Background: Management of pediatric post-transplantation lymphoproliferative disorder (PTLD) after hematopoietic stem cell (HSCT) and solid organ transplantation (SOT) is challenging.Aim: This study of 34 PTLD patients up to 19-years old diagnosed in Austria from 2000 to 2018 aimed at assessing initial characteristics, therapy, response, and outcome as well as prognostic markers of this rare pediatric disease.Methods and results: A retrospective data analysis was performed. Types of allografts were kidney (n = 12), liver (n = 7), heart (n = 5), hematopoietic stem cells (n = 4), lungs

Therapy of children with post‐transplantation lymphoproliferative disorder (PTLD) after hematopoietic stem cell (HSCT) and solid organ transplantation (SOT) can be challenging. In this retrospective study, we investigated PD‐L1 and PD1 expression in all PTLD categories of childhood and adolescence to see whether checkpoint inhibition with PD‐L1/PD1 inhibitors may serve as a therapy option. We included 21 patients aged 19 years or younger (at date of transplant) with PTLD following SOT or HSCT having adequate tumor samples available (n = 29). Using immunohistochemistry, we evaluated PD‐L1/PD1 expression on both tumor cells and cells of the microenvironment in all samples. Availability of consecutively matched tumor samples during 6 of 21 patients' disease courses also allowed an intra‐individual assessment of PD‐L1/PD1 expression. We observed lower PD‐L1 and higher PD1 expression in non‐destructive lesions, and higher PD‐L1 and lower PD1 expression in polymorphic and, in particular, in monomorphic PTLD, mostly diffuse large B‐cell lymphomas (DLBCL, n = 10/21). The amount of PD‐L1‐ and PD1‐positive cells changed in the opposite way in sequential biopsies of the same individual correlating well with the PTLD category. This is the first comprehensive pediatric study assessing PD‐L1 and PD1 expression on tumor cells and in the microenvironment of PTLD including not only monomorphic, but also non‐destructive early lesions. PD‐L1 expression of the tumor cells inversely correlated with PD1 expression in surrounding tissues, with the highest expression in DLBCL. Since PTLD can be therapeutically challenging, our results indicate a potential efficacy of checkpoint inhibitors if standard immune‐ and/or chemotherapy fail or are impossible. We therefore recommend routine staining of PD‐L1 and PD1 in all PTLD categories.

Summary Primary central nervous system (CNS) post‐transplant lymphoproliferative disorder (PTLD) in childhood is rare. Twenty‐five patients were retrieved from nine European Intergroup for Childhood Non‐Hodgkin’s Lymphoma and/or international Berlin–Frankfurt–Münster Study Group members. Types of allografts included kidney (n = 11), liver (n = 4), heart (n = 5), bowel (n = 1) and haematopoietic stem cells (n = 4). Eighteen were male, 16 ≥ 10 years old, 21 had monomorphic disease and 24 solid intracranial tumour masses. Four‐year event‐free and overall survival rates were 50% ± 10% and 74% ± 9% respectively. This report represents the largest paediatric series of CNS PTLD reported to date, showing favourable survival odds following systemic and intrathecal chemotherapy and rituximab administration.