Japanese encephalitis virus live attenuated vaccine strains display altered immunogenicity, virulence and genetic diversity

Comparative Pathogenesis of Two Lineages of Powassan Virus Reveals Distinct Clinical Outcome, Neuropathology, and Inflammation

Tick-borne flaviviruses (TBFV) can cause severe neuroinvasive disease which may result in death or long-term neurological deficit in over 50% of survivors. Multiple mechanisms for invasion of the central nervous system (CNS) by flaviviruses have been proposed including axonal transport, transcytosis, endothelial infection, and Trojan horse routes. Flaviviruses may utilize different or multiple mechanisms of neuroinvasion depending on the specific virus, infection site, and host variability. In this work we have shown that the infection of BALB/cJ mice with either Powassan virus lineage I (Powassan virus) or lineage II (deer tick virus) results in distinct spatial tropism of infection in the CNS which correlates with unique clinical presentations for each lineage. Comparative transcriptomics of infected brains demonstrates the activation of different immune pathways and downstream host responses. Ultimately, the comparative pathology and transcriptomics are congruent with different clinical signs in a murine model. These results suggest that the different disease presentations occur in clinical cases due to the inherent differences in the two lineages of Powassan virus.

Epitope(s) involving amino acids of the fusion loop of Japanese encephalitis virus envelope protein is(are) important to elicit protective immunity

Dengue vaccine candidates have been shown to improve vaccine safety and efficacy by altering the residues or accessibility of the fusion loop on the virus envelope protein domain II (DIIFL) in an ex vivo animal study. The current study aimed to comprehensively investigate the impact of DIIFL mutations on the antigenicity, immunogenicity, and protective efficacy of Japanese encephalitis virus (JEV) virus-like particles (VLPs) in mice. We found the DIIFL G106K/L107D (KD) and W101G/G106K/L107D (GKD) mutations altered the binding activity of JEV VLP to cross-reactive monoclonal antibodies but had no effect on their ability to elicit total IgG antibodies in mice. However, JEV VLPs with KD or GKD mutations induced significantly less neutralizing antibodies against JEV. Only 46% and 31% of the KD and GKD VLPs-immunized mice survived compared to 100% of the wild-type (WT) VLP-immunized mice after a lethal JEV challenge. In passive protection experiments, naïve mice that received sera from WT VLP-immunized mice exhibited a significantly higher survival rate of 46.7% compared to those receiving sera from KD VLP- and GKD VLP-immunized mice (6.7% and 0%, respectively). This study demonstrated that JEV DIIFL is crucial for eliciting potently neutralizing antibodies and protective immunity against JEV.

IMPORTANCE

Introduction of mutations into the fusion loop is one potential strategy for generating safe dengue and Zika vaccines by reducing the risk of severe dengue following subsequent infections, and for constructing live-attenuated vaccine candidates against newly emerging Japanese encephalitis virus (JEV) or Japanese encephalitis (JE) serocomplex virus. The monoclonal antibody studies indicated the fusion loop of JE serocomplex viruses primarily comprised non-neutralizing epitopes. However, the present study demonstrates that the JEV fusion loop plays a critical role in eliciting protective immunity in mice. Modifications to the fusion loop of JE serocomplex viruses might negatively affect vaccine efficacy compared to dengue and zika serocomplex viruses. Further studies are required to assess the impact of mutant fusion loop encoded by commonly used JEV vaccine strains on vaccine efficacy or safety after subsequent dengue virus infection.

Development of a live-attenuated chimeric vaccine against the emerging Usutu virus

Usutu virus (USUV) is an emerging arthropod-borne flavivirus that has expanded into multiple European countries during the past several decades. USUV infection in human has been linked to severe neurological complications, and no vaccine is now available against USUV. In this work, we develop a live-attenuated chimeric USUV vaccine (termed ChinUSUV) based on the full-length infectious cDNA clone of the licensed Japanese encephalitis virus (JEV) vaccine strain SA14-14-2. In vitro studies demonstrate that ChinUSUV replicates efficiently and maintains its genetic stability. Remarkably, ChinUSUV exhibits a significant attenuation phenotype in multiple mouse models even compared with the licensed JEV vaccine. A single immunization with ChinUSUV elicits potent IgG and neutralizing antibody responses as well as T cell response. Passive transfer of sera from ChinUSUV-immunized mice confers significant protection against lethal homologous challenge in suckling mice. Taken together, our results suggest that ChinUSUV represents a potential USUV vaccine candidate that merits further development.

Multiplexed multicolor antiviral assay amenable for high-throughput research

To curb viral epidemics and pandemics, antiviral drugs are needed with activity against entire genera or families of viruses. Here, we develop a cell-based multiplex antiviral assay for high-throughput screening against multiple viruses at once, as demonstrated by using three distantly related orthoflaviviruses: dengue, Japanese encephalitis and yellow fever virus. Each virus is tagged with a distinct fluorescent protein, enabling individual monitoring in cell culture through high-content imaging. Specific antisera and small-molecule inhibitors are employed to validate that multiplexing approach yields comparable inhibition profiles to single-virus infection assays. To facilitate downstream analysis, a kernel is developed to deconvolute and reduce the multidimensional quantitative data to three cartesian coordinates. The methodology is applicable to viruses from different families as exemplified by co-infections with chikungunya, parainfluenza and Bunyamwera viruses. The multiplex approach is expected to facilitate the discovery of broader-spectrum antivirals, as shown in a pilot screen of approximately 1200 drug-like small-molecules.

A Novel, Comprehensive A129 Mouse Model for Investigating Dengue Vaccines and Evaluating Pathogenesis

In search of a mouse model for use in evaluating dengue vaccines, we assessed A129 mice that lacked IFN-α/β receptors, rendering them susceptible to dengue virus (DENV) infection. To our knowledge, no reports have evaluated dengue vaccine efficiency using A129 mice. A129 mice were given a single intraperitoneal (IP) or subcutaneous (SC) injection of the vaccine, Dengvaxia. After 14 days of immunization via the IP or SC injection of Dengvaxia, the A129 mice exhibited notably elevated levels of anti-DENV immunoglobulin G and neutralizing antibodies (NAb) targeting all four DENV serotypes, with DENV-4 displaying the highest NAb levels. After challenge with DENV-2, Dengvaxia and mock-immunized mice survived, while only the mock group exhibited signs of morbidity. Viral genome levels in the serum and tissues (excluding the brain) were considerably lower in the immunized mice compared to those in the mock group. The SC administration of Dengvaxia resulted in lower viremia levels than IP administration did. Therefore, given that A129 mice manifest dengue-related morbidity, including viremia in the serum and other tissues, these mice represent a valuable model for investigating novel dengue vaccines and antiviral drugs and for exploring dengue pathogenesis.

Attenuated Chimeric GI/GIII Vaccine Candidate against Japanese Encephalitis Virus

Japanese encephalitis (JE) is a very severe disease characterized by high fatality rates and the development of permanent behavioral, psychiatric, and neurological sequelae among survivors. Japanese encephalitis virus (JEV), a flavivirus, is responsible for JE. In Asia, Genotype I (GI) has emerged as the dominant strain, replacing Genotype III (GIII). However, no clinically approved drug is available to treat JEV infection, and currently available commercial vaccines derived from JEV GIII strains provide only partial protection against GI. Utilizing a reverse genetics system, this study attempted to produce a novel chimeric JEV strain with high efficacy against JEV GI. Accordingly, a GI/GIII intertypic recombinant strain, namely SA14-GI env, was generated by substituting the E region of the GIII SA14-14-2 strain with that of the GI strain, K05GS. The neurovirulence of the mutant virus was significantly reduced in mice. Analysis of the immunogenicity of the chimeric virus revealed that it induced neutralizing antibodies against JEV GI in mice, and the protective efficacy of SA14-GI env was higher than that of SA14-14-2. These findings suggest that SA14-GI env may be a safe and effective live-attenuated vaccine candidate against JEV GI.

Novel approaches for the rapid development of rationally designed arbovirus vaccines

Vector-borne diseases, including those transmitted by mosquitoes, account for more than 17% of infectious diseases worldwide. This number is expected to rise with an increased spread of vector mosquitoes and viruses due to climate change and man-made alterations to ecosystems. Among the most common, medically relevant mosquito-borne infections are those caused by arthropod-borne viruses (arboviruses), especially members of the genera Flavivirus and Alphavirus. Arbovirus infections can cause severe disease in humans, livestock and wildlife. Severe consequences from infections include congenital malformations as well as arthritogenic, haemorrhagic or neuroinvasive disease. Inactivated or live-attenuated vaccines (LAVs) are available for a small number of arboviruses; however there are no licensed vaccines for the majority of these infections. Here we discuss recent developments in pan-arbovirus LAV approaches, from site-directed attenuation strategies targeting conserved determinants of virulence to universal strategies that utilize genome-wide re-coding of viral genomes. In addition to these approaches, we discuss novel strategies targeting mosquito saliva proteins that play an important role in virus transmission and pathogenesis in vertebrate hosts. For rapid pre-clinical evaluations of novel arbovirus vaccine candidates, representative in vitro and in vivo experimental systems are required to assess the desired specific immune responses. Here we discuss promising models to study attenuation of neuroinvasion, neurovirulence and virus transmission, as well as antibody induction and potential for cross-reactivity. Investigating broadly applicable vaccination strategies to target the direct interface of the vertebrate host, the mosquito vector and the viral pathogen is a prime example of a One Health strategy to tackle human and animal diseases.

Advances in Next-Generation Coronavirus Vaccines in Response to Future Virus Evolution

Coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread to more than 230 countries and territories worldwide since its outbreak in late 2019. In less than three years, infection by SARS-CoV-2 has resulted in over 600 million cases of COVID-19 and over 6.4 million deaths. Vaccines have been developed with unimaginable speed, and 11 have already been approved by the World Health Organization and given Emergency Use Listing. The administration of several first-generation SARS-CoV-2 vaccines has successfully decelerated the spread of COVID-19 but not stopped it completely. In the ongoing fight against viruses, genetic mutations frequently occur in the viral genome, resulting in a decrease in vaccine-induced antibody neutralization and widespread breakthrough infection. Facing the evolution and uncertainty of SARS-CoV-2 in the future, and the possibility of the spillover of other coronaviruses to humans, the need for vaccines with a broad spectrum of antiviral variants against multiple coronaviruses is recognized. It is imperative to develop a universal coronavirus or pan-coronavirus vaccine or drug to combat the ongoing COVID-19 pandemic as well as to prevent the next coronavirus pandemic. In this review, in addition to summarizing the protective effect of approved vaccines, we systematically summarize current work on the development of vaccines aimed at suppressing multiple SARS-CoV-2 variants of concern as well as multiple coronaviruses.

Contrasting the Practices of Virus Isolation and Characterization between the Early Period in History and Modern Times: The Case of Japanese Encephalitis Virus

Japanese encephalitis is a serious disease transmitted by mosquitoes. With its recent spread beyond the traditional territory of endemicity in Asia, the magnitude of global threat has increased sharply. While much of the current research are largely focused on changing epidemiology, molecular genetics of virus, and vaccination, little attention has been paid to the early history of virus isolation and phenotypic characterization of this virus. In this review, using this piece of history as an example, I review the transition of the concept and practice of virus isolation and characterization from the early period of history to modern times. The spectacular development of molecular techniques in modern times has brought many changes in practices as well as enormous amount of new knowledge. However, many aspects of virus characterization, in particular, transmission mechanism and host relationship, remain unsolved. As molecular techniques are not perfect in all respects, beneficial accommodation of molecular and biologic data is critically important in many branches of research. Accordingly, I emphasize exercising caution in applying only these modern techniques, point out unrecognized communication problems, and stress that JE research history is a rich source of interesting works still valuable even today and waiting to be discovered.

Investigation of immune response induction by Japanese encephalitis live‐attenuated and chimeric vaccines in mice

The Japanese encephalitis (JE) live‐attenuated vaccine SA14‐14‐2 and the chimeric vaccine IMOJEV (JE‐CV) are two kinds of vaccines available for use worldwide. JE‐CV was previously known as ChimeriVax‐JE, that consists of yellow fever vaccine 17D (YFV‐17D) from which the structural genes (prM/E) have been replaced with those of SA14‐14‐2. This study aimed to investigate the neutralizing antibody, protection efficacy, and specific T‐cell response elicited by both vaccines in mice. The neutralizing antibodies produced by JE‐CV were slightly lower than those produced by SA14‐14‐2, but the protection conferred by JE‐CV was considerably lower in the low vaccine dose immunization group. Furthermore, the JE‐CV did not induce a specific T‐cell response against JEV NS3, while it did induce a potent antigen‐specific T‐cell response against the viral backbone vaccine YFV. In conclusion, this study is the first detailed investigation of the cellular immune response to the two vaccines. Enzyme‐linked immunospot (ELISPOT) and flow staining suggest a more potent specific T‐cell response against the JEV antigen was elicited in mice immunized with SA14‐14‐2 but not JE‐CV. Using heterologous flaviviruses as a live‐attenuated vaccine backbone may unlikely generate an optimal T‐cell response against the vaccine strain virus and might affect the protective efficacy.

Microalgal drugs: A promising therapeutic reserve for the future

Over the decades, a variety of chemically synthesized drugs are being used to cure existing diseases but often these drugs could not be effectively employed for the treatment of serious and newly emerging diseases. Fortunately, in nature there occurs immense treasure of plants and microorganisms which are living jewels with respect to their richness of medically important metabolites of high value. Hence, amongst the existing microorganism(s), the marine world offers a plethora of biological entities that can contribute to alleviate numerous human ailments. Algae are one such photosynthetic microorganism found in both marine as well as fresh water which are rich source of metabolites known for their nutrient content and health benefits. Various algal species like Haematococcus, Diatoms, Griffithsia, Chlorella, Spirulina, Ulva, etc. have been identified and isolated to produce biologically active and pharmaceutically important high value compounds like astaxanthin, fucoxanthin, sulphur polysaccharides mainly galactose, rhamnose, xylose, fucose etc., which show antimicrobial, antifungal, anti-cancer, and antiviral activities. However, the production of either of these bio compounds is favored under conditions of stress. This review gives detailed information on various nutraceutical metabolites extracted from algae. Additionally focus has been made on the role of these bio compounds extracted from algae especially sulphur polysaccharides to treat several diseases with prospective treatment for SARS-CoV-2. Lastly it covers the knowledge gaps and future perspectives in this area of research.

Genetic Diversity Does Not Contribute to Attenuation of HeLa Passaged Wild-Type Yellow Fever Virus Strain French Viscerotropic Virus

The disease yellow fever was prevented by two live attenuated vaccines, strains 17D and French neurotropic vaccine (FNV), derived by serial passage of wild-type (WT) strains Asibi and French Viscerotropic virus (FVV), respectively. Both 17D and FNV displayed decreased genetic diversity and resistance to the antiviral Ribavirin compared to their WT parental strains, which are thought to contribute to their attenuated phenotypes. Subsequent studies found that only a few passages of WT strain FVV in HeLa cells resulted in an attenuated virus. In the current study, the genome sequence of FVV following five passages in HeLa cells (FVV HeLa p5) was determined through Next Generation Sequencing (NGS) with the aim to investigate the molecular basis of viral attenuation. It was found that WT FVV and FVV HeLa p5 virus differed by five amino acid substitutions: E-D155A, E-K331R, E-I412V, NS2A-T105A, and NS4B-V98I. Surprisingly, the genetic diversity and Ribavirin resistance of the FVV HeLa p5 virus were not statistically different to WT parent FVV. These findings suggest that while FVV HeLa p5 is attenuated, this is not dependent on a high-fidelity replication complex, characterized by reduced genetic diversity or increased Ribavirin stability, as seen with FNV and 17D vaccines.