The genes encoding the histone acetyl-transferases (HATs) CREB binding protein (CREBBP) and EP300 are recurrently mutated in the activated B cell-like and germinal center (GC) B cell-like subtypes of diffuse large B cell lymphoma (DLBCL). Here, we introduced a patient mutation into a human DLBCL cell line using CRISPR and deleted and in the GC B cell compartment of mice. CREBBP-mutant DLBCL clones exhibited reduced histone H3 acetylation, expressed significantly less MHCII, and grew faster than wild-type clones in s.c. and orthotopic xenograft models. Mice lacking Crebbp in GC B cells exhibited hyperproliferation of their GC compartment upon immunization, had reduced MHCII surface expression on GC cells, and developed accelerated MYC-driven lymphomas. Ep300 inactivation reproduced some, but not all, consequences of Crebbp inactivation. MHCII deficiency phenocopied the effects of CREBBP loss in spontaneous and serial transplantation models of MYC-driven lymphomagenesis, supporting the idea that the mutational inactivation of CREBBP promotes immune evasion. Indeed, the depletion of CD4 T cells greatly facilitated the engraftment of lymphoma cells in serial transplantation models. In summary, we provide evidence that both HATs are bona fide tumor suppressors that control MHCII expression and promote tumor immune control; mutational inactivation of CREBBP, but not of EP300, has additional cell-intrinsic engraftment and growth-promoting effects.

Interleukin‐6 (IL‐6) is a growth factor for normal B cells and plasma cell‐derived malignancies. Here, we show that the IL‐6 signaling pathway is also active in a subset of diffuse large B‐cell lymphoma (DLBCL) patients with particularly poor prognosis. Primary DLBCL cells and DLBCL cell lines expressing IL‐6R engraft and form orthotopic lymphomas in humanized mice that ectopically produce human IL‐6, and in mice reconstituted with a human immune system. We show that a subset of DLBCL cases have evolved mechanisms that ensure constitutive activation of the IL‐6 signaling pathway, i.e., the expression of both chains of the IL‐6R, the expression of the cytokine itself, and the mutational inactivation of a negative regulator of IL‐6 signaling, SOCS1. IL‐6 signaling promotes MYC‐driven lymphomagenesis in a genetically engineered model, and treatment with the IL‐6R‐specific antibody tocilizumab reduces growth of primary DLBCL cells and of DLBCL cell lines in various therapeutic settings. The combined results uncover the IL‐6 signaling pathway as a driver and negative prognosticator in aggressive DLBCL that can be targeted with a safe and well‐tolerated biologic.

The sphingosine-1-phosphate receptor S1PR2 and its downstream signaling pathway are commonly silenced in diffuse large B-cell lymphoma (DLBCL), either by mutational inactivation or through negative regulation by the oncogenic transcription factor FOXP1. In this study, we examined the upstream regulators of S1PR2 expression and have newly identified the transforming growth factor-β (TGF-β)/TGF-βR2/SMAD1 axis as critically involved in S1PR2 transcriptional activation. Phosphorylated SMAD1 directly binds to regulatory elements in the locus as assessed by chromatin immunoprecipitation, and the CRISPR-mediated genomic editing of, , or in DLBCL cell lines renders cells unresponsive to TGF-β-induced apoptosis. DLBCL clones lacking any 1 of the 3 factors have a clear growth advantage in vitro, as well as in subcutaneous xenotransplantation models, and in a novel model of orthotopic growth of DLBCL cells in the spleens and bone marrow of MISTRG mice expressing various human cytokines. The loss of induces hyperproliferation of the germinal center (GC) B-cell compartment of immunized mice and accelerates-driven lymphomagenesis in spontaneous and serial transplantation models. The specific loss of in murine GC B-cell phenocopies the effects of loss on GC B-cell hyperproliferation. Finally, we show that SMAD1 expression is aberrantly downregulated in >85% of analyzed DLBCL patients. The combined results uncover an important novel tumor suppressive function of the TGF-β/TGF-βR2/SMAD1/S1PR2 axis in DLBCL, and show that DLBCL cells have evolved to inactivate the pathway at the level of SMAD1 expression.

Key Points SMAD1 is silenced by hypermethylation in DLBCL cell lines and patient samples but not in peripheral blood B cells or lymph nodes. DAC treatment restores SMAD1 expression and reverses DLBCL growth in several xenotransplantation and patient-derived xenograft models.

Investigation of cancer cell lines is important for oncology research to characterize and understand mechanisms of cellular signaling and survival strategies in cancer. We analyzed the mutational profile of 11 diffuse large B-cell lymphoma (DLBCL) cell lines using a customized high throughput sequencing panel. We compared our data to previously published mutation data to better characterize these cell lines and establish consensus on the mutational status of some functionally relevant genes. With our targeted sequencing approach we detected 61 somatic mutations. The most frequently affected gene was TP53. MYD88 mutations were only seen in activated B-cell like cell lines. Overall comparison across different datasets revealed that just around 38% of mutations are reliable and can be validated by at least two independent observations whereas 24% of mutations could not be validated. Our analysis reveals considerable discrepancies regarding the mutational profile of some well-established cell lines.