CD33 and leukemia: However, as CD33 is present on normal hematopoietic stem cells (although lower than that on leukemic stem cells6), such an infusion schedule could prolong also cytopenia.13 A recent study showed that the effectiveness of AMG 330 was inferior against AML samples from patients with relapsed/refractory leukemia when compared with samples taken from patients at the time of first diagnosis.