Used in immunological research to study immune checkpoint pathways, particularly in cancer immunotherapy development. Serves as a binding partner for PD-1 receptor to modulate T-cell activity. Employed in protein-protein interaction assays, ELISA, and surface plasmon resonance (SPR) to screen and characterize therapeutic antibodies or inhibitors targeting the PD-1/PD-L2 pathway. Also utilized in structural studies to understand molecular binding mechanisms and support drug design. The His Tag facilitates easy purification and detection in recombinant expression systems.