The cleavages at the junctions of the flavivirus nonstructural (NS) proteins NS2A/NS2B, NS2B/NS3, NS3/NS4A, and NS4B/NS5 share an amino acid sequence motif and are presumably catalyzed by a virus-encoded protease. We constructed recombinant vaccinia viruses expressing various portions of the NS region of the dengue virus type 4 polyprotein. By analyzing immune precipitates of 35S-labeled lysates of recombinant virus-infected cells, we could monitor the NS2A/NS2B, NS2B/NS3, and NS3/NS4A cleavages. A polyprotein composed of NS2A, NS2B, and the N-terminal 184 amino acids of NS3 was cleaved at the NS2A/NS2B and NS2B/NS3 junctions, whereas a similar polyprotein containing only the first 77 amino acids of NS3 was not cleaved. This finding is consistent with the proposal that the N-terminal 180 amino acids of NS3 constitute a protease domain. Polyproteins containing NS2A and NS3 with large in-frame deletions of NS2B were not cleaved at the NS2A/NS2B or NS2B/NS3 junctions. Coinfection with a recombinant expressing NS2B complemented these NS2B deletions for NS2B/NS3 cleavage and probably also for NS2A/NS2B cleavage. Thus, NS2B is also required for the NS2A/NS2B and NS2B/NS3 cleavages and can act in trans. Other experiments showed that NS2B was needed, apparently in cis, for NS3/NS4A cleavage and for a series of internal cleavages in NS3. Indirect evidence that NS3 can also act in trans was obtained. Models are discussed for a two-component protease activity requiring both NS2B and NS3.
antibody-dependent enhancement ͉ nonhuman primate model ͉ Fc mutations ͉ cross-reactive mAb T he four dengue virus (DENV) serotypes (DENV-1 to DENV-4) are the most important arthropod-borne flaviviruses in terms of morbidity and geographic distribution. Up to 100 million DENV infections occur every year, mostly in tropical and subtropical areas where vector mosquitoes are abundant (1). Infection with any of the DENV serotypes may be asymptomatic or may lead to classic dengue fever or more severe dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS), which are increasingly common in the dengue endemic areas. Immunity to the same virus serotype (homotypic immunity) is life-long, whereas immunity to different serotypes (heterotypic immunity) lasts 2-3 months so that infection with a different serotype virus is possible (2). DHF/DSS often occurs in patients with second, heterotypic DENV infections or in infants with maternally transferred dengue immunity (3, 4). Severe dengue is a major cause of hospitalization, and fatality rates vary from Ͻ1% to 5% in children.Antibody-dependent enhancement (ADE) has been proposed as an underlying pathogenic mechanism of DHF/DSS (3). ADE occurs because preexisting subneutralizing antibodies and the infecting DENV form complexes that bind to Fc receptorbearing cells, leading to increased virus uptake and replication (4). ADE has been repeatedly demonstrated in vitro using dengue immune sera or monoclonal antibodies and cells of monocytic and recently, B lymphocytic lineages bearing Fc receptors (5-7). ADE of DENV-2 infection has also been demonstrated in monkeys infused with a human dengue immune serum (8).Infection with DENV or any other flavivirus induces broadly cross-reactive but weak or nonneutralizing antibodies (9, 10). These antibodies remain detectable for a long period and rise rapidly during a subsequent heterotypic infection as a result of an anamnestic response. A major subset of these cross-reactive antibodies is directed to immuno-dominant epitopes involving determinants mapped to the flavivirus-conserved fusion peptide in the envelope glycoprotein (E) (11-13). The functional activities of these cross-reactive antibodies are not well characterized.We have identified chimpanzee-human chimeric IgG1 mAbs capable of neutralizing or binding to one or more DENV serotypes (14, 15). Cross-reactive IgG 1A5 neutralizes DENV-1 and DENV-2 more efficiently than DENV-3 and DENV-4, and type-specific IgG 5H2 neutralizes DENV-4 at a high titer (14,15). Analysis of antigenic variants has localized the IgG 1A5 binding site to the conserved fusion peptide in E (11). Thus, IgG 1A5 shares many characteristics with the cross-reactive antibodies detected in flavivirus infections.We investigated the ability of IgG 1A5 to mediate enhancement of DENV replication in monocyte-derived cell lines and in juvenile rhesus monkeys after passive transfer. We also explored strategies to reduce ADE by mutational analysis of the key structures in the Fc of IgG 1A5. A 9-aa deletion at the N termin...
Abstract. The recombinant dengue virus type-4 vaccine candidate 2A⌬30 was attenuated in rhesus monkeys due to an engineered 30-nucleotide deletion in the 3Ј-untranslated region of the viral genome. A clinical trial to evaluate the safety and immunogenicity of a single dose of 2A⌬30 was conducted with 20 adult human volunteers. The vaccine candidate was well tolerated and did not cause systemic illness in any of the 20 volunteers. Viremia was detectable in 14 volunteers at a mean level of 1.6 log 10 plaque-forming units/ml of serum, although all 20 volunteers seroconverted with a seven-fold or greater increase in serum neutralizing antibody titer on day 28 post-vaccination (mean titer ϭ 1:580). A mild, asymptomatic, macular rash developed in 10 volunteers, and a transient elevation in the serum level of alanine aminotransferase was noted in five volunteers. The low level of reactogenicity and high degree of immunogenicity of this vaccine candidate warrant its further evaluation and its use to create chimeric vaccine viruses expressing the structural genes of dengue virus types 1, 2, and 3.
RNA segment 7 of the influenza A virus genome codes for at least two proteins, M1 and M2, which are synthesized from separate mRNA species. Sequence analysis of the M2 mRNA has shown that it contains an interrupted sequence of 689 nucleotides. The =51 virus-specific nucleotides comprising the 5'-end leader sequence of the M2 mRNA are the same as those found at the 5' end of the colinear M1 mRNA. Following the leader sequence of the M2 mRNA, where is a 271-nucleotide body region that is 3' coterminal with the M1 mRNA. Another small potential mRNA (mRNA3) related to RNA segment 7 has been found. mRNA3 has a leader sequence of =11 virus-specific nucleotides that are the same as the 5' end ofthe M1 and M2 mRNAs, followed by an interrupted sequence of 729 nucleotides, and then a body region of -271 nucleotides that is the same as that of the M2 mRNA. The nucleotide sequences found at the junctions of the interrupted sequences in M2 mRNA and mRNA3 are similar to those found at the splicing points of intervening sequences in eukaryotic mRNAs. In addition, both mRNAs contain 10-15 heterogeneous nonviral nucleotides at their 5' ends that appear to be derived from cellular RNAs used for priming the transcription of viral RNAs. Because the 5'-end sequences of the Ml mRNA and the M2 mRNA are the same and share the 5'-proximal initiation codon for protein synthesis, the first nine amino acids would be the same in the M1 and M2 protein and then the sequences would diverge. The =271-nucleotide body region of the M2 mRNA can be translated in the + 1 reading frame, and the sequence indicates that M1 and M2 overlap by 14 amino acids. The coding potential of the mRNA3 is for only nine amino acids, and these would be identical to the COOH-terminal region of the membrane protein (M1). We report here the results of experiments designed to determine the precise 5'-terminal nucleotides of the M2 mRNA, to demonstrate directly that translation of the M2 mRNA could occur in the second open frame, and to investigate whether the M2 mRNA was analogous to the NS2 mRNA in having an interrupted region.
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