Regression of Epstein-Barr virus-induced B-cell transformation in vitro involves virus-specific CD8+ T cells as the principal effectors and a novel CD4+ T-cell reactivity

Heightened Epstein-Barr virus immunity and potential cross-reactivities in multiple sclerosis

BACKGROUND

Epstein-Barr virus (EBV) is a likely prerequisite for multiple sclerosis (MS) but the underlying mechanisms are unknown. We investigated antibody and T cell responses to EBV in persons with MS (pwMS), healthy EBV-seropositive controls (HC) and post-infectious mononucleosis (POST-IM) individuals up to 6 months after disease resolution. The ability of EBV-specific T cell responses to target antigens from the central nervous system (CNS) was also investigated.

METHODS

Untreated persons with relapsing-remitting MS, POST-IM individuals and HC were, as far as possible, matched for gender, age and HLA-DRB1*15:01. EBV load was determined by qPCR, and IgG responses to key EBV antigens were determined by ELISA, immunofluorescence and Western blot, and tetanus toxoid antibody responses by multiplex bead array. EBV-specific T cell responses were determined ex vivo by intracellular cytokine staining (ICS) and cross-reactivity of in vitro-expanded responses probed against 9 novel Modified Vaccinia Ankara (MVA) viruses expressing candidate CNS autoantigens.

RESULTS

EBV load in peripheral blood mononuclear cells (PBMC) was unchanged in pwMS compared to HC. Serologically, while tetanus toxoid responses were unchanged between groups, IgG responses to EBNA1 and virus capsid antigen (VCA) were significantly elevated (EBNA1 p = 0.0079, VCA p = 0.0298) but, importantly, IgG responses to EBNA2 and the EBNA3 family antigens were also more frequently detected in pwMS (EBNA2 p = 0.042 and EBNA3 p = 0.005). In ex vivo assays, T cell responses to autologous EBV-transformed B cells and to EBNA1 were largely unchanged numerically, but significantly increased IL-2 production was observed in response to certain stimuli in pwMS. EBV-specific polyclonal T cell lines from both MS and HC showed high levels of autoantigen recognition by ICS, and several neuronal proteins emerged as common targets including MOG, MBP, PLP and MOBP.

DISCUSSION

Elevated serum EBV-specific antibody responses in the MS group were found to extend beyond EBNA1, suggesting a larger dysregulation of EBV-specific antibody responses than previously recognised. Differences in T cell responses to EBV were more difficult to discern, however stimulating EBV-expanded polyclonal T cell lines with 9 candidate CNS autoantigens revealed a high level of autoreactivity and indicate a far-reaching ability of the virus-induced T cell compartment to damage the CNS.

Membrane-bound CD95 ligand modulates CD19-mediated B cell receptor signaling and EBV activation

Post-transplant lymphoproliferative disorders (PTLDs) are associated with Epstein-Barr virus (EBV) infection in transplant recipients. Most of lymphoblastoid cell lines (LCLs) derived from EBV-immortalized B cells or PTLDs are sensitive to CD95-mediated apoptosis and cytotoxic T cell (CTL) killing. CD95 ligand (CD95L) exists as a transmembrane ligand (mCD95L) or a soluble form (sCD95L). Using recombinant mCD95L and sCD95L, we observed that sCD95L does not affect LCLs. While high expression of mCD95L in CTLs promotes apoptosis of LCLs, low expression induces clathrin-dependent CD19 internalization, caspase-dependent CD19 cleavage, and proteasomal/lysosomal-dependent CD19 degradation. The CD95L/CD95-mediated CD19 degradation impairs B cell receptor (BCR) signaling and inhibits BCR-mediated EBV activation. Interestingly, although inhibition of the caspase activity restores CD19 expression and CD19-mediated BCR activation, it fails to rescue BCR-mediated EBV lytic gene expression. EBV-specific CTLs engineered to overexpress mCD95L exhibit a stronger killing activity against LCLs. This study highlights that engineering EBV-specific CTLs to express a higher level of mCD95L could represent an attractive therapeutic approach to improve T cell immunotherapy for PTLDs.

EBV-induced T-cell responses in EBV-specific and nonspecific cancers

Epstein-Barr virus (EBV) is a ubiquitous human tumor virus associated with various malignancies, including B-lymphoma, NK and T-lymphoma, and epithelial carcinoma. It infects B lymphocytes and epithelial cells within the oropharynx and establishes persistent infection in memory B cells. With a balanced virus-host interaction, most individuals carry EBV asymptomatically because of the lifelong surveillance by T cell immunity against EBV. A stable anti-EBV T cell repertoire is maintained in memory at high frequency in the blood throughout persistent EBV infection. Patients with impaired T cell immunity are more likely to develop life-threatening lymphoproliferative disorders, highlighting the critical role of T cells in achieving the EBV-host balance. Recent studies reveal that the EBV protein, LMP1, triggers robust T-cell responses against multiple tumor-associated antigens (TAAs) in B cells. Additionally, EBV-specific T cells have been identified in EBV-unrelated cancers, raising questions about their role in antitumor immunity. Herein, we summarize T-cell responses in EBV-related cancers, considering latency patterns, host immune status, and factors like human leukocyte antigen (HLA) susceptibility, which may affect immune outcomes. We discuss EBV-induced TAA-specific T cell responses and explore the potential roles of EBV-specific T cell subsets in tumor microenvironments. We also describe T-cell immunotherapy strategies that harness EBV antigens, ranging from EBV-specific T cells to T cell receptor-engineered T cells. Lastly, we discuss the involvement of γδ T-cells in EBV infection and associated diseases, aiming to elucidate the comprehensive interplay between EBV and T-cell immunity.

Membranal and Blood-Soluble HLA Class II Peptidome Analyses Using Data-Dependent and Independent Acquisition

The interaction between HLA class II peptide complexes on antigen-presenting cells and CD4⁺ T cells is of fundamental importance for anticancer and antipathogen immunity as well as for the maintenance of immunological tolerance. To study CD4⁺ T cell reactivities, detailed knowledge of the presented peptides is necessary. In recent years, dramatic advances in the characterization of membranal and soluble HLA class I peptidomes could be observed. However, the same is not true for HLA class II peptidomes, where only few studies identify more than hundred peptides. Here we describe a MS-based workflow for the characterization of membranal and soluble HLA class II DR and DQ peptidomes. Using this workflow, we identify a total of 8595 and 3727 HLA class II peptides from Maver-1 and DOHH2 cells, respectively. Based on this data, a motif-based binding predictor is developed and compared to NetMHCIIpan 3.1. We then apply the workflow to human plasma, resulting in the identification of between 34 and 152 HLA-DR and between 100 and 180 HLA-DQ peptides, respectively. Finally, we implement a data-independent acquisition workflow to increase reproducibility and sensitivity of HLA class II peptidome characterizations.

Defective T-cell control of Epstein-Barr virus infection in multiple sclerosis

Mounting evidence indicates that infection with Epstein–Barr virus (EBV) has a major role in the pathogenesis of multiple sclerosis (MS). Defective elimination of EBV-infected B cells by CD8⁺ T cells might cause MS by allowing EBV-infected autoreactive B cells to accumulate in the brain. Here we undertake a comprehensive analysis of the T-cell response to EBV in MS, using flow cytometry and intracellular IFN-γ staining to measure T-cell responses to EBV-infected autologous lymphoblastoid cell lines and pools of human leukocyte antigen (HLA)-class-I-restricted peptides from EBV lytic or latent proteins and cytomegalovirus (CMV), in 95 patients and 56 EBV-seropositive healthy subjects. In 20 HLA-A2⁺ healthy subjects and 20 HLA-A2⁺ patients we also analysed CD8⁺ T cells specific for individual peptides, measured by binding to HLA-peptide complexes and production of IFN-γ, TNF-α and IL-2. We found a decreased CD8⁺ T-cell response to EBV lytic, but not CMV lytic, antigens at the onset of MS and at all subsequent disease stages. CD8⁺ T cells directed against EBV latent antigens were increased but had reduced cytokine polyfunctionality indicating T-cell exhaustion. During attacks the EBV-specific CD4⁺ and CD8⁺ T-cell populations expanded, with increased functionality of latent-specific CD8⁺ T cells. With increasing disease duration, EBV-specific CD4⁺ and CD8⁺ T cells progressively declined, consistent with T-cell exhaustion. The anti-EBNA1 IgG titre correlated inversely with the EBV-specific CD8⁺ T-cell frequency. We postulate that defective CD8⁺ T-cell control of EBV reactivation leads to an expanded population of latently infected cells, including autoreactive B cells.

A novel antibody discovery platform identifies anti-influenza A broadly neutralizing antibodies from human memory B cells

Monoclonal antibody isolation directly from circulating human B cells is a powerful tool to delineate humoral responses to pathological conditions and discover antibody therapeutics. We have developed a platform aimed at improving the efficiencies of B cell selection and V gene recovery. Here, memory B cells are activated and amplified using Epstein-Barr virus infection, co-cultured with CHO-muCD40L cells, and then assessed by functional screenings. An in vitro transcription and translation (IVTT) approach was used to analyze variable (V) genes recovered from each B cell sample and identify the relevant heavy/light chain pair(s). We achieved efficient amplification and activation of memory B cells, and eliminated the need to: 1) seed B cells at clonal level (≤1 cell/well) or perform limited dilution cloning; 2) immortalize B cells; or 3) assemble V genes into an IgG expression vector to confirm the relevant heavy/light chain pairing. Cross-reactive antibodies targeting a conserved epitope on influenza A hemagglutinin were successfully isolated from a healthy donor. In-depth analysis of the isolated antibodies suggested their potential uses as anti-influenza A antibody therapeutics and uncovered a distinct affinity maturation pathway. Importantly, our results showed that cognate heavy/light chain pairings contributed to both the expression level and binding abilities of our newly isolated VH1-69 family, influenza A neutralizing antibodies, contrasting with previous observations that light chains do not significantly contribute to the function of this group of antibodies. Our results further suggest the potential use of the IVTT as a powerful antibody developability assessment tool.

T-Cell Responses to EBV

Epstein-Barr virus (EBV) is arguably one of the most successful pathogens of humans, persistently infecting over ninety percent of the world's population. Despite this high frequency of carriage, the virus causes apparently few adverse effects in the vast majority of infected individuals. Nevertheless, the potent growth transforming ability of EBV means the virus has the potential to cause malignancies in infected individuals. Indeed, EBV is thought to cause 1% of human malignancies, equating to 200,000 malignancies each year. A clear factor as to why virus-induced disease is relatively infrequent in healthy infected individuals is the presence of a potent immune response to EBV, in particular, that mediated by T cells. Thus, patient groups with immunodeficiencies or whose cellular immune response is suppressed have much higher frequencies of EBV-induced disease and, in at least some cases, these diseases can be controlled by restoration of the T-cell compartment. In this chapter, we will primarily review the role the αβ subset of T cells in the control of EBV in healthy and diseased individuals.

Epstein-Barr virus and telomerase: from cell immortalization to therapy

Overcoming cellular senescence is strictly required for virus-driven tumors, including those associated with Epstein-Barr virus (EBV). This critical step is successfully accomplished by EBV through TERT expression and telomerase activation in infected cells. We herein review the complex interplay between EBV and TERT/telomerase in EBV-driven tumorigenesis. Evidence accumulated so far clearly indicates that elucidation of this issue may offer promising opportunities for the design of innovative treatment modalities for EBV-associated malignancies. Indeed, several therapeutic strategies for telomerase inhibition have been developed and are being investigated in clinical trials. In this respect, our recent finding that TERT inhibition sensitizes EBV+ lymphoma cells to antivirals through activation of EBV lytic replication is particularly promising and provides a rationale for the activation of clinical studies aimed at assessing the effects of combination therapies with TERT inhibitors and antivirals for the treatment of EBV-associated malignancies.

Adenovirus-based vaccines against rhesus lymphocryptovirus EBNA-1 induce expansion of specific CD8+ and CD4+ T cells in persistently infected rhesus macaques

The impact of Epstein-Barr virus (EBV) on human health is substantial, but vaccines that prevent primary EBV infections or treat EBV-associated diseases are not yet available. The Epstein-Barr nuclear antigen 1 (EBNA-1) is an important target for vaccination because it is the only protein expressed in all EBV-associated malignancies. We have designed and tested two therapeutic EBV vaccines that target the rhesus (rh) lymphocryptovirus (LCV) EBNA-1 to determine if ongoing T cell responses during persistent rhLCV infection in rhesus macaques can be expanded upon vaccination. Vaccines were based on two serotypes of E1-deleted simian adenovirus and were administered in a prime-boost regimen. To further modulate the response, rhEBNA-1 was fused to herpes simplex virus glycoprotein D (HSV-gD), which acts to block an inhibitory signaling pathway during T cell activation. We found that vaccines expressing rhEBNA-1 with or without functional HSV-gD led to expansion of rhEBNA-1-specific CD8(+) and CD4(+) T cells in 33% and 83% of the vaccinated animals, respectively. Additional animals developed significant changes within T cell subsets without changes in total numbers. Vaccination did not increase T cell responses to rhBZLF-1, an immediate early lytic phase antigen of rhLCV, thus indicating that increases of rhEBNA-1-specific responses were a direct result of vaccination. Vaccine-induced rhEBNA-1-specific T cells were highly functional and produced various combinations of cytokines as well as the cytolytic molecule granzyme B. These results serve as an important proof of principle that functional EBNA-1-specific T cells can be expanded by vaccination.

IMPORTANCE

EBV is a common human pathogen that establishes a persistent infection through latency in B cells, where it occasionally reactivates. EBV infection is typically benign and is well controlled by the host adaptive immune system; however, it is considered carcinogenic due to its strong association with lymphoid and epithelial cell malignancies. Latent EBNA-1 is a promising target for a therapeutic vaccine, as it is the only antigen expressed in all EBV-associated malignancies. The goal was to determine if rhEBNA-1-specific T cells could be expanded upon vaccination of infected animals. Results were obtained with vaccines that target EBNA-1 of rhLCV, a virus closely related to EBV. We found that vaccination led to expansion of rhEBNA-1 immune cells that exhibited functions fit for controlling viral infection. This confirms that rhEBNA-1 is a suitable target for therapeutic vaccines. Future work should aim to generate more-robust T cell responses through modified vaccines.

The EBV immunoevasins vIL-10 and BNLF2a protect newly infected B cells from immune recognition and elimination

Lifelong persistence of Epstein-Barr virus (EBV) in infected hosts is mainly owed to the virus' pronounced abilities to evade immune responses of its human host. Active immune evasion mechanisms reduce the immunogenicity of infected cells and are known to be of major importance during lytic infection. The EBV genes BCRF1 and BNLF2a encode the viral homologue of IL-10 (vIL-10) and an inhibitor of the transporter associated with antigen processing (TAP), respectively. Both are known immunoevasins in EBV's lytic phase. Here we describe that BCRF1 and BNLF2a are functionally expressed instantly upon infection of primary B cells. Using EBV mutants deficient in BCRF1 and BNLF2a, we show that both factors contribute to evading EBV-specific immune responses during the earliest phase of infection. vIL-10 impairs NK cell mediated killing of infected B cells, interferes with CD4+ T-cell activity, and modulates cytokine responses, while BNLF2a reduces antigen presentation and recognition of newly infected cells by EBV-specific CD8+ T cells. Together, both factors significantly diminish the immunogenicity of EBV-infected cells during the initial, pre-latent phase of infection and may improve the establishment of a latent EBV infection in vivo.

Longitudinal analysis of frequency and reactivity of Epstein-Barr virus-specific T lymphocytes and their association with intermittent viral reactivation

Persistent Epstein-Barr virus (EBV) infection is controlled tightly by virus-specific T cells. EBV infection is reactivated intermittently over time, even in apparently healthy carriers. Changes in frequency and reactivity of memory T cells, particularly of CD8(+) origin, have not been assessed in this context. It is hypothesized that viral reactivation is facilitated by diminished EBV-specific T-cell immunity. To this end, blood samples from 14 healthy donors were collected at irregular time intervals for a period of about 1 year. Samples were screened for both EBV plasma viremia and increases in viral load in PBMCs as parameters of EBV reactivation. PBMCs were subject to IFN-γ ELISPOT analysis using the autologous EBV-transformed lymphoblastoid cell line (EBV-LCL) or appropriate HLA class I-restricted EBV peptides as stimulators. Frequencies of epitope-specific CD8(+) T cells were monitored further using HLA tetramers and flow cytometry. Twelve of 14 donors exhibited signs of asymptomatic EBV reactivation. Viral reactivation was accompanied by either substantially decreased IFN-γ responses against autologous EBV-LCL (eight of 12 study participants) and/or increased responses against particular EBV peptides (six of 12 donors). In seven persons with HLA-A2 and/or -B8 alleles numbers of HLA tetramer-positive CD8(+) T cells also varied over time, but showed no correlation to episodes of detectable viral activity. In summary, IFN-γ reactivity of EBV-specific T cells is not constant. Viral reactivation is detected preferably at times of diminished EBV-LCL-specific cellular immunity. However, increased reactivity of single immunodominant CD8(+) EBV-specific T-cell clones may occur in response to virus replication.

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

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

T-cell immunity to Kaposi sarcoma-associated herpesvirus: recognition of primary effusion lymphoma by LANA-specific CD4+ T cells

T-cell immunity is important for controlling Kaposi sarcoma-associated herpesvirus (KSHV) diseases such as the endothelial cell malignancy Kaposi sarcoma, or the B-cell malignancy, primary effusion lymphoma (PEL). However, little is known about KSHV-specific T-cell immunity in healthy donors and immune control of disease. Using PBMCs from healthy KSHV-infected donors, we found weak ex vivo responses to the KSHV latent antigens LANA, vFLIP, vCyclin, and Kaposin, with LANA most frequently recognized. CD4(+) T-cell clones specific to LANA, a protein expressed in all KSHV-infected cells and malignancies, were established to determine whether they could recognize LANA-expressing cells. B-cell targets expressing or fed LANA protein were consistently recognized by the clones; however, most PEL cell lines were not. PELs express the KSHV protein vIRF3 that inhibits promoter function of the HLA class II transactivator, decreasing expression of genes controlled by this transactivator. Re-expressing the class II transactivator in the PELs increased expression of downstream targets such as HLA class II and restored recognition but not killing by the LANA-specific clones. We suggest that PELs are poorly controlled in vivo because of inefficient recognition and killing by T cells.

The company malaria keeps: how co-infection with Epstein-Barr virus leads to endemic Burkitt lymphoma

PURPOSE OF REVIEW

Co-infection with Plasmodium falciparum malaria and Epstein-Barr virus (EBV) are implicated in the cause of endemic Burkitt lymphoma (eBL), the most prevalent pediatric cancer in equatorial Africa. Although the causal association between EBV and eBL has been established, P. falciparum malaria's role is not as clearly defined. This review focuses on how malaria may disrupt EBV persistence and immunity.

RECENT FINDINGS

Two mutually compatible theories have been proposed. One suggests that P. falciparum malaria induces polyclonal B-cell expansion and lytic EBV reactivation, leading to the expansion of latently infected B cells and the likelihood of a c-myc translocation, a hallmark of Burkitt lymphoma tumors. The other advocates that EBV-specific T-cell immunity is impaired during P. falciparum malaria co-infection, either as a cause or consequence of enhanced EBV replication, leading to loss of viral control. Advancements in our ability to query the complexity of human responses to infectious diseases have stimulated interest in eBL pathogenesis.

SUMMARY

EBV is necessary but not sufficient to cause eBL. A more dynamic model encompasses incremental contributions from both chronic and acute P. falciparum malaria leading to alterations in EBV persistence and EBV-specific immunity that culminate in eBL. A better understanding of how P. falciparum malaria modifies EBV infections in children may allow us to anticipate reductions in eBL incidence coinciding with malaria control programs.

Decreased CD8+ T cell response to Epstein-Barr virus infected B cells in multiple sclerosis is not due to decreased HLA class I expression on B cells or monocytes

Background

Patients with multiple sclerosis (MS) have a decreased frequency of CD8⁺ T cells reactive to their own Epstein-Barr virus (EBV) infected B cells. We have proposed that this might predispose to the development of MS by allowing EBV-infected autoreactive B cells to accumulate in the central nervous system. The decreased CD8⁺ T cell response to EBV results from a general CD8⁺ T cell deficiency and also a decreased proportion of EBV-specific T cells within the total CD8⁺ T cell population. Because decreased HLA class I expression on monocytes and B cells has been reported in MS and could influence the generation and effector function of EBV-specific CD8⁺ T cells, the present study was undertaken to measure the expression of HLA molecules on B cells and monocytes in patients with MS.

Methods

We used flow cytometry to determine the proportions of T cells, natural killer cells, B cells and monocytes in peripheral blood mononuclear cells (PBMC) and to quantify the expression of HLA molecules on T cells, B cells and monocytes of 59 healthy subjects and 62 patients with MS who had not received corticosteroids or immunomodulatory therapy in the previous 3 months.

Results

The levels of HLA class I and class II molecules expressed on T cells, B cells and monocytes were normal in patients with MS, with the exception of two patients with secondary progressive MS with very low class II expression on B cells. In confirmation of previous studies we also found that the percentage of CD8⁺ T cells was significantly decreased whereas the percentage of CD4⁺ T cells and the CD4:CD8 ratio were significantly increased in patients with MS compared to healthy subjects.

Conclusions

The decreased CD8⁺ T cell response to EBV-infected B cells in MS patients is not due to decreased HLA class I expression on monocytes or B cells. In a small proportion of patients decreased HLA class II expression on B cells might impair the CD8⁺ T cell response to EBV by reducing CD4⁺ T cell help.

Cytotoxic CD4+ T cell responses to EBV contrast with CD8 responses in breadth of lytic cycle antigen choice and in lytic cycle recognition

EBV, a B lymphotropic herpesvirus, encodes two immediate early (IE)-, >30 early (E)-, and >30 late (L)-phase proteins during its replication (lytic) cycle. Despite this, lytic Ag-induced CD8 responses are strongly skewed toward IE and a few E proteins only, all expressed before HLA I presentation is blocked in lytically infected cells. For comparison, we examined CD4(+) T cell responses to eight IE, E, or L proteins, screening 14 virus-immune donors to overlapping peptide pools in IFN-γ ELISPOT assays, and established CD4(+) T cell clones against 12 defined epitopes for target-recognition assays. We found that the lytic Ag-specific CD4(+) T cell response differs radically from its CD8 counterpart in that it is widely distributed across IE, E, and L Ag targets, often with multiple reactivities detectable per donor and with IE, E, or L epitope responses being numerically dominant, and that all CD4(+) T cell clones, whether IE, E, or L epitope-specific, show strong recognition of EBV-transformed B cell lines, despite the lines containing only a small fraction of lytically infected cells. Efficient recognition occurs because lytic Ags are released into the culture and are acquired and processed by neighboring latently infected cells. These findings suggested that lytic Ag-specific CD4 responses are driven by a different route of Ag display than drives CD8 responses and that such CD4 effectors could be therapeutically useful against EBV-driven lymphoproliferative disease lesions, which contain similarly small fractions of EBV-transformed cells entering the lytic cycle.

Active lytic infection of human primary tonsillar B cells by KSHV and its noncytolytic control by activated CD4+ T cells

Kaposi sarcoma-associated herpesvirus (KSHV) is a B-lymphotropic virus whose primary site of replication is the oropharynx. KSHV can infect both T and B cells from primary tonsillar explant cultures. However, T cells do not support lytic replication, while B cells spontaneously produce substantial amounts of infectious virus. Here, we provide evidence for a mechanism by which activated T cells may promote or stabilize latency of KSHV infection in B cells. When mixed cultures of B cells and activated T cells were exposed to KSHV, little spontaneous virus production was observed. Removing T cells from the mix or treating the mixed culture with immune suppressants enhanced virus production. Adding back activated T cells to purified infected B cells efficiently suppressed KSHV production, primarily due to CD4(+) T cells. This suppressive activity required T cell activation and direct cell-cell contact, but not prior exposure to KSHV antigen. Suppression was not MHC restricted and did not result in killing of the target cell. We therefore propose that oropharyngeal T cells activated by a variety of stimuli can recognize ligands on infected target B cells, leading to signaling events that prevent spontaneous lytic activation and promote latent infection in this compartment.

Impaired Epstein-Barr virus-specific CD8+ T-cell function in X-linked lymphoproliferative disease is restricted to SLAM family-positive B-cell targets

X-linked lymphoproliferative disease (XLP) is a condition associated with mutations in the signaling lymphocytic activation molecule (SLAM)-associated protein (SAP; SH2D1A). SAP functions as an adaptor, binding to and recruiting signaling molecules to SLAM family receptors expressed on T and natural killer cells. XLP is associated with extreme sensitivity to primary Epstein-Barr virus (EBV) infection, often leading to a lethal infectious mononucleosis. To investigate EBV-specific immunity in XLP patients, we studied 5 individuals who had survived EBV infection and found CD8(+) T-cell responses numerically comparable with healthy donors. However, further investigation of in vitro-derived CD8(+) T-cell clones established from 2 of these donors showed they efficiently recognized SLAM ligand-negative target cells expressing EBV antigens, but showed impaired recognition of EBV-transformed, SLAM ligand-positive, lymphoblastoid cell lines (LCLs). Importantly, LCL recognition was restored when interactions between the SLAM receptors CD244 and natural killer-, T-, and B-cell antigen (NTBA) and their ligands on LCLs were blocked. We propose that XLP patients' particular sensitivity to EBV, and not to other viruses, reflects at least in part EBV's strict tropism for B lymphocytes and the often inability of the CD8(+) T-cell response to contain the primary infection of SLAM ligand-expressing target cells.

Role of CD4+ cytotoxic T lymphocytes in the control of viral diseases and cancer

Our knowledge on the physiological role of CD4(+) T lymphocytes has improved in the last decade: available data convincingly demonstrate that, besides the 'helper' activity, CD4(+) T cells may be also endowed with lytic properties. The cytotoxic function of these effector cells has a relevant role in the control of pathogenic infections and in mediating antitumor immune responses. On these bases, several immunotherapeutic approaches exploiting the cytotoxic properties of CD4(+) T cells are under investigation. This review summarizes available data supporting the functional and therapeutic relevance of cytotoxic CD4(+) T cells, with a particular focus on Epstein-Barr virus (EBV)-related disorders.

CD4+ T-cell clones recognizing human lymphoma-associated antigens: generation by in vitro stimulation with autologous Epstein-Barr virus-transformed B cells

Epstein-Barr virus (EBV)-specific T-cell preparations, generated by stimulating immune donor lymphocytes with the autologous virus-transformed B-lymphoblastoid cell line (LCL) in vitro, can be used to target EBV-positive malignancies. Although these preparations are enriched for EBV antigen-specific CD8(+) T cells, most also contain a CD4(+) T-cell population whose specificity is unknown. Here, we show that, although CD4(+) T-cell clones derived from such cultures recognize HLA class II-matched LCLs but not mitogen-activated B lymphoblasts, many (1) do not map to any known EBV antigen, (2) can be raised from EBV-naive as well as EBV-immune persons, and (3) can recognize a broad range of human B lymphoma-derived cell lines irrespective of EBV genome status, providing those lines to express the relevant HLA class II-restricting allele. Importantly, such CD4(+) clones not only produce IFNgamma but are also cytotoxic and can control the outgrowth of HLA-matched lymphoma cells in cocultivation assays. We infer that such CD4(+) T cells recognize cellular antigens that are preferentially up-regulated in EBV-transformed but not mitogen-activated B lymphoblasts and that are also expressed in a range of B-cell malignancies. Such antigens are therefore of potential value as targets for CD4(+) T cell-based immunotherapy.

Epitope specificity and clonality of EBV-specific CTLs used to treat posttransplant lymphoproliferative disease

In a recent phase II clinical trial using banked allogeneic CTL lines to treat EBV-associated posttransplant lymphoproliferative disease, a response rate of 52% was recorded 6 mo posttreatment. Tumor response was associated with an increase in both CTL/recipient HLA matches and CD4(+) T cells within the infused CTL lines. The present study was undertaken to correlate tumor response with CTL specificity. The majority of CTL lines infused recognized EBV-encoded nuclear Ag-3 proteins, but CTL protein specificity itself did not correlate with tumor response. Specificity in conjunction with donor/recipient functional HLA matching as opposed to HLA matching alone, however, was important for tumor response. CTL receptor TCR beta-chain variable gene subfamilies were polyclonal, with no preferential use of a particular family. However, tumor response was improved in those receiving CTL lines with polyclonal vs clonal distribution for subfamilies 2, 3, and 9. Interestingly, in five of six tumors (five Hodgkin's-like and one Burkitt's-like posttransplant lymphoproliferative disease) with restricted viral gene expression a complete response was recorded, although in some cases the tumor cells did not express the proteins recognized by the infused CTL. Thus CTL were advantageous when functionally HLA matched but for certain tumor types complete responses occurred in the absence of detectable specific CTL/tumor recognition. We suggest that either the allogenic CTL contained small, undetectable, EBV-specific, HLA-matched T cell populations or perhaps they stimulated nonspecific inflammatory responses in vivo, which were beneficial for tumor regression. These observations should be considered when designing and implementing CTL therapies.

The effects of acute malaria on Epstein-Barr virus (EBV) load and EBV-specific T cell immunity in Gambian children

BACKGROUND

To investigate how intense Plasmodium falciparum infection predisposes to Epstein-Barr virus (EBV)-positive Burkitt lymphoma (BL), we analyzed the effect of acute malaria on existing EBV-host balance.

METHODS

EBV genome loads in peripheral blood mononuclear cells were assayed by quantitative polymerase chain reaction, and EBV-specific CD8(+) T cell responses were assayed by interferon-gamma enzyme-linked immunospot assay.

RESULTS

Gambian children, from whom samples were obtained during an acute malaria attack and again up to 6 weeks later, had extremely high viral loads, reaching levels that in the United Kingdom are seen only in patients with infectious mononucleosis. Gambian control subjects (children and adults with no recent history of malaria) had lower median viral loads, although they were still >10-fold above the median for healthy UK adults. Limited experiments with EBV epitope peptides (restricted through the HLA-B 3501 and HLA-B 5301 alleles) also suggested an impairment of virus-specific CD8(+) T cell function in children with malaria, but only during acute disease.

CONCLUSIONS

Acute malaria is associated with sustained increase in EBV load and, possibly, a transient decrease in EBV-specific T cell surveillance. We infer that the unusually high set point of virus carriage in P. falciparum-challenged populations, allied with the parasite's capacity to act as a chronic B cell stimulus, probably contributes to the pathogenesis of endemic BL.

Adoptive cell therapy against EBV-related malignancies: a survey of clinical results

BACKGROUND

Epstein-Barr Virus (EBV) infection is associated with a heterogeneous group of tumors, including lymphoproliferative disorders, Hodgkin's disease, nasopharyngeal carcinoma and Burkitt's lymphoma. As such neoplastic disorders express viral antigens, they can be treated by adoptive immunotherapy strategies relying mostly on in vitro generation and expansion of virus-specific cytotoxic T lymphocytes (CTL), which can be administered to patients for both prophylaxis and treatment.

OBJECTIVE

We reviewed results obtained in all clinical trials reported thus far employing anti-EBV adoptive immunotherapy for different virus-related malignancies.

METHODS

'PTLD after HSCT', 'PTLD after SOT', 'NPC', 'HD', 'SCAEBV' and 'extranodal NK/T cell lymphoma', in combination with 'Adoptive immunotherapy' and 'Adoptive transfer', were used as search keys for papers in PubMed.

CONCLUSIONS

Although the heterogeneity of different studies precludes their collection for a meta-analysis, it can be inferred that adoptive therapy with EBV-specific CTL is safe, well tolerated and particularly effective in the case of most immunogenic tumors, like post-transplant lymphoproliferative disease.

Standardized and highly efficient expansion of Epstein-Barr virus-specific CD4+ T cells by using virus-like particles

Epstein-Barr virus (EBV)-specific T-cell lines generated by repeated stimulation with EBV-immortalized lymphoblastoid B-cell lines (LCL) have been successfully used to treat EBV-associated posttransplant lymphoproliferative disease (PTLD) in hematopoietic stem cell transplant recipients. However, PTLD in solid-organ transplant recipients and other EBV-associated malignancies respond less efficiently to this adoptive T-cell therapy. LCL-stimulated T-cell preparations are polyclonal and contain CD4(+) and CD8(+) T cells, but the composition varies greatly between lines. Because T-cell lines with higher CD4(+) T-cell proportions show improved clinical efficacy, we assessed which factors might compromise the expansion of this T-cell population. Here we show that spontaneous virus production by LCL and, hence, the presentation of viral antigens varies intra- and interindividually and is further impaired by acyclovir treatment of LCL. Moreover, the stimulation of T cells with LCL grown in medium supplemented with fetal calf serum (FCS) caused the expansion of FCS-reactive CD4(+) T cells, whereas human serum from EBV-seropositive donors diminished viral antigen presentation. To overcome these limitations, we used peripheral blood mononuclear cells pulsed with nontransforming virus-like particles as antigen-presenting cells. This strategy facilitated the specific and rapid expansion of EBV-specific CD4(+) T cells and, thus, might contribute to the development of standardized protocols for the generation of T-cell lines with improved clinical efficacy.

Conditional immortalization of human B cells by CD40 ligation

It is generally assumed that human differentiated cells have a limited life-span and proliferation capacity in vivo, and that genetic modifications are a prerequisite for their immortalization in vitro. Here we readdress this issue, studying the long-term proliferation potential of human B cells. It was shown earlier that human B cells from peripheral blood of healthy donors can be efficiently induced to proliferate for up to ten weeks in vitro by stimulating their receptor CD40 in the presence of interleukin-4. When we applied the same stimuli under conditions of modified cell number and culture size, we were surprised to find that our treatment induced B cells to proliferate throughout an observation period of presently up to 1650 days, representing more than 370 population doublings, which suggested that these B cells were immortalized in vitro. Long-term CD40-stimulated B cell cultures could be established from most healthy adult human donors. These B cells had a constant phenotype, were free from Epstein-Barr virus, and remained dependent on CD40 ligation. They had constitutive telomerase activity and stabilized telomere length. Moreover, they were susceptible to activation by Toll-like receptor 9 ligands, and could be used to expand antigen-specific cytotoxic T cells in vitro. Our results indicate that human somatic cells can evade senescence and be conditionally immortalized by external stimulation only, without a requirement for genetic manipulation or oncoviral infection. Conditionally immortalized human B cells are a new tool for immunotherapy and studies of B cell oncogenesis, activation, and function.

Repertoire and frequency of immune cells reactive to Epstein-Barr virus-derived autologous lymphoblastoid cell lines

Answers to questions about frequency and repertoire of immune cells, relative contributions made by different types of immune cells toward the total Epstein-Barr virus (EBV)-directed response and the variation of such responses in healthy persons have been elusive because of disparities in assays, antigen presenting cells, and antigenic sources used in previous experiments. In this study, we addressed these questions using an assay that allowed direct comparison of responses generated by different types of cells of the immune system. This short-term (20-hour) ex vivo assay measured interferon-gamma production by blood cells in response to autologous EBV-transformed lymphoblastoid cell lines (LCLs). Our experiments defined the variation in responses among persons and clearly distinguished 10 healthy EBV-immune from 10 healthy EBV-naive persons. In EBV-immune persons, 33% of responding cells were CD4(+), 43.3% were CD8(+), and 12.9% were gamma-delta T cells. LCL-reactive CD8(+) T cells were only 1.7-fold more frequent than similarly reactive CD4(+)T cells. Responses by gamma-delta T cells were 6-fold higher in seropositive than in seronegative persons. Our findings emphasize the importance of CD4(+) and gamma-delta T-cell responses and have implications for immunotherapy and for identifying defects in T-cell populations that might predispose to development of EBV-associated lymphomas.

Immunodominance of lytic cycle antigens in Epstein-Barr virus-specific CD4+ T cell preparations for therapy

BACKGROUND

Epstein-Barr virus (EBV) is associated with a number of human malignancies. EBV-positive post-transplant lymphoproliferative disease in solid organ and hematopoietic stem cell transplant recipients has been successfully treated by the adoptive transfer of polyclonal EBV-specific T cell lines containing CD4+ and CD8+ T cell components. Although patients receiving T cell preparations with a higher CD4+ T cell proportion show better clinical responses, the specificity of the infused CD4+ component has remained completely unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We generated LCL-stimulated T cell lines from 21 donors according to clinical protocols, and analyzed the antigen specificity of the CD4+ component in EBV-specific T cell preparations using a genetically engineered EBV mutant that is unable to enter the lytic cycle, and recombinantly expressed and purified EBV proteins. Surprisingly, CD4+ T cell lines from acutely and persistently EBV-infected donors consistently responded against EBV lytic cycle antigens and autoantigens, but barely against latent cycle antigens of EBV hitherto considered principal immunotherapeutic targets. Lytic cycle antigens were predominantly derived from structural proteins of the virus presented on MHC II via receptor-mediated uptake of released viral particles, but also included abundant infected cell proteins whose presentation involved intercellular protein transfer. Importantly, presentation of virion antigens was severely impaired by acyclovir treatment of stimulator cells, as currently performed in most clinical protocols.

CONCLUSIONS/SIGNIFICANCE

These results indicate that structural antigens of EBV are the immunodominant targets of CD4+ T cells in LCL-stimulated T cell preparations. These findings add to our understanding of the immune response against this human tumor-virus and have important implications for the improvement of immunotherapeutic strategies against EBV.

The switch from latent to productive infection in epstein-barr virus-infected B cells is associated with sensitization to NK cell killing

Following activation of Epstein-Barr virus (EBV)-infected B cells from latent to productive (lytic) infection, there is a concomitant reduction in the level of cell surface major histocompatibility complex (MHC) class I molecules and an impaired antigen-presenting function that may facilitate evasion from EBV-specific CD8+ cytotoxic T cells. In some other herpesviruses studied, most notably human cytomegalovirus (HCMV), evasion of virus-specific CD8+ effector responses via downregulation of surface MHC class I molecules is supplemented with specific mechanisms for evading NK cells. We now report that EBV differs from HCMV in this respect. While latently infected EBV-positive B cells were resistant to lysis by two NK lines and by primary polyclonal NK cells from peripheral blood, these effectors efficiently killed cells activated into the lytic cycle. Susceptibility to NK lysis coincided not only with downregulation of HLA-A, -B, and -C molecules that bind to the KIR family of inhibitory receptors on NK cells but also with downregulation of HLA-E molecules binding the CD94/NKG2A inhibitory receptors. Conversely, ULBP-1 and CD112, ligands for the NK cell-activating receptors NKG2D and DNAM-1, respectively, were elevated. Susceptibility of the virus-producing target cells to NK cell lysis was partially reversed by blocking ULBP-1 or CD112 with specific antibodies. These results highlight a fundamental difference between EBV and HCMV with regards to evasion of innate immunity.

CD4+ T-cell responses to Epstein-Barr virus (EBV) latent-cycle antigens and the recognition of EBV-transformed lymphoblastoid cell lines

There is considerable interest in the potential of Epstein-Barr virus (EBV) latent antigen-specific CD4+ T cells to act as direct effectors controlling EBV-induced B lymphoproliferations. Such activity would require direct CD4+ T-cell recognition of latently infected cells through epitopes derived from endogenously expressed viral proteins and presented on the target cell surface in association with HLA class II molecules. It is therefore important to know how often these conditions are met. Here we provide CD4+ epitope maps for four EBV nuclear antigens, EBNA1, -2, -3A, and -3C, and establish CD4+ T-cell clones against 12 representative epitopes. For each epitope we identify the relevant HLA class II restricting allele and determine the efficiency with which epitope-specific effectors recognize the autologous EBV-transformed B-lymphoblastoid cell line (LCL). The level of recognition measured by gamma interferon release was consistent among clones to the same epitope but varied between epitopes, with values ranging from 0 to 35% of the maximum seen against the epitope peptide-loaded LCL. These epitope-specific differences, also apparent in short-term cytotoxicity and longer-term outgrowth assays on LCL targets, did not relate to the identity of the source antigen and could not be explained by the different functional avidities of the CD4+ clones; rather, they appeared to reflect different levels of epitope display at the LCL surface. Thus, while CD4+ T-cell responses are detectable against many epitopes in EBV latent proteins, only a minority of these responses are likely to have therapeutic potential as effectors directly recognizing latently infected target cells.