CD33 and acute myeloid leukemia: The field of ADCs has grown rapidly since the first ADC, gemtuzumab ozogamicin (Mylotarg®,), a humanised IgG4 antibody targeting CD33 and conjugated to the DNA-cleaving agent calicheamicin, was approved by the FDA in 2000 for the treatment of CD33-expressing acute myeloid leukaemia (AML) [17].