Of five patients with myeloid neoplasms (three AML, two CML), one AML patient showed a biological response to daclizumab, with an impressive drop in white blood counts after the first dose, followed by relapse involving a CD25− clone and of the initial CD25+ clone after drug discontinuation. The gene discussed is IL2RA; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.