ATO sensitizes primary leukemia cells from prednisone poor-responder patients to dexamethasone. (A) Effect of ATO as single agent on 7 ALL patients who are described in Table 2. No cytotoxic effect could be detected in bone marrow leukocytes from a healthy donor at 0.33 μM ATO. (B) Response to increasing concentrations of DEX with or without 0.33 μM ATO on ALL cells from prednisone poor responders with T-ALL (Pt 1-2), pre-B-ALL (Pt 3-4), from prednisone good responders with T-ALL (Pt 5) and pre-B-ALL (Pt 6-7).