerns. A chimeric vaccine in which JE structural proteins are inserted into the 17D yellow fever vaccine backbone is one of several vaccines in development. There are no established antiviral treatments against JE. Interferon alpha was the most promising drug in small open trials, but a recent double-blind placebo controlled trial showed that it did not affect the outcome in children with JE.

Pathogenesis of flavivirus encephalitis

Within the flavivirus family, viruses that cause natural infections of the central nervous system (CNS) principally include members of the Japanese encephalitis virus (JEV) serogroup and the tick-borne encephalitis virus (TBEV) serocomplex. The pathogenesis of diseases involves complex interactions of viruses, which differ in neurovirulence potential, and a number of host factors, which govern susceptibility to infection and the capacity to mount effective antiviral immune responses both in the periphery and within the CNS. This chapter summarizes progress in the field of flavivirus neuropathogenesis. Mosquito-borne and tickborne viruses are considered together. Flavivirus neuropathogenesis involves both neuroinvasiveness (capacity to enter the CNS) and neurovirulence (replication within the CNS), both of which can be manipulated experimentally. Neuronal injury as a result of bystander effects may be a factor during flavivirus neuropathogenesis given that microglial activation and elaboration of inflammatory mediators, including IL-1β and TNF-α, occur in the CNS during these infections and may accompany the production of nitric oxide and peroxynitrite, which can cause neurotoxicity.

Ratios of subclinical to clinical Japanese encephalitis (JE) virus infections in vaccinated populations: evaluation of an inactivated JE vaccine by comparing the ratios with those in unvaccinated populations

Japanese encephalitis (JE) virus is characterized as a virus that produces a large number of subclinical infections. In this report, we estimated a ratio of subclinical to clinical infections in vaccinated human populations who acquired natural infection with JE virus, and evaluated protective capacity of the currently approved inactivated JE vaccine by comparing the ratio with those reported for unvaccinated populations. We developed a sensitive immunostaining method for detecting nonstructural 1 (NS1) antibody to demonstrate JE virus infection in vaccinated individuals. Serum samples collected from human populations in western Japan showed NS1 antibody prevalences of approximately 10% in an urban area in 1981 and 1995 and 20% in a rural area from 1982 through 1983. Analysis of annual change in NS1 antibody titer using paired samples provided a mean duration of NS1 antibody responses of approximately 2 years, indicating that 5% of the urban population or 10% of the rural population acquired natural JE virus infection in 1 year. Based on the number of JE cases from 1982 through 1991 and the number of people acquiring natural infection, and on the assumption that annual infection rates obtained in the present study areas are representative of the infection rate in entire Japan except for non-endemic northern areas, the ratio of subclinical to clinical infections in vaccinated populations was estimated to be 2000000:1, which was 2000-80000 times higher than the ratio previously reported for unvaccinated populations.

Japanese encephalitis vaccines: current vaccines and future prospects

Vaccination against JE ideally should be practiced in all areas of Asia where the virus is responsible for human disease. The WHO has placed a high priority on the development of a new vaccine for prevention of JE. Some countries in Asia (Japan, South Korea, North Korea, Taiwan, Vietnam, Thailand, and the PRC) manufacture JE vaccines and practice childhood immunization, while other countries suffering endemic or epidemic disease (India, Nepal, Laos, Cambodia, Bangladesh, Myanmar, Malaysia, Indonesia and the Philippines) have no JE vaccine manufacturing or policy for use. With the exception of the PRC, all countries practicing JE vaccination use formalin inactivated mouse brain vaccines, which are relatively expensive and are associated with rare but clinically significant allergic and neurological adverse events. New inactivated JE vaccines manufactured in Vero cells are in advanced preclinical or early clinical development in Japan, South Korea, Taiwan, and the PRC. An empirically derived, live attenuated vaccine (SA14-14-2) is widely used in the PRC. Trials in the PRC have shown SA14-14-2 to be safe and effective when administered in a two-dose regimen, but regulatory concerns over manufacturing and control have restricted international distribution. The genetic basis of attenuation of SA14-14-2 has been partially defined. A new live attenuated vaccine (ChimeriVax-JE) that uses a reliable flavivirus vaccine--yellow fever 17D--as a live vector for the envelope genes of SA14-14-2 virus is in early clinical trials and appears to be well tolerated and immunogenic after a single dose. Vaccinia and avipox vectored vaccines have also been tested clinically, but are no longer being pursued due to restricted effectiveness mediated by anti-vector immunity. Other approaches to JE vaccines--including naked DNA, oral vaccination, and recombinant subunit vaccines--have been reviewed.

Protective mechanisms induced by a Japanese encephalitis virus DNA vaccine: requirement for antibody but not CD8(+) cytotoxic T-cell responses

We have previously shown that a plasmid (pE) encoding the Japanese encephalitis virus (JEV) envelope (E) protein conferred a high level of protection against a lethal viral challenge. In the present study, we used adoptive transfer experiments and gene knockout mice to demonstrate that the DNA-induced E-specific antibody alone can confer protection in the absence of cytotoxic T-lymphocyte (CTL) functions. Plasmid pE administered by either intramuscular or gene gun injection produced significant E-specific antibodies, helper T (Th)-cell proliferative responses, and CTL activities. Animals receiving suboptimal DNA vaccination produced low titers of anti-E antibodies and were only partially or not protected from viral challenge, indicating a strong correlation between anti-E antibodies and the protective capacity. This observation was confirmed by adoptive transfer experiments. Intravenous transfer of E-specific antisera but not crude or T-cell-enriched immune splenocytes to sublethally irradiated hosts conferred protection against a lethal JEV challenge. Furthermore, experiments with gene knockout mice showed that DNA vaccination did not induce anti-E titers and protective immunity in Igmu(-/-) and I-Abeta(-/-) mice, whereas in CD8alpha(-/-) mice the pE-induced antibody titers and protective rate were comparable to those produced in the wild-type mice. Taken together, these results demonstrate that the anti-E antibody is the most critical protective component in this JEV challenge model and that production of anti-E antibody by pE DNA vaccine is dependent on the presence of CD4(+) T cells but independent of CD8(+) T cells.

T-cell activation and induction of antibodies and memory T cells by immunization with inactivated Japanese encephalitis vaccine

Mouse brain-derived inactivated Japanese encephalitis (JE) vaccine is the only currently internationally accepted vaccine against JE virus. We analyzed cellular and humoral immune responses to the JE vaccine in healthy adults in order to understand the protective immunity induced by this vaccine. Immunization with the JE vaccine induced T-cell activation in vivo, demonstrated by increase in the plasma levels of interleukin (IL)-2 and soluble CD8. JE virus-specific antibodies determined in radioimmunoprecipitation (RIP), hemagglutination inhibition (HI), and neutralization assays were also induced by immunization with the JE vaccine. JE virus-specific memory T cells were detected 60 days after immunization. These results suggest that protective immunity induced by the inactivated JE vaccine includes JE virus-specific T cells as well as antibodies with multiple biological activities.

Ethyleneglycol-bis-(beta-aminoethylether)tetraacetate as a blood anticoagulant: preservation of antigen-presenting cell function and antigen-specific proliferative response of peripheral blood mononuclear cells from stored blood

We examined the progressive and irreversible loss of antigen-specific lymphoproliferative responses in peripheral blood mononuclear cells (PBMC) obtained from blood exposed for prolonged periods to EDTA as an anticoagulant. The responses of these lymphocytes to interleukin-2 or to concanavalin A were, however, unaffected. The observed loss was not due to depletion of metal ions by EDTA, since the addition of several divalent cations to whole blood during storage in EDTA or to lymphocytes from EDTA-stored blood during antigen stimulation in vitro did not alleviate the defect. Reconstitution of antigen-specific T-cell lines or Percoll-purified T cells with adherent antigen-presenting cells in antigen stimulation assays revealed that the presenting cells and not the effector T-cells were the targets of EDTA-mediated damage. The anticoagulant heparin helped to circumvent this problem. Surprisingly, EGTA, another metal ion chelator, could successfully replace EDTA, with a marginal loss in antigen-specific responses. Lymphoproliferative responses to antigens of Japanese encephalitis virus (JEV) and Mycobacterium tuberculosis were both significantly preserved in EGTA. JEV antigen-specific responses of PBMC obtained from the blood of convalescent JEV patients and stored in EGTA for as long as 24 h (n = 20) were comparable to those of fresh PBMC (n = 10), while PBMC from blood stored in EDTA (n = 17) for 16 h or longer failed to respond. We recommend that EGTA be used as the anticoagulant of choice for applications that require the lymphocyte proliferation assay, especially when on-site testing facilities are not available.

New initiatives for the control of Japanese encephalitis by vaccination: minutes of a WHO/CVI meeting, Bangkok, Thailand, 13-15 October 1998

Japanese encephalitis (JE) is a leading cause of viral encephalitis in Asia that, in several countries, has been controlled effectively through national vaccine programs. However, in recent years, transmission has been recognized or has intensified in new locations where the available vaccines are either unaffordable or unlicensed. In addition, the near-eradication of poliomyelitis from Asia has elevated JE in the public health agenda of preventable childhood diseases, and surveillance of acute neurological infections to confirm polio eradication, simultaneously, has led to a greater awareness of the disease burden attributable to JE. The only internationally licensed JE vaccine, an inactivated mouse-brain derived vaccine, is efficacious but is problematic from the perspectives of reactogenicity, requirement for numerous doses, cost and reliance on a neurological tissue substrate. A live-attenuated vaccine distributed only in China also is efficacious and requires fewer doses; however, production and regulatory standards are unresolved. Several approaches toward developing novel JE vaccines that could fill the gap in JE vaccine need are under pursuit. The minutes and recommendations of a meeting of experts to discuss these issues, jointly sponsored by the World Health Organization and the Children's Vaccine Initiative in Bangkok, Thailand, 13-15 October, 1998, are presented.

Immunization with plasmid DNA encoding the envelope glycoprotein of Japanese Encephalitis virus confers significant protection against intracerebral viral challenge without inducing detectable antiviral antibodies

A plasmid DNA construct, pCMXENV encoding the envelope (E) glycoprotein of Japanese Encephalitis virus (JEV), was constructed. This plasmid expresses the E protein intracellularly, when transfected into Vero cells in culture. The ability of pCMXENV to protect mice from lethal JEV infection was evaluated using an intracerebral (i.c.) JEV challenge model. Several independent immunization and JEV challenge experiments were carried out and the results indicate that 51 and 59% of the mice are protected from lethal i.c. JEV challenge, when immunized with pCMXENV via intramuscular (i.m.) and intranasal (i.n.) routes respectively. None of the mice immunized with the vector DNA (pCMX) survived in any of these experiments. JEV-specific antibodies were not detected in pCMXENV-immunized mice either before or after challenge. JEV-specific T cells were observed in mice immunized with pCMXENV which increased significantly after JEV challenge indicating the presence of vaccination-induced memory T cells. Enhanced production of interferon-gamma (IFN-gamma) and complete absence of interleukin-4 (IL-4) in splenocytes of pCMXENV-immunized mice on restimulation with JEV antigens in vitro indicated that the protection is likely to be mediated by T helper (Th) lymphocytes of the Th1 sub-type. In conclusion, our results demonstrate that immunization with a plasmid DNA expressing an intracellular form of JEV E protein confers significant protection against i.c. JEV challenge even in the absence of detectable antiviral antibodies.

The anamnestic neutralizing antibody response is critical for protection of mice from challenge following vaccination with a plasmid encoding the Japanese encephalitis virus premembrane and envelope genes

For Japanese encephalitis (JE), we previously reported that recombinant vaccine-induced protection from disease does not prevent challenge virus replication in mice. Moreover, DNA vaccines for JE can provide protection from high challenge doses in the absence of detectable prechallenge neutralizing antibodies. In the present study, we evaluated the role of postchallenge immune responses in determining the outcome of JE virus infection, using mice immunized with a plasmid, pcDNA3JEME, encoding the JE virus premembrane (prM) and envelope (E) coding regions. In the first experiment, 10 mice were vaccinated once (five animals) or twice (remainder) with 100 micrograms of pcDNA3JEME. All of these mice showed low (6 of 10) or undetectable (4 of 10) levels of neutralizing antibodies. Interestingly, eight of these animals showed a rapid rise in neutralizing antibody following challenge with 10,000 50% lethal doses of JE virus and survived for 21 days, whereas only one of the two remaining animals survived. No unimmunized animals exhibited a rise of neutralizing antibody or survived challenge. Levels of JE virus-specific immunoglobulin M class antibodies were elevated following challenge in half of the unimmunized mice and in the single pcDNA3JEME-immunized mouse that died. In the second experiment, JE virus-specific primary cytotoxic T-lymphocyte (CTL) activity was detected in BALB/c mice immunized once with 100 micrograms of pcDNA3JEME 4 days after challenge, indicating a strong postchallenge recall of CTLs. In the third experiment, evaluation of induction of CTLs and antibody activity by plasmids containing portions of the prM/E cassette demonstrated that induction of CTL responses alone were not sufficient to prevent death. Finally, we showed that antibody obtained from pcDNA3JEME-immunized mice 4 days following challenge could partially protect recipient mice from lethal challenge. Taken together, these results indicate that neutralizing antibody produced following challenge provides the critical protective component in pcDNA3JEME-vaccinated mice.

Induction of Japanese encephalitis virus-specific cytotoxic T lymphocytes in humans by poxvirus-based JE vaccine candidates

Poxvirus-based recombinant Japanese encephalitis (JE) vaccine candidates, NYVAC-JEV and ALVAC-JEV, were examined for their ability to induce JE virus-specific cytotoxic T lymphocytes (CTLs) in a phase I clinical trial. These vaccine candidates encoded the JE virus premembrane (prM), envelope (E) and non-structural 1 (NS1) proteins. The volunteers received subcutaneous inoculations with each of these candidates on days 0 and 28, and blood was drawn 2 days before vaccination and on day 58. Anti-E and anti-NS1 antibodies were elicited in most vaccinees inoculated with NYVAC-JEV and in some vaccinees inoculated with ALVAC-JEV. Peripheral blood mononuclear cells (PBMCs) obtained from approximately one half of vaccines showed positive proliferation in response to stimulation with live JE virus. Cytotoxic assays demonstrated the presence of JE virus-specific CTLs in in vitro-stimulated PBMCs obtained from two NYVAC-JEV and two ALVAC-JEV vaccinees. Cell depletion tests using PBMCs from one NYVAC-JEV recipient indicated that the phenotype of CTLs was CD8+CD4-.

Particulate vaccine candidate for Japanese encephalitis induces long-lasting virus-specific memory T lymphocytes in mice

We previously reported that extracellular particles (EPs) composed of premembrane (prM) and envelope (E) proteins were released from cells infected with recombinant vaccinia viruses encoding Japanese encephalitis (JE) virus prM and E genes. In the present study, EPs were evaluated for induction of JE virus-specific antibody and specific T lymphocytes in mice. Six- to 8-week-old male Balb/c mice were inoculated intraperitoneally once or twice (at a 3-week interval) with purified EPs containing 1 microgram of E without adjuvant. Neutralizing antibody was detected and spleen cells proliferated against JE viral antigen 3 weeks after the second immunization with EPs. Neutralizing antibody and JE virus-specific T lymphocytes were also detected 10 months after immunization with EPs containing 2 micrograms of E. Spleen cells obtained from EP-immunized mice and stimulated in vitro with live JE virus, expressed JE virus-specific cytotoxic activity. The cytotoxic activity was reduced by treatment with anti-CD3 antibody and complement. These results indicate that immunization with EPs induces long-lasting specific antibody and memory T cells in mice.