Mechanism of differential Zika and dengue virus neutralization by a public antibody lineage targeting the DIII lateral ridge

Neutralizing antibodies to block viral entry and for identification of entry inhibitors

Neutralizing antibodies (NAbs) are naturally produced by our immune system to combat viral infections. Clinically, neutralizing antibodies with potent efficacy and high specificity have been extensively used to prevent and treat a wide variety of viral infections, including Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), Human Immunodeficiency Virus (HIV), Dengue Virus (DENV) and Hepatitis B Virus (HBV). An overwhelmingly large subset of clinically effective NAbs operates by targeting viral envelope proteins to inhibit viral entry into the host cell. Binding of viral envelope protein to the host receptor is a critical rate limiting step triggering a cascade of downstream events, including endocytosis, membrane fusion and pore formation to allow viral entry. In recent years, improved structural knowledge on these processes have allowed researchers to also leverage NAbs as an indispensable tool in guiding discovery of novel antiviral entry inhibitors, providing drug candidates with high efficacy and pan-genus specificity. This review will summarize the latest progresses on the applications of NAbs as effective entry inhibitors and as important tools to develop antiviral therapeutics by high-throughput drug screenings, rational design of peptidic entry inhibitor mimicking NAbs and in silico computational modeling approaches.

Antibodies from dengue patients with prior exposure to Japanese encephalitis virus are broadly neutralizing against Zika virus

Exposure to multiple mosquito-borne flaviviruses within a lifetime is not uncommon; however, how sequential exposures to different flaviviruses shape the cross-reactive humoral response against an antigen from a different serocomplex has yet to be explored. Here, we report that dengue-infected individuals initially primed with the Japanese encephalitis virus (JEV) showed broad, highly neutralizing potencies against Zika virus (ZIKV). We also identified a rare class of ZIKV-cross-reactive human monoclonal antibodies with increased somatic hypermutation and broad neutralization against multiple flaviviruses. One huMAb, K8b, binds quaternary epitopes with heavy and light chains separately interacting with overlapping envelope protein dimer units spanning domains I, II, and III through cryo-electron microscopy and structure-based mutagenesis. JEV virus-like particle immunization in mice further confirmed that such cross-reactive antibodies, mainly IgG3 isotype, can be induced and proliferate through heterologous dengue virus (DENV) serotype 2 virus-like particle stimulation. Our findings highlight the role of prior immunity in JEV and DENV in shaping the breadth of humoral response and provide insights for future vaccination strategies in flavivirus-endemic countries.

Application of germline antibody features to vaccine development, antibody discovery, antibody optimization and disease diagnosis

Although the efficacy and commercial success of vaccines and therapeutic antibodies have been tremendous, designing and discovering new drug candidates remains a labor-, time- and cost-intensive endeavor with high risks. The main challenges of vaccine development are inducing a strong immune response in broad populations and providing effective prevention against a group of highly variable pathogens. Meanwhile, antibody discovery faces several great obstacles, especially the blindness in antibody screening and the unpredictability of the developability and druggability of antibody drugs. These challenges are largely due to poorly understanding of germline antibodies and the antibody responses to pathogen invasions. Thanks to the recent developments in high-throughput sequencing and structural biology, we have gained insight into the germline immunoglobulin (Ig) genes and germline antibodies and then the germline antibody features associated with antigens and disease manifestation. In this review, we firstly outline the broad associations between germline antibodies and antigens. Moreover, we comprehensively review the recent applications of antigen-specific germline antibody features, physicochemical properties-associated germline antibody features, and disease manifestation-associated germline antibody features on vaccine development, antibody discovery, antibody optimization, and disease diagnosis. Lastly, we discuss the bottlenecks and perspectives of current and potential applications of germline antibody features in the biotechnology field.

Impact of structural dynamics on biological functions of flaviviruses

Flaviviruses comprise a number of mosquito- or tick-transmitted human pathogens of global public health importance. Advances in structural biology techniques have contributed substantially to our current understanding of the life cycle of these small enveloped RNA viruses and led to deep insights into details of virus assembly, maturation and cell entry. In addition to large-scale conformational changes and oligomeric rearrangements of envelope proteins during these processes, there is increasing evidence that smaller-scale protein dynamics (referred to as virus "breathing") can confer extra flexibility to these viruses for the fine-tuning of their interactions with the immune system and possibly with cellular factors they encounter in their complex ecological cycles in arthropod and vertebrate hosts. In this review, we discuss how work with tick-borne encephalitis virus has extended our view on flavivirus breathing, leading to the identification of a novel mechanism of antibody-mediated infection enhancement and demonstrating breathing intermediates of the envelope protein in the process of membrane fusion. These data are discussed in the context of other flaviviruses and the perspective of a potential role of virus breathing to cope with the requirements of adaptation and replication in evolutionarily very different hosts.

Serological cross-reactivity among common flaviviruses

The Flavivirus genus is made up of viruses that are either mosquito-borne or tick-borne and other viruses transmitted by unknown vectors. Flaviviruses present a significant threat to global health and infect up to 400 million of people annually. As the climate continues to change throughout the world, these viruses have become prominent infections, with increasing number of infections being detected beyond tropical borders. These include dengue virus (DENV), West Nile virus (WNV), Japanese encephalitis virus (JEV), and Zika virus (ZIKV). Several highly conserved epitopes of flaviviruses had been identified and reported to interact with antibodies, which lead to cross-reactivity results. The major interest of this review paper is mainly focused on the serological cross-reactivity between DENV serotypes, ZIKV, WNV, and JEV. Direct and molecular techniques are required in the diagnosis of Flavivirus-associated human disease. In this review, the serological assays such as neutralization tests, enzyme-linked immunosorbent assay, hemagglutination-inhibition test, Western blot test, and immunofluorescence test will be discussed. Serological assays that have been developed are able to detect different immunoglobulin isotypes (IgM, IgG, and IgA); however, it is challenging when interpreting the serological results due to the broad antigenic cross-reactivity of antibodies to these viruses. However, the neutralization tests are still considered as the gold standard to differentiate these flaviviruses.

Zika virus-like particle vaccine fusion loop mutation increases production yield but fails to protect AG129 mice against Zika virus challenge

Zika virus (ZIKV) is a mosquito-borne flavivirus with maternal infection associated with preterm birth, congenital malformations, and fetal death, and adult infection associated with Guillain-Barré syndrome. Recent widespread endemic transmission of ZIKV and the potential for future outbreaks necessitate the development of an effective vaccine. We developed a ZIKV vaccine candidate based on virus-like-particles (VLPs) generated following transfection of mammalian HEK293T cells using a plasmid encoding the pre-membrane/membrane (prM/M) and envelope (E) structural protein genes. VLPs were collected from cell culture supernatant and purified by column chromatography with yields of approximately 1-2mg/L. To promote increased particle yields, a single amino acid change of phenylalanine to alanine was made in the E fusion loop at position 108 (F108A) of the lead VLP vaccine candidate. This mutation resulted in a modest 2-fold increase in F108A VLP production with no detectable prM processing by furin to a mature particle, in contrast to the lead candidate (parent). To evaluate immunogenicity and efficacy, AG129 mice were immunized with a dose titration of either the immature F108A or lead VLP (each alum adjuvanted). The resulting VLP-specific binding antibody (Ab) levels were comparable. However, geometric mean neutralizing Ab (nAb) titers using a recombinant ZIKV reporter were significantly lower with F108A immunization compared to lead. After virus challenge, all lead VLP-immunized groups showed a significant 3- to 4-Log₁₀ reduction in mean ZIKV RNAemia levels compared with control mice immunized only with alum, but the RNAemia reduction of 0.5 Log₁₀ for F108A groups was statistically similar to the control. Successful viral control by the lead VLP candidate following challenge supports further vaccine development for this candidate. Notably, nAb titer levels in the lead, but not F108A, VLP-immunized mice inversely correlated with RNAemia. Further evaluation of sera by an in vitro Ab-dependent enhancement assay demonstrated that the F108A VLP-induced immune sera had a significantly higher capacity to promote ZIKV infection in FcγR-expressing cells. These data indicate that a single amino acid change in the fusion loop resulted in increased VLP yields but that the immature F108A particles were significantly diminished in their capacity to induce nAbs and provide protection against ZIKV challenge.

Zika virus (ZIKV) is transmitted by mosquitoes and is a serious health threat due to potential epidemic spread. Infection in adults may lead to Guillain-Barré syndrome, a neurological disorder, or may cause harm to a developing fetus resulting in preterm birth, fetal death, or devastating congenital malformations. There are currently no approved vaccines against ZIKV. We previously developed a lead candidate vaccine based on a virus-like particle (VLP) that was generated in tissue culture. This ZIKV shell is devoid of any viral genetic material. In previous studies, this lead VLP candidate generated neutralizing antibodies (nAbs) that recognized wild-type ZIKV and prevented viral replication in both mice and non-human primates. To increase production of the lead VLP candidate and decrease cost-of-goods, we introduced a single amino acid change, phenylalanine to alanine, in the envelope glycoprotein. This change resulted in a modest increase in VLP yield. However, this single amino acid change resulted in reduced induction of nAbs following immunization and no significant reduction of RNAemia following challenge compared to the lead candidate. The results of this study suggest this investigational vaccine candidate is not suitable for further vaccine development and that ZIKV VLP maturation may have an important role in protection.

A Small-Plaque Isolate of the Zika Virus with Envelope Domain III Mutations Affect Viral Entry and Replication in Mammalian but Not Mosquito Cells

An Asian Zika virus (ZIKV) isolated from a Thai patient that was serially passaged in Primary Dog Kidney (PDK) cells for attenuation displayed both big and small plaque-forming viruses by the 7th passage. Two small-plaque isolates were selected and purified for characterization as attenuated ZIKV candidates. In vitro growth kinetics showed significantly reduced titers for small-plaque isolates in Vero cells early post-infection compared to the parental ZIKV and a big-plaque isolate, but no significant difference was observed in C6/36 cells. Viral entry experiments elucidate that titer reduction likely occurred due to the diminished entry capabilities of a small-plaque isolate. Additionally, a small-plaque isolate displayed lowered neurovirulence in newborn mice compared to 100% lethality from infection with the parental ZIKV. Genomic analysis revealed the same three unique non-synonymous mutations for both small-plaque isolates: two on the envelope (E) protein at residues 310, alanine to glutamic acid (A310E), and 393, glutamic acid to lysine (E393K), and one on residue 355 of NS3, histidine to tyrosine (H355Y). Three-dimensional (3D) mapping suggests that the E protein mutations located on the receptor-binding and fusion domain III likely affect cell entry, tropism, and virulence. These ZIKV isolates and genotypic markers will be beneficial for vaccine development.

How Antibodies Recognize Pathogenic Viruses: Structural Correlates of Antibody Neutralization of HIV-1, SARS-CoV-2, and Zika

The H1N1 pandemic of 2009-2010, MERS epidemic of 2012, Ebola epidemics of 2013-2016 and 2018-2020, Zika epidemic of 2015-2016, and COVID-19 pandemic of 2019-2021, are recent examples in the long history of epidemics that demonstrate the enormous global impact of viral infection. The rapid development of safe and effective vaccines and therapeutics has proven vital to reducing morbidity and mortality from newly emerging viruses. Structural biology methods can be used to determine how antibodies elicited during infection or vaccination target viral proteins and identify viral epitopes that correlate with potent neutralization. Here we review how structural and molecular biology approaches have contributed to our understanding of antibody recognition of pathogenic viruses, specifically HIV-1, SARS-CoV-2, and Zika. Determining structural correlates of neutralization of viruses has guided the design of vaccines, monoclonal antibodies, and small molecule inhibitors in response to the global threat of viral epidemics.

The key amino acids of E protein involved in early flavivirus infection: viral entry

Flaviviruses are enveloped viruses that infect multiple hosts. Envelope proteins are the outermost proteins in the structure of flaviviruses and mediate viral infection. Studies indicate that flaviviruses mainly use envelope proteins to bind to cell attachment receptors and endocytic receptors for the entry step. Here, we present current findings regarding key envelope protein amino acids that participate in the flavivirus early infection process. Among these sites, most are located in special positions of the protein structure, such as the α-helix in the stem region and the hinge region between domains I and II, motifs that potentially affect the interaction between different domains. Some of these sites are located in positions involved in conformational changes in envelope proteins. In summary, we summarize and discuss the key envelope protein residues that affect the entry process of flaviviruses, including the process of their discovery and the mechanisms that affect early infection.

Substitutions at Loop Regions of TMUV E Protein Domain III Differentially Impair Viral Entry and Assembly

Flavivirus envelope protein (E) plays an important role in cellular infection, especially in virulence and antigenicity. E domain III of Tembusu virus (TMUV) is highly conserved among flaviviruses and contains four loop regions. However, the functions of the loop regions of TMUV E domain III in the viral life cycle have not yet been discovered. In this study, using a reverse genetics system, we performed site-directed mutagenesis on loops I, II, III, and IV of TMUV E domain III. Mutant 6 (S388A.G389A.K390A) showed better proliferation than the wild-type virus, while mutants 1-5 exhibited decreased in vitro infectivity, as determined by immunofluorescence assay (IFA). Based on a TMUV replicon system, the mutations exhibited no apparent effect on TMUV RNA replication. Subcellular fractionation assays and packaging system assays indicated that mutations in loops II-IV (T332A, T332S, S365A.S366A.T367A, and S388A.G389A.K390A, respectively) disrupted virion assembly. Moreover, loops I-IV played an important role in virus binding and entry, while mutant 6 (S388A.G389A.K390A) exhibited robust activity in virus entry. Taken together, our findings indicated the critical role of the loop regions in TMUV E domain III in the virus entry and assembly process.

Broadly neutralizing monoclonal antibodies protect against multiple tick-borne flaviviruses

Although Powassan virus (POWV) is an emerging tick-transmitted flavivirus that causes severe or fatal neuroinvasive disease in humans, medical countermeasures have not yet been developed. Here, we developed a panel of neutralizing anti-POWV mAbs recognizing six distinct antigenic sites. The most potent of these mAbs bind sites within domain II or III of the envelope (E) protein and inhibit postattachment viral entry steps. A subset of these mAbs cross-react with other flaviviruses. Both POWV type-specific and cross-reactive neutralizing mAbs confer protection in mice against POWV infection when given as prophylaxis or postexposure therapy. Several cross-reactive mAbs mapping to either domain II or III also protect in vivo against heterologous tick-transmitted flaviviruses including Langat and tick-borne encephalitis virus. Our experiments define structural and functional correlates of antibody protection against POWV infection and identify epitopes targeted by broadly neutralizing antibodies with therapeutic potential against multiple tick-borne flaviviruses.

Broad and potent neutralizing human antibodies to tick-borne flaviviruses protect mice from disease

Tick-borne encephalitis virus (TBEV) is an emerging human pathogen that causes potentially fatal disease with no specific treatment. Mouse monoclonal antibodies are protective against TBEV, but little is known about the human antibody response to infection. Here, we report on the human neutralizing antibody response to TBEV in a cohort of infected and vaccinated individuals. Expanded clones of memory B cells expressed closely related anti-envelope domain III (EDIII) antibodies in both groups of volunteers. However, the most potent neutralizing antibodies, with IC50s below 1 ng/ml, were found only in individuals who recovered from natural infection. These antibodies also neutralized other tick-borne flaviviruses, including Langat, louping ill, Omsk hemorrhagic fever, Kyasanur forest disease, and Powassan viruses. Structural analysis revealed a conserved epitope near the lateral ridge of EDIII adjoining the EDI-EDIII hinge region. Prophylactic or early therapeutic antibody administration was effective at low doses in mice that were lethally infected with TBEV.

Potent germline-like monoclonal antibodies: rapid identification of promising candidates for antibody-based antiviral therapy

In recent years, fully human monoclonal antibodies (mAbs) are making up an increasing share of the pharmaceutical market. However, to improve affinity and efficacy of antibodies, many somatic hypermutations could be introduced during affinity maturation, which cause several issues including safety and efficacy and limit their application in clinic. Here, we propose a special class of human mAbs with limited level of somatic mutations, referred to as germline-like mAbs. Remarkably, germline-like mAbs could have high affinity and potent neutralizing activity in vitro and in various animal models, despite lacking of extensive affinity maturation. Furthermore, the germline nature of these mAbs implies that they exhibit lower immunogenicity and can be elicited relatively fast in vivo compared with highly somatically mutated antibodies. In this review, we summarize germline-like mAbs with strong therapeutic and protection activity against various viruses that caused large-scale outbreaks in the last decade, including influenza virus H7N9, Zika virus, Dengue virus, Middle East respiratory syndrome coronavirus and severe acute respiratory syndrome coronavirus 2. We also illustrate underlying molecular mechanisms of these germline-like antibodies against viral infections from the structural and genetic perspective, thus providing insight into further development as therapeutic agents for the treatment of infectious diseases and implication for rational design of effective vaccines.

Landscape of Monoclonal Antibodies Targeting Zika and Dengue: Therapeutic Solutions and Critical Insights for Vaccine Development

The unprecedented 2015-2016 Zika outbreak in the Americas sparked global concern and drove the rapid deployment of vaccine and therapeutic countermeasures against this re-emerging pathogen. Alongside vaccine development, a number of potent neutralizing antibodies against Zika and related flaviviruses have been identified in recent years. High-throughput antibody isolation approaches have contributed to a better understanding of the B cell responses elicited following infection and/or vaccination. Structure-based approaches have illuminated species-specific and cross-protective epitopes of therapeutic value. This review will highlight previously described monoclonal antibodies with the best therapeutic potential against ZIKV and related flaviviruses, and discuss their implications for the rational design of better vaccine strategies.

Two immunogenic recombinant protein vaccine candidates showed disparate protective efficacy against Zika virus infection in rhesus macaques

Zika virus (ZIKV) infection has caused major public health problems recently. To develop subunit vaccines for ZIKV, we have previously constructed recombinant ZIKV envelope protein domain III (EDIII), and the entire ectodomain (E80, which comprises EDI, EDII and EDIII), as vaccine candidates and showed both of them being immunogenic and protective in murine models. In this follow-up study, we compared these vaccine candidates in non-human primates. Both of them elicited neutralizing antibody responses, but only E80 immunization inhibited ZIKV infection in both peripheral blood and monkey tissues, whereas EDIII increased blood ZIKV RNA through possibly antibody-dependent enhancement. Further investigations revealed that the virion-binding antibody response in E80 immunized monkeys persisted longer and stronger than in EDIII immunized monkeys. These results demonstrate that E80 is superior to EDIII as a vaccine candidate, and that the magnitude, quality and durability of virion-binding neutralizing antibodies are correlates of protection.

Hydrogen-deuterium exchange mass spectrometry identifies spatially distinct antibody epitopes on domain III of the Zika virus envelope protein

Zika Virus (ZIKV) has become a global public health concern because it causes fetal microcephaly and other neurological complications in humans. Currently, there are no approved treatments or vaccines for ZIKV infection. We describe here the detailed epitopes for six monoclonal antibodies (mAbs) that bind to domain III of the envelope protein of ZIKV, some of which have therapeutic potential. We show that by using hydrogen-deuterium exchange mass spectrometry (HDX-MS), we can identify three spatially distinct epitopes for the six mAbs investigated. The HDX-MS approach identified epitopes for three mAbs that agreed well with recently reported X-ray crystallography data. The HDX-MS determined epitopes for the other three anti-ZIKV mAbs for which there were no crystal structures, and the epitopes were confirmed by structure-guided mutagenesis and biolayer interferometry (BLI) competition binding assay. Our results have implications for the design of vaccine and antibody therapeutics against ZIKV and demonstrate the use of HDX-MS as a rapid and valid approach for epitope mapping.

Structural Basis of Zika Virus Specific Neutralization in Subsequent Flavivirus Infections

Zika virus (ZIKV), a mosquito-borne human flavivirus that causes microcephaly and other neurological disorders, has been a recent focus for the development of flavivirus vaccines and therapeutics. We report here a 4.0 Å resolution structure of the mature ZIKV in complex with ADI-30056, a ZIKV-specific human monoclonal antibody (hMAb) isolated from a ZIKV infected donor with a prior dengue virus infection. The structure shows that the hMAb interactions span across the E protein dimers on the virus surface, inhibiting conformational changes required for the formation of infectious fusogenic trimers similar to the hMAb, ZIKV-117. Structure-based functional analysis, and structure and sequence comparisons, identified ZIKV residues essential for neutralization and crucial for the evolution of highly potent E protein crosslinking Abs in ZIKV. Thus, this epitope, ZIKV’s “Achilles heel”, defined by the contacts between ZIKV and ADI-30056, could be a suitable target for the design of therapeutic antibodies.

Affinity-Restricted Memory B Cells Dominate Recall Responses to Heterologous Flaviviruses

Memory B cells (MBCs) can respond to heterologous antigens either by molding new specificities through secondary germinal centers (GCs) or by selecting preexisting clones without further affinity maturation. To distinguish these mechanisms in flavivirus infections and immunizations, we studied recall responses to envelope protein domain III (DIII). Conditional deletion of activation-induced cytidine deaminase (AID) between heterologous challenges of West Nile, Japanese encephalitis, Zika, and dengue viruses did not affect recall responses. DIII-specific MBCs were contained mostly within the plasma-cell-biased CD80⁺ subset, and few GCs arose following heterologous boosters, demonstrating that recall responses are confined by preexisting clonal diversity. Measurement of monoclonal antibody (mAb) binding affinity to DIII proteins, timed AID deletion, single-cell RNA sequencing, and lineage tracing experiments point to selection of relatively low-affinity MBCs as a mechanism to promote diversity. Engineering immunogens to avoid this MBC diversity may facilitate flavivirus-type-specific vaccines with minimized potential for infection enhancement.

Protective and enhancing interactions among dengue viruses 1-4 and Zika virus

Dengue viruses 1-4 (DENV 1-4) and Zika virus (ZIKV) are closely related flaviviruses transmitted by Aedes mosquitoes that co-circulate in Asia, the Americas, Africa, and Oceania. Here, we review recent and historical literature on in vitro experiments, animal models, and clinical and epidemiological studies to describe how the sequence of DENV 1-4 and ZIKV infections modulates subsequent dengue and Zika disease outcome. Overall, we find these interactions are asymmetric. Immunity from a prior DENV infection or a prior ZIKV infection can enhance future severe dengue disease for some DENV serotypes while protecting against other serotypes. Further, prior DENV immunity has not been shown to enhance future uncomplicated or severe Zika and instead appears to be protective. Interestingly, secondary ZIKV infection induces type-specific ZIKV immunity but only generates weakly cross-neutralizing anti-DENV/ZIKV immunity, consistent with risk of future dengue disease. In contrast, secondary DENV infection induces strongly cross-neutralizing antibodies that protect against subsequent severe dengue disease. These immunologic interactions may be explained by differences in virion structure between DENV 1-4 and ZIKV, which modulate thermostability, susceptibility to neutralization, and cell infectivity. Overall, these observations are important for the understanding and prediction of epidemics and the development and evaluation of dengue and Zika vaccines.

Mapping the diverse structural landscape of the flavivirus antibody repertoire

Flaviviruses are emerging arthropod-borne RNA viruses, causing a broad spectrum of life-threatening disease symptoms such as encephalitis and hemorrhagic fever. Successful vaccines exist against yellow fever virus, Japanese encephalitis virus and tick-borne encephalitis virus. However, vaccine development against other flaviviruses like dengue virus is not straightforward. This is partly because of the high sequence conservation and immunological cross-reactivity among flavivirus envelope glycoproteins leading to antibody mediated enhancement of disease. A comprehensive analyses of the structural landscape of humoral immune response against flaviviruses is crucial for antigen design. Here, we compare the available structural data of several flavivirus antibody complexes with a major focus on Zika virus and dengue virus and discuss the mapped epitopes, the stoichiometry of antibody binding and mechanisms of neutralization.

Integrated pipeline for the accelerated discovery of antiviral antibody therapeutics

The emergence and re-emergence of highly virulent viral pathogens with pandemic potential creates an urgent need for the accelerated discovery of antiviral therapeutics. Antiviral human monoclonal antibodies (mAbs) are promising candidates to prevent or treat severe viral diseases, but their long development timeframes limit their rapid deployment and use. Here, we report the development of an integrated sequence of technologies, including single-cell mRNA sequence analysis, bioinformatics, synthetic biology and high-throughput functional analysis, that enabled the rapid discovery of highly potent antiviral human mAbs, whose activity we validated in vivo. In a 78-day study modelling the deployment of a rapid response to an outbreak, we isolated more than 100 human mAbs specific for the Zika virus, assessed their function, identified 29 of those as having broadly neutralizing activity, and verified the therapeutic potency of the lead candidates in mice and non-human primate models of infection via the delivery of an antibody-encoding mRNA formulation and of the respective IgG antibody. The pipeline provides a roadmap for rapid antibody-discovery programs against viral pathogens of global concern.

Structural basis for Zika envelope domain III recognition by a germline version of a recurrent neutralizing antibody

Recent epidemics demonstrate the global threat of Zika virus (ZIKV), a flavivirus transmitted by mosquitoes. Although infection is usually asymptomatic or mild, newborns of infected mothers can display severe symptoms, including neurodevelopmental abnormalities and microcephaly. Given the large-scale spread, symptom severity, and lack of treatment or prophylaxis, a safe and effective ZIKV vaccine is urgently needed. However, vaccine design is complicated by concern that elicited antibodies (Abs) may cross-react with other flaviviruses that share a similar envelope protein, such as dengue virus, West Nile virus, and yellow fever virus. This cross-reactivity may worsen symptoms of a subsequent infection through Ab-dependent enhancement. To better understand the neutralizing Ab response and risk of Ab-dependent enhancement, further information on germline Ab binding to ZIKV and the maturation process that gives rise to potently neutralizing Abs is needed. Here we use binding and structural studies to compare mature and inferred-germline Ab binding to envelope protein domain III of ZIKV and other flaviviruses. We show that affinity maturation of the light-chain variable domain is important for strong binding of the recurrent VH3-23/VK1-5 neutralizing Abs to ZIKV envelope protein domain III, and identify interacting residues that contribute to weak, cross-reactive binding to West Nile virus. These findings provide insight into the affinity maturation process and potential cross-reactivity of VH3-23/VK1-5 neutralizing Abs, informing precautions for protein-based vaccines designed to elicit germline versions of neutralizing Abs.

An epidemiological survey of the current status of Zika and the immune interaction between dengue and Zika infection in Southern Taiwan

OBJECTIVES

This study was performed to examine the current status of Zika and the effects of pre-existing dengue immunity on Zika virus (ZIKV) infection in Southern Taiwan.

METHODS

A phylogenetic tree was used to analyze the phylogeny of detected ZIKVs. Paired sera from dengue patients were collected for the determination of dengue and Zika infection. Plaque reduction neutralization tests (PRNT) and quantitative reverse transcription PCR (qRT-PCR) were used to determine the titers of neutralizing antibodies and viruses, respectively. An antibody-dependent enhancement (ADE) assay was used to evaluate the effect of anti-dengue antibodies on ZIKV infection.

RESULTS

Epidemiological data indicated the continuous importation of ZIKV infection from neighboring Zika epidemic countries into Taiwan. A total of 78 dengue patients were enrolled and 21 paired serum samples were obtained. PRNT₉₀ results for the 21 samples identified eight cases of primary dengue infection and 13 cases of secondary dengue infection; two samples were positive for ZIKV (MR766). Results from the ADE assay indicated that convalescent sera from primary and secondary dengue infection patients displayed significant ADE of the ZIKV infection when compared to healthy controls (p < 0.05).

CONCLUSIONS

This study suggests that pre-existing dengue immunity facilitates ZIKV infection and that the continuous importation of ZIKV infection may pose a threat to indigenous Zika emergence in Southern Taiwan.