A role for tumour necrosis factor-alpha, Fas and Fas-Ligand in marrow failure associated with myelodysplastic syndrome

Treatment of myelodysplastic syndrome with agents interfering with inhibitory cytokines

Results of these trials provide evidence for biological activity and some clinical efficacy of agents potentially blocking inhibitory cytokines in patients with MDS. However, given the limited responses, it appears that factors additional to TNFalpha inhibitory activity contribute to the development of cytopenias in these patients. Further studies are warranted using anti-TNFalpha/anti-inhibitory cytokine approaches, either alone or in combination with other agents, capable of abrogating the effects of additional inhibitory mechanisms in MDS.

Stem cell factor regulation of Fas-mediated apoptosis of human erythroid precursor cells

Multiple cytokines regulate the development of erythrocytes. Increasing attention has been directed to the possible role of Fas and its cognate ligand (Fas-L), a subject of wide interest. Documentation of in vitro data supports the role of Fas and Fas-L in erythropoiesis. Several laboratories, including ours, investigated the opposing actions of erythropoietin (EPO) and stem cell factor (SCF) on Fas-mediated cell death of the erythroid cells. Only circumstantial in vivo evidence has accumulated concerning the issue. There are several reports suggesting that Fas-mediated cell death may have a role in some pathological conditions. Results of the accumulating findings and possible implications in clinical hematology are summarized in this review.

Self-renewal of multipotent long-term repopulating hematopoietic stem cells is negatively regulated by Fas and tumor necrosis factor receptor activation

Multipotent self-renewing hematopoietic stem cells (HSCs) are responsible for reconstitution of all blood cell lineages. Whereas growth stimulatory cytokines have been demonstrated to promote HSC self-renewal, the potential role of negative regulators remains elusive. Receptors for tumor necrosis factor (TNF) and Fas ligand have been implicated as regulators of steady-state hematopoiesis, and if overexpressed mediate bone marrow failure. However, it has been proposed that hematopoietic progenitors rather than stem cells might be targeted by Fas activation. Here, murine Lin(-)Sca1(+)c-kit(+) stem cells revealed little or no constitutive expression of Fas and failed to respond to an agonistic anti-Fas antibody. However, if induced to undergo self-renewal in the presence of TNF-alpha, the entire short and long-term repopulating HSC pool acquired Fas expression at high levels and concomitant activation of Fas suppressed in vitro growth of Lin(-)Sca1(+)c-kit(+) cells cultured at the single cell level. Moreover, Lin(-)Sca1(+)c-kit(+) stem cells undergoing self-renewal divisions in vitro were severely and irreversibly compromised in their short- and long-term multilineage reconstituting ability if activated by TNF-alpha or through Fas, providing the first evidence for negative regulators of HSC self-renewal.

Granulocyte colony-stimulating factor inhibits Fas-triggered apoptosis in bone marrow cells isolated from patients with refractory anemia with ringed sideroblasts

Treatment with granulocyte colony-stimulating factor (G-CSF) plus erythropoietin may synergistically improve hemoglobin levels and reduce bone marrow apoptosis in patients with refractory anemia with ringed sideroblasts (RARS). Fas-induced caspase activity is increased in RARS bone marrow cells. We showed that G-CSF significantly reduced Fas-mediated caspase-8 and caspase-3-like activity and the degree of nuclear apoptotic changes in bone marrow from nine RARS patients. A decrease in mitochondrial membrane potential and an increase in intracellular reactive oxygen species occurred in Fas-treated cells, but became significant only 24 h after changes in caspase activity and decrease in proliferation. G-CSF also reduced the magnitude of these late apoptotic changes. In CD34-selected normal cells, G-CSF induced myeloid colony growth, and an overall small decrease in the number of erythroid colonies. By contrast, G-CSF induced a 33-263% increase of erythroid colony formation in CD34+ cells from four of five RARS patients with severely reduced erythroid growth, while the normal or slightly reduced erythroid growth of three other patients was not influenced by G-CSF. This study suggests that G-CSF may reduce the pathologically increased caspase activity and concomitant apoptotic changes, and promote erythroid growth and differentiation of stem cells from RARS patients. Our data support the clinical benefit of G-CSF in this subgroup of myelodysplastic syndromes.

The role of apoptosis in the pathogenesis of the myelodysplastic syndromes

The paradoxical occurrence of peripheral cytopenias despite a normo/hypercellular marrow in myelodysplastic syndromes (MDS) has been attributed to excessive intramedullary hematopoietic cell apoptosis. It has also been postulated that abrogation of programmed cell death (PCD) may underlie MDS transformation to acute myeloid leukemia (AML). Despite overwhelming evidence for a role of aberrant apoptosis in myelodysplasia, the molecular mechanisms responsible for such changes have not been elucidated. This paper summarizes current evidence implicating a role for altered PCD in MDS and outlines potential cellular mechanisms whereby hematopoietic progenitor cell apoptosis may be dysregulated.

Shwachman-Diamond syndrome marrow cells show abnormally increased apoptosis mediated through the Fas pathway

Shwachman-Diamond syndrome (SDS) is an inherited bone marrow disorder with varying cytopenias and a strong predilection to myelodysplastic syndrome (MDS) and acute myeloid leukemia. Previously, it was found that the percentage of CD34(+) cells in bone marrow and the in vitro colony formation from CD34(+) cells of patients with SDS were markedly reduced. For these reasons, and because apoptosis is central in the pathogenesis of bone marrow dysfunction in MDS, this study was initiated to delineate the role of apoptosis in the pathogenesis of the marrow failure. Eleven children with SDS were studied. Compared to normal controls, patients' marrow mononuclear cells plated in clonogenic cultures showed a significantly higher tendency to undergo apoptosis. The defect in SDS was found in patients with and without MDS. Patients showed a more prominent decrease in colony formation and increased apoptosis after preincubation with activating anti-Fas antibody. Fas expression on marrow cells from patients was significantly higher than from normal controls. The difference between patients and controls for Fas expression was also significant for the following cell fraction subpopulations: CD34(-)/CD38(-), CD34(-)/CD38(+), and CD34(+). In conclusion, SDS hematopoietic progenitors are intrinsically flawed and have faulty proliferative properties and increased apoptosis. Bone marrow failure in SDS appears mediated by increased apoptosis as the central pathogenetic mechanism. This increased propensity for apoptosis is linked to increased expression of the Fas antigen and to hyperactivation of the Fas signaling pathway.

Mitochondrial disruption and limited apoptosis of erythroblasts are associated with high risk myelodysplasia. An ultrastructural analysis

AIMS

To investigate the ultrastructural characteristics of erythroblasts in myelodysplasia (MDS) which might be of additional importance in understanding its pathogenesis.

METHODS AND RESULTS

22 patients were classified according to FAB (French-American-British classification), IPSS (international prognostic score system), cytogenetic risk factors and transfusion dependency. Using electron microscopy, in 77% of the cases, nuclear abnormalities consisting of disrupted membranes and cystic/dilated perinuclear spaces were noted. In a limited number of patients (n=7), a low percentage of apoptosis in the erythroid lineage (mean 3.1+/-1.6%; median 3%: range 1-6) (normal controls: <0.5%) could be noted, primarily in mature erythroblasts and significantly associated with spongiform nuclear features. In all patients extensive cytoplasmic vacuolization and myelin figures in erythroblasts were demonstrated. In 55% of the cases, enlarged and abnormal mitochondria were observed, significantly associated with iron-accumulation. A significant inverse relation existed between the absence of apoptosis and more advanced, or high risk disease and cytogenetic risk factors. Mitochondrial abnormalities were significantly correlated with high risk disease as well with an increase in transfusion dependency.

CONCLUSIONS

These data indicate that in MDS apoptosis may play a role in early stages of disease. The overall prominent defects in mitochondria might be an additional defect that is involved in ineffective erythropoiesis.

Pro-apoptotic and anti-apoptotic effects of transferrin and transferrin-derived glycans on hematopoietic cells and lymphocytes

The aim of this study was to test the hypothesis that transferrin (Tf) has anti-apoptotic properties and thereby exerts a cytoprotective effect against tissue damage induced by irradiation and other cytotoxic modalities. This hypothesis was tested in several models, including in vitro human short-term marrow cultures, subpopulations of marrow cells, particularly, CD56(+) natural killer cells (and natural killer cell lines), and in vivo radioprotection of murine marrow cells. Reverse transcriptase polymerase chain reaction analysis was used for determination of cytokine mRNA. Preincubation of human marrow with Tf protected cells (except for a CD56(+) subpopulation) against cell death induced by gamma-irradiation, tumor necrosis factor-alpha (TNF-alpha), and agonistic anti-Fas monoclonal antibody. Deglycosylation of Tf abrogated this action of Tf; conversely, Tf-derived glycans (Tf-Gly) (but not glycans isolated from other proteins) mimicked the effects of the intact Tf molecule on apoptosis. Antibodies specific for the Tf receptor (CD71) did not block the effects of Tf or Tf-Gly on apoptosis. Determination of cytokine mRNA in the course of Fas-mediated apoptosis in the presence of Tf or Tf-Gly showed upregulation of mRNA for Fas ligand and TNF-alpha in CD56(+) and downregulation of these transcripts along with upregulation of mRNA for interleukin-10 in CD3(+) marrow cells. Under these conditions, a distinct increase in Fas-associated phosphatase-1 message was observed in CD3(+) cells that were protected by Tf or Tf-Gly against apoptosis. The in vitro data were confirmed in a murine in vivo model in which pretreatment of mice with Tf protected marrow cells against gamma-irradiation-induced cell death. These data suggest a role for Tf and particularly Tf-Gly in the regulation of programmed cell death, apparently via alterations in cytokine expression, and provide a basis for additional studies on the use of Tf in cytoprotective protocols.

Presence of activation-related m-RNA for EBV and CMV in the bone marrow of patients with myelodysplastic syndromes

The bone marrow (BM) in myelodysplastic syndromes (MDS) undergoes pathobiological changes that mimic an inflammatory process, and hence, an infectious etiology was suspected in these disorders. In the present report, we examined the bone marrow mononuclear cells (BMMNC) of 19 MDS patients and seven normal donors for the expression of one latency-related (Latency membrane protein 1 (LMP-1) and immediate early protein (IEP)) and one activation-related (BZLF and DNA-Pol) m-RNA each for two herpes viruses, Epstein-Barr virus (EBV) and cytomegalovirus (CMV), respectively. Reverse transcriptase polymerase chain reaction was used for this purpose. The latency-related transcripts (EBV-LMP-1 and CMV-IEP) were present in all the MDS and normal specimens. Intriguingly, 10/19 MDS specimens ( approximately 53%) and 2/7 normal donors ( approximately 28%) were positive for active EBV-BZLF (P=0.0067), while 2/19 MDS specimens ( approximately 11%) with 1/7 normal ( approximately 14%) showed active CMV-DNA-Pol (P=0.1588). Later, from another set of MDS patients (n=7) and normal donors (n=4), BM stromal cultures were established, which, at a 75% confluency, were overlaid with cord blood mononuclear cells (CBMNC). IEP was detectable in the CBMNC before and after co-incubation with MDS, as well as normal stroma. So, it was also present both in MDS and normal stromal cells. The other three were absent both in MDS and normal stromal layers. In CBMNC though, active EBV-BZLF and CMV-DNA-Pol m-RNA were detectable in one of seven MDS co-cultures each, albeit from different patients. None of the normal co-cultures showed active virus, either in stroma or CBMNC. Thus, the present report demonstrates, for the first time, the presence of active herpes viruses in the BMMNC of MDS patients and reveals the ability of the MDS stroma to support the viral activation.

Vascular endothelial cell growth factor is an autocrine promoter of abnormal localized immature myeloid precursors and leukemia progenitor formation in myelodysplastic syndromes

Vascular endothelial growth factor (VEGF) is a potent angiogenic peptide with biologic effects that include regulation of hematopoietic stem cell development, extracellular matrix remodeling, and inflammatory cytokine generation. To delineate the potential role of VEGF in patients with myelodysplastic syndrome (MDS), VEGF protein and receptor expression and its functional significance in MDS bone marrow (BM) were evaluated. In BM clot sections from normal donors, low-intensity cytoplasmic VEGF expression was detected infrequently in isolated myeloid elements. However, monocytoid precursors in chronic myelomonocytic leukemia (CMML) expressed VEGF in an intense cytoplasmic pattern with membranous co-expression of the Flt-1 or KDR receptors, or both. In situ hybridization confirmed the presence of VEGF mRNA in the neoplastic monocytes. In acute myelogenous leukemia (AML) and other MDS subtypes, intense co-expression of VEGF and one or both receptors was detected in myeloblasts and immature myeloid elements, whereas erythroid precursors and lymphoid cells lacked VEGF and receptor expression. Foci of abnormal localized immature myeloid precursors (ALIP) co-expressed VEGF and Flt-1 receptor, suggesting autocrine cytokine interaction. Antibody neutralization of VEGF inhibited colony-forming unit (CFU)-leukemia formation in 9 of 15 CMML and RAEB-t patient specimens, whereas VEGF stimulated leukemia colony formation in 12 patients. Neutralization of VEGF activity suppressed the generation of tumor necrosis factor-alpha and interleukin-1beta from MDS BM-mononuclear cells and BM-stroma and promoted the formation of CFU-GEMM and burst-forming unit-erythroid in methylcellulose cultures. These findings indicate that autocrine production of VEGF may contribute to leukemia progenitor self-renewal and inflammatory cytokine elaboration in CMML and MDS and thus provide a biologic rationale for ALIP and its adverse prognostic relevance in high-risk MDS.

Apoptosis in refractory anaemia with ringed sideroblasts is initiated at the stem cell level and associated with increased activation of caspases

Treatment with granulocyte colony-stimulating factor plus erythropoietin may improve haemoglobin levels in patients with ringsideroblastic anaemia (RARS) and reduce bone marrow apoptosis. We studied bone marrow from 10 RARS patients, two of whom were also investigated after successful treatment. Mononuclear, erythroid and CD34+ cells were analysed with regard to proliferation, apoptosis, clonogenic capacity and oncoprotein expression, in the presence or absence of Fas-agonist, Fas-blocking antibody 2 and caspase-3 inhibitor. During culture, RARS bone marrow cells showed higher spontaneous apoptosis (P < 0.05) and caspase activity (P < 0.05)) than bone marrow cells from healthy donors. Eight out of nine patients had reduced growth of erythroid colony-forming units (CFU-E) (< 10% of control) and granulocyte-macrophage CFU (CFU-GM) (< 50% of control) from CD34+ cells. Fas ligation increased apoptosis and decreased colony growth equally in RARS and controls, but caused significantly more caspase activation in RARS (P < 0.01). Fas-blocking antibody showed no significant inhibitory effect on spontaneous apoptosis or ineffective haematopoiesis, as measured using phosphatidylserine exposure, the terminal deoxynucleotide transferase-mediated dUTP-biotin nick-end labelling technique, caspase activity or clonogenic growth. Caspase inhibition reduced apoptosis, increased proliferation and enhanced erythroid colony growth from CD34+ cells in RARS, but showed no effect on normal cells. CFU-E improved > 1000% after successful treatment. Thus, erythroid apoptosis in RARS is initiated at the CD34+ level and growth factor treatment may improve stem cell function. Enhanced caspase activation at the stem cell level, albeit not mediated through endogenous activation of the Fas receptor, contributes to the erythroid apoptosis in RARS.

The role of apoptosis, proliferation, and the Bcl-2–related proteins in the myelodysplastic syndromes and acute myeloid leukemia secondary to MDS

Bone marrow CD34+ cell apoptosis (annexin V), proliferation (Ki-67), and Bcl-2-related protein expression was evaluated by flow cytometry in 102 patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia secondary to MDS (MDS-AML) and in 30 normal donors (NBM). Apoptosis was significantly increased in refractory anemia (RA)/RA with ringed sideroblasts (RARS) (56.9% [20.4%-93.6%]) and refractory anemia with excess blasts (RAEB) (51.2% [25.2%-76.6%]) compared with NBM (16.7% [3.4%-35.3%],P < .0001). In RA/RARS, apoptosis always exceeded proliferation (Ki-67-positivity, 26.1% [9.5%-47.8%]; apoptosis:proliferation ratio 2.08 [1.15-3.63]); whereas in RAEB, this ratio equalized (1.14 [0.93-2.08]) due to increased proliferation (40.4% [22%-69.5%]). Progression to RAEB in transformation (RAEB-t)/MDS-AML was associated with a significant reduction in apoptosis (22.3% [2.1%-53.2%];P < .0001) and proliferation (16.8% [1.9%-75.8%);P = .04; ratio 1.69 [0.16-12.21]). Pro-apoptotic (Bax/Bad) versus anti-apoptotic (Bcl-2/Bcl-X) Bcl-2-related protein ratios were increased in RA/RARS compared with NBM (2.57 [1.93-9.42] versus 1.89 [0.65-4.1]; P = .06), whereas disease progression was associated with significantly reduced ratios (1.16 [0.06-3.32]; P < .0001) due primarily to increased Bcl-2 expression. Apoptosis and Bax/Bad:Bcl-2/Bcl-X ratio were inversely correlated with both International Prognostic Scoring System score and cytogenetic risk group; highest levels observed in patients with low score and/or good risk cytogenetics. There was a trend toward an association between Bcl-2–related protein expression and apoptosis (P = .07). This study indicates that MDS progression arises through multiple hits that alter levels of CD34+cell apoptosis and proliferation. Early disease is associated with excessive apoptosis and elevated ratio of apoptosis to proliferation. Increased proliferative rates are observed in RAEB, whereas leukemic transformation arises through inhibition of apoptosis rather than excessive cell growth. Although disease progression is accompanied by a fall in pro-apoptotic versus anti-apoptotic Bcl-2–related protein ratios, heterogeneity in patterns of protein expression indicates that factors additional to Bcl-2 family members play a role in the deregulated apoptosis in MDS.

The role of apoptosis, proliferation, and the Bcl-2–related proteins in the myelodysplastic syndromes and acute myeloid leukemia secondary to MDS

Bone marrow CD34+ cell apoptosis (annexin V), proliferation (Ki-67), and Bcl-2-related protein expression was evaluated by flow cytometry in 102 patients with myelodysplastic syndrome (MDS) and acute myeloid leukemia secondary to MDS (MDS-AML) and in 30 normal donors (NBM). Apoptosis was significantly increased in refractory anemia (RA)/RA with ringed sideroblasts (RARS) (56.9% [20.4%-93.6%]) and refractory anemia with excess blasts (RAEB) (51.2% [25.2%-76.6%]) compared with NBM (16.7% [3.4%-35.3%],P &lt; .0001). In RA/RARS, apoptosis always exceeded proliferation (Ki-67-positivity, 26.1% [9.5%-47.8%]; apoptosis:proliferation ratio 2.08 [1.15-3.63]); whereas in RAEB, this ratio equalized (1.14 [0.93-2.08]) due to increased proliferation (40.4% [22%-69.5%]). Progression to RAEB in transformation (RAEB-t)/MDS-AML was associated with a significant reduction in apoptosis (22.3% [2.1%-53.2%];P &lt; .0001) and proliferation (16.8% [1.9%-75.8%);P = .04; ratio 1.69 [0.16-12.21]). Pro-apoptotic (Bax/Bad) versus anti-apoptotic (Bcl-2/Bcl-X) Bcl-2-related protein ratios were increased in RA/RARS compared with NBM (2.57 [1.93-9.42] versus 1.89 [0.65-4.1]; P = .06), whereas disease progression was associated with significantly reduced ratios (1.16 [0.06-3.32]; P &lt; .0001) due primarily to increased Bcl-2 expression. Apoptosis and Bax/Bad:Bcl-2/Bcl-X ratio were inversely correlated with both International Prognostic Scoring System score and cytogenetic risk group; highest levels observed in patients with low score and/or good risk cytogenetics. There was a trend toward an association between Bcl-2–related protein expression and apoptosis (P = .07). This study indicates that MDS progression arises through multiple hits that alter levels of CD34+cell apoptosis and proliferation. Early disease is associated with excessive apoptosis and elevated ratio of apoptosis to proliferation. Increased proliferative rates are observed in RAEB, whereas leukemic transformation arises through inhibition of apoptosis rather than excessive cell growth. Although disease progression is accompanied by a fall in pro-apoptotic versus anti-apoptotic Bcl-2–related protein ratios, heterogeneity in patterns of protein expression indicates that factors additional to Bcl-2 family members play a role in the deregulated apoptosis in MDS.

Excessive apoptosis in low risk myelodysplastic syndromes (MDS)

The paradox of peripheral cytopenias despite a normo/hypercellular marrow in MDS has been ascribed to excessive intramedullary hematopoietic cell apoptosis. Programmed cell death (PCD) in early disease might be triggered by the BM microenvironment, mediated either through inhibitory cytokines such as tumor necrosis factor alpha (TNF-alpha) or fas/fas ligand signaling or through a relative deficiency in hematopoietic growth factors. Intrinsic cellular defects giving rise to abnormalities in cell-cell or cell-stromal interaction, cell signaling or cell cycling may also underlie hematopoietic progenitor apoptosis. Alternatively, an early 'hit' in the multistep pathogenesis of MDS may result in a higher proliferative rate of the neoplastic clone. Increased apoptosis may thus represent a homeostatic process to control cell numbers. This paper shall summarize current evidence implicating a role for increased PCD in low risk MDS, outline possible etiologic factors and suggest potential therapeutic mechanisms whereby excessive hematopoietic progenitor cell apoptosis might be circumvented.

Increased apoptosis of bone marrow cells and preserved proliferative capacity of selected progenitors predict for clinical response to anti-inflammatory therapy in myelodysplastic syndromes

To determine the relation of apoptosis and clonal proliferation in the bone marrow (BM) to the effectiveness of a therapeutic protocol described to downmodulate monokine activity in patients with myelodysplastic syndromes (MDS). Prior to protocol therapy, BM stroma was cultivated and selected CD34(+) cells were studied in stroma and cytokine-dependent clonogenic assays. The TUNEL assay was used to establish the degree of apoptosis occurring in the marrow and CD34(+) population. The effectiveness of oral ciproloxacin 500 mg b. i.d., pentoxifylline 800 mg t.i.d., and dexamathasone 4 mg t.i.d. (CPD) antiinflammatory therapy was correlated with the intensity of cell apoptosis and proliferation of BM progenitor cells. Seventeen patients were studied. Twelve patients (10 transfusion dependent) received therapy for a median of 99 days (range 49-284). Toxicity caused four patients to discontinue the drug combination. Six patients fulfilled response criteria. Four patients became transfusion independent, and 50% reduction in the need for blood transfusions was noted in one patient. Blood parameters of one untransfused patient increased by >30%. Blood count remained unsupported in three patients, even at a median of 12 months after trial discontinuation. Apoptosis of marrow cells and selected CD34(+) progenitors was detected in a median of 49.5% (range 3. 6%-90%) and 10.6% (range 3.6%-100%; p < 0.01), respectively. In patients who responded to therapy, the median apoptosis rate in the bone marrow population was 71%, in contrast to the nonresponder's rate of 13% (p = 0.002). Overall clonogenic growth of selected precursors corresponded significantly with response to CPD protocol (p = 0.004). In some patients with MDS, ineffective hematopoiesis is related to high apoptotic index despite proliferation of the CD34(+) precursors. These patients seem to benefit from CPD cytokine modulatory therapeutic strategy.

Hematopoietic stem cell transplantation in patients with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a stem cell disorder, and hematopoietic stem cell transplantation is currently the only therapeutic modality that is potentially curative. Among patients with less advanced MDS (<5% marrow blasts), 3-year survivals of 65-70% are achievable with HLA-identical related and HLA-matched unrelated donors. The overall probability of disease recurrence in these patients is <5%. Among patients with advanced disease (>/=5% marrow blasts), about 35-45% and 25-30%, respectively, are surviving in remission after transplantation from a related or from an unrelated donor; the incidence of post-transplant relapse is 10-35%. The criteria proposed by the International Prognostic Scoring System (IPSS) derived from non-transplanted patients, also predict survival following transplantation. The development of new conditioning regimens has permitted successful hematopoietic stem cell transplants even in patients more than 60 years of age. Improved survival with transplants from unrelated volunteer donors may, in part, reflect selection of donors on the basis of high resolution (allele-level) HLA typing. Autologous stem cell transplantation may be beneficial for selected patients who have obtained a complete remission with conventional chemotherapy. Treatment-related morbidity and mortality, in particular after allogeneic transplantation, remain challenges that need to be addressed with innovative approaches.

Upregulation of interleukin-10 and inhibition of alloantigen responses by transferrin and transferrin-derived glycans

Previous studies have shown that critically timed administration of transferrin (Tf) facilitates induction of immunologic unresponsiveness. Here, we determined in mixed leukocyte culture (MLC) and in concanavalin A (ConA)-driven cultures the effect of exogenous Tf and Tf-derived glycans (Tf-Gly) on lymphocyte proliferation. In cultures of human blood lymphocytes, Tf inhibited selectively alloantigen-driven proliferation in MLC, but not ConA-stimulated lymphocyte proliferation. Deglycosylation of Tf abrogated the inhibitory effect of Tf on alloantigen-induced lymphocyte proliferation, and, consistent with a role for glycans, an effect qualitatively and quantitatively similar to Tf was exerted by purified Tf-Gly. Glycans isolated from other proteins, for example, immunoglobulin G (IgG) or fibrinogen, failed to inhibit alloantigen-induced proliferation selectively. Rather, they suppressed lymphocyte proliferation in a non-specific manner. Determination of cytokines in MLC supernatant showed a downregulation of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), IL-2, and IL-12 (p40), along with an upregulation of IL-10, a pattern entirely consistent with the observed effects of Tf and Tf-Gly on alloantigen-induced lymphocyte proliferation. The effect of Tf on MLC was directly IL-10-dependent. IL-10 levels were inversely correlated with lymphocyte proliferation and CD86 expression. Neutralization of IL-10 by anti-IL-10 monoclonal antibody (mAb) blocked the effect of Tf. The MLC-modulating effect of Tf (or Tf-Gly) was not dependent upon the Tf receptor CD71 but appeared to be mediated by a Gly-responsive receptor. These data suggest a role of Tf, and, in particular, Tf-Gly, in allo-interactions that is independent from the role of Tf in iron metabolism, and appears to involve co-stimulatory signals.

Negative regulators of hemopoiesis and stroma function in patients with myelodysplastic syndrome

The mechanism that leads to hemopoietic failure in patients with myelodysplastic syndrome (MDS) is not well understood. There is evidence, however, that regulatory molecules such as tumor necrosis factor (TNF)-alpha, Fas (CD95), and Fas-ligand, which negatively affect hemopoiesis by way of apoptosis are upregulated. Here we analyzed marrow samples from 80 patients with MDS in regard to TNF-alpha and Fas-ligand levels and a possible correlation with various disease parameters and risk factors. TNF-alpha levels were elevated in comparison to samples from normal marrow donors, however, no significant correlation with FAB subtype, cytogenetic risk group or score by the International Prognostic Scoring System (IPSS) was observed. However, there was an inverse correlation between the cytogenetic risk category (low, intermediate, high) and levels of soluble Fas-ligand. The major source of TNF-alpha were mononuclear (non-stromal) cells which appeared to produce TNF-alpha at maximum levels. Limiting dilution analysis of CD34+ precursor cells showed that individually assayed cells, removed from companion cells that presumably provided negative signals such as TNF-alpha or Fas-ligand, were able to generate progressively increasing numbers of colonies. Stromal layers derived from MDS marrow did not have an inhibitory effect. In fact, higher colony numbers were obtained from both normal and MDS marrow derived hemopoietic precursors propagated on irradiated stromal layers from MDS marrow than on stromal layers from normal marrow. These results show that substantial numbers of normal hemopoietic precursors persist in MDS marrow. However, differentiation into mature cells is inhibited by negative signals originating from accessory or abnormal hemopoietic precursors in the non-adherent marrow fraction.

Efficacy of N-acetylcysteine and all-trans retinoic acid in restoring in vitro effective hemopoiesis in myelodysplastic syndromes

We evaluated the in vitro effect on clonogenic potential (CFU-GM) and apoptosis in myelodysplastic syndromes (MDS) progenitors of an anti-oxidant (N-acetylcysteine, NAC) and/or a differentiating (all-trans retinoic acid, ATRA) agent. NAC significantly reduced apoptosis, both NAC and ATRA induced an increase in CFU-GM, but NAC seemed to be particularly effective in the high risk (HR) MDS. NAC + ATRA conferred a significant advantage in terms of CFU-GM with respect to NAC and ATRA alone. Tumor Necrosis Factor-alpha (TNF-alpha) levels decreased after incubation with NAC in the MDS samples. This study shows that ineffective hemopoiesis in MDS could benefit from both NAC and ATRA, suggesting that anti-oxidant treatment may play a role in guaranteeing MDS cell survival, predisposing them towards differentiation.

Achievements in Understanding and Treatment of Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) constitute a challenge for the biologist as well as for the treating physician. In Section I, Dr. Willman reviews the current classifications and disease mechanisms involved in this heterogeneous clonal hematopoietic stem cell disorder. A stepwise genetic progression model is proposed in which inherited or acquired genetic lesions promote the acquisition of “secondary” genetic events mainly characterized by gains and losses of specific chromosome regions. The genetic risk to develop MDS is likely multifactorial and dependent on various constellations of risk-producing and -protecting alleles. In Section II Dr. Barrett with Dr. Saunthararajah addresses the immunologic factors that may act as important secondary events in the development of severe pancytopenia. T cells from patients with MDS may suppress autologous erythroid and granulocytic growth in vitro, and T cell suppression by antithymocyte globulin or cyclosporine may significantly improve cytopenia, especially in refractory anemia. Recent studies have also demonstrated an increased vessel density in MDS bone marrow, and a phase II trial of thalidomide showed responses in a subgroup of MDS patients especially in those with low blast counts. In Section III Dr. Hellström-Lindberg presents results of allogeneic and autologous stem cell transplantation (SCT), intensive and low-dose chemotherapy. The results of allogeneic SCT in MDS are slowly improving but are still poor for patients with unfavorable cytogenetics and/or a high score according to the International Prognostic Scoring System. A recently published study of patients between 55-65 years old showed a disease-free survival (DFS) at 3 years of 39%. Consolidation treatment with autologous SCT after intensive chemotherapy may result in long-term DFS in a proportion of patients with high-risk MDS. Low-dose treatment with 5-azacytidine has been shown to significantly prolong the time to leukemic transformation or death in patients with high-risk MSA. Erythropoietin and granulocyte colony-stimulating factor may synergistically improve hemoglobin levels, particularly in sideroblastic anemia. Recent therapeutic advances have made it clear that new biological information may lead to new treatment modalities and, in combination with statistically developed predictive models, help select patients for different therapeutic options.

Detection of TNFalpha expression in the bone marrow and determination of TNFalpha production of peripheral blood mononuclear cells in myelodysplastic syndrome

TNFalpha is a highly active cytokine which plays an important role in the regulation of apoptotic cell death, a mechanism involved in the pathophysiology of myelodysplastic syndrome (MDS). In this study we investigated the expression of TNFalpha of the bone marrow trephine biopsies by immunohistochemical method and the TNFalpha production of peripheral blood mononuclear cells by ELISA method in 15 patients affected by MDS. Five of seven patients without excess of blasts showed high or intermediate TNFalpha expression in the bone marrow biopsies, whereas two patients with excess of blasts were negative and one had low expression. The five CMML patients revealed low or intermediate expression. The production of TNFalpha by the PBMC was analysed in 10 patients, four patients with RA and two with CMML produced higher level of TNFalpha which increased after stimulation with phorbol myristic acetate, but none of the RAEB patients revealed increase in TNFalpha production. In conclusion we suppose that increased TNFalpha expression and production by PBMC may be an indirect evidence of the role of increased apoptosis in low risk MDS patients.

A hypothesis for the pathogenesis of myelodysplastic syndromes: implications for new therapies

To guide development of new clinical strategies, a review of recent investigations in the pathobiology of MDS was performed. Articles were identified through a Medline search. Studies, including reviews, are cited in the references. A multistep pathogenesis is proposed. (1) Targeted injury or mutation within hemopoietic stem cells may be followed by an immunologic response adversely affecting progenitor survival. (2) Accelerated proliferation and premature death of marrow cells is amplified by apoptogenic cytokines (TNF-alpha, Fas ligand). (3) Establishment of an abnormal clone associated with telomere shortening. (4) Disease progression associated with loss of tumor suppressor activity. Opportunities for therapeutic interventions are possible at each step. Comparisons between the proposed pathogenesis of MDS and severe aplastic anemia (SAA) are also presented. Leukemia (2000) 14, 2-8.

Myelodysplastic syndrome and aplastic anemia: distinct entities or diseases linked by a common pathophysiology?

It is often difficult to distinguish myelodysplastic syndrome (MDS) from severe aplastic anemia (SAA) because both can present with profoundly hypocellular bone marrows. The distinction matters because although both conditions are complicated by pancytopenia, the risk of progression to acute leukemia is much greater in MDS. This chapter reexamines the relationship between SAA and MDS. The clinical and morphological features and pathophysiology of AA (including moderate and severe forms of acquired AA) are compared with MDS and hypoplastic MDS, with particular reference to new observations implicating autoimmune processes in both conditions. SAA and hypoplastic MDS (HMDS) are discussed in the light of these findings and attempts to separate nonevolving bone marrow failure syndromes from marrow failure progressing to acute leukemia are reviewed. The weight of evidence supports a common pathophysiology and, more speculatively, a common etiology for at least some forms of AA and MDS.

Achievements in Understanding and Treatment of Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) constitute a challenge for the biologist as well as for the treating physician. In Section I, Dr. Willman reviews the current classifications and disease mechanisms involved in this heterogeneous clonal hematopoietic stem cell disorder. A stepwise genetic progression model is proposed in which inherited or acquired genetic lesions promote the acquisition of “secondary” genetic events mainly characterized by gains and losses of specific chromosome regions. The genetic risk to develop MDS is likely multifactorial and dependent on various constellations of risk-producing and -protecting alleles. In Section II Dr. Barrett with Dr. Saunthararajah addresses the immunologic factors that may act as important secondary events in the development of severe pancytopenia. T cells from patients with MDS may suppress autologous erythroid and granulocytic growth in vitro, and T cell suppression by antithymocyte globulin or cyclosporine may significantly improve cytopenia, especially in refractory anemia. Recent studies have also demonstrated an increased vessel density in MDS bone marrow, and a phase II trial of thalidomide showed responses in a subgroup of MDS patients especially in those with low blast counts. In Section III Dr. Hellström-Lindberg presents results of allogeneic and autologous stem cell transplantation (SCT), intensive and low-dose chemotherapy. The results of allogeneic SCT in MDS are slowly improving but are still poor for patients with unfavorable cytogenetics and/or a high score according to the International Prognostic Scoring System. A recently published study of patients between 55-65 years old showed a disease-free survival (DFS) at 3 years of 39%. Consolidation treatment with autologous SCT after intensive chemotherapy may result in long-term DFS in a proportion of patients with high-risk MDS. Low-dose treatment with 5-azacytidine has been shown to significantly prolong the time to leukemic transformation or death in patients with high-risk MSA. Erythropoietin and granulocyte colony-stimulating factor may synergistically improve hemoglobin levels, particularly in sideroblastic anemia. Recent therapeutic advances have made it clear that new biological information may lead to new treatment modalities and, in combination with statistically developed predictive models, help select patients for different therapeutic options.

Recognition of major histocompatibility complex class II antigens by two anti-HLA-DR monoclonal antibodies on canine marrow cells correlates with effects on in vitro and in vivo hematopoiesis

BACKGROUND

The role of major histocompatibility complex class II antigens in hematopoiesis is not well defined. We have shown that in vitro depletion of HLA-DR+ cells from canine marrow (e.g., by anti-HLA-DR monoclonal antibody [mAb] H81.9 and complement) prevents hematopoietic recovery. In vivo administration of the same mAb H81.9 after transplantation of unmanipulated autologous marrow results in graft failure. In vitro mAb H81.9 inhibited colony formation from short-term and long-term marrow cultures.

METHODS AND RESULTS

We investigated the effect of another mAb, Ca1.41, which also recognizes nonpolymorphic determinants on human (HLA-DR) and canine major histocompatibility complex class II antigens but is reactive with a narrower spectrum of cells in both canine peripheral blood and marrow than mAb H81.9 (and other anti-HLA-DR mAbs). In contrast to all other anti-HLA-DR mAbs tested, Ca1.41 did not interfere with colony formation in short-term or long-term marrow cultures and spared a population of small mononuclear cells with low forward light scatter that was eliminated via apoptosis by exposure to mAb H81.9. These target cells included lymphocytes and CD34+ hemopoietic precursors that expressed MHC class II molecules as determined by mAb H81.9 but not by mAb Ca1.41. In addition, transmembrane signaling and up-regulation of interleukin-1beta mRNA occurred with mAb H81.9 but not with Ca1.41. Transplantation of autologous marrow treated in vitro cytolytically with mAb Ca1.41 allowed for complete hematopoietic reconstitution. Further, in vivo administration of Ca1.41 posttransplant did not lead to autologous graft failure as had been observed with mAb H81.9.

CONCLUSIONS

These results support the notion that major histocompatibility complex class II is expressed on early hematopoietic precursor cells but recognition is dependent upon the mAb used. Preliminary studies show that mAb H81.9 triggered transmembrane signaling, resulting in up-regulation of interleukin-1beta and apoptosis, although mAb Ca1.41 did not. The fact that Ca1.41 binding was modified in the presence of exogenous invariant chain-derived peptide suggests that both binding and signaling are peptide dependent.

Induction of negative regulators of haematopoiesis in human bone marrow cells by HLA-DR cross-linking

Tumour necrosis factor-alpha (TNF alpha) is up-regulated by cross-linking of major histocompatibility complex (MHC) class II [human leucocyte antigen (HLA)-DR] antigens on monocytes. This is done by a bacterial superantigen or anti-HLA-DR monoclonal antibody (MAb). We have previously shown that HLA-DR cross-linking results in inhibition of haematopoiesis and apoptosis. TNF alpha acts as a negative regulator of haematopoiesis. Here we investigated whether HLA-DR-mediated inhibition of haematopoiesis involved TNF alpha and TNF alpha-dependent secondary signals. Anti-HLA-DR MAb H81.9 up-regulated TNF alpha, as well as transforming growth factor beta, interleukin (IL)-1beta and IL-6 in human marrow cells at the ribonucleic acid (RNA) and protein level. The effect on TNF alpha was investigated further. Up-regulation was blocked by herbimycin A, consistent with a tyrosine kinase-dependent mechanism. Up-regulation was also blunted by the soluble TNF-receptor fusion protein TNFR:Fc, suggesting an autocrine amplification loop. Following TNF alpha up-regulation, there was increased expression of Fas (CD95) and Fas-ligand (Fas-L). Up-regulation of Fas and Fas-L was blocked by TNFR:Fc. Furthermore, MAb H81.9-induced apoptosis was prevented by anti-TNF alpha MAb and by the soluble Fas receptor, Fas-Ig, providing further evidence that the TNF effect was mediated via Fas. At the transcriptional level, cross-linking of HLA-DR by MAb H81.9 affects nuclear localization of NFkappaB, which is involved in the transcription of TNF alpha. NFkappaB activity is modified by changes in cellular redox potential, and we have shown that H81.9 affects redox potential as determined by the generation of nitric oxide. These data show that HLA-DR-initiated signals are able to trigger a cascade of negative regulators of haematopoiesis. This model provides an opportunity to dissect signalling pathways that may be involved in the development of spontaneous marrow failure, and to devise interventions aimed at protecting haematopoiesis.

Sequential activation of caspase-1 and caspase-3-like proteases during apoptosis in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are a group of hematopoietic disorders characterized by the concomitant presence of peripheral cytopenias and normocellular to hypercellular BM. This paradox has been proposed to be due to the presence of excessive proliferation matched by excessive intramedullary apoptosis of hematopoietic cells. When cultured in vitro MDS BM mononuclear cells (BMMC) undergo apoptosis within 4 h. We measured caspase-1-like and caspase-3-like activity in 22 MDS and 4 normal BM immediately following cell separation or after 4 h culture. When cultured in vitro, MDS BMMC demonstrated an increased apoptotic index within 4 h as measured by in situ end-labeling of fragmented DNA that was matched by a concurrent increase in caspase-3-like specific activity, and the two were significantly correlated. During the 4 h culture, a sequential activation of caspase-1-like and caspase-3-like activities was detected. Caspase-1-like specific activity was detected early and transiently at approximately 15 min, followed by a gradual increase in caspase-3-like-specific activity peaking at 2 h. When the broad-spectrum caspase inhibitor, Z-VAD.FMK, was included in the MDS BM aspirate 4 h culture, apoptosis was attenuated. We conclude that sequential activation of caspase-1-like and caspase-3-like activities may form the central biochemical pathway of apoptosis in BMMC from some MDS patients, and prevention of this process by caspase inhibitors may be of significant therapeutic value for these patients, in whom supportive care continues to be the mainstay of therapy.

Ineffective erythropoiesis in myelodysplastic syndromes: correlation with Fas expression but not with lack of erythropoietin receptor signal transduction

Ineffective erythropoiesis in myelodysplasia is characterized by a defect in erythroid progenitor growth and by abnormal erythroid differentiation. Increased apoptosis of erythroid, granulocytic and megakaryocytic lineages is thought to account for cytopenias. Erythropoietin (Epo)-induced BFU-E and CFU-E growth was studied in 25 myelodysplastic syndrome (MDS) marrow specimens and found to be drastically diminished. To investigate the functionality of Epo-R in MDS marrow, we focused on Epo-induced STAT5 activation. Epo was able to stimulate STAT5 DNA binding activity in all normal and 12/24 MDS marrows tested, with no correlation between the level of STAT5 activation and the development of erythroid colonies in response to Epo. In contrast, impaired proliferation of erythroid progenitors was related to an increased expression of the transmembrane mediator of apoptotic cell death Fas/CD95 on the glycophorin A+ subpopulation. Therefore we conclude that the stimulation of pro-apoptotic signals rather than the defect of anti-apoptotic pathways resulting from Epo-stimulated Jak2-STAT5 pathway, predominantly accounts for ineffective erythropoiesis in myelodysplasia.

Correlation of tumor necrosis factor alpha (TNF alpha) with high Caspase 3-like activity in myelodysplastic syndromes

Increased intramedullary apoptotic death of hematopoietic cells is thought to contribute to the ineffective hematopoiesis in myelodysplastic syndromes (MDS). Furthermore, high amounts of tumor necrosis factor alpha (TNF alpha) have previously been correlated with apoptosis in MDS marrows. The present studies were undertaken to examine the status of two key downstream effectors of TNF alpha signaling, i.e. Caspase 1 and Caspase 3 enzymes, using a fluorometric assay in the bone marrow aspirate mononuclear cells (BMMNC) in relation to apoptotic DNA fragmentation detected by in situ end-labeling (ISEL) of DNA and with localization of TNF alpha in the corresponding biopsies from 14 MDS patients. Both Caspase 1 and 3 were detectable in freshly harvested BMMNC, albeit median Caspase 3 levels (47.5 units/mg protein) being almost 10 times higher than Caspase 1 (4.0 units/mg protein). Upon short-term culture for 4 h in a serum-supplemented medium in vitro a significant increase was seen in Caspase 3 activity (58.8 +/- 13.9 at 0 h vs. 177.8 +/- 55.2 units/mg protein at 4 h, n = 14, P = 0.017) and in percent cells labeled by ISEL (apoptotic index or AI%: 0.76% +/- 0.25% vs. 3.99% +/- 1.1%, n = 14, P = 0.004, respectively). Caspase 1 activity increased after 15 min in culture. Interestingly, TNF alpha levels measured by immunohistochemistry correlated with the net increase in Caspase 3 activity after 4 h (p = 0.517, n = 13, P = 0.07) and the starting levels of Caspase 1 at 0 h correlated with the Caspase 3 levels attained at 4 h (p = 0.593, n = 13, P = 0.033). Additionally when TNF alpha-positive bone marrows (8/14) were compared with the negative marrows (6/14) the Caspase 3 levels were significantly higher in the TNF alpha-positive marrows (189.6 +/- 66.2 vs. 25.0 +/- 14.6 units/mg protein, respectively, P = 0.043). The increase in AI%, though not statistically significant, was also higher in the TNF alpha-positive marrows. Finally in HL60 cells the effects of different Caspase inhibitors and pentoxifylline (PTX) (interferes with lipid signaling of cytokines) on TNF alpha-induced apoptosis were evaluated. TNF alpha treatment significantly increased AI% (P < 0.003) as compared to the untreated controls. A co-treatment with three Caspase inhibitors, zVAD.FMK (inhibitor of Caspases 1 and 3, 10 microM/l), Ac.YVAD.FMK (Caspase 1 inhibitor, 1 microM/l), Ac.DEVD.FMK (Caspase 3 inhibitor, 10 microM/l) as well as PTX (250 microM/l) significantly curtailed the AI% induced by TNF alpha. The present studies thus identify the downstream effectors of TNF alpha-inducible apoptosis in MDS and so also the suppressors of TNF alpha apoptotic signaling. These results may have significant clinical implications in the therapy of MDS in the future.