Effects of ATO, etanercept, and TNF-α on apoptosis in normal marrow, MDS marrow, and ML1 cells. 1 × 10⁶ mononuclear cells/mL were exposed to ATO in the presence of etanercept for 1 hour, and TNF-α was added at the indicated concentrations for 20 hours. Results shown here were obtained with ATO at 5μM, etanercept at 5μg/mL, and TNF-α at 20 ng/mL. Apoptosis was determined by Annexin V and propidium iodide staining. Values are corrected for background apoptosis as described in “Materials and methods.” (A) Results represent the mean plus or minus SE of 3 independent experiments, each carried out in duplicates. Differences between normal and MDS marrows were significant (^*P < .01; ^**P < .05; ^***P < .002; unpaired t test). (B) CD34⁺ cells from a healthy control and 2 MDS patients (CMML, RA) were exposed to ATO as described for panel A (without etanercept and TNF-α). (C) CD34⁺ cells from healthy controls (normal bone marrow [NBM]) and MDS patients (RAEB) were exposed to ATO for 20 hours, and thymidine incorporation was determined to evaluate cell proliferation. As expected with CD34⁺ cells, spontaneous thymidine uptake was low, but it was further reduced by treatment with ATO or ATO + etanercept.