Identification of the site of Epstein-Barr virus persistence in vivo as a resting B cell

Epstein-Barr virus as a potentiator of autoimmune diseases

The Epstein-Barr virus (EBV) is epidemiologically associated with development of autoimmune diseases, including systemic lupus erythematosus, Sjögren syndrome, rheumatoid arthritis and multiple sclerosis. Although there is well-established evidence for this association, the underlying mechanistic basis remains incompletely defined. In this Review, we discuss the role of EBV infection as a potentiator of autoimmune rheumatic diseases. We review the EBV life cycle, viral transcription programmes, serological profiles and lytic reactivation. We discuss the epidemiological and mechanistic associations of EBV with systemic lupus erythematosus, Sjögren syndrome, rheumatoid arthritis and multiple sclerosis. We describe the potential mechanisms by which EBV might promote autoimmunity, including EBV nuclear antigen 1-mediated molecular mimicry of human autoantigens; EBV-mediated B cell reprogramming, including EBV nuclear antigen 2-mediated dysregulation of autoimmune susceptibility genes; EBV and host genetic factors, including the potential for autoimmunity-promoting strains of EBV; EBV immune evasion and insufficient host responses to control infection; lytic reactivation; and other mechanisms. Finally, we discuss the therapeutic implications and potential therapeutic approaches to targeting EBV for the treatment of autoimmune disease.

Epstein-Barr virus reactivation induces divergent abortive, reprogrammed, and host shutoff states by lytic progression

Viral infection leads to heterogeneous cellular outcomes ranging from refractory to abortive and fully productive states. Single cell transcriptomics enables a high resolution view of these distinct post-infection states. Here, we have interrogated the host-pathogen dynamics following reactivation of Epstein-Barr virus (EBV). While benign in most people, EBV is responsible for infectious mononucleosis, up to 2% of human cancers, and is a trigger for the development of multiple sclerosis. Following latency establishment in B cells, EBV reactivates and is shed in saliva to enable infection of new hosts. Beyond its importance for transmission, the lytic cycle is also implicated in EBV-associated oncogenesis. Conversely, induction of lytic reactivation in latent EBV-positive tumors presents a novel therapeutic opportunity. Therefore, defining the dynamics and heterogeneity of EBV lytic reactivation is a high priority to better understand pathogenesis and therapeutic potential. In this study, we applied single-cell techniques to analyze diverse fate trajectories during lytic reactivation in three B cell models. Consistent with prior work, we find that cell cycle and MYC expression correlate with cells refractory to lytic reactivation. We further found that lytic induction yields a continuum from abortive to complete reactivation. Abortive lytic cells upregulate NFκB and IRF3 pathway target genes, while cells that proceed through the full lytic cycle exhibit unexpected expression of genes associated with cellular reprogramming. Distinct subpopulations of lytic cells further displayed variable profiles for transcripts known to escape virus-mediated host shutoff. These data reveal previously unknown and promiscuous outcomes of lytic reactivation with broad implications for viral replication and EBV-associated oncogenesis.

Epstein-Barr virus reactivation induces divergent abortive, reprogrammed, and host shutoff states by lytic progression

Viral infection leads to heterogeneous cellular outcomes ranging from refractory to abortive and fully productive states. Single cell transcriptomics enables a high resolution view of these distinct post-infection states. Here, we have interrogated the host-pathogen dynamics following reactivation of Epstein-Barr virus (EBV). While benign in most people, EBV is responsible for infectious mononucleosis, up to 2% of human cancers, and is a trigger for the development of multiple sclerosis. Following latency establishment in B cells, EBV reactivates and is shed in saliva to enable infection of new hosts. Beyond its importance for transmission, the lytic cycle is also implicated in EBV-associated oncogenesis. Conversely, induction of lytic reactivation in latent EBV-positive tumors presents a novel therapeutic opportunity. Therefore, defining the dynamics and heterogeneity of EBV lytic reactivation is a high priority to better understand pathogenesis and therapeutic potential. In this study, we applied single-cell techniques to analyze diverse fate trajectories during lytic reactivation in two B cell models. Consistent with prior work, we find that cell cycle and MYC expression correlate with cells refractory to lytic reactivation. We further found that lytic induction yields a continuum from abortive to complete reactivation. Abortive lytic cells upregulate NFκB and IRF3 pathway target genes, while cells that proceed through the full lytic cycle exhibit unexpected expression of genes associated with cellular reprogramming. Distinct subpopulations of lytic cells further displayed variable profiles for transcripts known to escape virus-mediated host shutoff. These data reveal previously unknown and promiscuous outcomes of lytic reactivation with broad implications for viral replication and EBV-associated oncogenesis.

Epstein-Barr virus perpetuates B cell germinal center dynamics and generation of autoimmune-associated phenotypes in vitro

Human B cells encompass functionally diverse lineages and phenotypic states that contribute to protective as well as pathogenic responses. Epstein-Barr virus (EBV) provides a unique lens for studying heterogeneous B cell responses, given its adaptation to manipulate intrinsic cell programming. EBV promotes the activation, proliferation, and eventual outgrowth of host B cells as immortalized lymphoblastoid cell lines (LCLs) in vitro, which provide a foundational model of viral latency and lymphomagenesis. Although cellular responses and outcomes of infection can vary significantly within populations, investigations that capture genome-wide perspectives of this variation at single-cell resolution are in nascent stages. We have recently used single-cell approaches to identify EBV-mediated B cell heterogeneity in de novo infection and within LCLs, underscoring the dynamic and complex qualities of latent infection rather than a singular, static infection state. Here, we expand upon these findings with functional characterizations of EBV-induced dynamic phenotypes that mimic B cell immune responses. We found that distinct subpopulations isolated from LCLs could completely reconstitute the full phenotypic spectrum of their parental lines. In conjunction with conserved patterns of cell state diversity identified within scRNA-seq data, these data support a model in which EBV continuously drives recurrent B cell entry, progression through, and egress from the Germinal Center (GC) reaction. This "perpetual GC" also generates tangent cell fate trajectories including terminal plasmablast differentiation, which constitutes a replicative cul-de-sac for EBV from which lytic reactivation provides escape. Furthermore, we found that both established EBV latency and de novo infection support the development of cells with features of atypical memory B cells, which have been broadly associated with autoimmune disorders. Treatment of LCLs with TLR7 agonist or IL-21 was sufficient to generate an increased frequency of IgD-/CD27-/CD23-/CD38+/CD138+ plasmablasts. Separately, de novo EBV infection led to the development of CXCR3+/CD11c+/FCRL4+ B cells within days, providing evidence for possible T cell-independent origins of a recently described EBV-associated neuroinvasive CXCR3+ B cell subset in patients with multiple sclerosis. Collectively, this work reveals unexpected virus-driven complexity across infected cell populations and highlights potential roles of EBV in mediating or priming foundational aspects of virus-associated immune cell dysfunction in disease.

Time-resolved transcriptomes reveal diverse B cell fate trajectories in the early response to Epstein-Barr virus infection

Epstein-Barr virus infection of B lymphocytes elicits diverse host responses via well-adapted transcriptional control dynamics. Consequently, this host-pathogen interaction provides a powerful system to explore fundamental processes leading to consensus fate decisions. Here, we use single-cell transcriptomics to construct a genome-wide multistate model of B cell fates upon EBV infection. Additional single-cell data from human tonsils reveal correspondence of model states to analogous in vivo phenotypes within secondary lymphoid tissue, including an EBV+ analog of multipotent activated precursors that can yield early memory B cells. These resources yield exquisitely detailed perspectives of the transforming cellular landscape during an oncogenic viral infection that simulates antigen-induced B cell activation and differentiation. Thus, they support investigations of state-specific EBV-host dynamics, effector B cell fates, and lymphomagenesis. To demonstrate this potential, we identify EBV infection dynamics in FCRL4+/TBX21+ atypical memory B cells that are pathogenically associated with numerous immune disorders.

Epstein-Barr Virus Association with Breast Cancer: Evidence and Perspectives

Epstein-Barr virus (EBV) is an enveloped DNA virus that belongs to the gamma Herpesviridae family. The virus establishes a latent/lytic persistent infection, though it can be involved in cancer development in some subjects. Indeed, evidence supports an etiological role of EBV in undifferentiated nasopharyngeal carcinoma (NPC), a subset of gastric carcinomas and lymphomas. Additionally, EBV has been detected in breast carcinomas (BCs) although its role has not been established. In this review, we summarize epidemiological information regarding the presence of EBV in BC and we propose mechanistic models. However, additional epidemiological and experimental evidence is warranted to confirm these models.

Prevention of MS Requires Intervention on the Causes of the Disease: Reconciling Genes, Epigenetics, and Epstein Barr Virus

Prevention of multiple sclerosis requires intervention on modifiable causes of the condition making it necessary to establish what those causes are. MS is often stated to be a polygenic disease, with causal contributions from environmental factors and gene-environment interactions, implying an additive and independent relationship of these factors. Mechanistically there are no independent contributions of genes or environmental factors to traits. This model is unrealistic but still useful and underlies the concept of heritability, a foundational parameter in population genetics. However, it perpetuates a debate on an irreconcilable dichotomy about whether MS is primarily genetic or environmental. In particular, epidemiological evidence now exists for a causal, possibly even necessary, role for Epstein Barr Virus in MS. The additive model makes it unintuitive to reconcile MS as a genetic disease but also independently a viral illness. In this perspective it is argued that starting from a realistic interaction only model, based on broadly accepted biological premises, and working forward to explain why the classical additive model gives useful results, there is actually no paradox. An integrated approach using population genetic studies, immunology and molecular virology offers a particularly promising route to establish the elusive role of EBV in MS pathology, as EBV is a large and complex virus and its latency, dysregulated in most EBV-related pathologies, is hard to study in vivo. This approach may offer a route to prevention of MS altogether.

Neutralizing antibodies against Epstein-Barr virus infection of B cells can protect from oral viral challenge in the rhesus macaque animal model

Epstein-Barr virus (EBV) and related lymphocryptoviruses (LCVs) from nonhuman primates are transmitted through oral secretions, penetrate the mucosal epithelium, and establish persistent infection in B cells. To determine whether neutralizing antibodies against epithelial or B cell infection could block oral transmission and persistent LCV infection, we use rhesus macaques, the most accurate animal model for EBV infection by faithfully reproducing acute and persistent infection in humans. Naive animals are infused with monoclonal antibodies neutralizing epithelial cell infection or B cell infection and then challenged orally with recombinant rhesus LCV. Our data show that high-titer B cell-neutralizing antibodies alone, but not epithelial cell-neutralizing antibodies, can provide complete protection of rhesus macaques from oral LCV challenge, but not in all hosts. Thus, neutralizing antibodies against B cell infection are important targets for EBV vaccine development, but they may not be sufficient.

mAb infusion leads to high neutralizing titers in nonhuman primates

Protection of epithelial cells does not protect from lymphocryptovirus challenge

Neutralization of B cell infection alone provides partial protection in macaques

Detection of Epstein-Barr virus by a rapid and simple accelerated denaturation bubble-mediated strand exchange amplification method

Epstein-Barr Virus (EBV) is a tumor-associated virus naturally transmitted through saliva. This virus is the pathogen of infectious mononucleosis, which is closely related to the occurrence of nasopharyngeal carcinoma (NPC) and childhood lymphoma. Although a majority of EBV infected individuals exhibited good tolerance after primary infection, those who carry a viral load greater than the clinical cutoff value (COV), the upper level in healthy carriers, still suffer a high risk of cancer. Herein, a simple, rapid, and effective method, accelerated strand exchange amplification (ASEA), was developed for EBV detection, which could offer a strategy for non-invasive testing of EBV in saliva samples instead of blood samples as in traditional serology based methods and avoid bleeding during diagnosis. This approach could distinguish the genomic DNA of EBV and other species in saliva, and its limit of detection was as low as 1000 copies per mL, which was lower than the COV of EBV. Moreover, DNA extracted from saliva samples (n = 50) was employed as a template for EBV detection via qPCR and ASEA, the result of which showed that ASEA exhibited comparable sensitivity and specificity for actual sample diagnosis. Additionally, similar to conventional PCR, this method requires only one pair of primers and could be performed using a conventional fluorescence instrument, which makes this method easy to accomplish. Therefore, this rapid and effective method has the potential to provide rapid screening platforms for individuals with a high EBV load.

Targeted Delivery of BZLF1 to DEC205 Drives EBV-Protective Immunity in a Spontaneous Model of EBV-Driven Lymphoproliferative Disease

Epstein-Barr virus (EBV) is a human herpes virus that infects over 90% of the world's population and is linked to development of cancer. In immune-competent individuals, EBV infection is mitigated by a highly efficient virus-specific memory T-cell response. Risk of EBV-driven cancers increases with immune suppression (IS). EBV-seronegative recipients of solid organ transplants are at high risk of developing post-transplant lymphoproliferative disease (PTLD) due to iatrogenic IS. While reducing the level of IS may improve EBV-specific immunity and regression of PTLD, patients are at high risk for allograft rejection and need for immune-chemotherapy. Strategies to prevent PTLD in this vulnerable patient population represents an unmet need. We have previously shown that BZLF1-specific cytotoxic T-cell (CTL) expansion following reduced IS correlated with immune-mediated PTLD regression and improved patient survival. We have developed a vaccine to bolster EBV-specific immunity to the BZLF1 protein and show that co-culture of dendritic cells (DCs) loaded with a αDEC205-BZLF1 fusion protein with peripheral blood mononuclear cells (PMBCs) leads to expansion and increased cytotoxic activity of central-effector memory CTLs against EBV-transformed B-cells. Human-murine chimeric Hu-PBL-SCID mice were vaccinated with DCs loaded with αDEC205-BZLF1 or control to assess prevention of fatal human EBV lymphoproliferative disease. Despite a profoundly immunosuppressive environment, vaccination with αDEC205-BZLF1 stimulated clonal expansion of antigen-specific T-cells that produced abundant IFNγ and significantly prolonged survival. These results support preclinical and clinical development of vaccine approaches using BZLF1 as an immunogen to harness adaptive cellular responses and prevent PTLD in vulnerable patient populations.

The Epstein-Barr Virus-Encoded EBNA1 Protein Activates the Bone Morphogenic Protein (BMP) Signalling Pathway to Promote Carcinoma Cell Migration

The Epstein-Barr virus (EBV)-encoded nuclear antigen 1 (EBNA1) protein is expressed in all virus-associated malignancies, where it performs an essential role in the maintenance, replication and transcription of the EBV genome. In recent years, it has become apparent that EBNA1 can also influence cellular gene transcription. Here, we demonstrate that EBNA1 is able to stimulate the expression of the Transforming growth factor-beta (TGFβ) superfamily member, bone morphogenic protein 2 (BMP2), with consequential activation of the BMP signalling pathway in carcinoma cell lines. We show that BMP pathway activation is associated with an increase in the migratory capacity of carcinoma cells, an effect that can be ablated by the BMP antagonist, Noggin. Gene expression profiling of authentic EBV-positive nasopharyngeal carcinoma (NPC) tumours revealed the consistent presence of BMP ligands, established BMP pathway effectors and putative target genes, constituting a prominent BMP “signature” in this virus-associated cancer. Our findings show that EBNA1 is the major viral-encoded protein responsible for activating the BMP signalling pathway in carcinoma cells and supports a role for this pathway in promoting cell migration and possibly, metastatic spread.

Viral G protein-coupled receptors as modulators of cancer hallmarks

Herpesviruses encode transmembrane G protein-coupled receptors (GPCRs), which share structural homology to human chemokine receptors. These viral GPCRs include KSHV-encoded ORF74, EBV-encoded BILF1, and HCMV-encoded US28, UL33, UL78 and US27. Viral GPCRs hijack various signaling pathways and cellular networks, including pathways involved in the so-called cancer hallmarks as defined by Hanahan and Weinberg. These hallmarks describe cellular characteristics crucial for transformation and tumor progression. The cancer hallmarks involve growth factor-independent proliferation, angiogenesis, avoidance of apoptosis, invasion and metastasis, metabolic reprogramming, genetic instability and immune evasion amongst others. The role of beta herpesviruses modulating these cancer hallmarks is clearly highlighted by the proliferative and pro-angiogenic phenotype associated with KSHV infection which is largely ascribed to the ORF74-mediated modulation of signaling networks in host cells. For HCMV and Epstein-Bar encoded GPCRs, oncomodulatory effects have been described which contribute to the cancer hallmarks, thereby enhancing oncogenic development. In this review, we describe the main signaling pathways controlling the hallmarks of cancer which are affected by the betaherpesvirus encoded GPCRs. Most prominent among these involve the JAK-STAT, PI(3)K-AKT, NFkB and MAPK signaling nodes. These insights are important to effectively target these viral GPCRs and their signaling networks in betaherpesvirus-associated malignancies.

Immunosuppressive FK506 treatment leads to more frequent EBV-associated lymphoproliferative disease in humanized mice

Post-transplant lymphoproliferative disorder (PTLD) is a potentially fatal complication after organ transplantation frequently associated with the Epstein-Barr virus (EBV). Immunosuppressive treatment is thought to allow the expansion of EBV-infected B cells, which often express all eight oncogenic EBV latent proteins. Here, we assessed whether HLA-A2 transgenic humanized NSG mice treated with the immunosuppressant FK506 could be used to model EBV-PTLD. We found that FK506 treatment of EBV-infected mice led to an elevated viral burden, more frequent tumor formation and diminished EBV-induced T cell responses, indicative of reduced EBV-specific immune control. EBV latency III and lymphoproliferation-associated cellular transcripts were up-regulated in B cells from immunosuppressed animals, akin to the viral and host gene expression pattern found in EBV-PTLD. Utilizing an unbiased gene expression profiling approach, we identified genes differentially expressed in B cells of EBV-infected animals with and without FK506 treatment. Upon investigating the most promising candidates, we validated sCD30 as a marker of uncontrolled EBV proliferation in both humanized mice and in pediatric patients with EBV-PTLD. High levels of sCD30 have been previously associated with EBV-PTLD in patients. As such, we believe that humanized mice can indeed model aspects of EBV-PTLD development and may prove useful for the safety assessment of immunomodulatory therapies.

Dasatinib exacerbates splenomegaly of mice inoculated with Epstein-Barr virus-infected lymphoblastoid cell lines

Latent infection of Epstein-Barr virus (EBV) is associated with a poor prognosis in patients with B cell malignancy. We examined whether dasatinib, a multi kinase inhibitor, which is broadly used for chronic myeloid leukemia and Philadelphia chromosome-positive acute lymphoblastic leukemia is effective on EBV-positive B cell malignancies, using lymphoblastoid cell lines (LCLs) in vitro and in vivo. As a result, in vitro experiments showed that dasatinib induced cell death of the EBV-LCLs which was not accompanied with a lytic reactivation of EBVs. To evaluate the effectiveness in EBV latency type III represented by immunodeficiency lymphoma, LCL-inoculated immunodeficient NOD/shi-scid/Il2rg^nul (NOG) mice were treated with dasatinib. However, in vivo experiments revealed that dasatinib treatment exacerbated tumor cell infiltration into the spleen of LCL-inoculated NOG mice, whereas tumor size at the inoculated site was not affected by the treatment. These results suggest that dasatinib exacerbates the pathogenesis at least in some situations although the drug is effective in vitro. Hence, we should carefully examine a possibility of dasatinib repositioning for EBV⁺ B cell malignancies.

Pathogenesis of Human Gammaherpesviruses: Recent Advances

PURPOSE OF THIS REVIEW

Human gammaherpesviruses have complex lifecycles that drive their pathogenesis. KSHV and EBV are the etiological agents of multiple cancers worldwide. There is no FDA-approved vaccine for either KSHV or EBV. This review will describe recent progress in understanding EBV and KSHV lifecycles during infection.

RECENT FINDINGS

Determining how latency is established, particularly how non-coding RNAs influence latent and lytic infection, is a rapidly growing area of investigation into how gammaherpesviruses successfully persist in the human population. Many factors have been identified as restrictors of reactivation from latency, especially innate immune antagonism. Finally, new host proteins that play a role in lytic replication have been identified.

SUMMARY

In this review we discuss recent findings over the last 5 years on both host and viral factors that are involved in EBV and KSHV pathogenesis.

Translational profiling of B cells infected with the Epstein-Barr virus reveals 5' leader ribosome recruitment through upstream open reading frames

The Epstein-Barr virus (EBV) genome encodes several hundred transcripts. We have used ribosome profiling to characterize viral translation in infected cells and map new translation initiation sites. We show here that EBV transcripts are translated with highly variable efficiency, owing to variable transcription and translation rates, variable ribosome recruitment to the leader region and coverage by monosomes versus polysomes. Some transcripts were hardly translated, others mainly carried monosomes, showed ribosome accumulation in leader regions and most likely represent non-coding RNAs. A similar process was visible for a subset of lytic genes including the key transactivators BZLF1 and BRLF1 in cells infected with weakly replicating EBV strains. This suggests that ribosome trapping, particularly in the leader region, represents a new checkpoint for the repression of lytic replication. We could identify 25 upstream open reading frames (uORFs) located upstream of coding transcripts that displayed 5′ leader ribosome trapping, six of which were located in the leader region shared by many latent transcripts. These uORFs repressed viral translation and are likely to play an important role in the regulation of EBV translation.

Immune Control of γ-Herpesviruses

Vaccination against γ-herpesviruses has been hampered by our limited understanding of their normal control. Epstein–Barr virus (EBV)-transformed B cells are killed by viral latency antigen-specific CD8⁺ T cells in vitro, but attempts to block B cell infection with antibody or to prime anti-viral CD8⁺ T cells have protected poorly in vivo. The Doherty laboratory used Murid Herpesvirus-4 (MuHV-4) to analyze γ-herpesvirus control in mice and found CD4⁺ T cell dependence, with viral evasion limiting CD8⁺ T cell function. MuHV-4 colonizes germinal center (GC) B cells via lytic transfer from myeloid cells, and CD4⁺ T cells control myeloid infection. GC colonization and protective, lytic antigen-specific CD4⁺ T cells are now evident also for EBV. Subunit vaccines have protected only transiently against MuHV-4, but whole virus vaccines give long-term protection, via CD4⁺ T cells and antibody. They block infection transfer to B cells, and need include no known viral latency gene, nor any MuHV-4-specific gene. Thus, the Doherty approach of in vivo murine analysis has led to a plausible vaccine strategy for EBV and, perhaps, some insight into what CD8⁺ T cells really do.

Epstein-Barr virus (EBV) reactivation and therapeutic inhibitors

Epstein-Barr virus (EBV) is a ubiquitous human virus which infects almost all humans during their lifetime and following the acute phase, persists for the remainder of the life of the individual. EBV infects B lymphocytes leading to their immortalisation, with persistence of the EBV genome as an episome. In the latent phase, EBV is prevented from reactivating through efficient cytotoxic cellular immunity. EBV reactivates (lytic phase) under conditions of psychological stress with consequent weakening of cellular immunity, and EBV reactivation has been shown to occur in a subset of individuals with each of a variety of cancers, autoimmune diseases, the autoimmune-like disease, chronic fatigue syndrome/myalgic encephalitis and under other circumstances such as being an inpatient in an intensive care unit. Chronic EBV reactivation is an important mechanism in the pathogenesis of many such diseases, yet is rarely tested for in immunocompetent individuals. This review summarises the pathogenesis of EBV infection, EBV reactivation and its role in disease, and methods which may be used to detect it. Known inhibitors of EBV reactivation and replication are discussed, including drugs licensed for treatment of other herpesviruses, licensed or experimental drugs for various other indications, compounds at an early stage of drug development and nutritional constituents such as vitamins and dietary supplements.

Hypothesis: Multiple sclerosis is caused by three-hits, strictly in order, in genetically susceptible persons

Multiple Sclerosis is a chronic, progressive and debilitating neurological disease which, despite extensive study for over 100 years, remains of enigmatic aetiology. Drawn from the epidemiological evidence, there exists a consensus that there are environmental (possibly infectious) factors that contribute to disease pathogenesis that have not yet been fully elucidated. Here we propose a three-tiered hypothesis: 1) a clinic-epidemiological model of multiple sclerosis as a rare late complication of two sequential infections (with the temporal sequence of infections being important); 2) a proposal that the first event is helminthic infection with Enterobius Vermicularis, and the second is Epstein Barr Virus infection; and 3) a proposal for a testable biological mechanism, involving T-Cell exhaustion for Epstein-Barr Virus protein LMP2A. We believe that this model satisfies some of the as-yet unexplained features of multiple sclerosis epidemiology, is consistent with the clinical and neuropathological features of the disease and is potentially testable by experiment. This model may be generalizable to other autoimmune diseases.

Evaluation of the risk of lymphomagenesis in xenografts by the PCR-based detection of EBV BamHI W region in patient cancer specimens

Establishment of patient-derived tumor xenografts (PDXs) is hampered by lymphomagenesis mostly caused by the latently-infected Epstein-Barr virus (EBV) contained in patient cancer tissues. However, the character of patient tissues that result in lymphomagenesis after xenotransplantation is not elucidated. In this study, we analyzed the patient colorectal cancer (CRC) tissues and the PDXs established by their xenotransplantation. We found that 2 of 9 (22%) PDX tumors were EBV-associated human diffuse large B cell lymphoma which was formed by clonal proliferation of human B-cell lymphocytes, were strongly positive for EBER-ISH, and were classified as type III latency. Expression of EBV genes and RNAs, such as EBNAs, LMP1, EBER and EBV-associated microRNAs in patient CRC tissues were unlikely to be associated with lymphomagenesis in PDXs. In contrast, the positive PCR-based amplification of BamHI W region, a major internal repeat in EBV genome, in the patient CRC tissues was correlated with lymphomagenesis in PDXs. These results suggest that the detection of the EBV BamHI W region in the patient surgical specimens will be an effective way to predict the risk of lymphomagenesis in PDXs before xenotransplantation.

Drug Modulators of B Cell Signaling Pathways and Epstein-Barr Virus Lytic Activation

Epstein-Barr virus (EBV) is a ubiquitous human gammaherpesvirus that establishes a latency reservoir in B cells. In this work, we show that ibrutinib, idelalisib, and dasatinib, drugs that block B cell receptor (BCR) signaling and are used in the treatment of hematologic malignancies, block BCR-mediated lytic induction at clinically relevant doses. We confirm that the immunosuppressive drugs cyclosporine and tacrolimus also inhibit BCR-mediated lytic induction but find that rapamycin does not inhibit BCR-mediated lytic induction. Further investigation shows that mammalian target of rapamycin complex 2 (mTORC2) contributes to BCR-mediated lytic induction and that FK506-binding protein 12 (FKBP12) binding alone is not adequate to block activation. Finally, we show that BCR signaling can activate EBV lytic induction in freshly isolated B cells from peripheral blood mononuclear cells (PBMCs) and that activation can be inhibited by ibrutinib or idelalisib.IMPORTANCE EBV establishes viral latency in B cells. Activation of the B cell receptor pathway activates lytic viral expression in cell lines. Here we show that drugs that inhibit important kinases in the BCR signaling pathway inhibit activation of lytic viral expression but do not inhibit several other lytic activation pathways. Immunosuppressant drugs such as cyclosporine and tacrolimus but not rapamycin also inhibit BCR-mediated EBV activation. Finally, we show that BCR activation of lytic infection occurs not only in tumor cell lines but also in freshly isolated B cells from patients and that this activation can be blocked by BCR inhibitors.

Regulatory network analysis of Epstein-Barr virus identifies functional modules and hub genes involved in infectious mononucleosis

Epstein-Barr virus (EBV) is the most common cause of infectious mononucleosis (IM) and establishes lifetime infection associated with a variety of cancers and autoimmune diseases. The aim of this study was to develop an integrative gene regulatory network (GRN) approach and overlying gene expression data to identify the representative subnetworks for IM and EBV latent infection (LI). After identifying differentially expressed genes (DEGs) in both IM and LI gene expression profiles, functional annotations were applied using gene ontology (GO) and BiNGO tools, and construction of GRNs, topological analysis and identification of modules were carried out using several plugins of Cytoscape. In parallel, a human-EBV GRN was generated using the Hu-Vir database for further analyses. Our analysis revealed that the majority of DEGs in both IM and LI were involved in cell-cycle and DNA repair processes. However, these genes showed a significant negative correlation in the IM and LI states. Furthermore, cyclin-dependent kinase 2 (CDK2) - a hub gene with the highest centrality score - appeared to be the key player in cell cycle regulation in IM disease. The most significant functional modules in the IM and LI states were involved in the regulation of the cell cycle and apoptosis, respectively. Human-EBV network analysis revealed several direct targets of EBV proteins during IM disease. Our study provides an important first report on the response to IM/LI EBV infection in humans. An important aspect of our data was the upregulation of genes associated with cell cycle progression and proliferation.

Severe Epstein-Barr virus infection in primary immunodeficiency and the normal host

Epstein-Barr virus (EBV) infection is ubiquitous in humans, but the majority of infections have an asymptomatic or self-limiting clinical course. Rarely, individuals may develop a pathological EBV infection with a variety of life threatening complications (including haemophagocytosis and malignancy) and others develop asymptomatic chronic EBV viraemia. Although an impaired ability to control EBV infection has long been recognised as a hallmark of severe T-cell immunodeficiency, the advent of next generation sequencing has identified a series of Primary Immunodeficiencies in which EBV-related pathology is the dominant feature. Chronic active EBV infection is defined as chronic EBV viraemia associated with systemic lymphoproliferative disease, in the absence of immunodeficiency. Descriptions of larger cohorts of patients with chronic active EBV in recent years have significantly advanced our understanding of this clinical syndrome. In this review we summarise the current understanding of the pathophysiology and natural history of these diseases and clinical syndromes, and discuss approaches to the investigation and treatment of severe or atypical EBV infection.

Interplay of Murine Gammaherpesvirus 68 with NF-kappaB Signaling of the Host

Herpesviruses establish a chronic infection in the host characterized by intervals of lytic replication, quiescent latency, and reactivation from latency. Murine gammaherpesvirus 68 (MHV68) naturally infects small rodents and has genetic and biologic parallels with the human gammaherpesviruses (gHVs), Kaposi's sarcoma-associated herpesvirus and Epstein-Barr virus. The murine gammaherpesvirus model pathogen system provides a platform to apply cutting-edge approaches to dissect the interplay of gammaherpesvirus and host determinants that enable colonization of the host, and that shape the latent or lytic fate of an infected cell. This knowledge is critical for the development of novel therapeutic interventions against the oncogenic gHVs. The nuclear factor kappa B (NF-κB) signaling pathway is well-known for its role in the promotion of inflammation and many aspects of B cell biology. Here, we review key aspects of the virus lifecycle in the host, with an emphasis on the route that the virus takes to gain access to the B cell latency reservoir. We highlight how the murine gammaherpesvirus requires components of the NF-κB signaling pathway to promote replication, latency establishment, and maintenance of latency. These studies emphasize the complexity of gammaherpesvirus interactions with NF-κB signaling components that direct innate and adaptive immune responses of the host. Importantly, multiple facets of NF-κB signaling have been identified that might be targeted to reduce the burden of gammaherpesvirus-associated diseases.

Distribution and Molecular Characterization of Human Adenovirus and Epstein-Barr Virus Infections in Tonsillar Lymphocytes Isolated from Patients Diagnosed with Tonsillar Diseases

Surgically removed palatine tonsils provide a conveniently accessible source of T and B lymphocytes to study the interplay between foreign pathogens and the host immune system. In this study we have characterised the distribution of human adenovirus (HAdV), Epstein-Barr virus (EBV) and human cytomegalovirus (HCMV) in purified tonsillar T and B cell-enriched fractions isolated from three patient age groups diagnosed with tonsillar hypertrophy and chronic/recurrent tonsillitis. HAdV DNA was detected in 93 out of 111 patients (84%), while EBV DNA was detected in 58 patients (52%). The most abundant adenovirus type was HAdV-5 (68%). None of the patients were positive for HCMV. Furthermore, 43 patients (39%) showed a co-infection of HAdV and EBV. The majority of young patients diagnosed with tonsillar hypertrophy were positive for HAdV, whereas all adult patients diagnosed with chronic/recurrent tonsillitis were positive for either HAdV or EBV. Most of the tonsils from patients diagnosed with either tonsillar hypertrophy or chronic/recurrent tonsillitis showed a higher HAdV DNA copy number in T compared to B cell-enriched fraction. Interestingly, in the majority of the tonsils from patients with chronic/recurrent tonsillitis HAdV DNA was detected in T cells only, whereas hypertrophic tonsils demonstrated HAdV DNA in both T and B cell-enriched fractions. In contrast, the majority of EBV positive tonsils revealed a preference for EBV DNA accumulation in the B cell-enriched fraction compared to T cell fraction irrespective of the patients' age.

Epstein-Barr virus infection of infants: implications of early age of infection on viral control and risk for Burkitt lymphoma

Since its first description by Denis Burkitt, endemic Burkitt's lymphoma (BL), the most common childhood cancer in sub-Saharan Africa, has led scientists to search for clues to the origins of this malignancy. The discovery of Epstein-Barr virus (EBV) in BL cells over 50 years ago led to extensive sero-epidemiology studies and revealed that rather than being a virus restricted to areas where BL is endemic, EBV is ubiquitous in the world's population with an estimated greater than 90% of adults worldwide infected. A second pathogen, Plasmodium falciparum (P. falciparum) malaria is also linked to BL. In this review, we will discuss recent studies that indicate a role for P. falciparum malaria in dysregulating EBV infection, and increasing the risk for BL in children living where P. falciparum malaria transmission is high.

BH3 Profiling Reveals Selectivity by Herpesviruses for Specific Bcl-2 Proteins To Mediate Survival of Latently Infected Cells

Herpesviruses, including human cytomegalovirus (HCMV), Epstein-Barr virus (EBV), and Kaposi's sarcoma-associated herpesvirus, establish latency by modulating or mimicking antiapoptotic Bcl-2 proteins to promote survival of carrier cells. BH3 profiling, which assesses the contribution of Bcl-2 proteins towards cellular survival, was able to globally determine the level of dependence on individual cellular and viral Bcl-2 proteins within latently infected cells. Moreover, BH3 profiling predicted the sensitivity of infected cells to small-molecule inhibitors of Bcl-2 proteins.

EBV Persistence--Introducing the Virus

Persistent infection by EBV is explained by the germinal center model (GCM) which provides a satisfying and currently the only explanation for EBVs disparate biology. Since the GCM touches on every aspect of the virus, this chapter will serve as an introduction to the subsequent chapters. EBV is B lymphotropic, and its biology closely follows that of normal mature B lymphocytes. The virus persists quiescently in resting memory B cells for the lifetime of the host in a non-pathogenic state that is also invisible to the immune response. To access this compartment, the virus infects naïve B cells in the lymphoepithelium of the tonsils and activates these cells using the growth transcription program. These cells migrate to the GC where they switch to a more limited transcription program, the default program, which helps rescue them into the memory compartment where the virus persists. For egress, the infected memory cells return to the lymphoepithelium where they occasionally differentiate into plasma cells activating viral replication. The released virus can either infect more naïve B cells or be amplified in the epithelium for shedding. This cycle of infection and the quiescent state in memory B cells allow for lifetime persistence at a very low level that is remarkably stable over time. Mathematically, this is a stable fixed point where the mechanisms regulating persistence drive the state back to equilibrium when perturbed. This is the GCM of EBV persistence. Other possible sites and mechanisms of persistence will also be discussed.

Human complement receptor type 1/CD35 is an Epstein-Barr Virus receptor

Epstein-Barr virus (EBV) attachment to primary B cells initiates virus entry. Although CD21 is the only known receptor for EBVgp350/220, a recent report documents EBV-infected B cells from a patient genetically deficient in CD21. On normal resting B cells, CD21 forms two membrane complexes: one with CD19 and another with CD35. Whereas the CD21/CD19 complex is widely retained on immortalized and B cell tumor lines, the related complement-regulatory protein CD35 is lost. To determine the role(s) of CD35 in initial infection, we transduced a CD21-negative pre-B cell and myeloid leukemia line with CD35, CD21, or both. Cells expressing CD35 alone bound gp350/220 and became latently infected when the fusion receptor HLA II was coexpressed. Temporal, biophysical, and structural characteristics of CD35-mediated infection were distinct from CD21. Identification of CD35 as an EBV receptor uncovers a salient role in primary infection, addresses unsettled questions of virus tropism, and underscores the importance of EBVgp350/220 for vaccine development.

Immune regulation of human herpesviruses and its implications for human transplantation

Human herpesviruses including cytomegalovirus, Epstein-Barr virus, HHV6, HHV7, HHV8, Herpes simplex virus (HSV)-1 and HSV-2 and varicella zoster virus (VZV) have developed an intricate relationship with the human immune system. This is characterized by the interplay between viral immune evasion mechanisms that promote the establishment of a lifelong persistent infection and the induction of a broad humoral and cellular immune response, which prevents the establishment of viral disease. Understanding the immune parameters that control herpesvirus infection, and the strategies the viruses use to evade immune recognition, has been critical in understanding why immunological dysfunction in transplant patients can lead to disease, and in the development of immunological strategies to prevent and control herpesvirus associated diseases.

Latent and lytic Epstein-Barr virus gene expression in the peripheral blood of astronauts

Epstein-Barr virus (EBV) latent and replicative gene transcription was analyzed in peripheral blood B-lymphocytes from astronauts who flew on short-duration (∼11 days) Shuttle missions and long-duration (∼180 days) International Space Station (ISS) missions. Latent, immediate-early, and early gene replicative viral transcripts were detected in samples from six astronauts who flew on short-duration Shuttle missions, whereas viral gene transcription was mostly absent in samples from 24 healthy donors. Samples from six astronauts who flew on long-duration ISS missions were characterized by expanded expression of latent, immediate-early, and early gene transcripts and new onset expression of late replicative transcription upon return to Earth. These data indicate that EBV-infected cells are no longer expressing the restricted set of viral genes that characterize latency but are expressing latent and lytic gene transcripts. These data also suggest the possibility of EBV-related complications in future long-duration missions, in particular interplanetary travel.

Live-cell imaging reveals multiple interactions between Epstein-Barr virus nuclear antigen 1 and cellular chromatin during interphase and mitosis

Epstein-Barr virus (EBV) establishes a life-long latent infection in humans. In proliferating latently infected cells, EBV genomes persist as multiple episomes that undergo one DNA replication event per cell cycle and remain attached to the mitotic chromosomes. EBV nuclear antigen 1 (EBNA-1) binding to the episome and cellular genome is essential to ensure proper episome replication and segregation. However, the nature and regulation of EBNA-1 interaction with chromatin has not been clearly elucidated. This activity has been suggested to involve EBNA-1 binding to DNA, duplex RNA, and/or proteins. EBNA-1 binding protein 2 (EBP2), a nucleolar protein, has been proposed to act as a docking protein for EBNA-1 on mitotic chromosomes. However, there is no direct evidence thus far for EBP2 being associated with EBNA-1 during mitosis. By combining video microscopy and Förster resonance energy transfer (FRET) microscopy, we demonstrate here for the first time that EBNA-1 and EBP2 interact in the nucleoplasm, as well as in the nucleoli during interphase. However, in strong contrast to the current proposed model, we were unable to observe any interaction between EBNA-1 and EBP2 on mitotic chromosomes. We also performed a yeast double-hybrid screening, followed by a FRET analysis, that led us to identify HMGB2 (high-mobility group box 2), a well-known chromatin component, as a new partner for EBNA-1 on chromatin during interphase and mitosis. Although the depletion of HMGB2 partly altered EBNA-1 association with chromatin in HeLa cells during interphase and mitosis, it did not significantly impact the maintenance of EBV episomes in Raji cells.

Revisiting the effect of acute P. falciparum malaria on Epstein-Barr virus: host balance in the setting of reduced malaria endemicity

Burkitt's lymphoma (BL), an EBV-associated tumour, occurs at high incidence in populations where malaria is holoendemic. Previous studies in one such population suggested that acute P.falciparum infection impairs EBV-specific T-cell surveillance, allowing expansion of EBV infected B-cells from which BL derives. We re-examined the situation in the same area, The Gambia, after a reduction in malaria endemicity. Cellular immune responses to EBV were measured in children with uncomplicated malaria before (day 0) and after treatment (day 28), comparing EBV genome loads in blood and EBV-specific CD8⁺ T-cell numbers (assayed by MHC Class I tetramers and IFNγ ELISPOTS) with those seen in age- and sex-matched healthy controls. No significant changes were seen in EBV genome loads, percentage of EBV-specific CD8⁺ T-cells and IFNγ producing T-cells in acute versus convalescent samples, nor any difference versus controls. Regression assays performed also no longer detected any impairment of EBV-specific T-cell surveillance. Acute uncomplicated malaria infection no longer alters EBV-specific immune responses in children in The Gambia. Given the recent decline in malaria incidence in that country, we hypothesise that gross disturbance of the EBV-host balance may be a specific effect of acute malaria only in children with a history of chronic/recurrent malaria challenge.

Exploiting the interplay between innate and adaptive immunity to improve immunotherapeutic strategies for Epstein-Barr-virus-driven disorders

The recent demonstration that immunotherapeutic approaches may be clinically effective for cancer patients has renewed the interest for this strategy of intervention. In particular, clinical trials using adoptive T-cell therapies disclosed encouraging results, particularly in the context of Epstein-Barr-virus- (EBV-) related tumors. Nevertheless, the rate of complete clinical responses is still limited, thus stimulating the development of more effective therapeutic protocols. Considering the relevance of innate immunity in controlling both infections and cancers, innovative immunotherapeutic approaches should take into account also this compartment to improve clinical efficacy. Evidence accumulated so far indicates that innate immunity effectors, particularly NK cells, can be exploited with therapeutic purposes and new targets have been recently identified. We herein review the complex interactions between EBV and innate immunity and summarize the therapeutic strategies involving both adaptive and innate immune system, in the light of a fruitful integration between these immunotherapeutic modalities for a better control of EBV-driven tumors.

B-cell polyclonal activation and Epstein-Barr viral abortive lytic cycle are two key features in acute infectious mononucleosis

BACKGROUND

Acute infectious mononucleosis (AIM) is generally associated with a large EBV B cell reservoir cells and an intense B-cell polyclonal activation whereas the number of quiescent EBV-infected memory B cells in chronically EBV-infected healthy controls is very low.

OBJECTIVES

To evaluate the extent and functionality of ex vivo B-cell polyclonal activation, quantify the EBV DNA integrated in B cells, enumerate the functional EBV DNA reservoir in B cells and circulating B cells spontaneously secreting EBV antigens in AIM.

STUDY DESIGN

Circulating B cells and B cells differentiating into plamablasts and plasma cells, early (BZLF1)- and late viral antigen (gp350)-secreting-cells (SCs) were enumerated in six AIM patients and seven healthy EBV carriers.

RESULTS

In vitro B-cell polyclonal activation induced 8000-24,000 BZLF1- and 1000-3000gp350-SCs/10(6) B cells, respectively. These data suggest that only 11.1-19.5% of cells expressing BZLF1 synthesized gp350 and so completed the EBV-lytic cycle. Furthermore, circulating spontaneous BZLF1- and gp350-SCs that reflect ongoing viral replication were rare (20-120 and 10-30/10(6) B cells, respectively), and their low numbers contrasted with the high levels of circulating plasma cells (1.1-10.2% of CD19(+) B cells).

CONCLUSION

The in vivo terminal-B-cell differentiation into plasma cells could unmask EBV B-cell reservoir to specific cytotoxic T-cell response and combined with a predominant abortive functional-EBV-reservoir, strongly contribute to rapid decay of cellular EBV reservoir in AIM.

Inhibition of germinal centre apoptotic programmes by epstein-barr virus

To establish a persistent latent infection, Epstein-Barr virus (EBV) faces a challenge in that the virus-infected host cell must transit through the germinal centre reaction. This is a site of B cell differentiation where antibody responses are optimised, and the selection criteria for B cells are stringent. The germinal centre environment is harsh, and the vast majority of B cells here die by apoptosis. Only cells receiving adequate survival signals will differentiate fully to be released into the periphery as long-term memory B cells (the site of persistence). In this review, we detail the apoptotic pathways potentially encountered by EBV-infected B cells during the process of infection, and we describe the functions of those EBV-regulated cellular and viral genes that help promote survival of the host B cell.

Infectious agents and lymphoma

In the past 25 years revelations on the genesis of human cancer have come at an increasing pace. Research on oncogenic infectious agents, especially viruses, has helped us to understand the process of malignant transformation of cells because the cellular events in viral-driven transformation mirror, often brilliantly, basic cellular processes that culminate in cancer, even those not associated with viruses. Infectious agents, especially viruses, account for several of the most common malignancies-up to 20% of all cancers. Some of these cancers are endemic, with a high incidence in certain geographic locations, but sporadic/lower incidence in other parts of the world. Lymphomas arise frequently in association with infectious agents such as Epstein-Barr virus, human immunodeficiency virus, human herpes virus 8, Helicobacter pylori, and hepatitis C virus. In this review, we will focus on the association between infectious agents and lymphomas, with a look at the molecular mechanisms they use to disturb cell regulation and eventually result in cancer.

Prevalence of Epstein-Barr virus in tonsils and adenoids of United Arab Emirates nationals

OBJECTIVE

Given that Epstein-Barr virus (EBV) often inhabits human tonsils and adenoids, it remains to be distinctively determined its prevalence and in which cell and microenvironment the virus is present.

METHODS

To determine the prevalence of EBV in the tonsils and adenoids of the United Arab Emirates (UAE) nationals and to provide a basis for understanding the origin and biology of EBV-infected cells, the immunophenotype of all EBV-infected cells in 46 tonsils and 46 adenoids was determined by EBER in situ hybridization and immunohistochemistry with monoclonal antibodies to T cells (CD3), B cells (CD20), and epithelial cells (cytokeratin AE1/AE3), as well as immunostaining with antibodies to EBV latent membrane protein-1 (LMP-1).

RESULTS

EBV was found in 43% of tonsillectomy specimens and 15% of adenoidectomy specimens. All EBV-infected cells were found to be B lymphocytes. About 90% of the infected B cells are found in the interfollicular regions of tonsils and adenoids and the remaining 10% are found within the follicles. There is no significant association between EBV infection, age (P=0.324) and gender (P=0.442).

CONCLUSION

EBV is associated with tonsillar hypertrophy and is prevalent in 43% of our cases. EBV is only detected in B lymphocytes and we believe that B lymphocytes are sites of primary infection and latency. In situ hybridization is the gold standard for the detection of EBV in tissue.

Latent membrane protein 1 is dispensable for Epstein-Barr virus replication in human embryonic kidney 293 cells

Epstein Barr Virus (EBV) replicates in oral epithelial cells and gains entry to B-lymphocytes. In B-lymphocytes, EBV expresses a restricted subset of genes, the Latency III program, which converts B-lymphocytes to proliferating lymphoblasts. Latent Membrane Protein 1 (LMP1) and the other Latency III associated proteins are also expressed during virus replication. LMP1 is essential for virus replication and egress from Akata Burkitt Lymphoma cells, but a role in epithelial cell replication has not been established. Therefore, we have investigated whether LMP1 enhances EBV replication and egress from HEK293 cells, a model epithelial cell line used for EBV recombinant molecular genetics. We compared wild type (wt) and LMP1-deleted (LMP1Δ) EBV bacterial artificial chromosome (BAC) based virus replication and egress from HEK293. Following EBV immediate early Zta protein induction of EBV replication in HEK293 cells, similar levels of EBV proteins were expressed in wt- and LMP1Δ-infected HEK293 cells. LMP1 deletion did not impair EBV replication associated DNA replication, DNA encapsidation, or mature virus release. Indeed, virus from LMP1Δ-infected HEK293 cells was as infectious as EBV from wt EBV infected HEK cells. Trans-complementation with LMP1 reduced Rta expression and subsequent virus production. These data indicate that LMP1 is not required for EBV replication and egress from HEK293 cells.

Effects of storage and leukoreduction on lymphocytes and Epstein-Barr virus genomes in platelet concentrates

BACKGROUND

Epstein-Barr virus (EBV) persists in infected B lymphocytes in blood donors. Lymphocytes are viable during platelet (PLT) storage. The effects of storage and leukoreduction on lymphocytes and EBV genomes are evaluated.

STUDY DESIGN AND METHODS

Forty nonleukoreduced PLT concentrates were stored at 20 to 24°C for up to 7 days. EBV genomes in B cells were quantified on Days 1 and 5. Viable white blood cells (WBCs) and T and B cells were quantified in 10 of 40 units on Days 1, 3, 5, and 7 of storage. For the leukoreduction study, four pools of PLTs were leukoreduced within 24 hours of collection. B cells from before leukoreduction and all peripheral blood mononuclear cells from after leukoreduction were assayed for EBV.

RESULTS

Viable WBCs and T cells were stable whereas viable B cells were reduced to 71% of the Day 1 level by Day 5. A total of 31 of 37 (83.8%) units were EBV positive. Although EBV genomes remained stable in most units, 12 of 37 units demonstrated a median of 5.1 (range 2- to 134)-fold increase in EBV genomes per 105 B cells on Day 5. For the leukoreduction study, EBV genomes were detected in four of four pools before leukoreduction with a median of 3.8 (range, 0.2-93.6) EBV genomes per 105 B cells. EBV genomes were not detected in any of the postleukoreduction specimens.

CONCLUSIONS

Seventy percent of B lymphocytes are viable on Day 5 of PLT storage. Although the mean number of EBV genomes remained stable, a subset of units had increased EBV genomes during storage. Leukoreduction removed polymerase chain reaction-detectable EBV genomes from PLT pools.

Insights into the evolution of lymphomas induced by Epstein-Barr virus

Epstein-Barr virus (EBV) encodes a wealth of oncogenic instructions, including the abilities to drive a resting normal B cell to proliferate and to override apoptotic stimuli. EBV is found in almost all types of lymphomas at varying frequencies. However, the particular viral genes expressed differ considerably among tumors. We have examined the role of EBV in several lymphomas by conditionally evicting the extrachromosomal viral genome from tumor cells in vitro and have found a graded dependence on the virus. Tumor cells that express all the known latent viral genes have been found to depend on the virus to drive proliferation and to block apoptosis at least in part by repressing the proapoptotic protein Bim. Other tumor cells, which express fewer viral genes, also depend on the virus to block apoptosis, but rely on the virus to promote but not to drive proliferation. Lastly, tumor cells with the fewest viral genes expressed have been found to require EBV to prevent the inefficient induction of a Bim-independent apoptosis. We present a model for the evolution of EBV-induced lymphomas in which tumors are initially "addicted" to the virus for almost all oncogenic functions. These tumors are targets for the immune system because they express multiple immunogenic viral proteins. Therefore, EBV-induced tumors are under selective pressure to acquire cellular mutations that can replace viral functions. We posit that the heterogeneity in viral gene expression among different EBV-associated lymphomas reflects a dynamic process by which tumors evolve to be less dependent on the virus.

Epstein-Barr virus infection and chronic lymphocytic leukemia: a possible progression factor?

Epstein-Barr virus is pathogenically associated with a well defined group of lymphoid and epithelial tumors in which the virus directly drives transformation of infected cells. Recent evidence however indicates that this virus may infect a subpopulation of tumor cells in patients with chronic lymphocytic leukemia (CLL) and EBV infection has been also associated with Richter transformation in a fraction of cases. We herein review available data suggesting a possible role of EBV as a direct or micro-environmental progression factor in a subset of CLL.

Lymphomas differ in their dependence on Epstein-Barr virus

Epstein-Barr virus (EBV) encodes oncogenic information and, oftentimes concomitant with host immunosuppression, gives rise to malignancies in all major categories of lymphoma defined by the World Health Organization. Here, we conditionally evicted the viral extrachromosomal genome from tumor cells in vitro to examine the role of EBV in different lymphomas, including Burkitt lymphoma (BL) and posttransplant lymphoproliferative disorder. Cells derived from 2 canonical BLs were found to have the least dependence on the virus; some required EBV to prevent the inefficient induction of apoptosis. In contrast, cells derived from a subset of BL, Wp-restricted BL, required EBV to block a robust apoptotic program that involves the up-regulation of the proapoptotic protein Bim. Wp-restricted BL cells also relied on the virus to promote efficient proliferation, a distinction that highlights the multiple contributions EBV makes to affect proliferation of its host cells. Like Wp-BL cells, posttransplant lymphoproliferative disorder cells depended on the virus to inhibit apoptosis. They furthermore required the virus to drive them out of G(1)/G(0). Together, these results reveal a graded dependence on EBV among tumor cells that directly correlates with the number of viral genes expressed in the tumor cell.