Flow Cytometric Findings Indicative of Myelodysplasia Differ Depending on the Karyotype

Multiparameter flow cytometry (MFC) is increasingly being used as an adjunct to the diagnostic work-up in myelodysplastic syndromes (MDS). While many antigens have been described to be aberrantly expressed in MDS the findings are generally heterogeneous and there is no consistent finding that would be present in all cases with MDS. The aim of the present study therefore has been to assess the immunophenotype in cases with MDS with clearly defined cytogenetic abnormalities as well as with normal karyotypes. Bone marrow samples of a total of 115 patients with MDS have been analyzed in parallel by MFC and chromosome analysis. They had a complex (≥3) aberrant karyotype (n=7), a normal karyotype (n=74), a deletion of the long arm of chromosome 5 (del(5q), n=19), a deletion of the long arm of chromosome 20 (del(20q), n=8), or a monosomy 7 (−7, n=7), the latter three groups carrying the abnormality as sole chromosome aberration, respectively. A standardized panel of five-color combinations of antibodies has been applied for MFC allowing the detection of previously described aberrantly expressed antigens or antigen expression patterns. As compared to cases with other cytogenetics, in cases with a complex aberrant karyotype a higher bone marrow blast count (median 9.8 vs. 4.1%, p<0.001) as well as a higher frequency of coexpression of CD56 in granulocytes (70.0 vs. 25.9%, p=0.007) were found. Furthermore, the median side-scatter (SSC) signal in granulocytes was significantly lower in these cases (368 vs. 591, p=0.029). When combining the findings in the different cell lineages, significant differences between cases with complex aberrant karyotypes and those with other cytogenetics were found: the presence of more than 4 aberrantly expressed antigens on blasts, granulocytes or monocytes or the presence of >5% blasts were found in 80.0 vs. 29.0% of the cases (p=0.032). Cases with del(5q) as the sole chromosome abnormality more often featured a reduced SSC signal (94.7 vs. 69.3%, p=0.023) while an aberrant coexpression of CD56 on monocytes (21.1 vs. 54.5%, p=0.011) as well as the median number of aberrantly expressed antigens on monocytes (0.32 vs. 0.85, p<0.001) was lower in this group. Accordingly, at least 3 aberrantly expressed antigens on blasts, granulocytes or monocytes or a blast count >5% were found less frequently in cases with del(5q) as the sole chromosome abnormality as compared to other cases (36.8 vs. 69.9%, p=0.009). In cases with del(20q) as sole chromosome abnormality findings hardly differed from other cases with only a lack of CD13 expression in monocytes occurring more often (25.0 vs. 3.8%, p=0.058). Interestingly, in cases with −7 as sole chromosome abnormality a stronger SSC signal in blasts was observed as compared to other cases (median: 147 vs. 129, p=0.041) while the median number of aberrantly expressed antigens in granulocytes was lower (1.33 vs. 1.93, p=0.035). In cases with normal cytogenetics, a stronger SSC signal was found in granulocytes (median: 602 vs. 528, p=0.037) while the ratio of the SSC signal monocytes:lymphocytes was found to be lower (median: 3.0 vs. 3.3, p=0.044). Also the percentage of blasts was lower in these cases (median: 3.9 vs. 5.7%, p=0.032). With regard to the number of aberrantly expressed antigens on granulocytes and monocytes, however, at least 3 aberrantly expressed antigens were present more often in cases with normal cytogenetics (56.8 vs. 31.6%, p=0.016). These findings indicate that aberrantly expressed antigens are present in all of the analyzed cytogenetic subgroups of MDS. Importantly, the frequencies of findings typical for MDS differ between these groups. As a consequence, MFC panels used for the diagnostic work-up of MDS should be designed comprehensively to assure the detection of these diverse findings and should be evaluated prospectively.