Mechanism of Tim-3 regulation of CD8+T cell function

Abstract Tim-3 or transmembrane immunoglobulin and mucin domain-3 is a type I membrane protein expressed by various immune cell types, and has been shown to have a co-stimulatory role in T cells through the PI3K pathway. Tim-3 comprises extracellular, transmembrane and intracellular domains, the latter of which contains five tyrosine residues. We and others have shown that these tyrosines participate in TCR-mediated signaling pathways. Using LCMV infection, we also found that Tim-3 expression influences the formation of short-lived effector and memory precursor CD8+ T cells. We hypothesize that Tim-3 signaling through the tyrosine residues in its cytoplasmic domain modulates CD8+ T cell activation and differentiation. To test this hypothesis, we have used LCMV-specific TCR transgenic (P14) mice crossed to truncated version of Tim-3 and CD8+ conditional deletion of Tim-3. CD8+ T cell activation and memory were analyzed by flow cytometry after infection with LCMV Armstrong to induce an acute infection. The effects of Tim-3 on CD8+ T cells were found to be most prominent at the effector stage of infection and RNA sequencing has shown that loss of Tim-3 signaling promotes acquisition of a memory-like phenotype. Transcription factors T-bet and Blimp-1 were found to be lower in Tim-3 KO CD8+ T cells, while Tcf-1 maintained at higher levels in the absence of Tim-3 signaling. Cytokine production by effector CD8+ T cells was also found to be lower when Tim-3 was absent. Thus, we conclude that Tim-3 signaling via its cytoplasmic tyrosine residues plays a role in CD8+ T cells in an acute infection. These results may lead to a better understanding of CD8+ T cell activation and memory development in different settings. Supported by R01 AI138504-01A1