Used in immunological research to study T-cell activation and immune checkpoint pathways. Facilitates the development of cancer immunotherapies by enabling binding assays with PD-L1 and PD-L2 ligands. Commonly employed in ELISA, surface plasmon resonance, and protein-protein interaction studies to screen and characterize therapeutic antibodies. The His tag allows for easy purification and detection in recombinant systems. Supports drug discovery efforts targeting immune evasion in tumors and chronic infections.