期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2021
卷号：118
期号：39
DOI：10.1073/pnas.2024250118
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Despite the success of T cell–redirecting immunotherapies for blood cancers, toxic, off-target side effects prevent their safe application to other diseases. Part of the challenge lies in our incomplete understanding of T cell receptor (TCR) triggering. Although we know signaling requires TCR phosphorylation, how extracellular TCR/ligand binding produces intracellular phosphorylation is unclear. Using live-cell imaging, we found that just reducing TCR mobility induces T cell signaling. Since native ligands also restrict TCR mobility, our findings suggest that trapping TCRs in tight cell–cell interaction spaces, where large negative-regulatory phosphatases are depleted, might generally initiate T cell signaling. This implies that parameters beyond TCR–ligand affinity could be exploited to fine-tune the specificity and potency of T cell–redirecting agents.
T cell activation is initiated by T cell receptor (TCR) phosphorylation. This requires the local depletion of large receptor-type phosphatases from “close contacts” formed when T cells interact with surfaces presenting agonistic TCR ligands, but exactly how the ligands potentiate signaling is unclear. It has been proposed that TCR ligands could enhance receptor phosphorylation and signaling just by holding TCRs in phosphatase-depleted close contacts, but this has not been directly tested. We devised simple methods to move the TCR in and out of close contacts formed by T cells interacting with supported lipid bilayers (SLBs) and to slow the receptor’s diffusion in the contacts, using a series of anti-CD3ε Fab- and ligand-based adducts of the receptor. TCRs engaging a Fab extended with the large extracellular region of CD45 were excluded from contacts and produced no signaling. Conversely, allowing the extended Fab to become tethered to the SLB trapped the TCR in the close contacts, leading to very strong signaling. Importantly, attaching untethered anti-CD3ε Fab or peptide/MHC ligands, each of which were largely inactive in solution but both of which reduced TCR diffusion in close contacts approximately fivefold, also initiated signaling during cell/SLB contact. Our findings indicate that holding TCRs in close contacts or simply slowing their diffusion in phosphatase-depleted regions of the cell surface suffices to initiate signaling, effects we could reproduce in single-particle stochastic simulations. Our study shows that the TCR is preconfigured for signaling in a way that allows it to be triggered by ligands acting simply as receptor “traps.”
