Characterization of defective megakaryocytic development in patients with myelodysplastic syndromes

Megakaryocytic differentiation of progenitor cells was investigated in nine patients with low-risk myelodysplastic syndromes (MDS) (eight refractory a nemia [RA] and one RA with ringed sideroblasts [RARS]) and five patients,vi th high-risk MDS (two RA with excess of blasts [RAEB] and three RAEB in tra nsformation [RAEB-T]), Bone marrow-derived CD34(+) cells were enriched to a purity of 87% +/- 2% (mean +/- SEM) and assayed in short-term suspension c ultures in the presence of 10 ng/mL of PEGylated recombinant human megakary ocyte (MK) growth and development factor (PEG-rHuMGDF) and in addition to 5 0 ng/mL stem cell factor and 10 ng/mL interleukin-3, Cells of the megakaryo cytic lineage were identified by flow cytometric analysis of CD42b (GP1b) a nd mature MKs by morphologic criteria. Transcription of c-mpl receptor-spec ific mRNA in the CD34(+) cells of these patients was investigated by full-l ength reverse transcriptase polymerase chain reaction of the p form of c-mp l as well as of the alternative splice product c-mpl k, CD34(+) cells from seven healthy bone marrow donors served as controls. Differentiation along the MK pathway was stimulated in five patients with RA, C-mpl mRNA was expr essed in the CD34(+) cells in all cases, In three low-risk patients the cap acity for in vitro MK growth was absent or minimal even though mRNA for c-m pl receptor was detected in the CD34(+) cells of this group as well, In pat ients with high-risk MDS, PEG-rHuMGDF stimulated in vitro MK growth from CD 34(+) cells in only one of five cases. As in the patients with low-risk MDS , c-mpl mRNA for both c-mpl p and c-mpl k splicing products was detected. T hese results indicate that the in vitro response to stimulation with c-mpl ligand discriminates between two groups of patients with low-risk MDS and t hat the observed defect in megakaryocytic development is unrelated to the l evel of c-mpl expression in both low-risk and high-risk MDS. (C) 1999 Inter national Society for Experimental Hematology. Published by Elsevier Science Inc.