Used in immunological research to study immune checkpoint pathways, particularly in cancer immunotherapy development. Facilitates binding assays and interaction studies with ligands like PD-L1 and PD-L2. Employed in ELISA, surface plasmon resonance, and protein-protein interaction experiments to screen and characterize therapeutic antibodies or inhibitors. His tag enables easy purification and detection, making it valuable for in vitro studies aimed at modulating T-cell activation and immune response.