Siglec-3/CD33

Siglec-3 (CD33) defines the CD33-related Siglec subgroup and is a canonical myeloid differentiation marker, present on myeloblasts, promonocytes and monocytes while absent from mature granulocytes and lymphoid cells. Structurally it is a compact type I transmembrane receptor with a single V-set Ig domain, one C2-set domain and cytoplasmic ITIM motifs that mediate inhibitory signaling upon binding sialylated glycans. CD33 gained prominence as the target of the antibody-drug conjugate gemtuzumab ozogamicin in acute myeloid leukemia and is now pursued with bispecific and other conjugate formats. Genome-wide studies have also identified CD33 as a susceptibility locus for Alzheimer's disease through effects on microglial amyloid-beta uptake.