CD33

Class

Antibody-drug conjugate (anti-CD33 monoclonal antibody linked to calicheamicin)

Pathway

CD33-mediated internalization, calicheamicin-induced DNA double-strand breaks

CD33 is a cell-surface receptor found mainly on cells of the myeloid lineage, including monocytes, granulocyte precursors, and, importantly, the malignant blasts of acute myeloid leukemia (AML). Because CD33 is expressed broadly across AML cells but is largely absent from earlier blood-forming stem cells, it has long been considered an attractive handle for directing cytotoxic therapy specifically to leukemic cells. The main pharmacological strategy exploiting this target is the antibody-drug conjugate (ADC), in which a monoclonal antibody against CD33 is chemically linked to a potent DNA-damaging toxin, most notably calicheamicin. After the antibody binds CD33 on the cell surface, the complex is internalized by the cell, the linker is processed, and the toxin is released inside, causing breaks in the DNA double helix that trigger cell death. Other modalities under exploration, including CAR T-cells and radiolabeled antibodies, use the same CD33 recognition step but deliver a different killing mechanism, either engineered immune cells or localized radiation. Collectively, this mechanism matters mainly in myeloid malignancies, where selectively eliminating CD33-positive leukemic cells while sparing other tissues is the central therapeutic goal.