Used in research and development of immunotherapies targeting T-cell activation. Primarily applied in studies of immune modulation, especially in autoimmune diseases and transplant rejection. Binds specifically to the CD3 complex on T cells, enabling depletion or functional alteration of T-cell activity. Investigated in clinical settings for treatment of acute graft-versus-host disease and certain inflammatory conditions. Serves as a reference standard in bioassay development, flow cytometry, and quality control for biosimilar antibody products.