Identification of distinct subgroups of EBV-positive post-transplant diffuse large B-cell lymphoma.

Post-transplantation lymphoproliferative disorder is an aggressive complication of transplantation, most frequently of diffuse large B-cell lymphoma morphology and associated with Epstein-Barr virus (EBV) infection/reactivation. In this study the microenvironment of EBV (n=23) and EBV (n=9) post-transplant non-germinal center B-cell diffuse large B-cell lymphoma was characterized. Of EBV cases somatic hypermutation analysis, gene expression profiling, and extensive phenotyping were performed. Our results demonstrated variable cytotoxic T-cell infiltration and significantly increased CD163 M2 macrophage infiltration in EBV compared with EBV post-transplant diffuse large B-cell lymphoma. On the basis of IgM staining and hypermutation analysis, two EBV post-transplant diffuse large B-cell lymphoma subgroups were identified: IgM tumors lacking somatic hypermutations and IgM tumors harboring somatic hypermutations. IgM tumors arose late following transplantation (median interval: 16 months), mainly in kidney recipients. IgM tumors on the other hand arose early (median interval: 3 months, P-value=0.0032), almost exclusively following stem cell transplantation and were associated with worse outcome (median survival 1 month for IgM versus 41 months for IgM tumors, log-rank/Wilcoxon P-value 0.07/0.04). Notably, IgM tumors were characterized by plasma cell features (monotypic kappa/lambda expression, high MUM1 expression, and partial CD138 expression) and a high proliferation index. Consistent with the plasma cell phenotype, unfolded protein response signaling was upregulated. In contrast, IgM EBV post-transplant diffuse large B-cell lymphoma did not express kappa, lambda, IgD, or CD138 and expressed limited MUM1. In these tumors T-cell signaling was enhanced associated with increased T-cell infiltration compared with IgM cases. Overall, our results allow further molecular classification of EBV post-transplant diffuse large B-cell lymphoma and provide a rationale for the use of subtype-specific-targeted therapies (eg, bortezomib in IgM tumors). Our findings also provide a biological basis for the clinical differences between post-transplant lymphoproliferative disorder following solid organ and stem cell transplantation, which are regarded as different disorders.