Non-Hodgkin Lymphomas: Malignancies Arising from Mature B Cells.

Non-Hodgkin lymphomas (NHLs) are a diverse group of entities, both clinically and molecularly. Here, we review the evolution of classification schemes in B-cell lymphoma, noting the now standard WHO classification system that is based on immune cell-of-origin and molecular phenotypes. We review how lymphomas arise throughout the B-cell development process as well as the molecular and clinical features of prominent B-cell lymphomas. We provide an overview of the major progress that has occurred over the past decade in terms of our molecular understanding of these diseases. We discuss treatment options available and focus on a number of the diverse research tools that have been employed to improve our understanding of these diseases. We discuss the problem of heterogeneity in lymphomas and anticipate that the near future will bring significant advances that provide a measurable impact on NHL outcomes.

The whole-genome landscape of Burkitt lymphoma subtypes.

Burkitt lymphoma (BL) is an aggressive, MYC-driven lymphoma comprising 3 distinct clinical subtypes: sporadic BLs that occur worldwide, endemic BLs that occur predominantly in sub-Saharan Africa, and immunodeficiency-associated BLs that occur primarily in the setting of HIV. In this study, we comprehensively delineated the genomic basis of BL through whole-genome sequencing (WGS) of 101 tumors representing all 3 subtypes of BL to identify 72 driver genes. These data were additionally informed by CRISPR screens in BL cell lines to functionally annotate the role of oncogenic drivers. Nearly every driver gene was found to have both coding and non-coding mutations, highlighting the importance of WGS for identifying driver events. Our data implicate coding and non-coding mutations in IGLL5, BACH2, SIN3A, and DNMT1. Epstein-Barr virus (EBV) infection was associated with higher mutation load, with type 1 EBV showing a higher mutational burden than type 2 EBV. Although sporadic and immunodeficiency-associated BLs had similar genetic profiles, endemic BLs manifested more frequent mutations in BCL7A and BCL6 and fewer genetic alterations in DNMT1, SNTB2, and CTCF. Silencing mutations in ID3 were a common feature of all 3 subtypes of BL. In vitro, mass spectrometry-based proteomics demonstrated that the ID3 protein binds primarily to TCF3 and TCF4. In vivo knockout of ID3 potentiated the effects of MYC, leading to rapid tumorigenesis and tumor phenotypes consistent with those observed in the human disease.

TET2 Deficiency Sets the Stage for B-cell Lymphoma.

TET2 is a well-established tumor suppressor in the context of myeloid malignancies, but its role in lymphoma development has been less clear. In this issue of Cancer Discovery, Dominguez and colleagues report that TET2 function is critical for germinal center exit and plasma cell differentiation, and its deficiency can lead to B-cell lymphoma phenotypes.See related article by Dominguez et al., p. 1632.

Genetic convergence of rare lymphomas.

PURPOSE OF REVIEW: We review the genetic foundations of different rare lymphomas to examine their shared origins. These data indicate the potential application of genomics to improve the diagnosis and treatment of these rare diseases. RECENT FINDINGS: Next generation sequencing technologies have provided an important window into the genetic underpinnings of lymphomas. A growing body of evidence indicates that although some genetic alterations are specific to certain diseases, others are shared across different lymphomas. Many such genetic events have already demonstrated clinical utility, such as BRAF V600E that confers sensitivity to vemurafenib in patients with hairy cell leukemia. SUMMARY: The rareness of many lymphoma subtypes makes the conduct of clinical trials and recruitment of significant numbers of patients impractical. However, a knowledge of the shared genetic origins of these rare lymphomas has the potential to inform 'basket' clinical trials in which multiple lymphoma subtypes are included. These trials would include patients based on the presence of alterations in targetable driver genes. Such approaches would be greatly strengthened by a systematic assessment of significant patient numbers from each subtype using next generation sequencing.

GNA13 loss in germinal center B cells leads to impaired apoptosis and promotes lymphoma in vivo.

GNA13 is the most frequently mutated gene in germinal center (GC)-derived B-cell lymphomas, including nearly a quarter of Burkitt lymphoma and GC-derived diffuse large B-cell lymphoma. These mutations occur in a pattern consistent with loss of function. We have modeled the GNA13-deficient state exclusively in GC B cells by crossing the Gna13 conditional knockout mouse strain with the GC-specific AID-Cre transgenic strain. AID-Cre(+) GNA13-deficient mice demonstrate disordered GC architecture and dark zone/light zone distribution in vivo, and demonstrate altered migration behavior, decreased levels of filamentous actin, and attenuated RhoA activity in vitro. We also found that GNA13-deficient mice have increased numbers of GC B cells that display impaired caspase-mediated cell death and increased frequency of somatic hypermutation in the immunoglobulin VH locus. Lastly, GNA13 deficiency, combined with conditional MYC transgene expression in mouse GC B cells, promotes lymphomagenesis. Thus, GNA13 loss is associated with GC B-cell persistence, in which impaired apoptosis and ongoing somatic hypermutation may lead to an increased risk of lymphoma development.

The Chromatin Regulator CHD8 Is a Context-Dependent Mediator of Cell Survival in Murine Hematopoietic Malignancies.

Aberrant chromatin regulation is a frequent driver of leukemogenesis. Mutations in chromatin regulators often result in more stem-like cells that seed a bulk leukemic population. Inhibitors targeting these proteins represent an emerging class of therapeutics, and identifying further chromatin regulators that promote disease progression may result in additional drug targets. We identified the chromatin-modifying protein CHD8 as necessary for cell survival in a mouse model of BCR-Abl+ B-cell acute lymphoblastic leukemia. This disease has a poor prognosis despite treatment with kinase inhibitors targeting BCR-Abl. Although implicated as a risk factor in autism spectrum disorder and a tumor suppressor in prostate and lung cancer, the mechanism of CHD8's activity is still unclear and has never been studied in the context of hematopoietic malignancies. Here we demonstrate that depletion of CHD8 in B-ALL cells leads to cell death. While multiple B cell malignancies were dependent on CHD8 expression for survival, T cell malignancies displayed milder phenotypes upon CHD8 knockdown. In addition, ectopic expression of the Notch1 intracellular domain in a T cell malignancy partially alleviated the detrimental effect of CHD8 depletion. Our results demonstrate that CHD8 has a context-dependent role in cell survival, and its inhibition may be an effective treatment for B lymphoid malignancies.