Inhibition of EBV-mediated membrane fusion by anti-gHgL antibodies

Potent human monoclonal antibodies targeting Epstein-Barr virus gp42 reveal vulnerable sites for virus infection

Epstein-Barr virus (EBV) is linked to various malignancies and autoimmune diseases, posing a significant global health challenge due to the lack of specific treatments or vaccines. Despite its crucial role in EBV infection in B cells, the mechanisms of the glycoprotein gp42 remain elusive. In this study, we construct an antibody phage library from 100 EBV-positive individuals, leading to the identification of two human monoclonal antibodies, 2B7 and 2C1. These antibodies effectively neutralize EBV infection in vitro and in vivo while preserving gp42's interaction with the human leukocyte antigen class II (HLA-II) receptor. Structural analysis unveils their distinct binding epitopes on gp42, different from the HLA-II binding site. Furthermore, both 2B7 and 2C1 demonstrate potent neutralization of EBV infection in HLA-II-positive epithelial cells, expanding our understanding of gp42's role. Overall, this study introduces two human anti-gp42 antibodies with potential implications for developing EBV vaccines targeting gp42 epitopes, addressing a critical gap in EBV research.

Epstein-Barr virus gp42 antibodies reveal sites of vulnerability for receptor binding and fusion to B cells

Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with B cell lymphomas. EBV glycoprotein 42 (gp42) binds HLA class II and activates membrane fusion with B cells. We isolated gp42-specific monoclonal antibodies (mAbs), A10 and 4C12, which use distinct mechanisms to neutralize virus infection. mAb A10 was more potent than the only known neutralizing gp42 mAb, F-2-1, in neutralizing EBV infection and blocking binding to HLA class II. mAb 4C12 was similar to mAb A10 in inhibiting glycoprotein-mediated B cell fusion but did not block receptor binding, and it was less effective in neutralizing infection. Crystallographic structures of gH/gL/gp42/A10 and gp42/4C12 complexes revealed two distinct sites of vulnerability on gp42 for receptor binding and B cell fusion. Passive transfer of mAb A10 into humanized mice conferred nearly 100% protection from viremia and EBV lymphomas after EBV challenge. These findings identify vulnerable sites on EBV that may facilitate therapeutics and vaccines.

Non-overlapping epitopes on the gHgL-gp42 complex for the rational design of a triple-antibody cocktail against EBV infection

Epstein-Barr virus (EBV) is closely associated with cancer, multiple sclerosis, and post-acute coronavirus disease 2019 (COVID-19) sequelae. There are currently no approved therapeutics or vaccines against EBV. It is noteworthy that combining multiple EBV glycoproteins can elicit potent neutralizing antibodies (nAbs) against viral infection, suggesting possible synergistic effects. Here, we characterize three nAbs (anti-gp42 5E3, anti-gHgL 6H2, and anti-gHgL 10E4) targeting different glycoproteins of the gHgL-gp42 complex. Two antibody cocktails synergistically neutralize infection in B cells (5E3+6H2+10E4) and epithelial cells (6H2+10E4) in vitro. Moreover, 5E3 alone and the 5E3+6H2+10E4 cocktail confer potent in vivo protection against lethal EBV challenge in humanized mice. The cryo-EM structure of a heptatomic gHgL-gp42 immune complex reveals non-overlapping epitopes of 5E3, 6H2, and 10E4 on the gHgL-gp42 complex. Structural and functional analyses highlight different neutralization mechanisms for each of the three nAbs. In summary, our results provide insight for the rational design of therapeutics or vaccines against EBV infection.

Urgency and necessity of Epstein-Barr virus prophylactic vaccines

Epstein-Barr virus (EBV), a γ-herpesvirus, is the first identified oncogenic virus, which establishes permanent infection in humans. EBV causes infectious mononucleosis and is also tightly linked to many malignant diseases. Various vaccine formulations underwent testing in different animals or in humans. However, none of them was able to prevent EBV infection and no vaccine has been approved to date. Current efforts focus on antigen selection, combination, and design to improve the efficacy of vaccines. EBV glycoproteins such as gH/gL, gp42, and gB show excellent immunogenicity in preclinical studies compared to the previously favored gp350 antigen. Combinations of multiple EBV proteins in various vaccine designs become more attractive approaches considering the complex life cycle and complicated infection mechanisms of EBV. Besides, rationally designed vaccines such as virus-like particles (VLPs) and protein scaffold-based vaccines elicited more potent immune responses than soluble antigens. In addition, humanized mice, rabbits, as well as nonhuman primates that can be infected by EBV significantly aid vaccine development. Innovative vaccine design approaches, including polymer-based nanoparticles, the development of effective adjuvants, and antibody-guided vaccine design, will further enhance the immunogenicity of vaccine candidates. In this review, we will summarize (i) the disease burden caused by EBV and the necessity of developing an EBV vaccine; (ii) previous EBV vaccine studies and available animal models; (iii) future trends of EBV vaccines, including activation of cellular immune responses, novel immunogen design, heterologous prime-boost approach, induction of mucosal immunity, application of nanoparticle delivery system, and modern adjuvant development.

A high-throughput neutralizing assay for antibodies and sera evaluation against Epstein-Barr virus

BACKGROUND

Epstein-Barr virus (EBV) is a wide-spread human herpesvirus that is highly associated with infectious mononucleosis and several malignancies. Evaluation of EBV neutralizing antibody titers is important for serological studies, vaccine development and monoclonal antibody screening. The traditional method based on antibody inhibition of EBV transformation of B cells is very time-consuming. A more practical flow cytometry-based (FCM) approach to evaluate neutralizing titers is not amenable to achieving high-throughput evaluation of large-scale samples. A high-throughput approach is urgently needed.

RESULTS

Here, we present a rapid and high-throughput method based on high content imaging system (HCIS) analysis. EBV titers determined by the HCIS-based assay were similar to those obtained by the FCM-based assay. Neutralizing titers of sera and monoclonal antibodies measured by the HCIS-based assay strongly correlated with titers measured by the FCM-based assay. HCIS assays showed a strong correlation between B cell infection neutralizing titers and the anti-gp350 IgG titers in healthy EBV carriers and monkey sera. Finally, anti-gHgL IgG titers from sera of healthy EBV carriers significantly correlated with epithelial cell infection neutralizing titers.

CONCLUSIONS

This HCIS-based assay is a high-throughput assay to determine viral titers and evaluate neutralizing potentials of sera and monoclonal antibodies. This HCIS-based assay will aid the development of vaccines and therapeutic monoclonal antibody against EBV.

Epstein-Barr virus gH/gL has multiple sites of vulnerability for virus neutralization and fusion inhibition

Epstein-Barr virus (EBV) is nearly ubiquitous in adults. EBV causes infectious mononucleosis and is associated with B cell lymphomas, epithelial cell malignancies, and multiple sclerosis. The EBV gH/gL glycoprotein complex facilitates fusion of virus membrane with host cells and is a target of neutralizing antibodies. Here, we examined the sites of vulnerability for virus neutralization and fusion inhibition within EBV gH/gL. We developed a panel of human monoclonal antibodies (mAbs) that targeted five distinct antigenic sites on EBV gH/gL and prevented infection of epithelial and B cells. Structural analyses using X-ray crystallography and electron microscopy revealed multiple sites of vulnerability and defined the antigenic landscape of EBV gH/gL. One mAb provided near-complete protection against viremia and lymphoma in a humanized mouse EBV challenge model. Our findings provide structural and antigenic knowledge of the viral fusion machinery, yield a potential therapeutic antibody to prevent EBV disease, and emphasize gH/gL as a target for herpesvirus vaccines and therapeutics.

How EBV Infects: The Tropism and Underlying Molecular Mechanism for Viral Infection

The Epstein-Barr virus (EBV) is associated with a variety of human malignancies, including Burkitt's lymphoma, Hodgkin's disease, nasopharyngeal carcinoma and gastric cancers. EBV infection is crucial for the oncogenesis of its host cells. The prerequisite for the establishment of infection is the virus entry. Interactions of viral membrane glycoproteins and host membrane receptors play important roles in the process of virus entry into host cells. Current studies have shown that the main tropism for EBV are B cells and epithelial cells and that EBV is also found in the tumor cells derived from NK/T cells and leiomyosarcoma. However, the process of EBV infecting B cells and epithelial cells significantly differs, relying on heterogenous glycoprotein-receptor interactions. This review focuses on the tropism and molecular mechanism of EBV infection. We systematically summarize the key molecular events that mediate EBV cell tropism and its entry into target cells and provide a comprehensive overview.

Protective anti-gB neutralizing antibodies targeting two vulnerable sites for EBV-cell membrane fusion

Epstein-Barr virus (EBV) accounts for 200,000 new epithelial and B cell malignancy cases and 140,000 deaths annually. Glycoprotein B (gB) is the sole fusogen that is highly conserved and essential for all herpesvirus entry into target cells and thus, is attracting attention to identify potent antibodies to neutralize viral infection. Here, we discovered two anti-EBV gB neutralizing antibodies, 3A3 and 3A5, that effectively neutralized EBV infection of both B and epithelial cells. They also potently protected against EBV-induced lymphoproliferative disorders in humanized mice. Importantly, the 3A3 and 3A5 epitopes identified here represent the neutralizing antigenic sites to block EBV infection and membrane fusion. They are major targets of protective gB-specific neutralizing antibodies elicited by natural EBV infection in humans.

Epstein-Barr virus (EBV) infects more than 90% of the world’s adult population and accounts for a significant cancer burden of epithelial and B cell origins. Glycoprotein B (gB) is the primary fusogen essential for EBV entry into host cells. Here, we isolated two EBV gB-specific neutralizing antibodies, 3A3 and 3A5; both effectively neutralized the dual-tropic EBV infection of B and epithelial cells. In humanized mice, both antibodies showed effective protection from EBV-induced lymphoproliferative disorders. Cryoelectron microscopy analyses identified that 3A3 and 3A5 bind to nonoverlapping sites on domains D-II and D-IV, respectively. Structure-based mutagenesis revealed that 3A3 and 3A5 inhibit membrane fusion through different mechanisms involving the interference with gB-cell interaction and gB activation. Importantly, the 3A3 and 3A5 epitopes are major targets of protective gB-specific neutralizing antibodies elicited by natural EBV infection in humans, providing potential targets for antiviral therapies and vaccines.

Immunization with a self-assembling nanoparticle vaccine displaying EBV gH/gL protects humanized mice against lethal viral challenge

Epstein-Barr virus (EBV) is a cancer-associated pathogen responsible for 165,000 deaths annually. EBV is also the etiological agent of infectious mononucleosis and is linked to multiple sclerosis and rheumatoid arthritis. Thus, an EBV vaccine would have a significant global health impact. EBV is orally transmitted and has tropism for epithelial and B cells. Therefore, a vaccine would need to prevent infection of both in the oral cavity. Passive transfer of monoclonal antibodies against the gH/gL glycoprotein complex prevent experimental EBV infection in humanized mice and rhesus macaques, suggesting that gH/gL is an attractive vaccine candidate. Here, we evaluate the immunogenicity of several gH/gL nanoparticle vaccines. All display superior immunogenicity relative to monomeric gH/gL. A nanoparticle displaying 60 copies of gH/gL elicits antibodies that protect against lethal EBV challenge in humanized mice, whereas antibodies elicited by monomeric gH/gL do not. These data motivate further development of gH/gL nanoparticle vaccines for EBV.

A Neutralizing Antibody Targeting gH Provides Potent Protection against EBV Challenge In Vivo

Epstein-Barr virus (EBV) is an oncogenic herpesvirus that is associated with 200,000 new cases of cancer and 140,000 deaths annually. To date, there are no available vaccines or therapeutics for clinical usage. Recently, the viral heterodimer glycoprotein gH/gL has become a promising target for the development of prophylactic vaccines against EBV. Here, we developed the anti-gH antibody 6H2 and its chimeric version C6H2, which had full neutralizing activity in epithelial cells and partial neutralizing activity in B cells. C6H2 exhibited potent protection against lethal EBV challenge in a humanized mouse model. The cryo-electron microscopy (cryo-EM) structure further revealed that 6H2 recognized a previously unidentified epitope on gH/gL D-IV that is critical for viral attachment and subsequent membrane fusion with epithelial cells. Our results suggest that C6H2 is a promising candidate in the prevention of EBV-induced lymphoproliferative diseases (LPDs) and may inform the design of an EBV vaccine. IMPORTANCE Epstein-Barr virus (EBV) is a ubiquitous gammaherpesvirus that establishes lifelong persistence and is related to multiple diseases, including cancers. Neutralizing antibodies (NAbs) have proven to be highly effective in preventing EBV infection and subsequent diseases. Here, we developed an anti-EBV-gH NAb, 6H2, which blocked EBV infection in vitro and in vivo. This 6H2 neutralizing epitope should be helpful to understand EBV infection mechanisms and guide the development of vaccines and therapeutics against EBV infection.

Well Put Together—A Guide to Accessorizing with the Herpesvirus gH/gL Complexes

Herpesviruses are enveloped, double-stranded DNA viruses that infect a variety of hosts across the animal kingdom. Nine of these establish lifelong infections in humans, for which there are no cures and few vaccine or treatment options. Like all enveloped viruses, herpesviruses enter cells by fusing their lipid envelopes with a host cell membrane. Uniquely, herpesviruses distribute the functions of receptor engagement and membrane fusion across a diverse cast of glycoproteins. Two glycoprotein complexes are conserved throughout the three herpesvirus subfamilies: the trimeric gB that functions as a membrane fusogen and the heterodimeric gH/gL, the role of which is less clearly defined. Here, we highlight the conserved and divergent functions of gH/gL across the three subfamilies of human herpesviruses by comparing its interactions with a broad range of accessory viral proteins, host cell receptors, and neutralizing or inhibitory antibodies. We propose that the intrinsic structural plasticity of gH/gL enables it to function as a signal integration machine that can accept diverse regulatory inputs and convert them into a “trigger” signal that activates the fusogenic ability of gB.

A potent and protective human neutralizing antibody targeting a novel vulnerable site of Epstein-Barr virus

Epstein-Barr virus (EBV) is associated with a range of epithelial and B cell malignancies as well as autoimmune disorders, for which there are still no specific treatments or effective vaccines. Here, we isolate EBV gH/gL-specific antibodies from an EBV-infected individual. One antibody, 1D8, efficiently neutralizes EBV infection of two major target cell types, B cells and epithelial cells. In humanized mice, 1D8 provides protection against a high-dose EBV challenge by substantially reducing viral loads and associated tumor burden. Crystal structure analysis reveals that 1D8 binds to a key vulnerable interface between the D-I/D-II domains of the viral gH/gL protein, especially the D-II of the gH, thereby interfering with the gH/gL-mediated membrane fusion and binding to target cells. Overall, we identify a potent and protective neutralizing antibody capable of reducing the EBV load. The novel vulnerable site represents an attractive target that is potentially important for antibody and vaccine intervention against EBV infection.

Main Targets of Interest for the Development of a Prophylactic or Therapeutic Epstein-Barr Virus Vaccine

Epstein-Barr virus (EBV) is one of the most widespread viruses in the world; more than 90% of the planet's adult population is infected. Symptomatic primary infection by this Herpesviridae corresponds to infectious mononucleosis (IM), which is generally a benign disease. While virus persistence is often asymptomatic, it is responsible for 1.5% of cancers worldwide, mainly B cell lymphomas and carcinomas. EBV may also be associated with autoimmune and/or inflammatory diseases. However, no effective treatment or anti-EBV vaccine is currently available. Knowledge of the proteins and mechanisms involved in the different steps of the viral cycle is essential to the development of effective vaccines. The present review describes the main actors in the entry of the virus into B cells and epithelial cells, which are targets of interest in the development of prophylactic vaccines aimed at preventing viral infection. This review also summarizes the first vaccinal approaches tested in humans, all of which are based on the gp350/220 glycoprotein; while they have reduced the risk of IM, they have yet to prevent EBV infection. The main proteins involved in the EBV latency cycle and some of the proteins involved in the lytic cycle have essential roles in the oncogenesis of EBV. For that reason, these proteins are of interest for the development of therapeutic vaccines of which the objective is the stimulation of T cell immunity against EBV-associated cancers. New strategies aimed at broadening the antigenic spectrum, are currently being studied and will contribute to the targeting of the essential steps of the viral cycle, the objective being to prevent or treat the diseases associated with EBV.

The structural basis of herpesvirus entry

Herpesviruses are ubiquitous, double-stranded DNA, enveloped viruses that establish lifelong infections and cause a range of diseases. Entry into host cells requires binding of the virus to specific receptors, followed by the coordinated action of multiple viral entry glycoproteins to trigger membrane fusion. Although the core fusion machinery is conserved for all herpesviruses, each species uses distinct receptors and receptor-binding glycoproteins. Structural studies of the prototypical herpesviruses herpes simplex virus 1 (HSV-1), HSV-2, human cytomegalovirus (HCMV) and Epstein-Barr virus (EBV) entry glycoproteins have defined the interaction sites for glycoprotein complexes and receptors, and have revealed conformational changes that occur on receptor binding. Recent crystallography and electron microscopy studies have refined our model of herpesvirus entry into cells, clarifying both the conserved features and the unique features. In this Review, we discuss recent insights into herpesvirus entry by analysing the structures of entry glycoproteins, including the diverse receptor-binding glycoproteins (HSV-1 glycoprotein D (gD), EBV glycoprotein 42 (gp42) and HCMV gH-gL-gO trimer and gH-gL-UL128-UL130-UL131A pentamer), as well gH-gL and the fusion protein gB, which are conserved in all herpesviruses.

Epithelial cell infection by Epstein-Barr virus

Epstein-Barr Virus (EBV) is etiologically associated with multiple human malignancies including Burkitt lymphoma and Hodgkin disease as well as nasopharyngeal and gastric carcinoma. Entry of EBV into target cells is essential for virus to cause disease and is mediated by multiple viral envelope glycoproteins and cell surface associated receptors. The target cells of EBV include B cells and epithelial cells. The nature and mechanism of EBV entry into these cell types are different, requiring different glycoprotein complexes to bind to specific receptors on the target cells. Compared to the B cell entry mechanism, the overall mechanism of EBV entry into epithelial cells is less well known. Numerous receptors have been implicated in this process and may also be involved in additional processes of EBV entry, transport, and replication. This review summarizes EBV glycoproteins, host receptors, signal molecules and transport machinery that are being used in the epithelial cell entry process and also provides a broad view for related herpesvirus entry mechanisms.

Structural basis for the interaction of human herpesvirus 6B tetrameric glycoprotein complex with the cellular receptor, human CD134

A unique glycoprotein is expressed on the virus envelope of human herpesvirus 6B (HHV-6B): the complex gH/gL/gQ1/gQ2 (hereafter referred to as the HHV-6B tetramer). This tetramer recognizes a host receptor expressed on activated T cells: human CD134 (hCD134). This interaction is essential for HHV-6B entry into the susceptible cells and is a determinant for HHV-6B cell tropism. The structural mechanisms underlying this unique interaction were unknown. Herein we solved the interactions between the HHV-6B tetramer and the receptor by using their neutralizing antibodies in molecular and structural analyses. A surface plasmon resonance analysis revealed fast dissociation/association between the tetramer and hCD134, although the affinity was high (KD  = 18 nM) and comparable to those for the neutralizing antibodies (anti-gQ1: 17 nM, anti-gH: 2.7 nM). A competition assay demonstrated that the anti-gQ1 antibody competed with hCD134 in the HHV-6B tetramer binding whereas the anti-gH antibody did not, indicating the direct interaction of gQ1 and hCD134. A single-particle analysis by negative-staining electron microscopy revealed the tetramer's elongated shape with a gH/gL part and extra density corresponding to gQ1/gQ2. The anti-gQ1 antibody bound to the tip of the extra density, and anti-gH antibody bound to the putative gH/gL part. These results highlight the interaction of gQ1/gQ2 in the HHV-6B tetramer with hCD134, and they demonstrate common features among viral ligands of the betaherpesvirus subfamily from a macroscopic viewpoint.

Neutralizing Antibodies Protect against Oral Transmission of Lymphocryptovirus

Epstein-Barr virus (EBV) is a cancer-associated pathogen for which there is no vaccine. Successful anti-viral vaccines elicit antibodies that neutralize infectivity; however, it is unknown whether neutralizing antibodies prevent EBV acquisition. Here we assessed whether passively delivered AMMO1, a monoclonal antibody that neutralizes EBV in a cell-type-independent manner, could protect against experimental EBV challenge in two animal infection models. When present prior to a high-dose intravenous EBV challenge, AMMO1 prevented viremia and reduced viral loads to nearly undetectable levels in humanized mice. AMMO1 conferred sterilizing immunity to three of four macaques challenged orally with rhesus lymphocryptovirus, the EBV ortholog that infects rhesus macaques. The infected macaque had lower plasma neutralizing activity than the protected animals. These results indicate that a vaccine capable of eliciting adequate titers of neutralizing antibodies targeting the AMMO1 epitope may protect against EBV acquisition and are therefore highly relevant to the design of an effective EBV vaccine.

An anti-EBV mAb, AMMO1, limits viral replication following challenge in humanized mice

AMMO1 cross-reacts with and neutralizes rhesus lymphocryptovirus

Adequate levels of AMMO1 prevent oral acquisition of rhLCV in macaques

Protection afforded by neutralizing antibody provides proof of concept for EBV vaccines

Evaluation of Total and IgA-Specific Antibody Targeting Epstein-Barr Virus Glycoprotein 350 and Nasopharyngeal Carcinoma Risk

Background

We previously reported that higher levels of antibody targeting Epstein-Barr virus (EBV) glycoprotein350 (gp350), an EBV vaccine candidate, were protective against nasopharyngeal carcinoma (NPC) in genetically high-risk families from Taiwan. The current study attempted to extend this association to a general population cohort.

Methods

We compared total and IgA-specific gp350 antibody levels in 35 incident NPC cases and 81 disease-free controls from the Cancer Screening Program in Taiwan (23943 individuals recruited 1991-1992). Luciferase immunoprecipitation assays quantified gp350 antibody.

Results

Total EBVgp350 antibody levels were not higher in individuals who remained disease free compared to those who developed NPC (P = .11). This lack of a protective gp350 association persisted for cases diagnosed ≥5 years (odds ratio [OR] = 1.05; P = .91) and <5 years (OR = 1.85; P = .40) after blood draw. IgA-specific gp350 antibody levels were higher in cases than controls (OR = 7.03; P = .001). This increased risk was most pronounced for cases diagnosed <5 years after blood draw (OR = 11.7; P = .004).

Conclusion

Unlike our prior findings in those with a strong family history of NPC, total gp350 antibody levels were not protective against NPC development in this general population setting.

Epstein-Barr Virus and the Human Leukocyte Antigen Complex

Purpose

While most adults are infected Epstein-Barr virus (EBV), 3-5% remain uninfected. The human leukocyte antigen (HLA) complex, which controls many pathogens, may influence infection and disease associated with EBV.

Recent Findings

Numerous EBV proteins and miRNAs down-regulate HLA class I and II expression on the cell surface. HLA class II functions as a receptor for EBV entry into B cells. Specific HLA class II alleles correlate with the susceptibility of B cells to EBV infection in vitro and with EBV seropositivity or seronegativity of humans. HLA class I polymorphisms correlate with development and severity of EBV infectious mononucleosis and with the risk of several virus-associated malignancies including nasopharyngeal carcinoma, Hodgkin lymphoma, and post-transplant lymphoproliferative disease.

Significance

These findings indicate that while EBV has evolved to use MHC class II as a receptor for virus entry, polymorphisms in MHC class II and class I influence virus infection and disease.

Immunization with Components of the Viral Fusion Apparatus Elicits Antibodies That Neutralize Epstein-Barr Virus in B Cells and Epithelial Cells

Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with epithelial-cell cancers and B cell lymphomas. An effective EBV vaccine is not available. We found that antibodies to the EBV glycoprotein gH/gL complex were the principal components in human plasma that neutralized infection of epithelial cells and that antibodies to gH/gL and gp42 contributed to B cell neutralization. Immunization of mice and nonhuman primates with nanoparticle vaccines that displayed components of the viral-fusion machinery EBV gH/gL or gH/gL/gp42 elicited antibodies that potently neutralized both epithelial-cell and B cell infection. Immune serum from nonhuman primates inhibited EBV-glycoprotein-mediated fusion of epithelial cells and B cells and targeted an epitope critical for virus-cell fusion. Therefore, unlike the leading EBV gp350 vaccine candidate, which only protects B cells from infection, these EBV nanoparticle vaccines elicit antibodies that inhibit the virus-fusion apparatus and provide cell-type-independent protection from virus infection.

From recognition to execution-the HCMV Pentamer from receptor binding to fusion triggering

The β-herpesvirus human cytomegalovirus (HCMV) is the leading viral cause of neonatal developmental disabilities. In HCMV, the conserved herpesvirus glycoprotein B (gB) mediates membrane fusion between the viral and host cell membranes, whereas the trimeric gH/gL/gO or the pentameric gH/gL/UL128/UL130/UL31A complexes (Pentamer) bind to cell-specific receptors and provide the triggering signal to gB. Recent structural and functional studies have provided new insights into Pentamer structure, conformational flexibility, location of epitopes for neutralizing antibodies and potential binding sites for cell surface receptors. Together, these data suggest a model where receptor binding triggers a conformational change in Pentamer, allowing it to interact with gB and initiate the membrane fusion process.

An Antibody Targeting the Fusion Machinery Neutralizes Dual-Tropic Infection and Defines a Site of Vulnerability on Epstein-Barr Virus

Epstein-Barr virus (EBV) is a causative agent of infectious mononucleosis and is associated with 200,000 new cases of cancer and 140,000 deaths annually. Subunit vaccines against this pathogen have focused on the gp350 glycoprotein and remain unsuccessful. We isolated human antibodies recognizing the EBV fusion machinery (gH/gL and gB) from rare memory B cells. One anti-gH/gL antibody, AMMO1, potently neutralized infection of B cells and epithelial cells, the two major cell types targeted by EBV. We determined a cryo-electron microscopy reconstruction of the gH/gL-gp42-AMMO1 complex and demonstrated that AMMO1 bound to a discontinuous epitope formed by both gH and gL at the Domain-I/Domain-II interface. Integrating structural, biochemical, and infectivity data, we propose that AMMO1 inhibits fusion of the viral and cellular membranes. This work identifies a crucial epitope that may aid in the design of next-generation subunit vaccines against this major public health burden.

Perspectives of Phage-Eukaryotic Cell Interactions to Control Epstein-Barr Virus Infections

Recently, leading medical journals emphasized the importance of further studies on the potential application of bacterial viruses (phages) for the treatment of antibiotics-resistant infections outlining the present status of the therapy and perspectives for the future. Furthermore, a leading scientific journal pointed to the recent progress in research on phage interactions with eukaryotic cells (especially cells of the immune system) and potential implications of their results for our broader understanding of the role of phages – not only as “bacteria eaters” – but also as an important part of our body defense protecting against external and internal pathogenic invaders (as suggested previously). This illustrates how our understanding of the actual role and potential of phages is expanding and how worldwide interest in their use in medicine is growing. In this article we envision how this advancement of our knowledge about phages could be translated into the progress in combating herpesvirus infections especially those caused by Epstein–Barr virus (EBV).