T cell Ig and mucin domain-containing protein 3 is recruited to the immune synapse, disrupts stable synapse formation, and associates with receptor phosphatases

CD8(+) CTLs are adept at killing virally infected cells and Cancer cells and releasing cytokines (e.g., IFN-γ) to aid this response. However, during Cancer and chronic viral infections, such as with HIV, this CTL response is progressively impaired due to a process called T cell exhaustion. Previous work has shown that the glycoprotein T cell Ig and Mucin domain-containing protein 3 (TIM-3) plays a functional role in establishing T cell exhaustion. TIM-3 is highly upregulated on virus and tumor Ag-specific CD8(+) T cells, and antagonizing TIM-3 helps restore function of CD8(+) T cells. However, very little is known of how TIM-3 signals in CTLs. In this study, we assessed the role of TIM-3 at the immunological synapse as well as its interaction with proximal TCR signaling molecules in primary human CD8(+) T cells. TIM-3 was found within CD8(+) T cell lipid rafts at the immunological synapse. Blocking TIM-3 resulted in a significantly greater number of stable synapses being formed between TIM-3(hi)CD8(+) T cells and target cells, suggesting that TIM-3 plays a functional role in synapse formation. Further, we confirmed that TIM-3 interacts with Lck, but not the phospho-active form of Lck. Finally, TIM-3 colocalizes with receptor phosphatases CD45 and CD148, an interaction that is enhanced in the presence of the TIM-3 ligand, Galectin-9. Thus, TIM-3 interacts with multiple signaling molecules at the immunological synapse, and characterizing these interactions could aid in the development of therapeutics to restore Tim-3-mediated immune dysfunction.