Establishment and characterization of Japanese encephalitis virus-specific, human CD4(+) T-cell clones: flavivirus cross-reactivity, protein recognition, and cytotoxic activity

Duck Tembusu virus induces stronger cellular responses than Japanese encephalitis virus in primary duck neurons and fibroblasts

Duck Tembusu virus (DTMUV) and Japanese encephalitis virus (JEV) are mosquito-borne flaviviruses. These two viruses infect ducks; however, they show different neurological outcomes. The mechanism of DTMUV- and JEV-induced neuronal death has not been well investigated. In the present study, we examined the differences in the mechanisms involved in virus-induced cell death and innate immune responses between DTMUV KPS54A61 strain and JEV JaGAr-01 strain using primary duck neurons (DN) and duck fibroblasts (CCL-141). DN and CCL-141 were permissive for the infection and replication of these two viruses, which upregulated the expression of innate immunity genes. Both DTMUV and JEV induced cell death via a caspase-3-dependent manner; however, DTMUV triggered more cell death than JEV did in both CCL-141 and DN. These findings suggest that DTMUV infection causes apoptosis in duck neurons and fibroblasts more strongly than JEV. Levels of the mRNA expression of innate immunity-related genes after DTMUV infection were generally higher than levels after JEV infection, suggesting that DTMUV-induced immune response in duck cells may exhibit toxic effect rather than protective effects. This article is protected by copyright. All rights reserved.

Pre-existing Immunity to Japanese Encephalitis Virus Alters CD4 T Cell Responses to Zika Virus Inactivated Vaccine

The epidemic spread of Zika virus (ZIKV), associated with devastating neurologic syndromes, has driven the development of multiple ZIKV vaccines candidates. An effective vaccine should induce ZIKV-specific T cell responses, which are shown to improve the establishment of humoral immunity and contribute to viral clearance. Here we investigated how previous immunization against Japanese encephalitis virus (JEV) and yellow fever virus (YFV) influences T cell responses elicited by a Zika purified-inactivated virus (ZPIV) vaccine. We demonstrate that three doses of ZPIV vaccine elicited robust CD4 T cell responses to ZIKV structural proteins, while ZIKV-specific CD4 T cells in pre-immunized individuals with JEV vaccine, but not YFV vaccine, were more durable and directed predominantly toward conserved epitopes, which elicited Th1 and Th2 cytokine production. In addition, T cell receptor repertoire analysis revealed preferential expansion of cross-reactive clonotypes between JEV and ZIKV, suggesting that pre-existing immunity against JEV may prime the establishment of stronger CD4 T cell responses to ZPIV vaccination. These CD4 T cell responses correlated with titers of ZIKV-neutralizing antibodies in the JEV pre-vaccinated group, but not in flavivirus-naïve or YFV pre-vaccinated individuals, suggesting a stronger contribution of CD4 T cells in the generation of neutralizing antibodies in the context of JEV-ZIKV cross-reactivity.

Japanese Encephalitis Vaccines

Purpose of review

As an eminently vaccine-preventable disease, encephalitis caused by Japanese encephalitis virus (JEV) has attracted an unusually high degree of attention from those seeking to develop viral vaccines. Since the 1950s, all types of JEV vaccines including inactivated, recombinant and live attenuated ones have been licensed. As an example of an extremely successful endeavour, the time is ripe for reviewing the development of JEV vaccines and probing the reasons behind their uniform success.

Recent findings

Vaccines against JEV have come a long way since the first licensing in the mid-1950s of the mouse brain-grown-inactivated virus preparations, to the present day live-attenuated virus vaccines. A survey of the various inactivated and live vaccines developed against JEV provides a striking insight into the impressive safety and efficacy of all the vaccines available to prevent encephalitis from JEV. This review juxtaposes studies to understand naturally acquired immunity against JEV that have mostly been published post-2000, compares these with those elicited by vaccines and highlights the paucity of data on cell-mediated immune responses elicited by JEV vaccines.

Summary

This article not only seeks to make available the immense salient literature on this endeavour in one collection, but also queries the basis for the remarkable success of JEV vaccines, not least of which may be the ease of protecting against encephalitis caused by JEV. To conclude, the true test of the ingenuity of those dedicated to the pursuit of viral vaccines would be success against viral diseases such as HIV-AIDS and dengue that pose a far greater challenge to scientists.

Tick-Borne Encephalitis Virus: A Quest for Better Vaccines against a Virus on the Rise

Tick-borne encephalitis virus (TBEV), a member of the family Flaviviridae, is one of the most important tick-transmitted viruses in Europe and Asia. Being a neurotropic virus, TBEV causes infection of the central nervous system, leading to various (permanent) neurological disorders summarized as tick-borne encephalitis (TBE). The incidence of TBE cases has increased due to the expansion of TBEV and its vectors. Since antiviral treatment is lacking, vaccination against TBEV is the most important protective measure. However, vaccination coverage is relatively low and immunogenicity of the currently available vaccines is limited, which may account for the vaccine failures that are observed. Understanding the TBEV-specific correlates of protection is of pivotal importance for developing novel and improved TBEV vaccines. For affording robust protection against infection and development of TBE, vaccines should induce both humoral and cellular immunity. In this review, the adaptive immunity induced upon TBEV infection and vaccination as well as novel approaches to produce improved TBEV vaccines are discussed.

Cross-Reactive Immunity Among Flaviviruses

Flaviviruses consist of significant human pathogens responsible for hundreds of millions of infections each year. Their antigenic relationships generate immune responses that are cross-reactive to multiple flaviviruses and their widespread and overlapping geographical distributions, coupled with increases in vaccination coverage, increase the likelihood of exposure to multiple flaviviruses. Depending on the antigenic properties of the viruses to which a person is exposed, flavivirus cross-reactivity can be beneficial or could promote immune pathologies. In this review we describe our knowledge of the functional immune outcomes that arise from varied flaviviral immune statuses. The cross-reactive antibody and T cell immune responses that are protective versus pathological are also addressed.

T Lymphocytes as Measurable Targets of Protection and Vaccination Against Viral Disorders

Continuous epidemiological surveillance of existing and emerging viruses and their associated disorders is gaining importance in light of their abilities to cause unpredictable outbreaks as a result of increased travel and vaccination choices by steadily growing and aging populations. Close surveillance of outbreaks and herd immunity are also at the forefront, even in industrialized countries, where previously eradicated viruses are now at risk of re-emergence due to instances of strain recombination, contractions in viral vector geographies, and from their potential use as agents of bioterrorism. There is a great need for the rational design of current and future vaccines targeting viruses, with a strong focus on vaccine targeting of adaptive immune effector memory T cells as the gold standard of immunity conferring long-lived protection against a wide variety of pathogens and malignancies. Here, we review viruses that have historically caused large outbreaks and severe lethal disorders, including respiratory, gastric, skin, hepatic, neurologic, and hemorrhagic fevers. To observe trends in vaccinology against these viral disorders, we describe viral genetic, replication, transmission, and tropism, host-immune evasion strategies, and the epidemiology and health risks of their associated syndromes. We focus on immunity generated against both natural infection and vaccination, where a steady shift in conferred vaccination immunogenicity is observed from quantifying activated and proliferating, long-lived effector memory T cell subsets, as the prominent biomarkers of long-term immunity against viruses and their associated disorders causing high morbidity and mortality rates.

Cross-Reactivity and Anti-viral Function of Dengue Capsid and NS3-Specific Memory T Cells Toward Zika Virus

Zika virus (ZIKV), a flavivirus with homology to dengue virus (DENV), is spreading to areas of DENV hyper-endemicity. Heterologous T cell immunity, whereby virus-specific memory T cells are activated by variant peptides derived from a different virus, can lead to enhanced viral clearance or diminished protective immunity and altered immunopathology. In mice, CD8+ T cells specific for DENV provide in vivo protective efficacy against subsequent ZIKV infection. In humans, contrasting studies report complete absence or varying degrees of DENV/ZIKV T cell cross-reactivity. Moreover, the impact of cross-reactive T cell recognition on the anti-viral capacity of T cells remains unclear. Here, we show that DENV-specific memory T cells display robust cross-reactive recognition of ZIKV NS3 ex vivo and after in vitro expansion in respectively n = 7/10 and n = 9/9 dengue-immune individuals tested. In contrast, cross-reactivity toward ZIKV capsid is low or absent. Cross-reactive recognition of DENV or ZIKV NS3 peptides elicits similar production of the anti-viral effector mediators IFN-γ, TNF-α, and CD107a. We identify 9 DENV/ZIKV cross-reactive epitopes, 7 of which are CD4+ and 2 are CD8+ T cell epitopes. We also show that cross-reactive CD4+ and CD8+ T cells targeting novel NS3 epitopes display anti-viral effector potential toward ZIKV-infected cells, with CD8+ T cells mediating direct lyses of these cells. Our results demonstrate that DENV NS3-specific memory T cells display anti-viral effector capacity toward ZIKV, suggesting a potential beneficial effect in humans of pre-existing T cell immunity to DENV upon ZIKV infection.

Development of Virus-Like-Particle Vaccine and Reporter Assay for Zika Virus

Recent worldwide outbreaks of Zika virus (ZIKV) infection and the lack of an approved vaccine raise serious concerns regarding preparedness to combat this emerging virus. We used a virus-like particle (VLP)-based approach to develop a vaccine and a microneutralization assay for ZIKV. A synthetic capsid-premembrane-envelope (C-prM-E) gene construct of ZIKV was used to generate reporter virus particles (RVPs) that package a green fluorescent protein (GFP) reporter-expressing West Nile virus (WNV) replicon. The assay was adapted to a 96-well format, similar to the plaque reduction neutralization test (PRNT), and showed high reproducibility with specific detection of ZIKV neutralizing antibodies. Furthermore, C-prM-E and prM-E VLPs were tested as vaccine candidates in mice and compared to DNA vaccination. While the ZIKV prM-E construct alone was sufficient for generating VLPs, efficient VLP production from the C-prM-E construct could be achieved in the presence of the WNV NS2B-3 protease, which cleaves C from prM, allowing virus release. Immunization studies in mice showed that VLPs generated higher neutralizing antibody titers than those with the DNA vaccines, with C-prM-E VLPs giving slightly higher titers than those with prM-E VLPs. The superiority of C-prM-E VLPs suggests that inclusion of capsid may have benefits for ZIKV and other flaviviral VLP vaccines. To facilitate the VLP platform, we generated a stable cell line expressing high levels of ZIKV prM-E proteins that constitutively produce VLPs as well as a cell line expressing ZIKV C-prM-E proteins for RVP production. While several vaccine platforms have been proposed for ZIKV, this study describes a safe, effective, and economical VLP-based vaccine against ZIKV.IMPORTANCE To address the growing Zika virus epidemic, we undertook this study with two objectives: first, to develop a safe, effective, and economical vaccine for ZIKV, and second, to develop a rapid and versatile assay to detect the anti-ZIKV immune response. We generated a cell line stably expressing ZIKV prM-E that produces large amounts of VLPs in the supernatant and a ZIKV C-prM-E cell line that produces reporter virus particles upon transfection with a GFP replicon plasmid. The prM-E VLPs induced a strong neutralizing antibody response in mice that was better when the capsid was included. VLP-based vaccines showed significantly better neutralizing antibody responses than those with their DNA counterparts. The RVP-based microneutralization assay worked similarly to the PRNT assay, with a rapid GFP readout in a 96-well format. Our VLP-based platform provides a source for a ZIKV vaccine and diagnosis that can rapidly be adapted to current outbreaks.

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.

Mapping and analysis of West Nile virus-specific monoclonal antibodies: prospects for vaccine development

Seasonal epidemics of West Nile virus (WNV) infection now occur throughout North America, causing clinical symptoms ranging from fever to encephalitis. There are no specific treatment options or licensed vaccines. Several classically developed vaccine candidates are being evaluated in clinical trials. However, questions of safety and/or immunogenicity may limit their usefulness. Mapping of human and murine antibody repertoires against the WNV envelope protein after WNV infection have revealed important insights into the protective immune response against the virus. This review will give an overview of vaccines under development and summarize current data on E-protein antigenicity that could aid in the design of next generation WNV vaccines.

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.

Characterization of T cell receptors of Th1 cells infiltrating inflamed skin of a novel murine model of palladium-induced metal allergy

Metal allergy is categorized as a delayed-type hypersensitivity reaction, and is characterized by the recruitment of lymphocytes into sites of allergic inflammation. Because of the unavailability of suitable animal models for metal allergy, the role of T cells in the pathogenesis of metal allergy has not been explored. Thus, we developed a novel mouse model for metal allergy associated with infiltration of T cells by multiple injections of palladium (Pd) plus lipopolysaccharide into the footpad. Using this model, we characterized footpad-infiltrating T cells in terms of phenotypic markers, T cell receptor (TCR) repertoires and cytokine expression. CD3+ CD4+ T cells accumulated in the allergic footpads 7 days after Pd challenge. The expression levels of CD25, interleukin-2, interferon-γ and tumor necrosis factor, but not interleukin-4 and interleukin-5, increased in the footpads after challenge, suggesting CD4+ T helper 1 (Th1) cells locally expanded in response to Pd. Infiltrated T cells in the footpads frequently expressed AV18-1 and BV8-2 T cell receptor (TCR) chains compared with T cells in the lymph nodes and exhibited oligoclonality. T-cell clones identified from Pd-allergic mouse footpads shared identical CDR3 sequences containing AV18-1 and BV8-2. These results suggest that TCR AV18-1 and BV8-2 play dominant and critical parts in the antigen specificity of Pd-specific Th1 cells.

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.

Recombinant nucleocapsid-like particles from dengue-2 virus induce protective CD4+ and CD8+ cells against viral encephalitis in mice

Virus-like particles are a highly effective type of subunit vaccine that mimics the overall structure of virus particles without containing infectious genetic material. In this work, a particulate form of the recombinant capsid protein from dengue-2 was evaluated in mice to determine the level of protection against viral challenge and to measure the antigen-induced cell-mediated immunity (CMI). The nucleocapsid-like particles (NLPs) adjuvanted with alum did not induce antiviral antibodies. However, splenocytes from the immunized animals secreted high levels of IFN-gamma upon virus stimulation, and a significant protection rate was achieved after challenge with lethal dengue-2 virus. Finally, both IFN-gamma secretion and protection against viral encephalitis were demonstrated to be dependent on CD4(+) and CD8(+) cells. This study provides new evidences regarding the protective role of the CMI in the mouse model without the induction of neutralizing antibodies. Further studies in non-human primates or humanized mice should be carried out to elucidate the usefulness of the NLPs as a potential vaccine candidate against dengue disease.

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.

Complex adenovirus-mediated expression of West Nile virus C, PreM, E, and NS1 proteins induces both humoral and cellular immune responses

West Nile Virus (WNV), a member of the family Flaviviridae, was first identified in Africa in 1937. In recent years, it has spread into Europe and North America. The clinical manifestations of WNV infection range from mild febrile symptoms to fatal encephalitis. Two genetic lineages (lineages I and II) are recognized; lineage II is associated with mild disease, while lineage I has been associated with severe disease, including encephalitis. WNV has now spread across North America, significantly affecting both public and veterinary health. In the efforts to develop an effective vaccine against all genetic variants of WNV, we have studied the feasibility of inducing both neutralizing and cellular immune responses by de novo synthesis of WNV antigens using a complex adenoviral vaccine (CAdVax) vector. By expressing multiple WNV proteins from a single vaccine vector, we were able to induce both humoral and cellular immune responses in vaccinated mice. Neutralization assays demonstrated that the antibodies were broadly neutralizing against both lineages of WNV, with a significant preference for the homologous lineage II virus. The results from this study show that multiple antigens synthesized de novo from a CAdVax vector are capable of inducing both humoral and cellular immune responses against WNV and that a multiantigen approach may provide broad protection against multiple genetic variants of WNV.

A recombinant capsid protein from Dengue-2 induces protection in mice against homologous virus

In the present work, we study the immunogenicity and protective capacity of a recombinant capsid protein from Dengue-2 virus. The capsid gene was cloned under the T5 phage promoter and expressed in Escherichia coli. The recombinant protein was obtained mainly associated to the soluble fraction upon cellular disruption and exhibited a pattern of high aggregation, determined by gel filtration chromatography. The semipurified preparation was inoculated in mice and after three doses, no antiviral antibodies were induced. On the other hand, mice intracranially challenged with homologous lethal virus, exhibited statistically significant protection with respect to the control group. These results describe, for the first time, the protective capacity of the capsid protein of Dengue virus indicating the existence of a protector mechanism, which is totally independent of the antibodies. This lack of induction of antiviral antibodies makes the capsid protein an attractive vaccine candidate against dengue since eliminates the potential risk of the induction of antibody dependent enhancement associated to the current vaccines under study.

Changes in paracrine interleukin-2 requirement, CCR7 expression, frequency, and cytokine secretion of human immunodeficiency virus-specific CD4+ T cells are a consequence of antigen load

Virus-specific CD4+ T-cell responses are thought to be required for the induction and maintenance of many effective CD8+ T-cell and B-cell immune responses in experimental animals and humans. Although the presence of human immunodeficiency virus (HIV)-specific CD4+ T cells has been documented in patients at all stages of HIV infection, many fundamental questions regarding their frequency and function remain. A 10-color, 12-parameter flow cytometric panel was utilized to examine the frequency, memory phenotype (CD27, CCR7, and CD45RA), and cytokine production (interleukin-2 [IL-2], gamma interferon, and tumor necrosis factor alpha) of CD4+ T cells specific for HIV antigens as well as for adenovirus, Epstein-Barr virus (EBV), influenza H1N1 virus, influenza H3N2 virus, cytomegalovirus, varicella-zoster virus (VZV), and tetanus toxoid in normal controls, long-term nonprogressors (LTNP), and HIV-infected patients with progressive disease on or off therapy. The HIV-specific CD4+ T-cell responses in LTNP and patients on therapy were similar in frequency, phenotype, and cytokine production to responses directed against adenovirus, EBV, influenza virus, and VZV. HIV-specific CD4+ T cells from patients off antiretroviral therapy demonstrated a shift towards a CCR7(-) CD45RA(-) phenotype and a reduced percentage of IL-2-producing cells. The alterations in cytokine production during HIV viremia were found to be intrinsic to the HIV-specific CD4+ T cells and caused a requirement for IL-2 supplied exogenously for proliferation to occur. These observations suggest that many previously described changes in HIV-specific CD4+ T-cell function and phenotype are a consequence of high levels of antigen in viremic patients. In addition, defects in function and phenotype of HIV-specific CD4+ T cells are not readily discernible in the context of antiretroviral therapy but rather are similar to responses to other viruses.

CD4+ T-cell responses are required for clearance of West Nile virus from the central nervous system

Although studies have established that innate and adaptive immune responses are important in controlling West Nile virus (WNV) infection, the function of CD4(+) T lymphocytes in modulating viral pathogenesis is less well characterized. Using a mouse model, we examined the role of CD4(+) T cells in coordinating protection against WNV infection. A genetic or acquired deficiency of CD4(+) T cells resulted in a protracted WNV infection in the central nervous system (CNS) that culminated in uniform lethality by 50 days after infection. Mice surviving past day 10 had high-level persistent WNV infection in the CNS compared to wild-type mice, even 45 days following infection. The absence of CD4(+) T-cell help did not affect the kinetics of WNV infection in the spleen and serum, suggesting a role for CD4-independent clearance mechanisms in peripheral tissues. WNV-specific immunoglobulin M (IgM) levels were similar to those of wild-type mice in CD4-deficient mice early during infection but dropped approximately 20-fold at day 15 postinfection, whereas IgG levels in CD4-deficient mice were approximately 100- to 1,000-fold lower than in wild-type mice throughout the course of infection. WNV-specific CD8(+) T-cell activation and trafficking to the CNS were unaffected by the absence of CD4(+) T cells at day 9 postinfection but were markedly compromised at day 15. Our experiments suggest that the dominant protective role of CD4(+) T cells during primary WNV infection is to provide help for antibody responses and sustain WNV-specific CD8(+) T-cell responses in the CNS that enable viral clearance.

Recognition of conserved amino acid motifs of common viruses and its role in autoimmunity

The triggers of autoimmune diseases such as multiple sclerosis (MS) remain elusive. Epidemiological studies suggest that common pathogens can exacerbate and also induce MS, but it has been difficult to pinpoint individual organisms. Here we demonstrate that in vivo clonally expanded CD4+ T cells isolated from the cerebrospinal fluid of a MS patient during disease exacerbation respond to a poly-arginine motif of the nonpathogenic and ubiquitous Torque Teno virus. These T cell clones also can be stimulated by arginine-enriched protein domains from other common viruses and recognize multiple autoantigens. Our data suggest that repeated infections with common pathogenic and even nonpathogenic viruses could expand T cells specific for conserved protein domains that are able to cross-react with tissue-derived and ubiquitous autoantigens.

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.

Extensive cross-reactivity of CD4+ adenovirus-specific T cells: implications for immunotherapy and gene therapy

Adenovirus (Ad)-specific T-cell responses in healthy adult donors were investigated. Ad5, inactivated by methylene blue plus visible light, induced proliferation and gamma interferon (IFN-gamma) production in peripheral blood mononuclear cells of the majority of donors. Responding T cells were CD4(+) and produced IFN-gamma upon restimulation with infectious Ad5 and Ads of different subgroups. T-cell clones showed distinct cross-reactivity patterns recognizing Ad serotypes from either one subgroup (C), two subgroups (B and C), or three subgroups (A, B, and C). This cross-reactivity of Ad-specific T cells has relevance both for Ad-based gene therapy protocols, as well as for the feasibility of T-cell-mediated adoptive immunotherapy in recipients of an allogeneic stem cell transplantation.

Antigenic Structure of Flavivirus Proteins

The increased activity of Dengue virus in the tropical regions of the world and the recent movement of West Nile virus from the eastern to the western hemisphere emphasize the fact that vector-borne flaviviruses are medically important emerging infectious diseases. These facts warrant continued efforts to decode all facets of flavivirus immunology. This chapter reviews current understanding of the antigenic fine structure of flaviviral structural and nonstructural (NS) proteins and their involvement in B- an T-cell host responses. The virion structural glycoprotein E elicits both virus-neutralizing antibodies and antiviral Th-cell responses. Consistent with the current hypothesis of the MHC class I pathway of protein processing, immunodominant flaviviral Tc-cell epitopes mainly reside on the NS proteins. To prepare effective and inexpensive subunit vaccines, we will need to continue to better understand these structure-function relationships of flavivirus proteins.

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.

Yellow fever vector live-virus vaccines: West Nile virus vaccine development

By combining molecular-biological techniques with our increased understanding of the effect of gene sequence modification on viral function, yellow fever 17D, a positive-strand RNA virus vaccine, has been manipulated to induce a protective immune response against viruses of the same family (e.g. Japanese encephalitis and dengue viruses). Triggered by the emergence of West Nile virus infections in the New World afflicting humans, horses and birds, the success of this recombinant technology has prompted the rapid development of a live-virus attenuated candidate vaccine against West Nile virus.

Yellow fever virus encephalitis: properties of the brain-associated T-cell response during virus clearance in normal and gamma interferon-deficient mice and requirement for CD4+ lymphocytes

Viral encephalitis caused by neuroadapted yellow fever 17D virus (PYF) was studied in parental and gamma interferon (IFN-gamma)-deficient (IFN-gamma knockout [GKO]) C57BL/6 mice. The T-cell responses which enter the brain during acute fatal encephalitis of nonimmunized mice, as well as nonfatal encephalitis of immunized mice, were characterized for relative proportions of CD4+ and CD8+ cells, their proliferative responses, and antigen-specific expression of cytokines during stimulation in vitro. Unimmunized mice accumulated only low levels of T cells within the brain during fatal disease, whereas the brains of immunized mice contained higher levels of both T-cell subsets in response to challenge, with CD8+ cells increased relative to the CD4+ subset. The presence of T cells correlated with the time at which virus was cleared from the central nervous system in both parental and GKO mice. Lymphocytes isolated from the brains of challenged immunized mice failed to proliferate in vitro in response to T-cell mitogens or viral antigens; however, IFN-gamma, interleukin 4 (IL-4), and, to a lesser extent, IL-2 were detectable after stimulation. The levels of IFN-gamma, but not IL-2 or IL-4, were augmented in response to viral antigen, and this specificity was detectable in the CD4+ compartment. When tested for the ability to survive both immunization and challenge with PYF virus, GKO and CD8 knockout mice did not differ from parental mice (80 to 85% survival), although GKO mice exhibited a defect in virus clearance. In contrast, CD4 knockout and Igh-6 mice were unable to resist challenge. The data implicate antibody in conjunction with CD4+ lymphocytes bearing a Th1 phenotype as the critical factors involved in virus clearance in this model.

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.

Rapid determination of HLA B*07 ligands from the West Nile virus NY99 genome

Defined T cell epitopes for West Nile (WN) virus may be useful for developing subunit vaccines against WN virus infection and diagnostic reagents to detect WN virus-specific immune response. We applied a bioinformatics (EpiMatrix) approach to search the WN virus NY99 genome for HLA B*07 restricted cytotoxic T cell (CTL) epitopes. Ninety-five of 3,433 WN virus peptides scored above a predetermined cutoff, suggesting that these would be likely to bind to HLA B*07 and would also be likely candidate CTL epitopes. Compared with other methods for genome mapping, derivation of these ligands was rapid and inexpensive. Major histocompatibility complex ligands identified by this method may be used to screen T cells from WN virus-exposed persons for cell-mediated response to WN virus or to develop diagnostic reagents for immunopathogenesis studies and epidemiologic surveillance.

Immunogenicity and protective efficacy of the current inactivated Japanese encephalitis vaccine against different Japanese encephalitis virus strains

Mouse brain-derived, inactivated Japanese encephalitis (JE) vaccine has been internationally used for many years. It is believed that this vaccine made a great contribution to the reduction of JE patients in several countries. Mouse brain-derived, Beijing-1 and Nakayama JE vaccines induce high levels of neutralizing antibodies. High levels of induced antibodies are maintained at least for 3-4 yr. The induced antibodies are cross-reactive to heterologous strains; however, the neutralizing antibody titers against heterologous strains are usually lower than those against homologous strains. Considering that both Nakayama and Beijing-1 JE vaccines showed high levels of protective efficacy in Taiwan and Thailand where strains other than Nakayama and Beijing-1 were circulating, we conclude that the current inactivated JE vaccine can induce high levels of protective immunity against heterologous JE virus strains.

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.

Immunogenicity, genetic stability, and protective efficacy of a recombinant, chimeric yellow fever-Japanese encephalitis virus (ChimeriVax-JE) as a live, attenuated vaccine candidate against Japanese encephalitis

Yellow fever (YF) 17D vaccine virus, having a 60-year history of safe and effective use, is an ideal vector to deliver heterologous genes from other medically important flaviviruses. A chimeric YF/Japanese encephalitis (JE) virus (ChimeriVax-JE virus) was constructed by insertion of the premembrane and envelope (prME) genes of an attenuated human vaccine strain (SA14-14-2) of Japanese encephalitis (JE) virus between core and nonstructural (NS) genes of a YF 17D infectious clone. The virus grew to high titers in cell cultures and was not neurovirulent for 3- to 4-week-old mice at doses </=6 log10 plaque forming units (pfu) inoculated by the intracerebral (IC) route. In contrast, commercial YF 17D vaccine was highly neurovirulent for weanling mice by the same route. Mice inoculated subcutaneously with one dose of >/=10(3) pfu of ChimeriVax-JE virus were solidly protected against intraperitoneal challenge with a virulent JE virus. Genetic stability of the chimera was assessed by sequential passages in cell cultures or in mouse brain. All attenuating residues and the avirulent phenotype were preserved after 18 passages in cell cultures or 6 passages in mouse brains.