Functions of the unique N-terminal region of glycoprotein E in the pathogenesis of varicella-zoster virus infection

Chimeric adenovirus-based herpes zoster vaccine with the tPA signal peptide elicits a robust T-cell immune response

Herpes zoster (HZ), or shingles, is caused by reactivation of the varicella-zoster virus (VZV), which remains latent in the sensory ganglia until immunity wanes with age. The representative HZ vaccine, Shingrix is efficacious but causes side effects due to vaccine adjuvants. Therefore, the development of highly efficacious vaccines with minimal side effects is required. We developed chimeric adenovirus vector (ChimAd)-based HZ vaccine candidates encoding the VZV glycoprotein E (gE). These candidates include ChimAd-tPAgE, in which the signal peptide is replaced with tissue plasminogen activator (tPA), and ChimAd-WTgE, which retains the original signal peptide. C57BL/6 mice were immunized with VZV-vaccine candidates, and cellular and humoral immune responses were evaluated using interferon-γ ELISPOT and ELISA. The ChimAd-based HZ vaccines induced high levels of gE-specific antibodies and cell-mediated immunity. ChimAd-tPAgE (optimal dose: 1 × 107 IFU) elicited a more robust gE-specific T-cell response than Shingrix and Zostavax, showing potential as HZ prophylactic vaccines.

Structures of the Varicella Zoster Virus Glycoprotein E and Epitope Mapping of Vaccine-Elicited Antibodies

Background: Varicella zoster virus (VZV) is the causative agent for chickenpox and herpes zoster (HZ, shingles). HZ is a debilitating disease affecting elderly and immunocompromised populations. Glycoprotein E (gE) is indispensable for viral replication and cell-to-cell spread and is the primary target for anti-VZV antibodies. Importantly, gE is the sole antigen in Shingrix, a highly efficacious, AS01B-adjuvanted vaccine approved in multiple countries for the prevention of HZ, yet the three-dimensional (3D) structure of gE remains elusive. Objectives: We sought to determine the structure of VZV gE and to understand in detail its interactions with neutralizing antibodies. Methods: We used X-ray crystallography and cryo-electron microscopy to elucidate structures of gE bound by recombinant Fabs of antibodies previously elicited through vaccination with Zostavax, a live, attenuated vaccine. Results: The 3D structures resolve distinct central and C-terminal antigenic domains, presenting an array of diverse conformational epitopes. The central domain has two beta-sheets and two alpha helices, including an IgG-like fold. The C-terminal domain exhibits 3 beta-sheets and an Ig-like fold and high structural similarity to HSV1 gE. Conclusions: gE from VZV-infected cells elicits a human antibody response with a preference for the gI binding domain of gE. These results yield insights to VZV gE structure and immunogenicity, provide a framework for future studies, and may guide the design of additional herpesvirus vaccine antigens. Teaser: Structures of varicella zoster virus glycoprotein E reveal distinct antigenic domains and define epitopes for vaccine-elicited human antibodies.

Potent and long-lasting humoral and cellular immunity against varicella zoster virus induced by mRNA-LNP vaccine

Varicella zoster virus (VZV) is a highly contagious human herpes virus responsible for causing chickenpox (varicella) and shingles (herpes zoster). Despite the approval of a highly effective vaccine, Shingrix®, the global incidence of herpes zoster is increasing and the economic burden to the health care system and society are substantial due to significant loss of productivity and health complications, particularly among elderly and immunocompromised individuals. This is primarily because access to the vaccines remains mostly limited to countries within developed economies, such as USA and Canada. Therefore, similarly effective vaccines against VZV that are more accessible to the rest-of-the-world are necessary. In this study, we aimed to evaluate immunogenicity and memory response induced by three mRNA-LNP-based vaccine candidates targeting VZV's surface glycoprotein E (gE). C57BL/6 mice were immunized with each candidate vaccine, and humoral and cellular immune responses were assessed. Our results demonstrate that the mRNA-LNP-based vaccine candidates elicited robust and durable humoral responses specific to the gE antigen. Notably, mice vaccinated with the mRNA-LNP vaccines exhibited significantly higher antigen-specific T-cell cytokine production compared to the group receiving Shingrix®, the current standard of care vaccine. Additionally, mRNA-LNP vaccines induced long-lasting memory response, as evidenced by detection of persistent gE-specific Long-Lived Plasma Cells (LLPCs) and memory T cells four months after final immunization. These findings underscore the potential of our mRNA-LNP-based vaccine candidates in generating potent immune responses against VZV, offering promising prospects for their clinical development as an effective prophylactic vaccine against herpes zoster.

Immunogenicity in Mice Immunized with Recombinant Adenoviruses Expressing Varicella-Zoster Virus Envelope Glycoprotein E

Herpes zoster (HZ) is a disease caused by the reactivation of latent varicella-zoster virus (VZV). The subunit vaccine, Shingrix®, and live attenuated vaccine, Zostavax®, could be used as an HZ vaccine that prevents HZ from being developed due to the reactivation of latent VZV in the sensory ganglia due to aging, stress or immunosuppression. In this study, the recombinant adenoviruses rChAd63/gE expressing glycoprotein E (gE) of VZV based on chimpanzee adenovirus serotype 63 (ChAd63) were constructed and investigated for the immunogenicity of different immune pathways in C57BL/6 mice. The results showed similar CD4+ T and CD8+ T cell responses to Shingrix® were induced in mice vaccinated using rChAd63/gE via different immune pathways. This study elucidates that recombinant adenoviruses expressing VZV gE could be appropriate for further development as a new HZ vaccine candidate via different immune pathways.

Creating the "Dew Drop on a Rose Petal": the Molecular Pathogenesis of Varicella-Zoster Virus Skin Lesions

Varicella-zoster virus (VZV) is a human alphaherpesvirus that causes varicella (chicken pox) as the primary infection in a susceptible host. Varicella is very contagious through its transmission by direct contact with vesicular skin lesions that contain high titers of infectious virus and respiratory droplets. While the clinical manifestations of primary VZV infection are well recognized, defining the molecular mechanisms that drive VZV pathogenesis in the naive host before adaptive antiviral immunity is induced has been a challenge due to species specificity. This review focuses on advances made in identifying the differentiated human host cells targeted by VZV to cause varicella, the processes involved in viral takeover of these heterogenous cell types, and the host cell countermeasures that typically culminate in a benign illness. This work has revealed many unexpected and multifaceted mechanisms used by VZV to achieve its high prevalence and persistence in the human population.

Novel BC02 Compound Adjuvant Enhances Adaptive and Innate Immunity Induced by Recombinant Glycoprotein E of Varicella-Zoster Virus

Both adaptive and innate immunity responses are necessary for the efficient elimination of different pathogens. However, the magnitude, quality and desired type of immune response specific to the co-administered antigen is largely determined by adjuvants. BC02 (BCG CpG DNA compound adjuvants system 02) is a novel compound adjuvant with independent intellectual properties, which is composed of BCG CpG DNA biological adjuvant with Al(OH)₃ inorganic salt adjuvant acting as a delivery system. Its safety and strong adjuvant efficacy have been effectively verified in preclinical and clinical trials (Phase Ib, ClinicalTrials.gov Identifier: NCT04239313 and Phase II, ClinicalTrials.gov Identifier: NCT05284812). In this study, we report the level of cell-mediated immunity (CMI) and humoral immune response induced by the BC02 novel adjuvant combined with different doses of varicella-zoster virus (VZV) glycoprotein E (gE) in a mouse model. In addition, we conducted preliminary in vitro experiments to explore the enhancement of RAW264.7 cell immune activity by BC02 adjuvanted-gE experimental vaccine to activate innate immune response. The results showed that the BC02-adjuvanted low, medium or high dose of gE were highly effective in eliciting both CMI and humoral immune responses to the immunized mice, respectively. The production of gE-specific IFN-γ and IL-2-specific T cells was established within 28 days after booster immunization. In particular, the effect of BC02-adjuvanted medium dose of gE has been shown to be more prominent. Meanwhile, fluorescent antibody to membrane antigen (FAMA) and serum antibody plaque reduction tests have also shown that the BC02 adjuvanted-medium dose of gE antigen could induce the secretion of neutralizing antibodies against clinically isolated VZV strains in mice. In addition, our findings have shown that 1/25 dose of gE+BC02 medium dose experimental vaccine can significantly induce the secretion of innate immune cytokines TNF-A, MCP-1, IL-6 and GM-CSF and up-regulate the costimulatory molecules CD40, CD80 and I-A/I-E on RAW264.7 cells; and it has also been activated to form M2 macrophages. At the same time, RAW264.7 cells were stimulated for 12 h, and their phagocytosis was significantly enhanced. Taken together, these results suggest that the BC02 compound adjuvant offers a strategy to induce an appropriate innate and adaptive immunity against the different doses of the VZV gE protein to improve subunit vaccine efficacy, and BC02 may be a promising adjuvant candidate for subunit HZ vaccines.

Sirt3 deficiency induced down regulation of insulin degrading enzyme in comorbid Alzheimer's disease with metabolic syndrome

SIRT3 deacetylates mitochondrial proteins, thereby enhancing their function. We have previously demonstrated that Sirt3 gene deletion leads to brain mitochondrial dysfunction and neuroinflammation. We also reported that silencing of Sirt3 gene in APP/PS1 mice results in exacerbation of insulin resistance, neuroinflammation and β amyloid plaque deposition. To further understand how metabolic syndrome and amyloid pathology interact, we performed RNA-seq analysis of the brain samples of APP/PS1/Sirt3^-/- mice. Gene expression patterns were modulated in metabolic and inflammatory pathways by Sirt3 gene deletion, amyloid pathology, and the combination. Following Sirt3 gene deletion, a key finding was the decreased expression of insulin-degrading enzyme (IDE), an enzyme that regulates the levels of insulin and Aβ peptides. Western diet feeding of Sirt3^-/- and APP/PS1 mice resulted in decrease of IDE protein, parallel to Sirt3 downregulation. Conversely, activation of SIRT3 by nicotinamide riboside in vivo and in vitro resulted in IDE upregulation. SIRT3 activation in vivo also increased the levels of neprilysin, another Aβ degrading enzyme and decreased the levels of BACE1 which generates Aβ peptide suggesting SIRT3's role in amyloid plaque reduction. Our findings provide a plausible mechanism linking metabolic syndrome and amyloid pathology. SIRT3 may be a potential therapeutic target to treat AD.

Altered Surface Expression of Insulin-Degrading Enzyme on Monocytes and Lymphocytes from COVID-19 Patients Both at Diagnosis and after Hospital Discharge

Although the COVID-19 disease has developed into a worldwide pandemic, its pathophysiology remains to be fully understood. Insulin-degrading enzyme (IDE), a zinc-metalloprotease with a high affinity for insulin, has been found in the interactomes of multiple SARS-CoV-2 proteins. However, the relevance of IDE in the innate and adaptative immune responses elicited by circulating peripheral blood mononuclear cells is unknown. Here, we show that IDE is highly expressed on the surface of circulating monocytes, T-cells (both CD4⁺ and CD4⁻), and, to a lower extent, in B-cells from healthy controls. Notably, IDE’s surface expression was upregulated on monocytes from COVID-19 patients at diagnosis, and it was increased in more severe patients. However, IDE’s surface expression was downregulated (relative to healthy controls) 3 months after hospital discharge in all the studied immune subsets, with this effect being more pronounced in males than in females, and thus it was sex-dependent. Additionally, IDE levels in monocytes, CD4⁺ T-cells, and CD4⁻ T-cells were inversely correlated with circulating insulin levels in COVID-19 patients (both at diagnosis and after hospital discharge). Of note, high glucose and insulin levels downregulated IDE surface expression by ~30% in the monocytes isolated from healthy donors, without affecting its expression in CD4⁺ T-cells and CD4⁻ T-cells. In conclusion, our studies reveal the sex- and metabolism-dependent regulation of IDE in monocytes, suggesting that its regulation might be important for the recruitment of immune cells to the site of infection, as well as for glucometabolic control, in COVID-19 patients.

The Biology of Varicella-Zoster Virus Replication in the Skin

The replication of varicella-zoster virus (VZV) in skin is critical to its pathogenesis and spread. Primary infection causes chickenpox, which is characterised by centrally distributed skin blistering lesions that are rich in infectious virus. Cell-free virus in the cutaneous blistering lesions not only spreads to cause further cases, but infects sensory nerve endings, leading to the establishment of lifelong latency in sensory and autonomic ganglia. The reactivation of virus to cause herpes zoster is again characterised by localised painful skin blistering rash containing infectious virus. The development of in vitro and in vivo models of VZV skin replication has revealed aspects of VZV replication and pathogenesis in this important target organ and improved our understanding of the vaccine strain vOKa attenuation. In this review, we outline the current knowledge on VZV interaction with host signalling pathways, the viral association with proteins associated with epidermal terminal differentiation, and how these interconnect with the VZV life cycle to facilitate viral replication and shedding.

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.

Varicella-zoster virus: molecular controls of cell fusion-dependent pathogenesis

Varicella-zoster virus (VZV) is the causative agent of chicken pox (varicella) and shingles (zoster). Although considered benign diseases, both varicella and zoster can cause complications. Zoster is painful and can lead to post herpetic neuralgia. VZV has also been linked to stroke, related to giant cell arteritis in some cases. Vaccines are available but the attenuated vaccine is not recommended in immunocompromised individuals and the efficacy of the glycoprotein E (gE) based subunit vaccine has not been evaluated for the prevention of varicella. A hallmark of VZV pathology is the formation of multinucleated cells termed polykaryocytes in skin lesions. This cell-cell fusion (abbreviated as cell fusion) is mediated by the VZV glycoproteins gB, gH and gL, which constitute the fusion complex of VZV, also needed for virion entry. Expression of gB, gH and gL during VZV infection and trafficking to the cell surface enables cell fusion. Recent evidence supports the concept that cellular processes are required for regulating cell fusion induced by gB/gH-gL. Mutations within the carboxyl domains of either gB or gH have profound effects on fusion regulation and dramatically restrict the ability of VZV to replicate in human skin. This loss of regulation modifies the transcriptome of VZV infected cells. Furthermore, cellular proteins have significant effects on the regulation of gB/gH-gL-mediated cell fusion and the replication of VZV, exemplified by the cellular phosphatase, calcineurin. This review provides the current state-of-the-art knowledge about the molecular controls of cell fusion-dependent pathogenesis caused by VZV.

Modulation of Insulin Sensitivity by Insulin-Degrading Enzyme

Insulin-degrading enzyme (IDE) is a highly conserved and ubiquitously expressed metalloprotease that degrades insulin and several other intermediate-size peptides. For many decades, IDE had been assumed to be involved primarily in hepatic insulin clearance, a key process that regulates availability of circulating insulin levels for peripheral tissues. Emerging evidence, however, suggests that IDE has several other important physiological functions relevant to glucose and insulin homeostasis, including the regulation of insulin secretion from pancreatic β-cells. Investigation of mice with tissue-specific genetic deletion of Ide in the liver and pancreatic β-cells (L-IDE-KO and B-IDE-KO mice, respectively) has revealed additional roles for IDE in the regulation of hepatic insulin action and sensitivity. In this review, we discuss current knowledge about IDE’s function as a regulator of insulin secretion and hepatic insulin sensitivity, both evaluating the classical view of IDE as an insulin protease and also exploring evidence for several non-proteolytic functions. Insulin proteostasis and insulin sensitivity have both been highlighted as targets controlling blood sugar levels in type 2 diabetes, so a clearer understanding the physiological functions of IDE in pancreas and liver could led to the development of novel therapeutics for the treatment of this disease.

The N-terminus of varicella-zoster virus glycoprotein B has a functional role in fusion

Varicella-zoster virus (VZV) is a medically important alphaherpesvirus that induces fusion of the virion envelope and the cell membrane during entry, and between cells to form polykaryocytes within infected tissues during pathogenesis. All members of the Herpesviridae, including VZV, have a conserved core fusion complex composed of glycoproteins, gB, gH and gL. The ectodomain of the primary fusogen, gB, has five domains, DI-V, of which DI contains the fusion loops needed for fusion function. We recently demonstrated that DIV is critical for fusion initiation, which was revealed by a 2.8Å structure of a VZV neutralizing mAb, 93k, bound to gB and mutagenesis of the gB-93k interface. To further assess the mechanism of mAb 93k neutralization, the binding site of a non-neutralizing mAb to gB, SG2, was compared to mAb 93k using single particle cryogenic electron microscopy (cryo-EM). The gB-SG2 interface partially overlapped with that of gB-93k but, unlike mAb 93k, mAb SG2 did not interact with the gB N-terminus, suggesting a potential role for the gB N-terminus in membrane fusion. The gB ectodomain structure in the absence of antibody was defined at near atomic resolution by single particle cryo-EM (3.9Å) of native, full-length gB purified from infected cells and by X-ray crystallography (2.4Å) of the transiently expressed ectodomain. Both structures revealed that the VZV gB N-terminus (aa72-114) was flexible based on the absence of visible structures in the cryo-EM or X-ray crystallography data but the presence of gB N-terminal peptides were confirmed by mass spectrometry. Notably, N-terminal residues 109KSQD112 were predicted to form a small α-helix and alanine substitution of these residues abolished cell-cell fusion in a virus-free assay. Importantly, transferring the 109AAAA112 mutation into the VZV genome significantly impaired viral propagation. These data establish a functional role for the gB N-terminus in membrane fusion broadly relevant to the Herpesviridae.

Insights into the pathogenesis of varicella viruses

Purpose of review

Varicella zoster virus (VZV) is a highly contagious, neurotropic alpha herpes virus that causes varicella (chickenpox). VZV establishes lifelong latency in the sensory ganglia from which it can reactivate to induce herpes zoster (HZ), a painful disease that primarily affects older individuals and those who are immune-suppressed. Given that VZV infection is highly specific to humans, developing a reliable in vivo model that recapitulates the hallmarks of VZV infection has been challenging. Simian Varicella Virus (SVV) infection in nonhuman primates reproduces the cardinal features of VZV infections in humans and allows the study of varicella virus pathogenesis in the natural host. In this review, we summarize our current knowledge about genomic and virion structure of varicelloviruses as well as viral pathogenesis and antiviral immune responses during acute infection, latency and reactivation. We also examine the immune evasion mechanisms developed by varicelloviruses to escape the host immune responses and the current vaccines available for protecting individuals against chickenpox and herpes zoster.

Recent findings

Data from recent studies suggest that infected T cells are important for viral dissemination to the cutaneous sites of infection as well as site of latency and that a viral latency-associated transcript might play a role in the transition from lytic infection to latency and then reactivation.

Summary

Recent studies have provided exciting insights into mechanisms of varicelloviruses pathogenesis such as the critical role of T cells in VZV/SVV dissemination from the respiratory mucosa to the skin and the sensory ganglia; the ability of VZV/SVV to interfere with host defense; and the identification of VLT transcripts in latently infected ganglia. However, our understanding of these phenomena remains poorly understood. Therefore, it is critical that we continue to investigate host-pathogen interactions during varicelloviruses infection. These studies will lead to a deeper understanding of VZV biology as well as novel aspects of cell biology.

Development of adjuvanted recombinant zoster vaccine and its implications for shingles prevention

INTRODUCTION

GSK has developed a two-dose adjuvanted recombinant zoster vaccine (Shingrix, RZV) to protect people aged ≥50 years (50+) against herpes zoster (HZ) and its complications. RZV showed >90% efficacy against HZ, sustained over 4 years of follow-up, in all studied age groups.

AREAS COVERED

This article reviews the scientific rationale underlying the design of RZV; the clinical evidence demonstrating immunogenicity, safety, and efficacy in persons 50+; and the public health implications and cost-effectiveness.

EXPERT COMMENTARY

A decline in varicella zoster virus (VZV) immunity is associated with increased risk of HZ in adults 50+ and immunocompromised individuals. RZV was designed to restore levels of anti-VZV cellular and humoral immunity to prevent VZV reactivation. RZV includes the recombinant gE glycoprotein antigen, and Adjuvant System AS01_B which promotes cellular and antibody responses. In two Phase III studies in subjects aged 50+ and 70+ years, RZV efficacy against HZ compared to placebo was >90% and ≥89% against post-herpetic neuralgia (PHN). RZV is expected to dramatically impact HZ morbidity including its complications, and associated health-care costs. In the US population aged 50+ years, vaccination with RZV can be cost-effective compared to no vaccination and cost-saving compared to the currently available live-attenuated HZ vaccine (Zostavax, Merck).

Global aspects of viral glycosylation

Enveloped viruses encompass some of the most common human pathogens causing infections of different severity, ranging from no or very few symptoms to lethal disease as seen with the viral hemorrhagic fevers. All enveloped viruses possess an envelope membrane derived from the host cell, modified with often heavily glycosylated virally encoded glycoproteins important for infectivity, viral particle formation and immune evasion. While N-linked glycosylation of viral envelope proteins is well characterized with respect to location, structure and site occupancy, information on mucin-type O-glycosylation of these proteins is less comprehensive. Studies on viral glycosylation are often limited to analysis of recombinant proteins that in most cases are produced in cell lines with a glycosylation capacity different from the capacity of the host cells. The glycosylation pattern of the produced recombinant glycoproteins might therefore be different from the pattern on native viral proteins. In this review, we provide a historical perspective on analysis of viral glycosylation, and summarize known roles of glycans in the biology of enveloped human viruses. In addition, we describe how to overcome the analytical limitations by using a global approach based on mass spectrometry to identify viral O-glycosylation in virus-infected cell lysates using the complex enveloped virus herpes simplex virus type 1 as a model. We underscore that glycans often pay important contributions to overall protein structure, function and immune recognition, and that glycans represent a crucial determinant for vaccine design. High throughput analysis of glycosylation on relevant glycoprotein formulations, as well as data compilation and sharing is therefore important to identify consensus glycosylation patterns for translational applications.

Breadth and Functionality of Varicella-Zoster Virus Glycoprotein-Specific Antibodies Identified after Zostavax Vaccination in Humans

Herpes zoster (HZ) (shingles) is the clinical manifestation of varicella-zoster virus (VZV) reactivation. HZ typically develops as people age, due to decreased cell-mediated immunity. However, the importance of antibodies for immunity against HZ prevention remains to be understood. The goal of this study was to examine the breadth and functionality of VZV-specific antibodies after vaccination with a live attenuated HZ vaccine (Zostavax). Direct enumeration of VZV-specific antibody-secreting cells (ASCs) via enzyme-linked immunosorbent spot assay (ELISPOT assay) showed that Zostavax can induce both IgG and IgA ASCs 7 days after vaccination but not IgM ASCs. The VZV-specific ASCs range from 33 to 55% of the total IgG ASCs. Twenty-five human VZV-specific monoclonal antibodies (MAbs) were cloned and characterized from single-cell-sorted ASCs of five subjects (>60 years old) who received Zostavax. These MAbs had an average of ∼20 somatic hypermutations per VH gene, similar to those seen after seasonal influenza vaccination. Fifteen of the 25 MAbs were gE specific, whereas the remaining MAbs were gB, gH, or gI specific. The most potent neutralizing antibodies were gH specific and were also able to inhibit cell-to-cell spread of the virus in vitro Most gE-specific MAbs were able to neutralize VZV, but they required the presence of complement and were unable to block cell-to-cell spread. These data indicate that Zostavax induces a memory B cell recall response characterized by anti-gE > anti-gI > anti-gB > anti-gH antibodies. While antibodies to gH could be involved in limiting the spread of VZV upon reactivation, the contribution of anti-gE antibodies toward protective immunity after Zostavax needs further evaluation.IMPORTANCE Varicella-zoster virus (VZV) is the causative agent of chickenpox and shingles. Following infection with VZV, the virus becomes latent and resides in nerve cells. Age-related declines in immunity/immunosuppression can result in reactivation of this latent virus, causing shingles. It has been shown that waning T cell immunity correlates with an increased incidence of VZV reactivation. Interestingly, serum with high levels of VZV-specific antibodies (VariZIG; IV immunoglobulin) has been administered to high-risk populations, e.g., immunocompromised children, newborns, and pregnant women, after exposure to VZV and has shown some protection against chickenpox. However, the relative contribution of antibodies against individual surface glycoproteins toward protection from shingles in elderly/immunocompromised individuals has not been established. Here, we examined the breadth and functionality of VZV-specific antibodies after vaccination with the live attenuated VZV vaccine Zostavax in humans. This study will add to our understanding of the role of antibodies in protection against shingles.

Effects of Shield1 on the viral replication of varicella‑zoster virus containing FKBP‑tagged ORF4 and 48

The present study aimed to explore the effects of a stabilizing ligand, Shield-1, on the replication of recombinant varicella-zoster virus (VZV) containing FK506 binding protein (FKPB) tags in essential open reading frames (ORF) 4 and 48. A specific galactokinase (galK) selection method was conducted, following the addition of galK labels to VZV ORF4 and 48, using a SW102 VZV bacterial artificial chromosome (BAC) system. Subsequently, recombinant VZV containing FKPB tags in ORF4 and 48 was constructed by counterselection and homologous recombination. Recombinant viral plasmids containing FKPB-tagged VZV ORF4 and 48 were extracted and transfected into human acute retinal pigment epithelial ARPE-19 cells. The results demonstrated that the FKPB-tagged viral protein was rapidly degraded by proteases in recombinant virus-infected ARPE-19 cells. In addition, the recombinant VZVORF4-FKBP-ORF48-FKBP virus could not grow if a synthetic ligand of FKBP, Shield1, was not added to the ARPE-19 cell culture medium; however, the degradation of FKPB-tagged viral protein was prevented if Shield1 was added to the ARPE-19 cell culture medium, thereby allowing viral replication in ARPE-19 cells. These results indicated that Shield1 may regulate replication of recombinant VZVORF4-FKBP-ORF48-FKBP following transfection into human epithelial cells.

Dysregulated Glycoprotein B-Mediated Cell-Cell Fusion Disrupts Varicella-Zoster Virus and Host Gene Transcription during Infection

The highly conserved herpesvirus glycoprotein complex gB/gH-gL mediates membrane fusion during virion entry and cell-cell fusion. Varicella-zoster virus (VZV) characteristically forms multinucleated cells, or syncytia, during the infection of human tissues, but little is known about this process. The cytoplasmic domain of VZV gB (gBcyt) has been implicated in cell-cell fusion regulation because a gB[Y881F] substitution causes hyperfusion. gBcyt regulation is necessary for VZV pathogenesis, as the hyperfusogenic mutant gB[Y881F] is severely attenuated in human skin xenografts. In this study, gBcyt-regulated fusion was investigated by comparing melanoma cells infected with wild-type-like VZV or hyperfusogenic mutants. The gB[Y881F] mutant exhibited dramatically accelerated syncytium formation in melanoma cells caused by fusion of infected cells with many uninfected cells, increased cytoskeleton reorganization, and rapid displacement of nuclei to dense central structures compared to pOka using live-cell confocal microscopy. VZV and human transcriptomes were concurrently investigated using whole transcriptome sequencing (RNA-seq) to identify viral and cellular responses induced when gBcyt regulation was disrupted by the gB[Y881F] substitution. The expression of four vital VZV genes, ORF61 and the genes for glycoproteins gC, gE, and gI, was significantly reduced at 36 h postinfection for the hyperfusogenic mutants. Importantly, hierarchical clustering demonstrated an association of differential gene expression with dysregulated gBcyt-mediated fusion. A subset of Ras GTPase genes linked to membrane remodeling were upregulated in cells infected with the hyperfusogenic mutants. These data implicate gBcyt in the regulation of gB fusion function that, if unmodulated, triggers cellular processes leading to hyperfusion that attenuates VZV infection.

IMPORTANCE

The highly infectious, human-restricted pathogen varicella-zoster virus (VZV) causes chickenpox and shingles. Postherpetic neuralgia (PHN) is a common complication of shingles that manifests as prolonged excruciating pain, which has proven difficult to treat. The formation of fused multinucleated cells in ganglia might be associated with this condition. An effective vaccine against VZV is available but not recommended for immunocompromised individuals, highlighting the need for new therapies. This study investigated the viral and cellular responses to hyperfusion, a condition where the usual constraints of cell membranes are overcome and cells form multinucleated cells. This process hinders VZV and is regulated by a viral glycoprotein, gB. A combination of live-cell imaging and next-generation genomics revealed an alteration in viral and cellular responses during hyperfusion that was caused by the loss of gB regulation. These studies reveal mechanisms central to VZV pathogenesis, potentially leading to improved therapies.

Exocytosis of Varicella-Zoster Virus Virions Involves a Convergence of Endosomal and Autophagy Pathways

Varicella-zoster virus (VZV) is an extremely cell-associated herpesvirus with limited egress of viral particles. The induction of autophagy in VZV-infected monolayers is easily detectable; inhibition of autophagy leads to decreased VZV glycoprotein biosynthesis and diminished viral titers. To explain how autophagic flux could exert a proviral effect on the VZV infectious cycle, we postulated that the VZV exocytosis pathway following secondary envelopment may converge with the autophagy pathway. This hypothesis depended on known similarities between VZV gE and autophagy-related (Atg) Atg9/Atg16L1 trafficking pathways. Investigations were carried out with highly purified fractions of VZV virions. When the virion fraction was tested for the presence of autophagy and endosomal proteins, microtubule-associated protein 1 light chain (MAP1LC3B) and Ras-like GTPase 11 (Rab11) were detected. By two-dimensional (2D) and 3D imaging after immunolabeling, both proteins also colocalized with VZV gE in a proportion of cytoplasmic vesicles. When purified VZV virions were enumerated after immunoelectron microscopy, gold beads were detected on viruses following incubation with antibodies to VZV gE (∼100%), Rab11 (50%), and LC3B (30%). Examination of numerous electron micrographs demonstrated that enveloped virions were housed in single-membraned vesicles; viral particles were not observed in autophagosomes. Taken together, our data suggested that some viral particles after secondary envelopment accumulated in a heterogeneous population of single-membraned vesicular compartments, which were decorated with components from both the endocytic pathway (Rab11) and the autophagy pathway (LC3B). The latter cytoplasmic viral vesicles resembled an amphisome.

IMPORTANCE

VZV infection leads to increased autophagic flux, while inhibition of autophagy leads to a marked reduction in virus spread. In this investigation of the proviral role of autophagy, we found evidence for an intersection of viral exocytosis and autophagy pathways. Specifically, both LC3-II and Rab11 proteins copurified with some infectious VZV particles. The results suggested that a subpopulation of VZV particles were carried to the cell surface in single-walled vesicles with attributes of an amphisome, an organelle formed from the fusion of an endosome and an autophagosome. Our results also addressed the interpretation of autophagy/xenophagy results with mutated herpes simplex virus lacking its ICP34.5 neurovirulence gene (HSVΔ34.5). The VZV genome lacks an ICP34.5 ortholog, yet we found no evidence of VZV particles housed in a double-membraned autophagosome. In other words, xenophagy, a degradative process documented after infection with HSVΔ34.5, was not observed in VZV-infected cells.

Varicella-Zoster Virus Glycoproteins: Entry, Replication, and Pathogenesis

Varicella-zoster virus (VZV), an alphaherpesvirus that causes chicken pox (varicella) and shingles (herpes zoster), is a medically important pathogen that causes considerable morbidity and, on occasion, mortality in immunocompromised patients. Herpes zoster can afflict the elderly with a debilitating condition, postherpetic neuralgia, triggering severe, untreatable pain for months or years. The lipid envelope of VZV, similar to all herpesviruses, contains numerous glycoproteins required for replication and pathogenesis.

PURPOSE OF REVIEW

To summarize the current knowledge about VZV glycoproteins and their roles in cell entry, replication and pathogenesis.

RECENT FINDINGS

The functions for some VZV glycoproteins are known, such as gB, gH and gL in membrane fusion, cell-cell fusion regulation, and receptor binding properties. However, the molecular mechanisms that trigger or mediate VZV glycoproteins remains poorly understood.

SUMMARY

VZV glycoproteins are central to successful replication but their modus operandi during replication and pathogenesis remain elusive requiring further mechanistic based studies.

Role for the αV Integrin Subunit in Varicella-Zoster Virus-Mediated Fusion and Infection

Varicella-zoster virus (VZV) is an alphaherpesvirus that causes varicella and herpes zoster. Membrane fusion is essential for VZV entry and the distinctive syncytium formation in VZV-infected skin and neuronal tissue. Herpesvirus fusion is mediated by a complex of glycoproteins gB and gH-gL, which are necessary and sufficient for VZV to induce membrane fusion. However, the cellular requirements of fusion are poorly understood. Integrins have been implicated to facilitate entry of several human herpesviruses, but their role in VZV entry has not yet been explored. To determine the involvement of integrins in VZV fusion, a quantitative cell-cell fusion assay was developed using a VZV-permissive melanoma cell line. The cells constitutively expressed a reporter protein and short hairpin RNAs (shRNAs) to knock down the expression of integrin subunits shown to be expressed in these cells by RNA sequencing. The αV integrin subunit was identified as mediating VZV gB/gH-gL fusion, as its knockdown by shRNAs reduced fusion levels to 60% of that of control cells. A comparable reduction in fusion levels was observed when an anti-αV antibody specific to its extracellular domain was tested in the fusion assay, confirming that the domain was important for VZV fusion. In addition, reduced spread was observed in αV knockdown cells infected with the VZV pOka strain relative to that of the control cells. This was demonstrated by reductions in plaque size, replication kinetics, and virion entry in the αV subunit knockdown cells. Thus, the αV integrin subunit is important for VZV gB/gH-gL fusion and infection.

IMPORTANCE

Varicella-zoster virus (VZV) is a highly infectious pathogen that causes chickenpox and shingles. A common complication of shingles is the excruciating condition called postherpetic neuralgia, which has proven difficult to treat. While a vaccine is now available, it is not recommended for immunocompromised individuals and its efficacy decreases with the recipient's age. These limitations highlight the need for new therapies. This study examines the role of integrins in membrane fusion mediated by VZV glycoproteins gB and gH-gL, a required process for VZV infection. This knowledge will further the understanding of VZV entry and provide insight into the development of better therapies.

Immunogenicity of varicella zoster virus glycoprotein E DNA vaccine

In the present study a eukaryotic expression vector of varicella zoster virus (VZV) glycoprotein E (gE) was constructed and enabled to express in COS7 cells. Furthermore, a specific immune response against the VZV gE eukaryotic expression plasmid was induced in BALB/c mice. The VZV gE gene was amplified using polymerase chain reaction (PCR) and cloned into a eukaryotic expression vector, pcDNA3.1. The recombinant vector was subsequently transfected into COS7 cells using a liposome transfection reagent. The recombinant protein was instantaneously expressed by the transfected cells, as detected by immunohistochemistry, and the recombinant pcDNA-VZV gE plasmid was subsequently used to immunize mice. Tissue expression levels were analyzed by reverse transcription-PCR. In addition, the levels of serum antibodies and spleen lymphocyte proliferation activity were investigated. The amplified target gene included the full-length gE gene (~2.7 kb), and the recombinant expression vector induced gE expression in COS7 cells. In addition, the expression plasmid induced sustained expression in vivo following immunization of mice. Furthermore, the plasmid was capable of inducing specific antibody production and effectively stimulating T cell proliferation. Effective humoral and cellular immunity was triggered in the mice immunized with the VZV gE eukaryotic expression vector. The results of the present study laid the foundation for future research into a VZV DNA vaccine.

Global Mapping of O-Glycosylation of Varicella Zoster Virus, Human Cytomegalovirus, and Epstein-Barr Virus

Herpesviruses are among the most complex and widespread viruses, infection and propagation of which depend on envelope proteins. These proteins serve as mediators of cell entry as well as modulators of the immune response and are attractive vaccine targets. Although envelope proteins are known to carry glycans, little is known about the distribution, nature, and functions of these modifications. This is particularly true for O-glycans; thus we have recently developed a "bottom up" mass spectrometry-based technique for mapping O-glycosylation sites on herpes simplex virus type 1. We found wide distribution of O-glycans on herpes simplex virus type 1 glycoproteins and demonstrated that elongated O-glycans were essential for the propagation of the virus. Here, we applied our proteome-wide discovery platform for mapping O-glycosites on representative and clinically significant members of the herpesvirus family: varicella zoster virus, human cytomegalovirus, and Epstein-Barr virus. We identified a large number of O-glycosites distributed on most envelope proteins in all viruses and further demonstrated conserved patterns of O-glycans on distinct homologous proteins. Because glycosylation is highly dependent on the host cell, we tested varicella zoster virus-infected cell lysates and clinically isolated virus and found evidence of consistent O-glycosites. These results present a comprehensive view of herpesvirus O-glycosylation and point to the widespread occurrence of O-glycans in regions of envelope proteins important for virus entry, formation, and recognition by the host immune system. This knowledge enables dissection of specific functional roles of individual glycosites and, moreover, provides a framework for design of glycoprotein vaccines with representative glycosylation.

Comparative preclinical evaluation of AS01 versus other Adjuvant Systems in a candidate herpes zoster glycoprotein E subunit vaccine

The candidate vaccine HZ/su is being developed to prevent herpes-zoster disease (HZ). HZ occurrence is attributed to declines in varicella-zoster virus (VZV) specific T-cell immunity. HZ/su contains VZV antigen, gE, and Adjuvant System AS01_B (liposome-based formulation of MPL and QS-21). In clinical trials, AS01_B enhances CD4⁺ T-cell responses to gE. In clinical trials of other vaccines, Adjuvant Systems AS03 and AS04 also enhance antigen-specific CD4⁺ T-cell responses. Hence the purpose of this study was to evaluate gE formulated with AS01_B, AS01_E (50% less MPL and QS-21 than AS01_B), AS03 or AS04 in C57BL6 mice primed with live-attenuated VZV. Four-weeks post-vaccination, the gE-specific CD4⁺ T-cell response to gE/AS01_B was 5.4, 2.8 and 2.2-fold greater than those to gE/AS03, gE/AS04 and gE/AS03, respectively (p<0.001). Therefore in the VZV-primed mouse model, CD4⁺ T-cell responses to gE appeared most enhanced by AS01_B, and adds further support for the use of AS01_B in the HZ/su formulation.

A phase 1/2 study of an adjuvanted varicella-zoster virus subunit vaccine in autologous hematopoietic cell transplant recipients

Recombinant herpes zoster (HZ) vaccines may be an alternative to the live-attenuated HZ vaccine for immunocompromised individuals. This was a phase 1/2, randomized, observer-blind, placebo-controlled study in adults with multiple myeloma, non-Hodgkin lymphoma (B- or T-cell), Hodgkin lymphoma, or acute myeloid leukemia who had undergone autologous hematopoietic stem-cell transplant 50 to 70 days earlier. Subjects (N = 121) were randomized 1:1:1:1 to receive (at months 0, 1, 3) three doses of 50 μg varicella-zoster virus glycoprotein E (gE) adjuvanted with AS01B, 3 doses of gE adjuvanted with AS01E, 1 dose of saline followed by 2 doses of gE/AS01B, or 3 doses of saline. One month after the last dose (6 months after transplant), frequencies of CD4(+) T cells expressing ≥2 activation markers after induction with gE and anti-gE antibody concentrations were higher with all gE/AS01 regimens than with saline. Both responses persisted up to 1 year in subjects vaccinated with gE/AS01. Immune responses were higher in the gE/AS01B 3-dose group than in the gE/AS01B 2-dose group but not higher than in the gE/AS01E 3-dose group. One serious adverse event (pneumonia) was considered vaccine related. Both formulations and both schedules were immunogenic and well tolerated in this population. This study was registered at www.clinicaltrials.gov as #NCT00920218.

Molecular mechanisms of varicella zoster virus pathogenesis

Varicella zoster virus (VZV) is the causative agent of varicella (chickenpox) and zoster (shingles). Investigating VZV pathogenesis is challenging as VZV is a human-specific virus and infection does not occur, or is highly restricted, in other species. However, the use of human tissue xenografts in mice with severe combined immunodeficiency (SCID) enables the analysis of VZV infection in differentiated human cells in their typical tissue microenvironment. Xenografts of human skin, dorsal root ganglia or foetal thymus that contains T cells can be infected with mutant viruses or in the presence of inhibitors of viral or cellular functions to assess the molecular mechanisms of VZV-host interactions. In this Review, we discuss how these models have improved our understanding of VZV pathogenesis.

Safety and immunogenicity of three different formulations of an adjuvanted varicella-zoster virus subunit candidate vaccine in older adults: a phase II, randomized, controlled study

BACKGROUND

This study investigated the safety and immunogenicity of different formulations and schedules of a candidate subunit herpes zoster vaccine containing varicella-zoster virus glycoprotein E (gE) with or without the adjuvant system AS01B.

METHODS

In this phase II, single-blind, randomized, controlled study, adults aged ≥60years (N=714) received one dose of 100μggE/AS01B, two doses, two months apart, of 25, 50, or 100μggE/AS01B, or two doses of unadjuvanted 100μggE/saline. Frequencies of CD4(+) T cells expressing ≥2 activation markers following induction with gE were measured by intracellular cytokine staining and serum anti-gE antibody concentrations by ELISA.

RESULTS

Frequencies of gE-specific CD4(+) T cells were >3-fold higher after two doses of all gE/AS01B formulations than after one dose of 100μggE/AS01B or two doses of 100μggE/saline. Frequencies were comparable after two doses of 25, 50, or 100μggE/AS01B. Serum anti-gE antibody concentrations were comparable after two doses of 50 or 100μggE/AS01B and higher than in the other groups. Immune responses persisted for at least 36 months. Reactogenicities of all gE/AS01B formulations were similar but greater than with gE/saline.

CONCLUSIONS

The three formulations of gE/AS01B were immunogenic and well tolerated in adults aged ≥60years. Two vaccinations with gE/AS01B induced higher immune responses than one and the dose of gE impacted humoral but not cellular immune responses (NCT00434577).

Herpes simplex virus and varicella zoster virus, the house guests who never leave

Human alphaherpesviruses including herpes simplex viruses (HSV-1, HSV-2) and varicella zoster virus (VZV) establish persistent latent infection in sensory neurons for the life of the host. All three viruses have the potential to reactivate causing recurrent disease. Regardless of the homology between the different virus strains, the three viruses are characterized by varying pathologies. This review will highlight the differences in infection pattern, immune response, and pathogenesis associated with HSV-1 and VZV.

Cell-mediated immune responses to a varicella-zoster virus glycoprotein E vaccine using both a TLR agonist and QS21 in mice

Lack of adequate cell-mediated immunity (CMI) to varicella-zoster virus (VZV) has been associated with higher risks of developing herpes zoster (HZ) and associated post-herpetic neuralgia (PHN), and is of particular concern for older and immunocompromised individuals. Thus, the development of an effective HZ vaccine with a clinically acceptable safety profile that is capable of addressing decreased immunity would be highly desirable. In this study we compared the immunogenicity of different vaccine formulations containing VZV glycoprotein E (gE), an important target for CMI and antibody responses, in a VZV-primed mouse model. The formulations included recombinant gE, either unadjuvanted, or combined with aluminium salt or an Adjuvant System (AS01 or AS02), and CMI was used as the primary immunological endpoint. All adjuvanted vaccines induced gE- and/or VZV-specific CD4(+) T cell and antibody responses. A formulation of gE with an Adjuvant System containing the immunostimulants QS21 and 3-O-desacyl-4'-monophosphoryl lipid A (MPL) was shown to be more immunogenic than gE with aluminium salt or unadjuvanted gE (gE/saline). Both immunostimulants were shown to act synergistically in enhancing CMI responses. Formulations with AS01 elicited high frequencies of CD4(+) T cells producing IFN-γ and IL-2. These responses were dose-dependent with respect to both antigen and adjuvant. The gE/AS01(B) candidate vaccine induced higher frequencies of CD4(+) T cells producing IL-2 and/or IFN-γ than all other gE/AS01 formulations, supporting its use for clinical evaluations.

Investigation of varicella-zoster virus neurotropism and neurovirulence using SCID mouse-human DRG xenografts

Varicella-zoster virus (VZV) is a medically important human alphaherpesvirus. Investigating pathogenic mechanisms that contribute to VZV neurovirulence are made difficult by a marked host restriction. Our approach to investigating VZV neurotropism and neurovirulence has been to develop a mouse-human xenograft model in which human dorsal root ganglia (DRG) are maintained in severe compromised immunodeficient (SCID) mice. In this review, we will describe our key findings using this model in which we have demonstrated that VZV infection of SCID DRG xenograft results in rapid and efficient spread, enabled by satellite cell infection and polykaryon formation, which facilitates robust viral replication and release of infectious virus. In neurons that persist following this acute replicative phase, VZV genomes are present at low frequency with limited gene transcription and no protein synthesis, a state that resembles VZV latency in the natural human host. VZV glycoprotein I and interaction between glycoprotein I and glycoprotein E are critical for neurovirulence. Our work demonstrates that the DRG model can reveal characteristics about VZV replication and long-term persistence of latent VZV genomes in human neuronal tissues, in vivo, in an experimental system that may contribute to our knowledge of VZV neuropathogenesis.

[Varicella-zoster virus (VZV)]

Varicella-zoster virus (VZV) causes varicella in primary infection and zoster after reactivation from latency. Both herpes simplex virus (HSV) and VZV are classified into the same alpha-herpesvirus subfamily. Although most VZV genes have their HSV homologs, VZV has many unique biological characteristics. In this review, we summarized recent studies on 1) animal models for VZV infection and outcomes from studies using the models, including 2) viral dissemination processes from respiratory mucosa, T cells, to skin, 3) cellular receptors for VZV entry, 4) functions of viral genes required uniquely for in vivo growth and for establishment of latency, 5) host immune responses and viral immune evasion mechanisms, and 6) varicella vaccine and anti-VZV drugs.

Mutagenesis of varicella-zoster virus glycoprotein I (gI) identifies a cysteine residue critical for gE/gI heterodimer formation, gI structure, and virulence in skin cells

Varicella-zoster virus (VZV) is the alphaherpesvirus that causes chicken pox (varicella) and shingles (zoster). The two VZV glycoproteins gE and gI form a heterodimer that mediates efficient cell-to-cell spread. Deletion of gI yields a small-plaque-phenotype virus, ΔgI virus, which is avirulent in human skin using the xenograft model of VZV pathogenesis. In the present study, 10 mutant viruses were generated to determine which residues were required for the typical function of gI. Three phosphorylation sites in the cytoplasmic domain of gI were not required for VZV virulence in vivo. Two deletion mutants mapped a gE binding region in gI to residues 105 to 125. A glycosylation site, N116, in this region did not affect virulence. Substitution of four cysteine residues highly conserved in the Alphaherpesvirinae established that C95 is required for gE/gI heterodimer formation. The C95A and Δ105-125 (with residues 105 to 125 deleted) viruses had small-plaque phenotypes with reduced replication kinetics in vitro similar to those of the ΔgI virus. The Δ105-125 virus was avirulent for human skin in vivo. In contrast, the C95A mutant replicated in vivo but with significantly reduced kinetics compared to those of the wild-type virus. In addition to abolished gE/gI heterodimer formation, gI from the C95A or the Δ105-125 mutant was not recognized by monoclonal antibodies that detect the canonical conformation of gI, demonstrating structural disruption of gI in these viruses. This alteration prevented gI incorporation into virus particles. Thus, residues C95 and 105 to 125 are critical for gI structure required for gE/gI heterodimer formation, virion incorporation, and ultimately, effective viral spread in human skin.

Analysis of the functions of glycoproteins E and I and their promoters during VZV replication in vitro and in skin and T-cell xenografts in the SCID mouse model of VZV pathogenesis

The two VZV glycoproteins, gE and gI, are encoded by genes that are designated open reading frames, ORF67 and ORF68, located in the short unique region of the VZV genome. These proteins have homologs in the other alphaherpesviruses. Like their homologues, VZV gE and gI exhibit prominent co-localization in infected cells and form heterodimers. However, VZV gE is much larger than its homologues because it has a unique N-terminal domain, consisting of 188 amino acids that are not present in these other gene products. VZV gE also differs from the related gE proteins, in that it is essential for viral replication. Targeted mutations of gE that are compatible with VZV replication in cultured cells have varying phenotypes in skin and T-cell xenografts in the SCID mouse model of VZV pathogenesis in vivo. While gI is dispensable for growth in cultured cells in vitro, this glycoprotein is essential for VZV infection of differentiated human skin and T cells in vivo. The promoter regions of gE and gI are regulated by the cellular transactivator, specificity protein factor 1 (Sp1) in combination with the major VZV transactivator in reporter construct experiments and some Sp1 promoter elements are important for VZV virulence in vivo. Further analysis of VZV gE and gI functions and their interactions with other viral and host cell proteins are important areas for studies of VZV replication and pathogenesis.

Varicella-zoster virus glycoprotein E is a critical determinant of virulence in the SCID mouse-human model of neuropathogenesis

Varicella-zoster virus (VZV) is a neurotropic alphaherpesvirus. VZV infection of human dorsal root ganglion (DRG) xenografts in immunodeficient mice models the infection of sensory ganglia. We examined DRG infection with recombinant VZV (recombinant Oka [rOka]) and the following gE mutants: gEΔ27-90, gEΔCys, gE-AYRV, and gE-SSTT. gEΔ27-90, which lacks the gE domain that interacts with a putative receptor insulin-degrading enzyme (IDE), replicated as extensively as rOka, producing infectious virions and significant cytopathic effects within 14 days of inoculation. Since neural cells express IDE, the gE/IDE interaction was dispensable for VZV neurotropism. In contrast, gEΔCys, which lacks gE/gI heterodimer formation, was significantly impaired at early times postinfection; viral genome copy numbers increased slowly, and infectious virus production was not detected until day 28. Delayed replication was associated with impaired cell-cell spread in ganglia, similar to the phenotype of a gI deletion mutant (rOkaΔgI). However, at later time points, infection of satellite cells and other supportive nonneuronal cells resulted in extensive DRG tissue damage and cell loss such that cytopathic changes observed at day 70 were more severe than those for rOka-infected DRG. The replication of gE-AYRV, which is impaired for trans-Golgi network (TGN) localization, and the replication of gE-SSTT, which contains mutations in an acidic cluster, were equivalent to that of rOka, causing significant cytopathic effects and infectious virus production by day 14; genome copy numbers were equivalent to those of rOka. These experiments suggest that the gE interaction with cellular IDE, gE targeting to TGN sites of virion envelopment, and phosphorylation at SSTT are dispensable for VZV DRG infection, whereas the gE/gI interaction is critical for VZV neurovirulence.

Insulin degrading enzyme induces a conformational change in varicella-zoster virus gE, and enhances virus infectivity and stability

Varicella-zoster virus (VZV) glycoprotein E (gE) is essential for virus infectivity and binds to a cellular receptor, insulin-degrading enzyme (IDE), through its unique amino terminal extracellular domain. Previous work has shown IDE plays an important role in VZV infection and virus cell-to-cell spread, which is the sole route for VZV spread in vitro. Here we report that a recombinant soluble IDE (rIDE) enhances VZV infectivity at an early step of infection associated with an increase in virus internalization, and increases cell-to-cell spread. VZV mutants lacking the IDE binding domain of gE were impaired for syncytia formation and membrane fusion. Pre-treatment of cell-free VZV with rIDE markedly enhanced the stability of the virus over a range of conditions. rIDE interacted with gE to elicit a conformational change in gE and rendered it more susceptible to proteolysis. Co-incubation of rIDE with gE modified the size of gE. We propose that the conformational change in gE elicited by IDE enhances infectivity and stability of the virus and leads to increased fusogenicity during VZV infection. The ability of rIDE to enhance infectivity of cell-free VZV over a wide range of incubation times and temperatures suggests that rIDE may be useful for increasing the stability of varicella or zoster vaccines.