Evaluation of tick-borne encephalitis DNA vaccines in monkeys

Recent Advancements in Mosquito-Borne Flavivirus Vaccine Development

Lately, the global incidence of flavivirus infection has been increasing dramatically and presents formidable challenges for public health systems around the world. Most clinically significant flaviviruses are mosquito-borne, such as the four serotypes of dengue virus, Zika virus, West Nile virus, Japanese encephalitis virus and yellow fever virus. Until now, no effective antiflaviviral drugs are available to fight flaviviral infection; thus, a highly immunogenic vaccine would be the most effective weapon to control the diseases. In recent years, flavivirus vaccine research has made major breakthroughs with several vaccine candidates showing encouraging results in preclinical and clinical trials. This review summarizes the current advancement, safety, efficacy, advantages and disadvantages of vaccines against mosquito-borne flaviviruses posing significant threats to human health.

Tick-Borne Encephalitis Virus: A Quest for Better Vaccines against a Virus on the Rise

Tick-borne encephalitis virus (TBEV), a member of the family Flaviviridae, is one of the most important tick-transmitted viruses in Europe and Asia. Being a neurotropic virus, TBEV causes infection of the central nervous system, leading to various (permanent) neurological disorders summarized as tick-borne encephalitis (TBE). The incidence of TBE cases has increased due to the expansion of TBEV and its vectors. Since antiviral treatment is lacking, vaccination against TBEV is the most important protective measure. However, vaccination coverage is relatively low and immunogenicity of the currently available vaccines is limited, which may account for the vaccine failures that are observed. Understanding the TBEV-specific correlates of protection is of pivotal importance for developing novel and improved TBEV vaccines. For affording robust protection against infection and development of TBE, vaccines should induce both humoral and cellular immunity. In this review, the adaptive immunity induced upon TBEV infection and vaccination as well as novel approaches to produce improved TBEV vaccines are discussed.

An immunoinformatics-derived DNA vaccine encoding human class II T cell epitopes of Ebola virus, Sudan virus, and Venezuelan equine encephalitis virus is immunogenic in HLA transgenic mice

Immunoinformatics tools were used to predict human leukocyte antigen (HLA) class II-restricted T cell epitopes within the envelope glycoproteins and nucleocapsid proteins of Ebola virus (EBOV) and Sudan virus (SUDV) and the structural proteins of Venezuelan equine encephalitis virus (VEEV). Selected epitopes were tested for binding to soluble HLA molecules representing 5 class II alleles (DRB1*0101, DRB1*0301, DRB1*0401, DRB1*0701, and DRB1*1501). All but one of the 25 tested peptides bound to at least one of the DRB1 alleles, and 4 of the peptides bound at least moderately or weakly to all 5 DRB1 alleles. Additional algorithms were used to design a single "string-of-beads" expression construct with 44 selected epitopes arranged to avoid creation of spurious junctional epitopes. Seventeen of these 44 predicted epitopes were conserved between the major histocompatibility complex (MHC) of humans and mice, allowing initial testing in mice. BALB/c mice vaccinated with the multi-epitope construct developed statistically significant cellular immune responses to EBOV, SUDV, and VEEV peptides as measured by interferon (IFN)-γ ELISpot assays. Significant levels of antibodies to VEEV, but not EBOV, were also detected in vaccinated BALB/c mice. To assess immunogenicity in the context of a human MHC, HLA-DR3 transgenic mice were vaccinated with the multi-epitope construct and boosted with a mixture of the 25 peptides used in the binding assays. The vaccinated HLA-DR3 mice developed significant cellular immune responses to 4 of the 25 (16%) tested individual class II peptides as measured by IFN-γ ELISpot assays. In addition, these mice developed antibodies against EBOV and VEEV as measured by ELISA. While a low but significant level of protection was observed in vaccinated transgenic mice after aerosol exposure to VEEV, no protection was observed after intraperitoneal challenge with mouse-adapted EBOV. These studies provide proof of concept for the use of an informatics approach to design a multi-agent, multi-epitope immunogen and provide a basis for further testing aimed at focusing immune responses toward desired protective T cell epitopes.

Immunogenicity against Far Eastern and Siberian subtypes of tick-borne encephalitis (TBE) virus elicited by the currently available vaccines based on the European subtype: systematic review and meta-analysis

Tick-borne encephalitis (TBE) virus, which is usually divided into European, Far Eastern and Siberian subtypes, is a serious public health problem in several European and Asian countries. Vaccination is the most effective measure to prevent TBE; cross-subtype protection elicited by the TBE vaccines is biologically plausible since all TBE virus subtypes are closely related. This manuscript systematically explores available data on the cross-subtype immunogenicity elicited by the currently available Western vaccines based on the European subtype. Completed immunization course of 3 doses of both Western vaccines determined very high seroconversion/seropositivity rates against both Far Eastern and Siberian subtypes among previously flavivirus-naïve subjects. All but one study found no statistically significant difference in titers of neutralizing antibodies against strains belonging to homologous and heterologous subtypes. Pooled analysis of randomized controlled trials on head-to-head comparison of immunogenicity of Western and Russian TBE vaccines did not reveal differences in seroconversion rates against Far Eastern isolates in either hemagglutination inhibition (risk ratio = 0.98, p = 0.83) or enzyme-linked immunosorbent (risk ratio = 0.95, p = 0.44) assays after 2 vaccine doses. This suggests that, in regions where a heterogeneous TBE virus population circulates, vaccines based on the European subtype may be used alongside vaccines based on the Far Eastern subtype. Studies on the field effectiveness of TBE vaccines and investigation of vaccination failures, especially in countries where different subtypes co-circulate, will further elucidate TBE vaccination-induced cross-subtype protection.

RSV fusion (F) protein DNA vaccine provides partial protection against viral infection

The present study was conducted to investigate the feasibility and efficacy of a RSV F DNA vaccine incorporated with a mucosal adjuvant. Two DNA vaccine vectors (DRF-412 and DRF-412-P) were developed containing residues 412-524 of the RSV F gene. These antigenic regions were cloned into the phCMV1 DNA vaccine vector. One of the DNA vaccine vectors, DRF-412, contained the ctxA(2)B region of the cholera toxin gene as a mucosal adjuvant. The in vitro expressions of these DNA vectors were confirmed in Cos-7 cells by indirect immunofluorescence and Western blot analyses. In vivo expression of the cloned gene was further confirmed in mouse muscle tissue by immunohistological analysis. The active transcription of the RSV F gene in mouse muscle cells was confirmed by RT-PCR. The purified DRF-412 and DRF-412-P DNA vectors were used to immunize mice by intramuscular injections. Our results indicated that DRF-412 and DRF-412-P vaccine vectors were as effective as live RSV in inducing neutralization antibody, systemic Ab (IgG, IgG1, IgG2a, and IgG2b) responses, and mucosal antibody responses (Ig A). The Th1 (TNF-alpha, IL-12p70, IFN-gamma, IL-2) and Th2 (IL-10, IL-6) cytokine profiles were analyzed after stimulation of spleen cells from mice immunized with purified RF-412 protein. We observed that mice inoculated with vector DRF-412 induced a higher mixed Th1/Th2 cytokine immune response than DRF-412-P. Reverse transcriptase and quantitative real-time PCR (qRT-PCR) revealed that mice immunized with the DRF-412 vector contained less viral RNA in lung tissue and the lung immunohistology study confirmed that mice immunized with DRF-412 had better protection than those immunized with the DRF-412-P vector. These results indicate that the RSV DRF-412 vaccine vector, which contains the cholera toxin subunit ctxA2B as a mucosal adjuvant may provide a better DNA vaccination strategy against RSV.

Preclinical and clinical progress of particle-mediated DNA vaccines for infectious diseases

This review provides an overview of studies employing particle-mediated epidermal delivery (PMED) or the gene gun to administer DNA vaccines for infectious diseases in preclinical studies employing large animal models and in human clinical trials. It reviews the immunogenicity and protective efficacy of PMED DNA vaccines in nonhuman primates and swine and studies that have directly compared the effectiveness of PMED in these large animal models to existing licensed vaccines and intramuscular or intradermal delivery of DNA vaccines with a needle. Various clinical trials employing PMED have been completed and an overview of the immunogenicity, safety, and tolerability of this approach in humans is described. Finally, efforts currently in progress for commercial development of particle-mediated DNA vaccines are discussed.

Humoral and cellular immune response to RNA immunization with flavivirus replicons derived from tick-borne encephalitis virus

A new vaccination principle against flaviviruses, based on a tick-borne encephalitis virus (TBEV) self-replicating noninfectious RNA vaccine that produces subviral particles, has recently been introduced (R. M. Kofler, J. H. Aberle, S. W. Aberle, S. L. Allison, F. X. Heinz, and C. W. Mandl, Proc. Natl. Acad. Sci. USA 7:1951-1956, 2004). In this study, we evaluated the potential of the self-replicating RNA vaccine in mice in comparison to those of live, attenuated vaccines and a formalin-inactivated whole-virus vaccine (ImmunInject). For this purpose, mice were immunized using gene gun-mediated application of the RNA vaccine and tested for CD8+ T-cell responses, long-term duration, neutralizing capacity, and isotype profile of specific antibodies and protection against lethal virus challenge. We demonstrate that the self-replicating RNA vaccine induced a broad-based, humoral and cellular (Th1 and CD8+ T-cell response) immune response comparable to that induced by live vaccines and that it protected mice from challenge. Even a single immunization with 1 microg of the replicon induced a long-lasting antibody response, characterized by high neutralizing antibody titers, which were sustained for at least 1 year. Nevertheless, it was possible to boost this response further by a second injection with the RNA vaccine, even in the presence of a concomitant CD8+ T-cell response. In this way it was possible to induce a balanced humoral and cellular immune response, similar to infection-induced immunity but without the safety hazards of infectious agents. The results also demonstrate the value of TBEV replicon RNA for inducing protective long-lasting antiviral responses.

Immunogenicity of combination DNA vaccines for Rift Valley fever virus, tick-borne encephalitis virus, Hantaan virus, and Crimean Congo hemorrhagic fever virus

DNA vaccines for Rift Valley fever virus (RVFV), Crimean Congo hemorrhagic fever virus (CCHFV), tick-borne encephalitis virus (TBEV), and Hantaan virus (HTNV), were tested in mice alone or in various combinations. The bunyavirus vaccines (RVFV, CCHFV, and HTNV) expressed Gn and Gc genes, and the flavivirus vaccine (TBEV) expressed the preM and E genes. All vaccines were delivered by gene gun. The TBEV DNA vaccine and the RVFV DNA vaccine elicited similar levels of antibodies and protected mice from challenge when delivered alone or in combination with other DNAs. Although in general, the HTNV and CCHFV DNA vaccines were not very immunogenic in mice, there were no major differences in performance when given alone or in combination with the other vaccines.

DNA immunization against very virulent infectious bursal disease virus with VP2-4-3 gene and chicken IL-6 gene

The present study was to investigate the feasibility and efficiency of the DNA vaccine to protect chickens against very virulent infectious bursal disease virus (vvIBDV) infection. A plasmid DNA carrying VP2-4-3 genes of vvIBDV SH95 and a plasmid DNA carrying chicken interleukin-6 (ChIL-6) genes were constructed and designated as pALTER-MAX-VP2-4-3 and pALTER-MAX-ChIL-6 respectively. Several DNA vaccination experiments were performed: 1-week-old chickens were intramuscularly injected with only plasmid pcDNA3-VP2, pALTER-MAX-VP2-4-3 or mixture with pALTER-MAX-ChIL-6. The chickens at 4 weeks old were orally inoculated with vvIBDV SH95. The results showed that immunization with the mixture of pALTER-MAX-VP2-4-3 and pALTER-MAX-ChIL-6 three times conferred protection for 90% of chickens. Enzyme-linked immunosorbent assay (ELISA) antibody titres in chickens immunized together with pALTER-MAX-ChIL-6 were higher than those immunized simply with plasmid pcDNA3-VP2 or pALTER-MAX-VP2-4-3. IBDV was not detected in the bursa of the protected chickens at 8 days after challenge by RT-PCR. The results indicate that protection against vvIBDV can be achieved by using the VP2-4-3 gene of vvIBDV as a DNA vaccine. Furthermore, the simultaneous injection of ChIL-6 plasmid significantly increased the protection after challenge with the very virulent strain.

The role of particle-mediated DNA vaccines in biodefense preparedness

Particle-mediated epidermal delivery (PMED) of DNA vaccines is based on the acceleration of DNA-coated gold directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Professional antigen-presenting cells and keratinocytes in the skin are both targeted, resulting in antigen presentation via direct transfection and cross-priming mechanisms. Only a small number of cells need to be transfected to elicit humoral, cellular and memory responses, requiring only a low DNA dose. In recent years, data have accumulated on the utility of PMED for delivery of DNA vaccines against a number of viral pathogens, including filoviruses, flaviviruses, poxviruses, togaviruses and bunyaviruses. PMED DNA immunization of rodents and nonhuman primates results in the generation of neutralizing antibody, cellular immunity, and protective efficacy against a broad range of viruses of public health concern.

Epidermal delivery of protein and DNA vaccines

Targeting vaccines to the skin epidermis results in the activation of an immune inductive site that is rich in antigen-presenting cells. The superficial location of the skin makes it accessible to vaccine delivery. However, it is difficult to access the epidermis using needle and syringe delivery, and vaccine antigens are too large to be effectively delivered using standard topical formulations. Needle-free vaccine delivery systems have been developed for efficient delivery of particulate vaccines into the epidermal tissue. Particle-mediated epidermal delivery of DNA vaccines is based on the delivery of DNA-coated gold particles directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Alternatively, protein vaccines can be formulated into a dense powder, which can be propelled into the skin epidermis by epidermal powder immunisation using similar delivery devices and principles, but in this instance the protein is delivered to the extracellular space. Preclinical and clinical data will be reviewed, demonstrating applications of epidermal vaccine delivery to a wide range of experimental infectious disease vaccines.

Recent advancement in flavivirus vaccine development

Lately, the magnitude of cumulative diseases burden caused by flaviviruses, such as dengue virus, Japanese encephalitis virus, tick-borne encephalitis virus, West Nile virus and yellow fever virus, has reached an unprecedented level with the sizes of human and animal populations at risk increasing sharply. These diseases present highly complex medical, economic and ecologic problems, some effecting primarily human and others affecting human, livestock and wildlife. The large body of recent publications on the development of vaccines taking advantage of new generations of bio-engineering techniques clearly reflects the profound interests and deep sense of urgency in the scientific and medical communities in combating those diseases. This review reveals a collection of remarkable progresses thus far made in flaviviral vaccine research not only employing a diverse range of new strategies but also re-tooling old techniques to improve the existing vaccines. The efficacy and safety of some of the new vaccine candidates have been evaluated and proven in human clinical trials. Besides the technical advancement in vaccine development, in this review, the importance of somewhat neglected and yet critical subjects, such as adequacy of animal model, vaccine safety, vaccine formulation and delivery, complication in serodiagostics and economic factor, was examined in-depth.

Particle-mediated DNA vaccine delivery to the skin

Particle-mediated DNA vaccines employ a physical, intracellular delivery device to achieve the deposition of plasmid DNA-based expression vectors directly into the interior of cells of the skin. The resultant bolus of transient antigen expression in keratinocytes and trafficking dendritic cells results in the induction of humoral and cellular immune responses in various animal models and humans, mimicking characteristics of live or live-vectored vaccines. Ultimately, DNA vaccine success in the clinic will depend on both the successful intracellular delivery of a plasmid vector and an immunostimulator or adjuvant to maximise humoral and cellular immune responses to the encoded antigen(s). To this end, recent DNA vaccine clinical trials are confirming the importance of an intracellular delivery system, while preclinical studies in animal models are demonstrating the feasibility of augmenting responses through the use of DNA-encoded immunostimulators. Particle-mediated DNA vaccines represent a promising tool for developing candidate vaccines against some of the more difficult infectious, parasitic and oncologic disease targets.

Tick-borne flaviviruses

Tick-borne encephalitis (TBE), one of the most dangerous neuroinfections in Europe and Asia, is caused by tick-borne encephalitis virus (TBEV) and currently involves approximately 11,000 human cases annually, mostly in Russia. This chapter describes the main problems associated with the epidemiology, ecology, pathogenesis, and control of this disease. We have attempted to review the factors that influence the incidence and distribution of TBE, and to discuss possible reasons for the different clinical manifestations including most commonly observed asymptomatic infections, fever forms, acute encephalitis, and the less frequently registered biphasic milk fever and chronic encephalitis. Epidemiologic data concerning the other tick-borne flaviviruses, namely Louping ill virus, Langat virus, and Powassan virus that also produce encephalitis on a smaller scale, are also presented. Here we describe the history and current epidemiological role of Omsk hemorrhagic fever virus and Kyasanur forest disease virus, two viruses that are genetically closely related to TBEV, but produce hemorrhagic fever instead of encephalitis, and provide possible explanations for these differences. The other viruses in the tick-borne flavivirus group are also included despite the fact that they do not play an essential epidemiologic role in humans. This chapter contains a brief history of vaccination against TBE including the trials with live attenuated vaccine and reviews the modern trends in development of vaccine virus strains.

Tick-borne encephalitis and the impact of vaccination

TBE virus is endemic in many parts of Europe and Northern Asia, and in these regions it causes more than 10,000 severe cases of central nervous system disease in humans each year. The virus is primarily transmitted to humans when infected ticks take a blood meal, but infections due to the consumption of unpasteurized milk, primarily from goats, occur in certain regions. Based on genetic analyses, three closely related subtypes can be distinguished and are designated European, Siberian, and Far Eastern subtype according to their primary geographic distribution. Consistent with their close antigenic relationships, immunization studies in animals have revealed a high degree of cross-protection between virus strains belonging to different subtypes. The commercially available vaccines in Europe consist of highly purified inactivated whole TBE virus. Austria is the country with the highest coverage of TBE vaccination (86% of the total population) and this has led to a dramatic reduction in the annual number of clinical cases and proves under field conditions that vaccination is an effective means for the prophylaxis of TBE.

Vaccines and animal models for arboviral encephalitides

Arthropod-borne viruses ("arboviruses") cause significant human illness ranging from mild, asymptomatic infection to fatal encephalitis or hemorrhagic fever. The most significant arboviruses causing human illness belong to genera in three viral families, Togaviridae, Flaviviridae, and Bunyaviridae. These viruses represent a significant public health threat to many parts of the world, and, as evidenced by the recent introduction of the West Nile virus (WNV) to the Western Hemisphere, they can no longer be considered specific to any one country or region of the world. Like most viral diseases, there are no specific therapies for the arboviral encephalitides; therefore, effective vaccines remain the front line of defense for these diseases. With this in mind, the development of new, more effective vaccines and the appropriate animal models in which to test them become paramount. In fact, for many important arboviruses (e.g. California serogroup and St. Louis encephalitis viruses), there are currently no approved vaccines available for human use. For others, such as the alphaviruses, human vaccines are available only as Investigational New Drugs, and thus are not in widespread use. On the other hand, safe and effective vaccines against tick-borne encephalitis virus (TBEV) and Japanese encephalitis virus (JEV) have been in use for decades. New challenges in vaccine development have been met with new technologies in vaccine research. Many of the newer vaccines are now being developed by recombinant DNA technology. For example, chimeric virus vaccines have been developed using infectious clone technology for many of the arboviruses including, WNV, JEV, and TBEV. Other successful approaches have involved the use of naked DNA encoding and subsequently expressing the desired protective epitopes. Naked DNA vaccines have been used for TBEV and JEV and are currently under development for use against WNV. The development of less expensive, more authentic animal models to evaluate new vaccines against arboviral diseases will become increasingly important as these new approaches in vaccine research are realized. This article reviews the current status of vaccines, both approved for use and those in developmental stages, against the major arboviral encephalitides causing human disease. In addition, research on animal models, both past and present, for these diseases are discussed.

Comparison of individual and combination DNA vaccines for B. anthracis, Ebola virus, Marburg virus and Venezuelan equine encephalitis virus

Multiagent DNA vaccines for highly pathogenic organisms offer an attractive approach for preventing naturally occurring or deliberately introduced diseases. Few animal studies have compared the feasibility of combining unrelated gene vaccines. Here, we demonstrate that DNA vaccines to four dissimilar pathogens that are known biowarfare agents, Bacillus anthracis, Ebola (EBOV), Marburg (MARV), and Venezuelan equine encephalitis virus (VEEV), can elicit protective immunity in relevant animal models. In addition, a combination of all four vaccines is shown to be equally as effective as the individual vaccines for eliciting immune responses in a single animal species. These results demonstrate for the first time the potential of combined DNA vaccines for these agents and point to a possible method of rapid development of multiagent vaccines for disparate pathogens such as those that might be encountered in a biological attack.

Immunogenicity of a Japanese encephalitis DNA vaccine candidate in cynomolgus monkeys

A Japanese encephalitis (JE) vaccine candidate encoding JE virus premembrane (prM) and envelope (E) genes, designated pNJEME, was evaluated for safety and immunogenicity in non-human primate, cynomolgus monkeys. pNJEME was constructed using a vector (pNGVL4a) designed to address some of the safety concerns of DNA vaccine. In two different experiments, two immunizations with 300 microg of pNJEME by intramuscular (i.m.) injection, and 3 microg of pNJEME using a gene gun, and three immunizations by i.m. injection with 500 microg of pNJEME were performed. All the three protocols induced low to high levels of neutralizing antibody, indicating an ability of pNJEME to induce neutralizing antibody in monkeys with a wide individual variation in response to pNJEME. In one experiment designed to compare the DNA vaccine with a commercial inactivated JE vaccine, three immunizations by i.m. inoculation with 300 microg of pNJEME or by gene gun administration with 3 microg of pNJEME induced similar levels of neutralizing antibody to those induced by three immunizations with a human dose of the inactivated vaccine in most monkeys. After intranasal challenge with the Beijing P3 or JaTH160 strain of JE virus, pNJEME-immunized monkeys showed anamnestic neutralizing antibody responses, indicating that pNJEME induced memory B cells which were responsive to infection with JE virus. No systemic and local reactions were observed in any monkeys after i.m. or gene gun inoculations with plasmid DNAs.

Enhancing biosynthesis and secretion of premembrane and envelope proteins by the chimeric plasmid of dengue virus type 2 and Japanese encephalitis virus

We have constructed a series of plasmids encoding premembrane (prM) and envelope (E) protein genes of dengue virus type 2 (DEN-2). These plasmids included an authentic DEN-2 prM-E construct (pCBD2-14-6), and two chimeric constructs, 90% DEN-2 E-10% Japanese encephalitis (JE) virus E (pCB9D2-1J-4-3) and 80% DEN-2 E-20% JE E (pCB8D2-2J-2-9-1). Monoclonal antibody (MAb) reactivity indicated that all three plasmids expressed authentic DEN-2 virus E protein epitopes representative of flavivirus domains 1, 2, and 3. However, only the pCB8D2-2J-2-9-1 construct secreted high levels of prM, M (membrane), and E proteins into the culture fluid of plasmid-transformed COS-1 cells. The major portion of the prM and E proteins expressed by COS-1 cells transformed by pCBD2-14-6 or pCB9D2-4-3 plasmids remained membrane-bound. The results supported the notion that an unidentified membrane retention sequence is located between E-397 and E-436 of DEN-2 virus E protein. Replacing the carboxyl-terminal 20% of DEN-2 E (397-450) with the corresponding JE sequence had no effect on anti-DEN-2 MAb reactivity, indicating that this region is antigenically inert, although it is required for antigen secretion. Plasmid pCBD2-2J-2-9-1, which expressed secreted forms of prM/M and E that have the potential to form subviral particles, was superior to other constructs in stimulating an antibody response. Ninety percent neutralization titers ranging from 1:40 to >1:1000 were observed in seven of nine serum specimens from pCB8D2-2J-2-9-1-immunized mice. Eleven of twelve 2-day-old neonatal mice, derived from a pCB8D2-2J-2-9-1 immunized female mouse, survived intraperitoneal challenge of DEN-2 New Guinea C virus.

Tick-borne encephalitis

Tick-borne encephalitis (TBE) is one of the most dangerous human infections occurring in Europe and many parts of Asia. The etiological agent Tick-borne encephalitis virus (TBEV), is a member of the virus genus Flavivirus, of the family Flaviviridae. TBEV is believed to cause at least 11,000 human cases of encephalitis in Russia and about 3000 cases in the rest of Europe annually. Related viruses within the same group, Louping ill virus (LIV), Langat virus (LGTV) and Powassan virus (POWV), also cause human encephalitis but rarely on an epidemic scale. Three other viruses within the same group, Omsk hemorrhagic fever virus (OHFV), Kyasanur Forest disease virus (KFDV) and Alkhurma virus (ALKV), are closely related to the TBEV complex viruses and tend to cause fatal hemorrhagic fevers rather than encephalitis. This review describes the clinical manifestations associated with TBEV infections, the main molecular-biological properties of these viruses, and the different factors that define the incidence and severity of disease. The role of ticks and their local hosts in the emergence of new virus variants with different pathogenic characteristics is also discussed. This review also contains a brief history of vaccination against TBE including trials with live attenuated vaccine and modern tendencies in developing of vaccine virus strains.

Needle-free epidermal powder immunization

Due to the presence of a network of antigen-presenting cells and other cells with innate and adaptive immune functions, the skin is both a sensitive immune organ and a practical target site for vaccine administration. A handful of needle-free immunization technologies have emerged in recent years that aim to take advantage of these characteristics. Skin delivery technologies provide potentially safer alternatives to needle injection and promises increased efficacy in the prevention and/or therapy of infectious diseases, allergic disorders and cancer. In this review, we will cover advances in needle-free skin vaccination technologies and their potential applications to disease prevention and therapy. Emphasis will be placed on epidermal powder immunization and particle-mediated ('gene gun') DNA immunization, which use similar mechanical devices to deliver protein and DNA vaccines, respectively, into the viable epidermis.

Antibody prophylaxis and therapy for flavivirus encephalitis infections

The outbreak of West Nile (WN) encephalitis in the United States has rekindled interest in developing direct methods for prevention and control of human flaviviral infections. Although equine WN vaccines are currently being developed, a WN vaccine for humans is years away. There is also no specific therapeutic agent for flaviviral infections. The incidence of human WN virus infection is very low, which makes it difficult to target the human populations in need of vaccination and to assess the vaccine's economic feasibility. It has been shown, however, that prophylactic application of antiflaviviral antibody can protect mice from subsequent virus challenge. This model of antibody prophylaxis using murine monoclonal antibodies (MAbs) has been used to determine the timing of antibody application and specificity of applied antibody necessary for successful prophylaxis. The major flaviviral antigen is the envelope (E) glycoprotein that binds cellular receptors, mediates cell membrane fusion, and contains an array of epitopes that elicit virus-neutralizing and nonneutralizing antibodies. The protective efficacy of an E-glycoprotein-specific MAb is directly related to its ability to neutralize virus infectivity. The window for successful application of prophylactic antibody to prevent flaviviral encephalitis closes at about 4 to 6 days postinfection concomitant with viral invasion of the brain. Using murine MAbs to modify human disease results in a human antimouse antibody (HAMA) response that eventually limits the effectiveness of subsequent murine antibody applications. To reduce the HAMA response and make these MAbs more generally useful for humans, murine MAbs can be "humanized" or human MAbs with analogous reactivities can be developed. Antiflaviviral human or humanized MAbs might be practical and cost-effective reagents for preventing or modifying flaviviral diseases.

DNA-mediated vaccination against infectious bursal disease in chickens

The objective of the present study was to investigate the feasibility of a DNA vaccine to protect chickens against infectious bursal disease virus (IBDV) infection. A plasmid DNA carrying VP2, VP4, and VP3 genes of the standard challenge (STC) strain of IBDV was constructed and designated as pCR3.1-VP243-STC. One-day-old chickens were intramuscularly injected with the plasmid pCR3.1-VP243-STC once (group D1), twice (group D2), or three times (group D3) at weekly intervals. Chickens at 3 weeks old were orally inoculated with IBDV strain STC and observed for 10 days after challenge. Immunization twice (group D2) or three times (group D3) with the plasmid pCR3.1-VP243-STC conferred protection for 50-100 or 80-100% of chickens, respectively, as evidenced by the absence of clinical signs, mortality, and bursal atrophy. Although chickens vaccinated once (group D1) with the plasmid pCR3.1-VP243-STC did not have clinical signs, they exhibited varying degree of bursal atrophy after challenge. Enzyme-linked immunosorbent assay (ELISA) antibody titers in chickens protected by the plasmid pCR3.1-VP243-STC were significantly lower (P<0.05) than those not protected 10 days after challenge. IBDV antigen was not detected in the bursae of chickens that were protected by receiving the plasmid pCR3.1-VP243-STC twice or three times. The results indicate that the constructed plasmid pCR3.1-VP243-STC as a DNA vaccine provided efficacious protection for chickens against IBDV infection.

A recombinant Semliki Forest virus particle vaccine encoding the prME and NS1 proteins of louping ill virus is effective in a sheep challenge model

This study has examined the efficacy following intramuscular administration of a recombinant Semliki Forest virus (rSFV) vaccine, encoding the prME and NS1 proteins of louping ill virus (LIV), in sheep. Administration of rSFV-LIV vaccine resulted in transient detection at the injection site and draining lymph node only and no dissemination to distal sites. In addition, the recombinant vaccine offered complete protection against subcutaneous challenge with LIV, and partial protection following intranasal administration of LIV. Protected animals had no pathological changes normally associated with LIV infection, and had developed high antibody titres. In contrast, the two animals not protected exhibited classical clinical signs and neuropathological lesions of LIV infection. These findings indicate that rSFV-based vaccines have the potential to be developed as effective prototype vaccines for LIV.

Optimization of DNA immunization against human cytomegalovirus

The immune responses of mice injected with plasmids VR-gB and VR-gB Delta tm expressing the full-length membrane-anchored, or secreted forms of human cytomegalovirus (HCMV)-glycoprotein B (gB), respectively, and VR-pp65 expressing the HCMV-phosphoprotein 65 (pp65) were analyzed. Pretreatment of mice with the local anesthetic bupivacaine did not enhance antibody production, and IFN-alpha co-expressed with the immunizing plasmids induced a moderate increase in the antibody response. However, antibody response was higher in mice inoculated at three sites in the musculus quadriceps than in mice inoculated at one site with the same dose and in the same muscle. pVR-gB Delta tm induced significantly higher antibody titers than the construct expressing the membrane-anchored form of gB, and priming with pVR-gB Delta tm followed by boosting with the gB subunit resulted in high-titer antibody responses. Immunization with VR-pp65 induced dose-dependent CTL responses in about 50% of the mice at a dose of 50 microg. Co-expression of IFN-alpha did not affect the number of responding mice. These findings might be important for optimization of humoral and cellular immune responses to HCMV after DNA vaccination.

West Nile virus recombinant DNA vaccine protects mouse and horse from virus challenge and expresses in vitro a noninfectious recombinant antigen that can be used in enzyme-linked immunosorbent assays

Introduction of West Nile (WN) virus into the United States in 1999 created major human and animal health concerns. Currently, no human or veterinary vaccine is available to prevent WN viral infection, and mosquito control is the only practical strategy to combat the spread of disease. Starting with a previously designed eukaryotic expression vector, we constructed a recombinant plasmid (pCBWN) that expressed the WN virus prM and E proteins. A single intramuscular injection of pCBWN DNA induced protective immunity, preventing WN virus infection in mice and horses. Recombinant plasmid-transformed COS-1 cells expressed and secreted high levels of WN virus prM and E proteins into the culture medium. The medium was treated with polyethylene glycol to concentrate proteins. The resultant, containing high-titered recombinant WN virus antigen, proved to be an excellent alternative to the more traditional suckling-mouse brain WN virus antigen used in the immunoglobulin M (IgM) antibody-capture and indirect IgG enzyme-linked immunosorbent assays. This recombinant antigen has great potential to become the antigen of choice and will facilitate the standardization of reagents and implementation of WN virus surveillance in the United States and elsewhere.

Cutaneous DNA vaccination against Ebola virus by particle bombardment: histopathology and alteration of CD3-positive dendritic epidermal cells

We analyzed the localization of gold particles, expression of immunogenic protein, and histopathologic changes after vaccinating guinea pigs and mice with a DNA vaccine to the Ebola virus glycoprotein administered by cutaneous particle bombardment. Gold particles were deposited in all layers of the epidermis and in the dermis. Those in the epidermis were lost as the damaged layers sloughed, while those in the dermis were phagocytized by macrophages. Glycoprotein was demonstrated by immunohistochemistry primarily in keratinocytes in the epidermis and hair follicle epithelium and less frequently in dermal macrophages, fibroblasts, sebocytes, and cells that appeared to be Langerhans cells. The number of cells that expressed glycoprotein increased between 4 and 8 hours postvaccination, then decreased to near zero by 48 hours. The vaccine sites were histologically divisible into three zones. The central portion, zone 1, contained the most gold particles in the dermis and epidermis and had extensive tissue damage, including full-thickness epidermal necrosis. Zone 2 contained fewer gold particles in the epidermis and dermis and had less extensive necrosis. The majority of cells in which glycoprotein was expressed were in zone 2. Zone 3 contained gold particles only in the epidermis and had necrosis of only a few scattered cells. Regeneration of the epidermis in damaged areas was evident at 24 hours postvaccination and was essentially complete by day 5 in the mice and day 10 in the guinea pigs. Inflammatory changes were characterized by hemorrhage, edema, and infiltrates of neutrophils initially and by infiltrates of lymphocytes and macrophages at later times. In zone 1, inflammation affected both the epidermis and dermis. Peripherally, inflammation was relatively limited to the epidermis. CD3-positive dendritic epidermal cells were demonstrated in the epidermis and superficial hair follicles of unvaccinated immunocompetent mice and beige mice but not of SCID mice. These cells disappeared from all but the most peripheral portions of the vaccine sites of vaccinated mice within 24 hours. They reappeared slowly, failing to reach numbers comparable with unvaccinated mice by 35 days postvaccination. The epidermis of control guinea pigs also had CD3-positive cells, but they did not have dendrites. These findings should contribute to a better understanding of the mechanisms operating in response to DNA vaccination by particle bombardment.