Prognostic relevance of in vitro response to cell stimulation via surface IgD in binet stage a CLL

Ectonucleotidases in Blood Malignancies: A Tale of Surface Markers and Therapeutic Targets

Leukemia develops as the result of intrinsic features of the transformed cell, such as gene mutations and derived oncogenic signaling, and extrinsic factors, such as a tumor-friendly, immunosuppressed microenvironment, predominantly in the lymph nodes and the bone marrow. There, high extracellular levels of nucleotides, mainly NAD⁺ and ATP, are catabolized by different ectonucleotidases, which can be divided in two families according to substrate specificity: on one side those that metabolize NAD⁺, including CD38, CD157, and CD203a; on the other, those that convert ATP, namely CD39 (and other ENTPDases) and CD73. They generate products that modulate intracellular calcium levels and that activate purinergic receptors. They can also converge on adenosine generation with profound effects, both on leukemic cells, enhancing chemoresistance and homing, and on non-malignant immune cells, polarizing them toward tolerance. This review will first provide an overview of ectonucleotidases expression within the immune system, in physiological and pathological conditions. We will then focus on different hematological malignancies, discussing their role as disease markers and possibly pathogenic agents. Lastly, we will describe current efforts aimed at therapeutic targeting of this family of enzymes.

Expression of COBLL1 encoding novel ROR1 binding partner is robust predictor of survival in chronic lymphocytic leukemia

Chronic lymphocytic leukemia is a disease with up-regulated expression of the transmembrane tyrosine-protein kinase ROR1, a member of the Wnt/planar cell polarity pathway. In this study, we identified COBLL1 as a novel interaction partner of ROR1. COBLL1 shows clear bimodal expression with high levels in chronic lymphocytic leukemia patients with mutated IGHV and approximately 30% of chronic lymphocytic leukemia patients with unmutated IGHV. In the remaining 70% of chronic lymphocytic leukemia patients with unmutated IGHV, COBLL1 expression is low. Importantly, chronic lymphocytic leukemia patients with unmutated IGHV and high COBLL1 have an unfavorable disease course with short overall survival and time to second treatment. COBLL1 serves as an independent molecular marker for overall survival in chronic lymphocytic leukemia patients with unmutated IGHV. In addition, chronic lymphocytic leukemia patients with unmutated IGHV and high COBLL1 show impaired motility and chemotaxis towards CCL19 and CXCL12 as well as enhanced B-cell receptor signaling pathway activation demonstrated by increased PLCγ2 and SYK phosphorylation after IgM stimulation. COBLL1 expression also changes during B-cell maturation in non-malignant secondary lymphoid tissue with a higher expression in germinal center B cells than naïve and memory B cells. Our data thus suggest COBLL1 involvement not only in chronic lymphocytic leukemia but also in B-cell development. In summary, we show that expression of COBLL1, encoding novel ROR1-binding partner, defines chronic lymphocytic leukemia subgroups with a distinct response to microenvironmental stimuli, and independently predicts survival of chronic lymphocytic leukemia with unmutated IGHV.

BCR and chemokine responses upon anti-IgM and anti-IgD stimulation in chronic lymphocytic leukaemia

Dysregulation of B cell receptor (BCR) signalling is a hallmark of chronic lymphocytic leukaemia (CLL) pathology, and targeting BCR pathway kinases has brought great therapeutic advances. Activation of the BCR in lymphoid organs has been associated with CLL cell proliferation and survival, leading to progressive disease. While these responses are mediated predominantly by IgM, the role of IgD is less clear. Seeking to uncover downstream consequences of individual and combined stimulation of the two BCR isotypes, we found an amplification of IgD expression and IgD-mediated calcium signalling by previous stimulation of IgM in CLL. Furthermore, no heterologous downmodulation of the isotypes, as observed in healthy donors, was present. Only marginal downregulation of the expression of various chemokine receptors by α-IgM and α-IgD stimulation was found as compared to normal B cells. Consistently, calcium responses of CLL cells to different chemokines were only weakly affected by preceding BCR activation. In contrast, migration towards the two homeostatic chemokines CXCL12 and CCL21 was differentially regulated by IgM and IgD. While IgM activation reduced migration of CLL cells towards CXCL12, but not CCL21, IgD activation predominantly impacted on CCL21 but not CXCL12-mediated chemotaxis. This indicates that the preference for one chemokine over the other may depend on the functional presence of the two isotypes in CLL. Inhibitors against the kinases Syk, Lyn, and Btk antagonised both BCR- and chemokine-induced calcium signals.

Functional Differences between IgM and IgD Signaling in Chronic Lymphocytic Leukemia

BCR signaling is a central pathogenetic pathway in chronic lymphocytic leukemia (CLL). Most CLL cells express BCRs of IgM and IgD isotypes, but the contribution of these isotypes to functional responses remains incompletely defined. We therefore investigated differences between IgM and IgD signaling in freshly isolated peripheral blood CLL cells and in CLL cells cultured with nurselike cells, a model that mimics the lymph node microenvironment. IgM signaling induced prolonged activation of ERK kinases and promoted CLL cell survival, CCL3 and CCL4 chemokine secretion, and downregulation of BCL6, the transcriptional repressor of CCL3 In contrast, IgD signaling induced activation of the cytoskeletal protein HS1, along with F-actin polymerization, which resulted in rapid receptor internalization and failure to support downstream responses, including CLL cell survival and chemokine secretion. IgM and IgD receptor downmodulation, HS1 and ERK activation, chemokine secretion, and BCL6 downregulation were also observed when CLL cells were cocultured with nurselike cells. The Bruton's tyrosine kinase inhibitor ibrutinib effectively inhibited both IgM and IgD isotype signaling. In conclusion, through a variety of functional readouts, we demonstrate very distinct outcomes of IgM and IgD isotype activation in CLL cells, providing novel insight into the regulation of BCR signaling in CLL.

Microenvironment interactions and B-cell receptor signaling in Chronic Lymphocytic Leukemia: Implications for disease pathogenesis and treatment

Chronic Lymphocytic Leukemia (CLL) is a malignancy of mature B lymphocytes which are highly dependent on interactions with the tissue microenvironment for their survival and proliferation. Critical components of the microenvironment are monocyte-derived nurselike cells (NLCs), mesenchymal stromal cells, T cells and NK cells, which communicate with CLL cells through a complex network of adhesion molecules, chemokine receptors, tumor necrosis factor (TNF) family members, and soluble factors. (Auto-) antigens and/or autonomous mechanisms activate the B-cell receptor (BCR) and its downstream signaling cascade in secondary lymphatic tissues, playing a central pathogenetic role in CLL. Novel small molecule inhibitors, including the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib and the phosphoinositide-3-kinase delta (PI3Kδ) inhibitor idelalisib, target BCR signaling and have become the most successful new therapeutics in this disease. We here review the cellular and molecular characteristics of CLL cells, and discuss the cellular components and key pathways involved in the cross-talk with their microenvironment. We also highlight the relevant novel treatment strategies, focusing on immunomodulatory agents and BCR signaling inhibitors and how these treatments disrupt CLL-microenvironment interactions. This article is part of a Special Issue entitled: Tumor Microenvironment Regulation of Cancer Cell Survival, Metastasis, Inflammation, and Immune Surveillance edited by Peter Ruvolo and Gregg L. Semenza.

Molecular pathways: targeting the microenvironment in chronic lymphocytic leukemia--focus on the B-cell receptor

Interactions between malignant B lymphocytes and the tissue microenvironment play a major role in the pathogenesis of chronic lymphocytic leukemia (CLL) and other B-cell malignancies. The coexistence and coevolution of CLL cells with their tissue neighbors provided the basis for discovery of critical cellular and molecular drivers of the disease and identification of new therapeutic targets. Bone marrow stromal cells (BMSC), monocyte-derived nurselike cells (NLC), and T cells are key players in the CLL microenvironment, which activate and protect CLL cells within the tissues. CLL surface molecules, such as the B-cell antigen receptor (BCR), chemokine receptors, adhesion molecules, and TNF receptor superfamily members (e.g., CD40, BCMA, and BAFF-R) engage in cross-talk with respective tissue ligands. This cross-talk results in survival and expansion of the CLL clone, and protects CLL cells from conventional cytotoxic drugs. Inhibiting these pathways represents an alternative therapeutic strategy to more conventional chemoimmunotherapy. Here, we review central components of the CLL microenvironment, with a particular emphasis on BCR signaling, and we summarize the most relevant clinical advances with inhibitors that target the BCR-associated spleen tyrosine kinase/SYK (fostamatinib), Bruton's tyrosine kinase/BTK (ibrutinib), and PI3Kδ (idelalisib).

Variant B cell receptor isotype functions differ in hairy cell leukemia with mutated BRAF and IGHV genes

A functional B-cell receptor (BCR) is critical for survival of normal B-cells, but whether it plays a comparable role in B-cell malignancy is as yet not fully delineated. Typical Hairy Cell Leukemia (HCL) is a rare B-cell tumor, and unique in expressing multiple surface immunoglobulin (sIg) isotypes on individual tumor cells (mult-HCL), to raise questions as to their functional relevance. Typical mult-HCL also displays a mutated BRAF V(600)E lesion. Since wild type BRAF is a primary conduit for transducing normal BCR signals, as revealed by deletion modelling studies, it is as yet not apparent if mutated BRAF alters BCR signal transduction in mult-HCL. To address these questions, we examined BCR signalling in mult-HCL cases uniformly displaying mutated BRAF and IGHV genes. Two apparent functional sets were delineated by IgD co-expression. In sIgD^+ve mult-HCL, IgD mediated persistent Ca²⁺ flux, also evident via >1 sIgH isotype, linked to increased ERK activation and BCR endocytosis. In sIgD^−ve mult-HCL however, BCR-mediated signals and downstream effects were restricted to a single sIgH isotype, with sIgM notably dysfunctional and remaining immobilised on the cell surface. These observations reveal discordance between expression and function of individual isotypes in mult-HCL. In dual sIgL expressing cases, only a single sIgL was fully functional. We examined effects of anti-BCR stimuli on mult-HCL survival ex-vivo. Significantly, all functional non-IgD isotypes increased ERK1/2 phosphorylation but triggered apoptosis of tumor cells, in both subsets. IgD stimuli, in marked contrast retained tumor viability. Despite mutant BRAF, BCR signals augment ERK1/2 phosphorylation, but isotype dictates functional downstream outcomes. In mult-HCL, sIgD retains a potential to transduce BCR signals for tumor survival in-vivo. The BCR in mult-HCL emerges as subject to complex regulation, with apparent conflicting signalling by individual isotypes when co-expressed with sIgD. This suggests the possibility that mutant BRAF by-passes BCR constraints in mult-HCL.

B cell activation through CD40 and IL4R ligation modulates the response of chronic lymphocytic leukaemia cells to BAFF and APRIL

The two tumour necrosis factor family proteins BAFF (TNFSF13B) and APRIL (TNFSF13) and their receptors [BAFF-R (TNFRSF13C), TACI (TNFRSF13B), BCMA (TNFRSF17)] play a critical role in the survival of normal B cells. The sensitivity of normal B cells to BAFF and APRIL can be modulated by signals regulated by their receptors. This modulation, however, has not been extensively investigated in chronic lymphocytic leukaemia (CLL) cells. We evaluated the expression, regulation and signalling of BAFF and APRIL receptors in normal and in CLL cells upon stimulation through CD40+IL4R and BCR. We further analysed the prognostic value of BAFF and APRIL receptors expression in patients with CLL. BCMA expression was significantly higher on CLL cells than on normal B cells. BCR and CD40+IL4R stimulation promoted an increase in TACI and BCMA expression, cell viability and activation in normal B cells. A similar effect was observed in CLL cells after CD40+IL4R but not BCR stimulation. BCMA expression correlated with unmutated IGHV genes, poor-risk cytogenetics, and short progression-free survival. These findings further characterize the link between CD40+IL4R regulatory signals, BAFF, APRIL and their receptors and the survival of leukaemic cells and clinical features of CLL.

IgD cross-linking induces gene expression profiling changes and enhances apoptosis in chronic lymphocytic leukemia cells

Gene profile and functional changes upon IgD cross-linking were evaluated in chronic lymphocytic leukemia (CLL). Microarrays highlighted responsiveness to IgD in all cases, independently of clinico-biological characteristics. Stimulated samples exhibited the down-regulation of transcripts of B-cell receptor signaling and cell-adhesion at 24h and the up-modulation of differentiation and apoptosis genes at 48 h. A significant increase in apoptosis upon ligation was also documented. Furthermore, comparison between IgD and IgM stimulation displayed a differential transcriptional/functional response. In conclusion, CLL respond to IgD displaying expression changes and cell-death enhancement, indicating the apoptosis induction via-IgD as an alternative approach for CLL management.

Implications of new prognostic markers in chronic lymphocytic leukemia

Several prognostic markers based on genetic, phenotypic, and molecular characteristics of chronic lymphocytic leukemia (CLL) B cells have emerged in the past decade. The clinical utility of these newer prognostic indicators, alone or in combination with each other and other clinical predictive systems, is still being determined. This chapter attempts to define biologic and molecular underpinnings of 3 sets of prognostic indicators in CLL: genetic abnormalities quantified by FISH and/or defined by exploratory sensitive molecular techniques, expression of specific proteins in or on CLL cells (ie, CD38, CD49d, and ZAP-70), and the IGHV mutation status of a CLL clone. Although not demonstrated conclusively, each probably reflects the biologic properties of the leukemic cells of individual CLL patients. This reflection may be direct, indicating a specific property of the CLL cell itself, or indirect, representing how the CLL cell interacts with the host's microenvironment. The new tyrosine kinase inhibitors that are currently in clinical trials support this interpretation. These and other biology-based indicators of patient clinical course and outcome can be used as starting points from which to understand and treat CLL.

Enhanced outgrowth of EBV-transformed chronic lymphocytic leukemia B cells mediated by coculture with macrophage feeder cells

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the clonal expansion of CD5-expressing B lymphocytes that produce mAbs often reactive with microbial or autoantigens. Long-term culture of B-CLL clones would permit the collection and characterization of B-CLL mAbs to study antigen specificity and of B-CLL DNA to investigate molecular mechanisms promoting the disease. However, the derivation of long-term cell lines (eg, by EBV), has not been efficient. We have improved the efficiency of EBV B-CLL transformation of CpG oligonucleotide-stimulated cells by incubating patient peripheral blood mononuclear cells in the presence of an irradiated mouse macrophage cell line, J774A.1. Using this approach, peripheral blood mononuclear cells isolated from 13 of 21 B-CLL patients were transformed as documented by IGHV-D-J sequencing. Four clones grew and retained CD5 expression in culture for 2 to 4 months. However, despite documentation of EBV infection by expression of EBNA2 and LMP1, B-CLL cells died after removal of macrophage feeder cells. Nevertheless, using electrofusion technology, we generated 6 stable hetero-hybridoma cell lines from EBV-transformed B-CLL cells, and these hetero-hybridomas produced immunoglobulin. Thus, we have established enhanced methods of B-CLL culture that will enable broader interrogation of B-CLL cells at the genetic and protein levels.

CD38 and chronic lymphocytic leukemia: a decade later

This review highlights a decade of investigations into the role of CD38 in CLL. CD38 is accepted as a dependable marker of unfavorable prognosis and as an indicator of activation and proliferation of cells when tested. Leukemic clones with higher numbers of CD38(+) cells are more responsive to BCR signaling and are characterized by enhanced migration. In vitro activation through CD38 drives CLL proliferation and chemotaxis via a signaling pathway that includes ZAP-70 and ERK1/2. Finally, CD38 is under a polymorphic transcriptional control after external signals. Consequently, CD38 appears to be a global molecular bridge to the environment, promoting survival/proliferation over apoptosis. Together, this evidence contributes to the current view of CLL as a chronic disease in which the host's microenvironment promotes leukemic cell growth and also controls the sequential acquisition and accumulation of genetic alterations. This view relies on the existence of a set of surface molecules, including CD38, which support proliferation and survival of B cells on their way to and after neoplastic transformation. The second decade of studies on CD38 in CLL will tell if the molecule is an effective target for antibody-mediated therapy in this currently incurable leukemia.

ZAP-70 enhances migration of malignant B lymphocytes toward CCL21 by inducing CCR7 expression via IgM-ERK1/2 activation

ZAP-70 in chronic lymphocytic leukemia (CLL) has been associated with enhanced B-cell receptor (BCR) signaling, survival, and migration. We investigated whether ZAP-70 can directly govern migration and the underlying mechanisms. In the ZAP-70 stably transfected Ramos cell line, IgM stimulation, but no IgD, enhanced phosphorylation of ERK1/2, Akt and Syk, and delayed IgM and CD79b internalization. In contrast, in the Raji cell line, where ZAP-70 was constitutively phosphorylated, ERK1/2, but not Akt, was phosphorylated, suggesting that MAPK pathway mediates ZAP-70 effects. BCR stimulation modulated the expression of CCR7, CXCR4, CXCR5, CD44, CD49d, and CD62L, which were up-regulated in ZAP-70-positive CLL primary subclones. The most dramatic change after BCR engagement in ZAP-70-transfected cells was CCR7 up-regulation, this being impaired by ERK1/2 inhibition and translating into both increased signaling and migration toward CCL21. Primary CLL subclones with high ZAP-70 expression showed increased migration toward CCL21. In conclusion, ZAP-70 ectopic expression led to enhanced BCR signaling after IgM stimulation and increased the expression of CCR7 predominantly via ERK1/2, increasing the response and migration toward CCL21. In primary CLL samples, cellular subsets with high ZAP-70 expression had increased expression of adhesion molecules and chemokine receptors in addition to an enhanced ability to migrate toward CCL21.