Signaling events triggered by T cell receptor (TcR) stimulation are important targets for the development of common therapeutics for various autoimmune diseases. SLAP is a negative regulator of TcR-mediated signaling cascade via targeting TcR zeta chain for degradation through recruiting the ubiquitin ligase c-Cbl. In this study, we generated a transducible form of SH3 and SH2 domains of SLAP (ctSLAP Delta C) which can be specifically targeted to the cytoplasm of a cell. ctSLAP Delta C inhibited tyrosine phosphorylation of signaling mediators such as ZAP-70 and LAT involved in T cell activation, and effectively suppressed transcriptional activity of NFAT and NF kappa B upon TcR stimulation. The transduced ctSLAP Delta C in T cells blocked the secretion of T cell-specific cytokines such as IL-2, IFN gamma, IL-17A, and IL-4 and induced the expression of CD69 and CD25 on effector T cells without influencing the cell viability. Inhibition of TcR-mediated signaling via SLAP blocked the differentiation of naive T cells into Th1, Th2 or Treg cells with different sensitivity, suggesting that qualitative and quantitative intensity of TcR-mediated signaling in the context of polarizing cytokines environment may be a critical factor to determine the differentiation fate of naive T cells. These results suggest that cytoplasm-specific transduction of the SH3 and SH2 domains of SLAP has a therapeutic potential of being an immunosuppressive reagent for the treatment of various autoimmune diseases. (C) 2015 Elsevier Inc. All rights reserved.