Siglec-15 is a transmembrane glycoprotein of the siglecs family that participates in the immune regulatory systems through the recognition of their glycan ligands. Siglecs, short for sialic acid-binding immunoglobulin (Ig)-like lectins, are primarily expressed on the surface of immune cells and differentially control innate and adaptive immune responses. Mature human Siglec-15 consists of a 244 amino acid (aa) extracellular domain (ECD, Phe20 - Thr263) with two Ig-like domains, a 21 aa transmembrane segment (264-284), and a 44 aa cytoplasmic domain (285-328). Siglecs are attractive therapeutic targets because of their cell type-specific expression pattern, endocytic properties, high expression on certain lymphomas/leukemia, and ability to m