Zika virus serological diagnosis: commercial tests and monoclonal antibodies as tools

Zika virus (ZIKV), an emerging arthropod-borne virus (arbovirus) of the Flaviviridae family, is a current issue worldwide, particularly because of the congenital and neurological syndromes associated with infection by this virus. As the initial clinical symptoms of all diseases caused by this group are very similar, clinical diagnosis is difficult. Furthermore, laboratory diagnostic efforts have failed to identify specific and accurate tests for each virus of the Flaviviridae family due to the cross-reactivity of these viruses in serum samples. This situation has resulted in underreporting of the diseases caused by flaviviruses. However, many companies developed commercial diagnostic tests after the recent ZIKV outbreak. Moreover, health regulatory agencies have approved different commercial tests to extend the monitoring of ZIKV infections. Considering that a specific and sensitive diagnostic method for estimating risk and evaluating ZIKV propagation is still needed, this review aims to provide an update of the main commercially approved serological diagnostics test by the US Food and Drug Administration (FDA) and Brazilian National Health Surveillance Agency (ANVISA). Additionally, we present the technologies used for monoclonal antibody production as a tool for the development of diagnostic tests and applications of these antibodies in detecting ZIKV infections worldwide.

Identification of Theaflavin-3,3'-Digallate as a Novel Zika Virus Protease Inhibitor

Mounting evidence indicates that Zika virus (ZIKV) is closely related to neurological disorders such as microcephaly and Guillain-Barré syndrome. There are currently no effective vaccines and FDA-approved inhibitors against ZIKV infection. The flaviviral heterodimeric serine protease NS2B-NS3 plays an essential role in ZIKV maturation and replication, thus becoming a promising target in anti-ZIKV therapy. Herein, we developed a fluorescence-based screening assay to search for inhibitors targeting the ZIKV NS2B-NS3 protease (ZIKVpro), and identified theaflavin-3,3’-digallate (ZP10), a natural active compound derived from black tea, as a potent ZIKV protease inhibitor in vitro (IC_{50 =} 2.3 μM). ZP10 exhibited dose-dependent inhibitory effect on ZIKV replication (EC_{50 =} 7.65 μM). Western blot analysis suggested that ZP10 inhibited the cleavage processing of viral polyprotein precursor in cells either infected with ZIKV or expressing minimal self-cleaving proteinase NS2B-3 protease, resulting in inhibition of virus growth. Moreover, ZP10 was showed to directly bind to ZIKVpro, and a docking model further revealed that ZP10 interacted with several critical residues at the proteolytic cavity of the ZIKVpro. This study highlights that ZP10 has anti-ZIKV potency through ZIKVpro inhibition, which indicates its potential application in anti-ZIKV therapy.

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.

Quantum leap of monoclonal antibody (mAb) discovery and development in the COVID-19 era

In recent years the global market for monoclonal antibodies (mAbs) became a multi-billion-dollar business. This success is mainly driven by treatments in the oncology and autoimmune space. Instead, development of effective mAbs against infectious diseases has been lagging behind. For years the high production cost and limited efficacy have blocked broader application of mAbs in the infectious disease space, which instead has been dominated for almost a century by effective and cheap antibiotics and vaccines. Only very few mAbs against RSV, anthrax, Clostridium difficile or rabies have reached the market. This is about to change. The development of urgently needed and highly effective mAbs as preventive and therapeutic treatments against a variety of pathogens is gaining traction. Vast advances in mAb isolation, engineering and production have entirely shifted the cost-efficacy balance. MAbs against devastating diseases like Ebola, HIV and other complex pathogens are now within reach. This trend is further accelerated by ongoing or imminent health crises like COVID-19 and antimicrobial resistance (AMR), where antibodies could be the last resort. In this review we will retrace the history of antibodies from the times of serum therapy to modern mAbs and lay out how the current run for effective treatments against COVID-19 will lead to a quantum leap in scientific, technological and health care system innovation around mAb treatments for infectious diseases.

A complex between the Zika virion and the Fab of a broadly cross-reactive neutralizing monoclonal antibody revealed by cryo-EM and single particle analysis at 4.1 Å resolution

Zika virus (ZIKV) recently emerged as a major public health concern because it can cause fetal microcephaly and neurological disease such as the Guillain-Barré syndrome. A particularly potent class of broadly neutralizing antibodies (nAbs) targets a quaternary epitope located at the interface of two envelope proteins monomers, exposed at the surface of the mature virion. This “E-dimer-dependent epitope” (EDE), comprises the fusion loop of one monomer at the tip of domain II of E and a portion of the domains I and III of the adjacent monomer. Since this epitope largely overlaps with the binding site of the precursor membrane protein (prM) during Zika virion maturation, its molecular surface is evolutionary conserved in flaviviruses such as Dengue and Zika viruses, and can elicit antibodies that broadly neutralize various ZIKV strains. Here, we present a cryo-EM reconstruction at 4.1 Å resolution of the virion bound to the antigen binding fragment (Fab) of an antibody that targets this mutationally-constrained quaternary epitope. The Fab incompletely covers the surface of the virion as it does not bind next to its 5-fold icosahedral axes. The structure reveals details of the binding mode of this potent neutralizing class of antibodies and can inform the design of immunogens and vaccines targeting this conserved epitope.

Current Status of Zika Virus Vaccines: Successes and Challenges

The recently emerged Zika virus (ZIKV) spread to the Americas, causing a spectrum of congenital diseases including microcephaly in newborn and Guillain-Barré syndrome (GBS) in adults. The unprecedented nature of the epidemic and serious diseases associated with the viral infections prompted the global research community to understand the immunopathogenic mechanisms of the virus and rapidly develop safe and efficacious vaccines. This has led to a number of ZIKV vaccine candidates that have shown significant promise in human clinical trials. These candidates include nucleic acid vaccines, inactivated vaccines, viral-vectored vaccines, and attenuated vaccines. Additionally, a number of vaccine candidates have been shown to protect animals in preclinical studies. However, as the epidemic has waned in the last three years, further development of the most promising vaccine candidates faces challenges in clinical efficacy trials, which is needed before a vaccine is brought to licensure. It is important that a coalition of government funding agencies and private sector companies is established to move forward with a safe and effective vaccine ready for deployment when the next ZIKV epidemic occurs.

Isolation of Monoclonal Antibodies from Zika Virus-Infected Patient Samples

The combination of sorting antigen-specific memory B cells with determining immunoglobulin (Ig) genes at the single-cell level enables the isolation of monoclonal antibodies (mAbs) in individuals. This method requires a small amount of blood (usually 10 mL) and is rapid (less than 2 weeks to isolate antigen-specific mAbs). Due to the application of antigens as the bait to capture the specific memory B cells, the majority of isolated mAbs are true binders to the antigen, which increases the isolation efficiency. Here, applying this approach, we describe the characterization of mAbs against Zika virus from a convalescent patient sample. From 10 mL whole blood, we sorted 33 Zika envelope (E) protein-interacting single memory B cells. The Ig genes from 15 cells were determined, and 13 mAbs were found that bind to Zika E protein with varied binding affinities.

Structural Basis for Neutralization and Protection by a Zika Virus-Specific Human Antibody

We previously reported a human monoclonal antibody, ZK2B10, capable of protection against Zika virus (ZIKV) infection and microcephaly in developing mouse embryos. Here, we report the structural features and mechanism of action of ZK2B10. The crystal structure at a resolution of 2.32 Å revealed that the epitope is located on the lateral ridge of DIII of the envelope glycoprotein. Cryo-EM structure with mature ZIKV showed that the antibody binds to DIIIs around the icosahedral 2-fold, 3-fold, and 5-fold axes, a distinct feature compared to those reported for DIII-specific antibodies. The binding of ZK2B10 to ZIKV has no detectable effect on viral attachment to target cells or on conformational changes of the E glycoprotein in the acidic environment, suggesting that ZK2B10 functions at steps between the formation of the fusion intermediate and membrane fusion. These results provide structural and mechanistic insights into how ZK2B10 mediates protection against ZIKV infection.

Recombinant lipidated Zika virus envelope protein domain III elicits durable neutralizing antibody responses against Zika virus in mice

Background

The emergence of Zika virus (ZV) in tropical and subtropical areas of the world has created an urgent need for vaccines against ZV. However, approved vaccines that prevent ZV infection are not available. To develop an effective vaccine against ZV infection, a lipidated form of ZV envelope protein domain III that possesses an intrinsic adjuvant property was rationally designed. Our goal was to examine the immunogenicity of recombinant lipidated ZV envelope protein domain III (rLZE3) and evaluate its potential as a vaccine candidate against ZV.

Methods

Recombinant ZV envelope protein domain III (rZE3) and rLZE3 were prepared with an Escherichia coli-based system. Dendritic cell surface marker expression and cytokine production upon stimulation were analyzed to evaluate the function of rLZE3. Neutralizing antibody capacities were evaluated using focus reduction neutralization tests after immunization. To investigate the protective immunity in immunized mice, serum samples collected from immunized mice were adoptively transferred into AG129 mice, and then viremia levels and survival times were examined after ZV challenge.

Results

rLZE3 alone but not rZE3 alone efficiently activated dendritic cells in vitro and was taken up by dendritic cells in vivo. Immunization of C57BL/6 mice with rLZE3 alone (without exogenous adjuvant) could induce ZV-specific neutralizing antibody responses. Furthermore, serum samples obtained from rLZE3-immunized mice provided protection as indicated by a reduction in viremia levels and prolongation of survival times after ZV challenge.

Conclusion

These results indicate that rLZE3 is an excellent vaccine candidate and has great potential that should be evaluated in further preclinical studies.

Homologous prime-boost with Zika virus envelope protein and poly (I:C) induces robust specific humoral and cellular immune responses

The recent outbreaks of Zika virus (ZIKV) infection and the potential association with Guillain-Barré syndrome in adults and with congenital abnormalities have highlighted the urgency for an effective vaccine. The ZIKV Envelope glycoprotein (E_ZIKV) is the most abundant protein on the virus surface, and has been evaluated together with the pre-membrane protein (prM) of the viral coat as a vaccine candidate in clinical trials. In this study, we performed a head-to-head comparison of the immune response induced by different E_ZIKV-based vaccine candidates in mice. We compared different platforms (DNA, recombinant protein), adjuvants (poly (I:C), CpG ODN 1826) and immunization strategies (homologous, heterologous). The hierarchy of adjuvant potency showed that poly (I:C) was a superior adjuvant than CpG ODN. While poly (I:C) assisted immunization reached a plateau in antibody titers after two doses, the CpG ODN group required an extra immunization dose. Besides, the administration of poly (I:C) induced higher E_ZIKV-specific cellular immune responses than CpG ODN. We also show that immunization with homologous prime-boost E_ZIKV protein + poly (I:C) regimen induced a more robust humoral response than homologous DNA (pVAX-E_ZIKV) or heterologous regimens (DNA/protein or protein/DNA). A detailed analysis of cellular immune responses revealed that homologous (E_ZIKV + poly (I:C)) and heterologous (pVAX-E_ZIKV/E_ZIKV + poly (I:C)) prime-boost regimens induced the highest magnitude of IFN-γ secreting cells and cytokine-producing CD4⁺ T cells. Overall, our data demonstrate that homologous E_ZIKV + poly (I:C) prime-boost immunization is sufficient to induce more robust specific-E_ZIKV humoral and cellular immune responses than the other strategies that contemplate homologous DNA (pVAX-E_ZIKV) or heterologous (pVAX-E_ZIKV/E_ZIKV + poly (I:C), and vice-versa) immunizations.

Investigation of the immunogenicity of Zika glycan loop

Background

Zika virus (ZIKV) is a major human pathogen and member of the Flavivirus genus. Previous studies have identified neutralizing antibodies from Zika patients that bind to quaternary epitopes across neighboring envelope (E) proteins, called E dimer epitopes (EDE). An asparagine-linked glycan on the “glycan loop” (GL) of the ZIKV envelope protein protects the functionally important “fusion loop” on the opposite E subunit in the dimer, and EDE antibodies have been shown to bind to both of these loops. Human EDE antibodies have been divided into two subclasses based on how they bind to the glycan loop region: EDE1 antibodies do not require glycosylation for binding, while EDE2 antibodies strongly rely on the glycan for binding.

Methods

ZIKV GL was expressed on tobacco mosaic virus nanoparticles. Mice were immunized with GL or full-length monomeric E and the immune response was analyzed by testing the ability of sera and monoclonal antibodies to bind to GL and to neutralize ZIKV in in vitro cellular assay.

Results

We report here the existence of ZIKV moderately neutralizing antibodies that bind to E monomers through epitopes that include the glycan loop. We show that sera from human Zika patients contain antibodies capable of binding to the unglycosylated glycan loop in the absence of the rest of the envelope protein. Furthermore, mice were inoculated with recombinant E monomers and produced neutralizing antibodies that either recognize unglycosylated glycan loop or require glycan for their binding to monomeric E. We demonstrate that both types of antibodies neutralize ZIKV to some extent in a cellular virus neutralization assay.

Conclusions

Analogous to the existing EDE antibody nomenclature, we propose a new classification for antibodies that bind to E monomer epitopes (EME): EME1 and EME2 for those that do not require and those that do require glycan for binding to E, respectively.

Adjacent dimer epitope of envelope protein as an important region for Zika virus serum neutralization: a computational investigation

The recent emergence of Zika virus (ZIKV) has affected many countries, with severe clinical manifestations such as fetal microcephaly and Guillain-Barré syndrome. However, even though it is a major public health concern, there is no approved treatment available. Structural knowledge of the main neutralization regions of the envelope (E) protein of ZIKV and its interactions with neutralizing antibodies (nAbs) are crucial for the rational development of subunit vaccines and establishment of antibody-based interventions. In this study we screened from public data hot spot epitopes in conserved regions of ZIKV E protein that are nAbs targets. The result points to a conserved epitope located at domain II of the ZIKV E protein, namely adjacent dimer epitope, which is the ZIKV-117 and Z20 nAbs target. Although these two nAbs have been isolated from different donors, we have demonstrated, from structural and energetic details obtained by molecular dynamics of native and mutants, that hot spots residues of the epitope are the same for these nAbs, thereby indicating that they may share similar binding and neutralization mechanism. This convergence of information between these nAbs is important because both are potential targets for the development of therapies against ZIKV and only Z20 has its sequence and its complex structure with ZIKV E protein determined. Finally, these findings also contribute to existing knowledge, by fine mapping of the epitope/paratope residue pairs that are important for biotechnological development of therapies such as epitope mimetics for subunit vaccines and the rational design for antibody-based interventions against ZIKV. Communicated by Ramaswamy H. Sarma.

Analysis of a Therapeutic Antibody Cocktail Reveals Determinants for Cooperative and Broad Ebolavirus Neutralization

Structural principles underlying the composition of protective antiviral monoclonal antibody (mAb) cocktails are poorly defined. Here, we exploited antibody cooperativity to develop a therapeutic mAb cocktail against Ebola virus. We systematically analyzed the antibody repertoire in human survivors and identified a pair of potently neutralizing mAbs that cooperatively bound to the ebolavirus glycoprotein (GP). High-resolution structures revealed that in a two-antibody cocktail, molecular mimicry was a major feature of mAb-GP interactions. Broadly neutralizing mAb rEBOV-520 targeted a conserved epitope on the GP base region. mAb rEBOV-548 bound to a glycan cap epitope, possessed neutralizing and Fc-mediated effector function activities, and potentiated neutralization by rEBOV-520. Remodeling of the glycan cap structures by the cocktail enabled enhanced GP binding and virus neutralization. The cocktail demonstrated resistance to virus escape and protected non-human primates (NHPs) against Ebola virus disease. These data illuminate structural principles of antibody cooperativity with implications for development of antiviral immunotherapeutics.

Double Lock of a Human Neutralizing and Protective Monoclonal Antibody Targeting the Yellow Fever Virus Envelope

Yellow fever virus (YFV), a deadly human pathogen, is the prototype of the genus Flavivirus. Recently, YFV re-emerged in Africa and Brazil, leading to hundreds of deaths, with some cases imported to China. Prophylactic or therapeutic countermeasures are urgently needed. Previously, several human monoclonal antibodies against YFV were screened out by phage display. Here, we find that one of them, 5A, exhibits high neutralizing potency and good protection. Crystallographic analysis of the YFV envelope (E) protein in its pre- and post-fusion states shows conformations similar to those observed in other E proteins of flaviviruses. Furthermore, the structures of 5A in complex with the E protein in both states are resolved, revealing an invariant recognition site. Structural analysis and functional data suggest that 5A has high neutralization potency because it interferes with virus entry by preventing both virus attachment and fusion. These findings will be instrumental for immunogen or inhibitor design.

A high infectious simian adenovirus type 23 vector based vaccine efficiently protects common marmosets against Zika virus infection

Zika virus (ZIKV) has spread in many countries or territories causing severe neurologic complications with potential fatal outcomes. The small primate common marmosets are susceptible to ZIKV, mimicking key features of human infection. Here, a novel simian adenovirus type 23 vector-based vaccine expressing ZIKV pre-membrane-envelope proteins (Sad23L-prM-E) was produced in high infectious titer. Due to determination of immunogenicity in mice, a single-dose of 3×10⁸ PFU Sad23L-prM-E vaccine was intramuscularly inoculated to marmosets. This vaccine raised antibody titers of 10^4.07 E-specific and 10^3.13 neutralizing antibody (NAb), as well as robust specific IFN-γ secreting T-cell response (1,219 SFCs/10⁶ cells) to E peptides. The vaccinated marmosets, upon challenge with a high dose of ZIKV (10⁵ PFU) six weeks post prime immunization, reduced viremia by more than 100 folds, and the low level of detectable viral RNA (<10³ copies/ml) in blood, saliva, urine and feces was promptly eliminated when the secondary NAb (titer >10^3.66) and T-cell response (>726 SFCs/10⁶ PBMCs) were acquired 1–2 weeks post exposure to ZIKV, while non-vaccinated control marmosets developed long-term high titer of ZIKV (10^5.73 copies/ml) (P<0.05). No significant pathological lesions were observed in marmoset tissues. Sad23L-prM-E vaccine was detectable in spleen, liver and PBMCs at least 4 months post challenge. In conclusion, a prime immunization with Sad23L-prM-E vaccine was able to protect marmosets against ZIKV infection when exposed to a high dose of ZIKV. This Sad23L-prM-E vaccine is a promising vaccine candidate for prevention of ZIKV infection in humans.

Zika virus (ZIKV) is a member of the Flaviviridaefamily) and causes severe neurologic diseases. The development of safe and effective vaccine is urgent need. In this study, we constructed a novel simian adenovirus type 23 vector-based vaccine expressing ZIKV pre-membrane-envelope proteins (Sad23L-prM-E). By vaccinating the common marmosets with prime immunization of vaccine, and upon challenge with a high dose of ZIKV to the vaccinated marmosets, the immune response and protective efficacy of vaccine were extensively evaluated. The data suggested that Sad23L-prM-E vaccine could protect marmosets against a high dose of ZIKV challenge, which provided a promising vaccine for preventing ZIKV infection in humans.

A new class of broadly neutralizing antibodies that target the glycan loop of Zika virus envelope protein

Zika virus (ZIKV) infection poses a serious threat to human health. However, no licensed vaccine or therapeutic drug is currently available for ZIKV. We have previously shown that recombinant ZIKV E80 protein induced potent neutralizing antibody response and protected mice from lethal viral challenge. In the present study, we isolated five ZIKV neutralizing monoclonal antibodies (mAbs) from E80-immunized mice. These five mAbs specifically bound and neutralized Asian-lineage ZIKV strains. Epitope mapping revealed that all of the five mAbs recognized a novel linear epitope located on the glycan loop of E protein domain I. Sequence alignment revealed that the epitope was extremely conserved in ZIKV but highly variable between ZIKV and other flaviviruses. Thus, these five mAbs form a new class of anti-ZIKV antibodies exhibiting broad-spectrum neutralization on Asian-lineage ZIKV. A representative of this mAb class, 5F8, was found to exert inhibitory function in vitro primarily at the early stage of the post-attachment viral entry process. Importantly, mAb 5F8 was able to confer full protection in a mouse model of ZIKV lethal infection. Our results have strong implications for developing anti-ZIKV vaccines and therapeutic mAbs.

Potent Zika and dengue cross-neutralizing antibodies induced by Zika vaccination in a dengue-experienced donor

Zika virus (ZIKV) has caused significant disease, with widespread cases of neurological pathology and congenital neurologic defects. Rapid vaccine development has led to a number of candidates capable of eliciting potent ZIKV-neutralizing antibodies (reviewed in refs. ^1-3). Despite advances in vaccine development, it remains unclear how ZIKV vaccination affects immune responses in humans with prior flavivirus immunity. Here we show that a single-dose immunization of ZIKV purified inactivated vaccine (ZPIV)^4-7 in a dengue virus (DENV)-experienced human elicited potent cross-neutralizing antibodies to both ZIKV and DENV. Using a unique ZIKV virion-based sorting strategy, we isolated and characterized multiple antibodies, including one termed MZ4, which targets a novel site of vulnerability centered on the Envelope (E) domain I/III linker region and protects mice from viremia and viral dissemination following ZIKV or DENV-2 challenge. These data demonstrate that Zika vaccination in a DENV-experienced individual can boost pre-existing flavivirus immunity and elicit protective responses against both ZIKV and DENV. ZPIV vaccination in Puerto Rican individuals with prior flavivirus experience yielded similar cross-neutralizing potency after a single vaccination, highlighting the potential benefit of ZIKV vaccination in flavivirus-endemic areas.

Progress and applications of single-cell sequencing techniques

Single-cell sequencing (SCS) is a next-generation sequencing method that is mainly used to analyze differences in genetic and protein information between cells, to obtain genetic information on microorganisms that are difficult to cultivate at a single-cell level and to better understand their specific roles in the microenvironment. By sequencing the whole genome, transcriptome and epigenome of a single cell, the complex heterogeneous mechanisms involved in disease occurrence and progression can be revealed, further improving disease diagnosis, prognosis prediction and monitoring of the therapeutic effects of drugs. In this study, we mainly summarized the methods and application fields of SCS, which may provide potential references for its future clinical applications, including the analysis of embryonic and organ development, the immune system, cancer progression, and parasitic and infectious diseases as well as stem cell research, antibody screening, and therapeutic research and development.

Longitudinal analysis of the antibody repertoire of a Zika virus-infected patient revealed dynamic changes in antibody response

The Zika virus (ZIKV) is a mosquito-borne flavivirus that causes neonatal abnormalities and other disorders. Antibodies to the ZIKV envelope (E) protein can block infection. In this study, next-generation sequencing (NGS) of immunoglobulin heavy chain (IgH) mRNA transcripts was combined with single-cell PCR cloning of E-binding monoclonal antibodies for analysing antibody response in a patient from the early stages of infection to more than one year after the clearance of the virus. The patient's IgH repertoire 14 and 64 days after symptom onset showed dramatic dominant clonal expansion but low clonal diversity. IgH repertoire 6 months after disease-free status had few dominant clones but increased diversity. E-binding antibodies appeared abundantly in the repertoire during the early stages of infection but quickly declined after clearance of the virus. Certain VH genes such as VH5-10-1 and VH4-39 appeared to be preferentially enlisted for a rapid antibody response to ZIKV infection. Most of these antibodies require relatively few somatic hypermutations to acquire the ability to bind to the E protein, pointing to a possible mechanism for rapid defence against ZIKV infection. This study provides a unique and holistic view of the dynamic changes and characteristics of the antibody response to ZIKV infection.

Development of a Potent and Protective Germline-Like Antibody Lineage Against Zika Virus in a Convalescent Human

Zika virus (ZIKV) specific neutralizing antibodies hold great promise for antibody-based interventions and vaccine design against ZIKV infection. However, their development in infected patients remains unclear. Here, we applied next-generation sequencing (NGS) to probe the dynamic development of a potent and protective ZIKV E DIII-specific antibody ZK2B10 isolated from a ZIKV convalescent individual. The unbiased repertoire analysis showed dramatic changes in the usage of antibody variable region germline genes. However, lineage tracing of ZK2B10 revealed limited somatic hypermutation and transient expansion during the 12 months following the onset of symptoms. The NGS-derived, germline-like ZK2B10 somatic variants neutralized ZIKV potently and protected mice from lethal challenge of ZIKV without detectable cross-reactivity with Dengue virus (DENV). Site-directed mutagenesis identified two residues within the λ chain, N31 and S91, that are essential to the functional maturation of ZK2B10. The repertoire and lineage features unveiled here will help elucidate the developmental process and protective potential of E DIII-directed antibodies against ZIKV infection.

A Single Injection of Human Neutralizing Antibody Protects against Zika Virus Infection and Microcephaly in Developing Mouse Embryos

Zika virus (ZIKV) is a mosquito-transmitted flavivirus that is generally benign in humans. However, an emergent strain of ZIKV has become widespread, causing severe pre- and post-natal neurological defects. There is now an urgent need for prophylactic and therapeutic agents. To address this, we investigated six human monoclonal antibodies with ZIKV epitope specificity and neutralizing activity in mouse models of ZIKV infection and microcephaly. A single intraperitoneal injection of these antibodies conveyed distinct levels of adult and in utero protection from ZIKV infection, which closely mirrored their respective in vitro neutralizing activities. One antibody, ZK2B10, showed the most potent neutralization activity, completely protected uninfected mice, and markedly reduced tissue pathology in infected mice. Thus, ZK2B10 is a promising candidate for the development of antibody-based interventions and informs the rational design of ZIKV vaccine.

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Human antibodies against ZIKV are tested in mouse models

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In vitro neutralizing activity correlates with in vivo protection

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The most potent antibody, ZK2B10, provides protection against infection

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ZK2B10 markedly delays mortality

Development and Evaluation of a Universal and Supersensitive NS1-Based Luciferase Immunosorbent Assay to Detect Zika Virus-Specific IgG

Zika virus (ZIKV) causes rash, moderate fever, conjunctivitis, and arthralgia, and has serious connection with neurological complications; therefore, it is a major threat to public health. A rapid and supersensitive method for detecting anti-ZIKV antibodies in humans and animals is thus urgently required. Here, we report an NS1-based luciferase immunosorbent assay (LISA), developed to detect ZIKV-specific IgG. Fusion proteins including a reporter Nano-luciferase (NLuc) and various fragments of ZIKV NS1 protein were expressed in 293 T cells. LISA was performed using the above cell lysates containing the expressed fusion proteins. Sample panels of humans and animals infected with ZIKV were examined for sensitivity of LISA, relative to those of ZIKV RT-PCR, commercial NS1-based ELISA, and micro-neutralization (MN) assays. Specificity and potential cross-reactivity were also evaluated using various convalescent serum samples derived from patients infected with dengue virus (DENV), Japanese encephalitis virus (JEV), and hepatitis C virus (HCV). Results indicated the optimal antigenic domain for anti-ZIKV IgG detection was located within 172-352 amino acids (aa) of ZIKV NS1 protein. NS1-based LISA performs better than commercial ELISA in anti-ZIKV IgG detection. LISA was shown to be at least fourfold more sensitive than commercial ELISA, and could detect anti-ZIKV IgG in various animal hosts without the need of species-specific labeled antibody. This novel assay is potentially useful for the rapid and sensitive detection of anti-ZIKV IgG in human and animal samples.

Role of Zika Virus Envelope Protein Domain III as a Target of Human Neutralizing Antibodies

Zika virus (ZIKV) is a flavivirus that is structurally highly similar to the related viruses, dengue virus (DENV), West Nile virus, and yellow fever virus. ZIKV causes an acute infection that often results in mild symptoms but that can cause severe disease in rare instances. Following infection, individuals mount an adaptive immune response, composed of antibodies (Abs) that target the envelope (E) glycoprotein of ZIKV, which covers the surface of the virus. Groups have studied monoclonal antibodies and polyclonal immune sera isolated from individuals who recovered from natural ZIKV infections. Some of these antibodies bind to domain III of E (EDIII), but the functional importance of these antibodies is unknown. In this study, we aimed to determine if EDIII is a major target of the potent serum neutralizing antibodies present in people after ZIKV infection. By generating a chimeric virus containing ZIKV EDIII in a DENV4 virus backbone, our data show a minor role of EDIII-targeting antibodies in human polyclonal neutralization. These results reveal that while monoclonal antibody (MAb) studies are informative in identifying individual antibody epitopes, they can overestimate the importance of epitopes contained within EDIII as targets of serum neutralizing antibodies. Additionally, these results argue that the major target of human ZIKV neutralizing antibodies resides elsewhere in E; however, further studies are needed to assess the epitope specificity of the neutralizing response at the population level. Identification of the major epitopes on the envelope of ZIKV recognized by serum neutralizing antibodies is critical for understanding protective immunity following natural infection and for guiding the design and evaluation of vaccines.IMPORTANCE Zika virus is a flavivirus that was recently introduced to Latin America, where it caused a massive epidemic. Individuals infected with ZIKV generate an immune response composed of antibodies which bind to the envelope (E) protein. These anti-E antibodies are critical in protecting individuals from subsequent infection. Multiple groups have found that many ZIKV antibodies bind to domain III of E (EDIII), suggesting that this region is an important target of neutralizing antibodies. Here, we generated a chimeric virus containing ZIKV EDIII in a dengue virus backbone to measure ZIKV EDIII-specific antibody responses. We found that while polyclonal ZIKV immune serum contains antibodies targeting EDIII, they constitute only a small fraction of the total population of antibodies that neutralize ZIKV. Further studies are needed to define the main targets on the viral envelope recognized by human neutralizing antibodies, which is critical for guiding the development of ZIKV vaccines.

A Gorilla Adenovirus-Based Vaccine against Zika Virus Induces Durable Immunity and Confers Protection in Pregnancy

The teratogenic potential of Zika virus (ZIKV) has made the development of an effective vaccine a global health priority. Here, we generate two gorilla adenovirus-based ZIKV vaccines that encode for pre-membrane (prM) and envelope (E) proteins (GAd-Zvp) or prM and the ectodomain of E protein (GAd-Eecto). Both vaccines induce humoral and cell-mediated immune responses and prevent lethality after ZIKV challenge in mice. Protection is antibody dependent, CD8⁺ T cell independent, and for GAd-Eecto requires the complement component C1q. Immunization of GAd-Zvp induces antibodies against a key neutralizing epitope on domain III of E protein and confers durable protection as evidenced by memory B and long-lived plasma cell responses and challenge studies 9 months later. In two models of ZIKV infection during pregnancy, GAd-Zvp prevents maternal-to-fetal transmission. The gorilla adenovirus-based vaccine platform encoding full-length prM and E genes is a promising candidate for preventing congenital ZIKV syndrome and possibly infection by other flaviviruses.

Convalescent patient-derived monoclonal antibodies targeting different epitopes of E protein confer protection against Zika virus in a neonatal mouse model

The Zika virus (ZIKV) outbreak and its link to microcephaly triggered a public health concern. To examine antibody response in a patient infected with ZIKV, we used single-cell PCR to clone 31 heavy and light chain-paired monoclonal antibodies (mAbs) that bind to ZIKV envelope (E) proteins isolated from memory B cells of a ZIKV-infected patient. Three mAbs (7B3, 1C11, and 6A6) that showed the most potent and broad neutralization activities against the African, Asian, and American strains were selected for further analysis. mAb 7B3 showed an IC50 value of 11.6 ng/mL against the circulating American strain GZ02. Epitope mapping revealed that mAbs 7B3 and 1C11 targeted residue K394 of the lateral ridge (LR) epitope of the EDIII domain, but 7B3 has a broader LR epitope footprint and recognizes residues T335, G337, E370, and N371 as well. mAb 6A6 recognized residues D67, K118, and K251 of the EDII domain. Interestingly, although the patient was seronegative for DENV infection, mAb 1C11, originating from the VH3-23 and VK1-5 germline pair, neutralized both ZIKV and DENV1. Administration of the mAbs 7B3, 1C11, and 6A6 protected neonatal SCID mice infected with a lethal dose of ZIKV. This study provides potential therapeutic antibody candidates and insights into the antibody response after ZIKV infection.

Structures of enveloped virions determined by cryogenic electron microscopy and tomography

Enveloped viruses enclose their genomes inside a lipid bilayer which is decorated by membrane proteins that mediate virus entry. These viruses display a wide range of sizes, morphologies and symmetries. Spherical viruses are often isometric and their envelope proteins follow icosahedral symmetry. Filamentous and pleomorphic viruses lack such global symmetry but their surface proteins may display locally ordered assemblies. Determining the structures of enveloped viruses, including the envelope proteins and their protein-protein interactions on the viral surface, is of paramount importance. These structures can reveal how the virions are assembled and released by budding from the infected host cell, how the progeny virions infect new cells by membrane fusion, and how antibodies bind surface epitopes to block infection. In this chapter, we discuss the uses of cryogenic electron microscopy (cryo-EM) in elucidating structures of enveloped virions. Starting from a detailed outline of data collection and processing strategies, we highlight how cryo-EM has been successfully utilized to provide unique insights into enveloped virus entry, assembly, and neutralization.

Integrative Approaches in Structural Biology: A More Complete Picture from the Combination of Individual Techniques

With the recent technological and computational advancements, structural biology has begun to tackle more and more difficult questions, including complex biochemical pathways and transient interactions among macromolecules. This has demonstrated that, to approach the complexity of biology, one single technique is largely insufficient and unable to yield thorough answers, whereas integrated approaches have been more and more adopted with successful results. Traditional structural techniques (X-ray crystallography and Nuclear Magnetic Resonance (NMR)) and the emerging ones (cryo-electron microscopy (cryo-EM), Small Angle X-ray Scattering (SAXS)), together with molecular modeling, have pros and cons which very nicely complement one another. In this review, three examples of synergistic approaches chosen from our previous research will be revisited. The first shows how the joint use of both solution and solid-state NMR (SSNMR), X-ray crystallography, and cryo-EM is crucial to elucidate the structure of polyethylene glycol (PEG)ylated asparaginase, which would not be obtainable through any of the techniques taken alone. The second deals with the integrated use of NMR, X-ray crystallography, and SAXS in order to elucidate the catalytic mechanism of an enzyme that is based on the flexibility of the enzyme itself. The third one shows how it is possible to put together experimental data from X-ray crystallography and NMR restraints in order to refine a protein model in order to obtain a structure which simultaneously satisfies both experimental datasets and is therefore closer to the ‘real structure’.

ZIKV Envelope Domain-Specific Antibodies: Production, Purification and Characterization

Infection with Zika virus (ZIKV) came first to public attention after it was found to be associated with congenital microcephaly during the outbreak in Brazil (2015–2016). Diagnosis of ZIKV suffers from extensive cross-reactivity with other Flaviviruses, which are circulating in many ZIKV epidemic areas. Due to the fatal outcome of ZIKV infection during pregnancy, detailed knowledge about neutralizing and non-neutralizing epitopes is crucial for the development of robust detection systems of protective antibodies. Therefore, additional information about ZIKV immunogenicity and antibody response is required. In this project, we report the production, purification and characterization of six different polyclonal antibodies against ZIKV envelope (E) protein. The produced antibodies bind to isolated ZIKV E protein as well as to the surface of ZIKV particles, interestingly without being potently neutralizing. Surface plasmon resonance measurement showed that these antibodies bind with high affinity to ZIKV E protein. Epitope mapping revealed that the epitopes are distributed among the three ZIKV E domains with seven binding sites. These identified binding sites overlap only partially with the previously described epitopes recognized by neutralizing antibodies, which is in accordance with their lack of potent neutralizing activity. Additionally, these antibodies showed neither cross-reactivity nor potent neutralizing activity against West Nile virus, a related flavivirus. The gained set of data helps to extend our understanding about the distribution of neutralizing and non-/weak-neutralizing epitopes in ZIKV E protein, and provides a rationale for ZIKV vaccine design and development of robust detection assays for neutralizing antibodies.

Yeast-produced subunit protein vaccine elicits broadly neutralizing antibodies that protect mice against Zika virus lethal infection

Zika virus (ZIKV) infection is a serious public health concern due to its ability to induce neurological defects and its potential for rapid transmission at a global scale. However, no vaccine is currently available to prevent ZIKV infection. Here, we report the development of a yeast-derived subunit protein vaccine for ZIKV. The envelope protein domain III (EDIII) of ZIKV was produced as a secretory protein in the yeast Pichia pastoris. The yeast-derived EDIII could inhibit ZIKV infection in vitro in a dose-dependent manner, suggesting that it had acquired an appropriate conformation to bind to cellular receptors of ZIKV. Immunization with recombinant EDIII protein effectively induced antigen-specific binding antibodies and cellular immune responses. The resulting anti-EDIII sera could efficiently neutralize ZIKV representative strains from both Asian and African lineages. Passive transfer with the anti-EDIII neutralizing sera could confer protection against lethal ZIKV challenge in mice. Importantly, we found that purified anti-EDIII antibodies did not cross-react with closely related dengue virus (DENV) and therefore did not enhance DENV infection. Collectively, our results demonstrate that yeast-produced EDIII is a safe and effective ZIKV vaccine candidate.

Peptide-Based Subunit Vaccine Design of T- and B-Cells Multi-Epitopes against Zika Virus Using Immunoinformatics Approaches

The Zika virus disease, also known as Zika fever is an arboviral disease that became epidemic in the Pacific Islands and had spread to 18 territories of the Americas in 2016. Zika virus disease has been linked to several health problems such as microcephaly and the Guillain-Barré syndrome, but to date, there has been no vaccine available for Zika. Problems related to the development of a vaccine include the vaccination target, which covers pregnant women and children, and the antibody dependent enhancement (ADE), which can be caused by non-neutralizing antibodies. The peptide vaccine was chosen as a focus of this study as a safer platform to develop the Zika vaccine. In this study, a collection of Zika proteomes was used to find the best candidates for T- and B-cell epitopes using the immunoinformatics approach. The most promising T-cell epitopes were mapped using the selected human leukocyte antigen (HLA) alleles, and further molecular docking and dynamics studies showed a good peptide-HLA interaction for the best major histocompatibility complex-II (MHC-II) epitope. The most promising B-cell epitopes include four linear peptides predicted to be cross-reactive with T-cells, and conformational epitopes from two proteins accessible by antibodies in their native biological assembly. It is believed that the use of immunoinformatics methods is a promising strategy against the Zika viral infection in designing an efficacious multiepitope vaccine.

Generation of porcine monoclonal antibodies based on single cell technologies

The development of a rapid and efficient system to generate porcine monoclonal antibodies (mAbs) is an important step toward the discovery of critical neutralizing targets for designing rational vaccines against porcine viruses. In this study, we established a platform for producing porcine mAbs based on single cell technologies. First, we singled out an optimal donor from 507 pigs based on serum antibody neutralizing activity against porcine reproductive and respiratory syndrome virus (PRRSV). After identifying the contribution of IgG to the neutralizing activity, single CD45R⁺IgG⁺Ag⁺ B cells were sorted from peripheral blood mononuclear cells (PBMCs). Single B cell RT-PCR was performed using primers designed to cover the germline repertoire of the porcine VH/VL gene segments. Paired VH/VLs were cloned into a eukaryotic expression vector and transfected into 293T cells. We demonstrate that full-length porcine mAbs were produced, and antigen-specific mAbs were obtained after further validation. The approach reported in this study can be applied to generate porcine mAbs against any given antigen and may help with the screening of neutralizing antibodies against porcine pathogens.

Human Polyclonal Antibodies Prevent Lethal Zika Virus Infection in Mice

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus that represents a major threat to global health. ZIKV infections in adults are generally asymptomatic or present with mild symptoms. However, recent outbreaks of ZIKV have revealed that it can cause Congenital Zika Syndrome in neonates and Guillain-Barré syndrome in adults. Currently, no ZIKV-specific vaccines or antiviral treatments are available. In this study, we tested the efficacy of convalescent plasma IgG hyperimmune product (ZIKV-IG) isolated from individuals with high neutralizing anti-ZIKV titers as a therapeutic candidate against ZIKV infection using a model of ZIKV infection in Ifnar1^-/- mice. ZIKV-IG successfully protected mice from lethal ZIKV challenge. In particular, ZIKV-IG treatment at 24 hours after lethal ZIKV infection improved survival by reducing weight loss and tissue viral burden and improving clinical score. Additionally, ZIKV-IG eliminated ZIKV-induced tissue damage and inflammation in the brain and liver. These results indicate that ZIKV-IG is efficacious against ZIKV, suggesting this human polyclonal antibody is a viable candidate for further development as a treatment against human ZIKV infection.

Human Monoclonal Antibodies Potently Neutralize Zika Virus and Select for Escape Mutations on the Lateral Ridge of the Envelope Protein

The mosquito-borne Zika virus (ZIKV) has been causing epidemic outbreaks on a global scale. Virus infection can result in severe disease in humans, including microcephaly in newborns and Guillain-Barré syndrome in adults. Here, we characterized monoclonal antibodies isolated from a patient with an active Zika virus infection that potently neutralized virus infection in Vero cells at the nanogram-per-milliliter range. In addition, these antibodies enhanced internalization of virions into human leukemia K562 cells in vitro, indicating their possible ability to cause antibody-dependent enhancement of disease. Escape variants of the ZIKV MR766 strain to a potently neutralizing antibody, AC10, exhibited an amino acid substitution at residue S368 in the lateral ridge region of the envelope protein. Analysis of publicly availably ZIKV sequences revealed the S368 site to be conserved among the vast majority (97.6%) of circulating strains. We validated the importance of this residue by engineering a recombinant virus with an S368R point mutation that was unable to be fully neutralized by AC10. Four out of the 12 monoclonal antibodies tested were also unable to neutralize the virus with the S368R mutation, suggesting this region to be an important immunogenic epitope during human infection. Last, a time-of-addition infection assay further validated the escape variant and showed that all monoclonal antibodies inhibited virus binding to the cell surface. Thus, the present study demonstrates that the lateral ridge region of the envelope protein is likely an immunodominant, neutralizing epitope.IMPORTANCE Zika virus (ZIKV) is a global health threat causing severe disease in humans, including microcephaly in newborns and Guillain-Barré syndrome in adults. Here, we analyzed the human monoclonal antibody response to acute ZIKV infection and found that neutralizing antibodies could not elicit Fc-mediated immune effector functions but could potentiate antibody-dependent enhancement of disease. We further identified critical epitopes involved with neutralization by generating and characterizing escape variants by whole-genome sequencing. We demonstrate that the lateral ridge region, particularly the S368 amino acid site, is critical for neutralization by domain III-specific antibodies.

[The Recent Epidemic Spread of Zika Virus Disease]

Zika virus (ZIKV) is one of the members of the Spondweni serocomplex within the genus Flavivirus of the family Flaviviridae. The virus was first isolated from a serum specimen from a sentinel non-human primate in the Zika forest of Uganda in 1947. ZIKV is transmitted by Aedes aegypti and A. albopictus in an urban cycle and maintained in a sylvatic cycle between Aedes mosquitoes and monkeys in Africa and Asia. Initially, the virus was thought to cause only mild and nonspecific clinical symptoms in humans. However, ZIKV became a serious public health concern in recent years due to an association with congenital malformation known as microcephaly in newborns as well as Guillain-Barré syndrome and other neurologic disorders in adults. The severe nature of complications of ZIKV infection have led to an urgent need for a safe and effective vaccine worldwide including Japan. The first large outbreak of disease caused by ZIKV infection was reported from the island of Yap, Micronesia in 2007. It was followed by outbreaks in French Polynesia, Cook Islands, Ester Island, and New Caledonia in 2013 and 2014. In 2015, ZIKV outbreak was reported in Brazil and has spread across the Latin America, and the Caribbean. The exact prevalence of ZIKV infection has not been reported because of the absence of a standardized protocol for differential diagnosis and its clinical resemblance to dengue virus and other flavivirus infections. In Japan, the first human case of ZIK fever, who developed illness soon after returning from French Polynesia, was reported in 2013, and until 2017, 20 imported cases were documented. Currently, research on ZIKV has progressed remarkably thus this article aims to review recent progress in virology, epidemiology, and pathology of ZIKV infection.

Potent neutralizing antibodies elicited by dengue vaccine in rhesus macaque target diverse epitopes

There is still no safe and effective vaccine against dengue virus infection. Epidemics of dengue virus infection are increasingly a threat to human health around the world. Antibodies generated in response to dengue infection have been shown to impact disease development and effectiveness of dengue vaccine. In this study, we investigated monoclonal antibody responses to an experimental dengue vaccine in rhesus macaques. Variable regions of both heavy chain (VH) and light chain (VL) were cloned from single antibody-secreting B cells. A total of 780 monoclonal antibodies (mAbs) composed of paired VH and VL were characterized. Results show that the vaccination induces mAbs with diverse germline sequences and a wide range of binding affinities. Six potent neutralizing mAbs were identified among 130 dengue envelope protein binders. Critical amino acids for each neutralizing antibody binding to the dengue envelope protein were identified by alanine scanning of mutant libraries. Diverse epitopes were identified, including epitopes on the lateral ridge of DIII, the I-III hinge, the bc loop adjacent to the fusion loop of DII, and the β-strands and loops of DI. Significantly, one of the neutralizing mAbs has a previously unknown epitope in DII at the interface of the envelope and membrane protein and is capable of neutralizing all four dengue serotypes. Taken together, the results of this study not only provide preclinical validation for the tested experimental vaccine, but also shed light on a potential application of the rhesus macaque model for better dengue vaccine evaluation and design of vaccines and immunization strategies.

Dengue virus (DENV) is a leading cause of human illness in the tropics and subtropics, with about 40% of the world’s population living in areas at risk for infection. There are four DENV serotypes. Patients who have previously been infected by one dengue serotype may develop more severe symptoms such as bleeding and endothelial leakage upon secondary infection with another dengue serotype. This study reports the extensive cloning and analysis of 780 monoclonal antibodies (mAbs) from single B cells of rhesus macaques after immunization with an experimental dengue vaccine. We identified a panel of potent neutralizing mAbs with diverse epitopes on the DENV envelope protein. Antibodies in this panel were found to bind to the lateral ridge of DIII, the I-III hinge, the bc loop adjacent to the fusion loop of DII, and the β-strands and the loops of DI. We also isolated one mAb (d448) that can neutralize all four dengue serotypes and binds to a novel epitope at the interface of the DENV envelope and membrane proteins. Further investigation of these neutralizing monoclonal antibodies is warranted for better vaccine efficacy evaluation and vaccine design.

Characterization of two engineered dimeric Zika virus envelope proteins as immunogens for neutralizing antibody selection and vaccine design

The envelope protein of Zika virus (ZIKV) exists as a dimer on the mature viral surface and is an attractive antiviral target because it mediates viral entry. However, recombinant soluble wild-type ZIKV envelope (wtZE) might preferentially exist as monomer (monZE). Recently, it has been shown that the A264C substitution could promote formation of dimeric ZIKV envelope protein (ZE_A264C), requiring further characterization of purified ZE_A264C for its potential applications in vaccine development. We also noted that ZE_A264C, connected by disulfide bond, might be different from the noncovalent native envelope dimer on the virion surface. Because the antibody Fc fragment exists as dimer and is widely used for fusion protein construction, here we fused wtZE to human immunoglobulin G1 (IgG1) Fc fragment (ZE-Fc) for noncovalent wtZE dimerization. Using a multistep purification procedure, we separated dimeric ZE_A264C and ZE-Fc, revealing that they both exhibit typical β-sheet-rich secondary structures and stabilities similar to those of monZE. The binding activities of monZE, ZE_A264C, and ZE-Fc to neutralizing antibodies targeting different epitopes indicated that ZE_A264C and ZE-Fc could better mimic the native dimeric status, especially in terms of the formation of tertiary and quaternary epitopes. Both ZE_A264C and ZE-Fc recognize a ZIKV-sensitive cell line as does monZE, indicating that the two constructs are still functional. Furthermore, a murine immunization assay disclose that ZE_A264C and ZE-Fc elicit more neutralizing antibody responses than monZE does. These results suggest that the two immunogen candidates ZE_A264C and ZE-Fc have potential utility for neutralizing antibody selection and vaccine design against ZIKV.

Differential human antibody repertoires following Zika infection and the implications for serodiagnostics and disease outcome

Zika virus (ZIKV) outbreak in Americas led to extensive efforts to develop vaccines and ZIKV-specific diagnostics. In the current study, we use whole genome phage display library spanning the entire ZIKV genome (ZIKV-GFPDL) for in-depth immune profiling of IgG and IgM antibody repertoires in serum and urine longitudinal samples from individuals acutely infected with ZIKV. We observe a very diverse IgM immune repertoire encompassing the entire ZIKV polyprotein on day 0 in both serum and urine. ZIKV-specific IgG antibodies increase 10-fold between day 0 and day 7 in serum, but not in urine; these are highly focused on prM/E, NS1 and NS2B. Differential antibody affinity maturation is observed against ZIKV structural E protein compared with nonstructural protein NS1. Serum antibody affinity to ZIKV-E protein inversely correlates with ZIKV disease symptoms. Our study provides insight into unlinked evolution of immune response to ZIKV infection and identified unique targets for ZIKV serodiagnostics.

Engineering the PP7 Virus Capsid as a Peptide Display Platform

As self-assembling polyvalent nanoscale structures that can tolerate substantial genetic and chemical modification, virus-like particles are useful in a variety of fields. Here we describe the genetic modification and structural characterization of the Leviviridae PP7 capsid protein as a platform for the presentation of functional polypeptides. This particle was shown to tolerate the display of sequences from 1 kDa (a cell penetrating peptide) to 14 kDa (the Fc-binding double Z-domain) on its exterior surface as C-terminal genetic fusions to the coat protein. In addition, a dimeric construct allowed the presentation of exogenous loops between capsid monomers and the simultaneous presentation of two different peptides at different positions on the icosahedral structure. The PP7 particle is thereby significantly more tolerant of these types of polypeptide additions than Qβ and MS2, the other Leviviridae-derived VLPs in common use.

Serologic Tools and Strategies to Support Intervention Trials to Combat Zika Virus Infection and Disease

Zika virus is an emerging mosquito-borne flavivirus that recently caused a large epidemic in Latin America characterized by novel disease phenotypes, including Guillain-Barré syndrome, sexual transmission, and congenital anomalies, such as microcephaly. This epidemic, which was declared an international public health emergency by the World Health Organization, has highlighted shortcomings in our current understanding of, and preparation for, emerging infectious diseases in general, as well as challenges that are specific to Zika virus infection. Vaccine development for Zika virus has been a high priority of the public health response, and several candidates have shown promise in pre-clinical and early phase clinical trials. The optimal selection and implementation of imperfect serologic assays are among the crucial issues that must be addressed in order to advance Zika vaccine development. Here, I review key considerations for how best to incorporate into Zika vaccine trials the existing serologic tools, as well as those on the horizon. Beyond that, this discussion is relevant to other intervention strategies to combat Zika and likely other emerging infectious diseases.

Human antibody response to Zika targets type-specific quaternary structure epitopes

The recent Zika virus (ZIKV) epidemic in the Americas has revealed rare but serious manifestations of infection. ZIKV has emerged in regions endemic for dengue virus (DENV), a closely related mosquito-borne flavivirus. Cross-reactive antibodies confound studies of ZIKV epidemiology and pathogenesis. The immune responses to ZIKV may be different in people, depending on their DENV immune status. Here, we focus on the human B cell and antibody response to ZIKV as a primary flavivirus infection to define the properties of neutralizing and protective antibodies generated in the absence of preexisting immunity to DENV. The plasma antibody and memory B cell response is highly ZIKV type-specific, and ZIKV-neutralizing antibodies mainly target quaternary structure epitopes on the viral envelope. To map viral epitopes targeted by protective antibodies, we isolated 2 type-specific monoclonal antibodies (mAbs) from a ZIKV case. Both mAbs were strongly neutralizing in vitro and protective in vivo. The mAbs recognize distinct epitopes centered on domains I and II of the envelope protein. We also demonstrate that the epitopes of these mAbs define antigenic regions commonly targeted by plasma antibodies in individuals from endemic and nonendemic regions who have recovered from ZIKV infections.

Small-Animal Models of Zika Virus

Zika virus (ZIKV) infection can result in serious consequences, including severe congenital manifestations, persistent infection in the testes, and neurologic sequelae. After a pandemic emergence, the virus has spread to much of North and South America and has been introduced to many countries outside of ZIKV-endemic areas as infected travelers return to their home countries. Rodent models have been important in gaining a better understanding of the wide range of disease etiologies associated with ZIKV infection and for the initial phase of developing countermeasures to prevent or treat viral infections. We discuss herein the advantages and disadvantages of small-animal models that have been developed to replicate various aspects of disease associated with ZIKV infection.

Humoral Immune Responses Against Zika Virus Infection and the Importance of Preexisting Flavivirus Immunity

The recent emergence of Zika virus (ZIKV) in the western hemisphere has been linked to Guillain-Barre syndrome, congenital microcephaly, and devastating ophthalmologic and neurologic developmental abnormalities. The vast geographic spread and adverse disease outcomes of the 2015-2016 epidemic have elevated ZIKV from a previously understudied virus to one of substantial public health interest worldwide. Recent efforts to dissect immunological responses to ZIKV have provided significant insights into the functional quality and antigenic targets of ZIKV-induced B-cell responses. Several groups have demonstrated immunological cross-reactivity between ZIKV and other flaviviruses and have identified antibodies capable of both cross-neutralization, as well as antibody-dependent enhancement (ADE) of ZIKV infection. However, the impact of preexisting flavivirus immunity on ZIKV pathogenesis, the generation of protective responses, and in utero transmission of ZIKV infection remain unclear. Given the widespread endemicity of DENV in the areas most effected by the current ZIKV outbreak, the possibility of ADE is especially concerning and may pose unique challenges to the development and deployment of safe and immunogenic ZIKV vaccines. Here, we review current literature pertaining to ZIKV-induced B-cell responses and humoral cross-reactivity and discuss relevant considerations for the development of vaccines and therapeutics against ZIKV.