Direct visualization of antigen-specific CD8+ T cells during the primary immune response to Epstein-Barr virus In vivo

Epstein-Barr Virus-associated lymphoproliferative disorders: experimental and clinical developments

Epstein-Barr Virus (EBV), the first human virus related to oncogenesis, was initially identified in a Burkitt lymphoma cell line in 1964. EBV infects over 90% of the world's population. Most infected people maintain an asymptomatic but persistent EBV infection lifelong. However, in some individuals, EBV infection has been involved in the development of cancer and autoimmune disease. Nowadays, oncogenic potential of EBV has been intensively studied in a wide range of human neoplasms, including Hodgkin's lymphoma (HL), non-Hodgkin's lymphoma (NHL), nasopharyngeal carcinoma (NPC), gastric carcinoma (GC), etc. EBV encodes a series of viral protein and miRNAs, promoting its persistent infection and the transformation of EBV-infected cells. Although the exact role of EBV in the oncogenesis remains to be clarified, novel diagnostic and targeted therapeutic approaches are encouraging for the management of EBV-related malignancies. This review mainly focuses on the experimental and clinical advances of EBV-associated lymphoproliferative disorders.

Success and failure of the cellular immune response against HIV-1

The cellular immune response to HIV-1 has now been studied in extraordinary detail. A very large body of data provides the most likely reasons that the HIV-specific cellular immune response succeeds in a small number of people but fails in most. Understanding the success and failure of the HIV-specific cellular immune response has implications that extend not only to immunotherapies and vaccines for HIV-1 but also to the cellular immune response in other disease states. This Review focuses on the mechanisms that are most likely responsible for durable and potent immunologic control of HIV-1. Although we now have a detailed picture of the cellular immune responses to HIV-1, important questions remain regarding the nature of these responses and how they arise.

Measurement of CD8+ and CD4+ T Cell Frequencies Specific for EBV LMP1 and LMP2a Using mRNA-Transfected DCs

An EBV-specific cellular immune response is associated with the control of EBV-associated malignancies and lymphoproliferative diseases, some of which have been successfully treated by adoptive T cell therapy. Therefore, many methods have been used to measure EBV-specific cellular immune responses. Previous studies have mainly used autologous EBV-transformed B-lymphoblastoid cell lines (B-LCLs), recombinant viral vectors transfected or peptide pulsed dendritic cells (DCs) as stimulators of CD8⁺ and CD4⁺ T lymphocytes. In the present study, we used an interferon-γ (IFN-γ) enzyme-linked immunospot (ELISPOT) assay by using isolated CD8⁺ and CD4⁺ T cells stimulated with mRNA-transfected DCs. The frequency of latent membrane protein 1 (LMP1)-specific IFN-γ producing CD4⁺ T cells was significantly higher than that of LMP2a. The frequency of IFN-γ producing CD4⁺ T cells was significantly correlated with that of CD8⁺ T cells in LMP1-specific immune responses (r = 0.7187, Pc < 0.0001). To determine whether there were changes in LMP1- or LMP2a-specific immune responses, subsequent peripheral blood mononuclear cells (PBMCs) samples were analyzed. Significant changes were observed in 5 of the 10 donors examined, and CD4⁺ T cell responses showed more significant changes than CD8⁺ T cell responses. CD8⁺ and CD4⁺ T cells from EBV-seropositive donors secreted only the Th1 cytokines IFN-γ, TNF-α, and IL-2, while Th2 (IL-4) and Th17 (IL-17a) cytokines were not detected. CD4⁺ T cells secreted significantly higher cytokine levels than did CD8⁺ T cells. Analysis of EBV-specific T cell responses using autologous DCs transfected with mRNA might provide a comprehensive tool for monitoring EBV infection and new insights into the pathogenesis of EBV-associated diseases.

T Cell Cross-Reactivity between a Highly Immunogenic EBV Epitope and a Self-Peptide Naturally Presented by HLA-B*18:01+ Cells

T cell cross-reactivity underpins the molecular mimicry hypothesis in which microbial peptides sharing structural features with host peptides stimulate T cells that cross-react with self-peptides, thereby initiating and/or perpetuating autoimmune disease. EBV represents a potentially important factor in the pathogenesis of several T cell-mediated autoimmune disorders, with molecular mimicry a likely mechanism. In this study, we describe a human self-peptide (DELEIKAY) that is a homolog of a highly immunogenic EBV T cell epitope (SELEIKRY) presented by HLA-B*18:01. This self-peptide was shown to bind stably to HLA-B*18:01, and peptide elution/mass spectrometric studies showed it is naturally presented by this HLA molecule on the surface of human cells. A significant proportion of CD8(+) T cells raised from some healthy individuals against this EBV epitope cross-reacted with the self-peptide. A diverse array of TCRs was expressed by the cross-reactive T cells, with variable functional avidity for the self-peptide, including some T cells that appeared to avoid autoreactivity by a narrow margin, with only 10-fold more of the self-peptide required for equivalent activation as compared with the EBV peptide. Structural studies revealed that the self-peptide-HLA-B*18:01 complex is a structural mimic of the EBV peptide-HLA-B*18:01 complex, and that the strong antiviral T cell response is primarily dependent on the alanine/arginine mismatch at position 7. To our knowledge, this is the first report confirming the natural presentation of a self-peptide cross-recognized in the context of self-HLA by EBV-reactive CD8(+) T cells. These results illustrate how aberrant immune responses and immunopathological diseases could be generated by EBV infection.

Generation of human memory stem T cells after haploidentical T-replete hematopoietic stem cell transplantation

Memory stem T cells (TSCM) have been proposed as key determinants of immunologic memory. However, their exact contribution to a mounting immune response, as well as the mechanisms and timing of their in vivo generation, are poorly understood. We longitudinally tracked TSCM dynamics in patients undergoing haploidentical hematopoietic stem cell transplantation (HSCT), thereby providing novel hints on the contribution of this subset to posttransplant immune reconstitution in humans. We found that donor-derived TSCM are highly enriched early after HSCT. We showed at the antigen-specific and clonal level that TSCM lymphocytes can differentiate directly from naive precursors infused within the graft and that the extent of TSCM generation might correlate with interleukin 7 serum levels. In vivo fate mapping through T-cell receptor sequencing allowed defining the in vivo differentiation landscapes of human naive T cells, supporting the notion that progenies of single naive cells embrace disparate fates in vivo and highlighting TSCM as relevant novel players in the diversification of immunological memory after allogeneic HSCT.

Early virological and immunological events in asymptomatic Epstein-Barr virus infection in African children

Epstein-Barr virus (EBV) infection often occurs in early childhood and is asymptomatic. However, if delayed until adolescence, primary infection may manifest as acute infectious mononucleosis (AIM), a febrile illness characterised by global CD8+ T-cell lymphocytosis, much of it reflecting a huge expansion of activated EBV-specific CD8+ T-cells. While the events of AIM have been intensely studied, little is known about how these relate to asymptomatic primary infection. Here Gambian children (14-18 months old, an age at which many acquire the virus) were followed for the ensuing six months, monitoring circulating EBV loads, antibody status against virus capsid antigen (VCA) and both total and virus-specific CD8+ T-cell numbers. Many children were IgG anti-VCA-positive and, though no longer IgM-positive, still retained high virus loads comparable to AIM patients and had detectable EBV-specific T-cells, some still expressing activation markers. Virus loads and the frequency/activation status of specific T-cells decreased over time, consistent with resolution of a relatively recent primary infection. Six children with similarly high EBV loads were IgM anti-VCA-positive, indicating very recent infection. In three of these donors with HLA types allowing MHC-tetramer analysis, highly activated EBV-specific T-cells were detectable in the blood with one individual epitope response reaching 15% of all CD8+ T-cells. That response was culled and the cells lost activation markers over time, just as seen in AIM. However, unlike AIM, these events occurred without marked expansion of total CD8+ numbers. Thus asymptomatic EBV infection in children elicits a virus-specific CD8+ T-cell response that can control the infection without over-expansion; conversely, in AIM it appears the CD8 over-expansion, rather than virus load per se, is the cause of disease symptoms.

Antiviral T-cell therapy

Serious viral infections are a common cause of morbidity and mortality after allogeneic stem cell transplantation. They occur in the majority of allograft recipients and are fatal in 17–20%. These severe infections may be prolonged or recurrent and add substantially to the cost, both human and financial, of the procedure. Many features of allogeneic stem cell transplantation contribute to this high rate of viral disease. The cytotoxic and immunosuppressive drugs administered pretransplant to eliminate the host hematopoietic/immune system and any associated malignancy, the delay in recapitulating immune ontogeny post‐transplant, the immunosuppressive drugs given to prevent graft versus host disease (GvHD), and the effects of GvHD itself, all serve to make stem cell transplant recipients vulnerable to disease from endogenous (latent) and exogenous (community) viruses, and to be incapable of controlling them as quickly and effectively as most normal individuals.

Epstein-Barr virus-positive plasmacytoma in immunocompetent patients

AIMS

Extramedullary plasmacytomas are often localized, clinically indolent neoplasms, and affected patients usually respond to radiation therapy or limited cycles of chemotherapy. In contrast, plasmablastic lymphomas are clinically aggressive neoplasms composed of immunoblastic or plasmablastic cells and associated with more mature plasma cells in some cases. Patients with plasmablastic lymphoma usually have a poor prognosis despite aggressive chemotherapy. Evidence of Epstein-Barr virus (EBV) infection is uncommon in plasmacytoma, but common in plasmablastic lymphoma, and is therefore helpful in differential diagnosis. The aim of this study is to describe four cases of plasmacytoma arising in immunocompetent individuals that were diffusely positive for Epstein-Barr virus-encoded small RNA as shown by in-situ hybridization.

METHODS AND RESULTS

We describe the clinicopathological and immunophenotypic findings of four EBV-positive plasmacytomas arising in immunocompetent patients. These tumours were characterized by diffuse proliferation of mature-appearing plasma cells intermixed with a briskly reactive, CD8-positive, TIA-1-positive cytotoxic T-cell infiltrate. Long-term follow-up was available for all patients, and all were alive and free of disease at last follow-up (median 43.4 months).

CONCLUSIONS

We suggest the term EBV-positive plasmacytoma in immunocompetent patients for these lesions. It is essential to distinguish these tumours from plasmablastic lymphoma, as the latter diagnosis is associated with a much poorer prognosis, and patients require much more aggressive therapy.

Infectious mononucleosis

Infectious mononucleosis is a clinical entity characterized by pharyngitis, cervical lymph node enlargement, fatigue and fever, which results most often from a primary Epstein-Barr virus (EBV) infection. EBV, a lymphocrytovirus and a member of the γ-herpesvirus family, infects at least 90% of the population worldwide, the majority of whom have no recognizable illness. The virus is spread by intimate oral contact among adolescents, but how preadolescents acquire the virus is not known. During the incubation period of approximately 6 weeks, viral replication first occurs in the oropharynx followed by viremia as early as 2 weeks before onset of illness. The acute illness is marked by high viral loads in both the oral cavity and blood accompanied by the production of immunoglobulin M antibodies against EBV viral capsid antigen and an extraordinary expansion of CD8(+) T lymphocytes directed against EBV-infected B cells. During convalescence, CD8(+) T cells return to normal levels and antibodies develop against EBV nuclear antigen-1. A typical clinical picture in an adolescent or young adult with a positive heterophile test is usually sufficient to make the diagnosis of infectious mononucleosis, but heterophile antibodies are not specific and do not develop in some patients especially young children. EBV-specific antibody profiles are the best choice for staging EBV infection. In addition to causing acute illness, long-term consequences are linked to infectious mononucleosis, especially Hodgkin lymphoma and multiple sclerosis. There is no licensed vaccine for prevention and no specific approved treatment. Future research goals are development of an EBV vaccine, understanding the risk factors for severity of the acute illness and likelihood of developing cancer or autoimmune diseases, and discovering anti-EBV drugs to treat infectious mononucleosis and other EBV-spurred diseases.

Specificity and dynamics of effector and memory CD8 T cell responses in human tick-borne encephalitis virus infection

Tick-borne encephalitis virus (TBEV) is transferred to humans by ticks. The virus causes tick-borne encephalitis (TBE) with symptoms such as meningitis and meningoencephalitis. About one third of the patients suffer from long-lasting sequelae after clearance of the infection. Studies of the immune response during TBEV-infection are essential to the understanding of host responses to TBEV-infection and for the development of therapeutics. Here, we studied in detail the primary CD8 T cell response to TBEV in patients with acute TBE. Peripheral blood CD8 T cells mounted a considerable response to TBEV-infection as assessed by Ki67 and CD38 co-expression. These activated cells showed a CD45RA-CCR7-CD127- phenotype at day 7 after hospitalization, phenotypically defining them as effector cells. An immunodominant HLA-A2-restricted TBEV epitope was identified and utilized to study the characteristics and temporal dynamics of the antigen-specific response. The functional profile of TBEV-specific CD8 T cells was dominated by variants of mono-functional cells as the effector response matured. Antigen-specific CD8 T cells predominantly displayed a distinct Eomes+Ki67+T-bet+ effector phenotype at the peak of the response, which transitioned to an Eomes-Ki67-T-bet+ phenotype as the infection resolved and memory was established. These transcription factors thus characterize and discriminate stages of the antigen-specific T cell response during acute TBEV-infection. Altogether, CD8 T cells responded strongly to acute TBEV infection and passed through an effector phase, prior to gradual differentiation into memory cells with distinct transcription factor expression-patterns throughout the different phases.

Tick-borne encephalitis virus (TBEV) belongs to the flavivirus family and causes tick-borne encephalitis. This is a severe meningoencephalitic disease with no available treatment. Detailed studies of the immune response during human TBEV infection are essential to understand host responses to TBE and for the development of therapeutics. Herein, we studied the primary T cell-mediated immune response in patients diagnosed with TBEV infection. We show that CD8 T cells mount a vigorous TBEV-specific response within one week of hospitalization. Moreover, TBEV-specific CD8 T cells displayed a distinctive phenotypic and functional profile, paired with a distinct transcription factor expression-pattern during the peak of activation. In summary, this is the first comprehensive study of the CD8 T cell response during acute human TBEV infection, and provides a framework for understanding of CD8 T cell-mediated immunity in this emerging viral disease.

The interplay between Epstein-Barr virus and B lymphocytes: implications for infection, immunity, and disease

Human B cells are the primary targets of Epstein-Barr virus (EBV) infection. In most cases, EBV infection is asymptomatic because of a highly effective host immune response, but some individuals develop self-limiting infectious mononucleosis, while others develop EBV-associated lymphoid or epithelial malignancies. The viral and immune factors that determine the outcome of infection are not understood. The EBV life cycle includes a lytic phase, culminating in the production of new viral particles, and a latent phase, during which the virus remains largely silent for the lifetime of the host in memory B cells. Thus, in healthy individuals, there is a tightly orchestrated interplay between EBV and the host that allows the virus to persist. To promote viral persistence, EBV has evolved a variety of strategies to modulate the host immune response including inhibition of immune cell function, blunting of apoptotic pathways, and interfering with antigen processing and presentation pathways. In this article, we focus on mechanisms by which dysregulation of the host B cell and immune modulation by the virus can contribute to development of EBV+ B cell lymphomas.

EBV Persistence--Introducing the Virus

Persistent infection by EBV is explained by the germinal center model (GCM) which provides a satisfying and currently the only explanation for EBVs disparate biology. Since the GCM touches on every aspect of the virus, this chapter will serve as an introduction to the subsequent chapters. EBV is B lymphotropic, and its biology closely follows that of normal mature B lymphocytes. The virus persists quiescently in resting memory B cells for the lifetime of the host in a non-pathogenic state that is also invisible to the immune response. To access this compartment, the virus infects naïve B cells in the lymphoepithelium of the tonsils and activates these cells using the growth transcription program. These cells migrate to the GC where they switch to a more limited transcription program, the default program, which helps rescue them into the memory compartment where the virus persists. For egress, the infected memory cells return to the lymphoepithelium where they occasionally differentiate into plasma cells activating viral replication. The released virus can either infect more naïve B cells or be amplified in the epithelium for shedding. This cycle of infection and the quiescent state in memory B cells allow for lifetime persistence at a very low level that is remarkably stable over time. Mathematically, this is a stable fixed point where the mechanisms regulating persistence drive the state back to equilibrium when perturbed. This is the GCM of EBV persistence. Other possible sites and mechanisms of persistence will also be discussed.

Multiparameter Flow Cytometric Assays to Quantify Effector and Regulatory T-Cell Function in Multiple Sclerosis

The immune system plays a major pathological and regulatory role in multiple sclerosis (MS) and, therefore, is a focus of extensive research. Animal models of MS have been crucial in understanding the pathological processes in MS and developing certain treatments, however, all crucial aspects of the human disease may not be appropriately modeled. With the exception of detecting oligoclonal bands and IgG synthesis in cerebrospinal fluids of MS patients, there has not been major progress in the development of immunologic tests that can be used for diagnosis of MS. Further, due to the lack of validated immune assays, routine monitoring of the immune system following therapy initiation is not a part of standard patient care in MS. This is critical since immunomodulatory therapies used for MS treatment are not benign and, more importantly, there is a considerable variation in clinical responses in MS patients initiating such therapies. Flow cytometry is a powerful tool that can be used for studying both the phenotype and function of immune cells. The studies described here will demonstrate how flow cytometry can be used to apply current knowledge about the MS immune system to develop a diagnostic laboratory test for the immunologic monitoring of this disease. Importantly, we will also show that the multiparameter flow cytometry based assay developed by us can also be implemented for the immunologic evaluation of therapeutic success in MS patients.

Therapeutic implications of Epstein-Barr virus infection for the treatment of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is highly endemic in certain regions including the People’s Republic of China and Southeast Asia. Its etiology is unique and multifactorial, involving genetic background, epigenetic, and environment factors, including Epstein–Barr virus (EBV) infection. The presence of EBV in all tumor cells, aberrant pattern of antibodies against EBV antigens in patient sera, and elevated viral DNA in patient circulation as well as nasopharyngeal site underline the role of EBV during NPC development. In NPC tumors, EBV expresses latency type II, where three EBV-encoded proteins, Epstein–Barr nuclear antigen 1, latent membrane protein 1 and 2 (LMP1, 2), are expressed along with BamH1-A rightward reading frame 1, Epstein–Barr virus-encoded small nuclear RNAs, and BamH1-A rightward transcripts. Among all encoded proteins, LMP1 plays a central role in the propagation of NPC. Standard treatment of NPC consists of radiotherapy with or without chemotherapy for early stage, concurrent chemoradiotherapy in locally advanced tumors, and palliative systemic chemotherapy in metastatic disease. However, this standard care has limitations, allowing recurrences and disease progression in a certain proportion of cases. Although the pathophysiological link and molecular process of EBV-induced oncogenesis are not fully understood, therapeutic approaches targeting the virus may increase the cure rate and add clinical benefit. The promising results of early phase clinical trials on EBV-specific immunotherapy, epigenetic therapy, and treatment with viral lytic induction offer new options for treating NPC.

Epstein-Barr virus effect on frequency of functionally distinct T cell subsets in children with infectious mononucleosis

PURPOSE

Epstein-Barr virus is a common human pathogen which infects the great majority of population worldwide. A striking proliferation of CD8⁺ T cells is an immune response to EBV invasion of B lymphocytes during infectious mononucleosis. The aim of the study was to analyze frequencies of CD28⁺CD95⁻, CD28⁺CD95⁺, CD28⁻CD95⁺ T cell subsets putative naïve (T(N)), central (T(CM)) and effector memory (T(EM)) T cells in children with infectious mononucleosis.

MATERIAL/METHODS

Multiparameter flow cytometric analysis of CD4⁺ and CD8⁺ T cell subsets was performed in 19 children with acute infectious mononucleosis.

RESULTS

The CD4⁺/CD8⁺ ratio was found to be decreased (0.53) in children with infectious mononucleosis. Median T(N), T(CM), T(EM) frequencies were estimated to be 3.7, 4.5, 15.1% of CD8⁺ and 23, 59.3, 5.5% of CD4⁺ T cells, respectively. In the present study we demonstrated negative correlations between CD8⁺CD28⁺CD95⁺ and CD8⁺CD28⁻CD95⁺ T cells and both VCA IgM antibody titers and disease duration. However, no such correlation was found when subset of CD4⁺ T cells or CD8⁺CD28⁺CD95⁻ cells was compared.

CONCLUSIONS

We conclude that there is a rapid decrease in the number of memory CD8⁺ T cells in early acute stage of infectious mononucleosis.

Adoptive transfer of EBV specific CD8+ T cell clones can transiently control EBV infection in humanized mice

Epstein Barr virus (EBV) infection expands CD8⁺ T cells specific for lytic antigens to high frequencies during symptomatic primary infection, and maintains these at significant numbers during persistence. Despite this, the protective function of these lytic EBV antigen-specific cytotoxic CD8⁺ T cells remains unclear. Here we demonstrate that lytic EBV replication does not significantly contribute to virus-induced B cell proliferation in vitro and in vivo in a mouse model with reconstituted human immune system components (huNSG mice). However, we report a trend to reduction of EBV-induced lymphoproliferation outside of lymphoid organs upon diminished lytic replication. Moreover, we could demonstrate that CD8⁺ T cells against the lytic EBV antigen BMLF1 can eliminate lytically replicating EBV-transformed B cells from lymphoblastoid cell lines (LCLs) and in vivo, thereby transiently controlling high viremia after adoptive transfer into EBV infected huNSG mice. These findings suggest a protective function for lytic EBV antigen-specific CD8⁺ T cells against EBV infection and against virus-associated tumors in extra-lymphoid organs. These specificities should be explored for EBV-specific vaccine development.

Epstein Barr virus persistently infects more than 90% of the human adult population. While fortunately carried as an asymptomatic chronic infection in most individuals, it causes B cell lymphomas and carcinomas in some patients. Symptomatic primary EBV infection, called infectious mononucleosis, predisposes for some of these malignancies and is characterized by massive expansions of cytotoxic T cells, which are mostly directed against lytic EBV antigens that are expressed during virus particle production. Therefore, we investigated the protective role of lytic EBV antigen specific T cells during EBV infection and the contribution of lytic EBV infection to virus-associated tumor formation. We found that lytic EBV antigen specific T cells kill B cells with lytic virus replication and might thereby transiently control EBV infection in mice with human immune system components. Furthermore, we observed that EBV associated B cell tumors outside secondary lymphoid organs may require lytic replication for efficient formation. Thus, we suggest that lytic EBV antigens should be explored for vaccination against symptomatic EBV infection and EBV associated extra-lymphoid tumors.

Immunological changes and increased expression of myxovirus resistance protein a in thyroid tissue of patients with recent onset and untreated Graves' disease

BACKGROUND

Few studies have systematically examined the immune cells that infiltrate thyroid tissue at the time of the onset of Graves' disease (GD). The role of viruses in the pathogenesis of autoimmune thyroid diseases is controversial. The present study analyzed inflammatory responses with respect to signs of virus infection.

METHODS

Thyroid tissue was obtained from 22 patients with newly diagnosed and untreated GD, 24 patients with chronic GD, and 24 controls. Inflammation was assessed by immunostaining for CD4+ and CD8+ T cells, plasma cells (CD138+), and plasmacytoid dendritic cells (PDCs). The production of interferon-inducible myxovirus resistance protein A (MxA) was analyzed as a sign of virus infection.

RESULTS

The degree of thyroid inflammation and fibrosis was significantly higher in both patient groups compared with that in controls. The number of CD4+ T cells and plasma cells (activated B cells) was significantly higher in both patient groups. CD8+ cells were only present in patients with chronic disease. MxA expression and the number of PDCs increased only in patients with newly diagnosed GD. There was a strong positive correlation between the number of PDCs and the number of MxA+ leucocytes.

CONCLUSION

The increase in CD8+ T cells during the chronic stage of GD suggests that they may play a role in progression of the autoimmune process from early to chronic thyroiditis. Upregulation of MxA expression during the early stages of the disease, and the positive correlation between the number of PDCs and the number of MxA+ leucocytes, suggests that activated PDCs secrete type I IFNs at the lesion site, possibly in response to viral infection.

CD8+ T cell responses to lytic EBV infection: late antigen specificities as subdominant components of the total response

EBV elicits primary CD8(+) T cell responses that, by T cell cloning from infectious mononucleosis (IM) patients, appear skewed toward immediate early (IE) and some early (E) lytic cycle proteins, with late (L) proteins rarely targeted. However, L Ag-specific responses have been detected regularly in polyclonal T cell cultures from long-term virus carriers. To resolve this apparent difference between responses to primary and persistent infection, 13 long-term carriers were screened in ex vivo IFN-γ ELISPOT assays using peptides spanning the two IE, six representative E, and seven representative L proteins. This revealed memory CD8 responses to 44 new lytic cycle epitopes that straddle all three protein classes but, in terms of both frequency and size, maintain the IE > E > L hierarchy of immunodominance. Having identified the HLA restriction of 10 (including 7 L) new epitopes using memory CD8(+) T cell clones, we looked in HLA-matched IM patients and found such reactivities but typically at low levels, explaining why they had gone undetected in the original IM clonal screens. Wherever tested, all CD8(+) T cell clones against these novel lytic cycle epitopes recognized lytically infected cells naturally expressing their target Ag. Surprisingly, however, clones against the most frequently recognized L Ag, the BNRF1 tegument protein, also recognized latently infected, growth-transformed cells. We infer that BNRF1 is also a latent Ag that could be targeted in T cell therapy of EBV-driven B-lymphoproliferative disease.

Immunity to viruses: learning from successful human vaccines

For more than a century, immunologists and vaccinologists have existed in parallel universes. Immunologists have for long reveled in using 'model antigens', such as chicken egg ovalbumin or nitrophenyl haptens, to study immune responses in model organisms such as mice. Such studies have yielded many seminal insights about the mechanisms of immune regulation, but their relevance to humans has been questioned. In another universe, vaccinologists have relied on human clinical trials to assess vaccine efficacy, but have done little to take advantage of such trials for studying the nature of immune responses to vaccination. The human model provides a nexus between these two universes, and recent studies have begun to use this model to study the molecular profile of innate and adaptive responses to vaccination. Such 'systems vaccinology' studies are beginning to provide mechanistic insights about innate and adaptive immunity in humans. Here, we present an overview of such studies, with particular examples from studies with the yellow fever and the seasonal influenza vaccines. Vaccination with the yellow fever vaccine causes a systemic acute viral infection and thus provides an attractive model to study innate and adaptive responses to a primary viral challenge. Vaccination with the live attenuated influenza vaccine causes a localized acute viral infection in mucosal tissues and induces a recall response, since most vaccinees have had prior exposure to influenza, and thus provides a unique opportunity to study innate and antigen-specific memory responses in mucosal tissues and in the blood. Vaccination with the inactivated influenza vaccine offers a model to study immune responses to an inactivated immunogen. Studies with these and other vaccines are beginning to reunite the estranged fields of immunology and vaccinology, yielding unexpected insights about mechanisms of viral immunity. Vaccines that have been proven to be of immense benefit in saving lives offer us a new fringe benefit: lessons in viral immunology.

Primary immunodeficiencies predisposed to Epstein-Barr virus-driven haematological diseases

Epstein-Barr virus (EBV), a ubiquitous human herpesvirus, maintains lifelong subclinical persistent infections in humans. In the circulation, EBV primarily infects the B cells, and protective immunity is mediated by EBV-specific cytotoxic T cells (CTLs) and natural killer (NK) cells. However, EBV has been linked to several devastating diseases, such as haemophagocytic lymphohistiocytosis (HLH) and lymphoproliferative diseases in the immunocompromised host. Some types of primary immunodeficiencies (PIDs) are characterized by the development of EBV-associated complications as their predominant clinical feature. The study of such genetic diseases presents an ideal opportunity for a better understanding of the biology of the immune responses against EBV. Here, we summarize the range of PIDs that are predisposed to EBV-associated haematological diseases, describing their clinical picture and pathogenetic mechanisms.

MHC II tetramers visualize human CD4+ T cell responses to Epstein-Barr virus infection and demonstrate atypical kinetics of the nuclear antigen EBNA1 response

Characterization of the human EBV-specific CD4⁺ T cell response using MHC II tetramers reveals the latent EBV antigen response is more frequent than the lytic response with a delayed EBNA1 response that coincides with diminished cross-presentation.

Virus-specific CD4⁺ T cells are key orchestrators of host responses to viral infection yet, compared with their CD8⁺ T cell counterparts, remain poorly characterized at the single cell level. Here we use nine MHC II–epitope peptide tetramers to visualize human CD4⁺ T cell responses to Epstein–Barr virus (EBV), the causative agent of infectious mononucleosis (IM), a disease associated with large virus-specific CD8⁺ T cell responses. We find that, while not approaching virus-specific CD8⁺ T cell expansions in magnitude, activated CD4⁺ T cells specific for epitopes in the latent antigen EBNA2 and four lytic cycle antigens are detected at high frequencies in acute IM blood. They then fall rapidly to values typical of life-long virus carriage where most tetramer-positive cells display conventional memory markers but some, unexpectedly, revert to a naive-like phenotype. In contrast CD4⁺ T cell responses to EBNA1 epitopes are greatly delayed in IM patients, in line with the well-known but hitherto unexplained delay in EBNA1 IgG antibody responses. We present evidence from an in vitro system that may explain these unusual kinetics. Unlike other EBNAs and lytic cycle proteins, EBNA1 is not naturally released from EBV-infected cells as a source of antigen for CD4⁺ T cell priming.

Missing links in multiple sclerosis etiology. A working connecting hypothesis

The etiology of multiple sclerosis is still elusive despite an extended patchwork of mechanistic events has been accumulated. In this article, are tentatively identified from scattered literature sources new factors that may link well known characteristic of MS such as the central alteration of BBR selectivity, its association with EBV status and its biased distribution of the globe more comprehensively. The hypothesis proposes that the concomitant important rise in some heterophilic antibodies (anti Neu5Gc) which activate BBB endothelial cells and in the frequency of anti EBV committed T cells and of memory B infected cells with EBV contemporary to EBV infection play a major role in MS etiology. In addition, the hypothesis proposes new possible explanations for the elevated risk of MS in specific geographical area.

Epstein-Barr virus infection and posttransplant lymphoproliferative disorder

Epstein-Barr virus (EBV) is an important pathogen in recipients of solid organ transplants (SOT). Infection with EBV manifests as a spectrum of diseases/malignancies ranging from asymptomatic viremia through infectious mononucleosis to posttransplant lymphoproliferative disorder (PTLD). EBV disease and its associated PTLD is more frequently seen when primary EBV infection occurs after transplant, a common scenario in pediatric SOT recipients. Intensity of immunosuppressive therapies also influences the risk for PTLD. The use of EBV viral load monitoring facilitates the diagnosis and management of EBV/PTLD as well as being used to inform preemptive therapy with reduction of immunosuppression, the most effective intervention for prevention of and treatment for PTLD. Other therapies, including the rituximab (anti-CD20 monoclonal antibody) and traditional chemotherapy, are also useful in the treatment of established PTLD. The future development of standards for management based on EBV viral load and routine monitoring of EBV-specific CTL responses promise further improvement in outcomes with EBV and PTLD.

Temporal dynamics of the primary human T cell response to yellow fever virus 17D as it matures from an effector- to a memory-type response

The live attenuated yellow fever virus (YFV) 17D vaccine provides a good model to study immune responses to an acute viral infection in humans. We studied the temporal dynamics, composition, and character of the primary human T cell response to YFV. The acute YFV-specific effector CD8 T cell response was broad and complex; it was composed of dominant responses that persisted into the memory population, as well as of transient subdominant responses that were not detected at the memory stage. Furthermore, HLA-A2- and HLA-B7-restricted YFV epitope-specific effector cells predominantly displayed a CD45RA(-)CCR7(-)PD-1(+)CD27(high) phenotype, which transitioned into a CD45RA(+)CCR7(-)PD-1(-)CD27(low) memory population phenotype. The functional profile of the YFV-specific CD8 T cell response changed in composition as it matured from an effector- to a memory-type response, and it tended to become less polyfunctional during the course of this transition. Interestingly, activation of CD4 T cells, as well as FOXP3(+) T regulatory cells, in response to YFV vaccination preceded the kinetics of the CD8 T cell response. The present results contribute to our understanding of how immunodominance patterns develop, as well as the phenotypic and functional characteristics of the primary human T cell response to a viral infection as it evolves and matures into memory.

Behavioral, virologic, and immunologic factors associated with acquisition and severity of primary Epstein-Barr virus infection in university students

BACKGROUND

University students were studied prospectively to determine the incidence of and risk factors for acquisition of primary Epstein-Barr virus (EBV) infection and the virologic and immune correlates of disease severity.

METHODS

EBV antibody-negative freshmen participated in monthly surveillance until graduation. If antibodies developed, proximate samples were assayed for viral load by polymerase chain reaction. Lymphocyte and natural killer (NK) cell numbers and activation were measured by flow cytometry, and plasma cytokine levels were measured by a multiplex assay.

RESULTS

Of 546 students screened, 202 (37%) were antibody negative; 143 antibody-negative students were enrolled. During a median of 3 years of observation, 66 subjects experienced primary infection. Of these, 77% had infectious mononucleosis, 12% had atypical symptoms, and 11% were asymptomatic. Subjects reporting deep kissing with or without coitus had the same higher risk of infection than those reporting no kissing (P < .01). Viremia was transient, but median oral shedding was 175 days. Increases were observed in numbers of NK cells and CD8(+) T-cells but not in numbers of CD4(+) T-cells during acute infection. Severity of illness correlated positively with both blood EBV load (P = .015) and CD8(+) lymphocytosis (P = .0003).

CONCLUSIONS

Kissing was a significant risk for primary EBV infection. A total of 89% of infections were symptomatic, and blood viral load and CD8(+) lymphocytosis correlated with disease severity.

Qualitative host factors associated with immunological control of HIV infection by CD8 T cells

PURPOSE OF REVIEW

Despite significant technical advances that have permitted an increasingly more quantitative and detailed study of virus-specific cellular immunity over the past few years, our understanding of the nature of immunological control in rare cases of non-progressive HIV infection and diminished control in the majority of untreated chronically infected patients remains incomplete. This review will summarize recent findings and points of controversy within areas of active investigation of the cellular immune response to HIV.

RECENT FINDINGS

It is now appreciated that high frequencies of virus-specific CD8 T cells are readily detectable in chronic HIV infection, but do not restrict viral replication. For this reason, attention has shifted to qualitative features of the host immune response that might accurately determine the restriction of viral replication. A number of qualitative changes in the phenotype, cytokine secretion, and proliferative capacity of HIV-specific CD8 T cells of progressors have recently been described.

SUMMARY

Given that the desired response to the majority of vaccines in pre-clinical or clinical testing is to stimulate cellular immunity in an attempt to alter disease progression, understanding these qualitative features is of particular relevance. Further study will probably yield critical information for the means to stimulate effective immunity in vaccinees, prevent the loss of control of viral replication upon infection of vaccinees, or induce durable immunological control in humans already infected with HIV.

Short communication: impact of hepatitis C viral clearance on CD4+ T-lymphocyte course in HIV/HCV-coinfected patients treated with pegylated interferon plus ribavirin

The long-term impact of pegylated-interferon plus ribavirin (Peg-IFN-RBV) treatment outcome on CD4 T cell course in patients coinfected with human immunodeficiency virus (HIV) and hepatitis C virus (HCV) is unknown. The aim of this study was to investigate the impact of HCV-RNA clearance by standard anti-HCV therapy on long-term CD4 cells recovery in HIV/HCV patients on successful combined antiretroviral therapy (cART). We retrospectively enrolled HIV/HCV-coinfected patients on stable cART, treated with Peg-IFN-RBV between 2005 and 2009. CD4(+) T cell counts were registered at baseline (pre-Peg-IFN-RBV), after 6, 12, and 24 months of follow-up from therapy discontinuation. Multiple linear regression analysis was performed to identify independent predictors of CD4(+) T cell change following the anti-HCV treatment outcome. Of the 116 patients enrolled, 54 (46.6%) reached a sustained virological response (SVR) and 62 (53.4%) did not. Throughout a median follow-up of 24 months, the SVR group showed a mean annual increase in CD4(+) T cell from baseline of 84 cells/μl at 1 year and of a further 38 cells/μl within the second year (p=0.01, 0.001, respectively). A nonsignificant mean increase of 77 cells/μl occurred in the non-SVR group within month 24 (p=0.06). Variables associated with greater CD4 gains were higher nadir and lower pre-interferon CD4 counts, and lower body mass index (BMI). The achievement of SVR was not significantly associated with the change in CD4(+) count. The clearance of HCV replication did not affect the CD4(+) changes after Peg-IFN-RBV therapy in coinfected patients on efficient cART. Liver fibrosis and higher BMI were negative determinants of immune recovery.

Post-chemotherapy T-cell recovery is a marker of improved survival in patients with advanced thoracic malignancies

Background:

There is increasing interest in combining chemotherapy with immunotherapy. However, the effects of chemotherapy on the human immune system are largely unknown.

Methods:

Longitudinal changes in peripheral T-cell subsets in 40 patients with malignant mesothelioma (MM) or advanced non-small cell lung cancer (NSCLC) receiving platinum-based chemotherapy were assessed by flow cytometry and evaluated for associations with clinical outcome.

Results:

Proliferating T cells of all subsets were almost entirely depleted at day 8 following chemotherapy, but rapidly recovered above baseline levels. Regulatory T cells (Treg) were most profoundly depleted at this time point. A greater increase in CD8⁺ T-cell proliferation following one treatment cycle was associated with improved overall survival in univariate (hazard ratio (HR)=0.40; P<0.05) and multivariate (HR=0.17; P<0.01) analyses. A greater increase in the ratio of CD8⁺ T cell to Treg proliferation was also predictive of better prognosis.

Conclusion:

Chemotherapy potentially provides a favourable environment for the development of anti-tumour immunity through transient Treg depletion and regeneration of the T-cell pool. Change in CD8⁺ T-cell proliferation after one cycle of chemotherapy may represent a useful prognostic indicator in patients with MM and NSCLC.

Massive CD8 T cell response to primary HIV infection in the setting of severe clinical presentation

Acute HIV-1 infection causes a rapid total body depletion of CD4(+) T cells in most individuals and HIV-1-specific CD8(+) T cell expansion in response to viral replication. A numerically high CD8 T cell response may indicate limited T cell repertoire against HIV and rapid progression. We present a detailed evaluation of an acutely infected individual with a strong HIV-1-specific CD8 T cell response targeting multiple epitopes demonstrating that the upper limit of CD8 expansion in this setting may be much higher than previously reported and was likely driven by the narrow HIV-specific response.

T cell memory in the context of persistent herpes viral infections

The generation of a functional memory T cell pool upon primary encounter with an infectious pathogen is, in combination with humoral immunity, an essential process to confer protective immunity against reencounters with the same pathogen. A prerequisite for the generation and maintenance of long-lived memory T cells is the clearance of antigen after infection, which is fulfilled upon resolution of acute viral infections. Memory T cells play also a fundamental role during persistent viral infections by contributing to relative control and immuosurveillance of active replication or viral reactivation, respectively. However, the dynamics, the phenotype, the mechanisms of maintenance and the functionality of memory T cells which develop upon acute/resolved infection as opposed to chronic/latent infection differ substantially. In this review we summarize current knowledge about memory CD8 T cell responses elicited during α-, β-, and γ-herpes viral infections with major emphasis on the induction, maintenance and function of virus-specific memory CD8 T cells during viral latency and we discuss how the peculiar features of these memory CD8 T cell responses are related to the biology of these persistently infecting viruses.

Properties of end-stage human T cells defined by CD45RA re-expression

Persistent viral infections, inflammatory syndromes and ageing all induce the accumulation of highly differentiated CD45RA re-expressing memory T cells. These cells increase during ageing, especially in individuals who are infected with cytomegalovirus (CMV). These cells have decreased proliferative capacity, increased activation of senescence signalling pathways and greater susceptibility to apoptosis in vitro. However these cells are capable of multiple effector functions and thus bear all the hallmarks of short-lived effector T cells. This indicates that senescence signalling may govern the unique characteristics of effector T cells. In this article, we address the functional and migratory properties of these T cells and mechanisms that are involved in their generation. Finally we assess the potential for manipulation of their activity and whether this may improve immune function during ageing.

Distinct effector memory CD4+ T cell signatures in latent Mycobacterium tuberculosis infection, BCG vaccination and clinically resolved tuberculosis

Two billion people worldwide are estimated to be latently infected with Mycobacterium tuberculosis (Mtb) and are at risk for developing active tuberculosis since Mtb can reactivate to cause TB disease in immune-compromised hosts. Individuals with latent Mtb infection (LTBI) and BCG-vaccinated individuals who are uninfected with Mtb, harbor antigen-specific memory CD4⁺ T cells. However, the differences between long-lived memory CD4⁺ T cells induced by latent Mtb infection (LTBI) versus BCG vaccination are unclear. In this study, we characterized the immune phenotype and functionality of antigen-specific memory CD4⁺ T cells in healthy BCG-vaccinated individuals who were either infected (LTBI) or uninfected (BCG) with Mtb. Individuals were classified into LTBI and BCG groups based on IFN-γ ELISPOT using cell wall antigens and ESAT-6/CFP-10 peptides. We show that LTBI individuals harbored high frequencies of late-stage differentiated (CD45RA⁻CD27⁻) antigen-specific effector memory CD4⁺ T cells that expressed PD-1. In contrast, BCG individuals had primarily early-stage (CD45RA⁻CD27⁺) cells with low PD-1 expression. CD27⁺ and CD27⁻ as well as PD-1⁺ and PD-1⁻ antigen-specific subsets were polyfunctional, suggesting that loss of CD27 expression and up-regulation of PD-1 did not compromise their capacity to produce IFN-γ, TNF-α and IL-2. PD-1 was preferentially expressed on CD27⁻ antigen-specific CD4⁺ T cells, indicating that PD-1 is associated with the stage of differentiation. Using statistical models, we determined that CD27 and PD-1 predicted LTBI versus BCG status in healthy individuals and distinguished LTBI individuals from those who had clinically resolved Mtb infection after anti-tuberculosis treatment. This study shows that CD4⁺ memory responses induced by latent Mtb infection, BCG vaccination and clinically resolved Mtb infection are immunologically distinct. Our data suggest that differentiation into CD27⁻PD-1⁺ subsets in LTBI is driven by Mtb antigenic stimulation in vivo and that CD27 and PD-1 have the potential to improve our ability to evaluate true LTBI status.

Evidence of an oncogenic gammaherpesvirus in domestic dogs

In humans, chronic infection with the gammaherpesvirus Epstein-Barr virus is usually asymptomatic; however some infected individuals develop hematological and epithelial malignancies. The exact role of EBV in lymphomagenesis is poorly understood partly because of the lack of clinically relevant animal models. Here we report the detection of serological responses against EBV capsid antigens in healthy dogs and dogs with spontaneous lymphoma and that dogs with the highest antibody titers have B cell lymphoma. Moreover, we demonstrate the presence of EBV-like viral DNA and RNA sequences and Latent Membrane Protein-1 in malignant lymph nodes of dogs with lymphoma. Finally, electron microscopy of canine malignant B cells revealed the presence of classic herpesvirus particles. These findings suggest that dogs can be naturally infected with an EBV-like gammaherpesvirus that may contribute to lymphomagenesis and that dogs might represent a spontaneous model to investigate environmental and genetic factors that influence gammaherpesvirus-associated lymphomagenesis in humans.

Primary Epstein-Barr virus infection does not erode preexisting CD8⁺ T cell memory in humans

Acute Epstein-Barr virus (EBV) infection results in an unusually robust CD8(+) T cell response in young adults. Based on mouse studies, such a response would be predicted to result in attrition of preexisting memory to heterologous infections like influenza A (Flu) and cytomegalovirus (CMV). Furthermore, many studies have attempted to define the lymphocytosis that occurs during acute EBV infection in humans, but it is unclear whether bystander T cells contribute to it. To address these issues, we performed a longitudinal prospective study of primary EBV infection in humans. During acute EBV infection, both preexisting CMV- and Flu-specific memory CD8(+) T cells showed signs of bystander activation, including up-regulation of granzyme B. However, they generally did not expand, suggesting that the profound CD8(+) lymphocytosis associated with acute EBV infection is composed largely of EBV-specific T cells. Importantly, the numbers of CMV- and Flu-specific T cells were comparable before and after acute EBV infection. The data support the concept that, in humans, a robust CD8(+) T cell response creates a new memory CD8(+) T cell niche without substantially depleting preexisting memory for heterologous infections.

Natural and adoptive T-cell immunity against herpes family viruses after allogeneic hematopoietic stem cell transplantation

Reactivated infections with herpes family-related cytomegalovirus, Epstein-Barr virus and varicella zoster virus are serious and sometimes life-threatening complications for patients undergoing allogeneic hematopoietic stem cell transplantation. The pathogenesis of these infections critically involves the slow and inefficient recovery of antiviral T-cell immunity after transplantation. Although efficient drugs to decrease viral load during this vulnerable period have been developed, long-term control of herpes viruses and protection from associated diseases require the sufficient reconstitution of virus-specific memory T cells. To heal the deficiency by immunotherapeutic means, numerous research groups have developed antiviral vaccines and strategies based on the adoptive transfer of virus-specific T cells. This article summarizes the substantial progress made in this field during the past two decades and gives future perspectives about challenges that need to be addressed before antigen-specific immunotherapy against herpes family viruses can be implemented in general clinical practice.

Serological diagnosis of Epstein-Barr virus infection: Problems and solutions

Serological tests for antibodies specific for Epstein-Barr virus (EBV) antigens are frequently used to define infection status and for the differential diagnosis of other pathogens responsible for mononucleosis syndrome. Using only three parameters [viral capsid antigen (VCA) IgG, VCA IgM and EBV nuclear antigen (EBNA)-1 IgG],it is normally possible to distinguish acute from past infection: the presence of VCA IgM and VCA IgG without EBNA-1 IgG indicates acute infection, whereas the presence of VCA IgG and EBNA-1 IgG without VCA IgM is typical of past infection. However, serological findings may sometimes be difficult to interpret as VCA IgG can be present without VCA IgM or EBNA-1 IgG in cases of acute or past infection, or all the three parameters may be detected simultaneously in the case of recent infection or during the course of reactivation. A profile of isolated EBNA-1 IgG may also create some doubts. In order to interpret these patterns correctly, it is necessary to determine IgG avidity, identify anti-EBV IgG and IgM antibodies by immunoblotting, and look for heterophile antibodies, anti-EA (D) antibodies or viral genome using molecular biology methods. These tests make it possible to define the status of the infection and solve any problems that may arise in routine laboratory practice.

Adequate control of primary EBV infection and subsequent reactivations after cardiac transplantation in an EBV seronegative patient

EBV seronegative recipients of cardiac transplantation are at risk for development of post transplant lymphoproliferative disease following primary EBV infection due to the ongoing treatment with immunosuppressive drugs. Here we present detailed kinetics of the EBV-specific T-cell response following cardiac transplantation in an EBV seronegative recipient who developed a primary EBV infection 15weeks post transplantation and subsequent viral reactivations throughout follow up. The patient developed an EBV-specific CD8(+) T-cell response within 24days after first detection of the primary infection. Subsequently, an increased EBV-specific CD8(+) T-cell response developed upon viral reactivation, indicated by a threefold increase of EBV-specific CD8(+) T cells and increased IFNy production after stimulation with EBV-specific peptide pools. These data indicate that an EBV-specific T-cell response capable of adequate control of a primary EBV-infection and subsequent viral reactivations can develop in an EBV seronegative cardiac transplant recipient in the presence of severe immunosuppression.

Exploiting the interplay between innate and adaptive immunity to improve immunotherapeutic strategies for Epstein-Barr-virus-driven disorders

The recent demonstration that immunotherapeutic approaches may be clinically effective for cancer patients has renewed the interest for this strategy of intervention. In particular, clinical trials using adoptive T-cell therapies disclosed encouraging results, particularly in the context of Epstein-Barr-virus- (EBV-) related tumors. Nevertheless, the rate of complete clinical responses is still limited, thus stimulating the development of more effective therapeutic protocols. Considering the relevance of innate immunity in controlling both infections and cancers, innovative immunotherapeutic approaches should take into account also this compartment to improve clinical efficacy. Evidence accumulated so far indicates that innate immunity effectors, particularly NK cells, can be exploited with therapeutic purposes and new targets have been recently identified. We herein review the complex interactions between EBV and innate immunity and summarize the therapeutic strategies involving both adaptive and innate immune system, in the light of a fruitful integration between these immunotherapeutic modalities for a better control of EBV-driven tumors.

B-cell polyclonal activation and Epstein-Barr viral abortive lytic cycle are two key features in acute infectious mononucleosis

BACKGROUND

Acute infectious mononucleosis (AIM) is generally associated with a large EBV B cell reservoir cells and an intense B-cell polyclonal activation whereas the number of quiescent EBV-infected memory B cells in chronically EBV-infected healthy controls is very low.

OBJECTIVES

To evaluate the extent and functionality of ex vivo B-cell polyclonal activation, quantify the EBV DNA integrated in B cells, enumerate the functional EBV DNA reservoir in B cells and circulating B cells spontaneously secreting EBV antigens in AIM.

STUDY DESIGN

Circulating B cells and B cells differentiating into plamablasts and plasma cells, early (BZLF1)- and late viral antigen (gp350)-secreting-cells (SCs) were enumerated in six AIM patients and seven healthy EBV carriers.

RESULTS

In vitro B-cell polyclonal activation induced 8000-24,000 BZLF1- and 1000-3000gp350-SCs/10(6) B cells, respectively. These data suggest that only 11.1-19.5% of cells expressing BZLF1 synthesized gp350 and so completed the EBV-lytic cycle. Furthermore, circulating spontaneous BZLF1- and gp350-SCs that reflect ongoing viral replication were rare (20-120 and 10-30/10(6) B cells, respectively), and their low numbers contrasted with the high levels of circulating plasma cells (1.1-10.2% of CD19(+) B cells).

CONCLUSION

The in vivo terminal-B-cell differentiation into plasma cells could unmask EBV B-cell reservoir to specific cytotoxic T-cell response and combined with a predominant abortive functional-EBV-reservoir, strongly contribute to rapid decay of cellular EBV reservoir in AIM.

Detection and characterisation of alloreactive T cells

T cell alloreactivity is responsible for much of the morbidity and mortality associated with tissue transplantation and graft versus host disease. Immunoassays for ex vivo monitoring and quantitation of alloreactive T cells are being increasingly utilised to provide valuable information for individualised clinical management of transplant recipients. Here we describe detailed methodologies for both traditional and novel assays utilised for the detection, quantitation, and functional characterisation of alloreactive T cells and highlight the key advantages and disadvantages of each system.

Cell surface display of functional human MHC class II proteins: yeast display versus insect cell display

Reliable and robust systems for engineering functional major histocompatibility complex class II (MHCII) proteins have proved elusive. Availability of such systems would enable the engineering of peptide-MHCII (pMHCII) complexes for therapeutic and diagnostic applications. In this paper, we have developed a system based on insect cell surface display that allows functional expression of heterodimeric DR2 molecules with or without a covalently bound human myelin basic protein (MBP) peptide, which is amenable to directed evolution of DR2-MBP variants with improved T cell receptor (TCR)-binding affinity. This study represents the first example of functional display of human pMHCII complexes on insect cell surface. In the process of developing this pMHCII engineering system, we have also explored the potential of using yeast surface display for the same application. Our data suggest that yeast display is a useful system for analysis and engineering of peptide binding of MHCII proteins, but not suitable for directed evolution of pMHC complexes that bind with low affinity to self-reactive TCRs.

Impact of age on T cell signaling: a general defect or specific alterations?

Decreased immune responsiveness associated with aging is generally termed "immunosenescence". Several theories have been proposed to explain age-related declines in immune responses. Here, we will focus on and describe potential defects in T cell signal transduction from the membrane to the nucleus, leading to changes in the type, intensity and duration of the response as a major factor contributing to immunosenescence. We will first detail T cell signaling through the T cell receptor (TCR), CD28 and IL-2 receptor (IL-2R) and then discuss the observed age-related alterations to these signaling pathways. The role of membrane rafts in T cell signaling and T cell aging will be described. These factors will be considered in the context of the notion that age-related changes to T cell signaling may be attributed to changes in the functionality of the T cells due to shifts in T cell subpopulations with age. For this reason, we conclude by highlighting the application of multiparametric signaling analysis in leukocyte subsets using flow cytometry as a means to obtain a clearer picture with respect to age-related changes to immune signaling.

T cells and pathogenesis of hantavirus cardiopulmonary syndrome and hemorrhagic fever with renal syndrome

We previously hypothesized that increased capillary permeability observed in both hantavirus cardiopulmonary syndrome (HCPS) and hemorrhagic fever with renal syndrome (HFRS) may be caused by hantavirus-specific cytotoxic T cells attacking endothelial cells presenting viral antigens on their surface based on clinical observations and in vitro experiments. In HCPS, hantavirus-specific T cell responses positively correlated with disease severity. In HFRS, in one report, contrary to HCPS, T cell responses negatively correlated with disease severity, but in another report the number of regulatory T cells, which are thought to suppress T cell responses, negatively correlated with disease severity. In rat experiments, in which hantavirus causes persistent infection, depletion of regulatory T cells helped infected rats clear virus without inducing immunopathology. These seemingly contradictory findings may suggest delicate balance in T cell responses between protection and immunopathogenesis. Both too strong and too weak T cell responses may lead to severe disease. It is important to clarify the role of T cells in these diseases for better treatment (whether to suppress T cell functions) and protection (vaccine design) which may need to take into account viral factors and the influence of HLA on T cell responses.

Interleukin-2 rescues helpless effector CD8+ T cells by diminishing the susceptibility to TRAIL mediated death

CD8(+) T cells primed in the absence of CD4(+) T cell help are programmed to produce TRAIL, which results in Death receptor (DR5) mediated apoptosis upon restimulation. Here, we studied whether these 'helpless' effector CD8(+) T cells are consigned to an apoptotic fate or whether their helpless program can be altered by inflammatory or growth cytokines. We found that helpless CD8(+) T cells regained their full proliferative and functional capacity only when IL-2 was added to cell cultures, while IL-7 and IL-15, two common gamma chain cytokines associated with CD8(+) T cell homeostasis and memory, could only partly restore secondary expansion in helpless CD8(+) T cells. Recovery of functional CD8(+) T cell immunity by IL-2 was concomitant with induction of IL2Rα (CD25) expression, downregulation of TRAIL, and the upregulation of anti-apoptotic molecules Bcl-2 and FLIP. The addition of IL-2 to helpless CD8(+) T cells also interfered with DR5-mediated apoptosis induction, indicating that IL-2 affects several components of the TRAIL-DR5 pathway. Collectively, these data demonstrate that the helpless phenotype is not fixed, and that IL-2R signaling at the time of reactivation can play an important role in restoring CD8(+) T cell function.