Used in immunotherapy research for cancer treatment due to its high expression on tumor cells and limited presence in normal tissues. Serves as a target for monoclonal antibodies, antibody-drug conjugates (ADCs), and CAR-T cell therapies. The His tag facilitates purification and detection in laboratory settings, enabling development and testing of therapeutic agents. Plays a role in modulating T-cell responses, making it valuable in studying immune checkpoint pathways. Widely applied in preclinical studies to evaluate tumor targeting, immune activation, and treatment efficacy.