Expression of abnormal markers in myeloid CD34+ cells of patients with MDS is common, but few immunophenotypic data have been compiled so far. Based on the statement that CD7 and TdT are markers associated with a bad prognosis in acute myeloid leukemia, we intended to describe the incidence of their aberrant expression in CD34+ cells and its role helping to establish the diagnosis of MDS.
OBJECTIVES: To explore the aberrant expression of TdT and CD7 in myeloid CD34+ cells of MDS patients and to describe their possible correlation with cytogenetic features.
DESIGN AND METHODS: Bone marrow specimens from 45 patients with MDS were included in this study (17 RA, 12 RARS, 5 CMML, 9 RAEB, 2 RAEB-t). In addition, we analyzed 28 samples of bone marrow from patients with cytopenias, but no diagnosis of MDS, as a cohort control. Immunophenotyping was performed with the following combination of monoclonal antibodies: TdT FITC / CD7 PE/ CD34 PCy-5. A case was regarded as positive for any of these markers when their expression was described in at least, 25% of myeloid CD34+ cells. Besides, adequate cytogenetic data and FISH analysis of chromosomes 5, 7 and 8 were obtained from 42 out of the 45 MDS samples.
RESULTS: The percentage of CD34+ myeloid cells in MDS samples was fewer than 2% in 25 cases, ranged from 2–5% in 6 cases and was equal or greater than 5% in 14 cases. Aberrant expression of CD7 and/or TdT was observed in 28 cases: 20 were positive for CD7, 5 cases were positive for TdT and co-expression of both antigens was described in 3 cases. Prevalence of these abnormal markers was much higher in patients with MDS (28/45; 62%) than in the cohort control (2/28; 7%) . Besides, we identified at least one abnormal marker in 14 of the 16 patients with high risk MDS (9 RAEB, 5 CMML, 2 RAEB.t). According to the IPSS, karyotypes were divided into subgroups of favorable, intermediate or unfavorable, being classified 29 patients with favorable karyotypes and 13 patients with no favorable cytogenetics. In the first group, the abnormal expression of CD7 and/or TdT was detected in 13/29 patients (44.8%) and in 10/13 patients in the non-favourable group (76.9%).
CONCLUSIONS: CD7 and/or TdT expression in myeloid CD34 + cells may be helpful in establishing the diagnosis of MDS. Prevalence of these aberrancies seems to be higher in cases with no favorable karyotypes, but a larger number of patients will be required to state significant differences. Possible correlation between high risk MDS patients and immunophenotypic aberrancies suggests the convenience of following the outcome of those low risk MDS patients who have expression of any of these abnormal markers.