CD33 and acute myeloid leukemia: To overcome some of the limitations of GO, such as the non-uniform conjugation of the toxin with the antibody, the drug’s relatively slow internalization kinetics, and toxin extrusion via drug transporters, SGN-CD33A, a humanized CD33 antibody with engineered cysteines carrying a synthetic DNA cross-linking pyrrolobenzodiazepine dimer via a protease-cleavable linker, was developed and demonstrated increased potency in vitro against human AML cells while maintaining activity in the presence of drug transporters.