Human cytokines suppress apoptosis of leukaemic CD5+ B cells and preserve expression of bcl-2

Tumor Cell Survival Factors and Angiogenesis in Chronic Lymphocytic Leukemia: How Hot Is the Link?

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of neoplastic CD5+/CD19+ B lymphocytes in the blood. These cells migrate to and proliferate in the bone marrow and lymphoid tissues. Despite the development of new therapies for CLL, drug resistance and disease relapse still occur; novel treatment approaches are therefore still needed. Inhibition of the angiogenesis involved in the progression of CLL might be a relevant therapeutic strategy. The literature data indicate that vascular endothelial growth factor, angiopoietin-2, and matrix metalloproteinase-9 are pro-angiogenic factors in CLL. A number of other CLL factors might have pro-angiogenic activity: fibroblast growth factor-2, certain chemokines (such as CXCL-12 and CXCL-2), tumor necrosis factor-α, insulin-like growth factor-1, neutrophil gelatinase-associated lipocalin, and progranulin. All these molecules contribute to the survival, proliferation, and migration of CLL cells. Here, we review the literature on these factors' respective expression profiles and roles in CLL. We also summarize the main results of preclinical and clinical trials of novel agents targeting most of these molecules in a CLL setting. Through the eradication of leukemic cells and the inhibition of angiogenesis, these therapeutic approaches might alter the course of CLL.

Thioredoxin and hematologic malignancies

Thioredoxin (Trx) is an inflammation-inducible small oxidoreductase protein ubiquitously expressed in all organisms. Trx acts both intracellularly and extracellularly and is involved in a wide range of physiological cellular responses. Inside the cell, Trx alleviates oxidative stress by scavenging reactive oxygen species (ROS), regulates a variety of redox-sensitive signaling pathways as well as ROS-independent genes, and exerts cytoprotective effects. Outside the cell, Trx acts as growth factors or cytokines and promotes cell growth and many other cellular responses. Trx is also implicated in tumorigenesis. Trx is a proto-oncogene and is overexpressed in many cancers and correlates with poor prognosis. Trx stimulates cancer cell survival, promotes tumor angiogenesis, and inhibits both spontaneous apoptosis and drug-induced apoptosis. Inhibitors targeting Trx pathway provide a promising therapeutic strategy for cancer prevention and intervention. More recently, data from our laboratory demonstrate an important role of Trx in expanding long-term repopulating hematopoietic stem cells. In this chapter, we first provide an overview of Trx including its isoforms, compartmentation, and functions. We then discuss the roles of Trx in hematologic malignancies. Finally, we summarize the most recent findings from our lab on the use of Trx to enhance hematopoietic reconstitution following hematopoietic stem cell transplantation.

Restoring the functional immunogenicity of chronic lymphocytic leukemia using epigenetic modifiers

Chronic lymphocytic leukemia (CLL) is a malignancy arising from immune cells (B-lymphocytes) endowed with intrinsic antigen-presenting capabilities. Such a function however is lost during malignant transformation and CLL cells are well known for their inability to process and present antigens to the T-cell arm of the immune system. Instead, malignant CLL cells elicit a vast array of immune regulatory mechanisms conducive to T-cell dysfunction and immunosuppression. Previously, we have shown that treatment of CLL cells with the demethylating agent 5-aza-2'-deoxycytidine unleashed target antigen expression. Here we show for the first time that combining two epigenetic modifiers, 5-aza-2'-deoxycytidine and the histone deacetylase inhibitor LAQ824 effectively restores the immunogenicity of CLL cell lines as well as primary cells obtained from CLL patients. Indeed, such a combination induces the expression of novel and highly antigenic cancer-testis antigens (CTAs) and costimulatory molecules. These changes facilitate the formation of robust supramolecular activation complexes (SMAC) between CLL cells and responder T-cells leading to intracellular signaling, lytic granule mobilization, and polarization of functional and relevant T-cell responses. This cascade of T-cell activating events triggered by CLL cells with restored APC function, points to combined epigenetic modifier treatment as a potential immunotherapeutic strategy for CLL patients.

Rituximab for the treatment of patients with chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is a lymphoproliferative disorder that originates from antigen-experienced B lymphocytes that do not die and hence accumulate due to external survival signals or undergo apoptosis and are replenished by proliferating precursors. These neoplastic lymphocytes exhibit a characteristic immunophenotype of CD5(+)/CD19(+)/CD20(+)/HLA-DR+/CD23(+)/sIgdim. Thus, the CD20 antigen has been an appealing target for therapy. The introduction of the monoclonal antibody rituximab (anti-CD20) enabled an outstanding advance in CLL treatment. The introduction of this monoclonal antibody into chemotherapy regimens has dramatically improved complete response rates and progression-free survival in patients with both untreated and relapsed CLL. Although only preliminary data from phase III confirmatory trials have been reported, the FCR regimen, which combines fludarabine and cyclophosphamide with rituximab, is currently the most effective treatment regimen for CLL patients, and has also been demonstrated to significantly improve overall survival. The success of rituximab and the identification of other CLL lymphocyte surface antigens have spurred the development of a multitude of monoclonal antibodies targeting distinct proteins and epitopes in an attempt to target CLL cells more effectively.

Differential susceptibility of peripheral blood CD5+ and CD5- B cells to apoptosis in chronic hepatitis C patients

A body of evidence has suggested a close link between chronic hepatitis C virus (HCV) infection and B cell abnormalities, including mixed cryoglobulinemia, rheumatoid factor (RF) production, and lymphoproliferative disorders that may develop into non-Hodgkin's lymphoma. Recent studies have demonstrated the expansion of CD5(+) B cells in the peripheral blood of chronic hepatitis C patients (CHC). As CD5(+) B cells, which are capable of producing autoantibodies and RF, are apparently crucial for the development of HCV-associated pathogenesis, the fate of both the CD5(+) and CD5(-) B cell subsets upon chronic HCV infection is of interest. In this study, the degree to which chronic HCV infection induces apoptosis in each B cell subset was investigated. Our results demonstrated that peripheral CD5(-) B cells were more susceptible to apoptosis than CD5(+) B cells in CHC. Furthermore, plasma levels of IL-4, IL-10, and IL-12 were significantly elevated in CHC, thus suggesting that these interleukins protect CD5(+) B cells from apoptosis. The rationale for the differential susceptibility of distinct B cell subsets in CHC is also discussed with regard to extrahepatic manifestations associated with chronic HCV infection.

Expression of multidrug resistance-associated ABC transporters in B-CLL is independent of ZAP70 status

PURPOSE

To assess whether the poor prognosis of ZAP70-positive B-cell chronic lymphocytic leukemia (CLL) is associated with the overexpression of ABC transporter genes that are responsible for pleiotropic drug resistance.

MATERIALS AND METHODS

The transcript level of ten drug transporters was analyzed using semiquantitative and quantitative RT-PCR in control hematopoietic cells, in 41 CLL patient samples and in 5 lymphoma cell lines. ZAP70 status was determined by immunoblotting.

RESULTS

Of all analyzed transporters, MDR1, MDR2, MRP1, MRP4, MRP5, and MRP7 were expressed at a significantly higher level in B lymphocytes when compared with other hematopoietic cells in peripheral blood. A subgroup of 41 CLL patient samples showed similar or higher expression of these genes than control B cells, and CLL cells exhibited high expression when compared with multiple lymphoma cell lines. No significant correlation between ZAP70 expression and ABC transporter expression was observed.

CONCLUSION

The ZAP70 status is independent of the multidrug resistance phenotype in CLL.

A phase I/II study of rituximab and etanercept in patients with chronic lymphocytic leukemia and small lymphocytic lymphoma

Rituximab has modest activity in relapsed chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma but is associated with tumor necrosis factor-alpha (TNF-alpha) release that can cause CLL proliferation and inhibit apoptosis. We examined whether disruption of TNF-alpha by etanercept improves response to rituximab in CLL. Eligible patients had previously treated CLL with performance status 0-3. Patients received etanercept 25 mg subcutaneously twice weekly (weeks 1-5) and rituximab 375 mg/m(2) intravenously thrice weekly (weeks 2-5) using a phase I/II design. Primary end points were response and toxicity. The 36 enrolled patients had a median of two prior treatments; 50% were fludarabine refractory and 22% had del(17p13.1). Of the 34 response-evaluable patients, 10 (29%) responded, including 9 partial responses and 1 complete remission. Response was not affected by prior rituximab or fludarabine-refractory status, but no patients with del(17p13.1) responded. Median progression-free survival for responders was 9.0 months (range 1-43). Ten patients have had treatment-free intervals exceeding 12 months, including four who have remained untreated for 32, 43, 46 and 56 months. Adverse events were mild, including mild infusion reactions, transient cytopenias and grade 3 infections in 14% of the patients. The combination of etanercept and thrice weekly rituximab produces durable remissions in non-del(17p13.1) CLL patients and is well tolerated.

Lenalidomide for the treatment of B-cell malignancies

Lenalidomide is a novel anticancer agent that has made a major impact in the treatment of patients with B-cell malignancies. A more potent analog of thalidomide, lenalidomide was developed to enhance immunomodulatory properties with improved safety profile. Its antitumor activity seems mediated through modulation of both the cytokine and cellular tumor cell microenvironment. Preclinical as well as clinical observations demonstrate that lenalidomide downregulates production of various critical prosurvival cytokines in the tumor microenvironment while concurrently promoting activation of T- and natural killer (NK) cell-mediated antitumor response. Early clinical investigations noted its efficacy in relapsed and/or refractory multiple myeloma patients. Subsequently, larger randomized studies confirmed the clinical benefit of lenalidomide when added to dexamethasone compared with dexamethasone alone in previously treated myeloma patients resulting in its recent approval by the US Food and Drug Administration. Consequently, the role of lenalidomide in other B-cell malignancies has been investigated, with impressive results in chronic lymphocytic leukemia and non-Hodgkin's lymphoma. This review summarizes the data from various clinical investigations and highlights the impact of lenalidomide in the management of patients with B-cell malignancies.

Ex Vivo-activated Human Macrophages Kill Chronic Lymphocytic Leukemia Cells in the Presence of Rituximab: Mechanism of Antibody-dependent Cellular Cytotoxicity and Impact of Human Serum

Antibody-dependent cellular cytotoxicity (ADCC) is one of the mechanisms of tumor killing during antibody (Ab) immunotherapy, and a role for myeloid cells as effectors has been observed in several models. We are developing immunotherapy approaches based on administration of large numbers of ex vivo interferon-gamma-activated macrophages to cancer patients. With a quantitative assay measuring killing of nonproliferating tumor cells, we evaluated whether, in physiologic conditions, these macrophages synergize with the anti-CD20 Ab rituximab for killing primary B-cell chronic lymphocytic leukemia (B-CLL) cells. ADCC reached levels of 70% to 80% at effector to target ratios as low as 1:1. Macrophage recruitment by Ab-opsonized tumor cells did not result in enhanced cytokine secretion, suggesting that the cytokine shower observed in rituximab-treated patients is not caused by macrophage activation, and that cytokines have no role in CLL killing. We observed that uptake of tumor material by macrophages was not directly correlated to tumor killing. Nonetheless, experiments in the presence of cytochalasin D showed that ADCC occurred mainly by phagocytosis. Tumor killing was largely mediated by Fc gammaRI and inhibited by increasing concentration of serum. Importantly, complement deposition on B-CLL cells did not seem to enhance macrophage ADCC in this model, as complement-depleted and complement-repleted human plasmas exerted comparable inhibition.

The natural product honokiol induces caspase-dependent apoptosis in B-cell chronic lymphocytic leukemia (B-CLL) cells

B-cell chronic lymphocytic leukemia (B-CLL) remains an incurable disease that requires innovative new approaches to improve therapeutic outcome. Honokiol is a natural product known to possess potent antineoplastic and antiangiogenic properties. We examined whether honokiol can overcome apoptotic resistance in primary tumor cells derived from B-CLL patients. Honokiol induced caspase-dependent cell death in all of the B-CLL cells examined and was more toxic toward B-CLL cells than to normal mononuclear cells, suggesting greater susceptibility of the malignant cells. Honokiol-induced apoptosis was characterized by the activation of caspase-3, -8, and -9 and cleavage of poly(adenosine diphosphate-ribose) polymerase (PARP). Exposure of B-CLL cells to honokiol resulted in up-regulation of Bcl2-associated protein (Bax) and down-regulation of the expression of the key survival protein myeloid-cell leukemia sequence 1 (Mcl-1), which is associated with response to treatment in B-CLL patients. In addition, B-CLL cells pretreated with interleukin-4 (IL-4), a cytokine known to support B-CLL survival, underwent apoptosis when subsequently incubated with honokiol, indicating that honokiol could also overcome the prosurvival effects of IL-4. Furthermore, honokiol enhanced cytotoxicity induced by fludarabine, cladribine, or chlorambucil. These data indicate that honokiol is a potent inducer of apoptosis in B-CLL cells and should be examined for further clinical application either as a single agent or in combination with other anticancer agents. (Blood. 2005;106:690-697)

Intracellular IFN-γ expression by CD3+/CD8+ cell subset in B-CLL patients correlates with stage of the disease

Changes in the cytokine network may be responsible for malignant cell accumulation in B-cell chronic lymphocytic leukaemia (B-CLL). Among different cytokines of question interferon gamma (IFN-gamma) is indicated to prevent malignant cells from entering apoptosis. The aim of the study was to determine IFN-gamma production capacity of T-cell subsets and B lymphocytes in B-CLL patients in comparison with healthy individuals and during disease progression. Forty patients with newly diagnosed, untreated B-CLL and 20 healthy individuals were studied. The two- and three-colour flow cytometry techniques were used to detect intracellular cytokine expression. We detected statistically significantly higher percentage of both CD3+/CD4+/IFN-gamma+ and CD3+/CD8+/IFN-gamma+ in patients than in controls (P < 0.001 in both cases). Moreover the percentage of CD3+/CD8+/IFN-gamma+ cells correlated with stage of the disease (R = 0.39, P = 0.01) and parameters of disease progression like lymphocyte count and total tumour mass score (R = 0.33, P = 0.03 and R = 0.31, P = 0.04, respectively). By contrast, the percentage of CD19+/IFN-gamma+ cells in B-CLL group was lower than in controls (P < 0.01). These findings indicate that T-cell populations rather than malignant B cells are the source of IFN-gamma in B-CLL patients. The subset of CD3+/CD8+ cells expressing IFN-gamma seems to play a special role in the disease progression and more precise investigation should elucidate its role as a prognostic marker in B-CLL and a target for therapeutic strategies.

Prolegomenon for Chronic Lymphocytic Leukaemia

Chronic lymphocytic leukaemia (CLL) is a unique lymphoproliferative disorder that scarcely occurs under the age of 40; thereafter the incidence of CLL increases exponentially with age. CLL is characterized by progressive expansion of malignant CD5+ME+ B-cell clone accompanied by a myriad of cellular and humoral immune defects. Each of them might be linked to different clinically manifested complications such as increasing rate of infections, autoimmune disorders and disturbed immune surveillance against tumour cells. We assume that CLL occurs as a consequence of age-dependent, genetically related functional restrictions of the thymic microenvironment in supporting common lymphoid progenitor cells (CD5+ME+CD4-CD8-) to differentiate into mature T-cell and B-cell descendants. In conjunction with genetic abnormalities developing in B-cell progenitors, presumably expressing P glycoprotein (Pgp+), we postulate that developmentally altered T-cell descendants, along with quantitative imbalance among CD4+, their subsets and CD8+ lymphocytes in the peripheral blood, play an important additional role in facilitating the malignant B-cell clone emergence and in modulating the CLL clinical evolution. Namely, imbalance of any of T-cell-mediated cell interactive homeostatic mechanisms accompanied by imbalance in the production of various cytokines might in CLL influence leukaemic B-cell growth by deregulating inducer (c-myc and p53) and/or suppressor (bcl-2 and mutant p53) oncogenes responsible for the promotion or suppression of B-cell mitogenesis that may in turn further contribute to their impaired differentiation and/or differentiation arrest. In conclusion, CLL might be interpreted as a primary immunodeficiency syndrome developing in elderly population due to gradually evolving restriction of genetically controlled programs in the thymic microenvironment responsible for irregular maturation of common lymphoid progenitor cells that constitutively express CD5 antigen and ME receptor into T-cell and B-cell descendants.

STAT1 mediates differentiation of chronic lymphocytic leukemia cells in response to Bryostatin 1

Bryostatin 1 is known to exhibit in vitro and in vivo activity against chronic lymphocytic leukemia (CLL) cells by inducing their further maturation into plasma-like cells. Signal transducer and activator of transcription (STAT) proteins play a central role in B-lymphocyte growth and function and are aberrantly phosphorylated on serine residues in CLL cells. To determine whether STAT transcription factors are important in Bryostatin 1-induced differentiation of CLL cells, primary CLL cells were examined for signaling events following exposure to Bryostatin 1 in vitro. Western analysis and electrophoretic mobility shift assays revealed that Bryostatin 1 induced tyrosine phosphorylation and DNA binding of STAT1, yet there was no effect on constitutive serine phosphorylation of STAT1. Bryostatin 1-induced STAT1 activation occurred in a manner that was dependent on protein kinase C (PKC), mitogen-activated protein kinase (MAPK), and Janus tyrosine kinase (JAK) activation. Evidence indicates that Bryostatin 1 induces STAT1 activation through an interferon gamma (IFN gamma) autocrine loop. However, STAT1 activation by IFN gamma stimulation alone was not sufficient to induce differentiation. This insufficiency is due to the broader effect on gene expression caused by Bryostatin 1 compared with IFN gamma, as demonstrated by microarray analysis. Both up-regulation of CD22 expression and immunoglobulin M (IgM) production, markers of CLL differentiation, were inhibited by a decoy oligonucleotide for STAT1, indicating that STAT1 is necessary for Bryostatin 1-induced differentiation of CLL cells. This study implicates STAT transcription factors as important mediators of Bryostatin 1-induced differentiation of CLL cells and could possibly lead to improved therapeutic approaches for the treatment of CLL.

Induction of caspase-dependent programmed cell death in B-cell chronic lymphocytic leukemia by anti-CD22 immunotoxins

B cells of chronic lymphocytic leukemia (CLL) are long-lived in vivo, possibly because of defects in apoptosis. We investigated BL22, an immunotoxin composed of the Fv portion of an anti-CD22 antibody fused to a 38-kDa Pseudomonas exotoxin-A fragment. B cells from 22 patients with CLL were immunomagnetically enriched (96% purity) and were cultured with BL22 or an immunotoxin that does not recognize hematopoietic cells. The antileukemic activity of BL22 was correlated with CD22 expression, as determined by flow cytometry. BL22 induced caspase-9 and caspase-3 activation, poly(adenosine diphosphate [ADP]-ribose)polymerase (PARP) cleavage, DNA fragmentation, and membrane flipping. Cell death was associated with the loss of mitochondrial membrane potential and the down-regulation of Mcl-1 and X-chromosomal inhibitor of apoptosis protein (XIAP). Furthermore, BL22 induced a proapoptotic 18-kDa Bax protein and conformational changes of Bax. Z-VAD.fmk abrogated apoptosis, confirming that cell death was executed by caspases. Conversely, interleukin-4, a survival factor, inhibited spontaneous death in culture but failed to prevent immunotoxin-induced apoptosis. BL22 cytotoxicity was markedly enhanced when combined with anticancer drugs including vincristine. We also investigated HA22, a newly engineered immunotoxin, in which BL22 residues are mutated to improve target binding. HA22 was more active than BL22. In conclusion, these immunotoxins induce caspase-mediated apoptosis involving mitochondrial damage. Combination with chemotherapy is expected to improve the efficacy of immunotoxin treatment.

Inflammatory response: an unrecognised source of variability in the pharmacokinetics and pharmacodynamics of cancer chemotherapy

An important limitation in the use of chemotherapy in cancer treatment is that cytotoxic agents have small margins of safety compared with other drugs. The largely unpredictable pharmacokinetics of cytotoxic agents contribute significantly to differences in toxicity and efficacy between individuals. Over the past few decades, evidence has accumulated that the inflammatory response to conditions such as infection, degenerative disease, and cancer can greatly affect the disposition of drugs. A more recent finding is that the presence of an inflammatory response identifies patients with more aggressive disease and may also compromise the pharmacodynamics of anticancer drugs. In this review, we discuss the changes in the pharmacokinetics of drugs caused by the presence of inflammation. Also, we discuss the modulating role of inflammatory mediators on the pharmacokinetics and pharmacodynamics of cytotoxic agents. We argue that, overall, these factors identify inflammatory response as a potentially important factor in the interindividual variability of response and toxic effects to cancer chemotherapy.

B-chronic lymphocytic leukemia: practical aspects

B-CLL is the most common adult leukemia in the Western world. It is a neoplasia of mature looking B-monoclonal lymphocytes co-expressing the CD5 antigen (involving the blood, the bone marrow, the lymph nodes and related organs). Much new information about the nature of the neoplastic cells, including chromosomal and molecular changes as well as mechanisms participating in the survival of the leukemic clone have been published recently, in an attempt to elucidate the biology of the disease and identify prognostic subgroups. For the time being, clinical stage based on Rai and Binet staging systems remains the strongest predictor of prognosis and patients' survival, and therefore it affects treatment decisions. In the early stages treatment may be delayed until progression. When treatment is necessary according to well-established criteria, there are nowadays many different options. Chlorambucil has been the standard regimen for many years. During the last decade novel modalities have been tried with the emphasis on fludarabine and 2-chlorodeoxyadenosine and their combinations with other drugs. Such an approach offers greater probability of a durable complete remission but no effect on overall survival has been clearly proven so far. Other modalities, included in the therapeutic armamentarium, are monoclonal antibodies, stem cell transplantation (autologous or allogeneic) and new experimental drugs. Supportive care is an important part of patient management and it involves restoring hypogammaglobulinemia and disease-related anemia by polyvalent immunoglobulin administration and erythropoietin respectively.

Diminished peripheral blood memory B cells and accumulation of memory B cells in the salivary glands of patients with Sjögren's syndrome

OBJECTIVE

To delineate the mechanism of the abnormalities in B cell biology found in patients with primary Sjögren's syndrome (SS).

METHODS

The distribution of peripheral B cell subpopulations in 21 patients with primary SS was analyzed by immunofluorescence labeling and flow cytometry. Immunoglobulin rearrangements were analyzed in single B cells isolated from the peripheral blood and parotid glands by fluorescence-activated cell sorting.

RESULTS

A significant reduction in the number of peripheral CD27+ memory B cells was found in SS patients, including a significantly reduced number of CD27+/IgD+/IgM+/CD5+ memory B cells. Remarkably, SS patients with secondary lymphoma uniquely exhibited an increase in CD27-expressing peripheral B cells, including CD27(high) plasmablasts. Molecular analysis for mutated Ig gene rearrangements confirmed that CD27 expression distinguished naive and memory cells in SS. In contrast to the peripheral blood, the majority of parotid B cells from 1 patient examined exhibited both the mutational status and phenotype of memory B cells. Accordingly, the mutational frequencies of V(H) rearrangements were significantly greater in parotid B cells than in peripheral blood B cells, whereas the V(H) gene repertoire appeared to be very similar between the compartments.

CONCLUSION

These data indicate that there is an accumulation/retention of memory B cells in the inflamed salivary glands of SS patients. It is possible that preferential accumulation of CD27+ memory B cells in the inflamed parotid gland explains their reduction in the peripheral blood.

Th1/Th2 cytokine expression and its relationship with tumor growth in B cell non-Hodgkin's lymphoma (NHL)

AT helper 1 (Th1) immune response is considered more effective than T helper 2 (Th2) for anti-tumor immunity, but either response could potentially stimulate tumor cell growth in lymphomas. Moreover, both IL-4 and IL-2/IL-12 are used in experimental treatment models for non-Hodgkin's lymphoma (NHL) despite their differing ability to elicit Th2 or Th1 responses, respectively. Here, we investigate which T helper cytokines (Th1 or Th2) predominate in B cell NHL tissue and determine whether cytokine expression correlates with tumor cell growth, cell death, and survival in a series of 44 NHL patients. Overall, we observed both Th1 and Th2 cytokine expression at the mRNA level, detecting high levels of IFN-gamma, IL6 and IL-10 expression in the majority of tumors. Transcripts for the IL-12 subunits p35 (38 of 38) and p 40 (23 of 38) were frequently detected in NHL tissue, and high p40 levels were common in patients with a good prognosis. Furthermore, high IL-4 levels correlated with greater survival duration (P < 0.0024) but nor overall survival. Cytokine expression of IL-2, IFNgamma and IL-4 was significantly reduced in the high grade tumor group. Interestingly, there was a strong correlation between high IL-4 levels and reduced levels of apoptosis (P < 0.006) or proliferation (P < 0.0001), which has also been reported in leukemic models. This has important implications for the success of IL-4 as a treatment for low and high grade tumors.

Apoptosis induction by hypercross-linking of the surface antigen CD5 with anti-CD5 monoclonal antibodies in B cell chronic lymphocytic leukemia

We evaluated cells from 24 patients with B cell chronic lymphocytic leukemia (B-CLL) to determine apoptosis induced by CD5 hypercross-linking. Following the CD5 hypercross-linking with anti-CD5 monoclonal antibodies (MoAbs), we identified 10 patients where CD5 hypercross-linking induced apoptosis (group A) and 14 patients whose cells were resistant to the anti-CD5 MoAbs (group B). The programmed cell death pathway of the cells from patient group A was caspase-3 and poly (ADP-ribose) polymerase (PARP)-dependent, involved a reduction of the mitochondrial transmembrane potential DeltaPsi and a down-regulation of the anti-apoptotic Bcl-2, Mcl-1 and iNOS proteins. Early activation-associated molecules such as CD25 and CD69 were expressed at higher levels than in controls after 6 h of culture with anti-CD5 MoAb. The expression of CD5 and of CD72, the ligand for CD5, were significantly lower in group A compared with group B. Anti-CD20 MoAb had similar activity with anti-CD5 MoAb and the combination of the two MoAbs seemed to be additive. In this study, it is suggested that the cells from some B-CLL patients can be induced into programmed cell death by CD5 hypercross-linking with anti-CD5 MoAbs.

Non-malignant leukocytes delay spontaneous B-CLL cell apoptosis

Malignant B cells from chronic lymphocytic leukemia (B-CLL) patients have a long survival in vivo, although, in culture, they spontaneously die by apoptosis. Here, we analyzed the capacity of accessory leukocytes to modulate apoptosis of B-CLL cells in vitro. To this end, we performed long-term cultures using total mononuclear cells (TMC) from B-CLL patients and TMC depleted from monocytes, NK cells and T lymphocytes (B-CLL cells). In all the patients studied (n = 25) the presence of accessory leukocytes markedly prolonged the survival of B-CLL cells. The anti-apoptotic effect was exerted by monocytes and, to a lesser degree, NK cells, partially through the release of soluble factors. Indeed, accessory leukocytes separated from leukemic cells by semipermeable membranes were still able to prolong B-CLL cell survival. By flow cytometric analysis we found that the protective effect of non-malignant cells was associated with delayed down-regulation of Bcl-2 expression on leukemic cells. By contrast, the expression of Fas and Fas ligand proteins was unchanged in most samples. Our findings suggest that monocytes and NK cells, by delaying leukemic cell apoptosis, may play a role in B-CLL cell accumulation in vivo.

Interleukin-2 fusion protein with anti-CD3 single-chain Fv (sFv) selectively protects T cells from dexamethasone-induced apoptosis

Apoptosis of mature T cells may be an important pathophysiologic mechanism in diseases such as AIDS, cancer, and autoimmunity. In this study, in order to selectively protect T cells from dexamethasone (DEX)-induced apoptosis we constructed a fusion protein (anti-CD3sFv-IL-2) in which anti-CD3 single-chain Fv (sFv), the smallest unit of antibody recognizing the CD3 epsilon moiety of the T-cell receptor (TCR), was covalently linked to murine interleukin-2 (IL-2). Recombinant anti-CD3sFv protein was also expressed and used as a control. The purified anti-CD3sFv-IL-2 protein displayed IL-2 bioactivity in an IL-2 proliferation assay, which was inhibited by a neutralizing mIL-2 mAb. The anti-CD3sFv-IL-2 protein protected T lymphoma cells (S49.1) from DEX-induced apoptosis as demonstrated by oligonucleosomal genomic DNA fragmentation assay, and also recovered proliferation capacity of DEX-treated S49.1 cells and increased T cell composition both in DEX-treated spleen cell-populations and in DEX-treated mice, while the anti-CD3sFv protein did not. In addition, the anti-CD3sFv-IL-2 fusion protein was more efficient than a simple mixture of anti-CD3sFv and free rIL-2 in selectively protecting T cells from DEX-induced apoptosis. The levels of bcl-2 gene expression were significantly increased in DEX-treated T cells in the presence of the anti-CD3sFv-IL-2 protein. These studies indicate that the anti-CD3sFv-IL-2 fusion protein can selectively protect T cells from DEX-induced apoptosis and that the covalent linkage of anti-CD3sFv and IL-2 confines the anti-apoptotic effect of IL-2 to T cells.

Autologous plasma activates Akt/protein kinase B and enhances basal survival and resistance to DNA damage-induced apoptosis in B-chronic lymphocytic leukaemia cells

We have studied the actions of autologous plasma on both basal and DNA damage-induced apoptosis in B-chronic lymphocytic leukaemia (B-CLL) cells. Apoptosis was quantified using morphological criteria and Western blot analysis for the apoptosis-specific p85 fragment of poly(ADP ribose) polymerase. Cell viability was estimated using the methyl thiazol tetrazolium bromide dye reduction assay. Plasma cultures showed lower rates of basal apoptosis as well as a decreased cytotoxic response to chlorambucil and gamma-radiation compared with cultures in fetal calf serum. Experiments using neutralizing antibodies suggested that the protective actions of plasma could not be accounted for by interleukin 4, the interferons alpha or gamma or stromal cell-derived factor 1, each of which have been shown to protect B-CLL cells from apoptosis in vitro. Plasma addition to B-CLL cells resulted in rapid activation of the Akt protein kinase, a key signalling enzyme that has been implicated in anti-apoptotic signalling. LY294002, an inhibitor of phosphatidylinositol 3'-kinase, blocked Akt activation by plasma. To the best of our knowledge, this is the first report to show that factors present in plasma promote basal survival of B-CLL cells and resistance to cytotoxic drugs via stimulation of the Akt cytoprotective-signalling pathway. Pharmacological blockade of this pathway may have potential in the development of novel therapeutic strategies for B-CLL treatment.

Rituximab using a thrice weekly dosing schedule in B-cell chronic lymphocytic leukemia and small lymphocytic lymphoma demonstrates clinical activity and acceptable toxicity

PURPOSE

Rituximab has been reported to have little activity in small lymphocytic lymphoma (SLL)/chronic lymphocytic leukemia (CLL) and to be associated with significant infusion-related toxicity. This study sought to decrease the initial toxicity and optimize the pharmacokinetics with an alternative treatment schedule.

PATIENTS AND METHODS

Thirty three patients with SLL/CLL received dose 1 of rituximab (100 mg) over 4 hours. In cohort I (n = 3; 250 mg/m(2)) and cohort II (n = 7; 375 mg/m(2)) rituximab was administered on day 3 and thereafter three times weekly for 4 weeks using a standard administration schedule. Cohort III (n = 23; 375 mg/m(2)) administered rituximab similar to cohort II for the first two treatments and then over 1 hour thereafter.

RESULTS

A total of 33 CLL/SLL patients were enrolled; only one patient discontinued therapy because of infusion-related toxicity. Thirteen patients developed transient hypoxemia, hypotension, or dyspnea that were associated with significant changes in baseline interleukin-6, interleukin-8, tumor necrosis factor alpha, and interferon gamma compared with those not experiencing such reactions. Infusion-related toxicity occurred more commonly in older (median age 73 v 62 years; P =.02) patients with no other pretreatment clinical or laboratory features predicting occurrence of these events. The overall response rate was 45% (3% CR, 42% PR; 95% CI 28% to 64%). Median response duration for these 15 patients was 10 months (95% CI, 6.8-13.2; range, 3 to 17+).

CONCLUSION

Rituximab administered thrice weekly for 4 weeks demonstrates clinical efficacy and acceptable toxicity. Initial infusion-related events seem to be cytokine mediated and resolve by the third infusion making rapid administration possible. Future combination studies of rituximab with other therapies in CLL seem warranted.

Interleukin 4 therapy for patients with chronic lymphocytic leukaemia: a phase I/II study

Interleukin 4 (IL-4) is a pleiotropic type II cytokine which has been shown to have a direct killing effect on lymphoma and B-cell chronic lymphocytic leukaemia (B-CLL) cells in vitro. The clinical effects and toxicity of IL-4 treatment in patients with B-CLL were evaluated. Fourteen patients with B-CLL who were in partial remission after chemotherapy received one, two or three 8-week cycles of escalating doses (2, 4 or 6 microg/kg/d s.c.) of IL-4 for 3 d/week. Clinical response was analysed after each treatment cycle and toxicity was monitored continuously. Ten patients (71%) had progressive disease (PD) during IL-4 treatment. This was mainly attributable to an increase (two- to fourfold) of the blood lymphocyte count during IL-4 therapy. After cessation of IL-4 treatment, the lymphocytosis decreased spontaneously in 8 out of 12 evaluable patients. Splenomegaly remained unchanged in 7/7 patients, whereas enlarged lymph nodes were reduced by > 50% in 1/13 patients and by 25-50% in 4/13 patients. None of the patients achieved an objective tumour regression (complete or partial remission). A temporary increase (16-60%) of the platelet count was observed during IL-4 treatment. The platelet count decreased in 8/11 patients after the end of IL-4 therapy. World Health Organization (WHO) grade I/II fever, arthralgia and fatigue was observed in one-third of the patients and was more commonly seen with the highest dose (6 microg/kg/d). One patient developed pulmonary oedema and WHO grade III neutropenia was recorded in three patients. IL-4 was well tolerated by most patients in an outpatient setting. The anti-tumour activity observed in previous in vitro studies was not verified by the present in vivo trial which showed that IL-4 may instead increase the number of CLL cells in blood, indicating that IL-4 may have induced a stimulatory or antiapoptotic effect on the CLL cells in blood. These results may have important implications for the development of immunotherapy of CLL. In addition, the potential platelet-stimulatory effect of IL-4 warrants further studies.

Inhibition of in vitro spontaneous apoptosis by IL-7 correlates with Bcl-2 up-regulation, cortical/mature immunophenotype, and better early cytoreduction of childhood T-cell acute lymphoblastic leukemia

In normal T-cell development, IL-7 plays a nonredundant role as an antiapoptic factor by regulating Bcl-2 expression in pro-T cells. In the current study, we addressed the roles of IL-7 and related cytokines as apoptosis-modulating factors in precursor T-cell acute lymphoblastic leukemia (T-ALL). To this end, leukemic blasts from pediatric patients with T-ALL were prospectively investigated as to their responsiveness to IL-7, IL-4, and IL-2 (in terms of modulation of spontaneous apoptosis, assessed by flow cytometry), cytokine receptor expression profiles, and expression levels of Bcl-2 and Bax proteins. IL-7, in contrast to IL-4 and IL-2, was highly efficient in apoptosis inhibition , and this effect correlated with the expression levels of IL-7R chain and with the up-regulation of Bcl-2 protein expression (P&lt; .0001). Subclassification of T-ALL samples (n = 130) according to their in vitro IL-7 responses revealed that IL-7 refractory samples were more frequently positive for CD34 (P&lt; .0001) and the myeloid-associated antigen CD33 (P= .01), whereas IL-7 responsiveness was associated with an expression of more mature differentiation-associated T-cell antigens (CD1a, surface CD3, CD4/8; P &lt; .05). Furthermore, the extent of apoptosis inhibition by IL-7 in vitro quantitatively correlated with early cytoreduction as determined by the prednisone peripheral blood response on day 8 and cytoreduction in the marrow on day 15 (n = 87;P &lt; .05). Multivariate analysis of the apoptosis-related parameters investigated, including spontaneous apoptosis, its inhibition by IL-7, and expression levels of Bcl-2 and Bax, showed that only IL-7 responsiveness has an independent impact on early cytoreduction (P &lt; .05), thus indicating a potential prognostic relevance of IL-7 sensitivity in T-ALL.

Inhibition of in vitro spontaneous apoptosis by IL-7 correlates with Bcl-2 up-regulation, cortical/mature immunophenotype, and better early cytoreduction of childhood T-cell acute lymphoblastic leukemia

In normal T-cell development, IL-7 plays a nonredundant role as an antiapoptic factor by regulating Bcl-2 expression in pro-T cells. In the current study, we addressed the roles of IL-7 and related cytokines as apoptosis-modulating factors in precursor T-cell acute lymphoblastic leukemia (T-ALL). To this end, leukemic blasts from pediatric patients with T-ALL were prospectively investigated as to their responsiveness to IL-7, IL-4, and IL-2 (in terms of modulation of spontaneous apoptosis, assessed by flow cytometry), cytokine receptor expression profiles, and expression levels of Bcl-2 and Bax proteins. IL-7, in contrast to IL-4 and IL-2, was highly efficient in apoptosis inhibition , and this effect correlated with the expression levels of IL-7R chain and with the up-regulation of Bcl-2 protein expression (P< .0001). Subclassification of T-ALL samples (n = 130) according to their in vitro IL-7 responses revealed that IL-7 refractory samples were more frequently positive for CD34 (P< .0001) and the myeloid-associated antigen CD33 (P= .01), whereas IL-7 responsiveness was associated with an expression of more mature differentiation-associated T-cell antigens (CD1a, surface CD3, CD4/8; P < .05). Furthermore, the extent of apoptosis inhibition by IL-7 in vitro quantitatively correlated with early cytoreduction as determined by the prednisone peripheral blood response on day 8 and cytoreduction in the marrow on day 15 (n = 87;P < .05). Multivariate analysis of the apoptosis-related parameters investigated, including spontaneous apoptosis, its inhibition by IL-7, and expression levels of Bcl-2 and Bax, showed that only IL-7 responsiveness has an independent impact on early cytoreduction (P < .05), thus indicating a potential prognostic relevance of IL-7 sensitivity in T-ALL.

A conserved AU-rich element in the 3' untranslated region of bcl-2 mRNA is endowed with a destabilizing function that is involved in bcl-2 down-regulation during apoptosis

The control of mRNA stability is becoming recognized as a crucial point of gene expression regulation. A common element responsible for mRNA decay modulation is the adenine- and uracil-rich element that is found in the 3' untranslated region of numerous mRNAs subjected to fast expression changes in response to various stimuli. Previously we identified a post-transcriptional regulation level for the antiapoptotic bcl-2 gene, which could be involved in t(14;18) lymphoma-associated bcl-2 overexpression. Here we demonstrate that bcl-2 mRNA is endowed with an adenine- and uracil-rich element (ARE) characterized by high evolutionary conservation not only among all chordates examined, but even between chordates and the nematode Caenorhabditis elegans (ced-9 gene). As for other well-established destabilizing AREs, the insertion of the bcl-2 ARE downstream from stable beta-globin mRNA causes an enhanced decay of the beta-globin transcript, which proves its functional role. This possibility is corroborated by the fact that the pathway leading to the modulating activity of bcl-2 ARE is influenced by PKC, since the addition of DAG and TPA markedly attenuated the bcl-2 ARE destabilizing potential. Conversely, it is noteworthy that when C(2)-ceramide is added to the culture medium as the apoptotic agent, the beta-globin transcript harboring the bcl-2 ARE undergoes a dramatic increase in decay. This observation clearly indicates that the destabilizing function of bcl-2 ARE is enhanced by apoptotic stimuli and suggests that this element could be involved in a post-transcriptional mechanism of bcl-2 down-regulation during apoptosis. The half-life of the mRNA of bcl-2 in Jurkat cells is prolonged by PKC stimulation and shortened by C(2)-ceramide addition, strongly supporting the view that bcl-2 mRNA stability plays a physiological role in modulating bcl-2 expression, particularly in its down-regulation during apoptosis. Thus, this element becomes a new candidate for mediating those bcl-2 gene expression changes-from apoptosis-associated down-regulation to tumor-associated overexpression-observed thus far that profoundly influence single cell fate and tissue homeostasis.

Cytokine expression in B-CLL in relation to disease progression and in vitro activation

Earlier, we reported an association between low in vitro and in vivo IL-1 and IL-6 production, decreased IL-1beta and IL-10 mRNA expression and B cell chronic lymphocytic leukemia (B-CLL) disease progression. We have now further investigated cytokine mRNA transcription in B-CLL cells and cytokine serum levels in B-CLL patients. Reverse transcriptase polymerase chain reaction (RT-PCR) amplification of tumor necrosis factor (TNFalpha), IFNgamma, IL-6 and BCGF was equally often seen in non-progressive and progressive patients. However, 4 out of 23 non-progressive cases expressed mRNA for IL-12 while no IL-12 expression was seen in 15 progressive patients. No IL-12 was found in sera or supernatants from in vitro stimulated B-CLL cells, whereas TNFalpha and IL-10 were detected in sera from 51 and 31 of 65 B-CLL patients, respectively. TNFalpha values were significantly high in sera from patients in stages III and IV with disease progression. TNFalpha and IL-10 were also detected in culture supernatants from in vitro stimulated B-CLL cells, whereas IFNgamma was undetectable in these cultures and rarely positive in serum. Although further investigations are required, our data and that from previous reports indicate that B-CLL-derived cytokines are involved in B-CLL disease progression.

Adhesion to bone marrow stroma inhibits apoptosis of chronic lymphocytic leukemia cells

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of monoclonal long-lived B cells which are apparently resistant to normal apoptotic regulation. Since bone marrow stromal cells play an essential role in B lymphopoiesis, we have investigated whether stromal cells influence B-CLL cell survival. Our results indicate that intimate contact with stromal cells reduces B-CLL cell apoptosis and prevents the loss of bcl-2 protein expression. Binding of B-CLL cells to stromal cells requires simultaneous action of beta1 and beta2 integrins. The interaction between B-CLL cells and other cell types seems important for their survival and may represent an important mechanism underlying accumulation of malignant cells in B-CLL patients.

Transforming growth factor beta and tumor necrosis factor alpha inhibit both apoptosis and proliferation of activated rat hepatic stellate cells

Transforming growth factor beta (TGF-beta) as well as tumor necrosis factor alpha (TNF-alpha) gene expression are up-regulated in chronically inflamed liver. These cytokines were investigated for their influence on apoptosis and proliferation of activated hepatic stellate cells (HSCs). Spontaneous apoptosis in activated HSC was significantly down-regulated by 53% +/- 8% (P <.01) under the influence of TGF-beta and by 28% +/- 2% (P <.05) under the influence of TNF-alpha. TGF-beta and TNF-alpha significantly reduced expression of CD95L in activated HSCs, whereas CD95 expression remained unchanged. Furthermore, HSC apoptosis induced by CD95-agonistic antibodies was reduced from 96% +/- 2% to 51 +/- 7% (P <.01) by TGF-beta, and from 96% +/- 2% to 58 +/- 2% (P <.01) by TNF-alpha, suggesting that intracellular antiapoptotic mechanisms may also be activated by both cytokines. During activation, HSC cultures showed a reduced portion of cells in the G0/G1 phase and a strong increment of G2-phase cells. This increment was significantly inhibited (G1 arrest) by administration of TGF-beta and/or TNF-alpha to activated cells. In liver sections of chronically damaged rat liver (CCl4 model), using desmin and CD95L as markers for activated HSC, most of these cells did not show apoptotic signs (TUNEL-negative). Taken together, these findings indicate that TGF-beta and/or TNF-alpha both inhibit proliferation and also apoptosis in activated HSC in vitro. Both processes seem to be linked to each other, and their inhibition could represent the mechanism responsible for prolonged survival of activated HSC in chronic liver damage in vivo.

Apoptosis in B-chronic lymphocytic leukaemia

B-chronic lymphocytic leukaemia (B-CLL) is characterised by the progressive accumulation of monoclonal B cells, which may be the result of several factors leading to extended B-CLL cell lifespan, increased proliferative capacity and diminished cell death. Here we review the implications of several signals mediated by receptors, such as surface IgM, CD6 and CD40, for the B-CLL cell survival, together with data on gene modulation in relation to the apoptosis process in B-CLL cells. We also describe some features of the Fas/FasL system in B-CLL that hypothetically might contribute to the accumulation of leukaemic cells and the progression of the disease, by downregulating the apoptotic response or avoiding the autologous immune response.

Interleukin-10 inhibits the in vitro proliferation of human activated leukemic CD5+ B-cells

B-cell chronic lymphocytic leukemia (B-CLL) is characterised by the proliferation and accumulation of sIgM+/CD5+ B-cells that fail to progress to the final stages of B-cell development. Despite their developmental arrest, leukemic CD5+ B-cells can undergo proliferation in vitro in the presence of different activators including phorbol esters, antibodies to cell surface antigens and human cytokines. Interleukin-10 (IL-10) has recently been found to inhibit CLL B-cell function in vitro by inducing apoptosis and down-regulating expression of bcl-2. Here, we examined the effect of IL-10 on proliferation, RNA synthesis, immunoglobulin (IgM) secretion and viability of leukemic CD5+ B-cells induced by activation with the phorbol ester PMA, alone or in combination with anti-Ig. IL-10 reduced PMA and PMA/anti-Ig induced proliferation and RNA synthesis by 50-80% and 15-40% respectively. Although proliferation and RNA synthesis induced by PMA/anti-Ig could be enhanced by the addition of IL-2, IL-4, IL-13, IFN-gamma or TNF-alpha, the presence of these cytokines failed to abrogate the IL-10-mediated inhibition of leukemic CD5+ B-cell activation. In contrast to the effects on proliferation and RNA synthesis, IL-10 did not inhibit IgM secretion, and had only a minimal effect on the viability of activated cells. Our results indicate that IL-10 inhibits proliferation of leukemic CD5+ B-cells by a mechanism distinct from induction of apoptosis and support the proposal for the utilisation of IL-10 in the therapy of B-CLL.

B-Cell Chronic Lymphocytic Leukemia Cells Express a Functional Inducible Nitric Oxide Synthase Displaying Anti-Apoptotic Activity

The expression of different isoforms of nitric oxide synthase (NOS) was investigated in B-cell chronic lymphocytic leukemia (B-CLL) to delineate a possible role for nitric oxide (NO) in the control of apoptosis of the tumoral cells. By reverse transcription-polymerase chain reaction (RT-PCR), all B-CLL cells were found to express spontaneously inducible NOS (iNOS) mRNA, whereas endothelial constitutive NOS (ecNOS) mRNA was undetectable. The iNOS protein was detected by immunofluorescence in the cytoplasm of permeabilized leukemic cells and identified by Western blotting, using different anti-iNOS antibodies, as a protein of 135 kD in B-CLL cytoplasmic extracts. B-CLL cell lysates also displayed basal NOS enzymatic activity, as measured by the conversion of14C-labeled L-arginine into 14C-L-citrulline. Ligation of CD23, expressed on the vast majority of B-CLL cells, resulted in increased iNOS expression and activity. The NO released exerted an anti-apoptotic effect on B-CLL cells that was counteracted by NOS inhibitors and engagement of the APO-1/Fas pathway. Therefore, the existence of a functional iNOS in B-CLL cells will provide further insights into the mechanisms that control proliferation and apoptosis in these tumor cells.

© 1998 by The American Society of Hematology.

B-Cell Chronic Lymphocytic Leukemia Cells Express a Functional Inducible Nitric Oxide Synthase Displaying Anti-Apoptotic Activity

The expression of different isoforms of nitric oxide synthase (NOS) was investigated in B-cell chronic lymphocytic leukemia (B-CLL) to delineate a possible role for nitric oxide (NO) in the control of apoptosis of the tumoral cells. By reverse transcription-polymerase chain reaction (RT-PCR), all B-CLL cells were found to express spontaneously inducible NOS (iNOS) mRNA, whereas endothelial constitutive NOS (ecNOS) mRNA was undetectable. The iNOS protein was detected by immunofluorescence in the cytoplasm of permeabilized leukemic cells and identified by Western blotting, using different anti-iNOS antibodies, as a protein of 135 kD in B-CLL cytoplasmic extracts. B-CLL cell lysates also displayed basal NOS enzymatic activity, as measured by the conversion of14C-labeled L-arginine into 14C-L-citrulline. Ligation of CD23, expressed on the vast majority of B-CLL cells, resulted in increased iNOS expression and activity. The NO released exerted an anti-apoptotic effect on B-CLL cells that was counteracted by NOS inhibitors and engagement of the APO-1/Fas pathway. Therefore, the existence of a functional iNOS in B-CLL cells will provide further insights into the mechanisms that control proliferation and apoptosis in these tumor cells.

© 1998 by The American Society of Hematology.

Regulation of B-CLL apoptosis through membrane receptors and Bcl-2 family proteins

The accumulation of monoclonal chronic lymphocytic leukemia B (B-CLL) cells may be due to excessive proliferation and longevity. Clinical progression may thus come from a constitutive but altered expression of a number of genes that results in extended B-CLL cells life span, increased proliferative capacity and diminished cell death. B-CLL cells express a number of surface markers that characterise the normal B-cells phenotype. However, B-CLL cells are CD5 positive and most of them also express CD6, surface receptors that are present in just a small subset of normal B-cells. When exploring CD6 function, we found out that cross-linking of CD6 protected B-CLL from anti-IgM-induced apoptosis. CD6 activation blocked anti-IgM- induced Bax(alpha) up-regulation and, by doing so, corrected an imbalance in the Bcl-2/Bax ratio that accompanies apoptosis. Here, we review all surface receptors and cytokines that have been described as participating in the induction or protection of B-CLL apoptosis together with data on chemosensitivity and gene modulation, data on the Fas receptor/Fas ligand system, and the implications of all the latter for B-CLL cell survival.

Prognostic Significance of the Cell Cycle Inhibitor p27Kip1 in Chronic B-Cell Lymphocytic Leukemia

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of resting lymphocytes. The identification of p27kip1, a cyclin-dependent kinase inhibitor that contributes to cell cycle arrest and represents a link between extracellular signals and cell cycle, prompted us to study p27 protein in the lymphocytes from 88 patients with B-CLL and 32 patients with other chronic B-lymphoproliferative disorders. The expression of p27 protein was higher in B-CLL samples with variations among them. In B-CLL, p27 levels were independent of absolute number of circulating lymphocytes, but strongly correlated with both lymphocyte and total tumor mass (TTM) doubling time. High p27 expression was associated with a poorer overall prognosis. In vitro, there was an increased spontaneous survival of B-CLL cells expressing high p27 levels. Interleukin-4 (IL-4) upregulated p27 levels in B-CLL cells, while fludarabine decreased p27 levels. Thus, our results indicate that p27 may be a valuable kinetic marker in B-CLL by providing instantaneous estimation of the disease doubling time. In addition, these results suggest that there is a link between p27 expression and the ability of CLL cells to undergo apoptosis.

Prognostic Significance of the Cell Cycle Inhibitor p27Kip1 in Chronic B-Cell Lymphocytic Leukemia

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of resting lymphocytes. The identification of p27kip1, a cyclin-dependent kinase inhibitor that contributes to cell cycle arrest and represents a link between extracellular signals and cell cycle, prompted us to study p27 protein in the lymphocytes from 88 patients with B-CLL and 32 patients with other chronic B-lymphoproliferative disorders. The expression of p27 protein was higher in B-CLL samples with variations among them. In B-CLL, p27 levels were independent of absolute number of circulating lymphocytes, but strongly correlated with both lymphocyte and total tumor mass (TTM) doubling time. High p27 expression was associated with a poorer overall prognosis. In vitro, there was an increased spontaneous survival of B-CLL cells expressing high p27 levels. Interleukin-4 (IL-4) upregulated p27 levels in B-CLL cells, while fludarabine decreased p27 levels. Thus, our results indicate that p27 may be a valuable kinetic marker in B-CLL by providing instantaneous estimation of the disease doubling time. In addition, these results suggest that there is a link between p27 expression and the ability of CLL cells to undergo apoptosis.

Cytokines and cross-linking of sIgM augment PMA-induced activation of human leukaemic CD5+ B cells

Purified leukaemic CD5+ B cells obtained from patients with B cell chronic lymphocytic leukaemia (B-CLL) undergo activation and differentiation following in vitro stimulation with optimal concentrations of the phorbol ester PMA. This paper examines the ability of exogenous cytokines, anti-Ig antibodies, or combinations of these, to enhance or replace the activation signal provided by PMA to different populations of leukaemic B cells. Proliferation induced by PMA was enhanced 2-20-fold when the cells were co-cultured with either anti-Ig, IL-2, IL-4, IL-13, IFN-gamma or TNF-alpha. Moreover, the combination of anti-Ig, PMA and any one of the above cytokines further enhanced proliferation. Anti-Ig and exogenous cytokines were also capable of inducing proliferation in leukaemic B cells cultured with a non-mitogenic concentration of PMA. When taken together with the finding that IL-2, IL-4, IL-13, IFN-gamma and TNF-alpha prevent in vitro apoptosis of leukaemic CD5+ B cells, the results presented here suggest that these cytokines, in conjunction with signals delivered via sIg, may play a role in the proliferation of leukaemic B cells in vivo and, consequently, the pathogenesis of B-CLL.