Genetic analysis of varicella-zoster virus ORF0 to ORF4 by use of a novel luciferase bacterial artificial chromosome system

Identification and characterization of Varicella Zoster Virus circular RNA in lytic infection

This study investigates the role of circular RNAs (circRNAs) in the context of Varicella-Zoster Virus (VZV) lytic infection. We employ two sequencing technologies, short-read sequencing and long-read sequencing, following RNase R treatment on VZV-infected neuroblastoma cells to identify and characterize both cellular and viral circRNAs. Our large scanning analysis identifies and subsequent experiments confirm 200 VZV circRNAs. Moreover, we discover numerous VZV latency-associated transcripts (VLTs)-like circRNAs (circVLTslytic), which contain multiple exons and different isoforms within the same back-splicing breakpoint. To understand the functional significance of these circVLTslytic, we utilize the Bacteria Artificial Chromosome system to disrupt the expression of viral circRNAs in genomic DNA location. We reveal that the sequence flanking circVLTs' 5' splice donor plays a pivotal role as a cis-acting element in the formation of circVLTslytic. The circVLTslytic is dispensable for VZV replication, but the mutation downstream of circVLTslytic exon 5 leads to increased acyclovir sensitivity in VZV infection models. This suggests that circVLTslytic may have a role in modulating the sensitivity to antiviral treatment. The findings shed new insight into the regulation of cellular and viral transcription during VZV lytic infection, emphasizing the intricate interplay between circRNAs and viral processes.

Mutagenesis and functional analysis of the varicella-zoster virus portal protein

Herpesviruses replicate by cleaving concatemeric dsDNA into single genomic units that are packaged through an oligomeric portal present in preformed procapsids. In contrast to what is known about phage portal proteins, details concerning herpesvirus portal structure and function are not as well understood. A panel of 65 Varicella-Zoster virus (VZV) recombinant portal proteins with five amino acid in-frame insertions were generated by random transposon mutagenesis of the VZV portal gene, ORF54. Subsequently, 65 VZVLUC recombinant viruses (TNs) were generated via recombineering. Insertions were mapped to predicted portal domains (clip, wing, stem, wall, crown, and β-hairpin tunnel-loop) and recombinant viruses were characterized for plaque morphology, replication kinetics, pORF54 expression, and classified based on replication in non-complementing (ARPE19) or complementing (ARPE54C50) cell lines. The N- and C-termini were tolerant to insertion mutagenesis, as were certain clip sub-domains. The majority of mutants mapping to the wing, wall, β-hairpin tunnel loop, and stem domains were lethal. Elimination of the predicted ORF54 start codon revealed that the first 40 amino acids of the N-terminus were not required for viral replication. Stop codon insertions in the C-terminus showed that the last 100 amino acids were not required for viral replication. Lastly, a putative protease cleavage site was identified in the C-terminus of pORF54. Cleavage was likely orchestrated by a viral protease; however, processing was not required for DNA encapsidation and viral replication. The panel of recombinants should prove valuable in future studies to dissect mammalian portal structure and function.IMPORTANCEThough nucleoside analogs and a live-attenuated vaccine are currently available to treat some human herpesvirus family members, alternate methods of combating herpesvirus infection could include blocking viral replication at the DNA encapsidation stage. The approval of Letermovir provided proof of concept regarding the use of encapsidation inhibitors to treat herpesvirus infections in the clinic. We propose that small-molecule compounds could be employed to interrupt portal oligomerization, assembly into the capsid vertex, or affect portal function/dynamics. Targeting portal at any of these steps would result in disruption of viral DNA packaging and a decrease or absence of mature infectious herpesvirus particles. The oligomeric portals of herpesviruses are structurally conserved, and therefore, it may be possible to find a single compound capable of targeting portals from one or more of the herpesvirus subfamilies. Drug candidates from such a series would be effective against viruses resistant to the currently available antivirals.

Varicella-Zoster Virus ORF39 Transmembrane Protein Suppresses Interferon-Beta Promoter Activation by Interacting with STING

Varicella-Zoster virus (VZV) causes varicella in primary infection of children and zoster during reactivation in adults. Type I interferon (IFN) signaling suppresses VZV growth, and stimulator of interferon genes (STING) plays an important role in anti-VZV responses by regulating type I IFN signaling. VZV-encoded proteins are shown to inhibit STING-mediated activation of the IFN-β promoter. However, the mechanisms by which VZV regulates STING-mediated signaling pathways are largely unknown. In this study, we demonstrate that the transmembrane protein encoded by VZV open reading frame (ORF) 39 suppresses STING-mediated IFN-β production by interacting with STING. In IFN-β promoter reporter assays, ORF39 protein (ORF39p) inhibited STING-mediated activation of the IFN-β promoter. ORF39p interacted with STING in co-transfection assays, and this interaction was comparable to that of STING dimerization. The cytoplasmic N-terminal 73 amino acids region of ORF39P was not necessary for ORF39 binding and suppression of STING-mediated IFN-β activation. ORF39p also formed a complex containing both STING and TBK1. A recombinant VZV expressing HA-tagged ORF39 was produced using bacmid mutagenesis and showed similar growth to its parent virus. During HA-ORF39 virus infection, the expression level of STING was markedly reduced, and HA-ORF39 interacted with STING. Moreover, HA-ORF39 also colocalized with glycoprotein K (encoded by ORF5) and STING at the Golgi during virus infection. Our results demonstrate that the transmembrane protein ORF39p of VZV plays a role in evading the type I IFN responses by suppressing STING-mediated activation of the IFN-β promoter.

G-quadruplexes formed by Varicella-Zoster virus reiteration sequences suppress expression of glycoprotein C and regulate viral cell-to-cell spread

G-quadruplex (G4) formed by repetitive guanosine-rich sequences plays important roles in diverse cellular processes; however, its roles in viral infection are not fully understood. In this study, we investigated the genome-wide distribution of G4-forming sequences (G4 motifs) in Varicella-Zoster virus (VZV) and found that G4 motifs are enriched in the internal repeat short and the terminal repeat short regions flanking the unique short region and also in some reiteration (R) sequence regions. A high density of G4 motifs in the R2 region was found on the template strand of ORF14, which encodes glycoprotein C (gC), a virulent factor for viral growth in skin. Analyses such as circular dichroism spectroscopy, thermal difference spectra, and native polyacrylamide gel electrophoresis with oligodeoxynucleotides demonstrated that several G4 motifs in ORF14 form stable G4 structures. In transfection assays, gC expression from the G4-disrupted ORF14 gene was increased at the transcriptional level and became more resistant to suppression by G4-ligand treatment. The recombinant virus containing the G4-disrupted ORF14 gene expressed a higher level of gC mRNA, while it showed a slightly reduced growth. This G4-disrupted ORF14 virus produced smaller plaques than the wild-type virus. Our results demonstrate that G4 formation via reiteration sequences suppresses gC expression during VZV infection and regulates viral cell-to-cell spread.

A chemical method for generating live-attenuated, replication-defective DNA viruses for vaccine development

The development of a chemically attenuated, replication-incompetent virus vaccine can provide protection against diseases caused by DNA viruses. In this study, we have developed a method to produce live-attenuated, replication-defective viruses using centanamycin (CM), a chemical compound that alkylates the A-T-rich minor groove of the DNA and thereby blocks DNA replication. We tested the efficacy of CM to produce live-attenuated, replication-defective human cytomegalovirus, mouse cytomegalovirus, and herpes simplex virus-2 (HSV-2), suggesting a broad application for generating live-attenuated, replication-defective DNA viruses. Mass spectrometry analysis showed that CM alkylate viral DNA at the adenine-N3 position. Moreover, mice immunization with CM-attenuated mouse cytomegalovirus (MCMV) produced a robust immune response and reduced the viral load in immunized animals against challenges with live, wild-type MCMV. Our study offers a unifying and attractive therapeutic opportunity that chemically attenuated live DNA viruses can be readily developed as new frontline vaccines.

Rational Design of a Skin- and Neuro-Attenuated Live Varicella Vaccine: A Review and Future Perspectives

Primary varicella-zoster virus (VZV) infection causes varicella, which remains a prominent public health concern in children. Current varicella vaccines adopt the live-attenuated Oka strain, vOka, which retains the ability to infect neurons, establish latency and reactivate, leading to vaccine-associated zoster in some vaccinees. Therefore, it is necessary to develop a safer next-generation varicella vaccine to help reduce vaccine hesitancy. This paper reviews the discovery and identification of the skin- and neuro-tropic factor, the open reading frame 7 (ORF7) of VZV, as well as the development of a skin- and neuro-attenuated live varicella vaccine comprising an ORF7-deficient mutant, v7D. This work could provide insights into the research of novel virus vaccines based on functional genomics and reverse genetics.

Comparative Analysis of the Simian Varicella Virus and Varicella Zoster Virus Genomes

Varicella zoster virus (VZV) and simian varicella virus (SVV) cause varicella (chickenpox) in children and nonhuman primates, respectively. After resolution of acute disease, the viruses establish latent infection in neural ganglia, after which they may reactivate to cause a secondary disease, such as herpes zoster. SVV infection of nonhuman primates provides a model to investigate VZV pathogenesis and antiviral strategies. The VZV and SVV genomes are similar in size and structure and share 70–75% DNA homology. SVV and VZV DNAs are co-linear in gene arrangement with the exception of the left end of the viral genomes. Viral gene expression is regulated into immediate early, early, and late transcription during in vitro and in vivo infection. During viral latency, VZV and SVV gene expression is limited to transcription of a viral latency-associated transcript (VLT). VZV and SVV are closely related alphaherpesviruses that likely arose from an ancestral varicella virus that evolved through cospeciation into species-specific viruses.

Development of Robust Varicella Zoster Virus Luciferase Reporter Viruses for In Vivo Monitoring of Virus Growth and Its Antiviral Inhibition in Culture, Skin, and Humanized Mice

There is a continued need to understand varicella-zoster virus (VZV) pathogenesis and to develop more effective antivirals, as it causes chickenpox and zoster. As a human-restricted alphaherpesvirus, the use of human skin in culture and mice is critical in order to reveal the important VZV genes that are required for pathogenesis but that are not necessarily observed in the cell culture. We previously used VZV-expressing firefly luciferase (fLuc), under the control of the constitutively active SV40 promoter (VZV-BAC-Luc), to measure the VZV spread in the same sample. However, the fLuc expression was independent of viral gene expression and viral DNA replication programs. Here, we developed robust reporter VZV viruses by using bacterial artificial chromosome (BAC) technology, expressing luciferase from VZV-specific promoters. We also identified two spurious mutations in VZV-BAC that were corrected for maximum pathogenesis. VZV with fLuc driven by ORF57 showed superior growth in cells, human skin explants, and skin xenografts in mice. The ORF57-driven luciferase activity had a short half-life in the presence of foscarnet. This background was then used to investigate the roles for ORF36 (thymidine kinase (TK)) and ORF13 (thymidylate synthase (TS)) in skin. The studies reveal that VZV-∆TS had increased sensitivity to brivudine and was highly impaired for skin replication. This is the first report of a phenotype that is associated with the loss of TS.

Development of a skin- and neuro-attenuated live vaccine for varicella

Varicella caused by the primary infection of varicella-zoster virus (VZV) exerts a considerable disease burden globally. Current varicella vaccines consisting of the live-attenuated vOka strain of VZV are generally safe and effective. However, vOka retains full neurovirulence and can establish latency and reactivate to cause herpes zoster in vaccine recipients, raising safety concerns. Here, we rationally design a live-attenuated varicella vaccine candidate, v7D. This virus replicates like wild-type virus in MRC-5 fibroblasts and human PBMCs, the carrier for VZV dissemination, but is severely impaired for infection of human skin and neuronal cells. Meanwhile, v7D shows immunogenicity comparable to vOka both in vitro and in multiple small animal species. Finally, v7D is proven well-tolerated and immunogenic in nonhuman primates. Our preclinical data suggest that v7D is a promising candidate as a safer live varicella vaccine with reduced risk of vaccine-related complications, and could inform the design of other herpes virus vaccines.

Current varicella vaccines retain neurovirulence and can establish latency and reactivate. Here, the authors present preclinical results of a rationally-designed, skin- and neuro-attenuated varicella vaccine candidate, v7D, showing its attenuation in human skin and neuronal cells and its immunogenicity in small animal models and nonhuman primates

H84T BanLec has broad spectrum antiviral activity against human herpesviruses in cells, skin, and mice

H84T BanLec is a molecularly engineered lectin cloned from bananas with broad-spectrum antiviral activity against several RNA viruses. H84T BanLec dimers bind glycoproteins containing high-mannose N-glycans on the virion envelope, blocking attachment, entry, uncoating, and spread. It was unknown whether H84T BanLec is effective against human herpesviruses varicella-zoster virus (VZV), human cytomegalovirus (HCMV), and herpes simplex virus 1 (HSV-1), which express high-mannose N-linked glycoproteins on their envelopes. We evaluated H84T BanLec against VZV-ORF57-Luc, TB40/E HCMV-fLuc-eGFP, and HSV-1 R8411 in cells, skin organ culture, and mice. The H84T BanLec EC50 was 0.025 µM for VZV (SI50 = 4000) in human foreskin fibroblasts (HFFs), 0.23 µM for HCMV (SI50 = 441) in HFFs, and 0.33 µM for HSV-1 (SI50 = 308) in Vero cells. Human skin was obtained from reduction mammoplasties and prepared for culture. Skin was infected and cultured up to 14 days. H84T BanLec prevented VZV, HCMV and HSV-1 spread in skin at 10 µM in the culture medium, and also exhibited dose-dependent antiviral effects. Additionally, H84T BanLec arrested virus spread when treatment was delayed. Histopathology of HCMV-infected skin showed no overt toxicity when H84T BanLec was present in the media. In athymic nude mice with human skin xenografts (NuSkin mice), H84T BanLec reduced VZV spread when administered subcutaneously prior to intraxenograft virus inoculation. This is the first demonstration of H84T BanLec effectiveness against DNA viruses. H84T BanLec may have additional unexplored activity against other, clinically relevant, glycosylated viruses.

The architecture of the simian varicella virus transcriptome

Primary infection with varicella-zoster virus (VZV) causes varicella and the establishment of lifelong latency in sensory ganglion neurons. In one-third of infected individuals VZV reactivates from latency to cause herpes zoster, often complicated by difficult-to-treat chronic pain. Experimental infection of non-human primates with simian varicella virus (SVV) recapitulates most features of human VZV disease, thereby providing the opportunity to study the pathogenesis of varicella and herpes zoster in vivo. However, compared to VZV, the transcriptome and the full coding potential of SVV remains incompletely understood. Here, we performed nanopore direct RNA sequencing to annotate the SVV transcriptome in lytically SVV-infected African green monkey (AGM) and rhesus macaque (RM) kidney epithelial cells. We refined structures of canonical SVV transcripts and uncovered numerous RNA isoforms, splicing events, fusion transcripts and non-coding RNAs, mostly unique to SVV. We verified the expression of canonical and newly identified SVV transcripts in vivo, using lung samples from acutely SVV-infected cynomolgus macaques. Expression of selected transcript isoforms, including those located in the unique left-end of the SVV genome, was confirmed by reverse transcription PCR. Finally, we performed detailed characterization of the SVV homologue of the VZV latency-associated transcript (VLT), located antisense to ORF61. Analogous to VZV VLT, SVV VLT is multiply spliced and numerous isoforms are generated using alternative transcription start sites and extensive splicing. Conversely, low level expression of a single spliced SVV VLT isoform defines in vivo latency. Notably, the genomic location of VLT core exons is highly conserved between SVV and VZV. This work thus highlights the complexity of lytic SVV gene expression and provides new insights into the molecular biology underlying lytic and latent SVV infection. The identification of the SVV VLT homolog further underlines the value of the SVV non-human primate model to develop new strategies for prevention of herpes zoster.

Varicella-zoster virus (VZV)–a ubiquitous human pathogen–infects most individuals during childhood, leading to chickenpox, after which the virus persists in the host for decades. Later in life, VZV reactivates to cause shingles, frequently associated with difficult-to-treat chronic pain. Our limited understanding of the viral life-cycle hampers the development of more effective treatment options. Simian varicella virus (SVV) is the non-human primate homologue of VZV and causes a natural disease in Old World monkeys with clinical, pathological, and immunological features resembling human VZV infection. However, it is unclear how similar both viruses are at the molecular level. Here, we have revisited the genome-wide transcriptional activity of SVV during lytic infection of kidney epithelial cells derived from two non-human primate species and validated expression of newly identified viral transcripts in lung tissue from SVV-infected animals. Together, this has led to the identification of numerous alternative RNA isoforms, mostly unique to SVV, and some of which may have functional implications for the virus. Notably, we defined the SVV latency-associated transcript, which is highly similar to its VZV counterpart. In conclusion, our study shows the value of understanding the molecular biology of a given animal model and identifies potentially conserved mechanism of latency.

Mutagenesis of the Varicella-Zoster Virus Genome Demonstrates That VLT and VLT-ORF63 Proteins Are Dispensable for Lytic Infection

Primary varicella-zoster virus (VZV) infection leads to varicella and the establishment of lifelong latency in sensory ganglion neurons. Reactivation of latent VZV causes herpes zoster, which is frequently associated with chronic pain. Latent viral gene expression is restricted to the VZV latency-associated transcript (VLT) and VLT-ORF63 (VLT63) fusion transcripts. Since VLT and VLT63 encode proteins that are expressed during lytic infection, we investigated whether pVLT and pVLT-ORF63 are essential for VZV replication by performing VZV genome mutagenesis using CRISPR/Cas9 and BAC technologies. We first established that CRISPR/Cas9 can efficiently mutate VZV genomes in lytically VZV-infected cells through targeting non-essential genes ORF8 and ORF11 and subsequently show recovery of viable mutant viruses. By contrast, the VLT region was markedly resistant to CRISPR/Cas9 editing. Whereas most mutants expressed wild-type or N-terminally altered versions of pVLT and pVLT-ORF63, only a minority of the resulting mutant viruses lacked pVLT and pVLT-ORF63 coding potential. Growth curve analysis showed that pVLT/pVLT-ORF63 negative viruses were viable, but impaired in growth in epithelial cells. We confirmed this phenotype independently using BAC-derived pVLT/pVLT-ORF63 negative and repaired viruses. Collectively, these data demonstrate that pVLT and/or pVLT-ORF63 are dispensable for lytic VZV replication but promote efficient VZV infection in epithelial cells.

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.

Nectin-1 Is an Entry Mediator for Varicella-Zoster Virus Infection of Human Neurons

Varicella-zoster virus (VZV) maintains lifelong latency in neurons following initial infection and can subsequently be reactivated to result in herpes zoster or severe neurological manifestations such as encephalitis. Mechanisms of VZV neuropathogenesis have been challenging to study due to the strict human tropism of the virus. Although neuronal entry mediators of other herpesviruses, including herpes simplex virus, have been identified, little is known regarding how VZV enters neurons. Here, we utilize a human stem cell-based neuronal model to characterize cellular factors that mediate entry. Through transcriptional profiling of infected cells, we identify the cell adhesion molecule nectin-1 as a candidate mediator of VZV entry. Nectin-1 is highly expressed in the cell bodies and axons of neurons. Either knockdown of endogenous nectin-1 or incubation with soluble forms of nectin-1 produced in mammalian cells results in a marked decrease in infectivity of neurons. Notably, while addition of soluble nectin-1 during viral infection inhibits infectivity, addition after infection has no effect on infectivity. Ectopic expression of human nectin-1 in a cell line resistant to productive VZV infection confers susceptibility to infection. In summary, we have identified nectin-1 as a neuronal entry mediator of VZV. IMPORTANCE Varicella-zoster virus (VZV) causes chickenpox, gains access to neurons during primary infection where it resides lifelong, and can later be reactivated. Reactivation is associated with shingles and postherpetic neuralgia, as well as with severe neurologic complications, including vasculitis and encephalitis. Although the varicella vaccine substantially decreases morbidity and mortality associated with primary infection, the vaccine cannot prevent the development of neuronal latency, and vaccinated populations are still at risk for reactivation. Furthermore, immunocompromised individuals are at higher risk for VZV reactivation and associated complications. Little is known regarding how VZV enters neurons. Here, we identify nectin-1 as an entry mediator of VZV in human neurons. Identification of nectin-1 as a neuronal VZV entry mediator could lead to improved treatments and preventative measures to reduce VZV related morbidity and mortality.

Methods for the Manipulation of Herpesvirus Genome and the Application to Marek's Disease Virus Research

Herpesviruses are a group of double-strand DNA viruses that infect a wide range of hosts, including humans and animals. In the past decades, numerous methods have been developed to manipulate herpesviruses genomes, from the introduction of random mutations to specific genome editing. The development of genome manipulation methods has largely advanced the study of viral genes function, contributing not only to the understanding of herpesvirus biology and pathogenesis, but also the generation of novel vaccines and therapies to control and treat diseases. In this review, we summarize the major methods of herpesvirus genome manipulation with emphasis in their application to Marek’s disease virus research.

A Novel Human Skin Tissue Model To Study Varicella-Zoster Virus and Human Cytomegalovirus

The herpesviruses varicella-zoster virus (VZV) and human cytomegalovirus (HCMV) are endemic to humans. VZV causes varicella (chicken pox) and herpes zoster (shingles), while HCMV causes serious disease in immunocompromised patients and neonates. More effective, less toxic antivirals are needed, necessitating better models to study these viruses and evaluate antivirals. Previously, VZV and HCMV models used fetal tissue; here, we developed an adult human skin model to study VZV and HCMV in culture and in vivo While VZV is known to grow in skin, it was unknown whether skin could support an HCMV infection. We used TB40/E HCMV and POka VZV strains to evaluate virus tropism in skin organ culture (SOC) and skin xenograft mouse models. Adult human skin from reduction mammoplasties was prepared for culture on NetWells or mouse implantation. In SOC, VZV infected the epidermis and HCMV infected the dermis. Specifically, HCMV infected fibroblasts, endothelial cells, and hematopoietic cells, with some infected cells able to transfer infection. VZV and HCMV mouse models were developed by subcutaneous transplantation of skin into SCID/beige or athymic nude mice at 2 independent sites. Viruses were inoculated directly into one xenograft, and widespread infection was observed for VZV and HCMV. Notably, we detected VZV- and HCMV-infected cells in the contralateral, uninoculated xenografts, suggesting dissemination from infected xenografts occurred. For the first time, we showed HCMV successfully grows in adult human skin, as does VZV. Thus, this novel system may provide a much-needed preclinical small-animal model for HCMV and VZV and, potentially, other human-restricted viruses.IMPORTANCE Varicella-zoster virus and human cytomegalovirus infect a majority of the global population. While they often cause mild disease, serious illness and complications can arise. Unfortunately, there are few effective drugs to treat these viruses, and many are toxic. To complicate this, these viruses are restricted to replication in human cells and tissues, making them difficult to study in traditional animal models. Current models rely heavily on fetal tissues, can be prohibitively expensive, and are often complicated to generate. While fetal tissue models provide helpful insights, it is necessary to study human viruses in human tissue systems to fully understand these viruses and adequately evaluate novel antivirals. Adult human skin is an appropriate model for these viruses because many target cells are present, including basal keratinocytes, fibroblasts, dendritic cells, and lymphocytes. Skin models, in culture and xenografts in immunodeficient mice, have potential for research on viral pathogenesis, tissue tropism, dissemination, and therapy.

Current In Vivo Models of Varicella-Zoster Virus Neurotropism

Varicella-zoster virus (VZV), an exclusively human herpesvirus, causes chickenpox and establishes a latent infection in ganglia, reactivating decades later to produce zoster and associated neurological complications. An understanding of VZV neurotropism in humans has long been hampered by the lack of an adequate animal model. For example, experimental inoculation of VZV in small animals including guinea pigs and cotton rats results in the infection of ganglia but not a rash. The severe combined immune deficient human (SCID-hu) model allows the study of VZV neurotropism for human neural sub-populations. Simian varicella virus (SVV) infection of rhesus macaques (RM) closely resembles both human primary VZV infection and reactivation, with analyses at early times after infection providing valuable information about the extent of viral replication and the host immune responses. Indeed, a critical role for CD4 T-cell immunity during acute SVV infection as well as reactivation has emerged based on studies using RM. Herein we discuss the results of efforts from different groups to establish an animal model of VZV neurotropism.

Comparison of the Whole-Genome Sequence of an Oka Varicella Vaccine from China with Other Oka Vaccine Strains Reveals Sites Putatively Critical for Vaccine Efficacy

Varicella-zoster virus (VZV) infection results in varicella mostly in children. Reactivation of the virus causes herpes zoster (HZ), mostly in adults. A live attenuated vaccine (vOka-Biken) was originally derived from the parental strain pOka. Several live attenuated vaccines based on the Oka strain are currently available worldwide. In China, varicella vaccines have been licensed by four manufacturers. In this study, we analyze the whole-genome sequence (WGS) of vOka-BK produced by Changchun BCHT Biotechnology also known as Baike. vOka-BK WGS was compared against the genomic sequences of four other Oka strains: pOka, vOka-Biken, vOka-Varilrix from GlaxoSmithKline, and vOka-Varivax from Merck & Co. A previous study identified 137 single nucleotide polymorphisms (SNPs) shared by all vOkas. The current analysis used these data as a reference to compare with vOka-BK WGS and focused on 54 SNPs located in the unique regions of the genome. Twenty-eight nonsynonymous substitutions were identified, ORF62 and ORF55 featuring the most amino acid changes with 9 and 3, respectively. Among the 54 SNPs, 10 had a different mutation profile in vOka-BK compared to the other three vaccines. A comparison with the clade 3 strain Ellen, known to be attenuated, identified three shared amino acid changes: *130R in ORF0 and R958G and S628G in ORF62. This analysis provides the first comparison of a Chinese varicella vaccine to the other vaccines available worldwide and identifies sites potentially critical for VZV vaccine efficacy.IMPORTANCE Varicella, also known as chickenpox, is a highly contagious disease, caused by varicella-zoster virus (VZV). Varicella is a common childhood disease that can be prevented by a live attenuated vaccine. The first available vaccine was derived from the parental Oka strain in Japan in 1974. Several live attenuated vaccines based on the Oka strain are currently available worldwide. Among the four vaccines produced in China, the vaccine manufactured by Changchun BCHT Biotechnology, also known as Baike, has been reported to be very efficacious. Comparative genomic analysis of the Baike vaccine with other Oka vaccine strains identified sites that might be involved in vaccine efficacy, as well as important for the biology of the virus.

Bioluminescence Imaging as a Tool for Poxvirus Biology

Bioluminescence imaging, with luciferase as a reporter-encoding gene, has been successfully and widely used for studies to follow viral infection in an organism and to measure therapeutic efficacy of antiviral agents in small animal models. Bioluminescence is produced by the reaction of a luciferase enzyme stably inserted into the viral genome with a defined substrate systemically delivered into the animal. The light emitted is captured allowing the detection of viral infection sites and the quantification of viral replication in the context of tissues of a living animal. The goal of this chapter is to provide a technical background for the evaluation of poxvirus infection in cells and animals through bioluminescence imaging technology using luciferase-expressing recombinant poxviruses.

Anti-varicella-zoster virus activity of cephalotaxine esters in vitro

Harringtonine (HT) and homoharringtonine (HHT), alkaloid esters isolated from the genus Cephalotaxus, exhibit antitumor activity. A semisynthetic HHT has been approved for treatment of chronic myelogenous leukemia. In addition to antileukemic activity, HT and HHT are reported to possess potent antiviral activity. In this study, we investigated the effects of HT and HHT on replication of varicella-zoster virus (VZV) in vitro. HT and HHT, but not their biologically inactive parental alkaloid cephalotaxine (CET), significantly inhibited replication of recombinant VZV-pOka luciferase. Furthermore, HT and HHT, but not CET, strongly induced down-regulation of VZV lytic genes and exerted potent antiviral effects against a VZV clinical isolate. The collective data support the utility of HT and HHT as effective antiviral candidates for treatment of VZV-associated diseases.

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.

Varicella-zoster virus ORF7 interacts with ORF53 and plays a role in its trans-Golgi network localization

Varicella-zoster virus (VZV) is a neurotropic alphaherpesvirus that causes chickenpox and shingles. ORF7 is an important virulence determinant of VZV in both human skin and nerve tissues, however, its specific function and involved molecular mechanism in VZV pathogenesis remain largely elusive. Previous yeast two-hybrid studies on intraviral protein-protein interaction network in herpesviruses have revealed that VZV ORF7 may interact with ORF53, which is a virtually unstudied but essential viral protein. The aim of this study is to identify and characterize VZV ORF53, and to investigate its relationship with ORF7. For this purpose, we prepared monoclonal antibodies against ORF53 and, for the first time, characterized it as a ~40 kDa viral protein predominantly localizing to the trans-Golgi network of the infected host cell. Next, we further confirmed the interaction between ORF7 and ORF53 by co-immunoprecipitation and co-localization studies in both plasmid-transfected and VZV-infected cells. Moreover, interestingly, we found that ORF53 lost its trans-Golgi network localization and became dispersed in the cytoplasm of host cells infected with an ORF7-deleted recombinant VZV, and thus ORF7 seems to play a role in normal subcellular localization of ORF53. Collectively, these results suggested that ORF7 and ORF53 may function as a complex during infection, which may be implicated in VZV pathogenesis.

A SCID mouse-human lung xenograft model of varicella-zoster virus infection

Varicella pneumonia is one of the most serious, potentially life-threatening complications of primary varicella-zoster virus (VZV) infection in adults and immunocompromised individuals. However, studies on the lung pathogenesis of VZV infection as well as development and testing of antivirals have long been hindered by limited access to clinical samples and a lack of suitable animal models. In this study, we report for the first time the use of human lung xenografts in SCID mice for investigating VZV infection. Human fetal lung tissues grafted under the kidney capsule of SCID mice rapidly grew and developed mature structures closely resembling normal human lung. Following infection, VZV replicated and spread efficiently in human lung xenografts, where the virus targeted both alveolar epithelial and mesenchymal cells, and resulted in formation of large viral lesions. VZV particles were readily detected in the nuclei and cytoplasm of infected lung cells by electron microscopy. Additionally, VZV infection resulted in a robust pro-inflammatory cytokine response in human lung xenografts. In conclusion, infecting human lung xenografts in SCID mice provides a useful, biological relevant tool for future mechanistic studies on VZV lung pathogenesis, and may potentially facilitate the evaluation of new antiviral therapies for VZV lung infection.

1,2,3,4,6-Penta-O-galloyl-ß-D-glucose, a bioactive compound in Elaeocarpus sylvestris extract, inhibits varicella-zoster virus replication

The aim of this study was to establish the effect of a 70% ethanol extract of Elaeocarpus sylvestris (ESE) on varicella-zoster virus (VZV) replication and identify the specific bioactive component(s) underlying its activity. ESE induced a significant reduction in replication of the clinical strain of VZV. Activity-guided fractionation indicated that the ethyl acetate (EtOAc) fraction of ESE contains the active compound(s) inhibiting VZV replication. High-Performance Liquid Chromatography coupled to Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry (HPLC-Q-TOF-MS/MS) analysis of the EtOAc fraction of ESE facilitated the identification of 13 chemical components. Among these, 1,2,3,4,6-penta-O-galloyl-ß-D-glucose (PGG) markedly suppressed VZV-induced c-Jun N-terminal kinase (JNK) activation, expression of viral immediate-early 62 (IE62) protein and VZV replication. Our results collectively support the utility of PGG as a potential candidate anti-viral drug to treat VZV-associated diseases.

ORF7 of Varicella-Zoster Virus Is Required for Viral Cytoplasmic Envelopment in Differentiated Neuronal Cells

Although a varicella-zoster virus (VZV) vaccine has been used for many years, the neuropathy caused by VZV infection is still a major health concern. Open reading frame 7 (ORF7) of VZV has been recognized as a neurotropic gene in vivo, but its neurovirulent role remains unclear. In the present study, we investigated the effect of ORF7 deletion on VZV replication cycle at virus entry, genome replication, gene expression, capsid assembly and cytoplasmic envelopment, and transcellular transmission in differentiated neural progenitor cells (dNPCs) and neuroblastoma SH-SY5Y (dSY5Y) cells. Our results demonstrate that the ORF7 protein is a component of the tegument layer of VZV virions. Deleting ORF7 did not affect viral entry, viral genome replication, or the expression of typical viral genes but clearly impacted cytoplasmic envelopment of VZV capsids, resulting in a dramatic increase of envelope-defective particles and a decrease in intact virions. The defect was more severe in differentiated neuronal cells of dNPCs and dSY5Y. ORF7 deletion also impaired transmission of ORF7-deficient virus among the neuronal cells. These results indicate that ORF7 is required for cytoplasmic envelopment of VZV capsids, virus transmission among neuronal cells, and probably the neuropathy induced by VZV infection.IMPORTANCE The neurological damage caused by varicella-zoster virus (VZV) reactivation is commonly manifested as clinical problems. Thus, identifying viral neurovirulent genes and characterizing their functions are important for relieving VZV related neurological complications. ORF7 has been previously identified as a potential neurotropic gene, but its involvement in VZV replication is unclear. In this study, we found that ORF7 is required for VZV cytoplasmic envelopment in differentiated neuronal cells, and the envelopment deficiency caused by ORF7 deletion results in poor dissemination of VZV among neuronal cells. These findings imply that ORF7 plays a role in neuropathy, highlighting a potential strategy to develop a neurovirulence-attenuated vaccine against chickenpox and herpes zoster and providing a new target for intervention of neuropathy induced by VZV.

A distinct entorhinal cortex to hippocampal CA1 direct circuit for olfactory associative learning

Lateral and medial parts of entorhinal cortex (EC) convey nonspatial 'what' and spatial 'where' information, respectively, into hippocampal CA1, via both the indirect EC layer 2→ hippocampal dentate gyrus→CA3→CA1 and the direct EC layer 3→CA1 paths. However, it remains elusive how the direct path transfers distinct information and contributes to hippocampal learning functions. Here we report that lateral EC projection neurons selectively form direct excitatory synapses onto a subpopulation of morphologically complex, calbindin-expressing pyramidal cells (PCs) in the dorsal CA1 (dCA1), while medial EC neurons uniformly innervate all dCA1 PCs. Optogenetically inactivating the distinct lateral EC-dCA1 connections or the postsynaptic dCA1 calbindin-expressing PC activity slows olfactory associative learning. Moreover, optetrode recordings reveal that dCA1 calbindin-expressing PCs develop more selective spiking responses to odor cues during learning. Thus, our results identify a direct lateral EC→dCA1 circuit that is required for olfactory associative learning.

Deep Sequencing of Distinct Preparations of the Live Attenuated Varicella-Zoster Virus Vaccine Reveals a Conserved Core of Attenuating Single-Nucleotide Polymorphisms

The continued success of the live attenuated varicella-zoster virus vaccine in preventing varicella-zoster and herpes zoster is well documented, as are many of the mutations that contribute to the attenuation of the vOka virus for replication in skin. At least three different preparations of vOka are marketed. Here, we show using deep sequencing of seven batches of vOka vaccine (including ZostaVax, VariVax, VarilRix, and the Oka/Biken working seed) from three different manufacturers (VariVax, GSK, and Biken) that 137 single-nucleotide polymorphism (SNP) mutations are present in all vaccine batches. This includes six sites at which the vaccine allele is fixed or near fixation, which we speculate are likely to be important for attenuation. We also show that despite differences in the vaccine populations between preparations, batch-to-batch variation is minimal, as is the number and frequency of mutations unique to individual batches. This suggests that the vaccine manufacturing processes are not introducing new mutations and that, notwithstanding the mixture of variants present, VZV live vaccines are extremely stable.

IMPORTANCE

The continued success of vaccinations to prevent chickenpox and shingles, combined with the extremely low incidence of adverse reactions, indicates the quality of these vaccines. The vaccine itself is comprised of a heterogeneous live attenuated virus population and thus requires deep-sequencing technologies to explore the differences and similarities in the virus populations between different preparations and batches of the vaccines. Our data demonstrate minimal variation between batches, an important safety feature, and provide new insights into the extent of the mutations present in this attenuated virus.

Analysis of single nucleotide polymorphism among Varicella-Zoster Virus and identification of vaccine-specific sites

Varicella-zoster virus (VZV) is a causative agent for chickenpox and zoster. Live attenuated vaccines have been developed based on Oka and MAV/06 strains. In order to understand the molecular mechanisms of attenuation, complete genome sequences of vaccine and wild-type strains were compared and single nucleotide polymorphism (SNP) was analyzed. ORF22 and ORF62 contained the highest number of SNPs. The detailed analysis of the SNPs suggested 24 potential vaccine-specific sites. All the mutational events found in vaccine-specific sites were transitional, and most of them were substitution of AT to GC pair. Interestingly, 18 of the vaccine-specific sites of the vaccine strains appeared to be genetically heterogeneous. The probability of a single genome of vaccine strain to contain all 24 vaccine-type sequences was calculated to be less than 4%. The average codon adaptation index (CAI) value of the vaccine strains was significantly lower than the CAI value of the clinical strains.

In vitro system using human neurons demonstrates that varicella-zoster vaccine virus is impaired for reactivation, but not latency

Varicella-zoster virus (VZV) establishes latency in human sensory and cranial nerve ganglia during primary infection (varicella), and the virus can reactivate and cause zoster after primary infection. The mechanism of how the virus establishes and maintains latency and how it reactivates is poorly understood, largely due to the lack of robust models. We found that axonal infection of neurons derived from hESCs in a microfluidic device with cell-free parental Oka (POka) VZV resulted in latent infection with inability to detect several viral mRNAs by reverse transcriptase-quantitative PCR, no production of infectious virus, and maintenance of the viral DNA genome in endless configuration, consistent with an episome configuration. With deep sequencing, however, multiple viral mRNAs were detected. Treatment of the latently infected neurons with Ab to NGF resulted in production of infectious virus in about 25% of the latently infected cultures. Axonal infection of neurons with vaccine Oka (VOka) VZV resulted in a latent infection similar to infection with POka; however, in contrast to POka, VOka-infected neurons were markedly impaired for reactivation after treatment with Ab to NGF. In addition, viral transcription was markedly reduced in neurons latently infected with VOka compared with POka. Our in vitro system recapitulates both VZV latency and reactivation in vivo and may be used to study viral vaccines for their ability to establish latency and reactivate.

Functional analysis of human cytomegalovirus UL/b' region using SCID-hu mouse model

Human cytomegalovirus (HCMV) attenuated strains, Towne, and AD169, differ from prototypic pathogenic strains, such as Toledo, in that they are missing a ∼15-kb segment in the UL/b' region. In contrast to the attenuated strains, Toledo can replicate in human tissue implants in SCID (SCID-hu) mice. Thus, this model provides a unique in vivo system to study the mechanism of viral pathogenesis. Twenty-two ORFs have been annotated in the UL/b' region, including tissue-tropic genes encoded in a pentameric gH/gl complex. To differentiate the role of the pentameric gH/gl complex versus the functions of other ORFs in the 15-kb region in supporting viral growth in vivo, a series of recombinant viral strains were constructed and their ability to replicate in SCID-hu mice was tested. The mutations in the Towne and AD169 strains were repaired to restore their pentameric gH/gl complex and it was found that these changes did not rescue their inability to replicate in the SCID-hu mice. Subsequently four deletion viruses (D1, D2, D3, and D4) in the 15-kb region from the Toledo strain were created. It was demonstrated that D2 and D3 were able to grow in SCID-hu mice, while D1 and D4 were not viable. Interestingly, co-infection of the implant with the D1 and D4 viruses could compensate their respective growth defect in vivo. The results demonstrated that rescuing viral epithelial tropism is not sufficient to revert the attenuation phenotype of AD169 or Towne, and pathogenic genes are located in the segments missing in D1 and D4 viruses. J. Med. Virol. 88:1417-1426, 2016. © 2016 Wiley Periodicals, Inc.

Identification and BAC construction of Han, the first characterized HCMV clinical strain in China

Human cytomegalovirus (HCMV) is the leading infectious cause of birth defects, and may lead to severe or lethal diseases in immunocompromised individuals. Several HCMV strains have been identified and widely applied in research, but no isolate from China has been characterized. In the present study, we isolated, characterized and sequenced the first Chinese HCMV clinical strain Han, and constructed the novel and functional HCMV infectious clone Han-BAC-2311. HCMV Han was isolated from the urine sample of a Chinese infant with multiple developmental disorders. It expresses HCMV specific proteins and contains a representative HCMV genome with minor differences compared to other strains. By homologous recombination using mini-F derived BAC vector pUS-F6, the infectious clone Han-BAC-2311 was constructed containing representative viral genes across the HCMV genome. The insertion site and orientation of BAC sequence were confirmed by restriction enzyme digestion and Southern blotting. The reconstituted recombinant virus HanBAC-2311 expresses typical viral proteins with the same pattern as that of wild-type Han, and also displayed a similar growth kinetics to wild-type Han. The identification of the first clinical HCMV strain in China and the construction of its infectious clone will greatly facilitate the pathogenesis studies and vaccine development in China.

Insights into the function of tegument proteins from the varicella zoster virus

Chickenpox (varicella) is caused by primary infection with varicella zoster virus (VZV), which can establish long-term latency in the host ganglion. Once reactivated, the virus can cause shingles (zoster) in the host. VZV has a typical herpesvirus virion structure consisting of an inner DNA core, a capsid, a tegument, and an outer envelope. The tegument is an amorphous layer enclosed between the nucleocapsid and the envelope, which contains a variety of proteins. However, the types and functions of VZV tegument proteins have not yet been completely determined. In this review, we describe the current knowledge on the multiple roles played by VZV tegument proteins during viral infection. Moreover, we discuss the VZV tegument protein-protein interactions and their impact on viral tissue tropism in SCID-hu mice. This will help us develop a better understanding of how the tegument proteins aid viral DNA replication, evasion of host immune response, and pathogenesis.

Intermolecular Complementation between Two Varicella-Zoster Virus pORF30 Terminase Domains Essential for DNA Encapsidation

The herpesviral terminase complex is part of the intricate machinery that delivers a single viral genome into empty preformed capsids (encapsidation). The varicella-zoster virus (VZV) terminase components (pORF25, pORF30, and pORF45/42) have not been studied as extensively as those of herpes simplex virus 1 and human cytomegalovirus (HCMV). In this study, VZV bacterial artificial chromosomes (BACs) were generated with small (Δ30S), medium (Δ30M), and large (Δ30L) ORF30 internal deletions. In addition, we isolated recombinant viruses with specific alanine substitutions in the putative zinc finger motif (30-ZF3A) or in a conserved region (region IX) with predicted structural similarity to the human topoisomerase I core subdomains I and II (30-IXAla, 30-620A, and 30-622A). Recombinant viruses replicated in an ORF30-complementing cell line (ARPE30) but failed to replicate in noncomplementing ARPE19 and MeWo cells. Transmission electron microscopy of 30-IXAla-, 30-620A-, and 30-622A-infected ARPE19 cells revealed only empty VZV capsids. Southern analysis showed that cells infected with parental VZV (VZVLUC) or a repaired virus (30R) contained DNA termini, whereas cells infected with Δ30L, 30-IXAla, 30-620A, or 30-622A contained little or no processed viral DNA. These results demonstrated that pORF30, specifically amino acids 619 to 624 (region IX), was required for DNA encapsidation. A luciferase-based assay was employed to assess potential intermolecular complementation between the zinc finger domain and conserved region IX. Complementation between 30-ZF3A and 30-IXAla provided evidence that distinct pORF30 domains can function independently. The results suggest that pORF30 may exist as a multimer or participate in higher-order assemblies during viral DNA encapsidation.

IMPORTANCE

Antivirals with novel mechanisms of action are sought as additional therapeutic options to treat human herpesvirus infections. Proteins involved in the viral DNA encapsidation process have become promising antiviral targets. For example, letermovir is a small-molecule drug targeting HCMV terminase that is currently in phase III clinical trials. It is important to define the structural and functional characteristics of proteins that make up viral terminase complexes to identify or design additional terminase-specific compounds. The VZV ORF30 mutants described in this study represent the first VZV terminase mutants reported to date. Targeted mutations confirmed the importance of a conserved zinc finger domain found in all herpesvirus ORF30 terminase homologs but also identified a novel, highly conserved region (region IX) essential for terminase function. Homology modeling suggested that the structure of region IX is present in all human herpesviruses and thus represents a potential structurally conserved antiviral target.

A monoclonal antibody-based VZV glycoprotein E quantitative assay and its application on antigen quantitation in VZV vaccine

Varicella-zoster virus (VZV) is a highly infectious agent that causes varicella and herpes zoster (HZ), which may be associated with severe neuralgia. Vaccination is the most effective way to reduce the burden of the diseases. VZV glycoprotein E (gE) is the major and most immunogenic membrane protein that plays important roles in vaccine efficacy. A quantitative assay for gE content is desirable for the VZV vaccine process monitoring and product analysis. In this study, 70 monoclonal antibodies (mAbs) were obtained after immunizing mice with purified recombinant gE (rgE). The collection of mAbs was well-characterized, and a pair of high-affinity neutralization antibodies (capture mAb 4A2 and detection mAb 4H10) was selected to establish a specific and sensitive sandwich enzyme-linked immunosorbent assay (ELISA) to quantify the native and recombinant gE. The detection limit of this assay was found to be 1.95 ng/mL. Furthermore, a reasonably good correlation between the gE content (as measured by the mAb-based quantitative ELISA) and the virus titer (as measured by the "gold standard" plaque assay) was observed when both assays were performed for tracking the kinetics of virus growth during cell culture. A total of 16 batches of lyophilized VZV vaccine were tested using the newly developed quantitative ELISA and classical plaque assay, demonstrating reasonably good correlation between gE content and virus titer. Therefore, this mAb-based gE quantitative assay serves as a rapid, stable, and sensitive method for monitoring viral antigen content, one additional quantitative method for VZV vaccine process and product characterization. This quantitative ELISA may also serve as a complementary method for virus titering.

A bright future for bioluminescent imaging in viral research

Bioluminescence imaging (BLI) has emerged as a powerful tool in the study of animal models of viral disease. BLI enables real-time in vivo study of viral infection, host immune response and the efficacy of intervention strategies. Substrate dependent light emitting luciferase enzyme when incorporated into a virus as a reporter gene enables detection of bioluminescence from infected cells using sensitive charge-coupled device (CCD) camera systems. Advantages of BLI include low background, real-time tracking of infection in the same animal and reduction in the requirement for larger animal numbers. Transgenic luciferase-tagged mice enable the use of pre-existing nontagged viruses in BLI studies. Continued development in luciferase reporter genes, substrates, transgenic animals and imaging systems will greatly enhance future BLI strategies in viral research.

Deletion of the ORF9p acidic cluster impairs the nuclear egress of varicella-zoster virus capsids

The protein encoded by ORF9 is essential for varicella-zoster virus (VZV) replication. Previous studies documented its presence in the trans-Golgi network and its involvement in secondary envelopment. In this work, we deleted the ORF9p acidic cluster, destroying its interaction with ORF47p, and this resulted in a nuclear accumulation of both proteins. This phenotype results in an accumulation of primary enveloped capsids in the perinuclear space, reflecting a capsid de-envelopment defect.

Varicella zoster virus vaccines: potential complications and possible improvements

Varicella zoster virus (VZV) is the causative agent of varicella (chicken pox) and herpes zoster (shingles). After primary infection, the virus remains latent in sensory ganglia, and reactivates upon weakening of the cellular immune system due to various conditions, erupting from sensory neurons and infecting the corresponding skin tissue. The current varicella vaccine (v-Oka) is highly attenuated in the skin, yet retains its neurovirulence and may reactivate and damage sensory neurons. The reactivation is sometimes associated with postherpetic neuralgia (PHN), a severe pain along the affected sensory nerves that can linger for years, even after the herpetic rash resolves. In addition to the older population that develops a secondary infection resulting in herpes zoster, childhood breakthrough herpes zoster affects a small population of vaccinated children. There is a great need for a neuro-attenuated vaccine that would prevent not only the varicella manifestation, but, more importantly, any establishment of latency, and therefore herpes zoster. The development of a genetically-defined live-attenuated VZV vaccine that prevents neuronal and latent infection, in addition to primary varicella, is imperative for eventual eradication of VZV, and, if fully understood, has vast implications for many related herpesviruses and other viruses with similar pathogenic mechanisms.

β-l-1-[5-(E-2-bromovinyl)-2-(hydroxymethyl)-1,3-(dioxolan-4-yl)] uracil (l-BHDU) prevents varicella-zoster virus replication in a SCID-Hu mouse model and does not interfere with 5-fluorouracil catabolism

The alphaherpesvirus varicella-zoster virus (VZV) causes chickenpox and shingles. Current treatments are acyclovir (ACV) and its derivatives, foscarnet and brivudine (BVdU). Additional antiviral compounds with increased potency and specificity are needed to treat VZV, especially to treat post-herpetic neuralgia. We evaluated β-l-1-[5-(E-2-bromovinyl)-2-(hydroxymethyl)-1,3-(dioxolan-4-yl)] uracil (l-BHDU, 1) and 5'-O-valyl-l-BHDU (2) in three models of VZV replication: primary human foreskin fibroblasts (HFFs), skin organ culture (SOC) and in SCID-Hu mice with skin xenografts. The efficacy of l-BHDU in vivo and its drug-drug interactions were previously not known. In HFFs, 200μM l-BHDU was noncytotoxic over 3days, and l-BHDU treatment reduced VZV genome copy number and cell to cell spread. The EC50 in HFFs for l-BHDU and valyl-l-BHDU were 0.22 and 0.03μM, respectively. However, l-BHDU antagonized the activity of ACV, BVdU and foscarnet in cultured cells. Given its similar structure to BVdU, we asked if l-BHDU, like BVdU, inhibits 5-fluorouracil catabolism. BALB/c mice were treated with 5-FU alone or in combination with l-BHDU or BVdU. l-BHDU did not interfere with 5-FU catabolism. In SCID-Hu mice implanted with human skin xenografts, l-BHDU and valyl-l-BHDU were superior to ACV and valacyclovir. The maximum concentration (Cmax) levels of l-BHDU were determined in mouse and human tissues at 2h after dosing, and comparison of concentration ratios of tissue to plasma indicated saturation of uptake at the highest dose. For the first time, an l-nucleoside analog, l-BHDU, was found to be effective and well tolerated in mice.

The varicella-zoster virus portal protein is essential for cleavage and packaging of viral DNA

The varicella-zoster virus (VZV) open reading frame 54 (ORF54) gene encodes an 87-kDa monomer that oligomerizes to form the VZV portal protein, pORF54. pORF54 was hypothesized to perform a function similar to that of a previously described herpes simplex virus 1 (HSV-1) homolog, pUL6. pUL6 and the associated viral terminase are required for processing of concatemeric viral DNA and packaging of individual viral genomes into preformed capsids. In this report, we describe two VZV bacterial artificial chromosome (BAC) constructs with ORF54 gene deletions, Δ54L (full ORF deletion) and Δ54S (partial internal deletion). The full deletion of ORF54 likely disrupted essential adjacent genes (ORF53 and ORF55) and therefore could not be complemented on an ORF54-expressing cell line (ARPE54). In contrast, Δ54S was successfully propagated in ARPE54 cells but failed to replicate in parental, noncomplementing ARPE19 cells. Transmission electron microscopy confirmed the presence of only empty VZV capsids in Δ54S-infected ARPE19 cell nuclei. Similar to the HSV-1 genome, the VZV genome is composed of a unique long region (UL) and a unique short region (US) flanked by inverted repeats. DNA from cells infected with parental VZV (VZVLUC strain) contained the predicted UL and US termini, whereas cells infected with Δ54S contained neither. This result demonstrates that Δ54S is not able to process and package viral DNA, thus making pORF54 an excellent chemotherapeutic target. In addition, the utility of BAC constructs Δ54L and Δ54S as tools for the isolation of site-directed ORF54 mutants was demonstrated by recombineering single-nucleotide changes within ORF54 that conferred resistance to VZV-specific portal protein inhibitors. Importance: Antivirals with novel mechanisms of action would provide additional therapeutic options to treat human herpesvirus infections. Proteins involved in the herpesviral DNA encapsidation process have become promising antiviral targets. Previously, we described a series of N-α-methylbenzyl-N'-aryl thiourea analogs that target the VZV portal protein (pORF54) and prevent viral replication in vitro. To better understand the mechanism of action of these compounds, it is important to define the structural and functional characteristics of the VZV portal protein. In contrast to HSV, no VZV mutants have been described for any of the seven essential DNA encapsidation genes. The VZV ORF54 deletion mutant described in this study represents the first VZV encapsidation mutant reported to date. We demonstrate that the deletion mutant can serve as a platform for the isolation of portal mutants via recombineering and provide a strategy for more in-depth studies of VZV portal structure and function.

Clinical and molecular aspects of the live attenuated Oka varicella vaccine

VZV is a ubiquitous member of the Herpesviridae family that causes varicella (chicken pox) and herpes zoster (shingles). Both manifestations can cause great morbidity and mortality and are therefore of significant economic burden. The introduction of varicella vaccination as part of childhood immunization programs has resulted in a remarkable decline in varicella incidence, and associated hospitalizations and deaths, particularly in the USA. The vaccine preparation, vOka, is a live attenuated virus produced by serial passage of a wild-type clinical isolate termed pOka in human and guinea pig cell lines. Although vOka is clinically attenuated, it can cause mild varicella, establish latency, and reactivate to cause herpes zoster. Sequence analysis has shown that vOka differs from pOka by at least 42 loci; however, not all genomes possess the novel vOka change at all positions, creating a heterogeneous population of genetically distinct haplotypes. This, together with the extreme cell-associated nature of VZV replication in cell culture and the lack of an animal model, in which the complete VZV life cycle can be replicated, has limited studies into the molecular basis for vOka attenuation. Comparative studies of vOka with pOka replication in T cells, dorsal root ganglia, and skin indicate that attenuation likely involves multiple mutations within ORF 62 and several other genes. This article presents an overview of the clinical aspects of the vaccine and current progress on understanding the molecular mechanisms that account for the clinical phenotype of reduced virulence.

Interaction of allergy history and antibodies to specific varicella-zoster virus proteins on glioma risk

Glioma is the most common cancer of the central nervous system but with few confirmed risk factors. It has been inversely associated with chicken pox, shingles and seroreactivity to varicella virus (VZV), as well as to allergies and allergy-associated IgE. The role of antibody reactivity against individual VZV antigens has not been assessed. Ten VZV-related proteins, selected for high immunogenicity or known function, were synthesized and used as targets for antibody measurements in the sera of 143 glioma cases and 131 healthy controls selected from the San Francisco Bay Area Adult Glioma Study. Glioma cases exhibited significantly reduced seroreactivity compared to controls for six antigens, including proteins IE63 [odds ratio (OR) = 0.26, 95% confidence interval (CI): 0.12-0.58, comparing lowest quartile to highest) and the VZV-unique protein ORF2p (OR = 0.44, 95% CI: 0.21-0.96, lowest quartile to highest). When stratifying the study population into those with low and high self-reported allergy history, VZV protein seroreactivity was only associated inversely with glioma among individuals self-reporting more than two allergies. The data provide insight into both allergy and VZV effects on glioma: strong anti-VZV reactions in highly allergic individuals are associated with reduced occurrence of glioma. This result suggests a role for specificity in the anti-VZV immunity in brain tumor suppression for both individual VZV antigens and in the fine-tuning of the immune response by allergy. Anti-VZV reactions may also be a biomarker of effective CNS immunosurveillance owing to the tropism of the virus.

Bacterial artificial chromosome derived simian varicella virus is pathogenic in vivo

Background

Varicella zoster virus (VZV) is a neurotropic alphaherpesvirus that infects humans and results in chickenpox and herpes zoster. A number of VZV genes remain functionally uncharacterized and since VZV is an obligate human pathogen, rigorous evaluation of VZV mutants in vivo remains challenging. Simian varicella virus (SVV) is homologous to VZV and SVV infection of rhesus macaques (RM) closely mimics VZV infection of humans. Recently the SVV genome was cloned as a bacterial artificial chromosome (BAC) and BAC-derived SVV displayed similar replication kinetics as wild-type (WT) SVV in vitro.

Methods

RMs were infected with BAC-derived SVV or WT SVV at 4x10⁵ PFU intrabronchially (N=8, 4 per group, sex and age matched). We collected whole blood (PBMC) and bronchoalveolar lavage (BAL) at various days post-infection (dpi) and sensory ganglia during latent infection (>84 dpi) at necropsy and compared disease progression, viral replication, immune response and the establishment of latency.

Results

Viral replication kinetics and magnitude in bronchoalveolar lavage cells and whole blood as well as rash severity and duration were similar in RMs infected with SVV BAC or WT SVV. Moreover, SVV-specific B and T cell responses were comparable between BAC and WT-infected animals. Lastly, we measured viral DNA in sensory ganglia from both cohorts of infected RMs during latent infection.

Conclusions

SVV BAC is as pathogenic and immunogenic as WT SVV in vivo. Thus, the SVV BAC genetic system combined with the rhesus macaque animal model can further our understanding of viral ORFs important for VZV pathogenesis and the development of second-generation vaccines.

Regulation of the varicella-zoster virus ORF3 promoter by cellular and viral factors

The varicella zoster virus (VZV) immediate early 62 protein (IE62) activates most if not all identified promoters of VZV genes and also some minimum model promoters that contain only a TATA box element. Analysis of the DNA elements that function in IE62 activation of the VZV ORF3 promoter revealed that the 100 nucleotides before the translation start site of the ORF3 gene contains the promoter elements. This promoter lacks any functional TATA box element. Cellular transcription factors Sp1, Sp3 and YY1 bind to the promoter, and mutation of their binding sites inhibited ORF3 gene expression. VZV regulatory proteins, IE63 and ORF29, ORF61 and ORF10 proteins inhibited IE62-mediated activation of this promoter. Mutation of the Sp1/Sp3 binding site in the VZV genome did not alter VZV replication kinetics. This work suggests that Sp family proteins contribute to the activation of VZV promoters by IE62 in the absence of functional TATA box.

A herpes simplex virus 2 glycoprotein D mutant generated by bacterial artificial chromosome mutagenesis is severely impaired for infecting neuronal cells and infects only Vero cells expressing exogenous HVEM

We constructed a herpes simplex virus 2 (HSV-2) bacterial artificial chromosome (BAC) clone, bHSV2-BAC38, which contains full-length HSV-2 inserted into a BAC vector. Unlike previously reported HSV-2 BAC clones, the virus genome inserted into this BAC clone has no known gene disruptions. Virus derived from the BAC clone had a wild-type phenotype for growth in vitro and for acute infection, latency, and reactivation in mice. HVEM, expressed on epithelial cells and lymphocytes, and nectin-1, expressed on neurons and epithelial cells, are the two principal receptors used by HSV to enter cells. We used the HSV-2 BAC clone to construct an HSV-2 glycoprotein D mutant (HSV2-gD27) with point mutations in amino acids 215, 222, and 223, which are critical for the interaction of gD with nectin-1. HSV2-gD27 infected cells expressing HVEM, including a human epithelial cell line. However, the virus lost the ability to infect cells expressing only nectin-1, including neuronal cell lines, and did not infect ganglia in mice. Surprisingly, we found that HSV2-gD27 could not infect Vero cells unless we transduced the cells with a retrovirus expressing HVEM. High-level expression of HVEM in Vero cells also resulted in increased syncytia and enhanced cell-to-cell spread in cells infected with wild-type HSV-2. The inability of the HSV2-gD27 mutant to infect neuronal cells in vitro or sensory ganglia in mice after intramuscular inoculation suggests that this HSV-2 mutant might be an attractive candidate for a live attenuated HSV-2 vaccine.

ORF7 of varicella-zoster virus is a neurotropic factor

Varicella-zoster virus (VZV) is the causative agent of chickenpox and herpes zoster (shingles). After the primary infection, the virus remains latent in sensory ganglia and reactivates upon weakening of the cellular immune system due to various conditions, erupting from sensory neurons and infecting the corresponding skin tissue. The current varicella vaccine is highly attenuated in the skin and yet retains its neurovirulence and may reactivate and damage sensory neurons. The factors involved in neuronal invasion and establishment of latency are still elusive. Previously, we constructed a library of whole-gene deletion mutants carrying a bacterial artificial chromosome sequence and a luciferase marker in order to perform a comprehensive VZV genome functional analysis. Here, screening of dispensable gene deletion mutants in differentiated neuronal cells led to the identification of ORF7 as the first known, likely a main, VZV neurotropic factor. ORF7 is a virion component localized to the Golgi compartment in infected cells, whose deletion causes loss of polykaryon formation in epithelial cell culture. Interestingly, ORF7 deletion completely abolishes viral spread in human nervous tissue ex vivo and in an in vivo mouse model. This finding adds to our previous report that ORF7 is also a skin-tropic factor. The results of our investigation will not only lead to a better understanding of VZV neurotropism but could also contribute to the development of a neuroattenuated vaccine candidate against shingles or a vector for delivery of other antigens.

Sequencing and characterization of Varicella-zoster virus vaccine strain SuduVax

BACKGROUND

Varicella-zoster virus (VZV) causes chickenpox in children and shingles in older people. Currently, live attenuated vaccines based on the Oka strain are available worldwide. In Korea, an attenuated VZV vaccine has been developed from a Korean isolate and has been commercially available since 1994. Despite this long history of use, the mechanism for the attenuation of the vaccine strain is still elusive. We attempted to understand the molecular basis of attenuation mechanism by full genome sequencing and comparative genomic analyses of the Korean vaccine strain SuduVax.

RESULTS

SuduVax was found to contain a genome that was 124,759 bp and possessed 74 open reading frames (ORFs). SuduVax was genetically most close to Oka strains and these Korean-Japanese strains formed a strong clade in phylogenetic trees. SuduVax, similar to the Oka vaccine strains, underwent T- > C substitution at the stop codon of ORF0, resulting in a read-through mutation to code for an extended form of ORF0 protein. SuduVax also shared certain deletion and insertion mutations in ORFs 17, 29, 56 and 60 with Oka vaccine strains and some clinical strains.

CONCLUSIONS

The Korean VZV vaccine strain SuduVax is genetically similar to the Oka vaccine strains. Further comparative genomic and bioinformatics analyses will help to elucidate the molecular basis of the attenuation of the VZV vaccine strains.

Cloning of the herpes simplex virus type 1 genome as a novel luciferase-tagged infectious bacterial artificial chromosome

Herpes simplex virus type 1 (HSV-1) is a ubiquitous human pathogen of skin and mucous membranes. In the present study, the genome of the HSV-1 F strain was cloned as an infectious bacterial artificial chromosome (BAC) clone without any deletions of the viral genes. Additionally, a firefly luciferase cassette was inserted to generate a novel luciferase-expressing HSV-1 BAC. Importantly, the resulting recombinant HSV-1 BAC Luc behaved indistinguishably from the wild-type virus in Vero cells, and the luciferase activity could be easily quantified in vitro. Thus, this novel HSV-1 BAC system would serve as a powerful tool for gene function profiling.

Varicella-zoster virus immediate-early protein ORF61 abrogates the IRF3-mediated innate immune response through degradation of activated IRF3

Varicella-zoster virus (VZV) infection of differentiated cells within the host and establishment of latency likely requires evasion of innate immunity and limits secretion of antiviral cytokines. Here we report that its immediate-early protein ORF61 antagonizes the beta interferon (IFN-β) pathway. VZV infection down-modulated the Sendai virus (SeV)-activated IFN-β pathway, including mRNA of IFN-β and its downstream interferon-stimulated genes (ISGs), ISG54 and ISG56. Through a primary screening of VZV genes, we found that ORF61 inhibited SeV-mediated activation of IFN-β and ISRE (IFN-stimulated response element) promoter activities but only slightly affected NF-κB promoter activity, implying that the IFN-β pathway may be blocked in the IRF3 branch. An indirect immunofluorescence assay demonstrated that ectopic expression of ORF61 abrogated the detection of IRF3 in SeV-infected cells; however, it did not affect endogenous dormant IRF3 in noninfected cells. Additionally, ORF61 was shown to be partially colocalized with activated IRF3 in the nucleus upon treatment with MG132, an inhibitor of proteasomes, and the direct interaction between ORF61 and activated IRF3 was confirmed by a coimmunoprecipitation assay. Furthermore, Western blot analysis demonstrated that activated IRF3 was ubiquitinated in the presence of ORF61, suggesting that ORF61 degraded phosphorylated IRF3 via a ubiquitin-proteasome pathway. Semiquantitative reverse transcription-PCR (RT-PCR) analysis demonstrated that the level of ISG54 and ISG56 mRNAs was also downregulated by ORF61. Taken together, our results convincingly demonstrate that ORF61 down-modulates the IRF3-mediated IFN-β pathway by degradation of activated IRF3 via direct interaction, which may contribute to the pathogenesis of VZV infection.