Although a humanized anti-CD33 IgG4 antibody conjugated to the cytotoxic agent calicheamicin (gemtuzumab ozogamicin [GO]) was reapproved for treating newly diagnosed AML in relapsed/refractory (R/R) AML in adults and pediatric patients, treatment with GO continues to be associated with serious adverse effects (11, 12). The gene discussed is CD33; the disease is acute myeloid leukemia.