Interpatient variation in es nucleoside transporter expression in leukemic blasts from nine AML patients. The es transporter site content of fresh leukemic blasts was measured by flow cytometry in an equilibrium binding assay that used 5-(Sx8)-F, as in Fig 2. In these experiments, the equilibrium binding constants were obtained by fitting hyperbolas to the untransformed specific binding data. The histograms show B_max values ± SE for es site-specific binding of 5-(Sx8)-F in each blast sample, indicating sixfold variation among the patient samples examined.