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

Comparative Analysis of the Biosimilar and Innovative G-CSF Modulated Pathways on Umbilical Cord Blood-Derived Mononuclear Cells

Biosimilars of granulocyte colony-stimulating factor (G-CSF) have been routinely introduced into clinical practice. However, not functional genomics characterization has been performed yet in comparison with the innovator G-CSF. This study aimed to evaluate the transcriptomic changes in an in vitro model of umbilical cord blood cells (UBC) exposed to G-CSF for the identification of their modulated pathways. Umbilical cord blood cells-derived mononuclear cells (MNCs) were treated with biosimilar and innovator G-CSF for further gene expression profiling analysis using a microarray-based platform. Comparative analysis of biosimilar and innovator G-CSF gene expression signatures allowed us to identify the most commonly modulated pathways by both drugs. In brief, we observed predominantly upmodulation of transcripts related to PI3K-Akt, NF-kappaB, and tumor necrosis factor (TNF) signaling pathways as well as transcripts related to negative regulation of apoptotic process among others. In addition, hematopoietic colony-forming cell assays corroborate the G-CSF phenotypic effects over UBC-derived MNCs. In conclusion, our study suggests that G-CSF impacts UBC-derived cells through the modulation of several signaling pathways associated with cell survival, migration, and proliferation. The concordance observed between biosimilar and innovator G-CSF emphasizes their similarity in regards to their specificity and biological responses.

Revisiting use of growth factors in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) represent a heterogeneous group of clonal hematologic neoplasms characterized by morphologic dysplasia, aberrant hematopoiesis and peripheral blood refractory cytopenias. MDS is recognized to be associated with an increased risk of symptomatic anemia, infectious complications and bleeding diathesis, as well as a risk of progression to acute myeloid leukemia, particularly in patients with a high IPSS score. The advent of use of hematopoietic growth factors such as granulocyte colony-stimulating factor (G-CSF) and recombinant erythropoietin (EPO) has improved symptoms in MDS patients in addition to some data that suggest there might be an improvement in survival. G-CSF is an effective therapeutic option in MDS patients, and it should be considered for the management of refractory symptomatic cytopenias. G-CSF and EPO in combination can improve outcomes in appropriate MDS patients such as those with lower-risk MDS and refractory anemia with ring sideroblasts (RARS) . This article reviews use of growth factors for lower-risk MDS patients, and examines the data for G-CSF, EPO and thrombopietic growth factors (TPO) that are available or being developed as therapeutic modalities for this challenging disease.

The transporter ABCB7 is a mediator of the phenotype of acquired refractory anemia with ring sideroblasts

Refractory anemia with ring sideroblasts (RARS) is characterized by mitochondrial ferritin (FTMT) accumulation and markedly suppressed expression of the iron transporter ABCB7. To test the hypothesis that ABCB7 is a key mediator of ineffective erythropoiesis of RARS, we modulated its expression in hematopoietic cells. ABCB7 up and downregulation did not influence growth and survival of K562 cells. In normal bone marrow, ABCB7 downregulation reduced erythroid differentiation, growth and colony formation, and resulted in a gene expression pattern similar to that observed in intermediate RARS erythroblasts, and in the accumulation of FTMT. Importantly, forced ABCB7 expression restored erythroid colony growth and decreased FTMT expression level in RARS CD34+ marrow cells. Mutations in the SF3B1 gene, a core component of the RNA splicing machinery, were recently identified in a high proportion of patients with RARS and 11 of the 13 RARS patients in this study carried this mutation. Interestingly, ABCB7 exon usage differed between normal bone marrow and RARS, as well as within the RARS cohort. In addition, SF3B1 silencing resulted in downregulation of ABCB7 in K562 cells undergoing erythroid differentiation. Our findings support that ABCB7 is implicated in the phenotype of acquired RARS and suggest a relation between SF3B1 mutations and ABCB7 downregulation.

Myelodysplastic syndromes: an update on molecular pathology

The myelodysplastic syndromes (MDS) are a heterogeneous group of myeloid disorders characterised by impaired peripheral blood cell production due to bone marrow dysplasia affecting one or more of the major myeloid cell lines. MDS are one of five major categories of myeloid neoplasms according to the World Health Organization (WHO) classification system for haematological cancers. Given their cytological and cytogenetic heterogeneity, these diseases probably constitute a group of molecularly distinct entities with variable degrees of ineffective haematopoiesis and susceptibility to leukaemic transformation. Recent studies provide some insights into the physiopathology of MDS. In the early stages, one mechanism contributing to hypercellular marrow and peripheral blood cytopenia is a significant increase in programmed cell death (apoptosis) in haematopoietic cells. Furthermore, altered responses in relation to cytokines, the immune system and bone marrow stroma also contribute to the disease phenotype. Deletions of chromosome 5q31-q32 are the most common recurring cytogenetic abnormalities detected in MDS. The 5q- syndrome is a new entity recognised in the WHO classification since 2001 and is associated with a good prognosis. Haploinsufficiency of multiple genes mapping to the common deleted region at 5q31-32 may contribute to the pathogenesis of 5q- syndrome and other MDS with 5q- deletion. Many studies have demonstrated that altered DNA methylation and histone acetylation can alter gene transcription. Abnormal methylation of transcription promoter sites is universal in patients with MDS, and the number of involved loci is increased in high-risk disease and secondary leukaemias. A better understanding of the pathogenesis of MDS can contribute to the development of new treatments such as hypomethylating drugs, immunomodulatory agents such as lenalidomide, and immunosuppressive drugs aimed at reversing the specific alteration that results in improvement in patients with MDS.

Gene expression profiling of erythroblasts from refractory anaemia with ring sideroblasts (RARS) and effects of G-CSF

Refractory anaemia with ring sideroblasts (RARS) is characterized by anaemia, erythroid apoptosis, cytochrome c release and mitochondrial ferritin accumulation. Granulocyte-colony-stimulating factor (G-CSF) inhibits the first three of these features in vitro and in vivo. To dissect the molecular mechanisms underlying the RARS phenotype and anti-apoptotic effects of G-CSF, erythroblasts generated from normal (NBM) and RARS marrow CD34(+) cells were cultured +/-G-CSF and subjected to gene expression analysis (GEP). Several erythropoiesis-associated genes that were deregulated in RARS CD34(+) cells showed normal expression in erythroblasts, underscoring the importance of differentiation-specific GEP. RARS erythroblasts showed a marked deregulation of several pathways including apoptosis, DNA damage repair, mitochondrial function and the JAK/Stat pathway. ABCB7, transporting iron from mitochondria to cytosol and associated with inherited ring sideroblast formation was severely suppressed and expression decreased with differentiation, while increasing in NBM cultures. The same pattern was observed for the mitochondrial integrity gene MFN2. Other downregulated key genes included STAT5B, HSPA5, FANCC and the negative apoptosis regulator MAP3K7. Methylation status of key downregulated genes was normal. The mitochondrial pathway including MFN2 was significantly modified by G-CSF, and several heat shock protein genes were upregulated, as evidence of anti-apoptotic protection of erythropoiesis. By contrast, G-CSF had no effect on iron-transport or erythropoiesis-associated genes.

The role of rHuEpo in low-risk myelodysplastic syndrome patients

Myelodysplastic syndromes (MDS) are clonal disorders of the haemopoietic stem cell characterized by peripheral cytopenias that are the result of abnormal haemopoietic differentiation and maturation. Approximately 90% of MDS patients present with anemia at the beginning or during the course of the disease and often require transfusions. The rationale for treating anemic MDS patients with recombinant human erythropoietin (rHuEpo), alone or in combination with other growth factors, is based on the possibility of overcoming the defective proliferation and maturation of erythroid precursors through the inhibition of bone marrow apoptosis, the enhancement of the differentiation of preleukemic progenitor cells or the stimulation of the growth of residual normal haematopoietic cells. Clinical trails have shown that rHuEpo, alone or in combination with recombinant human granulocyte colony-stimulating factor, is a useful drug for the treatment of anemia in low-risk MDS patients, and the same trials have identified patients who are more likely to respond to maximize benefits, to minimize adverse effects, and to avoid misuse or abuse. However, further research is required to determine whether this treatment has any real impact on quality of life and on life expectancy, thus allowing recommendations to be made about rHuEpo use in MDS patients with a degree of certainty.

Avancées dans la prise en charge des syndromes myélodysplasiques

OBJECTIVES

Myelodysplastic syndromes (MDS) are a group of clonal hematologic disorder, which combine ineffective hematopoiesis and evolution to acute myeloid leukemia. Significant progress has been made in the understanding of the disease pathogenesis, diagnostics and classification. Promising new agents and innovative therapeutic strategies are currently used. In this article we will review these achievements and their impact on the treatment of MDS.

CURRENT KNOWLEDGE AND KEY POINTS

The pathogenesis of MDS involves abnormalities of the MDS clone itself such as abnormal apoptosis, signalling or epigenetic regulation and abnormalities of the microenvironment such as immune deregulation or increased angiogenesis, which represent potential therapeutic targets. There is currently no standard treatment for MDS and allogeneic stem cell transplantation remains the only curative strategy. However, besides conventional chemotherapy and growth factors, new agents including hypomethylating agents, antiangiogenic drugs, immune modulatory agents have proved effective.

FUTURE PROSPECTS AND PROJECTS

The interesting results achieved with these new agents show that it is necessary to continue investigation in order to improve therapeutic strategies in MDS.

Impact of growth factors in the regulation of apoptosis in low-risk myelodysplastic syndromes

Increased apoptosis of hematopoietic progenitors is a hallmark of myelodysplastic syndromes (MDS) and results in ineffective hematopoiesis. Erythroid apoptosis is thought to be the main mechanism underlying the severe anemia observed in the low-risk subgroups, refractory anemia (RA) and RA with ringed sideroblasts (RARS). Treatment with erythropoietin (Epo) alone or in combination with granulocyte colony-stimulating factor (G-CSF) may significantly improve anemia and reduce bone marrow apoptosis. A synergistic effect between Epo and G-CSF has been observed in the clinic, in particular in RARS. However, the molecular mechanisms beyond the anti-apoptotic effect of these growth factors have not been fully understood. This paper outlines the potential mechanisms underlying the augmented apoptosis during the erythroid differentiation in low-risk MDS as well as the anti-apoptotic effect of the growth factors.

Does continuous flow apheresis influence viability in allogeneic hematopoietic stem cell harvest?

One of the important clinical variables determining the success of hematopoietic stem cell transplantation is the number of viable CD34+ stem cells transfused to the patient. G-CSF mobilized peripheral blood stem cells from 17 healthy donors were collected by continuous flow apheresis. The median (range) proportions of early apoptotic (Annexin V-FITC(pos)/7-AAD(neg)) and viable (Annexin V-FITC(neg)/7-AAD(neg)) CD45(dim)CD34+ stem cells were 1.5 (0.9-3.7)% and 97.7 (82.8-100)% in the peripheral blood before apheresis and 2.6 (0.8-7.9)% and 97.3 (91.9-99)% in the apheresis products, respectively. Despite an increase in the number of apoptotic cells among all cell compartments, this was statistically significant only in CD34+ cells and granulocytes. The majority of the cells still retained their viability.

Erythropoietin plus granulocyte colony-stimulating factor is better than erythropoietin alone to treat anemia in low-risk myelodysplastic syndromes: results from a randomized single-centre study

Haemopoietic growth factors (HGF), i.e. erythropoietin [recombinant human erythropoietin (rHEPO)] or granulocyte colony stimulating factor (G-CSF), alone or in combination, have largely been used to treat anemia in myelodysplastic syndromes (MDS), but whether combined rHEPO and G-CSF is really superior to rHEPO alone is still under debate. In particular, randomized studies comparing front-line rHEPO vs rHEPO+G-CSF are still lacking. The aim of this study was to compare the effects of "standard" doses of rHEPO with the combination of rHEPO and G-CSF in the treatment of anemic patients with low-risk MDS in a prospective randomized trial. Anemic patients with low-risk MDS were randomly assigned to receive either rHEPO (10,000 IU s.c. three times a week) or the same dosage of rHEPO+G-CSF (300 mug s.c. twice a week) for a minimum of 8 weeks. Patients who were unresponsive to rHEPO were offered the combination therapy for another 8 weeks, whereas non-responders to rHEPO+G-CSF were considered "off study". Responders continued the treatment indefinitely. Both haematological response and changes in quality-of-life (QoL) scores (Functional Assessment of Cancer Therapy-Anemia) were recorded and evaluated. Thirty consecutive patients [10 refractory anemia (RA), 5 RA with ringed sideroblasts, 7 refractory cytopenia with multilineage dysplasia, 5 RA with less than 10% blasts and 3 5q-syndrome] were enrolled in the study. All of them (15 in the rHEPO arm and 15 in the rHEPO+G-CSF arm) were valuable after the first 8 weeks of treatment. Erythroid response was observed in 6/15 (40%) patients in the rHEPO arm and in 11/15 (73.3%) patients in the rHEPO+G-CSF arm. In 4/9 (44.4%) patients who were unresponsive to rHEPO, the addition of G-CSF induced erythroid response at 16 weeks. No relevant adverse effects were recorded for either treatment in any of the study patients. Erythroid response to HGF was associated with a relevant improvement in QoL. Twenty responders continued the treatment. Afterwards, 8/20 (40%) discontinued therapy because of the following: losing response (2), progression to high-risk MDS (3) and death due to other causes (3). The remaining 12 are still responding and continuing treatment, with a median follow-up of 28 months. Progression to acute leukemia was cumulatively observed in 4/30 (13.3%) patients (2 in each arm). Although our data were obtained from a relatively small cohort of patients, they indicate that the rHEPO+G-CSF treatment is more effective than rHEPO alone for correcting anemia in low-risk MDS patients and for making a relevant improvement in their QoL.

A non-randomised dose-escalating phase II study of thalidomide for the treatment of patients with low-risk myelodysplastic syndromes: the Thal-SMD-2000 trial of the Groupe Francais des Myelodysplasies

Patients (n=47) with low-risk myelodysplastic syndrome were treated with thalidomide [200 mg/d, increased by 200 mg/d/4 weeks up to week 16]. Responses were evaluated according to the International Working Group criteria at week 16 for 39 patients who received at least 8 weeks of treatment. Twenty-three (59%) patients showed haematological improvement (HI): four major erythroid response (HI-EM), 15 minor erythroid response, six major neutrophil response, two major platelet response. Side effects caused 22/39 to stop thalidomide before week 16. Nine of 23 responders continued thalidomide after week 16 [19% of trial patients] with sustained response in eight of nine. Six reached week 56, including the four HI-EM patients [13% of trial patients]. Nineteen of 36 red blood cell transfusion-dependent patients (53%) showed erythroid response, but only four became transfusion-independent. Among the 23 responders, the median duration of response was 260 d (range 30-650). Responses were sustained in all patients except one, and were observed between week 4 and week 8 in 85% of patients, at doses ranging from 200 to 400 mg. Only two patients responded at 600 mg/d and none at 800 mg/d. No clinical characteristics of responding versus non-responding patients were identified. The erythroid response rate was identical in all cytogenetic subgroups, including 5q31.1 deletions. Pretreatment vascular endothelial growth factor levels were lower in responders compared with non-responders (P=0.004). Microvessel density (MVD) increased and apoptosis decreased in four of six and in all six responders studied respectively whereas MVD and apoptosis were unchanged in three non-responders.

Antiapoptotic Role of Growth Factors in the Myelodysplastic Syndromes: Concordance BetweenIn vitroandIn vivoObservations

PURPOSE

Erythroid apoptosis in low-risk myelodysplastic syndrome (MDS) maybe mediated via mitochondrial release of cytochrome c and subsequent caspase activation. In the present study, we compared the in vitro and in vivo effects of proerythroid treatment with erythropoietin + granulocyte colony-stimulating factor (G-CSF) on myelodysplastic erythropoiesis regarding apoptosis and preferential growth of clones with cytogenetic abnormalities.

EXPERIMENTAL DESIGN

We enrolled 15 refractory anemia (RA) and 11 refractory anemia with ringed sideroblasts (RARS), including 5q- aberration, monosomy 7, and trisomy 8, before initiation of treatment and followed nine patients after successful treatment. The effects of G-CSF and erythropoietin were assessed. The expression of G-CSF receptor (G-CSFR) was explored during erythroid maturation. The relative growth of erythroid progenitors with cytogenetic aberrations in presence of erythropoietin was investigated.

RESULTS

Significant redistribution of cytochrome c was seen before treatment at all stages of erythroid differentiation. This release was blocked by G-CSF during the whole culture period and by erythropoietin during the latter phase. Both freshly isolated glycophorin A+ bone marrow cells and intermediate erythroblasts during cultivation retained their expression of G-CSFR. Cytochrome c release and caspase activation were significantly less pronounced in progenitors obtained from successfully treated nonanemic patients and showed no further response to G-CSF in vitro. Moreover, erythropoietin significantly promoted growth of cytogenetically normal cells from 5q- patients, whereas no such effect was observed on erythroblasts from monosomy 7 or trisomy 8 patients.

CONCLUSION

We conclude that growth factors such as erythropoietin and G-CSF can act both via inhibition of apoptosis of myelodysplastic erythroid precursors and via selection of cytogenetically normal progenitors.

Vital functions for lethal caspases

Caspases are a family of cysteine proteases expressed as inactive zymogens in virtually all animal cells. These enzymes play a central role in most cell death pathways leading to apoptosis but growing evidences implicate caspases also in nonapoptotic functions. Several of these enzymes, activated in molecular platforms referred to as inflammasomes, play a role in innate immune response by processing some of the cytokines involved in inflammatory response. Caspases are requested for terminal differentiation of specific cell types, whether this differentiation process leads to enucleation or not. These enzymes play also a role in T and B lymphocyte proliferation and, in some circumstances, appear to be cytoprotective rather than cytotoxic. These pleiotropic functions implicate caspases in the control of life and death but the fine regulation of their dual effect remains poorly understood. The nonapoptotic functions of caspases implicate that cells can restrict the proteolytic activity of these enzymes to selected substrates. Deregulation of the pathways in which caspases exert these nonapoptotic functions is suspected to play a role in the pathophysiology of several human diseases.

Early mitochondrial alterations in ATRA-induced cell death

All-trans retinoic acid (ATRA) induces differentiation and subsequent apoptosis in a variety of cell lines. Using the myeloid cell line P39, we show that ATRA disturbs mitochondrial functional activity long before any detectable signs of apoptosis occur. These early changes include diminished mitochondrial oxygen consumption, decreased calcium uptake by mitochondria and as a result, a lower mitochondrial matrix calcium concentration. Granulocyte colony-stimulating factor (G-CSF) increases mitochondrial respiration and calcium accumulation capacity and subsequently blocks ATRA-induced apoptosis. Nifedipine, a plasma membrane calcium channel blocker, inhibits apoptosis-related changes, such as the loss of the mitochondrial membrane potential and activation of caspases. Thus, the properties of ATRA and G-CSF to modulate mitochondrial respiration and intracellular calcium control are novel findings, which give insight into their precise molecular mode of action.

In patients with myelodysplastic syndromes response to rHuEPO and G-CSF treatment is related to an increase of cytogenetically normal CD34+ cells

The in vivo effect of recombinant human erythropoietin (rHuEpo) and granulocyte colony-stimulating factor (G-CSF) combined treatment on CD34(+) cells was evaluated by fluorescence in situ hybridization (FISH) in 13 myelodysplastic syndrome (MDS) patients with known cytogenetic abnormalities. After treatment, responsive patients presented a significantly lower proportion of FISH abnormal CD34(+) cells than before treatment (P = 0.003), and in comparison with unresponsive cases (P = 0.007). Response to treatment was associated with a reduced degree of apoptosis in CD34(+) cells (P = 0.021): however, no difference in telomere length was observed in responsive patients after growth factor administration. Although the number of patients analysed was relatively small, the present data suggest that, in MDS patients, response to rHuEpo and G-CSF may be related to the proliferation of karyotypically normal but potentially defective CD34(+) progenitor cells.

The Hematopoietic Stem Cell in Myelodysplasia

The mechanisms underlying hematopoietic stem cell or progenitor cell abnormalities in myelodysplastic syndromes (MDSs) remain poorly characterized. Current evidence exists for multiple intrinsic and extrinsic influences upon the stem cell in these disorders. These influences are outlined in this review and include: stem cell characteristics in MDSs, as compared with those in acute myelogenous leukemia; the role of increased apoptosis; the role of signaling pathway abnormalities; the influences of immune modulation; and the effect of stromal cells and stromal cell cytokine production. Despite numerous studies that have examined these factors, how they converge to produce a situation in which accelerated proliferation and accelerated death occur simultaneously remains largely an unexplored area. It is anticipated that future studies that focus on well-characterized and purified progenitor populations in these disorders will elucidate the process by which ineffective hematopoiesis results from the influences of stem cell abnormalities versus abnormalities in the stem cell's microenvironmental and immunologic milieu.

Membrane association of greasy grouper nervous necrosis virus protein A and characterization of its mitochondrial localization targeting signal

Localization of RNA replication to intracellular membranes is a universal feature of positive-strand RNA viruses. The betanodavirus greasy grouper (Epinephelus tauvina) nervous necrosis virus (GGNNV) is a positive-RNA virus with one of the smallest genomes among RNA viruses replicating in fish cells. To understand the localization of GGNNV replication complexes, we generated polyclonal antisera against protein A, the GGNNV RNA-dependent RNA polymerase. Protein A was detected at 5 h postinfection in infected sea bass cells. Biochemical fractionation experiments revealed that GGNNV protein A sedimented with intracellular membranes upon treatment with an alkaline pH and a high salt concentration, indicating that GGNNV protein A is tightly associated with intracellular membranes in infected cells. Confocal immunofluorescence microscopy and bromo-UTP incorporation studies identified mitochondria as the intracellular site of protein A localization and viral RNA synthesis. In addition, protein A fused with green fluorescent protein (GFP) was detected in the mitochondria in transfected cells and was demonstrated to be tightly associated with intracellular membranes by biochemical fractionation analysis and membrane flotation assays, indicating that protein A alone was sufficient for mitochondrial localization in the absence of RNA replication, nonstructural protein B, or capsid proteins. Three sequence analysis programs showed two regions of hydrophobic amino acid residues, amino acids 153 to 173 and 229 to 249, to be transmembrane domains (TMD) that might contain a membrane association domain. Membrane fraction analysis showed that the major domain is N-terminal amino acids 215 to 255, containing the predicted TMD from amino acids 229 to 249. Using GFP as the reporter by systematically introducing deletions of these two regions in the constructs, we further confirmed that the N-terminal amino acids 215 to 255 of protein A function as a mitochondrial targeting signal.

Apoptotic mechanisms in the control of erythropoiesis

Erythropoiesis is a complex multistep process encompassing the differentiation of hemopoietic stem cells to mature erythrocytes. The steps involved in this complex differentiation process are numerous and involve first the differentiation to early erythoid progenitors (burst-forming units-erythroid, BFU-E), then to late erythroid progenitors (colony-forming units-erythroid) and finally to morphologically recognizable erythroid precursors. A key event of late stages of erythropoiesis is nuclear condensation, followed by extrusion of the nucleus to produce enucleated reticulocytes and finally mature erythrocytes. During the differentiation process, the cells became progressively sensitive to erythropoietin that controls both the survival and proliferation of erythroid cells. A normal homeostasis of the erythropoietic system requires an appropriate balance between the rate of erythroid cell production and red blood cell destruction. Growing evidences outlined in the present review indicate that apoptotic mechanism play a relevant role in the control of erythropoiesis under physiologic and pathologic conditions. Withdrawal of erythropoietin or stimulation of death receptors such as Fas or TRAIL-Rs leads to activation of a subset of caspase-3, -7 and -8, which then cleave the transcription factors GATA-1 and TAL-1 and trigger apoptosis. In addition, there is evidence that a number of caspases are physiologically activated during erythroid differentiation and are functionally required for erythroid maturation. Several caspase substrates are cleaved in differentiating cells, including the protein acinus whose activation by cleavage is required for chromatin condensation. The studies on normal erythropoiesis have clearly indicated that immature erythroid precursors are sensitive to apoptotic triggering mediated by activation of the intrinsic and extrinsic apoptotic pathways. These apoptotic mechanisms are frequently exacerbated in some pathologic conditions, associated with the development of anemia (ie, thalassemias, multiple myeloma, myelodysplasia, aplastic anemia). The considerable progress in our understanding of the apoptotic mechanisms underlying normal and pathologic erythropoiesis may offer the way to improve the treatment of several pathologic conditions associated with the development of anemia.

Kostmann syndrome: severe congenital neutropenia associated with defective expression of Bcl-2, constitutive mitochondrial release of cytochrome c, and excessive apoptosis of myeloid progenitor cells

Kostmann syndrome, or severe congenital neutropenia (SCN), is an autosomal recessive disorder of neutrophil production. To investigate the potential role of apoptosis in SCN, bone marrow aspirates and biopsies were obtained from 4 patients belonging to the kindred originally described by Kostmann and 1 patient with SCN of unknown inheritance. An elevated degree of apoptosis was observed in the bone marrow of these patients, and a selective decrease in B-cell lymphoma-2 (Bcl-2) expression was seen in myeloid progenitor cells. Furthermore, in vitro apoptosis of bone marrow-derived Kostmann progenitor cells was increased, and mitochondrial release of cytochrome c was detected in CD34+ and CD33+ progenitors from patients, but not in controls. Administration of granulocyte colony-stimulating factor (G-CSF) restored Bcl-2 expression and improved survival of myeloid progenitor cells. In addition, cytochrome c release was partially reversed upon incubation of progenitor cells with G-CSF. In sum, these studies establish a role for mitochondria-dependent apoptosis in the pathogenesis of Kostmann syndrome and yield a tentative explanation for the beneficial effect of growth factor administration in these patients. (Blood. 2004;103:3355-3361)

The myelodysplastic syndromes: a matter of life or death

Apoptosis is upregulated in early myelodysplastic syndromes (MDS) and may contribute to the peripheral cytopenias commonly observed. Conversely, leukemic progression is associated with abrogation of programmed cell death (PCD). The stage of hematopoietic cell maturation at which defects in PCD arise and the underlying causes of apoptosis dysregulation remain unknown. This paper outlines the apoptotic process in normal hematopoietic cells and summarizes current data regarding the role, potential causes and clinical implications of altered apoptosis in MDS.

Tetraploid myeloid cells in donors of peripheral blood stem cells treated with rhG-CSF

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is frequently used to mobilize CD34+ cells in healthy donors and patient with malignant diseases prior to peripheral blood stem cell (PBSC) harvest. To analyze the effects of rhG-CSF on morphology and genotype of white blood cells, a novel multiparametric cell scanning system that combines morphologic, immune and genotypic analyses of the same cells was used. We report here that tetraploid myeloid cells are present in the peripheral blood of donors treated with rhG-CSF. The tetraploidy was detected in up to 0.6% of differentiated myeloid cells and all observed CD34+ cells were diploid. Thus, short treatment with rhG-CSF of PBSC donors induces numerfical chromosomal alterations in a small subset of mature myeloid cells.

A validated decision model for treating the anaemia of myelodysplastic syndromes with erythropoietin + granulocyte colony-stimulating factor: significant effects on quality of life

We have published previously a prototype of a decision model for anaemic patients with myelodysplastic syndromes (MDS), in which transfusion need and serum erythropoietin (S-Epo) were used to define three groups with different probabilities of erythroid response to treatment with granulocyte colony-stimulating factor (G-CSF) + Epo. S-Epo </= 500 U/l and a transfusion need of < 2 units/month predicted a high probability of response to treatment, S-Epo > 500 U/l and >/= 2 units/month for a poor response, whereas the presence of only one negative prognostic marker predicted an intermediate response. A total of 53 patients from a prospective study were included in our evaluation sample. Patients with good or intermediate probability of response were treated with G-CSF + Epo. The overall response rate was 42% with 28.3% achieving a complete and 13.2% a partial response to treatment. The response rates were 61% and 14% in the good and intermediate predictive groups respectively. The model retained a significant predictive value in the evaluation sample (P < 0.001). Median duration of response was 23 months. Scores for global health and quality of life (QOL) were significantly lower in MDS patients than in a reference population, and fatigue and dyspnoea was significantly more prominent. Global QOL improved in patients responding to treatment (P = 0.01). The validated decision model defined a subgroup of patients with a response rate of 61% (95% confidence interval 48-74%) to treatment with G-CSF + Epo. The majority of these patients have shown complete and durable responses.

Granulocyte colony-stimulating factor inhibits spontaneous cytochrome c release and mitochondria-dependent apoptosis of myelodysplastic syndrome hematopoietic progenitors

Low-risk myelodysplastic syndromes (MDS), including refractory anemia and sideroblastic anemia, are characterized by increased apoptotic death of erythroid progenitors. The signaling pathways that elicit this pathologic cell death in MDS have, however, remained unclear. Treatment with erythropoietin in combination with granulocyte colony-stimulating factor (G-CSF) may synergistically improve the anemia in patients with MDS, with a concomitant decrease in the number of apoptotic bone marrow precursors. Moreover, we have previously reported that G-CSF inhibits Fas-induced caspase activation in sideroblastic anemia (RARS). The present data demonstrate that almost 50% of erythroid progenitor cells derived from patients with MDS exhibit spontaneous release of cytochrome c from mitochondria with ensuing activation of caspase-9, whereas normal erythroid progenitors display neither of these features. G-CSF significantly inhibited cytochrome c release and suppressed apoptosis, most noticeably in cells from patients with sideroblastic anemia. Furthermore, inhibition of caspase-9 suppressed both spontaneous and Fas-mediated apoptosis of erythroid progenitors in all low-risk MDS cases studied. We propose that the increased sensitivity of MDS progenitor cells to death receptor stimulation is due to a constitutive activation of the mitochondrial axis of the apoptotic signaling pathway in these cells. These studies yield a mechanistic explanation for the beneficial clinical effects of growth factor administration in patients with MDS, and provide a model for the study of growth factor-mediated suppression of apoptosis in other bone marrow disorders.