Germinal Center B-cell Lymphoma Research Articles

Specific expression of miR-17-5p and miR-127 in testicular and central nervous system diffuse large B-cell lymphoma

Recent studies have shown that certain non-coding short RNAs, called miRNAs, play an important role in diffuse large B-cell lymphomas. Patients with diffuse large B-cell lymphoma have great diversity in both clinical characteristics, site of presentation and outcome. The aim of our study is to validate the differential expression in germinal center and non-germinal center diffuse large B-cell lymphoma,s and to study to the extent to which the primary site of differentiation is associated with the miRNA expression profile. We studied 50 cases of de novo diffuse large B-cell lymphoma for the expression of 15 miRNAs (miR-15a, miR-15b, miR-16, miR-17-3p, miR-17-5p, miR-18a, miR-19a, miR-19b, miR-20a, miR-21, miR-92, miR-127, miR-155, miR-181a and miR-221). Apart from 19 nodal cases without extranodal dissemination (stages I and II), we selected two groups with unambiguous stages I and II extranodal presentation; 9 cases of primary central nervous system, 11 cases of primary testicular and 11 cases of other primary extranodal diffuse large B-cell lymphomas. All cases were analyzed with qRT-PCR. In situ hybridization for the most differentially expressed miRNAs was performed to show miRNA expression in tumor cells, but not in background cells. MiR-21 and miR-19b showed the highest expression levels. No significant differences were seen between germinal center and non-germinal center diffuse large B-cell lymphomas in either the total or the nodal group for any of the 15 miRNAs. Two miRNAs showed significant differences in expression levels for diffuse large B-cell lymphoma subgroups according to the site of presentation. MiR-17-5p showed a significant higher expression level in the central nervous system compared with testicular and nodal diffuse large B-cell lymphomas (P<0.05). MiR-127 levels were significantly higher in testicular than in central nervous system and in nodal diffuse large B-cell lymphomas (P<0.05). We conclude that the location of diffuse large B-cell lymphoma is an important factor in determining the differential expression of miRNAs.

Global DNA methylation profiling reveals silencing of a secreted form of Epha7 in mouse and human germinal center B-cell lymphomas

Most human lymphomas originate from transformed germinal center (GC) B lymphocytes. While activating mutations and translocations of MYC, BCL2 and BCL6 promote specific GC lymphoma subtypes, other genetic and epigenetic modifications that contribute to malignant progression in the GC remain poorly defined. Recently, aberrant expression of the TCL1 proto-oncogene was identified in major GC lymphoma subtypes. TCL1 transgenic mice offer unique models of both aggressive GC and marginal zone B-cell lymphomas, further supporting a role for TCL1 in B-cell transformation. Here, restriction landmark genomic scanning was employed to discover tumor-associated epigenetic alterations in malignant GC and marginal zone B-cells in TCL1 transgenic mice. Multiple genes were identified that underwent DNA hypermethylation and decreased expression in TCL1 transgenic tumors. Further, we identified a secreted isoform of EPHA7, a member of the Eph family of receptor tyrosine kinases that are able to influence tumor invasiveness, metastasis and neovascularization. EPHA7 was hypermethylated and repressed in both mouse and human GC B-cell non-Hodgkin lymphomas, with the potential to influence tumor progression and spread. These data provide the first set of hypermethylated genes with the potential to complement TCL1-mediated GC B-cell transformation and spread.

M17, a gene specific for germinal center (GC) B cells and a prognostic marker for GC B-cell lymphomas, is dispensable for the GC reaction in mice

AbstractIn T-cell–dependent antibody responses, antigen-specific B cells undergo a phase of secondary antibody diversification in germinal centers (GCs). Somatic hypermutation (SHM) introduces mutations into the rearranged immunoglobulin (Ig) variable (V) region genes, and class-switch recombination (CSR) alters the Ig heavy (H) chain constant region. Aberrant SHM or CSR is thought to contribute to the development of GC-derived B-cell malignancies. Diffuse large B-cell lymphomas (DLBCLs) are a heterogeneous group of such GC-derived tumors. Based on their gene expression profile, DLBCLs can be divided into activated B-cell–like and GC-like subgroups. The human gene HGAL is predominantly expressed in GCs. It is also part of the gene expression signature of GC-like DLBCL, and its high expression in DLBCL has been associated with a better clinical prognosis. We have generated mice deficient of the HGAL homologue M17 in order to investigate its functional significance. The mutant animals form normal GCs, undergo efficient CSR and SHM, and mount T-cell–dependent antibody responses similar to wild-type controls. Thus, M17 is dispensable for the GC reaction, and its potential function in the pathogenesis of DLBCL remains elusive.

Detection of germinal center B-cell lymphoma in archival specimens: critical evaluation of Bcl-6 protein expression in diffuse large B-cell lymphoma of the tonsil

Expression of Bcl-6 and CD10, markers for the tumor of the germinal center (GC) B-cell derivation, has been studied in primary diffuse large B-cell lymphomas (DLBCLs) of the lymph node, gastrointestinal tract, and mediastinum. In these studies, the coexpression rate of CD10 and Bcl-6 was relatively constant at 30%∼40%, but the frequency of Bcl-6+ tumors varied from 55% to 100%, raising doubts about the usefulness of Bcl-6 expression in identifying the tumor of GC B-cell derivation. Because the expression of Bcl-6 in tumors of non-GC B-cell origin has recently been reported, we critically evaluated the expression of Bcl-6 and CD10 in primary DLBCLs of the tonsil, a relatively common tumor in Japan and Korea. The cases (n = 51) represented a consecutive series for any recent 2-year period at several teaching hospitals in Korea and Japan. Formalin-fixed, paraffin-embedded specimens were used for immunostaining. Staining for Bcl-6 and CD10 was positive in 44 (86%) and 22 cases (45%), respectively. However, among those positive for Bcl-6 (>10% Bcl-6+ tumor cells), 2 basic patterns were recognized: uniform and nonuniform. The uniform pattern was characterized by a dense population (>75%) and a consistent density in any given area, resembling the staining pattern observed in GC or follicular lymphoma (FL) (the “GC/FL” pattern). In contrast, the nonuniform pattern exhibited a varying density from area to area, as well as a less-dense population (<75%). The uniform pattern was observed in 26 cases (51%). All but 1 (95%) of the CD10+ tumors coexpressed Bcl-6, with most (82%) displaying the uniform pattern. We conclude that tumors showing a uniform pattern of Bcl-6 expression should be distinguished from those showing a nonuniform pattern, because the former most likely represent tumors of GC B-cell derivation and the latter most likely represent tumors of non-GC derivation. GC B-cell lymphoma thus defined accounted for 51% of tonsillar DLBCL, a proportion comparable to that of the nodal DLBCL. CD10 expression correlated with the “GC/FL” pattern, but appeared to be not essential for the identification of GC B-cell lymphoma. This study suggests that a significant proportion of tonsillar DLBCLs in Asia is of GC B-cell origin rather than of mucosa-associated lymphoid tissue origin. This finding may have significance for clinical management of these lymphomas.

Coexpression of Bcl-6 and CD10 in diffuse large B-cell lymphomas: Significance of Bcl-6 expression patterns in identifying germinal center B-cell lymphoma

Most follicular lymphomas (FLs) transform to diffuse lymphoma eventually, comprising a significant proportion of diffuse large B-cell lymphoma (DLBCL). Judging by bcl-2 rearrangement (bcl-2R), one third of DLBCLs are believed to be of FL derivation in the Western population. However, bcl-2R is not specific and is not detectable in every case of FL. In East Asia, FL is uncommon but DLBCL is not. The proportion of tumors of FL origin in DLBCL is not known in this region. The coexpression of Bcl-6 and CD10 proteins, a reliable marker to identify germinal center (GC) B-cell lymphoma including FL, was analyzed in primary nodal DLBCLs (n = 104) diagnosed at major hospitals in Seoul during a recent 2-year period, along with well-defined cases (n = 17) of nodal FL as controls. Bcl-2 protein expression (n = 77) was also studied along with bcl-2R (n = 64), by polymerase chain reaction. Formalin-fixed archival specimens were used in all these assays. The Bcl-6/CD10 coexpression was observed in 35 DLBCLs (34%) and 14 FLs (82%), and most of them showed a pattern of Bcl-6 expression similar to that of the GC. Bcl-2 expression or bcl-2R did not correlate with Bcl-6/CD10 coexpression. Histologically, compartmentalizing sclerosis was associated with a high rate of the coexpression (8 of 10). In conclusion, to detect GC B-cell lymphoma in routine biopsy specimens, a pattern of Bcl-6 staining similar to the GC must be identified. Bcl-6+/CD10+ GC B-cell lymphomas thus defined comprised one third of primary nodal DLBCLs in Korea. The incidence rate is similar to that in the West. The reasons for the discrepancy between the incidence of GC B-cell lymphoma and the paucity of the follicular pattern in East Asian subjects warrant further studies. HUM PATHOL 32:954-962. Copyright © 2001 by W.B. Saunders Company