Expression of Epstein-Barr virus-encoded growth-transformation-associated proteins in lymphoproliferations of bone-marrow transplant recipients

Distinct immunopathological mechanisms of EBV-positive and EBV-negative posttransplant lymphoproliferative disorders

EBV-positive and EBV-negative posttransplant lymphoproliferative disorders (PTLDs) arise in different immunovirological contexts and might have distinct pathophysiologies. To examine this hypothesis, we conducted a multicentric prospective study with 56 EBV-positive and 39 EBV-negative PTLD patients of the K-VIROGREF cohort, recruited at PTLD diagnosis and before treatment (2013-2019), and compared them to PTLD-free Transplant Controls (TC, n = 21). We measured absolute lymphocyte counts (n = 108), analyzed NK- and T cell phenotypes (n = 49 and 94), and performed EBV-specific functional assays (n = 16 and 42) by multiparameter flow cytometry and ELISpot-IFNγ assays (n = 50). EBV-negative PTLD patients, NK cells overexpressed Tim-3; the 2-year progression-free survival (PFS) was poorer in patients with a CD4 lymphopenia (CD4⁺ <300 cells/mm³ , p <  .001). EBV-positive PTLD patients presented a profound NK-cell lymphopenia (median = 60 cells/mm³ ) and a high proportion of NK cells expressing PD-1 (vs. TC, p = .029) and apoptosis markers (vs. TC, p < .001). EBV-specific T cells of EBV-positive PTLD patients circulated in low proportions, showed immune exhaustion (p = .013 vs. TC) and poorly recognized the N-terminal portion of EBNA-3A viral protein. Altogether, this broad comparison of EBV-positive and EBV-negative PTLDs highlight distinct patterns of immunopathological mechanisms between these two diseases and provide new clues for immunotherapeutic strategies and PTLD prognosis.

Carboxy-terminal sequence variation of LMP1 gene in Epstein-Barr-virus-associated mononucleosis and tumors from Serbian patients

Seven strains of Epstein-Barr virus (EBV) are defined based on C-terminal sequence variations of the latent membrane protein 1 (LMP1). Some strains, especially those with a 30-bp deletion, are thought to be related to tumorigenic activity and geographical localization. The aims of the study were to determine the prevalence of different LMP1 strains and to investigate sequence variation in the C-terminal region of LMP1 in Serbian isolates. This study included 53 EBV-DNA-positive plasma and tissue block samples from patients with mononucleosis syndrome, renal transplantation, and tumors, mostly nasopharyngeal carcinoma. The sequence of the 506-bp fragment of LMP1 C terminus was used for phylogenetic analyses and identification of LMP1 strains, deletions, and mutations. The majority of isolates were non-deleted (66%), and the rest had 30-bp, rare 69-bp, or yet unknown 27-bp deletions, which were not related to malignant or non-malignant isolate origin. However, the majority of 69-bp deletion isolates were derived from patients with nasopharyngeal carcinoma. Less than five 33-bp repeats were found in the majority of non-deleted isolates (68.6%), whereas most 69-bp deletion isolates (75%) had five or six repeats. Serbian isolates were assigned to four LMP1 strains: B95-8 (32.1%), China 1 (24.5%), North Carolina (NC; 18.9%), and Mediterranean (Med; 24.5%). In NC isolates, three new mutations unique for this strain were identified. EBV EBNA2 genotypes 1 and 2 were both found, with dominance of genotype 1 (90.7%). This study demonstrated noticeable geographical-associated characteristics in the LMP1 C terminus of investigated isolates.

Mobilizing the low-avidity T cell repertoire to kill tumors

Optimally, T cells destroy infected and transformed cells of the host. To be effective the T cell repertoire must have a sufficiently diverse number of T cell receptors (TCRs) to recognize the abundance of foreign and tumor antigens presented by MHC molecules. The T cell repertoire must also not be reactive toward self-antigens on healthy cells to prevent autoimmunity. Unlike antigens derived from pathogens, most tumor-associated antigens (TAA) are also self-antigens. Therefore, central and peripheral tolerance mechanisms delete or inhibit tumor-reactive T cells. Although there are T cells within the peripheral repertoire that recognize TAA, these T cells are not sufficient to prevent growth of clinically relevant tumors. We will discuss how this dysfunction results, in part, from the low functional avidity of T cells for tumor, or antigen presenting cells (APC) displaying TAA. We discuss the limitations of these low-avidity tumor-reactive T cells and review current immunotherapies aimed at enhancing the avidity and antitumor activity of the tumor-specific T cell repertoire.

Phenotypic and genotypic characteristics of new euploid–diploid lymphoblastoid B cell lines EBV+, normal human bone marrow derived, spontaneously overgrown in vitro

The present study describes the phenotypic and genotypic features of seven individual growth transformed, euploid-diploid EBV+ human B cell lines arisen spontaneously in vitro. The lines, obtained under general and standard culture conditions (un-manipulated), from seven individual bone marrow samples of 18 healthy young adults, Caucasian, of both sexes, display many traits of normal B cells and represent a mixture of EBV infected latently (latency type III) and producer cells (5-16% VCA+ by immunofluorescence) releasing seven individual different viral strains [Fruscalzo et al., 2001. DNA sequence heterogeneity within the Epstein-Barr virus family of repeats in the latent origin of replication. Gene 265, 165-173] similar to the B95-8 genotype as shown by results of Southern blot of BamHI-digested DNA fragment. These tests were planned to characterize more fully this panel of new bone marrow cell lines sharing normal B cell traits.

Potential selection of LMP1 variants in nasopharyngeal carcinoma

Seven distinct sequence variants of the Epstein-Barr virus latent membrane protein 1 (LMP1) have been identified by distinguishing amino acid changes in the carboxy-terminal domain. In this study the transmembrane domains are shown to segregate identically with the distinct carboxy-terminal amino acid sequences. Since strains of LMP1 have been shown to differ in abundance between blood and throat washes, nasopharyngeal carcinomas (NPCs) from areas of endemicity and nonendemicity with matching blood were analyzed by using a heteroduplex tracking assay to distinguish LMP1 variants. Striking differences were found between the compartments with the Ch1 strain prevalent in the NPCs from areas of endemicity and nonendemicity and the B958 strain prevalent in the blood of the endemic samples, whereas multiple strains of LMP1 were prevalent in the blood of the nonendemic samples. The possible selection against the B958 strain appearing in the tumor was highly significant (P < 0.0001). Sequence analysis of the full-length LMP1 variants revealed changes in many of the known and computer-predicted HLA-restricted epitopes with changes in key positions in multiple, potential epitopes for the specific HLA of the patients. These amino acid substitutions at key positions in the LMP1 epitopes may result in a reduced cytotoxic-T-lymphocyte response. These data indicate that strains with specific variants of LMP1 are more likely to be found in NPC. The predominance of specific LMP1 variants in NPC could reflect differences in the biologic or molecular properties of the distinct forms of LMP1 or possible immune selection.

Pathogenic roles for Epstein-Barr virus (EBV) gene products in EBV-associated proliferative disorders

Epstein-Barr virus (EBV) is associated with a still growing spectrum of clinical disorders, ranging from acute and chronic inflammatory diseases to lymphoid and epithelial malignancies. Based on a combination of in vitro and in vivo findings, EBV is thought to contribute in the pathogenesis of these diseases. The different EBV gene expression patterns in the various disorders, suggest different EBV-mediated pathogenic mechanisms. In the following pages, an overview of the biology of EBV-infection is given and functional aspects of EBV-proteins are discussed and their putative role in the various EBV-associated disorders is described. EBV gene expression patterns and possible pathogenic mechanisms are discussed. In addition, expression of the cellular genes upregulated by EBV in vitro is discussed, and a comparison with the in vivo situation is made.

Successful treatment of posttransplantation lymphoproliferative disorder (PTLD) following renal allografting is associated with sustained CD8(+) T-cell restoration

Posttransplantation lymphoproliferative disorder (PTLD) is a life-threatening Epstein-Barr virus (EBV)-associated B-cell malignancy occurring in 1% to 2% of renal transplantation patients. Host- and PTLD-related factors determining the likelihood of tumor response following reduction of immune suppression (IS) and antiviral therapy remain largely unknown. Standard therapy for PTLD is not well established. Eleven consecutive renal transplantation patients who developed EBV-positive PTLD 8 to 94 months after allografting were uniformly treated with acyclovir and IS reduction. All PTLDs were EBV-positive diffuse large B-cell lymphomas. Ten patients (91%) obtained a durable complete response (CR), and 9 (82%) have remained in continuous CR with a median follow-up of 29 months. Five patients (45%) lost their allograft. Of these, 4 patients had PTLD affecting the transplanted kidney. Peripheral blood CD8(+) T cells increased significantly (P =.0078) from baseline in 8 responders available for analysis. One of 2 patients whose absolute CD8(+) T-cell count subsequently dropped to baseline after IS reduction relapsed. The expanded CD8(+) T cells from 2 responders specifically recognized an immunodominant peptide from the EBV lytic gene BZLF-1. Another lytic EBV gene, thymidine kinase, was expressed in all 8 PTLDs tested. IS reduction and antiviral therapy for PTLD after renal transplantation is a highly successful therapeutic combination, but the risk of graft rejection is significant, particularly in patients with PTLD involving the renal allograft. A sustained expansion of CD8(+) T cells and a cellular immune response to EBV lytic antigens may be important for PTLD clearance in renal transplantation patients.

Adoptive transfer of autologous Epstein-Barr virus-specific cytotoxic T cells for nasopharyngeal carcinoma

Tumor cells from NPC patients are regularly and latently infected with EBV. To examine whether the virus serves as target for immune intervention of the cancer, we determined levels of EBV-specific CTLp in peripheral blood from NPC patients, long-term survivors of the cancer and healthy subjects. CTLp levels of test subjects varied between 3- 3,000/10(6) PBMCs. The plasma EBV burden increased when the CTLp level fell below 150, whereas the EBV burden of PBMCs was not correlated with CTLp level. Compared with healthy carriers, CTLp levels of patients were lower and varied over a wider range, between 3-1,500/10(6) PBMCs. The quantitative immune deficit was probably attributed to the tumor because, first, CTLp in survivors was restored to levels similar to those in healthy carriers after the tumor had been successfully treated. Second, the CTLp level changed as disease progressed, being lower in local disease, increased in locoregional disease and decreased again when the tumor metastasized. Based on these findings, 4 patients with advanced disease were infused with 5 x 10(7)-3 x 10(8) autologous EBV CTLs. The treatment was safe and unaccompanied by inflammatory or other complications, but whether it improved tumor control could not be discerned from the large tumor bulk. Nevertheless, the treatment regularly increased CTLp levels of patients, maintained it at higher levels for protracted periods and, in 3 patients, restored host surveillance of EBV replication, reducing the plasma EBV burden. Taken together, these results provided a rationale to further explore EBV as a target of immune intervention of NPC.

The cytoplasmic amino-terminus of the Latent Membrane Protein-1 of Epstein-Barr Virus: relationship between transmembrane orientation and effector functions of the carboxy-terminus and transmembrane domain

The Latent Membrane Protein 1 (LMP-1) protein of Epstein-Barr virus (EBV) is localized in the plasma membrane of the infected cell. LMP-1 possesses a hydrophobic membrane spanning domain, and charged, intracellular amino- and carboxy-termini. Two models have been proposed for the contribution of the amino-terminus to LMP-1's function: (i) as an effector domain, interacting with cellular proteins, or (ii) as a structural domain dictating the correct orientation of transmembrane domains and thereby positioning LMP-1's critical effector domains (i.e. the carboxy-terminus). However, no studies to date have addressed directly the structural contributions of LMP-1's cytoplasmic amino-terminus to function. This study was designed to determine if LMP-1's cytoplasmic amino-terminus (N-terminus) encodes information required solely for maintenance of proper topological orientation. We have constructed LMP-1 chimeras in which the cytoplasmic N-terminus of LMP-1 is replaced with an unrelated domain of similar size and charge, but of different primary sequence. Retention of the charged amino-terminal (N-terminal) cytoplasmic domain and first predicted transmembrane domain was required for correct transmembrane topology. The absolute primary sequence of the cytoplasmic N-terminus was not critical for LMP-1's cytoskeletal association, turnover, plasma membrane patching, oligomerization, Tumor Necrosis Factor Receptor-associated factor (TRAF) binding, NF-kappaB activation, rodent cell transformation and cytostatic activity. Furthermore, our results point to the hydrophobic transmembrane domain, independent of the cytoplasmic domains, as the primary LMP-1 domain mediating oligomerization, patching and cytoskeletal association. The cytoplasmic amino-terminus provides the structural information whereby proper transmembrane orientation is achieved.

Molecular pathogenesis of Epstein-Barr virus associated posttransplant lymphomas: new insights through latent membrane protein 1 fingerprinting

BACKGROUND

Fingerprint amino acid patterns within the carboxy terminus of the latent membrane protein (LMP1) oncoprotein of Epstein-Barr virus (EBV) allow individual strain identification at the molecular level. LMP1 is expressed in the tumor cells of EBV-associated posttransplant lymphomas (PTLs) and the LMP1 genome is also identified in lymphocytes of most donors of allogeneic bone marrow. Therefore, LMP1 genotyping in donor lymphocytes and PTL tumor cells, together with sex chromatin determination of tumor cells, allows to determine the origin of PTL tumor cells and the origin of individual EBV strains harboured by them.

METHODS

We traced the origin of aggressive PTLs occurring in six patients after allogeneic T cell-depleted stem cell transplantation (allo-SCT). DNA was extracted from donor lymphocytes and PTLs of recipients and amplified with LMP1-specific primers in each case. A comparative sequence analysis of the fingerprint LMP1 region identified in donor lymphocytes and lymphoma was performed.

RESULTS

One lymphoma of donor origin occurred after highly selected CD34+ PBSCT and contained the same LMP1 genotype as the donor lymphocytes. Three lymphomas of recipient origin had deletions within the carboxy terminus of LMP1, not identified in the donor strains. All lymphomas occurred in the setting of allo-SCT and had a rapid clinical course.

CONCLUSIONS

These results show that highly selected CD34+ PBSCT does not protect against transfer of EBV positive founder cells of donor type PTL and that, after allo-SCT, recipient type PTLs are not uncommon. Outgrowth of recipient type lymphoma may be favoured by LMP1 deletion variant strains present in recipient lymphocytes.

The generation of LMP2a-specific cytotoxic T lymphocytes for the treatment of patients with Epstein-Barr virus-positive Hodgkin disease

Based upon the success of using polyclonal, Epstein-Barr virus (EBV)-specific CTL lines for the prophylaxis and treatment of patients with post-transplant lymphoproliferative disease (PTLPD), there is now considerable incentive to develop CTL directed against the sub-dominant EBV antigens EBNA1, LMP1 and LMP2, which are expressed by the tumor cells of Hodgkin disease and nasopharyngeal carcinoma. To develop a system for generating LMP2a-specific CTL in vitro, we transfected autologous immature dendritic cells (DC), which had been grown in the absence of serum, with LMP2a RNA in the presence of the cationic lipid DOTAP. This transfection method did not adversely affect the DC in terms of immunophenotyping and they expressed high levels of HLA class I and II and critical costimulatory molecules. These LMP2a(+) DC, as compared to DC which had been transfected with irrelevant RNA, were shown to be highly immunostimulatory in autologous mixed lymphocyte reactions and, importantly, could stimulate the generation of CD8(+) and CD4(+) CTL which exclusively recognized LMP2a-expressing targets. This specific cytotoxicity was confirmed using antibody blocking experiments and cytotoxicity assays of the separated T cell subsets. Using this DC-based system we could also reactivate LMP2a-specific memory in EBV-seropositive donors whose polyclonal CTL response to LCL stimulation did not contain a LMP2a-specific component.

Mature dendritic cells pulsed with freeze–thaw cell lysates define an effective in vitro vaccine designed to elicit EBV-specific CD4+ and CD8+ T lymphocyte responses

Immunotherapy trials targeting the induction of tumor-reactive T-cell responses in cancer patients appear to hold significant promise. Because nonmutated lineage-specific antigens and mutated idiotypic antigens may be coexpressed by tumor cells, the use of autologous tumor material to promote the broadest range of antitumor T-cell specificities has significant clinical potential in cancer vaccination trials. As a model for vaccination in the cancer setting, we chose to analyze the promotion of T-cell responses against Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell line (B-LCL)–derived antigens in vitro. A series of bulk antigenic formats (freeze–thaw lysate, trifluoroacetic acid lysate, extracted membranes, affinity-purified MHC class I– and class II–presented peptides, acid-eluted peptides) prepared from EBV B-LCLs were tested for their ability to stimulate EBV B-LCL–reactive CD4+ and CD8+ T lymphocytes in vitro when pulsed onto autologous dendritic cells (DCs). DC presentation of freeze–thaw lysate material derived from (either autologous or allogeneic) EBV B-LCLs with an Mr of 10 kd or larger stimulated optimal anti-EBV B-LCL responsiveness from freshly isolated CD4+ and CD8+ peripheral blood T cells. These in vivo “memory” T-cell responses were observed only in EBV-seropositive donors. CD4+ T-cell responses to lysate-pulsed DCs were Th1 type (ie, strong interferon-γ and weak interleukin-5 responses). While CD8+ T-cell responses were also observed in interferon-γ Elispot assays and in cytotoxicity assays, these responses were of low frequency unless the DC stimulators were induced to “mature” after being fed with tumor lysates. Optimal-length, naturally processed, and MHC class I– or class II–presented tumor peptides were comparatively poorly immunogenic in this model system.

Mature dendritic cells pulsed with freeze–thaw cell lysates define an effective in vitro vaccine designed to elicit EBV-specific CD4+ and CD8+ T lymphocyte responses

Immunotherapy trials targeting the induction of tumor-reactive T-cell responses in cancer patients appear to hold significant promise. Because nonmutated lineage-specific antigens and mutated idiotypic antigens may be coexpressed by tumor cells, the use of autologous tumor material to promote the broadest range of antitumor T-cell specificities has significant clinical potential in cancer vaccination trials. As a model for vaccination in the cancer setting, we chose to analyze the promotion of T-cell responses against Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell line (B-LCL)–derived antigens in vitro. A series of bulk antigenic formats (freeze–thaw lysate, trifluoroacetic acid lysate, extracted membranes, affinity-purified MHC class I– and class II–presented peptides, acid-eluted peptides) prepared from EBV B-LCLs were tested for their ability to stimulate EBV B-LCL–reactive CD4+ and CD8+ T lymphocytes in vitro when pulsed onto autologous dendritic cells (DCs). DC presentation of freeze–thaw lysate material derived from (either autologous or allogeneic) EBV B-LCLs with an Mr of 10 kd or larger stimulated optimal anti-EBV B-LCL responsiveness from freshly isolated CD4+ and CD8+ peripheral blood T cells. These in vivo “memory” T-cell responses were observed only in EBV-seropositive donors. CD4+ T-cell responses to lysate-pulsed DCs were Th1 type (ie, strong interferon-γ and weak interleukin-5 responses). While CD8+ T-cell responses were also observed in interferon-γ Elispot assays and in cytotoxicity assays, these responses were of low frequency unless the DC stimulators were induced to “mature” after being fed with tumor lysates. Optimal-length, naturally processed, and MHC class I– or class II–presented tumor peptides were comparatively poorly immunogenic in this model system.

Selective amino acid substitutions of a subdominant Epstein-Barr virus LMP2-derived epitope increase HLA/peptide complex stability and immunogenicity: implications for immunotherapy of Epstein-Barr virus-associated malignancies

The latent membrane protein 2 is an immunogenic antigen expressed in Epstein-Barr virus (EBV)-associated tumors and consequently it may represent a target for specific cytotoxic T lymphocyte (CTL)-based immunotherapies. However, the efficacy of such a therapy is limited by the poor immunogenicity of the protein that induces weak CTL responses directed to the CLGGLLTMV (CLG) epitope only in the minority of EBV-seropositive donors. We have now demonstrated that selective peptide stimulation of peripheral blood lymphocytes induced CLG-specific CTL in all donors, suggesting that this epitope can be a suitable target for specific immunotherapies. We found that the CLG peptide has a low affinity for HLA-A*0201 and does not produce stable complexes, both factors that are likely to determine the strength of CTL responses to this epitope. Therefore, we synthesized and tested CLG analogues carrying single or combined amino acid substitutions to increase HLA/peptide stability. Among the analogues tested we identified two peptides which, compared to the natural epitope, showed higher affinity for HLA-A*0201 molecules, and produced stable complexes. These peptides demonstrated a potent, specific stimulatory capacity and could be used for selective CTL-based therapies.

Methylation status of the Epstein-Barr virus major latent promoter C in iatrogenic B cell lymphoproliferative disease. Application of PCR-based analysis

The Epstein-Barr virus (EBV) major latent promoter C drives the expression of viral nuclear proteins important in lymphocyte immortalization and as targets for immune surveillance by cytotoxic T cells. Hypermethylation of the C promoter silences its transcription. This promoter is methylated and silent in Burkitt's lymphoma, Hodgkin's disease, nasopharyngeal carcinoma, and nasal lymphoma. However, it is never methylated in the EBV-immortalized lymphoblastoid cell lines that serve as a model for EBV-associated lymphoproliferative disease. We have analyzed C promoter methylation in iatrogenic EBV-associated B-cell lymphoproliferative disease, mainly posttransplant lymphoma, using a sensitive polymerase chain reaction-based C promoter methylation assay. Our results showed heterogeneity in lymphoproliferative disease with methylation of viral DNA in specimens from 3 of 13 patients. In specimens from two of these patients, only methylated viral DNA was detected and viral nuclear antigen expression was correspondingly restricted. Heterogeneity in C promoter methylation and expression of associated transcripts may be an important determinant of the growth properties of lymphoproliferative lesions and may provide an explanation for the failure of some tumors to respond to withdrawal or reduction of immunosuppressive therapy.

Accessing Epstein-Barr virus-specific T-cell memory with peptide-loaded dendritic cells

The conventional means of studying Epstein-Barr virus (EBV)-induced cytotoxic T-lymphocyte (CTL) memory, by in vitro stimulation with the latently infected autologous lymphoblastoid cell line (LCL), has important limitations. First, it gives no information on memory to lytic cycle antigens; second, it preferentially amplifies the dominant components of latent antigen-specific memory at the expense of key subdominant reactivities. Here we describe an alternative approach, based on in vitro stimulation with epitope peptide-loaded dendritic cells (DCs), which allows one to probe the CTL repertoire for any individual reactivity of choice; this method proved significantly more efficient than stimulation with peptide alone. Using this approach we first show that reactivities to the immunodominant and subdominant lytic cycle epitopes identified by T cells during primary EBV infection are regularly detectable in the CTL memory of virus carriers; this implies that in such carriers chronic virus replication remains under direct T-cell control. We further show that subdominant latent cycle reactivities to epitopes in the latent membrane protein LMP2, though rarely undetectable in LCL-stimulated populations, can be reactivated by DC stimulation and selectively expanded as polyclonal CTL lines; the adoptive transfer of such preparations may be of value in targeting certain EBV-positive malignancies.

AIDS-related malignancies

In the US over one million persons are currently infected with the HIV, over half a million have had AIDS, and over 300,000 have died from AIDS. Worldwide, it is estimated that more than 17 million people are currently infected with HIV, and over 1,200,000 cases of AIDS have been reported to the World Health Organization. By some estimates, up to 40% of patients with AIDS will ultimately develop some form of cancer. Non-Hodgkin's lymphoma, Kaposi's sarcoma and invasive cervical cancer have a higher incidence in persons with HIV infection and all three are AIDS-defining illnesses. In addition, several reports suggest that a number of other malignancies may occur at an increased incidence in persons with HIV infection, including squamous-cell carcinoma of the head, neck and anus, plasmacytoma, melanoma, small-cell lung cancer, basal-cell cancer, and germ-cell tumours. Clinicians should become familiar with HIV-related malignancies as their incidence is expected to further increase as more effective therapies for HIV and associated opportunistic infections allow patients to live longer in an advanced state of immunodeficiency. In the current article, we will review the clinical and therapeutic aspects of the most common AIDS-related malignancies including non-Hodgkin's and Hodgkin's lymphomas, Kaposi's sarcoma and anogenital epithelial neoplasias.

Presence of Epstein-Barr virus latency type III at the single cell level in post-transplantation lymphoproliferative disorders and AIDS related lymphomas

AIMS

To investigate the expression pattern of Epstein-Barr virus (EBV) latent genes at the single cell level in post-transplantation lymphoproliferative disorders and acquired immunodefiency syndrome (AIDS) related lymphomas, in relation to cellular morphology.

METHODS

Nine post-transplantation lymphoproliferative disorders and three AIDS related lymphomas were subjected to immunohistochemistry using monoclonal antibodies specific for EBV nuclear antigen 1 (EBNA1) (2H4), EBNA2 (PE2 and the new rat anti-EBNA2 monoclonal antibodies 1E6, R3, and 3E9), and LMP1 (CS1-4 and S12). Double staining was performed combining R3 or 3E9 with S12.

RESULTS

R3 and 3E9 anti-EBNA2 monoclonal antibodies were more sensitive than PE2, enabling the detection of more EBNA2 positive lymphoma cells. Both in post-transplantation lymphoproliferative disorders and AIDS related lymphomas, different expression patterns were detected at the single cell level. Smaller neoplastic cells were positive for EBNA2 but negative for LMP1. Larger and more blastic neoplastic cells, sometimes resembling Reed-Sternberg cells, were LMP1 positive but EBNA2 negative (EBV latency type II). Morphologically intermediate neoplastic cells coexpressing EBNA2 and LMP1 (EBV latency type III), were detected using R3 and 3E9, and formed a considerable part of the neoplastic population in four of nine post-transplantation lymphoproliferative disorders and two of three AIDS related lymphomas. All samples contained a subpopulation of small tumour cells positive exclusively for Epstein-Barr early RNA and EBNA1. The relation between cellular morphology and EBV expression patterns in this study was less pronounced in AIDS related lymphomas than in post-transplantation lymphoproliferative disorders, because the AIDS related lymphomas were less polymorphic than the post-transplantation lymphoproliferative disorders.

CONCLUSIONS

In post-transplantation lymphoproliferative disorders and AIDS related lymphomas, EBV latency type III can be detected by immunohistochemistry in a subpopulation of tumour cells using sensitive monoclonal antibodies R3 and 3E9. Our data suggest that EBV infected tumour cells in these lymphomas undergo gradual changes in the expression of EBV latent genes, and that these changes are associated with changes in cellular morphology.

ICAM-1, soluble-CD23, and interleukin-10 concentrations in serum in renal-transplant recipients with Epstein-Barr virus reactivation

Primary and reactivated Epstein-Barr virus (EBV) infections after organ transplantation are associated with the development of posttransplant lymphoproliferative malignancies. Since viral reactivation frequently stays asymptomatic, early diagnosis and treatment are challenges during posttransplant patient monitoring. Both soluble-CD23 (sCD23) and intercellular adhesion molecule 1 (ICAM-1) cell surface expression as well as interleukin-10 (IL-10) production are closely associated with viral gene expression. Therefore, immunoglobulin M (IgM), IgG, IgA, sCD23, ICAM-1, and IL-10 concentrations were measured in serum samples from patients during EBV reactivation (n = 14) and were compared with those in samples from patients without EBV reactivation (n = 10) following renal transplantation. In addition, serum sCD23, ICAM-1, and IL-10 concentrations were measured longitudinally in weekly to biweekly samples from 10 patients with EBV reactivation for at least 20 weeks following transplantation. A significant elevation of sCD23 was found during viral reactivation (P < 0.05), whereas ICAM-1 levels showed a nonsignificant increase. The finding of a highly significant elevation of the serum IL-10 concentration during EBV reactivation (P < 0.001) may support speculations about its role in EBV-induced lymphoproliferation and in the development of opportunistic infections and secondary malignancies. Maximum serum IL-10 levels at the time of EBV reactivation were found in 7 of 10 patients. Well-defined ICAM-1 and sCD23 concentration peaks were found in 9 of 10 and 8 of 10 patients, respectively. Although both markers are not specific for EBV reactivation and therefore may not be useful for primary diagnosis, sCD23 and ICAM-1 might be potent tools for the clinical monitoring of EBV activity and virus-induced lymphoproliferation.

Isolation of Epstein-Barr Virus (EBV)-Specific Cytotoxic T Lymphocytes That Lyse Reed-Sternberg Cells: Implications for Immune-Mediated Therapy of EBV+ Hodgkin's Disease

A subset of Hodgkin's disease (HD) patients have detectable Epstein-Barr virus (EBV) genomes in the malignant Reed-Sternberg (R-S) cells. R-S cells express only a limited set of latent EBV proteins, but only LMP1 and LMP2 can potentially elicit a CD8+ cytotoxic T-lymphocyte (CTL) response. We have evaluated if either of these proteins could be used as targets for specific adoptive T-cell therapy for EBV-positive (EBV+) HD. The success of this strategy requires that R-S cells are susceptible to lysis by CD8+ CTL, and that CTL specific for LMP1 and LMP2 can be detected and potentially amplified in HD patients. Antigen presentation and CTL sensitivity was evaluated with an in vitro maintained, phenotypically representative R-S cell line, HDLM-2. The R-S cells were able to process and present viral proteins, and to be efficiently lysed by specific CTL in a Class I–restricted manner. Since CTL responses to LMP1 and LMP2 do not represent the dominant responses to EBV, we examined if CTL clones specific for these proteins could be isolated despite the presence of weak or nondetectable responses in polyclonal T-cell lines. LMP-specific clones were generated from individuals either by cloning from the polyclonal EBV-reactive T-cell lines or by direct stimulation of peripheral blood mononuclear cells (PBMC) with cells expressing LMP1 or LMP2 as the only EBV protein. Our ability to isolate CTL specific for LMP proteins from individuals with HD and the sensitivity of R-S cells for CTL-mediated lysis suggest that the pursuit of specific adoptive immunotherapy represents a viable strategy for the subset of HD patients with EBV+ tumors.

Human cytotoxic T lymphocyte responses to Epstein-Barr virus infection

Epstein-Barr virus (EBV) provides one of the most informative systems with which to study cytotoxic T lymphocyte (CTL) responses in humans. The virus establishes a highly immunogenic growth-transforming infection of B lymphocytes, associated with the coordinate expression of six virus-coded nuclear antigens (EBNAs 1, 2, 3A, 3B, 3C, -LP) and two latent membrane proteins (LMPs 1 and 2). This elicits both primary and memory CT8+ CTL responses that are markedly skewed toward HLA allele-specific epitopes drawn from the EBNA3A, 3B, 3C subset of latent proteins, with reactivities to other antigens being generally much less frequent. This hierarchy of immunodominance among the different latent proteins may at least partly reflect their differential accessibility to the HLA class I-processing pathway. Furthermore, CTLs to some of the immunodominant epitopes involve highly conserved T cell receptor (TCR) usage, a level of focusing which evidence suggests could have immunopathological consequences from cross-reactive recognition of other target structures. EBV is associated with a range of human tumors, and there is increasing interest in the possibility of targeting such malignancies using virus-specific CTLs. The dramatic reversal of EBV-driven lymphoproliferations in bone marrow transplant patients following CTL infusion demonstrates the potential of this approach, and here we discuss prospects for its extension to other EBV-positive tumors in which the immunodominant EBNA3A, 3B, 3C proteins are not expressed.

Epstein-Barr virus latent membrane protein 1 blocks p53-mediated apoptosis through the induction of the A20 gene

Two Epstein-Barr virus (EBV)-associated malignancies, nasopharyngeal carcinoma and posttransplant lymphoma, rarely have mutations in the p53 tumor suppressor gene, suggesting that a viral protein interferes with p53 function. The EBV oncogene, LMP1, induces expression of the cellular antiapoptotic genes bcl-2 and A20 and could in this way interfere with p53-mediated apoptosis. Two derivatives of the p53-null epithelial cell line H1299 were prepared, one of which (H1299-p53) stably expressed a temperature-sensitive (ts) p53 protein, and another (H1299-p53+LMP1) which stably expressed both ts-p53 and latent membrane protein 1 (LMP1). At the permissive temperature, the p53 protein in the H1299-p53 cell line transcriptionally activated two of its target genes, the cyclin-dependent kinase inhibitor p21 and the mdm2 gene product, in an LMP1-independent manner. Upon serum withdrawal at the permissive temperature, p53-mediated apoptosis was induced in 50 to 60% of the cells. In the H1299-p53 cell line which stably expressed LMP1, however, only 20 to 25% of the cells underwent apoptosis. While stable expression of LMP1 did not affect levels of bcl-2 family members in these cells, it did induce expression of A20. Stable expression of A20 in the H1299-p53 cell line inhibited p53-mediated apoptosis equivalent to inhibition by LMP1. The induction of A20 may underlie the ability of LMP1 to protect EBV-infected epithelial cells from p53-mediated apoptosis.

Differential tumorigenicity between Epstein-Barr virus genome-positive and genome-negative cell lines with t(11;14)(q13;q32) derived from mantle cell lymphoma

Epstein-Barr virus (EBV) genome has been detected in several human lymphoproliferative diseases, but the oncogenic function of EBV is not fully understood. We previously established EBV-positive (SP-50B) and EBV-negative (SP-53) cell lines with the t(11;14)(q13;q32) chromosome abnormality from a single patient with mantle cell lymphoma. Monoclonal EBV DNA in a circular episomal form was demonstrated in the SP-50B cells by Southern blot hybridization with the EBV-terminal fragment probe. SP-50B cells were positive for not only EBV-encoded nuclear antigen-1 (EBNA1) but also latent membrane protein-1 and EBNA2. None of the EBV-encoded proteins was expressed in SP-53 cells. The isogenic EBV-infected and EBV-free cell lines of neoplastic clones made it possible to examine a tumorigenic role of EBV. Only EBV-positive SP-50B cells possessed malignant phenotypes, such as growth ability in low serum, colony formation in soft agarose, and tumorigenicity in nude mice. On the other hand, a lymphoblastoid B-cell line established by infecting the patient's normal B lymphocytes in vitro with exogenous EBV had no tumorigenicity. These results suggested that EBV infection, if it occurred in neoplastic lymphoma cells, could play a role in acquisition of malignant phenotypes.

Expression of epstein-barr virus encoded nuclear antigen 1 in benign and malignant tissues harbouring EBV

AIMS

To determine levels of expression of Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) in benign and malignant tissues harbouring EBV in relation to EBNA1 promoter usage.

METHODS

Expression of EBNA1 was investigated by means of immunohistochemistry using a mixture of two EBNA1 specific monoclonal antibodies, 1H4-1 and 2B4-1. The presence of EBV was detected by EBER1/2 RNA in situ hybridisation. Detection of promoter specific EBNA1 transcripts was by RT-PCR analysis.

RESULTS

EBNA1 positive cells were detected in all 20 EBV associated B cell lymphomas, 18 of which had arisen in immunocompromised patients; in eight of nine EBV associated T cell lymphomas; in 11 of 27 EBV positive cases of Hodgkin's disease; and in reactive lymphoid tissue harbouring EBV, including four cases of infectious mononucleosis. A diffuse EBNA1 staining pattern was observed in most of the EBV associated B cell lymphomas and was comparable with the EBER1/2 staining pattern. In the T cell lymphomas the number of EBNA1 positive cells was usually considerably less than the number of EBER1/2 positive ones. RT-PCR analysis revealed that in tumours with restricted EBNA1 expression-that is, T cell lymphomas and Hodgkin's disease lesions, EBNA1 transcripts were usually generated only by the F/Q promoter, whereas in B cell lymphomas EBNA1 transcripts were usually generated by both the C/W and F/Q promoters.

CONCLUSIONS

EBNA1 is expressed in all types of tissue harbouring EBV, but the level of expression varies greatly. This may be the result of differential promoter usage.

Mature B cells are required for acute splenic infection, but not for establishment of latency, by murine gammaherpesvirus 68

Murine gammaherpesvirus 68 (gamma HV-68; also referred to as MHV-68) is a gammaherpesvirus which infects murid rodents. Previous studies showed that CD8 T cells are important for controlling gamma HV-68 replication during the first 2 weeks of infection and suggested a role for B cells in latent or persistent gamma HV-68 infection. To further define the importance of B cells and CD8 T cells during acute and chronic gamma HV-68 infection, we examined splenic infection in mice with null mutations in the transmembrane domain of the mu-heavy-chain constant region (MuMT; B-cell and antibody deficient) or in the beta2-microglobulin gene (beta2 -/-; CD8 deficient). Immunocompetent mice infected intraperitoneally with gamma HV-68 demonstrated peak splenic titers 9 to 10 days postinfection, cleared infectious virus 15 to 20 days postinfection, and harbored low levels of latent virus at 6 weeks postinfection. Beta2-/- mice showed peak splenic gamma HV-68 titers similar to those of normal mice but were unable to clear infectious virus completely from the spleen, demonstrating persistent infectious virus 6 weeks postinfection. These data indicate that CD8 T cells are important for clearing infectious gamma HV-68 from the spleen. Infected MuMT mice did not demonstrate detectable infectious gamma HV-68 in the spleen at any time after infection, indicating that mature B lymphocytes are necessary for acute splenic infection by gamma HV-68. Despite the lack of measurable acute infection, MuMT spleen cells harbored latent virus 6 weeks postinfection at a level about 100-fold higher than that in normal mice. These data demonstrate establishment of latency by a herpesvirus in an organ in the absence of acute viral replication in that organ. In addition, they demonstrate that gamma HV-68 can establish latency in a cell type other than mature B lymphocytes.

Human Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes home preferentially to and induce selective regressions of autologous EBV-induced B cell lymphoproliferations in xenografted C.B-17 scid/scid mice

C.B-17 scid/scid (severe combined immunodeficiency [SCID]) mice inoculated with peripheral blood lymphocytes from Epstein-Barr virus (EBV)-seropositive donors, or with EBV-transformed lymphoblastoid B cell lines (EBV-LCL), develop lethal human EBV+ B cell lymphoproliferative disorders (EBV-LPD) with characteristics similar to those arising in immunodeficient patients. Using this model, we examined the capacity of human effector cells to control human EBV-LPD. SCID mice received rabbit anti-asialo GM1 antiserum to abrogate endogenous natural killer-cell function. Preliminary experiments showed that adoptive transfer of peripheral blood mononuclear cells (PBMC), purified T cells, interleukin (IL) 2-activated PBMC or anti-CD3-activated T cells derived from EBV-seropositive donors did not result in improved survival of treated mice (in vivo effector/target ratio 2:1 to 1:1). In contrast, EBV-specific cytotoxic T lymphocytes (CTL), derived from EBV-seropositive donors and expanded in vitro, exhibited strong EBV-specific and HLA-restricted activity both in vitro and in vivo. SCID mice inoculated intraperitoneally with autologous but not with HLA-mismatched EBV-LCL had significantly improved survival relative to untreated mice after inoculation of EBV-specific CTL either intraperitoneally (P<0.001) or intravenously (P<0.001) (in vivo effector/target ratio 1:1). SCID mice bearing large subcutaneous EBV+ tumors and treated intravenously with 10(7) EBV-specific CTL achieved complete tumor regression. Both CTL- and CTL-plus-IL-2-treated mice survived significantly longer than untreated animals or animals treated with IL-2 alone (P = 0.0004 and P<0.02, respectively). SCID mice bearing two subcutaneous EBV+ tumors, one autologous and the other HLA mismatched to the EBV-specific CTL donor, had regression of only the autologous tumor after intravenous infusion of 10(7) EBV-specific CTL. Moreover, we could demonstrate preferential homing of PKH26-labeled EBV-specific CTL to autologous but not to HLA-mismatched EBV+ tumors as early as 24 h after intravenous adoptive transfer. Immunophenotypic analyses also demonstrated preferential infiltration of T cells into the autologous EBV+ tumor in SCID mice bearing both the autologous and either fully HLA-mismatched or genotypically related haplotype-sharing EBV+ tumors. The human T cells infiltrating EBV+ tumors were CD3+ and, predominantly, CD8+CD4-. Our results indicate that EBV-specific CTL preferentially localize to and infiltrate EBV+ tumors bearing the appropriate HLA antigens and thereafter induce targeted regressions of disease.

Down-regulation of Epstein-Barr virus nuclear antigen 1 in Reed-Sternberg cells of Hodgkin's disease

AIMS

To demonstrate Epstein-Barr virus (EBV) encoded nuclear antigen 1 (EBNA-1) gene expression in EBV associated disorders using a new monoclonal antibody (1H4-1) on routinely processed tissues.

METHODS

The pressure cooker antigen retrieval method was used for the immunohistochemical demonstration of EBNA-1 gene expression in formalin fixed, EBV positive tissues from Hodgkin's disease, infectious mononucleosis, HIV associated non-Hodgkin's lymphomas, post-transplant lymphomas, and undifferentiated nasopharyngeal carcinoma (NPC). EBV encoded EBNA-2, latent membrane protein 1 (LMP-1) and BZLF-1 gene expression was also examined using commercially available monoclonal antibodies.

RESULTS

Of the 34 EBER in situ hybridisation positive cases of Hodgkin's disease examined, none expressed EBNA-1 in the Reed-Sternberg cells. These cells were nevertheless strongly LMP-1 positive in all cases. Strong EBNA-1 staining was seen in all cases of EBER positive HIV associated non-Hodgkin's lymphoma (five of five), nasopharyngeal carcinoma (five of five), infectious mononucleosis (three of three), and post-transplant lymphoma (one of one). These cases also expressed LMP-1, EBNA-2 and BZLF-1, but at differing levels.

CONCLUSION

The pressure cooker antigen retrieval procedure is a sensitive and reliable adjunct to immunohistochemistry, especially with antibodies which are otherwise ineffective on routinely processed tissues. The EBNA-1 gene is not expressed at detectable levels in the malignant cells of Hodgkin's disease, but is consistently expressed in other EBV associated disorders. This finding has important implications for the role of EBNA-1 in the biology of EBV.

Crucial sequences within the Epstein-Barr virus TP1 promoter for EBNA2-mediated transactivation and interaction of EBNA2 with its responsive element

EBNA2 is one of the few genes of Epstein-Barr virus which are necessary for immortalization of human primary B lymphocytes. The EBNA2 protein acts as a transcriptional activator of several viral and cellular genes. For the TP1 promoter, we have shown previously that an EBNA2-responsive element (EBNA2RE) between -258 and -177 relative to the TP1 RNA start site is necessary and sufficient for EBNA2-mediated transactivation and that it binds EBNA2 through a cellular factor. To define the critical cis elements within this region, we cloned EBNA2RE mutants in front of the TP1 minimal promoter fused to the reporter gene for luciferase. Transactivation by EBNA2 was tested by transfection of these mutants in the absence and presence of an EBNA2 expression vector into the established B-cell line BL41-P3HR-1. The analysis revealed that two identical 11-bp motifs and the region 3' of the second 11-bp motif are essential for transactivation by EBNA2. Methylation interference experiments indicated that the same cellular factor in the absence of EBNA2 binds either one (complex I) or both (complex III) 11-bp motifs with different affinities, giving rise to two different specific protein-DNA complexes within the left-hand 54 bp of EBNA2RE. A third specific complex was shown previously to be present only in EBNA2-expressing cells and to contain EBNA2. Analysis of this EBNA2-containing complex revealed the same protection pattern as for complex III, indicating that EBNA2 interacts with DNA through binding of the cellular protein to the 11-bp motifs. Mobility shift assays with the different mutants demonstrated that one 11-bp motif is sufficient for binding the cellular factor, whereas for binding of EBNA2 as well as for efficient transactivation by EBNA2, both 11-bp motifs are required.

Viral infections in severely immunocompromised cancer patients

Immunocompromised cancer patients are susceptible to infection by many viral pathogens. The most serious morbidity results from active infection by members of the herpes virus family. Reactivation of latent virus occurs as a sequela of cytotoxic therapy and deficiency of cell-mediated immunity, especially cytotoxic responses, the major host protective defense. Herpes simplex virus and varicella zoster virus infections are problematic in patients with all types of cancer; cytomegalovirus infections cause life-threatening morbidity in bone marrow transplant patients. Several antiviral agents are highly active against these pathogens and different strategies of using them have resulted in reduced morbidity and mortality. Ultimately, the resolution of these infections is dependent on the control of the malignancy and the ability of the patient to mount an adequate immune response.

EBV gene expression, EBNA antibody responses and EBV+ peripheral blood lymphocytes in post-transplant lymphoproliferative disease

Epstein-Barr virus (EBV) is associated with the development of several B cell malignancies including Burkitt's lymphoma (BL), post-transplant lymphoproliferative disease (PTLD), and AIDS-related lymphomas. The latter two diseases result from EBV-driven B cell proliferation in the absence of normal immunosurveillance and as such, represent a heterogenous family of lymphoproliferative disorders. This article reviews studies on EBV gene expression and antibody development in PTLD and introduces recent information on the levels of EBV+ peripheral blood lymphocytes to discuss possible mechanisms of pathogenesis under varying conditions of immunosuppression.

Alterations of the p53 gene in Epstein-Barr virus-associated immunodeficiency-related lymphomas

Mutations of the p53 tumor suppressor gene are among the most common genetic alterations found in many different human malignancies, including those of the colon, lung, and breast. Alterations in wild-type p53 lead to loss of the suppressor function and thus contribute to tumorigenesis. The potential role of p53 mutations in a sampling of B-cell lymphomas, the majority of which were associated with Epstein-Barr virus (EBV), was investigated. Twenty-six biopsy specimens from immunocompromised patients, including allograft recipients and patients with AIDS, Wiscott-Aldrich syndrome, and human T-cell leukemia virus type 1 infection, in comparison with three Burkitt lymphomas and four Burkitt lymphoma cell lines were analyzed. Mutation in p53 was detected in all four Burkitt lymphoma cell lines as well as the three Burkitt lymphoma biopsy specimens. In patients with AIDS, 5 of 10 lymphomas were EBV positive, and 1 had a mutation in p53. Mutation in p53 was not detected in 14 EBV-positive lymphomas which arose in transplant recipients. These data indicate that with the exception of Burkitt lymphomas, p53 mutations are not involved in the majority EBV-positive B-cell lymphomas which develop in immunocompromised patients.

Manifestations of Epstein-Barr virus-associated disorders in liver

Epstein-Barr virus is a ubiquitous virus associated with a variety of different diseases and disorders. The manifestations of Epstein-Barr virus-associated diseases or disorders within the liver, which involve a broad spectrum of histologic and clinical features, ranging from hepatitis through lymphoproliferative disorders to lymphoma, are presented. An important aspect of Epstein-Barr virus expression and infection is the biology of the Epstein-Barr virus. Documentation of infection can be performed using serology to detect the interaction of Epstein-Barr virus with the immune system, and the detection of EBV proteins and use of molecular biologic techniques to identify the presence of EBV RNA, and DNA sequences. Of particular utility are in situ hybridization, Southern blot analysis, and polymerase chain reaction as diagnostic methods to identify specific RNA or DNA sequences. Epstein-Barr virus-associated diseases and disorders including infectious mononucleosis, sporadic fatal infectious mononucleosis, X-linked proliferative disorder (Duncan's disease), post-transplant lymphoproliferative disorders, lymphoma, and AIDS are discussed. The histopathologic findings present in liver associated with each disease are presented with illustrative examples. Handling the tissue and interaction with clinical services are also discussed as a method for appropriate diagnosis of Epstein-Barr virus-driven processes affecting the liver.

Epstein-Barr virus (EBV)-encoded membrane protein LMP1 from a nasopharyngeal carcinoma is non-immunogenic in a murine model system, in contrast to a B cell-derived homologue

Epstein-Barr virus (EBV)-encoded LMP1 gene derived from a nude mouse passaged nasopharyngeal carcinoma (NPC) of Chinese origin (C-LMP1) and its B cell (B95-8 prototype)-derived counterpart (B-LMP1) were compared for their ability to induce tumour rejection in a mouse mammary adenocarcinoma system. Each of the two LMP1 genes was introduced individually by retroviral vectors into a non-immunogenic mammary carcinoma line, S6C, that originated in an ACA (H-2f) mouse. Syngeneic ACA mice were immunised for 3 consecutive weeks with irradiated B- or C-LMP1 expressors or control cells. The immunised and control mice were then challenged with graded numbers of viable cells from the corresponding cell line. Only the B-LMP1 expressing cells were highly immunogenic. Up to 10(5) cells were rejected in pre-immunised mice, whereas at least 10(2) cells grew in non-immunised controls. No rejection response was detected against the C-LMP1 expressing cells which grew equally well in control and immunised mice, with a minimum inoculum of 10(2) cells in the majority of the clones. In a previous study, we found numerous sequence differences between B- and C-LMP1. The question of whether any of these differences is related to the non-immunogenicity of C-LMP1 needs further investigation. Meanwhile, our findings raise the possibility that the NPC cells may escape host rejection by the development of a non-immunogenic LMP1 variant under the impact of immunoselection.

HLA A2.1-restricted cytotoxic T cells recognizing a range of Epstein-Barr virus isolates through a defined epitope in latent membrane protein LMP2

Cytotoxic T-lymphocyte (CTL) responses induced by persistent Epstein-Barr virus (EBV) infection in normal B-lymphoid tissues could potentially be directed against EBV-positive malignancies if expression of the relevant viral target proteins is maintained in tumor cells. For malignancies such as nasopharyngeal carcinoma and Hodgkin's disease, this will require CTL targeting against the nuclear antigen EBNA1 or the latent membrane proteins LMP1 and LMP2. Here we analyze in detail a B95.8 EBV-reactivated CTL response which is specific for LMP2 and restricted through a common HLA allele, A2.1. We found that in vitro-reactivated CTL preparations from several A2.1-positive virus-immune donors contained detectable reactivity against A2.1-bearing target cells expressing either LMP2A or the smaller LMP2B protein from recombinant vaccinia virus vectors. Peptide sensitization experiments then mapped the A2.1-restricted response to a single epitope, the nonamer CLGGLLTMV (LMP2A residues 426 to 434), whose sequence accords well with the proposed peptide binding motif for A2.1. Most Caucasian and African virus isolates (whether of type 1 or type 2) were identical in sequence to B95.8 across this LMP2 epitope region, although 2 of 12 such isolates encoded a Leu-->Ile change at epitope position 6. In contrast, most Southeast Asian and New Guinean isolates (whether of type 1 or type 2) constituted a different virus group with a Cys-->Ser mutation at epitope position 1. CTLs raised against the B95.8-encoded epitope were nevertheless able to recognize these variant epitope sequences in the context of A2.1 whether they were provided exogenously as synthetic peptides or generated endogenously in B cells transformed with the variant viruses. A CTL response of this kind could have therapeutic potential in that it is directed against a protein expressed in many EBV-positive malignancies, is reactive across a range of virus isolates, and is restricted through a relatively common HLA allele.

High incidence of monoclonal EBV episomes in Hodgkin's disease and anaplastic large-cell KI-1-positive lymphomas in HIV-1-positive patients

A series of selected lymphoid malignancies (LMs) occurring in Italian HIV-1-infected (HIV+) patients, principally intravenous drug users, was investigated. In addition to small non-cleaved-cell (SNCC) and large-cell immunoblastic (LCI) non-Hodgkin's lymphomas (NHLs), a relatively high occurrence of anaplastic large-cell Ki-I-positive (ALC Ki-I+) lymphomas and Hodgkin's disease (HD) was observed, at variance with other reported series of HIV+ patients. Combined results of in situ hybridization and Southern-blot analyses, in conjunction with immunohistochemical detection of Epstein-Barr virus (EBV)-encoded latent membrane protein-I (LMP-I), showed an almost complete association of ALC Ki-I+ lymphomas and HD cases with EBV. The neoplastic cells of both these LMs also showed common immunophenotypic features such as frequent absence of B- and T-cell differentiation markers and expression of the Ki-I activation marker, while SNCC and LCI lymphomas were mainly of mature B-cell origin and Ki-I-. The concomitant high incidence of ALC Ki-I+ lymphomas and HD in a specific group of HIV+ patients, their almost complete association with EBV in clonal and episomal form and the great similarity in differentiation, activation and virological markers which they display suggest that these LMs are pathological variants of a continuous spectrum of HIV-I-associated disorders etiopathologically linked to EBV.

Multiple HLA A11-restricted cytotoxic T-lymphocyte epitopes of different immunogenicities in the Epstein-Barr virus-encoded nuclear antigen 4

Epstein-Barr virus (EBV), a ubiquitous herpesvirus, induces potent HLA class I-restricted cytotoxic T-lymphocyte (CTL) responses. Analyses of target antigen choice have shown that the very strong CTL responses which are often observed through the HLA A11 allele map are due almost entirely to a single transformation-associated EBV protein, the nuclear antigen EBNA4. Here, we sought to determine the number and relative immunogenicities of HLA A11-restricted epitopes within this 938-amino-acid protein. An initial screening with a series of recombinant vaccinia virus vectors encoding progressively truncated forms of EBNA4 was followed by peptide sensitization experiments using overlapping 14- or 15-mers from the entire sequence. These two approaches allowed the identification of five epitope regions located between residues 101 and 115, 416 and 429, 396 and 410, 481 and 495, and 551 and 564 of the EBNA4 molecule. CTL preparations from all seven HLA A11-positive donors tested had demonstrable reactivities against the 416-to-429 peptide, whereas reactivities against the other epitopes either tended to be lost on serial passage or, for some of the donors, were never detected. The immunodominance of the 416-to-429 epitope was further supported by peptide dilution assays using polyclonal effectors and by CTL cloning experiments. Analysis of the 416-to-429 region identified the nanomer 416-424 (IVTDFSVIK) as the cognate peptide. This peptide was able to sensitize targets to lysis by A11-restricted CTL clones at concentrations as low as 5 x 10(-14) M.

Recognition of the Epstein-Barr virus-encoded nuclear antigens EBNA-4 and EBNA-6 by HLA-A11-restricted cytotoxic T lymphocytes: implications for down-regulation of HLA-A11 in Burkitt lymphoma

Evasion from cytotoxic T-lymphocyte (CTL) surveillance may be an important step in the pathogenesis of Epstein-Barr virus (EBV)-carrying Burkitt lymphoma (BL) as suggested by the consistent down-regulation of all transformation-associated viral antigens, except EBV nuclear antigen 1 (EBNA-1), and of certain HLA class I alleles in BL biopsies and cell lines that maintain the tumor cell phenotype in vitro. The most common HLA class I defect recorded in BL lines is a selective down-regulation of HLA-A11. To gain some insight into the role of HLA-A11 down-regulation in pathogenesis of BL, we have investigated the target specificity of HLA-A11-restricted CTLs derived by stimulation of lymphocytes from three EBV-seropositive individuals with autologous EBV-transformed lymphoblastoid cell lines. Recombinant vaccinia viruses carrying the coding sequences for EBNA-1, -2A, -2B, -5, -3, -4, and -6 (also known as EBNA-1, -2A, -2B, -LP, -3a, -3b, and -3c, respectively) and EBV latent membrane protein 1 were used to induce high levels of expression of the relevant EBV antigen in fibroblasts derived from HLA class I-matched individuals. EBNA-4-expressing fibroblasts were the predominant target of HLA-A11-restricted CTLs in all three donors. A less pronounced and less regular EBNA-6-specific cytotoxic component was found in two of the donors.

Epstein-Barr virus infection in allogeneic marrow grafting: lessons for transplant physicians and virologists

The relationship between Epstein-Barr virus (EBV) and the host is profoundly disturbed by allogeneic bone marrow transplantation (BMT) because EBV resides in the recipient's hematopoietic system, which has to be destroyed in the majority of cases, and in the donor's hematopoietic system, i.e., the marrow graft. We have shown that EBV may be eradicated from some BMT recipients and that the virus may be transferred with the marrow graft. During the immediate post-transplant period oropharyngeal EBV excretion may occur which, by infecting passing B lymphocytes, may act as co-factor for acute graft-versus-host disease and help the virus to survive, despite the temporary depletion of its reservoir. The coexistence of totally different EBV strains in BMT recipients but not in healthy, untransfused controls, suggests that superinfection may by possible in case of immunodeficiency; alternatively, transfer of the virus by the reservoir itself (the B lymphocytes) might be the only effective route for superinfection. The generation of 'variant' strains during viral replication may form the basis of the vast polymorphism between wild-type EBV isolates in the population.