Used in immunological research to study T-cell activation and co-stimulatory signaling pathways. Serves as a ligand-binding target for developing immunotherapies, including cancer immunotherapy and treatments for autoimmune diseases. Employed in ELISA, surface plasmon resonance (SPR), and protein-protein interaction assays to screen and characterize therapeutic antibodies or drug candidates. The His tag facilitates easy purification and detection in recombinant protein applications.