[Show abstract][Hide abstract] ABSTRACT: Using an infectious cDNA clone we engineered seven mutations in the putative heparan sulfate- and receptor-binding motifs of the envelope protein of dengue virus serotype 2, strain 16681. Four mutant viruses, KK122/123EE, E202K, G304K, and KKK305/307/310EEE, were recovered following transfection of C6/36 cells. A fifth mutant, KK291/295EE, was recovered from C6/36 cells with a compensatory E295V mutation. All mutants grew in and mediated fusion of virus-infected C6/36 cells, but three of the mutants, KK122/123EE, E202K, G304K, did not grow in Vero cells without further modification. Two Vero cell lethal mutants, KK291/295EV and KKK307/307/310EEE, failed to replicate in DC-SIGN-transformed Raji cells and did not react with monoclonal antibodies known to block DENV attachment to Vero cells. Additionally, both mutants were unable to initiate negative-strand vRNA synthesis in Vero cells by 72h post-infection, suggesting that the replication block occurred prior to virus-mediated membrane fusion.
[Show abstract][Hide abstract] ABSTRACT: Humans develop polyclonal, serotype-specific neutralizing antibody responses after dengue virus (DENV) infection. Many mouse antibodies that neutralize DENV bind to the lateral ridge or A strand epitopes on domain III of the viral envelope (EDIII) protein. It has been assumed that these epitopes are also the main target of human neutralizing antibodies. Using recombinant dengue serotype 2 viruses with altered EDIII epitopes, we demonstrate that EDIII epitopes are not the main target of human neutralizing antibody.
Journal of Virology 01/2012; 86(7):4019-23. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Japanese encephalitis virus (JEV) is a human pathogenic, mosquito-borne flavivirus that is endemic/epidemic in Asia. JEV is rarely detected or isolated from blood or cerebrospinal fluid (CSF), and detection of IgM is generally diagnostic of the infection. The flavivirus nonstructural glycoprotein NS1 is released transiently during flavivirus replication. The aim of this study was to set up a quantitative JEV NS1 antigen capture assay. A soluble hexameric form of JEV NS1 protein was produced in a stable Drosophila S2 cell clone and purified from supernatant fluids. Two IgG1 monoclonal antibodies (MAbs) with high affinity against two different epitopes of JEV NS1 antigen were used to develop an antigen-capture assay with a limit of detection of 0.2ngml(-1) NS1. Up to 1μgml(-1) JEV NS1 protein was released in supernatants of mammalian cells infected with JEV but <10ngml(-1) was released in sera of virus-infected mice before the onset of encephalitis and death. Moreover, NS1 protein was detected at low levels (<10ngml(-1)) in 23.8% of sera and in 10.5% of CSF of patients diagnosed as IgM-positive for JEV. This quantitative test of NS1 protein is proposed for highly specific diagnosis of acute infection with JEV genotypes I to IV.
Journal of virological methods 06/2011; 179(1):8-16. · 2.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fifteen mutant dengue viruses were engineered and used to identify AAs in the molecular hinge of the envelope protein that are critical to viral infection. Substitutions at Q52, A54, or E133 reduced infectivity in mammalian cells and altered the pH threshold of fusion. Mutations at F193, G266, I270, or G281 affected viral replication in mammalian and mosquito cells, but only I270W had reduced fusion activity. T280Y affected the pH threshold for fusion and reduced replication in C6/36 cells. Three different mutations at L135 were lethal in mammalian cells. Among them, L135G abrogated fusion and reduced replication in C6/36 cells, but only slightly reduced the mosquito infection rate. Conversely, L135W replicated well in C6/36 cells, but had the lowest mosquito infection rate. Possible interactions between hinge residues 52 and 277, or among 53, 135, 170, 186, 265, and 276 required for hinge function were discovered by sequence analysis to identify compensatory mutations.
[Show abstract][Hide abstract] ABSTRACT: The FG extended loop in domain III of the dengue virus type 2 (DENV2) envelope protein is postulated to be a molecular determinant for host cell infectivity. To determine the contribution of the FG loop to virus infectivity, an infectious cDNA clone of DENV2 was manipulated by deleting amino acids in the loop (VEPGΔ) to mimic tick-borne flaviviruses or by substituting these AAs with RGD or RGDK/S to mimic motifs present in other mosquito-borne flaviviruses. We found the FG loop to be dispensable for infection of C6/36 cells but critical for infection of Aedes aegypti mosquito midguts and mammalian cells. All the FG loop mutants were able to bind to and enter mammalian cells but replication of VEPGΔ in Vero cells at 37 °C was delayed until acquisition of secondary mutations. Reduced binding of DENV2 type-specific monoclonal antibody 3H5 to mutant viruses confirmed the FG loop motif as its target epitope.
[Show abstract][Hide abstract] ABSTRACT: The flaviviral envelope (E) protein directs virus-mediated membrane fusion. To investigate membrane fusion as a requirement for virus growth, we introduced 27 unique mutations into the fusion peptide of an infectious cDNA clone of dengue 2 virus and recovered seven stable mutant viruses. The fusion efficiency of the mutants was impaired, demonstrating for the first time the requirement for specific FP AAs in optimal fusion. Mutant viruses exhibited different growth kinetics and/or genetic stabilities in different cell types and adult mosquitoes. Virus particles could be recovered following RNA transfection of cells with four lethal mutants; however, recovered viruses could not re-infect cells. These viruses could enter cells, but internalized virus appeared to be retained in endosomal compartments of infected cells, thus suggesting a fusion blockade. Mutations of the FP also resulted in reduced virus reactivity with flavivirus group-reactive antibodies, confirming earlier reports using virus-like particles.
[Show abstract][Hide abstract] ABSTRACT: The genetic stabilities of the three attenuation loci of the candidate dengue 2 (D2) PDK-53 vaccine virus were evaluated for the PDK-53 virus and PDK-53-vectored chimeric D2/1, D2/3, and D2/4 viruses following 10 sequential passages in Vero cells. Sequencing revealed that the dominant NS1-53-Asp and the NS3-250-Val attenuation loci were extremely stable, whereas reversion occurred at the 5'NCR-57-U locus in 10 of the 18 viral lineages tested. A more sensitive and quantitative assay, the TaqMan mismatch amplification mutation assay (TaqMAMA), was employed to more finely discriminate the level of reversion at the 5'NCR-57 locus. This rapid genetic assay permitted detection of <or=1% reversion of 5'NCR-57 U-to-C in viral populations. By TaqMAMA, various levels of reversion at 5'NCR-57 were detected in all 18 of the PDK-53-based viral lineages tested at Vero passage 10, but only 3 lineages had reversion levels>80% in the viral population. Chimeric viruses based on the PDK-53-V (all three mutations present) genetic background were more stable than those developed in the PDK-53-E (5'NCR and NS1 mutations present) background. The TaqMAMA can be applied in quality control analyses to ensure that attenuated vaccine seeds contain undetectable or minimal levels of reversion at a given attenuation locus.
Journal of Virological Methods 01/2006; 131(1):1-9. · 1.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Attenuation markers of the candidate dengue 2 (D2) PDK-53 vaccine virus are encoded by mutations that reside outside of the structural gene region of the genome. We engineered nine dengue virus chimeras containing the premembrane (prM) and envelope (E) genes of wild-type D1 16007, D3 16562, or D4 1036 virus within the genetic backgrounds of wild-type D2 16681 virus and the two genetic variants (PDK53-E and PDK53-V) of the D2 PDK-53 vaccine virus. Expression of the heterologous prM-E genes in the genetic backgrounds of the two D2 PDK-53 variants, but not that of wild-type D2 16681 virus, resulted in chimeric viruses that retained PDK-53 characteristic phenotypic markers of attenuation, including small plaque size and temperature sensitivity in LLC-MK(2) cells, limited replication in C6/36 cells, and lack of neurovirulence in newborn ICR mice. Chimeric D2/1, D2/3, and D2/4 viruses replicated efficiently in Vero cells and were immunogenic in AG129 mice. Chimeric D2/1 viruses protected adult AG129 mice against lethal D1 virus challenge. Two tetravalent virus formulations, comprised of either PDK53-E- or PDK53-V-vectored viruses, elicited neutralizing antibody titers in mice against all four dengue serotypes. These antibody titers were similar to the titers elicited by monovalent immunizations, suggesting that viral interference did not occur in recipients of the tetravalent formulations. The results of this study demonstrate that the unique attenuation loci of D2 PDK-53 virus make it an attractive vector for the development of live attenuated flavivirus vaccines.
Journal of Virology 12/2003; 77(21):11436-47. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: With the ability to colonize in the guts of a broad range of mosquito larvae, Bacillus cereus Cx5 has a potential to be utilized as a new host cell for the production of mosquito-larvicidal toxins aimed for mosquito control. However, the presence of one single (entFM) and two triple (hblCDA and nheABC) enterotoxin genes were previously confirmed in strain Cx5, raising concerns in its immediate use in the environment. Cx5 cells indeed showed recognizable levels of haemolytic and Vero cell cytotoxic activities. In this study, the single enterotoxin gene in B. cereus Cx5 (entCx5) has been inactivated in order to study the relationship between the presence of this gene and the cytotoxic and haemolytic activities found in the strain. We constructed a gene disruption plasmid, pTentCx5TV2, harbouring a truncated entCx5 gene in the temperature-sensitive shuttle vector, pUCTV2. After introducing the plasmid into B. cereus Cx5, we found that the plasmid was integrated via single crossover into the chromosome as expected at the entCx5 locus, disrupting the gene. Analysis of one mutant strain revealed that Vero cell cytotoxicity and haemolytic activity of the mutant were dramatically decreased compared to that of the wild type strain. This indicates an involvement of the entCx5 gene in haemolytic and Vero cell cytotoxic activities. The results also imply that there is a high possibility to generate an effective, and safe, host cell based on B. cereus Cx5 for the production of mosquito-larvicidal toxin.
World Journal of Microbiology and Biotechnology 01/2003; 19(8):831-837. · 1.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Chimeric dengue type 2/type 1 (DEN2/1) viruses, which contain the structural genes of the dengue-1 (16007) parental virus and the nonstructural genes of the DEN2-PDK53 virus, have been constructed. These DEN2/1 viruses induce high levels of DEN1 virus-specific neutralizing antibodies in mice. In this study, the DEN2/1 viruses induced DEN1 virus-specific neutralizing antibodies without the development of viremia in cynomolgus monkeys. Dengue virus-specific IgM antibodies were detected in the sera of the immunized animals as early as 3 days post-immunization. After challenge with the DEN1-16007 wild-type virus, only a low level of viremia was detected in chimeric DEN2/1 virus-immunized monkeys. A second challenge, with DEN2-16681 virus, was given while the levels of DEN2-specific neutralizing antibodies were very low: infectious Dengue 2 virus could not be detected in sera of the monkeys. A correlation between the level of neutralizing antibody and the incidence of viremia could not be found. In addition, there was no significant increase in the levels of interferon gamma and soluble interleukin 2 receptor in the sera of the challenged monkeys, which suggests a reduction in immunopathogenesis caused by T-cell activation. Our findings suggest that DEN2/1 viruses may used as a live-attenuated candidate vaccine because of their safety, broad immunogenicity, and lower immunopathogenicity.
The Southeast Asian journal of tropical medicine and public health 10/2002; 33(3):589-99. · 0.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The genome of a candidate dengue type 2 (DEN-2) vaccine virus, strain PDK-53, differs from its DEN-2 16681 parent by nine nucleotides. Using infectious cDNA clones, we constructed 18 recombinant 16681/PDK-53 viruses to analyze four 16681-to-PDK-53 mutations, including 5' noncoding region (5'NC)-57 C-to-T, premembrane (prM)-29 Asp-to-Val (the only mutation that occurs in the structural proteins), nonstructural protein 1 (NS1)-53 Gly-to-Asp, and NS3-250 Glu-to-Val. The viruses were studied for plaque size, growth rate, and temperature sensitivity in LLC-MK(2) cells, growth rate in C6/36 cells, and neurovirulence in newborn mice. All of the viruses replicated to peak titers of 10(7.3) PFU/ml or greater in LLC-MK(2) cells. The crippled replication of PDK-53 virus in C6/36 cells and its attenuation for mice were determined primarily by the 5'NC-57-T and NS1-53-Asp mutations. The temperature sensitivity of PDK-53 virus was attributed to the NS1-53-Asp and NS3-250-Val mutations. The 5'NC-57, NS1-53, and NS3-250 loci all contributed to the small-plaque phenotype of PDK-53 virus. Reversions at two or three of these loci in PDK-53 virus were required to reconstitute the phenotypic characteristics of the parental 16681 virus. The prM-29 locus had little or no effect on viral phenotype. Sequence analyses showed that PDK-53 virus is genetically identical to PDK-45 virus. Restriction of the three major genetic determinants of attenuation markers to nonstructural genomic regions makes the PDK-53 virus genotype attractive for the development of chimeric DEN virus vaccine candidates.
Journal of Virology 05/2000; 74(7):3011-9. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We constructed chimeric dengue type 2/type 1 (DEN-2/DEN-1) viruses containing the nonstructural genes of DEN-2 16681 virus or its vaccine derivative, strain PDK-53, and the structural genes (encoding capsid protein, premembrane protein, and envelope glycoprotein) of DEN-1 16007 virus or its vaccine derivative, strain PDK-13. We previously reported that attenuation markers of DEN-2 PDK-53 virus were encoded by genetic loci located outside the structural gene region of the PDK-53 virus genome. Chimeric viruses containing the nonstructural genes of DEN-2 PDK-53 virus and the structural genes of the parental DEN-1 16007 virus retained the attenuation markers of small plaque size and temperature sensitivity in LLC-MK(2) cells, less efficient replication in C6/36 cells, and attenuation for mice. These chimeric viruses elicited higher mouse neutralizing antibody titers against DEN-1 virus than did the candidate DEN-1 PDK-13 vaccine virus or chimeric DEN-2/DEN-1 viruses containing the structural genes of the PDK-13 virus. Mutations in the envelope protein of DEN-1 PDK-13 virus affected in vitro phenotype and immunogenicity in mice. The current PDK-13 vaccine is the least efficient of the four Mahidol candidate DEN virus vaccines in human trials. The chimeric DEN-2/DEN-1 virus might be a potential DEN-1 virus vaccine candidate. This study indicated that the infectious clones derived from the candidate DEN-2 PDK-53 vaccine are promising attenuated vectors for development of chimeric flavivirus vaccines.
Journal of Virology 05/2000; 74(7):3020-8. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: of the viruses replicated to peak titers of 107.3 PFU/ml or greater in LLC-MK2 cells. The crippled replication of PDK-53 virus in C6/36 cells and its attenuation for mice were determined primarily by the 5*NC-57-T and NS1-53-Asp mutations. The temperature sensitivity of PDK-53 virus was attributed to the NS1-53-Asp and NS3-250-Val mutations. The 5*NC-57, NS1-53, and NS3-250 loci all contributed to the small-plaque phenotype of PDK-53 virus. Reversions at two or three of these loci in PDK-53 virus were required to reconstitute the phenotypic characteristics of the parental 16681 virus. The prM-29 locus had little or no effect on viral phenotype. Sequence analyses showed that PDK-53 virus is genetically identical to PDK-45 virus. Restriction of the three major genetic determinants of attenuation markers to nonstructural genomic regions makes the PDK-53 virus genotype attractive for the development of chimeric DEN virus vaccine candidates.
Journal of Virology 04/2000; 74(7):3011-3019. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The neutralization of Japanese encephalitis virus (JEV) was studied using JEV-specific neutralizing (NT) monoclonal antibody (MAb) 503 that recognizes the envelope glycoprotein. Analysis using radiolabeled JEV and observations by confocal laser microscopy and electron microscopy indicated that the NT and protection activities of MAb 503 did not result from the prevention of the first step of JEV infection, binding of virus to the cell surface. Treatment with MAb 503 strongly inhibited JEV-induced cell fusion and internalization of JEV into the cells, and resulted in enhanced release of JEV-RNA from the cells. These observations suggested that the NT activity of MAb 503 is involved in the later steps of JEV infection.
The American journal of tropical medicine and hygiene 05/1998; 58(4):389-98. · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We identified nine nucleotide differences between the genomes of dengue-2 (DEN-2) 16681 virus and its vaccine derivative, strain PDK-53. These included a C-to-T (16681-to-PDK-53) mutation at nucleotide position 57 of the 5'-untranslated region, three silent mutations, and substitutions prM-29 Asp to Val, NS1-53 Gly to Asp, NS2A-181 Leu to Phe, NS3-250 Glu to Val, and NS4A-75 Gly to Ala. Unpassaged PDK-53 vaccine contained two genetic variants as a result of partial mutation at NS3-250. We constructed infectious cDNA clones for 16681 virus and each of the two PDK-53 variants. DEN-2 16681 clone-derived viruses were identical to the 16681 virus in plaque size and replication in LLC-MK2 cells, replication in C6/36 cells, E and prM epitopes, and neurovirulence for suckling mice. PDK-53 virus and both clone-derived PDK-53 variants were attenuated in mice. However, the variant containing NS3-250-Glu was less temperature sensitive and replicated better in C6/36 cells than did PDK-53 virus. The variant containing NS3-250-Val had smaller, more diffuse plaques, decreased replication, and increased temperature sensitivity in LLC-MK2 cells relative to PDK-53 virus. Both PDK-53 virus and the NS3-250-Val variant replicated poorly in C6/36 cells relative to 16681 virus. Unpassaged PDK-53 vaccine virus and the virus passaged once in LLC-MK2 cells had genomes of identical sequence, including the mixed NS3-250-Glu/Val locus. Although the NS3-250-Val mutation clearly affected virus replication in vitro, it was not a major determinant of attenuation for PDK-53 virus in suckling mice.