Used in immunological research to study T-cell activation and co-stimulatory signaling pathways. Facilitates binding assays with ligands such as CD80 and CD86 to analyze immune checkpoint interactions. Employed in protein-protein interaction studies due to the His tag, enabling easy purification and detection via nickel-affinity chromatography and anti-His antibodies. Serves as a critical reagent in developing and testing immunotherapies, including CAR-T cells and monoclonal antibodies targeting the CD28 pathway. Also utilized in surface plasmon resonance (SPR) and ELISA to quantify binding kinetics and affinity.