Proliferation and differentiation of myelodysplastic CD34+ cells in serum-free medium: response to individual colony-stimulating factors

[Management of myelodysplastic syndromes]

Myelodysplastic syndromes are heterogeneous diseases whose molecular characteristics have only been identified in recent years. Better identification of prognostic factors, larger access to allogeneic stem cell transplantation and the advent of new drugs notably hypomethylating agents (azacitidine, decitabine) and lenalidomide have improved patient outcome.

Deletion of Asxl1 results in myelodysplasia and severe developmental defects in vivo

Loss of Asxl1 results in myelodysplastic syndrome, whereas concomitant deletion of Tet2 restores HSC self-renewal and triggers a more severe disease phenotype distinct from that seen in single-gene knockout mice.

Somatic Addition of Sex Combs Like 1 (ASXL1) mutations occur in 10–30% of patients with myeloid malignancies, most commonly in myelodysplastic syndromes (MDSs), and are associated with adverse outcome. Germline ASXL1 mutations occur in patients with Bohring-Opitz syndrome. Here, we show that constitutive loss of Asxl1 results in developmental abnormalities, including anophthalmia, microcephaly, cleft palates, and mandibular malformations. In contrast, hematopoietic-specific deletion of Asxl1 results in progressive, multilineage cytopenias and dysplasia in the context of increased numbers of hematopoietic stem/progenitor cells, characteristic features of human MDS. Serial transplantation of Asxl1-null hematopoietic cells results in a lethal myeloid disorder at a shorter latency than primary Asxl1 knockout (KO) mice. Asxl1 deletion reduces hematopoietic stem cell self-renewal, which is restored by concomitant deletion of Tet2, a gene commonly co-mutated with ASXL1 in MDS patients. Moreover, compound Asxl1/Tet2 deletion results in an MDS phenotype with hastened death compared with single-gene KO mice. Asxl1 loss results in a global reduction of H3K27 trimethylation and dysregulated expression of known regulators of hematopoiesis. RNA-Seq/ChIP-Seq analyses of Asxl1 in hematopoietic cells identify a subset of differentially expressed genes as direct targets of Asxl1. These findings underscore the importance of Asxl1 in Polycomb group function, development, and hematopoiesis.

Mouse models of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are hematopoietic malignancies characterized by peripheral cytopenias in the face of normo- or hypercellular, dysplastic bone marrow that arise from mutations in the hematopoietic stem/progenitor cell (HSPC). The disease is characterized by multiple cytogenetic and molecular defects, which result in an extremely heterogeneous phenotype. Recently, significant efforts have been made to develop appropriate mouse models to study this complex disease. Because of the heterogeneity of MDS, no single model is able to capture the MDS phenotype in its entirety. In this review, we describe several MDS mouse models and discuss the advances made in our understanding of the different disease mechanisms within the malignant clone and the marrow microenvironment. In addition, we describe progress in xenotransplantation models of MDS and discuss questions that remain to be answered.

Expression and functional analysis of granulocyte colony-stimulating factor receptors on CD34++ cells in patients with myelodysplastic syndrome (MDS) and MDS-acute myeloid leukaemia

CD34++ cells from 45 patients with myelodysplastic syndrome (MDS) and MDS-acute myeloid leukaemia (MDS-AML) were observed by flow cytometry for the expression of granulocyte colony-stimulating factor receptor (G-CSFR). Ten patients had a significantly reduced expression of G-CSFR. Late stages of disease showed a higher proportion of either high or low G-CSFR expression than earlier stages. In MDS refractory anaemia (RA), G-CSFR was inversely related to CD33 expression. Most patients (9/10) with low G-CSFR expression had neutropenia of the peripheral blood. Neutropenia was less common in the normal group, but also occurred in the high expression group. No neutrophil response was observed following G-CSF administration to MDS-AML patients (6/6) with low G-CSFR expression. In the high expression group, patients (3/3) showed a response to G-CSF while, in the normal group (1/2), the response was minor. In the normal- or high-receptor-expressing groups, the receptors were functionally active in terms of apoptosis but not proliferation and clonogenic growth, although no clear correlation to receptor expression was observed. The G-CSFR signal transduction pathway in the normal and high group was not deficient of messenger RNA for either janus kinases (Jaks) or signal transducers and activators of transcription (Stats). These findings suggest that the lowered expression of G-CSFR may cause neutropenia in MDS and MDS-AML patients and, therefore, may partially explain the neutropenia in myelodysplastic patients.

Novel variant isoform of G-CSF receptor involved in induction of proliferation of FDCP-2 cells: relevance to the pathogenesis of myelodysplastic syndrome

Recent studies have shown that point mutations in granulocyte colony-stimulating factor receptor (G-CSFR) are involved in the pathogenesis of severe congenital neutropenia (SCN) and in the transformation of SCN to acute myelogenous leukemia (AML). It is reasonably speculated that the abnormalities in the signal transduction pathways for G-CSF could be partly responsible for the pathogenesis and the development to AML in patients with myelodysplastic syndromes (MDS). Therefore, we investigated the structural and functional abnormalities of the G-CSFR in 14 patients with MDS and 10 normal subjects. In in vitro colony forming assay, MDS samples showed reduced response to growth factors. However, G-CSF, but not GM-CSF and IL-3, enhanced clonal growth in three cases of high risk patients with MDS (RAEB, RAEB-t, and MDS having progressed to acute myeloid leukemia (AML)) and one low risk patient (RA). Eight out of 14 patients including above 4 patients demonstrated a common deletion of the G-CSFR cDNA; a deletion of three nucleotides (2128-2130) in the juxtamembrane domain of the G-CSFR, which resulted in a conversion of Asn(630)Arg(631) to Lys(630). To assess the functional activities of this deletion in the G-CSFR isoform, a mutant with the same three-nucleotide deletion was constructed by site-directed mutagenesis. FDCP-2 cells expressing the G-CSFR isoform responded to G-CSF, and exhibited proliferative responses than did those cells having wild-type G-CSFR. Moreover, these isoforms showed prolonged activation of STAT3 in response to G-CSF than did the wild-type. These results suggest that the deletion in the juxtamembrane domain of the G-CSFR gives a growth advantage to abnormal MDS clones and may contribute to the pathogenesis of MDS.

Growth characteristics of myelodysplastic CD34+ cells

Myelodysplastic syndromes (MDS) are a heterogeneous group of disorders of hematopoiesis entailing hyperproliferative and ineffective hematopoiesis associated with morphologic evidence of marrow cell dysplasia resulting in refractory cytopenia(s), and an increased risk of transformation into acute myeloblastic leukemia (AML). The administration of colony-stimulating factor(s) (CSFs) to patients with MDS increased blood neutrophil concentrations, in most patients, and it was anticipated to be of benefit to prevent infections. The progression to AML while being treated with CSFs has come under close scrutiny. In vitro studies are expected to produce more pertinent criteria for selection of patients who are likely to benefit, as well as the overall benefits of various therapies. For this purpose, in vitro colony assays are an excellent approach for investigation of the biologic characteristics of MDS progenitor cells. The stem cell phenotype CD34 is the one of the best markers of progenitor cells, and can be used for the purification of these cells to unify levels of maturation; a direct comparison of proliferative and differentiative capacity of MDS progenitor cells with normal CD34+ cells can thus be made. The properties of MDS CD34+ cells are described here in association with proliferation and differentiation, with special emphasis on the role of stem cell factor (a ligand for c-kit) in leukemic type growth of MDS CD34+ cells.

The evidence of clonal evolution with monosomy 7 in aplastic anemia following granulocyte colony-stimulating factor using the polymerase chain reaction

We present here the case of a Japanese female patient with aplastic anemia who developed monosomy 7 and clonal evolution following a treatment with recombinant human granulocyte colony-stimulating factor (rhG-CSF). At the onset of aplastic anemia, cytogenetic analysis was 46, XX and X-inactivation/methylation analysis revealed a polyclonal pattern. After 4 months of administration of rhG-CSF, she had 45, XX, -7 and a clonal pattern, although there were no morphological evidence of a myelodysplastic syndrome or leukemia. The ratio of monosomy 7 to normal analyzed by fluorescence in situ hybridization decreased after discontinuation of rhG-CSF and there were still no dysplastic changes and/or increased numbers of blasts. These results indicate that the acquisition of monosomy 7 following rhG-CSF treatment dose not always cause clonal evolution to induce hematological malignancies.

Proliferation and differentiation of myelodysplastic CD34+ cells

Myelodysplastic syndromes (MDS) are a heterogeneous group of disorders of hematopoiesis involving hyperproliferative and ineffective hematopoiesis associated with morphologic evidence of marrow cell dysplasia resulting in refractory cytopenia(s), and an increased risk of transformation into acute myeloblastic leukemia (AML). The administration of colony-stimulating factor(s) (CSFs) to patients with MDS increased blood neutrophil concentrations, in most patients, and was also expected to be beneficial and to prevent infections. However, the progression to AML during the treatment with CSFs was suspected in some patients. Therefore, extensive in vitro studies were expected to lead to the establishment of criteria for selection of patients who are likely to benefit from CSF's as well as to establish the overall value of the different types of CSFs therapy. For this purpose, in vitro colony assays provide an excellent tool for investigating the biologic characteristics of MDS progenitor cells. However, conditions of the culture must be such that each progenitor can express its full potential for proliferation and differentiation. Because of the above, MDS progenitor cells cannot be used because they carry an impairment in proliferation and differentiation. To address this problem, one needs to know how many cells are being handled and the maximum numbers of colonies and clusters expected. CD34, a stem cell phenotype, is at present one of the best markers of progenitor cells, and can be used for purposes of purification. Using a defined number of CD34+ cells, it was feasible to make direct investigations on MDS progenitor cells. In this review the properties of MDS progenitor cells are described, in association with proliferation and differentiation, with special emphasis on the phenotypic subpopulations of MDS CD34+ cells.

Inhibition of GM-CSF production by recombinant human interleukin-4: negative regulator of hematopoiesis

Interleukin-4 (IL-4), also known as B-cell stimulatory factor-1 (BSF-1), was initially identified as a T-cell product that mediates anti-IgM-induced DNA synthesis in B-lymphocytes. Various aspects of this highly pleiotropic cytokine have been described, including those on hematopoietic progenitor cells. However, the role of IL-4 in the hematopoietic system has been given different interpretations. Normal human hematopoietic progenitor cells do not proliferate under control of the autocrine system and cytokines are needed for proliferation and differentiation. However, IL-4 in itself does not support proliferation of these cells and if this is the case, the effects of IL-4 on hematopoietic progenitor cells still need to be investigated from the point of view of synergism with other cytokines as well as the control of accessory cells in the production of cytokines. We describe here some properties of IL-4 in association with cytokine production, with special emphasis on granulocyte-macrophage colony-stimulating factor (GM-CSF) production.

What is ineffective erythropoiesis in myelodysplastic syndromes?

The anaemia of MDS is multifactorial with intramedullary ineffective erythropoiesis resulting from an imbalance between erythroid proliferation, differentiation and apoptosis in favour of initial hypercellularity with high cell death through to a lower cellularity, lower death state with the eventual evolution of the leukaemic clone in many patients. The fundamental molecular abnormality(ies) in MDS, which produce the milieu for the heterogeneous molecular insults described (e.g., oncogene mutations) remains elusive. Many questions such as why MDS red cells are macrocytic and what are the precise cellular and molecular mechanisms of ineffective erythropoiesis remain unanswered but future study of the erythroid lineage should provide molecular clues to the earliest abnormalities in the pathogenesis of MDS.

Clonal analysis of peripheral blood and haemopoietic colonies in patients with aplastic anaemia and refractory anaemia using the polymorphic short tandem repeat on the human androgen-receptor (HUMARA) gene

The clonalities in white blood cells (WBC) of blood and nucleated bone marrow cells from patients with refractory anaemia and aplastic anaemia were examined by polymerase chain reaction (PCR) methods using the polymorphic short tandem repeat (STR) on the human androgen-receptor gene (HUMARA). Peripheral blood samples were obtained from 12 female patients, six with aplastic anaemia (AA) and six with refractory anaemia (RA). Peripheral blood was fractionated into granulocytes, lymphocytes, T lymphocytes and B lymphocytes. DNA was extracted from each fraction. Bone marrow samples were obtained from seven female patients (three with AA and four with RA). Sorted CD34 positive cells were cultured in a semisolid culture system. DNA was extracted from a 14-day haemopoietic colony. The clonal pattern was assessed using HUMARA gene STR polymorphism and the differential methylation pattern of nearby cytosine residues by PCR methods. Four of six (67%) AA and two of six (33%) RA patients had a monoclonal proliferating pattern in their granulocytes. The ratio of the numbers of minority colonies per majority colonies (m/M ratio) was examined for seven patients (three AA and four RA). In patients who had a clonal haemopoietic pattern in peripheral WBC the ratio was under 0.4 but not zero. In contrast, patients exhibiting a polyclonal pattern had an m/M ratio above 0.8. We concluded that some normal or heterogenous haemopoietic clones, not only MDS but also AA, may remain in the bone marrow, although almost all colonies were derived from a single pathogenic clone when the clonality pattern exhibited monoclonality in peripheral blood analysis.

Proliferation and differentiation of myelodysplastic CD34+ cells in serum-free medium: II. Response to combined colony-stimulating factors

To investigate the role of colony stimulating factors (CSFs) in the proliferation and differentiation of progenitor cells from myelodysplastic syndromes (MDS), marrow progenitor cells from 18 MDS patients were highly purified using CD34 monoclonal antibody and immunomagnetic microspheres (MDS CD34+ cells). These cells were cultured in serum-free medium with various combinations of five colony stimulating factors (CSFs): recombinant human interleukin-3 (rIL-3), granulocyte/macrophage-CSF (rGM-CSF), granulocyte-CSF (rG-CSF), macrophage-CSF (rM-CSF), and erythropoietin (rEP). Among the tested CSFs, such as rM-CSF, rG-CSF, rGM-CSF and rIL-3, a combination of the first three CSFs was the most effective stimulus for the proliferation of non-erythroid MDS progenitor cells. An increase of undifferentiated "blast" cell colonies in 5/18 MDS patients occurred and these 5 patients belonged to the high-risk group. In the presence of these three CSFs, rIL-3 had no effect on the proliferation and differentiation of MDS CD34+ cells; however, IL-3 was efficient for the proliferation of MDS CD34+ cells to the erythroid lineage. rGM-CSF or rIL-3 alone did not efficiently support proliferation and differentiation of CD34+ cells. M-CSF is present in normal human serum at a concentration of 550 +/- 110 U/ml, a concentration exceeding that used in this study (100 U/ml). Therefore, in vivo administration of G-CSF combined with GM-CSF to MDS patients may be one of the most effective CSF combinations for proliferation of MDS progenitor cells to the non-erythroid lineage. However, the effect on the capacity for differentiation was minimal, especially in patients belonging to the high-risk group.

Sequential administration of recombinant human granulocyte-macrophage colony-stimulating factor and human erythropoietin for treatment of myelodysplastic syndromes

Treatment of myelodysplastic syndromes (MDS) with recombinant human erythropoietin (Epo) is successful in only 10% to 25% of patients. We performed a pilot study in 10 anaemic patients with MDS to examine whether sequentially applied recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) and Epo improves haemoglobin levels and/or reduces red blood cell transfusion requirements. Morphological diagnoses of patients were refractory anaemia (RA) in 3 cases, RA with ring sideroblasts in 3 cases and RA with excess blasts in 4 cases. GM-CSF was given subcutaneously at a dose of 150 micrograms/m2/d during the initial 10 days. From day 11, Epo was administered by subcutaneous injections for 8 weeks at a dose of 100 U/kg/d and subsequently at an escalated dose of 200 U/kg/d in 3 patients. Changes in reticulocyte counts, haemoglobin levels, RBC support and ferrokinetic parameters were compared with pretreatment values. Two out of 8 evaluable patients showed a rise in haemoglobin levels at week 8 and 10, respectively, and lost their transfusion dependency for a period of 13 and 27 weeks. In 1 patient, haemoglobin level increased only after dose escalation of Epo (200 U/kg/d). Leukocyte counts remained uneffected by treatment with Epo, while 1 patient showed a 4-fold increase in platelet numbers. Toxicity was mild. Two patients died of pneumonia and global heart failure, respectively, unrelated to growth factor therapy. Based on this pilot study, we conclude that sequential treatment with GM-CSF and Epo does not increase erythroid responses in anaemic patients with MDS. Because of the delayed increase in haemoglobin in both responders, we surmise that the beneficial effects were induced by Epo alone.

Impaired proliferation and differentiation of myelodysplastic CD34+ cells

The myelodysplastic syndromes (MDS) are a heterogeneous group of disorders of hematopoiesis entailing hyperproliferative and ineffective hematopoiesis resulting in refractory cytopenia(s), and increased risk of transformation into acute myeloblastic leukemia (AML). The widely used classification defined by the French-American-British group (FAB) recognizes 5 cytological subtypes of different prognosis, based essentially on the presence and the frequency of marrow blasts. The percentage of marrow blasts does not exceed 30%, hence, direct investigations of biological and biochemical events of MDS blast cells have been hampered. The CD34 antigen is currently unique in its narrow specificity of expression on human lymphohematopoietic progenitor cells. This cell membrane phosphoglycoprotein has been used for immunologic blast cell purification, notwithstanding the frequency of marrow blasts, and has provided a set of tools for investigations of MDS i.e. a direct comparison of the nature of blast cells in each of the MDS subtypes, using immunologic, biologic, biochemical and molecular biological methodology. A combination of serum-free medium and a purification method for blast cells provided evidence that the progenitor cell growth abnormalities in these disorders involve a defect in the capacity of progenitor cells to respond to stimulation with growth factor(s), and has presented direct evidence for the manner in which myelodysplastic CD34+ cells are impaired.