A Quantitative Assay for Epstein-Barr Virus–Specific Immunity Shows Interferon-γ Producing CD8+ T Cells Increase During Immunosuppression Reduction to Treat Posttransplant Lymphoproliferative Disease

αβ and γδ T-cell responses to Epstein-Barr Virus: insights in immunocompetence, immune failure and therapeutic augmentation in transplant patients

Epstein-Barr Virus (EBV) is a human gamma herpes virus, which causes several diseases in immunocompetent (mononucleosis, chronic fatigue syndrome, gastric cancer, endemic Burkitt's lymphoma, head and neck cancer) and immunosuppressed (post-transplant lymphoproliferative disease, EBV-associated soft tissue tumors) patients. It elicits a complex humoral and cellular immune response with both innate and adaptive immune components. Substantial progress has been made in understanding the interplay of immune cells in EBV-associated diseases in recent years, and several therapeutic approaches have been developed to augment cellular immunity toward EBV for control of EBV-associated malignancy. This review will focus on recent developments in immunosuppressed transplant recipients.

In vitro and in vivo evidence that the switch from calcineurin to mTOR inhibitors may be a strategy for immunosuppression in Epstein-Barr virus-associated post-transplant lymphoproliferative disorder

Post-transplant lymphoproliferative disorder is a life-threatening complication of immunosuppression following transplantation mediated by failure of T cells to control Epstein-Barr virus (EBV)-infected and transformed B cells. Typically, a modification or reduction of immunosuppression is recommended, but insufficiently defined thus far. In order to help delineate this, we characterized EBV-antigen-specific T cells and lymphoblastoid cell lines from healthy donors and in patients with a kidney transplant in the absence or presence of the standard immunosuppressants tacrolimus, cyclosporin A, prednisolone, rapamycin, and mycophenolic acid. Phenotypes of lymphoblastoid cell-lines and T cells, T cell-receptor-repertoire diversity, and T-cell reactivity upon co-culture with autologous lymphoblastoid cell lines were analyzed. Rapamycin and mycophenolic acid inhibited lymphoblastoid cell-line proliferation. T cells treated with prednisolone and rapamycin showed nearly normal cytokine production. Proliferation and the viability of T cells were decreased by mycophenolic acid, while tacrolimus and cyclosporin A were strong suppressors of T-cell function including their killing activity. Overall, our study provides a basis for the clinical decision for the modification and reduction of immunosuppression and adds information to the complex balance of maintaining anti-viral immunity while preventing acute rejection. Thus, an immunosuppressive regime based on mTOR inhibition and reduced or withdrawn calcineurin inhibitors could be a promising strategy for patients with increased risk of or manifested EBV-associated post-transplant lymphoproliferative disorder.

Recent advances in understanding and managing infectious diseases in solid organ transplant recipients

Background: Undergoing solid organ transplantation (SOT) exposes the recipient to various infectious risks, including possible transmission of pathogen by the transplanted organ, post-surgical infections, reactivation of latent pathogens, or novel infections. Recent advances: In the last few years, the emergence of Zika virus has raised concerns in the transplant community. Few cases have been described in SOT patients, and these were associated mainly with moderate disease and favorable outcome; the notable exception is a recent case of fatal meningo-encephalopathy in a heart transplant recipient. Because of the advances in treating hepatitis C, several teams recently started to use organs from hepatitis C-positive donors. The worldwide increasing incidence of multidrug-resistant pathogens, as well as the increasing incidence of Clostridioidesdifficile infection, is of particular concern in SOT patients. In the field of mycology, the main recent therapeutic advance is the availability of isavuconazole for the treatment of invasive aspergillosis and mucormycosis. This drug has the advantage of minimal interaction with calcineurin inhibitors. Regarding the viral reactivations occurring after transplant, cytomegalovirus (CMV) infection is still a significant issue in SOT patients. The management of resistant CMV remains particularly difficult. The approval of letermovir, albeit in bone marrow transplantation, and the therapeutic trial of maribavir bring a ray of hope. Another advancement in management of post-transplant infections is the development of in vitro tests evaluating pathogen-specific immune response, such as immunodiagnostics for CMV and, more recently, tests for monitoring immunity against BK virus. Conclusion: The increasing number of organ transplantations, the use of newer immunosuppressive drugs, and high-risk donors continue to define the landscape of transplant infectious diseases in the current era.

Cancer and mTOR Inhibitors in Transplant Recipients

Malignancy is the second most common single cause of death observed in organ transplant recipients. The excess cancer risk is related to intensity and duration of immunosuppressive therapy and inversely to recipient age. Immunodeficiency and (chronic/oncogenic) viral infections together constitute a major risk. Nonmelanoma skin cancer, Kaposi sarcoma, and posttransplant lymphoproliferative disease have standardized incidence ratios exceeding 10- or 50-fold. The mammalian target of rapamycin (mTOR) inhibitors, sirolimus and everolimus, are increasingly used after organ transplantation with potential advantages in virus-associated posttransplant malignancies as well as anti-cancer properties. Despite a seemingly clear mechanism of action and solid rationale for their use in cancer therapy, mTORis have met only modest success rates in clinical trials with advanced malignancies except for specific tumors, such as Kaposi sarcoma and mantle cell lymphoma. Because mTORis are primarily cytostatic, not cytotoxic, the observed clinical efficacy is a reflection of disease stabilization rather than tumor regression. Nonmelanoma skin cancers, in particular cutaneous squamous cell carcinoma, have the highest standardized incidence ratios in transplant recipients. Recent meta-analyses and randomized trials on secondary prevention of squamous cell carcinoma observed a reduction in cumulative tumor load, suggesting most benefit to be gained by early conversion to an mTOR inhibitor-based maintenance regime. There is ongoing debate on the mechanisms involved including withdrawal of the carcinogenic effects of calcineurin inhibitors and/or their impact on chronic (oncogenic) viral infections. At present, there is, however, insufficient evidence for the primary use of mTORis as protective agents against most other cancer types.

Approaches for monitoring of non virus-specific and virus-specific T-cell response in solid organ transplantation and their clinical applications

Opportunistic viral infections are still a major complication following solid organ transplantation. Immune monitoring may allow the identification of patients at risk of infection and, eventually, the modulation of immunosuppressive strategies. Immune monitoring can be performed using virus-specific and non virus-specific assays. This article describes and summarizes the pros and cons of the different technical approaches. Among the assays based on non virus-specific antigens, the enumeration of T-cell subsets, the quantification of cytokines and chemokines and the quantification of intracellular adenosine triphosphate following mitogen stimulation are described and their clinical applications to determine the risk for viral infection are discussed. In addition, current specific methods available for monitoring viral-specific T-cell responses are summarized, such as peptide-MHC multimer staining, intracellular cytokine staining, enzyme-linked immunospot and virus-specific IFN-γ ELISA assays, and their clinical applications to determine the individual risk for opportunistic viral infections with human cytomegalovirus, Epstein-Barr virus and polyoma BK virus are discussed. The standardization of the procedure, the choice of the antigen(s) and the criteria to define cut-off values for positive responses are needed for some of these approaches before their implementation in the clinic. Nevertheless, immune monitoring combined with virological monitoring in transplant recipients is increasingly regarded as a helpful tool to identify patients at risk of infection as well as to assess treatment efficacy.

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.

Increased T-cell responses to Epstein-Barr virus with high viral load in patients with Epstein-Barr virus-positive diffuse large B-cell lymphoma

The immunological status of patients with Epstein-Barr virus-positive diffuse large B-cell lymphoma (EBV+ DLBCL) without obvious immunodeficiency has not been elucidated. A multicenter prospective study was conducted to assess pretreatment T-cell responses to EBV, EBV-DNA load and anti-EBV antibody in these patients. The proliferative and interferon (IFN)-γ-producing capacity of T-cells in response to autologous B-lymphoblastoid cell lines was determined using carboxyfluorescein diacetate succinimidyl ester (CFSE)-based assay. Frequencies of EBV-specific CD4+ T-cells in patients with EBV+ DLBCL (n = 13) were significantly higher than in healthy controls (HCs) (n = 16) after both ex vivo and in vitro stimulation. Frequencies of EBV-specific CD8+ T-cells in patients with EBV+ DLBCL tended to be higher than in HCs after in vitro stimulation. Patients with EBV+ DLBCL also showed increased immunoglobulin G (IgG) responses to lytic EBV-encoded antigens. Pretreatment plasma EBV-DNA level was significantly higher in patients with EBV+ DLBCL than in patients with EBV- DLBCL or HCs. In conclusion, EBV-specific T-cells showed increased reactivity, accompanied by higher levels of plasma virus DNA in patients with EBV+ DLBCL.

Clinical immune-monitoring strategies for predicting infection risk in solid organ transplantation

Infectious complications remain a leading cause of morbidity and mortality after solid organ transplantation (SOT), and largely depend on the net state of immunosuppression achieved with current regimens. Cytomegalovirus (CMV) is a major opportunistic viral pathogen in this setting. The application of strategies of immunological monitoring in SOT recipients would allow tailoring of immunosuppression and prophylaxis practices according to the individual's actual risk of infection. Immune monitoring may be pathogen-specific or nonspecific. Nonspecific immune monitoring may rely on either the quantification of peripheral blood biomarkers that reflect the status of a given arm of the immune response (serum immunoglobulins and complement factors, lymphocyte sub-populations, soluble form of CD30), or on the functional assessment of T-cell responsiveness (release of intracellular adenosine triphosphate following a mitogenic stimulus). In addition, various methods are currently available for monitoring pathogen-specific responses, such as CMV-specific T-cell-mediated immune response, based on interferon-γ release assays, intracellular cytokine staining or main histocompatibility complex-tetramer technology. This review summarizes the clinical evidence to date supporting the use of these approaches to the post-transplant immune status, as well as their potential limitations. Intervention studies based on validated strategies for immune monitoring still need to be performed.

Flow cytometry and solid organ transplantation: a perfect match

In the field of transplantation, flow cytometry serves a well-established role in pre-transplant crossmatching and monitoring immune reconstitution following hematopoietic stem cell transplantation. The capabilities of flow cytometers have continuously expanded and this combined with more detailed knowledge of the constituents of the immune system, their function and interaction and newly developed reagents to study these parameters have led to additional utility of flow cytometry-based analyses, particularly in the post-transplant setting. This review discusses the impact of flow cytometry on managing alloantigen reactions, monitoring opportunistic infections and graft rejection and gauging immunosuppression in the context of solid organ transplantation.

Detection of Epstein-Barr virus-specific memory CD4+ T cells using a peptide-based cultured enzyme-linked immunospot assay

Approaches to evaluate T-cell responses to Epstein-Barr virus (EBV) include enzyme-linked immunospot (ELISPOT), which quantifies cells capable of immediate interferon-γ secretion upon antigen stimulation. However, evaluation of expandable EBV-specific memory T cells in an ELISPOT format has not been described previously. We quantified EBV-specific T-cell precursors with high proliferative capacity by using a peptide-based cultured interferon-γ ELISPOT assay. Standard and cultured ELISPOT responses to overlapping peptide pools (15-mers overlapping by 11 amino acids) covering the lytic (BZLF1 and BMRF1) and latent (EBNA1, EBNA3a, EBNA3b, EBNA3c, LMP1 and LMP2) EBV proteins were evaluated in 20 healthy subjects with remote EBV infection and, for comparison, in four solid organ transplant recipients. Cultured ELISPOT responses to both lytic and latent EBV antigens were significantly higher than standard ELISPOT responses. The distribution of EBV-specific T-cell responses detected in healthy virus carriers showed more consistent cultured ELISPOT responses compared with standard ELISPOT responses. T-cell responses quantified by cultured ELISPOT were mainly mediated by CD4+ T cells and a marked pattern of immunodominance to latent-phase antigens (EBNA1 > EBNA3 family antigens > LMP2 > LMP1) was shown. Both the magnitude and distribution of EBV-specific T-cell responses were altered in solid organ transplant recipients; in particular, cultured ELISPOT responses were almost undetectable in a lung-transplanted patient with EBV-associated diseases. Analysis of T-cell responses to EBV by ELISPOT assays might provide new insights into the pathogenesis of EBV-related diseases and serve as new tools in the monitoring of EBV infection in immunocompromised patients.

Epidemiology of posttransplantation lymphoproliferative disorder in adult renal transplant recipients

BACKGROUND

There is little information in the literature describing the relationship between posttransplantation lymphoproliferative disorder (PTLD) incidence and presentation with both recipient Epstein-Barr virus (EBV) serostatus and EBV status of PTLD histology, particularly in the late posttransplantation period.

METHODS

This study reports the largest UK single-center, single-organ analysis of PTLD to date in a retrospective cohort study of 80 cases occurring in 4189 adult renal transplant recipients.

RESULTS

The incidence rate was 2.6 cases per 1000 patient-years (95% confidence interval [95% CI], 2.1-3.2) for PTLD, 1.8 (95% CI, 1.4-2.4) for non-Hodgkin's lymphoma, and 0.2 (95% CI, 0.07-4.2) for Hodgkin's lymphoma. Non-Hodgkin's lymphoma occurred at a rate 7.6 times that of the adult general population in England, whereas the rate for Hodgkin's lymphoma was 5.9 times. The incidence of PTLD was highest during the 10th to 14th posttransplantation years. Early-onset disease was associated with EBV-seronegative recipient status, EBV-positive histology, and the involvement of extranodal sites. PTLD occurring in EBV-seronegative recipients was associated with EBV nuclear antigen antibody deficiency, polymorphic disease, and the involvement of extranodal sites. EBV-negative histology occurred in 32% of cases at a median time to presentation of 109 months. PTLD involving the allograft, central nervous system, and skin was uncommon and occurred late.

CONCLUSION

The incidence of PTLD is highest in the late posttransplantation period. Close clinical surveillance and education for transplant recipients is required for the duration of time while immunosuppressed. Failure to detect EBV DNA in blood should not reassure, particularly in patients with symptoms such as abdominal pain, oropharyngeal complaints, neck lumps, and B-symptoms.

EBV-specific T-cell immunity in pediatric solid organ graft recipients with posttransplantation lymphoproliferative disease

BACKGROUND

Posttransplantation lymphoproliferative disease (PTLD) is an often Epstein-Barr virus (EBV)-associated mainly malignant complication after transplantation. We present data on EBV-specific T cells in children treated with rituximab with or without chemotherapy on the pediatric PTLD Pilot 2005 protocol.

METHODS

Peripheral blood mononuclear cells were isolated from 16 pediatric patients with PTLD, 4 transplanted children with EBV reactivation, and 18 healthy controls. EBV-specific T cells were quantified by flow cytometric detection of intracellular interferon-γ after stimulation with autologous EBV-transformed lymphoblastoid cell lines and correlated with EBV load in peripheral blood.

RESULTS

At diagnosis, PTLD patients had similar numbers of EBV-specific CD4 and CD8 T cells as healthy EBV-positive controls. EBV-specific T cells tended to be lower in early PTLD compared with late PTLD. During treatment with rituximab, CD4 and/or CD8 EBV-specific T cells increased in most patients, possibly reflecting restored immunocompetence due to a reduction of immunosuppression as well as antigenic stimulation by cross-presentation of EBV antigen from destroyed B cells. However, this increase did not predict response to rituximab or chemotherapy. EBV load and circulating B cells became undetectable in most patients during rituximab therapy. B-cell recovery after treatment was accompanied by redetection of EBV in peripheral blood, which was controlled by T-cell responses in 11 of 11 evaluable cases.

CONCLUSIONS

In pediatric PTLD patients, pretreatment EBV-specific T-cell numbers are in the range of healthy controls. These cells increased on reduction of immunosuppression and treatment with rituximab. Recurrence of EBV viremia during complete remission is matched by strong T-cell responses.

Adoptive T-cell immunotherapy from third-party donors: characterization of donors and set up of a T-cell donor registry

Infection with and reactivation of human cytomegalovirus (CMV), Epstein-Barr virus (EBV), and adenovirus (ADV) are frequent and severe complications in immunocompromised recipients after hematopoietic stem cell transplantation (HSCT) or solid organ transplantation (SOT). These serious adverse events are associated with significant morbidity and mortality. Donor lymphocyte infusions (DLIs) are often used to treat both viral infections and leukemia relapses after transplantation but are associated with potentially life-threatening graft-versus-host disease (GvHD). Adoptive immunotherapy with virus-specific cytotoxic effector T cells (CTLs) derived from seropositive donors can rapidly reconstitute antiviral immunity after HSCT and organ transplantation. Therefore, it can effectively prevent the clinical manifestation of these viruses with no significant acute toxicity or increased risk of GvHD. In conditions, where patients receiving an allogeneic cord blood (CB) transplant or a transplant from a virus-seronegative donor and since donor blood is generally not available for solid organ recipients, allogeneic third party T-cell donors would offer an alternative option. Recent studies showed that during granulocyte colony-stimulating factor (G-CSF) mobilization, the functional activity of antiviral memory T cells is impaired for a long period. This finding suggests that even stem cell donors may not be the best source of T cells. Under these circumstances, partially human leukocyte antigen (HLA)-matched virus-specific CTLs from healthy seropositive individuals may be a promising option. Therefore, frequency assessments of virus-specific memory T cells in HLA-typed healthy donors as well as in HSCT/SOT donors using a high throughput T-cell assay were performed over a period of 4 years at Hannover Medical School. This chapter will address the relevance and potential of a third-party T-cell donor registry and will discuss its clinical implication for adoptive T-cell immunotherapy.

CXCL13 as a novel marker for diagnosis and disease monitoring in pediatric PTLD

Posttransplant lymphoproliferative disease (PTLD) is a severe complication of immunosuppressive treatment in organ-grafted children. Early diagnosis of PTLD is hampered by both unspecific clinical symptoms and lack of easy accessible markers. The homeostatic chemokine CXCL13, which plays a crucial role in B-cell homing and lymphoid organ development, is expressed in some lymphomatous diseases. This study aims to investigate whether serum CXCL13 (sCXCL13) levels correlate with occurrence and regression of PTLD in pediatric solid-organ graft recipients. Serum samples from PTLD patients (n = 21), patients with Epstein-Barr virus (EBV) reactivation (n = 18), and healthy age-matched controls (n = 19) were tested for CXCL13 using a commercially available ELISA kit. sCXCL13 levels were significantly higher in PTLD patients than in healthy children. PTLD patients had also higher sCXCL13 values than pediatric solid-organ recipients with EBV reactivation. An increase in sCXCL13 levels was observed from EBV reactivation to PTLD diagnosis in most cases. Elevated sCXCL13 levels were detected up to 2 years prior to PTLD diagnosis and correlated well with response to cytoreductive treatment in individual patients. sCXCL13, thus, may be a readily available surrogate marker for the diagnosis of PTLD and for monitoring of response to treatment in patients with initially elevated sCXCL13 levels.

Reduction of immunosuppression as initial therapy for posttransplantation lymphoproliferative disorder(★)

Reduction of immunosuppression (RI) is commonly used to treat posttransplant lymphoproliferative disorder (PTLD) in solid organ transplant recipients. We investigated the efficacy, safety and predictors of response to RI in adult patients with PTLD. Sixty-seven patients were managed with RI alone and 30 patients were treated with surgical excision followed by adjuvant RI. The response rate to RI alone was 45% (complete response-37%, partial response-8%). The relapse rate in complete responders was 17%. Adjuvant RI resulted in a 27% relapse rate. The acute rejection rate following RI-containing strategies was 32% and a second transplant was feasible without relapse of PTLD. The median survival was 44 months in patients treated with RI alone and 9.5 months in patients who remained on full immunosuppression (p = 0.07). Bulky disease, advanced stage and older age predicted lack of response to RI. Survival analysis demonstrated predictors of poor outcome-age, dyspnea, B symptoms, LDH level, hepatitis C, bone marrow and liver involvement. Patients with none or one of these factors had a 3-year overall survival of 100% and 79%, respectively. These findings support the use of RI alone in low-risk PTLD and suggest factors that predict response and survival.

High incidence of post transplant lymphoproliferative disorder after antithymocyte globulin-based conditioning and ineffective prediction by day 28 EBV-specific T lymphocyte counts

The largest study on post-allogeneic hematopoietic cell transplant lymphoproliferative disorder (PTLD) epidemiology showed a cumulative incidence of 1.7% in patients receiving antithymocyte globulin (ATG). We had noted an apparently higher incidence in our transplant recipients whose conditioning included ATG. Therefore, we formally determined the incidence of PTLD through chart review. We also evaluated whether counts of EBV-specific T lymphocytes measured by cytokine flow cytometry could identify patients at risk of developing PTLD. Among 307 allogeneic transplant recipients, 25 (8.1%) developed PTLD. This was biopsy proven in 11 patients, and was fatal in seven patients. Patient age, EBV serostatus, donor type/match or GVHD did not influence PTLD risk significantly. Median onset of PTLD was 55 (range, 28-770) days post transplant. Day 28 EBV-specific T lymphocyte counts were not significantly different in 11 patients who developed PTLD and 31 non-PTLD patients matched for published risk factors for PTLD. In summary, when using conditioning with thymoglobulin 4.5 mg/kg, the incidence of PTLD is relatively high and cannot be predicted by day 28 cytokine flow cytometry-determined EBV-specific T lymphocyte counts. Thus, in this scenario PTLD prevention may be warranted, for example, using EBV DNAemia monitoring with preemptive therapy.

Post-transplant lymphoproliferative disorder in view of the new WHO classification: a more rational approach to a protean disease?

Post-transplant lymphoproliferative disorders (PTLDs) are serious, life-threatening complications of solid-organ transplantation (SOT) and bone marrow transplantation leading to a high mortality (30-60%). PTLD represents a heterogeneous group of lymphoproliferative diseases. They become clinically relevant because of the expansion of transplantation medicine together with the development of potent immunosuppressive drugs. Although the diagnostic morphological criteria of different forms of PTLD are commonly known, rapid and correct diagnosis is not always easy. Because of the limited number of clinical trials, a consensus is lacking on the optimal treatment of PTLD. This review focuses on incidence, risk factors, clinical picture of the disease and diagnostic tools including histopathology relating to the new classification introduced in 2008 by the World Health Organisation (WHO) and treatment of PTLD.

Post-transplant lymphoproliferative disorder following cytomegalovirus reactivation in a lung recipient

Post-transplant lymphoproliferative disorder (PTLD) is a life-threatening complication after lung transplantation, for which several risk factors including pretransplant seronegativity for Epstein-Barr virus are known. However, the impact of cytomegalovirus on PTLD remains to be determined. Here, we describe a case of Epstein-Barr virus-associated polymorphic PTLD that developed shortly after treatment for cytomegalovirus reactivation in a lung transplant recipient who was preoperatively seropositive for both cytomegalovirus and Epstein-Barr virus.

Diagnosis of post-transplant lymphoproliferative disorder in solid organ transplant recipients - BCSH and BTS Guidelines

A joint working group established by the Haemato-oncology subgroup of the British Committee for Standards in Haematology (BCSH) and the British Transplantation Society (BTS) has reviewed the available literature and made recommendations for the diagnosis and management of post-transplant lymphoproliferative disorder (PTLD) in adult recipients of solid organ transplants. This review details the risk factors predisposing to development, initial features and diagnosis. It is important that the risk of developing PTLD is considered when using post transplant immunosuppression and that the appropriate investigations are carried out when there are suspicions of the diagnosis. These must include tissue for histology and computed tomography scan to assess the extent of disease. These recommendations have been made primarily for adult patients, there have been some comments made with regard to paediatric practice.

Acquisition of polyfunctionality by Epstein-Barr virus-specific CD8+ T cells correlates with increased resistance to galectin-1-mediated suppression

Latent membrane antigen 1 and -2 (LMP-1/2)-specific CD8(+) T cells from newly diagnosed and relapsed Hodgkin's lymphoma (HL) patients display a selective functional impairment. In contrast, CD8(+) T cells specific for Epstein-Barr virus (EBV) nuclear proteins and lytic antigens retain normal T-cell function. Reversion to a dysfunctional phenotype of LMP-1/2-specific T cells is coincident with the regression of HL. To delineate the potential basis for this differential susceptibility for the loss of function, we have carried out a comprehensive functional analysis of EBV-specific T cells using ex vivo multiparametric flow cytometry in combination with assessment of antigen-driven proliferative potential. This analysis revealed that LMP-1/2-specific T cells from healthy virus carriers display a deficient polyfunctional profile compared to that of T cells specific for epitopes derived from EBV nuclear proteins and lytic antigens. Furthermore, LMP-specific T-cells are highly susceptible to galectin-1-mediated immunosuppression and are less likely to degranulate following exposure to cognate peptide epitopes and poorly recognized endogenously processed epitopes from virus-infected B cells. More importantly, ex vivo stimulation of these T cells with an adenoviral vector encoding multiple minimal CD8(+) T-cell epitopes as a polyepitope, in combination with a gammaC cytokine, interleukin-2, restored polyfunctionality and shielded these cells from the inhibitory effects of galectin-1.

Epstein-Barr virus, rapamycin, and host immune responses

PURPOSE OF REVIEW

To summarize recent advances that contribute to our understanding of the pathobiology of Epstein-Barr virus (EBV)-associated posttransplant lymphoproliferative disease (PTLD), the host immune response to virally infected B cells, and the molecular basis for the effects of mammalian target of rapamycin inhibitors on EBV+ B-cell lymphomas.

RECENT FINDINGS

Cytogenetic and genomic analyses support the concept that the underlying biology of EBV-associated PTLD is complex. Transplant recipients can generate and maintain significant populations of EBV-specific CD8+ memory T cells but the function of these cells may be impaired. EBV invokes multiple strategies to subvert and evade the host immune response. The phosphoinositide-3 kinase/Akt/mammalian target of rapamycin signal transduction pathway is a nexus for growth and survival signals in PTLD-associated EBV+ B-cell lymphomas.

SUMMARY

Multiple factors influence the development of EBV-associated PTLD including the host immune response to EBV, virally induced effects on the infected cell and the host immune system, and the type and intensity of immunosuppression.