Expression of the interferon regulatory factor 8/ICSBP-1 in human reactive lymphoid tissues and B-cell lymphomas: a novel germinal center marker

IRF8-mutant B cell lymphoma evades immunity through a CD74-dependent deregulation of antigen processing and presentation in MHCII complexes

The mechanism by which interferon regulatory factor 8 (IRF8) mutation contributes to lymphomagenesis is unknown. We modeled IRF8 variants in B cell lymphomas and found that they affected the expression of regulators of antigen presentation. Expression of IRF8 mutants in murine B cell lymphomas suppressed CD4, but not CD8, activation elicited by antigen presentation and downmodulated CD74 and human leukocyte antigen (HLA) DM, intracellular regulators of antigen peptide processing/loading in the major histocompatibility complex (MHC) II. Concordantly, mutant IRF8 bound less efficiently to the promoters of these genes. Mice harboring IRF8 mutant lymphomas displayed higher tumor burden and remodeling of the tumor microenvironment, typified by depletion of CD4, CD8, and natural killer cells, increase in regulatory T cells and T follicular helper cells. Deconvolution of bulk RNA sequencing data from IRF8-mutant human diffuse large B cell lymphoma (DLBCL) recapitulated part of the immune remodeling detected in mice. We concluded that IRF8 mutations contribute to DLBCL biology by facilitating immune escape.

IRF8-mutant B cell lymphoma evades immunity through a CD74-dependent deregulation of antigen processing and presentation in MHC CII complexes

In diffuse large B-cell lymphoma (DLBCL), the transcription factor IRF8 is the target of a series of potentially oncogenic events, including, chromosomal translocation, focal amplification, and super-enhancer perturbations. IRF8 is also frequently mutant in DLBCL, but how these variants contribute to lymphomagenesis is unknown. We modeled IRF8 mutations in DLBCL and found that they did not meaningfully impact cell fitness. Instead, IRF8 mutants, mapping either to the DNA-binding domain (DBD) or c-terminal tail, displayed diminished transcription activity towards CIITA, a direct IRF8 target. In primary DLBCL, IRF8 mutations were mutually exclusive with mutations in genes involved in antigen presentation. Concordantly, expression of IRF8 mutants in murine B cell lymphomas uniformly suppressed CD4, but not CD8, activation elicited by antigen presentation. Unexpectedly, IRF8 mutation did not modify MHC CII expression on the cell surface, rather it downmodulated CD74 and HLA- DM, intracellular regulators of antigen peptide processing/loading in the MHC CII complex. These changes were functionally relevant as, in comparison to IRF8 WT, mice harboring IRF8 mutant lymphomas displayed a significantly higher tumor burden, in association with a substantial remodeling of the tumor microenvironment (TME), typified by depletion of CD4, CD8, Th1 and NK cells, and increase in T-regs and Tfh cells. Importantly, the clinical and immune phenotypes of IRF8-mutant lymphomas were rescued in vivo by ectopic expression of CD74. Deconvolution of bulk RNAseq data from primary human DLBCL recapitulated part of the immune remodeling detected in mice and pointed to depletion of dendritic cells as another feature of IRF8 mutant TME. We concluded that IRF8 mutations contribute to DLBCL biology by facilitating immune escape.

Altered pathways and targeted therapy in double hit lymphoma

High-grade B-cell lymphoma with translocations involving MYC and BCL2 or BCL6, usually referred to as double hit lymphoma (DHL), is an aggressive hematological malignance with distinct genetic features and poor clinical prognosis. Current standard chemoimmunotherapy fails to confer satisfying outcomes and few targeted therapeutics are available for the treatment against DHL. Recently, the delineating of the genetic landscape in tumors has provided insight into both biology and targeted therapies. Therefore, it is essential to understand the altered signaling pathways of DHL to develop treatment strategies with better clinical benefits. Herein, we summarized the genetic alterations in the two DHL subtypes (DHL-BCL2 and DHL-BCL6). We further elucidate their implications on cellular processes, including anti-apoptosis, epigenetic regulations, B-cell receptor signaling, and immune escape. Ongoing and potential therapeutic strategies and targeted drugs steered by these alterations were reviewed accordingly. Based on these findings, we also discuss the therapeutic vulnerabilities that coincide with these genetic changes. We believe that the understanding of the DHL studies will provide insight into this disease and capacitate the finding of more effective treatment strategies.

Clinicopathological and Immunohistochemical Profile of Mantle Cell Lymphoma: An Institutional Experience

Introduction

Mantle cell lymphoma (MCL) is a biologically aggressive B-cell non-Hodgkin lymphoma (NHL) with distinctive morphologic, immunophenotypic, and molecular characteristics. Differentiation from other chronic lymphoproliferative disorders is essential for prognostication.

Aim

This paper aims to study the clinicopathological features of MCL with emphasis on immunohistochemical features and disease correlation.

Method

To do so, clinicopathological characteristics from 21 cases of MCL (14 males, seven females, M:F=2:1) diagnosed in the last five years i.e. 2015 to 2020, were retrospectively reviewed and correlated with immunohistochemistry (IHC) data. Particularly those pertaining to cyclin D1, SRY-box transcription factor 11 (SOX11), cluster of differentiation (CD) 5, CD23, MIB E3 ubiquitin protein ligase 1 (MIB1), tumor protein 53 (TP53), c-myelocytomatosis oncogene product (c-MYC), multiple myeloma oncogene 1 (MUM1), mouse double minute 2 homolog (MDM2), and Epstein-Barr virus latent membrane protein 1 (EBV-LMP1) expression with its aberrations.

Observations

This study shows that MCL constituted 4.2% (21/500) of all NHLs with a mean age of 57.5 years (median 60 years, range 30 to 80 years). The disease was nodal in 19, and extranodal in the remaining two cases. 14 of 21 (67%) had generalized lymphadenopathy and 71% had bone marrow (BM) involvement. The nodal involvement was diffuse in 9/17 (53%), 8/21 (38%) had a blastoid morphology, and an in-situ MCL pattern was not seen in any of the cases selected for the study. Cyclin D1 immunoexpression correlated well with SOX11; CD5-negative in five cases; and CD23-positive in three cases. TP53 and c-MYC expression were noted in 17/19 (89.4%) and 8/17 (47%), respectively. MUM1 registered positive in six cases. None of the cases showed immunopositivity for MDM2 and EBV-LMP1.

Conclusion

In essence, this study indicates that morphological and immunophenotypic subclassification of mantle cell lymphoma with a wider panel of IHC markers is essential for understanding disease biology and better prognostication.

Generation and characterization of the Eµ-Irf8 mouse model

In mature B-cell malignancies, chromosomal translocations often juxtapose an oncogenic locus to the regulatory regions of the immunoglobulin genes. These genomic rearrangements can associate with specific clinical/pathological sub-entities and inform diagnosis and treatment decisions. Recently, we characterized the t(14;16)(q32;q24) in diffuse large B-cell lymphoma (DLBCL), and showed that it targets the transcription factor IRF8, which is also somatically mutated in ~10% of DLBCLs. IRF8 regulates innate and adaptive immune responses mediated by myeloid/monocytic and lymphoid cells. While the role of IRF8 in human myeloid/dendritic-cell disorders is well established, less is known of its contribution to the pathogenesis of mature B-cell malignancies. To address this knowledge gap, we generated the Eµ-Irf8 mouse model, which mimics the IRF8 deregulation associated with t(14;16) of DLBCL. Eµ-Irf8 mice develop normally and display peripheral blood cell parameters within normal range. However, Eµ-Irf8 mice accumulate pre-pro-B-cells and transitional B-cells in the bone marrow and spleen, respectively, suggesting that the physiological role of Irf8 in B-cell development is amplified. Notably, in Eµ-Irf8 mice, the lymphomagenic Irf8 targets Aicda and Bcl6 are overexpressed in mature B-cells. Yet, the incidence of B-cell lymphomas is not increased in the Eµ-Irf8 model, even though their estimated survival probability is significantly lower than that of WT controls. Together, these observations suggest that the penetrance on the Irf8-driven phenotype may be incomplete and that introduction of second genetic hit, a common strategy in mouse models of lymphoma, may be necessary to uncover the pro-lymphoma phenotype of the Eµ-Irf8 mice.

miR-146a in Myasthenia Gravis Thymus Bridges Innate Immunity With Autoimmunity and Is Linked to Therapeutic Effects of Corticosteroids

Toll-like receptor (TLR)-mediated innate immune responses are critically involved in the pathogenesis of myasthenia gravis (MG), an autoimmune disorder affecting neuromuscular junction mainly mediated by antiacetylcholine receptor antibodies. Considerable evidence indicate that uncontrolled TLR activation and chronic inflammation significantly contribute to hyperplastic changes and germinal center (GC) formation in the MG thymus, ultimately leading to autoantibody production and autoimmunity. miR-146a is a key modulator of innate immunity, whose dysregulation has been associated with autoimmune diseases. It acts as inhibitor of TLR pathways, mainly by targeting the nuclear factor kappa B (NF-κB) signaling transducers, interleukin 1 receptor associated kinase 1 (IRAK1) and tumor necrosis factor (TNF) receptor associated factor 6 (TRAF6); miR-146a is also able to target c-REL, inducible T-cell costimulator (ICOS), and Fas cell surface death receptor (FAS), known to regulate B-cell function and GC response. Herein, we investigated the miR-146a contribution to the intrathymic MG pathogenesis. By real-time PCR, we found that miR-146a expression was significantly downregulated in hyperplastic MG compared to control thymuses; contrariwise, IRAK1, TRAF6, c-REL, and ICOS messenger RNA (mRNA) levels were upregulated and negatively correlated with miR-146a levels. Microdissection experiments revealed that miR-146a deficiency in hyperplastic MG thymuses was not due to GCs, but restricted to the GC-surrounding medulla, characterized by IRAK1 overexpression. We also showed higher c-REL and ICOS mRNA levels, and lower FAS mRNA levels, in GCs than in the remaining medulla, according to the contribution of these molecules in GC formation. By double immunofluorescence, an increased proportion of IRAK1-expressing dendritic cells and macrophages was found in hyperplastic MG compared to control thymuses, along with GC immunoreactivity for c-REL. Interestingly, in corticosteroid-treated MG patients intrathymic miR-146a and mRNA target levels were comparable to those of controls, suggesting that immunosuppressive therapy may restore the microRNA (miRNA) levels. Indeed, an effect of prednisone on miR-146a expression was demonstrated in vitro on peripheral blood cells. Serum miR-146a levels were lower in MG patients compared to controls, indicating dysregulation of the circulating miRNA. Our overall findings strongly suggest that defective miR-146a expression could contribute to persistent TLR activation, lack of inflammation resolution, and hyperplastic changes in MG thymuses, thus linking TLR-mediated innate immunity to B-cell-mediated autoimmunity. Furthermore, they unraveled a new mechanism of action of corticosteroids in inducing control of autoimmunity in MG via miR-146a.

IRF4 translocation status in pediatric follicular and diffuse large B-cell lymphoma patients enrolled in Children's Oncology Group trials

Large B-cell lymphoma with IRF4 rearrangement is a provisional entity in the 2017 World Health Organization classification. In order to characterize these lymphomas in children from the United States, IRF4 FISH and immunohistochemical stains were performed on 32 follicular lymphoma and diffuse large B-cell lymphoma (DLBCL) from Children's Oncology Group studies. Two DLBCLs (6%) had IRF4 rearrangements, one involving the ileocecal valve and another involving the tonsil and cerebrospinal fluid. Both cases had strong, diffuse IRF4/MUM1 immunohistochemical staining, which may be a pathologic clue to the diagnosis. Reclassification of these cases may have prognostic and therapeutic implications.

Increased expression of IRF8 in tumor cells inhibits the generation of Th17 cells and predicts unfavorable survival of diffuse large B cell lymphoma patients

The immunological pathogenesis of diffuse large B cell lymphoma (DLBCL) remains elusive. Searching for new prognostic markers of DLBCL is a crucial focal point for clinical scientists. The aim of the present study was to examine the prognostic value of interferon regulatory factor 8 (IRF8) expression and its effect on the development of Th17 cells in the tumor microenvironment of DLBCL patients. Flow cytometry, immunohistochemistry, and quantitative real-time PCR were used to detect the distribution of Th17 cells and related cytokines and IRF8 in tumor tissues from DLBCL patients. Two DLBCL cell lines (OCI-LY10 and OCI-LY1) with IRF8 knockdown or overexpression and two human B lymphoblast cell lines were co-cultured with peripheral blood mononuclear cells (PBMCs) in vitro to determine the effect of IRF8 on the generation of Th17 cells. Quantitative real-time PCR and Western blotting were used to investigate the involvement of retinoic acid receptor-related orphan receptor gamma t (RORγt) in the effect of IRF8 on Th17 cell generation. The survival of 67 DLBCL patients was estimated using the Kaplan-Meier method and log-rank analysis. The percentage of Th17 cells was lower in DLBCL tumor tissues than in PBMCs and corresponding adjacent benign tissues. Relative expression of interleukin (IL)-17A was lower, whereas that of interferon (IFN)-γ was higher in tumor tissues than in benign tissues. Co-culture with DLBCL cell lines inhibited the generation of Th17 cells in vitro. IRF8 upregulation was detected in DLBCL tumor tissues, and it was associated with decreased DLBCL patient survival. Investigation of the underlying mechanism suggested that IRF8 upregulation in DLBCL, through an unknown mechanism, inhibited Th17 cell generation by suppressing RORγt in neighboring CD4+ T cells. Tumor cells may express soluble or membrane-bound factors that inhibit the expression of RORγt in T cells within the tumor microenvironment. Our findings suggest that IRF8 expression could be a prognostic factor for DLBCL.

B cells gone rogue: the intersection of diffuse large B cell lymphoma and autoimmune disease

INTRODUCTION

Diffuse large B cell lymphoma (DLBCL) is characterized by genetic, genomic and clinical heterogeneity. Autoimmune diseases (AIDs) have recently been shown to represent significant risk factors for development of DLBCL.

AREAS COVERED

Studies that examined the relationships between AIDs and lymphoma in terms of pathogenesis, genetic lesions, and treatment were identified in the MEDLINE database using combinations of medical subject heading (MeSH) terms. Co-authors independently performed study selection for inclusion based on appropriateness of the study question and nature of the study design and sample size. Expert commentary: Identification of AID as a substantial risk factor for DLBCL raises new questions regarding how autoimmunity influences lymphomagenesis and disease behavior. It will be important to identify whether DLBCL cases arising in the setting of AID harbor inferior prognoses, and, if so, whether they also exhibit certain molecular abnormalities that may be targeted to overcome such a gap in clinical outcomes.

Increased expression of Toll-like receptors 7 and 9 in myasthenia gravis thymus characterized by active Epstein-Barr virus infection

Considerable data implicate the thymus as the main site of autosensitization to the acetylcholine receptor in myasthenia gravis (MG), a B-cell-mediated autoimmune disease affecting the neuromuscular junction. We recently demonstrated an active Epstein-Barr virus (EBV) infection in the thymus of MG patients, suggesting that EBV might contribute to the onset or maintenance of the autoimmune response within MG thymus, because of its ability to activate and immortalize autoreactive B cells. EBV has been reported to elicit and modulate Toll-like receptor (TLR) 7- and TLR9-mediated innate immune responses, which are known to favor B-cell dysfunction and autoimmunity. Aim of this study was to investigate whether EBV infection is associated with altered expression of TLR7 and TLR9 in MG thymus. By real-time PCR, we found that TLR7 and TLR9 mRNA levels were significantly higher in EBV-positive MG compared to EBV-negative normal thymuses. By confocal microscopy, high expression levels of TLR7 and TLR9 proteins were observed in B cells and plasma cells of MG thymic germinal centers (GCs) and lymphoid infiltrates, where the two receptors co-localized with EBV antigens. An increased frequency of Ki67-positive proliferating B cells was found in MG thymuses, where we also detected proliferating cells expressing TLR7, TLR9 and EBV antigens, thus supporting the idea that EBV-associated TLR7/9 signaling may promote abnormal B-cell activation and proliferation. Along with B cells and plasma cells, thymic epithelium, plasmacytoid dendritic cells and macrophages exhibited enhanced TLR7 and TLR9 expression in MG thymus; TLR7 was also increased in thymic myeloid dendritic cells and its transcriptional levels positively correlated with those of interferon (IFN)-β. We suggested that TLR7/9 signaling may be involved in antiviral type I IFN production and long-term inflammation in EBV-infected MG thymuses. Our overall findings indicate that EBV-driven TLR7- and TLR9-mediated innate immune responses may participate in the intra-thymic pathogenesis of MG.

Plasma cell and terminal B-cell differentiation in mantle cell lymphoma mainly occur in the SOX11-negative subtype

Mantle cell lymphoma is a mature lymphoid neoplasm characterized by the t(11;14)(q13;q32) and cyclin D1 overexpression. SOX11 is a transcription factor commonly overexpressed in these tumors but absent in most other mature B-cell lymphomas whose function is not well understood. Experimental studies have shown that silencing of SOX11 in mantle cell lymphoma cells promotes the shift from a mature B cell into an early plasmacytic differentiation phenotype, suggesting that SOX11 may contribute to tumor development by blocking the B-cell differentiation program. The relationship between SOX11 expression and terminal B-cell differentiation in primary mantle cell lymphoma and its relationship to the plasmacytic differentiation observed in occasional cases is not known. In this study we have investigated the terminal B-cell differentiation phenotype in 60 mantle cell lymphomas, 41 SOX11-positive and 19 SOX11-negative. Monotypic plasma cells and lymphoid cells with plasmacytic differentiation expressing cyclin D1 were observed in 7 (37%) SOX11-negative but in none of 41 SOX11-positive mantle cell lymphomas (P<0.001). Intense cytoplasmic expression of a restricted immunoglobulin light chain was significantly more frequent in SOX11-negative than -positive tumors (58 vs 13%) (P=0.001). Similarly, BLIMP1 and XBP1 expression was also significantly more frequent in SOX11-negative than in -positive cases (83 vs 34% and 75 vs 11%, respectively) (P=0.001). However, no differences in the expression of IRF4/MUM1 were observed among these subtypes of mantle cell lymphoma. In conclusion, these results indicate that SOX11-negative mantle cell lymphoma may be a particular subtype of this tumor characterized by more frequent morphological and immunophenotypic terminal B-cell differentiation features that may be facilitated by the absence of SOX11 transcription factor.

Loss of IRF8 Inhibits the Growth of Diffuse Large B-cell Lymphoma

IRF8 is a transcription factor with a critical role in B lymphocyte development and functions. Its role in human diffuse large B-cell lymphoma (DLBCL), however, remained elusive. In this study, using shRNA-mediated knockdown of IRF8 expression, we found that the loss of IRF8 significantly reduced the proliferation of DLBCL cells (P<0.05). Mechanistically, decreasing the levels of IRF8 led to a suppression of the phosphorylation of p38 and ERK, molecules critical for B cell proliferation. Furthermore, using a xenograft lymphoma mouse model, we found that the loss of IRF8 significantly inhibited the growth of lymphomas in vivo (P<0.05). Immunohistochemical analysis of human DLBCL tissues revealed that the levels of IRF8 were significantly greater in non-germinal center B-cell-like (non-GCB) subtype than that in GCB subtype (P<0.05). Analysis of public available data also suggested that the expression levels of IRF8 mRNA in human DLBCL tissues were inversely correlated with patients' overall survival time. Taken together, this study suggested that IRF8 may play an oncogenic role in human DLBCL by promoting cell proliferation.

Interferon regulatory factor 8 (IRF8) interacts with the B cell lymphoma 6 (BCL6) corepressor BCOR

B cell lymphoma 6 (BCL6) corepressor (BCOR) was discovered as a BCL6-interacting corepressor, but little is known about its other biological activities in normal B cell development and function. Previously, we found that interferon regulatory factor 8 (IRF8), also known as interferon consensus sequence-binding protein, directly targets a large number of genes in germinal center B cells including BCL6. In this study, we screened potential binding partners of IRF8 using a retrovirus-based protein complementation assay screen in a mouse pre-B cell line. We found that IRF8 interacts directly with BCOR and that the α-helical region of IRF8 and the BCL6 binding domain of BCOR are required for this interaction. In addition, IRF8 protein interacts directly with BCL6. Using an siRNA-mediated IRF8 knockdown mouse B cell lymphoma cell line, we showed that IRF8 represses Bcor and enhances Bcl6 transcription. Taken together, these data suggest that a complex comprising BCOR-BCL6-IRF8 modulates BCL6-associated transcriptional regulation of germinal center B cell function.

Chronic lymphocytic leukaemia: could immunological tolerance mechanisms be the origin of lymphoid neoplasms?

Immunological tolerance theory in chronic lymphocytic leukaemia (CLL): we suggest that B cells that express B-cell receptors (BCR) that recognize their own BCR epitopes are viewed by immune system as 'dangerous cells'. BCR autonomous signalling may induce constant receptor editing and mistakes in allelic exclusion. The fact that whole BCR recognizes a self-antigen or foreing antigen may be irrelevant in early B cell development. In early B cells, autonomous signalling induced by recognition of the BCR's own epitopes simulates an antigen-antibody engagement. In the bone marrow this interaction is viewed as recognition of self-molecules and induces receptor editing. In mature B cells autonomous signalling by the BCR may promote 'reversible anergy' and also may correct self-reactivity induced by the somatic hypermutation mechanisms in mutated CLL B cells. However, in unmutated CLL B cells, BCR autonomous signalling in addition to self-antigen recognition augments B cell activation, proliferation and genomic instability. We suggest that CLL originates from a coordinated normal immunologic tolerance mechanism to destroy self-reactive B cells. Additional genetic damage induced by tolerance mechanisms may immortalize self-reactive B cells and transform them into a leukemia.

A reporter mouse reveals lineage-specific and heterogeneous expression of IRF8 during lymphoid and myeloid cell differentiation

The IFN regulatory factor family member 8 (IRF8) regulates differentiation of lymphoid and myeloid lineage cells by promoting or suppressing lineage-specific genes. How IRF8 promotes hematopoietic progenitors to commit to one lineage while preventing the development of alternative lineages is not known. In this study, we report an IRF8-EGFP fusion protein reporter mouse that revealed previously unrecognized patterns of IRF8 expression. Differentiation of hematopoietic stem cells into oligopotent progenitors is associated with progressive increases in IRF8-EGFP expression. However, significant induction of IRF8-EGFP is found in granulocyte-myeloid progenitors and the common lymphoid progenitors but not the megakaryocytic-erythroid progenitors. Surprisingly, IRF8-EGFP identifies three subsets of the seemingly homogeneous granulocyte-myeloid progenitors with an intermediate level of expression of EGFP defining bipotent progenitors that differentiation into either EGFP(hi) monocytic progenitors or EGFP(lo) granulocytic progenitors. Also surprisingly, IRF8-EGFP revealed a highly heterogeneous pre-pro-B population with a fluorescence intensity ranging from background to 4 orders above background. Interestingly, IRF8-EGFP readily distinguishes true B cell committed (EGFP(int)) from those that are noncommitted. Moreover, dendritic cell progenitors expressed extremely high levels of IRF8-EGFP. Taken together, the IRF8-EGFP reporter revealed previously unrecognized subsets with distinct developmental potentials in phenotypically well-defined oligopotent progenitors, providing new insights into the dynamic heterogeneity of developing hematopoietic progenitors.

A capture-sequencing strategy identifies IRF8, EBF1, and APRIL as novel IGH fusion partners in B-cell lymphoma

The characterization of immunoglobulin heavy chain (IGH) translocations provides information on the diagnosis and guides therapeutic decisions in mature B-cell malignancies while enhancing our understanding of normal and malignant B-cell biology. However, existing methodologies for the detection of IGH translocations are labor intensive, often require viable cells, and are biased toward known IGH fusions. To overcome these limitations, we developed a capture sequencing strategy for the identification of IGH rearrangements at nucleotide level resolution and tested its capabilities as a diagnostic and discovery tool in 78 primary diffuse large B-cell lymphomas (DLBCLs). We readily identified IGH-BCL2, IGH-BCL6, IGH-MYC, and IGH-CCND1 fusions and discovered IRF8, EBF1, and TNFSF13 (APRIL) as novel IGH partners in these tumors. IRF8 and TNFSF13 expression was significantly higher in lymphomas with IGH rearrangements targeting these loci. Modeling the deregulation of IRF8 and EBF1 in vitro defined a lymphomagenic profile characterized by up-regulation of AID and/or BCL6, down-regulation of PRMD1, and resistance to apoptosis. Using a capture sequencing strategy, we discovered the B-cell relevant genes IRF8, EBF1, and TNFSF13 as novel targets for IGH deregulation. This methodology is poised to change how IGH translocations are identified in clinical settings while remaining a powerful tool to uncover the pathogenesis of B-cell malignancies.

IRF8 is associated with germinal center B-cell-like type of diffuse large B-cell lymphoma and exceptionally involved in translocation t(14;16)(q32.33;q24.1)

Chromosomal translocations involving the immunoglobulin loci represent frequent oncogenic events in B-cell lymphoma development. Although IRF8 (ICSBP-1) protein expression has been demonstrated in germinal center B-cells and related lymphomas in a single report, the IRF8 gene was not described as an immunoglobulin heavy chain (IGH) translocation partner. In a discovery-driven approach we searched for new translocation partners of IGH in diffuse large B-cell lymphoma (DLBCL) by long distance inverse polymerase chain reaction (LDI-PCR) and Sanger sequencing. A t(14;16)(q32.33;q24.1) IGH/IRF8 was detected in a CD5+de novo DLBCL, confirmed by translocation specific PCR and fluorescence in situ hybridization (FISH) analysis. No further IRF8 aberration could be identified either by LDI-PCR in an additional five CD5+DLBCLs or by FISH on 78 formalin-fixed paraffin-embedded biopsies. Subsequent screening for IRF8 by immunohistochemistry revealed IRF8 expression in 18/78 (23%), correlating with a germinal center B-cell-like (GCB) type of DLBCL. This hitherto unknown translocation t(14;16)(q32.33;q24.1) is likely to represent the initiator of a multistep lymphomagenesis in a CD5+de novo DLBCL.

Follicular lymphomas in children and young adults: a comparison of the pediatric variant with usual follicular lymphoma

Follicular lymphoma (FL), a common lymphoma in adults, occurs rarely in pediatric and young adult patients. Most pediatric cases have been described as grade 3, but the criteria to distinguish the pediatric variant of FL (PFL) from usual FL (UFL) seen in adults are not well defined. We undertook a study of FL in patients under the age of 30. We identified 63 cases, which were analyzed by morphology, immunohistochemistry, and polymerase chain reaction analysis of IGH@ and IGK@ clonality. These data were correlated with clinical findings including stage, treatment, and outcome. Among the 63 cases, 34 cases were classified as PFL: 22 presenting in lymph nodes, 8 in the Waldeyer ring, and 4 in the testis. Clonal immunoglobulin gene rearrangement was detected in 97% of PFL cases, but fluorescence in situ hybridization analysis showed an absence of the BCL2/IGH@ translocation in all cases tested. Twenty-nine cases were classified as UFL, 28 of which presented in lymph nodes. The nodal PFLs were observed exclusively in male patients in both children and young adults with a median age of 15 years. They showed marked head/neck predilection, blastoid cytologic features with a high proliferation rate, lack of BCL2 protein and t(14;18), low clinical stage at presentation, and good prognosis. PFLs involving the Waldeyer ring were distinguished by MUM1 expression, 50% (3/6) of which carried IRF4 breaks. BCL2 expression was common (63%) in the absence of BCL2/IGH@ translocation. UFLs were more common in female patients, exclusively in young adults (median age, 24 y), with no cases reported in patients under the age of 18. Twenty-five of 29 cases were of grade 1-2, and 4 cases were classified as grade 3A. They exhibited a higher clinical stage at presentation. Eighty-three percent expressed BCL2. Our results indicate that histologic and immunophenotypic criteria can reliably separate PFL and UFL and that UFL is exceptionally rare in the pediatric age group. PFL associated with particular anatomic sites have distinctive features and should be evaluated separately in future clinical and biological studies.

Uncovering the genetic architecture of multiple sclerosis

Multiple sclerosis (MS) is a disease in which genetic, environmental, and stochastic factors interact to trigger an inflammatory disease of the CNS that also has a neurodegenerative component. Over the past 3 years, progress in high-throughput technologies and analysis methods has synergized with the collaborative efforts of investigators studying MS genetics to enable the discovery of more than a dozen genes involved in making individuals susceptible to MS. These genes are beginning to suggest molecular pathways that may be particularly vulnerable to genetic variation in MS. Soon, a comprehensive map of common genetic variants affecting MS susceptibility will be assembled, and communal efforts will need to focus on the more challenging issue of understanding the genetic architecture of disease course and treatment response in MS. Early efforts integrating different dimensions of information, including genomics, imaging, transcriptomics, and proteomics, with precise phenotypic data from clinicians illustrate the way forward for prognostic algorithms in MS and suggest that these approaches will yield a new series of insights in the next decade.

Pathology, pathogenesis and molecular genetics of follicular NHL

Follicular lymphoma (FL) is a germinal centre-derived indolent B-cell lymphoma representing the second most common Non Hodgkin lymphoma in the Western world. This chapter focuses on the pathology of FL and summarizes the current knowledge about genetic and molecular features that are relevant for the pathogenesis of this neoplasm. The translocation t(14;18) is present in approximately 90% of FL leading to the upregulation of the anti-apoptotic protein BCL2, that may constitute a promising molecular target for therapeutic approaches. FL lacking the t(14;18) also exist, and B-cells carrying the t(14;18) can be detected in a subset of healthy individuals. In addition to the t(14;18), secondary genetic alterations are present in most FL and, more recently, deeper insights into the methylation and microRNA expression patterns in the tumour cells have been gained. The tumour microenvironment appears to be particularly important for the biology and the clinical course of FL.

Gene-expression profiling and not immunophenotypic algorithms predicts prognosis in patients with diffuse large B-cell lymphoma treated with immunochemotherapy

Diffuse large B-cell lymphomas (DLBCLs) can be divided into germinal-center B cell-like (GCB) and activated-B cell-like (ABC) subtypes by gene-expression profiling (GEP), with the latter showing a poorer outcome. Although this classification can be mimicked by different immunostaining algorithms, their reliability is the object of controversy. We constructed tissue microarrays with samples of 157 DLBCL patients homogeneously treated with immunochemotherapy to apply the following algorithms: Colomo (MUM1/IRF4, CD10, and BCL6 antigens), Hans (CD10, BCL6, and MUM1/IRF4), Muris (CD10 and MUM1/IRF4 plus BCL2), Choi (GCET1, MUM1/IRF4, CD10, FOXP1, and BCL6), and Tally (CD10, GCET1, MUM1/IRF4, FOXP1, and LMO2). GEP information was available in 62 cases. The proportion of misclassified cases by immunohistochemistry compared with GEP was higher when defining the GCB subset: 41%, 48%, 30%, 60%, and 40% for Colomo, Hans, Muris, Choi, and Tally, respectively. Whereas the GEP groups showed significantly different 5-year progression-free survival (76% vs 31% for GCB and activated DLBCL) and overall survival (80% vs 45%), none of the immunostaining algorithms was able to retain the prognostic impact of the groups (GCB vs non-GCB). In conclusion, stratification based on immunostaining algorithms should be used with caution in guiding therapy, even in clinical trials.

Genome-wide association study identifies a novel susceptibility locus at 6p21.3 among familial CLL

Prior genome-wide association (GWA) studies have identified 10 susceptibility loci for risk of chronic lymphocytic leukemia (CLL). To identify additional loci, we performed a GWA study in 407 CLL cases (of which 102 had a family history of CLL) and 296 controls. Moreover, given the strong familial risk of CLL, we further subset our GWA analysis to the CLL cases with a family history of CLL to identify loci specific to these familial CLL cases. Our top hits from these analyses were evaluated in an additional sample of 252 familial CLL cases and 965 controls. Using all available data, we identified and confirmed an independent association of 4 single-nucleotide polymorphisms (SNPs) that met genome-wide statistical significance within the IRF8 (interferon regulatory factor 8) gene (combined P values ≤ 3.37 × 10(-8)), located in the previously identified 16q24.1 locus. Subsetting to familial CLL cases, we identified and confirmed a new locus on chromosome 6p21.3 (combined P value = 6.92 × 10(-9)). This novel region harbors the HLA-DQA1 and HLA-DRB5 genes. Finally, we evaluated the 10 previously reported SNPs in the overall sample and replicated 8 of them. Our findings support the hypothesis that familial CLL cases have additional genetic variants not seen in sporadic CLL. Additional loci among familial CLL cases may be identified through larger studies.

MUM1/IRF4: A Review

MUM1/IRF4 protein is a member of the interferon regulatory factor (IRF) family of transcriptional factors initially described as downstream regulators of interferon signaling. The quantity of this factor varies within the hematopoietic system in a lineage and stage-specific way. It is considered to be a key regulator of several steps in lymphoid, myeloid, and dendritic cell differentiation and maturation. MUM1/IRF4 expression is observed in many lymphoid and myeloid malignancies, and may be a promising target for the treatment of some of these neoplasms. We reviewed the literature on MUM1/IRF4, with emphasis on the pathologic aspects of this marker in reactive and malignant hematologic and nonhematologic conditions.

The follicular lymphoma microenvironment: From tumor cell to host immunity

Follicular lymphoma (FL) is a neoplasm derived from follicular germinal center cells. Like the normal components of this lymphoid structure, FL cells interact with various immune cells, such as the follicular helper T cells, suppressor regulatory T cells, dendritic cells, and histiocytes, that define the tumor microenvironment. Gene expression studies have shown that the nature of the tumor microenvironment predicts survival in patients with FL and may influence the response to immunotherapy and risk of transformation. The immune system may either promote or constrain tumor cell development, depending on the relative distribution and activation status of various cell subpopulations. The prognostic value of germline genetic variants of some immune genes suggests that the host genetic background may also influence the biology of FL. Some efforts have been carried out to validate those findings and provide clinical tools that may be used at the time of diagnosis.

BCL6, MUM1, and CD10 expression in mantle cell lymphoma

Mantle cell lymphoma (MCL) characteristically express CD20, CD5, and cyclin-D1, carries the translocation t(11;14) (q13;q32) and typically has no expression of germinal center cell markers. So-called aberrant phenotypes such as CD5 negative and cyclin-D1-negative MCL have been described. Also few cases with CD10 and/or BCL-6 protein expression have been reported. We analyzed 127 MCL looking for the frequency of aberrant immunophenotype, CD10, BCL-6, and MUM1 expression. All cases were CD20 and cyclin-D1 positive, 96% expressed CD5, and 98% showed the t(11;14). BCL-6 expression was observed in 12% of the cases and MUM1 in 35%. No one case showed CD10 positivity in 30% or more neoplastic cells. Only 3 cases showed 10% to 20% of tumoral cells positive for CD10. MUM1 expression was observed in 67% of the BCL-6 positive cases. Thirty-two percent of the cases showed a MUM1+/BCL-6-/CD10- phenotype and 56% had a triple-negative-pattern. Aberrant phenotype is infrequent but not rare, and does not rule out a diagnosis of MCL in an otherwise typical case.

Differential expression of IRF8 in subsets of macrophages and dendritic cells and effects of IRF8 deficiency on splenic B cell and macrophage compartments

IRF8, a transcription factor restricted primarily to hematopoietic cells, is known to influence the differentiation and function of dendritic cells (DC), macrophages, granulocytes and B cells. In human tonsil, IRF8 is expressed at high levels by intrafollicular macrophages and DC, but at much lower levels by tingible body macrophages in germinal centers (GCs) and little, if at all, by follicular DC. Spleens of IRF8-deficient mice had reduced numbers of white pulp follicles and GCs that were irregular in shape. The frequency of follicular B cells was significantly reduced while the population of marginal zone (MZ) B cells was increased. In addition, MZ macrophages were reduced in number and abnormally distributed, while metallophilic macrophages were normal. These findings demonstrate differential requirements for IRF8 among distinct subsets of B cells, DC, and macrophages.

IFN regulatory factor 8 regulates MDM2 in germinal center B cells

IFN regulatory factor 8 (IRF8) is a transcription factor that affects the differentiation and function of myeloid, dendritic, and B cells. Herein we report that IRF8 regulates the expression of Mdm2, a suppressor of p53-dependent and -independent apoptosis pathways, in germinal center (GC) B cells. In GC B cells of IRF8-deficient mice, Mdm2 transcripts were greatly down-regulated, and MDM2 protein was poorly expressed in GC of Irf8(-/-) mice. Small interfering RNA-induced repression of IRF8 in a GC-derived B cell line resulted in decreased expression of MDM2 at the protein level but increased expression of p53 and p21. We found that IRF8 binds to the Mdm2 P2 promoter, and that cotransfection of an IRF8 expression vector with an Mdm2 reporter construct stimulated significant increases in reporter activity. Additionally, transcripts of the p53 target Pmaip1 (Noxa) were significantly increased in IRF8-deficient GC B cells as well as in the IRF8 knockdown B cell line. Finally, cells deficient in IRF8 exhibited growth suppression and increased sensitivity to apoptosis induced by etoposide or IL-21. These results suggest that by regulating MDM2, IRF8 might allow GC B cells to tolerate physiological DNA breaks that otherwise would trigger apoptosis.

IRF8 regulates myeloid and B lymphoid lineage diversification

Interferon regulatory factor 8 (IRF8) is a member of the IRF family of transcription factors whose members play critical roles in interferon (IFN) signaling pathways governing the establishment of innate immune responses by myeloid and dendritic cells. IRF8 is also expressed in lymphoid cells and recent studies have documented its involvement in B cell lineage specification, immunoglobulin light chain gene rearrangement, the distribution of mature B cells into the marginal zone and follicular B cell compartment, and the transcriptional regulation of critical elements of the germinal center reaction. Here we review the contributions of IRF8 to B cell development from hematopoietic stem cells in the bone marrow and its place in the hierarchical regulatory network governing specification and commitment to the B cell fate.

Follicular lymphomas with and without translocation t(14;18) differ in gene expression profiles and genetic alterations

Follicular lymphoma (FL) is genetically characterized by the presence of the t(14;18)(q32;q21) chromosomal translocation in approximately 90% of cases. In contrast to FL carrying the t(14;18), their t(14;18)-negative counterparts are less well studied about their immunohistochemical, genetic, molecular, and clinical features. Within a previously published series of 184 FLs grades 1 to 3A with available gene expression data, we identified 17 FLs lacking the t(14;18). Comparative genomic hybridization and high-resolution single nucleotide polymorphism (SNP) array profiling showed that gains/amplifications of the BCL2 gene locus in 18q were restricted to the t(14;18)-positive FL subgroup. A comparison of gene expression profiles showed an enrichment of germinal center B cell-associated signatures in t(14;18)-positive FL, whereas activated B cell-like, NFkappaB, proliferation, and bystander cell signatures were enriched in t(14;18)-negative FL. These findings were confirmed by immunohistochemistry in an independent validation series of 84 FLs, in which 32% of t(14;18)-negative FLs showed weak or absent CD10 expression and 91% an increased Ki67 proliferation rate. Although overall survival did not differ between FL with and without t(14;18), our findings suggest distinct molecular features of t(14;18)-negative FL.

New insights into the regulation of human B-cell differentiation

B lymphocytes provide the cellular basis of the humoral immune response. All stages of this process, from B-cell activation to formation of germinal centers and differentiation into memory B cells or plasma cells, are influenced by extrinsic signals and controlled by transcriptional regulation. Compared to naïve B cells, memory B cells display a distinct expression profile, which allows for their rapid secondary responses. Indisputably, many B-cell malignancies result from aberrations in the circuitry controlling B-cell function, particularly during the germinal centre (GC) reaction. Here, we review new insights into memory B-cell subtypes, recent literature on transcription factors regulating human B-cell differentiation and further evidence for B-cell lymphomagenesis emanating from errors during GC cell reactions.

Activation of the endoplasmic reticulum stress-associated transcription factor x box-binding protein-1 occurs in a subset of normal germinal-center B cells and in aggressive B-cell lymphomas with prognostic implications

X box-binding protein 1 (Xbp-1) is a transcription factor that is required for the terminal differentiation of B lymphocytes into plasma cells. The Xbp-1 gene is activated in response to endoplasmic reticulum stress signals, which generate a 50-kDa nuclear protein that acts as a potent transactivator and regulates the expression of genes related to the unfolded protein response. Activated Xbp-1 is essential for cell survival in plasma-cell tumors but its role in B-cell lymphomas is unknown. We analyzed the expression of activated Xbp-1 in reactive lymphoid tissues, 411 lymphomas and plasma-cell neoplasms, and 24 B-cell lines. In reactive tissues, Xbp-1 was only found in nuclear extracts. Nuclear expression of Xbp-1 was observed in occasional reactive plasma cells and in a subpopulation of Irf-4(+)/Bcl-6(-)/Pax-5(-) B cells in the light zones of reactive germinal centers, probably representing cells committed to plasma-cell differentiation. None of the low-grade lymphomas showed evidence of Xbp-1 activation; however, Xbp-1 activation was found in 28% of diffuse large B-cell lymphomas, independent of germinal or postgerminal center phenotype, as well as in 48% of plasmablastic lymphomas and 69% of plasma-cell neoplasms. Diffuse large B-cell lymphomas with nuclear Xbp-1 expression had a significantly worse response to therapy and shorter overall survival compared with negative tumors. These findings suggest that Xbp-1 activation may play a role in the pathogenesis of aggressive B-cell lymphomas.

The Germinal centre-derived lymphomas seen through their cellular microenvironment

The human lymph node is a complex tissue resulting from the microenvironmental organisation of different cell populations linked by topographical and/or functional relationships. Germinal centres (GCs) of lymphoid follicles contain a meshwork of follicular dendritic cells in addition to B-cells and some CD4(+) T cells. Moreover, there is a sharp demarcation around the whole follicle centre, which is highlighted by fibroblastic reticulum cells. On the whole, GC exerts a role in B cell physiology and malignancy. In GC-derived lymphomas, gene expression profiling studies have raised the possibility that survival of the affected patients may be associated with signatures preferentially expressed in non-malignant T cells and macrophages and/or dendritic cells. Immunohistological analyses in lymphoma biopsy samples have confirmed that the biological behaviour and tumour progression may be influenced by the tumour microenvironment. This review will examine GC-derived lymphomas, including follicular lymphomas, Hodgkin lymphomas and angioimmunoblastic T-cell lymphoma, through their integrated cellular microenvironment, highlighting those findings which may serve as a useful surrogate marker for tumour diagnosis or tumour progression, together with key molecules involved in tumour development.