Recurrent Abnormal Clones in Myelodysplastic Syndrome Marrow Originate from Cells at a Pluripotent Stem Level and Maintain Their Early Differentiation Potency.

OBJECTIVE: The present study aimed to investigate the origins and differentiation potencies of 4 common malignant clonal cell types (+8, 5q-/-5, 20q-/-20, 7q-/-7) in myelodysplastic syndrome (MDS) and to investigate whether the trisomy of chromosome 8 occurs subsequently to other chromosomal abnormalities.

METHODS: The present study analyzed a total of 46 cases of chromosomal abnormalities in MDS patients. The magnetic activated cell sorting technique (MACS) was used to sort the CD34(+)CD38(-) (pluripotent hematopoietic stem cells) and CD34(+)CD38(+) cells (committed progenitor cells) from the bone marrow mononuclear cells (BMNCs) of these patients; the sorted cells were then individually smeared. Meanwhile, cytospins were prepared from the remaining CD34(-) BMNCs after cell sorting. The clonal cell proportions in these three types of smears were detected by fluorescence in situ hybridization (FISH). Cases in which +8 was associated with another abnormality (2 cases each in combination with abnormalities in chromosomes 7, 5, and 20) were dually hybridized with the cep8 probe and another corresponding probe.

RESULTS: (1) for abnormalities of +8, 5q-/-5, 20q-/-20 or chromosome 7 involvements, clonal cells above the baseline level were detected in the pluripotent stem cell level. (2) The average clonal cell proportion in the committed progenitor cells of the 46 cases increased to 75.3% from 57.3% at the level of stem cell (p < 0.001). The groups with +8 and chromosome 5 abnormalities showed a statistically significant increase in clonal cells at the progenitor cell stage. At the individual level, 33 of 46 cases showed significant increases in clonal cells at the progenitor cell stage relative to the stem cell stage, whereas the clonal cell proportion in the CD34(-) BMNCs generally did not increase relative to the committed progenitor cell population. (3) The dual hybridization analysis showed that if +8 and another abnormality were present in the same abnormal clone according to G-banding, +8 always coexisted with the other chromosomal abnormality at the single cell level; there were no situations in which +8 occurred later than the other chromosomal abnormality.

CONCLUSION: It seems that the all malignant MDS clones originated at the pluripotent hematopoietic stem cell stage and that the proliferation and differentiation potencies were retained partly in these clonal cells. The present study failed to confirm that the trisomy 8 occurred subsequently to the other abnormalities, but some in vitro or transplant experiments maybe prove the succession of clonal origination.