- Open Access
Vaccination with dengue virus-like particles induces humoral and cellular immune responses in mice
© Zhang et al; licensee BioMed Central Ltd. 2011
- Received: 20 April 2011
- Accepted: 30 June 2011
- Published: 30 June 2011
The incidence of dengue, an infectious disease caused by dengue virus (DENV), has dramatically increased around the world in recent decades and is becoming a severe public health threat. However, there is currently no specific treatment for dengue fever, and licensed vaccine against dengue is not available. Vaccination with virus-like particles (VLPs) has shown considerable promise for many viral diseases, but the effect of DENV VLPs to induce specific immune responses has not been adequately investigated.
By optimizing the expression plasmids, recombinant VLPs of four antigenically different DENV serotypes DENV1-4 were successfully produced in 293T cells. The vaccination effect of dengue VLPs in mice showed that monovalent VLPs of each serotype stimulated specific IgG responses and potent neutralizing antibodies against homotypic virus. Tetravalent VLPs efficiently enhanced specific IgG and neutralizing antibodies against all four serotypes of DENV. Moreover, vaccination with monovalent or tetravalent VLPs resulted in the induction of specific cytotoxic T cell responses.
Mammalian cell expressed dengue VLPs are capable to induce VLP-specific humoral and cellular immune responses in mice, and being a promising subunit vaccine candidate for prevention of dengue virus infection.
- Dengue virus
Dengue viruses (DENV) are transmitted among humans by mosquitos, such as Aedes aegypti and Aedes albopictus . DENV infection may cause a self-limited febrile illness known as dengue fever (DF), or result in a life-threatening dengue hemorrhagic fever or dengue shock syndrome (DHF/DSS). It has been estimated that 50-100 million cases of DF and 250,000-500,000 cases of DHF occur annually , mainly in tropical and subtropical regions of the world. Dengue viruses, exist as four serotypes, belong to the family of Flaviviridae, genus Flavivirus. The virion contains a positive-sense single-strand RNA genome with a long open reading frame coding for capsid (C), premembrane(prM), and envelope(E) structural proteins, as well as seven non-structural(NS) proteins: NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5.
Because of the widespread geographical distribution and the severe clinical symptoms, dengue vaccine is urgently needed. However, licensed vaccine is not currently available for prevention of DENV infection. One major reason is the phenomenon of antibody dependent-enhancement (ADE), which is known as that a subsequent infection with an alternate serotype can enhance severity of dengue disease . One explanation of this phenomenon is that pre-existing non-neutralizing antibodies may enhance capacity of the new infecting DENV to access FcγR bearing cells. Therefore, DENV infection commonly lacks of antibody cross-protection among serotypes. Various strategies have been used to develop dengue vaccine. The most promising candidates are the live-attenuated tetravalent vaccines of which the clinical trials are in progress [4–7]. One example is the Sanofi Pasteur's dengue vaccine candidate, which is based on a backbone of yellow fever vaccine (YF 17D) replication genes and incorporates the envelope genes of the four dengue virus serotypes, entered its final stage of clinical development in Australia. However, concerns have been raised about interference in virus replication among serotypes . If the replication of four serotypes of vaccine viruses is not balanced, the replication of non-dominant serotypes can be interfered by dominant serotypes, which can result in preferential antibody response to the dominant strains and lead to a risk of developing more serious disease . Thus, an ideal dengue vaccine should induce neutralizing antibody responses against all four serotypes simultaneously and it must be safe to use.
To develop an effective and safe dengue vaccine, we tested the effect of recombinant dengue virus-like particles (VLPs). Virus-like particle vaccine has shown considerable promise as vaccine candidate for many viral diseases [10–13]. VLPs, which are similar to infectious virions in the structural and physicochemical features, are non-infectious particles and have advantages in safety and manufacturing. VLPs can be produced in multiple expression systems such as E.coli, yeast, baculovirus and mammalian cells. Recombinant VLPs can be efficiently taken up, internalized and processed by antigen presenting cells (APCs) , and capable to elicit strong humoral and cellular immune responses against viruses [14–16]. Recombinant VLPs of flaviviruses have been shown to be produced efficiently by co-expressing the prM and E proteins in the absence of C protein [17–19].
In this study, four serotypes of dengue virus-like particles containing recombinant prM and E proteins were generated in mammalian cells, and their immunogenicity was evaluated in BALB/c mice. The results showed that monovalent VLPs of each serotype could stimulate specific IgG and neutralizing antibody against homotypic virus, and tetravalent VLPs could induce specific IgG and neutralizing antibodies against all four serotypes of dengue virus. Moreover, vaccination with monovalent or tetravalent VLPs also resulted in the induction of specific cellular responses. Therefore, dengue VLPs can be a potential vaccine candidate for the prevention of dengue infection.
Cells and viruses
293T cells (ATCC No.CRL-11268) were cultured in Dulbecco's Modified Eagle Medium (DMEM; Gibco) supplemented with 10% heat-inactivated fetal bovine serum (FBS), penicillin (100 U/ml) and streptomycin (100 μg/ml) at 37°C with 5% CO2. C6/36 Aedes albopictus cells (ATCC No.CRL-1660) were grown at 28°C without CO2 in Eagle's Minimum Essential Medium (EMEM; Gibco) supplemented with FBS, penicillin and streptomycin as well.
Each serotype of dengue virus was passaged and propagated in C6/36 cells. The DENV-1 strain GZ01/95 and DENV-2 strain ZS01/01 were supplied by the Department of Microbiology, Zhongshan School of Medicine, Sun Yat-sen University, China. DENV-1 strain Hawaii, DENV-2 strain NGC, DENV-3 strain H87 and DENV-4 strain H241 were preserved by our laboratory. Strain GZ01/95, ZS01/01, H87 and H241 were used for RNA extraction and then VLPs expression plasmids construction while strain Hawaii, NGC, H87 and H241 were used for neutralization analysis. Japanese encephalitis virus (JEV) strain SA14-14-2 was also propagated in C6/36 cells and mainly used for cDNA cloning.
Construction of DENV VLP expression plasmids
The QIAamp Viral RNA Kit (Qiagen, Santa Clarita, CA) was used to extract genomic RNA of DENV1-4 and JEV from 140 μl C6/36 cells culture supernatant infected with each virus. The extracted RNA was subjected to RT using Transcriptor High Fidelity cDNA Synthesis Kit (Roche, Cat. No. 05081955001) to generate cDNA templates for amplification of target genes. The PCR segments were digested with NheI and NotI enzymes and inserted into NheI and NotI sites of pcDNA5/FRT vector.
Transient transfection of 293T cells with DENV VLP expression plasmids
293T cells were prepared in wells of 6-well plates one day earlier and were transfected with pD1-D4prME, pJD1-D4prME or pJD1-D4prMEΔ20%JEV for each well using lipofectamin2000 (Invitrogen, Cat no.11668019) according to instructions supplied by the manufacturer. Briefly, for each plasmid transfection, 8 μl lipofectamin2000 was diluted in 200 μl Opti-MEM (Gibco), and after incubating for 5 min at room temperature the diluted lipofectamin2000 was combined with diluted plasmid DNA (4 μg diluted in 200 μl Opti-MEM). After 20 min's incubation at room temperature, the mixture was added to each well with 80%-90% confluence of 293T cells. 48 hours post-transfection, cells and supernatants were harvested for future use.
Western blot analysis
Concentrated culture supernatants were applied to a NuPAGE 4-12% Bis-Tris gradient gel, and followed by electroblotting onto PVDF membrane. Non-denatured proteins were then probed with E protein specific rabbit polyclonal sera which were produced in our laboratory. A goat anti-rabbit IgG conjugated to HRP was used as the secondary antibody. The reactions were detected by 3,3' diaminobenzidine (DAB) reagent according to the manufacturer's instructions.
Purification of DENV VLPs and virions
For DENV1-4 VLPs purification, 293T cells in T175 flasks were transiently transfected with optimized plasmids of each serotype. The culture supernatants containing extracellular VLPs were harvested routinely every 2 days, continuously repeated 3 times. To purify DENV1-4 virions which were used for electron microscopy and mice immunization, C6/36 cells in T175 flasks were infected with DENV strain Hawaii, NGC, H87 and H241 respectively. At 7 days after infection, the supernatants were harvested and inactivated with 1:2000 β-propionolactone.
Cell supernatants collected from dengue VLPs production cells or dengue virus infected C6/36 cells were clarified by centrifugation at 10 000× g for 30 min followed by concentration using ultrafiltration system Vivaflow 200 (Sartorius stedim biotech). The concentrated culture supernatants were then purified by a two-step ultracentrifugation. The first step was a rate zonal centrifugation. Samples were added on the top of a 15-60% sucrose gradient and ultracentrifuged in a SW41 rotor (Beckman Coulter Inc.) at 38,000 rpm at 4 °C for 4 h. About 1 ml fractions were collected and pelleted by a second ultracentrifugation and then resuspended in PBS. The total protein concentrations of authentic virions and dengue VLPs were determined by Pierce BCA Protein Assay Kit.
Transmission Electron microscopy (TEM)
Purified dengue VLPs and dengue virions from sucrose density-gradient fractions were fixed with 2% glutaraldehyde. Small droplets of fixed samples were placed on copper formvar-coated grids for 1 min, then the grids were stained with sodium phosphotungstate for 1 min (excess samples of each step were removed). At last, the grids were visualized by TEM.
Four to six-week-old female BALB/c mice were purchased from Chinese Academy of Medical Sciences Breeding Laboratories and were intraperitoneally (i.p.) inoculated with monovalent DENV VLPs (100 μg per dose) or a tetravalent combination (25 μg of each serotype per dose) in Freund's complete adjuvant (Sigma) for priming and in Freund's incomplete adjuvant for two times of boosting at an interval of 2 weeks. Equal amount of DENV virions (100 μg for monovalent vaccine and 25 μg of each serotype for tetravalent vaccine) were used as controls with the same regimen. On days 0, 14 and 28, blood samples were collected through tail vein for measurement of serum IgG. At 2 weeks after the last inoculation, mice were sacrificed to collect serum for the neutralizing antibodies assay and separated splenocytes for testing cytotoxic T cell responses.
ELISA to measure serum IgG
VLPs specific serum IgG antibodies were titred by the binding capacity with rEIII protein, a recombinant protein that chimericly expressed DENV1-4 EIII domains in a certain order and previously produced in our laboratory. IgG titers were measured using enzyme-linked immunosorbent assay (ELISA). Briefly, 200 ng purified rEIII per well was coated on 96-well plates at 4°C overnight. Then, the plates were blocked with 5% skimmed milk in PBS for 1 h, and incubated with 2-fold serial diluted serum samples (starting from 1:50) at 37°C for 1 h. Bound IgG was detected by HRP-conjugated goat anti-mouse IgG (Sigma). After addition of 3,3', 3,5'-tetramethylbenzidine (TMB), absorbance was measured at 450 nm. The value which exceeds the mean+2 S.D. of negative control was considered positive.
Antibody neutralization assay
The neutralization ability of serum antibodies against DENV was determined using CPE-determination assays. Briefly, mice sera from all groups were heat-inactivated at 56°C for 30 min, then the sera were two-fold serial diluted from 1:5 to 1:160 in Eagle's medium supplemented with 1% heat-inactivated FBS, penicillin and streptomycin and mixed with 100TCID50 virus. After 1 h incubation at 37°C, 100 μl of virus-serum mixture was inoculated to the confluent monolayer of BHK-21 cells in 96-well plates. Every dilution of each serum was performed in quadruplicate. The plates were then incubated in a CO2 incubator at 37°C for 7 days. The neutralization titer was expressed as the maximum serum dilution at which the CPE of the virus was not observed in all four wells.
Enzyme Linked Immunospot (ELISPOT) Assay
The ELISPOT 96-well plates (BD) were coated with 100 μl of anti-mouse IFN-γ (5 μg/ml in coating buffer) at 4°C overnight. The following day, plates were washed and blocked with blocking solution for 2 h. Then, 100 μl freshly isolated splenocytes (5 × 105 cells) from the immunized mice were added to each well and stimulated with DENV VLPs at 37°C for 40 h. After cells were washed out, biotinylated anti-mouse IFN-γ was added to each well and incubated for 2 h at room temperature. Thereafter, the plates were washed and incubated for 1 h at room temperature with streptavidin-HRP. Finally, AEC substrate solution (BD) was added and spots were counted by ImmunoSpot® Analyzer (Cellular Technology Ltd.).
Statistical comparisons among groups were analyzed by one way ANOVA using SPSS 11.5. A P value less than 0.05 was considered statistically significant.
Production of DENV VLPs
To optimize the production of DENV VLPs, three types of expression plasmids encoding prM and E glycoproteins were constructed for each serotype (Figure 1A). E and prM proteins were chosen as two subunits of recombinant VLPs, because the former one constitutes the spikes on DENV membrane surface and is known as the major protective antigen of DENV to induce neutralizing antibodies, and the latter one is also embedded in the viral envelop and contributes to the stability of E protein. To test the secretion of DENV VLPs from transient transfected 293T cells, culture supernatants of 293T cells were collected and identified by western blot analysis for E protein expression (Figure 1B). Cells transfected with pD1-D4prME plasmids that express full length of prM and E proteins could express intracellular proteins (data not shown). However, due to the lack of signal sequence, they could not secret VLPs into tissue culture. When adding a JEV signal sequence at the N-terminal of full length of prM and E genes, cells transfected with expression plasmid pJD1prME could effectively secret VLPs, but cells transfected with pJD2-D4prME still could not secret VLPs. When both carrying a N-terminal JEV signal sequence and replacing C-terminal 20% regions of DENV E gene with the corresponding region of JEV E gene, all four constructs, pJD1-D4prMEΔ20%JEV, could secrete VLPs into tissue culture. Therefore, we chose pJD1prME and pJD2-D4prMEΔ20%JEV to express recombinant DENV1 and DENV2-4 VLPs in 293T cells, respectively.
DENV VLPs elicited virus specific IgG and neutralizing antibodies
The results that monovalent dengue VLPs could efficiently enhance specific IgG and develop neutralization antibodies, suggested that the tetravalent formulation of DENV VLPs, which was constituting of four types of DENV VLPs at equal amount, might be capable to stimulate neutralizing antibodies against all four serotypes of DENV. As generating balanced neutralizing antibodies to each serotype of a tetravalent dengue vaccine is desired for its safety and efficacy, a tetravalent dengue VLPs combination was applied to BALB/c mice for all priming and boosting immunizations as the regimen used for monovalent VLPs vaccination. Tetravalent dengue virions and PBS were again used as controls. The serum samples collected at Day 14, 28, and 42 post the initial tetravalent VLPs vaccination, were analyzed for rEIII specific IgG antibodies. The data showed that tetravalent virions could stimulate IgG antibodies against rEIII protein. Intriguingly, tetravalent VLPs could even achieved to a higher level than tetravalent virions could induce (Figure 3E). Moreover, neutralizing antibodies stimulated by tetravalent VLPs exhibited simultaneous blocking of DENV1-4 infections, and the blocking effect was comparable to tetravalent formula of virions (Figure 4B).
Therefore, similar as DENV virions, both monovalent and tetravalent formula of DENV VLPs could effectively induce virus specific IgG and produce high titer of protective neutralizing antibodies in vaccinated mice.
DENV VLPs induced virus-specific T cell responses
Despite many years of efforts, an effective dengue vaccine has not been developed. Various strategies have been applied to develop dengue vaccine, such as attenuated [22, 23], subunit [24, 25], chimeric [26, 27], and DNA [1, 28] vaccines. Previous studies have shown that co-expressed prM and E proteins of dengue virus could produce VLPs in mammalian cells, but the VLPs expression plasmids were often used as DNA vaccine [17, 20, 29]. Here we studied on recombinant dengue VLP vaccine as a new candidate. VLPs are similar to infectious virions in both structural and biochemical properties but are non-replicating and free of genome. Therefore, due to their preserved immunogenicity in native forms and better safety, VLPs have been used in many vaccine researches for prevention of viral diseases .
In order to optimize the production of dengue VLPs, three types of expression plasmids were constructed. The indirect fluorescent antibody (IFA) assay showed all constructs could express intracellular VLPs (data not shown). However, the western blot analysis of culturing supernatant showed that, pD1-D4prME constructs without signal peptide could not secret dengue VLPs. And except for pJD1prME, the constructs simply adding a JEV signal sequence could not secret dengue VLPs. All constructs which replaced the carboxy-terminal 20% of DENV E protein with corresponding JEV E protein could secret VLPs into cell culturing supernatant. Based on data from these express plasmids, pJD1prME and pJD2-D4prMEΔ20%JEV were identified as optimized VLP formation constructs for each DENV serotype. These data from different express plasmids indicated that i) signal peptide was one of the most important factors that influence downstream protein translocation and topology, thus dictating correct processing of dengue virus prM and E proteins by the host encoded signalase and endopeptidase . ii) the transmembrane domain of dengue E protein contains a strong ER retention signal [30, 31], replacement of the carboxy-terminal 20% of DENV E protein with the corresponding region of JEV provides extracellular secretion of DENV2-4 VLPs, but does not produce additional benefit to promote extracellular secretion of DENV-1 VLPs.
This was different from previous studies [29, 32], which showed that 20% JEV sequence replacement was absolutely necessary for DENV-1 and DENV-2 VLPs secretion; DENV-3 plasmids containing either the full-length DENV-3 E protein gene or the 20% JEV sequence replacement secreted VLPs to similar levels; Whereas DENV-4 VLPs were secreted to high levels by plasmids containing the full-length DENV-4 E protein gene but not by the chimeric plasmid containing 20% JEV E replacement. Considering that dengue viruses of different serotypes or even among different strains of the same type, their biological characteristics were not the same, thus it is essential to use different strategies when constructed dengue VLPs expression plasmids. As dengue particle assembly and secretion is influenced by interaction of prM and E , we inferred that the chimeric E (80%DENV and 20%JEV) of DENV2-4 could interact with DENV2-4 prM, which help to stabilize the interaction between prM and E and lead to efficient secretion of VLPs. As for DENV-1 (strain GZ01/95), its prM and E domains might interact stably enough, and the replacement of 20% C-terminal region of E would not improve more on this interaction, therefore DENV-1 VLPs showed similar secret pattern between pJD1prME and pJD1prMEΔ20%JEV plasmids.
The immunogenicity of dengue VLPs was evaluated using BALB/c mice. The analysis of humoral immune responses revealed that dengue VLPs, in either monovalent or tetravalent formula, induced high levels of rEIII-specific IgG. Because dengue virus-induced neutralizing antibodies can bind to virus and prevent virus from binding to host cell receptors, therefore inducing neutralizing antibodies is particularly important to block virus entry into target cells . In this study, either the monovalent or the tetravalent formula of dengue VLPs could efficiently trigger in vivo development of neutralizing antibodies. Furthermore, the tetravalent formula of VLPs was able to simultaneously induce balanced neutralizing antibodies against all four serotypes. All these results confirmed that all four serotypes of DENV VLPs prepared in this study preserved the antigenicity of prM and E proteins.
One of the marked advantages of VLPs is their ability to induce cellular immunity [34, 35]. Since IFN-γ constitutes a major mediator of the Th1 cell-mediated immune response and has been shown to play a key role in antiviral activity against dengue , in our study, cellular immune responses were assessed by IFN-γ releasing ability of VLPs-stimulated spleen cells. Spleen cells from mice vaccinated with dengue VLPs and virions produced comparable levels of IFN-γ after in vitro stimulation with dengue VLPs.
In conclusion, by optimizing the expression plasmids, we successfully generated recombinant DENV1-4 VLPs in mammalian cells. Furthermore, the vaccination effect of VLPs in mice showed that either monovalent or tetravalent formula of dengue VLPs could efficiently elicit virus specific humoral and cellular immune responses. These results supplied evidence that VLP vaccine may serve as a promising strategy for dengue vaccine development.
This work was supported by the grants (2006AA02A223) from National key projects of "863" High Technology R&D, Chinese Ministry of Science and Technology, and National Key Programs for Infectious Diseases, Ministry of Health.
- Ramanathan MP, Kuo YC, Selling BH, et al.: Development of a novel DNA SynCon™ tetravalent dengue vaccine that elicitsimmune responses against four serotypes. Vaccine 2009, 27: 6444-53. 10.1016/j.vaccine.2009.06.061View ArticlePubMedGoogle Scholar
- Centers for Disease Control and Prevention (CDC) DoV-bID-DF[http://cdc.gov/ncidod/dvbid/dengue]
- Chambers TJ, Hahn CS, Galler R, et al.: Flavivirus genome organization, expression, and replication. Ann Rev Microbiol 1990, 44: 649-88. 10.1146/annurev.mi.44.100190.003245View ArticleGoogle Scholar
- Sabchareon A, Lang J, Chanthavanich P, et al.: Safety and immunogenicity of tetravalent live-attenuated dengue vaccines in Thai adult volunteers: role of serotype concentration, ratio, and multiple doses. Am J Trop Med Hyg 2002, 66: 264-72.PubMedGoogle Scholar
- Sabchareon A, Lang J, Chanthavanich P, et al.: Safety and immunogenicity of a three dose regimen of two tetravalent live-attenuated dengue vaccines in five- to twelve-year-old Thai children. Pediatr Infect Dis J 2004, 23: 99-109. 10.1097/01.inf.0000109289.55856.27View ArticlePubMedGoogle Scholar
- Edelman R, Wasserman SS, Bodison SA, et al.: Phase I trial of 16 formulations of a tetravalent live-attenuated dengue vaccine. Am J Trop Med Hyg 2003, 69: 48-60.PubMedGoogle Scholar
- Innis BL, Eckels KH: Progress in development of a live-attenuated, tetravalent dengue virus vaccine by the United States Army Medical Research and Materiel Command. Am J Trop Med Hyg 2003, 69: 1-4.PubMedGoogle Scholar
- Imoto Jun-ichi, Konishi Eiji: Dengue tetravalent DNA vaccine increases its immunogenicity in mice when mixed with a dengue type 2 subunit vaccine or an inactivated Japanese encephalitis vaccine. Vaccine 2007, 25: 1076-84. 10.1016/j.vaccine.2006.09.059View ArticlePubMedGoogle Scholar
- Webster DanielP, Farrar Jeremy, Rowland-Jones Sarah: Progress towards a dengue vaccine. The Lancet Infectious Diseases 2009, 9: 678-87. 10.1016/S1473-3099(09)70254-3View ArticlePubMedGoogle Scholar
- Galarza JM, Latham T, Cupo A: Virus-like particle (VLP) vaccine conferred complete protection against a lethal influenza virus challenge. Viral Immunol 2005,18(1):244-51. 10.1089/vim.2005.18.244View ArticlePubMedGoogle Scholar
- Li C, Liu F, Liang M, Zhang Q, et al.: Hantavirus-like particles generated in CHO cells induce specific immune responses in C57BL/6 mice. Vaccine 2010, 28: 4294-4300. 10.1016/j.vaccine.2010.04.025View ArticlePubMedGoogle Scholar
- Weber J, Cheinsong-Popov R, Callow D, et al.: Immunogenicity of the yeast recombinant p17/p24:Ty virus-like particles (p24-VLP) in healthy volunteers. Vaccine 1995, 13: 831-4. 10.1016/0264-410X(94)00061-QView ArticlePubMedGoogle Scholar
- Sedlik C, Saron M, Sarraseca J, et al.: Recombinant parvovirus-like particles as an antigen carrier: a novel nonreplicative exogenous antigen to elicit protective antiviral cytotoxic T cells. Proc Natl Acad Sci USA 1997, 94: 7503-8. 10.1073/pnas.94.14.7503PubMed CentralView ArticlePubMedGoogle Scholar
- Murata K, Lechmann M, Qiao M, et al.: Immunization with hepatitis C virus-like particles protects mice from recombinant hepatitis C virus-vaccinia infection. Proc Natl Acad Sci USA 2003, 100: 6753-8. 10.1073/pnas.1131929100PubMed CentralView ArticlePubMedGoogle Scholar
- Pinto , Ligia A, Castle , et al.: HPV-16 L1 VLP vaccine elicits a broad-spectrum of cytokine responses in whole blood. Vaccine 2005, 23: 3555-64. 10.1016/j.vaccine.2005.01.146View ArticlePubMedGoogle Scholar
- Akahata Wataru, Yang Zhi-Yong, Andersen Hanne, et al.: A virus-like particle vaccine for epidemic Chikungunya virus protects nonhuman primates against infection. Nature Medicine 2010, 16: 334-8. 10.1038/nm.2105PubMed CentralView ArticlePubMedGoogle Scholar
- Chang GJ, Davis BS, Hunt AR, et al.: Flavivirus DNA vaccines: current status and potential. Ann NY Acad Sci 2001, 951: 272-85.View ArticlePubMedGoogle Scholar
- Putnak R, Porter K, Schmaljohn C: DNA vaccines for flaviviruses. Adv Virus Res 2003, 61: 445-68.View ArticlePubMedGoogle Scholar
- Lindenbach BD, Rice CM: Flaviviridae: the viruses and their replication. In Fields Virology. 4th edition. Edited by: Knipe DM, Howley PM. Philadelphia: Lippincott Williams & Willkins; 2001:991-1041.Google Scholar
- Chang GJ, Hunt AR, Davis B: A single intramuscular injection of recombinant plasmid DNA induces protective immunity and prevents Japanese encephalitis in mice. J Virol 2000, 74: 4244-52. 10.1128/JVI.74.9.4244-4252.2000PubMed CentralView ArticlePubMedGoogle Scholar
- Lobigs Mario, Lee Eva: Inefficient Signalase Cleavage Promotes Efficient Nucleocapsid Incorporation into Budding Flavivirus Membranes. J Virol 2004, 78: 178-86. 10.1128/JVI.78.1.178-186.2004PubMed CentralView ArticlePubMedGoogle Scholar
- Hoke CH Jr, Malinoski FJ, Eckels KH, et al.: Preparation of an attenuated dengue 4 (341750 Carib) virus vaccine. II. Safety and immunogenicity in humans. Am J Trop Med Hyg 1990, 43: 219-26.PubMedGoogle Scholar
- Edelman R, Tacket CO, Wasserman SS, et al.: A live attenuated dengue-1 vaccine candidate (45AZ5) passaged in primary dog kidney cell culture is attenuated and immunogenic for humans. J Infect Dis 1994, 170: 1448-55. 10.1093/infdis/170.6.1448View ArticlePubMedGoogle Scholar
- Staropoli I, Frenkiel MP, Megret F, et al.: Affinity-purified dengue-2 virus envelope glycoprotein induces neutralizing antibodies and protective immunity in mice. Vaccine 1997, 15: 1946-54. 10.1016/S0264-410X(97)00128-XView ArticlePubMedGoogle Scholar
- Simmons M, Nelson WM, Wu SJ, et al.: Evaluation of the protective efficacy of a recombinant dengue envelope B domain fusion protein against dengue 2 virus infection in mice. Am J Trop Med Hyg 1998, 58: 655-62.PubMedGoogle Scholar
- Bray M, Men R, Lai CJ: Monkeys immunized with intertypic chimeric dengue viruses are protected against wild-type virus challenge. J Virol 1996, 70: 4162-6.PubMed CentralPubMedGoogle Scholar
- Pletnev AG, Men R: Attenuation of the Langat tick-borne flavivirus by chimerization with mosquito-borne flavivirus dengue type 4. Proc Natl Acad Sci USA 1998, 95: 1746-51. 10.1073/pnas.95.4.1746PubMed CentralView ArticlePubMedGoogle Scholar
- Kochel T, Wu SJ, Raviprakash K, et al.: Inoculation of plasmids expressing the dengue-2 envelope gene elicit neutralizing antibodies in mice. Vaccine 1997, 15: 547-52. 10.1016/S0264-410X(97)00215-6View ArticlePubMedGoogle Scholar
- Chang GJ, Hunt AR, Holmes DA, et al.: Enhancing biosynthesis and secretion of premembrane and envelope proteins by the chimeric plasmid of dengue virus type 2 and Japanese encephalitis virus. Virology 2003, 306: 170-80. 10.1016/S0042-6822(02)00028-4View ArticlePubMedGoogle Scholar
- Hsieh SC, Liu IJ, King CC, et al.: A strong endoplasmic reticulum retention signal in the stem-anchor region of envelope glycoprotein of dengue virus type 2 affects the production of virus-like particles Virology. 2008,374(2):338-50.Google Scholar
- Hsieh SC, Tsai WY, Wang WK: The length of and nonhydrophobic residues in the transmembrane domain of dengue virus envelope protein are critical for its retention and assembly in the endoplasmic reticulum. J Virol 2010, 84: 4782-97. 10.1128/JVI.01963-09PubMed CentralView ArticlePubMedGoogle Scholar
- Purdy DE, Chang GJ: Secretion of noninfectious dengue virus-like particles and identification of amino acids in the stem region involved in intracellular retention of envelope protein. Virology 2005, 333: 239-250. 10.1016/j.virol.2004.12.036View ArticlePubMedGoogle Scholar
- Babu J Pradeep, Pattnaik1 Priyabrata, Gupta Nimesh, et al.: Immunogenicity of a recombinant envelope domain III protein of dengue virus type-4 with various adjuvants in mice. Vaccine 2008, 26: 4655-63. 10.1016/j.vaccine.2008.07.006View ArticlePubMedGoogle Scholar
- Schirmbeck R, Melber K, Kuhrober A, et al.: Immunization with soluble hepatitis B virus surface protein elicits murine H-2 class I-restricted CD8+ cytotoxic T lymphocyte responses in vivo. J Immunol 1994, 152: 1110-9.PubMedGoogle Scholar
- Greenstone HL, Nieland JD, de Visser KE, et al.: Chimeric papillomavirus virus-like particles elicit antitumor immunity against the E7 oncoprotein in an HPV16 tumor model. Proc Natl Acad Sci USA 1998,95(4):1800-5. 10.1073/pnas.95.4.1800PubMed CentralView ArticlePubMedGoogle Scholar
- Valdés I, Bernardo L, Gil L, et al.: A novel fusion protein domain III-capsid from dengue-2, in a highly aggregated form, induces a functional immune response and protection in mice. Virology 2009, 394: 249-58. 10.1016/j.virol.2009.08.029View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.