CD33 and leukemia: Gemtuzumab ozogamicin (GO), an antibody–drug conjugate composed of calicheamicin linked to a CD33-targeting monoclonal antibody, is Food and Drug Administration (FDA)-approved for adult patients with previously untreated CD33+ AML in combination with daunorubicin and cytarabine, based on the results of the Acute Leukemia French Association (ALFA)-0701 trial [3,4,5,6].