Glycoprotein D of herpes simplex virus (HSV) binds directly to HVEM, a member of the tumor necrosis factor receptor superfamily and a mediator of HSV entry

Peptides targeting the BTLA-HVEM complex can modulate T cell immune response

Immune checkpoints secure the proper function of the immune system and the maintenance of the BTLA-HVEM complex, an inhibitory immune checkpoint, is one of the pathways vital for T cell responsiveness to various stimuli. The present study reports the immunomodulatory potential of five peptides targeting the BTLA-HVEM complex on the activity of human T cells. Isolated T cells were exposed to the peptides alone or combined with CD3/CD28 mAb for 72 h or 120 h. The flow cytometry was used to evaluate the activation markers (CD69, CD62L, CD25), changes within the T cell memory compartment, proliferation rate, and apoptosis of T cells. The immunomodulatory effect of the peptides was visible as an increase in the percentage of CD4+ and CD8+ T cells expressing CD69 or CD25, a boost in T cell proliferation, and shifts in the T cell memory compartment. Pep(2) and Pep(5) were the most promising compounds, displaying a putative immune-restoring function.

In vitro reconstitution of herpes simplex virus 1 fusion identifies low pH as a fusion co-trigger

IMPORTANCE

HSV-1 causes lifelong, incurable infections and diseases ranging from mucocutaneous lesions to fatal encephalitis. Fusion of viral and host membranes is a critical step in HSV-1 infection of target cells that requires multiple factors on both the viral and host sides. Due to this complexity, many fundamental questions remain unanswered, such as the identity of the viral and host factors that are necessary and sufficient for HSV-1-mediated membrane fusion and the nature of the fusion trigger. Here, we developed a simplified in vitro fusion assay to examine the fusion requirements and identified low pH as a co-trigger for virus-mediated fusion in vitro. We hypothesize that low pH has a critical role in cell entry and, potentially, pathogenesis.

Immune checkpoints in rheumatoid arthritis: progress and promise

Rheumatoid arthritis (RA) is one of the most prevalent autoimmune inflammatory conditions, and while the mechanisms driving pathogenesis are yet to be completely elucidated, self-reactive T cells and immune checkpoint pathways have a clear role. In this review, we provide an overview of the importance of checkpoint pathways in the T cell response and describe the involvement of these in RA development and progression. We discuss the relationship between immune checkpoint therapy in cancer and autoimmune adverse events, draw parallels with the involvement of immune checkpoints in RA pathobiology, summarise emerging research into some of the lesser-known pathways, and the potential of targeting checkpoint-related pathways in future treatment approaches to RA management.

Effects of leucism on organ development and molecular mechanisms in Northern snakehead (Channa argus) beyond pigmentation alterations

Leucism, a widespread occurrence observed in Northern snakehead (Channa argus), bestows a striking white jade-like body coloration upon affected individuals and has gained substantial popularity in commercial breeding. While the visible manifestation of leucism in snakeheads is primarily limited to body coloration, it is crucial to explore the potential influence of leucism on organ development and elucidate the underlying molecular mechanisms. Through a comparative analysis of growth differences, our study revealed that at 150 days post-fertilization, the white variety exhibited an 8.5% higher liver index and intestinal index, but experienced a 20% and 38% decreased in spleen index and renal interstitial index, respectively, suggesting an enlarged digestive area but relatively smaller immune tissues. Nonetheless, no significant differences were observed in the intestinal flora between the two varieties, suggesting the exclusion of any exogenous impacts from symbiotic flora on the growth and development of the white variety. Importantly, transcriptome analysis demonstrated that the white variety exhibited higher expression levels of innate immune genes. Furthermore, annotation of the gene sets expressed in the liver and spleen revealed 76 and 35 genes respectively, with the white variety displaying lower expression in genes associated with "Viral protein interaction with cytokine and cytokine receptor", "Protein processing in endoplasmic reticulum", and "TNF signaling pathway", while exhibiting higher expression in "Estrogen signaling pathway". Notably, three genes, namely pcdhf 4, nlrc3 card 15-like, and a pol-like were identified in both the liver and spleen, indicating their potential involvement in altering the development and innate immunity of the white variety. This study reveals the systemic impact of leucism that extends beyond mere pigmentation alterations, highlighting the prominent characteristics of this phenotype and providing a foundation for future molecular breeding programs aimed at enhancing this variety.

Beyond the anti-PD-1/PD-L1 era: promising role of the BTLA/HVEM axis as a future target for cancer immunotherapy

Recent introduction of monoclonal antibodies targeting immune checkpoints to harness antitumor immunity has revolutionized the cancer treatment landscape. The therapeutic success of immune checkpoint blockade (ICB)-based therapies mainly relies on PD-1/PD-L1 and CTLA-4 blockade. However, the limited overall responses and lack of reliable predictive biomarkers of patient´s response are major pitfalls limiting immunotherapy success. Hence, this reflects the compelling need of unveiling novel targets for immunotherapy that allow to expand the spectrum of ICB-based strategies to achieve optimal therapeutic efficacy and benefit for cancer patients. This review thoroughly dissects current molecular and functional knowledge of BTLA/HVEM axis and the future perspectives to become a target for cancer immunotherapy. BTLA/HVEM dysregulation is commonly found and linked to poor prognosis in solid and hematological malignancies. Moreover, circulating BTLA has been revealed as a blood-based predictive biomarker of immunotherapy response in various cancers. On this basis, BTLA/HVEM axis emerges as a novel promising target for cancer immunotherapy. This prompted rapid development and clinical testing of the anti-BTLA blocking antibody Tifcemalimab/icatolimab as the first BTLA-targeted therapy in various ongoing phase I clinical trials with encouraging results on preliminary efficacy and safety profile as monotherapy and combined with other anti-PD-1/PD-L1 therapies. Nevertheless, it is anticipated that the intricate signaling network constituted by BTLA/HVEM/CD160/LIGHT involved in immune response regulation, tumor development and tumor microenvironment could limit therapeutic success. Therefore, in-depth functional characterization in different cancer settings is highly recommended for adequate design and implementation of BTLA-targeted therapies to guarantee the best clinical outcomes to benefit cancer patients.

Molecular determinants of the interaction between HSV-1 glycoprotein D and heparan sulfate

Literature has well-established the importance of 3-O-sulfation of neuronal cell surface glycan heparan sulfate (HS) to its interaction with herpes simplex virus type 1 glycoprotein D (gD). Previous investigations of gD to its viral receptors HVEM and nectin-1 also highlighted the conformational dynamics of gD's N- and C-termini, necessary for viral membrane fusion. However, little is known on the structural interactions of gD with HS. Here, we present our findings on this interface from both the glycan and the protein perspective. We used C-terminal and N-terminal gD variants to probe the role of their respective regions in gD/HS binding. The N-terminal truncation mutants (with Δ1-22) demonstrate equivalent or stronger binding to heparin than their intact glycoproteins, indicating that the first 22 amino acids are disposable for heparin binding. Characterization of the conformational differences between C-terminal truncated mutants by sedimentation velocity analytical ultracentrifugation distinguished between the "open" and "closed" conformations of the glycoprotein D, highlighting the region's modulation of receptor binding. From the glycan perspective, we investigated gD interacting with heparin, heparan sulfate, and other de-sulfated and chemically defined oligosaccharides using surface plasmon resonance and glycan microarray. The results show a strong preference of gD for 6-O-sulfate, with 2-O-sulfation becoming more important in the presence of 6-O-S. Additionally, 3-O-sulfation shifted the chain length preference of gD from longer chain to mid-chain length, reaffirming the sulfation site's importance to the gD/HS interface. Our results shed new light on the molecular details of one of seven known protein-glycan interactions with 3-O-sulfated heparan sulfate.

SUMOylation and Viral Infections of the Brain

The small ubiquitin-like modifier (SUMO) system regulates numerous biological processes, including protein localization, stability and/or activity, transcription, and DNA repair. SUMO also plays critical roles in innate immunity and antiviral defense by mediating interferon (IFN) synthesis and signaling, as well as the expression and function of IFN-stimulated gene products. Viruses including human immunodeficiency virus-1, Zika virus, herpesviruses, and coronaviruses have evolved to exploit the host SUMOylation system to counteract the antiviral activities of SUMO proteins and to modify their own proteins for viral persistence and pathogenesis. Understanding the exploitation of SUMO is necessary for the development of effective antiviral therapies. This review summarizes the interplay between viruses and the host SUMOylation system, with a special emphasis on viruses with neuro-invasive properties that have pathogenic consequences on the central nervous system.

Opportunities, Technology, and the Joy of Discovery

My grandparents were immigrants. My paternal grandfather was illiterate. Yet my parents were able to complete college and to become teachers. I had a conventional upbringing in a small town in Florida, graduating from high school in 1960. I was fortunate enough to graduate cum laude from Florida State University and to earn other credentials leading to faculty positions at outstanding institutions of higher education: the University of Chicago and Northwestern University. At a time when women were rarely the leaders of research groups, I was able to establish a well-funded research program and to make contributions to our understanding of viral entry into cells. My best research was done after I became confident enough to seek productive interactions with collaborators. I am grateful for the collaborators and collaborations that moved our field forward and for my trainees who have gone on to successes in many different careers. Expected final online publication date for the Annual Review of Virology, Volume 9 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Targeting the HVEM protein using a fragment of glycoprotein D to inhibit formation of the BTLA/HVEM complex

Cancer immunotherapy using blockade of immune checkpoints is mainly based on monoclonal antibodies. Despite the tremendous success achieved by using those molecules to block immune checkpoint proteins, antibodies possess some weaknesses, which means that there is still a need to search for new compounds as alternatives to antibodies. Many current approaches are focused on use of peptides/peptidomimetics to destroy receptor/ligand interactions. Our studies concern blockade of the BTLA/HVEM complex, which generates an inhibitory effect on the immune response resulting in tolerance to cancer cells. To design inhibitors of such proteins binding we based our work on the amino acid sequence and structure of a ligand of HVEM protein, namely glycoprotein D, which possesses the same binding site on HVEM as BTLA protein. To disrupt the BTLA and HVEM interaction we designed several peptides, all fragments of glycoprotein D, and tested their binding to HVEM using SPR and their ability to inhibit the BTLA/HVEM complex formation using ELISA tests and cellular reporter platforms. That led to identification of two peptides, namely gD(1-36)(K10C-D30C) and gD(1-36)(A12C-L25C), which interact with HVEM and possess blocking capacities. Both peptides are not cytotoxic to human PBMCs, and show stability in human plasma. We also studied the 3D structure of the gD(1-36)(K10C-D30C) peptide using NMR and molecular modeling methods. The obtained data reveal that it possesses an unstructured conformation and binds to HVEM in the same location as gD and BTLA. All these results suggest that peptides based on the binding fragment of gD protein represent promising immunomodulation agents for future cancer immunotherapy.

Herpes simplex virus interference with immunity: Focus on dendritic cells

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are highly prevalent in the human population. These viruses cause lifelong infections by establishing latency in neurons and undergo sporadic reactivations that promote recurrent disease and new infections. The success of HSVs in persisting in infected individuals is likely due to their multiple molecular determinants involved in escaping the host antiviral and immune responses. Importantly, HSVs infect and negatively modulate the function of dendritic cells (DCs), key immune cells that are involved in establishing effective and balanced immunity against viruses. Here, we review and discuss several molecular and cellular processes modulated by HSVs in DCs, such as autophagy, apoptosis, and the unfolded protein response. Given the central role of DCs in establishing optimal antiviral immunity, particular emphasis should be given to the outcome of the interactions occurring between HSVs and DCs.

Developments in Vaccination for Herpes Simplex Virus

Herpes simplex virus (HSV) is an alpha herpes virus, with two subtypes: HSV-1 and HSV-2. HSV is one of the most prevalent sexually transmitted infections. It is the cause of severe neonatal infections and a leading cause of infectious blindness in the Western world. As of 2016, 13.2% of the global population ages 15-49 were existing with HSV-2 infection and 66.6% with HSV-1. This high prevalence of disease and the fact that resistance to current therapies is on the rise makes it imperative to develop and discover new methods of HSV prevention and management. Among the arsenal of therapies/treatments for this virus has been the development of a prophylactic or therapeutic vaccine to prevent the complications of HSV reactivation. Our current understanding of the immune responses involved in latency and reactivation provides a unique challenge to the development of vaccines. There are no approved vaccines currently available for either prophylaxis or therapy. However, there are various promising candidates in the pre-clinical and clinical phases of study. Vaccines are being developed with two broad focuses: preventative and therapeutic, some with a dual use as both immunotherapeutic and prophylactic. Within this article, we will review the current guidelines for the treatment of herpes simplex infections, our understanding of the immunological pathways involved, and novel vaccine candidates in development.

HVEM structures and mutants reveal distinct functions of binding to LIGHT and BTLA/CD160

HVEM is a TNF (tumor necrosis factor) receptor contributing to a broad range of immune functions involving diverse cell types. It interacts with a TNF ligand, LIGHT, and immunoglobulin (Ig) superfamily members BTLA and CD160. Assessing the functional impact of HVEM binding to specific ligands in different settings has been complicated by the multiple interactions of HVEM and HVEM binding partners. To dissect the molecular basis for multiple functions, we determined crystal structures that reveal the distinct HVEM surfaces that engage LIGHT or BTLA/CD160, including the human HVEM-LIGHT-CD160 ternary complex, with HVEM interacting simultaneously with both binding partners. Based on these structures, we generated mouse HVEM mutants that selectively recognized either the TNF or Ig ligands in vitro. Knockin mice expressing these muteins maintain expression of all the proteins in the HVEM network, yet they demonstrate selective functions for LIGHT in the clearance of bacteria in the intestine and for the Ig ligands in the amelioration of liver inflammation.

The Structures and Functions of VZV Glycoproteins

The virions of all enveloped viruses, including those of the Herpesviridae, must bind to the cell surface then undergo a process of membrane fusion between the cell plasma membrane and the virus particle envelope. As for all herpesviruses, glycoproteins in the virion envelope are the modus operandi of these events.

The Hippocampal Vulnerability to Herpes Simplex Virus Type I Infection: Relevance to Alzheimer's Disease and Memory Impairment

Herpes simplex virus type 1 (HSV-1) as a possible infectious etiology in Alzheimer’s disease (AD) has been proposed since the 1980s. The accumulating research thus far continues to support the association and a possible causal role of HSV-1 in the development of AD. HSV-1 has been shown to induce neuropathological and behavioral changes of AD, such as amyloid-beta accumulation, tau hyperphosphorylation, as well as memory and learning impairments in experimental settings. However, a neuroanatomical standpoint of HSV-1 tropism in the brain has not been emphasized in detail. In this review, we propose that the hippocampal vulnerability to HSV-1 infection plays a part in the development of AD and amnestic mild cognitive impairment (aMCI). Henceforth, this review draws on human studies to bridge HSV-1 to hippocampal-related brain disorders, namely AD and aMCI/MCI. Next, experimental models and clinical observations supporting the neurotropism or predilection of HSV-1 to infect the hippocampus are examined. Following this, factors and mechanisms predisposing the hippocampus to HSV-1 infection are discussed. In brief, the hippocampus has high levels of viral cellular receptors, neural stem or progenitor cells (NSCs/NPCs), glucocorticoid receptors (GRs) and amyloid precursor protein (APP) that support HSV-1 infectivity, as well as inadequate antiviral immunity against HSV-1. Currently, the established diseases HSV-1 causes are mucocutaneous lesions and encephalitis; however, this review revises that HSV-1 may also induce and/or contribute to hippocampal-related brain disorders, especially AD and aMCI/MCI.

Placental Immune Responses to Viruses: Molecular and Histo-Pathologic Perspectives

As most recently demonstrated by the SARS-CoV-2 pandemic, congenital and perinatal infections are of significant concern to the pregnant population as compared to the general population. These outcomes can range from no apparent impact all the way to spontaneous abortion or fetal infection with long term developmental consequences. While some pathogens have developed mechanisms to cross the placenta and directly infect the fetus, other pathogens lead to an upregulation in maternal or placental inflammation that can indirectly cause harm. The placenta is a temporary, yet critical organ that serves multiple important functions during gestation including facilitation of fetal nutrition, oxygenation, and prevention of fetal infection in utero. Here, we review trophoblast cell immunology and the molecular mechanisms utilized to protect the fetus from infection. Lastly, we discuss consequences in the placenta when these protections fail and the histopathologic result following infection.

Fragments of gD Protein as Inhibitors of BTLA/HVEM Complex Formation-Design, Synthesis, and Cellular Studies

One of the major current trends in cancer immunotherapy is the blockade of immune checkpoint proteins that negatively regulate the immune response. This has been achieved through antibodies blocking PD-1/PD-L1 and CTLA-4/CD80/CD86 interactions. Such antibodies have revolutionized oncological therapy and shown a new way to fight cancer. Additional (negative) immune checkpoints are also promising targets in cancer therapy and there is a demand for inhibitors for these molecules. Our studies are focused on BTLA/HVEM complex, which inhibits T-cell proliferation and cytokine production and therefore has great potential as a new target for cancer treatment. The goal of the presented studies was the design and synthesis of compounds able to block BTLA/HVEM interactions. For that purpose, the N-terminal fragment of glycoprotein D (gD), which interacts with HVEM, was used. Based on the crystal structure of the gD/HVEM complex and MM/GBSA analysis performed on it, several peptides were designed and synthesized as potential inhibitors of the BTLA/HVEM interaction. Affinity tests, ELISA tests, and cellular-based reporter assays were performed on these compounds to check their ability to bind to HVEM and to inhibit BTLA/HVEM complex formation. For leading peptides candidates, all-atom and subsequent docking simulations with a coarse-grained force field were performed to determine their binding modes. To further evaluate their potential as drug candidates, their stability in plasma and their cytotoxicity effects on PBMCs were assessed. Our data indicate that the peptide gD(1-36)(K10C-T29C) is the best candidate as a future drug. It interacts with HVEM protein, blocks the BTLA/HVEM interaction, and is nontoxic to cells. The present study provides a new perspective on the development of BTLA/HVEM inhibitors that disrupt protein interactions.

Trivalent Glycoprotein Subunit Vaccine Prevents Neonatal Herpes Simplex Virus Mortality and Morbidity

Herpes simplex virus (HSV) can cause severe infection in neonates leading to mortality and lifelong morbidity. Prophylactic approaches, such as maternal immunization, could prevent neonatal HSV (nHSV) infection by providing protective immunity and preventing perinatal transmission. We previously showed that maternal immunization with a replication-defective HSV vaccine candidate, dl5-29, leads to transfer of virus-specific antibodies into the neonatal circulation and protects against nHSV neurological sequela and mortality (C. D. Patel, I. M. Backes, S. A. Taylor, Y. Jiang, et al., Sci Transl Med, 11:eaau6039, 2019, https://doi.org/10.1126/scitranslmed.aau6039). In this study, we evaluated the efficacy of maternal immunization with an experimental trivalent (gC2, gD2, and gE2) subunit vaccine to protect against nHSV. Using a murine model of nHSV, we demonstrated that maternal immunization with the trivalent vaccine protected offspring against nHSV-disseminated disease and mortality. In addition, offspring of immunized dams were substantially protected from behavioral pathology following HSV infection. This study supports the idea that maternal immunization is a viable strategy for the prevention of neonatal infections.IMPORTANCE Herpes simplex virus is among the most serious infections of newborns. Current antiviral therapies can prevent mortality if infection is recognized early and treated promptly. Most children who survive nHSV develop lifelong neurological and behavioral deficits, despite aggressive antiviral treatment. We propose that maternal immunization could provide protection against HSV for both mother and baby. To this end, we used a trivalent glycoprotein vaccine candidate to demonstrate that offspring are protected from nHSV following maternal immunization. Significantly, this approach protected offspring from long-term behavioral morbidity. Our results emphasize the importance of providing protective immunity to neonates during this window of vulnerability.

Pathogenesis of Herpes Stromal Keratitis: Immune Inflammatory Response Mediated by Inflammatory Regulators

Herpes stromal keratitis (HSK) is one of the primary diseases that cause vision loss or even blindness after herpes simplex virus (HSV)-1 infection. HSK-associated vision impairment is predominantly due to corneal scarring and neovascularization caused by inflammation. In the infected cornea, HSV can activate innate and adaptive immune responses of host cells, which triggers a cascade of reactions that leads to the release of inflammatory cytokines, chemokines, microRNA, and other regulatory factors that have stimulating or inhibitory effects on tissue. Physiologically, host cells show homeostasis. In this review, we summarize the factors involved in HSK pathogenesis from the perspective of immunity, molecules, and pathological angiogenesis. We also describe in detail the pathogenesis of chronic inflammatory lesions of the corneal stroma in response to HSV-1 infection.

Understanding T cell signaling using membrane reconstitution

T cells are central players of our immune system, as their functions range from killing tumorous and virus-infected cells to orchestrating the entire immune response. In order for T cells to divide and execute their functions, they must be activated by antigen-presenting cells (APCs) through a cell-cell junction. Extracellular interactions between receptors on T cells and their ligands on APCs trigger signaling cascades comprised of protein-protein interactions, enzymatic reactions, and spatial reorganization events, to either stimulate or repress T cell activation. Plasma membrane is the major platform for T cell signaling. Recruitment of cytosolic proteins to membrane-bound receptors is a common critical step in many signaling pathways. Membranes decrease the dimensionality of protein-protein interactions to enable weak yet biologically important interactions. Membrane resident proteins can phase separate into micro-islands that promote signaling by enriching or excluding signal regulators. Moreover, some membrane lipids can either mediate or regulate cell signaling by interacting with signaling proteins. While it is critical to investigate T cell signaling in a cellular environment, the large number of signaling pathways involved and potential crosstalk have made it difficult to obtain precise, quantitative information on T cell signaling. Reconstitution of purified proteins to model membranes provides a complementary avenue for T cell signaling research. Here, I review recent progress in studying T cell signaling using membrane reconstitution approaches.

Human Cytomegalovirus (HCMV) Reactivation in the Mammary Gland Induces a Proinflammatory Cytokine Shift in Breast Milk

A locally restricted human cytomegalovirus (HCMV) reactivation in the mammary gland commonly occurs in nearly every IgG-seropositive breastfeeding mother. This unique phenomenon can therefore be used to study the reactivation process in an immunocompetent healthy host. Breast milk contains a variety of immunoactive compounds, including immune cells, antibodies, growth factors, and cytokines supporting the newborn’s immature immune system. To characterize the impact of HCMV reactivation on breast milk cytokines, we analyzed longitudinal breast milk samples of four IgG-seropositive and three IgG-seronegative mothers of preterm infants using Proximity Extension Assay (PEA) technology (Olink Proteomics, Uppsala, Sweden). Cytokine profiling revealed elevated cytokine levels in IgG-seropositive mothers’ milk whey. Reactivating mothers showed higher levels of CC-chemokines (MCP-2, CCL19, and CCL20) and CXC-chemokines (IL-8, CXCL9, CXCL10, and CXCL11), such as the proinflammatory cytokine IL-17C, glycoprotein CD5, and TNFSF14. HCMV reactivation seems to influence the cytokine profile in human breast milk. This work could open the door for further studies analyzing distinct relations of the cytokine network as well as phenotypical and functional T cell properties in background of HCMV DNA dynamics in early lactation.

Immunomodulatory Bonds of the Partnership between Dendritic Cells and T Cells

By acquiring, processing, and presenting both foreign and self-antigens, dendritic cells (DCs) initiate T cell activation that is shaped through the immunomodulatory functions of a variety of cell-membrane-bound molecules including BTLA-HVEM, CD40-CD40L, CTLA-4-CD80/CD86, CD70-CD27, ICOS-ICOS-L, OX40-OX40L, and PD-L1-PD-1, as well as several key cytokines and enzymes such as interleukin-6 (IL-6), IL-12, IL-23, IL-27, transforming growth factor-beta 1 (TGF-β1), retinaldehyde dehydrogenase (Raldh), and indoleamine 2,3-dioxygenase (IDO). Some of these distinct immunomodulatory signals are mediated by specific subsets of DCs, therefore contributing to the functional specialization of DCs in the priming and regulation of immune responses. In addition to responding to the DC-mediated signals, T cells can reciprocally modulate the immunomodulatory capacities of DCs, further refining immune responses. Here, we review recent studies, particularly in experimental mouse systems, that have delineated the integrated mechanisms of crucial immunomodulatory pathways that enable specific populations of DCs and T cells to work intimately together as single functional units that are indispensable for the maintenance of immune homeostasis.

The Roles of Host and Viral Antibody Fc Receptors in Herpes Simplex Virus (HSV) and Human Cytomegalovirus (HCMV) Infections and Immunity

Herpesvirus infections are a leading cause of neurodevelopmental delay in newborns and end-organ disease in immunocompromised patients. One leading strategy to reduce the disease burden of herpesvirus infections such as herpes simplex virus (HSV) and human cytomegalovirus (HCMV) is to prevent primary acquisition by vaccination, yet vaccine development remains hampered by limited understanding of immune correlates of protection against infection. Traditionally, vaccine development has aimed to increase antibody titers with neutralizing function, which involves the direct binding of antibodies to viral particles. However, recent research has explored the numerous other responses that can be mediated by engagement of the antibody constant region (Fc) with Fc receptors (FcR) present on immune cells or with complement molecules. These functions include antiviral responses such as antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Uniquely, herpesviruses encode FcR that can act as distractor receptors for host antiviral IgG, thus enabling viral evasion of host defenses. This review focuses on the relative roles of neutralizing and non-neutralizing functions antibodies that target herpesvirus antigens for HSV and HCMV, as well as the roles of Fc-FcR interactions for both host defenses and viral escape.

Differential Requirements for gE, gI, and UL16 among Herpes Simplex Virus 1 Syncytial Variants Suggest Unique Modes of Dysregulating the Mechanism of Cell-to-Cell Spread

Like all the herpesviruses, herpes simplex virus encodes machinery that enables it to move through cell junctions to avoid neutralizing antibodies. This cell-to-cell spread mechanism requires the viral fusion machinery (gD, gH/gL, and gB) and numerous accessory proteins. Of all of these, minor alterations to only four proteins (gB, gK, UL20, or UL24) will dysregulate the fusion machinery, allowing the formation of syncytia. In contrast, removal of individual accessory proteins will block cell-to-cell spread, forcing the virus to transmit in a cell-free manner. In the context of a Syn variant, removal of a required accessory protein will block cell fusion, again forcing cell-free spread. This has been investigated most thoroughly for gBsyn variants, which lose their syncytial phenotype in the absence of several accessory proteins, including gE, gI, UL16, and UL21, which are known to physically interact. Recently it was found that UL21 is not needed for gKsyn-, UL20syn-, or UL24syn-induced cell fusion, and hence it was of interest to ascertain whether gE, gI, and UL16 are required for Syn variants other than gBsyn. Null mutants of these were each combined with seven syncytial variants distributed among gK, UL20, and UL24. Surprisingly, very different patterns of accessory protein requirements were revealed. Indeed, for the three gKsyn variants tested, two different patterns were found. Also, three mutants were able to replicate without causing cytopathic effects. These findings show that mutations that produce Syn variants dysregulate the cell-to-cell-spread machinery in unique ways and provide clues for elucidating how this virus moves between cells.IMPORTANCE Approximately 2/3 of adults worldwide are latently infected with herpes simplex virus 1. Upon reactivation, the virus has the ability to evade neutralizing antibodies by moving through cell junctions, but the mechanism of direct cell-to-cell spread is poorly understood. The machinery that assembles between cells includes the viral fusion proteins and various accessory proteins that prevent cells from fusing. Alterations in four proteins will dysregulate the machinery, allowing neighboring cells to fuse to make syncytia, but this can be prevented by removing various individual accessory proteins to further disable the machinery. Previously, the accessory protein UL21 was found to be important for the activity of some syncytial variants but not others. In this study, we discovered that UL16, gE, and gI all act differently in how they control the fusion machinery. A better understanding of the mechanism of cell-to-cell spread may enable the development of drugs that block it.

Surface Plasmon Resonance Reveals Direct Binding of Herpes Simplex Virus Glycoproteins gH/gL to gD and Locates a gH/gL Binding Site on gD

Herpes simplex virus (HSV) requires fusion between the viral envelope and host membrane. Four glycoproteins, gD, gH/gL, and gB, are essential for this process. To initiate fusion, gD binds its receptor and undergoes a conformational change that hypothetically leads to activation of gH/gL, which in turn triggers the fusion protein gB to undergo rearrangements leading to membrane fusion. Our model predicts that gD must interact with both its receptor and gH/gL to promote fusion. In support of this, we have shown that gD is structurally divided into two "faces": one for the binding receptor and the other for its presumed interaction with gH/gL. However, until now, we have been unable to demonstrate a direct interaction between gD and gH/gL. Here, we used surface plasmon resonance to show that the ectodomain of gH/gL binds directly to the ectodomain of gD when (i) gD is captured by certain anti-gD monoclonal antibodies (MAbs) that are bound to a biosensor chip, (ii) gD is bound to either one of its receptors on a chip, and (iii) gD is covalently bound to the chip surface. To localize the gH/gL binding site on gD, we used multiple anti-gD MAbs from six antigenic communities and determined which ones interfered with this interaction. MAbs from three separate communities block gD-gH/gL binding, and their epitopes encircle a geographical area on gD that we propose comprises the gH/gL binding domain. Together, our results show that gH/gL interacts directly with gD, supporting a role for this step in HSV entry.IMPORTANCE HSV entry is a multistep process that requires the actions of four glycoproteins, gD, gH/gL, and gB. Our current model predicts that gD must interact with both its receptor and gH/gL to promote viral entry. Although we know a great deal about how gD binds its receptors, until now we have been unable to demonstrate a direct interaction between gD and gH/gL. Here, we used a highly sensitive surface plasmon resonance technique to clearly demonstrate that gD and gH/gL interact. Furthermore, using multiple MAbs with defined epitopes, we have delineated a domain on gD that is independent of that used for receptor binding and which likely represents the gH/gL interaction domain. Targeting this interaction to prevent fusion may enhance both therapeutic and vaccine strategies.

Oncolytic herpes simplex virus tumor targeting and neutralization escape by engineering viral envelope glycoproteins

Oncolytic herpes simplex viruses (oHSVs) have been approved for clinical usage and become more and more popular for tumor virotherapy. However, there are still many issues for the oHSVs used in clinics and clinical trials. The main issues are the limited anti-tumor effects, intratumor injection, and some side effects. To overcome such challenges, here we review the genetic engineering of the envelope glycoproteins for oHSVs to target tumors specifically, and at the same time we summarize the many neutralization antibodies against the envelope glycoproteins and align the neutralization epitopes with functional domains of the respective glycoproteins for future identification of new functions of the glycoproteins and future engineering of the epitopes to escape from host neutralization.

Exploring First Interactions Between Ostreid Herpesvirus 1 (OsHV-1) and Its Host, Crassostrea gigas: Effects of Specific Antiviral Antibodies and Dextran Sulfate

Viral entry mechanisms of herpesviruses constitute a highly complex process which implicates several viral glycoproteins and different receptors on the host cell surfaces. This initial infection stage was currently undescribed for Ostreid herpes virus 1 (OsHV-1), a herpesvirus infecting bivalves including the Pacific oyster, Crassostrea gigas. To identify OsHV-1 glyproteins implicated in the attachment of the virus to oyster cells, three viral putative membrane proteins, encoded by ORF 25, 41, and 72, were selected and polyclonal antibodies against these targets were used to explore first interactions between the virus and host cells. In addition, effects of dextran sulfate, a negative charged sulfated polysaccharide, were investigated on OsHV-1 infection. Effects of antiviral antibodies and dextran sulfate were evaluated by combining viral DNA and RNA detection in spat (in vivo trials) and in oyster hemolymph (in vitro trials). Results showed that viral protein encoded by ORF 25 appeared to be involved in interaction between OsHV-1 and host cells even if other proteins are likely implicated, such as proteins encoded by ORF 72 and ORF 41. Dextran sulfate at 30 μg/mL significantly reduced the spat mortality rate in the experimental conditions. Taken together, these results contribute to better understanding the pathogenesis of the viral infection, especially during the first stage of OsHV-1 infection, and open the way toward new approaches to control OsHV-1 infection in confined facilities.

Analysis of herpes simplex type 1 gB, gD, and gH/gL on production of infectious HIV-1: HSV-1 gD restricts HIV-1 by exclusion of HIV-1 Env from maturing viral particles

BACKGROUND

We previously showed that the gM of HSV-1 could restrict the release of infectious HIV-1 from cells. In this study, we analyzed if the four HSV-1 glycoproteins (gD, gB, and gH/gL), which are the minimum glycoproteins required for HSV-1 entry, restricted the release of infectious HIV-1.

RESULTS

Of these four glycoproteins, gD and gH/gL restricted the production of infectious HIV-1 from cells transfected with an infectious molecular clone of HIV-1 (strain NL4-3) while gB had no significant effect. Pulse-chase analyses indicated that gD did not affect the biosynthesis and processing of gp160 into gp120/gp41, the transport of the gp120/gp41 to the cell surface, or the release of HIV-1 particles from the cell surface. Our analyses revealed that gD was incorporated into HIV-1 virus particles while gp120/gp41 was excluded from released virus particles. Truncated mutants of gD revealed that the cytoplasmic domain was dispensable but that a membrane bound gD was required for the restriction of release of infectious HIV-1. Finally, cell lines expressing gD also potently restricted the release of infectious virus.

CONCLUSIONS

Due to its ability to exclude HIV-1 gp120/gp41 from maturing virus, gD may provide a useful tool in deciphering mechanisms of Env incorporation into maturing virus particles.

Interaction between nectin-1 and the human natural killer cell receptor CD96

Regulation of Natural Killer (NK) cell activity is achieved by the integration of both activating and inhibitory signals acquired at the immunological synapse with potential target cells. NK cells express paired receptors from the immunoglobulin family which share common ligands from the nectin family of adhesion molecules. The activating receptor CD226 (DNAM-1) binds to nectin-2 and CD155, which are also recognized by the inhibitory receptor TIGIT. The third receptor in this family is CD96, which is less well characterized and may have different functions in human and mouse models. Human CD96 interacts with CD155 and ligation of this receptor activates NK cells, while in mice the presence of CD96 correlates with decreased NK cell activation. Mouse CD96 also binds nectin-1, but the effect of this interaction has not yet been determined. Here we show that human nectin-1 directly interacts with CD96 in vitro. The binding site for CD96 is located on the nectin-1 V-domain, which comprises a canonical interface that is shared by nectins to promote cell adhesion. The affinity of nectin-1 for CD96 is lower than for other nectins such as nectin-3 and nectin-1 itself. However, the affinity of nectin-1 for CD96 is similar to its affinity for herpes simplex virus glycoprotein D (HSV gD), which binds the nectin-1 V-domain during virus entry. The affinity of human CD96 for nectin-1 is lower than for its known activating ligand CD155. We also found that human erythroleukemia K562 cells, which are commonly used as susceptible targets to assess NK cell cytotoxicity did not express nectin-1 on their surface and were resistant to HSV infection. When expressed in K562 cells, nectin-1-GFP accumulated at cell contacts and allowed HSV entry. Furthermore, overexpression of nectin-1-GFP led to an increased susceptibility of K562 cells to NK-92 cell cytotoxicity.

A structural model of the immune checkpoint CD160-HVEM complex derived from HDX-mass spectrometry and molecular modeling

CD160 is a T cell coinhibitory molecule that interacts with the herpes virus entry mediator (HVEM) on antigen-presenting cells to provide an inhibitory signal to T cells. To date, the structure of CD160 and its complex with HVEM are unknown. Here, we have identified the fragments of CD160 interacting with HVEM using ELISA tests, hydrogen/deuterium studies, affinity chromatography and mass spectrometry (MS). By combining hydrogen/deuterium exchange and mass spectrometry (HDX-MS) we obtained key information about the tertiary structure of CD160, predicting the 3D structure of the CD160–HVEM complex. Our results provide insights into the molecular architecture of this complex, serving as a useful basis for designing inhibitors for future immunotherapies.

Signal Transduction Via Co-stimulatory and Co-inhibitory Receptors

T-cell receptor (TCR)-mediated antigen-specific stimulation is essential for initiating T-cell activation. However, signaling through the TCR alone is not sufficient for inducing an effective response. In addition to TCR-mediated signaling, signaling through antigen-independent co-stimulatory or co-inhibitory receptors is critically important not only for the full activation and functional differentiation of T cells but also for the termination and suppression of T-cell responses. Many studies have investigated the signaling pathways underlying the function of each molecular component. Co-stimulatory and co-inhibitory receptors have no kinase activity, but their cytoplasmic region contains unique functional motifs and potential phosphorylation sites. Engagement of co-stimulatory receptors leads to recruitment of specific binding partners, such as adaptor molecules, kinases, and phosphatases, via recognition of a specific motif. Consequently, each co-stimulatory receptor transduces a unique pattern of signaling pathways. This review focuses on our current understanding of the intracellular signaling pathways provided by co-stimulatory and co-inhibitory molecules, including B7:CD28 family members, immunoglobulin, and members of the tumor necrosis factor receptor superfamily.

Glycoprotein D of HSV-1 is dependent on tegument protein UL16 for packaging and contains a motif that is differentially required for syncytia formation

Glycoprotein D (gD) of herpes simplex virus type 1 (HSV-1) plays a key role in multiple events during infection including virus entry, cell-to-cell spread, and virus-induced syncytia formation. Here, we provide evidence that an arginine/lysine cluster located at the transmembrane-cytoplasm interface of gD critically contributes to viral spread and cell-cell fusion. Our studies began with the discovery that packaging of gD into virions is almost completely blocked in the absence of tegument protein UL16. We subsequently identified a novel, direct, and regulated interaction between UL16 and gD, but this was not important for syncytia formation. However, a mutational analysis of the membrane-proximal basic residues of gD revealed that they are needed for the gBsyn phenotype, salubrinal-induced fusion of HSV-infected cells, and cell-to-cell spread. Finally, we found that these same gD tail basic residues are not required for cell fusion induced by a gKsyn variant.

Experimental Dissection of the Lytic Replication Cycles of Herpes Simplex Viruses in vitro

Herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) produce lifelong infections and are highly prevalent in the human population. Both viruses elicit numerous clinical manifestations and produce mild-to-severe diseases that affect the skin, eyes, and brain, among others. Despite the existence of numerous antivirals against HSV, such as acyclovir and acyclovir-related analogs, virus variants that are resistant to these compounds can be isolated from immunosuppressed individuals. For such isolates, second-line drugs can be used, yet they frequently produce adverse side effects. Furthermore, topical antivirals for treating cutaneous HSV infections usually display poor to moderate efficacy. Hence, better or novel anti-HSV antivirals are needed and details on their mechanisms of action would be insightful for improving their efficacy and identifying specific molecular targets. Here, we review and dissect the lytic replication cycles of herpes simplex viruses, discussing key steps involved in cell infection and the processes that yield new virions. Additionally, we review and discuss rapid, easy-to-perform and simple experimental approaches for studying key steps involved in HSV replication to facilitate the identification of the mechanisms of action of anti-HSV compounds.

Inhibition of Herpes Simplex Virus-1 Entry into Human Cells by Nonsaccharide Glycosaminoglycan Mimetics

Although heparan sulfate (HS) has been implicated in facilitating entry of enveloped viruses including herpes simplex virus (HSV), small molecules that effectively compete with this abundant, cell surface macromolecule remain unknown. We reasoned that entry of HSV-1 involving its glycoprotein D (gD) binding to HS could be competitively targeted through small, synthetic, nonsaccharide glycosaminoglycan mimetics (NSGMs). Screening a library of NSGMs identified a small, distinct group that bound gD with affinities of 8-120 nM. Studies on HSV-1 entry into HeLa, HFF-1, and VK2/E6E7 cells identified inhibitors with potencies in the range of 0.4-1.0 μM. These synthetic NSGMs are likely to offer promising chemical biology probes and/or antiviral drug discovery opportunities.

CD147 Promotes Entry of Pentamer-Expressing Human Cytomegalovirus into Epithelial and Endothelial Cells

Human cytomegalovirus (HCMV) replicates in many diverse cell types in vivo, and entry into different cells involves distinct entry mechanisms and different envelope glycoproteins. HCMV glycoprotein gB is thought to act as the virus fusogen, apparently after being triggered by different gH/gL proteins that bind distinct cellular receptors or entry mediators. A trimer of gH/gL/gO is required for entry into all cell types, and entry into fibroblasts involves trimer binding to platelet-derived growth factor receptor alpha (PDGFRα). HCMV entry into biologically relevant epithelial and endothelial cells and monocyte-macrophages also requires a pentamer, gH/gL complexed with UL128, UL130, and UL131, and there is evidence that the pentamer binds unidentified receptors. We screened an epithelial cell cDNA library and identified the cell surface protein CD147, which increased entry of pentamer-expressing HCMV into HeLa cells but not entry of HCMV that lacked the pentamer. A panel of CD147-specific monoclonal antibodies inhibited HCMV entry into epithelial and endothelial cells, but not entry into fibroblasts. shRNA silencing of CD147 in endothelial cells inhibited HCMV entry but not entry into fibroblasts. CD147 colocalized with HCMV particles on cell surfaces and in endosomes. CD147 also promoted cell-cell fusion induced by expression of pentamer and gB in epithelial cells. However, soluble CD147 did not block HCMV entry and trimer and pentamer did not bind directly to CD147, supporting the hypothesis that CD147 acts indirectly through other proteins. CD147 represents the first HCMV entry mediator that specifically functions to promote entry of pentamer-expressing HCMV into epithelial and endothelial cells.IMPORTANCE Human cytomegalovirus infects nearly 80% of the world's population and causes significant morbidity and mortality. The current method of treatment involves the use of antiviral agents that are prone to resistance and can be highly toxic to patients; currently, there is no vaccine against HCMV available. HCMV infections involve virus dissemination throughout the body, infecting a wide variety of tissues; however, the mechanism of spread is not well understood, particularly with regard to which cellular proteins are utilized by HCMV to establish infection. This report describes the characterization of a newly identified cellular molecule that affects HCMV entry into epithelial and endothelial cells. These results will lead to a better understanding of HCMV pathogenesis and have implications for the development of future therapeutics.

The potential of currently unavailable herpes virus vaccines

INTRODUCTION

Despite overwhelming experimental work, there are no licensed vaccines against the most frequent Alphaherpesviruses, namely herpes simplex virus 1 and 2 (HSV1 and 2) nor against the Epstein-Barr virus (EBV), a member of the subfamily Gammaherpesvirus.

AREAS COVERED

Since the DNAs of both HSVs reside in the regional sensory ganglia in a latent state (i.e. as circularized episomal molecules), a corresponding vaccine might be useful for immunotherapy rather than for prevention of primary infection. Here we describe the design of a purified subunit vaccine as well as the preparation and efficacy of a recombinant fusion protein consisting of the gD ectodomain from our domestic attenuated HSV1 strain HSZP. The EBV vaccines considered so far, were destined for prevention of infectious mononucleosis (IM) or to prevent formation of EBV related tumors. To design the EBV peptide vaccine, at least 15 carefully selected immunogenic epitopes coming from 12 virus coded proteins were bound to synthetic micro-particle carriers along with a non-specific pathogen recognizing receptor (PRR) stimulating both the T as well as B lymphocytes.

EXPERT COMMENTARY

The efficacy of a novel EBV peptide in the rabbit model was based on criteria such as antibody formation (EA-D detected by ELISA, early and capsid proteins tested by immunoblot), presence of LMP1 antigen and of viral DNA in peripheral white blood cells. Out of 19 peptide combinations used for vaccination, at least 6 showed a satisfactory protective effect.

Implication of Soluble Forms of Cell Adhesion Molecules in Infectious Disease and Tumor: Insights from Transgenic Animal Models

Cell adhesion molecules (CAMs) are surface ligands, usually glycoproteins, which mediate cell-to-cell adhesion. They play a critical role in maintaining tissue integrity and mediating migration of cells, and some of them also act as viral receptors. It has been known that soluble forms of the viral receptors bind to the surface glycoproteins of the viruses and neutralize them, resulting in inhibition of the viral entry into cells. Nectin-1 is one of important CAMs belonging to immunoglobulin superfamily and herpesvirus entry mediator (HVEM) is a member of the tumor necrosis factor (TNF) receptor family. Both CAMs also act as alphaherpesvirus receptor. Transgenic mice expressing the soluble form of nectin-1 or HVEM showed almost complete resistance against the alphaherpesviruses. As another CAM, sialic acid-binding immunoglobulin-like lectins (Siglecs) that recognize sialic acids are also known as an immunoglobulin superfamily member. Siglecs play an important role in the regulation of immune cell functions in infectious diseases, inflammation, neurodegeneration, autoimmune diseases and cancer. Siglec-9 is one of Siglecs and capsular polysaccharide (CPS) of group B Streptococcus (GBS) binds to Siglec-9 on neutrophils, leading to suppress host immune response and provide a survival advantage to the pathogen. In addition, Siglec-9 also binds to tumor-produced mucins such as MUC1 to lead negative immunomodulation. Transgenic mice expressing the soluble form of Siglec-9 showed significant resistance against GBS infection and remarkable suppression of MUC1 expressing tumor proliferation. This review describes recent developments in the understanding of the potency of soluble forms of CAMs in the transgenic mice and discusses potential therapeutic interventions that may alter the outcomes of certain diseases.

Systematic screening of viral entry inhibitors using surface plasmon resonance

Viral binding and entry into host cells for various viruses have been studied extensively, yielding a detailed understanding of the overall viral entry process. As cell entry is an essential and requisite process by which a virus initiates infection, it is an attractive target for therapeutic intervention. The advantages of targeting viral entry are an extracellular target site, relatively easy access for biological interventions, and lower toxicity. Several cell-based strategies and biophysical techniques have been used to screen compounds that block viral entry. These studies led to the discovery of inhibitors against HIV, HCV, influenza, Ebola, and RSV. In recent years, several compounds screened by fragment-based drug discovery have been approved as drugs or are in the final stages of clinical trials. Among fragment screening technologies, surface plasmon resonance has been widely used because it provides accurate information on binding kinetics, allows real-time monitoring of ligand-drug interactions, requires very small sample amounts to perform analyses, and requires no modifications to or labeling of ligands. This review focuses on surface plasmon resonance-based schemes for screening viral entry inhibitors.

Global sensing of the antigenic structure of herpes simplex virus gD using high-throughput array-based SPR imaging

While HSV-2 typically causes genital lesions, HSV-1 is increasingly the cause of genital herpes. In addition, neonatal HSV infections are associated with a high rate of mortality and HSV-2 may increase the risk for HIV or Zika infections, reinforcing the need to develop an effective vaccine. In the GSK Herpevac trial, doubly sero-negative women were vaccinated with a truncated form of gD2 [gD2(284t)], then examined for anti-gD serum titers and clinical manifestations of disease. Surprisingly, few vaccinees were protected against genital HSV-2 but 86% were protected from genital HSV-1. These observations suggest that subtle differences in gD structure might influence a protective response. To better understand the antigenic structure of gD and how it impacts a protective response, we previously utilized several key anti-gD monoclonal antibodies (mAbs) to dissect epitopes in vaccinee sera. Several correlations were observed but the methodology limited the number of sera and mAbs that could be tested. Here, we used array-based surface plasmon imaging (SPRi) to simultaneously measure a larger number of protein-protein interactions. We carried out cross-competition or "epitope binning" studies with 39 anti-gD mAbs and four soluble forms of gD, including a form [gD2(285t)] that resembles the Herpevac antigen. The results from these experiments allowed us to organize the mAbs into four epitope communities. Notably, relationships within and between communities differed depending on the form of gD, and off-rate analysis suggested differences in mAb-gD avidity depending on the gD serotype and length. Together, these results show that gD1 and gD2 differ in their structural topography. Consistent with the Herpevac results, several mAbs that bind both gD1 and gD2 neutralize only HSV-1. Thus, this technology provides new insights into the antigenic structure of gD and provides a rationale as to how vaccination with a gD2 subunit may lead to protection from HSV-1 infection.

Herpes simplex virus glycoprotein D relocates nectin-1 from intercellular contacts

Herpes simplex virus (HSV) uses the cell adhesion molecule nectin-1 as a receptor to enter neurons and epithelial cells. The viral glycoprotein D (gD) is used as a non-canonical ligand for nectin-1. The gD binding site on nectin-1 overlaps with a functional adhesive site involved in nectin-nectin homophilic trans-interaction. Consequently, when nectin-1 is engaged with a cellular ligand at cell junctions, the gD binding site is occupied. Here we report that HSV gD is able to disrupt intercellular homophilic trans-interaction of nectin-1 and induce a rapid redistribution of nectin-1 from cell junctions. This movement does not require the receptor's interaction with the actin-binding adaptor afadin. Interaction of nectin-1 with afadin is also dispensable for virion surfing along nectin-1-rich filopodia. Cells seeded on gD-coated surfaces also fail to accumulate nectin-1 at cell contact. These data indicate that HSV gD affects nectin-1 locally through direct interaction and more globally through signaling.

B Virus (Macacine Herpesvirus 1) Divergence: Variations in Glycoprotein D from Clinical and Laboratory Isolates Diversify Virus Entry Strategies

B virus (Macacine herpesvirus 1) can cause deadly zoonotic disease in humans. Molecular mechanisms of B virus cell entry are poorly understood for both macaques and humans. Here we investigated the abilities of clinical B virus isolates to use entry receptors of herpes simplex viruses (HSV). We showed that resistant B78H1 cells became susceptible to B virus clinical strains upon expression of either human nectin-2 or nectin-1. Antibody against glycoprotein D (gD) protected these nectin-bearing cells from B virus infection, and a gD-negative recombinant B virus failed to enter these cells, indicating that the nectin-mediated B virus entry depends on gD. We observed that the infectivity of B virus isolates with a single amino acid substitution (D122N) in the IgV-core of the gD ectodomain was impaired on nectin-1-bearing cells. Computational homology-based modeling of the B virus gD-nectin-1 complex revealed conformational differences between the structures of the gD-122N and gD-122D variants that affected the gD-nectin-1 protein-protein interface and binding affinity. Unlike HSV, B virus clinical strains were unable to use herpesvirus entry mediator (HVEM) as a receptor, regardless of conservation of the gD amino acid residues essential for HSV-1 entry via HVEM. Based on the model of the B virus gD-HVEM interface, we predict that residues R7, R11, and G15 are largely responsible for the inability of B virus to utilize HVEM for entry. The ability of B virus to enter cells of a human host by using a combination of receptors distinct from those for HSV-1 or HSV-2 suggests a possible mechanism of enhanced neuropathogenicity associated with zoonotic infections.

IMPORTANCE

B virus causes brainstem destruction in infected humans in the absence of timely diagnosis and intervention. Nectins are cell adhesion molecules that are widely expressed in human tissues, including neurons and neuronal synapses. Here we report that human nectin-2 is a target receptor for B virus entry, in addition to the reported receptor human nectin-1. Similar to a B virus lab strain, B virus clinical strains can effectively use both nectin-1 and nectin-2 as cellular receptors for entry into human cells, but unlike HSV-1 and HSV-2, none of the clinical strains uses an HVEM-mediated entry pathway. Ultimately, these differences between B virus and HSV-1 and -2 may provide insight into the neuropathogenicity of B virus during zoonotic infections.

Retargeting of herpes simplex virus (HSV) vectors

Gene therapy applications depend on vector delivery and gene expression in the appropriate target cell. Vector infection relies on the distribution of natural virus receptors that may either not be present on the desired target cell or distributed in a manner to give off-target gene expression. Some viruses display a very limited host range, while others, including herpes simplex virus (HSV), can infect almost every cell within the human body. It is often an advantage to retarget virus infectivity to achieve selective target cell infection. Retargeting can be achieved by (i) the inclusion of glycoproteins from other viruses that have a different host-range, (ii) modification of existing viral glycoproteins or coat proteins to incorporate peptide ligands or single-chain antibodies (scFvs) that bind to the desired receptor, or (iii) employing soluble adapters that recognize both the virus and a specific receptor on the target cell. This review summarizes efforts to target HSV using these three strategies.

Tetraspanin CD151 Promotes Initial Events in Human Cytomegalovirus Infection

Human cytomegalovirus (HCMV), a betaherpesvirus, can cause life-threatening disease in immunocompromised individuals. Viral envelope glycoproteins that mediate binding to and penetration into target cells have been identified previously. In contrast, cellular proteins supporting HCMV during entry are largely unknown. In order to systematically identify host genes affecting initial steps of HCMV infection, a targeted RNA interference screen of 96 cellular genes was performed in endothelial cells by use of a virus strain expressing the full set of known glycoprotein H and L (gH/gL) complexes. The approach yielded five proviral host factors from different protein families and eight antiviral host factors, mostly growth factor receptors. The tetraspanin CD151 was uncovered as a novel proviral host factor and was analyzed further. Like endothelial cells, fibroblasts were also less susceptible to HCMV infection after CD151 depletion. Virus strains with different sets of gH/gL complexes conferring either broad or narrow cell tropism were equally impaired. Infection of CD151-depleted cells by a fluorescent virus with differentially labeled capsid and envelope proteins revealed a role of CD151 in viral penetration but not in adsorption to the cell. In conclusion, the tetraspanin CD151 has emerged as a novel host factor in HCMV entry and as a putative antiviral target.

IMPORTANCE

At present, the events at the virus-cell interface and the cellular proteins involved during the HCMV entry steps are scarcely understood. In this study, several host factors with putative roles in this process were identified. The tetraspanin CD151 was discovered as a previously unrecognized proviral host factor for HCMV and was found to support viral penetration into the target cells. The findings of this study shed light on the cellular contribution during the initial steps of HCMV infection and open a new direction in HCMV research.

In search for effective and definitive treatment of herpes simplex virus type 1 (HSV-1) infections

Herpes Simplex Virus type 1 (HSV-1) is a nuclear replicating enveloped virus.

Griffithsin and Carrageenan Combination To Target Herpes Simplex Virus 2 and Human Papillomavirus

Extensive preclinical evaluation of griffithsin (GRFT) has identified this lectin to be a promising broad-spectrum microbicide. We set out to explore the antiviral properties of a GRFT and carrageenan (CG) combination product against herpes simplex virus 2 (HSV-2) and human papillomavirus (HPV) as well as determine the mechanism of action (MOA) of GRFT against both viruses. We performed the experiments in different cell lines, using time-of-addition and temperature dependence experiments to differentiate inhibition of viral attachment from entry and viral receptor internalization. Surface plasmon resonance (SPR) was used to assess GRFT binding to viral glycoproteins, and immunoprecipitation and immunohistochemistry were used to identify the specific glycoprotein involved. We determined the antiviral activity of GRFT against HSV-2 to be a 50% effective concentration (EC₅₀) of 230 nM and provide the first evidence that GRFT has moderate anti-HPV activity (EC₅₀ = 0.429 to 1.39 μM). GRFT blocks the entry of HSV-2 and HPV into target cells but not the adsorption of HSV-2 and HPV onto target cells. The results of the SPR, immunoprecipitation, and immunohistochemistry analyses of HSV-2 combined suggest that GRFT may block viral entry by binding to HSV-2 glycoprotein D. Cell-based assays suggest anti-HPV activity through α₆ integrin internalization. The GRFT-CG combination product but not GRFT or CG alone reduced HSV-2 vaginal infection in mice when given an hour before challenge (P = 0.0352). While GRFT significantly protected mice against vaginal HPV infection when dosed during and after HPV16 pseudovirus challenge (P < 0.026), greater CG-mediated protection was afforded by the GRFT-CG combination for up to 8 h (P < 0.0022). These findings support the development of the GRFT-CG combination as a broad-spectrum microbicide.

Interleukin-22 and CD160 play additive roles in the host mucosal response to Clostridium difficile infection in mice

Our previous work has shown the significant up-regulation of Il22 and increased phosphorylation of signal transducer and activator of transcription 3 (STAT3) as part of the mucosal inflammatory response to Clostridium difficile infection in mice. Others have shown that phosphorylation of STAT3 at mucosal surfaces includes interleukin-22 (IL-22) and CD160-mediated components. The current study sought to determine the potential role(s) of IL-22 and/or CD160 in the mucosal response to C. difficile infection. Clostridium difficile-infected mice treated with anti-IL-22, anti-CD160 or a combination of the two showed significantly reduced STAT3 phosphorylation in comparison to C. difficile-infected mice that had not received either antibody. In addition, C. difficile-infected mice treated with anti-IL-22/CD160 induced a smaller set of genes, and at significantly lower levels than the untreated C. difficile-infected mice. The affected genes included pro-inflammatory chemokines and cytokines, and anti-microbial peptides. Furthermore, histopathological and flow cytometric assessments both showed a significantly reduced influx of neutrophils in C. difficile-infected mice treated with anti-IL-22/CD160. These data demonstrate that IL-22 and CD160 are together responsible for a significant fraction of the colonic STAT3 phosphorylation in C. difficile infection. They also underscore the additive effects of IL-22 and CD160 in mediating both the pro-inflammatory and pro-survival aspects of the host mucosal response in this infection.

A strategy for O-glycoproteomics of enveloped viruses--the O-glycoproteome of herpes simplex virus type 1

Glycosylation of viral envelope proteins is important for infectivity and interaction with host immunity, however, our current knowledge of the functions of glycosylation is largely limited to N-glycosylation because it is difficult to predict and identify site-specific O-glycosylation. Here, we present a novel proteome-wide discovery strategy for O-glycosylation sites on viral envelope proteins using herpes simplex virus type 1 (HSV-1) as a model. We identified 74 O-linked glycosylation sites on 8 out of the 12 HSV-1 envelope proteins. Two of the identified glycosites found in glycoprotein B were previously implicated in virus attachment to immune cells. We show that HSV-1 infection distorts the secretory pathway and that infected cells accumulate glycoproteins with truncated O-glycans, nonetheless retaining the ability to elongate most of the surface glycans. With the use of precise gene editing, we further demonstrate that elongated O-glycans are essential for HSV-1 in human HaCaT keratinocytes, where HSV-1 produced markedly lower viral titers in HaCaT with abrogated O-glycans compared to the isogenic counterpart with normal O-glycans. The roles of O-linked glycosylation for viral entry, formation, secretion, and immune recognition are poorly understood, and the O-glycoproteomics strategy presented here now opens for unbiased discovery on all enveloped viruses.

Information on site-specific O-glycosylation of viral envelope glycoproteins is generally very limited despite important functions. We present a powerful mass-spectrometry based strategy to globally identify O-glycosylation sites on viral envelope proteins of a given virus in the context of a productive infection. We successfully utilized the strategy to map O-linked glycosylation sites on the complex HSV-1 virus demonstrating that O-glycosylation is widely distributed on most envelope proteins. Moreover, we used genetically engineered keratinocytes lacking O-glycan elongation capacity to demonstrate that O-linked glycans are indeed important for HSV-1 biology as HSV-1 particles produced in these cells had significantly lower titers compared to wild-type keratinocytes. These tools enable wider discovery and detailed analysis of the role of site-specific O-glycosylation in virology.

Protein and oligonucleotide delivery systems for vaginal microbicides against viral STIs

Intravaginal delivery offers an effective option for localized, targeted, and potent microbicide delivery. However, an understanding of the physiological factors that impact intravaginal delivery must be considered to develop the next generation of microbicides. In this review, a comprehensive discussion of the opportunities and challenges of intravaginal delivery are highlighted, in the context of the intravaginal environment and currently utilized dosage forms. After a subsequent discussion of the stages of microbicide development, the intravaginal delivery of proteins and oligonucleotides is addressed, with specific application to HSV and HIV. Future directions may include the integration of more targeted delivery modalities to virus and host cells, in addition to the use of biological agents to affect specific genes and proteins involved in infection. More versatile and multipurpose solutions are envisioned that integrate new biologicals and materials into potentially synergistic combinations to achieve these goals.

Structural insight into equine lentivirus receptor 1

Equine lentivirus receptor 1 (ELR1) has been identified as a functional cellular receptor for equine infectious anemia virus (EIAV). Herein, recombinant ELR1 and EIAV surface glycoprotein gp90 were respectively expressed in Drosophila melanogaster S2 cells, and purified to homogeneity by Ni-NTA affinity chromatography and gel filtration chromatography. Gel filtration chromatography and analytical ultracentrifugation (AUC) analyses indicated that both ELR1 and gp90 existed as individual monomers in solution and formed a complex with a stoichiometry of 1:1 when mixed. The structure of ELR1 was first determined with the molecular replacement method, which belongs to the space group P42 21 2 with one molecule in an asymmetric unit. It contains eight antiparallel β-sheets, of which four are in cysteine rich domain 1 (CRD1) and two are in CRD2 and CRD3, respectively. Alignment of ELR1 with HVEM and CD134 indicated that Tyr61, Leu70, and Gly72 in CRD1 of ELR1 are important residues for binding to gp90. Isothermal titration calorimetry (ITC) experiments further confirmed that Leu70 and Gly72 are the critical residues.