Epstein-Barr Virus Genome Deletions in Epstein-Barr Virus-Positive T/NK Cell Lymphoproliferative Diseases.

The main target cells for Epstein-Barr virus (EBV) infection and persistence are B lymphocytes, although T and NK cells can also become infected. In this paper, we characterize the EBV present in 21 pediatric and adult patients who were treated in France for a range of diseases that involve infection of T or NK cells. Of these 21 cases, 5 pediatric patients (21%) and 11 adult patients (52%) were of Caucasian origin. In about 30% of the cases, some of the EBV genomes contain a large deletion. The deletions are different in every patient but tend to cluster near the BART region of the viral genome. Detailed investigation of a family in which several members have persistent T or NK cell infection by EBV indicates that the virus genome deletions arise or are selected independently in each individual patient. Genome sequence polymorphisms in the EBV in these T or NK cell diseases reflect the geographic origin of the patient and not a distinct type of EBV (the 21 cases studied included examples of both type 1 and type 2 EBV infection). Using virus produced from type 1 or type 2 EBV genomes cloned in bacterial artificial chromosome (BAC) vectors, we demonstrate infection of T cells in cord blood from healthy donors. Our results are consistent with transient infection of some T cells being part of normal asymptomatic infection by EBV in young children. IMPORTANCE EBV contributes to several types of human cancer. Some cancers and nonmalignant lymphoproliferative diseases involving T or NK cells contain EBV. These diseases are relatively frequent in Japan and China and have been shown sometimes to have deletions in the EBV genome in the disease cells. We identify further examples of deletions within the EBV genome associated with T or NK cell diseases, and we provide evidence that the virus genomes with these deletions are most likely selected in the individual cases, rather than being transmitted between people during infection. We demonstrate EBV infection of cord blood T cells by highly characterized, cloned EBV genomes and suggest that transient infection of T cells may be part of normal asymptomatic infection by EBV in young children.

The epitope arrangement on flavivirus particles contributes to Mab C10's extraordinary neutralization breadth across Zika and dengue viruses.

The human monoclonal antibody C10 exhibits extraordinary cross-reactivity, potently neutralizing Zika virus (ZIKV) and the four serotypes of dengue virus (DENV1-DENV4). Here we describe a comparative structure-function analysis of C10 bound to the envelope (E) protein dimers of the five viruses it neutralizes. We demonstrate that the C10 Fab has high affinity for ZIKV and DENV1 but not for DENV2, DENV3, and DENV4. We further show that the C10 interaction with the latter viruses requires an E protein conformational landscape that limits binding to only one of the three independent epitopes per virion. This limited affinity is nevertheless counterbalanced by the particle's icosahedral organization, which allows two different dimers to be reached by both Fab arms of a C10 immunoglobulin. The epitopes' geometric distribution thus confers C10 its exceptional neutralization breadth. Our results highlight the importance not only of paratope/epitope complementarity but also the topological distribution for epitope-focused vaccine design.

A protective Zika virus E-dimer-based subunit vaccine engineered to abrogate antibody-dependent enhancement of dengue infection.

Infections with dengue virus (DENV) and Zika virus (ZIKV) can induce cross-reactive antibody responses. Two immunodominant epitopes-one to precursor membrane protein and one to the fusion loop epitope on envelope (E) protein-are recognized by cross-reactive antibodies1-3 that are not only poorly neutralizing, but can also promote increased viral replication and disease severity via Fcγ receptor-mediated infection of myeloid cells-a process termed antibody-dependent enhancement (ADE)1,4,5. ADE is a significant concern for both ZIKV and DENV vaccines as the induction of poorly neutralizing cross-reactive antibodies may prime an individual for ADE on natural infection. In this report, we describe the design and production of covalently stabilized ZIKV E dimers, which lack precursor membrane protein and do not expose the immunodominant fusion loop epitope. Immunization of mice with ZIKV E dimers induces dimer-specific antibodies, which protect against ZIKV challenge during pregnancy. Importantly, the ZIKV E-dimer-induced response does not cross-react with DENV or induce ADE of DENV infection.

Human antibodies to the dengue virus E-dimer epitope have therapeutic activity against Zika virus infection.

The Zika virus (ZIKV) epidemic has resulted in congenital abnormalities in fetuses and neonates. Although some cross-reactive dengue virus (DENV)-specific antibodies can enhance ZIKV infection in mice, those recognizing the DENV E-dimer epitope (EDE) can neutralize ZIKV infection in cell culture. We evaluated the therapeutic activity of human monoclonal antibodies to DENV EDE for their ability to control ZIKV infection in the brains, testes, placentas, and fetuses of mice. A single dose of the EDE1-B10 antibody given 3 d after ZIKV infection protected against lethality, reduced ZIKV levels in brains and testes, and preserved sperm counts. In pregnant mice, wild-type or engineered LALA variants of EDE1-B10, which cannot engage Fcg receptors, diminished ZIKV burden in maternal and fetal tissues, and protected against fetal demise. Because neutralizing antibodies to EDE have therapeutic potential against ZIKV, in addition to their established inhibitory effects against DENV, it may be possible to develop therapies that control disease caused by both viruses.

Covalently linked dengue virus envelope glycoprotein dimers reduce exposure of the immunodominant fusion loop epitope.

A problem in the search for an efficient vaccine against dengue virus is the immunodominance of the fusion loop epitope (FLE), a segment of the envelope protein E that is buried at the interface of the E dimers coating mature viral particles. Anti-FLE antibodies are broadly cross-reactive but poorly neutralizing, displaying a strong infection enhancing potential. FLE exposure takes place via dynamic 'breathing' of E dimers at the virion surface. In contrast, antibodies targeting the E dimer epitope (EDE), readily exposed at the E dimer interface over the region of the conserved fusion loop, are very potent and broadly neutralizing. We here engineer E dimers locked by inter-subunit disulfide bonds, and show by X-ray crystallography and by binding to a panel of human antibodies that these engineered dimers do not expose the FLE, while retaining the EDE exposure. These locked dimers are strong immunogen candidates for a next-generation vaccine.

Dengue virus sero-cross-reactivity drives antibody-dependent enhancement of infection with zika virus.

Zika virus (ZIKV) was discovered in 1947 and was thought to lead to relatively mild disease. The recent explosive outbreak of ZIKV in South America has led to widespread concern, with reports of neurological sequelae ranging from Guillain Barré syndrome to microcephaly. ZIKV infection has occurred in areas previously exposed to dengue virus (DENV), a flavivirus closely related to ZIKV. Here we investigated the serological cross-reaction between the two viruses. Plasma immune to DENV showed substantial cross-reaction to ZIKV and was able to drive antibody-dependent enhancement (ADE) of ZIKV infection. Using a panel of human monoclonal antibodies (mAbs) to DENV, we showed that most antibodies that reacted to DENV envelope protein also reacted to ZIKV. Antibodies to linear epitopes, including the immunodominant fusion-loop epitope, were able to bind ZIKV but were unable to neutralize the virus and instead promoted ADE. Our data indicate that immunity to DENV might drive greater ZIKV replication and have clear implications for disease pathogenesis and future vaccine programs for ZIKV and DENV.

Recognition determinants of broadly neutralizing human antibodies against dengue viruses.

Dengue disease is caused by four different flavivirus serotypes, which infect 390 million people yearly with 25% symptomatic cases and for which no licensed vaccine is available. Recent phase III vaccine trials showed partial protection, and in particular no protection for dengue virus serotype 2 (refs 3, 4). Structural studies so far have characterized only epitopes recognized by serotype-specific human antibodies. We recently isolated human antibodies potently neutralizing all four dengue virus serotypes. Here we describe the X-ray structures of four of these broadly neutralizing antibodies in complex with the envelope glycoprotein E from dengue virus serotype 2, revealing that the recognition determinants are at a serotype-invariant site at the E-dimer interface, including the exposed main chain of the E fusion loop and the two conserved glycan chains. This 'E-dimer-dependent epitope' is also the binding site for the viral glycoprotein prM during virus maturation in the secretory pathway of the infected cell, explaining its conservation across serotypes and highlighting an Achilles' heel of the virus with respect to antibody neutralization. These findings will be instrumental for devising novel immunogens to protect simultaneously against all four serotypes of dengue virus.

A new class of highly potent, broadly neutralizing antibodies isolated from viremic patients infected with dengue virus.

Dengue is a rapidly emerging, mosquito-borne viral infection, with an estimated 400 million infections occurring annually. To gain insight into dengue immunity, we characterized 145 human monoclonal antibodies (mAbs) and identified a previously unknown epitope, the envelope dimer epitope (EDE), that bridges two envelope protein subunits that make up the 90 repeating dimers on the mature virion. The mAbs to EDE were broadly reactive across the dengue serocomplex and fully neutralized virus produced in either insect cells or primary human cells, with 50% neutralization in the low picomolar range. Our results provide a path to a subunit vaccine against dengue virus and have implications for the design and monitoring of future vaccine trials in which the induction of antibody to the EDE should be prioritized.

Structural analysis of a dengue cross-reactive antibody complexed with envelope domain III reveals the molecular basis of cross-reactivity.

Dengue virus infections are still increasing at an alarming rate in tropical and subtropical countries, underlying the need for a dengue vaccine. Although it is relatively easy to generate Ab responses to dengue virus, low avidity or low concentrations of Ab may enhance infection of FcR-bearing cells with clinical impact, posing a challenge to vaccine production. In this article, we report the characterization of a mAb, 2H12, which is cross-reactive to all four serotypes in the dengue virus group. Crystal structures of 2H12-Fab in complex with domain III of the envelope protein from three dengue serotypes have been determined. 2H12 binds to the highly conserved AB loop of domain III of the envelope protein that is poorly accessible in the mature virion. 2H12 neutralization varied between dengue serotypes and strains; in particular, dengue serotype 2 was not neutralized. Because the 2H12-binding epitope was conserved, this variation in neutralization highlights differences between dengue serotypes and suggests that significant conformational changes in the virus must take place for Ab binding. Surprisingly, 2H12 facilitated little or no enhancement of infection. These data provide a structural basis for understanding Ab neutralization and enhancement of infection, which is crucial for the development of future dengue vaccines.

Cell death gene expression profile: role of RIPK2 in dengue virus-mediated apoptosis.

Dengue virus (DENV) is a major emerging arthropod-borne pathogen, which infects individuals in both subtropical and tropical regions. Patients with DENV infection exhibit evidence of hepatocyte injury. However, the mechanisms of hepatocyte injury are unclear. Therefore we examined the expression of cell death genes during DENV-infection of HepG2 cells using real-time PCR arrays. The expression changes were consistent with activation of apoptosis and autophagy. Expression of the up-regulated genes, including RIPK2, HRK, TGF-ß, PERK, and LC3B, was confirmed by quantitative real-time PCR. RIPK2 belongs to the receptor-interacting protein family of serine/threonine protein kinases, which is a crucial mediator of multiple stress responses that leads to the activation of caspase, NF-κB and MAP kinases including JNK and p38. RIPK2 activity is inhibited by the p38 MAPK pathway inhibitor SB203580. The effect of SB203580 on RIPK2 expression and DENV-induced apoptosis was tested in DENV-infected HepG2 cells. The inhibition of RIPK2 expression by SB203580 significantly reduced apoptosis. SB203580 also significantly reduced DENV capsid protein (DENVC)-mediated apoptosis. Suppression of endogenous RIPK2 in DENV-infected HepG2 cells by small interfering RNA (siRNA) significantly decreased apoptosis suggesting for the first time that RIPK2 plays a role in DENV-mediated apoptosis.

Interaction of dengue virus envelope protein with endoplasmic reticulum-resident chaperones facilitates dengue virus production.

Dengue virus infection is an important mosquito-borne disease and a public health problem worldwide. A better understanding of interactions between human cellular host and dengue virus proteins will provide insight into dengue virus replication and cellular pathogenesis. The glycosylated envelope protein of dengue virus, DENV E, is processed in the endoplasmic reticulum of host cells and therefore reliant on host processing functions. The complement of host ER functions involved and nature of the interactions with DENV E has not been thoroughly investigated. By employing a yeast two-hybrid assay, we found that domain III of DENV E interacts with human immunoglobulin heavy chain binding protein (BiP). The relevance of this interaction was demonstrated by co-immunoprecipitation and co-localization of BiP and DENV E in dengue virus-infected cells. Using the same approach, association of DENV E with two other chaperones, calnexin and calreticulin was also observed. Knocking-down expression of BiP, calnexin, or calreticulin by siRNA significantly decreased the production of infectious dengue virions. These results indicate that the interaction of these three chaperones with DENV E plays an important role in virion production, likely facilitating proper folding and assembly of dengue proteins.

Sensitization to Fas-mediated apoptosis by dengue virus capsid protein.

Dengue fever (DF) and dengue hemorrhagic fever (DHF) are important public health problems in tropical regions. Abnormal hemostasis and plasma leakage are the main patho-physiological changes in DHF. However, hepatomegaly, hepatocellular necrosis and fulminant hepatic failure are occasionally observed in patients with DHF. Dengue virus-infected liver cells undergo apoptosis but the underlying molecular mechanism remains unclear. Using a yeast two-hybrid screen, we found that dengue virus capsid protein (DENV C) physically interacts with the human death domain-associated protein Daxx, a Fas-associated protein. The interaction between DENV C and Daxx in dengue virus-infected liver cells was also demonstrated by co-immunoprecipitation and double immunofluorescence staining. The two proteins were predominantly co-localized in the cellular nuclei. Fas-mediated apoptotic activity in liver cells constitutively expressing DENV C was induced by anti-Fas antibody, indicating that the interaction of DENV C and Daxx involves in apoptosis of dengue virus-infected liver cells.