DNA index and karyotype analysis in myelodysplasia

Immunophenotyping myelodysplastic neoplasms: the role of flow cytometry in the molecular classification era

The unique heterogenous landscape of myelodysplastic syndromes/neoplasms (MDS) has resulted in continuous redefinition of disease sub-entities, in view of the novel translational research data that have clarified several areas of the pathogenesis and the progression of the disease. The new international classifications (WHO 2022, ICC 2022) have incorporated genomic data defining phenotypical alterations, that guide clinical management of specific patient subgroups. On the other hand, for over a decade, multiparameter flow cytometry (MFC) has proven its value as a complementary diagnostic tool for these diseases and although it has never been established as a mandatory test for the baseline evaluation of MDS patients in international guidelines, it is almost universally adopted in everyday clinical practice for the assessment of suspected cytopenias through simplified scoring systems or elaborate analytical strategies for the detection of immunophenotypical dysplastic features in every hematopoietic cell lineage in the bone marrow (BM). In this review, we explore the clinically meaningful interplay of MFC data and genetic profiles of MDS patients, to reveal the currently existing and the potential future role of each methodology for routine clinical practice, and the benefit of the patients. We reviewed the existing knowledge and recent advances in the field and discuss how an integrated approach could lead to patient re-stratification and guide personalized management.

DNA content of granulocytes, monocytes, and lymphocytes in the bone marrow smears of patients with myelodysplastic syndromes

Recently, we have reported a high incidence of DNA hypodiploidy defined as DNA index (DI) in blasts/promyelocytes from 39 patients with myelodysplastic syndromes (MDS) found to be without a relationship to cytogenetics. In the present study the DNA content (DI) in granulocytes, monocytes, and lymphocytes measured in the same bone marrow smears from the above patients are reported. DNA hypodiploidy was found in mature cells, not only in myeloid cells (granulocytes and monocytes) but also in lymphocytes. A lower mean DI in each cell type of patients compared to controls was found. Pairwise comparison of the mean DI (+/-SE) in 32 patients with normal (n = 22) and abnormal (n = 10) cytogenetics and controls (n = 8) showed a significantly (P < 0.01) lower value for each group of patients, respectively, in all cell types. No difference was found between the two groups of patients. Presence of weak-Feulgen stained nuclei (DI < 0.40) in granulocytes and monocytes was more pronounced in patients expressing DNA hypodiploid immature cell populations, but only occasionally in lymphocytes, suggesting a link to an apoptotic event and intramedullary cell death. DNA hypodiploidy is shown to be a common feature even in mature cell populations in MDS bone marrows. Clonality, by means of DNA content, appears reasonable as regards the granulocytes and monocytes. DNA hypodiploid lymphocytes, on the other hand, might be small blasts (stem cells) or dying cell populations of unknown origin.

DNA image cytometry in MDS bone marrow smears

The nuclear DNA content, defined as DNA index (DI) in blasts/promyelocytes (bla/pro), were determined on Feulgen-stained bone marrow smears from 39 patients with myelodysplastic syndromes (MDS) and eight control subjects by the use of image cytometry (ICM). The DI in patients was compared to that of corresponding normal cell types, and to cytogenetic data available in 32/39 patients. The mean DI in bla/pro of patients with MDS was significantly (P < 0.01) lower compared to corresponding cell types in control subjects. By ICM, a DNA aneuploidy in bla/pro was found in 67% of the MDS patients, and 59% expressed DNA hypodiploidy. By cytogenetics, an abnormal karyotype was found in 31%, and 6/9 MDS patients with a 'hypodiploid' abnormal karyotype showed DNA hypodiploidy. Of patients with a normal karyotype (69%), seven (32%) showed a normal, 12 (55%) a lower, and three (14%) a higher DI compared to controls. No difference between groups of MDS patients was found. DNA hypodiploidy is suggested to be a common feature in MDS without a relationship to cytogenetics.

Prognostic relevance of serum thymidine kinase in primary myelodysplastic syndromes: relationship to development of acute myeloid leukaemia

The aim of this study was to evaluate the possible prognostic relevance of thymidine kinase serum levels (s-TK), an indirect marker of proliferative activity, in myelodysplastic syndromes (MDS). S-TK levels were monitored by means of a radioenzyme assay in 90 patients affected by MDS (22 refractory anaemia, RA; 17 RA with ring sideroblasts, RARS; 21 RA with blast excess, RAEB; 15 RAEB in transformation, RAEB-T; 15 chronic myelomonocytic leukaemia, CMMoL). Mean s-TK levels (U/microliter) measured at diagnosis were 11.9 +/- 12.6 for RA, 11.4 +/- 13.6 for RARS, 19.9 +/- 28.4 for RAEB, 39.6 +/- 34.3 for RAEB-T and 77.7 +/- 69.7 for CMMoL (normal values < 5 U/microliter). With the only exception of a weak relationship with lactate dehydrogenase, no correlation was found between initial s-TK values and other clinical or laboratory parameters, such as age, haemoglobin, white blood cell or platelet count, percentage of bone marrow blasts. MDS patients with s-TK > 38 U/microliters, a cut-off level selected by means of ROC statistical analysis, showed a significantly shorter survival than those with s-TK < 38 U/microliter (8.2 v 37.4 months, respectively; P < 0.0001). In particular, transformation in acute myeloid leukaemia (AML) occurred in 17/21 (81%) of patients with s-TK > 38 U/microliters and 9/69 (13%) of those with lower levels at diagnosis (P < 0.0001), independently of FAB subtype. High s-TK levels were also useful to predict evolution in AML during the course of the disease in patients with normal initial values. Multivariate analysis confirmed the independent prognostic value of s-TK on both overall survival and risk of acute transformation. We conclude that s-TK may be an important prognostic factor in MDS, strongly correlated with development of AML.

Differences in relative DNA content between human peripheral blood and bone marrow subpopulations--consequences for DNA index calculations

By sequentially staining for leukocyte differentiation antigens with monoclonal antibodies and for stainable DNA content with propidium iodide, we have evaluated the DNA ratios of normal peripheral blood and bone marrow subpopulations. In 19 peripheral blood samples the relative DNA content of the monocytes was higher than that of other subpopulations, with highly significant differences between the DNA ratios of the CD14+ monocytes, on the one hand, unlabeled controls, CD3+ T-lymphocytes, and CD20+ B-lymphocytes, on the other. In bone marrows from 16 healthy volunteers, the relative DNA content of the myelomonocytic subpopulations was higher than that of the T-lymphocytes with significant differences between the CD3+ lymphocytes, on the one hand, and the CD14+ monocytes, the CD13+ and CD33+ immature myeloid, the NAT9+ mature myeloid, and the AS-E1+ nucleated erythroid subpopulation, on the other. Since a mixture of peripheral blood mononuclear cells or T lymphocytes from healthy volunteers is often used as an external standard for DNA ploidy determinations, these data suggest that such a procedure could result in an overestimation of the DNA indices of most of the bone marrow subpopulations. Instead, we suggest the use of the DNA ratio of the CD14+ subpopulation from peripheral blood as standards for ploidy determinations for the myeloid bone marrow subpopulations.

Variation in DNA content of immature normal bone marrow cells

A variability in DNA content detected was found with image cytometry, in immature bone marrow cells from 13 healthy donors (median age 31 yr). The mean coefficient of variation (C.V.) of the DNA content was found to be significantly (P = 0.0002) higher in immature blasts and promyelocytes than in mature granulocytes, lymphocytes, and monocytes. The finding was not due to high DNA contents secondary to DNA-synthesis in immature cells, since the percentage of such cells with a reduced DNA content was also significantly (P = 0.0424-0.0002) increased. The error of the method expressed as the variance of multiple measurements has been found to be 0.0002-0.0004. A staining error has been found for some hydrolysis times, but not for times between 60 and 120 minutes. A measuring error was found for an average of 1.38 to 3.38% of the cells. If many normal cells with DNA-aneuploidy are sterile, this would explain the present findings as well as previous ones about intra-marrow cell death, and also the fact that the variability in DNA content could not be detected with cytogenetic or flow cytometric methods.

Comparison of acute myeloid leukemia occurring de novo or preceded by a myelodysplastic stage: differences in cellular DNA content

The DNA content of bone marrow cells in patients with acute leukemia preceded by a myelodysplastic stage (MDS-AML) was compared to that in patients with de novo AML. We studied granulocytes, lymphocytes, monocytes, and blasts/promyelocytes from Feulgen-stained bone marrow smears of 11 patients with de novo AML, ten patients with MDS-AML, and 13 apparently healthy controls. The mean amount of DNA per cell (DNA index; DI) in each cell population was determined using a digital video-based image-analyzing system (CAS-100). Analysis of variance (F test) showed a significant difference in the DNA content between de novo AML on one hand and MDS-AML and controls on the other as regards to blasts/promyelocytes (P < 0.01), lymphocytes (P < 0.05), and monocytes (P < 0.01), respectively. In three of 11 (27%) patients with de novo AML, a lower than normal limit DI was found both in immature and mature bone marrow cells. Patients with MDS-AML had those of DI values similar to normal controls. In consequence, a significantly reduced mean DI was found in patients with de novo AML in blasts/promyelocytes (P < 0.01), and monocytes (P < 0.05) compared to both normal controls and MDS-AML. Together with data published separately, suggesting differences in granulocyte morphology, clonality, and HLA-DR expression, these data suggest biological differences between the two diseases.

Flow cytometry: clinical applications in haematology

The time interval between the development of a new technique or methodology and its acceptance, if successful, as a recognized clinical application can be many years. The application of flow cytometry to reticulocyte counting, for example, has taken 8 years from the appearance of the first publication, and in 1990 it is still in its infancy as a clinical method. It is therefore a challenging task to anticipate which of the methodologies currently under development will achieve acceptance. It would be impossible to deal with all the candidates in the space available, and so a review is provided to those methods that may have potential applications in clinical haematology, together with some of the more practical details of methods that have recently been demonstrated to be viable in the clinical laboratory. The first category consists of leukocyte enumeration and studies on bone marrow, neutrophils, platelets and cellular DNA content, whilst the second covers reticulocyte counting and total red cell volume measurement. The contribution of flow cytometry to the field of immunophenotyping haematological disorders is probably unique in already being clinically acceptable. Finally, the question of quality control is addressed, as this is an essential prerequisite to the adoption of any new method in the clinical laboratory.