HLA class I associations with EBV+ post-transplant lymphoproliferative disorder

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.

Classic Hodgkin lymphoma post-transplant lymphoproliferative disorders (PTLD) are often preceded by discordant PTLD subtypes

Classic Hodgkin lymphoma (CHL) is the rarest post-transplant lymphoproliferative disorder (PTLD) subtype. Few cases of patients with metachronous discordant PTLD episodes including CHL-PTLD have been reported, but the incidence of and risk factors for this phenomenon are unknown. Patients with CHL-PTLD were identified from an institutional PTLD database. Of 13 patients identified with CHL-PTLD six (46%) had antecedent non-CHL-PTLD: three had polymorphic PTLD, two monomorphic PTLD, and one nondestructive PTLD. Patients with prior metachronous non-CHL-PTLD were younger at transplant and had a longer latency time to CHL-PTLD post-transplant. The prevalence of EBV seronegativity at transplant was high in both groups, but prolonged high-level EBV DNAemia only occurred in some with metachronous non-CHL-PTLD. In conclusion, patients with CHL-PTLD have metachronous non-CHL-PTLD diagnoses with discordant histology more commonly than previously recognized. Primary EBV infection with chronically elevated EBV viral loads may represent unique risk factors for CHL-PTLD following an initial non-CHL-PTLD event.

Association between HLA-A1 and -A2 types and Epstein-Barr virus status of post-transplant lymphoproliferative disorder

The susceptibility to Epstein-Barr virus (EBV)-related post-transplant lymphoproliferative disorder (PTLD) may be affected by the human leukocyte antigen (HLA) type. We investigated HLA-A and HLA-B allele frequencies, focusing on HLA-A1 and -A2, in a population-based case series of EBV + (n = 60) and EBV- (n = 44) PTLD after solid organ transplantation. The proportion of EBV + PTLD was highest in HLA-A1 homozygotes (100%), lower in carriers of HLA-A1/AX (79%), HLA-A1/A2 (55%), HLA-A2/AX (54%), and lowest in HLA-A2 homozygotes (37%). HLA-A1 type was overrepresented (22% versus 7%, p = 0.05) and HLA-A2 type underrepresented (57% versus 80%, p = 0.01) in patients with EBV + compared with EBV - PTLD. EBV + PTLD in HLA-A1 carriers developed almost exclusively in already EBV-seropositive individuals. EBV status of PTLD was not related to any other HLA-A or HLA-B type. Our findings suggest that HLA-A1 carriers may have an increased risk of EBV + PTLD due to a decreased ability to control the latent EBV infection.

Post-transplant lymphoproliferative disorders

Post-transplant lymphoproliferative disorders (PTLDs) are a group of conditions that involve uncontrolled proliferation of lymphoid cells as a consequence of extrinsic immunosuppression after organ or haematopoietic stem cell transplant. PTLDs show some similarities to classic lymphomas in the non-immunosuppressed general population. The oncogenic Epstein-Barr virus (EBV) is a key pathogenic driver in many early-onset cases, through multiple mechanisms. The incidence of PTLD varies with the type of transplant; a clear distinction should therefore be made between the conditions after solid organ transplant and after haematopoietic stem cell transplant. Recipient EBV seronegativity and the intensity of immunosuppression are among key risk factors. Symptoms and signs depend on the localization of the lymphoid masses. Diagnosis requires histopathology, although imaging techniques can provide additional supportive evidence. Pre-emptive intervention based on monitoring EBV levels in blood has emerged as the preferred strategy for PTLD prevention. Treatment of established disease includes reduction of immunosuppression and/or administration of rituximab (a B cell-specific antibody against CD20), chemotherapy and EBV-specific cytotoxic T cells. Despite these strategies, the mortality and morbidity remains considerable. Patient outcome is influenced by the severity of presentation, treatment-related complications and risk of allograft loss. New innovative treatment options hold promise for changing the outlook in the future.

HLA Associations and Risk of Posttransplant Lymphoproliferative Disorder in a Danish Population-Based Cohort

BACKGROUND

Posttransplant lymphoproliferative disorder (PTLD) is a feared complication to organ transplantation, associated with substantial morbidity and inferior survival. Risk factors for PTLD include T cell-depleting induction therapy and primary infection or reactivation of Epstein-Barr virus. Possible associations between certain HLA types and the risk of developing PTLD have been reported by other investigators; however, results are conflicting.

METHODS

We conducted a retrospective, population-based study on 4295 Danish solid organ transplant patients from the Scandiatransplant database. Having identified 93 PTLD patients in the cohort, we investigated the association of HLA types with PTLD, Epstein-Barr virus status and time to PTLD onset. The outcomes survival and PTLD were evaluated using Cox regression; mismatching, and the PTLD-specific mortality were evaluated in a competing risk analysis.

RESULTS

Risk of PTLD was associated with male sex (odds ratio, 1.70; 95% confidence interval, 1.07-2.71), and, in women, HLA-DR13 conferred an increased risk (odds ratio, 3.22; 95% confidence interval, 1.41-7.31). In multivariate analysis, HLA-B45 and HLA-DR13 remained independent predictive factors of PTLD. Mismatching in the B locus was associated with a reduced risk of PTLD (P < 0.001). Overall survival was poor after a PTLD diagnosis and was significantly worse than that in the remaining transplant cohort (P < 0.001).

CONCLUSIONS

Our data indicate risk-modifying HLA associations, which can be clinically useful after transplantation in personalized monitoring schemes. Given the strong linkage disequilibrium in the HLA region, the associations must be interpreted carefully. The large size, virtually complete ascertainment of cases and no loss to follow-up remain important strengths of the study.