Elliot, T. A. E. | bioRxiv Science

bioRxiv2025

Inhibitory TIGIT signalling is dependent on T cell receptor activation

TIGIT is an immune checkpoint receptor that can signal via cytoplasmic ITT-like and ITIM motifs to regulate T cell function. The signalling molecules that mediate inhibitory TIGIT signalling in T cells remain poorly defined, and it is not clear how TIGIT activation is regulated. Here, proximity proteomics was employed in Jurkat T cells to identify TIGIT-associating proteins upon engagement with its ligand CD155. This identified several ligation-specific TIGIT interactors, including proteins involved in signalling (Grb2 and SOS1), cytoskeletal regulation (CD2AP and SdcBP), and endocytosis (IST1 and SNX3). A TIGIT mutant (Y225A/Y231A) incapable of signalling via its inhibitory motifs prevented the recruitment of these proteins, indicating inhibitory signalling-specific engagement of these pathways. Strikingly, T cell receptor (TCR) stimulation was also needed for TIGIT to engage with these pathways. Mechanistically, phosphorylation of TIGIT required both CD155 ligation and TCR activation, which resulted in signalling and internalisation. These findings demonstrate that TIGIT signalling is context-dependent and restricted to T cells receiving simultaneous TCR activation. This establishes a regulatory mechanism that limits checkpoint control to when functionally required.

immunology↗

bioRxiv2021

Antigen and Checkpoint Receptor Recalibration of T Cell Receptor Signal Strength

How T cell receptor (TCR) signal strength modulates T cell function and to what extent this is modified by immune checkpoint blockade (ICB) are key questions in immunology. Using Nr4a3-Tocky mice as a digital read-out of NFAT pathway activity, we identify the rapid quantitative and qualitative changes that occur in CD4+ T cells in response to a range of TCR signalling strengths. We demonstrate that the time and dose dependent programming of distinct co-inhibitory receptors rapidly re-calibrates T cell activation thresholds. By developing a new in vivo model, we analyse the immediate effects of ICB on T cell re-activation. Our findings reveal that anti-PD1 but not anti-Lag3 immunotherapy leads to an increased TCR signal strength. We define a strong TCR signal metric of five genes specifically upregulated by anti-PD1 in T cells (TCR.strong), which can stratify clinical outcomes during anti-PD1 monotherapy in melanoma patients. Our study therefore reveals how analysis of TCR signal strength - and its manipulation - can provide powerful metrics for monitoring outcomes to immunotherapy. Key PointsO_LITCR signal strength-dependent programming of CD4+ T cells revealed over time in vivo C_LIO_LIInhibitory receptor expression is dynamic, TCR signal strength dependent, and rapidly re-calibrates T cell activation thresholds C_LIO_LIPD1 but not Lag3 blockade leads to a unique and increased TCR signal strength signature (coined TCR.strong) C_LIO_LITCR.strong metric stratifies melanoma patient survival in response to Nivolumab (anti-PD1) therapy C_LI

immunology↗