CD33 and acute myeloid leukemia: Gemtuzumab‐ozogamycin (GO), an humanized IgG4 monoclonal antibody conjugated with N‐acetyl‐γ calicheamicin dimethyl hydrazide, is directed against CD33, a trans‐membrane glycoprotein frequently expressed by leukemic blasts (85–90% of adult AML cases).1, 2