Identification and Characterization of U83A Viral Chemokine, a Broad and Potent β-Chemokine Agonist for Human CCRs with Unique Selectivity and Inhibition by Spliced Isoform

Human Herpes Virus-6 (HHV-6) Reactivation after Hematopoietic Cell Transplant and Chimeric Antigen Receptor (CAR)- T Cell Therapy: A Shifting Landscape

HHV-6B reactivation affects approximately half of all allogeneic hematopoietic cell transplant (HCT) recipients. HHV-6B is the most frequent infectious cause of encephalitis following HCT and is associated with pleiotropic manifestations in this setting, including graft-versus-host disease, myelosuppression, pneumonitis, and CMV reactivation, although the causal link is not always clear. When the virus inserts its genome in chromosomes of germ cells, the chromosomally integrated form (ciHHV6) is inherited by offspring. The condition of ciHHV6 is characterized by the persistent detection of HHV-6 DNA, often confounding diagnosis of reactivation and disease-this has also been associated with adverse outcomes. Recent changes in clinical practice in the field of cellular therapies, including a wider use of post-HCT cyclophosphamide, the advent of letermovir for CMV prophylaxis, and the rapid expansion of novel cellular therapies require contemporary epidemiological studies to determine the pathogenic role and spectrum of disease of HHV-6B in the current era. Research into the epidemiology and clinical significance of HHV-6B in chimeric antigen receptor T cell (CAR-T cell) therapy recipients is in its infancy. No controlled trials have determined the optimal treatment for HHV-6B. Treatment is reserved for end-organ disease, and the choice of antiviral agent is influenced by expected toxicities. Virus-specific T cells may provide a novel, less toxic therapeutic modality but is more logistically challenging. Preventive strategies are hindered by the high toxicity of current antivirals. Ongoing study is needed to keep up with the evolving epidemiology and impact of HHV-6 in diverse and expanding immunocompromised patient populations.

A bibliometric analysis: Ca2+ fluxes and inflammatory phenotyping by flow cytometry in peripheral blood mononuclear cells

Background

The immune system, composed of organs, tissues, cells, and proteins, is the key to protecting the body from external biological attacks and inflammation. The latter occurs in several pathologies, such as cancers, type 1 diabetes, and human immunodeficiency virus infection. Immunophenotyping by flow cytometry is the method of choice for diagnosing these pathologies. Under inflammatory conditions, the peripheral blood mononuclear cells (PBMCs) are partially activated and generate intracellular pathways involving Ca2+-dependent signaling cascades leading to transcription factor expression. Ca2+ signaling is typically studied by microscopy in cell lines but can present some limitations to explore human PBMCs, where flow cytometry can be a good alternative.

Objective

In this review, we dived into the research field of inflammation and Ca2+ signaling in PBMCs. We aimed to investigate the structure and evolution of this field in a physio-pathological context, and then we focused our review on flow cytometry analysis of Ca2+ fluxes in PBMCs.

Methods

From 1984 to 2022, 3865 articles on inflammation and Ca2+ signaling in PBMCs were published, according to The Clarivate Web of Science (WOS) database used in this review. A bibliometric study was designed for this collection and consisted of a co-citation and bibliographic coupling analysis.

Results

The co-citation analysis was performed on 133 articles: 4 clusters highlighted the global context of Ca2+ homeostasis, including chemical probe development, identification of the leading players in Ca2+ signaling, and the link with chemokine production in immune cell function. Next, the bibliographic coupling analysis combined 998 articles in 8 clusters. This analysis outlined the mechanisms of PBMC activation, from signal integration to cellular response. Further explorations of the bibliographic coupling network, focusing on flow cytometry, revealed 21 articles measuring cytosolic Ca2+ in PBMCs, with only 5 since 2016. This final query showed that Ca2+ signaling analysis in human PBMCs using flow cytometry is still underdeveloped and investigates mainly the cytosolic Ca2+ compartment.

Conclusion

Our review uncovers remaining knowledge gaps of intracellular players involved in Ca2+ signaling in PBMCs, such as reticulum and mitochondria, and presents flow cytometry as a solid option to supplement gold-standard microscopy studies.

Immunisation Using Novel DNA Vaccine Encoding Virus Membrane Fusion Complex and Chemokine Genes Shows High Protection from HSV-2

Herpes simplex virus 1 and 2 infections cause high unmet disease burdens worldwide. Mainly HSV-2 causes persistent sexually transmitted disease, fatal neonatal disease and increased transmission of HIV/AIDS. Thus, there is an urgent requirement to develop effective vaccines. We developed nucleic acid vaccines encoding a novel virus entry complex stabilising cell membrane fusion, 'virus-like membranes', VLM. Two dose intramuscular immunisations using DNA expression plasmids in a guinea pig model gave 100% protection against acute disease and significantly reduced virus replication after virus intravaginal challenge. There was also reduced establishment of latency within the dorsal root ganglia and spinal cord, but recurrent disease and recurrent virus shedding remained. To increase cellular immunity and protect against recurrent disease, cDNA encoding an inhibitor of chemokine receptors on T regulatory cells was added and compared to chemokine CCL5 effects. Immunisation including this novel human chemokine gene, newly defined splice variant from an endogenous virus genome, 'virokine immune therapeutic', VIT, protected most guinea pigs from recurrent disease and reduced recurrent virus shedding distinct from a gD protein vaccine similar to that previously evaluated in clinical trials. All DNA vaccines induced significant neutralising antibodies and warrant evaluation for new therapeutic treatments.

Viral G Protein-Coupled Receptors Encoded by β- and γ-Herpesviruses

Herpesviruses are ancient large DNA viruses that have exploited gene capture as part of their strategy to escape immune surveillance, promote virus spreading, or reprogram host cells to benefit their survival. Most acquired genes are transmembrane proteins and cytokines, such as viral G protein-coupled receptors (vGPCRs), chemokines, and chemokine-binding proteins. This review focuses on the vGPCRs encoded by the human β- and γ-herpesviruses. These include receptors from human cytomegalovirus, which encodes four vGPCRs: US27, US28, UL33, and UL78; human herpesvirus 6 and 7 with two receptors: U12 and U51; Epstein-Barr virus with one: BILF1; and Kaposi's sarcoma-associated herpesvirus with one: open reading frame 74. We discuss ligand binding, signaling, and structures of the vGPCRs in light of robust differences from endogenous receptors. Finally, we briefly discuss the therapeutic targeting of vGPCRs as future treatment of acute and chronic herpesvirus infections. Expected final online publication date for the Annual Review of Virology, Volume 9 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Comparative Analysis of Roseoloviruses in Humans, Pigs, Mice, and Other Species

Viruses of the genus Roseolovirus belong to the subfamily Betaherpesvirinae, family Herpesviridae. Roseoloviruses have been studied in humans, mice and pigs, but they are likely also present in other species. This is the first comparative analysis of roseoloviruses in humans and animals. The human roseoloviruses human herpesvirus 6A (HHV-6A), 6B (HHV-6B), and 7 (HHV-7) are relatively well characterized. In contrast, little is known about the murine roseolovirus (MRV), also known as murine thymic virus (MTV) or murine thymic lymphotrophic virus (MTLV), and the porcine roseolovirus (PRV), initially incorrectly named porcine cytomegalovirus (PCMV). Human roseoloviruses have gained attention because they can cause severe diseases including encephalitis in immunocompromised transplant and AIDS patients and febrile seizures in infants. They have been linked to a number of neurological diseases in the immunocompetent including multiple sclerosis (MS) and Alzheimer's. However, to prove the causality in the latter disease associations is challenging due to the high prevalence of these viruses in the human population. PCMV/PRV has attracted attention because it may be transmitted and pose a risk in xenotransplantation, e.g., the transplantation of pig organs into humans. Most importantly, all roseoloviruses are immunosuppressive, the humoral and cellular immune responses against these viruses are not well studied and vaccines as well as effective antivirals are not available.

Chemokine Subversion by Human Herpesviruses

Viruses use diverse molecular mechanisms to exploit and evade the immune response. Herpesviruses, in particular, encode functional chemokine and chemokine receptor homologs pirated from the host, as well as secreted chemokine-binding proteins with unique structures. Multiple functions have been described for herpesvirus chemokine components, including attraction of target cells, blockade of leukocyte migration, and modulation of gene expression and cell entry by the virus. Here we review current concepts about how human herpesvirus chemokines, chemokine receptors, and chemokine-binding proteins may be used to shape a proviral state in the host.

Analyses of Tissue Culture Adaptation of Human Herpesvirus-6A by Whole Genome Deep Sequencing Redefines the Reference Sequence and Identifies Virus Entry Complex Changes

Tissue-culture adaptation of viruses can modulate infection. Laboratory passage and bacterial artificial chromosome (BAC)mid cloning of human cytomegalovirus, HCMV, resulted in genomic deletions and rearrangements altering genes encoding the virus entry complex, which affected cellular tropism, virulence, and vaccine development. Here, we analyse these effects on the reference genome for related betaherpesviruses, Roseolovirus, human herpesvirus 6A (HHV-6A) strain U1102. This virus is also naturally “cloned” by germline subtelomeric chromosomal-integration in approximately 1% of human populations, and accurate references are key to understanding pathological relationships between exogenous and endogenous virus. Using whole genome next-generation deep-sequencing Illumina-based methods, we compared the original isolate to tissue-culture passaged and the BACmid-cloned virus. This re-defined the reference genome showing 32 corrections and 5 polymorphisms. Furthermore, minor variant analyses of passaged and BACmid virus identified emerging populations of a further 32 single nucleotide polymorphisms (SNPs) in 10 loci, half non-synonymous indicating cell-culture selection. Analyses of the BAC-virus genome showed deletion of the BAC cassette via loxP recombination removing green fluorescent protein (GFP)-based selection. As shown for HCMV culture effects, select HHV-6A SNPs mapped to genes encoding mediators of virus cellular entry, including virus envelope glycoprotein genes gB and the gH/gL complex. Comparative models suggest stabilisation of the post-fusion conformation. These SNPs are essential to consider in vaccine-design, antimicrobial-resistance, and pathogenesis.

Chemokines encoded by herpesviruses

Viruses use diverse strategies to elude the immune system, including copying and repurposing host cytokine and cytokine receptor genes. For herpesviruses, the chemokine system of chemotactic cytokines and receptors is a common source of copied genes. Here, we review the current state of knowledge about herpesvirus-encoded chemokines and discuss their possible roles in viral pathogenesis, as well as their clinical potential as novel anti-inflammatory agents or targets for new antiviral strategies.

Human Herpesviruses 6A, 6B, and 7

Human roseoloviruses include three different species, human herpesviruses 6A, 6B, and 7 (HHV-6A, HHV-6B, HHV-7), genetically related to human cytomegalovirus. They exhibit a wide cell tropism in vivo and, like other herpesviruses, induce a lifelong latent infection in humans. In about 1% of the general population, HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6). Many active infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. They also may cause serious diseases, particularly in immunocompromised individuals, including hematopoietic stem-cell transplant (HSCT) and solid-organ transplant recipients, and acquired immunodeficiency syndrome (AIDS) patients. This opportunistic pathogenic role is formally established for HHV-6 infection and less clear for HHV-7. It mainly concerns the central-nervous system, bone marrow, lungs, gastrointestinal tract, skin, and liver. As the best example, HHV-6 causes both exanthema subitum, a benign disease associated with primary infection, and severe encephalitis associated with virus reactivations in HSCT recipients. Diagnosis using serologic and direct antigen-detection methods currently exhibits limitations. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time polymerase-chain reaction (PCR). The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active infections, but there is currently no consensus regarding the indications of treatment or specifics of drug administration. Numerous questions about HHV-6A, HHV-6B, HHV-7 are still pending, concerning in particular clinical impact and therapeutic options in immunocompromised patients.

Piracy on the molecular level: human herpesviruses manipulate cellular chemotaxis

Cellular chemotaxis is important to tissue homeostasis and proper development. Human herpesvirus species influence cellular chemotaxis by regulating cellular chemokines and chemokine receptors. Herpesviruses also express various viral chemokines and chemokine receptors during infection. These changes to chemokine concentrations and receptor availability assist in the pathogenesis of herpesviruses and contribute to a variety of diseases and malignancies. By interfering with the positioning of host cells during herpesvirus infection, viral spread is assisted, latency can be established and the immune system is prevented from eradicating viral infection.

Laboratory and clinical aspects of human herpesvirus 6 infections

Human herpesvirus 6 (HHV-6) is a widespread betaherpesvirus which is genetically related to human cytomegalovirus (HCMV) and now encompasses two different species: HHV-6A and HHV-6B. HHV-6 exhibits a wide cell tropism in vivo and, like other herpesviruses, induces a lifelong latent infection in humans. As a noticeable difference with respect to other human herpesviruses, genomic HHV-6 DNA is covalently integrated into the subtelomeric region of cell chromosomes (ciHHV-6) in about 1% of the general population. Although it is infrequent, this may be a confounding factor for the diagnosis of active viral infection. The diagnosis of HHV-6 infection is performed by both serologic and direct methods. The most prominent technique is the quantification of viral DNA in blood, other body fluids, and organs by means of real-time PCR. Many active HHV-6 infections, corresponding to primary infections, reactivations, or exogenous reinfections, are asymptomatic. However, the virus may be the cause of serious diseases, particularly in immunocompromised individuals. As emblematic examples of HHV-6 pathogenicity, exanthema subitum, a benign disease of infancy, is associated with primary infection, whereas further virus reactivations can induce severe encephalitis cases, particularly in hematopoietic stem cell transplant recipients. Generally speaking, the formal demonstration of the causative role of HHV-6 in many acute and chronic human diseases is difficult due to the ubiquitous nature of the virus, chronicity of infection, existence of two distinct species, and limitations of current investigational tools. The antiviral compounds ganciclovir, foscarnet, and cidofovir are effective against active HHV-6 infections, but the indications for treatment, as well as the conditions of drug administration, are not formally approved to date. There are still numerous pending questions about HHV-6 which should stimulate future research works on the pathophysiology, diagnosis, and therapy of this remarkable human virus.

Targeting chemokines: Pathogens can, why can't we?

Chemoattractant cytokines, or chemokines, are the largest sub-family of cytokines. About 50 distinct chemokines have been identified in humans. Their principal role is to stimulate the directional migration of leukocytes, which they achieve through activation of their receptors, following immobilization on cell surface glycosaminoglycans (GAGs). Chemokine receptors belong to the G protein-coupled 7-transmembrane receptor family, and hence their identification brought great promise to the pharmaceutical industry, since this receptor class is the target for a large percentage of marketed drugs. Unfortunately, the development of potent and efficacious inhibitors of chemokine receptors has not lived up to the early expectations. Several approaches to targeting this system will be described here, which have been instrumental in establishing paradigms in chemokine biology. Whilst drug discovery programs have not yet elucidated how to make successful drugs targeting the chemokine system, it is now known that certain parasites have evolved anti-chemokine strategies in order to remain undetected by their hosts. What can we learn from them?

Analyses of germline, chromosomally integrated human herpesvirus 6A and B genomes indicate emergent infection and new inflammatory mediators

Human herpesvirus-6A (HHV-6A) is rarer than HHV-6B in many infant populations. However, they are similarly prevalent as germline, chromosomally integrated genomes (ciHHV-6A/B). This integrated form affects 0.1-1 % of the human population, where potentially virus gene expression could be in every cell, although virus relationships and health effects are not clear. In a Czech/German patient cohort ciHHV-6A was more common and diverse than ciHHV-6B. Quantitative PCR, nucleotide sequencing and telomeric integration site amplification characterized ciHHV-6 in 44 German myocarditis/cardiomyopathy and Czech malignancy/inflammatory disease (MI) patients plus donors. Comparisons were made to sequences from global virus reference strains, and blood DNA from childhood-infections from Zambia (HHV-6A mainly) and Japan (HHV-6B). The MI cohort were 86 % (18/21) ciHHV-6A, the cardiac cohort 65 % (13/20) ciHHV-6B, suggesting different disease links. Reactivation was supported by findings of 1) recombination between ciHHV-6A and HHV-6B genes in 20 % (4/21) of the MI cohort; 2) expression in a patient subset, of early/late transcripts from the inflammatory mediator genes chemokine receptor U51 and chemokine U83, both identical to ciHHV-6A DNA sequences; and 3) superinfection shown by deep sequencing identifying minor virus-variants only in ciHHV-6A, which expressed transcripts, indicating virus infection reactivates latent ciHHV-6A. Half the MI cohort had more than two copies per cell, median 5.2, indicative of reactivation. Remarkably, the integrated genomes encoded the secreted-active form of virus chemokines, rare in virus from childhood-infections. This shows integrated virus genomes can contribute new human genes with links to inflammatory pathology and supports ciHHV-6A reactivation as a source for emergent infection.

Classification of HHV-6A and HHV-6B as distinct viruses

Shortly after the discovery of human herpesvirus 6 (HHV-6), two distinct variants, HHV-6A and HHV-6B, were identified. In 2012, the International Committee on Taxonomy of Viruses (ICTV) classified HHV-6A and HHV-6B as separate viruses. This review outlines several of the documented epidemiological, biological, and immunological distinctions between HHV-6A and HHV-6B, which support the ICTV classification. The utilization of virus-specific clinical and laboratory assays for distinguishing HHV-6A and HHV-6B is now required for further classification. For clarity in biological and clinical distinctions between HHV-6A and HHV-6B, scientists and physicians are herein urged, where possible, to differentiate carefully between HHV-6A and HHV-6B in all future publications.

Activation of CCR2+ human proinflammatory monocytes by human herpesvirus-6B chemokine N-terminal peptide

Human monocytes expressing CCR2 with CD14 and CD16 can mediate antigen presentation, and promote inflammation, brain infiltration and immunosenescence. Recently identified roles are in human immunodeficiency virus infection, tuberculosis and parasitic disease. Human herpesvirus 6B (HHV-6B) encodes a chemokine, U83B, which is monospecific for CCR2, and is distinct from the related HHV-6A U83A, which activates CCR1, CCR4, CCR5, CCR6 and CCR8 on immune effector cells and dendritic cells. These differences could alter leukocyte-subset recruitment for latent/lytic replication and associated neuroinflammatory pathology. Therefore, cellular interactions between U83A and U83B could help dictate potential tropism differences between these viruses. U83A specificity is maintained in the 38-residue N-terminal spliced-truncated form. Here, we sought to determine the basis for the chemokine receptor specificity differences and identify possible applications. To do this we first analysed variation in a natural host population in sub-Saharan Africa where both viruses are equally prevalent and compared these to global strains. Analyses of U83 N-terminal variation in 112 HHV-6A and HHV-6B infections identified 6/38 U83A or U83B-specific residues. We also identified a unique single U83A-specific substitution in one U83B sequence, 'U83BA'. Next, the variation effects were tested by deriving N-terminal (NT) 17-mer peptides and assaying activation of ex vivo human leukocytes, the natural host and cellular target. Chemotaxis of CCR2+ leukocytes was potently induced by U83B-NT, but not U83BA-NT or U83A-NT. Analyses of the U83B-NT activated population identified migrated CCR2+, but not CCR5+, leukocytes. The U83BA-NT asparagine-lysine14 substitution disrupted activity, thus defining CCR2 specificity and acting as a main determinant for HHV-6A/B differences in cellular interactions. A flow-cytometry-based shape-change assay was designed, and used to provide further evidence that U83B-NT could activate CCR2+CD14+CD16+ monocytes. This defines a potential antiviral target for HHV-6A/B disease and novel peptide immunomodulator for proinflammatory monocytes.

Human Herpesvirus 6 and Neuroinflammation

Human herpesvirus (HHV-) 6A and HHV-6B are two distinct β-herpesviruses which have been associated with various neurological diseases, including encephalitis, meningitis, epilepsy, and multiple sclerosis. Although the reactivation of both viruses is recognized as the cause of some neurological complications in conditions of immunosuppression, their involvement in neuroinflammatory diseases in immunocompetent people is still unclear, and the mechanisms involved have not been completely elucidated. Here, we review the available data providing evidence for the capacity of HHV-6A and -6B to infect the central nervous system and to induce proinflammatory responses by infected cells. We discuss the potential role of both viruses in neuroinflammatory pathologies and the mechanisms which could explain virus-induced neuropathogenesis.

Immunomodulation and immunosuppression by human herpesvirus 6A and 6B

Like other members of the Herpesviridae family, human herpesvirus (HHV)-6A and HHV-6B have developed a wide variety of strategies to modulate or suppress host immune responses and, thereby, facilitate their own spread and persistence in vivo. Long considered two variants of the same virus, HHV-6A and HHV-6B have recently been reclassified as distinct viral species, although the established nomenclature has been maintained. In this review, we summarize the distinctive profiles of interaction of these two viruses with the human immune system. Both HHV-6A and HHV-6B display a tropism for CD4+ T lymphocytes, but they can also infect, in a productive or nonproductive fashion, other cells of the immune system. However, there are important differences regarding the ability of each virus to infect cytotoxic effector cells, as HHV-6A has been shown to productively infect several of these cells, whereas HHV-6B infects them inefficiently at best. In addition to direct cytopathic effects, both HHV-6A and HHV-6B can interfere with immunologic functions to varying degrees via cytokine modulation, including blockade of IL-12 production by professional antigen-presenting cells, modulation of cell-surface molecules essential for T-cell activation, and expression of viral chemokines and chemokine receptors. Some of these effects are related to signaling through and downregulation of the viral receptor, CD46, a key molecule linking innate and adaptive immune responses. Increasing attention has recently been focused on the importance of viral interactions with dendritic cells, which may serve both as targets of virus-mediated immunosuppression and as vehicles for viral transfer to CD4+ T cells. Our deepening knowledge of the mechanisms developed by HHV-6A and HHV-6B to evade immunologic control may lead to new strategies for the prevention and treatment of the diseases associated with these viruses. Moreover, elucidation of these viral mechanisms may uncover new avenues to therapeutically manipulate or modulate the immune system in immunologically mediated human diseases.

Complementation of the function of glycoprotein H of human herpesvirus 6 variant A by glycoprotein H of variant B in the virus life cycle

Human herpesvirus 6 (HHV-6) is a T-cell-tropic betaherpesvirus. HHV-6 can be classified into two variants, HHV-6 variant A (HHV-6A) and HHV-6B, based on genetic, antigenic, and cell tropisms, although the homology of their entire genomic sequences is nearly 90%. The HHV-6A glycoprotein complex gH/gL/gQ1/gQ2 is a viral ligand that binds to the cellular receptor human CD46. Because gH has 94.3% amino acid identity between the variants, here we examined whether gH from one variant could complement its loss in the other. Recently, we successfully reconstituted HHV-6A from its cloned genome in a bacterial artificial chromosome (BAC) (rHHV-6ABAC). Using this system, we constructed HHV-6ABAC DNA containing the HHV-6B gH (BgH) gene instead of the HHV-6A gH (AgH) gene in Escherichia coli. Recombinant HHV-6ABAC expressing BgH (rHHV-6ABAC-BgH) was successfully reconstituted. In addition, a monoclonal antibody that blocks HHV-6B but not HHV-6A infection neutralized rHHV-6ABAC-BgH but not rHHV-6ABAC. These results indicate that HHV-6B gH can complement the function of HHV-6A gH in the viral infectious cycle.

Human herpesvirus 6 glycoprotein complex formation is required for folding and trafficking of the gH/gL/gQ1/gQ2 complex and its cellular receptor binding

Human herpesvirus 6 (HHV-6) is a T-cell-tropic betaherpesvirus. A glycoprotein (g) complex that is unique to HHV-6, gH/gL/gQ1/gQ2, is a viral ligand for its cellular receptor, human CD46. However, whether complex formation or one component of the complex is required for CD46 binding and how the complex is transported in cells are open questions. Furthermore, in HHV-6-infected cells the gQ1 protein modified with N-linked glycans is expressed in two forms with different molecular masses: an 80-kDa form (gQ1-80K) and a 74-kDa form (gQ1-74K). Only gQ1-80K, but not gQ1-74K, forms the complex with gQ2, gH, and gL, and this four-component complex is incorporated into mature virions. Here, we characterized the molecular context leading to the maturation of gQ1 by expressing combinations of the individual gH/gL/gQ1/gQ2 components in 293T cells. Surprisingly, only when all four molecules were expressed was a substantial amount of gQ1-80K detected, indicating that all three of the other molecules (gQ2, gH, and gL) were necessary and sufficient for gQ1 maturation. We also found that only the tetrameric complex, and not its subsets, binds to CD46. Finally, a gQ2-null virus constructed in the BAC (bacterial artificial chromosome) system could not be reconstituted, indicating that gQ2 is essential for virus growth. These results show that gH, gL, gQ1, and gQ2 are all essential for the trafficking and proper folding of the gH/gL/gQ1/gQ2 complex and, thus, for HHV-6 infection.

[Human herpesvirus-6 and human herpesvirus-7 (HHV-6, HHV-7)]

human herpesvirus 6 (HHV-6) is the major causative agent of exanthem subitum which is one of popular diseases in infant, and establishes latent infections in adults of more than 90%. Recently, the encephalitis caused by reactivated- HHV-6 has been shown in patients after transplantation. In addition, the relationship HHV-6 and drug-induced hypersensitivity syndrome has also been reported. human herpesvirus 7 (HHV-7) was isolated from the stimulated-peripheral blood lymphocytes of a healthy individual, and also causes exanthema subitum. Both viruses are related viruses which belong to betaherpesvirus subfamily, and replicate and produce progeny viruses in T cells.

The cytomegalovirus UL146 gene product vCXCL1 targets both CXCR1 and CXCR2 as an agonist

Large DNA viruses, such as herpesvirus and poxvirus, encode proteins that target and exploit the chemokine system of their host. UL146 and UL147 in the cytomegalovirus (CMV) genome encode the two CXC chemokines vCXCL1 and vCXCL2. In this study, vCXCL1 was probed against a panel of the 18 classified human chemokine receptors. In calcium mobilization assays vCXCL1 acted as an agonist on both CXCR1 and CXCR2 but did not activate or block any of the other 16 chemokine receptors. vCXCL1 was characterized and compared with CXCL1/GROalpha, CXCL2/GRObeta, CXCL3/GROgamma, CXCL5/ENA-78, CXCL6/GCP-2, CXCL7/NAP-2 and CXCL8/IL-8 in competition binding, calcium mobilization, inositol triphosphate turnover, and chemotaxis assays using CXCR1- and CXCR2-expressing Chinese hamster ovary, 300.19, COS7, and L1.2 cells. The affinities of vCXCL1 for the CXCR1 and CXCR2 receptors were 44 and 5.6 nm, respectively, as determined in competition binding against radioactively labeled CXCL8. In calcium mobilization, phosphatidylinositol turnover, and chemotaxis assays, vCXCL1 acted as a highly efficacious activator of both receptors, with a rather low potency for the CXCR1 receptor but comparable with CXCL5 and CXCL7. It is suggested that CMV uses the UL146 gene product expressed in infected endothelial cells to attract neutrophils by activating their CXCR1 and CXCR2 receptors, whereby neutrophils can act as carriers of the virus to uninfected endothelial cells. In that way a lasting pool of CMV-infected endothelial cells could be maintained.

Human herpesvirus 6

Az 1986-ban felfedezett emberi 6-os herpeszvírus A és B változata molekuláris tulajdonságai alapján a legősibb emberi herpeszvírus. A B változat cseppfertőzéssel terjed a tünetmentes vírusürítő felnőttekről a két év alatti kisgyermekekre, akikben alkalmilag exanthema subitum jöhet létre. A vírus a CD4+ macrophagokat, lymphocytákat fertőzi, utóbbiakban élethossziglan lappangás, időnként a nyálmirigyekben vírustermeléssel járó perzisztencia alakul ki. Felnőttkorban ez a változat csontvelő- és szervátültetések kapcsán, immunszuppresszió talaján reaktiválódik, és akár halálos szövődményeket hoz létre. Sclerosis multiplex, idült fáradtság tünetegyüttes, Hodgkin- és nem Hodgkin-lymphomák kialakulásában kofaktor. A CD+-sejteket fertőző és bennük lappangó A változat közvetlen kórokozó képessége nem ismert. A HIV-fertőzést rendkívül erősen transzaktiváljain vitroés betegekben egyaránt. Papillomavírusok által okozott daganatokban is transzaktivátor. Mindkét vírusváltozat kórokozó képessége a megváltozott citokin- és kemokinegyensúlyon alapszik. A két változat elkülönítése szerológiailag nehézkes, erre a savóból vagy a fehérvérsejtekből végzett változatspecifikus PCR alkalmas. A súlyos komplikációk kezelésére, esetleg kemoprofilaxisára ganciclovir, esetleg foscarnet és cidofovir használható.

CCR5 signalling, but not DARC or D6 regulatory, chemokine receptors are targeted by herpesvirus U83A chemokine which delays receptor internalisation via diversion to a caveolin-linked pathway

Background

Herpesviruses have evolved chemokines and chemokine receptors, which modulate the recruitment of human leukocytes during the inflammatory response to infection. Early post-infection, human herpesvirus 6A (HHV-6A) infected cells express the chemokine receptor U51A and chemokine U83A which have complementary effects in subverting the CC-chemokine family thereby controlling anti-viral leukocyte recruitment. Here we show that, to potentiate this activity, the viral chemokine can also avoid clearance by scavenger chemokine receptors, DARC and D6, which normally regulate an inflammatory response. Conversely, U83A delays internalisation of its signalling target receptor CCR5 with diversion to caveolin rich membrane domains. This mechanism can redirect displaced human chemokines to DARC and D6 for clearance of the anti-viral inflammatory response, leaving the viral chemokine unchecked.

Methods

Cell models for competitive binding assays were established using radiolabeled human chemokines and cold U83A on CCR5, DARC or D6 expressing cells. Flow cytometry was used to assess specific chemotaxis of CCR5 bearing cells to U83A, and internalisation of CCR5 specific chemokine CCL4 after stimulation with U83A. Internalisation analyses were supported by confocal microscopy of internalisation and co-localisation of CCR5 with caveosome marker caveolin-1, after virus or human chemokine stimulation.

Results

U83A displaced efficiently human chemokines from CCR5, with a high affinity of 0.01nM, but not from DARC or D6. Signalling via CCR5 resulted in specific chemoattraction of primary human leukocytes bearing CCR5. However, U83A effective binding and signalling to CCR5 resulted in delayed internalisation and recycling up to 2 hours in the absence of continual re-stimulation. This resulted in diversion to a delayed caveolin-linked pathway rather than the rapid clathrin mediated endocytosis previously shown with human chemokines CCL3 or CCL4.

Conclusion

U83A diverts human chemokines from signalling, but not regulatory or scavenger, receptors facilitating their clearance, while occupying signalling receptors at the cell surface. This can enhance virus specific inflammation, facilitating dissemination to replication sensitive leukocytes while evading clearance; this has implications for linked neuro-inflammatory pathologies.

Microarray-based determination of the lytic cascade of human herpesvirus 6B

The lytic gene expression of several members of the human herpesvirus family has been profiled by using gene-expression microarrays; however, the lytic cascade of roseoloviruses has not been studied in similar depth. Based on the complete DNA genome sequences of human herpesvirus 6 variant A (HHV-6A) and variant B (HHV-6B), we constructed a cDNA microarray containing DNA probes to their predicted open reading frames, plus 914 human genes. Gene-expression profiling of HHV-6B strain Z29 in SupT1 cells over a 60 h time-course post-infection, together with kinetic classification of the HHV-6B genes in the presence of either cycloheximide or phosphonoacetic acid, allowed the placement of HHV-6B genes into defined kinetic classes. Eighty-nine HHV-6B genes were divided into four different expression kinetic classes: eight immediate-early, 44 early, 33 late and four biphasic. Clustering of genes with similar expression profiles implied a shared function, thus revealing possible roles of previously uncharacterized HHV-6B genes.

Predominant human herpesvirus 6 variant A infant infections in an HIV-1 endemic region of Sub-Saharan Africa

Human herpesvirus 6, HHV-6, commonly infects children, causing febrile illness and can cause more severe pathology, especially in an immune compromised setting. There are virulence distinctions between variants HHV-6A and B, with evidence for increased severity and neurotropism for HHV-6A. While HHV-6B is the predominant infant infection in USA, Europe and Japan, HHV-6A appears rare. Here HHV-6 prevalence, loads and variant genotypes, in asymptomatic compared to symptomatic infants were investigated from an African region with endemic HIV-1/AIDS. DNA was extracted from blood or sera from asymptomatic infants at 6 and 18 months age in a population-based micronutrient study, and from symptomatic infants hospitalised for febrile disease. DNA was screened by qualitative and quantitative real-time PCR, then genotyped by sequencing at variable loci, U46 (gN) and U47 (gO). HIV-1 serostatus of infants and mothers were also determined. HHV-6 DNA prevalence rose from 15% to 22% (80/371) by 18 months. At 6 months, infants born to HIV-1 positive mothers had lower HHV-6 prevalence (11%, 6/53), but higher HCMV prevalence (25%, 17/67). HHV-6 positive febrile hospitalized infants had higher HIV-1, 57% (4/7), compared to asymptomatic infants, 3% (2/74). HHV-6A was detected exclusively in 86% (48/56) of asymptomatic HHV-6 positive samples genotyped. Co-infections with both strain variants were linked with higher viral loads and found in 13% (7/56) asymptomatic infants and 43% (3/7) HIV-1 positive febrile infants. Overall, the results show HHV-6A as the predominant variant significantly associated with viremic infant-infections in this African population, distinct from other global cohorts, suggesting emergent infections elsewhere.

Role of dendritic cells infected with human herpesvirus 6 in virus transmission to CD4(+) T cells

Human herpesvirus 6 (HHV-6) is a ubiquitous betaherpesvirus that predominantly infects and replicates in CD4(+) T lymphocytes. However, the mechanism of HHV-6 transmission to T cells from the peripheral mucosa is unknown. Here we found that dendritic cells (DCs) can transmit HHV-6 to T cells, resulting in productive infection. In immature monocyte-derived DCs (MDDCs) infected with HHV-6, viral early and late antigens were expressed, and nucleocapsids containing a DNA core were observed, although few virions were detected in the cytoplasm by electron microscopy, indicating that the maturation of HHV-6 virions may be incomplete in MDDCs. However, HHV-6 transmission from MDDCs to stimulated CD4(+) T cells occurred efficiently in coculture of these cells, but not from MDDCs culture supernatants. This transmission was partially inhibited by treating the DCs with a viral DNA synthesis blocker, indicating that viral replication in MDDCs is required for this transmission. Furthermore, myeloid DCs and plasmacytoid DCs infected with HHV-6 could also transmit the virus to stimulated T cells. Thus, DCs may be the first cell population targeted by HHV-6 and could play an important role in the virus' transmission to T cells for their further propagation.

Immunomodulation by herpesvirus U51A chemokine receptor via CCL5 and FOG-2 down-regulation plus XCR1 and CCR7 mimicry in human leukocytes

Human herpesvirus-6A (HHV-6A) betachemokine-receptor U51A binds inflammatory modulators CCL2, CCL5, CCL11, CCL7, and CCL13. This unique specificity overlaps that of human chemokine receptors CCR1, CCR2, CCR3, and CCR5. In model cell lines, expression leads to CCL5 down-regulation with both constitutive and inducible signaling. Here, immunomodulation pathways are investigated in human leukocytes permissive for infection. Constitutive signaling was shown using inositol phosphate assays and inducible calcium signaling by response to CCL2, CCL5 and CCL11. Constitutive signaling targets were examined using an immune response-related microarray and RT-PCR, showing down-regulation of CCL5 and FOG-2, a hematopoietic transcriptional repressor. By RT-PCR and siRNA reversion, CCL5 and FOG-2 were shown down-regulated, during peak U51A expression post infection. Two further active ligands, XCL1 and CCL19, were identified, making U51A competitor to their human receptors, XCR1 and CCR7, on T lymphocytes, NK and dendritic cells. Finally, U51A-expressing cell lines and infected ex vivo leukocytes, showed migration towards chemokine-gradients, and chemokine internalization. Consequently, U51A may affect virus dissemination or host transmission by chemotaxis of infected cells to sites of chemokine secretion specific for U51A (for example the lymph node or lung, by CCL19 or CCL11, respectively) and evade immune-effector cells by chemokine diversion and down-regulation, affecting virus spread and inflammatory pathology.

CCR5 Delta32 polymorphism: associated with gallbladder cancer susceptibility

Inflammation of gallbladder is an established risk factor for gallbladder cancer (GBC) pathogenesis. Chemokine receptors play crucial role in antitumour immunity and are involved in inflammation and pathogenesis of cancers. Present study was aimed to examine the role of CCR5 Delta32 polymorphism in conferring genetic susceptibility to GBC. Present case-control study included 144 proven GBC patients and 210 healthy controls. Genotyping was done by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Statistically significant difference was observed in distribution of CCR5+/Delta32 genotype (P = 0.028) [odds ratio (OR) = 2.850; 95% confidence interval (CI) = 1.1-7.2] and CCR5 Delta32 allele (P = 0.012) (OR = 3.145, 95% CI = 1.2-7.7) in GBC patients which was conferring high risk. Stratification of GBC patients showed significant association of CCR5+/Delta32 genotype and CCR5 Delta32 allele with GBC patients with and without gallstones. Analysis based on age of onset and gender suggested significant association of CCR5 Delta32 allele with early onset (<50 years) of the disease but only marginal influence of gender in CCR5 Delta32-mediated risk of cancer. Risk was further modulated by tobacco usage and significantly increased risk was observed in tobacco users with CCR5+/Delta32 genotype. In conclusion, CCR5+/Delta32 genotype and CCR5 Delta32 allele confer significant risk for GBC particularly in patients with early onset and tobacco usage. Role of CCR5+/Delta32 polymorphism in GBC susceptibility is independent of gallstone formation.

The herpesvirus 8 encoded chemokines vCCL2 (vMIP-II) and vCCL3 (vMIP-III) target the human but not the murine lymphotactin receptor

Background

Large DNA-viruses such as herpesvirus and poxvirus encode proteins that target and exploit the chemokine system of their host. The Kaposi sarcoma- associated herpes virus (KSHV) encodes three chemokines. Two of these, vCCL2 and vCCL3, target the human lymphotactin receptor as an antagonist and a selective agonist, respectively. Therefore these virally endcoded chemokines have the potential to be used as tools in the study of lymphotactin receptor pathways in murine models.

Results

The activities of vCCL2, vCCL3, human lymphotactin (XCL1) and murine lymphotactin (mXCL1) were probed in parallel on the human and murine lymphotactin receptor (XCR1 and mXCR1) using a phosphatidyl-inositol assay. On the human XCR1, vCCL3, mXCL1 and XCL1 acted as agonists. In contrast, only mXCL1 was able to activate the murine lymphotactin receptor. Using the same assay, vCCL2 was able to block the response using any of the three agonists on the humane lymphotactin receptor with IC₅₀s of 2–3 nM. However, vCCL2 was unable to block the response of mXCL1 through the murine lymphotactin receptor.

Conclusion

This study shows that vCCL2 and vCCL3 cannot be used to investigate lymphotactin receptor pathways in murine models. These results also add vCCL2 and vCCL3 to a growing list of viral chemokines with known human chemokine receptor targets, which do not target the corresponding murine receptors. This fits with the observation that viral and endogenous ligands for the same human chemokine receptor tend to have relatively divergent amino-acid sequences, suggesting that these viruses have fine-tuned the design of their chemokines such that the action of the viral encoded chemokines cannot be expected to cross species barriers.

Chemokines and chemokine receptors encoded by cytomegaloviruses

CMVs carry several genes that are homologous to genes of the host organism. These include genes homologous to those encoding chemokines (CKs) and G protein-coupled receptors (GPCRs). It is generally assumed that these CMV genes were hijacked from the host genome during the long co-evolution of virus and host. In light of the important function of the CK and GPCR families in the normal physiology of the host, it has previously been hypothesized that the CMV homologs of these proteins, CMV vCKs and vGPCRs, may also have a significant impact on this physiology, such that lifelong maintenance and/or replication of the virus within the infected host is guaranteed. In addition, several of these homologs were reported to have a major impact in the pathogenesis of infection. In this review, the current state of knowledge on the CMV vCKs and vGPCRs will be discussed.

Downregulation of the T-cell receptor complex and impairment of T-cell activation by human herpesvirus 6 u24 protein

We have performed a screen aimed at identifying human herpesvirus 6 (HHV-6)-encoded proteins that modulate immune recognition. Here we show that the U24 protein encoded by HHV-6 variant A downregulates cell surface expression of the T-cell receptor (TCR)/CD3 complex, a complex essential to T-cell activation and the generation of an immune adaptive response. In the presence of U24, the TCR/CD3 complex is endocytosed but is not recycled back to the plasma membrane. Instead, it accumulates in early and late endosomes. Interestingly, whereas CD3 downregulation from the cell surface is normally associated with T-cell activation, U24 downregulates CD3 independently of T-cell activation. Moreover, we found that U24-expressing T cells are resistant to activation by antigen-presenting cells. HHV-6 has evolved a unique mechanism of inhibition of T-cell activation that may impair the establishment of an adaptive immune response. Furthermore, lymphocyte activation creates an environment favorable to the reactivation and replication of lymphotropic herpesviruses. Thus, by inhibiting T-cell activation, HHV-6 might limit its reactivation and thus minimize immune recognition.

HHV-6 and the immune system: mechanisms of immunomodulation and viral escape

Clinical and experimental evidence indicates that human herpesvirus 6 (HHV-6) can interfere with the function of the host immune system through a variety of mechanisms. Both HHV-6A and B can infect, either productively or nonproductively, several types of immune cells. The primary target for HHV-6 replication, both in vitro and in vivo, is the CD4+ T lymphocyte, a pivotal cell in the generation of humoral and cell-mediated adaptive immune responses. HHV-6A, but not B, also replicates in various cytotoxic effector cells, such as CD8+ T cells, gammadelta T cells and natural killer cells. In professional antigen-presenting cells like macrophages and dendritic cells, HHV-6 infection is typically nonproductive; yet, it induces dramatic functional abnormalities, including a selective suppression of IL-12, a critical cytokine in the generation of Th1-polarized antiviral immune responses. This and other immunomodulatory effects seem to be mediated by the engagement of the primary HHV-6 receptor, CD46. Moreover, HHV-6 infection results in a generalized loss of CD46 expression in lymphoid tissue, which may lead to an aberrant activation of autologous complement. Additional mechanisms of immunomodulation by HHV-6 include alterations in cell surface receptor expression and cytokine/chemokine production. HHV-6 can also modulate influence responses through the expression of virally-encoded homologs of chemokines and chemokine receptors. By modulating specific antiviral immune responses, HHV-6 can facilitate its own spread and persistence in vivo, as well as enhance the pathogenic effects of other agents, such as human immunodeficiency virus.

Virus-encoded chemokines, chemokine receptors and chemokine-binding proteins: new paradigms for future therapy

Over millions of years of coevolution with their hosts, viruses have learned the finest artifices of the immune system defense mechanisms and developed a variety of strategies for evading them. The chemokine system has been a primary target of these viral efforts because of the critical role it plays in the development of effective immune responses. Not only do chemokines control cellular recruitment at the site of infection, they also regulate the magnitude and character of the immune responses. Several viruses, and large DNA viruses in particular, have exploited the chemokine system by hijacking and reprogramming chemokine or chemokine-receptor genes, and/or secreting chemokine-binding proteins. In the past few years there has been intense investigation in this area, driven not only by the prospect of gaining a better understanding of viral-immune evasion mechanisms, but also by the possibility of targeting these molecules as part of future antiviral therapeutic approaches, as well as exploiting viral strategies of chemokine interference as novel therapies for inflammatory or neoplastic diseases.

Kaposi sarcoma-associated herpes virus targets the lymphotactin receptor with both a broad spectrum antagonist vCCL2 and a highly selective and potent agonist vCCL3

Large DNA viruses such as herpesvirus and poxvirus encode proteins that target and exploit the chemokine system of their host. These proteins have the potential to block or change the orchestrated recruitment of leukocytes to sites of viral infection. The genome of Kaposi sarcoma-associated herpes virus (KSHV) encodes three chemokine-like proteins named vCCL1, vCCL2, and vCCL3. In this study vCCL3 was probed in parallel with vCCL1 and vCCL2 against a panel of the 18 classified human chemokine receptors. In calcium mobilization assays vCCL1 acted as a selective CCR8 agonist, whereas vCCL2 was found to act as a broad spectrum chemokine antagonist of human chemokine receptors, including the lymphotactin receptor. In contrast vCCL3 was found to be a highly selective agonist for the human lymphotactin receptor XCR1. The potency of vCCL3 was found to be 10-fold higher than the endogenous human XCL1 chemokine in respect to phosphatidylinositol turnover and calcium mobilization as well as chemotaxis. High expression of XCR1 was found in placenta and neutrophils by real-time PCR. These data are consistent with reports of different expression profiles for vCCL2 and vCCL3 during the life cycle of KSHV, indicate a novel, sophisticated exploitation by the virus of specifically the lymphotactin receptor by both agonist and antagonist mechanisms, and suggest a unique physiological importance of this (somewhat overlooked) chemokine receptor.

Inhibition of HIV-1 infection by viral chemokine U83A via high-affinity CCR5 interactions that block human chemokine-induced leukocyte chemotaxis and receptor internalization

HIV-1 strains use C-C-chemokine receptor 5, CCR5, as a coreceptor for host transmission. Human CCR5 chemokine ligands inhibit binding and infection, whereas CCR5 mutations also inhibit infection by preventing surface expression, resulting in delayed progression to AIDS. Here, we describe a human herpesvirus 6 (HHV-6A) chemokine, U83A, which binds CCR5 with higher affinity than human chemokines, displacing their binding and leading to inhibition of chemotaxis of human leukocytes. Similarly, U83A inhibits infection by HIV-1 strains which use CCR5, but not the CXCR4, coreceptor. Unlike human CCR5 chemokine ligands which induce rapid CCR5 internalization mediated via clathrin, treatment with U83A prevents internalization. A spliced truncated U83A isoform, U83A-N, also binds CCR5 albeit with lower affinity, and this correlates with lower HIV-1 infection inhibition, whereas further truncation abolishes binding and any inhibition. Confocal microscopy confirms CCR5 internalization inhibition by U83A treatment, whereas labeled transferrin uptake shows that endocytosis via clathrin is unaltered. Previous results show that, although U83A-N is an antagonist, U83A is an agonist for CCR1, CCR4, CCR6, and CCR8 present on immune effector and antigen-presenting cells and here also shown for CCR5. Thus, U83A could act as a novel inhibitor of HIV-1 infection while also stimulating local immunity to the virus.

Biological and clinical advances in human herpesvirus-6 and -7 research

Since its isolation more than 20 years ago, human herpesvirus (HHV)-6 has been considered an opportunistic pathogen whose infection and/or reactivation is associated with diseases such as roseola, organ transplant anomalies and central nervous system disorders. The lack of relevant animal models, standardized diagnostic reagents and specific anti-HHV-6 drugs has impaired our ability to prove a causal relationship between the presence of this virus and the development of many diseases. Unless such models and reagents are developed and clinical trials performed, speculations on the role for this virus in various pathologies will continue to grow. In this review, recent biological, clinical and epidemiological research advances in the HHV-6 field as well as that of its closest relative, HHV-7, will be presented. Additionally, priority research areas that will help move the field forward are discussed.