Mature B cells leave the bone marrow as naïve B cells and migrate to the secondary lymphoid organs where they encounter the antigen for the first time. This interaction stimulates B cells to rapidly grow and form characteristic histological structures called germinal center. In the germinal centers, B cells are targeted by mechanisms of genetic editing of the immunoglobulin loci, namely somatic hypermutation and class switch recombination, undergo selection for high affinity immunoglobulin receptors and are committed to differentiate into memory B cells or plasma cells. GCs display two histological areas the dark and the light zone that have been characterized as functionally distinct compartments through which B cells recycle multiple times during the germinal center reaction. Overall design: Naïve, germinal center and memory B cells were isolated from three independent donors each.
MEF2B Instructs Germinal Center Development and Acts as an Oncogene in B Cell Lymphomagenesis.
Specimen part, Subject
View SamplesMost human B cell lymphomas (B-NHL) are derived from germinal centers (GCs), the structure where B-cells undergo class switch recombination (CSR) and somatic hypermutation (SHM) and are selected for high-affinity antibody production. The pathogenesis of B-NHL is associated with distinct genetic lesions, including chromosomal translocations and aberrant somatic hypermutation, which appear to arise from mistakes occurring during CSR and SHM. To ascertain the role of CSR and SHM in lymphomagenesis, we crossed three oncogene-driven (MYC, BCL6, MYC/BCL6) mouse models of B cell lymphoma with mice lacking activation-induced cytidine deaminase (AID), the enzyme required for both processes.
AID is required for germinal center-derived lymphomagenesis.
Specimen part
View SamplesSomatic mutations of the MLL2 methyltransferase gene represent a common genetic lesion in multiple cancer types. In diffuse large B cell lymphoma (DLBCL) and follicular lymphoma (FL) (collectively, over 70% of all lymphoma diagnoses), these mutations are highly recurrent and appear early during transformation, possibly in pre-malignant precursors. Here we show that FL- and DLBCL-associated MLL2 mutations impair its enzymatic activity and lead to diminished global H3K4 methylation in normal germinal-center (GC) B cells and DLBCL, consistent with the enrichment of MLL2 binding at enhancer and promoter regions marked by mono- and tri-methylation. Conditional deletion of Mll2 early during B cell development, but not after initiation of the GC reaction, leads to increased percentages and numbers of GC B cells, which feature a distinct transcriptional profile defined by the enrichment of cell-cycle regulatory and B-cell receptor signaling genes. Consistently, Mll2-deficient B cells exhibit proliferative advantage and accumulation in the S phase of the cell cycle, which is influenced by the number of cell divisions. While GC-specific loss of Mll2 was not sufficient to initiate malignant transformation, compound Mll2-deficient/BCL2-transgenic mice displayed an increased incidence of clonal lymphoproliferations resembling the features of human FL and DLBCL. These findings suggest that early MLL2 loss favors BCL2-induced lymphomagenesis by remodeling the epigenetic landscape of the cancer precursor cells. Eradication of MLL2-deficient cells may represent a rational therapeutic approach targeting early tumorigenic events.
Disruption of KMT2D perturbs germinal center B cell development and promotes lymphomagenesis.
Sex, Specimen part
View SamplesInactivating mutations of the gene encoding for the CREBBP acetyltransferase are highly frequent in diffuse large B cell lymphoma (DLBCL, 30% of cases) and follicular lymphoma (FL, 60% of cases), the two most common cancers derived from thegerminal-center (GC). However, the role of CREBBP inactivation in lymphomagenesisremains unclear. Using functional epigenomics and mouse genetics, here we definethe program modulated by CREBBP in primary human GC B cells and show thatCREBBP regulates enhancer/super-enhancer networks, with specific roles in GC/post-GC cell fate decisions. Conditional GC-specific deletion of Crebbp in the mouseperturbs the expression of a limited set of genes involved in the regulation of signaltransduction (BCR, TLR and CD40), lineage specification (NF-B and BCL6) andterminal B cell differentiation (PRDM1, IRF4). Consistently, Crebbp-deficient B cellsexhibit proliferative advantage and show impaired plasma cell differentiation. WhileGC-specific loss of Crebbp was not sufficient to initiate malignant transformation,compound Crebbp-haploinsufficient/BCL2-transgenic mice, mimicking the genetics ofFL and DLBCL, display an increased incidence of clonal lymphoid malignanciesrecapitulating the features of the human diseases. These findings establish CREBBPas a haploinsufficient tumor suppressor gene in GC B cells and provide insights intothe mechanisms and targes by which loss of CREBBP contributes to lymphomagenesis.
The CREBBP Acetyltransferase Is a Haploinsufficient Tumor Suppressor in B-cell Lymphoma.
Sex, Specimen part
View SamplesDiffuse large B-cell lymphoma (DLBCL), the most common form of lymphoma in adulthood, comprises multiple biologically and clinically distinct subtypes including germinal center B cell-like (GCB) and activated B cell like (ABC) DLBCL. Gene expression profile studies have shown that its most aggressive subtype, ABC-DLBCL, is associated with constitutive activation of the NF-kB transcription complex. However, except for a small fraction of cases, it remains unclear whether NF-kB activation in these tumors represents an intrinsic program of the tumor cell of origin or a pathogenetic event. Here we show that >50% of ABC-DLBCL and a smaller fraction of GCB-DLBCL carry somatic mutations at multiple genes, including negative (TNFAIP3/A20) and positive (CARD11, TRAF2, TRAF5, MAP3K7/TAK1 and TNFRSF11A/RANK) regulators of NF-kB. Of these, the A20 gene, which encodes for a ubiquitin-modifying enzyme involved in termination of NF-kB responses, is the most commonly affected one, with ~30% of the patients displaying biallelic inactivation by mutations and/or deletions, suggesting a tumor suppressor role. Less frequently, missense mutations of TRAF2 and CARD11 produce molecules with significantly enhanced ability to activate NF-kB. Thus, our results demonstrate that NF-kB activation in DLBCL is caused by genetic lesions affecting multiple genes, whose loss or activation may promote lymphomagenesis by leading to abnormally prolonged NF-kB responses.
Mutations of multiple genes cause deregulation of NF-kappaB in diffuse large B-cell lymphoma.
Specimen part, Cell line
View SamplesHeirarchical development of B-cells involves the induction and supression of large sets of genes that provide the basis for differentiation and, ultimately, antibody production.
Signatures of murine B-cell development implicate Yy1 as a regulator of the germinal center-specific program.
Specimen part
View SamplesThis SuperSeries is composed of the SubSeries listed below.
The B-cell receptor controls fitness of MYC-driven lymphoma cells via GSK3β inhibition.
No sample metadata fields
View SamplesSimilar to resting mature B cells, where the B-cell antigen receptor (BCR) is essential for cellular survival, surface BCR expression is conserved in most mature B cell lymphomas. The identification of activating BCR mutations and the growth disadvantage upon BCR knockdown of cells of certain lymphoma entities has led to the view that BCR signaling is required for tumour cell survival. Consequently, the BCR signaling machinery has become a new target in the therapy of B cell malignancies. Here, we studied the effects of BCR ablation on MYC-driven mouse B cell lymphomas and compared them to observations in human Burkitt lymphoma. Whereas BCR ablation did not, per se, significantly affect lymphoma growth, BCR-negative (BCR-) tumour cells rapidly disappeared in the presence of their BCR-expressing (BCR+) counterparts in vitro and in vivo. This required neither cellular contact, nor factors released by BCR+ tumour cells. Instead, BCR loss induced the rewiring of central carbon metabolism increasing the sensitivity of receptor-less lymphoma cells to nutrient restriction. The BCR attenuated GSK3 activity to support MYC-controlled gene expression. BCR- tumour cells exhibited increased GSK3 activity and were rescued from their competitive growth disadvantage by GSK3. BCR-negative lymphoma variants that restored competitive fitness, normalized GSK3 following constitutive activation of the MAPK pathway, commonly through Ras mutations. Similarly, in Burkitt lymphoma, activating RAS mutations may propagate Ig-crippled tumour cells, which usually represent a minority of the tumour bulk. Thus, while BCR expression enhances lymphoma cell fitness, BCR-targeted therapies may profit from combinations with drugs targeting BCR-less tumour cells.
The B-cell receptor controls fitness of MYC-driven lymphoma cells via GSK3β inhibition.
No sample metadata fields
View SamplesWe used RNA sequencing to characterize gene expression of Ly75+/+ B1-8hi and Ly75-/- B1-8hi B cells from the germinal center light zone (LZ) 12 h after forcing positive selection of the Ly75+/+ population with anti-DEC205-OVA. Overall design: We primed C57BL/6 hosts with OVA-alum i.p. and after 2 weeks we adoptively transferred a mixture of B1-8hi B cells in which 15% were Ly75+/+ CD45.1 (DECP) and 85% were Ly75-/- CD45.1/2 (DECN). We then immunized the animals with NP-OVA in the footpads and after 6 days we injected anti-DEC205-OVA. 12 h or 24 h after anti-DEC205-OVA injection we sorted B220+ CD38- CD95+ CD45.1+ CD45.2- CD83hi CXCR4lo (DECPLZ) and B220+ CD38- CD95+ CD45.1+ CD45.2+ CD83hi CXCR4lo (DECNLZ) cells for whole transcriptome analysis by mRNA sequencing.
Germinal Center Selection and Affinity Maturation Require Dynamic Regulation of mTORC1 Kinase.
Specimen part, Cell line, Subject
View SamplesWe used RNA sequencing to characterize gene expression of dendritic cells from mouse lymph node that, based on LIPSTIC labeling, underwent interaction with CD4+ T cells. Overall design: Antigen pulsed dendritic cells (DCs) were transferred into recipient mice, followed by antigen specific CD4+ T cells. Forty-eight hours after T cell transfer, endogenous dendritic cells were isolated by facs sorting from mouse lymph node and analyzed based on their in vivo LIPSTIC labeling.
Monitoring T cell-dendritic cell interactions in vivo by intercellular enzymatic labelling.
Specimen part, Cell line, Subject
View Samples