CD34(+) CD36(-) CELLS FROM MYELODYSPLASIA PATIENTS HAVE A LIMITED CAPACITY TO PROLIFERATE BUT CAN DIFFERENTIATE IN RESPONSE TO EPO AND MGF STIMULATION/

Myelodysplasia (MDS) is mostly characterized by a normal or increased number of normoblasts in the bone marrow and an impaired in vitro colo ny formation. In the present study we analyzed whether this might he d ue to a disconnection between proliferation and differentiation. CD34( +)/CD36(-) sorted bone marrow cells of 18 MDS patients were cultured i n a clonogenic and suspension culture assay in the presence of erythro poietin (Epo) and mast cell growth factor (MGF). Burst-forming units e rythroid (BFU-E, 75 +/- 88/10(4) CD34(+) cells, X +/- s.d.) and colony -forming units E (CFU-E) were observed in eight of the 13 cases (62%) with refractory anemia with or without ring sideroblasts (RA and RARS) and one of the five cases with RA with excess of blasts or in transfo rmation (RAEB and RAEB-T). Suspension cultures with CD34(+)/CD36(-) so rted cells with Epo plus MGF demonstrated an 8.9 +/- 6.5-fold expansio n after 7 days in cases with >10 BFU-E10(4) CD34(+)/CD36(-) cells whil e cases with <10 BFU-E/10(4) CD34(+)/CD36(-) cells demonstrated 1.0 +/ - 0.8-fold expansion especially in cases with RAEB/RAEB-T. FAGS and mo rphology analysis after 7 days of suspension culture demons?rated part ial differentiation along the erythroid lineage in cases with RA/RARS (75%) and RAEB/RAEB-T (66%) reflected by the presence of erythroblasts and normoblasts with variable expression of CD34, CD36 and Glycophori n A. In cases with erythroid colony formation 69 +/- 24% of the cells were CD34(-)/CD36(+) and in cases with <10 BFU-E/10(4) CD34(+) cells 1 8 +/- 16% of cells were CD34(-)/CD36(+). Iron staining showed the pres ence of ring sideroblasts in two cases with RARS indicating that the c ells originate from the abnormal erythroid clone. Finally, it was show n that cases with an impaired proliferative response demonstrate an en hanced binding of Annexin-V on CD34(+) cells during the first days of the cell suspension culture phase. These results suggest that a defect in the proliferative response is most pronouncedly expressed in MDS w hereas a subpopulation of cells retain the capacity to differentiate b etween transition to a terminated stage.