
<ArticleTitle>High affinity <prot><prot>interleukin-3</prot> receptor</prot> expression on blasts from patients with acute myelogenous leukemia correlates with cytotoxicity of a <prot>diphtheria toxin</prot>/<prot>IL-3</prot> fusion protein.</ArticleTitle>
<AbstractText>Diphtheria fusion proteins are a novel class of agents for the treatment of chemotherapy resistant AML. We prepared <prot>DT(388)</prot><prot>IL3</prot> composed of human <prot>interleukin-3</prot> (<prot>IL3</prot>) fused to the catalytic and translocation domain of <prot>diphtheria toxin</prot> (<prot>DT(388)</prot>) and assessed its activity on patient AML blasts. The number and affinity of <prot><prot>IL3</prot> receptors</prot> in circulating blasts was measured using a radiolabeled <prot>IL3</prot> agonist (SC-65461). Ninety-two percent of patients' blasts had both high and low affinity <prot><prot>IL3</prot> receptors</prot>. <prot>DT(388)<prot>IL3</prot></prot> cytotoxicity (1 log cell kill) was seen in nine of 25 samples (36%). There was a significant correlation between <prot>DT(388)<prot>IL3</prot></prot> log cell kill and blast high affinity <prot>IL3</prot> receptor density (P=0.0044). These results show that specific high affinity <prot>IL3</prot> binding is one factor important in the sensitivity of patients' leukemic blasts to <prot>DT(388)<prot>IL3</prot></prot>.</AbstractText>
