ANPEP and acute myeloid leukemia: As previously shown [20], the specific mAbs against CD13, WM15 (obtained after immunization with blasts from one AML patient [30]) and SJ1D1 (raised against CD13 from the myeloid cell line KG1 [31]) labelled to a similar extent CD13 expressed on the surface of AML (monoblastic, M5) U937 cells (Figure 1A).