CD4+ T-cell effectors inhibit Epstein-Barr virus-induced B-cell proliferation

A model of lymphocryptovirus-associated post-transplant lymphoproliferative disorder in immunosuppressed Mauritian cynomolgus macaques

Immunocompromised individuals are at risk for developing lymphocryptovirus-associated lymphoproliferative diseases, such as Epstein Barr virus (EBV)-associated B cell lymphomas and post-transplant lymphoproliferative disorder (PTLD). We previously reported development of cynomolgus lymphocryptovirus (CyLCV)-associated PTLD in Mauritian cynomolgus macaques (MCMs) undergoing hematopoietic stem cell transplantation (HSCT), which mirrored EBV-PTLD in transplant patients. Here, we sought to develop a MCM model of lymphocryptovirus-associated lymphoproliferative disease in immunosuppressed MCMs without HSCT. Five simian immunodeficiency virus (SIV)-infected, CD8α+ cell-depleted MCMs received an infusion of autologous B-lymphoblastoid cells transformed with CyLCV, followed by varying degrees of immunosuppression. Four of five infused macaques developed masses coincident with increasing CyLCV plasma viremia, and necropsies confirmed the presence of multicentric lymphomas, which most commonly manifested in lymph nodes, gastrointestinal tract, adrenal glands, and pancreas. Affected tissues harbored neoplastic lymphocytes double-positive for CD20 and CyLCV EBNA2 antigen, large frequencies of proliferating B cells, and high levels of cell-associated CyLCV DNA. In addition, longitudinal 18F-fluorodeoxyglucose positron-emission tomography (18F-FDG PET) of one MCM successfully detected lymphoproliferative disease in the adrenal glands prior to clinical signs of disease. These data demonstrate successful induction of lymphocryptovirus-associated PTLD-like disease in 4 of 5 MCMs, and thus support the use of MCMs as a preclinical NHP model of EBV-associated lymphoproliferative disease that could be employed to test novel diagnostic and therapeutic modalities.

Chronic HIV-1 Tat action induces HLA-DR downregulation in B cells: A mechanism for lymphoma immune escape in people living with HIV

Despite the success of combination antiretroviral therapy, people living with human immunodeficiency virus (HIV) still have an increased risk of Epstein-Barr virus (EBV)-associated B cell malignancies. In the HIV setting, B cell physiology is altered by coexistence with HIV-infected cells and the chronic action of secreted viral proteins, for example, HIV-1 Tat that, once released, efficiently penetrates noninfected cells. We modeled the chronic action of HIV-1 Tat on B cells by ectopically expressing Tat or TatC22G mutant in two lymphoblastoid B cell lines. The RNA-sequencing analysis revealed that Tat deregulated the expression of hundreds of genes in B cells, including the downregulation of a subset of major histocompatibility complex (MHC) class II-related genes. Tat-induced downregulation of HLA-DRB1 and HLA-DRB5 genes led to a decrease in HLA-DR surface expression; this effect was reproduced by coculturing B cells with Tat-expressing T cells. Chronic Tat presence decreased the NF-ᴋB pathway activity in B cells; this downregulated NF-ᴋB-dependent transcriptional targets, including MHC class II genes. Notably, HLA-DRB1 and surface HLA-DR expression was also decreased in B cells from people with HIV. Tat-induced HLA-DR downregulation in B cells impaired EBV-specific CD4+ T cell response, which contributed to the escape from immune surveillance and could eventually promote B cell lymphomagenesis in people with HIV.

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.

Lymph node targeted multi-epitope subunit vaccine promotes effective immunity to EBV in HLA-expressing mice

The recent emergence of a causal link between Epstein-Barr virus (EBV) and multiple sclerosis has generated considerable interest in the development of an effective vaccine against EBV. Here we describe a vaccine formulation based on a lymph node targeting Amphiphile vaccine adjuvant, Amphiphile-CpG, admixed with EBV gp350 glycoprotein and an engineered EBV polyepitope protein that includes 20 CD8+ T cell epitopes from EBV latent and lytic antigens. Potent gp350-specific IgG responses are induced in mice with titers >100,000 in Amphiphile-CpG vaccinated mice. Immunization including Amphiphile-CpG also induces high frequencies of polyfunctional gp350-specific CD4+ T cells and EBV-specific CD8+ T cells that are 2-fold greater than soluble CpG and are maintained for >7 months post immunization. This combination of broad humoral and cellular immunity against multiple viral determinants is likely to provide better protection against primary infection and control of latently infected B cells leading to protection against the development of EBV-associated diseases.

Epstein-Barr virus oral shedding and viremia and their association with oral hairy leukoplakia in HIV+ individuals

OBJECTIVE

To assess the oral shedding and viremia of Epstein-Barr virus (EBV) in HIV-positive patients and their relationship with oral hairy leukoplakia (OHL).

METHODOLOGY

A total of 94 HIV-positive patients were included in the study, in which blood and saliva samples were collected for EBV quantification. Data on gender, age, time of HIV seropositivity, combined antiretroviral therapy (cART), CD4+ T-cell counts, and HIV viral load were collected. OHL diagnosis was based on histopathological examination and EBV in situ hybridization.

RESULTS

The EBV load in the 94 HIV-positive patients was higher in saliva than in blood (2.4 and 1.6, respectively), and there was a positive correlation between EBV oral shedding and viremia (p = 0.001). Twenty (21.27%) patients had OHL and also a higher EBV load in saliva (mean log₁₀  = 3.11) compared to those who had no OHL (p = 0.045). Presence of OHL was only associated with age (p = 0.030).

CONCLUSION

In HIV-positive patients, the presence of OHL was associated with EBV oral shedding but not with viremia, regardless of the amount of circulating CD4+ T cells.

Human Cytomegalovirus pUL11, a CD45 Ligand, Disrupts CD4 T Cell Control of Viral Spread in Epithelial Cells

Human cytomegalovirus (HCMV) encodes numerous immunomodulatory genes that facilitate its persistence. Previously described mechanisms by which HCMV avoids T cell control typically involve evasion of detection by infected cells. Here, we show that the virus also inhibits T cells directly via an interaction between the pUL11 glycoprotein on infected cells and the CD45 phosphatase on T cells. The antiviral functions of CD4 T cells are impaired as a result of this interaction, largely via induced interleukin 10 (IL-10) secretion in the CD4 T cell central memory compartment, resulting in enhanced viral spread. This establishes CD45 as an inhibitory receptor that regulates antiviral T cell functions and has parallels with the manipulation of natural killer (NK) cells by HCMV. By coculturing donor T cells with HCMV-infected epithelial cells, we observed that CD4 T cells can respond to epithelial cell antigen presentation and can control HCMV spread via cytolytic and cytokine-dependent mechanisms. pUL11 impairs both mechanisms. We showed that pUL11-induced IL-10 secretion requires IL-2, mTOR, and T cell receptor signaling. This characterization of the effects of the pUL11-CD45 interaction may allow for the development of new antiviral therapies and treatments for inflammatory disorders. IMPORTANCE Human cytomegalovirus (HCMV) is adept at avoiding its host's immune defenses, both by evading detection and by directly inhibiting immune cells. This can lead to a loss of control of the infection, and dangerous disease can result, particularly in cases in which an individual's immune system is immature, weak, or suppressed. T cells form a crucial part of the response to HCMV and are used in cellular HCMV therapies. We show that an interaction between a viral glycoprotein (pUL11) and a T cell surface receptor (CD45) impairs T cell memory functions and allows for increased viral spread. This defines a new immunomodulatory strategy for the virus as well as a new T cell regulatory mechanism. These results are important, as they increase our understanding of how T cells function and how HCMV disrupts them. This will allow for the development of new antiviral therapies that restore T cell functions and indicates a new target for controlling pathological T cell disorders.

CD4+ Cytotoxic T cells - Phenotype, Function and Transcriptional Networks Controlling Their Differentiation Pathways

The two major subsets of peripheral T cells are classically divided into the CD4⁺ T helper cells and the cytotoxic CD8⁺ T cell lineage. However, the appearance of some effector CD4⁺ T cell populations displaying cytotoxic activity, in particular during viral infections, has been observed, thus breaking the functional dichotomy of CD4⁺ and CD8⁺ T lymphocytes. The strong association of the appearance of CD4⁺ cytotoxic T lymphocytes (CD4 CTLs) with viral infections suggests an important role of this subset in antiviral immunity by controlling viral replication and infection. Moreover, CD4 CTLs have been linked with anti-tumor activity and might also cause immunopathology in autoimmune diseases. This raises interest into the molecular mechanisms regulating CD4 CTL differentiation, which are poorly understood in comparison to differentiation pathways of other Th subsets. In this review, we provide a brief overview about key features of CD4 CTLs, including their role in viral infections and cancer immunity, and about the link between CD4 CTLs and immune-mediated diseases. Subsequently, we will discuss the current knowledge about transcriptional and epigenetic networks controlling CD4 CTL differentiation and highlight recent data suggesting a role for histone deacetylases in the generation of CD4 CTLs.

Epstein-Barr Virus and the Origin of Myalgic Encephalomyelitis or Chronic Fatigue Syndrome

Myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) affects approximately 1% of the general population. It is a chronic, disabling, multi-system disease for which there is no effective treatment. This is probably related to the limited knowledge about its origin. Here, we summarized the current knowledge about the pathogenesis of ME/CFS and revisit the immunopathobiology of Epstein-Barr virus (EBV) infection. Given the similarities between EBV-associated autoimmune diseases and cancer in terms of poor T cell surveillance of cells with EBV latency, expanded EBV-infected cells in peripheral blood and increased antibodies against EBV, we hypothesize that there could be a common etiology generated by cells with EBV latency that escape immune surveillance. Albeit inconclusive, multiple studies in patients with ME/CFS have suggested an altered cellular immunity and augmented Th2 response that could result from mechanisms of evasion to some pathogens such as EBV, which has been identified as a risk factor in a subset of ME/CFS patients. Namely, cells with latency may evade the immune system in individuals with genetic predisposition to develop ME/CFS and in consequence, there could be poor CD4 T cell immunity to mitogens and other specific antigens, as it has been described in some individuals. Ultimately, we hypothesize that within ME/CFS there is a subgroup of patients with DRB1 and DQB1 alleles that could confer greater susceptibility to EBV, where immune evasion mechanisms generated by cells with latency induce immunodeficiency. Accordingly, we propose new endeavors to investigate if anti-EBV therapies could be effective in selected ME/CFS patients.

Immunogenic particles with a broad antigenic spectrum stimulate cytolytic T cells and offer increased protection against EBV infection ex vivo and in mice

The ubiquitous Epstein-Barr virus (EBV) is the primary cause of infectious mononucleosis and is etiologically linked to the development of several malignancies and autoimmune diseases. EBV has a multifaceted life cycle that comprises virus lytic replication and latency programs. Considering EBV infection holistically, we rationalized that prophylactic EBV vaccines should ideally prime the immune system against lytic and latent proteins. To this end, we generated highly immunogenic particles that contain antigens from both these cycles. In addition to stimulating EBV-specific T cells that recognize lytic or latent proteins, we show that the immunogenic particles enable the ex vivo expansion of cytolytic EBV-specific T cells that efficiently control EBV-infected B cells, preventing their outgrowth. Lastly, we show that immunogenic particles containing the latent protein EBNA1 afford significant protection against wild-type EBV in a humanized mouse model. Vaccines that include antigens which predominate throughout the EBV life cycle are likely to enhance their ability to protect against EBV infection.

Human herpesviruses are tremendously successful pathogens that establish lifelong infection in a substantial proportion of the population. The oncogenic γ-herpesvirus EBV, like other herpesviruses, expresses a plethora of open-reading frames throughout its multifaceted life cycle. We have developed a prophylactic vaccine candidate in the form of immunogenic particles that contain several EBV antigens. This is in stark contrast to the vast majority of EBV vaccines candidates that contain only one or two EBV antigens. Our immunogenic particles were shown capable of stimulating several EBV-specific T-cell clones in vitro. The immunogenic particles were also capable of expanding cytolytic EBV-specific T cells ex vivo and provided a protective benefit in vivo when used as a prophylactic vaccine.

Antibodies conjugated with viral antigens elicit a cytotoxic T cell response against primary CLL ex vivo

Chronic lymphocytic leukemia (CLL) is the most frequent B cell malignancy in Caucasian adults. The therapeutic armamentarium against this incurable disease has recently seen a tremendous expansion with the introduction of specific pathway inhibitors and innovative immunotherapy. However, none of these approaches is curative and devoid of side effects. We have used B-cell-specific antibodies conjugated with antigens (AgAbs) of the Epstein-Barr virus (EBV) to efficiently expand memory CD4⁺ cytotoxic T lymphocytes (CTLs) that recognized viral epitopes in 12 treatment-naive patients with CLL. The AgAbs carried fragments from the EBNA3C EBV protein that is recognized by the large majority of the population. All CLL cells pulsed with EBNA3C-AgAbs elicited EBV-specific T cell responses, although the intensity varied across the patient collective. Interestingly, a large proportion of the EBV-specific CD4⁺ T cells expressed granzyme B (GrB), perforin, and CD107a, and killed CLL cells loaded with EBV antigens with high efficiency in the large majority of patients. The encouraging results from this preclinical ex vivo study suggest that AgAbs have the potential to redirect immune responses toward CLL cells in a high percentage of patients in vivo and warrant the inception of clinical trials.

Immunotherapy against cancer-related viruses

Approximately 12% of all cancers worldwide are associated with viral infections. To date, eight viruses have been shown to contribute to the development of human cancers, including Epstein-Barr virus (EBV), Hepatitis B and C viruses, and Human papilloma virus, among others. These DNA and RNA viruses produce oncogenic effects through distinct mechanisms. First, viruses may induce sustained disorders of host cell growth and survival through the genes they express, or may induce DNA damage response in host cells, which in turn increases host genome instability. Second, they may induce chronic inflammation and secondary tissue damage favoring the development of oncogenic processes in host cells. Viruses like HIV can create a more permissive environment for cancer development through immune inhibition, but we will focus on the previous two mechanisms in this review. Unlike traditional cancer therapies that cannot distinguish infected cells from non-infected cells, immunotherapies are uniquely equipped to target virus-associated malignancies. The targeting and functioning mechanisms associated with the immune response can be exploited to prevent viral infections by vaccination, and can also be used to treat infection before cancer establishment. Successes in using the immune system to eradicate established malignancy by selective recognition of virus-associated tumor cells are currently being reported. For example, numerous clinical trials of adoptive transfer of ex vivo generated virus-specific T cells have shown benefit even for established tumors in patients with EBV-associated malignancies. Additional studies in other virus-associated tumors have also been initiated and in this review we describe the current status of immunotherapy for virus-associated malignancies and discuss future prospects.

Efficient Culture of Human Naive and Memory B Cells for Use as APCs

The ability to culture and expand B cells in vitro has become a useful tool for studying human immunity. A limitation of current methods for human B cell culture is the capacity to support mature B cell proliferation. We developed a culture method to support the efficient activation and proliferation of naive and memory human B cells. This culture supports extensive B cell proliferation, with ∼10³-fold increases following 8 d in culture and 10⁶-fold increases when cultures are split and cultured for 8 more days. In culture, a significant fraction of naive B cells undergo isotype switching and differentiate into plasmacytes. Culture-derived (CD) B cells are readily cryopreserved and, when recovered, retain their ability to proliferate and differentiate. Significantly, proliferating CD B cells express high levels of MHC class II, CD80, and CD86. CD B cells act as APCs and present alloantigens and microbial Ags to T cells. We are able to activate and expand Ag-specific memory B cells; these cultured cells are highly effective in presenting Ag to T cells. We characterized the TCR repertoire of rare Ag-specific CD4⁺ T cells that proliferated in response to tetanus toxoid (TT) presented by autologous CD B cells. TCR Vβ usage by TT-activated CD4⁺ T cells differs from resting and unspecifically activated CD4⁺ T cells. Moreover, we found that TT-specific TCR Vβ usage by CD4⁺ T cells was substantially different between donors. This culture method provides a platform for studying the BCR and TCR repertoires within a single individual.

High Levels of IL-10 and CD4+CD25hi+ Treg Cells in Endemic Burkitt's Lymphoma Patients

Background: The interplay between Epstein-Barr virus infection, malaria, and endemic Burkitt’s Lymphoma is not well understood. Reports show diminished EBV-specific Th1 responses in children living in malaria endemic areas and deficiency of EBNA1-specific IFN-γ T cell responses in children with endemic Burkitt’s Lymphoma (eBL). This study, therefore, examined some factors involved in the loss of EBNA-1-specific T cell responses in eBL. Methods: T-cell subset frequencies, activation, and IFN-γ- or IL-4-specific responses were analyzed by flow-cytometry. Plasma cytokine levels were measured by ELISA. Results: CD4+ and CD8+ cells in age- and sex-matched healthy controls (n = 3) expressed more IFN-γ in response to all immunostimulants than in pediatric endemic BL (eBL) patients (n = 4). In healthy controls, IFN-γ expression was higher than IL-4 expression, whereas in eBL patients the expression of IL-4 by CD4+ cells to EBNA-1 was slightly higher than IFN-γ. Moreover, the blood levels of TNF-α was significantly lower (p = 0.004) while IL-10 was significantly higher (p = 0.038), in eBL patients (n = 21) compared to controls (n = 16). Additionally, the frequency of CD4+CD25hi+ T cells was higher in both age-matched acute uncomplicated malaria (n = 26) and eBL (n = 14) patients compared to healthy controls (n = 19; p = 0.000 and p = 0.027, respectively). Conclusion: The data suggest that reduced Th1 response in eBL might be due to increased levels of IL-10 and T reg cells.

Adoptive T-Cell Immunotherapy

Epstein-Barr virus (EBV) is associated with a range of malignancies involving B cells, T cells, natural killer (NK) cells, epithelial cells, and smooth muscle. All of these are associated with the latent life cycles of EBV, but the pattern of latency-associated viral antigens expressed in tumor cells depends on the type of tumor. EBV-specific T cells (EBVSTs) have been explored as prophylaxis and therapy for EBV-associated malignancies for more than two decades. EBVSTs have been most successful as prophylaxis and therapy for post-transplant lymphoproliferative disease (PTLD) , which expresses the full array of latent EBV antigens (type 3 latency), in hematopoietic stem-cell transplant (HSCT) recipients. While less effective, clinical studies have also demonstrated their therapeutic potential for PTLD post-solid organ transplant and for EBV-associated malignancies such as Hodgkin's lymphoma, non-Hodgkin's lymphoma, and nasopharyngeal carcinoma (NPC) that express a limited array of latent EBV antigens (type 2 latency). Several approaches are actively being pursued to improve the antitumor activity of EBVSTs including activation and expansion of T cells specific for the EBV antigens expressed in type 2 latency, genetic approaches to render EBVSTs resistant to the immunosuppressive tumor environment, and combination approaches with other immune-modulating modalities. Given the recent advances and renewed interest in cell therapy, we hope that EBVSTs will become an integral part of our treatment armamentarium against EBV-positive malignancies in the near-future.

EBV-Specific Immune Response: Early Research and Personal Reminiscences

Early research on Epstein-Barr virus (EBV) developed from serological observations that were made soon after the discovery of the virus. Indeed, the definition of the humoral response to a variety of EBV proteins dominated the early literature and was instrumental in providing the key evidence for the association of the virus with infectious mononucleosis (IM), Burkitt's lymphoma (BL), and nasopharyngeal carcinoma (NPC). Each of these disease associations involved a distinct pattern of serological reactivity to the EBV membrane antigens (MA), early antigens (EA), and the EBV nuclear antigen (EBNA). When it became generally accepted that the marked lymphocytosis , which is a hallmark of acute IM, was dominated by T cells, considerable effort was directed toward untangling the specificities that might be associated with restricting the proliferation of newly infected B cells. Early evidence was divided between support for both EBV non-specific and/or HLA non-restricted components. However, all results needed to be reassessed in light of the observation that T cells died by apoptosis within hours of separation from fresh blood from acute IM patients. The observation that EBV-infected cultures from immune (but not non-immune) individuals began to die (termed regression) about 10 days post-seeding, provided the first evidence of a specific memory response which was apparently capable of controlling the small pool of latently infected B cells which all immune individuals possess. In this early era, CD8(+) T cells were thought to be the effector population responsible for this phenomenon, but later studies suggested a role for CD4(+) cells. This historical review includes reference to key early observations in regard to both the specific humoral and cellular responses to EBV infection from the time of the discovery of the virus until 1990. As well, we have included personal recollections in regard to the events surrounding the discovery of the memory T cell response since we believe they add a human dimension to a chapter focussed on early history.

CD4 CTL: living up to the challenge

During thymic development, thymocytes expressing a T cell receptor consisting of an alpha and beta chain (TCRαβ), commit to either the cytotoxic- or T helper-lineage fate. This lineage dichotomy is controlled by key transcription factors, including the T helper (Th) lineage master regulator, the Th-inducing BTB/POZ domain-containing Kruppel-like zinc-finger transcription factor, ThPOK, (formally cKrox or Zfp67; encoded by Zbtb7b), which suppresses the cytolytic program in major histocompatibility complex (MHC) class II-restricted CD4(+) thymocytes and the Runt related transcription factor 3 (Runx3), which counteracts ThPOK in MHC class I restricted precursor cells and promotes the lineage commitment of CD8αβ(+) cytolytic T lymphocytes (CTL). ThPOK continues to repress the CTL gene program in mature CD4(+) T cells, even as they differentiate into effector Th cell subsets. The Th cell fate however is not fixed and two recent studies showed that mature, antigen-stimulated CD4(+) T cells have the flexibility to terminate the expression of ThPOK and functionally reprogram to cytotoxic effector cells. This unexpected plasticity of CD4(+) T cells results in the post-thymic termination of the Th lineage fate and the functional differentiation of distinct MHC class II-restricted CD4(+) CTL. The recognition of CD4 CTL as a defined separate subset of effector cells and the identification of the mechanisms and factors that drive their reprogramming finally create new opportunities to explore the physiological relevance of these effector cells in vivo and to determine their pivotal roles in both, protective immunity as well as in immune-related pathology.

Cytomegalovirus-seropositive children show inhibition of in vitro EBV infection that is associated with CD8+CD57+ T cell enrichment and IFN-γ

EBV, a human herpesvirus, is commonly acquired during childhood and persists latently in B cells. EBV seropositivity has been connected to immunomodulatory effects such as altered T and NK cell functional responses as well as protection against early IgE sensitization; however, owing to the asymptomatic presentation during childhood little is known regarding the infection process in children of different ages. In this study, we used mononuclear cells from cord blood and from 2- and 5-y-old EBV-naive children for in vitro EBV infection. We show that the degree of EBV-induced B cell activation and expansion differs between age groups and in particular in relationship to IFN-γ production capacity. EBV infection induced redistribution between B cell subsets with enrichment of IgD(+)CD27(+) cells (commonly referred to as non-switched memory) in infected cord blood cell cultures, and of IgD(-)CD27(+) cells (switched memory) in cell cultures from older children. We also related results to serostatus to CMV, a persistent herpesvirus that can affect differentiation status of T and NK cells. As compared with CMV(-) children, the EBV-induced enrichment of IgD(-)CD27(+) B cells was significantly reduced in infected cell cultures from CMV(+) children. This effect was associated with high levels of IFN-γ and frequencies of highly mature CD8(+)CD57(+) T cells in CMV(+) children. Our results demonstrate that both a child's age and serostatus to CMV will have an impact on EBV-induced B cell activation and expansion, and they point to the ability of viruses with immunomodulatory functions, such as CMV, to affect immune responses within the host system.

Trichodysplasia spinulosa-associated polyomavirus (TSV) and Merkel cell polyomavirus: correlation between humoral and cellular immunity stronger with TSV

Merkel Cell Polyomavirus (MCV) is a common infectious agent likely to be involved in the pathogenesis of most Merkel cell carcinomas (MCC). Trichodysplasia spinulosa-associated polyomavirus (TSV), which exhibit high seroprevalence in general population, has been detected in trichodysplasia spinulosa (TS) skin lesions suggesting an etiological role for this disease. Previous studies have shown strong MCV-specific T-cell responses, while no data exist on T-cell immunity against TSV. In order to characterize Th-cell immunity against TSV, and to allow comparisons with the MCV-specific Th-cell immunity, we studied TSV-specific proliferation, IFN-γ, IL-10 and IL-13, and MCV-specific IFN-γ and IL-10 responses in 51 healthy volunteers, and in one MCC patient. Recombinant TSV and MCV VP1 virus-like particles (VLPs) were used as antigens. A significant correlation was found between virus-specific Th-cell and antibody responses with TSV; with MCV it proved weaker. Despite significant homology in amino acid sequences, Th-cell crossreactivity was not evident between these viruses. Some subjects seronegative to both TSV and MCV exhibited Th-cell responses to both viruses. The agent initially priming these Th-cells remains an enigma. As CD8⁺ cells specific to MCV T-Ag oncoprotein clearly provide an important defense against established MCC, the MCV VP1-specific Th-cells may, by suppressing MCV replication with antiviral cytokines such as IFN-γ, significantly contribute to preventing the full process of oncogenesis.

Herpesviruses placating the unwilling host: manipulation of the MHC class II antigen presentation pathway

Lifelong persistent infection by herpesviruses depends on the balance between host immune responses and viral immune evasion. CD4 T cells responding to antigens presented on major histocompatibility complex class II (MHC-II) molecules are known to play an important role in controlling herpesvirus infections. Here we review, with emphasis on human herpesvirus infections, the strategies evolved to evade CD4 T cell immunity. These viruses target multiple points on the MHC class II antigen presentation pathway. The mechanisms include: suppression of CIITA to inhibit the synthesis of MHC class II molecules, diversion or degradation of HLA-DR molecules during membrane transport, and direct targeting of the invariant chain chaperone of HLA-DR.

Cutting edge: activation of virus-specific CD4 T cells throughout γ-herpesvirus latency

CD4 T cells are essential for immune control of γ-herpesvirus latency. We previously identified a murine MHC class II-restricted epitope in γ-herpesvirus-68 gp150 (gp150(67-83)I-A(b)) that elicits CD4 T cells that are maintained throughout long-term infection. However, it is unknown whether naive cells can be recruited into the antiviral CD4 T cell pool during latency. In this study, we generate a mouse transgenic for a gp150-specific TCR and show epitope-specific activation of transgenic CD4 T cells during acute and latent infections. Furthermore, although only dendritic cells can stimulate virus-specific CD8 T cells during latency, we show that both dendritic cells and B cells stimulate transgenic CD4 T cells. These studies demonstrate that naive CD4 T cells specific for a viral glycoprotein can be stimulated throughout infection, even during quiescent latency, suggesting that CD4 T cell memory is maintained in part by the continual recruitment of naive cells.

Long-term carriers generate Epstein-Barr virus (EBV)-specific CD4(+) and CD8(+) polyfunctional T-cell responses which show immunodominance hierarchies of EBV proteins

T cells simultaneously producing multiple cytokines and possessing cytotoxic capacity termed polyfunctional cells (PFCs) are increasingly recognized as the immune correlate of protection against pathogenic viruses. We investigated co-expression of four cytokines (interferon-γ, macrophage inflammatory protein 1-α, tumour necrosis factor-α and interleukin-2) and degranulation capacity (CD107a surface expression) of Epstein-Barr virus (EBV) -specific CD4(+) and CD8(+) T cells upon stimulation by overlapping peptides of EBV lytic (BZLF1) and latent (EBNA1, EBNA3 and LMP2) proteins, in 20 healthy Chinese long-term carriers. Two patients with post-transplant lymphoproliferative disorder (PTLD), who had impaired T-cell immunity, were studied for comparison. Both EBV-specific CD4(+) and CD8(+) PFCs were readily generated in long-term carriers and showed immunodominance hierarchies of latent proteins (EBNA1 > EBNA3/LMP2 and EBNA3 > LMP2 > EBNA1 for CD4(+) and CD8(+) T cells, respectively), as evidenced by a higher proportion of PFCs generated by immunodominant EBV proteins than by subdominant viral proteins. In contrast, the proportion of EBV-specific PFCs was markedly decreased in patients with PTLD. The EBV-specific PFCs produced more cytokine per cell than single-functional T cells and comprised different subsets. Five-functional CD4(+) and CD8(+) T cells were detected and four-functional CD4(+) T cells were mainly CD107a negative and expressed all four cytokines whereas four-functional CD8(+) T cells were mainly CD107a positive and expressed three of the four cytokines (interleukin-2-negative). We conclude that EBV-specific PFCs are generated in much higher proportions in the long-term carriers than in the patients with PTLD and maintain the immunodominant characteristics of the virus.

Identification of a sub-population of B cells that proliferates after infection with Epstein-Barr virus

Background

Epstein-Barr virus (EBV)-driven B cell proliferation is critical to its subsequent persistence in the host and is a key event in the development of EBV-associated B cell diseases. Thus, inquiry into early cellular events that precede EBV-driven proliferation of B cells is essential for understanding the processes that can lead to EBV-associated B cell diseases.

Methods

Infection with high titers of EBV of mixed, primary B cells in different stages of differentiation occurs during primary EBV infection and in the setting of T cell-immunocompromise that predisposes to development of EBV-lymphoproliferative diseases. Using an ex vivo system that recapitulates these conditions of infection, we correlated expression of selected B cell-surface markers and intracellular cytokines with expression of EBV latency genes and cell proliferation.

Results

We identified CD23, CD58, and IL6, as molecules expressed at early times after EBV-infection. EBV differentially infected B cells into two distinct sub-populations of latently infected CD23⁺ cells: one fraction, marked as CD23^hiCD58⁺IL6^- by day 3, subsequently proliferated; another fraction, marked as CD23^loCD58⁺, expressed IL6, a B cell growth factor, but failed to proliferate. High levels of LMP1, a critical viral oncoprotein, were expressed in individual CD23^hiCD58⁺ and CD23^loCD58⁺ cells, demonstrating that reduced levels of LMP1 did not explain the lack of proliferation of CD23^loCD58⁺ cells. Differentiation stage of B cells did not appear to govern this dichotomy in outcome either. Memory or naïve B cells did not exclusively give rise to either CD23^hi or IL6-expressing cells; rather memory B cells gave rise to both sub-populations of cells.

Conclusions

B cells are differentially susceptible to EBV-mediated proliferation despite expression of viral gene products known to be critical for continuous B cell growth. Cellular events, in addition to viral gene expression, likely play a critical role in determining the outcome of EBV infection. By indentifying cells predicted to undergo EBV-mediated proliferation, our study provides new avenues of investigation into EBV pathogenesis.

Epstein-Barr virus promotes interferon-alpha production by plasmacytoid dendritic cells

OBJECTIVE

Epstein-Barr virus (EBV) infection has been linked to systemic lupus erythematosus (SLE), as demonstrated by the presence of increased seroprevalence and elevated viral loads, but the mechanism of this linkage has not been elucidated. Increased interferon-alpha (IFNalpha) levels and signatures, which are associated with innate immune responses, have been found in patients with SLE. Plasmacytoid dendritic cells (PDCs) are innate immune cells that mediate viral immunity by producing large quantities of IFNalpha, but the role they play during infection with EBV remains unclear. To address this issue, we investigated the ability of EBV to promote IFNalpha production by PDCs in healthy subjects.

METHODS

Human PDCs were sorted and cultured in the presence of EBV, EBV-encoded RNA, and EBV double-stranded DNA. IFNalpha production by PDCs was measured by enzyme-linked immunosorbent assay, with the activation of these cells measured by flow cytometry.

RESULTS

We found that EBV DNA and RNA promoted IFNalpha production by human PDCs through engagement of Toll-like receptor 9 (TLR-9) and TLR-7, respectively, with the initial viral recognition by PDCs mediated by binding to class II major histocompatibility complex (MHC) molecules.

CONCLUSION

These data demonstrate that class II MHC-specific engagement by virus, with subsequent viral nucleic acid recognition, mediates IFNalpha production by PDCs. Our results suggest that elevated levels of IFNalpha found in SLE patients may be a result of aberrantly controlled chronic viral infection.

Persistent gamma-herpesvirus infection induces a CD4 T cell response containing functionally distinct effector populations

The direct effector mechanisms of CD4 T cells during gamma-herpesvirus 68 (gammaHV68)-persistent infection are less well understood than those of their CD8 T cell counterparts, although there is substantial evidence that CD4 T cells are critical for the control of persistent gamma-herpesvirus infection. Our results show that in gammaHV68-persistently infected mice, CD4 T cells are not cytokine polyfunctional, but there is a division of labor in the CD4 T cell compartment in which CD4 T cells polarize toward two distinct populations with different effector functions: IFN-gamma producers and CD107(+) cytolytic effectors. These two CD4 T cell effector populations degranulate and produce IFN-gamma during steady state without need for exogenous antigenic restimulation, which is fundamentally different from that observed with gammaHV68-specific CD8 T cells. By using anti-IFN-gamma Ab depletions and IFN-gamma-deficient mice, we show that CD4 T cell-mediated cytotoxicity in vivo is not dependent on IFN-gamma activity. In addition, our data show that purified CD4 T cells isolated from gammaHV68-latently infected mice have the capacity to inhibit gammaHV68 reactivation from latency. Our results support the concept that CD4 T cells are critical effectors for the control of gamma-herpesvirus latent infection, and they mediate this effect by two independent mechanisms: IFN-gamma production and cytotoxicity.

Protein kinase C theta regulates stability of the peripheral adhesion ring junction and contributes to the sensitivity of target cell lysis by CTL

Destruction of virus-infected cells by CTL is an extremely sensitive and efficient process. Our previous data suggest that LFA-1-ICAM-1 interactions in the peripheral supramolecular activation cluster (pSMAC) of the immunological synapse mediate formation of a tight adhesion junction that might contribute to the sensitivity of target cell lysis by CTL. Herein, we compared more (CD8(+)) and less (CD4(+)) effective CTL to understand the molecular events that promote efficient target cell lysis. We found that abrogation of the pSMAC formation significantly impaired the ability of CD8(+) but not CD4(+) CTL to lyse target cells despite having no effect of the amount of released granules by both CD8(+) and CD4(+) CTL. Consistent with this, CD4(+) CTL break their synapses more often than do CD8(+) CTL, which leads to the escape of the cytolytic molecules from the interface. CD4(+) CTL treatment with a protein kinase Ctheta inhibitor increases synapse stability and sensitivity of specific target cell lysis. Thus, formation of a stable pSMAC, which is partially controlled by protein kinase Ctheta, functions to confine the released lytic molecules at the synaptic interface and to enhance the effectiveness of target cell lysis.

Limited efficacy and unacceptable toxicity of cyclophosphamide for the induction of mixed chimerism and renal allograft tolerance in cynomolgus monkeys

To induce mixed chimerism and renal allograft tolerance in cynomolgus monkeys, cyclophosphamide (CP) and total body irradiation (TBI) were compared as part of a nonmyeloablative conditioning regimen. CP induced dose-dependent neutropenia and lymphopenia, but hematopoietic recovery was more rapid than that observed in the TBI group. Absolute B cell counts after CP were significantly higher (P<0.01) than those in the TBI group. With CP, a total dose of 200 mg/kg with CD154 blockade regularly induced multilineage chimerism. Nevertheless, the recipients failed to achieve long-term survival because of rejection (3 of 5), posttransplantation B cell lymphoma (1 of 5), and toxicities of CP (1 of 5). As previously reported, 3 Gy of TBI with either splenectomy or CD154 blockade induced mixed chimerism and renal allograft tolerance, with significantly less morbidity and mortality than that produced by CP. Thus, TBI is more effective and less toxic than CP as part of a nonmyeloablative regimen for the induction of mixed chimerism and renal allograft tolerance in cynomolgus monkeys.

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.

Complete responses of relapsed lymphoma following genetic modification of tumor-antigen presenting cells and T-lymphocyte transfer

Epstein-Barr virus (EBV)-associated tumors developing in immunocompetent individuals present a challenge to immunotherapy, since they lack expression of immunodominant viral antigens. However, the tumors consistently express viral proteins including LMP2, which are immunologically "weak" but may nonetheless be targets for immune T cells. We previously showed that a majority of cytotoxic T lymphocytes (CTLs) reactivated using EBV-transformed B-lymphoblastoid cells lines (LCLs) contained minor populations of LMP2-specific T cells and homed to tumor sites. However, they did not produce remissions in patients with bulky disease. We have now used gene transfer into antigen-presenting cells (APCs) to augment the expression and immunogenicity of LMP2. These modified APCs increased the frequency of LMP2-specific CTLs by up to 100-fold compared with unmodified LCL-APCs. The LMP2-specific population expanded and persisted in vivo without adverse effects. Nine of 10 patients treated in remission of high-risk disease remain in remission, and 5 of 6 patients with active relapsed disease had a tumor response, which was complete in 4 and sustained for more than 9 months. It is therefore possible to generate immune responses to weak tumor antigens by ex vivo genetic modification of APCs and the CTLs so produced can have substantial antitumor activity. This study is registered at http://www.cancer.gov/clinicaltrials (protocol IDs: BCM-H-9936, NCT00062868, NCT00070226).

Phase I/II studies to evaluate safety and immunogenicity of a recombinant gp350 Epstein–Barr virus vaccine in healthy adults

Two double-blind randomised controlled studies (phase I and I/II) were performed to assess for the first time the safety and immunogenicity of a recombinant subunit gp350 Epstein-Barr virus (EBV) vaccine in 148 healthy adult volunteers. All candidate vaccine formulations had a good safety profile and were well tolerated, with the incidence of solicited and unsolicited symptoms within a clinically acceptable range. One serious adverse event was reported in the phase I trial which was considered to be of suspected relationship to vaccination. The gp350 vaccine formulations were immunogenic and induced gp350-specific antibody responses (including neutralising antibodies).

HIV patients developing primary CNS lymphoma lack EBV-specific CD4+ T cell function irrespective of absolute CD4+ T cell counts

BACKGROUND

In chronic HIV infection, antiretroviral therapy-induced normalization of CD4(+) T cell counts (immune reconstitution [IR]) is associated with a decreased incidence of opportunistic diseases. However, some individuals remain at risk for opportunistic diseases despite prolonged normalization of CD4(+) T cell counts. Deficient Epstein-Barr virus (EBV)-specific CD4(+) T cell function may explain the occurrence of EBV-associated opportunistic malignancy-such as primary central nervous system (PCNS) lymphoma-despite recovery of absolute CD4(+) T cell counts.

METHODS AND FINDINGS

Absolute CD4(+) T cell counts and EBV-specific CD4(+) T cell-dependent interferon-gamma production were assessed in six HIV-positive individuals prior to development of PCNS lymphoma ("cases"), and these values were compared with those in 16 HIV-infected matched participants with no sign of EBV-associated pathology ("matched controls") and 11 nonmatched HIV-negative blood donors. Half of the PCNS lymphoma patients fulfilled IR criteria (defined here as CD4(+) T cell counts >or=500/microl blood). EBV-specific CD4(+) T cells were assessed 0.5-4.7 y prior to diagnosis of lymphoma. In 0/6 cases versus 13/16 matched controls an EBV-specific CD4(+) T cell response was detected (p = 0.007; confidence interval for odds ratio [0-0.40]). PCNS lymphoma patients also differed with regards to this response significantly from HIV-negative blood donors (p < 0.001, confidence interval for odds ratio [0-0.14]), but there was no evidence for a difference between HIV-negative participants and the HIV-positive matched controls (p = 0.47).

CONCLUSIONS

Irrespective of absolute CD4(+) T cell counts, HIV-positive patients who subsequently developed PCNS lymphoma lacked EBV-specific CD4(+) T cell function. Larger, ideally prospective studies are needed to confirm these preliminary data, and clarify the impact of pathogen-specific versus surrogate marker-based assessment of IR on clinical outcome.

Primary CD4+ T-cell responses provide both helper and cytotoxic functions during Epstein-Barr virus infection and transformation of fetal cord blood B cells

Most humans carry Epstein-Barr virus (EBV) in circulating memory B cells as a latent infection that is controlled by an immune response. When infected by EBV, B lymphocytes in fetal cord blood are readily transformed to lymphoblastoid cell lines (LCL). It is frequently assumed that this high efficiency of transformation is due to the absence of a primary immune response. However, cord blood lymphocytes stimulated with autologous LCL yield CD4+ T cells that can completely inhibit the growth of LCL by a major histocompatibility complex-restricted cytotoxic mechanism mediated by granulysin and granzyme B. Because EBV-transformed B cells maintain the phenotype of antigen-activated B-cell blasts, they can potentially receive inhibitory or helper functions from CD4+ T cells. To assess these functions, the effect of EBV-specific CD4+ T cells on the efficiency of virus transformation of autologous B cells was assayed. Paradoxically, although the cytotoxic CD4+ T-cell lines reduced EBV B-cell transformation at a high effector/target ratio of 10:1, they caused a twofold increase in B-cell transformation at the lower effector/target ratio of 1:1. Th1-polarized CD4+ T cells were more effective at inhibiting B-cell transformation, but Th2-polarized cell lines had reduced cytotoxic activity, were unable to inhibit LCL growth, and caused a 10-fold increase in transformation efficiency. Tonsil lymphoid follicles lacked NK cells and CD8+ T cells but contained CD4+ T cells. We propose that CD4+ T cells provide helper or cytotoxic functions to EBV-transformed B cells and that the balance of these functions within tonsil compartments is critical in establishing asymptomatic primary EBV infection and maintaining a stable lifelong latent infection.

Successful in vitro priming of EBV-specific CD8+ T cells endowed with strong cytotoxic function from T cells of EBV-seronegative children

Epstein-Barr virus (EBV)-seronegative transplant recipients are at high risk of developing EBV-associated post-transplant lymphoproliferative disorder (PTLD), and would maximally benefit from an EBV-directed T-cell therapy for prevention or treatment of PTLD. So far, efforts to activate CD8+ EBV-specific cytotoxic T lymphocytes (CTL) endowed with high specific cytotoxicity from EBV-seronegative children have failed. We compared the CD8+ CTL priming efficiency of three different modified activation protocols, based on lymphoblastoid cell lines (LCL) stimulation potentially enhanced by either LCL presentation through dendritic cells, or selection of IFN-gamma+ cultured cells, or culture in the presence of rhIL-12 and rhIL-7, according to the standard protocol for reactivation of EBV-specific CTL. We found that only specific LCL stimulation in the presence of rhIL-12 and rhIL-7 was able to reproducibly expand EBV-specific CD8+ CTL endowed with strong cytotoxic activity from truly EBV-seronegative children. The lines thus activated, which included specificities toward EBV latent and lytic proteins, showed high percentage CD8+ T cells, with <10% naïve CD8+/CCR7+/CD45RA+ cells. Overall, the total number of CD8+ central memory cells, and of CCR7 T-cell effectors was comparable to that observed in healthy EBV-seropositive controls. In conclusion, it is feasible to activate EBV-specific CD8+ CTL with suitable characteristics for in vivo employment from EBV-seronegative children.

Autophagy and antigen presentation

CD4(+) T cells co-ordinate adaptive immunity and are required for immunological memory establishment and maintenance. They are thought to primarily recognize extracellular antigens, which are endocytosed, processed by lysosomal proteases and then presented on major histocompatibility complex (MHC) class II. However, recent studies have demonstrated that viral, tumour and autoantigens can gain access to this antigen presentation pathway from within cells by autophagy. This review will discuss the autophagic pathways that contribute to endogenous MHC class II antigen processing. Furthermore, potential characteristics of autophagy substrates, qualifying them to access these pathways, and regulation of autophagy will be considered. Finally, I will suggest how antigen presentation after autophagy might contribute to immune surveillance of infected and transformed cells.

Virus-specific CD4+ T cells: ready for direct attack

CD4⁺ T cells are classically thought to orchestrate adaptive immune responses. But recent studies demonstrate that they can also kill infected cells directly. A new paper shows that highly efficient processing of Epstein Barr virus (EBV) glycoproteins for presentation on MHC class II makes virus-transformed B cells susceptible to lysis by CD4⁺ T cells. Thus, antiviral vaccines should aim to stimulate both helper and cytolytic CD4⁺ T cells.

Altered immunophenotypic parameters in infertile women. Possible role of herpes viremia

PROBLEM

Purpose of this study was to reveal any alteration in peripheral blood lymphocytic concentrations of a large cohort of infertile women and to investigate the possible role of herpes viremia in the peripheral immunostimulation.

METHOD OF STUDY

The immunophenotypic characteristics and the presence of herpes viruses DNA in the peripheral blood of 168 infertile women were studied.

RESULTS

Peripheral CD56+/CD16+ natural killer (NK) cell concentration, CD56+/CD16- NK cell concentration, white blood cell (WBC) concentration and lymphocyte concentration were statistically correlated to herpes viremia. Epstein-Barr virus (EBV) viremia is related with a limited reduction of CD56+/CD16- cell levels in the peripheral blood of infertile women with regard to the rest of herpes viruses. High T-lymphocyte concentration, CD4+ T-cell concentration and CD8+ T-cell concentration was observed in women positive for three different kinds of herpes viruses (triple viremia) in the peripheral blood.

CONCLUSIONS

Assuming that all women under study remained asymptomatic, these data suggest that subclinical herpesvirus viremia may be an important cause of peripheral immunostimulation in women with a history of infertility.

Continuous release of hepatitis C virus (HCV) by peripheral blood mononuclear cells and B-lymphoblastoid cell-line cultures derived from HCV-infected patients

In order to investigate hepatitis C virus (HCV) persistence and replication in peripheral blood mononuclear cells (PBMC) from a group of haemophilic individuals, HCV production and release to PBMC culture supernatants (SNs) from HCV singly infected patients and HIV/HCV co-infected patients was studied. HCV RNA+ SNs were found more frequently from HIV/HCV co-infected individuals (89.5 %) with poor reconstitution of their immune status than from singly HCV-infected patients (57 %) or from HIV/HCV co-infected individuals with a good response to highly active anti-retroviral therapy (50 %). The presence of the HCV genome in culture SNs was associated with lower CD4+ T-cell counts and with a more severe clinical picture of HIV infection. In spite of prolonged negative HCV viraemia, PBMC from HIV/HCV co-infected patients released the HCV genome after culture. HCV permissive PBMC allowed generation of HCV productive B cell lines with continuous HCV replication. These findings add further weight to the involvement of PBMCs in persistence of HCV infection and emphasize the role of B lymphocytes as HCV reservoirs.

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

T-cell memory to Epstein-Barr virus (EBV) was first demonstrated through regression of EBV-induced B-cell transformation to lymphoblastoid cell lines (LCLs) in virus-infected peripheral blood mononuclear cell (PBMC) cultures. Here, using donors with virus-specific T-cell memory to well-defined CD4 and CD8 epitopes, we reexamine recent reports that the effector cells mediating regression are EBV latent antigen-specific CD4+ and not, as previously assumed, CD8+ T cells. In regressing cultures, we find that the reversal of CD23+ B-cell proliferation was always coincident with an expansion of latent epitope-specific CD8+, but not CD4+, T cells; furthermore CD8+ T-cell clones derived from regressing cultures were epitope specific and reproduced regression when cocultivated with EBV-infected autologous B cells. In cultures of CD4-depleted PBMCs, there was less efficient expansion of these epitope-specific CD8+ T cells and correspondingly weaker regression. The data are consistent with an effector role for epitope-specific CD8+ T cells in regression and an auxiliary role for CD4+ T cells in expanding the CD8 response. However, we also occasionally observed late regression in CD8-depleted PBMC cultures, though again without any detectable expansion of preexisting epitope-specific CD4+ T-cell memory. CD4+ T-cell clones derived from such cultures were LCL specific in gamma interferon release assays but did not recognize any known EBV latent cycle protein or derived peptide. A subset of these clones was also cytolytic and could block LCL outgrowth. These novel effectors, whose antigen specificity remains to be determined, may also play a role in limiting virus-induced B-cell proliferation in vitro and in vivo.

Functional characterization of EBV-encoded nuclear antigen 1-specific CD4+ helper and regulatory T cells elicited by in vitro peptide stimulation

CD4(+) helper and regulatory T (Treg) cells play important but opposing roles in regulating host immune responses against cancer and other diseases. However, very little is known about the antigen specificity of CD4(+) Treg cells. Here we describe the generation of a panel of EBV-encoded nuclear antigen 1 (EBNA1)-specific CD4(+) T-cell lines and clones that recognize naturally processed EBNA1-P(607-619) and -P(561-573) peptides in the context of HLA-DQ2 and HLA-DR11, -DR12, and -DR13 molecules, respectively. Phenotypic and functional analyses of these CD4(+) T cells revealed that they represent EBNA1-specific CD4(+) T helper as well as Treg cells. CD4(+) Treg cells do not secrete interleukin (IL)-10 and transforming growth factor beta cytokines but express CD25, the glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR), and Forkhead Box P3 (Foxp3), and are capable of suppressing the proliferative responses of naive CD4(+) and CD8(+) T cells to stimulation with mitogenic anti-CD3 antibody. The suppressive activity of these CD4(+) Treg cells is mediated via cell-cell contact or in part by a cytokine-dependent manner. Importantly, these Treg cells suppress IL-2 secretion by CD4(+) effector T cells specific for either EBNA1 or a melanoma antigen, suggesting that these CD4(+) Treg cells induce immune suppression. These observations suggest that the success of peptide-based vaccines against EBV-associated cancer and other diseases may likely depend upon our ability to identify antigens/peptides that preferentially activate helper T cells and/or to design strategies to regulate the balance between CD4(+) helper and Treg cells.

Cytotoxic T lymphocyte therapy for Epstein-Barr virus+ Hodgkin's disease

Epstein Barr virus (EBV)⁺ Hodgkin's disease (HD) expresses clearly identified tumor antigens derived from the virus and could, in principle, be a target for adoptive immunotherapy with viral antigen–specific T cells. However, like most tumor-associated antigens in immunocompetent hosts, these potential targets are only weakly immunogenic, consisting primarily of the latent membrane protein (LMP)1 and LMP2 antigens. Moreover, Hodgkin tumors possess a range of tumor evasion strategies. Therefore, the likely value of immunotherapy with EBV-specific cytotoxic effector cells has been questioned. We have now used a combination of gene marking, tetramer, and functional analyses to track the fate and assess the activity of EBV cytotoxic T lymphocyte (CTL) lines administered to 14 patients treated for relapsed EBV⁺ HD. Gene marking studies showed that infused effector cells could further expand by several logs in vivo, contribute to the memory pool (persisting up to 12 mo), and traffic to tumor sites. Tetramer and functional analyses showed that T cells reactive with the tumor-associated antigen LMP2 were present in the infused lines, expanded in peripheral blood after infusion, and also entered tumor. Viral load decreased, demonstrating the biologic activity of the infused CTLs. Clinically, EBV CTLs were well tolerated, could control type B symptoms (fever, night sweats, and weight loss), and had antitumor activity. After CTL infusion, five patients were in complete remission at up to 40 mo, two of whom had clearly measurable tumor at the time of treatment. One additional patient had a partial response, and five had stable disease. The performance and fate of these human tumor antigen–specific T cells in vivo suggests that they might be of value for the treatment of EBV⁺ Hodgkin lymphoma.

PSK and Trx80 inhibit B-cell growth in EBV-infected cord blood mononuclear cells through T cells activated by the monocyte products IL-15 and IL-12

Epstein-Barr virus (EBV)–specific immunologic memory is not transferred from mother to child. In vitro infection of cord blood cells can therefore readily lead to the outgrowth of transformed B lymphocytes. We found that the immunomodulator polysaccharide K (PSK) or the mitogenic cytokine truncated thioredoxin (Trx80) inhibited the EBV-induced B-cell proliferation. Using signaling lymphocytic activation molecule (SLAM)–associated protein (SAP) induction as a sign for T- and natural killer (NK) cell activation, we could follow it without any need for cell separation because neither macrophages nor B lymphocytes express SAP. The results suggest the following scenario: EBV infected and activated B lymphocytes. Upon interacting with these cells, T cells became posed for responding to cytokines produced by monocytes. Both PSK and Trx80, which is a secreted C-terminally truncated thioredoxin, activated the monocytes, which then produced cytokines in the presence of the primed T cells. PSK induced interleukin-15 (IL-15), while Trx80 induced IL-12 production. Both cytokines activated the T cells for function. Phosphatidylinositol 3–(PI 3)–kinase and reactive oxygen species (ROSs) were involved in the PSK-induced activation of monocytes. Restimulation of the cultures with EBV-transformed B cells generated specific cytotoxic activity.

Recognition of Adult T-Cell Leukemia/Lymphoma Cells by CD4+ Helper T Lymphocytes Specific for Human T-Cell Leukemia Virus Type I Envelope Protein

PURPOSE

Human T-cell leukemia virus type I (HTLV-I) can cause an adult T-cell leukemia/lymphoma (ATLL). Because ATLL is a life-threatening lymphoproliferative disorder and is resistant to chemotherapy, the establishment and enhancement of T-cell immunity to HTLV-I through the development of therapeutic vaccines could be of value. Thus, the identification of HTLV-I epitopes for both CD8(+) and CD4(+) T cells should facilitate the development of effective vaccines. Although numerous HTLV-I epitopes for CTLs have been identified, few epitopes recognized by CD4(+) helper T cells against this virus have been described.

EXPERIMENTAL DESIGN

Synthetic peptides prepared from several regions of the HTLV-I envelope (Env) sequence that were predicted to serve as helper T-cell epitopes were prepared with use of computer-based algorithms and tested for their capacity to trigger in vitro helper T-cell responses using lymphocytes from normal volunteers.

RESULTS

The results show that the HTLV-I-Env(317-331), and HTLV-I-Env(384-398)-reactive helper T lymphocytes restricted by HLA-DQw6 and HLA-DR15, respectively, could recognize intact HTLV-I+ T-cell lymphoma cells and, as a consequence, secrete lymphokines. In addition, HTLV-I Env(196-210)-reactive helper T lymphocytes restricted by HLA-DR9 were able to directly kill HTLV-I+ lymphoma cells and recognize naturally processed antigen derived from killed HTLV-I+ lymphoma cells, which was presented to the helper T cells by autologous antigen-presenting cells.

CONCLUSIONS

The present findings hold relevance for the design and optimization of T-cell epitope-based immunotherapy against HTLV-I-induced diseases such as ATLL.

Epstein–Barr virus-specific cytotoxic T-lymphocytes for adoptive immunotherapy of post-transplant lymphoproliferative disease

Post-transplant lymphoproliferative disease (PTLD) refers to a collection of clinically and pathologically diverse tumours associated with iatrogenic immunosuppression following transplantation. In most cases, tumourigenesis results from a deficit in Epstein-Barr virus (EBV)-specific cytotoxic T-lymphocyte (CTL) activity that leads to uncontrolled EBV-driven outgrowth of latently infected B-lymphocytes. Conventional treatment for PTLD typically involves a reduction in immunosuppression, but this approach is frequently unsuccessful and mortality remains high. An alternative, adoptive immunotherapy, involving the administration of EBV-specific CTLs cultured in vitro has been developed with the aim of selectively reconstituting EBV-directed immunity and effecting targeted tumour destruction. This approach has been the subject of several clinical studies, and these provide encouraging evidence of its clinical efficacy. This review presents an overview of the pathogenesis of PTLD and examines current progress in the use of adoptive immunotherapy for its treatment.

T cell-based therapies for EBV-associated malignancies

Epstein-Barr virus (EBV) is associated with a number of human malignancies. The cells of these tumours express a range of EBV latent cycle gene products that have the potential to be exploited as targets for T cell-mediated immunological therapies. Considerable progress has been made in developing adoptive T cell transfer for EBV-associated post-transplant lymphoproliferative disease (PTLD) and clinical experience clearly demonstrates that EBV-specific T cell responses can be used to treat this EBV-associated malignancy. Adoptive T cell therapies for other EBV-associated malignancies are less advanced, although encouraging data are starting to emerge. Adoptive T cell transfer, however, does require significant levels of specialist laboratory support. Large-scale treatment of patients in geographical areas with a high prevalence of EBV-associated malignancy is likely to require the development of therapeutic vaccination strategies, a number of which are in development at present. Although it remains to be seen whether long-lasting sterilising immunity to EBV could be achieved, an alternative vaccine-based approach would be to develop a prophylactic vaccine to protect against primary EBV infection.

Dendritic cells initiate immune control of epstein-barr virus transformation of B lymphocytes in vitro

The initiation of cell-mediated immunity to Epstein-Barr virus (EBV) has been analyzed with cells from EBV-seronegative blood donors in culture. The addition of dendritic cells (DCs) is essential to prime naive T cells that recognize EBV-latent antigens in enzyme-linked immunospot assays for interferon γ secretion and eradicate transformed B cells in regression assays. In contrast, DCs are not required to control the outgrowth of EBV-transformed B lymphocytes from seropositive donors. Enriched CD4⁺ and CD8⁺ T cells mediate regression of EBV-transformed cells in seronegative and seropositive donors, but the kinetics of T-dependent regression occurs with much greater speed with seropositives. EBV infection of DCs cannot be detected by reverse transcription–polymerase chain reaction with primers specific for mRNA for the EBNA1 U and K exons. Instead, DCs capture B cell debris and generate T cells specific for EBV latency antigens. We suggest that the cross-presentation of EBV-latent antigens from infected B cells by DCs is required for the initiation of EBV-specific immune control in vivo and that future EBV vaccine strategies should target viral antigens to DCs.

Defective Control of Latent Epstein-Barr Virus Infection in Systemic Lupus Erythematosus

EBV infection is more common in patients with systemic lupus erythematosus (SLE) than in control subjects, suggesting that this virus plays an etiologic role in disease and/or that patients with lupus have impaired EBV-specific immune responses. In the current report we assessed immune responsiveness to EBV in patients with SLE and healthy controls, determining virus-specific T cell responses and EBV viral loads using whole blood recall assays, HLA-A2 tetramers, and real-time quantitative PCR. Patients with SLE had an approximately 40-fold increase in EBV viral loads compared with controls, a finding not explained by disease activity or immunosuppressive medications. The frequency of EBV-specific CD69+ CD4+ T cells producing IFN-gamma was higher in patients with SLE than in controls. By contrast, the frequency of EBV-specific CD69+ CD8+ T cells producing IFN-gamma in patients with SLE appeared lower than that in healthy controls, although this difference was not statistically significant. These findings suggest a role for CD4+ T cells in controlling, and a possible defect in CD8+ T cells in regulating, increased viral loads in lupus. These ideas were supported by correlations between viral loads and EBV-specific T cell responses in lupus patients. EBV viral loads were inversely correlated with the frequency of EBV-specific CD69+ CD4+ T cells producing IFN-gamma and were positively correlated with the frequencies of CD69+ CD8+ T cells producing IFN-gamma and with EBV-specific, HLA-A2 tetramer-positive CD8+ T cells. These results demonstrate that patients with SLE have defective control of latent EBV infection that probably stems from altered T cell responses against EBV.

Cytolytic CD4(+)-T-cell clones reactive to EBNA1 inhibit Epstein-Barr virus-induced B-cell proliferation

In the absence of immune surveillance, Epstein-Barr virus (EBV)-infected B cells generate neoplasms in vivo and transformed cell lines in vitro. In an in vitro system which modeled the first steps of in vivo immune control over posttransplant lymphoproliferative disease and lymphomas, our investigators previously demonstrated that memory CD4(+) T cells reactive to EBV were necessary and sufficient to prevent proliferation of B cells newly infected by EBV (S. Nikiforow et al., J. Virol. 75:3740-3752, 2001). Here, we show that three CD4(+)-T-cell clones reactive to the latent EBV antigen EBNA1 also prevent the proliferation of newly infected B cells from major histocompatibility complex (MHC) class II-matched donors, a crucial first step in the transformation process. EBNA1-reactive T-cell clones recognized B cells as early as 4 days after EBV infection through an HLA-DR-restricted interaction. They secreted Th1-type and Th2-type cytokines and lysed EBV-transformed established lymphoblastoid cell lines via a Fas/Fas ligand-dependent mechanism. Once specifically activated, they also caused bystander regression and bystander killing of non-MHC-matched EBV-infected B cells. Since EBNA1 is recognized by CD4(+) T cells from nearly all EBV-seropositive individuals and evades detection by CD8(+) T cells, EBNA1-reactive CD4(+) T cells may control de novo expansion of B cells following EBV infection in vivo. Thus, EBNA1-reactive CD4(+)-T-cell clones may find use as adoptive immunotherapy against EBV-related lymphoproliferative disease and many other EBV-associated tumors.

Lymphocyte data in Epstein-Barr-virus induced post-transplant lymphoproliferative disorder treated by rituximab

Viral infection is an important cause of morbidity and mortality in the post-allograft period. Recently, a new therapeutic approach was developed in post-transplant lymphoproliferative disorder (PTLD) induced by Epstein-Barr virus (EBV): the anti-CD20 monoclonal antibody or rituximab. We performed a single-center study on the treatment effectiveness of rituximab in three EBV-induced PTLD and evaluated biologic data, such as T and B lymphocytes count, during PTLD development and treatment. Before PTLD treatment, blood cell profile showed a severe T lymphopenia with a progressive increase of CD8+ cells and B lymphopenia. Secondly, during treatment, there appeared a T response, as in primary EBV, and a regressive B lymphopenia.

Contrasting roles of dendritic cells and B cells in the immune control of Epstein-Barr virus

The human gamma-herpesvirus, Epstein-Barr virus (EBV), has growth-transforming potential in vivo and in vitro. Despite this, most healthy carriers remain free of EBV-associated malignancies because of effective T cell-mediated immune control of the virus. A better understanding of these highly efficient control mechanisms is important in the development of new treatment strategies for EBV-associated malignancies. A rational approach to EBV immunotherapy requires answering two questions about the initiation of the protective EBV-specific immune response. The first question is, what is the antigen-presenting cell responsible for priming EBV specific immunity? Second, which viral antigen is central to protective EBV adaptive immunity seen in healthy carriers of the virus? We provide evidence in this review that dendritic cells rather than EBV-transformed B cells are responsible for orchestrating protective EBV immunity and that the EBV nuclear antigen 1 (EBNA1)-specific CD4+ T cell response probably plays a role in resistance against all types of EBV-associated malignancies in healthy carriers. This implies that EBNA1 targeting to dendritic cells should be a component of vaccine and immunotherapy development against EBV-associated malignancies.