Apoptosis of CD4+ T lymphocytes in human herpesvirus-6 infection

Transcriptomic profiling of thymic dysregulation and viral tropism after neonatal roseolovirus infection

Introduction

Herpesviruses, including the roseoloviruses, have been linked to autoimmune disease. The ubiquitous and chronic nature of these infections have made it difficult to establish a causal relationship between acute infection and subsequent development of autoimmunity. We have shown that murine roseolovirus (MRV), which is highly related to human roseoloviruses, induces thymic atrophy and disruption of central tolerance after neonatal infection. Moreover, neonatal MRV infection results in development of autoimmunity in adult mice, long after resolution of acute infection. This suggests that MRV induces durable immune dysregulation.

Methods

In the current studies, we utilized single-cell RNA sequencing (scRNAseq) to study the tropism of MRV in the thymus and determine cellular processes in the thymus that were disrupted by neonatal MRV infection. We then utilized tropism data to establish a cell culture system.

Results

Herein, we describe how MRV alters the thymic transcriptome during acute neonatal infection. We found that MRV infection resulted in major shifts in inflammatory, differentiation and cell cycle pathways in the infected thymus. We also observed shifts in the relative number of specific cell populations. Moreover, utilizing expression of late viral transcripts as a proxy of viral replication, we identified the cellular tropism of MRV in the thymus. This approach demonstrated that double negative, double positive, and CD4 single positive thymocytes, as well as medullary thymic epithelial cells were infected by MRV in vivo. Finally, by applying pseudotime analysis to viral transcripts, which we refer to as "pseudokinetics," we identified viral gene transcription patterns associated with specific cell types and infection status. We utilized this information to establish the first cell culture systems susceptible to MRV infection in vitro.

Conclusion

Our research provides the first complete picture of roseolovirus tropism in the thymus after neonatal infection. Additionally, we identified major transcriptomic alterations in cell populations in the thymus during acute neonatal MRV infection. These studies offer important insight into the early events that occur after neonatal MRV infection that disrupt central tolerance and promote autoimmune disease.

Human herpes virus 6 DNAemia is associated with worse survival after ex vivo T-cell depleted hematopoietic cell transplant

BACKGROUND

We examined the correlation between persistent HHV-6 DNAemia (p-HHV-6) and absolute lymphocyte counts (ALC), platelet counts (PLT) and all-cause mortality the 1-year after ex vivo T-cell depleted (TCD) hematopoietic cell transplant (HCT).

METHODS

We analyzed a cohort of adult TCD HCT recipients 2012-2016 prospectively monitored for plasma HHV-6 by qPCR from day +14 post-HCT (D+14) through D+100. P-HHV-6 was defined as ≥2 consecutive values of ≥500 copies/mL by D+100. PLT and ALC were compared between patients with and without p-HHV-6 using mixed model analysis of variance. Multivariable Cox proportional hazard models were used to identify the impact of p-HHV-6 on 1-year mortality.

RESULTS

Of 312 patients, 83 (27%) had p-HHV-6 by D+100. P-HHV-6 was associated with lower ALC and PLT in the first year post-HCT. In multivariable models, p-HHV-6 was associated with higher mortality by 1-year post-HCT (adjusted hazard ratio 2.97, 95% confidence intervals: 1.62-5.47, P=0.0005), after adjusting for age, antiviral treatment, and ALC at D+100.

CONCLUSIONS

P-HHV-6 was associated with lower ALC and PLT in the first year post-HCT. P-HHV-6 was an independent predictor of mortality in the first year after TCD HCT.

Post-allogeneic hematopoietic stem cell transplantation viral reactivations and viremias: a focused review on human herpesvirus-6, BK virus and adenovirus

Human cytomegalovirus and Epstein-Barr virus have been recognized as potential drivers of morbidity and mortality of patients undergoing allogeneic stem cell transplantation for years. Specific protocols for monitoring, prophylaxis and pre-emptive therapy are in place in many transplant settings. In this review, we focus on the next three most frequent viruses, human herpesvirus-6, BK virus and adenovirus, causing reactivation and/or viremia after allogeneic transplant, which are increasingly detected in patients in the post-transplant period owing to emerging techniques of molecular biology, recipients' characteristics, treatment modalities used for conditioning and factors related donors or stem cell source. Given the less frequent detection of an illness related to these viruses, there are often no specific protocols in place for the management of affected patients. While some patients develop significant morbidity (generally older), others may not need therapy at all (generally younger or children). Furthermore, some of the antiviral therapies used are potentially toxic. With the addition of increased risk of secondary infections, risk of graft failure or increased risk of graft-versus-host disease as well as the relationship with other post-transplant complications, the outcomes of patients with these viremias remain unsatisfactory and even long-term survivors experience increased morbidity.

Human herpesvirus 6A promotes glycolysis in infected T cells by activation of mTOR signaling

Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus worldwide. However, whether and how HHV-6 infection influences the metabolic machinery of the host cell to provide the energy and biosynthetic resources for virus propagation remains unknown. In this study, we identified that HHV-6A infection promotes glucose metabolism in infected T cells, resulting in elevated glycolytic activity with an increase of glucose uptake, glucose consumption and lactate secretion. Furthermore, we explored the mechanisms involved in HHV-6A-mediated glycolytic activation in the infected T cells. We found increased expressions of the key glucose transporters and glycolytic enzymes in HHV-6A-infected T cells. In addition, HHV-6A infection dramatically activated AKT-mTORC1 signaling in the infected T cells and pharmacological inhibition of mTORC1 blocked HHV-6A-mediated glycolytic activation. We also found that direct inhibition of glycolysis by 2-Deoxy-D-glucose (2-DG) or inhibition of mTORC1 activity in HHV-6A-infected T cells effectively reduced HHV-6 DNA replication, protein synthesis and virion production. These results not only reveal the mechanism of how HHV-6 infection affects host cell metabolism, but also suggest that targeting the metabolic pathway could be a new avenue for HHV-6 therapy.

Clinical Characteristics of Primary HHV-6B Infection in Children Visiting the Emergency Room

OBJECTIVE

This cohort study, based on the design of a prior study in the United States, was conducted to elucidate the clinical features of primary human herpesvirus-6B (HHV-6B) infection.

METHODS

Between June 2014 and May 2016, febrile children younger than 5 years who visited the emergency room (ER) and underwent blood examination were enrolled in this study.

RESULTS

Fifty-nine (12%) of the 491 patients were diagnosed with primary HHV-6B infection. The rates of both simple and complex febrile seizure were significantly higher in patients with primary HHV-6B infection than in those without (P < 0.001 and P = 0.008, respectively). The median age at primary HHV-6B infection was 15 months. Forty-seven (79.7%) of the 59 patients with primary HHV-6B infection were younger than 2-year-old. Clinical features were compared between HHV-6B-infected patients older and younger than 2 years. The frequency of apparent infection (exanthema subitum) was significantly higher in the younger patients (P = 0.01). The median leukocyte (P = 0.01) and lymphocyte (P < 0.001) counts in the patients older than 2 years were significantly lower than those in the younger patients.

CONCLUSIONS

Primary HHV-6B infection accounted for 12% of ER visits. Secondary febrile seizures, in particular the complex type, were considered to be a major contributor to the disease burden of primary HHV-6B infection. The timing of primary HHV-6B infection occurred at older ages than in past reports, and the frequency of inapparent infection was higher in older patients.

Human herpesvirus 6 viremia affects T-cell reconstitution after allogeneic hematopoietic stem cell transplantation

Human herpesvirus 6 (HHV6) viremia is a common cause of morbidity following allogeneic hematopoietic cell transplantation (HCT). We previously associated T-cell reconstitution with HHV6 viremia. Here, we investigated whether HHV6 viremia affects T-cell reconstitution after HCT in a time-dependent retrospective analysis. We included 273 pediatric patients (0.1-22.7 years; median follow-up, 58 months) receiving a first HCT between 2004 and 2014. HHV6 was screened weekly in plasma via polymerase chain reaction and occurred in 79 patients (29%) at a median time of 19 days after transplant. Main outcome of interest was immune reconstitution (IR) (CD3/CD4/CD8 T cells), measured biweekly until 12 weeks and monthly thereafter. Cox proportional-hazard models were used with IR and HHV6 as time-dependent variables in multivariate analysis with serotherapy in conditioning, graft source, graft-versus-host disease, age, and other viruses (Epstein-Barr virus, cytomegalovirus, and adenovirus) as covariates. Only patients with very high HHV6 viremia (>10⁵ copies/mL) showed hampered CD4⁺ (hazard ratio [HR], 0.913; 95% confidence interval [CI], 0.892-0.934; P < .001) and CD8⁺ (HR, 0.912; 95% CI, 0.891-0.933; P < .001) reconstitution in comparison with patients without HHV6, from ∼6 months after HCT. Especially naïve CD4⁺ IR was affected (P = .028) but not effector memory CD4⁺ IR (P = .33). Interestingly, T-cell reconstitution was improved in patients treated with antivirals (HR, 1.572; 95% CI, 1.463-1.690; P < .001). These findings suggest that HHV6 viremia affects late but not early T-cell reconstitution.

Unexpected High Incidence of Human Herpesvirus-6 Encephalitis after Naive T Cell-Depleted Graft of Haploidentical Stem Cell Transplantation in Pediatric Patients

The CD45RA T cell depletion (TCD) method has been used to deplete naive T cells, preventing graft-versus-host disease (GVHD) but preserving memory cells, providing immediate functional T cells with anti-infection, antileukemia, and antirejection effects. We describe a series of 25 consecutive high-risk patients with leukemia who received haploidentical hematopoietic stem cell transplantation (haplo-HSCT) with CD45RA TCD. Each patient received 2 cell products: 1 created by CD34 positive selection and the other through CD45RA depletion from the CD34 negative fraction by a CliniMACS device. CD45RA-depleted haplo-HSCT was well tolerated, with rapid engraftment and low risk of severe acute GVHD and chronic GVHD. Although this treatment achieved a good control of viral reactivations, such as cytomegalovirus and adenovirus, we observed an unexpectedly high rate of limbic encephalitis due to human herpesvirus-6 (HHV-6; 8 cases). Characteristically, the infection appeared early in almost all patients, just after the engraftment. Although no patient died from encephalitis, 1 patient showed neuropsychological sequelae, and another experienced secondary graft failure just after the HHV-6 reactivation.

HHV-6B infection, T-cell reconstitution, and graft-vs-host disease after hematopoietic stem cell transplantation

Successful and sustained CD4⁺ T-cell reconstitution is associated with increased survival after hematopoietic cell transplantation (HCT), but opportunistic infections may adversely affect the time and extent of immune reconstitution. Human herpesvirus 6B (HHV-6B) efficiently infects CD4⁺ T cells and utilizes as a receptor CD134 (OX40), a member of the TNF superfamily that antagonizes regulatory T-cell (T_reg) activity. Reactivation of HHV-6B has been associated with aberrant immune reconstitution and acute graft-versus-host disease (aGVHD) after HCT. Given that T_reg counts are negatively correlated with aGVHD severity, we postulate that one mechanism for the poor CD4⁺ T-cell reconstitution observed shortly after transplant may be HHV-6B infection and depletion of peripheral (extra-thymic) CD4⁺ T cells, including a subpopulation of T_reg cells. In turn, this may trigger a series of adverse events resulting in poor clinical outcomes such as severe aGVHD. In addition, recent evidence has linked HHV-6B reactivation with aberrant CD4⁺ T-cell reconstitution late after transplantation, which may be mediated by a different mechanism, possibly related to central (thymic) suppression of T-cell reconstitution. These observations suggest that aggressive management of HHV-6B reactivation in transplant patients may facilitate CD4⁺ T-cell reconstitution and improve the quality of life and survival of HCT patients.

Human Herpesvirus-6B Reactivation Is a Risk Factor for Grades II to IV Acute Graft-versus-Host Disease after Hematopoietic Stem Cell Transplantation: A Systematic Review and Meta-Analysis

Graft-versus-host disease (GVHD) is an important cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (HCT). Many studies have suggested that human herpesvirus-6B (HHV-6B) plays a role in acute GVHD (aGVHD) after HCT. Our objective was to systematically summarize and analyze evidence regarding HHV-6B reactivation and development of aGVHD. PubMed and EMBASE databases were searched using terms for HHV-6, HCT, and aGVHD, yielding 865 unique results. Case reports, reviews, articles focusing on inherited chromosomally integrated HHV-6, poster presentations, and articles not published in English were excluded. The remaining 467 articles were reviewed for the following requirements: a statistical analysis of HHV-6B reactivation and a GVHD was described, HHV-6B reactivation was defined by PCR, and blood (plasma, serum, or peripheral blood mononuclear cells) was used for HHV-6B PCR. Data were abstracted from publications that met these criteria (n = 33). Publications were assigned to 1 of 3 groups: (1) HHV-6B reactivation was analyzed as a time-dependent risk factor for subsequent aGVHD (n = 14), (2) aGVHD was analyzed as a time-dependent risk factor for subsequent HHV-6B reactivation (n = 1), and (3) analysis without temporal specification (n = 18). A statistically significant association (P < .05) between HHV-6B reactivation and aGVHD was observed in 10 of 14 studies (71%) in group 1, 0 of 1 study (0%) in Group 2, and 8 of 18 studies (44.4%) in Group 3. Of the 14 studies that analyzed HHV-6B as a risk factor for subsequent aGVHD, 11 performed a multivariate analysis and reported a hazard ratio, which reached statistical significance in 9 of these s tudies. Meta-analysis of these 11 studies demonstrated a statistically significant association between HHV-6B and subsequent grades II to IV aGVHD (hazard ratio, 2.65; 95% confidence interval, 1.89 to 3.72; P < .001).HHV-6B reactivation is associated with aGVHD, and when studies have a temporal component to their design, HHV-6B reactivation is associated with subsequent aGVHD. Further research is needed to investigate whether antiviral prophylaxis reduces incidence or severity of aGVHD.

Human herpesvirus 6A induces apoptosis of HSB-2 cells via a mitochondrion-related caspase pathway

Apoptosis plays an important role in the pathogenesis of viral infections. In this study, we investigated the cell death processes during productive HHV-6A infection and the underlying mechanisms. Annexin V-PI staining and electron microscopy indicated that HHV-6A is a strong inducer of apoptosis. HHV-6A infection decreased mitochondrial transmembrane potential and led to morphological changes of mitochondria. The cell death was associated with activation of caspase-3 and cleavage of DNA repair enzyme poly (ADP-ribose) polymerase, which is known to be an important substrate for activated caspase-3. Caspase-9 was activated significantly in HHV-6A-infected cells, whereas caspase-8 was not activated obviously. Moreover, HHV-6A infection upregulated Bax and downregulated Bcl-2. This is the first demonstration of mitochondrion-mediated, caspase-dependent apoptosis in HHV-6A-infected cells.

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.

Human herpesvirus 6A infects human embryonic fibroblasts and induces G2/M arrest and cell death

Human herpesvirus 6 (HHV-6) is a beta-herpesvirus capable of infecting cells from different origin. In this study, infection with HHV-6A of human embryonic fibroblasts (HEFs) was performed. Infected cells showed obvious cytopathic effects (CPE). PCR and immunohistochemical tests also confirmed that HEFs are susceptible to HHV-6A infection. The biological effects of HHV-6A infection on HEFs were studied. Infected cells showed decreased proliferation as measured by [(3)H] thymidine incorporation and cell counting. Further analysis demonstrated that infection with HHV-6A leads to cell cycle arrest at G2/M phase and increasing cell death. This is the first demonstration that infection of HEFs with HHV-6A causes profound alterations of cell properties.

Human herpesvirus 6A induces apoptosis of primary human fetal astrocytes via both caspase-dependent and -independent pathways

BACKGROUND

Human herpesvirus 6 (HHV-6) is a T-lymphtropic and neurotropic virus that can infect various types of cells. Sequential studies reported that apoptosis of glia and neurons induced by HHV-6 might act a potential trigger for some central nervous system (CNS) diseases. HHV-6 is involved in the pathogenesis of encephalitis, multiple sclerosis (MS) and fatigue syndrome. However, the mechanisms responsible for the apoptosis of infected CNS cells induced by HHV-6 are poorly understood. In this study, we investigated the cell death processes of primary human fetal astrocytes (PHFAs) during productive HHV-6A infection and the underlying mechanisms.

RESULTS

HHV-6A can cause productive infection in primary human fetal astrocytes. Annexin V-PI staining and electron microscopic analysis indicated that HHV-6A was an inducer of apoptosis. The cell death was associated with activation of caspase-3 and cleavage of poly (ADP-ribose) polymerase (PARP), which is known to be an important substrate for activated caspase-3. Caspase-8 and -9 were also significantly activated in HHV-6A-infected cells. Moreover, HHV-6A infection led to Bax up-regulation and Bcl-2 down-regulation. HHV-6A infection increased the release of Smac/Diablo, AIF and cytochrome c from mitochondria to cytosol, which induced apoptosis via the caspase-dependent and -independent pathways. In addition, we also found that anti-apoptotic factors such as IAPs and NF-κB decreased in HHV-6A infected PHFAs.

CONCLUSION

This is the first demonstration of caspase-dependent and -independent apoptosis in HHV-6A-infected glial cells. These findings would be helpful in understanding the mechanisms of CNS diseases caused by HHV-6.

The role of MAPK in CD4(+) T cells toll-like receptor 9-mediated signaling following HHV-6 infection

Human herpesvirus-6 (HHV-6) is an important immunosuppressive and immunomodulatory virus that primarily infects immune cells (mainly CD4(+) T cells) and strongly suppresses the proliferation of infected cells. Toll-like receptors are pattern-recognition receptors essential for the development of an appropriate innate immune defense against infection. To understand the role of CD4(+) T cells in the innate response to HHV-6 infection and the involvement of TLRs, we used an in vitro infection model and observed that the infection of CD4(+) T cells resulted in the activation of JNK/SAPK via up-regulation of toll-like receptor 9 (TLR9). Associated with JNK activation, annexin V-PI staining indicated that HHV-6A was a strong inducer of apoptosis. Apoptotic response associated cytokines, IL-6 and TNF-α also induced by HHV-6A infection.

An integrated approach to elucidate the intra-viral and viral-cellular protein interaction networks of a gamma-herpesvirus

Genome-wide yeast two-hybrid (Y2H) screens were conducted to elucidate the molecular functions of open reading frames (ORFs) encoded by murine γ-herpesvirus 68 (MHV-68). A library of 84 MHV-68 genes and gene fragments was generated in a Gateway entry plasmid and transferred to Y2H vectors. All possible pair-wise interactions between viral proteins were tested in the Y2H assay, resulting in the identification of 23 intra-viral protein-protein interactions (PPIs). Seventy percent of the interactions between viral proteins were confirmed by co-immunoprecipitation experiments. To systematically investigate virus-cellular protein interactions, the MHV-68 Y2H constructs were screened against a cellular cDNA library, yielding 243 viral-cellular PPIs involving 197 distinct cellar proteins. Network analyses indicated that cellular proteins targeted by MHV-68 had more partners in the cellular PPI network and were located closer to each other than expected by chance. Taking advantage of this observation, we scored the cellular proteins based on their network distances from other MHV-68-interacting proteins and segregated them into high (Y2H-HP) and low priority/not-scored (Y2H-LP/NS) groups. Significantly more genes from Y2H-HP altered MHV-68 replication when their expression was inhibited with siRNAs (53% of genes from Y2H-HP, 21% of genes from Y2H-LP/NS, and 16% of genes randomly chosen from the human PPI network; p<0.05). Enriched Gene Ontology (GO) terms in the Y2H-HP group included regulation of apoptosis, protein kinase cascade, post-translational protein modification, transcription from RNA polymerase II promoter, and IκB kinase/NFκB cascade. Functional validation assays indicated that PCBP1, which interacted with MHV-68 ORF34, may be involved in regulating late virus gene expression in a manner consistent with the effects of its viral interacting partner. Our study integrated Y2H screening with multiple functional validation approaches to create γ-herpes viral-viral and viral-cellular protein interaction networks.

Persistent infections by the herpesviruses Epstein Barr virus (EBV) and Kaposi's sarcoma herpesvirus (KSHV) are associated with tumor formation. To better understand how these and other related viruses interact with their host cells to promote virus replication and cause disease, we studied murine gamma-herpesvirus 68 (MHV-68). MHV-68 belongs to the same group of herpesviruses as EBV and KSHV, but has the advantage of being able to replicate efficiently in cell culture. Our study used genome-wide screens to identify 23 protein-protein interactions between the 80 MHV-68 proteins. Several of these interactions are likely to be important for assembling new viruses. We also discovered 243 interactions between MHV-68 and cellular proteins. To help prioritize cellular proteins for follow up studies, we developed a new computational tool to analyze our data. Proteins with high priority scores were more likely to affect viral replication than low priority proteins. Among the cellular proteins that had the greatest effect on MHV-68 replication was PCBP1, which negatively regulated MHV-68 late gene expression. This study identified many novel cellular proteins involved in MHV-68 replication and established a method to identify important proteins from high-throughput virus-cellular protein-protein interaction data sets.

Human herpesvirus 6 suppresses T cell proliferation through induction of cell cycle arrest in infected cells in the G2/M phase

Human herpesvirus 6 (HHV-6) is an important immunosuppressive and immunomodulatory virus that primarily infects immune cells and strongly suppresses the proliferation of infected cells. However, the mechanisms responsible for the regulation and suppression mediated by HHV-6 are still unknown. In this study, we examined the ability of HHV-6A to manipulate cell cycle progression in infected cells and explored the potential molecular mechanisms. We demonstrated that infection with HHV-6A imposed a growth-inhibitory effect on HSB-2 cells by inducing cell cycle arrest at the G(2)/M phase. We then showed that the activity of the Cdc2-cyclin B1 complex was significantly decreased in HHV-6A-infected HSB-2 cells. Furthermore, we found that inactivation of Cdc2-cyclin B1 in HHV-6A-infected cells occurred through the inhibitory Tyr15 phosphorylation resulting from elevated Wee1 expression and inactivated Cdc25C. The reduction of Cdc2-cyclin B1 activity in HHV-6-infected cells was also partly due to the increased expression of the cell cycle-regulatory molecule p21 in a p53-dependent manner. In addition, HHV-6A infection activated the DNA damage checkpoint kinases Chk2 and Chk1. Our data suggest that HHV-6A infection induces G(2)/M arrest in infected T cells via various molecular regulatory mechanisms. These results further demonstrate the potential mechanisms involved in immune suppression and modulation mediated by HHV-6 infection, and they provide new insights relevant to the development of novel vaccines and immunotherapeutic approaches.

Differential effect of human herpesvirus 6A on cell division and apoptosis among naive and central and effector memory CD4+ and CD8+ T-cell subsets

The immune responses of naive and different memory subsets of CD4(+) and CD8(+) T cells to human herpesvirus 6 (HHV-6) have not been previously investigated. We show that HHV-6A induces cell division, as measured by 5,6-carboxyfluorescein succinimidyl ester dye and flow cytometry, predominantly in two populations of effector memory CD4(+) and CD8(+) T cells (T(EM) and T(EMRA)); naïve (T(N)) and central memory (T(CM)) CD4(+) and CD8(+) T cells showed almost no cell division. In contrast, HHV-6A induced apoptosis primarily in T(N) and T(CM) CD4(+) and CD8(+) T cells, whereas T(EM) and T(EMRA) CD4(+) and CD8(+) T cells were resistant to HHV-6A-induced apoptosis. HHV-6A-induced apoptosis was associated with activation of caspase-8, caspase-9, and caspase-3, suggesting the involvement of death receptor and mitochondrial signaling pathways. In addition, HHV-6A induced secretion of interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), IL-8, and gamma interferon by peripheral blood mononuclear cells; TNF-alpha secretion was observed exclusively from CCR7(+) (T(N) plus T(CM)) CD4(+) T cells. These data show that HHV-6 differentially influences the functions of naïve T cells and different subsets of memory CD4(+) and CD8(+) T cells, which in part may be due to differential susceptibility to HHV-6A-induced apoptosis.

Angioimmunoblastic T-cell lymphoma: histological progression associates with EBV and HHV6B viral load

The clinical and histological presentations of angioimmunoblastic T-cell lymphoma (AITL) often mimic an infectious process. Epstein-Barr virus (EBV) and human herpes virus (HHV6) are known to be associated with AITL, but whether these viral infections play a role in its pathogenesis is unclear. It also remains to be investigated whether there might be other viruses associated with AITL. We first screened 26 well-characterised cases of AITL for herpesvirus by polymerase chain reaction (PCR) with universal primers and found evidence of only EBV and HHV6B infection. Subsequent PCR using virus-specific primers demonstrated EBV and HHV6B infection in 40/49 biopsies (36/42 cases) and 21/49 biopsies (19/42 cases) of AITL respectively with both viral infections found in 17/49 specimens (15/42 cases). Importantly, simultaneous infection with both viruses was found only in specimens showing histological pattern II (n = 2) or III (n = 15). Interestingly, among specimens containing both viruses, there was a tendency towards an inverse correlation between the EBV and HHV6B viral load as shown by quantitative PCR. In specimens positive only for EBV, the viral load was significantly higher in specimens with histological pattern III than those with pattern II. High EBV load was also significantly associated with B-cell monoclonality. Double EBV encoded small RNA (EBER) in situ hybridisation and immunohistochemistry indicated that EBV-infected B cells had a late postgerminal centre immunophenotype. Our results demonstrate an association between EBV and HHV6B infection and the histological progression of AITL, suggesting that these viruses may play a role in the pathogenesis of this lymphoma.

Questionable role of human herpesviruses in the pathogenesis of Kikuchi disease

CONTEXT

Kikuchi disease is a self-limiting febrile lymphadenopathy characterized by a patchy area of apoptosis. Kikuchi disease is thought to be caused by a virus, but this has not been clearly demonstrated. Human herpesviruses 6 and 7 (HHV-6 and HHV-7) are lymphotropic viruses that can induce apoptosis in infected lymphocytes. Recently, HHV-8 was reported to be a possible etiologic agent of Kikuchi disease.

OBJECTIVE

To investigate the incidence of HHV-6, HHV-7, and HHV-8 infection in patients with Kikuchi disease.

DESIGN

Seventy archival tissue specimens (from 50 Kikuchi disease cases and 20 control cases) were tested for the presence of HHV-6 and HHV-7 using a nested polymerase chain reaction, and for the presence of HHV-8 using single-step polymerase chain reaction. Immunohistochemistry for HHV-8 expression was carried out in those cases in which HHV-8 was detected using polymerase chain reaction.

RESULTS

Of the 50 cases with Kikuchi disease, 21 (42%) were HHV-6 positive and 32 (64%) were HHV-7 positive. Eight (40%) of the 20 control cases were HHV-6 positive and 9 (45%) were HHV-7 positive. Both HHV-6 and HHV-7 were detected in 15 (30%) of the cases with Kikuchi disease and in 3 (15%) of the control cases. Three (6%) of the 50 cases of Kikuchi disease were HHV-8 positive but revealed no positive cells on immunohistochemical analysis for HHV-8. Human herpesvirus 8 was not expressed in any of the control cases.

CONCLUSIONS

There was no association between the presence of HHV-6 or HHV-7 and Kikuchi disease. Because the HHV-8 genome but not protein was detected in a small proportion of the cases of Kikuchi disease, its potential causative role in this disease should be determined by further studies.

Polymorphisms at exon 4 of p53 and the susceptibility to herpesvirus types 6 and 1 infection in renal transplant recipients

In order to replicate their own genome in the host nucleus, herpesviruses have to overcome the barrier presented by p53 gene. Variants of codon 72 and codon 47 of exon four decrease the ability of p53 to induce apoptosis. In order to investigate the influence of this germline inheritance on the susceptibility to herpesvirus type 6 (HHV6) and 1 (HHV1) infection, we examined 78 renal transplant recipients and 151 controls. HHV6 infection was more frequent among the renal transplant patients (35.89%) than in the control population (11.25%) (P < 0.001). HHV1 infection rate was similar in renal transplant patients (7.28%) and controls (2.56%). HHV6-positive cases were more frequent among patients with codon 72 of p53 variants (60.71%) than among wild-type p53 patients (28.20%) (P = 0.001) despite the higher frequency of codon 72 of p53 wild-type variant in renal transplant patients compared with controls (64.1% vs. 36.4%; P < 0.001). The presence of a codon 72 of p53 germline variant genotype increased the risk for HHV6 infection more than five times (OR = 5.479; 95% CI = 1.992-15.069). Our data suggest that codon 72 of p53 polymorphism genotyping may be useful to screen for patients at higher risk for post-transplant infections hence identifying individuals that could benefit from preventive treatment.

Human herpesvirus 6B induces cell cycle arrest concomitant with p53 phosphorylation and accumulation in T cells

We studied the interactions between human herpesvirus 6B (HHV-6B) and its host cell. Productive infections of T-cell lines led to G1/S- and G2/M-phase arrest in the cell cycle concomitant with an increased level and enhanced DNA-binding activity of p53. More than 70% of HHV-6B-infected cells did not bind annexin V, indicating that the majority of cells were not undergoing apoptosis. HHV-6B infection induced Ser20 and Ser15 phosphorylation on p53, and the latter was inhibited by caffeine, an ataxia telangiectasia mutated kinase inhibitor. Thus, a productive HHV-6B infection suppresses T-cell proliferation concomitant with the phosphorylation and accumulation of p53.

Update on human herpesvirus 6 biology, clinical features, and therapy

Human herpesvirus 6 (HHV-6) is a betaherpesvirus that is closely related to human cytomegalovirus. It was discovered in 1986, and HHV-6 literature has expanded considerably in the past 10 years. We here present an up-to-date and complete overview of the recent developments concerning HHV-6 biological features, clinical associations, and therapeutic approaches. HHV-6 gene expression regulation and gene products have been systematically characterized, and the multiple interactions between HHV-6 and the host immune system have been explored. Moreover, the discovery of the cellular receptor for HHV-6, CD46, has shed a new light on HHV-6 cell tropism. Furthermore, the in vitro interactions between HHV-6 and other viruses, particularly human immunodeficiency virus, and their relevance for the in vivo situation are discussed, as well as the transactivating capacities of several HHV-6 proteins. The insight into the clinical spectrum of HHV-6 is still evolving and, apart from being recognized as a major pathogen in transplant recipients (as exemplified by the rising number of prospective clinical studies), its role in central nervous system disease has become increasingly apparent. Finally, we present an overview of therapeutic options for HHV-6 therapy (including modes of action and resistance mechanisms).

Human herpesvirus 6 infection arrests cord blood mononuclear cells in G(2) phase of the cell cycle

We here report that after infection with human herpesvirus 6A, human cord blood mononuclear cells accumulate in G(2)/M phase of the cell cycle. Experiments with foscarnet or ultraviolet (UV)-irradiated virus stocks pointed at an (immediate-)early, newly formed viral protein to be responsible for the arrest. At the molecular level, p53, cyclin B(1), cyclin A and tyrosine(15)-phosphorylated cdk1 accumulated after HHV-6A infection, indicating an arrest in G(2). However, no change was observed in the levels of downstream effectors of p53 in establishing a G(2) arrest, i.e. p21 and 14-3-3sigma. We thus conclude that the HHV-6A-induced G(2) arrest occurs independently of p53 accumulation.

Mathematical model to simulate the cellular dynamics of infection with human herpesvirus-6 in EBV-negative infectious mononucleosis

Acute infection with human herpesvirus-6 induces physiological cell proliferation in persons without major immune deficiency. It thus can serve as a parameter to validate a mathematical model designed to simulate cell proliferation under physiological and pathological conditions. Such a mathematical model is presented to simulate various cell changes of the T-cell immune system during the course of HHV-6 infection. Model development follows several steps, beginning with a basic model containing physiological T-cell pools to the introduction of infectious stimuli in the final model. A search algorithm designed to optimize the system parameters, as well as initial variables of the model, is presented. The results of simulation runs for acute HHV-6 infection of the final computational model correspond well to the data, as documented in human patients; they suggest that the computational model presented for the simulation of T-cell levels in a given viral infection may well serve as a tool for similar studies of other viral infections, including those that lead to cellular aplasia or neoplasia.

The varicella-zoster virus induces apoptosis in vitro in subpopulations of primary human peripheral blood mononuclear cells

Varicella-zoster virus (VZV), a member of Herpesviridae, subfamily alpha-Herpesvirinae, is pathogenic exclusively in the human. Chickenpox is the result of primary infection of VZV. During the viremic stage, VZV infects peripheral blood mononuclear cells (PBMC) and spreads to the periphery. In skin cells it causes typical lesions. Apoptosis has been demonstrated in different cell types by other alpha-herpesviruses. VZV-infected T lymphocytes, B lymphocytes, and monocytes, respectively, were examined in this in vitro study by flow cytometry, immunofluorescence and electron microscopy. All infected cell types showed signs of apoptosis: a lower DNA content, DNA fragmentation, loss of membrane integrity, and an altered nuclear morphology. The results observed led to the suggestion that VZV can induce apoptosis during infection in vivo in the PBMC subpopulations.

Human herpesvirus 6: molecular biology and clinical features

Human herpesvirus 6 (HHV-6) exists as distinct variants HHV-6A and HHV-6B. The complete genomes of HHV-6A and HHV-6B have been sequenced. HHV-6B contains 97 unique genes. CD46 is the cell receptor for HHV-6, explaining its broad tissue tropism but its restricted host-species range. HHV-6 utilizes a number of strategies to down-regulate the host immune response, including molecular mimicry by production of a functional chemokine and chemokine receptors. Immunosuppression is enhanced by depletion of CD4 T lymphocytes via direct infection of intra-thymic progenitors and by apoptosis induction. Infection is widespread in infants between 6 months and 2 years of age. A minority of infants develop roseola infantum, but undifferentiated febrile illness is more common. Reactivation from latency occurs in immunocompromised hosts. Organ-specific clinical syndromes occasionally result, but indirect effects including interactions with other viruses such as human immunodeficiency virus type 1 and human cytomegalovirus or graft dysfunction in transplant recipients may be more significant complications in this population. Recent advances in quantitative PCR are providing additional insights into the natural history of infection in paediatric populations and immunocompromised hosts.

Beta-herpesvirus challenges in the transplant recipient

Cytomegalovirus (CMV) has major consequences after allogeneic stem cell and solid organ transplantation. CMV may cause significant morbidity and mortality, and monitoring to detect reactivation to reduce disease or management of end organ disease is associated with increased resource utilization. Two other members of the beta-herpesvirus family, human herpesvirus (HHV) type 6 and HHV-7, are increasingly recognized as important pathogens in transplant recipients, either by direct infection (e.g., encephalitis, hepatitis, or pneumonitis) or via interaction with CMV. In addition to direct effects of CMV infection, such indirect effects as an increased risk for bacterial and fungal infections or impaired graft acceptance and function are important research topics. Diagnosis and treatment of CMV infection is currently more advanced than for HHV-6 and HHV-7.

Human herpesvirus 6 infection and cytomegalovirus-specific lymphoproliferative responses in allogeneic stem cell transplant recipients

The aim of this study was to investigate the effects of HHV-6 DNAemia on the CMV specific lymphoproliferative response after allogeneic stem cell transplantation. Twenty-one allogeneic stem cell transplantation (allo-SCT) patients were included in the study. The patients were either CMV seropositive and/or had CMV seropositive donors. We studied the effects of HHV-6 infection, documented by PCR, on CMV-specific lymphocyte proliferation response and on CMV infection documented by PCR. HHV-6 DNAemia correlated with the absence of CMV-specific lymphocyte proliferation responses after allo-SCT. Three of nine patients with persistent HHV-6 DNA had a CMV-specific lymphocyte proliferative response compared to 11 of 12 patients without persistent HHV-6 DNAemia (P = 0.02). Patients with higher HHV-6 DNA levels (>100 copies) were more likely than those with lower copy numbers not to develop a CMV-specific immune response (six of nine vs one of eight; P < 0.05). Patients who were repeatedly HHV-6 positive in three or more consecutive blood samples were also more likely to need repeated courses of preemptive antiviral therapy against CMV during the first 6 months after transplantation (P < 0.001). Our data indicate the possibility that HHV-6 can suppress the development of CMV-specific immune responses and thereby could predispose to development of late CMV disease.

The impact of human herpesvirus-6 and -7 infection on the outcome of liver transplantation

Human herpesvirus (HHV)-6 and -7 are novel members of the beta-herpesvirus family that maintain latency in the human host after primary infection. Reactivation from latency and/or increased degree of viral replication occurs during periods of immune dysfunction. The clinical effect of HHV-6 and HHV-7 reactivation in recipients of liver transplants is now being recognized. Clinical illnesses such as fever, rash, pneumonitis, encephalitis, hepatitis, and myelosuppression have been described in a number of anecdotal reports. Moreover, a growing body of evidence suggests that the more important effect of HHV-6 and HHV-7 reactivation on the outcomes of liver transplantation may be mediated indirectly by their interactions with the other beta-herpesvirus-cytomegalovirus (CMV). Coinfection among these three beta-herpesviruses in clinical syndromes that were classically ascribed to be solely caused by CMV has been shown and has raised substantial interest in the potential role of HHV-6 and HHV-7 as copathogens in the direct and indirect illnesses caused by CMV. This article reviews the current scientific data on the role and the magnitude of impact of HHV-6 and HHV-7 infection on the outcomes of liver transplantation.

Bovine herpesvirus 1 can infect CD4(+) T lymphocytes and induce programmed cell death during acute infection of cattle

Acute infection of cattle with bovine herpesvirus 1 (BHV-1) represses cell-mediated immunity, which can lead to secondary bacterial infections. Since BHV-1 can induce apoptosis of cultured lymphocytes, we hypothesized that these virus-host interactions occur in cattle. To test this hypothesis, we analyzed lymph nodes and peripheral blood mononuclear cells (PBMC) after calves were infected with BHV-1. In situ terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL) staining of lymphoid tissues (pharyngeal tonsil, cervical, retropharyngeal, and inguinal) was used to detect apoptotic cells. Calves infected with BHV-1 for 7 days revealed increased apoptotic cells near the corticomedullary junction in lymphoid follicles and in the subcapsular region. Increased frequency of apoptotic cells was also observed in the mucosa-associated lymphoid tissue lining the trachea and turbinate. Immunohistochemistry of consecutive sections from pharyngeal tonsil revealed that CD2(+) T lymphocytes were positive for the BHV-1 envelope glycoprotein gD. The location of these CD2(+) T lymphocytes in the germinal center suggested that they were CD4(+) T cells. Electron microscopy and TUNEL also revealed apoptotic and herpesvirus-infected lymphocytes from this area. Fluorescence-activated cell sorting analyses demonstrated that CD4(+) and CD8(+) T cells decreased in lymph nodes and PBMC after infection. The decrease in CD4(+) T cells correlated with an increase in apoptosis. CD4(+) but not CD8(+) lymphocytes were infected by BHV-1 as judged by in situ hybridization and PCR, respectively. Immediate-early (bovine ICP0) and early (ribonucleotide reductase) transcripts were detected in PBMC and CD4(+) lymphocytes prepared from infected calves. In contrast, a late transcript (glycoprotein C) was not consistently detected suggesting productive infection was not efficient. Taken together, these results indicate that BHV-1 can infect CD4(+) T cells in cattle, leading to apoptosis and suppression of cell-mediated immunity.