Epstein-Barr nuclear antigen 1-specific CD4(+) Th1 cells kill Burkitt's lymphoma cells

Epstein-Barr virus pathogenesis and emerging control strategies

Sixty years after its discovery as the first human tumour virus, Epstein-Barr virus (EBV)-specific therapies and vaccines have entered clinical trials. These might not only be applicable for EBV-associated malignancies, where the virus was originally discovered, but also to immunopathologies, including the autoimmune disease multiple sclerosis, which might be triggered in susceptible individuals by primary EBV infection. This Review discusses the surprisingly large spectrum of diseases that EBV seems to cause, as well as which of these might be treated by the therapeutic approaches that are currently being developed or are already clinically applied. New pharmacological inhibitors, antibody therapies, adoptive T cell therapies and active vaccinations are beginning to offer possibilities to target the various EBV infection programmes that are associated with different diseases. These novel developments might allow us to specifically target EBV rather than its host cells in virus-associated pathologies.

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.

Immune checkpoints in T cells during oncogenic γ-herpesvirus infections

Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) are two persistent oncogenic γ-herpesviruses with an exclusive tropism for humans. They cause cancers of lymphocyte, epithelial and endothelial cell origin, such as Burkitt's and Hodgkin's lymphoma, primary effusion lymphoma, nasopharyngeal carcinoma, and Kaposi sarcoma. Mutations in immune-related genes but also adverse events during immune checkpoint inhibition in cancer patients have revealed molecular requirements for immune control of EBV and KSHV. These include costimulatory and coinhibitory receptors on T cells that are currently explored or already therapeutically targeted in tumor patients. This review discusses these co-receptors and their influence on EBV- and KSHV-associated diseases. The respective studies reveal surprising specificities of some of these receptors for immunity to these tumor viruses, benefits of their blockade for some but not other virus-associated diseases, and that EBV- and KSHV-specific immune control should be monitored during immune checkpoint inhibition to prevent adverse events that might be associated with their reactivation during treatment.

Urgency and necessity of Epstein-Barr virus prophylactic vaccines

Epstein-Barr virus (EBV), a γ-herpesvirus, is the first identified oncogenic virus, which establishes permanent infection in humans. EBV causes infectious mononucleosis and is also tightly linked to many malignant diseases. Various vaccine formulations underwent testing in different animals or in humans. However, none of them was able to prevent EBV infection and no vaccine has been approved to date. Current efforts focus on antigen selection, combination, and design to improve the efficacy of vaccines. EBV glycoproteins such as gH/gL, gp42, and gB show excellent immunogenicity in preclinical studies compared to the previously favored gp350 antigen. Combinations of multiple EBV proteins in various vaccine designs become more attractive approaches considering the complex life cycle and complicated infection mechanisms of EBV. Besides, rationally designed vaccines such as virus-like particles (VLPs) and protein scaffold-based vaccines elicited more potent immune responses than soluble antigens. In addition, humanized mice, rabbits, as well as nonhuman primates that can be infected by EBV significantly aid vaccine development. Innovative vaccine design approaches, including polymer-based nanoparticles, the development of effective adjuvants, and antibody-guided vaccine design, will further enhance the immunogenicity of vaccine candidates. In this review, we will summarize (i) the disease burden caused by EBV and the necessity of developing an EBV vaccine; (ii) previous EBV vaccine studies and available animal models; (iii) future trends of EBV vaccines, including activation of cellular immune responses, novel immunogen design, heterologous prime-boost approach, induction of mucosal immunity, application of nanoparticle delivery system, and modern adjuvant development.

Burkitt lymphoma with a granulomatous reaction: an M1/Th1-polarised microenvironment is associated with controlled growth and spontaneous regression

AIMS

Burkitt lymphoma (BL) is an aggressive B-cell lymphoma that, in some instances, may show a granulomatous reaction associated with a favourable prognosis and occasional spontaneous regression. In the present study, we aimed to define the tumour microenvironment (TME) in four such cases, two of which regressed spontaneously.

METHODS AND RESULTS

All cases showed aggregates of tumour cells with the typical morphology, molecular cytogenetics and immunophenotype of BL surrounded by a florid epithelioid granulomatous reaction. All four cases were Epstein-Barr virus (EBV)-positive with type I latency. Investigation of the TME showed similar features in all four cases. The analysis revealed a proinflammatory response triggered by Th1 lymphocytes and M1 polarised macrophages encircling the neoplastic cells with a peculiar topographic distribution.

CONCLUSIONS

Our data provide an in-vivo picture of the role that specific immune cell subsets might play during the early phase of BL, which may be capable of maintaining the tumour in a self-limited state or inducing its regression. These novel results may provide insights into new potential therapeutic avenues in EBV-positive BL patients in the era of cellular immunotherapy.

Cytotoxic CD4+ T-cells specific for EBV capsid antigen BORF1 are maintained in long-term latently infected healthy donors

Epstein Barr Virus (EBV) infects more than 95% of the population whereupon it establishes a latent infection of B-cells that persists for life under immune control. Primary EBV infection can cause infectious mononucleosis (IM) and long-term viral carriage is associated with several malignancies and certain autoimmune diseases. Current efforts developing EBV prophylactic vaccination have focussed on neutralising antibodies. An alternative strategy, that could enhance the efficacy of such vaccines or be used alone, is to generate T-cell responses capable of recognising and eliminating newly EBV-infected cells before the virus initiates its growth transformation program. T-cell responses against the EBV structural proteins, brought into the newly infected cell by the incoming virion, are prime candidates for such responses. Here we show the structural EBV capsid proteins BcLF1, BDLF1 and BORF1 are frequent targets of T-cell responses in EBV infected people, identify new CD8+ and CD4+ T-cell epitopes and map their HLA restricting alleles. Using T-cell clones we demonstrate that CD4+ but not CD8+ T-cell clones specific for the capsid proteins can recognise newly EBV-infected B-cells and control B-cell outgrowth via cytotoxicity. Using MHC-II tetramers we show a CD4+ T-cell response to an epitope within the BORF1 capsid protein epitope is present during acute EBV infection and in long-term viral carriage. In common with other EBV-specific CD4+ T-cell responses the BORF1-specific CD4+ T-cells in IM patients expressed perforin and granzyme-B. Unexpectedly, perforin and granzyme-B expression was sustained over time even when the donor had entered the long-term infected state. These data further our understanding of EBV structural proteins as targets of T-cell responses and how CD4+ T-cell responses to EBV change from acute disease into convalescence. They also identify new targets for prophylactic EBV vaccine development.

Epstein-Barr virus is a widespread herpesvirus carried by most individuals. Whilst infection is usually asymptomatic, development of a prophylactic vaccine against EBV is desirable because of the virus’s association with infectious mononucleosis in primary infection and several cancers and autoimmune diseases during long-term virus carriage. Identifying T-cell responses that can recognise newly infected B-cells at very early stages of infection may provide novel targets for T-cell vaccination. Here we characterise T-cell responses against three virus proteins, BcLF1, BDLF1 and BORF1 that, as structural proteins of the virus particle, are delivered into the cell by the infecting virus. We find that all three proteins are recognised by T-cells from infected individuals. Moreover, isolated structural antigen-specific CD4+ T-cells rapidly recognise newly infected B-cells and prevent their outgrowth in vitro. As reported for CD4+ T-cells against other EBV proteins, structural antigen-specific CD4+ T-cells induced by primary EBV infection have cytotoxic function. However, we also demonstrate that, unusually, this cytotoxic function is retained in memory T-cells present in long-term infected individuals. Structural antigens may therefore represent useful targets for prophylactic EBV vaccine development to induce CD4+ T-cells able to rapidly eliminate virus-infected cells.

Interplay between IL-10, IFN-γ, IL-17A and PD-1 Expressing EBNA1-Specific CD4+ and CD8+ T Cell Responses in the Etiologic Pathway to Endemic Burkitt Lymphoma

Simple Summary

Endemic Burkitt lymphoma (eBL) is a common pediatric cancer in sub-Saharan Africa. The incidence of this aggressive B-cell cancer is linked to Plasmodium falciparum (Pf) malaria and Epstein–Barr virus (EBV) co-infections during childhood. Most eBL tumors contain EBV and are characterized by the Epstein–Barr Nuclear Antigen 1 (EBNA1) latency I pattern of viral gene expression. The aim of our study was to compare the phenotypes and functions of CD4⁺ and CD8⁺ T cell responses to EBNA1 in children diagnosed with eBL and in healthy EBV-seropositive children to highlight differences that contribute to the balance between anti-viral immunity and eBL pathogenesis.

Abstract

Children diagnosed with endemic Burkitt lymphoma (eBL) are deficient in interferon-γ (IFN-γ) responses to Epstein–Barr Nuclear Antigen1 (EBNA1), the viral protein that defines the latency I pattern in this B cell tumor. However, the contributions of immune-regulatory cytokines and phenotypes of the EBNA1-specific T cells have not been characterized for eBL. Using a bespoke flow cytometry assay we measured intracellular IFN-γ, IL-10, IL-17A expression and phenotyped CD4⁺ and CD8⁺ T cell effector memory subsets specific to EBNA1 for eBL patients compared to two groups of healthy children with divergent malaria exposures. In response to EBNA1 and a malaria antigen (PfSEA-1A), the three study groups exhibited strikingly different cytokine expression and T cell memory profiles. EBNA1-specific IFN-γ-producing CD4⁺ T cell response rates were lowest in eBL (40%) compared to children with high malaria (84%) and low malaria (66%) exposures (p < 0.0001 and p = 0.0004, respectively). However, eBL patients did not differ in CD8⁺ T cell response rates or the magnitude of IFN-γ expression. In contrast, eBL children were more likely to have EBNA1-specific CD4⁺ T cells expressing IL-10, and less likely to have polyfunctional IFN-γ⁺IL-10⁺ CD4⁺ T cells (p = 0.02). They were also more likely to have IFN-γ⁺IL-17A⁺, IFN-γ⁺ and IL-17A⁺ CD8⁺ T cell subsets compared to healthy children. Cytokine-producing T cell subsets were predominantly CD45RA⁺CCR7⁺ T_NAIVE-LIKE cells, yet PD-1, a marker of persistent activation/exhaustion, was more highly expressed by the central memory (T_CM) and effector memory (T_EM) T cell subsets. In summary, our study suggests that IL-10 mediated immune regulation and depletion of IFN-γ⁺ EBNA1-specific CD4⁺ T cells are complementary mechanisms that contribute to impaired T cell cytotoxicity in eBL pathogenesis.

Redirecting T Cells against Epstein-Barr Virus Infection and Associated Oncogenesis

The Epstein-Barr virus (EBV) is associated with lymphomas and carcinomas. For some of these, the adoptive transfer of EBV specific T cells has been therapeutically explored, with clinical success. In order to avoid naturally occurring EBV specific autologous T cell selection from every patient, the transgenic expression of latent and early lytic viral antigen specific T cell receptors (TCRs) to redirect T cells, to target the respective tumors, is being developed. Recent evidence suggests that not only TCRs against transforming latent EBV antigens, but also against early lytic viral gene products, might be protective for the control of EBV infection and associated oncogenesis. At the same time, these approaches might be more selective and cause less collateral damage than targeting general B cell markers with chimeric antigen receptors (CARs). Thus, EBV specific TCR transgenic T cells constitute a promising therapeutic strategy against EBV associated malignancies.

Membrane association of a model CD4+ T-cell vaccine antigen confers enhanced yet incomplete protection against murid herpesvirus-4 infection

Vaccination against γ-herpesviruses has proved difficult. CD4⁺ T cells are essential to contain infection, but how best to prime them and whether this can reduce viral loads remain unclear. To address these questions, we used ovalbumin (OVA) as a model antigen, delivering it with murine cytomegalovirus (MCMV) to protect mice against OVA-expressing murine herpesvirus-4 (MuHV-4). Membrane-associated OVA (mOVA) was more effective than soluble OVA, both to prime CD4⁺ T cells and as an effector target. It was also a better target than an OVA epitope limited to infected cells, suggesting that protective CD4⁺ T cells recognize infected cell debris rather than infected cells themselves. While MCMV-mOVA protected acutely against MuHV-4-mOVA, long-term protection was incomplete, even when OVA-specific CD8⁺ T cells and B cells were also primed. Thus, even optimized single-target vaccines may poorly reduce long-term γ-herpesvirus infections.

Infection and immune control of human oncogenic γ-herpesviruses in humanized mice

Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) comprise the oncogenic human γ-herpesvirus family and are responsible for 2-3% of all tumours in man. With their prominent growth-transforming abilities and high prevalence in the human population, these pathogens have probably shaped the human immune system throughout evolution for near perfect immune control of the respective chronic infections in the vast majority of healthy pathogen carriers. The exclusive tropism of EBV and KSHV for humans has, however, made it difficult in the past to study their infection, tumourigenesis and immune control in vivo. Mice with reconstituted human immune system components (humanized mice) support replication of both viruses with both persisting latent and productive lytic infection. Moreover, B-cell lymphomas can be induced by EBV alone and KSHV co-infection with gene expression hallmarks of human malignancies that are associated with both viruses. Furthermore, cell-mediated immune control by primarily cytotoxic lymphocytes is induced upon infection and can be probed for its functional characteristics as well as putative requirements for its priming. Insights that have been gained from this model and remaining questions will be discussed in this review. This article is part of the theme issue 'Silent cancer agents: multi-disciplinary modelling of human DNA oncoviruses'.

Post-translational modifications such as citrullination are excellent targets for cancer therapy

Under conditions of cellular stress, proteins can be post-translationally modified causing them to be recognized by the immune system. One such stress-induced post-translational modification (siPTM) is citrullination, the conversion of arginine residues to citrulline by peptidylarginine deiminase (PAD) enzymes. PAD enzymes are activated by millimolar concentrations of calcium which can occur during apoptosis, leading to precipitation of proteins, their subsequent uptake by B cells and stimulation of antibody responses. Detection of anti-citrullinated protein antibodies (ACPAs) is a diagnostic of rheumatoid arthritis (RA), where immune complexes stimulate inflammation around the joints. More recently, autophagy has been shown to play a role in the presentation of citrullinated peptides on MHC class II molecules to CD4⁺ helper T cells, suggesting that citrullination may be a way of alerting immune cells to cellular stress. Additionally, inflammation-induced IFNγ and concomitant MHC class II expression on target cells contributes to immune activation. Stressful conditions in the tumor microenvironment induce autophagy in cancer cells as a pro-survival mechanism. Cancer cells also over express PAD enzymes and in light of this the hypothesis that citrullinated peptides stimulate CD4⁺ T cell responses that would recognize these siPTM's produced during autophagy has been investigated. The induction of potent citrullinated peptide-specific CD4 responses has been shown in both humans and HLA transgenic mouse models. Responses in mouse models resulted in potent anti-tumour responses against tumours expressing either constitutive or IFNγ-inducible MHC class II. The anti-tumour effect relied upon direct recognition of tumours by specific CD4 T cells suggesting that citrullinated peptides are attractive targets for cancer vaccines.

Immune Control and Vaccination against the Epstein-Barr Virus in Humanized Mice

Mice with reconstituted human immune system components (humanized mice) offer the unique opportunity to test vaccines preclinically in the context of vaccine adjuvant sensing by human antigen presenting cells and priming of human cytotoxic lymphocyte populations. These features are particularly attractive for immune control of the Epstein–Barr virus (EBV), which represents the most potent growth-transforming pathogen in man and exclusively relies on cytotoxic lymphocytes for its asymptomatic persistence in the vast majority of healthy virus carriers. This immune control is particularly impressive because EBV infects more than 95% of the human adult population and persists without pathology for more than 50 years in most of them. This review will discuss the pathologies that EBV elicits in humanized mice, which immune responses control it in this model, as well as which passive and active vaccination schemes with adoptive T cell transfer and with virus-like particles or individual antigens, respectively, have been explored in this model so far. EBV-specific CD8⁺ T cell priming in humanized mice could provide crucial insights into how cytotoxic lymphocytes against other viruses and tumors might be elicited by vaccination in humans.

Immune Control of γ-Herpesviruses

Vaccination against γ-herpesviruses has been hampered by our limited understanding of their normal control. Epstein–Barr virus (EBV)-transformed B cells are killed by viral latency antigen-specific CD8⁺ T cells in vitro, but attempts to block B cell infection with antibody or to prime anti-viral CD8⁺ T cells have protected poorly in vivo. The Doherty laboratory used Murid Herpesvirus-4 (MuHV-4) to analyze γ-herpesvirus control in mice and found CD4⁺ T cell dependence, with viral evasion limiting CD8⁺ T cell function. MuHV-4 colonizes germinal center (GC) B cells via lytic transfer from myeloid cells, and CD4⁺ T cells control myeloid infection. GC colonization and protective, lytic antigen-specific CD4⁺ T cells are now evident also for EBV. Subunit vaccines have protected only transiently against MuHV-4, but whole virus vaccines give long-term protection, via CD4⁺ T cells and antibody. They block infection transfer to B cells, and need include no known viral latency gene, nor any MuHV-4-specific gene. Thus, the Doherty approach of in vivo murine analysis has led to a plausible vaccine strategy for EBV and, perhaps, some insight into what CD8⁺ T cells really do.

Primary EBV Infection Induces an Acute Wave of Activated Antigen-Specific Cytotoxic CD4+ T Cells

Primary EBV infection drives highly cytotoxic virus-specific CD4⁺ T cell responses.

EBV-specific memory CD4⁺ T cells are polyfunctional but lack cytotoxic activity.

Acute EBV-specific CD4-CTLs differ transcriptionally from classical memory CD4-CTLs.

CD4⁺ T cells are essential for immune protection against viruses, yet their multiple roles remain ill-defined at the single-cell level in humans. Using HLA class II tetramers, we studied the functional properties and clonotypic architecture of EBV-specific CD4⁺ T cells in patients with infectious mononucleosis, a symptomatic manifestation of primary EBV infection, and in long-term healthy carriers of EBV. We found that primary infection elicited oligoclonal expansions of T_H1-like EBV-specific CD4⁺ T cells armed with cytotoxic proteins that responded immediately ex vivo to challenge with EBV-infected B cells. Importantly, these acutely generated cytotoxic CD4⁺ T cells were highly activated and transcriptionally distinct from classically described cytotoxic CD4⁺ memory T cells that accumulate during other persistent viral infections, including CMV and HIV. In contrast, EBV-specific memory CD4⁺ T cells displayed increased cytokine polyfunctionality but lacked cytotoxic activity. These findings suggested an important effector role for acutely generated cytotoxic CD4⁺ T cells that could potentially be harnessed to improve the efficacy of vaccines against EBV.

Heterologous prime-boost vaccination protects against EBV antigen-expressing lymphomas

The Epstein-Barr virus (EBV) is one of the predominant tumor viruses in humans, but so far no therapeutic or prophylactic vaccination against this transforming pathogen is available. We demonstrated that heterologous prime-boost vaccination with the nuclear antigen 1 of EBV (EBNA1), either targeted to the DEC205 receptor on DCs or expressed from a recombinant modified vaccinia virus Ankara (MVA) vector, improved priming of antigen-specific CD4+ T cell help. This help supported the expansion and maintenance of EBNA1-specific CD8+ T cells that are most efficiently primed by recombinant adenoviruses that encode EBNA1. These combined CD4+ and CD8+ T cell responses protected against EBNA1-expressing T and B cell lymphomas, including lymphoproliferations that emerged spontaneously after EBNA1 expression. In particular, the heterologous EBNA1-expressing adenovirus, boosted by EBNA1-encoding MVA vaccination, demonstrated protection as a prophylactic and therapeutic treatment for the respective lymphoma challenges. Our study shows that such heterologous prime-boost vaccinations against EBV-associated malignancies as well as symptomatic primary EBV infection should be further explored for clinical development.

Pushing the Right Buttons: Improving Efficacy of Therapeutic DNA Vectors

Gene therapy represents a potent therapeutical application for regenerative medicine. So far, viral and nonviral approaches suffer from major drawbacks hindering efficient gene therapeutic applicability: the immunogenicity of viral systems on the one hand, and the low gene transfer efficiency of nonviral systems on the other hand. Therefore, there is a high demand for improvements of therapeutical systems at several levels. This review summarizes different DNA vector modifications to enhance biological efficacy and efficiency of therapeutical vectors, aiming for low toxicity, high specificity, and biological efficacy-the cornerstones for successful translation of gene therapy into the clinic. We aim to provide a step-by-step instruction to optimize their vectors to achieve the desired outcome of gene therapy. Our review provides the means to either construct a potent gene therapeutic vector de novo or to specifically address a bottleneck in the chain of events mandatory for therapeutic success. Although most of the introduced techniques can be translated into different areas, this review primarily addresses improvements for applications in transient gene therapy in the field of tissue engineering.

The elucidation of non-classical MHC class II antigen processing through the study of viral antigens

By convention, CD4+ T cells are activated predominantly by Major Histocompatibility Complex class II-bound peptides derived from extracellular (exogenous) antigens. It has been known for decades that alternative sources of antigen, particularly those synthesized within the antigen-presenting cell, can also supply peptides but the impact on TCD4+ responses, sometimes considerable, has only recently become appreciated. This review focuses on the contributions that studies of viral antigen have made to this shift in perspective, concluding with discussions of relevance to rational vaccine design, autoimmunity and cancer immunotherapy.

Cytotoxic CD4 T Cells-Friend or Foe during Viral Infection?

CD4 T cells with cytotoxic function were once thought to be an artifact due to long-term in vitro cultures but have in more recent years become accepted and reported in the literature in response to a number of viral infections. In this review, we focus on cytotoxic CD4 T cells in the context of human viral infections and in some infections that affect mice and non-human primates. We examine the effector mechanisms used by cytotoxic CD4 cells, the phenotypes that describe this population, and the transcription factors and pathways that lead to their induction following infection. We further consider the cells that are the predominant targets of this effector subset and describe the viral infections in which CD4 cytotoxic T lymphocytes have been shown to play a protective or pathologic role. Cytotoxic CD4 T cells are detected in the circulation at much higher levels than previously realized and are now recognized to have an important role in the immune response to viral infections.

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.

The Differentiation and Protective Function of Cytolytic CD4 T Cells in Influenza Infection

CD4 T cells that recognize peptide antigen in the context of class II MHC can differentiate into various subsets that are characterized by their helper functions. However, increasing evidence indicates that CD4 cells with direct cytolytic activity (CD4 CTL) play a role in chronic as well as acute infections, such as influenza A virus (IAV) infection. In the last couple of decades, techniques to measure the frequency and activity of these cytolytic cells has demonstrated their abundance in infections, such as human immunodeficiency virus, mouse pox, murine gamma herpes virus, cytomegalovirus, Epstein-Barr virus, and influenza among others. We now appreciate a greater role for CD4 CTL as direct effectors in viral infections and antitumor immunity through their ability to acquire perforin-mediated cytolytic activity and contribution to lysis of virally infected targets or tumors. As early as the 1980s, CD4 T cell clones with cytolytic potential were identified after influenza virus infection, yet much of this early work was dependent on in vitro culture and little was known about the physiological relevance of CD4 CTL. Here, we discuss the direct role CD4 CTL play in protection against lethal IAV infection and the factors that drive the generation of perforin-mediated lytic activity in CD4 cells in vivo during IAV infection. While focusing on CD4 CTL generated during IAV infection, we pull comparisons from the literature in other antiviral and antitumor systems. Further, we highlight what is currently known about CD4 CTL secondary and memory responses, as well as vaccination strategies to induce these potent killer cells that provide an extra layer of cell-mediated immune protection against heterosubtypic IAV infection.

T-Cell Responses to EBV

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

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.

Epstein-Barr virus genetic variation in lymphoblastoid cell lines derived from Kenyan pediatric population

Epstein-Barr virus (EBV) is associated with Burkitt’s lymphoma (BL), and in regions of sub-Saharan Africa where endemic BL is common, both the EBV Type 1 (EBV-1) and EBV Type 2 strains (EBV-2) are found. Little is known about genetic variation of EBV strains in areas of sub-Saharan Africa. In the present study, spontaneous lymphoblastoid cell lines (LCLs) were generated from samples obtained from Kenya. Polymerase chain reaction (PCR) amplification of the EBV genome was done using multiple primers and sequenced by next-generation sequencing (NGS). Phylogenetic analyses against the published EBV-1 and EBV-2 strains indicated that one sample, LCL10 was closely related to EBV-2, while the remaining 3 LCL samples were more closely related to EBV-1. Moreover, single nucleotide polymorphism (SNP) analyses showed clustering of LCL variants. We further show by analysis of EBNA-1, BLLF1, BPLF1, and BRRF2 that latent genes are less conserved than lytic genes in these LCLs from a single geographic region. In this study we have shown that NGS is highly useful for deciphering detailed inter and intra-variations in EBV genomes and that within a geographic region different EBV genetic variations can co-exist, the implications of which warrant further investigation. The findings will enhance our understanding of potential pathogenic variants critical to the development and maintenance of EBV-associated malignancies.

The immunology of Epstein-Barr virus-induced disease

Epstein-Barr virus (EBV) is usually acquired silently early in life and carried thereafter as an asymptomatic infection of the B lymphoid system. However, many circumstances disturb the delicate EBV-host balance and cause the virus to display its pathogenic potential. Thus, primary infection in adolescence can manifest as infectious mononucleosis (IM), as a fatal illness that magnifies the immunopathology of IM in boys with the X-linked lymphoproliferative disease trait, and as a chronic active disease leading to life-threatening hemophagocytosis in rare cases of T or natural killer (NK) cell infection. Patients with primary immunodeficiencies affecting the NK and/or T cell systems, as well as immunosuppressed transplant recipients, handle EBV infections poorly, and many are at increased risk of virus-driven B-lymphoproliferative disease. By contrast, a range of other EBV-positive malignancies of lymphoid or epithelial origin arise in individuals with seemingly intact immune systems through mechanisms that remain to be understood.

Elevation of c-MYC disrupts HLA class II-mediated immune recognition of human B cell tumors

Elevated levels of the transcription factor c-myc are strongly associated with various cancers, and in particular B cell lymphomas. Although many of c-MYC's functions have been elucidated, its effect on the presentation of Ag through the HLA class II pathway has not been reported previously. This is an issue of considerable importance, given the low immunogenicity of many c-MYC-positive tumors. We report in this paper that increased c-MYC expression has a negative effect on the ability of B cell lymphomas to functionally present Ags/peptides to CD4(+) T cells. This defect was associated with alterations in the expression of distinct cofactors as well as interactions of antigenic peptides with class II molecules required for the presentation of class II-peptide complexes and T cell engagement. Using early passage Burkitt's lymphoma (BL) tumors and transformed cells, we show that compared with B lymphoblasts, BL cells express decreased levels of the class II editor HLA-DM, lysosomal thiol-reductase GILT, and a 47-kDa enolase-like protein. Functional Ag presentation was partially restored in BL cells treated with a c-MYC inhibitor, demonstrating the impact of this oncogene on Ag recognition. This restoration of HLA class II-mediated Ag presentation in early passage BL tumors/cells was linked to enhanced HLA-DM expression and a concurrent decrease in HLA-DO in BL cells. Taken together, these results reveal c-MYC exerts suppressive effects at several critical checkpoints in Ag presentation, which contribute to the immunoevasive properties of BL tumors.

Antigen-armed antibodies targeting B lymphoma cells effectively activate antigen-specific CD4+ T cells

The treatment of non-Hodgkin lymphomas has benefited enormously from the introduction of monoclonal antibody-based therapies. However, the efficacy of these treatments varies with lymphoma subtypes and typically decreases with subsequent relapses. Here, we report on antigen-armed antibodies (AgAbs) as a potential treatment of B-cell lymphoma. AgAbs include antigens from ubiquitous pathogens, such as Epstein-Barr virus (EBV), that persist in their host and elicit strong lifelong T-cell responses. They act as vectors by introducing antigen directly into tumor cells to induce an antigen-specific CD4(+) T-cell response against these cells. We have fused antibodies targeting human B-cell surface receptors (CD19-22) to immunodominant T-cell antigens from EBV proteins, including EBNA1, EBNA3B, and EBNA3C. Exposure of EBV-transformed B cells and of Burkitt lymphoma cells to AgAbs led to antigen presentation, T-cell recognition, and target cell killing. The efficiency of AgAb action paralleled the abundance of the targeted molecules on lymphoma cells as well as their HLA class II expression levels. AgAbs can also induce activation and proliferation of EBV-specific memory CD4(+) T cells ex vivo. These studies show the potential of AgAbs as an effective therapeutic strategy against B-cell lymphomas.

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.

Macroautophagy Proteins Assist Epstein Barr Virus Production and Get Incorporated Into the Virus Particles

Epstein Barr virus (EBV) persists as a latent herpes virus infection in the majority of the adult human population. The virus can reactivate from this latent infection into lytic replication for virus particle production. Here, we report that autophagic membranes, which engulf cytoplasmic constituents during macroautophagy and transport them to lysosomal degradation, are stabilized by lytic EBV replication in infected epithelial and B cells. Inhibition of autophagic membrane formation compromises infectious particle production and leads to the accumulation of viral DNA in the cytosol. Vice versa, pharmacological stimulation of autophagic membrane formation enhances infectious virus production. Atg8/LC3, an essential macroautophagy protein and substrate anchor on autophagic membranes, was found in virus preparations, suggesting that EBV recruits Atg8/LC3 coupled membranes to its envelope in the cytosol. Our data indicate that EBV subverts macroautophagy and uses autophagic membranes for efficient envelope acquisition during lytic infection.

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Macroautophagic membranes are stabilized during lytic EBV replication.

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Inhibition of macroautophagic membrane formation reduces EBV production.

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Stimulation of macroautophagic membrane formation boosts EBV production.

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Without macroautophagic membranes EBV DNA accumulates in the cytosol.

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Macroautophagic membranes get incorporated into EBV particles.

A whole recombinant yeast-based therapeutic vaccine elicits HBV X, S and Core specific T cells in mice and activates human T cells recognizing epitopes linked to viral clearance

Chronic hepatitis B infection (CHB) is characterized by sub-optimal T cell responses to viral antigens. A therapeutic vaccine capable of restoring these immune responses could potentially improve HBsAg seroconversion rates in the setting of direct acting antiviral therapies. A yeast-based immunotherapy (Tarmogen) platform was used to make a vaccine candidate expressing hepatitis B virus (HBV) X, surface (S), and Core antigens (X-S-Core). Murine and human immunogenicity models were used to evaluate the type and magnitude of HBV-Ag specific T cell responses elicited by the vaccine. C57BL/6J, BALB/c, and HLA-A*0201 transgenic mice immunized with yeast expressing X-S-Core showed T cell responses to X, S and Core when evaluated by lymphocyte proliferation assay, ELISpot, intracellular cytokine staining (ICS), or tumor challenge assays. Both CD4+ and CD8+ T cell responses were observed. Human T cells transduced with HBc18-27 and HBs183-91 specific T cell receptors (TCRs) produced interferon gamma (IFNγ following incubation with X-S-Core-pulsed dendritic cells (DCs). Furthermore, stimulation of peripheral blood mononuclear cells (PBMCs) isolated from CHB patients or from HBV vaccine recipients with autologous DCs pulsed with X-S-Core or a related product (S-Core) resulted in pronounced expansions of HBV Ag-specific T cells possessing a cytolytic phenotype. These data indicate that X-S-Core-expressing yeast elicit functional adaptive immune responses and supports the ongoing evaluation of this therapeutic vaccine in patients with CHB to enhance the induction of HBV-specific T cell responses.

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

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

IMPORTANCE

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

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.

Expression, purification, and immunogenic characterization of Epstein-Barr virus recombinant EBNA1 protein in Pichia pastoris

Epstein-Barr virus (EBV) is a ubiquitous human herpesvirus associated with the development of both lymphoid and epithelial tumors. EBNA1 is the only viral protein expressed in all EBV-associated malignancies and plays important roles in EBV latency. Thus, EBNA1 is thought to be a promising antigen for immunotherapy of all EBV-associated malignancies. This study was undertaken to produce recombinant EBNA1 protein in Pichia pastoris and evaluate its immunogenicity. The truncated EBNA1 (E1ΔGA, codons 390-641) was expressed as a secretory protein with an N-terminal histidine tag in the methylotrophic yeast P. pastoris and purified by Ni-NTA affinity chromatography. The purified proteins were then used as antigens to immunize BALB/c mice for production of polyclonal antibodies. Western blot analysis showed that the polyclonal antibodies specifically recognized the EBNA1 protein in B95-8 cell lysates. The recombinant E1ΔGA also induced strong lymphoproliferative and Th1 cytokine responses in mice. Furthermore, mice immunized with E1ΔGA developed CD4+ and CD8+ T cell responses. These findings showed that the yeast-expressed E1ΔGA retained good immunogenicity and might be a promising vaccine candidate against EBV-associated malignancies.

Modulation of HIV peptide antigen specific cellular immune response by synthetic α- and β-defensin peptides

Defensin peptides have their direct role in host defense against microbial infection as innate molecules and also thought to contribute to adaptive immunity by recruiting naïve T-cells and immature dendritic cells at the site of infection through CCR6 receptor. The main aim of the present study is to investigate the efficacy of defensins for the induction of cell mediated immune response against the peptide antigen of HIV-1 encapsulated in PLG microparticles through intranasal (IN) route in mice model. To characterized, we have analyzed T-cell proliferation, Th1/Th2 cytokines, β-chemokines production and IFN-γ/perforin secretion from CD4(+)/CD8(+) T-cells in response to HIV immunogen alone and with defensins at different mucosal site i.e. lamina propria (LP), spleen (SP) and peyer's patches (PP). The cellular immunogenicity of HIV peptide with defensin formulations showed a significantly higher (p<0.001) proliferation response as compared to individual HIV peptide. The enhanced cytokines measurement profile showed mixed Th1 and Th2 type of peptide specific immune response by the incorporation of defensins. In the continuation, enhancement in MIP-1α and RANTES level was also observed in HIV peptide-defensin formulations. The FACS data had revealed that CD4(+)/CD8(+) T-cells showed significantly (p<0.001) higher IFN-γ and perforin secretion in HIV with defensin peptide formulations than HIV antigen alone group. Thus, the study emphasized here that defensin peptides have a potential role as mucosal adjuvant, might be responsible for the induction of cell mediated immunity when administered in mice through IN route with HIV peptide antigen.

Potential cellular functions of Epstein-Barr Nuclear Antigen 1 (EBNA1) of Epstein-Barr Virus

Epstein-Barr Nuclear Antigen 1 (EBNA1) is a multifunctional protein encoded by EBV. EBNA1’s role in maintaining EBV in latently proliferating cells, by mediating EBV genome synthesis and nonrandom partitioning to daughter cells, as well as regulating viral gene transcription, is well characterized. Less understood are the roles of EBNA1 in affecting the host cell to provide selective advantages to those cells that harbor EBV. In this review we will focus on the interactions between EBNA1 and the host cell that may provide EBV-infected cells selective advantages beyond the maintenance of EBV.

A20 controls macrophage to elicit potent cytotoxic CD4(+) T cell response

Emerging evidence indicates that CD4(+) T cells possess cytotoxic potential for tumor eradication and perforin/granzyme-mediated cytotoxicity functions as one of the important mechanisms for CD4(+) T cell-triggered cell killing. However, the critical issue is how the cytotoxic CD4(+) T cells are developed. During the course of our work that aims at promoting immunostimulation of APCs by inhibition of negative regulators, we found that A20-silenced Mф drastically induced granzyme B expression in CD4(+) T cells. As a consequence, the granzyme-highly expressing CD4(+) T cells exhibited a strong cytotoxic activity that restricted tumor development. We found that A20-silenced Mф activated cytotoxic CD4(+) T cells by MHC class-II restricted mechanism and the activation was largely dependent on enhanced production of IFN-γ.

How human tumor viruses make use of autophagy

Viruses commandeer regulatory pathways of their hosts to optimize their success as cellular parasites. The human tumor viruses, Epstein-Barr Virus (EBV), Kaposi’s Sarcoma Herpesvirus (KSHV), Hepatitis B Virus (HBV), and Hepatitis C Virus (HCV) all affect autophagy for their own ends. EBV and KSHV regulate it during latent infections, a phase when no progeny virus is produced, while HBV and HCV use autophagy to promote their productive infections. Here we shall compare and contrast how these human tumor viruses regulate autophagy and what they gain by the appropriation of this cellular pathway.

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.

Tumor-specific CD4+ T cells develop cytotoxic activity and eliminate virus-induced tumor cells in the absence of regulatory T cells

The important role of tumor-specific cytotoxic CD8⁺ T cells is well defined in the immune control of the tumors, but the role of effector CD4⁺ T cells is poorly understood. In the current research, we have used a murine retrovirus-induced tumor cell line of C57BL/6 mouse origin, namely FBL-3 cells, as a model to study basic mechanisms of immunological control and escape during tumor formation. This study shows that tumor-specific CD4⁺ T cells are able to protect against virus-induced tumor cells. We show here that there is an expansion of tumor-specific CD4⁺ T cells producing cytokines and cytotoxic molecule granzyme B (GzmB) in the early phase of tumor growth. Importantly, we demonstrate that in vivo depletion of regulatory T cells (Tregs) and CD8⁺ T cells in FBL-3-bearing DEREG transgenic mice augments IL-2 and GzmB production by CD4⁺ T cells and increases FV-specific CD4⁺ T-cell effector and cytotoxic responses leading to the complete tumor regression. Therefore, the capacity to reject tumor acquired by tumor-reactive CD4⁺ T cells largely depends on the direct suppressive activity of Tregs. We suggest that a cytotoxic CD4⁺ T-cell immune response may be induced to enhance resistance against oncovirus-associated tumors.

EBNA3B-deficient EBV promotes B cell lymphomagenesis in humanized mice and is found in human tumors

Epstein-Barr virus (EBV) persistently infects more than 90% of the human population and is etiologically linked to several B cell malignancies, including Burkitt lymphoma (BL), Hodgkin lymphoma (HL), and diffuse large B cell lymphoma (DLBCL). Despite its growth transforming properties, most immune-competent individuals control EBV infection throughout their lives. EBV encodes various oncogenes, and of the 6 latency-associated EBV-encoded nuclear antigens, only EBNA3B is completely dispensable for B cell transformation in vitro. Here, we report that infection with EBV lacking EBNA3B leads to aggressive, immune-evading monomorphic DLBCL-like tumors in NOD/SCID/γc-/- mice with reconstituted human immune system components. Infection with EBNA3B-knockout EBV (EBNA3BKO) induced expansion of EBV-specific T cells that failed to infiltrate the tumors. EBNA3BKO-infected B cells expanded more rapidly and secreted less T cell-chemoattractant CXCL10, reducing T cell recruitment in vitro and T cell-mediated killing in vivo. B cell lines from 2 EBV-positive human lymphomas encoding truncated EBNA3B exhibited gene expression profiles and phenotypic characteristics similar to those of tumor-derived lines from the humanized mice, including reduced CXCL10 secretion. Screening EBV-positive DLBCL, HL, and BL human samples identified additional EBNA3B mutations. Thus, EBNA3B is a virus-encoded tumor suppressor whose inactivation promotes immune evasion and virus-driven lymphomagenesis.

Cytotoxic CD4 T cells in antiviral immunity

CD4 T cells that acquire cytotoxic phenotype and function have been repeatedly identified in humans, mice, and other species in response to many diverse pathogens. Since CD4 cytotoxic T cells are able to recognize antigenic determinants unique from those recognized by the parallel CD8 cytotoxic T cells, they can potentially contribute additional immune surveillance and direct effector function by lysing infected or malignant cells. Here, we briefly review much of what is known about the generation of cytotoxic CD4 T cells and describe our current understanding of their role in antiviral immunity. Furthering our understanding of the many roles of CD4 T cells during an anti-viral response is important for developing effective vaccine strategies that promote long-lasting protective immunity.

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.

Cytosolic DNA-activated human dendritic cells are potent activators of the adaptive immune response

Recent studies in cell lines and genetically engineered mice have demonstrated that cytosolic dsDNA could activate dendritic cells (DCs) to become effector APCs. Recognition of DNA might be a major factor in antimicrobial immune responses against cytosolic pathogens and also in human autoimmune diseases such as systemic lupus erythematosus. However, the role of cytosolic dsDNA in human DC activation and its effects on effector T and B cells are still elusive. In this study, we demonstrate that intracellular dsDNA is a potent activator of human monocyte-derived DCs as well as primary DCs. Activation by dsDNA depends on NF-κB activation, partially on the adaptor molecule IFN-promoter stimulator-1 and the novel cytosolic dsDNA receptor IFI16, but not on the previously recognized dsDNA sentinels absent in melanoma 2, DNA-dependent activator of IFN regulatory factor 3, RNA polymerase III, or high-mobility group boxes. More importantly, we report for the first time, to our knowledge, that human dsDNA-activated DCs, rather than LPS- or inflammatory cytokine mixture-activated DCs, represent the most potent inducers of naive CD4(+) T cells to promote Th1-type cytokine production and generate CD4(+) and CD8(+) cytotoxic T cells. dsDNA-DCs, but not LPS- or mixture-activated DCs, induce B cells to produce complement-fixing IgG1 and IgG3 Abs. We propose that cytosolic dsDNA represents a novel, more effective approach to generate DCs to enhance vaccine effectiveness in reprogramming the adaptive immune system to eradicate infectious agents, autoimmunity, allergy, and cancer.

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

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

Shifting the equilibrium in cancer immunoediting: from tumor tolerance to eradication

The continual interaction of the immune system with a developing tumor is thought to result in the establishment of a dynamic state of equilibrium. This equilibrium depends on the balance between effector and regulatory T-cell compartments. Whereas regulatory T cells can infiltrate and accumulate within tumors, effector T cells fail to efficiently do so. Furthermore, effector T cells that do infiltrate the tumor become tightly controlled by different regulatory cellular subsets and inhibitory molecules. The outcome of this balance is critical to survival, and whereas in some cases the equilibrium can rapidly result in the elimination of the transformed cells by the immune system, in many other cases the tumor manages to escape immune control. In this review, we discuss relevant work focusing on the establishment of the intratumor balance, the dynamic changes in the populations of effector and regulatory T cells within the tumor, and the role of the tumor vasculature and its activation state in the recruitment of different T-cell subsets. Finally, we also discuss work associated to the manipulation of the immune response to tumors and its impact on the infiltration, accumulation, and function of tumor-reactive lymphocytes within the tumor microenvironment.

Infectious agents in human cancers: lessons in immunity and immunomodulation from gammaherpesviruses EBV and KSHV

Members of the herpesvirus family have evolved the ability to persist in their hosts by establishing a reservoir of latently infected cells each carrying the viral genome with reduced levels of viral protein synthesis. In order to spread within and between hosts, in some cells, the quiescent virus will reactivate and enter lytic cycle replication to generate and release new infectious virus particles. To allow the efficient generation of progeny viruses, all herpesviruses have evolved a wide variety of immunomodulatory mechanisms to limit the exposure of cells undergoing lytic cycle replication to the immune system. Here we have focused on the human gammaherpesviruses Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) that, uniquely among the eight human herpesviruses identified to date, have growth transforming potential. Most people infected with these viruses will not develop cancer, viral growth-transforming activity being kept under control by the host's antigen-specific immune responses. Nonetheless, EBV and KSHV are associated with several malignancies in which various viral proteins, either predominantly or exclusively latency-associated, are expressed; at least some of these proteins also have immunomodulatory activities. Of these malignancies, some are the result of a disrupted virus/immune balance through genetic, infectious or iatrogenic immune suppression. Others develop in people that are not overtly immune suppressed and likely modulate the immunological response. This latter aspect of immune modulation by EBV and KSHV forms the basis of this review.

Cytolytic CD4(+) T cells in viral immunity

It is generally believed that the role of CD4(+) T cells is to coordinate the different arms of the adaptive immune system to shape an effective response against a pathogen and regulate nonessential or deleterious activities. However, a growing body of evidence suggests that effector CD4(+) T cells can directly display potent antiviral activity themselves. The presence of cytolytic CD4(+) T cells has been demonstrated in the immune response to numerous viral infections in both humans and in animal models and it is likely that they play a critical role in the control of viral replication in vivo. This article describes the current research on virus-specific cytolytic CD4(+) T cells, with a focus on HIV-1 infection and the implications that this immune response has for vaccine design.

Prospects of a novel vaccination strategy for human gamma-herpesviruses

Due to the oncogenic potential associated with persistent infection of human gamma-herpesviruses, including Epstein-Barr virus (EBV or HHV-4) and Kaposi's sarcoma-associated herpesvirus (KSHV or HHV-8), vaccine development has focused on subunit vaccines. However, the results using an animal model of mouse infection with a related rodent virus, murine gamma-herpesvirus 68 (MHV-68, γHV-68, or MuHV-4), have shown that the only effective vaccination strategy is based on live attenuated viruses, including viruses engineered to be incapable of establishing persistence. Vaccination with a virus lacking persistence would eliminate many potential complications. Progress in understanding persistent infections of EBV and KSHV raises the possibility of engineering a live attenuated virus without persistence. Therefore, we should keep the option open for developing a live EBV or KSHV vaccine.

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

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