Abstract • 32

The clonogenic properties of bone marrow (BM) CD 34+ progenitors in 12 adults with MDS (FAB: RA: 4, RARS: 1, RAEB: 2, RAEBT: 2, CMML: 3; median age: 60 range 19-74) and 4 children (CMML/JMML; age : 3.5 age 1,6-4) was studied. All had features of dysplasia in at least 2 lines and were transfusion dependent. BM mononuclear cells (MNC from normal individuals or MDS patients were lymphocyte and monocyte depleted and CD 34+ population selected with paramagnetic beads (Dynal, Oslo). From another aliquot 5 ×10mL MNC were used to prepare stromal layers in aMEM in the presence of hydrocortisone, foetal calf and horse serum. At 4-6 weeks confluent stroma was seeded in cross-culture assays with 5× 103 control or MDS CD 34+ cells and cultured for 5 days without any growth factors. Aggregates (>20 cells) were scored as CFU-bl. Stroma non-adherent cells were eluted and cultured in the CFU-GM assay. CD34+ Lin-cells (median 92%) from MDS patients produced significantly lower CFU-bl (median 28 [SD 52.82]) than control cells (median 147.5 [SD 54.49];p=0.0002). The stroma non-adhesive progenitors were also significantly reduced (median 24 [SD82.191]) compared to control samples (230 [SD5.05];p = 7.35). The median % surface area covered by stroma was 80 {SD 30.42] compared to normal (98 [SD4.541];p=0.001) and they supported poorly the proliferation of control CFU-bl (86[SD 58.96]p=0.05). Stroma also survived poorly and lifted in 6 patients at 6 weeks. When cells from patients with CMML were compared to those from JMML, the latter produced significantly higher numbers of CFU-bl (128.5 [SD 21.85] vs 21 [SD 13.5]; p=0.0003) while their stroma non-adhesive precursors were significantly reduced (35.5[SD 0.87] vs 179 [SD 144.85]; p = 0.05). It is concluded that CD 34+Li- precursors from MDS patients have a poor proliferative capacity and their stroma supports haematopoiesis suboptimally. However, in JMML patients stroma adherent precursors gave appropriate clonogenic responses and the stroma behaved normally.