Used in immunological research to study T-cell activation and co-stimulatory signaling pathways. Serves as a ligand for 4-1BB (CD137), playing a key role in enhancing T-cell proliferation, survival, and cytokine production. Applied in the development of cancer immunotherapies, particularly in evaluating immune checkpoint modulation. Utilized in vitro and in vivo to support the expansion of activated T cells and to assess the function of immune cell populations. Also employed in protein-protein interaction studies and immunoassay development due to its tagged format, enabling detection and purification.