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While studying c-Myc protein expression in several Burkitt lymphoma cell lines and in lymph nodes from a mouse model bearing a translocated

Activating mutations of MYD88 (MYD88L265P being the far most frequent) are found in most cases of Waldenström macroglobulinemia (WM) as well as in various aggressive B-cell lymphoma entities with features of plasma cell (PC) differentiation, such as activated B-cell type diffuse large B-cell lymphoma (DLBCL). To understand how MYD88 activation exerts its transformation potential, we developed a new mouse model in which the MYD88L252P protein, the murine ortholog of human MYD88L265P, is continuously expressed in CD19 positive B-cells together with the Yellow Fluorescent Protein (Myd88L252P mice). In bone marrow, IgM B and plasma cells were expanded with a CD138 expression continuum from IgMhigh CD138low to IgMlow CD138high cells and the progressive loss of the B220 marker. Serum protein electrophoresis (SPE) longitudinal analysis of 40 Myd88L252P mice (16 to 56 weeks old) demonstrated that ageing was first associated with serum polyclonal hyper gammaglobulinemia (hyper Ig) and followed by a monoclonal immunoglobulin (Ig) peak related to a progressive increase in IgM serum levels. All Myd88L252P mice exhibited spleen enlargement which was directly correlated with the SPE profile and was maximal for monoclonal Ig peaks. Myd88L252P mice exhibited very early increased IgM PC differentiation. Most likely due to an early increase in the Ki67 proliferation index, IgM lymphoplasmacytic (LP) and plasma cells continuously expanded with age being first associated with hyper Ig and then with monoclonal Ig peak. This peak was consistently associated with a spleen LP-like B-cell lymphoma. Clonal expression of both membrane and secreted µ chain isoforms was demonstrated at the mRNA level by high throughput sequencing. The Myd88L252P tumor transcriptomic signature identified both proliferation and canonical NF-κB p65/RelA activation. Comparison with MYD88L265P WM showed that Myd88L252P tumors also shared the typical lymphoplasmacytic transcriptomic signature of WM bone marrow purified tumor B-cells. Altogether these results demonstrate for the first time that continuous MYD88 activation is specifically associated with clonal transformation of differentiating IgM B-cells. Since MYD88L252P targets the IgM PC differentiation continuum, it provides an interesting preclinical model for development of new therapeutic approaches to both WM and aggressive MYD88 associated DLBCLs.

Diffuse large B-cell lymphoma (DLBCL) is the most frequent lymphoid malignancy affecting adults. The NF-κB transcription factor family is activated by 2 main pathways, the canonical and the alternative NF-κB activation pathway, with different functions. The alternative NF-κB pathway leads to activation of the transcriptionally active RelB NF-κB subunit. Alternative NF-κB activation status and its role in DLBCL pathogenesis remain undefined. Here, we reveal a frequent activation of RelB in a large cohort of DLBCL patients and cell lines, independently of their activated B-cell–like or germinal center B-cell–like subtype. RelB activity defines a new subset of patients with DLBCL and a peculiar gene expression profile and mutational pattern. Importantly, RelB activation does not correlate with the MCD genetic subtype, enriched for activated B-cell–like tumors carrying MYD88L265P and CD79B mutations that cooperatively activate canonical NF-κB, thus indicating that current genetic tools to evaluate NF-κB activity in DLBCL do not provide information on the alternative NF-κB activation. Furthermore, the newly defined RelB-positive subgroup of patients with DLBCL exhibits a dismal outcome after immunochemotherapy. Functional studies revealed that RelB confers DLBCL cell resistance to DNA damage–induced apoptosis in response to doxorubicin, a genotoxic agent used in the front-line treatment of DLBCL. We also show that RelB positivity is associated with high expression of cellular inhibitor of apoptosis protein 2 (cIAP2). Altogether, RelB activation can be used to refine the prognostic stratification of DLBCL and may contribute to subvert the therapeutic DNA damage response in a segment of patients with DLBCL.

The need to identify new therapeutic approaches to the treatment of cancers of the B lymphoid lineage is crucial. Unlike CRISPR/Cas technology, antisense strategies result in transient modifications of gene expression and lack mutagenic effects at the DNA level. Here, we provide evidence for efficient knockdown of c-REL and RELA expression after treatment with splice switching antisense oligonucleotides (SSO) inducing exon skipping and reading frameshifts. We also developed a tool to facilitate the choice of exons for on purpose inhibition of mouse and human gene expression. Interestingly, treatments with morpholino SSO targeting the c-REL exon 2 donor splice site or RELA exon 5 acceptor splice site elicited very efficient knockdown in diffuse large B cell lymphoma (DLBCL) cell lines and antibody-secreting cells derived from primary human B cells. Consistent with the clinical relevance of c-REL activation in DLBCLs, treatment with c-REL SSO induced major alterations in NF-κB and TNF signalling pathways and strongly decreased cell viability. Altogether, SSO-mediated knockdown is a powerful approach to transiently inhibit the expression of given genes in B-lineage cells that should pave the way for cancer treatments, provided optimized ligand-conjugations for in vivo delivery.Graphical Abstract

Here, we created a conditional transgenic mouse model with insertion of a sequence coding for both MYD88L252P and the Yellow Fluorescent Protein (YFP) into the rosa26-locus. B-cell specific induction of the transgene constantly led to spleen enlargement with expansion of YFP positive B-cells in 8-12 month-old mice, with a moderate B-cell proliferation increase. Being clonal or oligoclonal, these B-cells exhibited a marked morphological and immunophenotypic lymphoplasmocytic aspect with a plasma cell transcriptomic signature and a serum immunoglobulin M peak. Therefore, continuous activation of MYD88 in mice can lead on its own to a lymphoma close to Waldenström Macroglobulinemia.Key pointB-cell specific enforced expression of MYD88L252P leads to a clonal indolent lymphoplasmocytic B-cell lymphoma with a serum IgM peak.

EBV infects and immortalizes B cells in vitro and in vivo. It is the causative agent of most immune deficiency–related lymphoproliferative disorders and is associated with various lymphomas. EBV latency III–transformed B cells are known to express two immunosuppressive molecules, IL-10 and PD-L1, two characteristics of regulatory B cells (Bregs). In this study, we show that, in addition to secretion of the Breg immunosuppressive cytokines IL-10, IL-35, and TGF-β1, EBV latency III–transformed B cells were able to repress proliferation of their autologous T cells preactivated by CD2, CD3, and CD28. This inhibitory effect was likely caused by CD4+ T cells because EBV latency III–transformed B cells induced a strong proliferation of isolated autologous CD8 T cells. Indeed, EBV was able to promote expansion of autologous FOXP3+ CD39high CTLA4+, Helios+, GITR+, LAG3+ CD4 T cells (i.e., regulatory T cells [Tregs]). Two types of Tregs were induced: unconventional CD25neg and conventional CD25pos Tregs. These Tregs expressed both the latency-associated peptide (LAP) and the PD-1 receptor, two markers of functional Tregs. Expansion of both Treg subtypes depended on PD-L1, whose expression was under the control of LMP1, the main EBV oncogene. These results demonstrate that, like Bregs, EBV latency III–transformed B cells exhibit strong immunoregulatory properties. These data provide clues to the understanding of how after EBV primo-infection, EBV-proliferating B cells can survive in an aggressive immunological environment and later emerge to give rise to EBV-associated B cell lymphomas such as in elderly patients.

International audience

Transformation of an indolent B-cell lymphoma is associated with a more aggressive clinical course and poor survival. The role of immune surveillance in the transformation of a B-cell indolent lymphoma towards a more aggressive form is poorly documented. To experimentally address this question, we used the L.CD40 mouse model, which is characterized by B-cell specific continuous CD40 signaling, responsible for spleen indolent clonal or oligoclonal B-cell lymphoma after one year in 60% cases. Immunosuppression was obtained either by T/NK cell depletion or by treatment with the T-cell immunosuppressive drug cyclosporin A. Immunosuppressed L.CD40 mice had larger splenomegaly with increased numbers of B-cells in both spleen and peripheral blood. High-throughput sequencing of immunoglobulin variable segments revealed that clonal expansion was increased in immunosuppressed L.CD40 mice. Tumor B cells of immunosuppressed mice were larger with an immunoblastic aspect, both on blood smears and spleen tissue sections, with increased proliferation rate and increased numbers of activated B-cells. Collectively, these features suggest that immune suppression induced a shift from indolent lymphomas into aggressive ones. Thus, as a preclinical model, immunosuppressed L.CD40 mice reproduce aggressive transformation of an indolent B-cell tumor and highlight the role of the immune surveillance in its clinical course, opening new perspective for immune restoration therapies.

Transformation of an indolent B-cell lymphoma is associated with a more aggressive clinical course and poor survival. The role of immune surveillance in the transformation of a B-cell indolent lymphoma towards a more aggressive form is poorly documented. To experimentally address this question, we used the L.CD40 mouse model, which is characterized by B-cell specific continuous CD40 signaling, responsible for spleen indolent clonal or oligoclonal B-cell lymphoma after one year in 60% cases. Immunosuppression was obtained either by T/NK cell depletion or by treatment with the T-cell immunosuppressive drug cyclosporin A. Immunosuppressed L.CD40 mice had larger splenomegaly with increased numbers of B-cells in both spleen and peripheral blood. High-throughput sequencing of immunoglobulin variable segments revealed that clonal expansion was increased in immunosuppressed L.CD40 mice. Tumor B cells of immunosuppressed mice were larger with an immunoblastic aspect, both on blood smears and spleen tissue sections, with increased proliferation rate and increased numbers of activated B-cells. Collectively, these features suggest that immune suppression induced a shift from indolent lymphomas into aggressive ones. Thus, as a preclinical model, immunosuppressed L.CD40 mice reproduce aggressive transformation of an indolent B-cell tumor and highlight the role of the immune surveillance in its clinical course, opening new perspective for immune restoration therapies.Summary statementHighlighting the role of immune surveillance, transformation of indolent B-cell lymphoma into an aggressive malignancy is experimentally reproduced after T-cell immune suppression in the L.CD40 preclinical mouse model.

Escape from immune control must be important in the natural course of B-cell lymphomas, especially for those with activation of NF-κB. The pre-clinical LMP1/CD40-expressing transgenic mouse model is characterized by B-cell specific CD40 signaling responsible for NF-κB continuous activation with a spleen monoclonal B-cell tumor after 1 year in 60% of cases. LMP1/CD40 tumors B-cells expressed high levels of PD-L1. This expression was dependent on activation of either NF-κB, JAK1/JAK2 or BTK pathways since these pathways were activated in tumor B-cells and ex vivo treatment with the inhibitory molecules PHA-408, ruxolitinib and ibrutinib led to decrease of its expression. Treatment of LMP1/CD40-expressing lymphomatous mice with an anti-PD-L1 monoclonal antibody induced tumor regression with decreased spleen content, activation and proliferation rate of B-cells as well as a marked increase in T-cell activation, as assessed by CD62L and CD44 expression. These results highlight the interest of therapies targeting the PD-1/PD-L1 axis in activated lymphomas with PD-L1 expression, with possible synergies with tyrosine kinase inhibitors.

The repair DNA polymerase β (Polβ), when overexpressed, plays a critical role in generating genetic instability via its interference with the genomic replication program. Up-regulation of Polβ has been reported in many tumor types that exhibit genetic aberrations, including EBV-related B-cell lymphomas. However, the mechanisms responsible for its overexpression have never been examined. Here, we report that both expression and activity of Polβ, in EBV-immortalized B cells, are induced by several natural genetic variants of LMP1, an oncoprotein associated with the vast majority of EBV-related tumors. Conversely, we found that the expression of Polβ decreased when LMP1 signaling was down-regulated by a dominant negative of LMP1 or an inhibitor of the nuclear factor-κB (NF-κB) pathway, the main transduction pathway activated by LMP1, strongly supporting a role of NF-κB in the LMP1-mediated Polβ regulation. Using electrophoretic mobility shift assay experiments from several EBV-immortalized B-cell nuclear extracts, we identified an LMP1-dependent p50/c-Rel heterodimer on a proximal κB binding site (−211 to −199nt) of the Polβ promoter. This result was correlated with a specific Polβ κB transcriptional activity. Taken together, our data enlighten a new mechanism responsible for Polβ overexpression in EBV-infected cells, mediated by LMP1 and dependent on NF-κB activation. [Cancer Res 2009;69(12):5177–85]

In Hodgkin's disease (HD), both neoplastic Reed-Sternberg (RS) cells and bystander B-lymphocytes may be infected by Epstein-Barr virus (EBV). We postulated that if tumorigenic EBV strains did exist, they would be preferentially found in consistently EBV-associated tumors, such as RS cells, and differ significantly from the strains present in other, non-pathological sites of the same patients. In the present study we have compared LMP1-BNLF1 polymorphism of EBV strains infecting RS cells and B-lymphocytes in lymph nodes effected by HD on the one hand, and bystander B-lymphocytes in reactive lymph nodes on the other. It appeared that viral strains detected in HD tissues including RS cells and bystander B-lymphocytes were infected by different, but related EBV strains and were four times more polymorphic than EBV strains infecting bystander B-lymphocytes of reactive lymph nodes. The question arises as to the biological significance of these observations and the origin and chronology of multiple infections in the same patient. Since RS cells are derived from B-lymphocytes it is conceivable that the latter events could have occurred during the proliferation of bystander B-lymphocytes and their EBV episome following an antigenic stimulation.

International audience; Background: Diffuse large B-cell lymphoma (DLBCL) is a fatal malignancy that needs to identify new targets for additional therapeutic options. This study aimed to clarify the clinical and biological significance of endogenous neurotrophin (nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF)) in DLBCL biopsy samples and cell lines.METHODS: We analysed expression of NGF, BDNF, and their receptors (Trk, p75(NTR)) in 51 biopsies and cell lines by immunohistochemistry, immunofluorescence, and western blotting. To investigate the biological role of BDNF/TrkB/p75(NTR) axis, effects of neurotrophin signalling inhibition were determined on tumour cell survival and vascular endothelial growth factor (VEGF) secretion. The pharmacological pan-Trk inhibitor K252a was used for in vitro and in vivo studies.RESULTS: A BDNF/TrkB axis was expressed in all biopsies, which was independent of the germinal centre B-cell (GCB)/non-GCB profile. p75(NTR), TrkB, and BDNF tumour scores were significantly correlated and high NGF expression was significantly associated with MUM1/IRF4, and the non-GCB subtype. Diffuse large B-cell lymphoma cell lines co-expressed neurotrophins and their receptors. The full-length TrkB receptor was found in all cell lines, which was also phosphorylated at Tyr-817. p75(NTR) was associated to Trk and not to its cell death co-receptor sortilin. In vitro, inhibition of neurotrophin signalling induced cell apoptosis. K252a caused cell apoptosis, decreased VEGF secretion, and potentiated rituximab effect, notably in less rituximab-sensitive cells. In vivo, K252a significantly reduced tumour growth and potentiated the effects of rituximab in a GCB-DLBCL xenograft model.CONCLUSIONS: This work argues for a pro-survival role of endogenous neurotrophins in DLBCLs and inhibition of Trk signalling might be a potential treatment strategy for rituximab resistant subgroups.

Epstein–Barr virus (EBV) is associated with Hodgkin’s disease (HD). However, EBV-positive Reed–Sternberg (RS) cells and EBV-positive B lymphocytes co-exist in the same EBV-positive lymph node affected by HD. In a previous report, using total lymph node DNA, the presence of two distinct EBV strains was demonstrated, but their cellular localization (i.e. RS cells vs B lymphocytes) could not be determined. To address this question, three patients with EBV-associated HD were selected in the present study and single-cell PCR of the latent membrane protein-1 (LMP-1) gene from isolated RS cells was performed. In one case, it was clear that RS cells and B lymphocytes were infected by different EBV strains. In the two remaining cases, only one band was detected from total lymph node DNA. However, single-cell PCR showed that RS cells in each sample were infected by single EBV strains, which were different from those detected in lymphoblastoid cell lines derived from EBV-positive B lymphocytes of lymph node cell suspensions from these two patients.

EBV-immortalized B cells induce a complex immune response such that the virus persists as a clinically silent infection for the lifetime of the infected host. B7-H1, also called PD-L1, is a cosignaling molecule of the B7 family that can inhibit activated T cell effectors by interaction with its receptor PD-1. In this work, we have studied the dependence of B7-H1 on NF-κB and c-Myc, the two main transcription factors in EBV latency III proliferating B cells, on various lymphoblastoid and Burkitt lymphoma cell lines, some of them being inducible or not for the EBV latency III program and/or for c-Myc. We found that B7-H1 repressed killing of EBV-immortalized B cells by their autologous T and NK cells. At the mRNA level, NF-κB was a weak inducer whereas c-Myc was a strong repressor of B7-H1 expression, an effect mediated by STAT1 inhibition. At the protein level, B7-H1 molecules were stored in both degradative and unconventional secretory lysosomes. Surface membrane B7-H1 molecules were constitutively internalized and proteolyzed in lysosomes. The EBV latency III program increased the amounts of B7-H1–containing secretory lysosomes and their export to the surface membrane. By repressing actin polymerization, c-Myc blocked secretory lysosome migration and B7-H1 surface membrane export. In addition to B7-H1, various immunoregulatory molecules participating in the immunological synapse are stored in secretory lysosomes. By playing on actin polymerization, c-Myc could thus globally regulate the immunogenicity of transformed B cells, acting on export of secretory lysosomes to plasma membrane.

International audience; BACKGROUND: In Epstein-Barr virus-associated Hodgkin's lymphomas, neoplastic Reed-Sternberg cells and surrounding non-tumor B-cells contain different variants of the LMP1-BNLF1 oncogene. In this study, we raised the question of functional properties of latent membrane protein 1 (LMP1) natural variants from both Reed-Sternberg and non-tumor B-cells. DESIGN AND METHODS: Twelve LMP1 natural variants from Reed-Sternberg cells, non-tumor B-cells of Hodgkin's lymphomas and from B-cells of benign reactive lymph nodes were cloned, sequenced and stably transfected in murine recombinant interleukin-3-dependent Ba/F3 cells to search for relationships between LMP1 cellular origin and oncogenic properties as well as nuclear factor-kappaB activation, and apoptosis protection. RESULTS: LMP1 variants of Reed-Sternberg cell origin were often associated with increased mutation rate and with recurrent genetic events, such as del15bp associated with S to N replacement at codon 309, and four substitutions I85L, F106Y, I122L, and M129I. Oncogenic potential (growth factor-independence plus clonogenicity) was consistently associated with LMP1 variants from Reed-Sternberg cells, but inconstantly for LMP1-variants from non-tumor B-cells. Analysis of LMP1 variants from both normal B-cells and Reed-Sternberg cells indicates that protection against apoptosis through activation of nuclear factor-kappaB - whatever the cellular origin of LMP1 - was maintained intact, regardless of the mutational pattern. CONCLUSIONS: Taken together, our results demonstrate that preserved nuclear factor-kappaB activity and protection against apoptosis would be the minimal prerequisites for all LMP1 natural variants from both normal and tumor cells in Hodgkin's lymphomas, and that oncogenic potential would constitute an additional feature for LMP1 natural variants in Reed-Sternberg cells.

The Epstein-Barr virus (EBV) latency III program imposed by EBNA2 and LMP1 is directly responsible for immortalization of B cells in vitro and is thought to mediate most immunodeficiency-related posttransplant lymphoproliferative diseases in vivo. To answer the question whether and how this proliferation program is related to c-Myc, we have established the transcriptome of both c-Myc and EBV latency III proliferation programs using a Lymphochip specialized microarray. In addition to EBV-positive latency I Burkitt lymphoma lines and lymphoblastoid cell lines (LCLs), we used an LCL expressing an estrogen-regulatable EBNA2 fusion protein (EREB2-5) and derivative B-cell lines expressing a constitutively active or tetracycline-regulatable c- myc gene. A total of 897 genes were found to be fourfold or more up- or downregulated in either one or both proliferation programs compared to the expression profile of resting EREB2-5 cells. A total of 661 (74%) of these were regulated similarly in both programs. Numerous repressed genes were known targets of STAT1, and most induced genes were known to be upregulated by c-Myc and to be involved in cell proliferation. In keeping with the gene expression patterns, inactivation of c-Myc by a chemical inhibitor or by conditional expression of dominant-negative c-Myc and Max mutants led to proliferation arrest of LCLs. Most genes differently regulated in both proliferation programs corresponded to genes induced by NF-κB in LCLs, and many of them coded for immunoregulatory and/or antiapoptotic molecules. Thus, c-Myc and NF-κB are the two main transcription factors responsible for the phenotype, growth pattern, and biological properties of cells driven into proliferation by EBV.

Overexpression and activation of TPM3-ALK tyrosine kinase fusion protein is a causal oncogenic event in the development of Anaplastic Large Cell Lymphoma and Inflammatory Myofibroblastic ALK-positive tumours. Thus, the development of ALK specific tyrosine kinase inhibitors is a current therapeutic challenge. Animal models are essential to assess, in vivo, the efficiency of ALK-oncogene inhibitors and to identify new and/or additional therapeutic targets in the ALK tumorigenesis pathway. Using the tetracycline system to allow conditional and concomitant TPM3-ALK and luciferase expression, we have developed a unique transplant model for bioluminescent TPM3-ALK-induced fibroblastic tumours in athymic nude mice. The reversible TPM3-ALK expression allowed us to demonstrate that this oncogene is essential for the tumour growth and its maintenance. In addition, we showed that this model could be used to precisely assess tumour growth inhibition upon ALK chemical inactivation. As proof of principle, we used the general tyrosine kinase inhibitor herbimycin A to inhibit ALK oncoprotein activity. As expected, herbimycin A treatment reduced tumour growth as assessed both by tumour volume measurement and bioluminescent imaging. We conclude that this transplant model for TPM3-ALK-induced tumours represents a valuable tool not only to accurately and rapidly evaluate in vivo ALK-targeted therapies but also to gain insight into the mechanism of ALK-positive tumour development.

We examined lymph nodes and tonsils from patients with infectious mononucleosis by combined detection of EBV-encoded RNA and a specific marker of natural killer (NK) cells, PEN5. A small number of Epstein-Barr virus (EBV) latently infected nonneoplastic NK cells were detected. Our data demonstrate that NK cells are natural targets of EBV and that infection of these cells is an early event observed during primary EBV infection.

This report describes two cases of human herpesvirus-8 (HHV-8)–associated large cell lymphoma of the bowel in human immunodeficiency virus (HIV)–positive men. Immunohistochemistry provides evidence of HHV-8 infection of the lymphoma cells (LNA1+, vIL-6+). In both cases, lymphoma cells were coinfected by the Epstein-Barr virus. One case was of B-cell lineage, but the second one was of null phenotype with isolated expression of the CD3 molecule. However, in the latter case, assessment of B- or T-cell clonality remained elusive. The chief finding for these two cases was the lack of history of primary effusion lymphoma. There was an apparent restriction of the tumor to the large bowel in the first case. For the second case, the bowel tumor was preceded by lymph node and liver involvement. The cases suggest that the incidence of HHV-8 infection in large cell lymphoma arising in the setting of HIV infection (other than primary effusion lymphoma) may be underestimated and that the detection of the viral gene products would be appropriate for greater understanding of the pathogenesis of these tumors. HUM PATHOL 33:846-849. Copyright 2002, Elsevier Science (USA). All rights reserved.

Epstein-Barr virus (EBV) classically infects and transforms B lymphocytes in vitro, yielding lymphoblastoid cell lines (LCLs). In contrast to other herpesviruses, EBV is not described as an infectious agent for monocytes. However, recent papers described in vitro infection of monocytes leading to abortive or transient viral expression. In the present study, we report the characterization of E1, a monocytic cell line infected and transformed by EBV. This cell line was derived from an LCL by a drastic electroporation and selection of neomycin-resistant cells, unfavorable to B-cell outgrowth. E1 expressed surface molecules of monocytic lineage (CD14, major histocompatibility complex class II, and CD80) and the c-fmsgene, a highly specific marker for the monocytic lineage. This cell line is able to phagocytose and secrete proinflammatory monokines tumor necrosis factor alpha, interleukin-6 (IL-6), and IL-8. E1 cells are tumorigenic after injection in nude mice, and a monocytic cell line obtained from one of these tumors (TE1) displayed immunophenotype and functional properties similar to those of E1. We detected the presence of the EBV genome in both cell lines, as well as expression of theEBNA-1andLMP-1, but notEBNA-2, viral genes, characteristic of a type II latency. LMP-1 influences the phenotype of these monocytic cell lines, as demonstrated by down-regulation of cell proliferation and membrane intercellular adhesion molecule 1 expression due to anLMP-1antisense strategy. This is the first description of a latently infected human monocytic cell line and the first direct demonstration of an instrumental role for LMP-1 in the proliferation of EBV-transformed cell lines expressing a type II latency.

Abstract 5233 Introduction In Activated B-Cell like Diffuse Large B-Cell Lymphomas (ABC DLBCLs) the most commonly affected gene is TNFAIP3, which encodes A20, an ubiquitin modifying enzyme involved in the negative regulation of NF-κB signaling. A20 is itself a target gene of NF-κB and needs to be induced in order to exert its negative feedback effect on NF-κB. Mutations resulting in the inactivation of A20 have been found in a significant proportion of ABC DLBCL cases (Compagno M et al, Nature 2009). The tumor suppressor role of A20 was established by the reintroduction of wild-type A20 in some mutant A20 lymphoma B-cell lines promoting apoptosis, supposedly due to the loss of the ability to inactivate NF-κB. However, a protective effect of A20 against apoptotic stimuli was demonstrated in some cell types. In endothelial cells, A20 protects from TNF- and Fas-mediated apoptosis by inhibiting caspase-8 activation (Daniel S et al, Blood 2004). We thus wanted to understand the relationship between A20 expression, NF-κB activation and protection against apoptosis in B-cells. Methods We have cloned cDNAs coding for wild-type A20 (A20wt), for IκBαS32,36A (constitutively active form of IκBα), and for luciferase (as a control) into a doxycycline double-inducible episomal vector pRT-1, and stably transfected these vectors into an EBV positive lymphoblastoid B-cells line. Induction of p53 mediated apoptosis was performed by treatment of cells with Fludarabine*, whereas induction of caspase-8 dependant was performed with agonist antibodies against Fas (CD95). Results Both A20 and IκBαS32,36A overexpression suppressed NF-κB activity with downregulation of NF-κB target genes. Loss of NF-κB activation by induction of IκBαS32,36A led to increase of spontaneous apoptosis. Oppositely, loss of NF-κB activation by induction of A20 led to decrease of spontaneous apoptosis. Compared with luciferase transfected cells, no effect of A20 overexpression was seen after treatment of cells with anti-CD95 antibodies. Caspase-9 cleavage was significantly decreased and increase of TP53 protein levels was lower in A20 overexpressing cells after Fludarabine* treatment. By contrast, Fludarabine* treatment of IκBαS32,36A expressing cells led to an increase of both TP53 protein levels and caspase-9 cleavage. Therefore, A20 negatively modulated mitochondrial apoptosis pathway despite NF-κB downregulation. Conclusions These results suggest that A20 may exert an anti-apoptotic effect on its own independently of NF-κB activation. We are now looking after the functional properties of A20 natural mutants. Indeed, we can hypothesize that A20 mutants described in ABC DLBCLs have lost their negative feedback effect on NF-κB, but not their protective effect against apoptosis. So, A20 mutants may actively contribute to oncogenesis through their own protective effect on tumor cells. Disclosures: No relevant conflicts of interest to declare.

Not only Burkitt lymphoma (BL) with the translocation of MYC, but also diffuse large B-cell lymphoma (DLBCL) by other mechanisms (mutation, amplification, promoter dysregulation…) are associated with dysregulation of c-Myc, the master transcription factor for proliferation. DLBCL’s are classified in two subgroups: “Germinal center B-cell” (GCB) without and “activated B-cell” (ABC) with constitutive NF-κB activation. This constitutive activation of NF-κB can be the result of genetic alterations (MYD88, A20, TRAF2, and TRAF5) or the activation of B-cell receptor or CD40. These features raise the question of the synergy of action between NF-κB and c-Myc in ABC-DLBCL. We analyzed the effect of a continuous activation of c-Myc in a context of over-activation of NF-κB by several inductors. Our results show that overexpression of c-Myc in the context of induction of NF-κB, i) by EBV latency III program, provides a selective advantage to those cells (gene expression in favor of a high metabolism, intense proliferation and protection against apoptosis), ii) by TLR9 (in vivo and in vitro model) increases the survival and proliferation of B lymphocytes of λc-Myc mice (increase of activated B cells, splenomegaly, increased B cells proliferation, modification of tumor microenvironment), and iii) by CD40, induces a very aggressive B lymphomagenesis in CD40/Myc double transgenic mice, the tumors have a phenotype close to ABC-DLBCL. These results suggest that c-Myc is an NF-κB co-transforming event in aggressive lymphomas with an activated phenotype by NF-κB, such as ABC-DLBCL., A l’instar du lymphome de Burkitt (LB) avec la translocation de MYC, les lymphomes diffus à grandes cellules B (DLBCL) par d'autres mécanismes (mutation, amplification, dérégulation du promoteur) sont associés à une dérégulation de c-Myc, facteur de transcription maitre de la prolifération. Les DLBCL sont classés en deux sous-groupes: « centre germinatif » (GCB) et « cellule B activée » (ABC) avec activation constitutive de NF-κB. Cette activation constitutive de NF-κB peut être le résultat d'altérations génétiques (MYD88, A20, TRAF2 et TRAF5) ou de l'activation du BCR ou CD40. Ces caractéristiques soulèvent la question de la synergie d’action entre NF-κB et c-Myc dans les ABC-DLBCL. Nous avons analysé l’effet d'une activation continue de c-Myc dans un contexte de sur-activation de NF-κB par plusieurs inducteurs. Nos résultats montrent que la surexpression de c-Myc dans un contexte d'induction de NF-κB, i) par le programme EBV latence III, apporte un avantage sélectif à ces cellules (expression génique en faveur d'un métabolisme élevé, prolifération intense et protection contre apoptose), ii) par le TLR9 (modèle in vivo et in vitro), augmente la survie et la prolifération des lymphocytes B des souris λc-Myc (augmentation des cellules B activées, splénomégalie, augmentation de la prolifération des lymphocytes B, modification du microenvironnement tumoral), et iii) par CD40, induit une lymphomagenèse B très agressive dans les souris doubles transgéniques CD40/Myc, les tumeurs ont un phénotype proche des ABC-DLBCL. Ces résultats suggèrent que c-Myc est un événement co-transformant dans les lymphomes agressifs avec un phénotype activé par NF-κB, tel que les ABC-DLBCL.