Myeloid Cell Marker : CD 33

CD33 (Siglec‑3) is a sialic‑acid‑binding transmembrane glycoprotein expressed on myeloid lineage cells — including myeloid progenitors, monocytes, granulocytes and some dendritic cells — and on most acute myeloid leukemia (AML) blasts. It’s used diagnostically to identify myeloid cells and serves as a therapeutic target for antibody–drug conjugates and other immune‑targeted treatments; it also modulates innate immune signaling.

CD33 positive means cells express the CD33 surface protein, a myeloid-lineage marker detected by flow cytometry. It indicates myeloid or monocytic origin and is commonly present on normal myeloid precursors and in many cases of acute myeloid leukemia and related disorders. CD33 positivity helps classify disease, guide targeted therapies (e.g., anti-CD33 agents), and monitor treatment response, but is not disease-specific.

Yes — CD33 (Siglec-3) is a myeloid-lineage surface antigen expressed on immature and mature myeloid cells, including monocytes, macrophages, granulocytes (neutrophils), certain dendritic cells, and myeloid progenitors. It is commonly present on acute myeloid leukemia blasts and generally absent or low on lymphoid cells. CD33 is used diagnostically and as a therapeutic target in myeloid malignancies.

CD33‑positive AML is treated with standard induction chemotherapy (e.g., cytarabine plus an anthracycline) often combined with the CD33‑targeted antibody‑drug conjugate gemtuzumab ozogamicin. After remission, patients receive consolidation chemotherapy and/or allogeneic stem‑cell transplant if eligible. Relapsed/refractory cases may use gemtuzumab or other targeted agents based on co‑mutations, with vigilant supportive care and monitoring for liver toxicity and VOD.

Leukemia‑associated CD markers include: B‑cell ALL—CD19, CD10, CD22 (±CD20); T‑cell ALL—CD3, CD7, CD2; AML—myeloid markers CD33, CD13, CD117 (often CD34, HLA‑DR); CLL—CD5 with CD19 and CD23 (CD20 dim); hairy cell leukemia—CD11c, CD25, CD103. Patterns and combinations, not single markers, guide diagnosis. Flow cytometry detects these markers and confirms lineage and treatment planning.

Approximately 85–90% of acute myeloid leukemia (AML) cases express CD33 on blast cells. Expression frequency and intensity vary by AML subtype and patient, but CD33 positivity is common enough that CD33-directed therapies are used clinically. Reported frequencies range slightly in the literature; clinicians confirm CD33 expression by flow cytometry before prescribing CD33-targeted agents.