c-myc overexpression activates alternative pathways for intracellular proteolysis in lymphoma cells.

Burkitt's lymphoma (BL) is a highly malignant B-cell tumour characterized by chromosomal translocations that constitutively activate the c-myc oncogene. Here we show that BL cells are resistant to apoptosis and do not accumulate ubiquitin conjugates in response to otherwise toxic doses of inhibitors of the proteasome. Deubiquitinating enzymes and the cytosolic subtilisin-like protease tripeptidylpeptidase II are upregulated in BLs, and could be rapidly induced by the overexpression of c-myc in normal B cells carrying oestrogen-driven recombinant Epstein-Barr virus. Apoptosis was induced by inhibiting tripeptidylpeptidase II, suggesting that the activity of this protease may be required for the survival of BL cells. We thus show that there is a regulatory link between c-myc activation and changes in proteolysis that may affect malignant transformation.

A minimal glycine-alanine repeat prevents the interaction of ubiquitinated I kappaB alpha with the proteasome: a new mechanism for selective inhibition of proteolysis.

The Epstein-Barr virus nuclear antigen 1 contains a glycine-alanine repeat that inhibits in cis MHC class I-restricted presentation. We report here that insertion of a minimal glycine-alanine repeat motif in different positions of I kappaB alpha protects this NF-kappaB inhibitor from signal-induced degradation dependent on ubiquitin-proteasome, and decreases its basal turnover in vivo resulting in constitutive dominant-negative mutants. The chimeras are phosphorylated and ubiquitinated in response to tumor necrosis factor alpha, but are then released from NF-kappaB and fail to associate with the proteasome. This explains how functionally competent I kappaB alpha is protected from proteasomal disruption and identifies the glycine-alanine repeat as a new regulator of proteolysis.

Lysis of tumor biopsy cells by autologous T lymphocytes activated in mixed cultures and propagated with T cell growth factor.

Blood lymphocytes from tumor patients were cocultivated with allogeneic lymphocytes (MLC) or autologous tumor cells (ATS), and their cytotoxicity was characterized. The main objective of the study was the lysis of autologous tumor biopsy cells by such effectors. Lymphocytes of patients activated in MLC lysed allogeneic third-party cells and in some cases also lysed autologous tumor cells. Allogeneic but not autologous PHA blasts were also damaged by these effectors. The cytotoxic potential of MLC-activated lymphocytes from healthy donors was similar; allogeneic tumors and phytohemagglutinin (PHA) blasts but not autologous PHA blasts were lysed. The cytotoxicity of lymphocytes activated in ATS were specific for the stimulator because they acted only on the autologous tumor cells. Allogeneic tumors and autologous and allogeneic PHA blasts were not lysed. The pattern of cytotoxicity with regard to this target panel was maintained when the MLC or ATS cultures were further propagated with TCGF. Results obtained in cold target competition assays suggested (a) activated lymphocyte lyse the third party tumor targets because of alloantigen recognition; (b) in MLC several different sets of alloreactive cytotoxic lymphocytes are present simultaneously; and (c) the alloreactive cells are different than those that act on the autologous tumor cells. Thus, the lysis of allogeneic tumor cells by lymphocytes of the patient is not due to recognition of cross-reacting tumor-related antigens, and the autotumor cytotoxicity of the patients' MLC-activated lymphocytes if performed by specifically reacting cells.

The life span of major histocompatibility complex-peptide complexes influences the efficiency of presentation and immunogenicity of two class I-restricted cytotoxic T lymphocyte epitopes in the Epstein-Barr virus nuclear antigen 4.

We have investigated the reactivity to two human histocompatibility leukocyte antigen (HLA) A11-restricted cytotoxic T lymphocyte (CTL) epitopes derived from amino acids 416-424 (IVTDFSVIK, designated IVT) and 399-408 (AVFDRKSVAK, designated AVF) of the Epstein-Barr virus (EBV) nuclear antigen (EBNA) 4. A strong predominance of CTL clones specific for the IVT epitope was demonstrated in polyclonal cultures generated by stimulation of lymphocytes from the EBV-seropositive donor BK with the autologous B95.8 virus-transformed lymphoblastoid cell line (LCL). This was not due to intrinsic differences of CTL efficiency since clones specific for the two epitopes lysed equally well A11-positive phytohemagglutinin blasts and LCLs pulsed with the relevant synthetic peptide. Irrespective of the endogenous levels of EBNA4 expression, untreated LCLs were lysed more efficiently by the IVT-specific effectors, suggesting that a higher density of A11-IVT complexes is presented at the cell surface. In accordance, 10-50-fold higher amounts of IVT peptides were found in high-performance liquid chromatography fractions of acid extracts corresponding to an abundance of about 350-12,800 IVT and 8-760 AVF molecules per cell. Peptide-mediated competition of CTL sensitization, transport assays in streptolysin-O permeabilized cells, and induction of A11 expression in the transporter associated with antigen presentation-deficient T2/A11 transfectant demonstrated that the IVT and AVF peptides bind with similar affinities to A11, are translocated with equal efficiency to the endoplasmic reticulum, and form complexes of comparable stability over a wide range of temperature and pH conditions. A rapid surface turnover of A11 molecules containing the AVF peptide was demonstrated in metabolically active T2/A11 cells corresponding to a half-life of approximately 3.5 as compared to approximately 2 h for molecules induced at 26 degrees C in the absence of exogenous peptides and >12 h for IVT-containing complexes. This difference in persistence is likely to determine the representation of individual class I-restricted CTL epitopes within the cell surface pool of molecules, and may be an important factor contributing to their immunogenicity.

Epitope-dependent selection of highly restricted or diverse T cell receptor repertoires in response to persistent infection by Epstein-Barr virus.

The T cell receptor (TCR) repertoires of cytotoxic responses to the immunodominant and subdominant HLA A11-restricted epitopes in the Epstein-Barr virus (EBV) nuclear antigen-4 were investigated in four healthy virus carriers. The response to the subdominant epitope (EBNA4 399-408, designated AVF) was highly restricted with conserved Vbeta usage and identical length and amino acid motifs in the third complementarity-determining regions (CDR3), while a broad repertoire using different combinations of TCR-alpha/beta V and J segments and CDR3 regions was selected by the immunodominant epitope (EBNA4 416-424, designated IVT). Distinct patterns of interaction with the A11-peptide complex were revealed for each AVF- or IVT-specific TCR clonotype by alanine scanning mutagenesis analysis. Blocking of cytotoxic function by antibodies specific for the CD8 coreceptor indicated that, while AVF-specific TCRs are of high affinity, the oligoclonal response to the IVT epitope includes both low- and high-affinity TCRs. Thus, comparison of the memory response to two epitopes derived from the same viral antigen and presented through the same MHC class I allele suggests that immunodominance may correlate with the capacity to maintain a broad TCR repertoire.

T cell responses and virus evolution: loss of HLA A11-restricted CTL epitopes in Epstein-Barr virus isolates from highly A11-positive populations by selective mutation of anchor residues.

Epstein-Barr virus (EBV) is a B lymphotropic herpesvirus of humans that elicits strong HLA class I-restricted cytotoxic T lymphocyte (CTL) responses. An influence of such responses on virus evolution was first suggested by our finding that EBV isolates from the highly HLA A11-positive Papua New Guinea (PNG) population carried a lys-thr mutation at residue 424 of the nuclear antigen EBV-encoded nuclear antigen (EBNA4) that destroyed the immunodominant target epitope for A11-restricted CTL recognition. Here we turn to a much larger population, Southern Chinese, where the A11 allele is again present in over 50% of the individuals. Each of 23 EBV isolates analyzed from this population were also mutated in the EBNA4 416-424 epitope, the mutations selectively involving one of the two anchor residues in positions 2 (417 val-leu) or 9 (424 lys-asp, -arg or -thr) that are critical for A11-peptide interaction. The majority of the Chinese isolates and all 10 PNG isolates also carried mutations affecting positions 1 and 2 of the next most immunodominant A11-restricted epitope, EBNA4 residues 399-408. These changes clearly affected antigenicity since A11-positive lymphoblastoid cell lines (LCLs) carrying these mutant EBV strains were not recognized by A11-restricted CTLs raised against the prototype B95.8 virus. Furthermore, Chinese donors naturally infected with these mutant viruses did not mount detectable A11-restricted CTL responses on in vitro stimulation with autologous LCL cells carrying either the B95.8 or their endogenous EBV strain. In two different highly A11-positive populations, therefore, immune pressure appears to have selected for resident EBV strains lacking immunodominant A11-restricted CTL epitopes.

Interleukin 10 pretreatment protects target cells from tumor- and allo-specific cytotoxic T cells and downregulates HLA class I expression.

Interleukin 10 (IL-10) is a cytokine with a variety of reported effects including inhibition of monocyte major histocompatibility complex (MHC) class II-dependent antigen presentation, type 1 helper T cell cytokine production, and inhibition of T cell proliferation. Herein we report the effect of IL-10 pretreatment on antigen presentation to tumor- and allo-specific CD8+ cytotoxic T lymphocytes (CTL). Prior incubation of human melanoma cells with recombinant IL-10 (rIL-10) for 48-72 h resulted in a dose-dependent, up to 100% inhibition, of autologous CTL-mediated, HLA-A2.1-restricted, tumor-specific lysis. Allo-specific CTL cytotoxicity against Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL) was also inhibited, demonstrating a protective effect also on lymphoid cells. In contrast, IL-10 pretreatment of allogeneic LCL or K562 targets had either no effect or slightly enhanced cytotoxic activity mediated by freshly isolated or IL-2-activated natural killer cells. Flow cytometric analysis with monoclonal antibodies against HLA-A2, or nonpolymorphic determinants of MHC class I proteins, revealed a 20-50% reduction in cell-surface expression, whereas intercellular adhesion molecules 1, and 2, and lymphocyte function-associated antigen 3 levels were not affected. In addition, relative to untreated target cells, IL-10 pretreated tumor cells were unaltered in their capacity to affect CTL-mediated lysis by cold target inhibition, demonstrating that the effect of IL-10 is unrelated to the initial binding of CTL to their targets. These results are compatible with an effect of IL-10 on the MHC class I antigen presentation pathway, and suggest a novel mechanism of immune tolerance, based on escape from CTL-mediated tumor and allo-transplant rejection.

HLA-A11 epitope loss isolates of Epstein-Barr virus from a highly A11+ population.

Cytotoxic T lymphocytes (CTLs) control viral infections by recognizing viral peptides presented by major histocompatibility complex (MHC) class I molecules. Human leukocyte antigen (HLA)-A11-restricted CTLs that recognize peptide residues 416 to 424 of the Epstein-Barr virus (EBV) nuclear antigen-4 frequently dominate EBV-induced responses in A11+ Caucasian donors. This epitope is conserved in type A EBV strains from Caucasians and central African populations, where A11 is relatively infrequent. However, strains from highly A11+ populations in New Guinea carry a lysine-to-threonine mutation at residue 424 that abrogates CTL recognition and binding of the peptide to nascent A11 molecules. The results suggest that evolution of a widespread and genetically stable virus such as EBV is influenced by pressure from MHC-restricted CTL responses.

Effect of interferon-alpha 1 from E. coli on some cell functions.

Interferon-alpha 1 from Escherichia coli transformed with a hybrid plasmid containing a human leukocyte complementary DNA insert, induces resistance to virus in appropriate target cells. It also shares the following properties with natural leukocyte interferon (IFN). (i) It enhances natural killing activity of human lymphocytes, (ii) it enhances antibody-dependent cell-mediated cytotoxicity, (iii) it suppresses antigen- and mitogen-induced leukocyte migration inhibition, (iv) it inhibits growth of IFN-sensitive Burkitt lymphoma cells. Since these activities are exhibited by a cloned protein species, they are due to IFN itself and not to other human proteins.

Epstein-Barr virus promotes genomic instability in Burkitt's lymphoma.

Epstein-Barr virus (EBV) has been implicated in the pathogenesis of human malignancies but the mechanisms of oncogenesis remain largely unknown. Genomic instability and chromosomal aberrations are hallmarks of malignant transformation. We report that EBV carriage promotes genomic instability in Burkitt's lymphoma (BL). Cytogenetic analysis of EBV- and EBV+ BL lines and their sublines derived by EBV conversion or spontaneous loss of the viral genome revealed a significant increase in dicentric chromosomes, chromosome fragments and chromatid gaps in EBV-carrying cells. Expression of EBV latency I was sufficient for this effect, whereas a stronger effect was observed in cells expressing latency III. Telomere analysis by fluorescent in situ hybridization revealed an overall increase of telomere size and prevalence of telomere fusion and double strand-break fusion in dicentric chromosomes from EBV+ cells. Phosphorylated H2AX, a reporter of DNA damage and ongoing repair, was increased in virus-carrying cells in the absence of exogenous stimuli, whereas efficient activation of DNA repair was observed in both EBV+ and EBV- cells following treatment with etoposide. These findings point to induction of telomere dysfunction and DNA damage as important mechanisms for EBV oncogenesis.

Viral immunopathology of human tumors.

Virally induced tumors provide the strongest case of host surveillance against neoplastic cells and their precursors. Human cancers associated with Epstein-Barr virus, hepatitis B virus, papilloma virus and human T cell leukemia virus infection are responsible for approximately 15-20% of the total incidence of cancer world-wide. Current work in each of these virus/tumor systems seeks to understand the mechanisms of viral action and to identify strategies of immune intervention that may allow us to prevent viral infection or to control its potentially life-threatening consequences.

Short-lived green fluorescent proteins for quantifying ubiquitin/proteasome-dependent proteolysis in living cells.

The ubiquitin/proteasome-dependent proteolytic pathway is an attractive target for therapeutics because of its critical involvement in cell cycle progression and antigen presentation. However, dissection of the pathway and development of modulators are hampered by the complexity of the system and the lack of easily detectable authentic substrates. We have developed a convenient reporter system by producing N-end rule and ubiquitin fusion degradation (UFD)-targeted green fluorescent proteins that allow quantification of ubiquitin/proteasome-dependent proteolysis in living cells. Accumulation of these reporters serves as an early predictor of G2/M arrest and apoptosis in cells treated with proteasome inhibitors. Comparison of reporter accumulation and cleavage of fluorogenic substrates demonstrates that the rate-limiting chymotrypsin-like activity of the proteasome can be substantially curtailed without significant effect on ubiquitin-dependent proteolysis. These reporters provide a new powerful tool for elucidation of the ubiquitin/proteasome pathway and for high throughput screening of compounds that selectively modify proteolysis in vivo.

Activation of cytotoxic activity of human blood lymphocytes by tumor-promoting compounds.

Three categories of tumor promoters and chemically related but inactive substances were tested for their effect on the cytotoxic activity of human blood lymphocytes against K562 and Daudi targets. Lymphocytes incubated overnight in the presence of phorbol esters 12-O-tetradecanoylphorbol-13-acetate and phorbol-12,13-dibutyrate [P(Bu)2] had enhanced function. Incubation with 4-alpha-phorbol-12,13-didecanoate was without effect. Enhancing activity was also exerted by the indole alkaloids, teleocidin and lyngbyatoxin A, and the polyacetates, aplysiatoxin and debromoaplysiatoxin, but not by dihydroteleocidin. Only the tumor-promoting compounds activated the cytotoxic potential. The substances acted in a dose-dependent manner with optimal activity at characteristic concentrations. Overnight incubation of lymphocytes at 4 degrees did not change their spontaneous cytotoxicity but abolished the enhancing effect of P(Bu)2. Thus, P(Bu)2-induced activation occurred only on metabolically active cells. The activation did not require DNA synthesis. Similar to controls, the P(Bu)2-treated cells required divalent cations and an intact cytoskeleton in order to perform their lytic function. Experiments with the various metabolic inhibitors indicate that phorbol ester treatment does not induce an alternative cytotoxic mechanism since, as with untreated lymphocytes, P(Bu)2-activated cells require contact with the target and intact secretory functions. The enhanced cytolytic potential was not due to induction of alpha-interferon (IFN-alpha) production, as shown by the fact that the effect was not abolished by addition of anti-IFN antibodies during the P(Bu)2 treatment of lymphocytes or during the cytotoxic assay. However, the presence of antiserum against IFN reduced the cytotoxic potential of control cells, suggesting that endogenous IFN production contributes to the maintenance of lytic function in cultured cells. If this mechanism is counteracted by addition of anti-IFN serum, the phorbol esters can provide an alternative activation signal. When P(Bu)2-activated lymphocytes were subsequently treated with IFN-alpha or IFN-gamma, their lytic capacity was further increased. These results indicate that P(Bu)2 and IFN activate cytotoxic potential through different pathways.

T-cell response to B-cells and Epstein-Barr virus antigens in infectious mononucleosis.

After Epstein-Barr virus (EBV) infection in vivo, B-cells with latent virus infection persist indefinitely through life. These cells grow in vitro on explanation and can be established as immortal B-cell lines. To reconcile the unlimited growth potential in vitro with the maintenance of a low proportion of B-cells infected by EBV in vivo, a strict in vivo control mechanism has to be postulated. Certain aspects of this control are apparent when the primary infection is followed by infectious mononucleosis. This is characterized by lymphocytosis and the presence of activated T-cells. The T-cell proliferation is probably the manifestation of the immune response against EBV antigens. However, the reaction of T-cells upon encounter of B-blasts is also likely to contribute to the events. At present, it is difficult to detect an EBV-specific component in the action of the T-cells in the acute phase of mononucleosis exerted on B-cells. However, for the clinical course of the disease the activation of T-cells is important. The activated T-cells may control and also eliminate the B-cells infected by EBV. In addition to the immunity which develops during the disease, th immunoregulatory mechanism is likely to have a role in the inhibition of B-cell proliferation.

Identification and characterization of an Epstein-Barr virus-specific T-cell response in the pathologic tissue of a patient with Hodgkin's disease.

Several lines of evidence indicate that an impairment of EBV-specific immune responses may contribute to the pathogenesis of Hodgkin's disease (HD). At present, however, it is not clear whether a defective immunity to EBV is a characteristic restricted to EBV-associated HD cases or a more generalized phenomenon, part of the inherent immune deficiency of HD patients. In this study, we have addressed this issue by analyzing EBV-specific responses in infiltrating T lymphocytes (TILs) from one HD biopsy, where the virus was confined to a small proportion of apparently normal lymphocytes. TIL cultures were established using low amounts of recombinant interleukin 2 and in the absence of specific stimulation, conditions that preferentially induce the proliferation of in vivo activated T cells. An EBV-specific cytotoxic component was revealed by the capacity of these TILs to lyse autologous EBV-positive lymphoblastoid cell lines (LCLs) obtained by spontaneous transformation from the lesion but not HLA-mismatched LCLs and autologous phytohemagglutinin blasts. This cytotoxic activity closely resembled that of EBV-specific memory T cells, which may be reactivated from the blood lymphocytes of healthy donors by in vitro stimulation with autologous LCLs. The use of a panel of appropriately HLA-matched B95.8-transformed LCLs as targets in standard 51Cr release assays revealed EBV-specific cytotoxic responses to be restricted mainly through the A11 and B44 HLA alleles with a minor HLA-A26-restricted component. Using autologous fibroblasts infected with recombinant vaccinia viruses expressing the EBV latent antigens, the TIL culture was shown to recognize latent membrane protein 2 and, to a lesser extent, EBV-encoded nuclear antigen 6. In addition, a strong proliferative response was induced by coculture of TILs with autologous but not with allogeneic LCLs or autologous phytohemagglutinin blasts. Six CD4-positive, EBV-specific T-cell clones were isolated by limiting dilution. The study of cytokine mRNA expression, carried out by reverse transcriptase-assisted PCR, revealed that three of these T-cell clones expressed a Th0 phenotype, whereas 1 had a Th2 phenotype. These findings are consistent with the presence in this HD lesion of an ongoing immune response against EBV-carrying cells and suggest that the complex immune deficiency that characterizes HD patients probably does not include a generalized, constitutional defect of EBV-specific T-cell responses.

Immunological characterization of Hodgkin's and non-Hodgkin's lymphoma patients with high antibody titers against Epstein-Barr virus-associated antigens.

We have studied nine Hodgkin's lymphoma (HD) and ten non-Hodgkin's lymphoma (NHL) patients with extraordinarily high anti-viral capsid antigen (VCA) titers (greater than 5120). Controls were 13 HD and 23 NHL patients with anti-VCA titers between 40 and 2560. High anti-VCA titers were present in NHL patients at the time of diagnosis or within 16 months, whereas the rise of anti-VCA titers in HD patients appeared to be a late event during the clinical course of the disease (mean time from diagnosis, 68 months). In particular, we have asked whether the exceptionally high anti-Epstein-Barr virus (EBV) titers in some HD and NHL patients can be correlated to some of the EBV-specific and -nonspecific parameters of cell-mediated immunity. The battery of non-EBV-specific immunological tests included the assessment of natural killer cell activity and the analysis of T-lymphocyte subclasses according to surface markers, together with spontaneous and mitogen-induced DNA synthesis and their helper or suppressor activity on PWM-generated immunoglobulin synthesis. Outgrowth inhibition (Ol) and leukocyte migration inhibition were used to assess EBV-specific cell-mediated immunity. The majority of the high-titer HD and NHL patients showed a drastically reduced OKT4:OKT8 ratio in their peripheral lymphocyte population. Low-titer HD and NHL patients showed no such reduction. There was no strict correlation between the number of OKT8-positive cells and suppressor activity in the functional PWM-induced immunoglobulin production test. Part of the high-titer HD patients showed defective cellular responses in the outgrowth inhibition test, directed against the proliferation of EBV-transformed (EBV-determined nuclear antigen-positive) cells. Some of them showed also a deficient leukocyte migration inhibition response to EBV-determined nuclear antigen but, interestingly, not to early antigen-VCA. In the NHL group, only one of the high-titer patients showed a similar defect. None of the low-titer HD and NHL patients showed such defects.

Cell-mediated immune reactions in three patients with malignant lymphoproliferative diseases in remission and abnormally high Epstein-Barr virus antibody titers.

Two patients with Hodgkin's disease in remission and one chronic lymphatic leukemia patient with extraordinarily high anti-Epstein-Barr virus (EBV) (viral capsid antigen) antibody titers (greater than 10,000) were selected to study a spectrum of cell-mediated immune responses, including natural killer, interferon-boosted killer, antibody-dependent lymphocytotoxicity, and T-cell-mediated reactions. The purpose was to compare these reactions in patients with immunosuppression and a high EBV load who can hold their EBV-carrying cells under control with the corresponding reactions in patients with EBV-carrying lymphoproliferative disease. In contrast to the latter group, the three patients of the present study showed a less profound and less general suppression of the immune responses. Multiple effector mechanisms probably safeguard against the proliferation of EBV-transformed B-cells. Clinically manifest EBV-carrying lymphoproliferative disease occurs only in very severe immunodeficiencies effecting multiple effectors.

Cellular immune defects to Epstein-Barr virus-determined antigens in young males.

Three males with the X-linked lymphoproliferative syndrome (XLP) with hypo- or agammaglobulinemia following Epstein-Barr virus (EBV) infection and two males with the chronic mononucleosis syndrome were investigated for immune responses to EBV-determined antigens. Males with XLP showed profound cellular immune defects. Markedly diminished responses of natural killer cell and interferon-activated killer cell activities and impaired leukocyte migration inhibition responses to phytohemagglutinin were determined in patients with XLP. The two patients with chronic mononucleosis showed less severe defects. All patients showed partial or complete impairment of their EBV-specific immune responses as measured by leukocyte migration inhibition. EBV-specific antibodies were markedly diminished against EBV-associated nuclear antigen, early antigen, and viral capsid antigen in males with XLP. In contrast, patients with chronic mononucleosis had elevated antibodies to most EBV-specific antigens. Individuals with life-threatening EBV-induced lymphoproliferative disorders may exhibit multiple defective immune mechanisms against the virus.

Oxidative stress enables Epstein-Barr virus-induced B-cell transformation by posttranscriptional regulation of viral and cellular growth-promoting factors.

Infection of human B lymphocytes by Epstein-Barr virus (EBV) leads to the establishment of immortalized lymphoblastoid cell lines (LCLs) that are widely used as a model of viral oncogenesis. An early consequence of infection is the induction of DNA damage and activation of the DNA damage response, which limits the efficiency of growth transformation. The cause of the DNA damage remains poorly understood. We have addressed this question by comparing the response of B lymphocytes infected with EBV or stimulated with a potent B-cell mitogen. We found that although the two stimuli induce comparable proliferation during the first 10 days of culture, the EBV-infected blasts showed significantly higher levels of DNA damage, which correlated with stronger and sustained accumulation of reactive oxygen species (ROS). Treatment with ROS scavengers decreased DNA damage in both mitogen-stimulated and EBV-infected cells. However, while mitogen-induced proliferation was slightly improved, the proliferation of EBV-infected cells and the establishment of LCLs were severely impaired. Quenching of ROS did not affect the kinetics and magnitude of viral gene expression but was associated with selective downregulation of the viral LMP1 and phosphorylated cellular transcription factor STAT3 that have key roles in transformation. Analysis of the mechanism by which high levels of ROS support LMP1 expression revealed selective inhibition of viral microRNAs that target the LMP1 transcript. Our study provides novel insights into the role of EBV-induced oxidative stress in promoting B-cell immortalization and malignant transformation.

Epstein-Barr virus: adaptation to a life within the immune system.

Epstein-Barr virus has developed multiple strategies to ensure its long-term persistence in the infected B cells of immunocompetent hosts. These include the establishment of cell-phenotype-specific programs of viral gene expression and the transduction of cellular genes that modulate immune responses. Cytotoxic T cells may specifically influence the evolution of this genetically stable virus.