Mechanisms and manipulation of force dependent behavior in T cell biology

总结 TCR识别由MHC蛋白结合和呈递的肽是细胞免疫的基础。tcr识别 pMHC的作用最常通过传统受体-配体理论的透镜来观察，其中细胞反应 被认为是由溶液结合亲和力或动力学控制的。虽然这是经常发生的情况，工作在 过去的几年已经表明，来自施加在膜结合TCR上的机械力的复杂性， pMHC可以深刻影响T细胞信号传导。值得注意的是捕获键： 在相互作用的细胞之间形成的TCR-pMHC复合物的寿命的增强。捕捉债券可以导致 信号输出的大变化，可以大大增强T细胞的敏感性。展示了 调节T细胞反应的机械力，以强亲和力识别但不能导致免疫应答的配体， 捕捉债券产生改变或甚至没有T细胞信号传导。依赖于力量的行为与广泛的 一系列T细胞生物学过程，包括胸腺教育，对病毒或肿瘤抗原的反应，以及病毒 逃跑尽管已经证明了机械力在TCR识别中的重要性，但我们只 对TCR如何形成捕获或恢复为滑动键有初步了解。我们（PI Evavold）最近 成功操纵TCR捕获键（今年发表在《科学》杂志上），但这是通过 筛选文库，并且不了解机制。因此，我们缺乏预测力的模型， TCR的依赖行为，以及这如何影响生物学，这反过来又影响我们预测 免疫原性，评估突变的后果，并阻碍我们理解T细胞特异性的能力。 然而，最近，我们开发了一个全面的框架来识别，操纵和预测力 TCR-pMHC相互作用的依赖性行为。与以前的努力不同，我们的框架直接解决了 机制在这里，我们将进一步发展，完善和应用我们的框架。我们的假设是， 通过能量的透镜，力的依赖行为将提供关于如何和为什么这样做的缺失的机理细节 捕获键出现在TCR中，允许它们的合理预测和操纵，并允许考虑力 包括在T细胞识别抗原的评估中。我们的三个目标是：1）进一步发展我们的 力依赖性TCR行为的机械框架; 2）解释如何从 TCR界面的自然变化以及捕获键如何调节T细胞生物学;以及3）使用合理的捕获键 通过基因工程来更好地控制小鼠的病毒感染。总的来说，这项提案中的工作将阐明 T细胞机械生物学的基础机制，将捕获键置于正式的机械基础上， 提供了预测和有效操纵TCR捕获键并最终操纵T细胞生物学的手段。

Summary TCR recognition of peptides bound and presented by MHC proteins underlies cellular immunity. TCR recognition of pMHC is most often viewed through the lens of traditional receptor-ligand theory, where cellular responses are presumed to be governed by solution binding affinities or kinetics. While this is often the case, work over the past several years has shown that complexities from mechanical forces exerted on membrane bound TCR and pMHC can profoundly influence T cell signaling. Of notable interest are catch bonds: force dependent enhancements of the lifetimes of TCR-pMHC complexes formed between interacting cells. Catch bonds can lead to large changes in signaling output and can greatly enhance T cell sensitivity. Demonstrating the importance of mechanical forces in tuning T cell responses, ligands that are recognized with strong affinity but fail to result in catch bonds yield altered or even no T cell signaling. Force-dependent behavior has been implicated in a wide range of T cell biological processes, including thymic education, responses to viral or tumor antigens, and viral escape. Although the importance of mechanical force in TCR recognition has been demonstrated, we have only a rudimentary understanding of how TCRs form catch or revert to slip bonds. We (PI Evavold) have had recent success in manipulating TCR catch bonds (published in Science this year) but this was achieved through screening libraries and without an understanding of mechanism. We thus lack predictive models for force dependent behavior in TCRs and in turn how this affects biology, which in turn impacts our ability to predict immunogenicity, assess the consequences of mutations, and hinders our ability to understand T cell specificity. Recently, however, we developed a comprehensive framework to identify, manipulate, and predict force dependent behavior in TCR-pMHC interactions. Unlike prior efforts, our framework directly addresses mechanism. Here, we will further develop, refine, and apply our framework. Our driving hypothesis is that viewing force dependent behavior through the lens of energy will provide the missing mechanistic detail of how and why catch bonds emerge in TCRs, allow their rational prediction and manipulation, and permit force considerations to be included in assessments of T cell recognition of antigen. Our three Aims are to 1) further develop our mechanistic framework for force dependent TCR behavior; 2) explain how changes to catch bonds emerge from natural variations in TCR interfaces and how catch bonds regulate T cell biology; and 3) Use rational catch bond engineering to better control viral infection in mice. Overall, the work in this proposal will illuminate the opaque mechanisms that underlie T cell mechanobiology, place catch bonds on a formal mechanistic footing, and provide the means to predict and productively manipulate TCR catch bonds and ultimately T cell biology.