The Expression Pattern of CD33 Antigen Can Differentiate Leukemic from Normal Progenitor Cells in Acute Myeloid Leukemia

Leukemic stem cells (LSC) in acute myeloid leukemia (AML), defined by CD34 and CD38 antigens also express CD33 similar to normal hematopoietic stem cells. Residual LSC are believed to be responsible for relapse in AML after chemotherapy. Leukemic progenitor cell compartments were defined by CD34 and CD38 expression by flow cytometry in 61 new cases of AML. In each of four compartments thus defined, CD34+CD38−, CD34+CD38+, CD34−CD38− and CD34−CD38+, the pattern and intensity of expression of CD33 were studied in comparison to similar progenitor cell compartments in normal bone marrow and peripheral blood stem cell harvests. Post induction bone marrow samples from 10/61 cases were studied for aberrant CD33 expression. The intensity and pattern of expression of CD33 in AML progenitor cells were significantly different compared to normal progenitor cells. In two cases who were in morphological remission post induction, aberrant CD33 expressing progenitor cells were detectable at a frequency of 1.6 and 0.5 % respectively in the bone marrow. Aberrant CD33 expression in bone marrow LSC identified as CD34+CD38− cells in the CD45 dim/low side scatter region on flow cytometry may be useful as minimal residual disease marker after AML therapy. The method involves the use of a limited number of reagents and can be applied to all cases of AML.