CD33 is widely expressed in AML and is present in nearly all patients1,2
It is expressed on leukemic blasts in approximately 90% of patients, regardless of cytogenetic or molecular abnormalities2
Simplified hypothetical model of stem and progenitor cells in the human hematopoietic system, showing expressions of CD33. Adapted from Walter et al 2012.
CD33 is absent from normal hematopoietic stem cells and is not found outside the hematopoietic system, making it an ideal target2-4
AML=acute myeloid leukemia; B=B-progenitor; BFU-E=burst-forming unit, erythroid; CFU-GM=colony-forming unit, granulocyte-monocyte; CFU-Meg=colony-forming unit, megakaryocytic; T=T-progenitor.
1. O’Hear C, Heiber JF, Schubert I, Fey G, Geiger TL. Anti-CD33 chimeric antigen receptor targeting of acute myeloid leukemia. Haematologica. 2015;100(3):336-344. 
2. Ehninger A, Kramer M, Röllig C, et al; Study Alliance Leukemia. Distribution and levels of cell surface expression of CD33 and CD123 in acute myeloid leukemia. Blood Cancer J. 2014;4:e218. doi:10.1038/bcj.2014.39.
3. Walter RB, Appelbaum FR, Estey EH, Bernstein ID. Acute myeloid leukemia stem cells and CD33-targeted immunotherapy. Blood. 2012;119(26):6198-6208.
4. Hoyer JD, Grogg KL, Hanson CA, Gamez JD, Dogan A. CD33 detection by immunohistochemistry in paraffin-embedded tissues: a new antibody shows excellent specificity and sensitivity for cells of myelomonocytic lineage. Am J Clin Pathol. 2008;129(2):316-323.