Charting differences between tumors and normal tissue is a mainstay of cancer research. However, clonal tumor expansion from complex normal tissue architectures potentially obscures cancer-specific events, including divergent epigenetic patterns. Using whole-genome bisulfite sequencing of normal B cell subsets, we observed broad epigenetic programming of selective transcription factor binding sites coincident with the degree of B cell maturation. By comparing normal B cells to malignant B cells from 268 patients with chronic lymphocytic leukemia (CLL), we showed that tumors derive largely from a continuum of maturation states reflected in normal developmental stages. Epigenetic maturation in CLL was associated with an indolent gene expression pattern and increasingly favorable clinical outcomes. We further uncovered that most previously reported tumor-specific methylation events are normally present in non-malignant B cells. Instead, we identified a potential pathogenic role for transcription factor dysregulation in CLL, where excess programming by EGR and NFAT with reduced EBF and AP-1 programming imbalances the normal B cell epigenetic program.

The generation and functions of human peripheral blood (PB) IgM CD27+ B cells to migrate to B-cell follicles and undergo germinal center (GC) B-cell differentiation, whereas activated IgG + memory B cells preferentially showed a plasma cell (PC) fate. This observation was supported by reverse regulation of B-cell lymphoma 6 and PR domain containing 1 and differential BTB and CNC homology 1, basic leucine zipper transcription factor 2 expression. Moreover, IgM

Unmutated CLL derives from unmutated mature CD5+ B cells and mutated CLL derives from CD5+CD27+ post–germinal center B cells.

Lymphomas are assumed to originate at different stages of lymphocyte development through chromosomal aberrations. Thus, different lymphomas resemble lymphocytes at distinct differentiation stages and show characteristic morphologic, genetic, and transcriptional features. Here, we have performed a microarray-based DNA methylation profiling of 83 mature aggressive B-cell non-Hodgkin lymphomas (maB-NHLs) characterized for their morphologic, genetic, and transcriptional features, including molecular Burkitt lymphomas and diffuse large B-cell lymphomas. Hierarchic clustering indicated that methylation patterns in maB-NHLs were not strictly associated with morphologic, genetic, or transcriptional features. By supervised analyses, we identified 56 genes de novo methylated in all lymphoma subtypes studied and 22 methylated in a lymphoma subtype-specific manner. Remarkably, the group of genes de novo methylated in all lymphoma subtypes was significantly enriched for polycomb targets in embryonic stem cells. De novo methylated genes in all maB-NHLs studied were expressed at low levels in lymphomas and normal hematopoietic tissues but not in nonhematopoietic tissues. These findings, especially the enrichment for polycomb targets in stem cells, indicate that maB-NHLs with different morphologic, genetic, and transcriptional background share a similar stem cell-like epigenetic pattern. This suggests that maB-NHLs originate from cells with stem cell features or that stemness was acquired during lymphomagenesis by epigenetic remodeling. (Blood. 2009; 113:2488-2497 IntroductionAberrant DNA methylation is a hallmark of cancer. Virtually all cancer types are associated with alterations of the methylome. These include global DNA hypomethylation, mostly targeting DNA repeats, and hypermethylation of CpG islands located in the promoter regions of tumor suppressor genes. [1][2][3][4] It is widely accepted that tumor suppressor gene inactivation by DNA hypermethylation allows the tumor clone to obtain a selective (eg, proliferative) advantage. However, recent reports have provided evidence for an instructive mechanism behind aberrant DNA methylation in cancer, which might indicate that specific sequences are predisposed to acquire epigenetic alterations. [5][6][7][8][9] Remarkably, 3 independent reports have recently shown that a highly significant proportion of genes becoming hypermethylated in cancer were already repressed at the embryonic stem cell (ESC) stage by polycomb group (PcG) marks. 7-9 These findings are considered to support the "cancer stem cell theory" in which The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked ''advertisement'' in accordance with 18 USC section 1734. For personal use only. on May 13, 2018. by guest www.bloodjournal.org From aberrant epigenetic changes of PcG target genes occurring in a cell with stem cell features might represent the ...

The origin of IgM+CD27+ B lymphocytes with mutated IgV genes, which account for ∼20% of human peripheral blood (PB) B cells, is controversially discussed. A generation in a primary diversification pathway, in T cell–independent immune responses, or in T cell–dependent germinal center (GC) reactions has been proposed. We show here that IgM+IgD+CD27+ and IgM+IgD−/lowCD27+ B cell subsets carry, like class-switched memory B cells, mutations in the Bcl6 gene as a genetic trait of a GC experience. Moreover, the identification of PB IgM+IgD+CD27+ B cells clonally related to GC-derived IgG+ memory B cells with shared and distinct IgV gene mutations demonstrates the GC origin also of the former subset. These findings provide genetic evidence for a GC derivation of somatically mutated IgM+ B cells and indicate that adult humans harbor a large population of IgM+IgD+ post-GC memory B cells. Furthermore, the analysis revealed that a highly diverse and often very large population of memory B cells is generated from a given GC B cell clone, and that (preferentially IgM) memory B cells are generated already early in the GC reaction. This provides novel insights into the dynamics of GC reactions and the generation of a memory B cell repertoire.

SummaryTumor cell survival critically depends on heterotypic communication with benign cells in the microenvironment. Here, we describe a survival signaling pathway activated in stromal cells by contact to B cells from patients with chronic lymphocytic leukemia (CLL). The expression of protein kinase C (PKC)-βII and the subsequent activation of NF-κB in bone marrow stromal cells are prerequisites to support the survival of malignant B cells. PKC-β knockout mice are insusceptible to CLL transplantations, underscoring the in vivo significance of the PKC-βII-NF-κB signaling pathway in the tumor microenvironment. Upregulated stromal PKC-βII in biopsies from patients with CLL, acute lymphoblastic leukemia, and mantle cell lymphoma suggests that this pathway may commonly be activated in a variety of hematological malignancies.

A key feature of the adaptive immune system is the generation of memory B and T cells and long-lived plasma cells, providing protective immunity against recurring infectious agents. Memory B cells are generated in germinal center (GC) reactions in the course of T cell-dependent immune responses and are distinguished from naive B cells by an increased lifespan, faster and stronger response to stimulation and expression of somatically mutated and affinity matured immunoglobulin (Ig) genes. Approximately 40% of human B cells in adults are memory B cells, and several subsets were identified. Besides IgG and IgA memory B cells, ∼50% of peripheral blood memory B cells express IgM with or without IgD. Further smaller subpopulations have additionally been described. These various subsets share typical memory B cell features, but likely also fulfill distinct functions. IgM memory B cells appear to have the propensity for refined adaptation upon restimulation in additional GC reactions, whereas reactivated IgG B cells rather differentiate directly into plasma cells. The human memory B-cell pool is characterized by (sometimes amazingly large) clonal expansions, often showing extensive intraclonal IgV gene diversity. Moreover, memory B-cell clones are frequently composed of members of various subsets, showing that from a single GC B-cell clone a variety of memory B cells with distinct functions is generated. Thus, the human memory B-cell compartment is highly diverse and flexible. Several B-cell malignancies display features suggesting a derivation from memory B cells. This includes a subset of chronic lymphocytic leukemia, hairy cell leukemia and marginal zone lymphomas. The exposure of memory B cells to oncogenic events during their generation in the GC, the longevity of these B cells and the ease to activate them may be key determinants for their malignant transformation.

Following individual development by means of the 'sandwich method' the duration of egg, larval, and pupal stages, as well as of adult maturation feeding of the spruce bark beetle (Ips typographus) was measured at constant temperatures in the range between 12" and 33°C. At 20°C complete development from egg to adult emerging from pupa averaged 29 days. The proportion of the duration of larval development relative to total preimaginal development increased with temperature. Developmental rates, i.e. the speed of development increased linearly with temperature in a range between 15" and 25°C. Based on linear regressions, lower developmental thresholds were calculated to be 10.6"C (eggs), 8.2"C (larvae), 9.9"C (pupae), and 8.3"C (preimaginal development egg to pupa), respectively. Differing heat sums reported in the literature matched ours when recalculated with our developmental thresholds. A nonlinear model (Logan/Lactin) was fitted to the data which allowed to describe development in the entire temperature range. It further permits to identify lower and upper ( FZ 40°C) developmental thresholds as well as optimum temperatures (30-33°C) of the instars.