STAP-2_Derived Peptide Suppresses TCR-Mediated Signals to Initiate Immune Responses

Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that contains pleckstrin and Src homology 2¯like domains, as well as a proline-rich region in its C-terminal region. Our previous study demonstrated that STAP-2 positively regulates TCR signaling by associating with TCR-proximal CD3f ITAMs and the lymphocyte-specific protein tyrosine kinase. In this study, we identify the STAP-2 interacting regions of CD3f ITAMs and show that the STAP-2¯derived synthetic peptide (iSP2) directly interacts with the ITAM sequence and blocks the interactions between STAP-2 and CD3f ITAMs. Cell-penetrating iSP2 was delivered into human and murine T cells. iSP2 suppressed cell proliferation and TCR-induced IL-2 production. Importantly, iSP2 treatment suppressed TCR-mediated activation of naive CD4⁺ T cells and decreased immune responses in CD4⁺ T cell¯mediated experimental autoimmune encephalomyelitis. It is likely that iSP2 is a novel immunomodulatory tool that modulates STAP-2-mediated activation of TCR signaling and represses the progression of autoimmune diseases.