Prognostic value of in vitro bone marrow culture in refractory anaemia with excess of myeloblasts

Role of physiologic concentrations of stem cell factor in leukemic type growth of myelodysplastic CD34+ cells

The stem cell factor (SCF: a ligand for c-kit) plays a central role in the growth of myelodysplastic (MDS) progenitor cells with leukemic type growth. In this study, the role of physiologic concentrations of SCF on the proliferation and differentiation on MDS progenitor cells was further analyzed in the presence of combined cytokines. For this purpose, marrow CD34+ cells were purified up to 94% for 12 normal individuals and 90% for 18 MDS patients, using monoclonal antibodies and immunomagnetic microspheres. The purified CD34+ cells were cultured for 14 days with saturating doses of cytokines, including recombinant human macrophage colony stimulating factor (rM-CSF), granulocyte-CSF (rG-CSF), granulocyte/macrophage-CSF (rGM-CSF), interleukin-3 (rIL-3) and rSCF. The clonal growth of MDS CD34+ cells supported by a combination of all the above cytokines was then subdivided into the two patterns of leukemic or non-leukemic. The role of various concentrations of rSCF (0, 0.5, 5, 50 and 500 ng ml(-1)), with or without the above cytokines, in proliferation and differentiation of MDS CD34+ cells was analyzed in each group. The physiologic concentration of SCF at 5 ng ml(-1) significantly increased undifferentiated 'blast cell' colonies or clusters in leukemic type growth of MDS CD34+ cells over that seen in normal CD34+ cells. SCF is present in plasma at a level of ng ml(-1). This means that progenitor cells are continuously exposed to stimulation by SCF in vivo and that MDS leukemic cells have a growth advantage over normal blasts.

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.

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.

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.

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.

Myelodysplastic syndromes. Pathogenesis, diagnosis and treatment

Our understanding of the biology of leukemia and myelodysplasia is still only partial. The diagnosis of myelodysplasia is often based on quantitative and qualitative findings in the peripheral blood and bone marrow. These findings are often shared by other disorders. There is a need for sensitive and inexpensive laboratory tests to determine clonality and karyotypic abnormalities in this disorder. Future classifications of these syndromes will need to be based on morphologic and biologic markers that are closely linked to disease progression, response to treatment, and survival. Our limited understanding of the pathogenesis of MDS decreases the specificity and effectiveness of our therapeutic interventions. Agents that are minimally toxic such as CRA, danazol, 1,25-dihydroxyvitamin D3, androgens, and pyridoxine are seldom useful. Antileukemic therapy and allogeneic bone marrow transplantation have a major role to play in patients younger than 45 years of age; in older patients these treatment modalities remain controversial because of their toxicity. Hematopoietic growth factors, used alone or in combination, may improve the quality of life and improve survival of patients with MDS. Growth factors may also decrease treatment-related mortality associated with chemotherapy and bone marrow transplantation and render these treatment modalities available for a higher percentage of patients. The development of more specific differentiating agents may permit hematopoietic differentiation while minimizing side effects.

Circulating CD34+ cells: an adverse prognostic factor in the myelodysplastic syndromes

As part of an epidemiological survey of myelodysplastic syndromes (MDS) in southern Tasmania, 62 MDS patients identified over a 2 year period were tested for the presence of CD34, the human progenitor cell antigen (HPCA), in their peripheral blood. The results were correlated with transformation to acute myeloid leukemia (AML) and patient survival, and CD34+ status was compared as a prognostic indicator with Bournemouth score, cytogenetics, and CFU-GM colony growth which were also assessed. Circulating CD34+ cells were found in 23 of the 62 MDS patients; 9 of the 23 patients with circulating CD34+ cells transformed to AML, as compared with none of the 39 CD34 negative patients (P less than 0.0001); and 11 of the 23 patients with circulating CD34+ cells were dead at the end of the 2 year period, as opposed to 6 of the 39 with no CD34+ cells (P less than 0.03). The Bournemouth score was also significantly associated with transformation to AML (P less than 0.0001) and poor survival (P less than 0.04). These were the only significant associations of the possible prognostic factors studied with either transformation or survival. In summary, the presence of circulating CD34+ cells was significantly associated with both progression to AML and poor survival and was found to be a better prognostic indicator than cytogenetics or CFU-GM colony growth.

Biology of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) represent a diverse spectrum of disorders ranging from refractory anemia to a preleukemic state. Peripheral cytopenias, cellular marrow, dysplasias and dysfunctions of myeloid and lymphoid cells constitute hematological hallmarks, and are caused by ineffective hemopoiesis. Investigations of cell cultures and cellular functions indicate that the disease originates in a stem cell pluripotent to all myeloid cells and possibly lymphoid cells as well. The disease commonly runs a chronic indolent course, often terminating in acute leukemia or nonleukemic death, notably infections and/or hemorrhage due to cytopenias and cellular dysfunctions. Clonal expansion or clonal evolution appears to be related to the disease progression with a greater degree of malignancy. However, the initial sequence of events causing damage to stem cells is still undefined.

Leukocyte-derived inhibitory activity in patients with myelodysplastic syndrome

Leukocyte-derived inhibitory activity inhibiting the entry of normal progenitor cells of granulocytes and macrophages (CFU-GM) into the S-phase of a cell cycle was investigated in 16 patients with different forms of myelodysplastic syndrome (MDS). The presence of this inhibitory activity was analysed in medium conditioned with low-density cells obtained from peripheral blood of MDS patients. The inhibition rate was measured by 3H-thymidine suicide technique with subsequent cultivation of pretreated cells in semisolid agar medium. Low-density cells from MDS patients of various types were studied: from the twelve patients with refractory anaemia (RA or RAS) only three were positive, one patient with chronic myelomonocytic leukaemia (CMML) was negative while one patient with refractory anaemia with excess of blasts (RAEB) and two patients with RAEB in transformation (RAEB-T) were positive with respect of the described test. In two patients with RA, who underwent a long-term investigation, the production of leukocyte-derived inhibitory activity preceded the development of disease into RAEB or RAEB-T. In five positive cases, supernatants were incubated with antiserum against human placental ferritin; with one exception, the inhibitory activity was neutralized.

Significance of in vitro cultures in myelodysplastic syndromes

Bone marrow samples from 20 controls, 41 patients suffering from various types of myelodysplasia and 19 suffering from ANLL were investigated by in vitro cultures. The cultures were stimulated by various concentrations of leucocyte conditioned medium (LCM) and PHA-stimulated conditioned medium (PCM) and were examined after 7 and 14 d. We found that, in clinically stable MDS, growth patterns and dose-response to CM's were mostly within the normal range. With progressive blastic transformation, these features became abnormal with an increase in cluster growth. Clusters responding to a high dose of LCM, persisting after 14 d and enhanced by PCM may represent 'early' clonogenic cells. These clusters were found in progressive MDS with increased numbers of blast cells. Clusters formed by 'late' clonogenic cells were found in normal bone marrow and stable MDS. In ANLL the disturbance of proliferation and maturation seems to be much more pronounced than in progressive MDS with blastic transformation. We conclude that the interpretation of in vitro bone marrow culture data in terms of a disorderly arrangement of clonogenic cells in MDS and ANLL is facilitated by comparing different conditioned medium stimulations and by scoring after different time intervals.

Colony assays of hematopoietic progenitor cells and correlations to clinical situations

The production of blood cells is a dynamic process that is noticeably aberrant during disease. The availability of colony assays in vitro that allow detection of hematopoietic stem and progenitor cells for the neutrophil, monocyte-macrophage, erythroid and/or megakaryocyte lineages has been of importance for the present understanding of the mechanisms controlling the proliferation, self-renewal capacity, and differentiation of morphologically nonrecognizable immature cells which give rise to the mature progeny circulating in the blood. It is through the use of these assays that the existence of potentially relevant stimulatory and inhibitory feedback interactions has been demonstrated. Abnormalities in these interactions, which may be of significance during leukemia and related disorders, have been uncovered. This communication will discuss regulatory interactions detected via the colony assays, their potential relevance physiologically and pathologically, and the use of these assays for diagnosis, prognosis, and for monitoring the clinical status of patients.

Prognostic value of the combined suicide level of granulocyte progenitors and the labelling index of precursors in preleukemic states and oligoblastic leukemias

Although abnormalities in granulopoiesis detected by means of bone marrow cytology, culture and kinetic studies have provided prognostic data in preleukemic states and oligoblastic leukemias, this information cannot be applied to individual cases. In order to determine the indications for treatment and the form it should take in a given case, data would be required concerning the probability of impending transformation into acute leukemia. In 45 studies involving 34 patients who were followed for 10-42 months, a combination of a rise in the proportion of granulocyte precursors in S-phase, indicated by a colony-forming cell suicide rate of over 40%, and a low labelling index of myeloblasts and promyelocytes, was always followed by the onset of acute leukemia within 10 months. Sequential studies in 13 patients revealed an increase in cluster-forming cells and in the suicide level in the second study. The changed kinetics of granulopoietic proliferation may provide an indication for chemotherapy.

Refractory anemia with excess of blast cells: prognostic factors and effect of treatment with androgens or cytosine arabinoside. Results of a prospective trial in 58 patients. Cooperative Group for the Study of Aplastic and Refractory Anemias

The results of a prospective study of 58 patients with refractory anemia and partial blastic infiltration of the bone marrow lead to the following conclusions. The median survival (12 months from diagnosis) is shorter and the rate of acute leukemia as cause of death (60%) higher than in other retrospective series. This group of patients, however, appears to be a "continuum" of preleukemic states with more or less rapid evolution, so that the exclusion of the most severe cases appears unjustified. Based on the degree of bone marrow blastosis, and also on the degree of blood cytopenias, the anomalies of 59 Fe incorporation kinetics and the bone marrow stem-cell cultures, it is possible to derive a plausible prognosis for individual patients, which could aid the choice of therapy. Androgen therapy does not accelerate leukemic evolution, but does not improve the bone marrow insufficiency. Cytosine-arabinoside at low dosage exhibited no toxicity, but did not delay the appearance of overt leukemia.