RELATIONSHIP BETWEEN CD8+ T-CELL PHENOTYPE AND FUNCTION, EPSTEIN-BARR VIRUS LOAD, AND CLINICAL OUTCOME IN PEDIATRIC RENAL TRANSPLANT RECIPIENTS: A PROSPECTIVE STUDY1

Transplantation for congenital heart disease is associated with an increased risk of Epstein-Barr virus-related post-transplant lymphoproliferative disorder in children

BACKGROUND

Children undergoing heart transplant are at higher risk of developing post-transplant lymphoproliferative disorder (PTLD) than other solid organ recipients. The factors driving that risk are unclear. This study investigated risk factors for PTLD in children transplanted at 1 of 2 United Kingdom pediatric cardiac transplantation centers.

METHODS

All children (<18 years, n = 200) transplanted at our institution over a 16-year period were analyzed. Freedom from PTLD was assessed using the Kaplan-Meier method and Cox proportional regression.

RESULTS

PTLD occurred in 17 of 71 children transplanted for congenital heart disease (CHD) and 18 of 129 transplanted for acquired cardiomyopathy (ACM). The cumulative incidence of all PTLD was 21.1% at 5 years after transplant. Median time from transplant to PTLD was 2.9 years (interquartile range: 0.9-4.6). Negative Epstein-Barr virus (EBV) serostatus pre-transplant (adjusted hazard ratio [HR]: 2.7, 95% CI: 1.3-5.6, p = 0.01) and underlying CHD (adjusted HR: 3.2, 95% CI: 1.4-7.4, p = 0.007) were independently associated with higher risk of PTLD. Age at thymectomy was significantly different between children with CHD and ACM (0.4 vs 5.5 years, p < 0.01). Median CD4⁺ and CD8⁺ T lymphocyte counts at 2 years after transplant were significantly lower in children transplanted for CHD vs ACM (CD4⁺: 391/µl vs 644/µl, p = 0.01; CD8⁺: 382/µl vs 500/µl, p = 0.01). At 5 years after transplant, those differences persisted among patients who developed PTLD (CD4⁺, 430/µl vs 963/µl, p < 0.01 and CD8⁺, 367/µl vs 765/µl, p < 0.01).

CONCLUSION

Underlying CHD is an independent risk factor for PTLD and is associated with a younger age at thymectomy. A persistent association with altered T lymphocyte subsets may contribute to the impaired response to primary EBV infection and increase the risk of PTLD.

Pediatric renal transplantation: A retrospective single-center study on epidemiology and morbidity due to EBV

Pediatric R-Tx patients are at high risk of developing EBV primary infection. Although high DNA replication is a risk factor for PTLD, some patients develop PTLD with low viral load. In this retrospective single-center study including all pediatric patients having received R-Tx (2003-2012 period), we aimed to identify risk factors for uncontrolled reactions to EBV (defined as the presence of a viral load >10 000 copies/mL or PTLD). A Cox proportional hazard model was performed. A total of 117 patients underwent R-Tx at a mean age of 9.7 ± 5.3 years, 46 of them being seronegative for EBV at the time of R-Tx. During follow-up, 54 patients displayed positive EBV viral load, 22 of whom presenting with primary infection. An uncontrolled reaction to EBV was observed in 24 patients, whilst 4 patients developed PTLD. Univariate and multivariate analyses suggested the following risk factors for an uncontrolled reaction: age below 5 years, graft from a deceased donor, ≥5 HLA mismatches, EBV-seronegative status at the time of R-Tx, and a secondary post-Tx loss of anti-EBNA. Monitoring anti-EBNA after R-Tx may contribute to the early identification of patients at risk for uncontrolled reaction.

Risk of posttransplant lymphoproliferative disorder associated with use of belatacept

Purpose

Published evidence on a rare but serious malignancy associated with use of the first biological agent approved for long-term maintenance immunosuppression in renal transplant recipients is reviewed.

Summary

Belatacept (Nulojix, Bristol-Myers Squibb) is approved by the Food and Drug Administration for use in combination therapy to prevent renal graft rejection in patients who are Epstein-Barr virus seropositive. Belatacept appears to offer some advantages over calcineurin inhibitor-based regimens (e.g., no need for therapeutic drug monitoring), but its use poses a risk of posttransplant lymphoproliferative disorder (PTLD), a rapidly progressing and often lethal malignancy. The efficacy and safety of more-intensive and less-intensive belatacept regimens were established in two Phase III clinical trials, which found that rates of patient and graft survival were comparable to those in cyclosporine users; belatacept was shown to be superior in preserving renal function. The occurrence of PTLD, particularly PTLD involving the central nervous system, in 0–4% of belatacept-treated patients in clinical trials prompted postmarketing initiatives: (1) implementation of a risk evaluation and mitigation strategy (REMS) program to help ensure the safe and proper use of belatacept, (2) longitudinal studies to better define the risks and outcomes of belatacept therapy, and (3) a manufacturer-created patient registry to track belatacept use and encourage voluntary reporting of associated adverse events.

Conclusion

Appropriate patient selection and adherence to REMS requirements, including patient counseling and facilitation of registry enrollment, are essential in mitigating the increased risk of PTLD associated with belatacept therapy.

Epidemiology and morbidity of Epstein-Barr virus infection in pediatric renal transplant recipients: a multicenter, prospective study

BACKGROUND

The epidemiology and morbidity of Epstein-Barr virus (EBV) infection in pediatric renal transplant recipients have been characterized insufficiently.

METHODS

In a prospective, multicenter study among 106 pediatric kidney allograft recipients aged 11.4 ± 5.9 years, we investigated the epidemiology of EBV infection and the relationship between EBV load, EBV serology, and EBV-related morbidity (posttransplant lymphoproliferative disease [PTLD] or symptomatic EBV infection, defined as flu-like symptoms or infectious mononucleosis).

RESULTS

EBV primary infection occurred in 27 of 43 (63%) seronegative patients and reactivation/reinfection in 28 of 63 (44%) seropositive patients. There was no association between the degree or duration of EBV load and EBV-related morbidity: The vast majority (17 of 18 [94%]) of patients with a high, persistent EBV load remained PTLD-free throughout a follow-up of 5.0 ± 1.3 years, while 2 of 3 (66%) patients with EBV-related PTLD exhibited only a low EBV load beforehand. Eight of 18 (44%) patients with a high, persistent EBV load remained asymptomatic during a follow-up of 5.3 ± 2.9 years. Multivariate analysis identified the EBV high-risk (D(+)/R(-)) serostatus (odds ratio [OR], 7.07; P < .05), the presence of human leukocyte antigen (HLA)-DR7 (OR, 5.65; P < .05), and the intensity of the immunosuppressive therapy (OR, 1.53; P < .01) as independent risk factors for the development of a symptomatic EBV infection.

CONCLUSIONS

Presence of EBV high-risk seroconstellation, HLA-DR7, and intensity of immunosuppressive therapy are significant risk factors for a symptomatic EBV infection, whereas there is no close association between the degree or duration of EBV load and EBV-related morbidity. Clinical Trials Registration. NCT00963248.

[Outcomes of pediatric renal transplantation in France]

Significant progress has been observed in pediatric renal transplantation over the last 20 years, leading to an increase in graft and patient survival. Mortality is low and is mainly due to infections, neoplasias and complications related to the initial disease. Graft survival is 67% at 10 years. Factors which influence graft survival are: donor type (results are better with a live donor), donor age, recipient age (with 2 periods at risk:<2 years old and teenagers), HLA incompatibilities, and recurrence of the initial disease. Chronic allograft nephropathy (CAN) is the major cause of late graft loss. Poor compliance, especially in teenagers, may lead to late rejections and graft loss. Calcineurin inhibitors nephrotoxicity is in part responsible for the development of CAN, thus treatments and the role of mTOR inhibitors will probably evolve. These different factors are discussed in this article.

Presence of monoclonal T-cell populations in B-cell post-transplant lymphoproliferative disorders

As has been previously shown, the lack of immune surveillance plays a major role in the unchecked proliferation of Epstein-Barr virus (EBV)-infected B cells in the pathogenesis of B-cell post-transplant lymphoproliferative disorders. We hypothesised that the lack of immune surveillance should possibly also affect T cells, and this should lead to subsequent emergence of T-cell clones. The presence of both B- and T-cell clones in post-transplant lymphoproliferative disorders samples has rarely been demonstrated in the past. We systematically evaluated 26 B-cell post-transplant lymphoproliferative disorder, 23 human immune deficiency virus-associated B-cell lymphoma and 10 immune-competent diffuse large B-cell lymphoma samples for B- and T-cell clonality (polymerase chain reaction and heteroduplex analysis using BIOMED-2 protocol), T-cell subsets (immunohistochemistry) and EBV association (in situ hybridisation using EBER). One-half of B-cell post-transplant lymphoproliferative disorders showed evidence of monoclonal T-cell expansion, and among the T cells present in the tissue samples, CD8-positive cells predominated. Although 9/13 (69%) B-cell post-transplant lymphoproliferative disorders with the presence of monoclonal T-cell population had a CD4:CD8 ratio of ≤0.4, 0/13 of the cases without monoclonal T-cell expansion had a ratio ≤0.4 (P = 0.002). Only 2/26 (8%) demonstrated significant cytological atypia in the CD3/CD8-positive cells. There was no association between EBV and presence of T-cell clones. T-cell clones were not identified in lymphomas other than B-cell post-transplant lymphoproliferative disorders. Among 53.8% cases of EBV-positive B-cell post-transplant lymphoproliferative disorders with associated clonal expansion of T-cells tested, none had EBV-positive T cells. We conclude that half of B-cell post-transplant lymphoproliferative disorders are associated with clonal expansion of CD8-positive T cells, most of which do not amount to the coexistence of a T-cell post-transplant lymphoproliferative disorders.

Predictors of outcome in post-transplant lymphoproliferative disorder: an evaluation of tumor infiltrating lymphocytes in the context of clinical factors

We hypothesized that the number of tumor infiltrating cytotoxic T-cells (CTCs) and regulatory T-cells (Tregs), shown to have prognostic value in other lymphoproliferative disorders, could predict survival in post-transplant lymphoproliferative disorder (PTLD). Sixty-two patients were diagnosed with PTLD between 1987 and 2007, with 44 cases representing monomorphic B-cell PTLDs with diffuse aggressive morphologic features. Of these 44 cases, 31 had sufficient tissue for further study. On univariate analysis, high tumor infiltrating CD3(+) T-cell (> or =550/10 hpf) and TIA-1(+) CTC (> or =300/10 hpf) counts were associated with favorable overall survival (OS), PTLD-specific survival (PTLD-SS), and progression-free survival (PFS) while Treg counts were not predictive of outcome. However, on multivariate analysis, clinical factors were the most powerful predictor of PTLD outcome (performance status and CHOP as first line therapy for OS; performance status and number of extranodal sites for both PTLD-SS and PFS).

Post-transplant lymphoproliferative disorders: role of viral infection, genetic lesions and antigen stimulation in the pathogenesis of the disease

Post-transplant lymphoproliferative disorders (PTLD) are a life-threatening complication of solid organ transplantation or, more rarely, hematopoietic stem cell transplantation. The majority of PTLD is of B-cell origin and associated with Epstein–Barr virus (EBV) infection. PTLD generally display involvement of extranodal sites, aggressive histology and aggressive clinical behavior. The molecular pathogenesis of PTLD involves infection by oncogenic viruses, namely EBV, as well as genetic or epigenetic alterations of several cellular genes. At variance with lymphoma arising in immunocompetent hosts, whose genome is relatively stable, a fraction of PTLD are characterized by microsatellite instability as a consequence of defects in the DNA mismatch repair mechanism. Apart from microsatellite instability, molecular alterations of cellular genes recognized in PTLD include alterations of cMYC, BCL6, TP53, DNA hypermethylation, and aberrant somatic hypermutation of protooncogenes. The occurrence of IGV mutations in the overwhelming majority of PTLD documents that malignant transformation targets germinal centre (GC) B-cells and their descendants both in EBV–positive and EBV–negative cases. Analysis of phenotypic markers of B-cell histogenesis, namely BCL6, MUM1 and CD138, allows further distinction of PTLD histogenetic categories. PTLD expressing the BCL6+/MUM1+/-/CD138− profile reflect B-cells actively experiencing the GC reaction, and comprise diffuse large B-cell lymphoma (DLBCL) centroblastic and Burkitt lymphoma. PTLD expressing the BCL6−/MUM1+/CD138− phenotype putatively derive from B-cells that have concluded the GC reaction, and comprise the majority of polymorphic PTLD and a fraction of DLBCL immunoblastic. A third group of PTLD is reminiscent of post-GC and preterminally differentiated B-cells that show the BCL6−/MUM1+/CD138+ phenotype, and are morphologically represented by either polymorphic PTLD or DLBCL immunoblastic.

Significance of Epstein-Barr virus (EBV) load and Interleukin-10 in post-transplant lymphoproliferative disorders

The complex relationship between EBV, IL-10 and lymphomagenesis has been widely investigated and several studies have highlighted the diagnostic value of EBV DNA copies and serum IL-10, that may be considered as tumor markers. Notwithstanding the great number of data published in the last few years on the behavior of EBV DNA copies in the peripheral blood of transplanted patients, a threshold value significant for impending or overt post-transplant lymphoproliferative disorder (PTLD) has not yet been defined. Too many factors, both technical and clinicopathological, may affect the results of clinical studies, making their comparison difficult. On the contrary, although the role of IL-10 in PTLDs has been well documented, a sufficient number of studies exploring sensitivity and specificity of serum IL-10 measurement is lacking. The aim of this review is to summarise data on EBV load quantification and serum IL-10 detection in transplanted patients, providing clinicians with wide and useful information in order to improve bedside management of transplanted patients with regard to PTLDs occurrence and treatment.

Monitoring of Epstein-Barr virus load and antibody in pediatric renal transplant patients

BACKGROUND

Epstein-Barr virus (EBV) infection can lead to life-threatening post-transplant lymphoproliferative disorder (PTLD). The aim of the present study was to establish EBV monitoring methods to prevent PTLD.

METHODS

EBV-DNA load was investigated, using real-time polymerase chain reaction (PCR) and anti-EBV antibody titers, in peripheral blood mononuclear cells of 21 renal transplant patients (seven recipients who were EBV-seronegative, R[-]; 14 who were EBV-seropositive, R[+]) before grafting. The mean age at entry and the mean follow-up period was 7.8 years of age (range, 3.3-12.0 years) and 1.8 years (range, 0.4-4.0 years), respectively, in the R(-) group, and 12.5 years of age (range, 3.9-17.7 years) and 3.8 years (range, 0.8-8.2 years) in the R(+) group, respectively.

RESULTS

The mean maximum load of the EBV genome was 1071 copies/microg DNA (range, 106-20700 copies/microg DNA) in the R(-) group, and 61 copies/microg DNA (range, <50-552 copies/microg DNA) in the R(+) group. During follow up no patient in the R(+) group had any noticeable symptoms that could be related to EBV, but three recipients in the R(-) group developed EBV-related symptoms including adenoid hypertrophy, cervical lymphadenopathy, and PTLD (B cell lymphoma), in one patient each. In the R(-) group the first leukocyte-associated viremia was detected at 30-180 days, and seroconversion at 43-266 days after transplantation.

CONCLUSIONS

Viral DNA detection using PCR is a useful tool for EBV surveillance, but the maximum EBV load was not markedly elevated (2474 copies/microg DNA) in a patient with PTLD. Therefore, EBV surveillance using only monitoring of EBV load in peripheral leukocyte may be insufficient. Histology may therefore be necessary to accurately diagnose PTLD.

Quantitative analysis of EBV-specific CD4/CD8 T cell numbers, absolute CD4/CD8 T cell numbers and EBV load in solid organ transplant recipients with PLTD

Post transplant lymphoproliferative disease (PTLD) in solid organ transplant (SOT) recipients is assumed to be the result of impaired Epstein-Barr Virus (EBV)-specific cellular immunity. We analyzed the absolute CD4 and CD8 T cell counts as well as the EBV-specific CD4 and CD8 T cell responses in relation to EBV load in SOT recipients with PTLD. A prospective, single center study was initiated and 10 immunosuppressed patients with diagnosis of PTLD were analyzed and compared to 3 patients without PTLD (2 SOT recipients with EBV-reactivation, 1 patient with Infectious Mononucleosis) and 6 healthy EBV positive controls. EBV-specific CD8 T cells were enumerated using HLA class I tetramers and the IFN-gamma cytokine secretion assay. EBNA1-specific CD4 T cells were analyzed after protein stimulation and EBV load was quantified by real-time PCR. Absolute CD8 T cell counts were highly variable in all 19 cases analyzed. In contrast, the absolute EBV-specific CD8 T cell count was found to be low in 7/9 patients with PTLD (<5/microl whole blood). These frequencies were similar to absolute EBV-specific CD8 T cell numbers observed in healthy EBV positive donors, but much lower compared to patients with EBV reactivation but no PTLD. Absolute CD4 T cell counts were significantly lower in PTLD patients (mean: 336/microl+/-161 vs. controls 1008/microl+/-424, p=0.0001), with EBNA1-specific CD4 T cell responses being also low, but highly variable. Moreover, low absolute CD4 T cell counts (<230/microl) were associated with an elevated EBV load (>1000 copies/microg DNA). We conclude that SOT recipients with PTLD have an inadequate functional EBV-specific T cell response. Our data suggest that the frequency and function of circulating EBV-specific CD8 T cells are dependent on absolute CD4 T cell counts. Further studies are needed to verify if a low absolute CD4 T cell count presents a risk factor for the development of PTLD in SOT recipients.

Review of Epstein–Barr virus and post-transplant lymphoproliferative disorder post-solid organ transplantation (Review Article)

Post-transplant lymphoproliferative disorder (PTLD) following solid organ transplantation is an important form of post-transplant malignancy. PTLD is typically associated with Epstein-Barr virus (EBV) and occurs in the setting of profound immunosuppression resulting in a deficiency of EBV-specific cytotoxic T lymphocytes (CTL). Predisposing factors include EBV mismatch between donor and recipient, use of immunosuppression especially T-cell depletive therapies and genetic predisposition of recipients. The standard approach has been to reduce immunosuppression but is often insufficient to induce tumour regression. Further understanding of the immunobiology of PTLD has resulted in improved monitoring techniques (including EBV viral load determined by polymerase chain reaction) and newer treatment options. Recent work has highlighted a potential role for dendritic cells in both the pathogenesis and treatment of PTLD. Current treatment modalities include adoptive immunotherapy using ex vivo generated autologous EBV-specific CTL or allogeneic CTL, cytokine therapies, antiviral agents, and more recently, rituximab and dendritic-cell based therapies. This review focuses on the developments and progress in the pathogenesis, diagnosis and treatment of PTLD.

Post-transplant lymphoproliferative disorders: molecular basis of disease histogenesis and pathogenesis

Post-transplant lymphoproliferative disorders (PTLD) represent a serious complication of solid organ and allogeneic bone marrow transplantation. PTLD generally display B-cell lineage derivation, involvement of extranodal sites, aggressive histology and clinical behaviour, and frequent association with EBV infection. The occurrence of IgV mutations in the overwhelming majority of PTLD documents that malignant transformation targets germinal centre (GC) B-cells and their descendants both in EBV-positive and EBV-negative cases. Analysis of phenotypic markers of B-cell histogenesis, namely BCL6, MUM-1 and CD138, allows further distinction of PTLD histogenetic categories. PTLD expressing the BCL6(+)/MUM1(+/-)/CD138(-) profile reflect B-cells actively experiencing the GC reaction and comprise diffuse large B-cell lymphoma (DLBCL) centroblastic and Burkitt lymphoma. PTLD expressing the BCL6(-)/MUM1(+)/CD138(-) phenotype putatively derive from B-cells that have concluded the GC reaction and comprise the majority of polymorphic PTLD and a fraction of DLBCL. A third group of PTLD is reminiscent of post-GC and pre- terminally differentiated B-cells that show the BCL6(-)/MUM1(+)/CD138(+) phenotype and are morphologically represented by either polymorphic PTLD or DLBCL immunoblastic. The molecular pathogenesis of PTLD involves infection by oncogenic viruses, namely Epstein-Barr virus, as well as genetic or epigenetic alterations of several cellular genes. At variance with lymphoma arising in immunocompetent hosts, whose genome is relatively stable, a fraction of PTLD are characterized by microsatellite instability as a consequence of defects in the DNA mismatch repair mechanism. Apart from microsatellite instability, molecular alterations of cellular genes recognized in PTLD include alterations of c-MYC, BCL-6, p53, DNA hypermethylation, and aberrant somatic hypermutation of proto-oncogenes.

EBV-specific memory CD8+ T cell phenotype and function in stable solid organ transplant patients

Immune responses to EBV in immunosuppressed (IS) solid organ transplant (SOTx) recipients have not been well characterized. Here we evaluate the phenotype and function of EBV-specific CD8+ T cells in peripheral blood isolated from "stable" IS SOTx recipients. The EBV-specific CD8+ T cell memory subset distribution in the peripheral blood of patients was examined by flow cytometric analysis using HLA-A2 tetramers incorporating BMLF1 (lytic), and LMP2 and EBNA3A (latent)-derived peptides, in conjunction with mAbs against the CD45RO, CD45RA, and CD62L markers. The ability of CD8+ T cells to produce IFN-gamma in response to the same EBV-derived peptides was measured by ELISPOT assay. Patients and healthy normal donors exhibited similar anti-EBV CD8+ T cell frequencies and specificities against the EBV epitopes evaluated. When compared to healthy normal donors, an overall significant expansion of the CD8+ T cell "effector memory" (CD45RO+/CD62L-) pool, including that of EBV "latent" (LMP2 and EBNA3A)-specific CD8+ T cells was detected in IS SOTx patients. However, the patients' EBV-specific CD8+ T cells showed decreased IFN-gamma production to the EBV-peptide stimulation. These results indicate that the impairment of EBV-specific CD8+ T cell activity is not due to clonal depletion, but is mainly due to impaired functional activation.

Third dose of basiliximab in pediatric renal transplantation

Antibody induction therapy is frequently used in pediatric renal transplantation to reduce risk of early rejection. We previously reported lower rates of human herpes virus type 6 (HHV-6) reactivation in patients receiving monoclonal antibody induction with basiliximab, compared to patients receiving antithymocyte globulin/antilymphocyte globulin treatment. Subclinical rejection events were still present in many patients in the first 6 months after transplantation. This prompted a third dose of basiliximab to be administered at day 21 in addition to the standard two doses given immediately prior to transplantation and on day 4. No significant reduction of subclinical rejections was noted in the 11 patients receiving triple dosing of basiliximab. Two patients developed an allergic reaction responsive to intravenous fluids, steroids, and antihistamines with full resolution within 30 minutes of administration. There was no increase in de novo infection or reactivation of HHV-6 or Epstein-Barr virus in this group compared to patients receiving two doses of basiliximab. The goal of reduction of early subclinical rejection events was not achieved with the third dosing of basiliximab in this initial group of pediatric renal transplant patients. However, 63.6% of patients receiving triple basiliximab remained free of clinical and/or subclinical rejection for the first 6 months posttransplant compared to only 36.4% remaining rejection-free for the same interval in the group who received the conventional two doses of basiliximab.