Role of the CD40 and CD95 (APO-1/Fas) antigens in the apoptosis of human B-cell malignancies

A CD40 Signalosome anchored in lipid rafts leads to constitutive activation of NF-kappaB and autonomous cell growth in B cell lymphomas

B cell lineage non-Hodgkin's lymphomas (NHL-B) are neoplastic B cells that show dysregulated B lymphocyte growth characteristics. Unlike normal B cells, aggressive NHL-B cells show constitutive expression of nuclear NF-kappaB by maintaining an assembled, scaffold-like signaling platform, called a Signalosome within the lipid raft microdomain, extending from the cell membrane. The CD40 Signalosome appears to be initiated through autochthonous production and cognate binding of CD154 (CD40L, gp39) to CD40 by the lymphoma cell. Constitutive expression of NF-kappaB in NHL-B can be downregulated by treatment with antibodies to CD40 or CD154 that disrupt Signalosomes, inhibit lymphoma cell growth, and induce cell death. CD40 Signalosomes may provide a potentially vulnerable target for therapeutic intervention in NHL-B cells.

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.

Sensitization to TRAIL-induced apoptosis and modulation of FLICE-inhibitory protein in B chronic lymphocytic leukemia by actinomycin D

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent activator of the cell death pathway and exerts tumoricidal activity in vivo with minimal toxicity. In order to investigate the therapeutic potential of TRAIL in B chronic lymphocytic leukemia (B-CLL) we have analyzed the expression of TRAIL receptors (TRAIL-Rs) in leukemic cells from B-CLL patients and their in vitro sensitivity to apoptosis induced by recombinant human TRAIL. We have found TRAIL-R1 and -R2 death receptor, and TRAIL-R3 and -R4 decoy receptor mRNA expression in most of the 57 B-CLL patients studied (R1 82%, R2 100%, R3 96% and R4 82%). TRAIL-R1 and R2 proteins were expressed on the surface and within the cells, whereas R3 and R4 decoy receptors were almost exclusively expressed in the cytoplasm. Despite TRAIL death receptor expression, B-CLL cells were relatively resistant to induction of apoptosis by recombinant human TRAIL (300 ng/ml). However, the susceptibility to TRAIL-induced apoptosis was increased by treatment of B-CLL cells with actinomycin D (Act D). Western blot analysis showed higher constitutive expression of the long form of FLICE-inhibitory protein (FLIP(L)) in B-CLL as compared to normal tonsillar B cells. Act D treatment down-regulated both long and short FLIP expression, which was correlated with the increase in B-CLL sensitivity to TRAIL. Although the surface TRAIL death receptor expression was up-regulated both by cell culture and by Act D treatment, the changes were not correlated with a gain in susceptibility to TRAIL. In addition, neither decoy receptors nor Bcl-2 expression were affected by Act D. Our findings suggest the possible involvement of FLIP in regulating TRAIL-mediated apoptosis in B-CLL.

Survival of leukemic B cells promoted by engagement of the antigen receptor

Chronic lymphocytic leukemia (CLL) is an incurable leukemia characterized by the slow but progressive accumulation of cells in a CD5+ B-cell clone. Like the nonmalignant counterparts, B-1 cells, CLL cells often express surface immunoglobulin with the capacity to bind autologous structures. Previously there has been no established link between antigen-receptor binding and inhibition of apoptosis in CLL. In this work, using primary CLL cells from untreated patients with this disease, it is demonstrated that engagement of surface IgM elicits a powerful survival program. The response includes inhibition of caspase activity, activation of NF-kappaB, and expression of mcl-1, bcl-2, and bfl-1 in the tumor cells. Blocking phosphatidylinositol 3-kinase (PI3-K), a critical mediator of signals through the antigen receptor, completely abrogated mcl-1 induction and impaired survival in the stimulated cells. These data support the contention that CLL cell survival is promoted by antigen for which the malignant clone has affinity, and suggest that pharmacologic interference with antigen-receptor-derived signals has potential for therapy in patients with CLL.

Caspase 8 activation independent of Fas (CD95/APO-1) signaling may mediate killing of B-chronic lymphocytic leukemia cells by cytotoxic drugs or gamma radiation

Ligation of the cell-surface Fas molecule by its ligand (Fas-L) or agonistic anti-Fas monoclonal antibodies results in the cleavage and activation of the cysteine protease procaspase 8 followed by the activation of procaspase 3 and by apoptosis. In some leukemia cell lines, cytotoxic drugs induce expression of Fas-L, which may contribute to cell killing through the ligation of Fas. The involvement of Fas, Fas-L, and caspase 8 was studied in the killing of B-cell chronic lymphocytic leukemia (B-CLL) cells by chlorambucil, fludarabine, or gamma radiation. Spontaneous apoptosis was observed at 24-hour incubation, with additional apoptosis induced by each of the cytotoxic treatments. Although Fas mRNA expression was elevated after exposure to chlorambucil, fludarabine, or gamma radiation, Fas protein levels only increased after irradiation. Therefore, Fas expression may be regulated by multiple mechanisms that allow the translation of Fas mRNA only in response to restricted cytotoxic stimuli. None of the cytotoxic stimuli studied here induced Fas-L expression. An agonistic anti-Fas monoclonal antibody (CH-11) did not significantly augment apoptosis induction by any of the death stimuli. A Fas-blocking antibody (ZB4) did not inhibit spontaneous, chlorambucil-, fludarabine-, or radiation-induced apoptosis. However, procaspase 8 processing was induced by all cytotoxic stimuli. These data suggest that the Fas/Fas-L signaling system does not play a major role in the induction of apoptosis in B-CLL cells treated with cytotoxic drugs or radiation. However, Fas-independent activation of caspase 8 may play a crucial role in the regulation of apoptosis in these cells.

Upstream mediators of the Fas apoptotic transduction pathway are defective in B-chronic lymphocytic leukemia

Data concerning the presence and the functionality of Fas receptor in malignant B-cells are controversial. We have analyzed Fas molecules on B-cells from patients with B-chronic lymphocytic leukemia (B-CLL) cells. We observed a large variability, both of percentage of Fas-positive cells and of intensity of Fas level. Fas triggering was inefficient in inducing apoptosis whatever the number of Fas-positive B-cells, the amount of Fas receptors. B-cells were also resistant to etoposide treatment, but able to undergo apoptosis after dexamethasone treatment. We suggest that the Fas apoptotic pathway is altered in B-CLL patients at the initial step(s) of apoptotic machinery.

Reference values for peripheral blood B-lymphocyte subpopulations: a basis for multiparametric immunophenotyping of abnormal lymphocytes

BACKGROUND AND OBJECTIVES

Immunophenotyping has become a useful tool for the differential diagnosis of chronic B-cell lymphoproliferative disorders. The aim of this work was to determine reference values of normal B-cell subpopulations.

MATERIAL AND METHODS

Blood samples from 38 healthy volunteers were analyzed by multidimensional flow cytometry, using a panel of directly conjugated antibodies. Results were expressed as percent of positive B cells and as median fluorescence intensity, an indirect assessment of the expression level.

RESULTS

CD20, CD22, CD24, CD40, CD79a, CD79b, FMC7, CD11a, CD18, CD44 were positive in the whole B cell population, whereas CD10, CD86, CD103, CD154 and FasL were almost absent from the B-lymphocyte population. 75% were IgD positive. The kappa/lambda ratio was 1.5. CD5, CD23, CD25, CD38, CD43, CD54, CD62L, CD80 and CD95 were positive in different B-cell subpopulations. The utility of all these markers in the differential diagnosis of chronic B-cell lymphoproliferative disorders is discussed.

CONCLUSION

In order to interpret a pathological immunophenotype, it is necessary to refer to quantitative and qualitative values of normal B-cell subpopulations.

Increased serum levels of soluble Fas in progressive B-CLL

Clinical progression of B-cell chronic lymphocytic leukemia (B-CLL) depends on survival and accumulation of leukemic cells, regulated in part by physical cell contact and soluble molecules. Here we have studied the Fas/FasL system in relation to clinical progression in B-CLL. Serum levels of soluble Fas (sFas) and FasL (sFasL) were determined by ELISA in 43 progressive and 40 non-progressive B-CLL patients and in 21 control individuals. Correlation between sFas serum levels and clinical progression, stage and survival were statistically analyzed. We found high levels of sFas in B-CLL sera correlated with disease progression (p<0.01). In addition, higher sFas levels were found in patients in stages II, III and IV in comparison to patients in stage 0 (p<0.05, p<0.01, p<0.03, respectively). Survival was significantly shorter for patients with > or =6 ng/ml sFas serum levels, although a multivariate analysis did not show sFas to be a significant independent prognostic factor. Fresh B-CLL cells showed only low levels of membrane expression, which were not correlated to sFas levels in serum. In vitro activation of B-CLL cells increased Fas expression, as reported earlier, and induced cells to release sFas into the supernatant. In conclusion, our results indicate that sFas in serum may be a useful parameter for the prediction of clinical progression in B-CLL.

In vivo gene transfer of CD40 ligand into colon cancer cells induces local production of cytokines and chemokines, tumor eradication and protective antitumor immunity

The interaction between CD40 ligand (CD40L, CD154) and its receptor CD40 on antigen-presenting cells, is essential for the initiation of cell-mediated and humoral immune responses. In this study, we investigated the antitumor effect of in vivo gene transfer of CD40L to tumor cells using an adenoviral vector (AdCMVmCD40L) in a murine CT-26 colon cancer model. We found that injection of AdCMVmCD40L caused tumor regression in a dose-dependent manner. A complete regression of tumor was observed in 81% of mice treated with 10(9) p.f.u. of AdCMVmCD40L. The antitumor effect induced by CD40L was mediated by CD8+ T cells and was associated with the generation of tumor-specific cytolytic T lymphocytes (CTL). Animals that eradicated the tumor were protected against tumor cell rechallenge, and both CD4+ and CD8+ T cells were involved in specific protective immunity. Treatment with AdCMVmCD40L in one tumor nodule also caused complete regression of established tumors at distant sites. The antitumor effect elicited by AdCMVmCD40L was associated with the intratumoral production of IL-12 and IFN-gamma and with an increased intratumoral expression of chemokines such as MIP- 1alpha, MIP-1beta, MIP-2, RANTES, and eotaxin. These data demonstrate that intratumoral injection of AdCMVmCD40L induces a powerful cascade of chemokines and cytokines in the tumor mass and stimulates an efficient antitumor immunity leading to regression of established colon cancer and protection against tumor cell rechallenge.

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

Follicular lymphoma (FL) and B-cell chronic lymphocytic leukemia (B-CLL) are paradigmatic examples of lymphoid malignancies in which the relevant biological mechanisms are alterations in the control of apoptosis rather than an exaggerated proliferation. This explains why low-grade B-cell neoplasms still fail to be cured with current approaches. It is becoming increasingly clear that the defective apoptosis of FL and B-CLL has to be ascribed not only to intrinsic defects of the neoplastic cells, but also to extrinsic factors that influence their behavior. Malignant B cells retain the capacity to respond to microenvironmental signals, but have devised a monothematic responsiveness. They have a specific sensitivity to anti-apoptotic signals that favor their survival, whereas they seem to have become insensitive to pro-apoptotic signals. Bystander, nontumoral cells play a fundamental (though not sufficient) role both in the onset and in the progression of these diseases. The survival of leukemic cells appears to be dependent on direct cell-cell contacts. The localization of malignant B cells in bone marrow or neoplastic follicles is not a passive adhesion phenomenon but a crucial step for their survival. Bidirectional malignant lymphocyte-nontumoral cell interactions may lead to the amplification of a microenvironment able to inhibit the apoptosis of neoplastic B cells. The pressure of antigenic selection and the role of the tumor necrosis factor receptor family through the functional survival signal provided by CD40 together with the crippled death signal exerted by CD95 are new prominent characters on the stage.

CD40 activation does not protect chronic lymphocytic leukemia B cells from apoptosis induced by cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTLs) can kill target cells by the granule/exocytosis pathway or the Fas-mediated apoptosis pathway. The sensitivity of chronic lymphocytic leukemia (CLL) B cells to CTL-mediated apoptosis before and after CD40 activation was examined. Resting or CD40-activated CLL cells were found to be equally sensitive to class I–restricted CTL-mediated killing. Despite expressing CD95, the CD40-activated CLL target cells were found to be resistant to apoptosis induced by CH11, an IgM CD95 monoclonal antibody (mAb). Consistent with this, inhibitors of caspases, which are involved in the Fas-induced apoptotic pathway (eg, N-carbobenzoxy-Val-Ala-Asp fluoromethyl ketone [z-VAD-fmk]), were unable to block destruction of CLL target cells by CTL. In addition, preincubation of the effector T cells with the anti-Fas ligand mAb NOK-2 failed to inhibit their subsequent ability to kill CLL target cells. On the other hand, CTL activity was blocked by inhibitors of the granule exocytosis pathway such as ethylene-glyco-tetra-acetic acid or concanamycin A. These results indicate that CD40 activation does not impair the sensitivity of CLL cells to Fas-independent CTL-mediated apoptosis.

CD40 activation does not protect chronic lymphocytic leukemia B cells from apoptosis induced by cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTLs) can kill target cells by the granule/exocytosis pathway or the Fas-mediated apoptosis pathway. The sensitivity of chronic lymphocytic leukemia (CLL) B cells to CTL-mediated apoptosis before and after CD40 activation was examined. Resting or CD40-activated CLL cells were found to be equally sensitive to class I–restricted CTL-mediated killing. Despite expressing CD95, the CD40-activated CLL target cells were found to be resistant to apoptosis induced by CH11, an IgM CD95 monoclonal antibody (mAb). Consistent with this, inhibitors of caspases, which are involved in the Fas-induced apoptotic pathway (eg, N-carbobenzoxy-Val-Ala-Asp fluoromethyl ketone [z-VAD-fmk]), were unable to block destruction of CLL target cells by CTL. In addition, preincubation of the effector T cells with the anti-Fas ligand mAb NOK-2 failed to inhibit their subsequent ability to kill CLL target cells. On the other hand, CTL activity was blocked by inhibitors of the granule exocytosis pathway such as ethylene-glyco-tetra-acetic acid or concanamycin A. These results indicate that CD40 activation does not impair the sensitivity of CLL cells to Fas-independent CTL-mediated apoptosis.

CD40 ligand in CLL pathogenesis and therapy

Advances in immunology during the past three decades have facilitated our understanding of the biology of specific lymphoid neoplasms including chronic lymphocytic leukemia (CLL). Investigations in our laboratory have focused on CD40, a critical regulator of B cell survival and differentiation, and its ligand, CD154 (CD40L). We have established that in some cases of CLL the malignant cells express both CD40 and CD154, and on the basis of those observations, proposed a model for CLL tumor growth due to CD40-CD154 interactions within and among the malignant cells, and for the occurrence of autoimmune syndromes in some cases of CLL. Here, we include an update on our studies regarding CD154 expression in CLL, a review of the data regarding the consequences of CD40 engagement in CLL B cells, and a discussion of these findings in the context of the complex and potentially opposite outcomes that have been reported for CD40-mediated signals in CLL. The implications for therapy, such as by impedance to CD154-CD40 interaction using antibody to CD154, or by selective inhibitors of NF-kappa B, are considered.

Differences in IgE isotype switching induced by anti-CD40 monoclonal antibody and cytokines among subtypes of chronic B lymphoid leukemias

OBJECTIVE

Immunologic differences among the chronic B lymphoid leukemias defined by the French-American-British (FAB) classification were evaluated with respect to IgE isotype switching induced by anti-CD40 monoclonal antibody (mAb) and cytokines.

MATERIALS AND METHODS

We immunocytochemically studied IgE isotype switching of leukemic B cells from 25 cases and three cell lines established from the leukemias after stimulation with anti-CD40 mAb, plus each of the following cytokines: interleukin 2 (IL-2); IL-4; IL-10; tumor necrosis factor alpha (TNF-alpha); and transforming growth factor beta (TGF-beta). Also, genomic Cepsilon and Cepsilon transcripts were analyzed by polymerase chain reaction and reverse transcriptase polymerase chain reaction.

RESULTS

Leukemic cells from hairy cell leukemia variant and its cell line, with deletion of the Cepsilon gene, did not undergo IgE isotype switching in response to any of the stimuli. In contrast, a cell line (FH-5) established from chronic lymphocytic leukemia cells, bearing the Cepsilon gene, underwent the highest level of IgE isotype switching on stimulation with anti-CD40 mAb and IL-4. This response was correlated with the production of Cepsilon transcripts. IL-4, IL-10, and TNF-alpha induced higher levels of IgE isotype switching than the others. No IgE isotype switching was observed in any of the non-Hodgkin's lymphomas examined, except mantle cell lymphoma and lymphoplasmacytic lymphoma. Percentages of CD40(+) cells in five cases with follicular lymphoma were significantly lower than the other leukemias.

CONCLUSIONS

IgE isotype switching induced by anti-CD40 mAb with cytokines other than IL-4 was first demonstrated, whereas none of the non-Hodgkin's lymphomas except mantle cell lymphoma and lymphoplasmacytic lymphoma showed IgE isotype switching in response to any of the stimuli. Cells of follicular lymphoma were suggested to be different from cells of the other leukemias.

Biology of chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (CLL) lies at the cross-roads of hematology, immunology and oncology for at least three major reasons: (a) it is the prototype of human malignancies that primarily involve defects in the induction of apoptosis; (b) CLL patients develop a severe immunodeficiency with progressive hypogammaglobulinemia; and (c) they have a high prevalence of autoimmune phenomena. Recent advances in the biology of the malignant cell in CLL lead to a scenario comprised of two basic elements: first, CLL cells are optimally organized to survive in their niches because their ability to undergo apoptosis is severely hampered; second, they have a microenvironment-dependence that promotes their extended survival, a situation that arises most probably through direct cell-to-cell contacts. In addition, CLL cells themselves are the major accessory cells in CLL, but are inefficient antigen-presenting cells. This latter defect may provide a clue to reinterpret the events of immunodeficiency and autoimmunity.

Accessory cells, cytokine loops and cell-to-cell interactions in chronic lymphocytic leukemia

In addition to the extensive work that has been conducted in order to understand better the biological features of the leukemic population in B-cell chronic lymphocytic leukemia (CLL), over the years considerable interest has been directed towards other related studies that may have important implications for the accumulation of the leukemic clone and for the immunoparesis typical of this disease. In the present review article, we discuss some of these areas of investigation and, in particular, we focus on: (1) the multiple abnormalities recorded within the T and cytotoxic compartment of patients with CLL; (2) cytokine loops occurring in this disease, with particular emphasis on the cytokines that appear to play a more critical role; and (3) the cell-to-cell cross talk that may be actively operational in CLL. These findings will be discussed in relation with the possible implications that each of them have in the expansion and clinical behavior of a disease that is increasingly proving its heterogeneity.

An oral CD40 ligand gene therapy against lymphoma using attenuated Salmonella typhimurium

CD40 ligand (CD40L) has a great potential as a novel treatment for B-cell lymphoma (BCL). It has previously been demonstrated that a nonvirulent strain of Salmonella typhimurium mutant (ST) can be used not only as a vehicle in oral genetic immunization via the intestinal mucosa, but also as an enhancer of interferon γ– and tumor necrosis factor –mediated immunity. After confirming that human CD40L can up-regulate expression of Fas, B7-1, and B7-2 molecules on murine BCL cells in vitro, we transfected the human CD40L gene intoS typhimurium mutant (ST40L), which was administrated orally to determine whether it was able to prevent the growth of BCL in mice. Expression of human CD40L was confirmed immunohistochemically with protein being detected in the Peyer's patches of mice immunized with ST40L. Moreover, human soluble CD40L had been detectable until 7 to 8 weeks after oral administration of ST40L. Although ST alone exhibited some protective effects, ST40L demonstrated a significantly greater protection against the development of CD40 positive BCL compared with the control. In the surviving mice that had been treated with ST40L, a small and hard nodule was formed at the injection site, which was found to be composed of infiltrating lymphocytes expressing Fas ligand. These results have the potential to be a simple, effective, and above all, safe immune-gene therapy against BCL.

CD40 ligand-induced apoptosis is Fas-independent in human multiple myeloma cells

We and others previously demonstrated that human multiple myeloma (MM) cells express CD40 and have an active CD40-growth regulatory pathway. This study characterizes the growth outcome of soluble (gp39) or membrane-bound recombinant human CD40-ligand (rCD40L) and its relationship with Fas-dependent apoptosis. Contrary to the moderate growth-stimulatory effect of the CD40-MAb G28.5, gp39 inhibited 3H-thymidine uptake of the plasma dyscrasia lines ARH-77, U266, and HS-Sultan in a dose-dependent fashion by up to 82%. By comparison, RPMI 8226 cells were resistant to CD40L-growth modulation, which may be attributable to a single base substitution (TCA-->TTA, serine-->leucine) at the 3rd cysteine-rich extramembrane region of CD40. Gp39 similarly reduced myeloma clonogenic colony (MCC) formation in patient primary bone marrow cultures by 50% (40-76%; n=6). Studies using transfectant L cells that constitutively expressed CD40L showed that membrane-bound CD40L inhibited the growth of ARH-77, U266, and HS-Sultan cells (66%, 63%, and 32%, respectively), whereas untransfected L cells did not. Growth inhibition by gp39 or CD40L+ L cells was neutralized by coincubation with the CD40L antibodies 5c8 or LL48. CD40L-treatment increased apoptotic activity of MM cells, as defined by oligonucleosomal DNA fragmentation and an increased binding to annexin V (16-28%). All three untreated CD40-responsive MM lines expressed the Fas/Apo-1/CD95 antigen (65-92% CD95+). However, only ARH-77 cells responded to the growth inhibitory effect of the CD95-agonistic antibody CH-11. CD95 expression was not affected significantly by gp39 treatment, and growth inhibition by CH-11 was additive to gp39 (from 42% to 64% decrease in 3H-thmidine uptake). Conversely, the CD95 antagonist antibody ZB4 reversed the Fas-dependent growth inhibitory process but did not significantly alter gp39-mediated growth outcome. Gp39 treatment lowered the expression of TNFR-associated factors TRAF4 and TRAF6 by 38% and 32%, respectively, whereas detectable levels of TRAF1,2,3, and 5 levels remained unchanged. Our observations indicate that the CD40L-binding inhibits human MM cell growth and increases its apoptotic activity. This growth inhibitory effect corresponds to lower levels of cytoplasmic TRAF signaling elements, and appears independent of the Fas-signaling pathway. CD40 receptor mutation may lead to unresponsiveness to CD40 growth modulation in multiple myeloma cells.

Immunostimulatory CpG-oligonucleotides cause proliferation, cytokine production, and an immunogenic phenotype in chronic lymphocytic leukemia B cells

Bacterial DNA and synthetic CpG-oligodeoxynucleotides (ODNs) derived thereof have attracted attention because they activate cells of the immune system in a sequence-dependent manner. Here we investigated the potential of CpG-ODNs to cause proliferation, cytokine production, and regulation of surface molecules in human B-chronic lymphocytic leukemia (CLL) cells. CpG-ODN induced proliferation in both B-CLL cells and normal B cells; however, only B-CLL cells increased proliferative responses when CpG-ODN was added to co-cultures of CD40-ligand transfected mouse fibroblasts (CD40LF) and B cells. Production of interleukin-6 and tumor necrosis factor  was detectable at borderline levels, using CpG-ODN as the only stimulus. In contrast, when CpG-ODN was added to co-cultures of B cells and CD40LF, a strong increase in cytokine production occurred in B-CLL cells as well as in normal B cells. The surface molecules CD40, CD58, CD80, CD86, CD54, and MHC class I molecules were up-regulated in B-CLL cells, whereas CD95 expression was not influenced by CpG-ODN stimulation. The same pattern of surface molecule regulation was observed in normal B cells, but up-regulation of CD40 was significantly stronger in B-CLL cells. Costimulation with CpG-ODN and CD40LF resulted in further up-regulation of CD58, CD80, CD86, and MHC class I molecules. In contrast, CD95 expression induced by CD40-ligation was inhibited by CpG-ODN. CpG-ODN activated B-CLL cells acquired a strong stimulatory capacity toward T cells in allogeneic mixed lymphocyte reaction. This effect was completely inhibited by a combination of anti-CD80 and anti-CD86 monoclonal antibody. Taken together, these findings suggest the possible use of CpG-ODN for immunotherapeutic strategies in patients with B-CLL.

Sequential cis-platinum and fludarabine with or without arabinosyl cytosine in patients failing prior fludarabine therapy for chronic lymphocytic leukemia: a phase II study

Patients with chronic lymphocytic leukemia (CLL) who fail fludarabine (Fluda) therapy have a poor response to subsequent salvage regimens and a poor prognosis. This study was undertaken to determine the efficacy and toxicity of a cis-platinum, (cis-p)fluda and arabinosyl cytosine (ara-C) combination in patients who were refractory to fluda or had relapsed following prior fluda therapy for CLL. Forty-one patients who had progressive CLL were treated on study. Eleven patients (27%) were sensitive to fluda and thirty (73%) refractory prior to study entry. Therapy consisted of cis-p 100 mg/m2 continuous intravenous (i.v.) infusion over 4 days, fluda 30 mg/m2 i.v. over 15 minutes on Days 3 and 4 either given alone (PF) or with ara-C 500 mg/m2 i.v. over 1 hour on Day 4 (PFA). The median number of PF or PFA courses received was two. No patient achieved a complete response. Eight patients (19%) achieved a partial response (PR), 28 were taken off study with progressive or refractory disease and 5 had induction deaths. The overall median survival was 6 months, 15 months in responding patients, and 4 months in non-responding patients. Rai stage I-II patients had a median survival of 7 months and stage III-IV patients had a median survival of 3 months. Major toxicities (myelosuppression, sepsis, renal failure and tumor lysis syndrome) were frequent. In conclusion, it can be said that the PF and PFA regimens have equivalent modest activity in patients with progressive CLL following prior fluda therapy, predominantly among patients whose disease was sensitive to fluda at last prior exposure. Ara-C did not add to the activity of the cis-p/fluda combination in this study group.

Apoptosis regulating proteins as targets of therapy for haematological malignancies

Most chemotherapeutic agents used in the treatment of haematological malignancies cause cell death by inducing apoptosis through undefined means. The discovery of the proteins involved in apoptosis and the description of apoptotic pathways suggest new potential targets for therapeutic intervention. Both 'intrinsic' and 'extrinsic' pathways can be activated separately, but activation of caspases appears central to most apoptotic pathways. Novel approaches attempt to induce apoptosis by directly targeting a portion of an apoptotic pathway. Agents that trigger signalling of Fas or tumour necrosis factor- (TNF-) related apoptosis inducing ligand (TRAIL) receptor seek to induce the extrinsic pathway at the cell surface. The BCL-2 family of proteins seems central to the regulation of those apoptotic pathways that involve mitochondrial sequestration or the release of cytochrome c, with subsequent activation of Apaf-1, caspase-9 and caspase-3. The activity of this family may depend upon both the phosphorylation state of different members and the relative level of pro- and anti-apoptotic members. New agents such as the staurosporine analogue UCN-01 and bryostatin are thought to affect apoptosis induction by altering BCL-2 phosphorylation. Others, such as BCL-2 antisense and ATRA attempt to modulate the protein levels to promote apoptosis. Direct activation of caspase-3 is a probable target, but as yet no agent with this direct function is in trial. Clinical trials of several agents have been completed or are underway. It is likely that agents that target particular points in apoptosis pathways will have antileukaemia/lymphoma activity, however, the optimal utilisation may involve combination with other more conventional agents that also activate apoptosis.

Apoptosis, proliferation and NF-kappaB activation induced by agonistic Fas antibodies in the human myeloma cell line OH-2: amplification of Fas-mediated apoptosis by tumor necrosis factor

Tumor necrosis factor (TNF) is known to be a growth factor for several myeloma cell lines. However, in the presence of the agonistic Fas antibody CH 11, TNF enhanced the level of apoptosis in cultures of the human myeloma cell line OH-2. This pro-apoptotic effect of TNF was explained at least in part by a TNF-mediated enhancement of Fas expression. TNF induces proliferation of OH-2 by activating nuclear transcription factor kappa-B (NF-kappaB). The proliferative effect of TNF on OH-2 cells was abrogated by CH11, but this was not caused by an inhibition of the translocation of NF-kappaB. On the contrary, CH11 could by itself activate NF-kappaB in OH-2 cells, and in the presence of an inhibitor of caspase-1 induce proliferation of the cells. The relationship between stimulation of TNF receptors and Fas and the level of NF-kappaB activation was also examined in three other myeloma cell lines. RPMI-8226 cells showed NF-kappaB activation by TNF, but contrary to OH-2, not by CH11. Unstimulated U-266 and JJN-3 cells had high levels of activated NF-kappaB. This shows that NFkappa-B is either constitutively activated or inducible in myeloma cells. Modulation of Fas expression and inhibition of NF-kappaB activation can potentially be of therapeutic importance in multiple myeloma.

CD47 ligation induces caspase-independent cell death in chronic lymphocytic leukemia

Thrombospondin forms a 'molecular bridge' between phagocytic and apoptotic cells through interaction with alphavbeta3/CD36. We report here that engagement of CD47, a newly described thrombospondin receptor, by immobilized monoclonal antibody against CD47 or by thrombospondin induced in all B-cell chronic lymphocytic leukemia clones the cytoplasmic features of apoptosis (cell shrinkage, decrease in mitochondrial transmembrane potential and phosphatidylserine externalization) without the nuclear features (chromatin condensation, appearance of single-stranded DNA, DNA fragmentation and cleavage of poly ADP-ribose polymerase). These cytoplasmic events of apoptosis were not prevented by the addition of caspase inhibitor z-VAD-fmk, or by the presence of survival factors (such as interleukin-4 and gamma interferon) or cell activation. Morphological studies confirmed the integrity of the nucleus and showed swelling of the mitochondria. This caspase-independent death pathway may be relevant to the development of alternate therapeutic strategies in chronic lymphocytic leukemia, which remains an incurable disease.

Ligation of CD28 In Vivo Induces CD40 Ligand Expression and Promotes B Cell Survival

Functional activation of T cells requires ligation of Ag receptors with specific peptides presented by MHC molecules on APCs concurrent with appropriate contacts of cell surface accessory molecules. Among these accessory molecules, interactions between CD28/CTLA-4 with B7 family members (CD80 and CD86) and CD40 with CD40 ligand (CD40L) play a decisive role in regulating the progression of balanced immune responses. However, most information regarding the role of accessory molecules in immune responses has been derived in the context of signals from the TCRs. Little understanding has been achieved regarding the consequence of ligation of costimulation molecules in absence of signals from the TCR. By employing an in vivo murine system, we show, herein, that ligation of CD28 alone with anti-CD28 Abs leads to a dramatic enlargement of the peripheral lymphoid organs characterized primarily by the expansion of B cells. B cells from anti-CD28-treated mice are resistant to spontaneous and anti-IgM-induced apoptosis. These cells are also unsusceptible to FasL-mediated apoptosis. Interestingly, this in vivo effect of CD28 on B cells is largely mediated by inducing the expression of CD40L, since coadministration of a blocking Ab against CD40L inhibited CD28-mediated B cell survival and expansion. Therefore, CD28-mediated expression of CD40L may play an important role in the regulation of lymphocyte homeostasis.

fas-mediated lysis of chronic lymphocytic leukaemia cells: role of type I versus type II cytokines and autologous fasL-expressing T cells

Given the known role of the fas cytolytic pathway in B-cell regulation, we evaluated whether fas-fasL interactions might induce chronic lymphocytic leukaemia (CLL) cell death. De novo CLL cells expressed a low level of surface fas, and were not lysed by fasL-bearing cells. CLL cells cultured in media containing the type I cytokines interleukin (IL)-12 or interferon (IFN)-alpha had increased fas expression, and were readily lysed by fasL-bearing cells. In contrast, the type II cytokine IL-4 did not increase CLL cell fas, and abrogated type I cytokine-induced fas up-regulation. With prolonged culture, IL-4 exposed CLL cells expressed an intermediate level of fas; however, such CLL cells were resistant to fas-mediated lysis. These results indicate that IL-4 inhibits fas-mediated killing of CLL cells at the level of both fas receptor expression and post-receptor events. Additionally, we have defined in vitro culture conditions which generate fasL-bearing T cells from CLL patients; such T cells efficiently mediated fas-based lysis of autologous fas-positive CLL cells. We therefore conclude that type I and type II cytokines differentially regulate the fas pathway in CLL cells, and that a combination of type I cytokines and fasL-expressing T cells may represent a new approach to the immunotherapy of CLL.

Expression of functional CD40 in human hepatocellular carcinoma

CD40, a member of the tumor necrosis factor receptor (TNFR) family, plays a crucial role in the survival, proliferation, and differentiation in B cells. However, the expression of CD40 other than in B cells has not been well studied. Therefore, we investigated the expression and function of CD40 in hepatocellular carcinomas (HCCs). Expression of CD40 mRNA in 6 established HCC cell lines was analyzed by reverse-transcription polymerase chain reaction (RT-PCR) and CD40 expression on cell surface was examined by flow cytometrical analysis. We also examined the expression of CD40 in human HCC tissues (45 cases) and nontumor liver tissues (30 cases) by immunohistochemistry. To examine the function of CD40 in HCC cells, we investigated the effect of CD40 signaling on anti-Fas antibody and TNF-alpha-induced apoptosis in HepG2 cells. In addition, intracellular levels of cysteine protease P32 (CPP32) protein in HepG2 cells were also determined by Western blotting. We have shown that 6 HCC cell lines constitutively expressed CD40 mRNA and membrane-bound CD40 antigen, which was slightly up-regulated by interferon gamma (IFN-gamma). In addition, 60% of human HCC tissues demonstrated positive staining for CD40, whereas nontumor tissues showed little detectable staining. In HepG2 cells, CD40 stimulation does not affect cell viability, but significantly inhibited Fas and TNFR-mediated apoptosis in a dose-dependent manner by blocking the activation of CPP32. From these results, we conclude that CD40 expression in HCCs plays an important role in tumor biology, especially the resistance against Fas and TNFR-mediated apoptosis.

FADD expression and caspase activation in B-cell lymphomas resistant to Fas-mediated apoptosis

We have previously shown that malignant B cells from non-Hodgkin's lymphomas (NHL) are resistant to Fas-mediated apoptosis. To determine the mechanisms underlying this resistance, we analysed by Western blotting the expression of several apoptotic regulators, caspase 3, caspase 8, FADD and poly(ADP-ribose) polymerase (PARP) in fresh lymphoma cells, isolated from 16 B-NHL biopsy samples of different histological subtypes, and displaying variable levels of Fas expression. The profiles of expression of these apoptotic regulators were monitored in cell lysates at different times following Fas with or without CD40 stimulation. Expression of FADD and of the uncleaved forms of PARP, caspase 3 and caspase 8 were detected in all untreated NHL samples. Low levels of PARP cleavage were noted in three untreated samples. Fas stimulation alone induced neither significant apoptosis nor significant changes in the expression profiles of FADD, caspases 3 and 8 and PARP in the 16 samples, except for variations in FADD and caspase 8 expression levels in a minority of samples. Fas/CD40 co-stimulation induced apoptosis and cleavage of caspase 3, caspase 8 and PARP in the five NHLs tested; expression of FADD was not modified. Our results showed (1) that induction of apoptosis in B-NHLs by Fas/CD40 co-stimulation used the same caspase executioner machinery as the normal Fas pathway, and (2) that NHL cells which resisted Fas-mediated apoptosis displayed no defect in either expression or functionality of caspases 3 and 8, nor in FADD expression. The dysfunction underlying NHL resistance to apoptosis must therefore lie upstream of caspase 8, or could alternatively be influenced by anti-apoptotic regulators of the Bcl-2 family.

A novel B-CLL specific nuclear protein (p44/46)

Our previous results indicated some diversities in electrophoretic patterns of proteins from different cellular fractions, i.e. nuclear, mitochondrial, microsomal and cytosolic isolated from mononuclear cells from the peripheral blood of B cell chronic lymphocytic leukemia (B-CLL) patients and healthy donors. Major differences were observed in electrophoretic banding of nuclear proteins from normal and transformed cells, especially in molecular mass region of 37 52 kDa. Electrophoretically-specific nuclear protein with molecular mass of 44/46 kDa of cells originating from B-CLL patients was used for raising polyclonal antiserum. As it was determined by Western blot technique (with alkaline phosphatase) obtained antiserum recognized 44/46 kDa antigen of nuclear fraction from B-CLL and acute lymphoblastic leukemia (ALL) cells, but not from normal ones. Our preliminary data were revealed that this antiserum shows no crossreactivity with leukemic nuclear proteins of patients with T cell chronic lymphocytic leukemia (T-CLL) and neither with nuclear polypeptides from either normal or cancerous (adenocarcinoma) stomach and colon mucosa. Immunological analysis was shown that higher expression of this particular antigen seems to correlate with progression of B-CLL.

[Mechanisms of tumor escape from immunologic response]

INTRODUCTION

The rationale for immune control of cancer is now better defined via the immunovirology of transforming viruses, definition of human tumor antigens recognized by T-lymphocytes, and cellular and humoral components of the anticancer response. Nonetheless tumors can escape from immune surveillance. To better define immunomodulation strategies, we describe some of the various strategies developed by transformed cells to evade the immune response.

CURRENT KNOWLEDGE AND KEY POINTS

Both the lack of specific tumor antigen and down-regulation of major histocompatibility complex (MHC) molecule expression hamper recognition of neoplastic cells by T-lymphocytes. In presence of defective expression of ligands for the T-cell co-stimulatory receptors, tumor recognition may lead to the development of tolerance instead of specific cytotoxic activity. Tumor cell counter-attack against effector T-cells has also been described, using either inhibitory cytokines (IL-10), apoptosis induction (via Fas signalling), functional inactivation (disruption of normal CD40/CD40 ligand interactions), or induction of anergy.

FUTURE PROSPECTS AND PROJECTS

Despite the many different mechanisms of tumor escape, the immune system has developed efficient counter-attacks. For instance, natural killer cells may detect and destroy tumor cells that lack class 1 MHC molecules and thus escape from specific T-lymphocyte cytolysis. Moreover, immunogenicity can be restored, at least in vitro, by different means such as tumor cell stimulation by cytokines or CD40, suggesting that therapeutic strategies will soon be developed in order to stimulate an efficient antitumoral immune response.

IFN-alpha stimulates proliferation and cytokine secretion of CD40-stimulated B cell chronic lymphocytic leukemia cells in vitro

Interferon (IFN)-alpha has a therapeutic effect in several B cell malignancies, including low-grade non-Hodgkin's lymphoma (NHL), multiple myeloma, and hairy cell leukemia, whereas its efficacy in the treatment of B cell chronic lymphocytic leukemia (B-CLL) is rather limited. In the present study, we investigated the effect of IFN-alpha on the biologic functions of B-CLL cells, which were stimulated by cross-linking of the CD40 antigen. In cell samples from 16 B-CLL patients, the addition of IFN-alpha to CD40-stimulated purified B-CLL cells caused a significant increase in [3H]thymidine uptake (p < 0.003). In B-CLL cells maximally activated by CD40 cross-linking and interleukin-2 (IL-2)/IL-10, proliferation was not further enhanced or inhibited by IFN-alpha. In contrast, proliferation of normal tonsillar B cells stimulated by the combination CD40/IL-2/IL-10 was significantly inhibited by IFN-alpha. Because B-CLL activation might be enhanced by induction of the autocrine growth factor tumor necrosis factor-alpha (TNF-alpha), we investigated the effect of IFN-alpha on the secretion of B cell tropic cytokines. In fact, IFN-alpha significantly stimulated the secretion of IL-6 and TNF-alpha in CD40-activated B-CLL cells (p < 0.01). Although exogenous addition of TNF-alpha did not influence activation of CD40-stimulated B-CLL cells, neutralization of TNF-alpha by polyclonal antibodies led to a complete inhibition of CD40-mediated proliferation of B-CLL cells, suggesting that enhanced proliferation and increased cytokine production by CD40-activated B-CLL cells are independent IFN-alpha-mediated events. The studies presented here provide evidence that IFN-alpha mediates costimulatory signals in the context of T cell-mediated B-CLL cell activation.

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.

Downregulation of the CD95 receptor and defect CD40-mediated signal transduction in B-chronic lymphocytic leukemia cells

Cross-linking of the CD40 receptors has been shown to induce protein tyrosine kinases (PTK) phosphorylation and prevent apoptosis in Bcl-2 negative germinal center B cells. The expression of CD40 on B chronic lymphocytic leukemia (B-CLL) cells was found to be similar to that of normal B cells. Activation of normal B cells with soluble anti-CD40 monoclonal antibody (mAb) induced tyrosine phosphorylation, prolonged survival and prevented apoptosis. However, activation of CD40 on B-CLL cells using soluble anti-CD40 mAb does not influence survival or apoptosis. Normal B cells entered apoptosis when cultured in the presence of soluble anti-CD95 mAb. This process was independent of PTK activity. On B-CLL cells, the CD95 molecules were downregulated and a transient PTK signal was observed when cross-linking of the receptor by soluble anti-CD95 mAb occurred. Interestingly, B-CLL cells did not enter apoptosis in the presence of anti-CD95 mAb. Our study indicates that survival signals mediated through the CD40 molecule and death signals mediated through the CD95 molecule used different intracellular pathways in control donor B cells. In contrast, B-CLL cells do not respond to these signals. The leukemic B cells showed a defective CD40-mediated signal transduction and downregulated CD95 receptor expression. As a consequence, no apoptosis could be induced in B-CLL cells by a soluble anti-CD95 mAb. The abnormalities of these receptors may contribute to the long-lived status of B-CLL cells.

Sensitivity to Fas-mediated apoptosis is null or weak in B-cell non-Hodgkin's lymphomas and is moderately increased by CD40 ligation

The Fas receptor (APO-1/CD95) is capable of inducing apoptosis of lymphoid cells and is expressed in some non-Hodgkin's lymphomas (NHLs). Fas expression is up-regulated at the surface of normal B cells upon triggering of the CD40 receptor. In this report, we investigated the sensitivity of NHLs to Fas-mediated apoptosis induced by anti-Fas monoclonal antibodies (MAbs) and its possible modulation by CD40 ligation in 18 NHL biopsy samples of various histological subtypes. Flow cytometric analysis showed that the fraction of Fas-expressing lymphoma cells was highly variable from sample to sample (from 1% to 93%, mean value 46%). The frequency of apoptotic cells was not significantly increased upon treatment with an anti-Fas MAb compared with control MAb in the 18 NHL cases analysed. The sensitivity of lymphoma cells to Fas-mediated apoptosis was correlated neither with the histological subtypes nor with the level of Fas expression. Activation of neoplastic B cells by CD40 ligation resulted in significant increases in Fas expression and Fas-induced apoptosis among the five B-NHL cases tested. The overall increase in apoptotic rates was moderate and remained lower in tumour samples than in control CD40-activated normal tonsil B cells. Altogether, our results indicate that the sensitivity to Fas-induced apoptosis is null or weak in NHL cells, irrespective of their histological subtype, and that it can be increased to a moderate and variable degree by CD40 ligation on neoplastic B cells. This may be an impediment to the development of Fas-based therapies for NHLs.

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.