Mechanisms and manipulation of force dependent behavior in T cell biology

总结 TCR 对 MHC 蛋白结合和呈递的肽的识别是细胞免疫的基础。 TCR识别 pMHC 的作用最常通过传统受体-配体理论的视角来看待，其中细胞反应 推测受溶液结合亲和力或动力学控制。虽然这种情况经常发生，但请仔细研究 过去几年的研究表明，施加在膜结合 TCR 上的机械力带来的复杂性 pMHC 可以深刻影响 T 细胞信号传导。值得注意的是捕捉债券：力依赖 相互作用细胞之间形成的 TCR-pMHC 复合物的寿命延长。捕获债券可以引领 信号输出的巨大变化，可以大大增强 T 细胞的敏感性。展示的重要性 调节 T 细胞反应的机械力，配体以强亲和力被识别，但未能产生 catch 债券产量发生改变，甚至没有 T 细胞信号传导。依赖力的行为与广泛的 T 细胞生物学过程的范围，包括胸腺教育、对病毒或肿瘤抗原的反应以及病毒 逃脱。虽然机械力在TCR识别中的重要性已经被证明，但我们只知道 对 TCR 如何形成捕获键或恢复滑移键的基本了解。我们（PI Evavold）最近有 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，我们缺乏力的预测模型 TCR 的依赖性行为，以及它如何影响生物学，进而影响我们的预测能力 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综合框架来识别、操纵和预测力 TCR-pMHC 相互作用中的依赖性行为。与之前的努力不同，我们的框架直接解决 机制。在这里，我们将进一步开发、完善和应用我们的框架。我们的驾驶假设是观看 通过能量透镜的力依赖行为将提供缺失的机制细节，说明如何以及为什么 Catch Bonds出现在TCR中，允许其合理预测和操纵，并允许考虑力 纳入 T 细胞抗原识别评估。我们的三个目标是 1) 进一步发展我们的 力相关 TCR 行为的机械框架； 2) 解释捕获债券的变化是如何产生的 TCR 界面的自然变化以及捕获键如何调节 T 细胞生物学； 3）使用合理的捕获债券 工程以更好地控制小鼠的病毒感染。总体而言，本提案中的工作将阐明不透明的问题 T 细胞机械生物学基础的机制，将捕获键置于正式的机械基础上，以及 提供预测和有效操纵 TCR 捕获键以及最终 T 细胞生物学的方法。

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.