It is expressed on myeloid progenitors, monocytes, myeloid dendritic cells and less so, on macrophages and granulocytes.3 Although it is restricted mainly to the myeloid lineage, low levels of CD33 expression has been reported on some lymphoid cells, including the earliest precursors of human fetal thymocytes and human CD34(+) postnatal thymocytes.4 In addition, activated NK cells and T cells can also express CD33.5 CD33 is expressed on the majority of AML cells and the level of CD33 seems to correlate with the disease prognosis.6 This evidence concerns the gene CD33 and acute myeloid leukemia.