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

The IPTA Nashville consensus conference on post-transplant lymphoproliferative disorders after solid organ transplantation in children: IV-consensus guidelines for the management of post-transplant lymphoproliferative disorders in children and adolescents

The International Pediatric Transplant Association convened an expert consensus conference to assess current evidence and develop recommendations for various aspects of care relating to post-transplant lymphoproliferative disorders (PTLD) after pediatric solid organ transplantation. This report addresses the outcomes of deliberations by the PTLD Management Working Group. A strong recommendation was made for reduction in immunosuppression as the first step in management. Similarly, strong recommendations were made for the use of the anti-CD20 monoclonal antibody (rituximab) as was the case for chemotherapy in selected scenarios. In some scenarios, there is uncoupling of the strength of the recommendations from the available evidence in situations where such evidence is lacking but collective clinical experiences drive decision-making. Of note, there are no large, randomized phase III trials of any treatment for PTLD in the pediatric age group. Current gaps and future research priorities are highlighted.

The IPTA Nashville Consensus Conference on Post-Transplant lymphoproliferative disorders after solid organ transplantation in children: III - Consensus guidelines for Epstein-Barr virus load and other biomarker monitoring

The International Pediatric Transplant Association convened an expert consensus conference to assess current evidence and develop recommendations for various aspects of care relating to post-transplant lymphoproliferative disorders after solid organ transplantation in children. In this report from the Viral Load and Biomarker Monitoring Working Group, we reviewed the existing literature regarding the role of Epstein-Barr viral load and other biomarkers in peripheral blood for predicting the development of PTLD, for PTLD diagnosis, and for monitoring of response to treatment. Key recommendations from the group highlighted the strong recommendation for use of the term EBV DNAemia instead of "viremia" to describe EBV DNA levels in peripheral blood as well as concerns with comparison of EBV DNAemia measurement results performed at different institutions even when tests are calibrated using the WHO international standard. The working group concluded that either whole blood or plasma could be used as matrices for EBV DNA measurement; optimal specimen type may be clinical context dependent. Whole blood testing has some advantages for surveillance to inform pre-emptive interventions while plasma testing may be preferred in the setting of clinical symptoms and treatment monitoring. However, EBV DNAemia testing alone was not recommended for PTLD diagnosis. Quantitative EBV DNAemia surveillance to identify patients at risk for PTLD and to inform pre-emptive interventions in patients who are EBV seronegative pre-transplant was recommended. In contrast, with the exception of intestinal transplant recipients or those with recent primary EBV infection prior to SOT, surveillance was not recommended in pediatric SOT recipients EBV seropositive pre-transplant. Implications of viral load kinetic parameters including peak load and viral set point on pre-emptive PTLD prevention monitoring algorithms were discussed. Use of additional markers, including measurements of EBV specific cell mediated immunity was discussed but not recommended though the importance of obtaining additional data from prospective multicenter studies was highlighted as a key research priority.

Outcomes of children treated for multiple Epstein-Barr virus-associated post-transplant tumors

BACKGROUND

After solid organ transplantation, children are at risk for Epstein-Barr virus-associated post-transplant lymphoproliferative disorder and smooth muscle tumors. Little is known about the clinical course, Epstein-Barr viral load variations, and optimal treatment for such patients. We set forth to understand the course of repeated episodes of post-transplant lymphoproliferative disorder and smooth muscle tumors.

METHODS

We performed a retrospective chart review of patients up to 21 years old with solid organ transplantation and post-transplant lymphoproliferative disorder at the Children's Hospital of Philadelphia from January 2003 through June 30, 2020.

RESULTS

Six patients had multiple episodes of Epstein-Barr virus-associated post-transplant lymphoproliferative disorder and smooth muscle tumors. When the second episode was discovered, only one patient was symptomatic. Histology differed from diagnosis in four patients. Treatment included viral-specific T-lymphocytes (2), rituximab (3), reduction in immunosuppression alone (1). Five patients had complete response, and one had stable disease, but three patients developed a subsequent tumor. Two patients developed Epstein-Barr virus-associated smooth muscle tumors. Of these six patients, four are alive. The deaths were not related to their tumors.

CONCLUSIONS

Despite a complete response to initial therapy, children are at risk for repeated episodes of Epstein-Barr virus-associated post-transplant lymphoproliferative disorder and smooth muscle tumors. Histology and location were not typically consistent with initial diagnosis, suggesting these are second primaries rather than recurrences. Disease may be managed with individualized treatment plans but EBV-specific T cells need further study in such tumors.

Post-transplant lymphoproliferative disorders (PTLD) in adolescents and young adults: A category in need of definition

Post-transplant lymphoproliferative disorders are a well-recognized complication of solid organ and stem cell transplantation. Much data has accumulated with respect to the pathobiology and clinical behavior of these lesions in the general post-transplant population as well as in the pediatric and adult age groups. However, information as to these lesions in the adolescent and young adult populations, which bridge the pediatric and adult groups, is limited. In this review, the focus is on this unique population of PTLD patients and their proliferations.

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.

Reinforcement of cell-mediated immunity driven by tumor-associated Epstein-Barr virus (EBV)-specific T cells during targeted B-cell therapy with rituximab

Introduction

In immunocompromised patients, Epstein-Barr virus (EBV) infection or reactivation is associated with increased morbidity and mortality, including the development of B-cell lymphomas. The first-line treatment consists of reduction of immunosuppression and administration of rituximab (anti-CD20 antibody). Furthermore, the presence of EBV-specific T cells against latent EBV proteins is crucial for the control of EBV-associated diseases. Therefore, in addition to effective treatment strategies, appropriate monitoring of T cells of high-risk patients is of great importance for improving clinical outcome. In this study, we hypothesized that rituximab-mediated lysis of malignant EBV-infected B cells leads to the release and presentation of EBV-associated antigens and results in an augmentation of EBV-specific effector memory T-cell responses.

Methods

EBV-infected B lymphoblastoid cell lines (B-LCLs) were used as a model for EBV-associated lymphomas, which are capable of expressing latency stage II and III EBV proteins present in all known EBV-positive malignant cells. Rituximab was administered to obtain cell lysates containing EBV antigens (AC^EBV). Efficiency of cross-presentation of EBV-antigen by B-LCLs compared to cross-presentation by professional antigen presenting cells (APCs) such as dendritic cells (DCs) and B cells was investigated by in vitro T-cell immunoassays. Deep T-cell profiling of the tumor-reactive EBV-specific T cells in terms of activation, exhaustion, target cell killing, and cytokine profile was performed, assessing the expression of T-cell differentiation and activation markers as well as regulatory and cytotoxic molecules by interferon-γ (IFN-γ) EliSpot assay, multicolor flow cytometry, and multiplex analyses.

Results

By inhibiting parts of the cross-presentation pathway, B-LCLs were shown to cross-present obtained exogenous AC^EBV-derived antigens mainly through major histocompatibility complex (MHC) class I molecules. This mechanism is comparable to that for DCs and B cells and resulted in a strong EBV-specific CD8⁺ cytotoxic T-cell response. Stimulation with AC^EBV-loaded APCs also led to the activation of CD4⁺ T helper cells, suggesting that longer peptide fragments are processed via the classical MHC class II pathway. In addition, B-LCLs were also found to be able to take up exogenous antigens from surrounding cells by endocytosis leading to induction of EBV-specific T-cell responses although to a much lesser extent than cross-presentation of AC^EBV-derived antigens. Increased expression of activation markers CD25, CD71 and CD137 were detected on EBV-specific T cells stimulated with AC^EBV-loaded APCs, which showed high proliferative and cytotoxic capacity as indicated by enhanced EBV-specific frequencies and increased secretion levels of cytotoxic effector molecules (e.g. IFN-γ, granzyme B, perforin, and granulysin). Expression of the regulatory proteins PD-1 and Tim-3 was induced but had no negative impact on effector T-cell functions.

Conclusion

In this study, we showed for the first time that rituximab-mediated lysis of EBV-infected tumor cells can efficiently boost EBV-specific endogenous effector memory T-cell responses through cross-presentation of EBV-derived antigens. This promotes the restoration of antiviral cellular immunity and presents an efficient mechanism to improve the treatment of CD20⁺ EBV-associated malignancies. This effect is also conceivable for other therapeutic antibodies or even for therapeutically applied unmodified or genetically modified T cells, which lead to the release of tumor antigens after specific cell lysis.

[The diagnostic value of whole blood Epstein-Barr virus DNA load in lymphoproliferative diseases after allogeneic hematopoietic stem cell transplantation]

Objectives: To investigate the diagnostic value of whole blood quantitative PCR for DNA load of Epstein-Barr virus (EBV) in post-transplant lymphoproliferative disease (PTLD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) . Methods: A total of 694 patients with hematologic diseases who underwent allo-HSCT at the Hematology Department of Peking University First Hospital from April 2004 to April 2019 were included, and their data were retrospectively analyzed. Results: ①Among the 694 cases, 29 cases (22 males and 7 females, with a median age of 22 (1-52) years) developed PTLD after allo-HSCT with a cumulative incidence of 4.2% and a median onset time of 2.1 (0.8-20.6) months. ② Univariate analysis showed that age<30 years, diagnosis with aplastic anemia, human leukocyte antigen (HLA) mismatch, use of antithymocyte globulin (ATG) in preconditioning regimens, and EBV reactivation were the risk factors for the occurrence of PTLD. Multivariate analysis showed that EBV reactivation was an independent risk factor for the occurrence of PTLD. ③Further analysis of EBV reactivation cases showed that the peak value of EBV-DNA load was significantly higher in the PTLD group than that in the non-PTLD group (P<0.001) and the incidence of PTLD increased with the increase of EBV-DNA load. Receiver operating characteristic (ROC) curve analysis indicated that PTLD was more likely to be diagnosed when the EBV-DNA load was >1.19×10(6) copies/ml (sensitivity 0.800 and specificity 0.768) . ④All patients with PTLD received rituximab-based treatment, with an overall response rate of 86.2% and an overall survival rate of 54.3%. Conclusion: The PTLD occurrence after allo-HSCT is highly correlated with EBV reactivation, and the higher the EBV-DNA load, the greater the risk of PTLD occurrence. The dynamic monitoring of EBV-DNA load plays an important role in predicting PTLD occurrence.

Distinct immunopathological mechanisms of EBV-positive and EBV-negative posttransplant lymphoproliferative disorders

EBV-positive and EBV-negative posttransplant lymphoproliferative disorders (PTLDs) arise in different immunovirological contexts and might have distinct pathophysiologies. To examine this hypothesis, we conducted a multicentric prospective study with 56 EBV-positive and 39 EBV-negative PTLD patients of the K-VIROGREF cohort, recruited at PTLD diagnosis and before treatment (2013-2019), and compared them to PTLD-free Transplant Controls (TC, n = 21). We measured absolute lymphocyte counts (n = 108), analyzed NK- and T cell phenotypes (n = 49 and 94), and performed EBV-specific functional assays (n = 16 and 42) by multiparameter flow cytometry and ELISpot-IFNγ assays (n = 50). EBV-negative PTLD patients, NK cells overexpressed Tim-3; the 2-year progression-free survival (PFS) was poorer in patients with a CD4 lymphopenia (CD4⁺ <300 cells/mm³ , p <  .001). EBV-positive PTLD patients presented a profound NK-cell lymphopenia (median = 60 cells/mm³ ) and a high proportion of NK cells expressing PD-1 (vs. TC, p = .029) and apoptosis markers (vs. TC, p < .001). EBV-specific T cells of EBV-positive PTLD patients circulated in low proportions, showed immune exhaustion (p = .013 vs. TC) and poorly recognized the N-terminal portion of EBNA-3A viral protein. Altogether, this broad comparison of EBV-positive and EBV-negative PTLDs highlight distinct patterns of immunopathological mechanisms between these two diseases and provide new clues for immunotherapeutic strategies and PTLD prognosis.

Patient risk stratification and tailored clinical management of post-transplant CMV-, EBV-, and BKV-infections by monitoring virus-specific T-cell immunity

Background

Despite routine post-transplant viral monitoring and pre-emptive therapy, viral infections remain a major cause of allogeneic hematopoietic cell transplantation-related morbidity and mortality.

Objective

We here aimed to prospectively assess the kinetics and the magnitude of cytomegalovirus-(CMV), Epstein Barr virus-(EBV), and BK virus-(BKV)-specific T cell responses post-transplant and evaluate their role in guiding therapeutic decisions by patient risk-stratification.

Study design

The tri-virus-specific immune recovery was assessed by Elispot, in 50 consecutively transplanted patients, on days +20, +30, +60, +100, +150, +200 post-transplant and in case of reactivation, weekly for 1 month.

Results

The great majority of the patients experienced at least one reactivation, while over 40% of them developed multiple reactivations from more than one of the tested viruses, especially those transplanted from matched or mismatched unrelated donors. The early reconstitution of virus-specific immunity (day +20), favorably correlated with transplant outcomes. Εxpanding levels of CMV-, EBV-, and BKV-specific T cells (VSTs) post-reactivation coincided with decreasing viral load and control of infection. Certain cut-offs of absolute VST numbers or net VST cell expansion post-reactivation were determined, above which, patients with CMV or BKV reactivation had >90% probability of complete response (CR).

Conclusion

Immune monitoring of virus-specific T-cell reconstitution post-transplant may allow risk-stratification of virus reactivating patients and enable patient-tailored treatment. The identification of individuals with high probability of CR will minimize unnecessary overtreatment and drug-associated toxicity while allowing candidates for pre-emptive intervention with adoptive transfer of VSTs to be appropriately selected.

Innate and Adaptive Immune Correlates of Chronic and Self-limiting EBV DNAemia in Solid-organ Transplant Recipients

BACKGROUND

Epstein-Barr virus (EBV) DNAemia is a major risk factor for posttransplant lymphoproliferative disorder; however, immune correlates of EBV DNAemia in the transplant setting are limited.

METHODS

Peripheral blood mononuclear cells were collected from 30 transplant recipients with self-limiting EBV DNAemia (SLD; n = 11) or chronic EBV DNAemia (CD; n = 19) at enrollment and 4-8 weeks later. Mass cytometry was used to characterize innate and T-cell immune correlates of EBV DNAemia. Furthermore, flow cytometry was used to measure the frequency of EBV-specific T-cell responses between groups following stimulation with an EBV-infected cell lysate.

RESULTS

Unsupervised analysis of the innate compartment (CD3CD19 cells) identified 5 CD11c clusters at higher abundance in the SLD group (false discovery rate ≤ 1%). These clusters expressed CD11b, CD45RO, CD14, CD123, CD127, and CD38, among others. Unsupervised profiling of the T-cell compartment (CD3CD19) revealed 2 CD4 T-cell clusters at higher frequency among those with SLD (false discovery rate ≤ 1%), which expressed CD45RA, CCR7, CD27, CD28, and CD40L-suggestive of a naive T cell (TN). Manual biaxial gating confirmed increased frequencies of conventional dendritic cells (3.1% versus 2.1%; P = 0.023) and CD4 TN (4.4% versus 1.9%; P = 0.018) among those with SLD. Last, frequencies of interferon-γ-producing EBV-specific CD4 T cells were significantly lower in the CD group relative to those with SLD (4243 versus 250 cells/10 cells; P = 0.015).

CONCLUSIONS

CD is associated with a reduction of CD11c cells, CD4 TN, and interferon-γ-producing EBV-specific CD4 T cells, suggesting an interplay between innate and adaptive immune compartments may be important for regulating EBV DNAemia.

Joining Efforts for PTLD: Lessons Learned from Comparing the Approach and Treatment Strategies Across the Pediatric and Adult Age Spectra

PURPOSE OF REVIEW

Post-transplant lymphoproliferative disorders are a rare and heterogeneous group of diseases, where large prospective studies have been difficult to perform and treatment paradigms are often based on retrospective studies. Here, we critically analyze and present the clinical algorithms commonly used for this disease, with a special focus on the challenges and differences of the approaches in the adult and pediatric populations.

RECENT FINDINGS

Clinical trials exploring combinations of immunochemotherapies with a sequential and risk-stratified strategy have demonstrated exciting results, but are hampered from specialty and age-determined silos. Approaches introducing novel-targeted therapies and cellular therapies are currently being explored with a goal of joining efforts across the pediatric and adult age spectra. We propose that future therapeutic approaches would benefit from combining pediatric and adult PTLD efforts, gaining from the experience garnered from the age- and subtype-specific tailored strategies, with the aim of limiting treatment-related toxicities while maximizing the efficacy. Joining of efforts holds enormous potential for accelerating access to novel therapeutic strategies for PTLD in the near future.

Virus-specific T cells in pediatric renal transplantation

After pediatric kidney transplantation, immunosuppressive therapy causes an increased risk of severe viral complications, especially from cytomegalovirus (CMV), BK polyomavirus (BKPyV) or Epstein-Barr virus (EBV), and less frequent from adenovirus (ADV). However, suitable predictive markers for the individual outcome of viral infections are missing and the therapeutic management remains a challenge to the success of pediatric kidney transplantation. Virus-specific T cells are known for controlling viral replication and there is growing evidence that virus-specific T cells may serve as a prognostic marker to identify patients at risk for viral complications. This review provides an overview of the usability of virus-specific T cells for improving diagnostic and therapeutic management of viral infections with reference to the necessity of antiviral prophylaxis, timing of pre-emptive therapy, and dosing of immunosuppressive medication after pediatric kidney transplantation. Several studies demonstrated that high levels of virus-specific T cells are associated with decrease of virus load and favorable outcome, whereas lack of virus-specific T cells coincided with virus-induced complications. Accordingly, the additional monitoring of virus-specific T cells aims to personalize the management of antiviral therapy, identify overimmunosuppression, and avoid unnecessary therapeutic interventions. Prospective randomized trials in pediatric kidney recipients comparing standard antiviral and immunosuppressive regimens with T cell-guided therapeutic interventions are needed, before monitoring of virus-specific T cells is implemented in the routine care of pediatric kidney graft recipients.

Biomarkers for PTLD diagnosis and therapies

Post-transplant lymphoproliferative disorder (PTLD) represents a spectrum of lymphoproliferative disorders and is a serious complication of pediatric transplantation. The majority of PTLD are associated with Epstein Barr virus (EBV) and the characteristic EBV+ B cell lymphomas are the leading post-transplant malignancy in children. EBV+ PTLD remains a formidable issue in pediatric transplantation and is thought to result from impaired immunity to EBV as a result of immunosuppression. However, the key viral and immune factors that determine whether EBV+ PTLD develops remain unknown. Recently, there has been much interest in developing biomarkers in order to improve and achieve more personalized approaches, in the clinical diagnosis, management, and treatment of EBV+ PTLD. Here, we review the status of immune-, viral-, and B cell lymphoma-derived candidates for biomarkers of EBV+ PTLD.

Skewed T cell responses to Epstein-Barr virus in long-term asymptomatic kidney transplant recipients

Kidney transplant recipients (KTRs) abnormally replicate the Epstein Barr Virus (EBV). To better understand how long-term immunosuppression impacts the immune control of this EBV re-emergence, we systematically compared 10 clinically stable KTRs to 30 healthy controls (HCs). The EBV-specific T cell responses were determined in both groups by multiparameter flow cytometry with intra cellular cytokine staining (KTRs n = 10; HCs n = 15) and ELISpot-IFNγ assays (KTRs n = 7; HCs n = 7). The T/B/NK cell counts (KTRs n = 10; HCs n = 30) and the NK/T cell differentiation and activation phenotypes (KTRs n = 10; HCs n = 15/30) were also measured. We show that in KTRs, the Th1 effector CD4+ T cell responses against latent EBV proteins are weak (2/7 responders). Conversely, the frequencies total EBV-specific CD8+T cells are conserved in KTRs (n = 10) and span a wider range of EBNA-3A peptides (5/7responders) than in HCs (5/7responders). Those modifications of the EBV-specific T cell response were associated with a profound CD4+ T cell lymphopenia in KTRs compared to HCs, involving the naïve CD4+ T cell subset, and a persistent activation of highly-differentiated senescent CD8+ T cells. The proportion of total NK / CD8+ T cells expressing PD-1 was also increased in KTRs. Noteworthy, PD-1 expression on CD8+ T cells normalized with time after transplantation. In conclusion, we show modifications of the EBV-specific cellular immunity in long term transplant recipients. This may be the result of both persistent EBV antigenic stimulation and profound immunosuppression induced by anti-rejection treatments. These findings provide new insights into the immunopathology of EBV infection after renal transplantation.

Post-transplant lymphoproliferative disorders, Epstein-Barr virus infection, and disease in solid organ transplantation: Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

PTLD with the response-dependent sequential use of RIS, rituximab, and cytotoxic chemotherapy is recommended. Evidence gaps requiring future research and alternate treatment strategies including immunotherapy are highlighted.

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.

The Immune Response to Epstein Barr Virus and Implications for Posttransplant Lymphoproliferative Disorder

Posttransplant lymphoproliferative disorder (PTLD) is a serious complication in organ transplant recipients and is most often associated with the Epstein Barr virus (EBV). EBV is a common gammaherpes virus with tropism for B lymphocytes and infection in immunocompetent individuals is typically asymptomatic and benign. However, infection in immunocompromised or immunosuppressed individuals can result in malignant B cell lymphoproliferations, such as PTLD. EBV+ PTLD can arise after primary EBV infection, or because of reactivation of a prior infection, and represents a leading malignancy in the transplant population. The incidence of EBV+ PTLD is variable depending on the organ transplanted and whether the recipient has preexisting immunity to EBV but can be as high as 20%. It is generally accepted that impaired immune function due to immunosuppression is a primary cause of EBV+ PTLD. In this overview, we review the EBV life cycle and discuss our current understanding of the immune response to EBV in healthy, immunocompetent individuals, in transplant recipients, and in PTLD patients. We review the strategies that EBV uses to subvert and evade host immunity and discuss the implications for the development of EBV+ PTLD.

The "ABC" of Virus-Specific T Cell Immunity in Solid Organ Transplantation

Transplant patients are at increased risk of viral complications due to impaired control of viral replication, resulting from HLA mismatching between graft and host and the immunosuppression needed to avert alloimmune reactions. In the past decade, quantitative viral load measurements have become widely available to identify patients at risk and to inform treatment decisions with respect to immunosuppressive drugs and antiviral therapies. Because viral loads are viewed as the result of viral replication and virus-specific immune control, virus-specific T cell monitoring has been explored to optimize management of adenovirus, BK polyomavirus and cytomegalovirus ("ABC") in transplant patients. Although most studies are descriptive using different technologies, the overall results show that the quantity and quality of virus-specific T cells inversely correlate with viral replication, whereby strong cellular immune responses are associated with containment of viral replication. The key obstacles to the introduction of assays for virus-specific T cells into clinical practice is the definition of reliable cutoffs for clinical decision making, the poor negative predictive value of some assays, and the absence of interventional trials justifying changes of antiviral treatment or immunosuppression. More clinical research is needed using optimized assays and targets before standardization and commutability can be envisaged as achieved for viral load testing.

Malignancies after pediatric kidney transplantation: more than PTLD?

Post-transplant lymphoproliferative disease (PTLD) is the most frequent malignant complication of transplantation in childhood. Even with modern post-transplant immunosuppressive strategies, 1-2% of all kidney transplant recipients will develop PTLD within the first 5 years after transplantation, and the risk remains high even thereafter as long as immunosuppression is required. In addition to PTLD, adult kidney transplant recipients have an increased incidence of other immunosuppression-related malignancies, such as non-melanoma skin cancer or Kaposi's sarcoma. It is foreseeable that pediatric transplant recipients will face similar complications during their adult life. Not only immunosuppression but also other risk factors have been identified for some of these malignancies. Strategies addressing these risk factors during childhood may contribute to life-long cancer prevention. Furthermore, early recognition and regular screening may facilitate early diagnosis and treatment, thereby reducing transplant-related morbidity. In this review we focus on malignant complications after renal transplantation and discuss known risk factors. We also review current screening strategies for malignancies during post-transplant follow-up.

Posttransplant lymphoproliferative disease after pediatric solid organ transplantation

Patients after solid organ transplantation (SOT) carry a substantially increased risk to develop malignant lymphomas. This is in part due to the immunosuppression required to maintain the function of the organ graft. Depending on the transplanted organ, up to 15% of pediatric transplant recipients acquire posttransplant lymphoproliferative disease (PTLD), and eventually 20% of those succumb to the disease. Early diagnosis of PTLD is often hampered by the unspecific symptoms and the difficult differential diagnosis, which includes atypical infections as well as graft rejection. Treatment of PTLD is limited by the high vulnerability towards antineoplastic chemotherapy in transplanted children. However, new treatment strategies and especially the introduction of the monoclonal anti-CD20 antibody rituximab have dramatically improved outcomes of PTLD. This review discusses risk factors for the development of PTLD in children, summarizes current approaches to therapy, and gives an outlook on developing new treatment modalities like targeted therapy with virus-specific T cells. Finally, monitoring strategies are evaluated.