Preleukaemia and myelodysplastic syndromes today

The clinical picture of myelodysplastic syndromes (MDS) results from the expansion of an abnormal clone of haemopoietic stem cells that has undergone premalignant transformation. Different types of "oncogene" may be involved in this process, some of which code for growth factors and their receptors, some for membrane or cytoplasmic proteins and some for nuclear binding proteins. The insults causing gene mutations are not known, though chemical, viral or radiation damage could be important. The most striking feature of MDS is the inadequate production of dysplastic, poorly functional cells as a result of impaired differentiation and premature cell death in the bone marrow. Treatment is currently directed to supportive therapy with blood components and antibiotics, attempts to stimulate proliferation and differentiation with recombinant human growth factors, and, in a few cases, bone marrow transplantation. Chemotherapy alone has met with little success.

Circulating erythropoietin in patients with myelodysplastic syndromes

Serum concentration of erythropoietin (Epo) has been measured by radioimmunoassay in 46 patients with myelodysplastic syndromes. There is an overall inverse relationship between the level of Epo and the degree of anaemia but a wide range of Epo response between patients with similar haemoglobin concentrations. No differences were found between the different FAB groups, but the highest Epo levels were found in those patients with erythroid hypoplasia in the bone marrow. It is suggested that the intensity of erythroid activity in the marrow, as well as the degree of anaemia, may be a factor determining serum Epo concentration.

The application of X-chromosome gene probes to the diagnosis of myeloproliferative disease

X-chromosome DNA probes for the phosphoglycerate kinase (PGK) and hypoxanthine phosphoribosyl transferase (HPRT) genes were used to study clonality in haemopoietic cells from 63 women with myeloproliferative disease, idiopathic erythrocytosis, secondary erythrocytosis or normal red cell volumes. A total of 25 women (39%) were heterozygous for one of the polymorphisms associated with these genes. Clonality was demonstrated in five out of six patients with polycythaemia vera (PV) and in three other patients with myeloproliferative disease. In all cases of PV, including the patient in whom clonality was not demonstrated, cultures of peripheral blood showed growth of endogenous erythroid colonies.

Oncogenes in the myelodysplastic syndrome

The conversion of normal haemopoietic stem cells to myelodysplastic and then to leukaemic cells is marked by a number of events leading to progressive genetic changes in the abnormal clonal population. Cytogenetic evidence points to abnormalities at specific chromosomal locations, commonly involving chromosomes 5 and 7, where there are a particular concentration of genes directly involved in the regulation of haemopoietic proliferation and differentiation. These include GM-CSF, IL-3, M-CSF, erythropoietin and others. Other genes that may be involved in the preleukaemic process are so-called 'oncogenes' such as met on chromosome 7q and fms on 5q (which codes for the M-CSF receptor) that may be deleted or translocated. The ras gene family is activated by point mutations in a wide variety of malignant states, including myelodysplasia and acute myeloblastic leukaemia. At the present time we do not know the cause of these genetic lesions, their functional significance or the sequence in which they occur.

DNA index and karyotype analysis in myelodysplasia

DNA index (DI) determined by flow cytometry and karyotype determined by conventional methods were obtained on bone marrow samples from 43 haematologically normal subjects and 54 patients with myelodysplastic syndrome (MDS). Twenty one patients had a clonal karyotype abnormality but an additional five had a DI outside the normal range, showing evidence of aneuploidy that was not available from chromsome preparations. When patients were grouped into those with excess chromosomal material, those with diploid karyotypes, and those with a loss of chromosomal material, there was a significant difference among the mean DIs of each group, normal subjects being different from all patient groups. In these patients DI measurements were of value when carried out together with conventional chromsomal analysis in gaining the maximum amount of genetic information when a satisfactory karyotype might not be available or where failure of an abnormal cell population to proliferate might give an incomplete cytogenetic picture. The contribution of non-clonal chromsome loss to the DI is probably significant but has not been quantitated.

Multidrug resistance in haemopoietic cell lines, myelodysplastic syndromes and acute myeloblastic leukaemia

Resistance to cytotoxic agents is a common clinical problem encountered in the treatment of human myelodysplastic syndromes (MDS) and acute myeloblastic leukaemia (AML). Cellular acquisition of the multidrug resistance (MDR) phenotype confers loss of sensitivity to a wide range of structurally dissimilar anti-neoplastic agents. This state can arise through increased expression of the mdrl (P-glycoprotein) gene. We have used the mdrl gene probe to investigate adriamycin resistant (HL60/AR) and vinblastine resistant (CEM/VLB100) human leukaemic cell lines. In addition, peripheral blood or bone marrow cells from 66 patients with MDS and AML have been screened for gene amplification and 40 cases for increased mRNA expression. P-glycoprotein gene amplification was observed only in the (CEM/VLB100) and not in the HL60/AR on any other leukaemic cell line. Gene amplification was not found in any patient's cells. Eighteen out of 40 patients showed an increase (2----20) of mdrl mRNA expression. These results are not only of significance in understanding the biology of human drug resistance but have practical importance in the design of anti-leukaemic therapy.

Effect of 5637-conditioned medium on peripheral blood granulocyte-macrophage progenitors in normal subjects and patients with the myelodysplastic syndrome

There was no overall increase in PB-CFU-GM from normal subjects, or MDS patients, when exogenous CSA (5637-CM) was added to the culture medium. However, there was a sub-group of MDS patients (seven of 35) whose PB-CFU-GM numbers were significantly stimulated by 5637-CM. In addition, there were 11 (out of 48) MDS patients with undetectable PB-CFU-GM in assays without exogenous CSA but only two when 5637-CM was added (p less than 0.01). This sub-group is of particular interest as it is known that those without detectable PB-CFU-GM tend to have significantly shorter survival times than others. The mechanism of the functional abnormality is yet to be determined.

Primary acquired sideroblastic erythropoiesis in non-anaemic and minimally anaemic subjects

Six patients had primary sideroblastic erythropoiesis together with a haemoglobin concentration of 12.0 g/dl or higher. In four cases this was associated with macrocytosis. Other abnormalities included failure of erythroid progenitor growth from peripheral blood in three cases and occasional dysplastic appearances in neutrophils and megakaryocytes. Sideroblastic erythropoiesis seems to be an early manifestation of the myelodysplastic syndrome and may present clinically at a pre-anaemic stage.

Effects of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) on single CD34-positive hemopoietic progenitors from human bone marrow

To determine the extent accessory cells mediate the effects of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) on human hemopoietic progenitors in vitro, we added this hemopoietin to liquid cultures of single CD34-positive marrow cells. These were selected on a fluorescence-activated cell sorter using the HPCA-1 (My10) antibody. Myeloid, erythroid and a few mixed clones developed in 13% of wells in the apparent absence of accessory cells at the beginning of culture. Although accessory cells were generated quickly from the myeloid progenitors and could have mediated the action of rhGM-CSF, this was not the case in the majority of the erythroid clones in which no other cell types were recorded. We conclude that rhGM-CSF can act directly on a subset of erythroid progenitors and probably induces a substantial number of myeloid clones directly.

Myelodysplasia, chemical exposure, and other environmental factors

This paper describes a case-control study of the occupational and environmental exposures of patients with myelodysplasia. The methodology, first described in Canada for solid tumors, estimates lifetime exposures to a number of potential toxic hazards or carcinogens. This pilot study confirms that the methodology, with the use of questionnaires and interviews, can estimate exposures to specific chemicals and shows some significant associations with myelodysplasia, including exposure to petrol or diesel compounds.

c-myc protein kinetics during growth and differentiation of CD34 (MY10)-positive blast cells from normal human marrow

We have used flow cytometry to quantitate nuclear c-myc protein, at each phase of the cell cycle, during in-vitro differentiation of CD34-positive stem cells isolated from normal human bone marrow by the monoclonal antibody, MY10. Mean c-myc protein levels in CD34-positive cells, consisting of greater than 70% blasts, are lower than a marrow fraction containing myeloid cells of intermediate maturation, but have an invariant proportional relationship, with regard to nuclear mass, over the cell cycle. The majority of these primitive cells are non-cycling, as revealed by DNA content. Under our assay conditions, nuclear c-myc protein distribution over the cell cycle did not change as these progenitors entered a proliferative phase in culture. In cultures containing factors supporting myeloid maturation, mean G0/G1 p62c-myc levels initially decline, then rise above starting values as promyelocytes and myelocytes differentiate from CD34-positive cells, and as proliferation begins. With further myeloid maturation, and while cell numbers are increasing, c-myc protein continues to increase. C-myc protein kinetics differ in cultures in which macrophages, rather than myeloid cells, predominate. These data indicate that a complex relationship exists between c-myc gene expression and proliferation, maturation and lineage in haemopoietic cells, and lend support to the notion that early down regulation may be causally associated with the differentiation process.

In vitro growth of myeloid and erythroid progenitor cells from myelodysplastic patients in response to recombinant human granulocyte-macrophage colony-stimulating factor

Marrow progenitor cells from 14 myelodysplastic (MDS) patients and 17 normal donors were assayed in semisolid cultures supplemented with increasing doses of recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) or medium conditioned by 5637 bladder carcinoma cells (5637CM). At doses of supplements shown to be optimal for colony formation in cultures of normal marrow, myeloid (day 14) colony numbers were subnormal in 10 of 14 MDS marrows cultured in 5637CM and in 8 of 14 cultures containing rhGM-CSF (2.5 ng/ml). However, a high dose of rhGM-CSF (20 ng/ml) raised myeloid colony numbers in cultures of many MDS marrows, so that 9 of 14 now yielded colonies within the normal range; increased levels of 5637CM failed to do this. Erythroid colony growth was poor in 13 of 14 MDS marrow cultures supplemented with erythropoietin in addition to 5637CM or rhGM-CSF. High concentrations of rhGM-CSF did not increase erythroid growth. These data suggest that myeloid progenitors from the MDS clone may have a decreased responsiveness to hemopoietins which can be overcome at high concentrations of growth factors.

Enrichment of CD34 (My10)-positive myeloid and erythroid progenitors from human marrow and their growth in cultures supplemented with recombinant human granulocyte-macrophage colony-stimulating factor

Myeloid and erythroid progenitor cells were enriched from human marrow by selecting CD34-positive (CD34 + ve) cells, labeled with the My10 (HPCA-1) antibody, using a fluorescence-activated cell sorter. Seventy-one percent of CD34 + ve cells were blasts and most of these were too primitive to be identified by standard morphological criteria. On average, 9.5% of CD34 + ve cells formed clones after 14 days of culture in semisolid medium supplemented with erythropoietin and medium conditioned by 5637 bladder carcinoma cells. Over 2.5% of CD34 + ve cells were day-14 myeloid colony-forming cells and 2.4% were erythroid colony (burst)-forming progenitors. The remaining progenitors formed myeloid and erythroid clusters. A subpopulation of day-14 myeloid colony-forming cells failed to respond to recombinant human granulocyte-macrophage colony-stimulating factor (rhuGM-CSF) after accessory cells were removed during enrichment, so it appears that this factor can induce myeloid growth indirectly as well as directly. Recombinant human GM-CSF also supported erythroid colony-formation in cultures of CD34 + ve cells, which suggests that this hemopoietin may act directly on erythroid progenitors.

Assessment of DNA content and cell cycle distribution of erythroid and myeloid cells from bone marrow

A method is described for the measurement of DNA index and cell cycle distribution in purified erythroid and myeloid populations from human bone marrow. Erythroid cells were prepared after complement mediated lysis of non-erythroid marrow cells. Myeloid cells were obtained by fluorescence activated cell sorting by forward and wide angle light scatter. Mononuclear marrow cells were prepared with a density gradient. Nuclei prepared from the separated populations were stained with propidium iodide. Myeloid cells had a higher DNA index than erythroid cells, and the mononuclear preparation had an intermediate value. There were more erythroid than myeloid cells in the S and G2M phases of the cell cycle. These lineage differences are particularly relevant when considering data derived from unseparated bone marrow cells, and further experiments are needed to determine the origin of these anomalies.

RAS mutations in myelodysplasia detected by amplification, oligonucleotide hybridization, and transformation

Members of the RAS gene family have been implicated in many neoplasms with activating mutations around amino acid positions 12 and 61. We have assessed the mutational activation of H, K, and NRAS in myelodysplasia (MDS) by polymerase chain reaction and hybridization with synthetic oligonucleotide probes. Using this method, point mutations in codons 12/13 and 61 of these RAS genes were detected in 20 of 50 patients including two with refractory anemia with ringed sideroblasts (RARS). Ten normal individuals had no detectable RAS mutations. In 11 instances, DNA from patients with detectable RAS mutations were shown to register in either NIH3T3 focus-forming or nude mouse tumorigenicity assays. In addition, one patient (RARS) was shown to have an activated NRAS gene detected by a tumorigenicity assay and Southern blot analyses. Two MDS patients had mutations detected in two different RAS genes. DNA from one of these patients was observed to give rise to transformants with activated N and HRAS. Two patients with detectable NRAS mutations in the MDS stage progressed to AML and DNA from the AML stage registered positively in a transformation assay with NRAS activation. These results show that RAS mutations can occur at early, as well as late, stages of leukemic progression. The incidence of RAS mutations appears to be significantly higher in CMML than in the other subgroups (p = 0.02).

Effect of phytohaemagglutinin on the synthesis and secretion of ferritin in peripheral blood lymphocytes

Stimulation of lymphocytes with phytohaemagglutinin (PHA) causes an increase in the rate of ferritin and total protein synthesis which is not enhanced by supplementing the medium with iron. There is an increase in intracellular ferritin content which is amplified by the presence of iron but this is also observed in the absence of PHA stimulation. The increased cellular ferritin is greater for heart type ferritin than for spleen type ferritin. Ferritin secreted into the medium from the cells shows a relative preponderance of spleen type ferritin compared to the intracellular protein. The data shows a dissociation between ferritin synthesis, cellular accumulation and secretion for which the mechanisms have still to be elucidated.