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

Abstract

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.

Natural Killer Cells in Post-Transplant Lymphoproliferative Disorders

“…While most adult transplant recipients have encountered EBV before transplantation, pediatric transplant recipients are less likely to and therefore more frequently develop primary EBV primary infection after transplantation. A recent study by our team observed that the NK cells of adult PTLD patients overexpress the HLA-DR activation marker, with the highest levels observed in patients who acquired primary EBV infection post-transplant [32]. In that same study, NK cell activation was associated with high EBV loads and seemed to cause NK cell apoptosis, as those patients also presented with high proportions of IFN-γ-producing NK cells, PD-1 overexpression and profound NK cell lymphopenia [32] (Figure 1).…”

“…A recent study by our team observed that the NK cells of adult PTLD patients overexpress the HLA-DR activation marker, with the highest levels observed in patients who acquired primary EBV infection post-transplant [32]. In that same study, NK cell activation was associated with high EBV loads and seemed to cause NK cell apoptosis, as those patients also presented with high proportions of IFN-γ-producing NK cells, PD-1 overexpression and profound NK cell lymphopenia [32] (Figure 1). Altogether, the different alterations of NK cells that have been described at EBV-positive PTLD diagnosis seem to be directly related to the interaction between EBV and NK cells in the context of immunosuppression and reduced presence of adaptive T lymphocytes.…”

“…In contrast with T cells, NK cell exhaustion probably results from the progressive loss of expression of several activating receptors, followed by the accumulation of inhibiting receptors, including the expression of inhibitory immune checkpoints, such as PD-1, Tim-3 and Lag-3, leading to cell dysfunction [45] (Figure 1). Another alteration of the NK cell phenotype at EBVpositive PTLD diagnosis, which often appears alongside one or several of the previously mentioned alterations, is the expression of the PD-1 receptor [32,34]. PD-1 expression by NK cells is rare in healthy individuals [46], but is often observed in association with gammaherpesvirus infection in kidney transplant recipients with chronic EBV reactivation [47], in pediatric thoracic recipients with high EBV loads [34], and in human-herpesvirus-8 (HHV-8)-related Kaposi sarcoma patients [44].…”

“…NK cells are known to play a major role in the control of EBV infection in the early post-transplant period, as NK cell reconstitution in peripheral blood reaches normal values within the first month after SOT or HSCT, several months before T cell and B cell restoration [27][28][29][30][31]. In a recent study in adult SOT recipients, NK cell lymphopenia was observed in 70% of EBV-positive PTLD diagnoses [32]. In that same study, the proportion of peripheral blood CD56 bright CD16 − and CD56 dim CD16 + NK cells was similar between PTLD patients and transplant controls, independently of SOT type.…”

“…In pediatric EBV-positive PTLD patients with high PD-1 expression by NK cells, the low functional capacity of NK cells, in terms of both IFN-γ production and CD107a cytotoxicity marker expression, can be recovered after in vitro PD-1/PD-L1 blockade [34]. A study of adult lung recipients observed diminished NK cell cytotoxicity against various lymphoma cell lines at PTLD diagnosis [33], while IFN-γ production after IL-12 and IL-18 stimulation was superior in NK cells of adult SOT recipients at PTLD diagnosis, compared to transplant controls [32,33]. Treatment with anti-PD-1 antibodies resulted in increased cytotoxicity and IFN-γ production of peripheral NK cells from multiple myeloma patients carrying high proportions of PD-1 + NK cells, suggesting that PD-1 could be a target for an immunotherapeutic strategy in EBV-positive PTLD patients [52].…”