ICE processing and PARP cleavage in ex vivo-derived leukemia cells. Extracts obtained from cells treated with the indicated cytotoxic drugs were processed as described in methodology and analyzed by immunoblotting for ICE processing and PARP cleavage. Mononuclear cells containing more than 95% of leukemia blasts were separated from whole heparinized blood by Ficoll-Paque gradient centrifugation. Because of the shortage of patient material, the experiment has been performed once only.