CD9 antigen (CD9)

CD9 antigen, also known as Tetraspanin-29, is a cell surface glycoprotein belonging to the tetraspanin (TM4SF) family [1, 5, 8]. It features four transmembrane domains and organizes tetraspanin-enriched microdomains (TEMs) that act as platforms for signaling and adhesion by coordinating interactions between integrins, growth factor receptors, and other membrane proteins [3, 11, 12]. CD9 is critically involved in diverse physiological processes, including sperm-egg fusion, platelet aggregation, and immune cell activation [1, 2, 5, 8]. In oncology, CD9 plays a complex, context-dependent role; it can act as a metastasis suppressor in some cancers (e.g., lung, breast) while promoting tumor progression and chemoresistance in others (e.g., glioblastoma, gastric cancer) [2, 4, 8, 10]. Beyond cancer, it is a primary marker for exosomes and regulates the entry and egress of several viruses, including HIV-1 and coronaviruses [1, 2, 8, 11]. Therapeutic strategies targeting CD9, such as monoclonal antibodies (e.g., ALB6, 5H9), are being explored for cancer and infectious diseases, though development faces challenges due to CD9's role in platelet activation and its broad tissue distribution [2, 4, 11].

Other names

Tetraspanin-29TSPAN29MIC3MRP-1 (Motility-related protein 1)p24 antigenBTCC-1DRAP-275H9 antigenCell growth-inhibiting gene 2 proteinBA2

Inhibition of cell migration and metastasis, induction of apoptosis in malignant cells, disruption of tetraspanin-enriched microdomains (TEMs), and blocking of exosome-mediated intercellular communication [2, 4, 11].