Japanese encephalitis: development of new candidate vaccines

Evaluation of the adjuvant effect of imiquimod and CpG ODN 1826 in chimeric DNA vaccine against Japanese encephalitis

Vaccines represent a significant milestone in the history of human medical science and serve as the primary means for controlling infectious diseases. In recent years, the geographical distribution of Japanese encephalitis viruses (JEV) of various genotypes has become increasingly complex, which provides a rationale for the development of safer and more effective vaccines. The advent of subunit and nucleic acid vaccines, especially propelled by advancements in genetic engineering since the 1980s, has accelerated the application of novel adjuvants. These novel vaccine adjuvants have diversified into toll-like receptor (TLR) agonists, complex adjuvants, nanoparticles and so on. However, the efficacy of adjuvant combinations can vary depending on the host system, disease model, or vaccine formulation, sometimes resulting in competitive or counteractive effects. In our previous study, we constructed a pJME-LC3 chimeric DNA vaccine aimed at inducing an immune response through autophagy induction. Building on this, we investigated the impact of the TLR7/8 agonist imiquimod (IMQ) and the TLR9 agonist CpG ODN 1826 as adjuvants on the immunogenicity of the Japanese encephalitis chimeric DNA vaccine. Our findings indicate that the combination of the pJME-LC3 vaccine with IMQ and CpG ODN 1826 adjuvants enhanced the innate immune response, promoting the maturation and activation of antigen-presenting cells in the early immune response. Furthermore, it played a regulatory and optimizing role in subsequent antigen-specific immune responses, resulting in effective cellular and humoral immunity and providing prolonged immune protection. The synergistic effect of IMQ and CpG ODN 1826 as adjuvants offers a novel approach for the development of Japanese encephalitis nucleic acid vaccines.

Japanese Encephalitis Virus NS4A Protein Interacts with PTEN-Induced Kinase 1 (PINK1) and Promotes Mitophagy in Infected Cells

The nonstructural protein 4A (NS4A) of flaviviruses has been implicated as a "central organizer" of the membrane-bound replication complex during virus replication. However, its role in the host responses to virus infection is not understood. Using the yeast-two-hybrid library screen, we identified a multitude of host proteins interacting with the Japanese encephalitis virus (JEV) NS4A protein. Several of these interacting proteins are known to localize to the mitochondria. One of these proteins was PTEN-induced kinase 1 (PINK1), a serine/threonine-protein kinase known for its role in mitophagy. Here, we demonstrate the JEV-NS4A localization to the mitochondria and its interaction with PINK1 in Huh7 cells during JEV infection. The JEV-infected cells showed an enhanced mitophagy flux with a concomitant decline in the mitochondrial mass. We present data showing that JEV-NS4A alone was sufficient to induce mitophagy. Interference with mitochondrial fragmentation and mitophagy resulted in reduced virus propagation. Overall, our study provides the first evidence of mitochondrial quality control dysregulation during JEV infection, largely mediated by its NS4A protein. IMPORTANCE The JEV-infected mammalian cells show an enhanced mitophagy flux with a concomitant decline in the mitochondrial mass. We show that the NS4A protein of JEV localized to the mitochondria and interacted with PINK1 in Huh7 cells during infection with the virus and demonstrate that JEV-NS4A alone is sufficient to induce mitophagy. The study provides the first evidence of mitochondrial quality control dysregulation during JEV infection, largely mediated by its NS4A protein.

The dominant roles of ICAM-1-encoding gene in DNA vaccination against Japanese encephalitis virus are the activation of dendritic cells and enhancement of cellular immunity

We investigated the cellular immune responses elicited by a plasmid DNA vaccine encoding prM-E protein from the Japanese encephalitis (JE) virus (JEV) with or without various forms of intercellular adhesion molecule (ICAM)-1 gene to maximize the immune responses evoked by the JE DNA vaccine. We observed that co-immunization with the construct containing murine ICAM-1 gene (pICAM-1) resulted in a significant increase in the percentage of CD4(+)T cells, high level of JEV-specific cytotoxic T lymphocyte response, and high production of T helper 1 (Th1)-type cytokines in splenic T cells. Furthermore, the co-expression of ICAM-1 and DNA immunogens was found to be more effective in generating T cell-mediated immune responses than those induced by immunization with pJME in combination with pICAM-1. Our results suggested that ICAM-1 enhanced T cell receptor signaling and activated Th1 immune responses in the JEV model system by increasing the induction of CD4(+)Th1 cell subset and activating dendritic cells.

Japanese encephalitis: a review of the Indian perspective

Japanese encephalitis virus (JEV) causes Japanese encephalitis, which is a leading form of viral encephalitis in Asia, with around 50,000 cases and 10,000 deaths per year in children below 15 years of age. The JEV has shown a tendency to extend to other geographic regions. Case fatality averages 30% and a high percentage of the survivors are left with permanent neuropsychiatric sequelae. Currently, there is no cure for JEV, and treatment is mainly supportive. Patients are not infectious, but should avoid further mosquito bites. A number of antiviral agents have been investigated; however, none of these have convincingly been shown to improve the outcome of JEV. In this review, the current knowledge of the epidemiology and the pathogenesis of this deadly disease have been summarized.

Development of a pilot-scale production process and characterization of a recombinant Japanese encephalitis virus envelope domain III protein expressed in Escherichia coli

Japanese encephalitis virus (JEV) is the most important cause of encephalitis in most Asian regions. JEV envelope domain III (JEV EDIII) protein is involved in binding to host receptors, and it contains specific epitopes that elicit virus-neutralizing antibodies. A highly immunogenic, recombinant JEV EDIII protein was expressed in Escherichia coli. In order to take this vaccine candidate for further studies, recombinant JEV EDIII protein was produced employing a pilot-scale fermentation process. Recombinant JEV EDIII protein expressed as inclusion bodies (IBs) was solubilized in 8 M urea and renatured by on-column refolding protocol in the presence of glycerol. A three-step purification process comprising of affinity chromatography, ion-exchange chromatography (IEX) based on salt, and IEX based on pH was developed. About ~124 mg of highly purified and biologically active EDIII protein was obtained from 100 g of biomass. Biological function of the purified EDIII protein was confirmed by their ability to generate EDIII-specific antibodies in mice that could neutralize the virus. These findings suggest that recombinant JEV EDIII protein in combination with compatible adjuvant is highly immunogenic and elicit high-titer neutralizing antibodies. Thus, recombinant JEV EDIII protein produced at large scale can be a potential vaccine candidate.

Fenofibrate reduces mortality and precludes neurological deficits in survivors in murine model of Japanese encephalitis viral infection

BACKGROUND

Japanese encephalitis (JE), the most common form of viral encephalitis occurs periodically in endemic areas leading to high mortality and neurological deficits in survivors. It is caused by a flavivirus, Japanese encephalitis virus (JEV), which is transmitted to humans through mosquitoes. No effective cure exists for reducing mortality and morbidity caused by JEV infection, which is primarily due to excessive inflammatory response. Fenofibrate, a peroxisome proliferator-activated receptor-α (PPARα) agonist is known to resolve inflammation by repressing nuclear factor-κB (NF-κB) and enhancing transcription of anti-oxidant and anti-inflammatory genes. In addition, fenofibrate also up-regulates a class of proteins, cytochrome P4504Fs (Cyp4fs), which are involved in detoxification of the potent pro-inflammatory eicosanoid, leukotriene B(4) (LTB(4)) to 20-hydroxy LTB(4).

METHODOLOGY/PRINCIPAL FINDINGS

The neuroprotective effect of fenofibrate was examined using in vitro (BV-2 microglial cell line) and in vivo (BALB/c mice) models of JEV infection. Mice were treated with fenofibrate for 2 or 4 days prior to JEV exposure. Pretreatment with fenofibrate for 4 but not 2 days reduced mortality by 80% and brain LTB(4) levels decreased concomitantly with the induction of Cyp4f15 and 4f18, which catalyze detoxification of LTB(4) through hydroxylation. Expression of cytokines and chemokine decreased significantly as did microglial activation and replication of the JEV virus.

CONCLUSIONS/SIGNIFICANCE

Fenofibrate confers neuroprotection against Japanese encephalitis, in vivo, in mouse model of JEV infection. Thus, fenofibrate, a PPARα agonist that is commonly used as a hypolipidemic drug could potentially be used for prophylaxis during JE epidemics to reduce mortality and morbidity.

Cross protection against lethal West Nile virus challenge in mice immunized with recombinant E protein domain III of Japanese encephalitis virus

Japanese encephalitis virus (JEV) and West Nile virus (WNV) are closely related mosquito-borne flaviviruses that cause severe encephalitic diseases with global impact. Cross protection among JEV and WNV has been previously described, and most cross reactive epitopes were identified within the domain II of E protein (EDII). In this study, the E protein domain III (EDIII) of JEV was successfully expressed in Escherichia coli, purified by a Ni-NTA column and characterized by Western blotting assay. Competitive inhibition assay showed that this recombinant JEV EDIII blocks the entry of JEV into BHK-21 cells. Mice immunized with the recombinant JEV EDIII developed high IgG and neutralizing antibodies titers against JEV. Most importantly, antibodies induced by JEV EDIII could neutralize WNV in vitro and partially protected mice against lethal WNV challenge. These results demonstrate that immunization with JEV EDIII induces cross-protective immunity against WNV infection, indicating a possible role of EDIII for the cross-protection among flavivirus.

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

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

Development of a vaccine to prevent Japanese encephalitis: a brief review

Japanese encephalitis (ICD 10: A83.0) is an important specific viral encephalitis caused by the Japanese encephalitis virus, a virus of the Flavivirus group. Millions of people, especially those in endemic areas of developing countries in Asia, are at high risk from this infection. Therefore proper management to deal with this virus is essential. There is no specific treatment for Japanese encephalitis virus. Supportive and symptomatic treatments are usually used, which emphasize the importance of prevention in this specific neurological disorder. Vector control or vaccination can be used to prevent the disease. Because the existing Japanese encephalitis vaccine poses some undesirable problems, a new vaccine is needed. The process of developing a new vaccine is briefly discussed.

Past, present, and future of Japanese encephalitis

Japanese encephalitis (JE), a vector-borne viral disease, is endemic to large parts of Asia and the Pacific. An estimated 3 billion people are at risk, and JE has recently spread to new territories. Vaccination programs, increased living standards, and mechanization of agriculture are key factors in the decline in the incidence of this disease in Japan and South Korea. However, transmission of JE is likely to increase in Bangladesh, Cambodia, Indonesia, Laos, Myanmar, North Korea, and Pakistan because of population growth, intensified rice farming, pig rearing, and the lack of vaccination programs and surveillance. On a global scale, however, the incidence of JE may decline as a result of large-scale vaccination programs implemented in China and India.

Evaluation of Japanese encephalitis virus DNA vaccine candidates in rhesus monkeys [Macaca mulatta]

We have previously described DNA vaccine candidates against Japanese encephalitis virus (JEV) that were immunogenic in mice. Present study was conducted to evaluate their immunogenicity in rhesus monkeys (Macaca mulatta) and compare it with the commercial mouse brain-derived, formalin-inactivated vaccine. Groups of four monkeys were immunized with either pMEa (expressing the anchored form of the envelope protein along with the pre-membrane protein of JEV) or pMEs (expressing the secretory form of the envelope protein along with pre-membrane protein of JEV) by intra-muscular (IM, using needle) or intra-dermal (ID, using gene gun) routes. Following primary immunization with 1mg plasmid DNA given IM, or 5 microg plasmid DNA given ID, the monkeys were boosted after 1 and 2 months with 0.5mg DNA given IM or 5 microg DNA given ID, and observed for a period of 6 months. After the second booster, most of the monkeys sero-converted and developed JEV neutralizing antibodies, albeit of low titer. Importantly however, following a sham challenge with the mouse brain-derived inactivated JEV vaccine given 6 months after immunization, the neutralizing antibody titers rose rapidly indicating a vigorous anamnestic response. Based on the JEV neutralizing antibody response following the vaccination and the extent of anamnestic response generated in the immunized monkeys, plasmid pMEa was superior to pMEs. This study indicates that the JEV candidate DNA vaccine is capable of generating protective levels of JEV neutralizing antibodies in rhesus monkeys and prime the immune system effectively against a subsequent exposure to JEV.

Effect of pre-existing anti-tick-borne encephalitis virus immunity on neutralising antibody response to the Vero cell-derived, inactivated Japanese encephalitis virus vaccine candidate IC51

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in Asia with a case fatality rate up to 35% and long-term sequelae up to 75%. This active-controlled, randomized, multi-centre, observer-blind, phase III trial investigated the neutralising antibody response to the new Japanese encephalitis (JE) vaccine IC51 in subjects with (N=81) and without (N=339) pre-existing tick-borne encephalitis (TBE) vaccine induced antibodies as determined by TBE enzyme-linked immunosorbent assay IgG (ELISA). Neutralising antibody response was statistically superior in TBE ELISA-positive subjects compared to TBE ELISA-negative subjects after the first (p<0.0001) but not after the second vaccination with IC51. Thus, pre-existing vaccine-induced TBE immunity enhances the neutralising JEV-specific antibody response after a single IC51 vaccination.

Current use and development of vaccines for Japanese encephalitis

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS/CONCLUSION

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

Immunization with West Nile virus envelope domain III protects mice against lethal infection with homologous and heterologous virus

The Japanese encephalitis virus (JEV) serocomplex-group consists of mosquito-borne flaviviruses, which include West Nile virus (WNV) and JEV, and both may cause severe encephalitis in humans. WNV has spread rapidly across the United States since its introduction in 1999 and its geographical distribution within the western hemisphere is expected to further expand, whereas, JEV is the most common cause of viral encephalitis in Southeast Asia, China and India. Currently, there is no registered human vaccine or specific therapy to prevent or treat WNV infection. Here we describe the efficacy of recombinant domain III (DIII) of WNV glycoprotein E in a mouse model. It induces high neutralizing antibody titers, as well as, protection against lethal WNV infection in C57BL/6 mice. This vaccine preparation also afforded partial protection against lethal JEV infection.

Immunogenicity and protective efficacy of the E. coli-expressed domain III of Japanese encephalitis virus envelope protein in mice

Domain III of Japanese encephalitis virus (JEV) envelope protein (E-DIII) was synthesized in E. coli as a fusion protein containing maltose-binding protein (MBP-E-DIII) or six contiguous histidine residues (His-E-DIII) at its N-terminus. MBP-E-DIII was found both in the soluble as well as the insoluble fraction of the bacterial lysate, while His-E-DIII was found exclusively in the inclusion bodies. These purified proteins were examined in mice for their immunogenicity in presence of an aluminium hydroxide based-adjuvant Alhydrogel and Freund's adjuvant. While both proteins generated anti-JEV antibodies that neutralized JEV activity in vitro, His-E-DIII generated higher antibody titers than MBP-E-DIII. Mice immunized with His-E-DIII in presence of Alhydrogel generated antibody titers similar to those induced by the commercial vaccine and protected mice against lethal JEV challenge.