Epstein-barr virus nuclear antigen 1 sequences in endemic and sporadic Burkitt's lymphoma reflect virus strains prevalent in different geographic areas

Sequence variation of the Epstein-Barr virus nuclear antigen 1 (EBNA1) gene in chronic lymphocytic leukemia and healthy volunteer subjects

Epstein-Barr virus-related malignancies have been linked to variations in the sequences of EBV genes, notably EBNA1. Therefore, the purpose of this study was to examine the DBD/DD domain and USP7 binding domain sequences at the C-terminus of the EBNA1 gene in patients with chronic lymphocytic leukemia (CLL). This study included 40 CLL patients and 21 healthy volunteers. Using commercial kits, total DNA was extracted from buffy coat samples, and each sample was tested for the presence of the EBV genome. The C-terminus of EBNA1 was then amplified from positive samples, using nested PCR. Sanger sequencing was used to identify mutations in the PCR products, and the results were analyzed using MEGA11 software. The mean ages of CLL patients and healthy individuals were 61.07 ± 10.2 and 59.08 ± 10.3, respectively. In the EBNA-1 amplicons from CLL patients and healthy individuals, 38.5% and 16.7%, respectively, harbored mutations in the DBD/DD domain of the C-terminal region of the EBNA1 gene (P = 0.378). The mutation frequency at locus 97,320 was significantly higher in CLL patients than in healthy individuals (P = 0.039). Three EBV subtypes based on residue 487 were detected. The frequency of alanine, threonine, and valine in both groups was 88, 8, and 4 percent, respectively (P = 0.207). Moreover, all of the isolates from healthy donors had alanine at this position. The findings indicated that the presence of threonine or valine at residue 487 as well as a synonymous substitution at residue 553 in the C-terminal region of EBNA1 might be involved in the pathogenesis of EBV in CLL patients.

Unstable EBV latency drives inflammation in multiple sclerosis patient derived spontaneous B cells

Epidemiological studies have demonstrated that Epstein-Barr virus (EBV) is a known etiologic risk factor, and perhaps prerequisite, for the development of MS. EBV establishes life-long latent infection in a subpopulation of memory B cells. Although the role of memory B cells in the pathobiology of MS is well established, studies characterizing EBV-associated mechanisms of B cell inflammation and disease pathogenesis in EBV (+) B cells from MS patients are limited. Accordingly, we analyzed spontaneous lymphoblastoid cell lines (SLCLs) from multiple sclerosis patients and healthy controls to study host-virus interactions in B cells, in the context of an individual's endogenous EBV. We identify differences in EBV gene expression and regulation of both viral and cellular genes in SLCLs. Our data suggest that EBV latency is dysregulated in MS SLCLs with increased lytic gene expression observed in MS patient B cells, especially those generated from samples obtained during "active" disease. Moreover, we show increased inflammatory gene expression and cytokine production in MS patient SLCLs and demonstrate that tenofovir alafenamide, an antiviral that targets EBV replication, decreases EBV viral loads, EBV lytic gene expression, and EBV-mediated inflammation in both SLCLs and in a mixed lymphocyte assay. Collectively, these data suggest that dysregulation of EBV latency in MS drives a pro-inflammatory, pathogenic phenotype in memory B cells and that this response can be attenuated by suppressing EBV lytic activation. This study provides further support for the development of antiviral agents that target EBV-infection for use in MS.

Epstein-Barr virus latency programs dynamically sensitize B cells to ferroptosis

Epstein–Barr virus (EBV) contributes to Burkitt lymphoma and post-transplant lymphoproliferative disease (PTLD). EBV-transforming programs activate lipid metabolism to convert B cells into immortalized lymphoblastoid cell lines (LCL), a PTLD model. We found that stages of EBV transformation generate lipid reactive oxygen species (ROS) byproducts to varying degrees, and that a Burkitt-like phase of B cell outgrowth requires lipid ROS detoxification by glutathione peroxidase 4 and its cofactor glutathione. Perturbation of this redox defense in early stages of transformation or in Burkitt cells triggered ferroptosis, a programmed cell death pathway. LCLs were less dependent on this defense, a distinction tied to EBV latency programs. This highlights ferroptosis induction as a potential therapeutic approach for prevention or treatment of certain EBV+ lymphomas.

Epstein–Barr virus (EBV) causes 200,000 cancers annually. Upon B cell infection, EBV induces lipid metabolism to support B cell proliferation. Yet, little is known about how latent EBV infection, or human B cell stimulation more generally, alter sensitivity to ferroptosis, a nonapoptotic form of programmed cell death driven by iron-dependent lipid peroxidation and membrane damage. To gain insights, we analyzed lipid reactive oxygen species (ROS) levels and ferroptosis vulnerability in primary human CD19+ B cells infected by EBV or stimulated by key B cell receptors. Prior to the first mitosis, EBV-infected cells were exquisitely sensitive to blockade of glutathione biosynthesis, a phenomenon not observed with B cell receptor stimulation. Subsequently, EBV-mediated Burkitt-like hyperproliferation generated elevated levels of lipid ROS, which necessitated SLC7A11-mediated cystine import and glutathione peroxidase 4 (GPX4) activity to prevent ferroptosis. By comparison, B cells were sensitized to ferroptosis induction by combinatorial CD40-ligand and interleukin-4 stimulation or anti–B cell receptor and Toll-like receptor 9 stimulation upon GPX4 inhibition but not with SLC7A11 blockade. EBV transforming B cells became progressively resistant to ferroptosis induction upon switching to the latency III program and lymphoblastoid physiology. Similarly, latency I Burkitt cells were particularly vulnerable to blockade of SLC7A11 or GPX4 or cystine withdrawal, while latency III Burkitt and lymphoblastoid cells were comparatively resistant. The selenocysteine biosynthesis kinase PSTK was newly implicated as a cellular target for ferroptosis induction including in Burkitt cells, likely due to roles in GPX4 biosynthesis. These results highlight ferroptosis as an intriguing therapeutic target for the prevention or treatment of particular EBV-driven B cell malignancies.

EBV Genome Mutations and Malignant Proliferations

The Epstein-Barr virus (EBV) is a DNA virus with a relatively stable genome. Indeed, genomic variability is reported to be around 0.002%. However, some regions are more variable such as those carrying latency genes and specially EBNA1, -2, -LP, and LMP1. Tegument genes, particularly BNRF1, BPLF1, and BKRF3, are also quite mutated. For a long time, it has been considered for this ubiquitous virus, which infects a very large part of the population, that particular strains could be the cause of certain diseases. However, the mutations found, in some cases, are more geographically restricted rather than associated with proliferation. In other cases, they appear to be involved in oncogenesis. The objective of this chapter is to provide an update on changes in viral genome sequences in malignancies associated with EBV. We focused on describing the structure and function of the proteins corresponding to the genes mentioned above in order to understand how certain mutations of these proteins could increase the tumorigenic character of this virus. Mutations described in the literature for these proteins were identified by reporting viral and/or cellular functional changes as they were described.

Reframing Burkitt lymphoma: virology not epidemiology defines clinical variants

In 1964, Epstein-Barr virus (EBV) was identified in a biopsy from a patient with Burkitt lymphoma (BL) launching a new field of study into this ubiquitous human virus. Almost 60 years later, insights into the role of EBV in lymphomagenesis are still emerging. While all BL carry the hallmark c-myc translocation, the epidemiologic classification of BL (e.g., endemic, sporadic or immunodeficiency-associated) has traditionally been used to define BL clinical variants. However, recent studies using molecular methods to characterize the transcriptional and genetic landscape of BL have identified several unique features are observed that distinguish EBV+ BL including a high level of activation induced deaminase mutation load, evidence of antigen selection in the B cell receptor, and a decreased mutation frequency of TCF3/ID3, all found predominantly in EBV+ compared to EBV- BL. In this review, the focus will be on summarizing recent studies that have done in depth characterization of genetic and transcriptional profiles of BL, describing the differences and similarities of EBV+ and EBV- BL, and what they reveal about the etiology of BL. The new studies put forth a compelling argument that the association with EBV should be the defining etiologic feature of clinical variants of BL. This reframing of BL has important implications for therapeutic interventions for BL that distinguish the EBV+ from the EBV- lymphomas.

Epstein-Barr virus molecular epidemiology and variants identification in head and neck squamous cell carcinoma

Epstein-Barr virus (EBV) is known as one of the most widespread oncogenic viruses. Head and neck squamous cell carcinoma (HNSCC) is triggered by various risk factors. The aim of the present study was to determine the EBV infection rate, genotyping and variants frequency in HNSCC patients. In this cross-sectional study, 156 patients with HNSCC were enrolled. Formalin fixed paraffin embedded (FFPE) tissue samples were selected from hospitals affiliated to Iran University of Medical Sciences, Tehran, Iran. The EBV EBNA-3C, EBNA-1 and LMP-1 genes were amplified by PCR and then analyzed and confirmed by nucleotide sequencing. CLC work bench 5, MEGA6 and SPSS v.21 software were used for analysis the raw data. The mean age ± SD (years) of the all patients (n = 156) was 60.5 ± 12.6, in which of 121(77.6%) males it was 60.7 ± 11.9 and of 35 (22.4%) females it was 59.7 ± 14.9. Totally, 20 samples (12.8%) were found to be infected with EBV genome. The EBV genotypes 1 and 2 were calculated 90% (18/20) and 10% (2/20), respectively. vLMP-1 found in 40% (4/10) of all LMP-1 tested samples. Furthermore, the EBNA-1 predominant variants were P-ala followed by P-thr and also there were three P-ala-v2 sub variants. Statistics could not find any significant associations although there were some potentials. By our preliminary study in Iran, it revealed that EBV-1 is the predominant Epstein-Barr virus genotype in head and neck squamous cell carcinoma patients. vLMP-1 isolates showed lower survival rate than others. EBNA-1 variants had no significant association with any specific disease complication.

A reliable Epstein-Barr Virus classification based on phylogenomic and population analyses

The Epstein-Barr virus (EBV) infects more than 90% of the human population, playing a key role in the origin and progression of malignant and non-malignant diseases. Many attempts have been made to classify EBV according to clinical or epidemiological information; however, these classifications show frequent incongruences. For instance, they use a small subset of genes for sorting strains but fail to consider the enormous genomic variability and abundant recombinant regions present in the EBV genome. These could lead to diversity overestimation, alter the tree topology and misinterpret viral types when classified, therefore, a reliable EBV phylogenetic classification is needed to minimize recombination signals. Recombination events occur 2.5-times more often than mutation events, suggesting that recombination has a much stronger impact than mutation in EBV genomic diversity, detected within common ancestral node positions. The Hierarchical Bayesian Analysis of Population Structure (hierBAPS) resulted in the differentiation of 12 EBV populations showed seven monophyletic and five paraphyletic. The populations identified were related to geographic location, of which three populations (EBV-p1/Asia/GC, EBV-p2/Asia II/Tumors and EBV-p4/China/NPC) were related to tumor development. Therefore, we proposed a new consistent and non-simplistic EBV classification, beneficial in minimizing the recombination signal in the phylogeny reconstruction, investigating geography relationship and even infer associations to human diseases. These EBV classifications could also be useful in developing diagnostic applications or defining which strains need epidemiological surveillance.

Sequence Variation of Epstein-Barr Virus: Viral Types, Geography, Codon Usage, and Diseases

Epstein-Barr virus causes most cases of infectious mononucleosis and posttransplant lymphoproliferative disease. It contributes to several types of cancer, including Hodgkin's lymphoma, Burkitt's lymphoma, diffuse large B cell lymphoma, nasopharyngeal carcinoma, and gastric carcinoma. EBV genome variation is important because some of the diseases associated with EBV have very different incidences in different populations and geographic regions, and differences in the EBV genome might contribute to these diseases. Some specific EBV genome alterations that appear to be significant in EBV-associated cancers are already known, and current efforts to make an EBV vaccine and antiviral drugs should also take account of sequence differences in the proteins used as targets.

One hundred thirty-eight new Epstein-Barr virus (EBV) genome sequences have been determined. One hundred twenty-five of these and 116 from previous reports were combined to produce a multiple-sequence alignment of 241 EBV genomes, which we have used to analyze variation within the viral genome. The type 1/type 2 classification of EBV remains the major form of variation and is defined mostly by EBNA2 and EBNA3, but the type 2 single-nucleotide polymorphisms (SNPs) at the EBNA3 locus extend into the adjacent gp350 and gp42 genes, whose products mediate infection of B cells by EBV. A small insertion within the BART microRNA region of the genome was present in 21 EBV strains. EBV from saliva of U.S. patients with chronic active EBV infection aligned with the wild-type EBV genome with no evidence of WZhet rearrangements. The V3 polymorphism in the Zp promoter for BZLF1 was found to be frequent in nasopharyngeal carcinoma cases from both Hong Kong and Indonesia. Codon usage was found to differ between latent and lytic cycle EBV genes, and the main forms of variation of the EBNA1 protein have been identified.

IMPORTANCE Epstein-Barr virus causes most cases of infectious mononucleosis and posttransplant lymphoproliferative disease. It contributes to several types of cancer, including Hodgkin's lymphoma, Burkitt's lymphoma, diffuse large B cell lymphoma, nasopharyngeal carcinoma, and gastric carcinoma. EBV genome variation is important because some of the diseases associated with EBV have very different incidences in different populations and geographic regions, and differences in the EBV genome might contribute to these diseases. Some specific EBV genome alterations that appear to be significant in EBV-associated cancers are already known, and current efforts to make an EBV vaccine and antiviral drugs should also take account of sequence differences in the proteins used as targets.

EBNA1: Oncogenic Activity, Immune Evasion and Biochemical Functions Provide Targets for Novel Therapeutic Strategies against Epstein-Barr Virus- Associated Cancers

The presence of the Epstein-Barr virus (EBV)-encoded nuclear antigen-1 (EBNA1) protein in all EBV-carrying tumours constitutes a marker that distinguishes the virus-associated cancer cells from normal cells and thereby offers opportunities for targeted therapeutic intervention. EBNA1 is essential for viral genome maintenance and also for controlling viral gene expression and without EBNA1, the virus cannot persist. EBNA1 itself has been linked to cell transformation but the underlying mechanism of its oncogenic activity has been unclear. However, recent data are starting to shed light on its growth-promoting pathways, suggesting that targeting EBNA1 can have a direct growth suppressing effect. In order to carry out its tasks, EBNA1 interacts with cellular factors and these interactions are potential therapeutic targets, where the aim would be to cripple the virus and thereby rid the tumour cells of any oncogenic activity related to the virus. Another strategy to target EBNA1 is to interfere with its expression. Controlling the rate of EBNA1 synthesis is critical for the virus to maintain a sufficient level to support viral functions, while at the same time, restricting expression is equally important to prevent the immune system from detecting and destroying EBNA1-positive cells. To achieve this balance EBNA1 has evolved a unique repeat sequence of glycines and alanines that controls its own rate of mRNA translation. As the underlying molecular mechanisms for how this repeat suppresses its own rate of synthesis in cis are starting to be better understood, new therapeutic strategies are emerging that aim to modulate the translation of the EBNA1 mRNA. If translation is induced, it could increase the amount of EBNA1-derived antigenic peptides that are presented to the major histocompatibility (MHC) class I pathway and thus, make EBV-carrying cancers better targets for the immune system. If translation is further suppressed, this would provide another means to cripple the virus.

Carcinoma-risk variant of EBNA1 deregulates Epstein-Barr Virus episomal latency

Epstein-Barr Virus (EBV) latent infection is a causative co-factor for endemic Nasopharyngeal Carcinoma (NPC). NPC-associated variants have been identified in EBV-encoded nuclear antigen EBNA1. Here, we solve the X-ray crystal structure of an NPC-derived EBNA1 DNA binding domain (DBD) and show that variant amino acids are found on the surface away from the DNA binding interface. We show that NPC-derived EBNA1 is compromised for DNA replication and episome maintenance functions. Recombinant virus containing the NPC EBNA1 DBD are impaired in their ability to immortalize primary B-lymphocytes and suppress lytic transcription during early stages of B-cell infection. We identify Survivin as a host protein deficiently bound by the NPC variant of EBNA1 and show that Survivin depletion compromises EBV episome maintenance in multiple cell types. We propose that endemic variants of EBNA1 play a significant role in EBV-driven carcinogenesis by altering key regulatory interactions that destabilize latent infection.

Genome-wide analysis of Epstein-Barr virus (EBV) isolated from EBV-associated gastric carcinoma (EBVaGC)

Epstein-Barr virus (EBV) is linked to the development of a variety of malignancies, including EBV-associated gastric carcinoma (EBVaGC). In this study, EBVaGC was detected in 15 (7.3%) of 206 GC cases. To identify the EBV genomic variation, EBV genomic sequences isolated from 9 EBVaGC biopsy specimens were successfully retrieved, designated EBVaGC1 to EBVaGC9. By comparative analysis of these strains with another 6 completely sequenced EBV strains, EBV-wild type, B95–8, AG876, GD1, GD2, and HKNPC1, it was demonstrated that EBVaGC1 to 9 were most closely related to the GD1 strain. Phylogenetic analysis of the GC biopsy specimen-derived EBV (GC-EBV) genomes was subsequently performed to assess their genomic diversity and it exhibited the greatest divergence from the type 2 strain, AG876. Compared with the reference EBV strain GD1, they harbored 961 variations in total, including 919 substitutions, 23 insertions, and 19 deletions. Single nucleotide polymorphism (SNP) density varied substantially across all known open reading frames and was highest in latency-associated genes. Moreover, we identified 2 interstrain recombinants at the EBNA1 locus, which provided a further mechanism for the generation of diversity. Some T-cell epitope sequences in EBNA1 and LMP2A genes showed extensive variation across strains, which implied their importance in the development of vaccines and T-cell therapy. In conclusion, we reported the first genome-wide view of sequence variation of EBV isolated from primary EBVaGC biopsy specimens, which might serve as an effective method for further understanding the genomic variations contribute to EBVaGC carcinogenesis and treatment.

Identifying Patient-Specific Epstein-Barr Nuclear Antigen-1 Genetic Variation and Potential Autoreactive Targets Relevant to Multiple Sclerosis Pathogenesis

Background

Epstein-Barr virus (EBV) infection represents a major environmental risk factor for multiple sclerosis (MS), with evidence of selective expansion of Epstein-Barr Nuclear Antigen-1 (EBNA1)-specific CD4+ T cells that cross-recognize MS-associated myelin antigens in MS patients. HLA-DRB1*15-restricted antigen presentation also appears to determine susceptibility given its role as a dominant risk allele. In this study, we have utilised standard and next-generation sequencing techniques to investigate EBNA-1 sequence variation and its relationship to HLA-DR15 binding affinity, as well as examining potential cross-reactive immune targets within the central nervous system proteome.

Methods

Sanger sequencing was performed on DNA isolated from peripheral blood samples from 73 Western Australian MS cases, without requirement for primary culture, with additional FLX 454 Roche sequencing in 23 samples to identify low-frequency variants. Patient-derived viral sequences were used to predict HLA-DRB1*1501 epitopes (NetMHCII, NetMHCIIpan) and candidates were evaluated for cross recognition with human brain proteins.

Results

EBNA-1 sequence variation was limited, with no evidence of multiple viral strains and only low levels of variation identified by FLX technology (8.3% nucleotide positions at a 1% cut-off). In silico epitope mapping revealed two known HLA-DRB1*1501-restricted epitopes (‘AEG’: aa 481–496 and ‘MVF’: aa 562–577), and two putative epitopes between positions 502–543. We identified potential cross-reactive targets involving a number of major myelin antigens including experimentally confirmed HLA-DRB1*15-restricted epitopes as well as novel candidate antigens within myelin and paranodal assembly proteins that may be relevant to MS pathogenesis.

Conclusions

This study demonstrates the feasibility of obtaining autologous EBNA-1 sequences directly from buffy coat samples, and confirms divergence of these sequences from standard laboratory strains. This approach has identified a number of immunogenic regions of EBNA-1 as well as known and novel targets for autoreactive HLA-DRB1*15-restricted T cells within the central nervous system that could arise as a result of cross-reactivity with EBNA-1-specific immune responses.

Sequence Variation Analysis of Epstein-Barr Virus Nuclear Antigen 1 Gene in the Virus Associated Lymphomas of Northern China

Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is the only viral protein expressed in all EBV-positive tumors as it is essential for the maintenance, replication and transcription of the virus genome. According to the polymorphism of residue 487 in EBNA1 gene, EBV isolates can be classified into five subtypes: P-ala, P-thr, V-val, V-leu and V-pro. Whether these EBNA1 subtypes contribute to different tissue tropism of EBV and are consequently associated with certain malignancies remain to be determined. To elucidate the relationship, one hundred and ten EBV-positive lymphoma tissues of different types from Northern China, a non-NPC endemic area, were tested for the five subtypes by nested-PCR and DNA sequencing. In addition, EBV type 1 and type 2 classification was typed by using standard PCR assays across type-specific regions of the EBNA3C genes. Four EBNA1 subtypes were identified: V-val (68.2%, 75/110), P-thrV (15.5%, 17/110), V-leuV (3.6%, 4/110) and P-ala (10.9%, 12/110). The distribution of the EBNA1 subtypes in the four lymphoma groups was not significantly different (p = 0.075), neither was that of the EBV type 1/type 2 (p = 0.089). Compared with the previous data of gastric carcinoma (GC), nasopharyngeal carcinoma (NPC) and throat washing (TW) from healthy donors, the distribution of EBNA1 subtypes in lymphoma differed significantly (p = 0.016), with a little higher frequency of P-ala subtype. The EBV type distribution between lymphoma and the other three groups was significantly different (p = 0.000, p = 0.000, p = 0.001, respectively). The proportion of type 1 and type 2 mixed infections was higher in lymphoma than that in GC, NPC and TW. In lymphomas, the distribution of EBNA1 subtypes in the three EBV types was not significantly different (p = 0.546). These data suggested that the variation patterns of EBNA1 gene may be geographic-associated rather than tumor-specific and the role of EBNA1 gene variations in tumorigenesis needs more extensive and deep explorations.

Detection of nasopharyngeal carcinoma in Morocco (North Africa) using a multiplex methylation-specific PCR biomarker assay

Background

Silencing of tumor suppressor genes (TSGs) or activation of oncogenes by, e.g., aberrant promoter methylation, may be early events during carcinogenesis. The methylation status of such genes can be used for early detection of cancer. We are pursuing this approach in our efforts to develop markers for early detection and follow-up of nasopharyngeal carcinoma (NPC). We set out to develop this approach to allow identification of NPC from Morocco and then also compared with NPC samples from different geographical locations and different ethnicity with different NPC incidences, Epstein-Barr virus (EBV) prevalence, and environments.

Results

By multiplex methylation-specific PCR (MMSP), multiple relevant genes can be detected simultaneously, to achieve high sensitivity and specificity. The strong association of EBV with NPC is also very useful in such an approach. We have initially screened for 12 potential marker genes including EBV genes coding for EBV nuclear antigen 1 (EBNA1) and latent membrane protein-1 (LMP1) and ten potential TSGs obtained from previously published data. The resulting assay included EBNA1, LMP1, and three cellular TSGs: ITGA9, RASSF1A, and P16. We evaluated this assay on 64 NPC patient biopsies from Morocco, Italy, and China compared to deoxyribonucleic acid (DNA) from 20 nasopharyngeal control tissues. In the Moroccan NPC cohort (n = 44), prevalence of the EBNA1 gene showed the highest sensitivity (36/44; 82 %) with 94 % specificity. Out of eight (18 %) EBNA1 negative Moroccan samples, only three were positive for at least one methylated cellular gene. By detection of cellular marker genes, the sensitivity increased from 82 to 89 % (39/44). In the whole material of 64 biopsies from three geographical locations, at least any one marker (viral or cellular) could be detected in 91 % of biopsies with 90 % specificity. In a pilot evaluating assay performance on serum DNA from NPC and controls including samples from Italy (n = 11) and China (n = 5), at least any one marker from the MMSP assay could be detected in 88 %, but the specificity was only 50 %.

Conclusions

An MMSP assay has the potential for detection of NPC by screening in high-risk populations. Serum-derived DNA seems not as good as earlier published NPC swab DNA for screening purpose.

Epstein-Barr virus genetic variation in lymphoblastoid cell lines derived from Kenyan pediatric population

Epstein-Barr virus (EBV) is associated with Burkitt’s lymphoma (BL), and in regions of sub-Saharan Africa where endemic BL is common, both the EBV Type 1 (EBV-1) and EBV Type 2 strains (EBV-2) are found. Little is known about genetic variation of EBV strains in areas of sub-Saharan Africa. In the present study, spontaneous lymphoblastoid cell lines (LCLs) were generated from samples obtained from Kenya. Polymerase chain reaction (PCR) amplification of the EBV genome was done using multiple primers and sequenced by next-generation sequencing (NGS). Phylogenetic analyses against the published EBV-1 and EBV-2 strains indicated that one sample, LCL10 was closely related to EBV-2, while the remaining 3 LCL samples were more closely related to EBV-1. Moreover, single nucleotide polymorphism (SNP) analyses showed clustering of LCL variants. We further show by analysis of EBNA-1, BLLF1, BPLF1, and BRRF2 that latent genes are less conserved than lytic genes in these LCLs from a single geographic region. In this study we have shown that NGS is highly useful for deciphering detailed inter and intra-variations in EBV genomes and that within a geographic region different EBV genetic variations can co-exist, the implications of which warrant further investigation. The findings will enhance our understanding of potential pathogenic variants critical to the development and maintenance of EBV-associated malignancies.

Genome-wide analysis of wild-type Epstein-Barr virus genomes derived from healthy individuals of the 1,000 Genomes Project

Most people in the world (∼90%) are infected by the Epstein–Barr virus (EBV), which establishes itself permanently in B cells. Infection by EBV is related to a number of diseases including infectious mononucleosis, multiple sclerosis, and different types of cancer. So far, only seven complete EBV strains have been described, all of them coming from donors presenting EBV-related diseases. To perform a detailed comparative genomic analysis of EBV including, for the first time, EBV strains derived from healthy individuals, we reconstructed EBV sequences infecting lymphoblastoid cell lines (LCLs) from the 1000 Genomes Project. As strain B95-8 was used to transform B cells to obtain LCLs, it is always present, but a specific deletion in its genome sets it apart from natural EBV strains. After studying hundreds of individuals, we determined the presence of natural EBV in at least 10 of them and obtained a set of variants specific to wild-type EBV. By mapping the natural EBV reads into the EBV reference genome (NC007605), we constructed nearly complete wild-type viral genomes from three individuals. Adding them to the five disease-derived EBV genomic sequences available in the literature, we performed an in-depth comparative genomic analysis. We found that latency genes harbor more nucleotide diversity than lytic genes and that six out of nine latency-related genes, as well as other genes involved in viral attachment and entry into host cells, packaging, and the capsid, present the molecular signature of accelerated protein evolution rates, suggesting rapid host–parasite coevolution.

Epstein-Barr Virus: From the Detection of Sequence Polymorphisms to the Recognition of Viral Types

The Epstein-Barr virus is etiologically linked with the development of benign and malignant diseases, characterized by their diversity and a heterogeneous geographic distribution across the world. The virus possesses a 170-kb-large genome that encodes for multiple proteins and non-coding RNAs. Early on there have been numerous attempts to link particular diseases with particular EBV strains, or at least with viral genetic polymorphisms. This has given rise to a wealth of information whose value has been difficult to evaluate for at least four reasons. First, most studies have looked only at one particular gene and missed the global picture. Second, they usually have not studied sufficient numbers of diseased and control cases to reach robust statistical significance. Third, the functional significance of most polymorphisms has remained unclear, although there are exceptions such as the 30-bp deletion in LMP1. Fourth, different biological properties of the virus do not necessarily equate with a different pathogenicity. This was best illustrated by the type 1 and type 2 viruses that markedly differ in terms of their transformation abilities, yet do not seem to cause different diseases. Reciprocally, environmental and genetic factors in the host are likely to influence the outcome of infections with the same virus type. However, with recent developments in recombinant virus technology and in the availability of high throughput sequencing, the tide is now turning. The availability of 23 complete or nearly complete genomes has led to the recognition of viral subtypes, some of which possess nearly identical genotypes. Furthermore, there is growing evidence that some genetic polymorphisms among EBV strains markedly influence the biological and clinical behavior of the virus. Some virus strains are endowed with biological properties that explain crucial clinical features of patients with EBV-associated diseases. Although we now have a better overview of the genetic diversity within EBV genomes, it has also become clear that defining phenotypic traits evinced by cells infected by different viruses usually result from the combination of multiple polymorphisms that will be difficult to identify in their entirety. However, the steadily increasing number of sequenced EBV genomes and cloned EBV BACS from diseased and healthy patients will facilitate the identification of the key polymorphisms that condition the biological and clinical behavior of the viruses. This will allow the development of preventative and therapeutic approaches against highly pathogenic viral strains.

Epstein-Barr Virus Strain Variation

What is wild-type Epstein-Barr virus and are there genetic differences in EBV strains that contribute to some of the EBV-associated diseases? Recent progress in DNA sequencing has resulted in many new Epstein-Barr virus (EBV) genome sequences becoming available. EBV isolates worldwide can be grouped into type 1 and type 2, a classification based on the EBNA2 gene sequence. Type 1 transforms human B cells into lymphoblastoid cell lines much more efficiently than type 2 EBV and molecular mechanisms that may account for this difference in cell transformation are now becoming understood. Study of geographic variation of EBV strains independent of the type 1/type 2 classification and systematic investigation of the relationship between viral strains, infection and disease are now becoming possible. So we should consider more directly whether viral sequence variation might play a role in the incidence of some EBV-associated diseases.

Unexpected patterns of Epstein-Barr virus transcription revealed by a high throughput PCR array for absolute quantification of viral mRNA

We have validated a flexible, high-throughput and relatively inexpensive RT-QPCR array platform for absolute quantification of Epstein-Barr virus transcripts in different latent and lytic infection states. Several novel observations are reported. First, during infection of normal B cells, Wp-initiated latent gene transcripts remain far more abundant following activation of the Cp promoter than was hitherto suspected. Second, EBNA1 transcript levels are remarkably low in all forms of latency, typically ranging from 1 to 10 transcripts per cell. EBNA3A, -3B and -3C transcripts are likewise very low in Latency III, typically at levels similar to or less than EBNA1 transcripts. Thirdly, a subset of lytic gene transcripts is detectable in Burkitt lymphoma lines at low levels, including: BILF1, which has oncogenic properties, and the poorly characterized LF1, LF2 and LF3 genes. Analysis of seven African BL biopsies confirmed this transcription profile but additionally revealed significant expression of LMP2 transcripts.

The V-val subtype Epstein-Barr virus nuclear antigen 1 promotes cell survival after serum withdrawal

Epstein-Barr virus (EBV) can establish latent infection and has been associated with various human cancers. Epstein-Barr nuclear antigen 1 (EBNA1) is the only viral protein that is expressed in all EBV-associated malignant tissues. The N- and C-terminal domains of EBNA1, which are connected by internal glycine/alanine-rich short repeat sequences of various sizes, show sequence divergence across EBV strains isolated from around the world. At least five subtypes have been described, according to the amino acid at residue 487: P-ala, P-thr, V-val, V-pro, and V-leu. Whether the variations of EBNA-1 contribute to the pathogenesis of EBV or simply reflect the geographical distribution of EBV remain to be investigated. Furthermore, the cell effects conferred by EBNA1 subtypes that differ from that of the B95.8 prototype, which belongs to the P-ala subtype, remain to be elucidated. In this study, PCR was amplified with the full-length V-val EBNA1 gene from the CG3 cell line, an EBV-carrying lymphoblastoid cell line derived from a Taiwanese chronic myeloid leukemia patient. Plasmids expressing His-tagged EBNA1 fusion proteins in E. coli were constructed and used to raise antibodies in rabbit. The V-val EBNA1 gene was then cloned into a eukaryotic expression vector and successfully expressed in the transfected cultured cells. Expression of V-val EBNA1 rendered 293 cells able to undergo serum‑independent cell proliferation, providing them with anti-apoptotic abilities, which are two characteristics of cancer cells. These data suggested that use of EBNA1 originally derived from tumor cells, rather than the more commonly utilized prototype, when investigating the potential role of EBNA1 in the oncogenesis of EBV-associated malignancies, is crucial.

Epstein-Barr virus utilizes Ikaros in regulating its latent-lytic switch in B cells

Ikaros is a zinc finger DNA-binding protein that regulates chromatin remodeling and the expression of genes involved in the cell cycle, apoptosis, and Notch signaling. It is a master regulator of lymphocyte differentiation and functions as a tumor suppressor in acute lymphoblastic leukemia. Nevertheless, no previous reports described effects of Ikaros on the life cycle of any human lymphotropic virus. Here, we demonstrate that full-length Ikaros (IK-1) functions as a major factor in the maintenance of viral latency in Epstein-Barr virus (EBV)-positive Burkitt's lymphoma Sal and MutuI cell lines. Either silencing of Ikaros expression by small hairpin RNA (shRNA) knockdown or ectopic expression of a non-DNA-binding isoform induced lytic gene expression. These effects synergized with other lytic inducers of EBV, including transforming growth factor β (TGF-β) and the hypoxia mimic desferrioxamine. Data from chromatin immunoprecipitation (ChIP)-quantitative PCR (qPCR) and ChIP-sequencing (ChIP-seq) analyses indicated that Ikaros did not bind to either of the EBV immediate early genes BZLF1 and BRLF1. Rather, Ikaros affected the expression of Oct-2 and Bcl-6, other transcription factors that directly inhibit EBV reactivation and plasma cell differentiation, respectively. IK-1 also complexed with the EBV immediate early R protein in coimmunoprecipitation assays and partially colocalized with R within cells. The presence of R alleviated IK-1-mediated transcriptional repression, with IK-1 then cooperating with Z and R to enhance lytic gene expression. Thus, we conclude that Ikaros plays distinct roles at different stages of EBV's life cycle: it contributes to maintaining latency via indirect mechanisms, and it may also synergize with Z and R to enhance lytic replication through direct association with R and/or R-induced alterations in Ikaros' functional activities via cellular signaling pathways.

IMPORTANCE

This is the first report showing that the cellular protein Ikaros, a known master regulator of hematopoiesis and critical tumor suppressor in acute lymphoblastic leukemia, also plays important roles in the life cycle of Epstein-Barr virus in B cells.

Identification of a novel variant of LMP-1 of EBV in patients with endemic Burkitt lymphoma in western Kenya

Background

Epstein Barr virus (EBV) is a gammaherpesvirus that is associated with nasopharyngeal carcinoma (NPC) and endemic Burkitt lymphoma (eBL). EBV carries several latent genes that contribute to oncogenesis including the latent membrane protein 1 (LMP-1), a known oncogene and constitutively active CD40 homolog. Variation in the C terminal region of LMP-1 has been linked to NPC pathogenesis, but little is known regarding LMP-1 variation and eBL.

Results

In the present study, peripheral blood samples were obtained from 38 eBL patients and 22 healthy controls in western Kenya, where the disease is endemic. The LMP-1 C-terminal region from these samples was sequenced and analyzed. The frequency of a 30 base pair deletion of LMP-1 previously linked to NPC was not associated with eBL compared to healthy controls. However a novel LMP-1 variant was identified, called K for Kenya and for the G318K mutation that characterizes it. The K variant LMP-1 was found in 40.5% of eBL sequences and 25.0% of healthy controls. All K variant sequences contained mutations in both of the previously described minimal T cell epitopes in the C terminal end of LMP-1. These mutations occurred in the anchor residue at the C-terminal binding groove of both epitopes, a pocket necessary for MHC loading.

Conclusions

Overall, our results suggest that there is a novel K variant of LMP-1 in Kenya that may be associated with eBL. Further studies are necessary to determine the functional implications of the LMP-1 variant on early events in eBL genesis.

Combining HLA-DR risk alleles and anti-Epstein-Barr virus antibody profiles to stratify multiple sclerosis risk

Background:

Risk factors for multiple sclerosis (MS) include human leukocyte antigen (HLA)-DR and Epstein-Barr virus (EBV)-specific antibody responses, including an epitope within EBV nuclear antigen 1 (EBNA-1) that is of recent interest.

Objective:

The objective of this paper is to assess case-control associations between MS risk and anti-EBV antibody levels as well as HLA-DR profiles, gender and age in a population-based cohort.

Methods:

Serological responses to EBV were measured in 426 MS patients and 186 healthy controls. HLA-DR typing was performed using sequence-based methods.

Results:

MS patients had significantly higher levels of antibodies against epitope-specific and polyspecific EBNA-1 and viral capsid antigen (VCA), compared with controls (all p < 10−15). In regression analyses, anti-EBNA-1 and anti-VCA antibody levels, protective HLA-DR*04/07/09 alleles and gender (all p < 0.003) contributed independently to a model that classified cases and controls with an odds ratio > 20 (sensitivity 92%, specificity 64%). Notably, the strong influence of high-risk HLA-DR alleles was abrogated after inclusion of EBV serology results.

Conclusions:

The ability to discriminate MS cases and controls can be substantially enhanced by including anti-EBV serology as well as HLA-DR risk profiles. These findings support the relevance of EBV-specific immunity in MS pathogenesis, and implicate both HLA-dependent and HLA-independent immune responses against EBNA-1 as prominent disease risk factors.

Different patterns of Epstein-Barr virus latency in endemic Burkitt lymphoma (BL) lead to distinct variants within the BL-associated gene expression signature

Epstein-Barr virus (EBV) is present in all cases of endemic Burkitt lymphoma (BL) but in few European/North American sporadic BLs. Gene expression arrays of sporadic tumors have defined a consensus BL profile within which tumors are classifiable as "molecular BL" (mBL). Where endemic BLs fall relative to this profile remains unclear, since they not only carry EBV but also display one of two different forms of virus latency. Here, we use early-passage BL cell lines from different tumors, and BL subclones from a single tumor, to compare EBV-negative cells with EBV-positive cells displaying either classical latency I EBV infection (where EBNA1 is the only EBV antigen expressed from the wild-type EBV genome) or Wp-restricted latency (where an EBNA2 gene-deleted virus genome broadens antigen expression to include the EBNA3A, -3B, and -3C proteins and BHRF1). Expression arrays show that both types of endemic BL fall within the mBL classification. However, while EBV-negative and latency I BLs show overlapping profiles, Wp-restricted BLs form a distinct subgroup, characterized by a detectable downregulation of the germinal center (GC)-associated marker Bcl6 and upregulation of genes marking early plasmacytoid differentiation, notably IRF4 and BLIMP1. Importantly, these same changes can be induced in EBV-negative or latency I BL cells by infection with an EBNA2-knockout virus. Thus, we infer that the distinct gene profile of Wp-restricted BLs does not reflect differences in the identity of the tumor progenitor cell per se but differences imposed on a common progenitor by broadened EBV gene expression.

Epstein-barr virus sequence variation-biology and disease

Some key questions in Epstein-Barr virus (EBV) biology center on whether naturally occurring sequence differences in the virus affect infection or EBV associated diseases. Understanding the pattern of EBV sequence variation is also important for possible development of EBV vaccines. At present EBV isolates worldwide can be grouped into Type 1 and Type 2, a classification based on the EBNA2 gene sequence. Type 1 EBV is the most prevalent worldwide but Type 2 is common in parts of Africa. Type 1 transforms human B cells into lymphoblastoid cell lines much more efficiently than Type 2 EBV. Molecular mechanisms that may account for this difference in cell transformation are now becoming clearer. Advances in sequencing technology will greatly increase the amount of whole EBV genome data for EBV isolated from different parts of the world. Study of regional variation of EBV strains independent of the Type 1/Type 2 classification and systematic investigation of the relationship between viral strains, infection and disease will become possible. The recent discovery that specific mutation of the EBV EBNA3B gene may be linked to development of diffuse large B cell lymphoma illustrates the importance that mutations in the virus genome may have in infection and human disease.

Acute or chronic life-threatening diseases associated with Epstein-Barr virus infection

Infectious mononucleosis (IM) is one of the representative, usually benign, acute diseases associated with primary Epstein-Barr virus (EBV) infection. IM is generally self-limiting and is characterized mostly by transient fever, lymphadenopathy and hepatosplenomegaly. However, very rarely primary EBV infection results in severe or fatal conditions such as hemophagocytic lymphohistiocytosis together with fulminant hepatitis designated as severe or fatal IM or EBV-associated hemophagocytic lymphohistiocytosis alone. In addition, chronic EBV-associated diseases include Burkitt's lymphoma, undifferentiated nasopharyngeal carcinoma, Hodgkin lymphoma, T-cell lymphoproliferative disorder (LPD)/lymphoma, natural killer-cell LPD including leukemia or lymphoma, gastric carcinoma, pyothorax-associated lymphoma and senile B-cell LPD as well as chronic active EBV infection and LPD/lymphoma in patients with immunodeficiency. The number of chronic life-threatening diseases linked to the EBV infection is increasingly reported and many of these diseases have a poor prognosis. This review will focus on the historical, pathogenetic, diagnostic, therapeutic and prophylactic issues of EBV-associated life-threatening diseases.

A multiplex calibrated real-time PCR assay for quantitation of DNA of EBV-1 and 2

Accurate and highly sensitive tests for the diagnosis of active Epstein-Barr virus (EBV) infection are essential for the clinical management of individuals infected with EBV. A calibrated quantitative real-time PCR assay for the measurement of EBV DNA of both EBV-1 and 2 subtypes was developed, combining the detection of the EBV DNA and a synthetic DNA calibrator in a multiplex PCR format. The assay displays a wide dynamic range and a high degree of accuracy even in the presence of 1μg of human genomic DNA. This assay measures with the same efficiency EBV DNA from strains prevalent in different geographic areas. The clinical sensitivity and specificity of the system were evaluated by testing 181 peripheral blood mononuclear cell (PBMCs) and plasma specimens obtained from 21 patients subjected to bone marrow transplantation, 70 HIV-seropositive subjects and 23 healthy controls. Patients affected by EBV-associated post-transplant lymphoprolipherative disorders had the highest frequency of EBV detection and the highest viral load. Persons infected with HIV had higher levels of EBV DNA load in PBMCs and a higher frequency of EBV plasma viremia compared to healthy controls. In conclusion, this new assay provides a reliable high-throughput method for the quantitation of EBV DNA in clinical samples.

Functional modulation of the metastatic suppressor Nm23-H1 by oncogenic viruses

Evidence over the last two decades from a number of disciplines has solidified some fundamental concepts in metastasis, a major contributor to cancer associated deaths. However, significant advances have been made in controlling this critical cellular process by focusing on targeted therapy. A key set of factors associated with this invasive phenotype is the nm23 family of over twenty metastasis-associated genes. Among the eight known isoforms, Nm23-H1 is the most studied potential anti-metastatic factor associated with human cancers. Importantly, a growing body of work has clearly suggested a critical role for Nm23-H1 in limiting tumor cell motility and progression induced by several tumor viruses, including Epstein-Barr virus (EBV), Kaposi's sarcoma associated herpes virus (KSHV) and human papilloma virus (HPV). A more in depth understanding of the interactions between tumor viruses encoded antigens and Nm23-H1 will facilitate the elucidation of underlying mechanism(s) which contribute to virus-associated cancers. Here, we review recent studies to explore the molecular links between human oncogenic viruses and progression of metastasis, in particular the deregulation of Nm23-H1 mediated suppression.

EBNA1 and LMP1 variants in multiple sclerosis cases and controls

BACKGROUND

Prior infection with Epstein-Barr virus (EBV) is an established risk factor for multiple sclerosis (MS). Some findings from observational studies, including possible epidemics and differences in prevalence, may be explained if different strains of EBV conferred different MS risk.

METHODS

DNA was extracted from peripheral lymphocytes obtained from 66 MS cases and 66 age- and cohort-matched controls. Nested polymerase chain reaction (PCR) was performed to amplify the N- and C-terminus regions of EBNA1 and the hyper-variable region of the LMP1 gene. For EBNA1, we compared the presence of the prototype B95.8 vs variant sequence and the presence of multiple strains in MS cases and controls. For LMP1, we considered differences in the proportions of mutations between cases and controls.

RESULTS

Comparing the proportion of mutant sequence between MS cases and controls in the EBNA1 N-terminal (0/28 vs 1/27) and C-terminal regions (3/40 vs 8/36) revealed no significant differences (P > 0.05). No individual variants in LMP1 were associated with risk of MS (all P > 0.05). Neither EBNA1 nor LMP1 variation was associated with anti-EBNA1 IgG antibody titers.

CONCLUSIONS

These findings do not support a strong role for variation in EBNA1 N-terminus, EBNA1 C-terminus or LMP1 contributing to MS risk.

Epstein–Barr virus latent gene sequences as geographical markers of viral origin: unique EBNA3 gene signatures identify Japanese viruses as distinct members of the Asian virus family

Polymorphisms in Epstein–Barr virus (EBV) latent genes can identify virus strains from different human populations and individual strains within a population. An Asian EBV signature has been defined almost exclusively from Chinese viruses, with little information from other Asian countries. Here we sequenced polymorphic regions of the EBNA1, 2, 3A, 3B, 3C and LMP1 genes of 31 Japanese strains from control donors and EBV-associated T/NK-cell lymphoproliferative disease (T/NK-LPD) patients. Though identical to Chinese strains in their dominant EBNA1 and LMP1 alleles, Japanese viruses were subtly different at other loci. Thus, while Chinese viruses mainly fall into two families with strongly linked ‘Wu’ or ‘Li’ alleles at EBNA2 and EBNA3A/B/C, Japanese viruses all have the consensus Wu EBNA2 allele but fall into two families at EBNA3A/B/C. One family has variant Li-like sequences at EBNA3A and 3B and the consensus Li sequence at EBNA3C; the other family has variant Wu-like sequences at EBNA3A, variants of a low frequency Chinese allele ‘Sp’ at EBNA3B and a consensus Sp sequence at EBNA3C. Thus, EBNA3A/B/C allelotypes clearly distinguish Japanese from Chinese strains. Interestingly, most Japanese viruses also lack those immune-escape mutations in the HLA-A11 epitope-encoding region of EBNA3B that are so characteristic of viruses from the highly A11-positive Chinese population. Control donor-derived and T/NK-LPD-derived strains were similarly distributed across allelotypes and, by using allelic polymorphisms to track virus strains in patients pre- and post-haematopoietic stem-cell transplant, we show that a single strain can induce both T/NK-LPD and B-cell-lymphoproliferative disease in the same patient.

EBNA1 sequences in Argentinean pediatric acute and latent Epstein-Barr virus infection reflect circulation of novel South American variants

Epstein-Barr virus (EBV) is related to the development of lymphomas and is also the etiological agent for infectious mononucleosis (IM). Sequence variation of the EBNA1 gene, consistently expressed in all EBV-positive cells, has been widely studied. Based on the amino acid at codon 487 five major EBNA1 variants have been described, two closely related prototypic variants (P-ala and P-thr) and three variant sequences (V-leu, V-val, and V-pro). Sub-variants were then further classified based on mutations other than the originally described. While several studies proposed associations with tumors and/or anatomical compartments, others argued in favor of a geographical distribution of these variants. In the present study, EBNA1 variants in 11 pediatric patients with IM and 19 pediatric EBV lymphomas from Argentina were compared as representatives of benign and malignant infection in children, respectively. A 3-month follow-up study of EBNA1 variants in peripheral blood cells and in oral secretions of patients with IM was performed. A new V-ala variant which includes five V-ala sub-variants and three new V-leu sub-variants was described. These data favor the geographical association hypothesis since no evidence for a preferential compartment distribution of EBNA1 variants and sub-variants was found. This is the first study to characterize EBNA1 variants in pediatric patients with infection mononucleosis worldwide.

Quantitative studies of Epstein-Barr virus-encoded microRNAs provide novel insights into their regulation

Epstein-Barr virus (EBV) has been shown to encode at least 40 microRNAs (miRNAs), an important class of molecules that negatively regulate the expression of many genes through posttranscriptional mechanisms. Here, we have used real-time PCR assays to quantify the levels of EBV-encoded BHRF1 and BART miRNAs in latently infected cells and in cells induced into the lytic cycle. During latency, BHRF1 miRNAs were seen only in cells with detectable Cp- and/or Wp-initiated EBNA transcripts, while the BART miRNAs were expressed in all forms of latent infection. Surprisingly, levels of different BART miRNAs were found to vary up to 50-fold within a cell line. However, this variation could not be explained by differential miRNA turnover, as all EBV miRNAs appeared to be remarkably stable. Following entry into the virus lytic cycle, miR-BHRF1-2 and -1-3 were rapidly induced, coincident with the onset of lytic BHRF1 transcripts, while miR-BHRF1-1 expression was delayed until 48 h and correlated with the appearance of Cp/Wp-initiated EBNA transcripts. In contrast, levels of BART miRNAs were relatively unchanged during virus replication, despite dramatic increases in BART transcription. Finally, we show that BHRF1 and BART miRNAs were delayed relative to the induction of BHRF1 and BART transcripts in freshly infected primary B cell cultures. In summary, our data show that changes in BHRF1 and BART transcription are not necessarily reflected in altered miRNA levels, suggesting that miRNA maturation is a key step in regulating steady-state levels of EBV miRNAs.

Expansion of EBNA1-specific effector T cells in posttransplantation lymphoproliferative disorders

Immunosuppression resulting in impaired Epstein-Barr virus (EBV)-specific T-cell immunity is involved in the pathogenesis of EBV-positive post-transplantation lymphoproliferative disorder (EBV(+) PTLD). Restoration of EBV-specific T-cell immunity by adoptive immunotherapy can induce remission. EBV-nuclear antigen-1 (EBNA1) is unique in being expressed in all cases of EBV(+) PTLD. Recent data demonstrate that EBNA1 is not immunologically silent and can be exploited as a T-cell target. There are no data on EBNA1-specific T cells in PTLD. EBNA1-specific T cells capable of proliferation, interferon-γ release, and CD107a/b degranulation were assayed in 14 EBV(+) PTLD diagnostic blood samples and 19 healthy controls. EBNA1-specific CD4(+) T cells predominated and were expanded in 10 of 14 patients and 19 of 19 controls. Although human leukocyte antigen class I alleles influenced the magnitude of the response, EBNA1-specific CD8(+) effector T cells were successfully generated in 9 of 14 EBV(+) PTLD patients and 16 of 19 controls. The majority of PTLD patients had a polymorphism in an EBNA1 epitope, and T-cell recognition was greatly enhanced when EBNA1 peptides derived from the polymorphic epitope were used. These results indicate that EBNA1-specific T cells should be included in adoptive immunotherapy for PTLD. Furthermore, expansion protocols should use antigenic sequences from relevant EBV strains.

Strains of Epstein-Barr virus infecting multiple sclerosis patients

Both epidemiological and experimental studies have indicated that the ubiquitous herpesvirus Epstein-Barr virus (EBV) plays a role in the pathogenesis of multiple sclerosis (MS). Some features of MS epidemiology, such as the decline in risk among migrants from high to low MS prevalence areas, suggest the presence of variant EBV strains that increase MS risk. The objective of this study was to investigate whether genetic variability in EBV is associated with MS. Genes encoding for two EBV antigens (EBNA1 and BRRF2) were sequenced in EBV isolates from 40 MS patients and a similar number of control subjects. These viral antigens were chosen for analysis because they are known to stimulate atypical immune responses in MS. Extensive sequence polymorphism was observed within the EBNA1 and BRRF2 genes in isolates from both MS patients and controls. Interestingly, several single nucleotide polymorphisms within the EBNA1 gene, and one within the BRRF2 gene, were found to occur at marginally different frequencies in EBV strains infecting MS patients versus controls. Although this study does not find a simple causal relationship between EBV strains and the occurrence of MS, the existence of haplotypes that occur at different frequencies in MS patients versus controls may provide an area for future study of the role of EBV strain variation in multiple sclerosis.

Variations of Epstein-Barr virus nuclear antigen 1 gene in gastric carcinomas and nasopharyngeal carcinomas from Northern China

The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1), the only viral protein consistently expressed in all EBV-associated tumors, is classified into five distinct subtypes: P-ala, P-thr, V-leu, V-val and V-pro based on the signature changes at amino acid residue 487. By now, whether the EBNA1 subtypes preferentially associate with particular malignancies or represent geographical polymorphism remains controversial. In China, most studies of the EBNA1 variations focused on nasopharyngeal carcinoma (NPC) in endemic area, among which some suggested the V-val subtype is preferentially associated with NPC. To characterize the variations of EBNA1 in NPC non-endemic area in China and to explore the association of EBNA1 variations with EBV-associated gastric carcinoma (EBVaGC) and NPC, the C-terminal sequences of EBNA1 were analyzed for 41 EBVaGC, 41 NPC biopsies and 55 throat washing (TW) samples from healthy donors in Northern China. Three major patterns of the EBNA1 variations, V-val, P-thrV and V-leuV, were observed, and V-val was the most common subtype in all the three groups, followed by P-thrV and V-leuV. The distribution of the EBNA1 subtypes among EBVaGC, NPC and healthy donors was not significantly different (P>0.05). In addition, preferential linkages between EBNA1 subtypes and EBNA3C variants were found to exist. There was no evidence that particular EBNA1 subtypes are preferentially associated with EBVaGC or NPC in Northern China, suggesting that EBNA1 gene variations are geographically restricted rather than tumor-specific polymorphisms.

The extent of genetic diversity of Epstein-Barr virus and its geographic and disease patterns: a need for reappraisal

Epstein-Barr virus (EBV) is a ubiquitous, gamma-1 lymphotrophic virus etiologically linked to nasopharyngeal carcinoma (NPC), endemic to Southern China, and Burkitt lymphoma (BL), endemic to equatorial Africa, both of which are rare elsewhere in the world. Why EBV is associated with different malignancies in different geographic regions remains puzzling and may be related to EBV genotypic variability through specific disease and geographic associations. We review the literature on sequence variation in EBV genes, focusing on LMP-1, EBNA-1, and BZLF-1 and their distribution by geography and disease. Given the limitations of current studies, definitive conclusions regarding the link between EBV genotypes, disease and geography are not possible. We suggest that the true extent of EBV diversity is likely to be greater than is currently recognized. Additional studies conducted in carefully selected populations, that are sufficiently powered to provide robust estimates, and that utilize testing approaches that permit full characterization of viral diversity are needed to further our understanding of patterns of EBV genetic variation and their association with malignancies in different regions.

Widespread sequence variation in Epstein-Barr virus nuclear antigen 1 influences the antiviral T cell response

Epstein-Barr virus (EBV) nuclear antigen (EBNA) 1 is perhaps the most widely studied EBV protein, because of its critical role in maintaining the EBV episome and its expression in all EBV-associated malignancies. Much of this research has focused exclusively on the EBV wild-type (wt) strain (B95-8). Sequence analysis of the gene encoding for EBNA1 in EBV isolates from 43 Caucasians has now revealed considerable EBNA1 sequence divergence from the EBV wt strain in the majority of isolates from this population group. Importantly, T cell recognition of an endogenously processed HLA-B8 - binding EBNA1 epitope was greatly influenced by this sequence polymorphism.

Epstein-Barr virus genetic variation in Vietnamese patients with nasopharyngeal carcinoma: full-length analysis of LMP1

Genetic variation in tumor virus genes and its impact on function might contribute to the understanding of geographic differences in risks for virus-associated tumors. This is particularly true for the genes known to contribute to the biology of the tumor. It is has been proposed that Epstein-Barr virus (EBV) gene variation has a role in the high risk of nasopharyngeal carcinoma (NPC) in South-East Asia. NPC is among the five most common cancers in Vietnam. EBV-NPC cells always express EBV nuclear antigen 1 (EBNA1) and also frequently latent membrane protein 1 and 2 (LMP1 & LMP2). To investigate EBV gene variation in Vietnamese NPC patients we analyzed the full length of LMP1 gene including its promoter region, and the N-termini of both EBNA1 and LMP2A genes from five NPC biopsies. We detected two EBV variants V1 and V2 based on the LMP1 nucleotide sequence pattern compared with the prototype B95-8 and some available sequences including Chinese variants. The V1 variant shows strong similarity to a variant dominant in Southern China (China 1), while the V2 variant is similar to a Thai variant SEA 2 and partly identity with GD1 in the C-terminus. The promoter region and transmembrane domain of the SEA 2-like samples contained some specific differences compared with previously published variants. In contrast, analysis of EBNA1 N- and LMP2A N-termini only revealed minor changes. Our findings reinforces that the polymorphisms of whole LMP1 sequence should be considered in future EBV molecular epidemiology studies in different geographic populations.

A major EBNA1 variant from Asian EBV isolates shows enhanced transcriptional activity compared to prototype B95.8

Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) has an instrumental role in maintaining EBV latent infection by controlling EBV episome replication and regulating viral transcription. It is a ubiquitously expressed protein during latent viral infection and in EBV-associated tumors. The EBNA1 C-terminus interacts functionally with the Qp and Cp that control viral gene expression in latency I/II and III, respectively. EBNA1 has been classified into five subtypes due to sequence variation in the DNA-interacting C-terminus. By DNA sequence analysis of its C-terminus, we detected a main sub-variant (V-val-v1) of EBNA1 with valine located in both positions 487 and 528 from matched samples including NPC biopsies and peripheral blood taken from Vietnamese (9), Chinese (12) NPC patients and healthy donors (5). In the FR-region of oriP from nine NPC biopsies from Vietnam we also frequently found substitutions, deletions and variable numbers of repeats. Using a luciferase reporter system, EBNA1 and FR both derived from Asian isolates induced higher transcriptional activity than those from B95-8 virus.

Analysis of Epstein-Barr virus latent gene expression in endemic Burkitt's lymphoma and nasopharyngeal carcinoma tumour cells by using quantitative real-time PCR assays

Studies of Epstein-Barr virus (EBV)-positive cell lines have identified several forms of virus latency, but the patterns of virus gene expression in EBV-positive tumour cells appear more variable. However, it is unclear to what extent these differences merely reflect the increased sensitivities of different detection methods. Here, the design and validation of novel real-time RT-PCR assays to quantify relative levels of EBV transcripts are described. When the new assays were used to screen a collection of endemic Burkitt's lymphoma tumours, abundant Qp-driven EBNA1 expression was found, whereas the other latent transcripts (with the exception of LMP2A) were either absent or detectable only at trace levels. Analysis of 12 nasopharyngeal carcinoma biopsies revealed significant levels of EBNA1 and LMP2A transcripts in almost every case but, in contrast to previous reports, LMP1 expression was undetectable. These new quantitative assays may help to provide a clearer picture of EBV gene expression in tumour material.

Cytomegalovirus and Epstein-Barr virus subtypes—The search for clinical significance

Cytomegalovirus (CMV) as well as Epstein Barr virus (EBV) genomes include regions which show in part substantial polymorphisms. Characterization of several polymorphic regions led to the identification of various CMV and EBV subtypes. Within the last years there have been undertaken numerous efforts to find out whether the diverse subtypes differentially contribute to clinical manifestations. However, although some associations have been described so far between a certain virus subtype and the development of individual diseases these analyses were greatly complicated by the huge genomic background of CMV and EBV, by the large variety of individual host-virus relations and by differences in the geographic or demographic subtype distribution. In addition, it was shown meanwhile that a substantial proportion of virus infections is due to mixed infections with different subtypes. In this review we will give an overview of the current knowledge concerning the clinical significance of individual CMV and EBV subtypes, defined by characterization of selected polymorphisms. In addition, we also focus on recent analyses which show that infection with mixed virus subtype populations may be disadvantageous compared to single virus subtype infections.

The genome of Epstein-Barr virus type 2 strain AG876

Two Epstein-Barr virus (EBV) types are known, EBV1 and EBV2, which possess substantially diverged alleles for latency genes EBNA-2, EBNA-3A, EBNA-3B and EBNA-3C but are thought to be otherwise similar. We report the first complete EBV2 genome sequence, for strain AG876, as 172,764 bp. The sequence was interpreted as containing at least 80 protein coding genes. Comparison with the published EBV1 sequence demonstrated that the two sequences are collinear and, outside the known diverged alleles, generally very close. The EBNA-1 gene was identified as another diverged locus, although its variation is believed not to correlate with EBV type. Patterns of substitution between the two genomes presented a wide spectrum of classes of change. No evidence was seen for involvement of B-cell-specific hypermutation systems in generation of the diverged alleles. Overall, genomic comparisons indicated that the two EBV types should be regarded as belonging to the same virus species.

Suppression of Epstein-Barr nuclear antigen 1 (EBNA1) by RNA interference inhibits proliferation of EBV-positive Burkitt’s lymphoma cells

PURPOSE

Epstein-Barr virus (EBV) is associated with the development of several lymphoid and epithelial malignancies, including Burkitt's lymphoma. The EBV latent protein, EBV Nuclear Antigen 1 (EBNA1), is detectable in almost all types of EBV-associated tumors and is essential for replication and maintenance of the latent episome of EBV. We here examined whether the RNA interference (RNAi) technique could be employed to suppress expression of EBNA1 in EBV-positive Burkitt's lymphoma cells.

METHODS

A Raji cell line expressing small hairpin RNAs (shRNAs) against EBNA1 was established and EBNA1 mRNA level was determined by real-time RT-PCR analysis. We investigated the effects of EBNA1 silence on lymphoma cell growth and cell cycle progression.

RESULTS

Transfection of an EBNA1 RNAi plasmid resulted in substantial loss of EBNA1 mRNA and significantly inhibited proliferation of Raji cells relative to the control plasmid case. Suppression of EBNA1 was also associated with downregulation of EBV oncogene EBNA2, a decreased PCNA labeling index and increased G0/G1 fraction in cell cycle analysis.

CONCLUSIONS

These findings point to potential therapeutic applications for vector-mediated siRNA delivery to control EBV-associated malignant disorders.

Epstein-Barr virus nuclear antigen 2 (EBNA2) gene deletion is consistently linked with EBNA3A, -3B, and -3C expression in Burkitt's lymphoma cells and with increased resistance to apoptosis

Most Epstein-Barr virus (EBV)-positive Burkitt's lymphomas (BLs) carry a wild-type EBV genome and express EBV nuclear antigen 1 (EBNA1) selectively from the BamHI Q promoter (latency I). Recently we identified a distinct subset of BLs carrying both wild-type and EBNA2 gene-deleted (transformation-defective) viral genomes. The cells displayed an atypical "BamHI W promoter (Wp)-restricted" form of latency where Wp (rather than Qp) was active and EBNA1, -3A, -3B, -3C, and -LP were expressed in the absence of EBNA2 or latent membrane proteins 1 and 2. Here we present data strongly supporting the view that the EBNA2-deleted genome is transcriptionally active in these cells and the wild-type genome is silent. Single-cell cloning of three parental Wp-restricted BL lines generated clones carrying either both viral genomes or the EBNA2-deleted genome only, never clones with the wild-type genome only. All rescued clones displayed the Wp-restricted form of latency characteristic of the parent line and retained the original parent cell phenotype. Interestingly, Wp-restricted parent lines and derived clones were markedly more resistant to inducers of apoptosis than standard latency I BL lines. Furthermore, in vitro infection of EBV-negative BL lines with an EBNA2 gene-deleted virus generated EBV-positive converts with Wp-restricted latency and a similarly marked apoptosis resistance. We postulate that, in the subset of BLs displaying Wp-restricted latency, infection of a tumor progenitor cell with an EBNA2 gene-deleted virus has provided that cell with a survival advantage through broadening antigen expression to include the EBNA3 proteins.

Proposed guidelines for diagnosing chronic active Epstein-Barr virus infection

Since the initial report of unusual manifestations possibly associated with chronic active Epstein-Barr virus (EBV) infection (CAEBV), nearly three decades have passed. During this period, reported cases with this entity have dramatically increased in the world. Additionally, recent development of diagnostic procedures, including molecular biological and immunological techniques, have provided us with the ability to define certain diseases, especially malignant disorders. Guidelines, derived mainly from the current literature and recent experiences with CAEBV in Japan, for diagnosing CAEBV are proposed to clarify this enigmatic disease.

V-val subtype of Epstein-Barr virus nuclear antigen 1 preferentially exists in biopsies of nasopharyngeal carcinoma

Epstein-Barr virus (EBV) has been suggested to be involved in pathogenesis of nasopharyngeal carcinoma (NPC). However, EBV infection is ubiquitous, whereas NPC occurs with strong geographic and racial distribution. Whether a substrain of EBV contributes to this phenomenon remains uncertain. Epstein-Barr virus nuclear antigen 1 (EBNA-1) is one of the most frequently detected EBV proteins in NPC tissues. Based on the polymorphism of amino acids at position 487, EBNA-1 is classified into five subtypes: P-ala, P-thr, V-val, V-leu and V-pro. To examine the relationship between subtypes of EBNA-1 and NPC, we determined the subtypes of EBNA-1 in biopsies of NPC, peripheral blood lymphocytes (PBL), and throat washings (TWs) obtained in endemic and non-endemic areas of NPC within China. The results revealed that V-val was the only subtype detected in NPC tissue, whereas three subtypes of EBNA-1, V-val, P-ala, and P-thr, were detected in PBL and TWs irrespective of origin, and mixed infection of V-val and P-ala was also observed. In addition, the variations of V-val derived from biopsies of NPC were identical to those derived from PBL and TWs in the context of N-terminus and C-terminus of EBNA-1. These facts indicate that a substrain of EBV with V-val subtype of EBNA-1 infects NPC preferentially and a susceptibility to a particular EBV isolate in the nasopharynx may exist during development of NPC.

Epstein-Barr virus signal transduction and B-lymphocyte growth transformation

Latent EBV growth transformation of resting B-cells into indefinitely proliferating cell lines is a successful viral strategy for survival in its host and the basis of several human malignancies. EBV transforms cell growth through viral proteins that modify cell gene expression at the level of transcription or by appropriating signaling pathways. Analyses of the EBV-transforming protein LMP1 have begun to reveal that this receptor transduces critical signals by appropriating the TNF receptor signal transduction pathway to activate NF-kappaB and MAPK. While this has brought an important aspect into clearer focus, future progress in delineating the underlying mechanism of transformation, which will be essential to devising effective therapies to treat EBV-associated malignancies, will depend on resolving the intricacies of TRAF signal transduction. Since expression of cytokines, receptors, and anti-apoptotic proteins are regulated by TRAF signaling, another critical issue is delineating the genes that are specifically targeted by LMP1 in order to transform B-lymphocyte growth.

Identification of a naturally processed HLA-DR-restricted T-helper epitope in Epstein-Barr virus nuclear antigen type 1

Epstein-Barr virus nuclear antigen type 1 (EBNA1), the only viral protein that is unequivocally expressed in all Epstein-Barr virus (EBV)-associated malignant diseases, is essential for viral DNA replication and maintenance of the viral episome in infected cells. A glycine-alanine repeat domain inhibits antigen processing through the ubiquitin-proteasome pathway for presentation on human leukocyte antigen (HLA) class I molecules. EBNA1 is not protected from the HLA class II processing pathway, and CD4+ HLA class II-restricted T cells recognize the antigen. CD4+ T-helper (Th) cells play critical roles in initiating, regulating, and maintaining immune responses against viral infections and tumors, so that inclusion of EBNA1 as a target antigen may improve immunotherapy for EBV-associated cancers. In this study, the authors used the TEPITOPE software program to predict promiscuous class II epitope candidates. After several HLA-DR-restricted peptides were identified by in vitro analysis of the T-cell response to synthetic peptides, a T-cell clone was established that was specific for one of the peptides. Functional studies were performed with this clone. The CD4+ T helper cells specific for the HLA-DR15-restricted peptide EBNA1(482) (AEGLRALLARSHVER) recognized naturally processed EBNA1 protein. This epitope was presented by several HLA-DR alleles, including DR4, DR7, and DR11. The inclusion of the promiscuous, naturally processed EBNA1(482) epitope in vaccine constructs could enhance immune responses against EBV-positive cancers.