Gene Expression Analysis of B-Cell Post Transplant Lymphoproliferative Disorders Provides Insights into Disease Biology.

Background: B-cell post transplant lymphoproliferative disorders (PTLDs) encompass a diverse group of entities, the majority representing EBV-driven lymphoproliferations, which arise in the setting of iatrogenic immunosuppression. Their pathogenesis, especially the genetic relationship of PTLD with other types of B-cell non-Hodgkin lymphomas (B-NHLs), is not well understood and the association of polymorphic PTLD (P-PTLD) with monomorphic PTLD (M-PTLD) is presently unclear. Thus, in order to address these issues we analyzed gene expression profiles of PTLD and compared them with those derived from other types of B-NHL, normal B-cell subsets, and B-cell derived cell lines.

Material and methods: Paraffin embedded and H&E stained sections were used for morphologic analysis and PTLD were classified according to the WHO classification. Phenotypic characterization was performed using a comprehensive panel of antibodies and in situ hybridization for EBER. Frozen tissue from PTLD, different B-NHL, purified normal B-cell subsets, EBV-transformed lymphoblastoid cell lines (LCLs) and multiple myeloma cell lines, was used to generate complementary RNA (cRNA) that was hybridized to HGU95 arrays (Affymetrix). Gene expression data were analyzed using unsupervised and supervised clustering algorithms and classifiers were generated to determine the relationship between PTLD and cells corresponding to different stages of mature B-cell development.

Results: The 12 PTLD analyzed represented an infectious mononucleosis-like (IM-like) lesion, 5 P-PTLD, and 6 M-PTLD. All P-PTLD and 5 M-PTLD had late-germinal center (GC)/post-GC phenotypes and 8 PTLD, including the IM-like lesion, were EBV+, while 4 PTLD were EBV−. The expression profiles of late GC/post GC PTLD appeared homogeneous and distinct from other B-NHL, however no segregation of P-PTLD and M-PTLD or EBV+ and EBV− PTLD was noted. Surprisingly, on supervised analysis, only 4 genes were expressed at higher levels in PTLD compared to B-NHL and normal B-cell subsets (BLIMP-1, XBP-1, IFITM3, PCMT1) and only 2 genes were differentially upregulated in EBV+ PTLD (CD27 ligand, MTDH). The expression profiles of PTLD appeared most similar to LCLs.

Conclusions: B-cell PTLDs of late-GC/post-GC phenotype represent a distinct type of B-NHL, which are possibly derived from activated B-cells. Despite morphologic distinctions, P-PTLD and M-PTLD have overlapping genetic profiles suggesting disease heterogeneity within different categories.