The proliferation center microenvironment and prognostic markers in chronic lymphocytic leukemia/small lymphocytic lymphoma

Early reappearance of intraclonal proliferative subpopulations in ibrutinib-resistant chronic lymphocytic leukemia

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib represents an effective strategy for treatment of chronic lymphocytic leukemia (CLL), nevertheless about 30% of patients eventually undergo disease progression. Here we investigated by flow cytometry the long-term modulation of the CLL CXCR4dim/CD5bright proliferative fraction (PF), its correlation with therapeutic outcome and emergence of ibrutinib resistance. By longitudinal tracking, the PF, initially suppressed by ibrutinib, reappeared upon early disease progression, without association with lymphocyte count or serum beta-2-microglobulin. Somatic mutations of BTK/PLCG2, detected in 57% of progressing cases, were significantly enriched in PF with a 3-fold greater allele frequency than the non-PF fraction, suggesting a BTK/PLCG2-mutated reservoir resident within the proliferative compartments. PF increase was also present in BTK/PLCG2-unmutated cases at progression, indicating that PF evaluation could represent a marker of CLL progression under ibrutinib. Furthermore, we evidence different transcriptomic profiles of PF at progression in cases with or without BTK/PLCG2 mutations, suggestive of a reactivation of B-cell receptor signaling or the emergence of bypass signaling through MYC and/or Toll-Like-Receptor-9. Clinically, longitudinal monitoring of the CXCR4dim/CD5bright PF by flow cytometry may provide a simple tool helping to intercept CLL progression under ibrutinib therapy.

The complexities of T-cell dysfunction in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy characterized by profound alterations and defects in the T-cell compartment. This observation has gained renewed interest as T-cell treatment strategies, which are successfully applied in more aggressive B-cell malignancies, have yielded disappointing results in CLL. Despite ongoing efforts to understand and address the observed T-cell defects, the exact mechanisms and nature underlying this dysfunction remain largely unknown. In this review, we examine the supporting signals from T cells to CLL cells in the lymph node niche, summarize key findings on T-cell functional defects, delve into potential underlying causes, and explore novel strategies for reversing these deficiencies. Our goal is to identify strategies aimed at resolving CLL-induced T-cell dysfunction which, in the future, will enhance the efficacy of autologous T-cell-based therapies for CLL patients.

Translation of Data from Animal Models of Cancer to Immunotherapy of Breast Cancer and Chronic Lymphocytic Leukemia

The field of clinical oncology has been revolutionized over the past decade with the introduction of many new immunotherapies the existence of which have depended to a large extent on experimentation with both in vitro analysis and the use of various animal models, including gene-modified mice. The discussion below will review my own laboratory's studies, along with those of others in the field, on cancer immunotherapy. Our own studies have predominantly dwelt on two models of malignancy, namely a solid tumor model (breast cancer) and lymphoma. The data from our own laboratory, and that of other scientists, highlights the novel information so obtained, and the evidence that application of such information has already had an impact on immunotherapy of human oncologic diseases.

B Cell Subsets and Immune Checkpoint Expression in Patients with Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is characterized by dysfunctional B cells. Immune checkpoint molecules such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed death-1 (PD-1) are upregulated in patients with CLL and may correlate with prognostic markers such as beta-2 microglobulin (B2M). The aim of this study was to evaluate the levels of immune checkpoints on B cell subsets and to further correlate them with B2M levels in patients with CLL. We recruited 21 patients with CLL and 12 controls. B cell subsets and the levels of immune checkpoint expression were determined using conventional multi-color flow cytometry. Basal levels of B2M in patients with CLL were measured using an enzyme-linked immunosorbent assay. Patients with CLL had increased levels of activated B cells when compared to the control group, p < 0.001. The expression of PD-1 and CTLA-4 were increased on activated B cells and memory B cells, p < 0.05. There were no associations between B2M levels and the measured immune checkpoints on B cell subsets, after adjusting for sex and age. In our cohort, the patients with CLL expressed elevated levels of PD-1 and CTLA-4 immune checkpoints on activated and memory B cell subsets. However, there was no correlation between these immune checkpoint expressions and B2M levels.

The Role of the Microenvironment and Cell Adhesion Molecules in Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy whose progression largely depends on the lymph node and bone marrow microenvironment. Indeed, CLL cells actively proliferate in specific regions of these anatomical compartments, known as proliferation centers, while being quiescent in the blood stream. Hence, CLL cell adhesion and migration into these protective niches are critical for CLL pathophysiology. CLL cells are lodged in their microenvironment through a series of molecular interactions that are mediated by cellular adhesion molecules and their counter receptors. The importance of these adhesion molecules in the clinic is demonstrated by the correlation between the expression levels of some of them, in particular CD49d, and the prognostic likelihood. Furthermore, novel therapeutic agents, such as ibrutinib, impair the functions of these adhesion molecules, leading to an egress of CLL cells from the lymph nodes and bone marrow into the circulation together with an inhibition of homing into these survival niches, thereby preventing disease progression. Several adhesion molecules have been shown to participate in CLL adhesion and migration. Their importance also stems from the observation that they are involved in promoting, directly or indirectly, survival signals that sustain CLL proliferation and limit the efficacy of standard and novel chemotherapeutic drugs, a process known as cell adhesion-mediated drug resistance. In this respect, many studies have elucidated the molecular mechanisms underlying cell adhesion-mediated drug resistance, which have highlighted different signaling pathways that may represent potential therapeutic targets. Here, we review the role of the microenvironment and the adhesion molecules that have been shown to be important in CLL and their impact on transendothelial migration and cell-mediated drug resistance. We also discuss how novel therapeutic compounds modulate the function of this important class of molecules.

Proliferative Signals in Chronic Lymphocytic Leukemia; What Are We Missing?

Chronic lymphocytic leukemia (CLL) cells cycle between lymphoid tissue sites where they actively proliferate, and the peripheral blood (PB) where they become quiescent. Strong evidence exists for a crucial role of B cell receptor (BCR) triggering, either by (self-)antigen or by receptor auto-engagement in the lymph node (LN) to drive CLL proliferation and provide adhesion. The clinical success of Bruton's tyrosine kinase (BTK) inhibitors is widely accepted to be based on blockade of the BCR signal. Additional signals in the LN that support CLL survival derive from surrounding cells, such as CD40L-presenting T helper cells, myeloid and stromal cells. It is not quite clear if and to what extent these non-BCR signals contribute to proliferation in situ. In vitro BCR triggering, in contrast, leads to low-level activation and does not result in cell division. Various combinations of non-BCR signals delivered via co-stimulatory receptors, Toll-like receptors (TLRs), and/or soluble cytokines are applied, leading to comparatively modest and short-lived CLL proliferation in vitro. Thus, an unresolved gap exists between the condition in the patient as we now understand it and applicable knowledge that can be harnessed in the laboratory for future therapeutic applications. Even in this era of targeted drugs, CLL remains largely incurable with frequent relapses and emergence of resistance. Therefore, we require better insight into all aspects of CLL growth and potential rewiring of signaling pathways. We aim here to provide an overview of in vivo versus in vitro signals involved in CLL proliferation, point out areas of missing knowledge and suggest future directions for research.

Mechanisms of Resistance to Targeted Therapies in Chronic Lymphocytic Leukemia

Even if treatment options for Chronic Lymphocytic Leukemia (CLL) patients have changed dramatically in the past few years, with the approval of targeted therapeutic agents, the disease remains incurable. Beside intrinsic genetic features characterizing the leukemic cell, signals coming from the microenvironment have a key role in promoting cell survival and in protecting CLL cells from the action of drugs. Consequently, the identification of previously unrecognized genetic lesions is important in risk-stratification of CLL patients and is progressively becoming a critical tool for choosing the best therapeutic strategy. Significant efforts have also been dedicated to define microenvironment-dependent mechanisms that sustain leukemic cells favoring survival, proliferation, and accumulation of additional genetic lesions. Furthermore, understanding the molecular and biological mechanisms, potentially driving disease progression and chemoresistance, is the first step to design therapies that could be effective in high-risk patients. Significant progress has been made in the identification of the different mechanisms through which patients relapse after "new" and "old" therapies. These studies have led to the development of targeted strategies to overcome, or even prevent, resistance through the design of novel agents or their combination.In this chapter we will give an overview of the main therapeutic options for CLL patients and review the mechanisms of resistance responsible for treatment failure. Potential strategies to overcome or prevent resistance will be also discussed.

High-resolution melting analysis for rapid and sensitive MYD88 screening in chronic lymphocytic leukemia

High resolution melting (HRM) assay is a novel technology for the fast, high-throughput, sensitive, post-PCR analysis of genetic mutations. Myeloid differentiation primary response 88 (MYD88) mutations are frequently reported in chronic lymphocytic leukemia (CLL) and confer a worse prognosis. The objective of the present study was to assess the value of HRM analysis for the rapid screening of MYD88 mutations in patients with CLL. Genomic DNA samples were extracted from the bone marrow of 129 newly diagnosed patients with CLL. A plasmid with an MYD88-L265P mutation was constructed, and the p.L265P substitution, which is the predominant MYD88 mutation in CLL, was detected using HRM analysis and direct sequencing. The plasmid pCMV-MYD88-L265P-Mu was successfully constructed as a positive control, and was verified by direct sequencing. The normalized and shifted melting curves of 6/129 (4.65%) samples were clearly different from those of other patients by HRM analysis. In addition, the 794T>C mutation in MYD88 was identified in 6 (4.65%) patients by direct sequencing. Sensitivity evaluation revealed that the HRM assay had a higher sensitivity (to 1% dilution) than direct sequencing, in addition to being convenient and time-saving. The MYD88 p.L256P mutation has been implicated to be associated with adverse prognosis in CLL. HRM analysis has the potential to be a routine prescreening technique to identify the MYD88 p.L256P mutation and may facilitate the clinical treatment of CLL.

Exosome-carried microRNA-based signature as a cellular trigger for the evolution of chronic lymphocytic leukemia into Richter syndrome

Even if considered a cumulative and not a proliferative CD5+ B-cell neoplasm, chronic lymphocytic leukemia (CLL) has a proliferation rate higher than that recognized earlier, especially in the lymphoid tissues. Some patients with CLL develop a clinical syndrome entitled Richter syndrome (RS). Understanding CLL genetics and epigenetics may help to elucidate the molecular basics of the clinical heterogeneity of this type of malignancy. In the present project we aimed to identify a microRNA species that can predict the evolution of therapy-resistant CLL towards RS. In the first phase of our study, microRNA-19b was identified as a possible target, and in the second phase, we transfected three different CLL cell lines with microRNA-19b mimic and inhibitor and assessed the potential role on leukemia cells in vitro. The mechanism by which miR-19b acts were identified as the upregulation of Ki67 and downregulation of p53. This was further supported through RT-PCR and western blotting on CLL cell lines, as well as by next generation sequencing on two patients diagnosed with CLL that evolved into RS.

Chronic lymphocytic leukemia with proliferation centers in bone marrow is associated with younger age at initial presentation, complex karyotype, and TP53 disruption

The presence of expanded proliferation centers (PCs) in lymph nodes involved by chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma has been associated with adverse clinical outcomes, but the frequency and significance of PCs in bone marrow (BM) remain unclear. The study group included 36 patients with BM involvement by CLL in which PCs were present. We compared this group with 110 randomly selected BM samples involved by CLL without morphologically discernable PCs. Patients with PCs in BM were younger (median age, 53 years [range,18-71 years] versus 58 years [range, 31-82 years]; P = .007), more frequently experienced B symptoms (27.8% versus 8.2%, P = .0076), more often had Rai stage IV disease (30.6% versus 17.3%, P = .02) and higher serum lactate dehydrogenase (P = .0037) and β₂-microglobulin (P = .0001) levels, and lower hemoglobin (P = .026) and platelet counts (P = .0422). TP53 alterations were more common in patients with PCs in BM (45.4% versus 18.7%; P = .0049), as was a complex karyotype (26.4% versus 9%; P = .019). There were no significant differences in the frequency of ZAP70 or CD38 positivity or IGHV mutation status. The median time to first treatment was shorter in patients with PCs in BM (7 months versus 19 months, P = .047), and the frequency of Richter syndrome was higher (14% versus 4%, P = .041). Patients with PCs in BM had significantly shorter overall survival compared with the control group (median, 249.3 months versus undefined; P = .0241). These data suggest that identification of PCs in BM samples involved by CLL is associated with adverse prognostic features.

Identification of new phosphorylation sites of CD23 in B-cells of patients with chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (B-CLL) is the most common lymphoproliferative disorder in adults. Patients with B-CLL strongly express the CD23 - C type of lectin (low affinity IgE receptor, Fc epsilon RII), which is linked to B cell activation and proliferation. Phosphorylation in lymphocytes is tightly associated with regulation of protein activities, functional regulation and cell signaling, and may thus affect initiation and/or progression of the disease. Here we report changes in the phosphorylation of CD23 on threonine (pThr314) and two serine residues (pSer254, pSer265) in B lymphocytes of B-CLL patients, using a flow cytometry approach. The majority of tested patients with active forms of B-CLL presented a notable overexpression of CD23 along with pThr314, pSer254, and pSer265 CD23 phosphorylation positivity. Moreover, we have experimentally stimulated the CD23 phosphorylations in a subset of peripheral blood lymphocytes of healthy controls by phorbol-12-myristate-13-acetate treatment. This affects the activation of competent phosphorylation mediating kinases, resulting in the enhanced phosphorylation pattern. Together, these data confirm that CD23 protein is phosphorylated in B cells of B-CLL patients, report the identification of new CD23 phosphorylation sites, and suggest a possible role(s) of such phosphorylations in the activation of CD23 during the process of lymphocytic activation in B-CLL.

Targeting the Adenosinergic Axis in Chronic Lymphocytic Leukemia: A Way to Disrupt the Tumor Niche?

Targeting adenosine triphosphate (ATP) metabolism and adenosinergic signaling in cancer is gaining momentum, as increasing evidence is showing their relevance in tumor immunology and biology. Chronic lymphocytic leukemia (CLL) results from the expansion of a population of mature B cells that progressively occupies the bone marrow (BM), the blood, and peripheral lymphoid organs. Notwithstanding significant progress in the treatment of these patients, the cure remains an unmet clinical need, suggesting that novel drugs or drug combinations are needed. A unique feature of CLL is its reliance on micro-environmental signals for proliferation and cell survival. We and others have shown that the lymphoid niche, an area of intense interactions between leukemic and bystander non-tumor cells, is a typically hypoxic environment. Here adenosine is generated by leukemic cells, as well as by cells of myeloid origin, acting through autocrine and paracrine mechanisms, ultimately affecting tumor growth, limiting drug responses, and skewing the immune cells towards a tolerant phenotype. Hence, understanding the mechanisms through which this complex network of enzymes, receptors, and metabolites functions in CLL, will pave the way to the use of pharmacological agents targeting the system, which, in combination with drugs targeting leukemic cells, may get us one step closer to curing these patients.

ZAP70 expression enhances chemokine-driven chronic lymphocytic leukemia cell migration and arrest by valency regulation of integrins

The ζ-associated protein of 70 kDa (ZAP70) is expressed in the aggressive form of B-cell chronic lymphocytic leukemia (CLL). Moreover, the integrin very late antigen (VLA)-1 is highly expressed on subtypes of CLL that are associated with high proliferation rates in the lymph node context. We herein identify a critical role for ZAP70 in chemokine-mediated, inside-out signaling to integrins in trisomy 12 carrying Ohio State University-CLL cell lines derived from a patient with previously treated CLL. We found that ZAP70-positive CLL cells migrated significantly better toward ligands of the lymph node homing chemokine receptors CCR7 and CXCR4 compared with ZAP70-negative cells. In addition, ZAP70-expressing CLL cells adhered more efficiently to integrin ligands under static conditions. We discovered that ZAP70 expression controls chemokine-driven clustering of the integrins VLA-4 and lymphocyte function-associated antigen-1. More precisely, chemokine stimulation resulted in a ZAP70-dependent integrin valency regulation on CLL cells, whereas high-affinity regulation of integrins was independent of ZAP70. Consequently, ZAP70-expressing CLL cells show increased chemokine-driven arrest on immobilized integrin ligands and on chemokine-presenting endothelial cells under physiologic flow conditions. Hence, we describe a novel mechanism showing how ZAP70 controls chemokine-driven valency regulation of integrins and arrest of CLL cells on endothelial cells, a process that might contribute to CLL disease progression.-Laufer, J. M., Lyck, R., Legler, D. F. ZAP70 expression enhances chemokine-driven chronic lymphocytic leukemia cell migration and arrest by valency regulation of integrins.

PD-1/PD-L1 inhibitors in haematological malignancies: update 2017

The introduction of PD-1/PD-L1 pathway inhibitors is an important landmark in solid oncology with unprecedented practice-changing activity in various types of solid tumours. Among haematological malignancies, PD-1/PD-L1 inhibitors have been successful, so far, only in the treatment of classical Hodgkin lymphoma, which typically exhibits an over-expression of PD-1 ligands (PD-L1, PD-L2) due to alterations in chromosome 9p24.1. Such positive outcomes led to the US Food and Drug Administration approval of nivolumab use in relapsed Hodgkin lymphoma in 2016 as the first haematological indication. Although the results in other lymphoid malignancies have not been so striking, blockade of the PD-1/PD-L1 axis has led to meaningful responses in other lymphoma types such as diffuse large B-cell lymphoma, follicular lymphoma or several T-cell lymphomas. Monotherapy with PD-1/PD-L1 inhibitors in chronic lymphocytic leukaemia and multiple myeloma has been unsatisfactory, suggesting that a combinational approach with other synergistic drugs is needed. In the case of multiple myeloma, immunomodulatory agents together with corticosteroids represent the most promising combinations. Among myeloid malignancies, the anti-PD-1 monoclonal antibodies are examined dominantly in acute myeloid leukaemia and myelodysplastic syndromes in combination with potentially synergistic hypomethylating drugs such as 5-azacitidine, resulting in promising outcomes that warrant further investigation. We have described all available clinical results of PD-1/PD-L1 inhibitors in haematological malignancies and discussed related toxicities, as well as highlighted crucial preclinical studies in this review.

The kinase inhibitors R406 and GS-9973 impair T cell functions and macrophage-mediated anti-tumor activity of rituximab in chronic lymphocytic leukemia patients

Small molecules targeting kinases involved in B cell receptor signaling are showing encouraging clinical activity in chronic lymphocytic leukemia (CLL) patients. Fostamatinib (R406) and entospletinib (GS-9973) are ATP-competitive inhibitors designed to target spleen tyrosine kinase (Syk) that have shown clinical activity with acceptable toxicity in trials with CLL patients. Preclinical studies with these inhibitors in CLL have focused on their effect in patient-derived leukemic B cells. In this work we show that clinically relevant doses of R406 and GS-9973 impaired the activation and proliferation of T cells from CLL patients. This effect could not be ascribed to Syk-inhibition given that we show that T cells from CLL patients do not express Syk protein. Interestingly, ζ-chain-associated protein kinase (ZAP)-70 phosphorylation was diminished by both inhibitors upon TCR stimulation on T cells. In addition, we found that both agents reduced macrophage-mediated phagocytosis of rituximab-coated CLL cells. Overall, these results suggest that in CLL patients treated with R406 or GS-9973 T cell functions, as well as macrophage-mediated anti-tumor activity of rituximab, might be impaired. The potential consequences for CLL-treated patients are discussed.

Diagnostic Utility of Lymphoid Enhancer Binding Factor 1 Immunohistochemistry in Small B-Cell Lymphomas

OBJECTIVES

Recent studies have shown that lymphoid enhancer binding factor 1 (LEF1) is a useful marker for chronic lymphocytic B-cell leukemia (CLL)/small lymphocytic lymphoma. Yet, it is not still being widely used in a diagnostic setting. In this study, we document the experience with LEF1 immunohistochemistry during routine diagnostics.

METHODS

In total, 191 B-cell lymphoma cases from Hammersmith Hospital, Imperial College NHS Healthcare Trust (London, UK) were investigated by immunohistochemistry for LEF1 during routine diagnostic workup. These cases included both bone marrow trephines and lymph node biopsy specimens. The monoclonal antibody clone EPR2029Y was used.

RESULTS

LEF1 expression was strong and diffuse (>70% of cells) in most cases. Few CLL cases showed a staining in proliferation centers only. Seventy-seven of 80 CLL cases expressed LEF1. Other entities expressing LEF1 included one of 38 follicular lymphomas, two of 33 marginal zone lymphomas, and one diffuse large B-cell lymphoma with a background of follicular lymphoma grade 3B. Sensitivity for LEF1 for the diagnosis of CLL was 0.96, and specificity was 0.93.

CONCLUSIONS

In this study, we could demonstrate the diagnostic utility of LEF1. LEF1 is a sensitive and specific marker for CLL and is helpful in the diagnosis of diagnostically challenging small B-cell lymphomas.

Chronic lymphocytic leukemia cells diversify and differentiate in vivo via a nonclassical Th1-dependent, Bcl-6-deficient process

Xenografting primary tumor cells allows modeling of the heterogeneous natures of malignant diseases and the influences of the tissue microenvironment. Here, we demonstrate that xenografting primary chronic lymphocytic leukemia (CLL) B lymphocytes with activated autologous T cells into alymphoid mice results in considerable CLL B cell division and sizable T cell expansion. Nevertheless, most/all CD5⁺CD19⁺ cells are eventually lost, due in part to differentiation into antibody-secreting plasmablasts/plasma cells. CLL B cell differentiation is associated with isotype class switching and development of new IGHV-D-J mutations and occurs via an activation-induced deaminase-dependent pathway that upregulates IRF4 and Blimp-1 without appreciable levels of the expected Bcl-6. These processes were induced in IGHV-unmutated and IGHV-mutated clones by Th1-polarized T-bet⁺ T cells, not classical T follicular helper (Tfh) cells. Thus, the block in B cell maturation, defects in T cell action, and absence of antigen-receptor diversification, which are often cardinal characteristics of CLL, are not inherent but imposed by external signals and the microenvironment. Although these activities are not dominant features in human CLL, each occurs in tissue proliferation centers where the mechanisms responsible for clonal evolution operate. Thus, in this setting, CLL B cell diversification and differentiation develop by a nonclassical germinal center-like reaction that might reflect the cell of origin of this leukemia.

The outcome of B-cell receptor signaling in chronic lymphocytic leukemia: proliferation or anergy

Biologists and clinicians agree that the B-cell receptor influences the behavior of chronic lymphocytic leukemia, and promising new drugs are aimed at receptor-associated kinases. Engagement of surface immunoglobulin by antigen is a key driver of malignant cells with outcome influenced by the nature of the cell, the level of stimulation and the microenvironment. Analysis of surface immunoglobulin-mediated signaling in the two major disease subsets defined by IGHV mutational status reveals bifurcation of responses toward proliferation or anergy. Mutated chronic lymphocytic leukemia, generally of relatively good prognosis, is mainly, but not exclusively, driven towards anergy in vivo. In contrast, unmutated chronic lymphocytic leukemia shows less evidence for anergy in vivo retaining more responsiveness to surface immunoglobulin M-mediated signaling, possibly explaining increased tumor progression. Expression and function of surface immunoglobulin M in unmutated chronic lymphocytic leukemia appear rather homogeneous, but mutated chronic lymphocytic leukemia exhibits a highly heterogeneous profile that may relate to further variable clinical behavior within this subset. Anergy should increase susceptibility to apoptosis but, in leukemic cells, this may be countered by overexpression of the B-cell lymphoma-2 survival protein. Maintained anergy spreads to chemokines and adhesion molecules, restraining homing and migration. However, anergy is not necessarily completely benign, being able to reverse and regenerate surface immunoglobulin M-mediated responses. A two-pronged attack on proliferative and anti-apoptotic pathways may succeed. Increased understanding of how chronic lymphocytic leukemia cells are driven to anergy or proliferation should reveal predictive biomarkers of progression and of likely response to kinase inhibitors, which could assist therapeutic decisions.

Phorbol myristate acetate, but not CD40L, induces the differentiation of CLL B cells into Ab-secreting cells

In this study, we investigated the capacity of chronic lymphocytic leukemia (CLL) B cells to undergo terminal differentiation into Ig-secreting plasma cells in T cell-independent and T cell-dependent responses. We used a two-step model involving stimulation with phorbol myristate acetate (PMA) and CD40L, together with cytokines (PMA/c and CD40L/c), for 7 days. We describe immunophenotypic modifications, changes in the levels of mRNA and protein for transcription factors and morphological and functional events occurring during the differentiation of CLL B cells into antibody-secreting cells (ASCs). The induction of differentiation differed significantly between the CD40L/c and PMA/c culture systems. The PMA/c culture system allowed CLL B cells to differentiate into IgM-secreting cells with an immunophenotype and molecular profile resembling those of preplasmablasts. By contrast, CD40L/c-stimulated cells had a phenotype and morphology similar to those of activated B cells and resembling those of the CLL B cells residing in the lymph node and bone marrow. These data suggest that the CLL B cells are not frozen permanently at a stage of differentiation and are able to differentiate into ASCs as appropriate stimulation are provided. The data presented here raise questions about the molecular processes and stimulation required for CLL B-cell differentiation and about the inability of CD40 ligand to induce differentiation of the CLL B cells.

Lymphocytes from chronic lymphocytic leukaemia undergo ABL1-linked amoeboid motility and homotypic interaction as an early adaptive change to ex vivo culture

BACKGROUND

Those stimuli that together promote the survival, differentiation and proliferation of the abnormal B-lymphocytes of chronic lymphocytic leukaemia (CLL) are encountered within tissues, where together they form the growth-supporting microenvironment. Different tissue-culture systems promote the survival of the neoplastic lymphocytes from CLL, partly replicating the in vivo tissue environment of the disorder. In the present study, we focussed on the initial adaptive changes to the tissue culture environment focussing particularly on migratory behaviour and cellular interactions.

METHODS

A high-density CLL culture system was employed to test CLL cell-responses using a range of microscopic techniques and flow cytometric analyses, supported by mathematical measures of cell shape-change and by biochemical techniques. The study focussed on the evaluation of changes to the F-actin cytoskeleton and cell behaviour and on ABL1 signalling processes.

RESULTS

We showed that the earliest functional response by the neoplastic lymphocytes was a rapid shape-change caused through rearrangement of the F-actin cytoskeleton that resulted in amoeboid motility and promoted frequent homotypic interaction between cells. This initial response was functionally distinct from the elongated motility that was induced by chemokine stimulation, and which also characterised heterotypic interactions between CLL lymphocytes and accessory cells at later culture periods. ABL1 is highly expressed in CLL lymphocytes and supports their survival, it is also recognised however to have a major role in the control of the F-actin cytoskeleton. We found that the cytoplasmic fraction of ABL1 became co-localised with F-actin structures of the CLL lymphocytes and that the ABL1 substrate CRKL became phosphorylated during initial shape-change. The ABL-inhibitor imatinib mesylate prevented amoeboid movement and markedly reduced homotypic interactions, causing cells to acquire a globular shape to rearrange F-actin to a microvillus form that closely resembled that of CLL cells isolated directly from circulation.

CONCLUSION

We suggest that ABL1-induced amoeboid motility and homotypic interaction represent a distinctive early response to the tissue environment by CLL lymphocytes. This response is separate from that induced by chemokine or during heterotypic cell-contact, and may play a role in the initial entry and interactions of CLL lymphocytes in tissues.

The CD37-targeted antibody-drug conjugate IMGN529 is highly active against human CLL and in a novel CD37 transgenic murine leukemia model

Therapeutic regimens for chronic lymphocytic leukemia (CLL) have increasingly utilized monoclonal antibodies since the chimeric anti-CD20 antibody rituximab was introduced. Despite improved clinical outcomes, current CLL therapies are not curative. Therefore, antibodies with greater efficacy and novel targets are desirable. One promising target is CD37, a tetraspanin protein highly expressed on malignant B-cells in CLL and non-Hodgkin lymphoma. Although several novel CD37-directed therapeutics are emerging, detailed preclinical evaluation of these agents is limited by lack of appropriate animal models with spontaneous leukemia expressing the human CD37 (hCD37) target. To address this, we generated a murine CLL model that develops transplantable hCD37+ leukemia. Subsequently, we engrafted healthy mice with this leukemia to evaluate IMGN529, a novel hCD37-targeting antibody-drug conjugate. IMGN529 rapidly eliminated peripheral blood leukemia and improved overall survival. In contrast, the antibody component of IMGN529 could not alter disease course despite exhibiting substantial in vitro cytotoxicity. Furthermore, IMGN529 is directly cytotoxic to human CLL in vitro, depletes B-cells in patient whole blood and promotes killing by macrophages and natural killer cells. Our results demonstrate the utility of a novel mouse model for evaluating anti-human CD37 therapeutics and highlight the potential of IMGN529 for treatment of CLL and other CD37-positive B-cell malignancies.

Roles of Rho GTPases in leucocyte and leukaemia cell transendothelial migration

Leucocytes migrate into and out of blood vessels at multiple points during their development and maturation, and during immune surveillance. In response to tissue damage and infection, they are rapidly recruited through the endothelium lining blood vessels into the tissues. Leukaemia cells also move in and out of the bloodstream during leukaemia progression. Rho GTPases are intracellular signalling proteins that regulate cytoskeletal dynamics and are key coordinators of cell migration. Here, we describe how different members of the Rho GTPase family act in leucocytes and leukaemia cells to regulate steps of transendothelial migration. We discuss how inhibitors of Rho signalling could be used to reduce leucocyte or leukaemia cell entry into tissues.

The pathogenesis of chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is characterized by the clonal expansion of CD5(+)CD23(+) B cells in blood, marrow, and second lymphoid tissues. Gene-expression profiling and phenotypic studies suggest that CLL is probably derived from CD5(+) B cells similar to those found in the blood of healthy adults. Next-generation sequencing has revealed recurrent genetic lesions that are implicated in CLL pathogenesis and/or disease progression. The biology of CLL is entwined with its microenvironment, in which accessory cells can promote leukemia cell growth and/or survival. Recently, much attention has been focused on the CLL B cell receptor (BCR) and on chemokine receptors that enable CLL cells to home to lymphoid tissues and to establish the leukemia microenvironment. Agents that can interfere with BCR signaling or chemokine-receptor signaling, or that target surface antigens selectively expressed on CLL cells, promise to have significant therapeutic benefit in patients with this disease.

Apoptotic and proliferative characteristics of proliferation centers in lymph node sections of patients with chronic lymphocytic leukemia

We have analyzed the immunohistochemical expression of a wide range of molecules along with the proliferation rate separately in the proliferation centers (PCs) and in the rest of the tumor area, in lymph node or spleen sections of patients with chronic lymphocytic leukemia (CLL). Fas, FasL and c-FLIP were observed both within and outside the PCs in all cases. However, only the difference in FasL expression between the PCs and the non-PC areas attained statistical significance. Median survivin expression in the PCs was higher compared to the non-PC areas. Cleaved caspase 3 was expressed at very low levels both within and outside PCs, while BCL-2 protein was expressed at high levels in all cases in both tumor compartments. Multivariate analysis demonstrated that concurrent overexpression of Fas/FasL/c-FLIP in the PCs was correlated with worse outcome for progression-free survival as well as for overall survival.

The PD-1/PD-L1 axis contributes to T-cell dysfunction in chronic lymphocytic leukemia

Chronic lymphocytic leukemia is marked by profound defects in T-cell function. Programmed death-1 is a receptor involved in tumor-mediated immunosuppression through binding of the PD-L1 ligand. Multiparametric flow cytometry and immunohistochemistry were used to study PD-1/PD-L1 expression. Functional assays were used to determine the involvement of the PD-1/PD-L1 axis in T-cell responses. PD-1 expression by CD4(+) and CD8(+) T lymphocytes was significantly higher in 117 chronic lymphocytic leukemia patients than in 33 donors of a comparable age. CD4(+) and CD8(+) T lymphocytes from chronic lymphocytic leukemia patients displayed increased numbers of effector memory and terminally differentiated cells, respectively, when compared to controls. The number of effector memory CD4(+) and terminally differentiated CD8(+) lymphocytes positively associated with a more advanced stage of disease, treatment requirements and unfavorable genomic aberrations. Furthermore, leukemic lymphocytes expressed higher levels of PD-L1 than circulating B lymphocytes from normal donors. PD-1 and PD-L1 surface expression spiked in proliferating T and B lymphocytes, suggesting that this interaction works efficiently in activated environments. Within chronic lymphocytic leukemia proliferation centers in the lymph node, CD4(+)/PD-1(+) T lymphocytes were found to be in close contact with PD-L1(+) chronic lymphocytic leukemia cells. Lastly, functional experiments using recombinant soluble PD-L1 and blocking antibodies indicated that this axis contributes to the inhibition of IFN-γ production by CD8(+) T cells. These observations suggest that pharmacological manipulation of the PD-1/PD-L1 axis may contribute to restoring T-cell functions in the chronic lymphocytic leukemia microenvironment.

CXCL12 is a costimulator for CD4+ T cell activation and proliferation in chronic lymphocytic leukemia patients

Activated T cells from patients with chronic lymphocytic leukemia (CLL) provide survival and proliferative signals to the leukemic clone within lymphoid tissues. Recruitment of both, CLL cells and T lymphocytes, to this supportive microenvironment greatly depends on CXCL12 production by stromal and myeloid cells. CXCL12 also supplies survival stimuli to leukemic B cells, but whether it exerts stimulatory effects on T lymphocytes from CLL patients is unknown. In order to evaluate the capacity of CXCL12 to increase CD4(+) T cell activation and proliferation in CLL patients, peripheral blood mononuclear cells were cultured with or without recombinant human CXCL12 or autologous nurse-like cells, and then T cell activation was induced by anti-CD3 mAb. CXCL12 increases the proliferation and the expression of CD25, CD69, CD154, and IFNγ on CD3-stimulated CD4(+) T cells from CLL patients, similarly in T cells from ZAP-70(+) to ZAP-70(-) patients. Autologous nurse-like cells establish a close contact with CD4(+) T cells and increase their activation and proliferation partially through a CXCR4-dependent mechanism. In addition, we found that activated T cells in the presence of CXCL12 enhance the activation and proliferation of the leukemic clone. In conclusion, CXCL12 production by lymphoid tissue microenvironment in CLL patients might play a key dual role on T cell physiology, functioning not only as a chemoattractant but also as a costimulatory factor for activated T cells.

Targeting the microenvironment in chronic lymphocytic leukemia offers novel therapeutic options

Chronic lymphocytic leukemia (CLL) cells display features consistent with a defect in apoptosis and exhibit prolonged survival in vivo. Survival of these malignant cells is influenced by interactions with non-leukemic cells located in permissive niches in lymphoid organs. Leukemic cells subvert the normal architecture of the lymphoid organs, recruiting stromal cells, dendritic cells and T lymphocytes, all reported as playing active roles in the survival and proliferation of CLL. The same survival-promoting environment also rescues/protects leukemic cells from cytotoxic therapies, giving way to disease relapse. This review summarizes and discusses current knowledge about the intricate network of soluble and cell-bound signals regulating the life and death of CLL cells in different districts. At the same time, it seeks to hone in on which discrete molecular elements are best suited as targets for treating this still incurable disease.

Chronic lymphocytic leukemia/small lymphocytic lymphoma with cyclin D1 positive proliferation centers do not have CCND1 translocations or gains and lack SOX11 expression

Cyclin D1 expression, usually absent in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), has been described in the proliferation centers (PC) of some CLL/SLL. The prevalence of this finding is uncertain, as is the explanation for its occurrence and whether these cases have any other unique features. Cyclin D1 immunohistochemical staining was therefore investigated in 57 extramedullary CLL/SLL biopsies. In 6 cases, cyclin D1 immunofluorescence followed by CCND1 fluorescence in situ hybridization (FISH) and PC targeted analysis was performed using a Bioview Duet system. Excluding the prospectively selected cases that had the targeted FISH studies, cyclin D1+ PC were identified in 20% of cases. The cyclin D1+ CLL did not appear pathologically or phenotypically distinctive, though 46% had an interfollicular growth pattern. The cyclin D1+ PCs were SOX11- and lacked CCND1 translocations and gains in 5 of 5 informative cases. The recognition of cyclin D1 expression in PC of a significant minority of CLL/SLL can be a diagnostic aid and should not lead to the diagnosis of focal mantle cell lymphoma.

CD73-generated extracellular adenosine in chronic lymphocytic leukemia creates local conditions counteracting drug-induced cell death

Extracellular adenosine (ADO), generated from ATP or ADP through the concerted action of the ectoenzymes CD39 and CD73, elicits autocrine and paracrine effects mediated by type 1 purinergic receptors. We have tested whether the expression of CD39 and CD73 by chronic lymphocytic leukemia (CLL) cells activates an adenosinergic axis affecting growth and survival. By immunohistochemistry, CD39 is widely expressed in CLL lymph nodes, whereas CD73 is restricted to proliferation centers. CD73 expression is highest on Ki-67(+) CLL cells, adjacent to T lymphocytes, and is further localized to perivascular areas. CD39(+)/CD73(+) CLL cells generate ADO from ADP in a time- and concentration-dependent manner. In peripheral blood, CD73 expression occurs in 97/299 (32%) CLL patients and pairs with CD38 and ZAP-70 expression. CD73-generated extracellular ADO activates type 1 purinergic A2A receptors that are constitutively expressed by CLL cells and that are further elevated in proliferating neoplastic cells. Activation of the ADO receptors increases cytoplasmic cAMP levels, inhibiting chemotaxis and limiting spontaneous drug-induced apoptosis of CLL cells. These data are consistent with the existence of an autocrine adenosinergic loop, and support engraftment of leukemic cells in growth-favorable niches, while simultaneously protecting from the action of chemotherapeutic agents.

Chronic lymphocytic leukemia: the pathologist's view of lymph node microenvironment

Chronic lymphocytic leukemia (CLL), an indolent B-cell malignancy frequently diagnosed in the elderly, is characterized by the relentless accumulation of CD5+ monoclonal B cells that proliferate in the appropriate tissue microenvironments. Despite many advances achieved by molecular and functional studies, our knowledge of the reciprocal relationship between the CLL cell and its microenvironment at the tissue level is still largely incomplete. In this review we present the relevant current information on the tissue microenvironmental features of CLL, focusing on the events that appear to occur in the lymph node. Special attention is devoted to analyzing the properties of both neoplastic and nonneoplastic bystander cells within proliferation centers, the mysterious structures that likely represent the actual proliferative compartment.

Pitfalls in lymphoma pathology: avoiding errors in diagnosis of lymphoid tissues

The complexity involved in the histological interpretation of lymph nodes and other lymphoid tissue specimens suspected of harbouring lymphoma is underappreciated. As with other histology specimens, the quality of sections and background information are crucial but so, increasingly, is the appropriate use of immunocytochemistry and a variety of molecular analyses. Within the UK National Health Service, progressive regional centralisation is ongoing, to ensure access to specialist expertise and a full range of testing beyond traditional stains. This is to be welcomed but there remains a need to maintain skills in smaller district hospitals, to ensure lymphoma recognition in unexpected circumstances, to permit clinically useful interim diagnoses when needed urgently and to sustain training in haematopathology among junior pathologists. In this review a range of potential pitfalls in lymphoid tissue pathology is outlined, arising at all stages from specimen preparation to reporting. Knowledge of such pitfalls, some of which are common while others are rare but of vital clinical importance, should help increase confidence in lymphoma diagnosis among histopathologists.

Aberrant interferon-signaling is associated with aggressive chronic lymphocytic leukemia

The type I interferons (IFNs) normally suppress tumor growth by phosphorylating and activating the signal transducer and activator of transcription 1 (STAT1), but also briefly activate STAT3, which promotes cell growth. In chronic lymphocytic leukemia (CLL) cells, the duration of IFN-mediated STAT3 phosphorylation was found to exhibit significant interpatient variability and was prolonged in cells with high risk features, such as 11q- and 17p-deletions involving ataxia telangiectasia mutated (ATM) and p53. This aberrant signaling pattern was associated with a paradoxical increase in cell size and number in response to IFN and similar alterations in IFN-signaling and responses were seen in cell lines that developed in the absence of p53 or ATM. However, direct inhibition of p53 or ATM failed to cause these changes, and CLL cells with aggressive clinical features were found to also express high levels of reactive oxygen species (ROS), which decrease tyrosine phosphatase activity. Prolonged IFN-mediated STAT3 phosphorylation and lowered phosphatase activity could be reversed by antioxidants. These findings suggest that increased ROS levels may corrupt IFN-signaling processes in aggressive CLL cells, causing IFN to be used as a growth factor rather than a tumor suppressor. Antioxidants or STAT3 kinase inhibitors might improve the outcome of IFN therapy in CLL by restoring normal signaling.

Chronic Lymphocytic Leukemia, Small Lymphocytic Lymphoma, and Monoclonal B-Cell Lymphocytosis

Chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL), and monoclonal B-cell lymphocytosis (MBL) are clonal proliferations of small, mature B cells. CLL and SLL are considered neoplastic, although they are indolent and many patients with these lymphomas never require treatment. Most MBL cases share immunophenotypic and genetic features with CLL and SLL but have a small burden of clonal cells. This review focuses on the pathologic features of CLL, SLL, and MBL and their differential diagnoses. Guidelines are provided to separate the entities from one another and to avoid pitfalls in distinguishing these entities from other lymphomas and from reactive lymphoid proliferations.

Most morphologic features in chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) do not reliably predict underlying FISH genetics or immunoglobulin heavy chain variable region somatic mutational status

Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is common in the Western world. Genetic abnormalities detected by fluorescence in situ hybridization (FISH) and immunoglobulin heavy chain variable gene region (IGHV) mutational status are well-known independent prognostic indicators in CLL/SLL. Given the requirement for specialized testing to detect such aberrations, we investigated whether morphologic features may predict the presence of a more or less favorable genetic profile. Forty-one SLL cases were morphologically evaluated for expanded proliferation centers, increased large cells outside of proliferation centers, and nuclear contour irregularities (NCI) in small and large tumor cells. ZAP-70 immunohistochemistry and FISH (deletions of 13q14, p53 and ATM and trisomy 12) were successful in all cases. IGHV mutational status was determined in 26/41 cases. Significant NCI in both small and large cells correlated with the presence of an unfavorable FISH abnormality (ie, ATM or p53 deletions). However, despite good specificity (94%), the sensitivity (57%) of this finding is inadequate for routine use. No other significant associations with morphologic features were identified. Strong ZAP-70 positivity correlated with unmutated IGHV (P=0.001), rendering ZAP-70 IHC a useful surrogate for IGHV mutational status. ZAP-70 positivity predicted against finding a favorable FISH deletion 13q14 (P=0.023). Although we only studied 41 cases, we corroborated their validity using Kaplan-Meier overall survival analysis. In conclusion, morphologic features in SLL are not a reliable predictor of underlying genetic status. Thus, we propose a practical, cost-effective approach to the work-up of these cases, which should be driven by clinical necessity.

Expanded and highly active proliferation centers identify a histological subtype of chronic lymphocytic leukemia ("accelerated" chronic lymphocytic leukemia) with aggressive clinical behavior

BACKGROUND

The concept of "accelerated" chronic lymphocytic leukemia is frequently used by both pathologists and clinicians. However, neither histological criteria to define this form of chronic lymphocytic leukemia nor its clinical correlates and prognostic impact have been formally defined in large series of patients.

DESIGN AND METHODS

Tissue biopsies from 100 patients with chronic lymphocytic leukemia were analyzed for the size of proliferation centers and their proliferation rate as assessed by mitosis count and Ki-67 immunostaining. Histological patterns were correlated with main clinico-biological features and outcome.

RESULTS

A suspicion of disease transformation was the main reason for carrying out tissue biopsy, which was performed at a median time of 14 months (range, 0 to 204 months) after the diagnosis of chronic lymphocytic leukemia. The biopsy showed histological transformation to diffuse large B-cell lymphoma in 22 cases. In the remaining 78 patients, the presence of expanded proliferation centers (broader than a 20x field) and high proliferation rate (either >2.4 mitoses/proliferation center or Ki-67 >40%/proliferation center) predicted a poor outcome and were selected to define a highly proliferative group. Thus, 23 patients with either expanded proliferation centers or high proliferation rate were considered as having "accelerated" chronic lymphocytic leukemia. These patients displayed particular features, including higher serum lactate dehydrogenase levels and more frequently elevated ZAP-70 than "non-accelerated" cases. The median survival from biopsy of patients with "non-accelerated" chronic lymphocytic leukemia, "accelerated" chronic lymphocytic leukemia and transformation to diffuse large B-cell leukemia was 76, 34, and 4.3 months, respectively (P<0.001).

CONCLUSIONS

The presence of expanded and/or highly active proliferation centers identifies a group of patients with "accelerated" chronic lymphocytic leukemia characterized by an aggressive clinical behavior.

NF-kappaB as a therapeutic target in chronic lymphocytic leukemia

IMPORTANCE OF THE FIELD

NF-kappaB includes a family of transcription factors that play a critical role in the biology of normal lymphocytes and it is aberrantly activated in chronic lymphocytic leukemia (CLL) cells. Here, we review the role of constitutive NF-kappaB activation in CLL pathogenesis and its potential as a therapeutic target for CLL treatment.

AREAS COVERED IN THIS REVIEW

This review highlights the different strategies reported to inhibit NF-kappaB signaling in CLL cells. They include both IkappaB kinase inhibitors and several natural compounds that act at different steps of the pathway.

WHAT THE READER WILL GAIN

Targeting NF-kappaB leads to apoptosis of CLL cells, corroborating the role of NF-kappaB in the survival and clonal expansion of these tumoral cells. Moreover, several studies confirmed a synergistic effect between NF-kappaB inhibitors and other antitumoral agents and that inhibition of NF-kappaB could overcome the microenvironmental protection of CLL cells.

TAKE HOME MESSAGE

NF-kappaB is a relevant target in CLL and inhibitors of this prosurvival pathway, alone or in combination, represent a novel therapeutic strategy for the treatment of CLL patients.

Chronic lymphocytic leukaemia: a disease of activated monoclonal B cells

B cell-type chronic lymphocytic leukaemia (CLL) has long been considered a disease of resting lymphocytes. However, cell surface and intracellular phenotypes suggest that most CLL cells are activated cells, although only a small subset progresses beyond the G1 stage of the cell cycle. In addition, traditional teaching says that CLL cells divide rarely, and therefore the build-up of leukaemic cells is due to an inherent defect in cell death. However, in vivo labelling of CLL cells indicates a much more active rate of cell birth than originally estimated, suggesting that CLL is a dynamic disease. Here we review the observations that have led to these altered views of the activation state and proliferative capacities of CLL cells and also provide our interpretation of these observations in light of their potential impact on patients.

CXCL12-induced chemotaxis is impaired in T cells from patients with ZAP-70-negative chronic lymphocytic leukemia

BACKGROUND

T cells from patients with chronic lymphocytic leukemia may play an important role in contributing to the onset, sustenance, and exacerbation of the disease by providing survival and proliferative signals to the leukemic clone within lymph nodes and bone marrow.

DESIGN AND METHODS

By performing chemotaxis assays towards CXCL12, CCL21 and CCL19, we sought to evaluate the migratory potential of T cells from chronic lymphocytic leukemia patients. We next analyzed the chemokine-induced migration of T cells, dividing the chronic lymphocytic leukemia samples according to their expression of the poor prognostic factors CD38 and ZAP-70 in leukemic cells determined by flow cytometry.

RESULTS

We found that T cells from patients with chronic lymphocytic leukemia are less responsive to CXCL12, CCL21 and CCL19 than T cells from healthy adults despite similar CXCR4 and CCR7 expression. Following separation of the patients into two groups according to ZAP-70 expression, we found that T cells from ZAP-70-negative samples showed significantly less migration towards CXCL12 compared to T cells from ZAP-70-positive samples and that this was not due to defective CXCR4 down-regulation, F-actin polymerization or to a lesser expression of ZAP-70, CD3, CD45, CD38 or CXCR7 on these cells. Interestingly, we found that leukemic cells from ZAP-70-negative samples seem to be responsible for the defective CXCR4 migratory response observed in their T cells.

CONCLUSIONS

Impaired migration towards CXCL12 may reduce the access of T cells from ZAP-70-negative patients to lymphoid organs, creating a less favorable microenvironment for leukemic cell survival and proliferation.

AID protein expression in chronic lymphocytic leukemia/small lymphocytic lymphoma is associated with poor prognosis and complex genetic alterations

The biological behavior of chronic lymphocytic leukemia and small lymphocytic lymphoma is unpredictable. Nonetheless, non-mutated IgV(H) gene rearrangement, ATM (11q22-23) and p53 (17p13) deletion are recognized as unfavorable prognosticators in chronic lymphocytic leukemia. The mRNA expression of activation-induced cytidine deaminase (AID), an enzyme indispensable for somatic hypermutation processes, was claimed to be predictive of non-mutated chronic lymphocytic leukemia cells in blood. Here, we evaluated AID protein expression compared with known molecular and immunohistochemical prognostic indicators in 71 chronic lymphocytic leukemia/small lymphocytic lymphoma patients using a tissue microarray approach. We found AID heterogeneously expressed in tumor cells as shown by colocalization analysis for CD5 and CD23. Ki-67 positive paraimmunoblasts of the proliferation centers displayed the highest expression. This observation is reflected by a significant association of AID positivity with a high proliferation rate (P=0.012). ATM deletion was detected in 10% (6/63) of patients and p53 deletion in 19% (13/67) of patients. Moreover, both ATM (P=0.002) and p53 deletion (P=0.004) were significantly associated with AID. IgV(H) gene mutation was seen in 45% (27/60) of patients. Twenty-five percent (17/69) of patients with AID-positive chronic lymphocytic leukemia/small lymphocytic lymphoma displayed a shorter survival than AID-negative chronic lymphocytic leukemia/small lymphocytic lymphoma patients (61 vs 130 months, P=0.001). Although there was a trend, we could not show an association with the IgV(H) gene mutation status. Taken together, our study shows that AID expression is an indicator of an unfavorable prognosis in chronic lymphocytic leukemia/small lymphocytic lymphoma patients, although it is not a surrogate marker for the IgV(H) status. Furthermore, the microenvironment of proliferation centers seems to influence AID regulation and might be an initiating factor in its transformation.

Ribosome-associated nucleophosmin 1: increased expression and shuttling activity distinguishes prognostic subtypes in chronic lymphocytic leukaemia

Two distinct groups of chronic lymphocytic leukaemia (CLL) are distinguished by the presence or absence of somatic hypermutation of the immunoglobulin heavy-chain gene. CLL without somatic hypermutation has an adverse outcome, but the precise biological differences that underlie this more aggressive clinical-course are unclear. Using a proteomic approach, we found that the two prognostic forms of CLL were consistently distinguished according to their protein expression pattern. The most important difference observed related to the different expression of nucleophosmin 1 between the two forms of CLL. This different expression was not related to apoptosis, proliferation or gene mutation. However, co-immunoprecipitation experiments identified an association between nucleophosmin 1 and ribosomal proteins. Using immunocytofluorescence, nucleophosmin 1 expression was identified in the nucleoli and nucleoplasm of all cells, but in a proportion of cells, nucleophosmin had been transferred from the nucleoplasm to the cytoplasm. Both the fluorescent intensity, and the frequency of cytoplasmic nucleophosmin 1 expression, was higher in CLL without somatic hypermutation. We propose therefore, that nucleophosmin 1, in association with ribosomal proteins, undergoes nucleo-cytoplasmic shuttling in CLL. This process is most prominent in un-mutated CLL and may signify altered protein biosynthesis.

An impaired transendothelial migration potential of chronic lymphocytic leukemia (CLL) cells can be linked to ephrin-A4 expression

Chronic lymphocytic leukemia (CLL) cell migration into lymphoid tissues is an important aspect of the pathobiology of this disease. Here, we investigated the role of ephrin-A4 (EFNA4) in the transendothelial migration (TEM) capacity of CLL and normal B cells through interacting with endothelial EphA2 (erythropoietin-producing hepatocellular carcinoma). CLL cells showed a remarkable impairment in the adhesion to and transmigration through human umbilical vein endothelial cell (HUVEC) monolayers, correlating with their higher EFNA4 expression. In vitro, TEM was mediated by EFNA4 binding to endothelial EphA2 receptor, which is highly expressed in tumor necrosis factor-alpha-activated HUVECs as well as in the CD31(+) endothelial cells of human lymph nodes. The pretreatment of CLL cells with EphA2 homodimers further impaired their adhesion to and transmigration through HUVEC monolayers, whereas pretreatment of HUVECs with EFNA4 homodimers improved those phenomena in both CLL and normal B cells, suggesting that EFNA4 signaling negatively contributed to TEM. In fact, EFNA4 signaling into CLL cells significantly reduced their adhesion to intercellular adhesion molecule 1, vascular cell adhesion molecule 1, and several extracellular matrix molecules and impaired CCL-19-mediated TEM and chemotaxis. Our results suggest that EFNA4-EphA2 interactions are involved in CLL cell trafficking between blood and the tissues and therefore may become a therapeutic target in the future.