The indispensable role of microenvironment in the natural history of low-grade B-cell neoplasms

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.

Understanding CLL biology through mouse models of human genetics

Rapid advances in large-scale next-generation sequencing studies of human samples have progressively defined the highly heterogeneous genetic landscape of chronic lymphocytic leukemia (CLL). At the same time, the numerous challenges posed by the difficulties in rapid manipulation of primary B cells and the paucity of CLL cell lines have limited the ability to interrogate the function of the discovered putative disease "drivers," defined in human sequencing studies through statistical inference. Mouse models represent a powerful tool to study mechanisms of normal and malignant B-cell biology and for preclinical testing of novel therapeutics. Advances in genetic engineering technologies, including the introduction of conditional knockin/knockout strategies, have opened new opportunities to model genetic lesions in a B-cell-restricted context. These new studies build on the experience of generating the MDR mice, the first example of a genetically faithful CLL model, which recapitulates the most common genomic aberration of human CLL: del(13q). In this review, we describe the application of mouse models to the studies of CLL pathogenesis and disease transformation from an indolent to a high-grade malignancy (ie, Richter syndrome [RS]) and treatment, with a focus on newly developed genetically inspired mouse lines modeling recurrent CLL genetic events. We discuss how these novel mouse models, analyzed using new genomic technologies, allow the dissection of mechanisms of disease evolution and response to therapy with greater depth than previously possible and provide important insight into human CLL and RS pathogenesis and therapeutic vulnerabilities. These models thereby provide valuable platforms for functional genomic analyses and treatment studies.

A retinoic acid-dependent stroma-leukemia crosstalk promotes chronic lymphocytic leukemia progression

In chronic lymphocytic leukemia (CLL), the non-hematopoietic stromal microenvironment plays a critical role in promoting tumor cell recruitment, activation, survival, and expansion. However, the nature of the stromal cells and molecular pathways involved remain largely unknown. Here, we demonstrate that leukemic B lymphocytes induce the activation of retinoid acid synthesis and signaling in the microenvironment. Inhibition of RA-signaling in stromal cells causes deregulation of genes associated with adhesion, tissue organization and chemokine secretion including the B-cell chemokine CXCL13. Notably, reducing retinoic acid precursors from the diet or inhibiting RA-signaling through retinoid-antagonist therapy prolong survival by preventing dissemination of leukemia cells into lymphoid tissues. Furthermore, mouse and human leukemia cells could be distinguished from normal B-cells by their increased expression of Rarγ2 and RXRα, respectively. These findings establish a role for retinoids in murine CLL pathogenesis, and provide new therapeutic strategies to target the microenvironment and to control disease progression.

The stromal microenvironment plays a key role in the expansion of chronic lymphocytic leukemia. Here, the authors use the Eµ-TCL1 mouse model to show that leukemic B-cells induce the activation of retinoic acid synthesis in stromal cells of the lymphoid microenvironment, and that impacting on retinoic acid signalling via diet or chemical inhibition prolonged survival by preventing leukemia dissemination and accumulation in lymphoid tissues.

Identification and characterization of distinct IL-17F expression patterns and signaling pathways in chronic lymphocytic leukemia and normal B lymphocytes

Chronic lymphocytic leukemia (CLL) is characterized by a progressive accumulation of B lymphocytes. T cell abnormalities are a common feature of CLL and contribute to impaired immune function in these patients. T cells are ineffective in eliminating the leukemic clone and may actually promote tumor growth and survival. Previous work from our laboratory documented elevated circulating levels of IL-17A-producing Th17 cells in CLL patients as compared to healthy age-matched control subjects. These high circulating Th17 levels associated with better prognostic markers and significantly longer overall survival, even among patients whose clones used unmutated IGHVs (U-CLL). Recent studies suggest that Th17 cells are heterogeneous, expressing different profiles of cytokines, and that different subsets of Th17s mediate different biological functions. In the present study, we found significantly higher levels of IL-17F-expressing CD4⁺ T cells in CLL versus healthy peripheral blood mononuclear cells following in vitro stimulation in the presence of Th17-promoting cytokines. Furthermore, the differentiation of IL-17F-expressing Th17 cells was significantly enhanced when purified CD4⁺ T cells from CLL patients were cultured in the presence of autologous CLL B cells. Lastly, single-cell network profiling revealed that IL-17F triggers NFκB phosphorylation in T and B cells from patients with CLL, but not age-matched healthy controls. Taken together, our data suggest that the phenotype of Th17 cells in CLL patients is distinct from healthy individuals, expressing higher levels of IL-17F, and that B and T cells from CLL patients are particularly responsive to IL-17F, as compared to healthy age-matched control individuals.

DLL4 regulates NOTCH signaling and growth of T acute lymphoblastic leukemia cells in NOD/SCID mice

Activation of the NOTCH pathway occurs commonly in T acute lymphoblastic leukemia (T-ALL) mainly due to mutations in NOTCH1 or alterations in FBW7 and is involved in the regulation of cell proliferation and survival. Since mutations hit different domains of the receptor, they are predicted to heterogeneously perturb ligand-induced NOTCH1 activity. Moreover, T-ALL cells also co-express NOTCH3 receptors which could be triggered by different ligands. In this study, we aimed to investigate the role of DLL4 in the regulation of NOTCH signaling in T-ALL cells in the context of different types of NOTCH1 mutation or wild-type NOTCH receptor, as well as the effects of DLL4 neutralization on T-ALL engraftment in mice. We found that NOTCH signaling can be stimulated in T-ALL cells in vitro by either human or murine DLL4 with heterogeneous effects, according to NOTCH1/FBW7 mutation status, and that these effects can be blocked by antibodies neutralizing DLL4, NOTCH1 or NOTCH2/3. In vivo, DLL4 is expressed in the spleen and the bone marrow (BM) of NOD/SCID mice bearing T-ALL xenografts as well as the BM of T-ALL patients. Importantly, DLL4 blockade impaired growth of T-ALL cells in NOD/SCID mice and increased leukemia cell apoptosis. These results show that DLL4 is an important component of the tumor microenvironment which contributes to the early steps of T-ALL cell growth.

"Role of the B-cell receptor and the microenvironment in chronic lymphocytic leukemia''

Despite significant progress in treatment, chronic lymphocytic leukemia (CLL) remains an incurable disease. Advances have been made to understand the molecular pathogenesis underlying CLL progression and treatment resistance. We here review the available evidences concerning the role of the B-cell receptor (BCR) and the tumor microenvironment interactions in CLL pathogenesis. Antigen likely has a key role in the selection of the tumoral clone, the mutational status of immunoglobulin genes is a strong prognostic predictor and BCR signaling has been postulated to have a role for CLL trafficking and interaction with the stromal microenvironment. There is also important evidence, favoring a role for the microenvironment in CLL pathogenesis. Most, if not all, proliferative events occur in the lymph nodes and bone marrow, where leukemic cells receive through microenvironment interactions survival signals aiming to avoid apoptosis and acquire favorable tumoral growing conditions. In addition, the tumoral microenvironment appears to be the site where the acquisition of additional genetic lesions in the clone occur, which should greatly influence clinical outcome. The advent of new tyrosine kinase inhibitors which seem to be able to modulate microenvironment interactions and circumvent the p53 deletion have generated significant promise by raising the possibility that they could provide significant progress in disease treatment.

T cells from indolent CLL patients prevent apoptosis of leukemic B cells in vitro and have altered gene expression profile

T cells may have a role in sustaining the leukemic clone in chronic lymphocytic leukemia (CLL). In this study, we have examined the ability of T cells from CLL patients to support the survival of the leukemic B cells in vitro. Additionally, we compared global gene expression of T cells from indolent CLL patients with healthy individuals and multiple myeloma (MM) patients. Apoptosis of purified leukemic B cells was inhibited in vitro when co-cultured with increasing numbers of autologous T cells (p < 0.01) but not autologous B and T cells of normal donors. The anti-apoptotic effect exceeded that of the anti-apoptotic cytokine IL-4 (p = 0.002) and was greater with CD8+ cells (p = 0.02) than with CD4+ cells (p = 0.05). The effect was depended mainly on cell-cell contact although a significant effect was also observed in transwell experiments (p = 0.05). About 356 genes involved in different cellular pathways were deregulated in T cells of CLL patients compared to healthy individuals and MM patients. The results of gene expression profiling were verified for 6 genes (CCL4, CCL5 (RANTES), XCL1, XCL2, KLF6, and TRAF1) using qRT-PCR and immunoblotting. Our results demonstrate that CLL-derived T cells can prevent apoptosis of leukemic B cells and have altered expression of genes that may facilitate the survival of the leukemic clone.

Coming full circle: 70 years of chronic lymphocytic leukemia cell redistribution, from glucocorticoids to inhibitors of B-cell receptor signaling

Chronic lymphocytic leukemia (CLL) cells proliferate in pseudofollicles within the lymphatic tissues, where signals from the microenvironment and BCR signaling drive the expansion of the CLL clone. Mobilization of tissue-resident cells into the blood removes CLL cells from this nurturing milieu and sensitizes them to cytotoxic drugs. This concept recently gained momentum after the clinical activity of kinase inhibitors that target BCR signaling (spleen tyrosine kinase, Bruton tyrosine kinase, PI3Kδ inhibitors) was established. Besides antiproliferative activity, these drugs cause CLL cell redistribution with rapid lymph node shrinkage, along with a transient surge in lymphocytosis, before inducing objective remissions. Inactivation of critical CLL homing mechanism (chemokine receptors, adhesion molecules), thwarting tissue retention and recirculation into the tissues, appears to be the basis for this striking clinical activity. This effect of BCR-signaling inhibitors resembles redistribution of CLL cells after glucocorticoids, described as early as in the 1940s. As such, we are witnessing a renaissance of the concept of leukemia cell redistribution in modern CLL therapy. Here, we review the molecular basis of CLL cell trafficking, homing, and redistribution and similarities between old and new drugs affecting these processes. In addition, we outline how these discoveries are changing our understanding of CLL biology and therapy.

Signaling pathways activated by the B-cell receptor in chronic lymphocytic leukemia

Over the past decade, several features of the B-cell receptor (BCR) complex have emerged as major markers for prognostic classification of B-cell chronic lymphocytic leukemia (B-CLL). In particular, the absence of somatic mutations within the immunoglobulin variable heavy chain genes (IGHV), the presence of ZAP-70 and a higher ability of the BCR to translate signals within the cell have been associated with an aggressive clinical course. Indeed, the stratification of patients with B-CLL based on BCR features suggests that heterogeneity of B-CLL clinical courses may reflect BCR signaling differences that have arisen during the evolution of leukemia. Therefore, characterizing BCR signaling profiles may help to identify signaling markers useful for patient stratification, disease monitoring and therapeutic targeting in B-CLL.

TCL1A and ATM are co-expressed in chronic lymphocytic leukemia cells without deletion of 11q

Chronic lymphocytic leukemia is characterized by the accumulation of B cells that are resistant to apoptosis. This resistance is induced by pro-survival stimuli from the microenvironment. TCL1 and ATM are central to the pathogenesis of the disease and associated with more aggressive disease. Their protein products have recently been shown to physically interact in leukemic cells and to impact on NF-κB signaling, which is a key regulator of apoptosis. In the present study we show that TCL1 and ATM are significantly co-expressed and up-regulated in malignant cells compared to non-malignant B cells, and that expression of TCL1 is partially deregulated by aberrant DNA-methylation. In addition, complex external stimuli induce essentially similar TCL1 and ATM time-course kinetics. In line with a coordinative regulation of NF-κB signaling by TCL1, its knockdown induced apoptosis in primary leukemia cells. These findings suggest that both genes functionally cooperate to modulate similar apoptosis-related cellular pathways.

Lymph node-induced immune tolerance in chronic lymphocytic leukaemia: a role for caveolin-1

Emerging evidence indicates that the tumour microenvironment (TME) regulates the behaviour of chronic lymphocytic leukaemia (CLL). However, the precise mechanism and molecules involved in this process remain unknown. Gene expression profiles of CLL cells from lymph node (LN), bone marrow (BM) and peripheral blood (PB) indicate overexpression of a tolerogenic signature in CLL cells in lymph nodes (LN-CLL). Based on their role in B cell biology, the progression of CLL, or immune regulation, a few genes of this 83-gene signature were selected for further analyses. We observed a significant correlation between the clinical outcomes and the expression of CAV1 (P = 0·041), FGFR1 isoform 8 (P = 0·032), PTPN6 (P = 0·031) and ZWINT (P < 0·001). CAV1, a molecule involved in the regulation of tumour progression in other cancers, was seven-fold higher in LN-CLL cells compared to BM- and PB-CLL cells. Knockdown of CAV1 expression in CLL cells resulted in significantly decreased migration (P = 0·016) and proliferation (P = 0·04). When CAV1 was knocked down in B and T cell lines, we observed an inability to form immune synapses. Furthermore, CAV1 knockdown in CLL cells impaired their ability to form immune synapses with autologous T lymphocytes and allogeneic, healthy T cells. Subsequent analyses of microarray data showed differential expression of cytoskeletal genes, specifically those involved in actin polymerization. Therefore, we report a novel role for CAV1 in tumour-induced immunosuppression during the progression of CLL.

The impact of CDK inhibition in human malignancies associated with pronounced defects in apoptosis: advantages of multi-targeting small molecules

Malignant cells in chronic lymphocytic leukemia (CLL) and related diseases are heterogeneous and consist primarily of long-lived resting cells in the periphery and a minor subset of dividing cells in proliferating centers. Both cell populations have different molecular signatures that play a major role in determining their sensitivity to therapy. Contemporary approaches to treating CLL are heavily reliant on cytotoxic chemotherapeutics. However, none of the current treatment regimens can be considered curative. Pharmacological CDK inhibitors have extended the repertoire of potential drugs for CLL. Multi-targeted CDK inhibitors affect CDKs involved in regulating both cell cycle progression and transcription. Their interference with transcriptional elongation represses anti-apoptotic proteins and, thus, promotes the induction of apoptosis. Importantly, there is evidence that treatment with CDK inhibitors can overcome resistance to therapy. The pharmacological CDK inhibitors have great potential for use in combination with other therapeutics and represent promising tools for the development of new curative treatments for CLL.

Inhibiting B-cell receptor signaling pathways in chronic lymphocytic leukemia

B-cell receptor (BCR) signaling is a central pathologic mechanism in B-cell malignancies, including chronic lymphocytic leukemia (CLL), in which it promotes leukemia cell survival and proliferation, and modulates CLL cell migration and tissue homing. BCR signaling now can be targeted with new, small molecule inhibitors of the spleen tyrosine kinase (Syk), Bruton's tyrosine kinase (Btk), or phosphoinositide 3'-kinase (PI3K) isoform p110δ (PI3Kδ), which have recently entered the clinical stage and show promising results in patients with CLL. During the first weeks of therapy, these agents characteristically induce rapid resolution of lymphadenopathy and organomegaly, accompanied by a transient surge in lymphocyte counts due to "mobilization" of tissue-resident CLL cells into the blood. Then, often after months of continuous therapy, a major proportion of patients achieve remissions. This article reviews key biologic aspects of BCR-associated kinases in CLL and other B cell neoplasias, and develops perspectives for future development of this exciting new class of kinase inhibitors.

The Bruton tyrosine kinase inhibitor PCI-32765 thwarts chronic lymphocytic leukemia cell survival and tissue homing in vitro and in vivo

B-cell receptor (BCR) signaling is a critical pathway in the pathogenesis of several B-cell malignancies, including chronic lymphocytic leukemia (CLL), and can be targeted by inhibitors of BCR-associated kinases, such as Bruton tyrosine kinase (Btk). PCI-32765, a selective, irreversible Btk inhibitor, is a novel, molecularly targeted agent for patients with B-cell malignancies, and is particularly active in patients with CLL. In this study, we analyzed the mechanism of action of PCI-32765 in CLL, using in vitro and in vivo models, and performed correlative studies on specimens from patients receiving therapy with PCI-32765. PCI-32765 significantly inhibited CLL cell survival, DNA synthesis, and migration in response to tissue homing chemokines (CXCL12, CXCL13). PCI-32765 also down-regulated secretion of BCR-dependent chemokines (CCL3, CCL4) by the CLL cells, both in vitro and in vivo. In an adoptive transfer TCL1 mouse model of CLL, PCI-32765 affected disease progression. In this model, PCI-32765 caused a transient early lymphocytosis, and profoundly inhibited CLL progression, as assessed by weight, development, and extent of hepatospenomegaly, and survival. Our data demonstrate that PCI-32765 effectively inhibits CLL cell migration and survival, possibly explaining some of the characteristic clinical activity of this new targeted agent.

Post-transcriptional silencing of Notch2 mRNA in chronic lymphocytic [corrected] leukemic cells of B-CLL patients

Environmental and genomic stresses induce different pathological conditions and one of them is blood cancer. This escalating load of disease with a constant threat to life requires an intensive comprehensive response. For our understanding about the cancer treatment capabilities, novel medicinal platforms should be strived to explore among the existing conventional and molecular approaches that have already been proven to be successful in fighting against genetic diseases. Several DNA therapeutics previously studied are currently in clinical settings. RNA interfering antisense oligonucleotide (AS-ODN) is the most experimentally advanced molecular therapeutic which has the potential to modify the gene activity resulting in the down regulation of particular protein. In this study, we focused on the inhibition of Notch2 function in B-cell chronic lymphocytic leukemia (B-CLL) by AS-ODN (phosphorothioate oligomers) targeted to the initiation codon region of the Notch2 mRNA. We investigated the in vitro ability of four such oligomers to reduce the expression of Notch2 gene in peripheral blood mononuclear cells from B-CLL patients. Our findings implicate that AS-ODNs specifically designed for the region of 314-333 neucleotides (AS1) of Notch2 inhibits its gene expression better than other AS-ODNs designed for other regions and respond in a dose dependent manner. The results of cell proliferation assay for the evaluation of AS1 in gene silencing, infer that the number of cells were reduced to 80% (P < 0.001). Our results implicate that using the AS-ODNs against specific Notch2 nucleotide sequence can be used as future therapeutic agent with the ability of Notch2 down regulation, which is the root problem in the pathogenicity of B-CLL.

CD40 stimulation sensitizes CLL cells to lysosomal cell death induction by type II anti-CD20 mAb GA101

Sensitivity of chronic lymphocytic leukemia (CLL) cells to anti-CD20 mAbs is low and, therefore, the efficacy of monotherapy with current anti-CD20 mAbs is limited. At present, it is not known whether sensitivity of CLL cells to CD20 mAbs is modulated by microenvironmental stimuli. We have shown previously that in vitro CD40 stimulation of peripheral blood-derived CLL cells results in resistance to cytotoxic drugs. In the present study, we show that, in contrast, CD40 stimulation sensitizes CLL cells to the recently described novel type II anti-CD20 mAb GA101. Cell death occurred without cross-linking of GA101 and involved a lysosome-dependent mechanism. Combining GA101 with various cytotoxic drugs resulted in additive cell death, not only in CD40-stimulated CLL cells, but also in p53-dysfunctional CLL cells. Our findings indicate that GA101 has efficacy against chemoresistant CLL, and provide a rationale for combining cytotoxic drugs with anti-CD20 mAbs.

Immunologic aspects of monoclonal B-cell lymphocytosis

Monoclonal B-cell lymphocytosis (MBL) is a preclinical hematologic condition wherein small numbers of clonal B cells can be detected in the blood of otherwise healthy individuals. Most MBL have a surface immunophenotype nearly identical to that of chronic lymphocytic leukemia (CLL), though other phenotypes can also be identified. MBL has been shown to be a precursor state for CLL, but most MBL clones are quite small and apparently have minimal potential to progress of CLL or other B-cell lymphoproliferative disorder (B-LPD). The investigation of MBL as a precursor state for CLL will likely lead to important insights into mechanisms of disease pathogenesis. The review will cover clinical and translational aspects of MBL, with a particular emphasis on the prevalence of MBL; the relationship between MBL, CLL, and other B-LPDs; and the capacity of MBL to modulate the normal B- and T-cell compartments.

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.

Two novel aspirin analogues show selective cytotoxicity in primary chronic lymphocytic leukaemia cells that is associated with dual inhibition of Rel A and COX-2

OBJECTIVES

Non-steroidal anti-inflammatory drugs have been shown to induce apoptosis in primary B-cell chronic lymphocytic leukaemia (CLL) cells, but the molecular mechanisms that underpin this observation have not been fully elucidated. Here, we have analysed the effect two novel aspirin analogues, 2-hydroxy benzoate zinc (2HBZ) and 4-hydroxy benzoate zinc (4HBZ), on primary CLL samples.

MATERIALS AND METHODS

Cytotoxic effects of 2HBZ and 4HBZ were analysed in primary CLL cells derived from 52 patients, and normal B- and T-lymphocytes. Mechanisms of action of these agents were also elucidated.

RESULTS

Both analogues induced apoptosis in a dose-dependent and time-dependent manner. Apoptosis was associated with activation of caspase-3 that could be partially abrogated by the caspase-9 inhibitor (Z-LEHD.fmk). Importantly, both agents demonstrated preferential cytotoxicity in CLL cells when compared to normal B- and T-lymphocytes. In terms of their molecular mechanisms of action, 4HBZ and 2HBZ inhibited COX-2 transcription and protein expression and this was associated with upstream inhibition of transcription factor Rel A. Co-culture of CLL cells with CD40 ligand-expressing mouse fibroblasts significantly increased COX-2 expression and inhibited spontaneous apoptosis. Importantly, the most potent analogue, 4HBZ, overcame pro-survival effects of the co-culture system and significantly repressed COX-2. Finally, elevated COX-2 expression was associated with poor prognostic subsets and increased sensitivity to 4HBZ.

CONCLUSIONS

Our results demonstrate therapeutic potential of 4HBZ and are consistent with a mechanism involving suppression of Rel A nuclear translocation and inhibition of COX-2 transcription.

Bone marrow stromal cell-derived vascular endothelial growth factor (VEGF) rather than chronic lymphocytic leukemia (CLL) cell-derived VEGF is essential for the apoptotic resistance of cultured CLL cells

Chronic lymphocytic leukemia (CLL) cells feature a pronounced apoptotic resistance. The vascular endothelial growth factor (VEGF) possesses a role in this apoptotic block, although underlying functional mechanisms and the involvement of the microenvironment are unclear. In this study, the VEGF status in CLL was assessed by enzyme-linked immunosorbent assay and immunofluorescence. VEGF receptor 2 (VEGFR2) phosphorylation was determined flow cytometrically and by immunofluorescence. For co-culture, CLL cells were cultivated on a monolayer of the bone marrow-derived stromal cell (BMSC) line HS5. Secreted VEGF was neutralized using the monoclonal antibody mAb293 (R&D Systems, Minneapolis, MN, USA). To block protein secretion, we used Brefeldin A. VEGF was downregulated in BMSCs by small interfering RNA (siRNA), and we assessed survival by annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) staining. CLL cells express and secrete VEGF and possess phosphorylated VEGFR2. This positive VEGF status is not sufficient to prevent spontaneous apoptosis in vitro. Coculture with BMSCs, which secrete vast amounts of VEGF, maintains in vitro CLL cell survival. Blockage of secreted VEGF using the monoclonal antibody mAb293 significantly reduced the survival support for cocultured CLL cells. Both general blockage of protein secretion by Brefeldin A in BMSCs, but not in CLL cells, and siRNA-mediated downregulation of VEGF in BMSCs, significantly reduced the coculture-mediated survival support for CLL cells. It can be concluded that BMSC-derived proteins and VEGF, in particular, but not CLL cell-derived VEGF, is essentially involved in the coculture-mediated survival support for CLL cells. Hence, therapeutic targeting of VEGF signaling might be a promising approach to overcome the apoptotic resistance CLL cells feature within their natural microenvironment.

Targeting macrophages in classical Hodgkin's lymphoma may seem rational, but is it safe?

A few reports have linked increased numbers of tissue macrophages with treatment failure and reduced lifespan in classical Hodgkin's lymphoma (HL) patients. Some investigators even suggested to target the macrophages in HL with biologic therapy, thus eliminating them from the tumor microenvironment. This review explores the risk: benefit equation of such approach as well as what the author believes is the driving force behind the 'great' migration of macrophages in HL. This article unravels the inflammatory pathways and immune alterations in classical HL that lead to a complex network consisting of T-cells, numerous cytokines, macrophages, and other cells. Macrophages are thought to play a crucial role in tumor antigen processing and presentation tasks, Reed-Sternberg (RS) cell phagocytosis, and antibody-dependent cellular cytotoxicity, therefore their extinction may be hazardous. The author believes RS cells should be targeted by the biologics, not the macrophages, and links his hopes with the existing investigational anti-CD30 therapies in relapsed/refractory classical HL.

Reconstitution of PTEN activity by CK2 inhibitors and interference with the PI3-K/Akt cascade counteract the antiapoptotic effect of human stromal cells in chronic lymphocytic leukemia

Evidence suggests that tumor microenvironment is critically involved in supporting survival of chronic lymphocytic leukemia (CLL) cells. However, the molecular mechanisms of this effect and the clinical significance are not fully understood. We applied a microenvironment model to explore the interaction between CLL cells and stromal cells and to elucidate the role of phosphatidylinositol 3 kinase (PI3-K)/Akt/phosphatase and tensin homolog detected on chromosome 10 (PTEN) cascade in this process and its in vivo relevance. Primary human stromal cells from bone marrow, lymph nodes, and spleen significantly inhibited spontaneous apoptosis of CLL cells. Pan-PI3-K inhibitors (LY294002, wortmannin, PI-103), isotype-specific inhibitors of p110α, p110β, p110γ, and small interfering RNA against PI3-K and Akt1 counteracted the antiapoptotic effect of the stromal cells. Induction of apoptosis was associated with a decrease in phosphatidylinositol-3,4,5-triphosphate, PI3-K-p85, and dephosphorylation of phosphatidylinositol-dependent kinase-1 (PDK-1), Akt1, and PTEN. Freshly isolated peripheral blood mononuclear cells from patients with CLL (n = 44) showed significantly higher levels of phosphorylated Akt1, PDK-1, PTEN, and CK2 than healthy persons (n = 8). CK2 inhibitors (4,5,6,7-tetrabromo-1H-benzotriazole, apigenin, and 5,6-dichloro-1-β-D-ribofuranosylbenzimidazol) decreased phosphorylation of PTEN and Akt, induced apoptosis in CLL cells, and enhanced the response to fludarabine. In conclusion, bone marrow microenvironment modulates the PI3-K/Akt/PTEN cascade and prevents apoptosis of CLL cells. Combined inhibition of PI3-K/Akt and recovery of PTEN activity may represent a novel therapeutic concept for CLL.

Influence of bone marrow stromal microenvironment on forodesine-induced responses in CLL primary cells

Forodesine, a purine nucleoside phosphorylase inhibitor, displays in vitro activity in chronic lymphocytic leukemia (CLL) cells in presence of dGuo, which is the basis for an ongoing clinical trial in patients with fludarabine-refractory CLL. Initial clinical data indicate forodesine has significant activity on circulating CLL cells, but less activity in clearing CLL cells from tissues such as marrow. In tissue microenvironments, lymphocytes interact with accessory stromal cells that provide survival and drug-resistance signals, which may account for residual disease. Therefore, we investigated the impact of marrow stromal cells (MSCs) on forodesine-induced response in CLL lymphocytes. We demonstrate that spontaneous and forodesine-induced apoptosis of CLL cells was significantly inhibited by human and murine MSCs. Forodesine-promoted dGuo triphosphate (dGTP) accumulation and GTP and ATP depletion in CLL cells was inhibited by MSCs, providing a mechanism for resistance. Also, MSCs rescued CLL cells from forodesine-induced RNA- and protein-synthesis inhibition and stabilized and increased Mcl-1 transcript and protein levels. Conversely, MSC viability was not affected by forodesine and dGuo. Collectively, MSC-induced biochemical changes antagonized forodesine-induced CLL cell apoptosis. This provides a biochemical mechanism for MSC-derived resistance to forodesine and emphasizes the need to move toward combinations with agents that interfere with the microenvironment's protective role for improving current therapeutic efforts.

NF-kappaB as a prognostic marker and therapeutic target in chronic lymphocytic leukemia

Chronic lymphocytic leukemia is the most common adult leukemia and is currently incurable with conventional chemotherapeutic agents. Over the last few years, significant discoveries have been made regarding the biology that underpins this disease. These new insights have allowed us to develop more rational prognostic tools and identify promising novel therapeutic targets. In this review, we highlight the importance of both constitutive and inducible DNA binding of the transcription factor NF-kappaB in chronic lymphocytic leukemia. We describe the current knowledge regarding the activity and function of specific NF-kappaB subunits in this disease, and discuss the complex mechanisms that regulate NF-kappaB activation in vivo. In addition, we provide compelling evidence for the utility of the NF-kappaB subunit, Rel A, as a prognostic marker and as a therapeutic target in this disease, and we also describe how this protein may contribute to the drug resistance commonly encountered with this condition.

In vivo intraclonal and interclonal kinetic heterogeneity in B-cell chronic lymphocytic leukemia

Clonal evolution and outgrowth of cellular variants with additional chromosomal abnormalities are major causes of disease progression in chronic lymphocytic leukemia (CLL). Because new DNA lesions occur during S phase, proliferating cells are at the core of this problem. In this study, we used in vivo deuterium ((2)H) labeling of CLL cells to better understand the phenotype of proliferating cells in 13 leukemic clones. In each case, there was heterogeneity in cellular proliferation, with a higher fraction of newly produced CD38+ cells compared with CD38- counterparts. On average, there were 2-fold higher percentages of newly born cells in the CD38+ fraction than in CD38- cells; when analyzed on an individual patient basis, CD38+ (2)H-labeled cells ranged from 6.6% to 73%. Based on distinct kinetic patterns, interclonal heterogeneity was also observed. Specifically, 4 patients exhibited a delayed appearance of newly produced CD38+ cells in the blood, higher leukemic cell CXC chemokine receptor 4 (CXCR4) levels, and increased risk for lymphoid organ infiltration and poor outcome. Our data refine the proliferative compartment in CLL based on CD38 expression and suggest a relationship between in vivo kinetics, expression of a protein involved in CLL cell retention and trafficking to solid tissues, and clinical outcome.

The microenvironment in mature B-cell malignancies: a target for new treatment strategies

Despite major therapeutic advances, most mature B-cell malignancies remain incurable. Compelling evidence suggests that crosstalk with accessory stromal cells in specialized tissue microenvironments, such as the bone marrow and secondary lymphoid organs, favors disease progression by promoting malignant B-cell growth and drug resistance. Therefore, disrupting the crosstalk between malignant B cells and their milieu is an attractive novel strategy for treating selected mature B-cell malignancies. Here we summarize the current knowledge about the cellular and molecular interactions between neoplastic B lymphocytes and accessory cells that shape a supportive microenvironment, and the potential therapeutic targets that are emerging, together with the new problems they raise. We discuss clinically relevant aspects and provide an outlook into future biologically oriented therapeutic strategies. We anticipate a paradigm shift in the treatment of selected B-cell malignancies, moving from targeting primarily the malignant cells toward combining cytotoxic drugs with agents that interfere with the microenvironment's proactive role. Such approaches hopefully will help eliminating residual disease, thereby improving our current therapeutic efforts.

Expression of activation-induced cytidine deaminase in malignant lymphomas infiltrating the bone marrow

Somatic hypermutation of immunoglobulin genes and class switch recombination are pivotal processes in the germinal center (GC) reaction and have been implicated in the development of malignant B-cell lymphoma. Both processes require the enzyme activation-induced cytidine deaminase (AID). Expression of AID is largely restricted to GC B cells and B cells that undergo class switch recombination outside the GC. AID is also expressed in many B-cell lymphomas. This study investigates the expression of AID of malignant lymphomas infiltrating the bone marrow. Bone marrow trephines (n=130) with infiltration of Hodgkin lymphoma and non-Hodgkin lymphoma of B cell and T-cell type and trephines with reactive lymphoid follicles (n=16) were analyzed immunohistochemically for AID protein. AID is expressed in bone marrow infiltrates of malignant lymphomas. AID was generally detected in lymphomas of GC origin. Tumor cells of hairy cell leukemia are mostly AID. There is apparently no different expression of AID found in bone marrow infiltrates of malignant lymphomas compared with a control group with nodal malignant lymphoma infiltrates (n=105). These results suggest that the expression pattern of AID in lymphoma infiltrates in the bone marrow reflects that of extramedullary lymphoma infiltrates.

11q22.3 deletion in B-chronic lymphocytic leukemia is specifically associated with bulky lymphadenopathy and ZAP-70 expression but not reduced expression of adhesion/cell surface receptor molecules

The presence of chromosome abnormalities promotes tumor progression in B-chronic lymphocytic leukemia (CLL). However, the molecular pathways that are relevant to tumor progression remain unclear. In this study, we screened for common chromosome abnormalities [13q14 del, 11q22.3 (ATM) del, 17p13 (p53) del and trisomy 12] by fluorescent in situ hybridization in 40 B-CLL patients. Each of the four chromosome abnormality groups was compared to several clinical factors related to lymphocyte behaviour in CLL. The 11q22.3 (ATM) deletion group was significantly associated with the presence of bulky abdominal/mediastinal lymphadenopathy (P = 0.014). We hypothesized that this phenotype would be associated with an altered transcription pattern of genes. Class comparison analysis by significance analysis of microarrays on a subset of CLL samples (n = 14) indicated that a number of cell surface receptor and adhesion related genes were under-expressed in the 11q22.3 deletion group (CD44, CD11a, PTPRC, CD79a, chemokine ligand 17 and chemokine receptor type 6). The presence of additional prognostic factors, such as CD38 and immunoglobulin heavy chain variable region mutational status, may also influence the transcriptional pathways between the two groups. Therefore, we employed a novel analysis technique for the correlation of log(2) gene expression ratios with the percentage of each tumor that carried the 11q22.3 deletion. Using Spearman's correlation, ZAP-70, chemokine ligand 17, BSAP (PAX5), CD7, LAG3 and PTPR6 were significantly correlated with the percentage of cells with the 11q22.3 deletion. However, the down-regulation of cell surface receptors and adhesion molecules observed by class comparison could not be confirmed to be specific for the 11q22.3 deletion by this method.

Exploration of factors affecting the onset and maturation course of follicular lymphoma through simulations of the germinal center

Genetic mutations frequently observed in human follicular lymphoma (FL) B-cells result in aberrant expression of the anti-apoptotic protein bcl-2 and surface immunoglobulins (Igs) which display one or more novel variable (V) region N-glycosylation motifs. In the present study, we develop a simulation model of the germinal center (GC) to explore how these mutations might influence the emergence and clonal expansion of key mutants which provoke FL development. The simulations employ a stochastic method for calculating the cellular dynamics, which incorporates actual IgV region sequences and a simplified hypermutation scheme. We first bring our simulations into agreement with experimental data for well-characterized normal and bcl-2(+) anti-hapten GC responses in mice to provide a model for understanding how bcl-2 expression leads to permissive selection and memory cell differentiation of weakly competitive B-cells. However, as bcl-2 expression in the GC alone is thought to be insufficient for FL development, we next monitor simulated IgV region mutations to determine the emergence times of key mutants displaying aberrant N-glycosylation motifs recurrently observed in human FL IgV regions. Simulations of 26 germline V(H) gene segments indicate that particular IgV regions have a dynamical selective advantage by virtue of the speed with which one or more of their key sites can generate N-glycosylation motifs upon hypermutation. Separate calculations attribute the high occurrence frequency of such IgV regions in FL to an ability to produce key mutants at a fast enough rate to overcome stochastic processes in the GC that hinder clonal expansion. Altogether, these simulations characterize three pathways for FL maturation through positively selected N-glycosylations, namely, via one of two key sites within germline V(H) region gene segments, or via a site in the third heavy chain complementarity-determining region (CDR-H3) that is generated from VDJ recombination.

In vivo dynamics of stable chronic lymphocytic leukemia inversely correlate with somatic hypermutation levels and suggest no major leukemic turnover in bone marrow

Although accumulating evidence indicates that chronic lymphocytic leukemia (CLL) is a disease with appreciable cell dynamics, it remains uncertain whether this also applies to patients with stable disease. In this study, (2)H(2)O was administered to a clinically homogeneous cohort of nine stable, untreated CLL patients. CLL dynamics in blood and bone marrow were determined and compared with normal B-cell dynamics in blood from five healthy individuals who underwent a similar (2)H(2)O labeling protocol. Average CLL turnover rates (0.08-0.35% of the clone per day) were approximately 2-fold lower than average B-cell turnover rates from healthy individuals (0.34-0.89%), whereas the rate at which labeled CLL cells in blood disappeared (0.00-0.39% of B cells per day) was approximately 10-fold lower compared with labeled B cells from healthy individuals (1.57-4.24% per day). Leukemic cell turnover variables inversely correlated with the level of somatic hypermutation of the CLL clone (IgVH mutations). Although CLL cells in bone marrow had a higher level of label enrichment than CLL cells in blood, no difference between proliferation rates and proapoptotic and antiapoptotic profiles of CLL cells from these compartments was observed. These data suggest that, in stable disease, there is a biological relationship between the degree of somatic hypermutation of the CLL clone and its dynamics in vivo. Furthermore, in contrast to lymph nodes, the bone marrow does not seem to be a major CLL proliferation site.

The novel nuclear factor-kappaB inhibitor LC-1 is equipotent in poor prognostic subsets of chronic lymphocytic leukemia and shows strong synergy with fludarabine

PURPOSE

We have recently shown that the novel nuclear factor-kappaB (NF-kappaB) inhibitor LC-1 is effective in primary chronic lymphocytic leukemia (CLL) cells. Here we elucidated the mechanism of action of LC-1, evaluated its relative cytotoxicity in prognostic subsets, and investigated its potential synergistic interaction with fludarabine.

EXPERIMENTAL DESIGN

Ninety-six fully characterized CLL cases were assessed for in vitro sensitivity to LC-1 and fludarabine. In selected cases, caspase activation, inhibition of Rel A DNA binding, and the transcription of CFLAR, BIRC5, and BCL2 were measured before and after exposure to LC-1. In addition, the efficacy of LC-1 was assessed in the presence of the survival factors CD154 and interleukin-4, and the potential synergistic interaction between LC-1 and fludarabine was evaluated.

RESULTS

Cell death was associated with caspase-3 activation mediated via activation of both caspase-8 and caspase-9. Apoptosis was preceded by a reduction of nuclear Rel A DNA binding and inhibition of CFLAR, BIRC5, and BCL2 transcription. Importantly, LC-1 overcame the cytoprotective effects by interleukin-4 and CD40 ligand and was equipotent in CLL cells derived from good and bad prognostic subsets. LC-1 exhibited strong synergy with fludarabine, and the combination produced a highly significant mean dose reduction index for fludarabine of > 1,000.

CONCLUSIONS

In view of imminent first-in-man study of LC-1 in Cardiff, these data show an important mechanistic rationale for the use of LC-1 in this disease. Furthermore, it validates the concept of targeting nuclear factor-kappaB in CLL and identifies the therapeutic potential of LC-1 in combination with fludarabine even in patients with fludarabine resistance.

Microenvironmental influences in chronic lymphocytic leukaemia: the role of antigen stimulation

Several studies suggest that immune-mediated pathways are important in the pathogenesis of chronic lymphocytic leukaemia (CLL). The in vivo accumulation of leukaemic lymphocytes is facilitated by interactions of CLL cells with other cells and soluble factors that probably occur more often within the microenvironment through classical receptor-ligand interactions. These include CD40L-CD40 and chemokine-chemokine receptor interactions as well as B cell receptor (BCR) engagement by (auto)antigens. Indeed, the categorizations of CLL patients based on immunoglobulin heavy variable (IGHV) gene mutations and structure of the clone's BCR suggest that CLL patient outcome could be a reflection of ongoing BCR signalling in the context of other co-signals.

Constitutively activated Notch signaling is involved in survival and apoptosis resistance of B-CLL cells

Notch signaling is involved in tumorigenesis, but its role in B-chronic lymphocytic leukemia (B-CLL) pathogenesis is not completely defined. This study examined the expression and activation of Notch receptors in B-CLL cells and the role of Notch signaling in sustaining the survival of these cells. Our results show that B-CLL cells but not normal B cells constitutively express Notch1 and Notch2 proteins as well as their ligands Jagged1 and Jagged2. Notch signaling is constitutively activated in B-CLL cells, and its activation is further increased in B-CLL cells, which resist spontaneous apoptosis after 24-hour ex vivo culture. Notch stimulation by a soluble Jagged1 ligand increases B-CLL cell survival and is accompanied by increased nuclear factor-kappa B (NF-kappaB) activity and cellular inhibitor of apoptosis protein 2 (c-IAP2) and X-linked inhibitor of apoptosis protein (XIAP) expression. In contrast, Notch-signaling inhibition by the gamma-secretase inhibitor I (GSI; z-Leu-Leu-Nle-CHO) and the specific Notch2 down-regulation by small-interfering RNA accelerate spontaneous B-CLL cell apoptosis. Apoptotic activity of GSI is accompanied by reduction of NF-kappaB activity and c-IAP2 and XIAP expression. Overall, our findings show that Notch signaling plays a critical role in B-CLL cell survival and apoptosis resistance and suggest that it could be a novel potential therapeutic target.

Significantly shorter telomeres in T-cells of patients with ZAP-70+/CD38+ chronic lymphocytic leukaemia

In contrast to other B-cell neoplasias, chronic lymphocytic leukaemia (CLL) is characterized by increased non-leukaemic T-cells. In order to assess their replicative history, telomere length was analyzed in subsets of leucocytes from CLL patients. Naive and memory T-cells from ZAP-70(+)/CD38(+) patients exhibited significantly shorter average telomere lengths than ZAP-70(-)/CD38(-) patients. Compared to the age-related percentiles of telomere length values from healthy individuals practically all values of the naive and memory T-cells from the ZAP-70(+)/CD38(+) CLL patients fell below the 50th percentile. This indicated an extensive expansion and a role for T-cells in ZAP-70(+)/CD38(+) CLL patients.

CD40 ligand protects from TRAIL-induced apoptosis in follicular lymphomas through NF-kappaB activation and up-regulation of c-FLIP and Bcl-xL

The TNF family member TRAIL is emerging as a promising cytotoxic molecule for antitumor therapy. However, its mechanism of action and the possible modulation of its effect by the microenvironment in follicular lymphomas (FL) remain unknown. We show here that TRAIL is cytotoxic only against FL B cells and not against normal B cells, and that DR4 is the main receptor involved in the initiation of the apoptotic cascade. However, the engagement of CD40 by its ligand, mainly expressed on a specific germinal center CD4(+) T cell subpopulation, counteracts TRAIL-induced apoptosis in FL B cells. CD40 induces a rapid RNA and protein up-regulation of c-FLIP and Bcl-x(L). The induction of these antiapoptotic molecules as well as the inhibition of TRAIL-induced apoptosis by CD40 is partially abolished when NF-kappaB activity is inhibited by a selective inhibitor, BAY 117085. Thus, the antiapoptotic signaling of CD40, which interferes with TRAIL-induced apoptosis in FL B cells, involves NF-kappaB-mediated induction of c-FLIP and Bcl-x(L) which can respectively interfere with caspase 8 activation or mitochondrial-mediated apoptosis. These findings suggest that a cotreatment with TRAIL and an inhibitor of NF-kappaB signaling or a blocking anti-CD40 Ab could be of great interest in FL therapy.

Lymphoma microenvironment: culprit or innocent?

Studies are revealing that lymphoid neoplasms are characterized by well-defined chromosome translocations and by the accumulation of subsequent molecular alterations involving mainly the cell cycle and/or apoptotic pathways. However, survival of B and T tumor cells is also dependent on the interactions with the accompanying cells that comprise the lymphoma microenvironment. Although non-tumor cells can contribute both positive and negative signals to the lymphoma cells, in this review we present compelling evidence of the essential influence of the tumor microenvironment on the initiation and progression of specific lymphoma types, highlighting some new therapeutic approaches that target the lymphoma microenvironment.

Pharmacological inhibitors of NF-kappaB accelerate apoptosis in chronic lymphocytic leukaemia cells

Nuclear factor-kappaB (NF-kappaB) is a transcription factor that plays a critical role in the inappropriate survival of various types of malignant cells. Chronic lymphocytic leukaemia (CLL) is the most common B-cell malignancy in the Western world. Although overexpression and regulation of NF-kappaB has been described in CLL, its function remains unclear. Exposure of CLL cells to BAY117082 or Kamebakaurin, potent pharmacological inhibitors of the NF-kappaB pathway, accelerated apoptosis in approximately 70% of cases. Sensitivity to NF-kappaB pathway inhibitors was not related to the prognostic markers VH status, CD38 or Zap70 expression, or to the levels of nuclear NF-kappaB. Normal peripheral B cells were resistant to the apoptosis-inducing effects of these compounds. Cell death induced by the inhibitors was associated with activation of caspase-9 and -3, and loss of mitochondrial membrane polarization, but did not involve changes in the expression of Bcl-2 or Mcl-1. Inhibitors caused an increase in c-jun NH2-terminal kinase activity in CLL, but this did not appear to be important for apoptosis. Microarray analysis identified some potential novel NF-kappaB target genes, including interleukin-16- and the Bcl-2- related survival protein Bcl-w. These results demonstrate that a substantial proportion of CLL are dependent on NF-kappaB for enhanced survival and suggest that inhibition of NF-kappaB may have therapeutic potential.

Deregulated expression of fat and muscle genes in B-cell chronic lymphocytic leukemia with high lipoprotein lipase expression

Lipoprotein lipase (LPL) is a prognostic marker in B-cell chronic lymphocytic leukemia (B-CLL) related to immunoglobulin V(H) gene (IgV(H))mutational status. We determined gene expression profiles using Affymetrix U133A GeneChips in two groups of B-CLLs selected for either high ('LPL+', n=10) or low ('LPL-', n=10) LPL mRNA expression. Selected genes were verified by real-time PCR in an extended patient cohort (n=42). A total of 111 genes discriminated LPL+ from LPL- B-CLLs. Of these, the top three genes associated with time to first treatment were Septin10, DMD and Gravin (P</=0.01). The relationship of LPL+ and LPL- B-CLL gene expression signatures to 52 tissues was statistically analyzed. The LPL+ B-CLL expression signature, represented by 64 genes was significantly related to fat, muscle and PB dendritic cells (P<0.001). Exploration of microarray data to define functional alterations related to the biology of LPL+ CLL identified two functional modules, fatty acid degradation and MTA3 signaling, as being altered with higher statistical significance. Our data show that LPL+ B-CLL cells have not only acquired gene expression changes in fat and muscle-associated genes but also in functional pathways related to fatty acid degradation and signaling which may ultimately influence CLL biology and clinical outcome.

T and B cells in B-chronic lymphocytic leukaemia: Faust, Mephistopheles and the pact with the Devil

A large number of human malignancies are associated with decreased numbers of circulating T cells. B-CLL, in this regard, represents an anomaly since there is not only high numbers of circulating B cells, characteristic of the malignancy, but also a massive expansion of both CD4 and CD8 T cells. These T cells for the most part may probably not represent a leukaemia-specific TCR-dependent expansion. On the contrary, these T cells, especially the CD4 subset, might support a "microenvironment" sustaining the growth of the leukaemic B cell clone. Conversely, the leukaemic B cells may produce membrane-bound as well as soluble factors that stimulate the proliferation of these T cells in an antigen independent manner. In addition to these T cells lacking anti-leukaemic reactivity, there exist spontaneously occurring leukaemia-specific T cells recognizing several leukaemia-associated antigens, e.g. the tumour derived idiotype, survivin and telomerase. Both CD4 and CD8 leukaemia-specific T cells have been identified using proliferation and gamma-IFN assays. These reactive T cells can lyse autologous tumour cells in an MHC class I and II restricted manner. Spontaneously occurring leukaemia-specific T cells are more frequently noted at an indolent stage rather than in progressive disease. Preliminary results from vaccination trials using whole tumour cell preparations as vaccine have demonstrated that vaccination may induce a leukaemia-specific T cell response, which might be associated with clinical benefits. Extended clinical trials are required to establish the therapeutic effects of vaccination in B-CLL. Studies in our laboratory as well as those of others indicate that whole tumour cell antigen in the form of apoptotic bodies or RNA loaded on to dendritic cells may be a suitable vaccine candidate. Patients with low stage disease may maximally benefit from this form of therapy.

Targeting endoplasmic reticulum protein transport: a novel strategy to kill malignant B cells and overcome fludarabine resistance in CLL

Previous studies showed that chronic lymphocytic leukemia (CLL) cells exhibit certain mitochondrial abnormalities including mtDNA mutations, increased superoxide generation, and aberrant mitochondrial biogenesis, which are associated with impaired apoptosis and reduced sensitivity to fludarabine. Here we report that CLL cells and multiple myeloma cells are highly sensitive to brefeldin A, an inhibitor of endoplasmic reticulum (ER) to Golgi protein transport currently being developed as a novel anticancer agent in a prodrug formulation. Of importance, brefeldin A effectively induced apoptosis in fludarabine-refractory CLL cells. Disruption of protein trafficking by brefeldin A caused the sequestration of the prosurvival factors APRIL and VEGF in the ER, leading to abnormal ER swelling and a decrease in VEGF secretion. Such ER stress and blockage of secretory protein traffic eventually resulted in Golgi collapse, activation of caspases, and cell death. Notably, the cellular sensitivity to this compound appeared to be independent of p53 status. Taken together, these findings suggest that malignant B cells may be highly dependent on ER-Golgi protein transport and that targeting this process may be a promising therapeutic strategy for B-cell malignancies, especially for those that respond poorly to conventional treatments.

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.

Clonal selection in the bone marrow involvement of follicular lymphoma

To characterize the pathways of bone marrow (BM) involvement of follicular lymphoma (FL), we performed morphological and immunophenotypical analysis of tumor cells from lymph nodes (LNs) and corresponding BMs in 21 patients with FL. In three cases, genealogical trees were constructed based on the immunoglobulin variable region heavy chain (IgV(H)) gene sequences of tumor clones from LNs and BMs. Results showed that FLs within the BMs display identical or lower cytological grades than in the LNs. In the majority of cases, different proportions of tumor cells expressed bcl-2, CD10 and Ki67 in LNs and BMs. Tumor cells in the BM showed ongoing somatic hypermutation of the IgV(H) genes; the distribution of these mutations was highly consistent with antigen selection. The topology of the genealogical trees revealed that different subclones populate the LN and BM and BM infiltration may occur at different points of the clonal evolution of FL. Early descendants of the original tumor clone and derivatives of diversified tumor clones may invade the BM. These results suggest that the BM involvement of FL is associated with intensive clonal selection of tumor cells, and the BM provides a microenvironment similar to the germinal centers of LNs, where tumor cells retain their biological nature.

Induction of CD95 upregulation does not render chronic lymphocytic leukemia B-cells susceptible to CD95-mediated apoptosis

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by a progressive accumulation of long-lived and well-differentiated clonal B-lymphocytes in peripheral blood, lymphoid tissue and bone marrow. Although B-CLL pathogenesis is not entirely understood, the progressive increase in lymphocyte counts coupled with the very low proportion of proliferating cells suggests that B-CLL may be primarily determined by defective apoptosis. Consistently, freshly analyzed CLL B-cells express very low levels of membrane CD95, one of the best-known receptors involved in triggering apoptosis. In this study, CD95 upregulation on CLL B-cells was induced by culturing clonal B-cells in the presence of supernatants from preactivated autologous T-lymphocytes. Intracellular cytokine staining of preactivated autologous T-lymphocytes using monoclonal antibodies (moAbs) specific for Th1 or Th2 cytokines, namely interleukin (IL)-2, IL-4, IL-5, IL-10 and interferon (IFN)-gamma, showed these cells to be positive for IL-2 and IFN-gamma. Blocking experiments using moAbs specific for IL-2 and/or IFN-gamma revealed that CD95 upregulation on CLL B-cells was mainly driven by IFN-gamma. However, CD95-expressing CLL B-cells were demonstrated to be resistant to CD95-mediated apoptosis, thus arguing against strategies aimed at exploiting CD95-mediated apoptosis for immunotherapy of B-CLL.

Fibromodulin, an extracellular matrix protein: characterization of its unique gene and protein expression in B-cell chronic lymphocytic leukemia and mantle cell lymphoma

Fibromodulin is an extracellular matrix protein normally produced by collagen-rich tissues; the fibromodulin gene has been found to be the most overexpressed gene in B-cell chronic lymphocytic leukemia. In this study, fibromodulin was expressed at the gene level (reverse transcription-polymerase chain reaction [RT-PCR]) in all patients with B-CLL (n = 75) and in most (5 of 7) patients with mantle cell lymphoma (MCL). No mutations in the fibromodulin gene were detected. Fibromodulin was also detected at the protein level in the cytoplasm of the B-CLL cells and in the supernatant after in vitro cultivation, but not at the cell surface. Fibromodulin was not found in patients with T-cell chronic lymphocytic leukemia (T-CLL), B-cell prolymphocytic leukemia (B-PLL), T-cell prolymphocytic leukemia (T-PLL), hairy cell leukemia, follicular lymphoma, lymphoplasmacytic lymphoma, multiple myeloma, acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), or chronic myelogenous leukemia (CML) or in 36 hematologic cell lines. Normal blood mononuclear cells (T and B lymphocytes, monocytes), tonsil B cells, and granulocytes did not express fibromodulin. Activation (phorbol 12-myristate 13-acetate [PMA]/ionomycin) of normal T and B lymphocytes induced weak fibromodulin gene expression, but not to the extent seen in freshly isolated B-CLL cells. The reason for the exclusive ectopic expression of fibromodulin in B-CLL and MCL is unknown. However, its unique protein expression makes it likely that fibromodulin is involved in the pathobiology of B-CLL and MCL. (Blood. 2005;105:4828-4835)