CD63 is a member of the tetraspanin superfamily, a cluster of cell surface associated membrane proteins with four transmembrane domains [PubMed: 31882993, PubMed: 25921073]. Tetraspanins have been shown to be involved in many cellular functions including cell motility, adhesion, differentiation,activation, immune response, and tumor cell migration and invasion. Post translational modification of CD63 results in its ability to organize and form tetraspanin-enriched microdomains (TEMs) on membranes. The formation of TEMs allows interaction with components such as integrin molecules, immunoglobulins, proteoglycans, cadherins, and signaling molecules on the cell surface [PubMed: 31882993, PubMed: 15992681]. CD63 is highly enriched in late endosomal and lysosomal compartments after being endocytosed from the cell surface through the clathrin-coated vesicles.