CD33 and acute myeloid leukemia: The expression of CD33 is largely restricted to the myeloid lineage and recently gained much interest as a target for immunotherapy of AML and other CD33-expressing malignancies, initially with the antibody-drug conjugate Gemtuzumab Ozagamicin, followed by bispecific antibody conjugates, antibody-cytokine conjugates, and lately CD33-CAR T cells (9, 24–26).