The Nanomechanical Properties of CLL Cells Are Linked to the Actin Cytoskeleton and Are a Potential Target of BTK Inhibitors

Chronic lymphocytic leukemia (CLL) is an incurable disease characterized by an intense trafficking of the leukemic cells between the peripheral blood and lymphoid tissues. It is known that the ability of lymphocytes to recirculate strongly depends on their capability to rapidly rearrange their cytoskeleton and adapt to external cues; however, little is known about the differences occurring between CLL and healthy B cells during these processes. To investigate this point, we applied a single-cell optical (super resolution microscopy) and nanomechanical approaches (atomic force microscopy, real-time deformability cytometry) to both CLL and healthy B lymphocytes and compared their behavior. We demonstrated that CLL cells have a specific actomyosin complex organization and altered mechanical properties in comparison to their healthy counterpart. To evaluate the clinical relevance of our findings, we treated the cells in vitro with the Bruton's tyrosine kinase inhibitors and we found for the first time that the drug restores the CLL cells mechanical properties to a healthy phenotype and activates the actomyosin complex. We further validated these results in vivo on CLL cells isolated from patients undergoing ibrutinib treatment. Our results suggest that CLL cells' mechanical properties are linked to their actin cytoskeleton organization and might be involved in novel mechanisms of drug resistance, thus becoming a new potential therapeutic target aiming at the normalization of the mechanical fingerprints of the leukemic cells.

Emerging Strategies in 3D Culture Models for Hematological Cancers

In vitro cell cultures are fundamental and necessary tools in cancer research and personalized drug discovery. Currently, most cells are cultured using two-dimensional (2D) methods, and drug testing is mainly performed in animal models. However, new and improved methods that implement three-dimensional (3D) cell-culturing techniques provide compelling evidence that more advanced experiments can be performed, yielding valuable new insights. In 3D cell-culture experiments, the cell environment can be manipulated to mimic the complexity and dynamicity of the human tissue microenvironment, possibly leading to more accurate representations of cell-to-cell interactions, tumor biology, and predictions of drug response. The 3D cell cultures can also potentially provide alternative ways to study hematological cancers and are expected to eventually bridge the gap between 2D cell culture and animal models. The present review provides an overview of the complexity of the lymphoid microenvironment and a summary of the currently used 3D models that aim at recreating it for hematological cancer research. We here dissect the differences and challenges between, and potential advantages of, different culture methods and present our vision of the most promising future strategies in the hematological field.

PYK2 is overexpressed in chronic lymphocytic leukaemia: A potential new therapeutic target

Chronic Lymphocytic Leukaemia (CLL) is the most common adult B-cell leukaemia and despite improvement in patients' outcome, following the use of targeted therapies, it remains incurable. CLL supportive microenvironment plays a key role in both CLL progression and drug resistance through signals that can be sensed by the main components of the focal adhesion complex, such as FAK and PYK2 kinases. Dysregulations of both kinases have been observed in several metastatic cancers, but their role in haematological malignancies is still poorly defined. We characterized FAK and PYK2 expression and observed that PYK2 expression is higher in leukaemic B cells and its overexpression significantly correlates with their malignant transformation. When targeting both FAK and PYK2 with the specific inhibitor defactinib, we observed a dose-response effect on CLL cells viability and survival. In vivo treatment of a CLL mouse model showed a decrease of the leukaemic clone in all the lymphoid organs along with a significant reduction of macrophages and of the spleen weight and size. Our results first define a possible prognostic value for PYK2 in CLL, and show that both FAK and PYK2 might become putative targets for both CLL and its microenvironment (e.g. macrophages), thus paving the way to an innovative therapeutic strategy.

Protocol for generation of 3D bone marrow surrogate microenvironments in a rotary cell culture system

In this protocol, we describe how to generate 3D culture surrogates of chronic lymphocytic leukemia (CLL) and multiple myeloma (MM) bone marrow microenvironments. We detail the use of culturing scaffolds populated with BM stromal cells and tumor cells in the RCCS™ bioreactor. This 3D culture can efficiently recapitulate tumor-stroma crosstalk and allows the testing of drugs such as ibrutinib and bortezomib. Moreover, this protocol can be used for the generation of other and more complex tumor microenvironments.

For complete details on the use and execution of this protocol, please refer to Belloni et al. (2018) and Barbaglio et al. (2021).

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Step-by-step generation of a 3D bone marrow microenvironment for CLL and MM

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Set up of a dynamic 3D culture in an RCCS™ bioreactor

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Integrative analysis of the 3D scaffolds in response to drug treatment

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Three-dimensional co-culture model of chronic lymphocytic leukemia bone marrow microenvironment predicts patient-specific response to mobilizing agents

Chronic Lymphocytic Leukemia (CLL) cells disseminate into supportive tissue microenvironments. To investigate the mechanisms involved in leukemic cell tissue retention we developed a 3D bone marrow (BM) microenvironment that recreates CLL - BM-stromal cells interactions inside a scaffold within a bioreactor. Our system allows the parallel analysis of CLL cells retained inside the scaffold and those released in the presence/absence of pharmacological agents, mimicking tissue and circulating cell compartments, respectively. CLL cells can be retained within the scaffold only in the presence of microenvironmental elements, which through direct contact down-regulate the expression of HS1 cytoskeletal protein in CLL cells. Consist with this, the expression of HS1 was lower in CLL cells obtained from patients' BM versus CLL cells circulating in the PB. Moreover, we demonstrate that CLL cells with inactive-HS1, impaired cytoskeletal activity and a more aggressive phenotype are more likely retained within the scaffold despite the presence of Ibrutinib, whose mobilizing effect is mainly exerted on those with active-HS1, ensuing dynamic cytoskeletal activity. This differential effect would not otherwise be assessable in a traditional 2D system and may underlie a distinctive resistance of single CLL clones. Notably, CLL cells mobilized in the peripheral blood of patients during Ibrutinib therapy exhibited activated HS1, underscoring that our model reliably mirrors the in vivo situation. The 3D model described herein is suitable to reproduce and identify critical CLL-BM interactions, opening the way to pathophysiological studies and the evaluation of novel targeted therapies in an individualized manner.

3D-STED Super-Resolution Microscopy Reveals Distinct Nanoscale Organization of the Hematopoietic Cell-Specific Lyn Substrate-1 (HS1) in Normal and Leukemic B Cells

HS1, the hematopoietic homolog of cortactin, acts as a versatile actin-binding protein in leucocytes. After phosphorylation, it is involved in GTPase and integrin activation, and in BCR, TCR, and CXCR4 downstream signaling. In normal and leukemic B cells, HS1 is a central cytoskeletal interactor and its phosphorylation and expression are prognostic factors in chronic lymphocytic leukemia (CLL) patients. We here introduce for the first time a super-resolution imaging study based on single-cell 3D-STED microscopy optimized for revealing and comparing the nanoscale distribution of endogenous HS1 in healthy B and CLL primary cells. Our study reveals that the endogenous HS1 forms heterogeneous nanoclusters, similar to those of YFP-HS1 overexpressed in the leukemic MEC1 cell line. HS1 nanoclusters in healthy and leukemic B cells form bulky assemblies at the basal sides, suggesting the recruitment of HS1 for cell adhesion. This observation agrees with a phasor-FLIM-FRET and STED colocalization analyses of the endogenous MEC1-HS1, indicating an increased interaction with Vimentin at the cell adhesion sites. In CLL cells isolated from patients with poor prognosis, we observed a larger accumulation of HS1 at the basal region and a higher density of HS1 nanoclusters in the central regions of the cells if compared to good-prognosis CLL and healthy B cells, suggesting a different role for the protein in the cell types analyzed. Our 3D-STED approach lays the ground for revealing tiny differences of HS1 distribution, its functionally active forms, and colocalization with protein partners.

3D Bioprinting Allows the Establishment of Long-Term 3D Culture Model for Chronic Lymphocytic Leukemia Cells

Chronic Lymphocytic Leukemia (CLL) represents the most common leukemia in the western world and remains incurable. Leukemic cells organize and interact in the lymphoid tissues, however what actually occurs in these sites has not been fully elucidated yet. Studying primary CLL cells in vitro is very challenging due to their short survival in culture and also to the fact that traditional two-dimensional in vitro models lack cellular and spatial complexity present in vivo. Based on these considerations, we exploited for the first time three-dimensional (3D) bioprinting to advance in vitro models for CLL. This technology allowed us to print CLL cells (both primary cells and cell lines) mixed with the appropriate, deeply characterized, hydrogel to generate a scaffold containing the cells, thus avoiding the direct cell seeding onto a precast 3D scaffold and paving the way to more complex models. Using this system, we were able to efficiently 3D bioprint leukemic cells and improve their viability in vitro that could be maintained up to 28 days. We monitored over time CLL cells viability, phenotype and gene expression, thus establishing a reproducible long-term 3D culture model for leukemia. Through RNA sequencing (RNAseq) analysis, we observed a consistent difference in gene expression profile between 2D and 3D samples, indicating a different behavior of the cells in the two different culture settings. In particular, we identified pathways upregulated in 3D, at both day 7 and 14, associated with immunoglobulins production, pro-inflammatory molecules expression, activation of cytokines/chemokines and cell-cell adhesion pathways, paralleled by a decreased production of proteins involved in DNA replication and cell division, suggesting a strong adaptation of the cells in the 3D culture. Thanks to this innovative approach, we developed a new tool that may help to better mimic the physiological 3D in vivo settings of leukemic cells as well as of immune cells in broader terms. This will allow for a more reliable study of the molecular and cellular interactions occurring in normal and neoplastic conditions in vivo, and could also be exploited for clinical purposes to test individual responses to different drugs.

Modeling the Leukemia Microenviroment In Vitro

Over the last decade, the active role of the microenvironment in the pathogenesis, development and drug resistance of B cell malignancies has been clearly established. It is known that the tissue microenvironment promotes proliferation and drug resistance of leukemic cells suggesting that successful treatments of B cell malignancies must target the leukemic cells within these compartments. However, the cross-talk occurring between cancer cells and the tissue microenvironment still needs to be fully elucidated. In solid tumors, this lack of knowledge has led to the development of new and more complex in vitro models able to successfully mimic the in vivo settings, while only a few simplified models are available for haematological cancers, commonly relying only on the co-culture with stabilized stromal cells and/or the addition of limited cocktails of cytokines. Here, we will review the known cellular and molecular interactions occurring between monoclonal B lymphocytes and their tissue microenvironment and the current literature describing innovative in vitro models developed in particular to study chronic lymphocytic leukemia (CLL). We will also elaborate on the possibility to further improve such systems based on the current knowledge of the key molecules/signals present in the microenvironment. In particular, we think that future models should be developed as 3D culture systems with a higher level of cellular and molecular complexity, to replicate microenvironmental-induced signaling. We believe that innovative 3D-models may therefore improve the knowledge on pathogenic mechanisms leading to the dissemination and homing of leukemia cells and consequently the identification of therapeutic targets.

B lymphocytes contribute to stromal reaction in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a prominent stromal reaction that has been variably implicated in both tumor growth and tumor suppression. B-lymphocytes have been recently implicated in PDAC progression but their contribution to the characteristic stromal desmoplasia has never been assessed before. In the present work, we aimed to verify whether B-lymphocytes contribute to stromal cell activation in PDAC. CD19⁺ B-lymphocytes purified from peripheral blood of patients with PDAC were cultivated in the presence of human pancreatic fibroblasts and cancer-associated fibroblasts. Released pro-fibrotic soluble factors and collagen production were assessed by ELISA and Luminex assays. Quantitative RT-PCR was used to assess fibroblast activation in the presence of B cells. The expression of selected pro-fibrotic and inflammatory molecules was confirmed on PDAC tissue sections by multi-color immunofluorescence studies. We herein demonstrate that B-cells from PDAC patients (i) produce the pro-fibrotic molecule PDGF-B and stimulate collagen production by fibroblasts; (ii) express enzymes implicated in extracellular matrix remodeling including LOXL2; and (iii) produce the chemotactic factors CCL-4, CCL-5, and CCL-11. In addition we demonstrate that circulating plasmablasts are expanded in the peripheral blood of patients with PDAC, stimulate collagen production by fibroblasts, and infiltrate pancreatic lesions. Our results indicate that PDAC is characterized by perturbations of the B-cell compartment with expansion of B-lymphocyte subsets that directly contribute to the stromal reaction observed at disease site. These findings provide an additional rationale for modulating B-cell activity in patients with pancreatic cancer.

Computational analysis of the evolutionarily conserved Missing In Metastasis/Metastasis Suppressor 1 gene predicts novel interactions, regulatory regions and transcriptional control

Missing in Metastasis (MIM), or Metastasis Suppressor 1 (MTSS1), is a highly conserved protein, which links the plasma membrane to the actin cytoskeleton. MIM has been implicated in various cancers, however, its modes of action remain largely enigmatic. Here, we performed an extensive in silico characterisation of MIM to gain better understanding of its function. We detected previously unappreciated functional motifs including adaptor protein (AP) complex interaction site and a C-helix, pointing to a role in endocytosis and regulation of actin dynamics, respectively. We also identified new functional regions, characterised with phosphorylation sites or distinct hydrophilic properties. Strong negative selection during evolution, yielding high conservation of MIM, has been combined with positive selection at key sites. Interestingly, our analysis of intra-molecular co-evolution revealed potential regulatory hotspots that coincided with reduced potentially pathogenic polymorphisms. We explored databases for the mutations and expression levels of MIM in cancer. Experimentally, we focused on chronic lymphocytic leukaemia (CLL), where MIM showed high overall expression, however, downregulation on poor prognosis samples. Finally, we propose strong conservation of MTSS1 also on the transcriptional level and predict novel transcriptional regulators. Our data highlight important targets for future studies on the role of MIM in different tissues and cancers.

Inhibition of chronic lymphocytic leukemia progression by full-length chromogranin A and its N-terminal fragment in mouse models

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of leukemic B cells in peripheral blood, bone marrow (BM) and lymphoid tissues, and by their recirculation between these compartments. We observed that circulating chromogranin A (CgA) and its N-terminal fragment (called vasostatin-1, CgA_1-76), two neuroendocrine secretory polypeptides that enhance the endothelial barrier function, are present in variable amounts in the blood of CLL patients. Studies in animal models showed that daily administration of full-length human CgA_1-439 (0.3 μg, i.v., or 1.5 μg/mouse, i.p.) can reduce the BM/blood ratio of leukemic cells in Eμ-TCL1 mice, a transgenic model, and decrease BM, lung and kidney infiltration in Rag2^−/−γc^−/− mice engrafted with human MEC1 CLL cells, a xenograft model. This treatment also reduced the loss of body weight and improved animal motility. In vitro, CgA enhanced the endothelial barrier integrity and the trans-endothelial migration of MEC1 cells, with a bimodal dose-response curve. Vasostatin-1, but not a larger fragment consisting of N-terminal and central regions of CgA (CgA_1-373), inhibited CLL progression in the xenograft model, suggesting that the C-terminal region is crucial for CgA activity and that the N-terminal domain contains a site that is activated by proteolytic cleavage. These findings suggest that circulating full-length CgA and its fragments may contribute to regulate leukemic cell trafficking and reduce tissue infiltration in CLL.

Synthetic high-density lipoproteins as targeted monotherapy for chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) remains incurable despite the introduction of new drugs. Therapies targeting receptors and pathways active specifically in malignant B cells might provide better treatment options. For instance, in B cell lymphoma, our group has previously shown that scavenger receptor type B-1 (SR-B1), the high-affinity receptor for cholesterol-rich high-density lipoproteins (HDL), is a therapeutic target. As evidence suggests that targeting cholesterol metabolism in CLL cells may have therapeutic benefit, we examined SR-B1 expression in primary CLL cells from patients. Unlike normal B cells that do not express SR-B1, CLL cells express the receptor. As a result, we evaluated cholesterol-poor synthetic HDL nanoparticles (HDL NP), known for targeting SR-B1, as a therapy for CLL. HDL NPs potently and selectively induce apoptotic cell death in primary CLL cells. HDL NPs had no effect on normal peripheral blood mononuclear cells from healthy individuals or patients with CLL. These data implicate SR-B1 as a target in CLL and HDL NPs as targeted monotherapy for CLL.

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.

Targeting Macrophages Sensitizes Chronic Lymphocytic Leukemia to Apoptosis and Inhibits Disease Progression

The role of monocytes/macrophages in the development and progression of chronic lymphocytic leukemia (CLL) is poorly understood. Transcriptomic analyses show that monocytes/macrophages and leukemic cells cross talk during CLL progression. Macrophage depletion impairs CLL engraftment, drastically reduces leukemic growth, and favorably impacts mouse survival. Targeting of macrophages by either CSF1R signaling blockade or clodrolip-mediated cell killing has marked inhibitory effects on established leukemia also. Macrophage killing induces leukemic cell death mainly via the TNF pathway and reprograms the tumor microenvironment toward an antitumoral phenotype. CSF1R inhibition reduces leukemic cell load, especially in the bone marrow, and increases circulating CD20(+) leukemic cells. Accordingly, co-targeting TAMs and CD20-expressing leukemic cells provides a survival benefit in the mice. These results establish the important role of macrophages in CLL and suggest therapeutic strategies based on interfering with leukemia-macrophage interactions.

Abstract 1023: Duration of signaling through IgM and IgD receptors differentially influences cell survival and BCL6-regulated CCL3/4 chemokine production in Chronic Lymphocytic Leukemia (CLL)

B-cell receptor (BCR) signaling is a central pathogenetic mechanism in CLL. Most CLL cells express both IgM and IgD receptors, and increased responsiveness to IgM stimulation correlates with poor disease outcome and with expression of IGHV-unmutated immunoglobulin receptors (U-CLL). In contrast, the relevance of IgD signaling remains poorly understood.

The aim of the present study is to characterize functional differences between IgM and IgD signaling in CLL in terms of protection from in vitro apoptosis, BCR signaling activation and CCL3/4 chemokine secretion and to explore the mechanism through which CCL3/4 are regulated, with a focus on their transcriptional repressor BCL6.

CLL cells were stimulated with anti-IgM and anti-IgD; 48-hour cell viability and BCR expression were analyzed by flow cytometry; phosphorylation of the BCR-signaling related molecules HS1 and ERK after 2, 5, 15, 30, 60 minutes of stimulation were analyzed by Western Blot and flow cytometry; BCL6 protein expression by Western Blot and CCL3/4 secretion by ELISA were tested after 3, 6, 9, 12, 24 hours of stimulation.

Anti-IgM stimulation protected CLL cells from in vitro apoptosis to a greater extent than anti-IgD and U-CLL were more responsive to anti-IgM as compared to cells carrying IGHV-mutated receptors (M-CLL) (p = 0.0022; n = 13 M-CLL vs. n = 11 U-CLL). In line with this finding, U-CLL expressed higher levels of surface IgM, as compared to M-CLL (p<0.0001; n = 40 M-CLL vs. n = 33 U-CLL). IgM stimulation induced protracted HS1 and ERK phosphorylation up to 30 minutes following receptor engagement, as analyzed in 10 M-CLL and 10 U-CLL cases. In contrast, IgD stimulation induced short-lived phosphorylation of both proteins, which rapidly returned to baseline. U-CLL cells were more responsive than M-CLL to both anti-IgM and anti-IgD stimulation. High CCL3/4 secretion was detected after anti-IgM, in particular in U-CLL. Surprisingly low, if any, induction of both chemokines was detected after stimulation of IgD receptors. Interestingly, increased CCL3/4 production and concomitant BCL6 protein downregulation were observed after 6 and up to 12 hours following anti-IgM but not anti-IgD stimulation.

In conclusion, IgM stimulation induces a long-lived signaling response, increased CLL-cell survival and CCL3/4 secretion, in particular in U-CLL; in contrast, IgD signaling is short-lived and has minimal effects on protection from apoptosis and chemokine secretion. BCL6 protein downregulation induced by anti-IgM parallels CCL3/4 production, suggesting a functional link between BCL6 expression and CCL3/4. Taken together, these evidences suggest that the differential functional outcomes of IgM and IgD signaling might be related to the duration of the signaling response and support the relevance of IgM signaling in CLL pathogenesis.

Citation Format: Elisa ten Hacken, Cristina Scielzo, Susan O'Brien, William G. Wierda, Michael J. Keating, Paolo Ghia, Federico Caligaris-Cappio, Jan A. Burger. Duration of signaling through IgM and IgD receptors differentially influences cell survival and BCL6-regulated CCL3/4 chemokine production in Chronic Lymphocytic Leukemia (CLL). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1023. doi:10.1158/1538-7445.AM2015-1023

Establishment and Characterization of PCL12, a Novel CD5+ Chronic Lymphocytic Leukaemia Cell Line

Immortalized cell lines representative of chronic lymphocytic leukemia (CLL) can assist in understanding disease pathogenesis and testing new therapeutic agents. At present, very few representative cell lines are available. We here describe the characterization of a new cell line (PCL12) that grew spontaneously from the peripheral blood (PB) of a CLL patient with progressive disease and EBV infection. The CLL cell origin of PCL12 was confirmed after the alignment of its IGH sequence against the “original” clonotypic sequence. The IGH gene rearrangement was truly unmutated and no CLL-related cytogenetic or genetic lesions were detected. PCL12 cells express CD19, CD20, CD5, CD23, low levels of IgM and IgD and the poor-outcome-associated prognostic markers CD38, ZAP70 and TCL1. In accordance with its aggressive phenotype the cell line is inactive in terms of LYN and HS1 phosphorylation. BcR signalling pathway is constitutively active and anergic in terms of p-ERK and Calcium flux response to α-IgM stimulation. PCL12 cells strongly migrate in vitro in response to SDF-1 and form clusters. Finally, they grow rapidly and localize in all lymphoid organs when xenotrasplanted in Rag2^-/-γc^-/- mice. PCL12 represents a suitable preclinical model for testing pharmacological agents.

From a 2DE-gel spot to protein function: lesson learned from HS1 in chronic lymphocytic leukemia

The identification of molecules involved in tumor initiation and progression is fundamental for understanding disease's biology and, as a consequence, for the clinical management of patients. In the present work we will describe an optimized proteomic approach for the identification of molecules involved in the progression of Chronic Lymphocytic Leukemia (CLL). In detail, leukemic cell lysates are resolved by 2-dimensional Electrophoresis (2DE) and visualized as "spots" on the 2DE gels. Comparative analysis of proteomic maps allows the identification of differentially expressed proteins (in terms of abundance and post-translational modifications) that are picked, isolated and identified by Mass Spectrometry (MS). The biological function of the identified candidates can be tested by different assays (i.e. migration, adhesion and F-actin polymerization), that we have optimized for primary leukemic cells.

An overview of chronic lymphocytic leukaemia biology

Chronic lymphocytic leukaemia (CLL) is characterised by accumulation of CD5(+) monoclonal B cells in primary and secondary lymphoid tissues. Genetic defects and stimuli originating from the microenvironment concur to the selection and expansion of the malignant clone. Several lines of evidence, including molecular and functional analysis of the monoclonal immunoglobulin, support the hypothesis that stimulation through the B-cell receptor affects life and death of leukaemic cells. The microenvironment also has a critical role in the survival and accumulation of leukaemic cells within lymphoid organs where signals delivered from the surrounding cells are likely crucial in inducing proliferation. Nevertheless, several major biological issues still remain to be solved including regulation of the balance between proliferation and survival of leukaemic cells and the links between emerging gene abnormalities and microenvironment. In this context, mouse models are helpful tools in understanding disease mechanisms and in evaluating the efficacy of novel therapeutic agents.

How the microenvironment shapes chronic lymphocytic leukemia: the cytoskeleton connection

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation in primary and secondary lymphoid tissues of CD5+ B cells that have the same B cell receptor (BCR) rearrangement. Genetic alterations and different stimuli originating from the microenvironment cooperate in the selection and expansion of the malignant clone. Molecular and functional analyses suggest that stimulation through the BCR affects the destiny of leukemic cells in terms of life or death. Microenvironmental signals are crucial for this process, inducing proliferation and leading to the survival and accumulation of leukemic cells within lymphoid organs. Nevertheless, a number of major biological issues still remain to be solved, including the relationships between cell proliferation and cell accumulation within lymphoid organs as well as the mechanisms that regulate CLL cell migration and recirculation between peripheral blood and lymphoid tissues. We focused on the role played by the cytoskeleton, given its relevance in controlling cellular shape, mobility, and homing. We hypothesize that hematopoietic cell-specific Lyn substrate 1 (HS1), a putative prognostic marker in CLL that interacts with distinct cytoskeleton adapters in leukemic B-lymphocytes, could regulate the CLL cell cytoskeleton.

CLL-like monoclonal B-cell lymphocytosis: are we all bound to have it?

CLL-like monoclonal B-cell lymphocytosis (MBL) shares a unique immunophenotype with chronic lymphocytic leukemia (CLL), and represents the vast majority of clonal B-cell expansions found in the peripheral blood of otherwise healthy subjects. Along with the improvement of laboratory techniques and the widespread availability of multiparameter flow cytometry, the finding of tiny aberrant B-cell populations became more frequent, prompting the need for clinical and biological definition of the nature of this condition and its relationship with leukemia development. MBL seems to be a melting-pot containing several entities, identical in terms of phenotype but with extremely different risks of leukemia development (from low to none) that seem to correlate with the number of B lymphocytes. CLL-like MBL observed in the clinical setting ("Clinical MBL"), usually being characterized by lymphocytosis, demonstrated a sizeable, even if low (1.1-1.4% per year), risk of leukemic progression, but represents a minority of all MBL cases. The vast majority of CLL-like MBL are detected in general population screenings and do not likely have a risk of CLL that is substantially higher than that of unaffected individuals. Interestingly, MBL frequency increases with age, being virtually undetectable under 40 years of age but being present in 50-75% of the people older than 90 years. It has been proposed that MBL could be interpreted as an epiphenomenon of a chronic and persistent antigenic stimulation. The (rare) possibility to evolve into a frank leukemia might then depend on biological and molecular factors insofar unknown that may modify the modality of cell reaction as well as the potential to acquire further genetic abnormalities. Therefore, the real challenge of the next years in the MBL research field is not to increase the sensitivity of detection, neither to implement screening protocols to be applied to the general population, rather to unravel the biologic features that, at individual level, will identify those (few) cases that are at risk of developing a progressive disease.

Expression and function of toll like receptors in chronic lymphocytic leukaemia cells

Mature B-cells can recognize microbial antigens via B-cell-receptor (BCR) in a specific way and via Toll-like receptors (TLR) in a costimulatory manner. A wealth of information is gathering on the possible role of antigenic stimulation in the natural history of Chronic Lymphocytic Leukaemia (CLL). However little is known regarding the repertoire and function of TLR in CLL cells. The TLR family includes 10 different transmembrane proteins devoted to recognize specific pathogen-associated molecular patterns and to alarm immunocompetent cells to trigger an immune response. Here, we studied fresh leukaemic cells for the expression pattern of TLR1 to TLR10, NOD1, NOD2 and SIGIRR (also known as TIR8). CLL cells were found to express several pattern recognition receptors including TLR1, TLR2, TLR6, TLR10, NOD1 and NOD2. The specific TLR expressed by CLL cells were functional. Leukaemic cells, upon stimulation with TLR1/2/6 ligands, such as bacterial lipopeptides, activated the nuclear factor-kappaB signalling pathway, expressed CD86 and CD25 activation molecules, and were protected from spontaneous apoptosis. These findings further support the hypothesis that CLL cells resemble antigen-activated B-cells and suggest a potential role of TLR in modulating CLL cell response in the context of specific antigen recognition.

Age-dependent accumulation of monoclonal CD4+CD8+ double positive T lymphocytes in the peripheral blood of the elderly

Multicolour flow cytometric analysis enabled the identification of monoclonal B-cell lymphocytosis (MBL), frequently resembling chronic lymphocytic leukaemia, at a rather high frequency in peripheral blood (PB) samples from an elderly population. PB T lymphocytes from 103 otherwise healthy subjects >65 years of age and 51 younger donors (<65 years) were analysed. Besides CD4(+) and CD8(+) single positive (SP) cells, CD4(+)CD8(+) double positive (DP) mature T lymphocytes were present in both series and could be further distinguished into CD4(high)CD8(low) and CD4(low)CD8(high) subsets. An age-dependent increase of both DP T-cell subsets was observed, while SP T cells remained stable throughout life. Flow cytometry and polymerase chain reaction analysis of the TRBV expression profiles showed the presence of a TRBV restriction within CD4(+)CD8(+) DP cells in more than half (53/103; 55.3%) of the individuals >65 years of age, regardless the actual number of DP T cells observed. Clonal expansions were more prominent within the CD4(high)CD8(low) subset, accounting for most circulating DP clones (47/103; 45.6%). A few cases showed more than one (up to three) monoclonal expansion. Clonal CD4(low)CD8(high) DP T-lymphocyte expansions were detected in only 10/103 samples (9.7%) and showed a close phenotypic similarity to the rare T-cell large granular lymphocyte leukaemias. The similarities between DP clones and MBL in the elderly may help to better understand the mechanisms of immunosenescence and their relationships with the development of lymphoproliferative disorders.

From normal to clonal B cells: Chronic lymphocytic leukemia (CLL) at the crossroad between neoplasia and autoimmunity

Chronic lymphocytic leukemia (CLL) is a B-cell malignancy endowed with a number of features that recall autoimmune disorders, including the CD5 expression and the development of autoimmune manifestations restricted to self antigens expressed by hematopoietic cells. Several evidences strongly support the possibility that an antigenic stimulation through the B-cell receptor (BCR) is involved in the selection and possibly also the expansion of the malignant clone. Though all evidences suggest specific Ag recognition and possibly stimulation at different time-points, the nature of the Ag(s) is still unknown. It appears likely that CLL cells derive from a pool of auto/polyreactive CD5(+) B cells. Hence CLL appears to be a B-cell malignancy triggered or facilitated in its development and evolution by an auto-Ag. The crucial issues have become to what extent this deleterious binding capacity is central to the natural history of the disease and how it relates to the malignant transformation of the cell.

Identification of proangiogenic TIE2-expressing monocytes (TEMs) in human peripheral blood and cancer

Tumor-infiltrating myeloid cells, including tumor-associated macrophages (TAMs), have been implicated in tumor progression. We recently described a lineage of mouse monocytes characterized by expression of the Tie2 angiopoietin receptor and required for the vascularization and growth of several tumor models. Here, we report that TIE2 expression in human blood identifies a subset of monocytes distinct from classical inflammatory monocytes and comprised within the less abundant "resident" population. These TIE2-expressing monocytes (TEMs) accounted for 2% to 7% of blood mononuclear cells in healthy donors and were distinct from rare circulating endothelial cells and progenitors. In human cancer patients, TEMs were observed in the blood and, intriguingly, within the tumors, where they represented the main monocyte population distinct from TAMs. Conversely, TEMs were hardly detected in nonneoplastic tissues. In vitro, TEMs migrated toward angiopoietin-2, a TIE2 ligand released by activated endothelial cells and angiogenic vessels, suggesting a homing mechanism for TEMs to tumors. Purified human TEMs, but not TEM-depleted monocytes, markedly promoted angiogenesis in xenotransplanted human tumors, suggesting a potentially critical role of TEMs in human cancer progression. Human TEMs may provide a novel, biologically relevant marker of angiogenesis and represent a previously unrecognized target of cancer therapy.

ZAP-70 is expressed by normal and malignant human B-cell subsets of different maturational stage

ZAP-70 tyrosine kinase is involved in signalling pathways following T-cell receptor stimulation and was originally described only in T cells and natural killer cells. ZAP-70 expression has been reported in normal mouse B lineage cells and in human malignant B lymphocytes, mainly in chronic lymphocytic leukemia (CLL) where it correlates with clinical outcome. We analyzed several B-cell lines and ex vivo malignant B cells, ranging from acute lymphoblastic leukemia to multiple myeloma and reflecting different stages of B-cell differentiation, and they showed ZAP-70 expression regardless their maturation stage. We then analyzed by Western blot and flow cytometry different human normal B-lymphocyte subpopulations: naïve, germinal center and memory B cells from tonsils, CD19+ CD5+ cells from cord blood and CD19+ lymphocytes from peripheral blood. All expressed ZAP-70 protein, though at different levels depending on their differentiation, activation and tissue localization. In addition, ZAP-70 expression levels could be modulated following stimulation via the B-cell receptor. These findings implicate a potential role of ZAP-70 in the signalling pathway of B lymphocytes at different maturational stages, indicate that ZAP-70 expression is not a CLL-specific feature among B-cell malignancies and suggest that the absence of ZAP-70 rather than its presence should be considered abnormal for malignant B lymphocytes.

HS1 protein is differentially expressed in chronic lymphocytic leukemia patient subsets with good or poor prognoses

We used a proteomic approach for identifying molecules involved in the pathogenesis of chronic lymphocytic leukemia (CLL). We investigated 14 patients who were completely concordant for IgV(H) mutational status (unmutated vs. mutated), CD38 expression (positive vs. negative), and clinical behavior (progressive vs. stable); these patients were characterized as having either poor or good prognoses. The 2 patient subsets differed in the expression of hematopoietic lineage cell-specific protein 1 (HS1). In patients with poor prognoses, most HS1 protein was constitutively phosphorylated, whereas only a fraction was phosphorylated in patients with good prognoses. This difference was investigated in a larger cohort of 26 unselected patients. The survival curve of all 40 patients analyzed revealed that patients with predominately phosphorylated HS1 experience a significantly shorter median survival time. As HS1 is a protein pivotal in the signal cascade triggered by B cell receptor (BCR) stimulation, we studied its pattern of expression following BCR engagement. Normal mature B cells stimulated by anti-IgM shifted the non- or less-phosphorylated form of HS1 toward the more phosphorylated form. Naive B cells showed both HS1 forms while memory B cells expressed mainly the phosphorylated fraction. These data indicate a central role for antigen stimulation in CLL and suggest a new therapeutic target for patients with aggressive disease.

Differential effects on CLL cell survival exerted by different microenvironmental elements

Selected microenvironmental stimuli confer to leukemic cells a growth advantage and an extended survival. We aimed at dissecting the differential support provided by the different cellular components of the microenvironment where CLL cells accumulate. To this end we cultured purified CLL cells in vitro in the presence or absence of different accessory cells (stromal cells, autologous T lymphocytes) and/or soluble molecules (IL-4, sCD40L) and assessed the leukemic cell response in terms of cell viability and chemoattracting capacity. The results indicate that both T lymphocytes and stromal cells are involved in sustaining the survival of leukemic B cells, but indicate that their support is different in terms of time of onset and duration. T cells have a short-term support activity while stromal cells provide long-term support.

Monoclonal CD5+ and CD5- B-lymphocyte expansions are frequent in the peripheral blood of the elderly

The responsiveness and diversity of peripheral B-cell repertoire decreases with age, possibly because of B-cell clonal expansions, as suggested by the incidence of serum monoclonal immunoglobulins and of monoclonal chronic lymphocytic leukemia (CLL)-like B lymphocytes in clinically silent adults. We phenotyped peripheral blood cells from 500 healthy subjects older than 65 years with no history or suspicion of malignancies and no evidence of lymphocytosis. In 19 cases (3.8%) a kappa/lambda ratio of more than 3:1 or less than 1:3 was found: 9 were CD5+, CD19+, CD23+, CD20low, CD79blow, sIglow (classic CLL-like phenotype); 3 were CD5+, CD19+, CD23+, CD20high, CD79blow, sIglow (atypical CLL-like), and 7 were CD5-, CD19+, CD20high, CD23-, CD79bbright, FMC7+, sIgbright (non-CLL-like). In 2 subjects, 2 phenotypically distinct unrelated clones were concomitantly evident. No cases were CD10+. Polymerase chain reaction (PCR) analysis demonstrated a monoclonal rearrangement of IgH genes in 15 of 19 cases. No bcl-1 or bcl-2 rearrangements were detected. Using a gating strategy based on CD20/CD5/CD79 expression, 13 additional CLL-like B-cell clones were identified (cumulative frequency of classic CLL-like: 5.5%). Thus, phenotypically heterogeneous monoclonal B-lymphocyte expansions are common among healthy elderly individuals and are not limited to classic CLL-like clones but may have the phenotypic features of different chronic lymphoproliferative disorders, involving also CD5- B cells.

The characterization of chemokine production and chemokine receptor expression reveals possible functional cross-talks in AML blasts with monocytic differentiation

OBJECTIVE

The mechanisms regulating the trafficking of leukemic myeloid blasts are poorly understood. A differential expression of chemokines and chemokine receptors might account for some aspects of the pattern of invasion and accumulation of leukemic cells. We aimed at defining the pattern of chemokine and chemokine receptor expression of acute myeloid leukemia (AML) blasts in comparison with their putative normal cell counterparts.

PATIENTS AND METHODS

Twenty-five cases of AML were analyzed by flow cytometry for the expression of several chemokine receptors and by RT-PCR for the expression of relevant chemokines. For selected chemokines, the production was confirmed by ELISA. AML blasts were also assessed for their migration capacity in response to autologous supernatants and recombinant chemokines.

RESULTS

Undifferentiated AML (MO-M1 and some M2) express only CXCR4 on their surface and produce mainly inflammatory chemokines, resembling normal CD34+ progenitors. More differentiated AML (M4-M5 and some M2) have a more diversified receptor repertoire and, besides CXCR4, express the receptors for inflammatory chemokines and produce both constitutive and inflammatory chemokines, resembling resting and activated monocytes. In particular, M4-M5 blasts produce MCP-1 and MIP-3alpha and also express their specific receptors (CCR2 and, to a lesser extent, CCR6) and migrate in vitro in response to MCP-1 and MIP-3alpha and to their own supernatant. A significant correlation between extramedullary involvement and coexpression of MCP-1/CCR2 was found.

CONCLUSIONS

These data suggest that chemokines and their receptors segregate within the different FAB subtypes and, by allowing cross-talk among members of the malignant clone, might help to explain some aspects of the pattern of invasion in AML with monocytic differentiation.

CD100/Plexin-B1 interactions sustain proliferation and survival of normal and leukemic CD5+ B lymphocytes

Growth and survival of chronic B-cell tumors are favored by the malignant cell's capacity to respond to selected microenvironmental stimuli provided by nontumoral bystander cells. To investigate which mechanisms operate in these crosstalks and whether they are malignancy-related or reproduce the mechanisms used by normal B cells we have studied the expression and functional role of semaphorin CD100 (now called Sema4D) in chronic lymphocytic leukemia (CLL) cells and normal CD5+ B cells. We demonstrate here that (1) leukemic and normal CD5+ B lymphocytes uniformly express CD100; (2) the CD100 high-affinity receptor Plexin-B1 is expressed by bone marrow stromal cells, follicular dendritic cells, and activated T lymphocytes, and is thus available to CD100+ lymphocytes in different specific microenvironments; and (3) upon interaction between CD100 and Plexin-B1 both CLL and normal CD5+ B cells increase their proliferative activity and extend their life span. These findings establish that Plexin-B1 is an easily accessible receptor for CD100 within the immune system. The encounter of CD100+ leukemic cells with Plexin-B1 may promote the proliferation and survival of malignant cells. The crosstalk operated by the CD100/Plexin-B1 interaction is not malignancy related but reproduces a mechanism used by normal CD5+ B cells.

The pattern of CD38 expression defines a distinct subset of chronic lymphocytic leukemia (CLL) patients at risk of disease progression

Chronic lymphocytic leukemia (CLL) has a variable clinical course. CD38 expression and IgV(H) gene mutational status are independent predictors of prognosis, but their relationships and the CD38 cutoff level are unknown. Using cytofluorography, we analyzed CD38 in 148 patients, in 108 of whom we were able to evaluate IgV(H) mutations, make correlations with disease history, and assess cumulative survival. Three different patient groups were identified by the CD38 expression pattern: a group homogeneously CD38(-), a group homogeneously CD38(+), and a group characterized by a bimodal profile, because of the concomitant presence of variable proportions of 2 distinct populations, one CD38(+) and one CD38(-). In CD38 bimodal expression patients the CD38(+) subset was significantly more represented in the bone marrow than in the peripheral blood. For IgV(H) mutations, 11.4% of CD38(-), 84.6% of CD38(+), and 68.0% of CD38 bimodal expression patients had no mutation. CD38 expression, IgV(H) mutational status, and traditional prognostic factors were concordant. The progression rate was 12.9% for CD38(-), 75.0% for CD38(+), and 63.3% for CD38 bimodal expression patients. Only 25.8% of the CD38(-) patients but 63.3% of the bimodal and 75.0% of CD38(+) patients were treated. The presence of a CD38(+) population, albeit small, correlated with the development of autoimmune manifestations. The CD38(-) group has not yet reached the median survival, which is 183 months in the CD38(+) group and 156 months in the CD38 bimodal expression group, regardless of the size of the CD38(+) population. The presence of a distinct CD38(+) population within the leukemic clone, rather than a numerical cutoff definition, correlates with IgV(H) gene mutational status and, irrespective of its size, identifies CLL patients who will have progressive disease.