Dafsolimab is a murine-derived IgG2b monoclonal antibody targeting the CD3 molecule. As an anti-CD3 antibody, its primary application has historically been in basic immunology research and as a crucial tool reagent in biomedical science. It is used to study T-cell activation, signal transduction, and in vitro functional assays. In clinical contexts, early murine anti-CD3 antibodies (like OKT3) were used as potent immunosuppressants to prevent organ transplant rejection, but their use was limited by the development of human anti-mouse antibodies (HAMA) and significant cytokine release syndrome. Dafsolimab likely represents this class of foundational research or early therapeutic tools.