Immunization with recombinant adenovirus synthesizing the secretory form of Japanese encephalitis virus envelope protein protects adenovirus-exposed mice against lethal encephalitis

A seroepidemiological survey of adenovirus type 7 circulation among healthy adults in China and in Sierra Leone, West Africa

Adenovirus type 7 (HAdV7) is one of the most pathogenic human adenoviruses (HAdVs) and can cause severe illness and even death, particularly in people with weakened immune systems. Many countries worldwide have experienced epidemics of this highly contagious pathogen, including China and Sierra Leone; however, studies describing the seroprevalence of anti-HAdV7 neutralizing antibodies (nAbs) are still lacking. Herein, we established an efficient neutralization assay based on a recombinant luciferase-expressing HAdV7 virus (HAd7-Luc) to monitor historical HAdV7 infections and predict outbreak distributions. Among the 2,350 serum samples collected from eight sites in China and Sierra Leone in this cross-sectional serological survey, the overall proportion of anti-HAdV7-seropositive individuals was nearly 60%, with higher seroprevalence rates in Sierra Leone than in China. Regionally, HAdV7 nAb titers were higher in China than in Sierra Leone and showed a geographic variation across different regions. Regardless of the location, the seropositive rate of HAdV7 nAb was lower than that of HAdV5 nAb, as was the nAb titer. The prevalence rates of antibodies against HAdV7 and HAdV5 were both related to age but not to sex. In addition, serologic cross-reactions were rarely observed among people infected with HAdV7 and HAdV5. These results indicate a humoral immune response acquired through endemic HAdV7 infection and enrich the understanding of not only the epidemiological prevention and control of HAdV7 but also the clinical application of HAdV7-based vaccines or gene therapy tools.

Adenovirus vector-based vaccines as forefront approaches in fighting the battle against flaviviruses

Flaviviruses are arthropod-borne viruses (arboviruses) that have been recently considered among the significant public health problems in defined geographical regions. In this line, there have been vaccines approved for some flaviviruses including dengue virus (DENV), Japanese encephalitis virus (JEV), yellow fever virus (YFV), and tick-borne encephalitis virus (TBEV), although the efficiency of such vaccines thought to be questionable. Surprisingly, there are no effective vaccine for many other hazardous flaviviruses, including West Nile and Zika viruses. Furthermore, in spite of approved vaccines for some flaviviruses, for example DENV, alternative prophylactic vaccines seem to be still needed for the protection of a broader population, and it originates from the unsatisfying safety, and the efficacy of vaccines that have been introduced. Thus, adenovirus vector-based vaccine candidates are suggested to be effective, safe, and reliable. Interestingly, recent widespread use of adenovirus vector-based vaccines for the COVID-19 pandemic have highlighted the importance and feasibility of their widespread application. In this review, the applicability of adenovirus vector-based vaccines, as promising approaches to harness the diseases caused by Flaviviruses, is discussed.

Mucosal Vaccination: A Promising Alternative Against Flaviviruses

The Flaviviridae are a family of positive-sense, single-stranded RNA enveloped viruses, and their members belong to a single genus, Flavivirus. Flaviviruses are found in mosquitoes and ticks; they are etiological agents of: dengue fever, Japanese encephalitis, West Nile virus infection, Zika virus infection, tick-borne encephalitis, and yellow fever, among others. Only a few flavivirus vaccines have been licensed for use in humans: yellow fever, dengue fever, Japanese encephalitis, tick-borne encephalitis, and Kyasanur forest disease. However, improvement is necessary in vaccination strategies and in understanding of the immunological mechanisms involved either in the infection or after vaccination. This is especially important in dengue, due to the immunological complexity of its four serotypes, cross-reactive responses, antibody-dependent enhancement, and immunological interference. In this context, mucosal vaccines represent a promising alternative against flaviviruses. Mucosal vaccination has several advantages, as inducing long-term protective immunity in both mucosal and parenteral tissues. It constitutes a friendly route of antigen administration because it is needle-free and allows for a variety of antigen delivery systems. This has promoted the development of several ways to stimulate immunity through the direct administration of antigens (e.g., inactivated virus, attenuated virus, subunits, and DNA), non-replicating vectors (e.g., nanoparticles, liposomes, bacterial ghosts, and defective-replication viral vectors), and replicating vectors (e.g., Salmonella enterica, Lactococcus lactis, Saccharomyces cerevisiae, and viral vectors). Because of these characteristics, mucosal vaccination has been explored for immunoprophylaxis against pathogens that enter the host through mucosae or parenteral areas. It is suitable against flaviviruses because this type of immunization can stimulate the parenteral responses required after bites from flavivirus-infected insects. This review focuses on the advantages of mucosal vaccine candidates against the most relevant flaviviruses in either humans or animals, providing supporting data on the feasibility of this administration route for future clinical trials.

Novel Japanese encephalitis virus NS1-based vaccine: Truncated NS1 fused with E. coli heat labile enterotoxin B subunit

BACKGROUND

Current vaccines against Japanese encephalitis virus (JEV) of flaviviruses have some disadvantages, such as the risk of virulent reversion. Non-structural protein NS1 is conserved among flaviviruses and confers immune protection without the risk of antibody-dependent enhancement (ADE). Therefore, NS1 has become a promising vaccine candidate against flaviviruses.

METHODS

A NS1-based vaccine (LTB-NS1_∆63) with a truncated NS1 protein (NS1_∆63) fused to E. coli heat-labile enterotoxin B subunit (LTB) was expressed in E.coli and explored for its ability to induce immune responses. Safety of LTB-NS1_∆63 was assessed by determining its toxicity in vitro and in vivo. Protective capability of LTB-NS1_∆63 and its-induced antisera was evaluated in the mice challenged with JEV by analyzing mortality and morbidity.

FINDINGS

LTB-NS1_∆63 induced immune responses to a similar level as LTB-NS1, but more robust than NS1_∆63 alone, particularly in the context of oral immunization of mice. Oral vaccination of LTB-NS1_∆63 led to a higher survival rate than that of NS1_∆63 or live-attenuated JEV vaccine SA14-14-2 in the mice receiving lethal JEV challenge. LTB-NS1_∆63 protein also significantly decreases the morbidity of JEV-infected mice. In addition, passive transfer of LTB-NS1_∆63-induced antisera provides a protection against JEV infection in mice.

INTERPRETATION

NS1_∆63 bears JEV NS1 antigenicity. Besides, LTB-NS1_∆63 could serve as a novel protein-based mucosa vaccine targeting JEV and other flaviviruses.

FUNDING

This work was supported by the National Natural Science Foundation, Jiangxi Province Science and Technology Committee, Education Department of Jiangxi Province.

The potential of adenoviral vaccine vectors with altered antigen presentation capabilities

Introduction: Despite their appeal as vaccine vectors, adenoviral vectors are yet unable to induce protective immune responses against some weakly immunogenic antigens. Additionally, the maximum doses of adenovirus-based vaccines are limited by vector-induced toxicity, causing vector elimination and diminished immune responses against the target antigen. In order to increase immune responses to the transgene, while maintaining a moderate vector dose, new technologies for improved transgene presentation have been developed for adenoviral vaccine vectors.Areas covered: This review provides an overview of different genetic-fusion adjuvants that aim to improve antigen presentation in the context of adenoviral vector-based vaccines. The influence on both T cell and B cell responses are discussed, with a main focus on two technologies: MHC class II-associated invariant chain and virus-like-vaccines.Expert opinion: Different strategies have been tested to improve adenovirus-based vaccinations with varying degrees of success. The reviewed genetic adjuvants were designed to increase antigen processing and MHC presentation, or promote humoral immune responses with an improved conformational antigen display. While none of the introduced technologies is universally applicable, this review shall give an overview to identify potential improvements for future vaccination approaches.

The truncated E protein of DTMUV provide protection in young ducks

Duck Tembusu virus (DTMUV) is a major pathogen of duck industry in China. In the current study, we generated different constructs containing envelope (E) protein, pre-membrane-envelope (prM-E) protein, and C-terminally truncated E protein of the DTMUV. The constructed proteins could induce specific antibody responses in young ducks. When ducklings were immunized with the constructed proteins, they were 100% protected against DTMUV infection. Furthermore, the fluorescent signal of the truncated E protein was stronger than other constructed proteins, when Bac-to-Bac baculovirus expression system was applied. Our data demonstrated that the truncated E protein used in the current study could be applied as a potential vaccine candidate to control DTMUV infection in young ducks.

Seroepidemiological investigation of HAdV-4 infection among healthy adults in China and in Sierra Leone, West Africa

An apparent increase in the frequency of human adenovirus type 4 (HAdV-4) infections among general populations has been observed over the past 10 years. However, available epidemiological data that may reflect previous viral circulation and assist in predicting potential outbreaks are sparse, particularly in mainland China and Africa. In this study, a convenient neutralization assay for use in the surveillance of historical HAdV-4 infections was established based on a recombinant luciferase-expressing virus. Subsequently, the neutralizing antibodies (nAbs) of 1013 healthy adult serum samples from China and Sierra Leone were evaluated. Our results showed that over 50% of the participants from China and nearly 70% of donors from Sierra Leone had detectable nAbs against HAdV-4 despite the few infection cases officially reported in these regions. Furthermore, the prevalence of nAbs to HAdV-4 is lower than that to HAdV-5, and both varied by geographic location. In addition, the seropositive rates of both HAdV-4 and HAdV-5 nAbs increased with age. However, the nAbs stimulated by HAdV-4 remained stable at low (≤200) levels among the different age groups, whereas moderate (201–1000) or high (>1000) nAb levels were produced by HAdV-5 and tended to decrease with age. These results elucidate the human humoral immune response against HAdV-4 and revealed that this virus may be an underestimated causative agent of respiratory disease among adults in China and West Africa, demonstrating the importance of HAdV-4 surveillance and providing useful insights for the future development of HAdV-4-based vaccines.

Prevalence of serum neutralizing antibodies to adenovirus type 5 (Ad5) and 41 (Ad41) in children is associated with age and sanitary conditions

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Serum neutralizing antibodies to Ad5 and Ad41 in adults and children were titrated.

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Prevalence of NAb in children was associated with age and sanitary conditions.

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NAb titer distribution pattern was very different between Ad5 an Ad41.

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Ad41 vectored vaccine candidates might have a bright future.

Neutralizing antibody (NAb) can dampen the immunogenicity of adenovirus (Ad) vector-based vaccine. Vector systems based on human adenovirus type 41 (Ad41) have been constructed and used to develop recombinant vaccines. Here, we attempted to study the seroprevalence of NAbs to Ad5 and Ad41 among children and adults in Qinghai province, China. The positive rates (titer ⩾ 40) of Ad5 and Ad41 NAb in adults from Xining city were 75.7% and 94.7%, respectively. The moderate/high-positive rates (titer ⩾ 160) of NAb were quite close between the two viruses in adults (70.4% for Ad5 and 73.5% for Ad41). Age-dependent increase of NAb seroprevalence was observed for both viruses in children. NAb-positive rate of Ad41 reached 50% at 3.3–4.6 years of age for children from Chengxi district, Xining city, approximately 1.5 years earlier than that of Ad5 did. Interestingly, NAb level was also associated with sanitary conditions among young children. For Ad5, 8–15% children (0.2–3.0 years of age) from city or town, where the sanitations were relatively better, had moderate/high-positive NAb, while the same rate was 62% for children from villages. For Ad41, 22% children from city, 47% from town and 88% from villages possessed moderate/high-positive NAb. The possible influence of NAb titer distributions on the application of Ad41-vectored vaccines was discussed in detail. Our results suggested that children from places with poor sanitations should be included for comprehensive Ad NAb seroprevalence studies, and provided insights to the applications of Ad41 vectors.

Trimeric knob protein specifically distinguishes neutralizing antibodies to different human adenovirus species: potential application for adenovirus seroepidemiology

Adenoviruses (Ads) are non-enveloped DNA viruses that have been extensively studied and used as vectors for gene therapy and several potential vaccines. There are 57 Ad serotypes in seven species (A-G), and Ad neutralizing antibody (NAb) titres can vary by serotype and geographical location. Until now serotype- and species-specific antibodies have been detected by neutralization or haemagglutination inhibition assays. These expensive and cumbersome methods of adenovirus typing have mainly been used in epidemiological studies. Our prior work demonstrated that NAbs against the fiber protein are commonly generated during natural Ad infection in humans and the trimeric knob is preferentially recognized by fiber-induced NAbs. In this study, we expressed nine trimeric knob proteins from representative Ad serotypes of human Ad (HAdV)-A-F in Escherichia coli and found no cross-reactivity of these recombinant proteins with rabbit hyperimmune sera (among HAdV-A-F or within HAdV-C). Results of the ELISA based on Ad2 and Ad5 (both HAdV-C) knob proteins were consistent with those of neutralization assays, indicating that the trimeric knob protein would be a good candidate antigen for detecting Ad serotype-specific NAbs in sera from naturally infected subjects. We also demonstrated the primary seroepidemiology of nine Ad serotypes in 274 children using the knob-based ELISA. These results have potential implications for epidemiology of Ad serotypes and future development of Ad-based vaccines and gene therapy.

Japanese encephalitis: development of new candidate vaccines

Japanese encephalitis (JE) is the most common form of viral encephalitis that appears in the form of frequent epidemics of brain fever throughout Southeast Asia, China and India. The disease is caused by a Flavivirus named Japanese encephalitis virus that is spread to humans by mosquitoes. An internationally approved mouse brain-derived inactivated vaccine has been available that is relatively expensive, gives immunity of uncertain duration and is not completely safe. Cell culture-derived inactivated and attenuated JE vaccines are in use in China, but these are not produced as per the norms acceptable in most countries. Several new promising JE vaccine candidates have been developed, some of which are under different stages of clinical evaluation. These new candidate JE vaccines have the potential to generate long-lasting immunity at low cost.

A serological survey of human adenovirus serotype 2 and 5 circulating pediatric populations in Changchun, China, 2011

Background

Efficacy of recombinant adenovirus serotype 5 (rAd5) vaccine vectors for human immunodeficiency virus type 1 (HIV-1) and other pathogens have been shown to be limited by high titers of pre-existing Ad5 neutralizing antibodies (NAbs) in the developing world.

Results

Using a secreted embryonic alkaline phosphatase (SEAP) neutralization assay, 50% serum neutralization titers against rAd2 and rAd5 vectors were measured in samples from 274 infants and young children in northeast China. The pediatric population was found to be 59.6% and 43.3% seropositive for rAd2 and rAd5, respectively. Of all participants, 44.9% had moderate and high (> 200) and 25.6% had high (>1000) Ad2 NAb titers, compared with the corresponding rates of 26.6% and 9.3% against Ad5. Marked age-dependent increases in NAb titers to both Ad serotypes were observed across five age groups, with the exception of infants in the 0-6-month group commonly having relatively high titers due to pre-existing maternal antibodies.

Conclusions

Our data suggest that Ad-based therapies may be suitible for children in the 7-12-month age range in this region.

Clinical development of IMOJEV ®--a recombinant Japanese encephalitis chimeric vaccine (JE-CV)

INTRODUCTION

Japanese encephalitis (JE) is a disease of the central nervous system (CNS) caused by Japanese encephalitis virus (JEV). JE is endemic in most of the South-East Asian countries and in some parts of the Western Pacific. As mosquito control is ineffective, currently vaccination is the only available control measure. A mouse brain-derived inactivated JE vaccine (MBDV) has been in use for a long time; however, it is not feasible for mass vaccination due to the ethical and safety issues. With the World Health Organization (WHO) appealing for the development of novel, safe and affordable JE vaccines, several vaccine candidates have been developed in the recent times and IMOJEV ® is one among them.

AREAS COVERED

This review presents a brief account of various developmental, immunological and ethical issues related to IMOJEV® and provides an in-depth account of its clinical development and efficacy in comparison to other JE vaccines.

EXPERT OPINION

IMOJEV® is a safe and efficacious vaccine. If made affordable through financial assistance from health agencies or by its production in set ups where operational costs are lower, it may become an ideal vaccine for mass vaccination in JE endemic regions.

Impact of preexisting adenovirus vector immunity on immunogenicity and protection conferred with an adenovirus-based H5N1 influenza vaccine

The prevalence of preexisting immunity to adenoviruses in the majority of the human population might adversely impact the development of adaptive immune responses against adenovirus vector-based vaccines. To address this issue, we primed BALB/c mice either intranasally (i.n.) or intramuscularly (i.m.) with varying doses of wild type (WT) human adenovirus subtype 5 (HAd5). Following the development of immunity against HAd5, we immunized animals via the i.n. or i.m. route of inoculation with a HAd vector (HAd-HA-NP) expressing the hemagglutinin (HA) and nucleoprotein (NP) of A/Vietnam/1203/04 (H5N1) influenza virus. The immunogenicity and protection results suggest that low levels of vector immunity (<520 virus-neutralization titer) induced by priming mice with up to 10(7) plaque forming units (p.f.u.) of HAd-WT did not adversely impact the protective efficacy of the vaccine. Furthermore, high levels of vector immunity (approximately 1500 virus-neutralization titer) induced by priming mice with 10(8) p.f.u. of HAd-WT were overcome by either increasing the vaccine dose or using alternate routes of vaccination. A further increase in the priming dose to 10(9) p.f.u. allowed only partial protection. These results suggest possible strategies to overcome the variable levels of human immunity against adenoviruses, leading to better utilization of HAd vector-based vaccines.

Pre-clinical evaluation of a replication-competent recombinant adenovirus serotype 4 vaccine expressing influenza H5 hemagglutinin

BACKGROUND

Influenza virus remains a significant health and social concern in part because of newly emerging strains, such as avian H5N1 virus. We have developed a prototype H5N1 vaccine using a recombinant, replication-competent Adenovirus serotype 4 (Ad4) vector, derived from the U.S. military Ad4 vaccine strain, to express the hemagglutinin (HA) gene from A/Vietnam/1194/2004 influenza virus (Ad4-H5-Vtn). Our hypothesis is that a mucosally-delivered replicating Ad4-H5-Vtn recombinant vector will be safe and induce protective immunity against H5N1 influenza virus infection and disease pathogenesis.

METHODOLOGY/PRINCIPAL FINDINGS

The Ad4-H5-Vtn vaccine was designed with a partial deletion of the E3 region of Ad4 to accommodate the influenza HA gene. Replication and growth kinetics of the vaccine virus in multiple human cell lines indicated that the vaccine virus is attenuated relative to the wild type virus. Expression of the HA transgene in infected cells was documented by flow cytometry, western blot analysis and induction of HA-specific antibody and cellular immune responses in mice. Of particular note, mice immunized intranasally with the Ad4-H5-Vtn vaccine were protected against lethal H5N1 reassortant viral challenge even in the presence of pre-existing immunity to the Ad4 wild type virus.

CONCLUSIONS/SIGNIFICANCE

Several non-clinical attributes of this vaccine including safety, induction of HA-specific humoral and cellular immunity, and efficacy were demonstrated using an animal model to support Phase 1 clinical trial evaluation of this new vaccine.

Viral Vaccines in India: An Overview

Viruses cause a large number of diseases in humans, some of which are fatal, while others are highly debilitating. A majority of viral diseases attack infants and young children, while others strike people in their prime. Development of preventive measures against viral diseases is, therefore, of paramount importance. Vaccination is the most cost-effective medical intervention for preventing mortality and morbidity against infectious diseases. A number of effective and safe vaccines are currently available against several viral diseases of significant medical importance. Many of these manufactured in India, are at par with international standards and are affordable. For many other viral diseases, for which vaccines are currently not available, research is underway at various national laboratories, as well as in the private sector companies in India. The present overview highlights the various vaccine preventable viral diseases that are of special importance to India and aims to provide a glimpse of the various vaccines that are currently available, or are under development in India.

Induction and comparison of SIV immunity in Ad5 naïve and Ad5 immune non-human primates using an Ad5 [E1-, E2b-] based vaccine

The effectiveness of recombinant Adenovirus serotype 5 (Ad5) vectors to induce immune responses against targeted antigens has been limited by the presence of pre-existing or Ad5 vaccine induced anti-vector immunity. The Ad5 [E1-, E2b-] platform, a recombinant Ad5 with additional deletions, has been previously reported by us to induce immune responses in the presence of Ad5 immunity. In an Ad5 immune non-human primate (NHP) model, an Ad5 [E1-, E2b-] construct expressing HIV-1 Gag induced immune responses in the presence of pre-existing Ad5 immunity. In the present study we expand on these prior observations by comparing the cell mediated immune (CMI) responses induced by Ad5 [E1-, E2b-]-SIV-gag/nef in Ad5 naïve and Ad5 immune NHP. Additionally, NHP were immunized with an Ad5 [E1-, E2b-]-HIV-pol construct following two homologous administrations of Ad5 [E1-, E2b-]-SIV-gag/nef to determine if an immune response could be induced against a third antigen in the presence of vaccine induced Ad5 immunity. Positive CMI responses, as assessed by interferon-gamma (IFN-γ) secreting lymphocytes, were induced against all three antigens. These CMI responses increased over a course of multiple immunizations and the response profiles observed in Ad5 naïve and Ad5 immune NHP were similar. No influence of the major histocompatibility complex on CMI responses was observed. These data indicate that the new Ad5 [E1-, E2b-] platform based vaccine could be used for homologous vaccination regimes to induce robust CMI responses in the presence of Ad5 vector immunity.

Japanese encephalitis virus-infected macrophages induce neuronal death

Inflammation in the central nervous system (CNS) in Japanese encephalitis (JE) is shown to be the result of microglial activation that leads to the release of various proinflammatory mediators. Peripheral macrophages have been reported to infiltrate into the CNS in JE, though their contribution to the inflammatory process is yet to be elucidated. In this study, using an in vitro macrophage model, we have shown that upon JE virus infection, these cells secrete various soluble factors which may significantly add to the existing inflammatory milieu and lead to apoptotic or necrotic death of neurons. However, it is difficult to quantify the extent of involvement of either the microglia or infiltrating macrophages in the inflammatory processes.

IMOJEV(®): a Yellow fever virus-based novel Japanese encephalitis vaccine

Japanese encephalitis (JE) is a disease of the CNS caused by Japanese encephalitis virus (JEV). The disease appears in the form of frequent outbreaks in most south- and southeast Asian countries and the virus has become endemic in several areas. There is no licensed therapy available and disease control by vaccination is considered to be most effective. Mouse brain-derived inactivated JE vaccines, although immunogenic, have several limitations in terms of safety, availability and requirement for multiple doses. Owing to these drawbacks, the WHO called for the development of novel, safe and more efficacious JE vaccines. Several candidate vaccines have been developed and at least three of them that demonstrated strong immunogenicity after one or two doses of the vaccine in animal models were subsequently tested in various clinical trials. One of these vaccines, IMOJEV(®) (JE-CV and previously known as ChimeriVax™-JE), is a novel recombinant chimeric virus vaccine, developed using the Yellow fever virus (YFV) vaccine vector YFV17D, by replacing the cDNA encoding the envelope proteins of YFV with that of an attenuated JEV strain SA14-14-2. IMOJEV was found to be safe, highly immunogenic and capable of inducing long-lasting immunity in both preclinical and clinical trials. Moreover, a single dose of IMOJEV was sufficient to induce protective immunity, which was similar to that induced in adults by three doses of JE-VAX(®), a mouse brain-derived inactivated JE vaccine. Recently, Phase III trials evaluating the immunogenicity and safety of the chimeric virus vaccine have been successfully completed in some JE-endemic countries and the vaccine manufacturers have filed an application for vaccine registration. IMOJEV may thus be licensed for use in humans as an improved alternative to the currently licensed JE vaccines.

A complex adenovirus vaccine against chikungunya virus provides complete protection against viraemia and arthritis

Chikungunya virus, a mosquito-borne alphavirus, recently caused the largest epidemic ever seen for this virus. Chikungunya disease primarily manifests as a painful and debilitating arthralgia/arthritis, and no effective drug or vaccine is currently available. Here we describe a recombinant chikungunya virus vaccine comprising a non-replicating complex adenovirus vector encoding the structural polyprotein cassette of chikungunya virus. A single immunisation with this vaccine consistently induced high titres of anti-chikungunya virus antibodies that neutralised both an old Asian isolate and a Réunion Island isolate from the recent epidemic. The vaccine also completely protected mice against viraemia and arthritic disease caused by both virus isolates.

Bioinformatics in new generation flavivirus vaccines

Flavivirus infections are the most prevalent arthropod-borne infections world wide, often causing severe disease especially among children, the elderly, and the immunocompromised. In the absence of effective antiviral treatment, prevention through vaccination would greatly reduce morbidity and mortality associated with flavivirus infections. Despite the success of the empirically developed vaccines against yellow fever virus, Japanese encephalitis virus and tick-borne encephalitis virus, there is an increasing need for a more rational design and development of safe and effective vaccines. Several bioinformatic tools are available to support such rational vaccine design. In doing so, several parameters have to be taken into account, such as safety for the target population, overall immunogenicity of the candidate vaccine, and efficacy and longevity of the immune responses triggered. Examples of how bio-informatics is applied to assist in the rational design and improvements of vaccines, particularly flavivirus vaccines, are presented and discussed.

Identification and characterization of Japanese encephalitis virus envelope protein gene from swine

AIMS

Identification and characterization of Japanese encephalitis virus (JEV) envelope protein gene from swine.

METHODS AND RESULTS

Genomic RNA was separated from JEV isolated strain Henan-09-03, and used as templates for cDNA synthesis of E gene. The cDNA of E gene was amplified by RT-PCR and cloned into the pMD19-T-Vector and confirmed by sequencing. The cloned gene was then subcloned into the pET-32a and was introduced into Escherichia coli BL21 (DE3) for expression. The E protein was purified by Ni chelating column-based affinity chromatography. The molecular weight of expressed protein was about 50 kDa. Compared with the published sequence of SA14 (AF495589), the homology of the nucleotide sequence was 98% and the seven mutations resulting in amino acid substitutions at Leu 36 Ser, Leu107 Val, Ala167 Thr, Asn 230 Ser, Leu 340 Pro, Asn 430 Ile, Phe 448 Leu. Phylogenetic analysis of the E sequence of isolated strain classified it within genotype III of the JEV. The result of Western blotting indicated that the antigenicity of the protein was specific.

CONCLUSIONS

The stable expression of the protein and the analysis of its antigenic specificity provide the foundation for developing the ELISA early stage diagnosis kit.

SIGNIFICANCE AND IMPACT OF THE STUDY

As coating antigen, the recombinant E protein served a good source in the indirect ELISA method for the detection of JEV antibody.

Mucosal immunity induced by adenovirus-based H5N1 HPAI vaccine confers protection against a lethal H5N2 avian influenza virus challenge

Development of effective vaccines against highly pathogenic avian influenza (HPAI) H5N1 viruses is a global public health priority. Considering the difficulty in predicting HPAI H5N1 pandemic strains, one strategy used in their design includes the development of formulations with the capacity of eliciting broad cross-protective immunity against multiple viral antigens. To this end we constructed a replication-defective recombinant adenovirus-based avian influenza virus vaccine (rAdv-AI) expressing the codon-optimized M2eX-HA-hCD40L and the M1-M2 fusion genes from HPAI H5N1 human isolate. Although there were no significant differences in the systemic immune responses observed between the intramuscular prime-intramuscular boost regimen (IM/IM) and the intranasal prime-intramuscular boost regimen (IN/IM), IN/IM induced more potent CD8(+) T cell and antibody responses at mucosal sites than the IM/IM vaccination, resulting in more effective protection against lethal H5N2 avian influenza (AI) virus challenge. These findings suggest that the strategies used to induce multi-antigen-targeted mucosal immunity, such as IN/IM delivery of rAdv-AI, may be a promising approach for developing broad protective vaccines that may be more effective against the new HPAI pandemic strains.

Expression of Japanese encephalitis virus envelope protein in transgenic tobacco plants

The virus envelope (E) protein of Japanese encephalitis virus induces virus-neutralizing antibodies and is therefore a potential vaccine antigen. In a mammalian system, co-expression of another viral structural protein prM is necessary for proper expression and folding of E protein. Transgenic tobacco plants were produced carrying JEV cDNA encoding prM and E proteins under the control of the CaMV 35S promoter. E protein, however, was not detectable in these plants. In vitro translation studies showed that the presence of the prM sequence inhibited transgene expression in the plant system. Accordingly, JEV E protein could be expressed in transgenic tobacco plants only without the prM protein.

New insights on adenovirus as vaccine vectors

Adenovirus (Ad) vectors were initially developed for treatment of genetic diseases. Their usefulness for permanent gene replacement was limited by their high immunogenicity, which resulted in rapid elimination of transduced cells through induction of T and B cells to antigens of Ad and the transgene product. The very trait that excluded their use for sustained treatment of genetic diseases made them highly attractive as vaccine carriers. Recently though results showed that Ad vectors based on common human serotypes, such as serotype 5, may not be ideal as vaccine carriers. A recently conducted phase 2b trial, termed STEP trial, with an AdHu5-based vaccine expressing antigens of human immunodeficiency virus 1 (HIV-1) not only showed lack of efficacy in spite of the vaccine's immunogenicity, but also suggested an increased trend for HIV acquisition in individuals that had circulating AdHu5 neutralizing antibodies prior to vaccination. Alternative serotypes from humans or nonhuman primates (NHPs), to which most humans lack pre-existing immunity, have been vectored and may circumvent the problems encountered with the use of AdHu5 vectors in humans. In summary, although Ad vectors have seen their share of setbacks in recent years, they remain viable tools for prevention or treatment of a multitude of diseases.

Strategies to overcome host immunity to adenovirus vectors in vaccine development

The first clinical evaluations of adenovirus (Ad)-based vectors for gene therapy were initiated in the mid-1990s and led to great anticipation for future utility. However, excitement surrounding gene therapy, particularly Ad-based therapy, was diminished upon the death of Jesse Gelsinger, and recent discouraging results from the HIV vaccine STEP trial have brought efficacy and safety issues to the forefront again. Even so, Ad vectors are still considered among the safest and most effective vaccine vectors. Innate and pre-existing immunity to Ad mediate much of the acute toxicities and reduced therapeutic efficacies observed following vaccination with this vector. Thus, innovative strategies must continue to be developed to reduce Ad-specific antigenicity and immune recognition. This review provides an overview and critique of the most promising strategies, including results from preclinical trials in mice and nonhuman primates, which aim to revive the future of Ad-based vaccines.

A preliminary and comparative evaluation of a novel Ad5 [E1-, E2b-] recombinant-based vaccine used to induce cell mediated immune responses

Adenovirus vectors have been shown to be highly effective as vaccine platforms capable of inducing both humoral and cell mediated immune (CMI) responses. An Ad serotype 5 vector containing unique deletions in the E2b region (Ad5 [E1-, E2b-]) has been reported to have several advantages over conventional Adenovirus serotype 5 (Ad5) vectors deleted in only the E1 region (Ad5 [E1-]), including increased carrying capacity and diminished viral late gene expression. Here, we evaluated a novel Ad5 [E1-, E2b-] vector utilizing the E.C7 cell line for viral packaging. Its' effectiveness as a potential vaccine platform as compared to the currently utilized Ad5 [E1-]-based platform was assessed in both Ad5 naïve and Ad5 immune mice. We employed the HIV-1 Gag gene as the antigenic transgene expressed by the novel vector. Cellular expression of the Gag was confirmed by Western Blot analysis. Dose response studies using three intradermal immunizations of 10(7) to 10(10) virus particles (VP) of each construct revealed that immunization with 10(10)VP resulted in the maximum immunological response. Multiple immunizations of Ad naïve BALB/c mice with an Ad5 [E1-, E2b]-gag vaccine resulted in higher ELISpot CMI responses as compared to mice immunized with an Ad5 [E1-]-gag vaccine. More importantly, multiple immunizations of Ad5 immune BALB/c mice with an Ad5 [E1-, E2b]-gag vaccine resulted in significant increases in ELISpot CMI responses when compared to Ad5 immune mice vaccinated with an Ad5 [E1-]-gag vector. Preliminary studies in three Ad5 immune non-human primates (NHP) demonstrated that vaccination with Ad5 [E1-, E2b-]-gag-induced elevated levels of interferon-gamma and IL-2 secreting lymphocytes as assessed by ELISpot assays. These studies indicate that the novel Ad5 [E1-, E2b-] viral vector can be utilized as a potential vaccine platform to induce elevated CMI responses as compared to current generation Ad5 [E1-] viral vectors even in the presence of pre-existing Ad5 immunity.

Nasal delivery of an adenovirus-based vaccine bypasses pre-existing immunity to the vaccine carrier and improves the immune response in mice

Pre-existing immunity to human adenovirus serotype 5 (Ad5) is common in the general population. Bypassing pre-existing immunity could maximize Ad5 vaccine efficacy. Vaccination by the intramuscular (I.M.), nasal (I.N.) or oral (P.O.) route with Ad5 expressing Ebola Zaire glycoprotein (Ad5-ZGP) fully protected naïve mice against lethal challenge with Ebola. In the presence of pre-existing immunity, only mice vaccinated I.N. survived. The frequency of IFN-γ+ CD8+ T cells was reduced by 80% and by 15% in animals vaccinated by the I.M. and P.O. routes respectively. Neutralizing antibodies could not be detected in serum from either treatment group. Pre-existing immunity did not compromise the frequency of IFN-γ+ CD8+ T cells (3.9±1% naïve vs. 3.6±1% pre-existing immunity, PEI) nor anti-Ebola neutralizing antibody (NAB, 40±10 reciprocal dilution, both groups). The number of INF-γ+ CD8+ cells detected in bronchioalveolar lavage fluid (BAL) after I.N. immunization was not compromised by pre-existing immunity to Ad5 (146±14, naïve vs. 120±16 SFC/million MNCs, PEI). However, pre-existing immunity reduced NAB levels in BAL by ∼25% in this group. To improve the immune response after oral vaccination, the Ad5-based vaccine was PEGylated. Mice given the modified vaccine did not survive challenge and had reduced levels of IFN-γ+ CD8+ T cells 10 days after administration (0.3±0.3% PEG vs. 1.7±0.5% unmodified). PEGylation did increase NAB levels 2-fold. These results provide some insight about the degree of T and B cell mediated immunity necessary for protection against Ebola virus and suggest that modification of the virus capsid can influence the type of immune response elicited by an Ad5-based vaccine.

Construction and evaluation of a chimeric pseudoinfectious virus vaccine to prevent Japanese encephalitis

Multiple vaccines exist to control Japanese encephalitis (JE), but all suffer from problems. We have developed a new type of flavivirus vaccine, a pseudoinfectious virus (RepliVAX WN) that prevents West Nile virus (WNV)-induced disease. Here, we describe production of a chimeric RepliVAX (RepliVAX JE) that expresses the JE virus (JEV) prM and E proteins. Our prototype RepliVAX JE replicated poorly in cells, but blind passage produced a better-growing derivative, and analyses of this derivative allowed us to engineer a second-generation RepliVAX (RepliVAX JE.2) that grew to high titers. RepliVAX JE.2 elicited neutralizing antibodies in both mice and hamsters and provided 100% protection from a lethal challenge with JEV or WNV, respectively. These results demonstrate the utility our RepliVAX platform for producing a JE vaccine.

Multi-antigen vaccines based on complex adenovirus vectors induce protective immune responses against H5N1 avian influenza viruses

There are legitimate concerns that the highly pathogenic H5N1 avian influenza virus could adapt for human-to-human transmission and cause a pandemic similar to the 1918 "Spanish flu" that killed 50 million people worldwide. We have developed pandemic influenza vaccines by incorporating multiple antigens from both avian and Spanish influenza viruses into complex recombinant adenovirus vectors. In vaccinated mice, these vaccines induced strong humoral and cellular immune responses against pandemic influenza virus antigens, and protected vaccinated mice against lethal H5N1 virus challenge. These results indicate that this multi-antigen, broadly protective vaccine may serve as a safer and more effective approach than traditional methods for development of a pandemic influenza vaccine.

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.

Vaccine to confer to nonhuman primates complete protection against multistrain Ebola and Marburg virus infections

Filoviruses (Ebola and Marburg viruses) are among the deadliest viruses known to mankind, with mortality rates nearing 90%. These pathogens are highly infectious through contact with infected body fluids and can be easily aerosolized. Additionally, there are currently no licensed vaccines available to prevent filovirus outbreaks. Their high mortality rates and infectious capabilities when aerosolized and the lack of licensed vaccines available to prevent such infectious make Ebola and Marburg viruses serious bioterrorism threats, placing them both on the category A list of bioterrorism agents. Here we describe a panfilovirus vaccine based on a complex adenovirus (CAdVax) technology that expresses multiple antigens from five different filoviruses de novo. Vaccination of nonhuman primates demonstrated 100% protection against infection by two species of Ebola virus and three Marburg virus subtypes, each administered at 1,000 times the lethal dose. This study indicates the feasibility of vaccination against all current filovirus threats in the event of natural hemorrhagic fever outbreak or biological attack.

Tumor necrosis factor receptor-1-induced neuronal death by TRADD contributes to the pathogenesis of Japanese encephalitis

While a number of studies have documented the neurotropism of Japanese encephalitis virus (JEV), little is known regarding the molecular mechanism of neuronal death following viral infection. The tumor necrosis factor receptor (TNFR)-associated death domain (TRADD) has been suggested to be the crucial signal adaptor that mediates all intracellular responses from TNFR-1. Using mouse (Neuro2a) and human (SK-N-SH) neuroblastoma cell lines, we have shown that the altered expression of TNFR-1 and TRADD following JEV infection regulates the downstream apoptotic cascades. Activation of TRADD led to mitochondria-mediated neuronal apoptosis. As TRADD-knockout animals or deficient cell lines are unavailable, it has been difficult to definitively address the physiological role of TRADD in diseases pathology following JEV infection. We circumvented this problem by silencing TRADD expression with small-interfering RNA (siRNA) and have found that TRADD is required for TNFR-1-initiated neuronal apoptosis following in vitro infection with JEV. Interestingly, siRNA against TRADD also decreased the viral load in Neuro2a cells. Furthermore, siRNA against TRADD increased the survival of JEV-infected mice by altering the expression of pro apoptotic versus antiapoptotic molecules. These studies show that the engagement of TNFR-1 and TRADD following JEV infection plays a crucial role in neuronal apoptosis.

Seroprevalence of neutralizing antibodies to adenovirus type 5 among children in India: implications for recombinant adenovirus-based vaccines

We determined the levels of adenovirus 5 (Ad5) neutralizing antibodies in children in India less than 2 years of age. The results clearly show an age-dependent increase in Ad5-specific immunity, with 7- to 12-month-old children having the lowest levels of Ad5 immunity. This opens up the scope for the use of recombinant Ad5-based vaccines in this age group.

Neuroprotection conferred by astrocytes is insufficient to protect animals from succumbing to Japanese encephalitis

Astrocytes play a key role in regulating aspects of inflammation and in the homeostatic maintenance of the central nervous system (CNS). However, the role of astrocytes in viral encephalitis mediated inflammation is not well documented. As Japanese encephalitis virus (JEV) infection is localized to neurons and considering the importance of astrocytes in supporting neuronal survival and function, we have exploited an experimental model of Japanese encephalitis (JE) to better understand the role of astrocytes in JE. Suckling mice pups were inoculated with the virus and 2 and 4 days later we analyzed a panel of molecules characteristic of reactive astrogliosis. We show that JEV infection increases the expression of astrocyte-specific glial fibrillary acidic protein (GFAP), the glutamate aspartate transporter (GLAST), glutamate transporter-1 (GLT-1) and ceruloplasmin (CP). The transcript levels of growth factors produced predominantly by activated astrocytes such as nerve growth factor (NGF) and ciliary neurotrophin factor (CNTF) were elevated following JEV infection. The transcript level of brain-derived neurotrophic factor (BDNF) was also elevated following JEV infection. Both NGF and CNTF were capable of preventing ROS mediated neuronal death following in vitro JEV infection to a certain extent. Taken altogether, these data indicate that increased astrogliosis following JEV infection is accompanied by the enhanced ability of astrocytes to detoxify glutamate, inactivate free radical and produce neurotrophic factors that are involved in neuronal protection. However, this elevated physiological state of astrocyte is insufficient in conferring neuroprotection, as infected animals eventually succumb to infection. The response of astrocytes to JE can be amplified to modulate the adaptive response of brain to induce neuroprotection.

Proinflammatory mediators released by activated microglia induces neuronal death in Japanese encephalitis

While a number of studies have documented the importance of microglia in central nervous system (CNS) response to injury, infection and disease, little is known regarding its role in viral encephalitis. We therefore, exploited an experimental model of Japanese Encephalitis, to better understand the role played by microglia in Japanese Encephalitis Virus (JEV) infection. Lectin staining performed to assess microglial activation indicated a robust increase in reactive microglia following infection. A difference in the topographic distribution of activated, resting, and phagocytic microglia was also observed. The levels of various proinflammatory mediators, such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (Cox-2), IL-6, IL-1beta, TNF-alpha, and MCP-1 that have been implicated in microglial response to an activational state was significantly elevated following infection. These cytokines exhibited region selective expression in the brains of infected animals, with the highest expression observed in the hippocampus. Moreover, the expression of neuronal specific nuclear protein NeuN was markedly downregulated during progressive infection indicating neuronal loss. In vitro studies further confirmed that microglial activation and subsequent release of various proinflammatory mediators induces neuronal death following JEV infection. Although initiation of immune responses by microglial cells is an important protective mechanism in the CNS, unrestrained inflammatory responses may result in irreparable brain damage. Our findings suggest that the increased microglial activation following JEV infection influences the outcome of viral pathogenesis. It is likely that the increased microglial activation triggers bystander damage, as the animals eventually succumb to infection.

Status and challenges of filovirus vaccines

Vaccines that could protect humans against the highly lethal Marburg and Ebola viruses have eluded scientists for decades. Classical approaches have been generally unsuccessful for Marburg and Ebola viruses and pose enormous safety concerns as well. Modern approaches, in particular those using vector-based approaches have met with success in nonhuman primate models although success against Ebola has been more difficult to achieve than Marburg. Despite these successes, more work remains to be done. For the vector-based vaccines, safety in humans and potency in the face of pre-existing anti-vector immunity may be critical thresholds for licensure. The immunological mechanism(s) by which these vaccines protect has not yet been convincingly determined. Licensure of these vaccines for natural outbreaks may be possible through clinical trials although this will be very difficult; licensure may also be possible by pivotal efficacy studies in animal models with an appropriate challenge. Nevertheless, nonhuman primate studies have shown that protection against Marburg and Ebola is possible and there is hope that one day a vaccine will be licensed for human use.

Recombinant adenovirus expressing GP5 and M fusion proteins of porcine reproductive and respiratory syndrome virus induce both humoral and cell-mediated immune responses in mice

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important contagious agents of swine in the world. PRRSV infection poses a challenge to current vaccination strategies. In this study, three replication-defective adenovirus recombinants were developed as potential vaccine against PRRSV in a mouse model. Three groups of BALB/c mice (24 mice per group) were inoculated subcutaneously twice at 2-week intervals with the recombinants expressing PRRSV GP5 (rAd-GP5), M (rAd-M), and M-GP5 fusion protein (rAd-M-GP5). Two additional groups were injected with wild-type adenovirus (wtAd) or PBS as control. The results showed that the mice inoculated with recombinant adenoviruses developed PRRSV-specific antibodies, cellular immune response by 2 weeks post second inoculation. However, only mice immunized with recombinant adenovirus rAd-M-GP5 developed significantly higher titers of neutralizing antibodies to PRRSV and produced stronger lymphocyte proliferation responses compared to mice immunized with rAd-M or rAd-GP5 alone. It was also found that mice immunized with rAd-M-GP5 were primed for significant higher levels of anti-PRRSV CTL responses than mice immunized with rAd-M. Mice receiving rAd-GP5 also mounted PRRSV-specific response, but levels were lower. It suggested that the recombinant adenovirus expressing M-GP5 fusion protein might be an attractive candidate vaccine to be tested for preventing PRRSV infection.