Induction of protective immunity in animals vaccinated with recombinant vaccinia viruses that express PreM and E glycoproteins of Japanese encephalitis virus

Advances in vaccinia virus-based vaccine vectors, with applications in flavivirus vaccine development

Historically, virulent variola virus infection caused hundreds of millions of deaths. The smallpox pandemic in human beings has spread for centuries until the advent of the attenuated vaccinia virus (VV) vaccine, which played a crucial role in eradicating the deadly contagious disease. Decades of exploration and utilization have validated the attenuated VV as a promising vaccine vehicle against various lethal viruses. In this review, we focus on the advances in VV-based vaccine vector studies, including construction approaches of recombinant VV, the impact of VV-specific pre-existing immunity on subsequent VV-based vaccines, and antigen-specific immune responses. More specifically, the recombinant VV-based flaviviruses are intensively discussed. Based on the publication data, this review aims to provide valuable insights and guidance for future VV-based vaccine development.

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.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Generation and characterization of a new mammalian cell line continuously expressing virus-like particles of Japanese encephalitis virus for a subunit vaccine candidate

Background

Japanese encephalitis virus (JEV) is the most important cause of epidemic encephalitis in most Asian regions. There is no specific treatment available for Japanese encephalitis, and vaccination is the only effective way to prevent JEV infection in humans and domestic animals. The purpose of this study is to establish a new mammalian cell line stably and efficiently expressing virus-like particle of JEV for potential use of JEV subunit vaccine.

Results

We generated a new cell clone (BJ-ME cells) that stably produces a secreted form of Japanese encephalitis virus (JEV) virus-like particle (VLP). The BJ-ME cells were engineered by transfecting BHK-21 cells with a code-optimized cDNA encoding JEV prM and E protein expression plasmid. Cell line BJ-ME can stably produces a secreted form of Japanese encephalitis virus virus-like particle (JEV-VLP) which contains the JEV envelope glycoprotein (E) and membrane protein (M). The amount of JEV-VLP antigen released into the culture fluid of BJ-ME cells was as high as 15–20 μg/ml. JEV-VLP production was stable after multiple cell passages and 100% cell expression was maintained without detectable cell fusion or apoptosis. Cell culture fluid containing the JEV-VLP antigen could be harvested five to seven times continuously at intervals of 4–6 days while maintaining the culture. Mice immunized with the JEV-VLP antigen with or without adjuvant developed high titers of neutralizing antibodies and 100% protection against lethal JEV challenge.

Conclusion

These results suggest that the recombinant JEV-VLP antigen produced by the BJ-ME cell line is an effective, safe and affordable subunit Japanese encephalitis vaccine candidate, especially for domestic animals such as pig and horse.

Japanese encephalitis: the virus and vaccines

Japanese encephalitis (JE) is an infectious disease of the central nervous system caused by Japanese encephalitis virus (JEV), a zoonotic mosquito-borne flavivirus. JEV is prevalent in much of Asia and the Western Pacific, with over 4 billion people living at risk of infection. In the absence of antiviral intervention, vaccination is the only strategy to develop long-term sustainable protection against JEV infection. Over the past half-century, a mouse brain-derived inactivated vaccine has been used internationally for active immunization. To date, however, JEV is still a clinically important, emerging, and re-emerging human pathogen of global significance. In recent years, production of the mouse brain-derived vaccine has been discontinued, but 3 new cell culture-derived vaccines are available in various parts of the world. Here we review current aspects of JEV biology, summarize the 4 types of JEV vaccine, and discuss the potential of an infectious JEV cDNA technology for future vaccine development.

Japanese Encephalitis Virus Generated Neurovirulence, Antigenicity, and Host Immune Responses

In response to a JE virus attack, infected body cells start secretion of different cytokines and activate innate immune response. Virus starts neuronal invasion by entering into nerve cells and inflecting the central nervous system. It avoids exposure of body’s natural immunity and generates neurotrophic effects. Virus causes acute susceptibility to CNS and establishes encephalitis syndrome that results in very high fatality in children. In survivors, JEV inhibits the growth and proliferation of NCPs and imposes permanent neuronal disorders like cognitive, motor, and behavioral impairments. However, body cells start TCR mediated interactions, to recognize viral antigens with class I MHC complex on specific target cells, and operate mass killing of virus infected cells by increased CTL activity. Thus, both cell mediated and antibody interactions plays a central role in protection against JEV. In the present review article virus generated neurovirulence, antigenicity, and host immune responses are described in detail. More emphasis is given on diagnosis, clinical care, and active immunization with well-designed potential antiflavivirus vaccines. Further, for achieving an elite success against JEV, global eradication strategies are to be needed for making vaccination program more responsible and effective in endemic areas.

Immunogenicity and growth inhibitory efficacy of the prime-boost immunization regime with DNA followed by recombinant vaccinia virus carrying the P29 gene of Babesia gibsoni in dogs

In recent studies, heterologous prime-boost approaches, employing plasmid DNA and viral vector pathogen-delivering sequences, have been considered an effective protection strategy for intracellular parasite infections. Here, we evaluated the efficacy of such a strategy against the canine Babesia gibsoni infection. The DNA (pCAGGS-P29) and recombinant vaccinia virus (vvP29) both encoding the P29 of B. gibsoni were used in this study. The dogs were immunized 3 times with priming DNA and boosted once with recombinant virus. The dogs immunized with P29 developed a significant level of IgG2 antibody against P29. The response was strongly boosted by the inoculation of vvP29. The peripheral IFN-gamma responses of the dogs immunized with P29 were significantly higher than those of controls after the parasite inoculation. Moreover, the P29 immunized group showed a significantly low level of parasitemia. In conclusion, this study supports the efficacy of a prime-boost strategy for dogs against canine B. gibsoni infection.

The prM-independent packaging of pseudotyped Japanese encephalitis virus

As noted in other flaviviruses, the envelope (E) protein of Japanese encephalitis virus (JEV) interacts with a cellular receptor and mediates membrane fusion to allow viral entry into target cells, thus eliciting neutralizing antibody response. The formation of the flavivirus prM/E complex is followed by the cleavage of precursor membrane (prM) and membrane (M) protein by a cellular signalase. To test the effect of prM in JEV biology, we constucted JEV-MuLV pseudotyped viruses that express the prM/E protein or E only. The infectivity and titers of JEV pseudotyped viruses were examined in several cell lines. We also analyzed the neutralizing capacities with anti-JEV sera from JEV-immunized mice. Even though prM is crucial for multiple stages of JEV biology, the JEV-pseudotyped viruses produced with prM/E or with E only showed similar infectivity and titers in several cell lines and similar neutralizing sensitivity. These results showed that JEV-MuLV pseudotyped viruses did not require prM for production of infectious pseudotyped viruses.

Expression and characterization of bovine lactoperoxidase by recombinant vaccinia virus

Lactoperoxidase (LPO) is a 78 kDa heme-containing oxidation-reduction enzyme present in milk, found in physiological fluids of mammals. LPO has an antimicrobial activity, and presumably contribute to the protective functions of milk against infectious diseases. In this study, recombinant vaccinia virus expressing bovine LPO (vv/bLPO) was constructed. In rabbit kidney (RK13) cells infected with vv/bLPO, recombinant bLPO was detected in both cell extracts and culture supernatants. Tunicamycin treatment decreased the molecular weight of recombinant bLPO, indicating that recombinant bLPO contains a N-linked glycosylation site. The replication of recombinant vaccinia viruses expressing bovine lactoferrin (vv/bLF) at a multiplicity of infection (moi) of 5 plaque-forming units (PFU)/cell was inhibited by antiviral activity of recombinant bLF, suggesting that vv/bLF has an antiviral effect against vaccinia virus. On the other hand, the replication of vv/bLPO at a moi of 5 PFU/cell was not inhibited by antiviral activity of recombinant bLPO, indicating that this recombinant virus could be used as a suitable viral vector. These results indicate that a combination of bLPO and vaccinia virus vector may be useful for medical and veterinary applications in vivo.

Immunization with pseudotype baculovirus expressing envelope protein of Japanese encephalitis virus elicits protective immunity in mice

BACKGROUND

Japanese encephalitis (JE) is a serious infection and disease in southern and eastern Asia. The design and development of safer and more efficacious vaccines against Japanese encephalitis virus (JEV) is a high-priority target in the world. Recently, baculovirus pseudotyped with vesicular stomatitis virus glycoprotein (VSVG) was described as an attractive gene delivery vehicle in mammalian cells and a potential vector for vaccine development. In the present study, we constructed a recombinant pseudotype baculovirus encoding the JEV envelope (E) protein and demonstrated that it could elicit high protective immunity in mice.

METHODS

Recombinant pseudotype baculovirus (BV-G-E) was generated by inserting JEV E gene fragment into pFastBac-VSV/G vector. BALB/c mice were immunized with BV-G-E and challenged with JEV wild-type strain. The neutralization antibody, interferon (IFN)-gamma expression and release, and survival rate were analysed and compared with the group of immunized with inactivated vaccine and DNA vaccine (pc-E) encoding the same gene of JEV.

RESULTS

We demonstrated that intramuscular injections of BV-G-E at various doses into mice produced higher levels of JEV-specific neutralizing antibodies, IFN-gamma and better protective efficacy against a lethal challenge with JEV than that of pc-E. Furthermore, BV-G-E could elicit a higher level of cellular immunity response and provide equal protective efficacy against JEV challenge compared to inactivated vaccine.

CONCLUSIONS

Our data demonstrate that BV-G-E elicited higher levels of protective immunity compared to DNA vaccine and that pseudotype baculovirus-mediated gene delivery can be utilized as an alternative strategy to develop new generations of vaccines against JEV infection.

Third-generation flavivirus vaccines based on single-cycle, encapsidation-defective viruses

Flaviviruses are arthropod-borne pathogens that cause significant disease on all continents of the world except Antarctica. Flavivirus diseases are particularly important in tropical regions where arthropod vectors are abundant. Live-attenuated virus vaccines (LAVs) and inactivated virus vaccines (INVs) exist for some of these diseases. LAVs are economical to produce and potent, but are not suitable for use in the immunocompromised. INVs are safer, but are more expensive to produce and less potent. Despite the success of both classes of these first-generation flavivirus vaccines, problems associated with their use indicate a need for improved products. Furthermore, there are no suitable vaccines available for important emerging flavivirus diseases, notably dengue and West Nile encephalitis (WNE). To address these needs, new products, including LAVs, INVs, viral-vectored, genetically engineered LAVs, naked DNA, and subunit vaccines are in various stages of development. Here we describe the current state of these first- and second-generation vaccine candidates, and compare these products to our recently described single-cycle, encapsidation defective flavivirus vaccine: RepliVAX. RepliVAX can be propagated in C-expressing cells (or as a unique two-component virus) using methods similar to those used to produce today's economical and potent LAVs. However, due to deletion of most of the gene for the C protein, RepliVAX cannot spread between normal cells, and is unable to cause disease in vaccinated animals. Nevertheless, RepliVAX is potent and efficacious in animal models for WNE and Japanese encephalitis, demonstrating its utility as a third-generation flavivirus vaccine that should be potent, economical to produce, and safe in the immunocompromised.

Enhancement of humoral and cellular immunity in mice against Japanese encephalitis virus using a DNA prime-protein boost vaccine strategy

A synthetic multi-epitope gene containing critical epitopes of the Japanese encephalitis virus (JEV) envelope gene was cloned into both prokaryotic and eukaryotic expression vectors. The recombinant plasmid and purified recombinant protein (heterologously expressed in Escherichia coli) were used as immunogens in a mouse model. The results indicate that both the recombinant protein and the DNA vaccine induce humoral and cellular immune responses. Neutralising antibody titres in mice in the pcDNA-TEP plus rEP group increased considerably relative to mice immunised using either pcDNA-TEP or rEP alone (P<0.05). Furthermore, the highest levels of interleukin (IL)-2, interferon-gamma and IL-4 were induced following priming with the DNA vaccine and boosting with the recombinant protein. Together these findings demonstrate that a DNA-recombinant protein prime-boost vaccination strategy can produce high levels of antibody and trigger significant T cell responses in mice, highlighting the potential value of such an approach in the prevention of JEV infection.

Chimeric coronavirus-like particles carrying severe acute respiratory syndrome coronavirus (SCoV) S protein protect mice against challenge with SCoV

We tested the efficacy of coronavirus-like particles (VLPs) for protecting mice against severe acute respiratory syndrome coronavirus (SCoV) infection. Coexpression of SCoV S protein and E, M and N proteins of mouse hepatitis virus in 293T or CHO cells resulted in the efficient production of chimeric VLPs carrying SCoV S protein. Balb/c mice inoculated with a mixture of chimeric VLPs and alum twice at an interval of four weeks were protected from SCoV challenge, as indicated by the absence of infectious virus in the lungs. The same groups of mice had high levels of SCoV-specific neutralizing antibodies, while mice in the negative control groups, which were not immunized with chimeric VLPs, failed to manifest neutralizing antibodies, suggesting that SCoV-specific neutralizing antibodies are important for the suppression of viral replication within the lungs. Despite some differences in the cellular composition of inflammatory infiltrates, we did not observe any overt lung pathology in the chimeric-VLP-treated mice, when compared to the negative control mice. Our results show that chimeric VLP can be an effective vaccine strategy against SCoV infection.

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

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

Japanese encephalitis for a reference to international travelers

Japanese encephalitis (JE) is an inflammatory disease in the central nervous system caused by infection with Japanese encephalitis virus (JEV). JE is a disease with a high fatality rate and endemic and epidemic in East, Southeast, and South Asia. High morbidity is noted in children living in the endemic area. JEV is maintained mainly between vector mosquitoes and pigs in nature. The risk of JE increases as the number of vector mosquitoes increases. The expansion of JEV-endemic area depends on irrigated rice field and pig farming. These environments that are suitable for infectious cycle of JEV exist widely in Asia today. The effective and safe vaccine is available in endemic countries and for international travelers. JE vaccination is strongly recommended to those who visit the JEV-endemic regions, especially in the rainy season.

LC16m8: an attenuated smallpox vaccine

The frequency of moderate to severe adverse reactions associated with smallpox vaccines currently stockpiled in the US, and the continued threat of bioterrorism have prompted the development of effective vaccines with improved safety profiles. LC16m8, an attenuated, replicating smallpox vaccine derived from the Lister strain of vaccinia, is currently licensed in Japan where it was safely used in over 50,000 children in the 1970s. It has been shown to have markedly less neurotoxicity than unattenuated vaccines in nonclinical studies. LC16m8 is immunogenic after a single dose, and recent studies in two different animal models have demonstrated protective efficacy equivalent to that of the only FDA-licensed smallpox vaccine. This article reviews the history and available scientific literature regarding LC16m8 and provides comparisons to other smallpox vaccines.

Prime-boost immunization with DNA followed by a recombinant vaccinia virus expressing P50 induced protective immunity against Babesia gibsoni infection in dogs

A heterologous prime-boost immunization regime with priming DNA followed by recombinant vaccinia virus expressing relevant antigens has been shown to induce effective immune responses against several infectious pathogens. In this study, we constructed a recombinant plasmid and vaccinia virus, both of which expressed P50 of Babesia gibsoni, to investigate the immunogenicity and protective efficacy of a heterologous prime-boost immunization against canine babesiosis. The dogs immunized with the prime-boost regime developed a significantly high level of specific antibody against P50 when compared with the control groups, and the antibody level was strongly increased after a booster immunization with a recombinant vaccinia virus. The prime-boost immunization regime induced a specific IgG2 antibody response and IFN-gamma production in dogs. Two weeks after the booster immunization with a recombinant vaccinia virus expressing P50, the dogs were challenged with B. gibsoni patasites. The dogs immunized with the prime-boost regime showed partial protection, manifested as a significantly low level of parasitemia and a 2-day delay of the peak parasitemia. These results indicated that such a heterologous prime-boost immunization approach might be useful against B. gibsoni infection in dogs.

An attenuated LC16m8 smallpox vaccine: analysis of full-genome sequence and induction of immune protection

The potential threat of smallpox bioterrorism has made urgent the development of lower-virulence vaccinia virus vaccines. An attenuated LC16m8 (m8) vaccine was developed in 1975 from the Lister strain used in the World Health Organization smallpox eradication program but was not used against endemic smallpox. Today, no vaccines can be tested with variola virus for efficacy in humans, and the mechanisms of immune protection against the major intracellular mature virion (IMV) and minor extracellular enveloped virion (EEV) populations of poxviruses are poorly understood. Here, we determined the full-genome sequences of the m8, parental LC16mO (mO), and grandparental Lister (LO) strains and analyzed their evolutionary relationships. Sequence data and PCR analysis indicated that m8 was a progeny of LO and that m8 preserved almost all of the open reading frames of vaccinia virus except for the disrupted EEV envelope gene B5R. In accordance with this genomic background, m8 induced 100% protection against a highly pathogenic vaccinia WR virus in mice by a single vaccination, despite the lack of anti-B5R and anti-EEV antibodies. The immunogenicity and priming efficacy with the m8 vaccine consisting mainly of IMV were as high as those with the intact-EEV parental mO and grandparental LO vaccines. Thus, mice vaccinated with 10(7) PFU of m8 produced low levels of anti-B5R antibodies after WR challenge, probably because of quick clearance of B5R-expressing WR EEV by strong immunity induced by the vaccination. These results suggest that priming with m8 IMV provides efficient protection despite undetectable levels of immunity against EEV.

Selection of immunodominant fragments from envelope gene for vaccine against Japanese encephalitis virus in DNA priming–protein boosting protocols

Fragmentation of E gene of JEV into smaller fragments, none of the fragments either in plasmids form or in recombinant protein form can induce optimal protection against the virus infection. It is only when DNA priming-protein boosting strategies are used then the N-terminal E(A) and the C-terminal E(B) showed full protection against JEV as those induced by commercial vaccine, provided both fragments are preceded in the N-terminal by a signal peptide M(15) derived from C-terminal of prM gene in JEV genome. When the subfragments of E(A): E(A1) and E(A2) and E(B): E(B1) and E(B2) are tested, only E(A1) subfragment can replace E(A) in protein boosting to induce optimal protection against JEV, E(A2), E(B1), E(B2) in plasmid or protein forms are not. Therefore, along the E gene (978-2330 bp) N-terminal, E(A1) (978-1580 bp) and C-terminal E(B) (1851-2330 bp) are the most effective in inducing immunity against JEV but not the middle fragment E(A2) (1518-1877 bp) (see for orientation of E(A1), E(A2) and E(B) in E gene). Under the notion that molecular complexity determines the outcome of immune response of the host, E(B) being shorter, simpler in molecular structure and can be easily expressed in soluble form in E. coli (as opposed to insoluble E(A1)), E(B) probably will be the choice as a candidate vaccine to protect the host against JEV infection.

Japanese encephalitis subunit vaccine composed of virus-like envelope antigen particles purified from serum-free medium of a high-producer J12#26 cell clone

A stable cell clone, J12#26, which continuously secretes large amounts of the envelope (E) antigen of Japanese encephalitis (JE) virus (J. Virol. 77 (2003) 8745) was adapted to serum-free medium. The J12#26 antigen possessed hemagglutinating activity, as well as the viral E and M proteins. More than 10 and 1mg of the antigen quantified with the licensed JE vaccine (JE-VAX) as a standard by E-ELISA and protein determination, respectively, were recovered from 500 ml of serum-free medium by membrane ultrafiltration, Sephacryl S-300 chromatography, sucrose gradient centrifugation and Sephadex G-25 chromatography. SDS-PAGE and Western blot analyses confirmed the high yield and purity of the J12#26 E antigen, which was comprised of small spherical virus-like particles (VLP) of approximately 25 nm in diameter. This antigen induced in mice without adjuvant neutralizing antibody (NT Ab) titers, as high as or higher than the licensed JE vaccine, and complete protection against challenge with wild-type virus. These results suggest that the J12#26 antigen is a promising second-generation JE subunit vaccine.

Construction of recombinant pseudorabies virus expressing NS1 protein of Japanese encephalitis (SA14-14-2) virus and its safety and immunogenicity

The bivalent genetic engineering vaccine of Japanese encephalitis (JE) and Aujeszkj disease (AD) was developed to provide a novel approach to prevent and control these two diseases. NS1 gene of Japanese encephalitis virus (JEV) SA14-14-2 strain was produced by reverse transcriptase-mediated PCR (RT-PCR) and was cloned into vector pUSK to form recombinant plasmid (designed as pUSK-NS1). A co-transfection experiment was performed in porcine kidney (PK-15) cells with pUSK-NS1 and the genome of the vector virus (PRV TK(-)/gG(-)/LacZ(+) mutant). By plaque purification, PCR detection and southern hybridization, recombinant pseudorabies virus (PRV) expressing NS1 protein of JEV was acquired and named TK(-)/gG(-)/NS1(+). Western blot analysis and ELISA demonstrated the NS1 protein expression. To evaluate the recombinant virus's potential application, we characterized the safety and immune responses in Balb/c mice and swine. The safety test indicated that, when receiving the recombinant virus at a concentration of 10(6.0)pfu, no virulence of the recombinant virus to the mice, piglets and pregnant sows was observed. The vaccinated animals could acquire protective immunity against lethal challenge of the virulent PRV Ea strain and develop a good humoral and cellular immune response against JEV. The above results revealed that the recombinant virus could be a suitable candidate vaccine strain for developing a novel genetic vaccine to combat pseudorabies and Japanese encephalitis in the pig industry.

Sub-fragments of the envelope gene are highly protective against the Japanese encephalitis virus lethal infection in DNA priming—protein boosting immunization strategies

The envelope (E) gene of Japanese encephalitis virus (JEV) plays a major protective role against JEV infection. In order to locate the part of E gene that is responsible for this protection, an N-terminal fragment EA (nucleotide number 933-1877 bp of JEV genome) and a C-terminal fragment EB (nucleotide number 1851-2330 bp of JEV genome) from E gene were prepared. Both of these fragments were used in the form of recombinant proteins (rEA and rEB) and plasmid DNA (pEA, pM15EA and pEB) for immunizations. Recombinant EA protein (rEA) was previously found to be non-protective because it was expressed in an insoluble form. Plasmid EA (pEA) was also found to be non-protective unless it is preceded by a 15 mer signal peptide derived from the very C-terminal of the membrane gene (M) of JEV to form pM15EA plasmid indicating the importance of the signal peptide in the expression of EA immunogenicity. Although pM15EA and pEB are both immunogenic and protective against JEV lethal infection, the protection by both fragments however is not optimal. Even when pM15EA and pEB were used together for immunization, maximum protection as those induced by control vaccine was not achieved. However, if individual fragments (EA or EB) were used in a DNA priming-protein boosting or protein priming-DNA boosting strategy, high levels of protection were achieved by both fragments. This was especially true for EA fragment where the level of protection against JEV lethal infection was equal to that induced by commercially available vaccine alone. The protection correlated very well with the neutralizing antibody titers and the T helper cell involved in this process in mainly the Th1 type.

Development of a recombinant vaccine against Japanese encephalitis

Japanese encephalitis (JE) is the major form of viral encephalitis in much of the South-East Asia, India, and China. The disease is caused by a mosquito-borne virus known as Japanese encephalitis virus (JEV). The virus spreads in the form of epidemics, although several endemic areas for JEV activity are known. In recent years, JEV has spread to newer geographic locations such as Australia and Pakistan, and thus has become an important emerging virus infection in these areas. A mouse brain-derived, formalin-inactivated vaccine is available for immunization against JE. Because the formalin-inactivated JEV vaccine has limitations in terms of safety, availability, and cost, attempts are being made to develop improved vaccine using the recombinant DNA technology. This article reviews various attempts in this direction and summarizes the latest developments such as the recombinant yellow fever virus- or the plasmid DNA-based JEV vaccine.

Stable high-producer cell clone expressing virus-like particles of the Japanese encephalitis virus e protein for a second-generation subunit vaccine

We produced and characterized a cell clone (J12#26 cells) that stably expresses Japanese encephalitis virus (JEV) cDNA, J12, which encodes the viral signal peptide, premembrane (prM), and envelope (E) proteins (amino acid positions 105 to 794). Rabbit kidney-derived RK13 cells were transfected with a J12 expression plasmid, selected by resistance to marker antibiotics, and cloned by two cycles of a limiting-dilution method in the presence of antibiotics, a procedure that prevents the successful generation of E-producing cell clones. J12#26 cells secreted virus-like particles containing the authentic E antigen (E-VLP) into the culture medium in a huge enzyme-linked immunosorbent assay-equivalent amount (2.5 micro g per 10(4) cells) to the internationally licensed JE vaccine JE-VAX. E-VLP production was stable after multiple cell passages and persisted over 1 year with 100% expressing cells without detectable cell fusion, apoptosis, or cell death, but was suspended when the cells grew to 100% confluency and contact inhibition occurred. Mice immunized with the purified J12#26 E-antigen without adjuvant developed high titers of neutralizing antibodies for at least 7 months and 100% protection against intraperitoneal challenge with 5 x 10(6) PFU of JEV when examined according to the JE vaccine standardization protocol. These results suggest that the recombinant E-VLP antigen produced by the J12#26 cell clone is an effective, safe, and low-cost second-generation subunit JE vaccine.

Inoculation of plasmids encoding Japanese encephalitis virus PrM-E proteins with colloidal gold elicits a protective immune response in BALB/c mice

We established a simple and effective method for DNA immunization against Japanese encephalitis virus (JEV) infection with plasmids encoding the viral PrM and E proteins and colloidal gold. Inoculation of plasmids mixed with colloidal gold induced the production of specific anti-JEV antibodies and a protective response against JEV challenge in BALB/c mice. When we compared the efficacy of different inoculation routes, the intravenous and intradermal inoculation routes were found to elicit stronger and more sustained neutralizing immune responses than intramuscular or intraperitoneal injection. After being inoculated twice, mice were found to resist challenge with 100,000 times the 50% lethal dose (LD(50)) of JEV (Beijing-1 strain) even when immunized with a relatively small dose of 0.5 micro g of plasmid DNA. Protective passive immunity was also observed in SCID mice following transfer of splenocytes or serum from plasmid DNA- and colloidal gold-immunized BALB/c mice. The SCID mice resisted challenge with 100 times the LD(50) of JEV. Analysis of histological sections detected expression of proteins encoded by plasmid DNA in the tissues of intravenously, intradermally, and intramuscularly inoculated mice 3 days after inoculation. DNA immunization with colloidal gold elicited encoded protein expression in splenocytes and might enhance immune responses in intravenously inoculated mice. This approach could be exploited to develop a novel DNA vaccine.

Canine herpesvirus ORF2 is a membrane protein modified by N-linked glycosylation

Canine herpesvirus (CHV) ORF2, located downstream of the glycoprotein C (gC) gene, has homologues with some of the alphaherpesviruses. To characterize CHV OFR2, a recombinant CHV carrying a LacZ gene in the ORF2 locus, and recombinant vaccinia virus expressing ORF2 protein were constructed. Northern blot analysis revealed ORF2 and a gamma2 class late gene, and its protein product was detectable in CHV-infected cells reacted with ORF2 protein antiserum. Tunicamycin and N-glycosidase F treatment revealed that the ORF2 protein was modified by N-linked glycosylation. Fractionation and immune fluorescence analyses of the CHV-infected cells showed the ORF2 as a membrane protein transportable to the surface of infected cells. In vitro, the ORF2 protein did not affect viral replication and cell-to-cell viral spreading. Present findings represent the first evidence pointing to the CHV ORF2 as a membrane protein modified by an N-linked glycosylation.

Expression of canine interferon-gamma by a recombinant vaccinia virus and its antiviral effect

A recombinant vaccinia virus-expressing canine interferon (IFN)-gamma (vv/cIFN-gamma) was constructed. In rabbit kidney (RK13) and canine A72 cells infected with vv/cIFN-gamma, IFN activity was detected in the culture supernatants of both cell types. Canine IFN-gamma was also detected in both cell extracts by Western blot. The activity of the recombinant canine IFN-gamma in RK13 cells was higher than that in A72 cells. The vv/cIFN-gamma could not grow in A72 cells at a low multiplicity of infection, probably due to the antiviral activity of the canine IFN-gamma produced. Although exogenous IFN-gamma did not inhibit the growth of vaccinia virus, addition of anti-canine IFN-gamma serum recovered the growth of the vv/cIFN-gamma on A72 cells in a dose-dependent manner. These results suggest that the growth of vv/cIFN-gamma was inhibited by IFN-gamma produced in a paracrine and autocrine manner. In addition, the recombinant canine IFN-gamma inhibited the multiplication of canine herpesvirus, pseudorabies virus and canine adenovirus type 1 in Madin-Darby canine kidney cells. The antiviral effect of canine IFN-gamma was more effective than that of canine IFN-beta. From the present studies, we concluded the recombinant virus may be a useful suicide viral vector.

Prevention of vertical transmission of Neospora caninum in BALB/c mice by recombinant vaccinia virus carrying NcSRS2 gene

Neospora caninum infection is the major cause of bovine abortion. To develop a vaccine against N. caninum infection, recombinant vaccinia viruses carrying NcSRS2 and NcSAG1 genes (vv/Nc-p43 and vv/Nc-p36, respectively) were constructed and were tested in a mouse model. Vaccination of dams with vv/Nc-p43 appeared to confer effective protection against vertical transmission to offspring, though that with vv/Nc-p36 only provided partial protection. Moreover, the vv/Nc-p43 vaccination provoked cellular immune responses and antibody production against N. caninum. In conclusion, it is expected that vv/Nc-p43 can be used as an effective live vaccine to prevent vertical transmission of N. caninum in natural hosts.

Protective efficacy of vaccination by recombinant vaccinia virus against Neospora caninum infection

The recombinant vaccinia viruses expressing the surface protein of Neospora caninum tachyzoite, NcSAG1 or NcSRS2, were constructed. The vaccination with these recombinant viruses could protect effectively the parasite invasion in a mouse model system. The vaccine efficacy of NcSRS2 was higher than that of NcSAG1. The present study indicated that a high level of IgG1 Ab production to parasite is important for clearance of parasite at the early stage of infection and that T cell response has a crucial role for protection against the intracellular infection at the late stage of infection. The recombinant vaccinia viruses might be applicable as vaccine against N. caninum infection in a natural host.

Purified dengue 2 virus envelope glycoprotein aggregates produced by baculovirus are immunogenic in mice

The full-length dengue 2 virus envelope glycoprotein (Egp) was expressed in insect cells by recombinant (r) baculovirus and found to form multimeric aggregates that were recovered in the void volume of gel filtration columns and by ultracentrifugation. An immunoblot confirmed that rEgp aggregrates disrupted with SDS sample buffer released a monomeric form that migrated with a molecular weight similar to native dengue 2 virus Egp on polyacrylamide gels. The rEgp aggregates reacted strongly with a panel of monoclonal antibodies specific for the native Egp and which identify critical structural and functional epitopes. The rEgp aggregates were purified by ultracentrifugation through 30% sucrose, and were shown to be the major protein band on a polyacrylamide gel and corresponding immunoblot. Purified rEgp aggregates in combination with aluminum hydroxide induced high titer neutralizing antibodies in adult mice. The generation of full-length dengue 2 rEgp aggregates in insect cells facilitated development of a simple, effective procedure for purification of the recombinant protein, and represents a good approach for producing highly immunogenic dengue 2 rEgp as a component of a subunit vaccine.

A single intramuscular injection of recombinant plasmid DNA induces protective immunity and prevents Japanese encephalitis in mice

Plasmid vectors containing Japanese encephalitis virus (JEV) premembrane (prM) and envelope (E) genes were constructed that expressed prM and E proteins under the control of a cytomegalovirus immediate-early gene promoter. COS-1 cells transformed with this plasmid vector (JE-4B clone) secreted JEV-specific extracellular particles (EPs) into the culture media. Groups of outbred ICR mice were given one or two doses of recombinant plasmid DNA or two doses of the commercial vaccine JEVAX. All mice that received one or two doses of DNA vaccine maintained JEV-specific antibodies 18 months after initial immunization. JEVAX induced 100% seroconversion in 3-week-old mice; however, none of the 3-day-old mice had enzyme-linked immunosorbent assay titers higher than 1:400. Female mice immunized with this DNA vaccine developed plaque reduction neutralization antibody titers of between 1:20 and 1:160 and provided 45 to 100% passive protection to their progeny following intraperitoneal challenge with 5,000 PFU of virulent JEV strain SA14. Seven-week-old adult mice that had received a single dose of JEV DNA vaccine when 3 days of age were completely protected from a 50, 000-PFU JEV intraperitoneal challenge. These results demonstrate that a recombinant plasmid DNA which produced JEV EPs in vitro is an effective vaccine.

Expression of canine interferon-beta by a recombinant vaccinia virus

A recombinant vaccinia virus expressing canine interferon (IFN)-beta was constructed (vv/cIFN-beta). In rabbit kidney (RK13) and canine A72 cells infected with vv/cIFN-beta, the recombinant canine IFN-beta was detected in both cell extracts and supernatants, and the IFN activities of the culture supernatants were also detected. Inhibition of N-linked glycosylation by tunicamycin treatment indicated that the recombinant canine IFN-beta was modified by N-linked glycosylation in a different way between RK13 and A72 cells, and that N-linked glycosylation is essential for its secretion. The growth of vv/cIFN-beta at a low multiplicity of infection was inhibited by antiviral activity of canine IFN-beta, indicating that this recombinant virus could be used as a suicide viral vector.

Monoclonal antibody inhibition of Neospora caninum tachyzoite invasion into host cells

Monoclonal antibodies were produced against Neospora caninum tachyzoites to identify antigens which may play a role during invasion of host cells. Confocal laser microscopy showed that most antigens recognised by the mAb were located on the surface, but one mAb, 1A5, reacted to the apical end of the parasite. Some mAbs, which recognised 70, 42 and 36kDa parasite proteins, significantly inhibited the invasion of the parasite in vitro. The mAbs which recognised 42 and 36kDa parasite protein, reacted with Nc-p43 and Nc-p36 expressed by vaccinia virus and Escherichia coli, respectively. These results suggest that a 70kDa protein, Nc-p43 and Nc-p36 are involved in the invasion of the parasite into host cells.

Expression of recombinant Toxoplasma gondii P24

The gene encoding Toxoplasma gondii P24 has been reported previously. To determine the function of P24 against immune systems in the near future, we prepared recombinant P24 antigens using Escherichia coli, insect cells infected with recombinant baculovirus and mammalian cells infected with recombinant vaccinia virus. The P24 antigens derived from E. coli, insect cells and mammalian cells were detected with mouse immune sera against P24 or T. gondii homogenates by Western blot analysis; these corresponded to the authentic P24 and secreted into the supernatants of the insect and mammalian cell cultures. These proteins were not effected by tunicamycin treatment in cultured cells, indicating that recombinant P24 did not contain N-linked sugars. Recombinant P24 was separated by two-dimensional electrophoresis and analyzed by Western blotting. From these results, P24 was acidic protein and had identical isoelectric point with the authentic P24.

Cloning and expression of a 48-kilodalton Babesia caballi merozoite rhoptry protein and potential use of the recombinant antigen in an enzyme-linked immunosorbent assay

A cDNA expression library prepared from Babesia caballi merozoite mRNA was screened with a monoclonal antibody BC11D against the rhoptry protein of B. caballi merozoite. A cDNA encoding a 48-kDa protein of B. caballi was cloned and designated BC48. The complete nucleotide sequence of the BC48 gene had 1,828 bp and was shown to contain no intron. Southern blotting analysis indicated that the BC48 gene contained more than two copies in the B. caballi genome. Computer analysis suggested that this sequence contained an open reading frame of 1,374 bp with a coding capacity of approximately 52 kDa. The recombinant protein expressed by the vaccinia virus vector in horse cells had an apparent molecular mass of 48 kDa, which was the same as that of the native B. caballi 48-kDa protein. Moreover, recombinant proteins expressed by the pGEX4T expression vector in Escherichia coli as glutathione S-transferase fusion proteins were used for antigen in an enzyme-linked immunosorbent assay (ELISA). The ELISA was able to differentiate very clearly between B. caballi-infected horse sera and B. equi-infected horse sera or noninfected normal horse sera. These results suggest that this simple and highly sensitive test might be applicable to the detection of B. caballi-infected horses in the field.

Immunization with plasmid DNA encoding the envelope glycoprotein of Japanese Encephalitis virus confers significant protection against intracerebral viral challenge without inducing detectable antiviral antibodies

A plasmid DNA construct, pCMXENV encoding the envelope (E) glycoprotein of Japanese Encephalitis virus (JEV), was constructed. This plasmid expresses the E protein intracellularly, when transfected into Vero cells in culture. The ability of pCMXENV to protect mice from lethal JEV infection was evaluated using an intracerebral (i.c.) JEV challenge model. Several independent immunization and JEV challenge experiments were carried out and the results indicate that 51 and 59% of the mice are protected from lethal i.c. JEV challenge, when immunized with pCMXENV via intramuscular (i.m.) and intranasal (i.n.) routes respectively. None of the mice immunized with the vector DNA (pCMX) survived in any of these experiments. JEV-specific antibodies were not detected in pCMXENV-immunized mice either before or after challenge. JEV-specific T cells were observed in mice immunized with pCMXENV which increased significantly after JEV challenge indicating the presence of vaccination-induced memory T cells. Enhanced production of interferon-gamma (IFN-gamma) and complete absence of interleukin-4 (IL-4) in splenocytes of pCMXENV-immunized mice on restimulation with JEV antigens in vitro indicated that the protection is likely to be mediated by T helper (Th) lymphocytes of the Th1 sub-type. In conclusion, our results demonstrate that immunization with a plasmid DNA expressing an intracellular form of JEV E protein confers significant protection against i.c. JEV challenge even in the absence of detectable antiviral antibodies.

Biosynthesis and interaction of glycoproteins E and I of canine herpesvirus

In cells infected with canine herpesvirus (CHV), the mature form of glycoprotein E (gE) had a molecular weight of 94 kDa, and that of glycoprotein I (gI) had a broad range of molecular weights of 55-62 kDa. gE and gI formed a complex like gE and gI of other alphaherpesviruses. When cells were infected with the gI minus mutant of CHV (gI/Z), the mature form of the 94 kDa gE was not formed, but a 76 kDa gE polypeptide was found. Similarly, no mature gI was formed in cells infected with the gE minus mutant of CHV (gE/Z), but a 40 kDa gI polypeptide was formed. When cells were coinfected with gE/Z and gI/Z, the molecular masses of gE and gI were increased from 76 to 94 kDa and from 40 to 55-62 kDa, respectively. We constructed vaccinia virus recombinants which expressed CHV gE or CHV gI. Only when cells were coinfected with both the vaccinia recombinant which expressed gE and the vaccinia recombinant which expressed gI, gE and gI were processed into their mature forms. Our results suggest that the presence of both gE and gI is necessary for efficient processing of the precursors of gE and gI to their mature forms.

Protection against lethal Japanese encephalitis virus infection of mice by immunization with the highly attenuated MVA strain of vaccinia virus expressing JEV prM and E genes

Genes encoding the glycosylated precursor of the membrane (prM) and envelope (E) proteins of a Korean strain of Japanese encephalitis virus (JEV) were inserted into the genome of the host-range restricted, highly attenuated, and safety-tested MVA strain of vaccinia virus. MVA recombinants containing the JEV genes, under strong synthetic or modified H5 vaccinia virus promoters, were isolated. Synthesis of JEV prM and E proteins was detected by immunofluorescence microscopy, flow cytometry, and polyacrylamide gel electrophoresis. Mice inoculated and boosted by various routes with either of the MVA recombinants produced JEV neutralizing antibodies, that had titres comparable with those induced by an inactivated JEV vaccine, as well as haemagglutination-inhibiting antibodies. Mice immunized with 2 x 10(6) infectious units of MVA/JEV recombinants by intramuscular or intraperitoneal routes were completely protected against a 10(5) LD50 JEV challenge at 9 weeks of age.

Degradation of Japanese encephalitis virus by neutrophils

The ability of neutrophils to degrade the phagocytosed Japanese encephalitis (JE) virion, via triggering of the respiratory burst and generation of toxic radicals has been investigated. JEV or JEV-induced macrophage derived factor (MDF) induces increase in intracellular oxidative signals with generation of superoxide anion (O2-), via activation of cytosolic NADPH and subsequent formation of hydrogen peroxide, with maximum activity on day 7 post infection. The response was sensitive to anti-MDF antibody treatment. Further, the study revealed rapid degradation of phagocytosed JE viral protein and nucleic acid. The viral protein degradation was partially dependent on the generation of toxic oxygen species as it could be abrogated by pretreatment of the cells with staurosporine.

DNA-based and alphavirus-vectored immunisation with prM and E proteins elicits long-lived and protective immunity against the flavivirus, Murray Valley encephalitis virus

The immunogenicity and protective efficacy of DNA-based vaccination with plasmids encoding the membrane proteins prM and E of the flavivirus Murray Valley encephalitis virus (MVE) were investigated. Gene gun-mediated intradermal delivery of DNA encoding the prM and E proteins elicited long-lived, virus-neutralising antibody responses in three inbred strains of mice and provided protection from challenge with a high titer inoculum of MVE. Intramuscular DNA vaccination by needle injection also induced MVE-specific antibodies that conferred resistance to challenge with live virus but failed to reduce virus infectivity in vitro. The two routes of DNA-based vaccination with prM and E encoding plasmids resulted in humoral immunty with distinct IgG subtypes. MVE-specific IgG1 antibodies were always prevalent after intradermal DNA vaccination via a gene gun but not detected when mice were immunised with DNA by the intramuscular route or infected with live virus. We also tested a Semliki Forest virus replicon as vector for a flavivirus prM and E protein-based subunit vaccine. Single-cycle infections in mice vaccinated with packaged recombinant replicon particles elicited durable, MVE-specific, and virus-neutralising antibody responses.

Identification and characterization of the glycoprotein E and I genes of canine herpesvirus

We have determined the sequence of the gE and gI genes of canine herpesvirus (CHV), DFD-6 strain. The gE ORF codes for a 522 a.a. polypeptide with a signal sequence at the amino-terminus and a trans-membrane domain at the carboxy-terminus. The gI ORF codes for a 259 a.a. polypeptide with a signal sequence but no trans-membrane domain. Comparison with another line of CHV indicated that the DFD-6 gI gene underwent a frame-shift mutation which caused the loss of the trans-membrane domain. Antibodies against the gE and gI polypeptides detected a 94 kDa gE and a broad band of gI (55-62 kDa) in DFD-6 infected cells, respectively. The precursor of DFD-6 gE is modified to the mature form by N-linked glycosylation only in the presence of gI. Together with the fact that the gI- mutant of DFD-6 produced smaller plaques, it is suggested that the truncated DFD-6 gI is functional. The precursor of DFD-6 gI is modified to the mature form by N-linked glycosylation only in the presence of gE.

DNA immunization with Japanese encephalitis virus nonstructural protein NS1 elicits protective immunity in mice

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is a zoonotic pathogen that is prevalent in some Southeast Asian countries and causes acute encephalitis in humans. To evaluate the potential application of gene immunization to JEV infection, we characterized the immune responses from mice intramuscularly injected with plasmid DNA encoding JEV glycoproteins, including the precursor membrane (prM) plus envelope (E) proteins and the nonstructural protein NS1. When injected with the plasmid expressing prM plus E, 70% of the immunized mice survived after a lethal JEV challenge, whereas when immunized with the plasmid expressing NS1, 90% of the mice survived after a lethal challenge. As a control, the mice immunized with the DNA vector pcDNA3 showed a low level (40%) of protection, suggesting a nonspecific adjuvant effect of the plasmid DNA. Despite having no detectable neutralizing activity, the NS1 immunization elicited a strong antibody response exhibiting cytolytic activity against JEV-infected cells in a complement-dependent manner. By contrast, immunization with a construct expressing a longer NS1 protein (NS1'), containing an extra 60-amino-acid portion from the N terminus of NS2A, failed to protect mice against a lethal challenge. Biochemical analyses revealed that when individually expressed, NS1 but not NS1' could be readily secreted as a homodimer in large quantity and could also be efficiently expressed on the cell surface. Interestingly, when NS1 and NS1' coexisted in cells, the level of NS1 cell surface expression was much lower than that in cells expressing NS1 alone. These data imply that the presence of partial NS2A might have a negative influence on an NS1-based DNA vaccine. The results herein clearly illustrate that immunization with DNA expressing NS1 alone is sufficient to protect mice against a lethal JEV challenge.

Particulate vaccine candidate for Japanese encephalitis induces long-lasting virus-specific memory T lymphocytes in mice

We previously reported that extracellular particles (EPs) composed of premembrane (prM) and envelope (E) proteins were released from cells infected with recombinant vaccinia viruses encoding Japanese encephalitis (JE) virus prM and E genes. In the present study, EPs were evaluated for induction of JE virus-specific antibody and specific T lymphocytes in mice. Six- to 8-week-old male Balb/c mice were inoculated intraperitoneally once or twice (at a 3-week interval) with purified EPs containing 1 microgram of E without adjuvant. Neutralizing antibody was detected and spleen cells proliferated against JE viral antigen 3 weeks after the second immunization with EPs. Neutralizing antibody and JE virus-specific T lymphocytes were also detected 10 months after immunization with EPs containing 2 micrograms of E. Spleen cells obtained from EP-immunized mice and stimulated in vitro with live JE virus, expressed JE virus-specific cytotoxic activity. The cytotoxic activity was reduced by treatment with anti-CD3 antibody and complement. These results indicate that immunization with EPs induces long-lasting specific antibody and memory T cells in mice.

A 27 amino acid coding region of JE virus E protein expressed in E. coli as fusion protein with glutathione-S-transferase elicit neutralizing antibody in mice

We have recently shown that neutralizing epitope(s) exist near the C-terminal of JE virus E-protein by expressing the coding gene cDNA fragments as fusion proteins with protein A. Among four cDNA fragments, the fragment (B3) carrying the coding sequence of amino acid number 373-399 of E protein elicited the highest neutralizing (N) antibody titer (1:75). To exclude the possible influence of protein A contained in the expressed gene products on the mouse immune response, we expressed (B3) using pGEX-3X expression vector as fusion with glutathione-S transferase (GST). The mice immunized with recombinant GST-B3 fusion protein induced an immune response (mean average ELISA: 3364; N: 1:75) almost similar to that by recombinant protein A-B3 fusion protein (mean average ELISA: 3476; N: 1:75). While hemagglutination-inhibition (HI) antibodies were not induced by this fusion protein. These results indicate that 27 amino acid sequence on the E protein (373-399) was sufficient to induce neutralizing antibodies without association with protein A moiety.

Immunization with recombinant vaccinia viruses expressing structural and part of the nonstructural region of tick-borne encephalitis virus cDNA protect mice against lethal encephalitis

Three recombinant vaccinia viruses containing different fragments of tick-borne encephalitis virus (TBEV) cDNA representing the 5'-noncoding region (5'NCR), all structural and part of the nonstructural regions were constructed. Western blot analysis showed that E and NS1 proteins were expressed and processed correctly in cells infected with recombinant viruses vC-NS1 (coding for C-prM-E-NS1 region) and vC-NS3 (coding for C-prM-E-NS1-NS2A-NS2B-NS3 region). In contrast, in cells infected with recombinant virus v5'C-NS2A (coding for 5'NCR and C-prM-E-NS1-NS2A regions) expression of NS1 protein was greatly reduced and no E protein was detected. Immunization of mice with vC-NS3 induced high levels of TBEV-specific antibodies and protected them against intraperitoneal challenge with 10(7) LD50 of TBEV. The level of protection was very similar to the level of protection achieved by immunization with commercially available inactivated TBEV vaccine. Although the immunization of mice with recombinants vC-NS1 and v5'C-NS2A induced much lower levels of TBEV-specific antibodies, they were still protected against intraperitoneal challenge with 10(4) and 10(3.6) LD50 of TBEV, respectively. The high level of protection against TBEV infection achieved by the immunization of mice with the recombinant vaccinia virus vC-NS3 makes this virus a very attractive candidate for development of a live recombinant vaccine against TBEV.

Recognition of nonstructural protein peptides by cytotoxic T lymphocytes raised against Japanese encephalitis virus

We have previously reported that Lyt2+ cytotoxic T lymphocytes (CTL) can be raised against Japanese encephalitis virus (JEV) in BALB/c mice. In order to confirm the presence of H-2Kd-restricted CTL and to examine their cross-recognition of West Nile virus (WNV), we tested the capacity of anti-JEV CTL to lyse uninfected syngeneic target cells that were pulsed with synthetic peptides. The sequence of the synthetic peptides was predicted based upon the H-2Kd binding consensus motif. We show here that preincubation of uninfected syngeneic targets (P388D1) with JEV NS1- and NS3-derived peptides [NS1 (891-899) and NS3 (1804-1812)], but not with JEV NS5-derived peptide [NS5 (3370-3378)], partially sensitized them for lysis by polyclonal anti-JEV CTL. These results indicate the CTL recognition of NS1- and NS3-derived peptides of JEV.

Finer mapping of neutralizing epitope(s) on the C-terminal of Japanese encephalitis virus E-protein expressed in recombinant Escherichia coli system

In order to localize denaturation-resistant neutralizing epitope(s) in the C-terminal 180 amino acids of Japanese encephalitis (JE) virus E-protein, four recombinant clones encoding different or overlapping nucleotide sequences were constructed by PCR from a recombinant plasmid pS22. The amplified fragments were cloned into PCR 1000 vector, and then transferred into Escherichia coli expression vector pRIT2T. The inserted genes were expressed as fusion proteins with protein-A and examined for their antigenicity and immunogenicity by Western blotting and mouse immunization, respectively. Among the four recombinant fusion proteins, the highest neutralizing antibody titre was obtained by the one expressed by the recombinant clone pRIT2T-B3, which carried the coding sequence of amino acid number 373-399 of JE virus E protein. The results indicated that this short region of 27 amino acids sequence near the C-terminal of JE virus E protein possesses neutralizing epitope(s). These data should assist in the design of an efficient subunit vaccine against JE virus infection in future.

Human immunodeficiency virus type 1 reverse transcriptase: enhancement of activity by interaction with cellular topoisomerase I

A number of studies have suggested that topoisomerase I (topo I) activity may be important in human immunodeficiency virus type 1 (HIV-1) replication. Specifically it has been reported that purified virus particles have topo I activity and that inhibitors of this enzyme can inhibit virus replication in vitro. We have investigated a possible association of HIV-1 gag proteins with topo I activity. We found that whereas the gag-encoded proteins by themselves do not have activity, the nucleocapsid protein p15 can interact with and enhance the activity of cellular topo I. Furthermore it could be demonstrated that topo I markedly enhanced HIV-1 reverse transcriptase activity in vitro and that this could be inhibited by the topo I-specific inhibitor camptothecin. The findings suggest that cellular topo I plays an important role in the reverse transcription of HIV-1 RNA and that the recruitment of this enzyme may be an important step in virus replication.