EXPERIMENTAL AND CLINICAL TRANSPLANTATION

Key words : Biliary atresia, Burkitt lymphoma, Epstein-Barr virus, Glycogen storage disease, Progressive familial intrahepatic cholestasis

Solid-organ transplant (SOT) is an effective treatment modality for children with end-stage organ failure.¹ However, because the patients require lifelong immunosuppression to maintain graft health and prevent rejection, they are vulnerable to viral infections such as Epstein-Barr virus (EBV).² Posttransplant lymphoproliferative disorder (PTLD) represents a significant and potentially devastating complication following SOT; it is primarily associated with EBV and predominantly affects transplant recipients who are seronegative for EBV before transplant. The pivotal role of EBV in PTLD pathogenesis resides in the ability of EBV to transform and immortalize B cells, leading to uncontrolled proliferation, particularly in the immunosuppressed state associated with organ transplant.^3,4

Incidence rates of PTLD have noticeably increased in recent years, likely due to the rising frequency of SOT, increased clinical awareness, and advancements in diagnostic methodologies. Typically, PTLD presents within the first year after transplant, as solitary or multiple nodular lesions, with a preference for the transplanted organs and the reticuloendothelial system.⁵ The incidence of PTLD changes according to the type of transplanted organ. The highest incidence occurs in lung (6.5%-20%) and intestinal transplants (11.8%-17.2%), followed by heart (3.5%-13.2%), liver (2%-5.7%), and kidney (1.2%-6.9%) transplants.^6-11 The involvement of anatomic sites is a combination of the degree of immunosuppression and lymphoid tissue load within the transplanted organ.5 Risk factors of PTLD include EBV-naive recipients with EBV-seropositive donors, younger age at SOT, aggressive and high trough levels of immunosuppression (especially with anti-thymocyte globulin and tacrolimus), and being within the first year after SOT.¹²

Several determinants influence PTLD outcomes, including the nature of PTLD (T or natural killer cell PTLD, EBV-negative PTLD), the presence of monoclonal disease, and the patient’s performance status according to the World Health Organization or Eastern Cooperative Oncology Group classification.¹³ The impact of lesion localization on survival remains inconclusive, except for the central nervous system and multisite PTLD.¹⁴

We systematically reviewed the evolving trends in PTLD incidence rates, the anatomic sites implicated at presentation, and the intricate interplay between these sites and relevant clinical outcomes. Our study focused on the clinical features and treatment outcomes of pediatric patients with PTLD, with emphasis on patient survival and associated clinical ramifications.

Materials and Methods

We conducted a retrospective review of medical records from pediatric SOT recipients of liver transplant (LT) and kidney transplant (KT) at the Baskent University Ankara Hospital Organ Transplant Center between January 1, 2017, and January 1, 2024. The study was approved by the Institutional Review Board of our center (No. KA24-63). Clinical suspicion of PTLD arose when SOT recipients exhibited persistent lymphadenopathy or tumorous lesions that were subsequently confirmed through pathology examination and classified according to the World Health Organization system. Patients were categorized into malignant and benign groups based on pathology findings. Early PTLD was defined as occurrence within the first year after transplant. The association with EBV was determined through in situ hybridization of EBV-encoded RNA in tissue specimens. The EBV viral loads in patients were quantified via real-time polymerase chain reaction (PCR) targeting EBV DNA in peripheral blood samples. Patient characteristics were reviewed, including clinical features at transplant (underlying disease, transplanted organ, age at transplant, and EBV serology status of donor and recipient), posttransplant history (rejection episodes and immunosuppression treatment), and PTLD specifics (clinical presentation, histopathology diagnosis, EBV detection, treatment, and outcome assessment).

The immunosuppression protocol of our center was as follows: 10 mg/kg prednisolone was given at the operation theater, then tapered to 1 mg/kg, and gradually decreased over 3 to 6 months. Mycophenolate mofetil was administered to all patients at a dose of 1200 mg/m2, and patients were weaned from the drug in 3 months. Tacrolimus was the main immunosuppressive agent, and the levels were targeted at 10 to12 ng/mL immediately after surgery, 6 to 8 ng/mL during the first month, and 4 to 6 ng/mL during the first year posttransplant.

Causes of death were evaluated by the researchers based on the review of medical reports. The PTLD-related mortality was defined as death for which PTLD was the etiological cause of pathophysiology, including infection due to rituximab immunosuppression or chemotherapy (at the time of treatment of PTLD), oncological complications such as tumor compression to vital organs, bleeding, or organ rejection due to a reduction in immunosuppression (RIS). Death from sepsis that was deemed unrelated to PTLD chemotherapy or organ failure while PTLD was in remission was considered a death unrelated to PTLD.

We performed statistical analysis using SPSS software (version 25.0).

During the study period, 10 patients (9 LT, 1 KT; 3 male and 7 female) were diagnosed with PTLD, yielding an incidence of 8.7% among pediatric LT recipients (9 of 103 recipients). The mean age at PTLD diagnosis was 46.4 months (range 10-120 mo, SD 5 mo), and the mean age at transplant was 21.5 months (range 6-84 mo, SD 0.5 mo). The mean time from transplant to PTLD diagnosis was 21.2 months (range 2-60 mo, SD 6.5 mo). The most common underlying diagnoses were biliary atresia (5 cases), progressive familial intrahepatic cholestasis type 2 (2 cases), glycogen storage disease type 1a (1 case), Crigler-Najjar syndrome (1 case), and renal artery stenosis (1 case). Before transplant, 7 of 10 recipients were EBV-naive. Tacrolimus alone was the immunosuppression treatment at PTLD diagnosis in 7 of 10 patients, and the remaining 3 patients received tacrolimus plus mycophenolate mofetil. Tacrolimus was switched to everolimus in 4 of 10 patients and to sirolimus in the 6 remaining patients. Early PTLD was diagnosed in 4 of 10 patients.

Common symptoms at PTLD diagnosis included fever, lymphadenopathy, hepatosplenomegaly, dyspnea, and diarrhea. The most commonly involved lymphadenopathy sites were mediastinal, intra-abdominal, and cervical regions; 90% of biopsies revealed early polymorphic PTLD, according to positive results for CD20 and EBV-encoded small RNA. One patient, admitted after KT, was diagnosed with Burkitt lymphoma of the abdomen. The results of the EBV PCR tests were positive in all patients at diagnosis. Subsequently, 7 of the 10 patients were treated with rituximab (375 mg/m²/wk for 4 wk). Of the 3 remaining patients, who did not receive rituximab, 2 were treated with RIS plus weekly intravenous immunoglobulin (IVIG) therapy and 1 was treated with chemotherapy for non-Hodgkin lymphoma based on the NHL Berlin-Frankfurt-Münster 90 protocols (NHL-BFM-90). For 2 of the 7 rituximab-treated patients, IVIG therapy was given as secondary immunoprophylaxis for 6 to 12 months after rituximab therapy. All patients achieved remission for PTLD. There was no graft loss due to PTLD therapy. The mean time from transplant until the last follow-up or death was 22.9 months (range 3-60 mo, SD 2.5 mo). The details of clinical features, therapy results, and outcomes of the patients are given in Table 1.

Mortality occurred in 2 patients due to causes unrelated to PTLD (hepatic insufficiency in patient 4 and sepsis in patient 7).

We evaluated 10 PTLD cases in pediatric SOT recipients over the last 7 years. In our study, the total incidence of PTLD after LT was 8.7% which was consistent with the literature.^5,10,12 Generally, LT recipients are younger than KT recipients at the time of development of PTLD. We considered that this age difference may be due to the common cause of liver insufficiency, ie, biliary atresia, which could lead to an earlier discovery of PFIC in LT cases versus KT cases. Incidence of PTLD is higher in LT recipients, and LT recipients tend to be diagnosed at an early age, so the combination of LT (vs KT) and younger age (vs older age) is a known risk factor for PTLD. The clinical spectrum of our PTLD cases was similar to the details in previously published reports, ie, the median age at the time of PTLD was around 4 years (46.4 mo; range 10-120 mo, SD 5 mo); however, the time from transplant to PTLD diagnosis was longer than reported in the literature.^12,15,16 Most transplant recipients who develop PTLD are diagnosed during the first year after transplant; in our cohort, the mean time from transplant to PTLD diagnosis was 21.2 months.

Initial symptoms of PTLD were most often fever (100%), followed by lymphadenopathy in cervical, intra-abdominal, and axillary regions (60%), and gastrointestinal symptoms such as diarrhea (20%). Only 2 patients presented with mediastinal mass and dyspnea. In a study by Jeong and colleagues, most patients with PTLD were admitted because of fever (55.6%) or gastrointestinal complaints (61.1%).¹⁷ Among episodes of PTLD, lymph nodes and gastrointestinal sites accounted for most cases, and this was consistent with the previous reports from our institution.^18,19 The most commonly involved lymphadenopathy sites were mediastinal, intra-abdominal, and cervical regions.

We observed that 70% of recipients were EBV-naive, whereas 60% of donors were seropositive for EBV before transplant, as in compliance with the previous reports. We think the young age in LT recipients has caused a tendency towards being seronegative for EBV and in turn, caused PTLD. All of the patients had positive results for EBV PCR tests at the time of PTLD diagnosis. The evaluation of the hospital records of the patients revealed that EBV PCR positivity preceded the symptomatic EBV disease; however, unfortunately there is not an established cutoff for EBV PCR positivity to guide the treatment.⁶ The RIS regimen was applied to all patients; however, they progressed to clinical EBV disease and PTLD. A widely acceptable cutoff for preemptive treatment of EBV infection in SOT patients could be established in further studies.

With a single exception (patient 8, with PTLD-Burkitt lymphoma), our patients all were at the stage known as early polymorphic PTLD, with positive results for CD20 and EBV-encoded small RNA. This observation was in agreement with previously published data that showed only 10% of the PTLD cases are of T-cell origin.^5,20

All 10 of our patients were on tacrolimus therapy: 7 patients were on tacrolimus alone, and 3 patients were on tacrolimus plus mycophenolate mofetil. Despite the fact that we could not reach the mean tacrolimus trough levels at the development time of PTLD, the reality of the difficulty to maintain stabilized levels of tacrolimus in children may have caused a tendency toward PTLD.

We observed that ganciclovir, acyclovir, and valganciclovir were administered as antiviral therapy to 50%, 20%, and 10% of our patients, respectively. Acyclovir and ganciclovir inhibit EBV lytic replication but do not affect latent infection.²¹ However, many centers use antiviral prophylaxis in high-risk patients; a recent meta-analysis has suggested that antiviral use both prophylactically and preemptively in EBV-naive patients did not affect the incidence of PTLD.²²

For more than 30 years, RIS has been a common clinical approach for the initial treatment of PTLD; in accordance with this established trend, we observed that RIS was applied in all of the patients in our study; however, only 1 patient (patient 5) benefited from this intervention and did not need any further treatment.²³ Seven of our patients received rituximab (375 mg/m²/wk: for 4 wk in 5 patients and 2 wk in 2 patients). The PTLD of all patients who were treated with rituximab was resolved with a follow-up period of 3 to 60 months. The only patient (patient 8) who was diagnosed with the monomorphic form, ie, PTLD-Burkitt lymphoma, was treated with NHL-BFM-90 chemotherapy and remains in remission after 36 months.

In previous studies, patients with early PTLD have been treated with IVIG, either alone or in combination with antivirals.²⁴ However, the prophylactic benefit of IVIG on PTLD remains uncertain. Two prospective trials in patients given prophylactic IVIG did not find any effect on EBV disease, incidence of PTLD, and EBV viral load.^25,26 In another study, KT registry data revealed a significant reduction in PTLD incidence in transplant recipients treated with prophylactic IVIG, although this protective effect did not go beyond the first year after transplant.²⁷ In 2 of our patients (patient 3 and patient 6), despite remission with rituximab, we extended IVIG therapy after rituximab because these 2 patients experienced frequent bacterial infections and EBV PCR positivity with increasing titers. After initiation of IVIG therapy every 21 days, the EBV PCR results from these 2 patients became negative, and the patients required no additional hospitalization due to infection. After initiation of secondary prophylaxis with IVIG, these 2 patients were free of PTLD and infections at 12 months (patient 3) and 18 months (patient 6). Further studies are required to clarify whether patients benefit from primary or secondary prophylaxis with IVIG.

A highlight of our retrospective study is that patients diagnosed early in the disease course of PTLD exhibited milder manifestations versus the patients diagnosed with Burkitt lymphoma. Notably, all patients achieved remission, with rituximab coupled with RIS as the effective treatment in cases of early polymorphic PTLD. Although PTLD was previously considered a fatal complication of SOT, outcomes have improved, and active EBV infection monitoring may further reduce this complication in pediatric SOT recipients. Despite these advances, we urge clinicians to remain vigilant to diagnose PTLD at early stages.

Volume: 22 Issue: 10 October 2024 - Supplement - 5

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