The genome sequence of herpes simplex virus type 2

Molecular Evolution of Herpes Simplex Virus 2 Complete Genomes: Comparison between Primary and Recurrent Infections

Herpes simplex virus 1 (HSV-1) and HSV-2 are large, double-stranded DNA viruses that cause lifelong persistent infections characterized by periods of quiescence and recurrent disease. How HSV evolves within an infected individual experiencing multiple episodes of recurrent disease over time is not known. We determined the genome sequences of viruses isolated from two subjects in the Herpevac Trial for Women who experienced primary HSV-2 genital disease and compared them with sequences of viruses isolated from the subsequent fifth or sixth episode of recurrent disease in the same individuals. Each of the HSV-2 genome sequences was initially obtained using next-generation sequencing and completed with Sanger sequencing. Polymorphisms over the entire genomes were mapped, and amino acid variants resulting from nonsynonymous changes were analyzed based on the secondary and tertiary structures of a previously crystallized protein. A phylogenetic reconstruction was used to assess relationships among the four HSV-2 samples, other North American sequences, and reference sequences. Little genetic drift was detected in viruses shed by the same subjects following repeated reactivation events, suggesting strong selective pressure on the viral genome to maintain sequence fidelity during reactivations from its latent state within an individual host. Our results also demonstrate that some primary HSV-2 isolates from North America more closely resemble the HG52 laboratory strain from Scotland than the low-passage-number clinical isolate SD90e from South Africa or laboratory strain 333. Thus, one of the sequences reported here would be a logical choice as a reference strain for inclusion in future studies of North American HSV-2 isolates.IMPORTANCE The extent to which the HSV-2 genome evolves during multiple episodes of reactivation from its latent state within an infected individual is not known. We used next-generation sequencing techniques to determine whole-genome sequences of four viral samples from two subjects in the Herpevac Trial. The sequence of each subject's well-documented primary isolate was compared with the sequence of the isolate from their fifth or sixth episode of recurrent disease. Only 19 genetic polymorphisms unique to the primary or recurrent isolate were identified, 10 in subject A and 9 in subject B. These observations indicate remarkable genetic conservation between primary and recurrent episodes of HSV-2 infection and imply that strong selection pressures exist to maintain the fidelity of the viral genome during repeated reactivations from its latent state. The genome conservation observed also has implications for the potential success of a therapeutic vaccine.

Pharmacological Induction of Heme Oxygenase-1 Impairs Nuclear Accumulation of Herpes Simplex Virus Capsids upon Infection

Heme oxygenase-1 (HO-1) is an inducible enzyme that is expressed in response to physical and chemical stresses, such as ultraviolet radiation, hyperthermia, hypoxia, reactive oxygen species (ROS), as well as cytokines, among others. Its activity can be positively modulated by cobalt protoporphyrin (CoPP) and negatively by tin protoporphirin (SnPP). Once induced, HO-1 degrades iron-containing heme into ferrous iron (Fe²⁺), carbon monoxide (CO) and biliverdin. Importantly, numerous products of HO-1 are cytoprotective with anti-apoptotic, anti-oxidant, anti-inflammatory, and anti-cancer effects. The products of HO-1 also display antiviral properties against several viruses, such as the human immunodeficiency virus (HIV), influenza, hepatitis B, hepatitis C, and Ebola virus. Here, we sought to assess the effect of modulating HO-1 activity over herpes simplex virus type 2 (HSV-2) infection in epithelial cells and neurons. There are no vaccines against HSV-2 and treatment options are scarce in the immunosuppressed, in which drug-resistant variants emerge. By using HSV strains that encode structural and non-structural forms of the green fluorescent protein (GFP), we found that pharmacological induction of HO-1 activity with CoPP significantly decreases virus plaque formation and the expression of virus-encoded genes in epithelial cells as determined by flow cytometry and western blot assays. CoPP treatment did not affect virus binding to the cell surface or entry into the cytoplasm, but rather downstream events in the virus infection cycle. Furthermore, we observed that treating cells with a CO-releasing molecule (CORM-2) recapitulated some of the anti-HSV effects elicited by CoPP. Taken together, these findings indicate that HO-1 activity interferes with the replication cycle of HSV and that its antiviral effects can be recapitulated by CO.

Highly conserved intragenic HSV-2 sequences: Results from next-generation sequencing of HSV-2 UL and US regions from genital swabs collected from 3 continents

INTRODUCTION

Understanding the variability in circulating herpes simplex virus type 2 (HSV-2) genomic sequences is critical to the development of HSV-2 vaccines.

METHODS

Genital lesion swabs containing ≥ 107log10 copies HSV DNA collected from Africa, the USA, and South America underwent next-generation sequencing, followed by K-mer based filtering and de novo genomic assembly. Sites of heterogeneity within coding regions in unique long and unique short (UL_US) regions were identified. Phylogenetic trees were created using maximum likelihood reconstruction.

RESULTS

Among 46 samples from 38 persons, 1468 intragenic base-pair substitutions were identified. The maximum nucleotide distance between strains for concatenated UL_US segments was 0.4%. Phylogeny did not reveal geographic clustering. The most variable proteins had non-synonymous mutations in < 3% of amino acids.

CONCLUSIONS

Unenriched HSV-2 DNA can undergo next-generation sequencing to identify intragenic variability. The use of clinical swabs for sequencing expands the information that can be gathered directly from these specimens.

A Herpes Simplex Virus Type 2 Deleted for Glycoprotein D Enables Dendritic Cells to Activate CD4+ and CD8+ T Cells

Herpes simplex virus type 2 (HSV-2) is highly prevalent in the human population producing significant morbidity, mainly because of the generation of genital ulcers and neonatal encephalitis. Additionally, HSV-2 infection significantly increases the susceptibility of the host to acquire HIV and promotes the shedding of the latter in the coinfected. Despite numerous efforts to create a vaccine against HSV-2, no licensed vaccines are currently available. A long-standing strategy, based on few viral glycoproteins combined with adjuvants, recently displayed poor results in a Phase III clinical study fueling exploration on the development of mutant HSV viruses that are attenuated in vivo and elicit protective adaptive immune components, such as antiviral antibodies and T cells. Importantly, such specialized antiviral immune components are likely induced and modulated by dendritic cells, professional antigen presenting cells that process viral antigens and present them to T cells. However, HSV interferes with several functions of DCs and ultimately induces their death. Here, we propose that for an attenuated mutant virus to confer protective immunity against HSV in vivo based on adaptive immune components, such virus should also be attenuated in dendritic cells to promote a robust and effective antiviral response. We provide a background framework for this idea, considerations, as well as the means to assess this hypothesis. Addressing this hypothesis may provide valuable insights for the development of novel, safe, and effective vaccines against herpes simplex viruses.

The Product of the Herpes Simplex Virus 2 UL16 Gene Is Critical for the Egress of Capsids from the Nuclei of Infected Cells

The herpes simplex virus (HSV) UL16 gene is conserved throughout the Herpesviridae and encodes a poorly understood tegument protein. The HSV-1 UL16 protein forms complexes with several viral proteins, including UL11, gE, VP22, and UL21. We previously demonstrated that HSV-2 UL21 was essential for virus propagation due to the failure of DNA-containing capsids (C capsids) to exit the nucleus. We hypothesized that if a UL16/UL21 complex was required for nuclear egress, HSV-2 lacking UL16 would have a phenotype similar to that of HSV-2 lacking UL21. Deletion of HSV-2 UL16 (Δ16) resulted in a 950-fold reduction in virus propagation in mouse L cell fibroblasts and a 200-fold reduction in virus propagation in Vero cells that was fully reversed upon the repair of Δ16 (Δ16R) and partially reversed by infecting UL16-expressing cells with Δ16. The kinetics of viral gene expression in cells infected with Δ16 were indistinguishable from those of cells infected with Δ16R or the parental virus. Additionally, similar numbers of capsids were isolated from the nuclei of cells infected with Δ16 and the parental virus. However, transmission electron microscopy, fluorescence in situ hybridization experiments, and fluorescent capsid localization assays all indicated a reduction in the ability of Δ16 C capsids to exit the nucleus of infected cells. Taken together, these data indicate that, like UL21, UL16 is critical for HSV-2 propagation and suggest that the UL16 and UL21 proteins may function together to facilitate the nuclear egress of capsids.IMPORTANCE HSV-2 is a highly prevalent sexually transmitted human pathogen that is the main cause of genital herpes infections and is fueling the epidemic transmission of HIV in sub-Saharan Africa. Despite important differences in the pathological features of HSV-1 and HSV-2 infections, HSV-2 is understudied compared to HSV-1. Here we demonstrate that a deletion of the HSV-2 UL16 gene results in a substantial inhibition of virus replication due to a reduction in the ability of DNA-containing capsids to exit the nucleus of infected cells. The phenotype of this UL16 mutant resembles that of an HSV-2 UL21 mutant described previously by our laboratory. Because UL16 and UL21 interact, these findings suggest that a complex containing both proteins may function together in nuclear egress.

HSV1 latent transcription and non-coding RNA: A critical retrospective

Virologists have invested great effort into understanding how the herpes simplex viruses and their relatives are maintained dormant over the lifespan of their host while maintaining the poise to remobilize on sporadic occasions. Piece by piece, our field has defined the tissues in play (the sensory ganglia), the transcriptional units (the latency-associated transcripts), and the responsive genomic region (the long repeats of the viral genomes). With time, the observed complexity of these features has compounded, and the totality of viral factors regulating latency are less obvious. In this review, we compose a comprehensive picture of the viral genetic elements suspected to be relevant to herpes simplex virus 1 (HSV1) latent transcription by conducting a critical analysis of about three decades of research. We describe these studies, which largely involved mutational analysis of the notable latency-associated transcripts (LATs), and more recently a series of viral miRNAs. We also intend to draw attention to the many other less characterized non-coding RNAs, and perhaps coding RNAs, that may be important for consideration when trying to disentangle the multitude of phenotypes of the many genetic modifications introduced into recombinant HSV1 strains.

Herpesvirus Capsid Assembly and DNA Packaging

Herpes simplex virus type I (HSV-1) is the causative agent of several pathologies ranging in severity from the common cold sore to life-threatening encephalitic infection. During productive lytic infection, over 80 viral proteins are expressed in a highly regulated manner, resulting in the replication of viral genomes and assembly of progeny virions. The virion of all herpesviruses consists of an external membrane envelope, a proteinaceous layer called the tegument, and an icosahedral capsid containing the double-stranded linear DNA genome. The capsid shell of HSV-1 is built from four structural proteins: a major capsid protein, VP5, which forms the capsomers (hexons and pentons), the triplex consisting of VP19C and VP23 found between the capsomers, and VP26 which binds to VP5 on hexons but not pentons. In addition, the dodecameric pUL6 portal complex occupies 1 of the 12 capsid vertices, and the capsid vertex specific component (CVSC), a heterotrimer complex of pUL17, pUL25, and pUL36, binds specifically to the triplexes adjacent to each penton. The capsid is assembled in the nucleus where the viral genome is packaged into newly assembled closed capsid shells. Cleavage and packaging of replicated, concatemeric viral DNA requires the seven viral proteins encoded by the UL6, UL15, UL17, UL25, UL28, UL32, and UL33 genes. Considerable advances have been made in understanding the structure of the herpesvirus capsid and the function of several of the DNA packaging proteins by applying biochemical, genetic, and structural techniques. This review is a summary of recent advances with respect to the structure of the HSV-1 virion capsid and what is known about the function of the seven packaging proteins and their interactions with each other and with the capsid shell.

Validation of a membrane touch biosensor for the qualitative detection of IgG class antibodies to herpes simplex virus type 2

A 1920s dead-stop end-point titration technique revisited for blood antibody analysis.

Production of a fragment of glycoprotein G of herpes simplex virus type 2 and evaluation of its diagnostic potential

INTRODUCTION

Herpes simplex virus type 2 (HSV-2) is the most common cause of genital herpes. Glycoprotein G (gG) is a prototype antigen for type-specific serodiagnosis distinguishing between HSV type 1 (HSV-1) and HSV-2 infections. As immunological diagnosis kits for accurate differentiation between HSV-1 and HSV-2 antibodies can be expensive, there is a need to develop a convenient, sensitive, specific and cost-effective serodiagnostic kit.

METHODS

We successfully expressed a fragment of gG comprising residues 321-580 of HSV-2 with histidine tag (gG(321-580His)) in a Bac-to-Bac baculovirus expression system, which had an antigenicity similar to its native counterpart. An indirect enzyme-linked immunosorbent assay (ELISA) was developed using gG(321-580His) as the diagnostic antigen and evaluated by comparison with a commercial HerpeSelect 2 ELISA immunoglobulin G kit as reference.

RESULTS

In testing 318 field serum samples, the diagnostic relative sensitivity and specificity of the developed gG(321-580His)-ELISA test in qualitative comparison with the commercial kit were 93.81% and 96.74%, respectively, and the accuracy was 94.65%.

CONCLUSION

The study indicates that gG(321-580His) has a high diagnostic potential for HSV-2 virus serodiagnosis in humans.

Regulation of Herpes Simplex Virus Glycoprotein-Induced Cascade of Events Governing Cell-Cell Fusion

Receptor-dependent herpes simplex virus (HSV)-induced cell-cell fusion requires glycoproteins gD, gH/gL, and gB. Our current model posits that during fusion, receptor-activated conformational changes in gD activate gH/gL, which subsequently triggers the transformation of the prefusion form of gB into a fusogenic state. To examine the role of each glycoprotein in receptor-dependent cell-cell fusion, we took advantage of our discovery that fusion by wild-type herpes simplex virus 2 (HSV-2) glycoproteins occurs twice as fast as that achieved by HSV-1 glycoproteins. By sequentially swapping each glycoprotein between the two serotypes, we established that fusion speed was governed by gH/gL, with gH being the main contributor. While the mutant forms of gB fuse at distinct rates that are dictated by their molecular structure, these restrictions can be overcome by gH/gL of HSV-2 (gH2/gL2), thereby enhancing their activity. We also found that deregulated forms of gD of HSV-1 (gD1) and gH2/gL2 can alter the fusogenic potential of gB, promoting cell fusion in the absence of a cellular receptor, and that deregulated forms of gB can drive the fusion machinery to even higher levels. Low pH enhanced fusion by affecting the structure of both gB and gH/gL mutants. Together, our data highlight the complexity of the fusion machinery, the impact of the activation state of each glycoprotein on the fusion process, and the critical role of gH/gL in regulating HSV-induced fusion. IMPORTANCE Cell-cell fusion mediated by HSV glycoproteins requires gD, gH/gL, gB, and a gD receptor. Here, we show that fusion by wild-type HSV-2 glycoproteins occurs twice as fast as that achieved by HSV-1 glycoproteins. By sequentially swapping each glycoprotein between the two serotypes, we found that the fusion process was controlled by gH/gL. Restrictions imposed on the gB structure by mutations could be overcome by gH2/gL2, enhancing the activity of the mutants. Under low-pH conditions or when using deregulated forms of gD1 and gH2/gL2, the fusogenic potential of gB could only be increased in the absence of receptor, underlining the exquisite regulation that occurs in the presence of receptor. Our data highlight the complexity of the fusion machinery, the impact of the activation state of each glycoprotein on the fusion process, and the critical role of gH/gL in regulating HSV-induced fusion.

Genotyping of herpes simplex virus type 1 by whole-genome sequencing

A previous phylogenetic analysis based on 32 full-length sequences of herpes simplex virus type 1 (HSV-1) suggested three major phylogenetic groups (phylogroups) with distinct geographic distribution: (1) western strains from Europe and North America, (2) isolates from Asia and one American strain and (3) isolates from Africa only. Here, we sequenced the genomes of additional 10 clinical HSV-1 isolates from Germany, and subsequently compared these sequences to 40 published HSV-1 genomes. The present data demonstrate that HSV-1 is the most diverse human alphaherpesvirus (mean pairwise p-distance of 0.756 %) and confirm the tripartite tree. However, as the German isolates cluster with strains of both phylogroups I and II, it is demonstrated that the latter is also present in Europe and thus is a Eurasian phylogroup. Tree-order scans indicate that HSV-1 evolution is massively influenced by recombination including all investigated strains regardless of the areal distribution of the phylogroups. Numerous recombination events in the evolution of HSV-1 may also influence genotyping as the present HSV-1 genotyping schemes do not yield results consistent with phylogroup classification. Genotyping of HSV-1 is currently based on analyses of intragenic sequence polymorphisms of US2, glycoprotein G (gG, US4) and gI (US7). Each of the 10 German HSV-1 isolates displayed a different US2/gG/gI-genotype combination, but clustered either in phylogroup I or II. In conclusion, the phylogroup concept provides a HSV-1 typing scheme that largely reflects human migration history, whereas the analysis of single-nucleotide polymorphisms fails to render significant biological properties, but allows description of individual genetic traits.

Current Concepts for Genital Herpes Simplex Virus Infection: Diagnostics and Pathogenesis of Genital Tract Shedding

Herpes simplex virus 2 (HSV-2) is a DNA virus that is efficiently transmitted through intimate genital tract contact and causes persistent infection that cannot be eliminated. HSV-2 may cause frequent, symptomatic self-limited genital ulcers, but in most persons infection is subclinical. However, recent studies have demonstrated that the virus is frequently shed from genital surfaces even in the absence of signs or symptoms of clinical disease and that the virus can be transmitted during these periods of shedding. Furthermore, HSV-2 shedding is detected throughout the genital tract and may be associated with genital tract inflammation, which likely contributes to increased risk of HIV acquisition. This review focuses on HSV diagnostics, as well as what we have learned about the importance of frequent genital HSV shedding for (i) HSV transmission and (ii) genital tract inflammation, as well as (iii) the impact of HSV-2 infection on HIV acquisition and transmission. We conclude with discussion of future areas of research to push the field forward.

No Evidence of Pritelivir Resistance Among Herpes Simplex Virus Type 2 Isolates After 4 Weeks of Daily Therapy

BACKGROUND

Pritelivir is a novel helicase-primase inhibitor in clinical development for treatment of herpes simplex virus type 2 (HSV-2) infections. In preclinical work, resistance-mediating mutations were identified in the HSV-2 genome at 3 loci in the UL5 gene and 1 locus in UL52.

METHODS

To evaluate whether daily pritelivir treatment results in emergence of resistance-mediating mutations, we analyzed HSV-2 strains detected in genital swab specimens from trial participants who were randomly assigned to receive different dosages of pritelivir. We sequenced resistance regions from 87 participants' samples, the UL5 gene in 73 samples from 44 participants, and the UL52 gene in 71 samples from 43 participants.

RESULTS

We found no evidence that pritelivir induced known resistance-mediating mutations or for amino acid variation at other loci. In one participant's HSV-2 isolate, we found a previously unidentified mutation close to the putative resistance-mediating region in UL5 and subsequently determined in vitro susceptibility to pritelivir. We characterized mutations from 32 cultivated HSV-2 isolates previously found to be susceptible to pritelivir in vitro and identified several novel mutations that most likely reflect preexisting variation in circulating HSV-2.

CONCLUSIONS

This study demonstrates evidence of retained susceptibility of HSV-2 to pritelivir in immunocompetent persons following daily therapy for up to 28 days.

Systemic immunodominant CD8 responses with an effector-like phenotype are induced by intravaginal immunization with attenuated HSV vectors expressing HIV Tat and mediate protection against HSV infection

Mucosal HSV infection remains a public health issue in developing and developed world. However, an effective vaccine is still missing, partly because of the incomplete knowledge of correlates of protection. In this study we have investigated the kinetics and quality of immunity elicited by an attenuated HSV1 vector expressing the immunomodulatory Tat protein of HIV-1 (HSV1-Tat). Animals were immunized by intravaginal (IVag) or intradermal (ID) route with HSV1-Tat or with a control HSV1 vector expressing the LacZ gene (HSV1-LacZ) and immune responses were characterized in different anatomical districts. IVag immunization with HSV1-Tat enhanced both expansion and memory phases of HSV-specific immunodominant CD8 responses at systemic, but not local, level and induced short- and long-term protection against mucosal challenge. Conversely, ID immunization with HSV1-Tat favored HSV-subdominant CD8 responses, which protected mice only at early time points after immunization. IVag immunization, in particular with HSV1-Tat, compared to ID immunization, induced the differentiation of CD8(+) T lymphocytes into short-lived effector (SLEC) and effector memory (Tem) cells, generating more robust recall responses associated with increased control of virus replication. Notably, systemic SLEC and Tem contributed to generate protective local secondary responses, demonstrating their importance for mucosal control of HSV. Finally, IgG responses were observed mostly in IVag HSV1-Tat immunized animals, although seemed dispensable for protection, which occurred even in few IgG negative mice. Thus, HSV1 vectors expressing Tat induce protective anti-HSV1 immune responses.

Murine gammaherpesvirus 68 ORF35 is required for efficient lytic replication and latency

Murine gammaherpesvirus (MHV) 68, a natural pathogen of field mice, is related to human gammaherpesviruses, Epstein–Barr virus (EBV; human herpesvirus 4) and Kaposi’s sarcoma-associated herpesvirus (KSHV; human herpesvirus 8). The ORF35 of MHV-68 and its homologues of EBV and KSHV are located in the gene cluster composed of ORF34–ORF38 in which each gene overlaps with adjacent genes. Although MHV-68 ORF35 was reported to be an essential gene, its function during infection is presently unknown. In this study, we show, by analysing ORF35-transfected cells, that three serine residues in the C terminus are responsible for the phosphorylation and that the ORF35 protein forms homo-oligomers via a predicted coiled-coil motif. The ORF35 protein expressed by transfection was preferentially located in the cytoplasm of cells uninfected or infected with MHV-68. The recombinant virus lacking ORF35 (35S virus) exhibited genome replication and expression of lytic proteins comparable to those of the WT virus, but reduced levels of virus production, suggesting that the ORF35 protein acts at the virion assembly and/or egress step. Lytic replication in the lung after intranasal infection and the frequency of ex vivo reactivation from latency after intraperitoneal infection were lower in 35S virus-infected mice than in mice infected with the WT or marker-reverted virus. Our results indicate that ORF35 is not essential for MHV-68 lytic replication, but plays an important role in efficient viral replication and reactivation from latency.

[Diagnosis and therapy of genitoanal ulcers of infectious etiology]

BACKGROUND/OBJECTIVES

In this review article the diagnostic and therapeutic principles of genital ulcers of infectious etiology are highlighted. Besides frequent causative infections rare but relevant diseases in the differential diagnosis are discussed in detail.

MATERIAL AND METHODS

A Pubmed literature search was carried out, guidelines from different task groups and clinical experiences are presented.

RESULTS

Infections with herpes simplex virus (first) and syphilis (second) are still the most common causes of infectious genital ulcers. An endemic occurrence, previously rare in Europe, has been observed in recent years. Particular risk groups, such as men who have sex with men (MSM), sex workers or sex tourists are affected. Even less common locations, such as the mouth or the rectum, lymphogranuloma venereum (LGV) and atypical clinical symptoms (e.g. pelvic pain in pelvic lymphadenopathy with LGV) must be considered in the differential diagnosis.

CONCLUSION

In recent years sexually transmitted infections (STI) have shown a significant increase in western industrialized nations. In all cases with unclear findings in the genital and anal areas (and also in the oral cavity) STI diseases must be reconsidered in the differential diagnosis.

Herpes Simplex Virus: The Interplay Between HSV, Host, and HIV-1

Herpes simplex virus proteins interact with host (human) proteins and create an environment conducive for its replication. Genital ulceration due to herpes simplex virus type 2 (HSV-2) infections is an important clinical manifestation reported to increase the risk of human immunodeficiency virus type 1 (HIV-1) acquisition and replication in HIV-1/HSV-2 coinfection. Dampening the innate and adaptive immune responses of the skin-resident dendritic cells, HSV-2 not only helps itself, but creates a "yellow brick road" for one of the most dreaded viruses HIV, which is transmitted mainly through the sexual route. Although, data from clinical trials show that HSV-2 suppression reduces HIV-1 viral load, there are hardly any reports presenting conclusive evidence on the impact of HSV-2 coinfection on HIV-1 disease progression. Be that as it may, understanding the interplay between these three characters (HSV, host, and HIV-1) is imperative. This review endeavors to collate studies on the influence of HSV-derived proteins on the host response and HIV-1 replication. Studying such complex interactions may help in designing and developing common strategies for the two viruses to keep these "partners in crime" at bay.

Herpes Simplex Vaccines: Prospects of Live-attenuated HSV Vaccines to Combat Genital and Ocular infections

Herpes simplex virus type-1 (HSV-1) and its closely related type-2 (HSV-2) viruses cause important clinical manifestations in humans including acute ocular disease and genital infections. These viruses establish latency in the trigeminal ganglionic and dorsal root neurons, respectively. Both viruses are widespread among humans and can frequently reactivate from latency causing disease. Currently, there are no vaccines available against herpes simplex viral infections. However, a number of promising vaccine approaches are being explored in pre-clinical investigations with few progressing to early phase clinical trials. Consensus research findings suggest that robust humoral and cellular immune responses may partially control the frequency of reactivation episodes and reduce clinical symptoms. Live-attenuated viral vaccines have long been considered as a viable option for generating robust and protective immune responses against viral pathogens. Varicella zoster virus (VZV) belongs to the same alphaherpesvirus subfamily with herpes simplex viruses. A live-attenuated VZV vaccine has been extensively used in a prophylactic and therapeutic approach to combat primary and recurrent VZV infection indicating that a similar vaccine approach may be feasible for HSVs. In this review, we summarize pre-clinical approaches to HSV vaccine development and current efforts to test certain vaccine approaches in human clinical trials. Also, we discuss the potential advantages of using a safe, live-attenuated HSV-1 vaccine strain to protect against both HSV-1 and HSV-2 infections.

CD1d Expression and Invariant NKT Cell Responses in Herpesvirus Infections

Invariant natural killer T (iNKT) cells are a highly conserved subset of unconventional T lymphocytes that express a canonical, semi-invariant T cell receptor and surface markers shared with the natural killer cell lineage. iNKT cells recognize exogenous and endogenous glycolipid antigens restricted by non-polymorphic CD1d molecules, and are highly responsive to the prototypical agonist, α-galactosylceramide. Upon activation, iNKT cells rapidly coordinate signaling between innate and adaptive immune cells through the secretion of proinflammatory cytokines, leading to the maturation of antigen-presenting cells, and expansion of antigen-specific CD4+ and CD8+ T cells. Because of their potent immunoregulatory properties, iNKT cells have been extensively studied and are known to play a pivotal role in mediating immune responses against microbial pathogens including viruses. Here, we review evidence that herpesviruses manipulate CD1d expression to escape iNKT cell surveillance and establish lifelong latency in humans. Collectively, published findings suggest that iNKT cells play critical roles in anti-herpesvirus immune responses and could be harnessed therapeutically to limit viral infection and viral-associated disease.

Genome Sequencing and Analysis of Geographically Diverse Clinical Isolates of Herpes Simplex Virus 2

Herpes simplex virus 2 (HSV-2), the principal causative agent of recurrent genital herpes, is a highly prevalent viral infection worldwide. Limited information is available on the amount of genomic DNA variation between HSV-2 strains because only two genomes have been determined, the HG52 laboratory strain and the newly sequenced SD90e low-passage-number clinical isolate strain, each from a different geographical area. In this study, we report the nearly complete genome sequences of 34 HSV-2 low-passage-number and laboratory strains, 14 of which were collected in Uganda, 1 in South Africa, 11 in the United States, and 8 in Japan. Our analyses of these genomes demonstrated remarkable sequence conservation, regardless of geographic origin, with the maximum nucleotide divergence between strains being 0.4% across the genome. In contrast, prior studies indicated that HSV-1 genomes exhibit more sequence diversity, as well as geographical clustering. Additionally, unlike HSV-1, little viral recombination between HSV-2 strains could be substantiated. These results are interpreted in light of HSV-2 evolution, epidemiology, and pathogenesis. Finally, the newly generated sequences more closely resemble the low-passage-number SD90e than HG52, supporting the use of the former as the new reference genome of HSV-2.

IMPORTANCE

Herpes simplex virus 2 (HSV-2) is a causative agent of genital and neonatal herpes. Therefore, knowledge of its DNA genome and genetic variability is central to preventing and treating genital herpes. However, only two full-length HSV-2 genomes have been reported. In this study, we sequenced 34 additional HSV-2 low-passage-number and laboratory viral genomes and initiated analysis of the genetic diversity of HSV-2 strains from around the world. The analysis of these genomes will facilitate research aimed at vaccine development, diagnosis, and the evaluation of clinical manifestations and transmission of HSV-2. This information will also contribute to our understanding of HSV evolution.

Global Diversity within and between Human Herpesvirus 1 and 2 Glycoproteins

Human herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) are large-genome DNA viruses that establish a persistent infection in sensory neurons and commonly manifest with recurring oral or genital erosions that transmit virus. HSV encodes 12 predicted glycoproteins that serve various functions, including cellular attachment, entry, and egress. Glycoprotein G is currently the target of an antibody test to differentiate HSV-1 from HSV-2; however, this test has shown reduced capacity to differentiate HSV strains in East Africa. Until the recent availability of 26 full-length HSV-1 and 36 full-length HSV-2 sequences, minimal comparative information was available for these viruses. In this study, we use a variety of sequence analysis methods to compare all available sequence data for HSV-1 and HSV-2 glycoproteins, using viruses isolated in Europe, Asia, North America, the Republic of South Africa, and East Africa. We found numerous differences in diversity, nonsynonymous/synonymous substitution rates, and recombination rates between HSV-1 glycoproteins and their HSV-2 counterparts. Phylogenetic analysis revealed that while most global HSV-2 glycoprotein G sequences did not form clusters within or between continents, one clade (supported at 60.5%) contained 37% of the African sequences analyzed. Accordingly, sequences from this African subset contained unique amino acid signatures, not only in glycoprotein G, but also in glycoproteins I and E, which may account for the failure of sensitive antibody tests to distinguish HSV-1 from HSV-2 in some African individuals. Consensus sequences generated in the study can be used to improve diagnostic assays that differentiate HSV-1 from HSV-2 in global populations.

IMPORTANCE

Human herpes simplex viruses 1 and 2 (HSV-1 and HSV-2) are large DNA viruses associated with recurring oral or genital erosions that transmit virus. Up to 12 HSV-1 and HSV-2 glycoproteins are involved in HSV cell entry or are required for viral spread in animals, albeit some are dispensable for replication in vitro. The recent availability of comparable numbers of full-length HSV-1 and HSV-2 sequences enabled comparative analysis of gene diversity of glycoproteins within and between HSV types. Overall, we found less glycoprotein sequence diversity within HSV-2 than within the HSV-1 strains studied, while at the same time, several HSV-2 glycoproteins were evolving under less selective pressure. Because HSV glycoproteins are the focus of antibody tests to detect and differentiate between infections with the two strains and are constituents of vaccines in clinical-stage development, these findings will aid in refining the targets for diagnostic tests and vaccines.

Genomic, phylogenetic, and recombinational characterization of herpes simplex virus 2 strains

Herpes simplex virus 2 (HSV-2) is a major global pathogen, infecting 16% of people 15 to 49 years old worldwide and causing recurrent genital ulcers. Little is known about viral factors contributing to virulence, and there are currently only two genomic sequences available. In this study, we determined nearly complete genomic sequences of six additional HSV-2 isolates, using Illumina MiSeq. We report that HSV-2 has a genomic overall mean distance of 0.2355%, which is less than that of HSV-1. There were approximately 100 amino-acid-encoding and indels per genome. Microsatellite mapping found a bias toward intergenic regions in the nonconserved microsatellites and a genic bias in all detected tandem repeats. Extensive recombination between the HSV-2 strains was also strongly implied. This was the first study to analyze multiple HSV-2 sequences, and the data will be valuable in future evolutionary, virulence, and structure-function studies.

IMPORTANCE

HSV-2 is a significant worldwide pathogen, causing recurrent genital ulcers. Here we present six nearly complete HSV-2 genomic sequences, and, with the addition of two previously sequenced strains, for the first time genomic, phylogenetic, and recombination analysis was performed on multiple HSV-2 genomes. Our results show that microsatellite mapping found a bias toward intergenic regions in the nonconserved microsatellites and a genic bias in all detected tandem repeats and confirm that chimpanzee herpesvirus 1 (ChHV-1) is a separate species and that each of the HSV-2 strains is a genomic mosaic.

Antiviral activity of theaflavin digallate against herpes simplex virus type 1

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Black tea theaflavins show significant anti-herpes simplex virus type 1 (HSV-1) effect on both A549 and Vero cells.

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Theaflavin is able to inhibit the entry of HSV-1 to its host by blocking the adsorption and penetration processes.

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Application of these agents as natural topical remedy to prevent and treat HSV-1 infection and spreading is promising.

Tea is the second most consumed drink in the world. The beneficial effects of tea have been mostly attributed to its catechin content. Black tea is derived from the leaves of Camellia sinensis plant, and it is rich in theaflavin polyphenols, in particular theaflavin (TF1), theaflavin-3-monogallate (TF2A), theaflavin-3′-monogallate (TF2B), and theaflavin-3,3′-digallate (TF3). Vero and A549 cells were used to evaluate the effect of purified individual black tea theaflavins as anti-herpes simplex virus 1 agents. With the rise of HSV resistant strains, there is a critical need to develop novel antiherpesviral treatments. Results of the cytotoxicity assay tested by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium] showed that TF1, TF2, and TF3 are not toxic to Vero and A549 cells at a concentration up to 75 μM. The antiviral activity of the individual theaflavins was tested by plaque reduction assay, MTS assay, flow cytometric analysis and confocal microscopy observations. The results showed that TF1, TF2, and TF3 exhibit potent, dose-dependent anti-HSV-1 effect, with TF3 being the most efficient in both Vero and A549 cells. A concentration of 50 μM TF3 and above was sufficient to inhibit >99% of the production of HSV-1 viral particles. The anti-HSV-1 effect of TF3 is due to a direct effect on the virions, and treating Vero or A549 cells with TF3 for 1 h prior to infection, or treating the cells at different times post infection does not inhibit HSV-1 production. TF3 is stable at vaginal pH, indicating its potential to be a promising natural and affordable remedy against herpes simplex viral infections.

Short nucleotide sequences in herpesviral genomes identical to the human DNA

In 2010, we described many similar DNA sequences in human and viral genomes, including herpesviral ones. The data obtained allowed us to suggest that these motifs may provide the antiviral protection by mating with a complementary potential target and destroying it by the catalytic way like small interfering RNA, siRNA. Since we have analyzed these viruses as a group, two major issues seemed to us curious: (1) the number of such motifs in genomes of various herpesvirus types, and (2) distribution of these motifs in an individual viral genome. Here we searched only the herpesviral genomes for short (>20nt) continuous sequences (hits) that are totally identical to the sequences of human DNA. We found that different viral genes and genomes of different herpesviruses contain different amount of such hits. Assuming like in previous paper that the density of these hits in viral genes is associated with the probability to be targets for cellular siRNA, we consider the genomic allocation of this density as a hypothetical targetome map of the human herpesviruses. We combined all nine types of herpesviruses in the three groups according the hit concentration in their genomes and found that the resulting sequence corresponds to the type of cellular pathology caused by a virus. We do not assert now that this trend also relates to other human viruses or other viruses in general. As the GenBank continues to fill, it would be highly advisable to conduct further relevant research. We also suggested that a high hits concentration we found in the gene RL1 (ICP34.5) of the herpes simplex virus type 1 (HSV1) can make this gene a likely target for putative cellular endogenous siRNA. Artificial blockade of the gene RL1 attaches oncolytic properties to HSV1, and we do not exclude the possibility that part of the HSV1 population in humans with blocked RL1 in vivo, may participate in early anti-cancer protection during the reactivation of the virus from the latent state.

HSV-2 immediate-early protein US1 inhibits IFN-β production by suppressing association of IRF-3 with IFN-β promoter

HSV-2 is the major cause of genital herpes, and its infection increases the risk of HIV-1 acquisition and transmission. After initial infection, HSV-2 can establish latency within the nervous system and thus maintains lifelong infection in humans. It has been suggested that HSV-2 can inhibit type I IFN signaling, but the underlying mechanism has yet to be determined. In this study, we demonstrate that productive HSV-2 infection suppresses Sendai virus (SeV) or polyinosinic-polycytidylic acid-induced IFN-β production. We further reveal that US1, an immediate-early protein of HSV-2, contributes to such suppression, showing that US1 inhibits IFN-β promoter activity and IFN-β production at both mRNA and protein levels, whereas US1 knockout significantly impairs such capability in the context of HSV-2 infection. US1 directly interacts with DNA binding domain of IRF-3, and such interaction suppresses the association of nuclear IRF-3 with the IRF-3 responsive domain of IFN-β promoter, resulting in the suppression of IFN-β promoter activation. Additional studies demonstrate that the 217-414 aa domain of US1 is critical for the suppression of IFN-β production. Our results indicate that HSV-2 US1 downmodulates IFN-β production by suppressing the association of IRF-3 with the IRF-3 responsive domain of IFN-β promoter. Our findings highlight the significance of HSV-2 US1 in inhibiting IFN-β production and provide insights into the molecular mechanism by which HSV-2 evades the host innate immunity, representing an unconventional strategy exploited by a dsDNA virus to interrupt type I IFN signaling pathway.

Herpes simplex virus 2 (HSV-2) infected cell proteins are among the most dominant antigens of a live-attenuated HSV-2 vaccine

Virion glycoproteins such as glycoprotein D (gD) are believed to be the dominant antigens of herpes simplex virus 2 (HSV-2). We have observed that mice immunized with a live HSV-2 ICP0^- mutant virus, HSV-2 0ΔNLS, are 10 to 100 times better protected against genital herpes than mice immunized with a HSV-2 gD subunit vaccine (PLoS ONE 6:e17748). In light of these results, we sought to determine which viral proteins were the dominant antibody-generators (antigens) of the live HSV-2 0ΔNLS vaccine. Western blot analyses indicated the live HSV-2 0ΔNLS vaccine elicited an IgG antibody response against 9 or more viral proteins. Many antibodies were directed against infected-cell proteins of >100 kDa in size, and only 10 ± 5% of antibodies were directed against gD. Immunoprecipitation (IP) of total HSV-2 antigen with 0ΔNLS antiserum pulled down 19 viral proteins. Mass spectrometry suggested 44% of immunoprecipitated viral peptides were derived from two HSV-2 infected cells proteins, RR-1 and ICP8, whereas only 14% of immunoprecipitated peptides were derived from HSV-2’s thirteen glycoproteins. Collectively, the results suggest the immune response to the live HSV-2 0ΔNLS vaccine includes antibodies specific for infected cell proteins, capsid proteins, tegument proteins, and glycoproteins. This increased breadth of antibody-generating proteins may contribute to the live HSV-2 vaccine’s capacity to elicit superior protection against genital herpes relative to a gD subunit vaccine.

A single intramuscular vaccination of mice with the HSV-1 VC2 virus with mutations in the glycoprotein K and the membrane protein UL20 confers full protection against lethal intravaginal challenge with virulent HSV-1 and HSV-2 strains

Herpes Simplex Virus type-1 (HSV-1) and type-2 (HSV-2) establish life-long infections and cause significant orofacial and genital infections in humans. HSV-1 is the leading cause of infectious blindness in the western world. Currently, there are no available vaccines to protect against herpes simplex infections. Recently, we showed that a single intramuscular immunization with an HSV-1(F) mutant virus lacking expression of the viral glycoprotein K (gK), which prevents the virus from entering into distal axons of ganglionic neurons, conferred significant protection against either virulent HSV-1(McKrae) or HSV-2(G) intravaginal challenge in mice. Specifically, 90% of the mice were protected against HSV-1(McKrae) challenge, while 70% of the mice were protected against HSV-2(G) challenge. We constructed the recombinant virus VC2 that contains specific mutations in gK and the membrane protein UL20 preventing virus entry into axonal compartments of neurons, while allowing efficient replication in cell culture, unlike the gK-null virus, which has a major defect in virus replication and spread. Intramuscular injection of mice with 10⁷ VC2 plaque forming units did not cause any significant clinical disease in mice. A single intramuscular immunization with the VC2 virus protected 100% of mice against lethal intravaginal challenge with either HSV-1(McKrae) or HSV-2(G) viruses. Importantly, vaccination with VC2 produced robust cross protective humoral and cellular immunity that fully protected vaccinated mice against lethal disease. Quantitative PCR did not detect any viral DNA in ganglionic tissues of vaccinated mice, while unvaccinated mice contained high levels of viral DNA. The VC2 virus may serve as an efficient vaccine against both HSV-1 and HSV-2 infections, as well as a safe vector for the production of vaccines against other viral and bacterial pathogens.

Identification of novel virus-specific antigens by CD4⁺ and CD8⁺ T cells from asymptomatic HSV-2 seropositive and seronegative donors

Reactivation of latent herpes simplex virus 2 (HSV-2) infections can be characterized by episodic recurrent genital lesions and/or viral shedding. We hypothesize that infected (HSV-2(pos)) asymptomatic individuals have acquired T cell responses to specific HSV-2 antigen(s) that may be an important factor in controlling their recurrent disease symptoms. Our proteomic screening technology, ATLAS, was used to characterize the antigenic repertoire of T cell responses in infected (HSV-2(pos)) and virus-exposed seronegative (HSV-2(neg)) subjects. T cell responses, determined by IFN-γ secretion, were generated to gL, UL2, UL11, UL21, ICP4, ICP0, ICP47 and UL40 with greater magnitude and/or frequency among cohorts of exposed HSV-2(neg) or asymptomatic HSV-2(pos) individuals, compared to symptomatic recurrent HSV-2(pos) subjects. T cell antigens recognized preferentially among individuals who are resistant to infection or who are infected and have mild or no clinical disease may provide new targets for the design of vaccines aimed at treating and/or preventing HSV-2 infection.

Update on herpes virus infections of the nervous system

Herpes simplex viruses types 1 and 2 (HSV-1 and HSV-2) are human neurotropic viruses that establish latent infection in dorsal root ganglia (DRG) for the entire life of the host. From the DRG they can reactivate to cause human morbidity and mortality. Although they vary, in part, in the clinical disorders they cause, and in their molecular structure, they share several features that govern the biology of their infection of the human nervous system. HSV-1 is the causative agent of encephalitis, corneal blindness, and several peripheral nervous system disorders; HSV-2 is responsible for meningoencephalitis in neonates and meningitis in adults. The biology of their ability to establish latency, maintain it for the entire life of the host, reactivate, and cause primary and recurrent disease is being studied in animal models and in humans. This review covers recent advances in understanding the biology and pathogenesis of HSV-related disease.

Inhibitors of signal peptide peptidase (SPP) affect HSV-1 infectivity in vitro and in vivo

Recently we have shown that the highly conserved herpes simplex virus glycoprotein K (gK) binds to signal peptide peptidase (SPP), also known as minor histocompatibility antigen H13. In this study we have demonstrated for the first time that inhibitors of SPP, such as L685,458, (Z-LL)2 ketone, aspirin, ibuprofen and DAPT, significantly reduced HSV-1 replication in tissue culture. Inhibition of SPP activity via (Z-LL)2 ketone significantly reduced viral transcripts in the nucleus of infected cells. Finally, when administered during primary infection, (Z-LL)2 ketone inhibitor reduced HSV-1 replication in the eyes of ocularly infected mice. Thus, blocking SPP activity may represent a clinically effective and expedient approach to the reduction of viral replication and the resulting pathology.

A single viral gene determines lethal cross-species neurovirulence of baboon herpesvirus HVP2

Alpha-herpesviruses can produce more severe infections in non-natural host species than in their natural host. Isolates of the baboon alpha-herpesvirus Papiine herpesvirus 2 (HVP2) are either very neurovirulent in mice (subtype nv) or non-virulent (subtype ap), but no such difference is evident in the natural baboon host. Comparative genome sequencing was used to identify subtype-specific sequence differences (SSDs) between HVP2nv and HVP2ap isolates. Some genes were identified that despite exhibiting sequence variation among isolates did not have any SSDs, while other genes had comparatively high levels of SSDs. Construction of genomic recombinants between HVP2nv and HVP2ap isolates mapped the mouse neurovirulence determinant to within three genes. Construction of gene-specific recombinants demonstrated that the UL39 ORF is responsible for determining the lethal neurovirulence phenotype of HVP2 in mice. These results demonstrate that differences in a single viral gene can determine the severity of herpesvirus infection in a non-natural host species.

Binding of HSV-1 glycoprotein K (gK) to signal peptide peptidase (SPP) is required for virus infectivity

Glycoprotein K (gK) is a virion envelope protein of herpes simplex virus types 1 (HSV-1) and 2 (HSV-2), which plays important roles in virion entry, morphogenesis and egress. Two-hybrid and pull-down assays were utilized to demonstrate that gK and no other HSV-1 genes specifically binds to signal peptide peptidase (SPP), also known as minor histocompatibility antigen H13. SPP dominant negative mutants, shRNA against SPP significantly reduced HSV-1 replication in vitro. SPP also affected lysosomes and ER responses to HSV-1 infection. Thus, in this study we have shown for the first time that gK, despite its role in fusion and egress, is also involved in binding the cytoplasmic protein SPP. These results also suggest that SPP plays an important role in viral replication and possibly virus pathogenesis. This makes SPP unique in that its function appears to be required by the virus as no other protein can compensate its loss in terms of viral replication.

Helicase-primase inhibitor pritelivir for HSV-2 infection

BACKGROUND

Pritelivir, an inhibitor of the viral helicase-primase complex, exhibits antiviral activity in vitro and in animal models of herpes simplex virus (HSV) infection. We tested the efficacy and safety of pritelivir in otherwise healthy persons with genital HSV-2 infection.

METHODS

We randomly assigned 156 HSV-2-positive persons with a history of genital herpes to receive one of four doses of oral pritelivir (5, 25, or 75 mg daily, or 400 mg weekly) or placebo for 28 days. Participants obtained daily swabs from the genital area for HSV-2 testing, which was performed with a polymerase-chain-reaction assay. Participants also maintained a diary of genital signs and symptoms. The primary end point was the rate of genital HSV shedding.

RESULTS

HSV shedding among placebo recipients was detected on 16.6% of days; shedding among pritelivir recipients was detected on 18.2% of days among those receiving 5 mg daily, 9.3% of days among those receiving 25 mg daily, 2.1% of days among those receiving 75 mg daily, and 5.3% of days among those receiving 400 mg weekly. The relative risk of viral shedding with pritelivir, as compared with placebo, was 1.11 (95% confidence interval [CI], 0.65 to 1.87) with the 5-mg daily dose, 0.57 (95% CI, 0.31 to 1.03) with the 25-mg daily dose, 0.13 (95% CI, 0.04 to 0.38) with the 75-mg daily dose, and 0.32 (95% CI, 0.17 to 0.59) with the 400-mg weekly dose. The percentage of days with genital lesions was also significantly reduced, from 9.0% in the placebo group to 1.2% in both the group receiving 75 mg of pritelivir daily (relative risk, 0.13; 95% CI, 0.02 to 0.70) and the group receiving 400 mg weekly (relative risk, 0.13; 95% CI, 0.03 to 0.52). The rate of adverse events was similar in all groups.

CONCLUSIONS

Pritelivir reduced the rates of genital HSV shedding and days with lesions in a dose-dependent manner in otherwise healthy men and women with genital herpes. (Funded by AiCuris; ClinicalTrials.gov number, NCT01047540.).

Taxonomy

This chapter addresses the classification and taxonomy of viruses with special attention to viruses that show pneumotropic properties. Information provided in this chapter supplements that provided in other chapters in Parts II–V of this volume that discuss individual viral pathogens.

Genomic sequences of a low passage herpes simplex virus 2 clinical isolate and its plaque-purified derivative strain

Herpes simplex virus 2 is an important human pathogen as the causative agent of genital herpes, neonatal herpes, and increased risk of HIV acquisition and transmission. Nevertheless, the only genomic sequence that has been completed is the attenuated HSV-2 HG52 laboratory strain. In this study we defined the genomic sequence of the HSV-2 SD90e low passage clinical isolate and a plaque-purified derivative, SD90-3P. We found minimal sequence differences between SD90e and SD90-3P. However, in comparisons with the HSV-2 HG52 reference genome sequence, the SD90e genome ORFs contained numerous point mutations, 13 insertions/deletions (indels), and 9 short compensatory frameshifts. The indels were true sequence differences, but the compensatory frameshifts were likely sequence errors in the original HG52 sequence. Because HG52 virus is less virulent than other HSV-2 strains and may not be representative of wildtype HSV-2 strains, we propose that the HSV-2 SD90e genome serve as the new HSV-2 reference genome.

Herpes Simplex Virus UL14 Protein Blocks Apoptosis

We report that an HSV-2 UL14 protein expressing cell line (14/HEp-2) was more resistant to apoptosis induced by osmotic shock and certain drugs than its parental cell line. Furthermore, HSV-1 UL14 protein deletion virus (UL14D) showed weaker inhibition of apoptosis compared to the rescued virus UL14R. The protein's anti-apoptotic function may derive from its heat shock protein-like properties.

Single dose of glycoprotein K (gK)-deleted HSV-1 live-attenuated virus protects mice against lethal vaginal challenge with HSV-1 and HSV-2 and induces lasting T cell memory immune responses

Background

Herpes simplex virus type-1(HSV-1) and HSV-2 are important human pathogens that cause significant ocular and urogenital complications, respectively. We have previously shown that HSV-1 virions lacking glycoprotein K (gK) are unable to enter into neurons via synaptic axonal membranes and be transported in either retrograde or anterograde manner. Here, we tested the ability of HSV-1 (F) gK-null to protect against lethal challenge with either highly virulent ocular HSV-1 (McKrae strain), or genital HSV-2 (G strain). The gK-null virus vaccine efficiently protected mice against lethal vaginal infection with either HSV-1(McKrae) or HSV-2 (G).

Results

Female mice were immunized via a single intramuscular injection with 10⁶ PFU of the gK-null virus. Immunized mice were treated with Depo-Provera fourteen days after vaccination and were challenged via the vaginal route one week later. Ninety percent of mice vaccinated with the gK-null virus survived HSV-1 (McKrae) challenge, while 70% of these mice survived after HSV-2 (G) challenge. Moreover, all vaccinated mice exhibited substantially reduced disease symptoms irrespective of HSV-1 or HSV-2 challenge as compared to the mock vaccinated challenge group. T-cell memory immune responses to specific glycoprotein B (gB) and glycoprotein D (gD) peptide epitopes were detectable at 7 months post vaccination.

Conclusions

These results suggest that the highly attenuated, non-neurotropic gK-null virus may be used as an effective vaccine to protect against both virulent HSV-1 and HSV-2 genital infections and induce lasting immune responses.

Using HSV-1 genome phylogenetics to track past human migrations

We compared 31 complete and nearly complete globally derived HSV-1 genomic sequences using HSV-2 HG52 as an outgroup to investigate their phylogenetic relationships and look for evidence of recombination. The sequences were retrieved from NCBI and were then aligned using Clustal W. The generation of a maximum likelihood tree resulted in a six clade structure that corresponded with the timing and routes of past human migration. The East African derived viruses contained the greatest amount of genetic diversity and formed four of the six clades. The East Asian and European/North American derived viruses formed separate clades. HSV-1 strains E07, E22 and E03 were highly divergent and may each represent an individual clade. Possible recombination was analyzed by partitioning the alignment into 5 kb segments, performing individual phylogenetic analysis on each partition and generating a.phylogenetic network from the results. However most evidence for recombination spread at the base of the tree suggesting that recombination did not significantly disrupt the clade structure. Examination of previous estimates of HSV-1 mutation rates in conjunction with the phylogenetic data presented here, suggests that the substitution rate for HSV-1 is approximately 1.38 × 10(-7) subs/site/year. In conclusion, this study expands the previously described HSV-1 three clade phylogenetic structures to a minimum of six and shows that the clade structure also mirrors global human migrations. Given that HSV-1 has co-evolved with its host, sequencing HSV-1 isolated from various populations could serve as a surrogate biomarker to study human population structure and migration patterns.

Molecular characterization of clinical isolates of herpes simplex virus type 1 collected in a tertiary-care hospital in Dublin, Ireland

Herpes simplex virus type 1 (HSV-1) is a ubiquitous human pathogen. While there has been extensive research into the evolutionary relationships among herpesviruses, there is little data on the evolutionary relationship of HSV-1 based on sequence analysis of clinical isolates. The present study aims to be the first to document the molecular epidemiology and genetic diversity and frequency of recombination of HSV-1 (n = 42) clinical isolates in Ireland. The entire 1,171 bp of the gI-1 gene and 717 bp of the gG-1 gene of 42 clinical Irish isolates were amplified, sequenced and the phylogenies reconstructed. Putative recombinants were examined using bootscan analysis. Phylogenetic reconstruction of the nucleotide sequence alignments of the entire genes of amplified glycoproteins gI and gG suggested that three distinct HSV-1 genogroups were circulating in the Irish population. At least 15 HSV-1 intergenic recombinants with a recombination point between gI and gG, and 11 HSV-1 intragenic recombinants were detected. There was no evident association between genetic group and gender, disease recurrence or anatomical site of infection. Genital isolates (n = 30) belonged to all genogroups. However, two HSV-1 isolates, Irl 31 and Irl32, from a patient with severe mucocutaneous infection nonresponsive to acyclovir and isolated over a prolonged period were both intragenic and intergenic recombinants. The detection of variability and recombination in gG and gI genes of both HSV-1 may provide a mechanism to evade the host immune response thereby maintaining the viral genome. The variability and recombination detected may also have implications for the detection, diagnosis and treatment of HSV.

Pandoraviruses: amoeba viruses with genomes up to 2.5 Mb reaching that of parasitic eukaryotes

Ten years ago, the discovery of Mimivirus, a virus infecting Acanthamoeba, initiated a reappraisal of the upper limits of the viral world, both in terms of particle size (>0.7 micrometers) and genome complexity (>1000 genes), dimensions typical of parasitic bacteria. The diversity of these giant viruses (the Megaviridae) was assessed by sampling a variety of aquatic environments and their associated sediments worldwide. We report the isolation of two giant viruses, one off the coast of central Chile, the other from a freshwater pond near Melbourne (Australia), without morphological or genomic resemblance to any previously defined virus families. Their micrometer-sized ovoid particles contain DNA genomes of at least 2.5 and 1.9 megabases, respectively. These viruses are the first members of the proposed "Pandoravirus" genus, a term reflecting their lack of similarity with previously described microorganisms and the surprises expected from their future study.

Novel deletion in glycoprotein G forms a cluster and causes epidemiologic spread of herpes simplex virus type 2 infection

The herpes simplex virus type 2 (HSV-2) glycoprotein G (gG-2) gene of 106 clinical isolates was analyzed and six isolates were identified with 63 nucleotides comprising 21 amino acids (aa) deleted in the immunodominant region. Compared with strain HG52, variations in the gG-2 gene were found at 276 and 27 sites in nucleotide and aa sequences, respectively, in the 106 strains. Significant variations in both nucleotides and aa were accumulated in the immunodominant region rather than in the other regions (P < 0.001), indicating that the immunodominant region might be indispensable in vivo and a hot spot for variation. The frequency of 21 aa-deleted strains (HSVΔ21/gG-2) among clinical isolates was 5%, indicating the advantage of this deletion of gG-2 for epidemiological expansion. Phylogenetic analysis of the 106 strains indicated that the HSVΔ21/gG-2 strains formed a cluster among the various variations but that their genomes showed different endonuclease digestion patterns. The antibody titers to total HSV antigens of patients infected with wild HSV-2 and HSVΔ21/gG-2 were similar, but patients with HSVΔ21/gG-2 had a lower antibody titer to gG-2 than those with wild HSV-2 (P < 0.001). HSVΔ21/gG-2 might be less immnunogenic and reduce antibody production to gG-2, while its pathogenicity in humans was not distinguished in its clinical manifestations. Thus, infection with HSVΔ21/gG-2 caused genital lesions similar to wild HSV-2 infection, but evaded the immune response to gG-2 to allow epidemiological spread, indicating the importance of this deletion in the immunodominant region of gG-2 in the pathogenesis and transmission of genital herpes.

The Us2 gene product of herpes simplex virus 2 is a membrane-associated ubiquitin-interacting protein

The Us2 gene encodes a tegument protein that is conserved in most members of the Alphaherpesvirinae. Previous studies on the pseudorabies virus (PRV) Us2 ortholog indicated that it is prenylated, associates with membranes, and spatially regulates the enzymatic activity of the MAP (mitogen-activated protein) kinase ERK (extracellular signal-related kinase) through direct binding and sequestration of ERK at the cytoplasmic face of the plasma membrane. Here we present an analysis of the herpes simplex virus 2 (HSV-2) Us2 ortholog and demonstrate that, like PRV Us2, HSV-2 Us2 is a virion component and that, unlike PRV Us2, it does not interact with ERK in yeast two-hybrid assays. HSV-2 Us2 lacks prenylation signals and other canonical membrane-targeting motifs yet is tightly associated with detergent-insoluble membranes and localizes predominantly to recycling endosomes. Experiments to identify cellular proteins that facilitate HSV-2 Us2 membrane association were inconclusive; however, these studies led to the identification of HSV-2 Us2 as a ubiquitin-interacting protein, providing new insight into the functions of HSV-2 Us2.

Role of immediate early protein ICP27 in the differential sensitivity of herpes simplex viruses 1 and 2 to leptomycin B

Leptomycin B (LMB) is a highly specific inhibitor of CRM1, a cellular karyopherin-β that transports nuclear export signal-containing proteins from the nucleus to the cytoplasm. Previous work has shown that LMB blocks herpes simplex virus 1 (HSV-1) replication in Vero cells and that certain mutations in viral immediate early protein ICP27 can confer LMB resistance. However, little is known of the molecular mechanisms involved. Here we report that HSV-2, a close relative of HSV-1, is naturally resistant to LMB. To see whether the ICP27 gene determines this phenotypic difference, we generated an HSV-1 mutant that expresses the HSV-2 ICP27 instead of the HSV-1 protein. This recombinant was fully sensitive to LMB, indicating that one or more other viral genes must be important in determining HSV-2's LMB-resistant phenotype. In additional work, we report several findings that shed light on how HSV-1 ICP27 mutations can confer LMB resistance. First, we show that LMB treatment of HSV-1-infected cells leads to suppression of late viral protein synthesis and a block to progeny virion release. Second, we identify a novel type of ICP27 mutation that can confer LMB resistance, that being the addition of a 100-residue amino-terminal affinity purification tag. Third, by studying infections where both LMB-sensitive and LMB-resistant forms of ICP27 are present, we show that HSV-1's sensitivity to LMB is dominant to its resistance. Together, our results suggest a model in which the N-terminal portion of ICP27 mediates a nonessential activity that interferes with HSV-1 replication when CRM1 is inactive. We suggest that LMB resistance mutations weaken or abrogate this activity.

HSV-2 specifically down regulates HLA-C expression to render HSV-2-infected DCs susceptible to NK cell killing

Both NK cells and CTLs kill virus-infected and tumor cells. However, the ways by which these killer cells recognize the infected or the tumorigenic cells are different, in fact almost opposite. CTLs are activated through the interaction of the TCR with MHC class I proteins. In contrast, NK cells are inhibited by MHC class I molecules. The inhibitory NK receptors recognize mainly MHC class I proteins and in this regard practically all of the HLA-C proteins are recognized by inhibitory NK cell receptors, while only certain HLA-A and HLA-B proteins interact with these receptors. Sophisticated viruses developed mechanisms to avoid the attack of both NK cells and CTLs through, for example, down regulation of HLA-A and HLA-B molecules to avoid CTL recognition, leaving HLA-C proteins on the cell surface to inhibit NK cell response. Here we provide the first example of a virus that through specific down regulation of HLA-C, harness the NK cells for its own benefit. We initially demonstrated that none of the tested HSV-2 derived microRNAs affect NK cell activity. Then we show that surprisingly upon HSV-2 infection, HLA-C proteins are specifically down regulated, rendering the infected cells susceptible to NK cell attack. We identified a motif in the tail of HLA-C that is responsible for the HSV-2-meduiated HLA-C down regulation and we show that the HLA-C down regulation is mediated by the viral protein ICP47. Finally we show that HLA-C proteins are down regulated from the surface of HSV-2 infected dendritic cells (DCs) and that this leads to the killing of DC by NK cells. Thus, we propose that HSV-2 had developed this unique and surprising NK cell-mediated killing strategy of infected DC to prevent the activation of the adaptive immunity.

Approximately 20% of all humans are latently and asymptomatically infected with HSV-2. This suggests that the virus developed mechanisms to avoid immune cell detection; many of which are still unknown. Infected cells are killed mainly by two lymphocyte populations; NK cells and CTLs that belong to the innate and the adaptive immunity, respectively. While the killing machinery of these two cell types is similar, almost identical, the ways by which they discriminate between infected and uninfected cells is different. CTLs are activated, primarily by DCs, to become effector cells. They then recognize virus-derived peptides in the groove of MHC class I molecules and eliminate the virally infected cells. In contrast, NK cells recognize infected cells through several NK cell activating receptors, while the recognition of MHC class I proteins by NK cells leads to inhibition of NK cell killing. Viruses, such as HIV, developed mechanisms to interfere with the function of both NK cells and CTLs via targeting of specific MHC class I proteins. Here we show that HSV-2 developed a MHC class I-dependent mechanism in which the virus, through specific targeting of HLA-C by the viral protein ICP47, harness the NK cells for its own benefit, probably to avoid the activation of adaptive immune response.

The herpes simplex virus 2 UL21 protein is essential for virus propagation

Herpes simplex virus 2 (HSV-2) is an important human pathogen that is the major cause of genital herpes infections and a significant contributor to the epidemic spread of human immunodeficiency virus infections. The UL21 gene is conserved throughout the Alphaherpesvirinae subfamily and encodes a tegument protein that is dispensable for HSV-1 and pseudorabies virus replication in cultured cells; however, its precise functions have not been determined. To investigate the role of UL21 in the HSV-2 replicative cycle, we constructed a UL21 deletion virus (HSV-2 ΔUL21) using an HSV-2 bacterial artificial chromosome, pYEbac373. HSV-2 ΔUL21 was unable to direct the production of infectious virus in noncomplementing cells, whereas the repaired HSV-2 ΔUL21 strain grew to wild-type (WT) titers, indicating that UL21 is essential for virus propagation. Cells infected with HSV-2 ΔUL21 demonstrated a 2-h delay in the kinetics of immediate early viral gene expression. However, this delay in gene expression was not responsible for the inability of cells infected with HSV-2 ΔUL21 to produce virus insofar as late viral gene products accumulated to WT levels by 24 h postinfection (hpi). Electron and fluorescence microscopy studies indicated that DNA-containing capsids formed in the nuclei of ΔUL21-infected cells, while significantly reduced numbers of capsids were located in the cytoplasm late in infection. Taken together, these data indicate that HSV-2 UL21 has an early function that facilitates viral gene expression as well as a late essential function that promotes the egress of capsids from the nucleus.

Genome-wide prediction of vaccine targets for human herpes simplex viruses using Vaxign reverse vaccinology

Herpes simplex virus (HSV) types 1 and 2 (HSV-1 and HSV-2) are the most common infectious agents of humans. No safe and effective HSV vaccines have been licensed. Reverse vaccinology is an emerging and revolutionary vaccine development strategy that starts with the prediction of vaccine targets by informatics analysis of genome sequences. Vaxign (http://www.violinet.org/vaxign) is the first web-based vaccine design program based on reverse vaccinology. In this study, we used Vaxign to analyze 52 herpesvirus genomes, including 3 HSV-1 genomes, one HSV-2 genome, 8 other human herpesvirus genomes, and 40 non-human herpesvirus genomes. The HSV-1 strain 17 genome that contains 77 proteins was used as the seed genome. These 77 proteins are conserved in two other HSV-1 strains (strain F and strain H129). Two envelope glycoproteins gJ and gG do not have orthologs in HSV-2 or 8 other human herpesviruses. Seven HSV-1 proteins (including gJ and gG) do not have orthologs in all 40 non-human herpesviruses. Nineteen proteins are conserved in all human herpesviruses, including capsid scaffold protein UL26.5 (NP_044628.1). As the only HSV-1 protein predicted to be an adhesin, UL26.5 is a promising vaccine target. The MHC Class I and II epitopes were predicted by the Vaxign Vaxitop prediction program and IEDB prediction programs recently installed and incorporated in Vaxign. Our comparative analysis found that the two programs identified largely the same top epitopes but also some positive results predicted from one program might not be positive from another program. Overall, our Vaxign computational prediction provides many promising candidates for rational HSV vaccine development. The method is generic and can also be used to predict other viral vaccine targets.