Cross-reactive T-cell responses to the nonstructural regions of dengue viruses among dengue fever and dengue hemorrhagic fever patients in Malaysia

Regional Variation of the CD4 and CD8 T Cell Epitopes Conserved in Circulating Dengue Viruses and Shared with Potential Vaccine Candidates

As dengue expands globally and many vaccines are under trials, there is a growing recognition of the need for assessing T cell immunity in addition to assessing the functions of neutralizing antibodies during these endeavors. While several dengue-specific experimentally validated T cell epitopes are known, less is understood about which of these epitopes are conserved among circulating dengue viruses and also shared by potential vaccine candidates. As India emerges as the epicenter of the dengue disease burden and vaccine trials commence in this region, we have here aligned known dengue specific T cell epitopes, reported from other parts of the world with published polyprotein sequences of 107 dengue virus isolates available from India. Of the 1305 CD4 and 584 CD8 epitopes, we found that 24% and 41%, respectively, were conserved universally, whereas 27% and 13% were absent in any viral isolates. With these data, we catalogued epitopes conserved in circulating dengue viruses from India and matched them with each of the six vaccine candidates under consideration (TV003, TDEN, DPIV, CYD-TDV, DENVax and TVDV). Similar analyses with viruses from Thailand, Brazil and Mexico revealed regional overlaps and variations in these patterns. Thus, our study provides detailed and nuanced insights into regional variation that should be considered for itemization of T cell responses during dengue natural infection and vaccine design, testing and evaluation.

Dengue and COVID-19: two sides of the same coin

BACKGROUND

Many countries in Asia and Latin America are currently facing a double burden of outbreaks due to dengue and COVID-19. Here we discuss the similarities and differences between the two infections so that lessons learnt so far from studying both infections will be helpful in further understanding their immunopathogenesis and to develop therapeutic interventions.

MAIN BODY

Although the entry routes of the SARS-CoV-2 and the dengue virus (DENV) are different, both infections result in a systemic infection, with some similar clinical presentations such as fever, headache, myalgia and gastrointestinal symptoms. However, while dengue is usually associated with a tendency to bleed, development of micro and macrothrombi is a hallmark of severe COVID-19. Apart from the initial similarities in the clinical presentation, there are further similarities between such as risk factors for development of severe illness, cytokine storms, endothelial dysfunction and multi-organ failure. Both infections are characterised by a delayed and impaired type I IFN response and a proinflammatory immune response. Furthermore, while high levels of potent neutralising antibodies are associated with protection, poorly neutralising and cross-reactive antibodies have been proposed to lead to immunopathology by different mechanisms, associated with an exaggerated plasmablast response. The virus specific T cell responses are also shown to be delayed in those who develop severe illness, while varying degrees of endothelial dysfunction leads to increased vascular permeability and coagulation abnormalities.

CONCLUSION

While there are many similarities between dengue and SARS-CoV-2 infection, there are also key differences especially in long-term disease sequelae. Therefore, it would be important to study the parallels between the immunopathogenesis of both infections for development of more effective vaccines and therapeutic interventions.

Longitudinal Analysis of Dengue Virus-Specific Memory T Cell Responses and Their Association With Clinical Outcome in Subsequent DENV Infection

Memory T cells resulting from primary dengue virus (DENV) infection are hypothesized to influence the clinical outcome of subsequent DENV infection. However, the few studies involving prospectively collected blood samples have found weak and inconsistent associations with outcome and variable temporal trends in DENV-specific memory T cell responses between subjects. This study used both ex-vivo and cultured ELISPOT assays to further evaluate the associations between DENV serotype-cross-reactive memory T cells and severity of secondary infection. Using ex-vivo ELISPOT assays, frequencies of memory T cells secreting IFN-γ in response to DENV structural and non-structural peptide pools were low in PBMC from multiple time points prior to symptomatic secondary DENV infection and showed a variable response to infection. There were no differences in responses between subjects who were not hospitalized (NH, n=6) and those who were hospitalized with dengue hemorrhagic fever (hDHF, n=4). In contrast, responses in cultured ELISPOT assays were more reliably detectable prior to secondary infection and showed more consistent increases after infection. Responses in cultured ELISPOT assays were higher in individuals with hDHF (n=8) compared to NH (n=9) individuals before the secondary infection, with no difference between these groups after infection. These data demonstrate an association of pre-existing DENV-specific memory responses with the severity of illness in subsequent DENV infection, and suggest that frequencies of DENV-reactive T cells measured after short-term culture may be of particular importance for assessing the risk for more severe dengue disease.

Identification and selection of immunodominant B and T cell epitopes for dengue multi-epitope-based vaccine

Dengue virus (DENV) comprises four serotypes (DENV1-4) which cause 390 million global infections with 500,000 hospitalizations and 25,000 fatalities annually. Currently, the only FDA approved DENV vaccine is the chimeric live-attenuated vaccine, Dengvaxia®, which is based on the yellow fever virus (YFV) genome that carries the prM and E genes of the respective DENV 1, 2, 3, and 4 serotypes. However, it has lower efficacies against serotypes DENV1 (51%) and DENV2 (34%) when compared with DENV3 (75%) and DENV4 (77%). The absence of T cell epitopes from non-structural (NS) and capsid (C) proteins of the yellow fever vaccine strain might have prevented Dengvaxia® to elicit robust cellular immune responses, as CD8⁺ T cell epitopes are mainly localized in the NS3 and NS5 regions. Multi-epitope-based peptide vaccines carrying CD4⁺, CD8⁺ T cell and B cell epitopes represent a novel approach to generate specific immune responses. Therefore, assessing and selecting epitopes that can induce robust B and T cell responses is a prerequisite for constructing an efficient multi-epitope peptide vaccine. Potent B and T cell epitopes can be identified by utilizing immunoinformatic analysis, but the immunogenicity of the epitopes have to be experimentally validated. In this review, we presented T cell epitopes that have been predicted by bioinformatic approaches as well as recent experimental validations of CD4⁺ and CD8⁺ T cell epitopes by ex-vivo stimulation of PBMCs with specific peptides. Immunoproteomic analysis could be utilized to uncover HLA-specific epitopes presented by DENV-infected cells. Based on various approaches, immunodominant epitopes capable of inducing strong immune responses could be selected and incorporated to form a universally applicable multi-epitope-based peptide dengue vaccine.

Conserved epitopes with high HLA-I population coverage are targets of CD8+ T cells associated with high IFN-γ responses against all dengue virus serotypes

Cytotoxic CD8⁺ T cells are key for immune protection against viral infections. The breadth and cross-reactivity of these responses are important against rapidly mutating RNA viruses, such as dengue (DENV), yet how viral diversity affect T cell responses and their cross-reactivity against multiple variants of the virus remains poorly defined. In this study, an integrated analysis was performed to map experimentally validated CD8⁺ T cell epitopes onto the distribution of DENV genome sequences across the 4 serotypes worldwide. Despite the higher viral diversity observed within HLA-I restricted epitopes, mapping of 609 experimentally validated epitopes sequences on 3985 full-length viral genomes revealed 19 highly conserved epitopes across the four serotypes within the immunogenic regions of NS3, NS4B and NS5. These conserved epitopes were associated with a higher magnitude of IFN-γ response when compared to non-conserved epitopes and were restricted to 13 HLA class I genotypes, hence providing high coverage among human populations. Phylogeographic analyses showed that these epitopes are largely conserved in most of the endemic regions of the world, and with only some of these epitopes presenting distinct mutated variants circulating in South America and Asia.This study provides evidence for the existence of highly immunogenic and conserved epitopes across serotypes, which may impact design of new universal T-cell-inducing vaccine candidates that minimise detrimental effects of viral diversification and at the same time induce responses to a broad human population.

Dysfunctional Innate Immune Responses and Severe Dengue

Although infection with the dengue virus (DENV) causes severe dengue, it causes a mild self-limiting illness in the majority of individuals. There is emerging evidence that an aberrant immune response in the initial stages of infection lead to severe disease. Many inflammatory cytokines, chemokines, and lipid mediators are significantly higher in patients with severe dengue compared to those who develop mild infection, during febrile phase of illness. Monocytes, mast cells, and many other cells of the immune system, when infected with the DENV, especially in the presence of poorly neutralizing antibodies, leads to production of pro-inflammatory cytokines and inhibition of interferon signaling pathways. In addition, production of immunosuppressive cytokines such as IL-10 further leads to inhibition of cellular antiviral responses. This dysregulated and aberrant immune response leads to reduced clearance of the virus, and severe dengue by inducing a vascular leak and excessive inflammation due to high levels of inflammatory cytokines. Individuals with comorbid illnesses could be prone to more severe dengue due to low grade endotoxemia, gut microbial dysbiosis and an altered phenotype of innate immune cells. The immunosuppressive and inflammatory lipid mediators and altered phenotype of monocytes are likely to further act on T cells and B cells leading to an impaired adaptive immune response to the virus. Therefore, in order to identify therapeutic targets for treatment of dengue, it would be important to further characterize these mechanisms in order for early intervention. In this review, we discuss the differences in the innate immune responses in those who progress to develop severe dengue, compared to those with milder disease in order to understand the mechanisms that lead to severe dengue.

Two Is Better Than One: Evidence for T-Cell Cross-Protection Between Dengue and Zika and Implications on Vaccine Design

Dengue virus (DENV, family Flaviviridae, genus Flavivirus) exists as four distinct serotypes. Generally, immunity after infection with one serotype is protective and lifelong, though exceptions have been described. However, secondary infection with a different serotype can result in more severe disease for a minority of patients. Host responses to the first DENV infection involve the development of both cross-reactive antibody and T cell responses, which, depending upon their precise balance, may mediate protection or enhance disease upon secondary infection with a different serotype. Abundant evidence now exists that responses elicited by DENV infection can cross-react with other members of the genus Flavivirus, particularly Zika virus (ZIKV). Cohort studies have shown that prior DENV immunity is associated with protection against Zika. Cross-reactive antibody responses may enhance infection with flaviviruses, which likely accounts for the cases of severe disease seen during secondary DENV infections. Data for T cell responses are contradictory, and even though cross-reactive T cell responses exist, their clinical significance is uncertain. Recent mouse experiments, however, show that cross-reactive T cells are capable of mediating protection against ZIKV. In this review, we summarize and discuss the evidence that T cell responses may, at least in part, explain the cross-protection seen against ZIKV from DENV infection, and that T cell antigens should therefore be included in putative Zika vaccines.

Dengue Virus-Specific Humoral and T Cellular Immune Response in Italian Residents and Travelers Returning from Endemic Areas

Dengue virus (DENV), a member of the family Flaviviridae, is the causative agent of dengue fever, the most prevalent mosquito-borne viral illness in humans, representing a major public health concern in the tropical countries. Although humoral immunity to DENV has been extensively studied and widely used, little is known about the potential diagnostic use of T cell response for DENV diagnosis. The aim of our study was to characterize the T cell immunity in subjects with acute or past DENV infection, using an original and easy to perform ex vivo ELISpot assay, and to evaluate the role of cross-reactivity between the four DENV serotypes and between DENV and Zika virus (ZIKV). As controls, DENV-seronegative healthy subjects were enrolled and a cutoff of positive DENV-specific T cell response was calculated. DENV-specific T cell response for at least one DENV serotype was detected among all DENV-specific neutralization positive subject. Furthermore, our data showed that in acute DENV infection, the DENV-specific effector memory T cell response against the relevant serotype was predominant. However, a high level of cross-reactivity among all DENV serotypes was also documented. DENV-specific T cell response was almost undetectable among DENV-seronegative subjects with ZIKV acute infection, supporting the hypothesis that the assay could be useful in differential diagnosis between ZIKV and DENV infection.

Association of dengue virus-specific polyfunctional T-cell responses with clinical disease severity in acute dengue infection

INTRODUCTION

Although the role of dengue virus (DENV)-specific T cells in the pathogenesis of acute dengue infection is emerging, the functionality of virus-specific T cells associated with milder clinical disease has not been well studied. We sought to investigate how the functionality of DENV-NS3 and DENV-NS5 protein-specific T cells differ in patients with dengue fever (DF) and dengue hemorrhagic fever (DHF).

METHODS

Using intracellular cytokine assays, we assessed the production of interferon γ (IFNγ), tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-1β (MIP-1β), and CD107a expression in adult patients with acute DF (n = 21) and DHF (n = 22).

RESULTS

Quadruple cytokine-producing, polyfunctional DENV-NS3- and DENV-NS5-specific T cells were more frequent in those with DF when compared to those with DHF. While DENV-NS3- and DENV-NS5-specific T cells in patients with DF expressed IFNγ > TNF-α > MIP-β > CD107a, T cells of those with DHF predominantly expressed CD107a > MIP-1β > IFNγ > TNF-α. Overall production of IFNγ or TNF-α by DENV-NS3- and DENV-NS5-specific T cells was significantly higher in patients with DF. The majority of NS3-specific T cells in patients with DF (78.6%) and DHF (68.9%) were single-cytokine producers; 76.6% of DENV-NS5-specific T cells in those with DF and 77.1% of those with DHF, produced only a single cytokine. However, no significant association was found with polyfunctional T-cell responses and the degree of viraemia.

CONCLUSIONS

Our results suggest that the functional phenotype of DENV-specific T cells are likely to associate with clinical disease severity.

Human T Cell Response to Dengue Virus Infection

DENV is a major public health problem worldwide, thus underlining the overall significance of the proposed Program. The four dengue virus (DENV) serotypes (1-4) cause the most common mosquito-borne viral disease of humans, with 3 billion people at risk for infection and up to 100 million cases each year, most often affecting children. The protective role of T cells during viral infection is well-established. Generally, CD8 T cells can control viral infection through several mechanisms, including direct cytotoxicity, and production of pro-inflammatory cytokines such as IFN-γ and TNF-α. Similarly, CD4 T cells are thought to control viral infection through multiple mechanisms, including enhancement of B and CD8 T cell responses, production of inflammatory and anti-viral cytokines, cytotoxicity, and promotion of memory responses. To probe the phenotype of virus-specific T cells, epitopes derived from viral sequences need to be known. Here we discuss the identification of CD4 and CD8 T cell epitopes derived from DENV and how these epitopes have been used by researchers to interrogate the phenotype and function of DENV-specific T cell populations.

Longitudinal Analysis of Memory B and T Cell Responses to Dengue Virus in a 5-Year Prospective Cohort Study in Thailand

Prior exposure to dengue virus (DENV) has a profound impact on the outcome of infection, which varies according to the interval between infections. Antibodies secreted by B cells and cytokines secreted by T cells are thought to contribute both to protective immunity against DENV and the pathogenesis of dengue disease. We analyzed peripheral blood mononuclear cells (PBMC) collected from Thai children over a 5-year prospective cohort study to define the dynamics of DENV-specific memory B and T cell responses and the impact of symptomatic or subclinical DENV infections. To measure B cell responses, PBMC were stimulated with IL-2 plus R848 and culture supernatants were tested for DENV-binding antibodies by ELISA. To measure T cell responses, PBMC were stimulated in dual-color ELISPOT assays with overlapping peptide pools of structural and non-structural proteins from the four DENV types. B cell responses were low to one or more DENV types prior to symptomatic infection and increased with reactivity to all four types after infection. Subjects who had a subclinical infection or who did not experience a DENV infection during the study period showed strong memory B cell responses to all four DENV types. T cell responses to DENV peptides demonstrated a cytokine hierarchy of IFN-γ > IL-2 > IFN-γ/IL-2. T cell responses were low or absent prior to secondary infections. The trends in T cell responses to DENV peptides over 3 year post-infection were highly variable, but subjects who had experienced a secondary DENV1 infection showed higher cytokine responses compared to subjects who had experienced a secondary DENV2 or subclinical infection. The longitudinal nature of our study demonstrates persistent memory B cell responses over years and a lasting but variable impact of secondary DENV infection on DENV-specific T cell responses.

Influence of chemokines on the endothelial permeability and cellular transmigration during dengue

During a pathogenic infection, an inflammatory process is triggered in which several inflammatory mediators, such as cytokines, chemokines, growth factors, complement system components, nitric oxide, and others induce integrity alteration on the endothelial barrier. Chemokines are responsible for regulating leukocyte trafficking under homeostatic conditions as well as activating immune system cells under inflammatory conditions. They are crucial molecules in the early stages of infection, leading to the recruitment of immune cells, namely neutrophils, monocytes, natural killer (NK) cells, natural killer T cells (NKT), dendritic cells (DC), T lymphocytes and all cells expressing chemokine receptors for inflammatory sites. Other functions, such as collagen production, tissue repair, a proliferation of hematopoietic precursors and angiogenesis, are also performed by these molecules. Chemokines, amongst inflammatory mediators, play a key role in dengue immunopathogenesis. Dengue fever is a disease caused by the dengue virus (DENV). It is characterized by a broad spectrum of clinical manifestations ranging from asymptomatic cases to mild and severe symptomatic ones. As for the latter, the appearance of hemorrhagic manifestations and changes in vascular permeability may lead the patient to develop cavitary effusions, organ involvement, and even death. As chemokines exert an influence on various homeostatic and inflammatory processes, acting vigorously on vascular endothelial activation and cell migration, the main purpose of this chapter is to discuss the influence of chemokines on the alteration of endothelial permeability and migration of T lymphocytes in DENV infection.

Quantification of dengue virus specific T cell responses and correlation with viral load and clinical disease severity in acute dengue infection

Background

In order to understand the role of dengue virus (DENV) specific T cell responses that associate with protection, we studied their frequency and phenotype in relation to clinical disease severity and resolution of viraemia in a large cohort of patients with varying severity of acute dengue infection.

Methodology/Principal findings

Using ex vivo IFNγ ELISpot assays we determined the frequency of dengue viral peptide (DENV)-NS3, NS1 and NS5 responsive T cells in 74 adult patients with acute dengue infection and examined the association of responsive T cell frequency with the extent of viraemia and clinical disease severity. We found that total DENV-specific and DENV-NS3-specific T cell responses, were higher in patients with dengue fever (DF), when compared to those with dengue haemorrhagic fever (DHF). In addition, those with DF had significantly higher (p = 0.02) DENV-specific T cell responses on day 4 of infection compared to those who subsequently developed DHF. DENV peptide specific T cell responses inversely correlated with the degree of viraemia, which was most significant for DENV-NS3 specific T cell responses (Spearman’s r = -0.47, p = 0.0003). The frequency of T cell responses to NS1, NS5 and pooled DENV peptides, correlated with the degree of thrombocytopenia but had no association with levels of liver transaminases. In contrast, total DENV-IgG inversely correlated with the degree of thrombocytopenia and levels of liver transaminases.

Conclusions/Significance

Early appearance of DENV-specific T cell IFNγ responses before the onset of plasma leakage, appears to associate with milder clinical disease and resolution of viraemia, suggesting a protective role in acute dengue infection.

In order to understand the role of dengue virus (DENV) specific T cell responses in protection against infection, we studied T cell cytokine production in relation to clinical disease severity and resolution of viraemia in a large cohort of patients with varying severity of acute dengue infection. We found that DENV-specific T cell responses were higher in patients with dengue fever, when compared to those with dengue haemorrhagic fever. In addition, early appearance of DENV-specific T cell responses was significantly associated with milder clinical disease (p = 0.02). DENV peptide specific T cell responses inversely correlated with the degree of viraemia, which was most significant for DENV-NS3 specific T cell responses (Spearman’s r = -0.47, p = 0.0003). The frequency of NS1, NS5 and pooled DENV peptides, correlated with the degree of thrombocytopenia but had no association with liver transaminases. Our data suggest that early appearance of DENV-specific T cell IFNγ responses appear to associate with milder clinical disease and resolution of viraemia, suggesting a protective role in acute dengue infection.

HLA-directed bioinformatics approach for genome-wide mapping of dengue CTL epitopes

Aim: In silico approach was used to predict cytotoxic T lymphocyte (CTL) epitopes from the proteome of all four dengue serotypes. Methods: The immune epitope database analysis resource was used to analyze the CTL epitopes of dengue serotypes. The prediction of epitopes was done against nine high frequency HLA class I alleles occurring worldwide. Results: A total of 2784 epitopes were predicted from all four dengue virus proteomes. Immune epitope database analysis resource tool predicted 202 epitopes as positive for immunogenecity. A total of 39 of 257 consensus epitopes predicted were present in all four serotypes. This study identified nine new class I-restricted epitopes. Conclusion: Mapping of these potentially immunogenic dengue epitopes paves the way for future investigation of their utility as vaccine candidates to prevent or treat dengue virus infections.

Development of Peptide Vaccines in Dengue

Dengue is one of the most important arboviral infections worldwide, infecting up to 390 million people and causing 25,000 deaths annually. Although a licensed dengue vaccine is available, it is not efficacious against dengue serotypes that infect people living in South East Asia, where dengue is an endemic disease. Hence, there is an urgent need to develop an efficient dengue vaccine for this region. Data from different clinical trials indicate that a successful dengue vaccine must elicit both neutralizing antibodies and cell mediated immunity. This can be achieved by designing a multi-epitope peptide vaccine comprising B, CD8+ and CD4+ T cell epitopes. As recognition of T cell epitopes are restricted by human leukocyte antigens (HLA), T cell epitopes which are able to recognize several major HLAs will be preferentially included in the vaccine design. While peptide vaccines are safe, biocompatible and cost-effective, it is poorly immunogenic. Strategies to improve its immunogenicity by the use of long peptides, adjuvants and nanoparticle delivery mechanisms are discussed.

How Can Elispot Add Information to Improve Knowledge on Tropical Diseases?

Elispot has been used as an important tool for detecting immune cells' products and functions and has facilitated the understanding of host-pathogen interaction. Despite the incredible diversity of possibilities, two main approaches have been developed: the immunopathogenesis and diagnosis/prognosis of infectious diseases as well as cancer research. Much has been described on the topics of allergy, autoimmune diseases, and HIV-Aids, however, Elispot can also be applied to other infectious diseases, mainly leishmaniasis, malaria, some viruses, helminths and mycosis usually classified as tropical diseases. The comprehension of the function, concentration and diversity of the immune response in the infectious disease is pointed out as crucial to the development of infection or disease in humans and animals. In this review we will describe the knowledge already obtained using Elispot as a method for accessing the profile of immune response as well as the recent advances in information about host-pathogen interaction in order to better understand the clinical outcome of a group of tropical and neglected diseases.

Use of a Recombinant Gamma-2 Herpesvirus Vaccine Vector against Dengue Virus in Rhesus Monkeys

Research on vaccine approaches that can provide long-term protection against dengue virus infection is needed. Here we describe the construction, immunogenicity, and preliminary information on the protective capacity of recombinant, replication-competent rhesus monkey rhadinovirus (RRV), a persisting herpesvirus. One RRV construct expressed nonstructural protein 5 (NS5), while a second recombinant expressed a soluble variant of the E protein (E85) of dengue virus 2 (DENV2). Four rhesus macaques received a single vaccination with a mixture of both recombinant RRVs and were subsequently challenged 19 weeks later with 1 × 10⁵ PFU of DENV2. During the vaccine phase, plasma of all vaccinated monkeys showed neutralizing activity against DENV2. Cellular immune responses against NS5 were also elicited, as evidenced by major histocompatibility complex class I (MHC-I) tetramer staining in the one vaccinated monkey that was Mamu-A*01 positive. Unlike two of two unvaccinated controls, two of the four vaccinated monkeys showed no detectable viral RNA sequences in plasma after challenge. One of these two monkeys also showed no anamnestic increases in antibody levels following challenge and thus appeared to be protected against the acquisition of DENV2 following high-dose challenge. Continued study will be needed to evaluate the performance of herpesviral and other persisting vectors for achieving long-term protection against dengue virus infection.IMPORTANCE Continuing studies of vaccine approaches against dengue virus (DENV) infection are warranted, particularly ones that may provide long-term immunity against all four serotypes. Here we investigated whether recombinant rhesus monkey rhadinovirus (RRV) could be used as a vaccine against DENV2 infection in rhesus monkeys. Upon vaccination, all animals generated antibodies capable of neutralizing DENV2. Two of four vaccinated monkeys showed no detectable viral RNA after subsequent high-dose DENV2 challenge at 19 weeks postvaccination. Furthermore, one of these vaccinated monkeys appeared to be protected against the acquisition of DENV2 infection on the basis of undetectable viral loads and the lack of an anamnestic antibody response. These findings underscore the potential utility of recombinant herpesviruses as vaccine vectors.

Differential humoral and cellular immunity induced by vaccination using plasmid DNA and protein recombinant expressing the NS3 protein of dengue virus type 3

Background

The dengue non-structural 3 (NS3) is a multifunctional protein, containing a serine-protease domain, located at the N-terminal portion, and helicase, NTPase and RTPase domains present in the C-terminal region. This protein is considered the main target for CD4+ and CD8+ T cell responses during dengue infection, which may be involved in protection. However, few studies have been undertaken evaluating the use of this protein as a protective antigen against dengue, as well as other flavivirus. In the present work we evaluated the potential of the NS3 (protease domain) as a protective antigen by comparing the administration of a recombinant protein versus a DNA vaccine in the mouse model.

Results

BALB/c mice were immunized with the recombinant protein NS3-DEN3 via intraperitoneal and with plasmid pcDNA3/NS3-DEN3 intramuscularly and the immune response was evaluated. The activity of T lymphocytes was analyzed by the MTT assay, and cells of mice immunized with the recombinant protein showed no activity when stimulated with the homologous protein. However, cells from mice immunized with DNA, responded to stimulation with the recombinant protein. When the expression (RT-PCR) and cytokine production (ELISA) was evaluated in the splenocytes, different behavior depending on the type of immunization was observed, splenocytes of mice immunized with the recombinant protein expressed cytokines such as IL-4, IL-10 and produced high concentrations of IL-1, IL-6 and TNFα. Splenocytes from mice immunized with DNA expressed IL-2 and IFNγ and did not produce IL-6. In addition, immunization with the recombinant protein induced the production of antibodies that are detected up to a dilution 1:3200 by ELISA and Western blot assays, however, the serum of mice immunized with DNA presented no detectable antibody titers.

Conclusion

The results obtained in this study show that administration of pcDNA3/NS3-DEN3 induces a favorable response in the activation of T lymphocytes with low production of specific antibodies against NS3-DEN3.

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.

Recombinant Dengue 2 Virus NS3 Helicase Protein Enhances Antibody and T-Cell Response of Purified Inactivated Vaccine

Dengue virus purified inactivated vaccines (PIV) are highly immunogenic and protective over the short term, but may be poor at inducing cell-mediated immune responses and long-term protection. The dengue nonstructural protein 3 (NS3) is considered the main target for T-cell responses during viral infection. The amino (N)-terminal protease and the carboxy (C)-terminal helicase domains of DENV-2 NS3 were expressed in E. coli and analyzed for their immune-potentiating capacity. Mice were immunized with DENV-2 PIV with and without recombinant NS3 protease or NS3 helicase proteins, and NS3 proteins alone on days 0, 14 and 28. The NS3 helicase but not the NS3 protease was effective in inducing T-cell responses quantified by IFN-γ ELISPOT. In addition, markedly increased total IgG antibody titer against virus antigen was seen in mice immunized with the PIV/NS3 helicase combination in the ELISA, as well as increased neutralizing antibody titer measured by the plaque reduction neutralization test. These results indicate the potential immunogenic properties of the NS3 helicase protein and its use in a dengue vaccine formulation.

Analysis of cell-mediated immune responses in support of dengue vaccine development efforts

Dengue vaccine development has made significant strides, but a better understanding of how vaccine-induced immune responses correlate with vaccine efficacy can greatly accelerate development, testing, and deployment as well as ameliorate potential risks and safety concerns. Advances in basic immunology knowledge and techniques have already improved our understanding of cell-mediated immunity of natural dengue virus infection and vaccination. We conclude that the evidence base is adequate to argue for inclusion of assessments of cell-mediated immunity as part of clinical trials of dengue vaccines, although further research to identify useful correlates of protective immunity is needed.

Functionality of dengue virus specific memory T cell responses in individuals who were hospitalized or who had mild or subclinical dengue infection

Background

Although antibody responses to dengue virus (DENV) in naturally infected individuals have been extensively studied, the functionality of DENV specific memory T cell responses in relation to clinical disease severity is incompletely understood.

Methodology/Principal findings

Using ex vivo IFNγ ELISpot assays, and by determining cytokines produced in ELISpot supernatants, we investigated the functionality of DENV-specific memory T cell responses in a large cohort of individuals from Sri Lanka (n=338), who were naturally infected and were either hospitalized due to dengue or had mild or sub clinical dengue infection. We found that T cells of individuals with both past mild or sub clinical dengue infection and who were hospitalized produced multiple cytokines when stimulated with DENV-NS3 peptides. However, while DENV-NS3 specific T cells of those with mild/sub clinical dengue infection were more likely to produce only granzyme B (p=0.02), those who were hospitalized were more likely to produce both TNFα and IFNγ (p=0.03) or TNFα alone.

We have also investigated the usefulness of a novel T cell based assay, which can be used to determine the past infecting DENV serotype. 92.4% of DENV seropositive individuals responded to at least one DENV serotype of this assay and none of the seronegatives responded. Individuals who were seronegative, but had received the Japanese encephalitis vaccine too made no responses, suggesting that the peptides used in this assay did not cross react with the Japanese encephalitis virus.

Conclusions/significance

The types of cytokines produced by DENV-specific memory T cells appear to influence the outcome of clinical disease severity. The novel T cell based assay, is likely to be useful in determining the past infecting DENV serotype in immune-epidemiological studies and also in dengue vaccine trials.

Although dengue viral infections cause severe clinical disease, the majority of individuals infected with the dengue virus (DENV) develop asymptomatic infection. The function of DENV specific memory T cells in relation to past clinical disease severity is incompletely understood. In this study, we sought to investigate the function of DENV specific memory T cell responses in a large cohort (n = 338) of individuals who were naturally infected with the DENV but developed varying severity of clinical disease. We found that T cells of individuals who were hospitalized due to dengue and those with mild/sub clinical dengue infection produced multiple cytokines when stimulated with DENV-NS3 peptides. In addition, we have also validated a novel T cell based assay, which can be used to determine the past infecting DENV serotype. We found that 92.4% of DENV seropositive individuals responded to at least one DENV serotype of this assay and none of the seronegatives responded. Moreover, the peptides used in this assay did not cross react with Japanese encephalitis virus. Therefore, this assay is likely to be useful in determining the past infecting DENV serotype in immune-epidemiological studies and also in dengue vaccine trials.

Clinical outcome and genetic differences within a monophyletic Dengue virus type 2 population

The exact mechanisms of interplay between host and viral factors leading to severe dengue are yet to be fully understood. Even though previous studies have implicated specific genetic differences of Dengue virus (DENV) in clinical severity and virus attenuation, similar studies with large-scale, whole genome screening of monophyletic virus populations are limited. Therefore, in the present study, we compared 89 whole genomes of DENV-2 cosmopolitan clade III isolates obtained from patients diagnosed with dengue fever (DF, n = 58), dengue hemorrhagic fever (DHF, n = 30) and dengue shock syndrome (DSS, n = 1) in Singapore between July 2010 and January 2013, in order to determine the correlation of observed viral genetic differences with clinical outcomes. Our findings showed no significant difference between the number of primary and secondary infections that progressed to DHF and DSS (p>0.05) in our study cohort. Despite being highly homogenous, study isolates possessed 39 amino acid substitutions of which 10 substitutions were fixed in three main groups of virus isolates. None of those substitutions were specifically associated with DHF and DSS. Notably, two evolutionarily unique virus groups possessing C-P43T+NS1-S103T+NS2A-V83I+NS3-R337K+ NS3-I600T+ NS5-P136S and NS2A-T119N mutations were exclusively found in patients with DF, the benign form of DENV infections. Those mutants were significantly associated with mild disease outcome. These observations indicated that disease progression into DHF and DSS within our patient population was more likely to be due to host than virus factors. We hypothesize that selection for potentially less virulent groups of DENV-2 in our study cohort may be an evolutionary adaptation of viral strains to extend their survival in the human-mosquito transmission cycle.

Elucidating the role of T cells in protection against and pathogenesis of dengue virus infections

Dengue viruses (DENV) cause significantly more human disease than any other arbovirus, with hundreds of thousands of cases leading to severe disease in thousands annually. Antibodies and T cells induced by primary infection with DENV have the potential for both positive (protective) and negative (pathological) effects during subsequent DENV infections. In this review, we summarize studies that have examined T-cell responses in humans following natural infection and vaccination. We discuss studies that support a role for T cells in protection against and those that support a role for the involvement of T cells in the pathogenesis of severe disease. The mechanisms that lead to severe disease are complex, and T-cell responses are an important component that needs to be further evaluated for the development of safe and efficacious DENV vaccines.

Immunodominance changes as a function of the infecting dengue virus serotype and primary versus secondary infection

Dengue virus (DENV) is the causative agent of dengue fever (DF). This disease can be caused by any of four DENV serotypes (DENV1 to -4) which share 67 to 75% sequence homology with one another. The effect of subsequent infections with different serotypes on the T cell repertoire is not fully understood. We utilized mice transgenic for human leukocyte antigens (HLA) lacking the alpha/beta interferon (IFN-α/β) receptor to study responses to heterologous DENV infection. First, we defined the primary T cell response to DENV3 in the context of a wide range of HLA molecules. The primary DENV3 immune response recognized epitopes derived from all 10 DENV proteins, with a significant fraction of the response specific for structural proteins. This is in contrast to primary DENV2 infection, in which structural proteins are a minor component of the response, suggesting differential antigen immunodominance as a function of the infecting serotype. We next investigated the effect of secondary heterologous DENV infection on the T cell repertoire. In the case of both DENV2/3 and DENV3/2 heterologous infections, recognition of conserved/cross-reactive epitopes was either constant or expanded compared to that in homologous infection. Furthermore, in heterologous infection, previous infection with a different serotype impaired the development of responses directed to serotype-specific but not conserved epitopes. Thus, a detrimental effect of previous heterotypic responses might not be due to dysfunctional and weakly cross-reactive epitopes dominating the response. Rather, responses to the original serotype might limit the magnitude of responses directed against epitopes that are either cross-reactive to or specific for the most recently infecting serotype.

IMPORTANCE

DENV transmission occurs in more than 100 countries and is an increasing public health problem in tropical and subtropical regions. At present, no effective antiviral therapy or licensed vaccine exists, and treatment is largely supportive in nature. Disease can be caused by any of the four DENV serotypes (DENV1 to -4), which share a high degree of sequence homology with one another. In this study, we have addressed the question of how the T cell repertoire changes as a function of infections with different serotypes and of subsequent heterologous secondary infections. This is of particular interest in the field of dengue viruses, in which secondary infections with different DENV serotypes increase the risk of severe disease. Our results on the evolution of the immune response after primary and secondary infections provide new insights into HLA-restricted T cell responses against DENV relevant for the design of a vaccine against DENV.

Invariant NKT cell response to dengue virus infection in human

BACKGROUND

Dengue viral infection is a global health threat without vaccine or specific treatment. The clinical outcome varies from asymptomatic, mild dengue fever (DF) to severe dengue hemorrhagic fever (DHF). While adaptive immune responses were found to be detrimental in the dengue pathogenesis, the roles of earlier innate events remain largely uninvestigated. Invariant natural killer T (iNKT) cells represent innate-like T cells that could dictate subsequent adaptive response but their role in human dengue virus infection is not known. We hypothesized that iNKT cells play a role in human dengue infection.

METHODS

Blood samples from a well-characterized cohort of children with DF, DHF, in comparison to non-dengue febrile illness (OFI) and healthy controls at various time points were studied. iNKT cells activation were analyzed by the expression of CD69 by flow cytometry. Their cytokine production was then analyzed after α-GalCer stimulation. Further, the CD1d expression on monocytes, and CD69 expression on conventional T cells were measured.

RESULTS

iNKT cells were activated during acute dengue infection. The level of iNKT cell activation associates with the disease severity. Furthermore, these iNKT cells had altered functional response to subsequent ex vivo stimulation with α-GalCer. Moreover, during acute dengue infection, monocytic CD1d expression was also upregulated and conventional T cells also became activated.

CONCLUSION

iNKT cells might play an early and critical role in the pathogenesis of severe dengue viral infection in human. Targeting iNKT cells and CD1d serve as a potential therapeutic strategy for severe dengue infection in the future.

Recombinant dengue 2 virus NS3 protein conserves structural antigenic and immunological properties relevant for dengue vaccine design

The NS3 protein is a multifunctional non-structural protein of flaviviruses implicated in the polyprotein processing. The predominance of cytotoxic T cell lymphocytes epitopes on the NS3 protein suggests a protective role of this protein in limiting virus replication. In this work, we studied the antigenicity and immunogenicity of a recombinant NS3 protein of the Dengue virus 2. The full-length NS3 gene was cloned and expressed as a His-tagged fusion protein in Escherichia coli. The pNS3 protein was purified by two chromatography steps. The recombinant NS3 protein was recognized by anti-protease NS3 polyclonal antibody and anti-DENV2 HMAF by Western Blot. This purified protein was able to stimulate the secretion of high levels of gamma interferon and low levels of interleukin-10 and tumor necrosis factor-α in mice splenocytes, suggesting a predominantly Th-1-type T cell response. Immunized BALB/c mice with the purified NS3 protein showed a strong induction of anti-NS3 IgG antibodies, essentially IgG2b, as determined by ELISA. Immunized mice sera with recombinant NS3 protein showed specific recognition of native dengue protein by Western blotting and immunofluorescence techniques. The successfully purified recombinant protein was able to preserv the structural and antigenic determinants of the native dengue protein. The antigenicity shown by the recombinant NS3 protein suggests its possible inclusion into future DENV vaccine preparations.

Lack of clinical manifestations in asymptomatic dengue infection is attributed to broad down-regulation and selective up-regulation of host defence response genes

Objectives

Dengue represents one of the most serious life-threatening vector-borne infectious diseases that afflicts approximately 50 million people across the globe annually. Whilst symptomatic infections are frequently reported, asymptomatic dengue remains largely unnoticed. Therefore, we sought to investigate the immune correlates conferring protection to individuals that remain clinically asymptomatic.

Methods

We determined the levels of neutralizing antibodies (nAbs) and gene expression profiles of host immune factors in individuals with asymptomatic infections, and whose cognate household members showed symptoms consistent to clinical dengue infection.

Results

We observed broad down-regulation of host defense response (innate, adaptive and matrix metalloprotease) genes in asymptomatic individuals as against symptomatic patients, with selective up-regulation of distinct genes that have been associated with protection. Selected down-regulated genes include: TNF α (TNF), IL8, C1S, factor B (CFB), IL2, IL3, IL4, IL5, IL8, IL9, IL10 and IL13, CD80, CD28, and IL18, MMP8, MMP10, MMP12, MMP15, MMP16, and MMP24. Selected up-regulated genes include: RANTES (CCL5), MIP-1α (CCL3L1/CCL3L3), MIP-1β (CCL4L1), TGFβ (TGFB), and TIMP1.

Conclusion

Our findings highlight the potential association of certain host genes conferring protection against clinical dengue. These data are valuable to better explore the mysteries behind the hitherto poorly understood immunopathogenesis of subclinical dengue infection.

Clinical and immunological markers of dengue progression in a study cohort from a hyperendemic area in Malaysia

Background

With its elusive pathogenesis, dengue imposes serious healthcare, economic and social burden on endemic countries. This study describes the clinical and immunological parameters of a dengue cohort in a Malaysian city, the first according to the WHO 2009 dengue classification.

Methodology and Findings

This longitudinal descriptive study was conducted in two Malaysian hospitals where patients aged 14 and above with clinical symptoms suggestive of dengue were recruited with informed consent. Among the 504 participants, 9.3% were classified as non-dengue, 12.7% without warning signs, 77.0% with warning signs and 1.0% with severe dengue based on clinical diagnosis. Of these, 37% were misdiagnosed as non-dengue, highlighting the importance of both clinical diagnosis and laboratory findings. Thrombocytopenia, prolonged clotting time, liver enzymes, ALT and AST served as good markers for dengue progression but could not distinguish between patients with and without warning signs. HLA-A*24 and -B*57 were positively associated with Chinese and Indians patients with warning signs, respectively, whereas A*03 may be protective in the Malays. HLA-A*33 was also positively associated in patients with warning signs when compared to those without. Dengue NS1, NS2A, NS4A and NS4B were found to be important T cell epitopes; however with no apparent difference between with and without warning signs patients. Distinction between the 2 groups of patients was also not observed in any of the cytokines analyzed; nevertheless, 12 were significantly differentially expressed at the different phases of illness.

Conclusion

The new dengue classification system has allowed more specific detection of dengue patients, however, none of the clinical parameters allowed distinction of patients with and without warning signs. While the HLA-A*33 may be predictive marker for development of warning signs; larger studies will be needed to support this findings.

T cell responses in dengue viral infections

Dengue viral infections are the commonest mosquito borne viral infection in the world, affecting more than 100 countries and 390 million individuals annually. Currently, there are no effective antiviral drugs or an effective vaccine to prevent infection. A main hurdle in developing a safe and effective vaccine has been our poor understanding of the complex nature of the protective immune response in acute dengue infection and the presence of four dengue virus (DV) serotypes that are highly homologous. The role of DV specific T cells in the pathogenesis of severe clinical disease in not clear. It has been speculated that highly cross reactive T cells for the previous infecting heterologous DV serotype, which produce pro-inflammatory cytokines, contribute to disease pathogenesis. These cross reactive T cells are believed to be suboptimal in clearing the infection with the current DV-serotype. However, other studies have shown that cross-reactive DV-specific T cells are absent or present in very low frequency during acute infection, appearing only during the convalescent period in the majority of patients. Furthermore, significant apoptosis of T cells occurs in severe acute clinical disease. Overall therefore, it is unclear what role T cells play in contributing to disease pathogenesis during acute dengue infection. Existing data have been complicated by cross-reactivity in T cells assays. These findings can now be re-evaluated in the light of novel technologies to identify serotype-specific T cell responses.

Effects of cocktail of four local Malaysian medicinal plants (Phyllanthus spp.) against dengue virus 2

Background

The absence of commercialized vaccines and antiviral agents against dengue has made the disease a major health concern around the world. With the current dengue virus transmission rate and incidences, the development of antiviral drugs is of vital need. The aim of this project was to evaluate the possibility of developing a local medicinal plant, Phyllanthus as an anti-dengue agent.

Methods

Cocktail (aqueous and methanolic) extracts were prepared from four species of Phyllanthus (P.amarus, P.niruri, P.urinaria, and P.watsonii) and their polyphenolic compounds were identified via HPLC and LC-MS/MS analysis. MTS assay was then carried out to determine the maximal non-toxic dose (MNTD) of the extracts, followed by screening of the in vitro antiviral activity of aqueous cocktail extracts against DENV2 by means of time-of-addition (pre-, simultaneous and post-) using RT-qPCR. The differentially expressed proteins in the treated and infected cells were analysed with two dimensional gel electrophoresis experiments.

Results

Several active compounds including gallic acid, geraniin, syringin, and corilagen have been identified. The MNTD of both aqueous and methanolic extracts on Vero cells were 250.0 μg/ml and 15.63 μg/ml respectively. Phyllanthus showed strongest inhibitory activity against DENV2 with more than 90% of virus reduction in simultaneous treatment. Two-dimensional analysis revealed significantly altered levels of thirteen proteins, which were successfully identified by tandem MS (MS/MS). These altered proteins were involved in several biological processes, including viral entry, viral transcription and translation regulations, cytoskeletal assembly, and cellular metabolisms.

Conclusions

Phyllanthus could be potentially developed as an anti-DENV agent.

The battle between infection and host immune responses of dengue virus and its implication in dengue disease pathogenesis

Dengue virus (DENV) is a mosquito-transmitted single stranded RNA virus belonging to genus Flavivirus. The virus is endemic in the tropical and subtropical countries of the world, causing diseases classified according to symptoms and severity (from mild to severe) as dengue fever, dengue hemorrhagic fever, and dengue shock syndrome. Among a variety of human cell types targeted by DENV, monocytes, macrophages, and dendritic cells are members of innate immunity, capable of mounting rapid inflammatory responses. These cells are also major antigen presenting cells, responsible for activating the adaptive immunity for long-term memory. This paper is an overview of the current understanding of the following mutually affected aspects: DENV structure, viral infectivity, cellular receptors, innate immune response, and adaptive immunity.

Expression, purification, and evaluation of diagnostic potential and immunogenicity of a recombinant NS3 protein from all serotypes of dengue virus

Dengue is one of the major public health concerns in the world. Since all the four serotypes are actively circulating in Mexico, there is a need to develop an efficient diagnosis system to improve case management of the patients. There exist few studies evaluating the use of the NS3 protein as a protective antigen against dengue virus (DENV). In this paper we show the expression of a recombinant NS3 protein from all serotypes of dengue virus (GST-DVNS3-1-4) and report a reliable "in-house detection system" for the diagnosis of dengue infection which was field-tested in a small village (Tezonapa) in the state of Veracruz, Mexico. The fusion proteins were immunogenic, inducing antibodies to be able to recognize to antigens up to a 1 : 3200 dilution. The purified proteins were used to develop an in-house detection system (ELISA) and were further tested with a panel of 239 serum samples. The in-house results were in excellent agreement with the commercial kits with κ = 0.934 ± 0.064 (95%  CI = 0.808-1.061), and κ = 0.872 ± 0.048 (95%  CI = 0.779-0.965) for IgM and IgG, respectively. The agreement between the NS1 antigen detection versus the rNS3 ELISA, κ = 0.837 ± 0.066 (95%  CI = 0.708-0.966), was very good. Thus, these results demonstrate that recombinant NS3 proteins have potential in early diagnosis of dengue infections.

Cellular and cytokine correlates of severe dengue infection

Background

The occurrence of dengue haemorrhagic fever (DHF) is thought to result from a complex interplay between the virus, host genetics and host immune factors. Existing published data are not consistent, in part related to relatively small sample sizes. We set out to determine possible associations between dengue virus (DEN-V) NS3 specific T cells and cytokine and chemokine levels and the pathogenesis of severe disease in a large cohort of individuals with DHF.

Methodology/Principal Findings

By using ex vivo IFNγ ELISpot assays we determined DENV-NS3 specific responses in patients with varying severity of DHF. Other cytokines produced by DENV-NS3 specific T cells were determined by using multiple bead array analysis (MBAA). We also determined the serum cytokine levels using MBAA, lymphocyte subsets and Annexin V expression of lymphocytes in patients with varying severity of DHF. Of the 112 DHF patients studied, 29 developed shock. Serum IL-10 and IP-10 levels positively and significantly correlated with T cell apoptosis while IL-10 levels inversely correlated with T cell numbers. In contrast, TGFß showed a very significant (P<0.0001) and positive correlation (Spearman’s R = 0.65) with the platelet counts, consistent with platelet release. We found that whilst patients with severe dengue had lower total T cell numbers, the DV-NS3 specific T cells persisted and produced high levels of IFNγ but not TNFα, IL-3, IL-13, IL-2, IL-10 or IL-17.

Conclusions/Significance

Our data suggest that serum IL-10, TNFα and TGFβ differentially associate with dengue disease severity.

Identification of serotype-specific T cell responses to highly conserved regions of the dengue viruses

Determining previous infecting dengue virus (DENV) serotypes has been difficult due to highly cross-reactive immune responses from previous DENV infections. Determining the correlates of serotype-specific immune responses would be crucial in understanding dengue transmission in the community and would also help to determine the correlates of protective immune responses. Therefore, we set out to define highly conserved, serotype-specific regions of the DENVs. Serotype-specific and highly conserved regions of the four DENV serotypes were identified using Basic Local Alignment Search Tool (BLAST) searches and custom perl scripts. Using ex-vivo and cultured enzyme-linked immunospot (ELISPOT) assays, we identified serotype-specific T cell epitopes within the four DENV serotypes in healthy adult donors from Sri Lanka. We identified T cell responses to 19 regions of the four DENV serotypes. Six peptides were from the NS2A region and four peptides were from the NS4A region. All immune donors responded to peptides of at least two DENV serotypes, suggesting that heterologous infection is common in Sri Lanka. Eight of 20 individuals responded to at least two peptides of DENV-4, despite this serotype not being implicated previously in any of the epidemics in Sri Lanka. The use of these regions to determine past and current infecting DENV serotypes will be of value to characterize further the dynamics of silent dengue transmission in the community. In addition, these T cell responses to these regions could be used to characterize DENV serotype-specific immune responses and thus possibly help us to understand the immune correlates of a protective immune response.

Conserved MHC class I-presented dengue virus epitopes identified by immunoproteomics analysis are targets for cross-serotype reactive T-cell response

Dengue fever and dengue hemorrhagic fever are significant global public health problems, and understanding the overall immune response to infection will contribute to appropriate management of the disease and its potentially severe complications. Live attenuated and subunit vaccine candidates, which are under clinical evaluation, induce primarily an antibody response to the virus and minimal cross-reactive T-cell responses. Currently, there are no available tools to assess protective T-cell responses during infection or after vaccination. In this study, we utilize an immunoproteomics process to uncover novel HLA-A2-specific epitopes derived from dengue virus (DV)-infected cells. These epitopes are conserved, and we report that epitope-specific cytotoxic lymphocytes (CTLs) are cross-reactive against all 4 DV serotypes. These epitopes have potential as new informational and diagnostic tools to characterize T-cell immunity in DV infection and may serve as part of a universal vaccine candidate complementary to current vaccines in trial.

Induction of a protective response in mice by the dengue virus NS3 protein using DNA vaccines

The dengue non-structural 3 (NS3) is a multifunctional protein, containing a serino-protease domain, located at the N-terminal portion, and helicase, NTPase and RTPase domains present in the C-terminal region. This protein is considered the main target for CD4+ and CD8+ T cell responses during dengue infection, which may be involved in protection. However, few studies have been undertaken evaluating the use of this protein as a protective antigen against dengue, as well as other flavivirus. In the present work, we investigate the protective efficacy of DNA vaccines based on the NS3 protein from DENV2. Different recombinant plasmids were constructed, encoding either the full-length NS3 protein or only its functional domains (protease and helicase), fused or not to a signal peptide (t-PA). The recombinant proteins were successfully expressed in transfected BHK-21 cells, and only plasmids encoding the t-PA signal sequence mediated protein secretion. Balb/c mice were immunized with the different DNA vaccines and challenged with a lethal dose of DENV2. Most animals immunized with plasmids encoding the full-length NS3 or the helicase domain survived challenge, regardless of the presence of the t-PA. However, some mice presented clinical signs of infection with high morbidity (hind leg paralysis and hunched posture), mainly in animal groups immunized with the DNA vaccines based on the helicase domain. On the other hand, inoculation with plasmids encoding the protease domain did not induce any protection, since mortality and morbidity rates in these mouse groups were similar to those detected in the control animals. The cellular immune response was analyzed by ELISPOT with a specific-CD8+ T cell NS3 peptide. Results revealed that the DNA vaccines based on the full-length protein induced the production of INF-γ, thus suggesting the involvement of this branch of the immune system in the protection.

Insights into HLA-restricted T cell responses in a novel mouse model of dengue virus infection point toward new implications for vaccine design

The frequency of dengue virus (DENV) infection has increased dramatically in the last few decades, and the lack of a vaccine has led to significant morbidity and mortality worldwide. To date, a convenient murine system to study human T cell responses to DENV has not been available. Mice transgenic for HLA are widely used to model human immune responses, and it has been shown that mouse-passaged DENV is able to replicate to significant levels in IFN-α/βR(-/-) mice. To cover a wide range of HLA phenotypes, we backcrossed IFN-α/βR(-/-) mice with HLA A*0201, A*0101, A*1101, B*0702, and DRB1*0101-transgenic mice. A DENV proteome-wide screen identified a total of 42 epitopes across all HLA-transgenic IFN-α/βR(-/-) strains tested. In contrast, only eight of these elicited responses in the corresponding IFN-α/βR(+/+) mice. We were able to identify T cell epitopes from 9 out of the 10 DENV proteins. However, the majority of responses were derived from the highly conserved nonstructural proteins NS3 and NS5. The relevance of this model is further demonstrated by the fact that most of the epitopes identified in our murine system are also recognized by PBMC from DENV-exposed human donors, and a dominance of HLA B*0702-restricted responses has been detected in both systems. Our results provide new insights into HLA-restricted T cell responses against DENV, and we describe in this study a novel murine model that allows the investigation of T cell-mediated immune mechanisms relevant to vaccine design.

Susceptible and protective HLA class 1 alleles against dengue fever and dengue hemorrhagic fever patients in a Malaysian population

Background

The human leukocyte antigen alleles have been implicated as probable genetic markers in predicting the susceptibility and/or protection to severe manifestations of dengue virus (DENV) infection. In this present study, we aimed to investigate for the first time, the genotype variants of HLA Class 1(-A and -B) of DENV infected patients against healthy individuals in Malaysia.

Methodology/Principal Findings

This study was carried out with 92 dengue disease patients and 95 healthy controls from three different ethnic groups (Malay, Chinese and Indian) in Malaysia. All patients with clinical and laboratory confirmation of DENV infection were typed for the HLA-A and B loci, using polymerase chain reaction-sequence specific primer techniques. In our total population, a significant increase for HLA-B*53 (P = 0.042, Pc = 1.008) allele and a significant decrease for A*03 (P = 0.015, Pc = 0.18, OR = 5.23, 95% CI = 1.19–23.02) and B*18 (P = 0.017, Pc = 0.408) alleles were noted in DHF patients as compared to healthy donors. We also observed that in the Malay DHF patients, allele B*13 (P = 0.049, Pc = 1.176, OR = 0.18, 95% CI = 0.03–0.90) was present at a significantly higher frequency in this population while allele HLA-B*18 (P = 0.024, Pc = 0.576) was seen to be negatively associated with DHF.

Conclusions/Significance

These are the first findings on genetic polymorphisms in our population and we conclude that: (1) In our total population, HLA-B*53 probably involve in disease susceptibility, while the HLA-A*03 and HLA-B*18 may confer protection from progression to severe disease; (2) In the Malay population, HLA-B*13 and B*18 are probably associated in disease susceptibility and protection, respectively. These results could furnish as a valuable predictive tool to identify ethnically different individuals at risk and/or protection from severe forms of DENV infection and would provide valuable informations for the design of future dengue vaccine.

Meta-analysis of all immune epitope data in the Flavivirus genus: inventory of current immune epitope data status in the context of virus immunity and immunopathology

A meta-analysis was performed in order to inventory the immune epitope data related to viruses in the genus Flavivirus. Nearly 2000 epitopes were captured from over 130 individual Flavivirus-related references identified from PubMed and reported as of September 2009. This report includes all epitope structures and associated immune reactivity from the past and current literature, including: the epitope distribution among pathogens and related strains, the epitope distribution among different pathogen antigens, the number of epitopes defined in human and animal models of disease, the relationship between epitopes identified in different disease states following natural (or experimental) infection, and data from studies focused on candidate vaccines. We found that the majority of epitopes were defined for dengue virus (DENV) and West Nile virus (WNV). The prominence of DENV and WNV data in the epitope literature is likely a reflection of their overall worldwide impact on human disease, and the lack of vaccines. Conversely, the relatively smaller number of epitopes defined for the other viruses within the genus (yellow fever and Japanese encephalitis virus) most likely reflects the presence of established prophylaxis and/or their more modest impact on morbidity and mortality globally. Through this work we hope to provide useful data to those working in the area of Flavivirus research.

Identification of a dengue virus-specific HLA-A*0201-restricted CD8+ T cell epitope

In this study, a combination of epitope-prediction programs and in vitro assays was used to identify dengue virus (DENV)-specific CD8(+) T cell epitopes. Peripheral blood mononuclear cells (PBMCs) isolated from patients who recovered from dengue fever were stimulated with candidate epitope peptides derived from DENV, which were predicted by using SYFPEITHI and RANKpep epitope-prediction programs. The IFN-gamma ELISpot results and the results of intracellular staining of IFN-gamma showed that peptides NS4b_40 (TLYAVATTI), E_256 (QEGAMHTAL), NS3_205 (LPAIVREAI), NS5_210 (SRNSTHEMY), and NS3_207 (AIVREAIKR) could induce the recall response of CD8(+) T cells. Furthermore, the results of the MHC-peptide complex stabilization assay revealed that peptide NS4b_40 (TLYAVATTI) has a high affinity for HLA-A*0201 molecules. The IFN-gamma ELISpot results and staining of intracellular IFN-gamma confirmed that this peptide could induce high-level CD8(+) T cell response in HLA-A*0201 positive PBMCs. Peptide NS4b_40 (TLYAVATTI) was identified as a novel DENV-specific HLA-A*0201-restricted CD8(+) T cell epitope.

Identification of Dengue-specific B-Cell Epitopes by Phage-display Random Peptide Library

BACKGROUND

Dengue is the most important human viral disease transmitted by arthropod vectors. The availability of random peptide libraries (RPL) displayed on phage has provided a powerful tool for selecting sequences that mimic epitopes from microorganisms that are useful for diagnostic and vaccine development purposes. In this paper, we describe peptides that resemble the antigenic structure of B-cell epitopes of dengue virus identified from a phage-peptide library using human sera containing polyclonal antibodies against dengue virus.

MATERIALS AND METHODS

Eighteen phage clones were isolated from the phage-display peptide library, J404, by affinity selection using human antisera against dengue virus type 3. These clones were tested for reactivity by ELISA with a panel of hyperimmune ascitic fluids (HAFs) containing antibodies either against all four dengue serotypes, West Nile virus (WNV) or Eastern equine encephalitis virus (EEEV) with control ascitic fluid (NAF) used as a negative control.

RESULTS

Eight clones were recognized by HAFs against the four dengue serotypes, of which four significantly inhibited binding of anti-dengue antibodies to the virus. Two peptides with similar sequences to regions of NS3 and NS4B non-structural dengue virus proteins were identified.

CONCLUSION

Our results suggest that these peptides could be used for the development of diagnostic tools for the detection of dengue virus infection and for a potential vaccine against this pathogen.

The history and evolution of human dengue emergence

Dengue viruses (DENV) are the most important human arboviral pathogens. Transmission in tropical and subtropical regions of the world includes a sylvatic, enzootic cycle between nonhuman primates and arboreal mosquitoes of the genus Aedes, and an urban, endemic/epidemic cycle principally between Aedes aegypti, a mosquito that exploits peridomestic water containers as its larval habitats, and human reservoir hosts that are preferred for blood feeding. Genetic studies suggest that all four serotypes of endemic/epidemic DENV evolved independently from ancestral, sylvatic viruses and subsequently became both ecologically and evolutionarily distinct. The independent evolution of these four serotypes was accompanied by the expansion of the sylvatic progenitors' host range in Asia to new vectors and hosts, which probably occurred gradually over a period of several hundred years. Although many emerging viral pathogens adapt to human replication and transmission, the available evidence indicates that adaptation to humans is probably not a necessary component of sylvatic DENV emergence. These findings imply that the sylvatic DENV cycles in Asia and West Africa will remain a potential source of re-emergence. Sustained urban vector control programs and/or human vaccination will be required to control DEN because the enzootic vectors and primate reservoir hosts are not amenable to interventions.

Scientific consultation on cell mediated immunity (CMI) in dengue and dengue vaccine development

Dengue is a re-emerging arboviral disease of great public health importance. Limited understanding of protective immune responses against dengue has hampered advancement of dengue vaccine candidates. Demonstrating an immunological correlate of protection has been limited to associating quantitative neutralizing antibody titers with clinical outcomes following infection. There have been a number of studies investigating the role of cell mediated immunity (CMI) in natural infections and these have demonstrated roles in both virus clearance and potentiating disease. Vaccine developers have extended the exploratory study of CMI in natural infection to the study of dengue vaccine recipients. Primary infections and monovalent vaccine administration generates dengue type-specific T-cell responses. Secondary infection, vaccination of flavivirus primed individuals, or administration of multivalent vaccine candidates results in broad, cross-reactive T-cell responses, similar to the broadening of antibody patterns. However, the precise function of CMI in protection or disease pathology remains ill-defined and, at present, there is no evidence to suggest that CMI can be utilized as a correlate of protection. Nonetheless, the study of CMI in natural infection and following vaccine administration should continue in an attempt to improve the understanding of dengue immunopathology, vaccine candidate immunogenicity, and potential correlates of protection.

Vascular endothelium: the battlefield of dengue viruses

Increased vascular permeability without morphological damage to the capillary endothelium is the cardinal feature of dengue haemorrhagic fever (DHF)/dengue shock syndrome (DSS). Extensive plasma leakage in various tissue spaces and serous cavities of the body, including the pleural, pericardial and peritoneal cavities in patients with DHF, may result in profound shock. Among various mechanisms that have been considered include immune complex disease, T-cell-mediated, antibodies cross-reacting with vascular endothelium, enhancing antibodies, complement and its products, various soluble mediators including cytokines, selection of virulent strains and virus virulence, but the most favoured are enhancing antibodies and memory T cells in a secondary infection resulting in cytokine tsunami. Whatever the mechanism, it ultimately targets vascular endothelium (making it a battlefield) leading to severe dengue disease. Extensive recent work has been done in vitro on endothelial cell monolayer models to understand the pathophysiology of vascular endothelium during dengue virus (DV) infection that may be translated to help understand the pathogenesis of DHF/DSS. The present review provides a broad overview of the effects of DV infection and the associated host responses contributing towards alterations in vascular endothelial cell physiology and damage that may be responsible for the DHF/DSS.

Evaluation of recombinant Kunjin replicon SIV vaccines for protective efficacy in macaques

Persistent gag-specific T cell immunity would be a useful component of an effective HIV vaccine. The Flavivirus Kunjin replicon was previously engineered to persistently express HIV gag and was shown to induce protective responses in mice. We evaluated Kunjin replicon virus-like-particles expressing SIVgag-pol in pigtail macaques. Kunjin-specific antibodies were induced, but no SIV-specific T cell immunity were detected. Following SIVmac251 challenge, there was no difference in SIV viremia or retention of CD4 T cells between Kunjin-SIVgag-pol vaccine immunized animals and controls. An amnestic SIV gag-specific CD8 T cell response associated with control of viremia was observed in 1 of 6 immunized animals. Refinements of this vector system and optimization of the immunization doses, routes, and schedules are required prior to clinical trials.