Mechanisms and manipulation of force dependent behavior in T cell biology

摘要 MHC蛋白结合和呈递的多肽的TCR识别是细胞免疫的基础。TCR识别 最常通过传统的受体-配体理论来看待pMHC，在该理论中，细胞反应 被认为是由溶液结合亲和力或动力学决定的。虽然这种情况经常是这样的，但请在 过去几年的研究表明，由于机械力作用于膜结合的TCR和 PMHC可以深刻地影响T细胞信号转导。值得注意的是捕捉债券：取决于力 增强相互作用细胞之间形成的TCR-pMHC复合体的寿命。捕捉债券可以领先 使信号输出发生较大变化，并能大大提高T细胞的敏感性。证明了 调节T细胞反应的机械力，这种配体被认为具有很强的亲和力，但无法导致 捕捉债券的收益率改变了，甚至没有T细胞信号。力依赖行为已经牵涉到了广泛的 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 逃走。尽管机械力在TCR识别中的重要性已经被证明，但我们只有 对TCR如何形成接球或回复到滑移联系有一个初步的了解。我们(Pi Evavold)最近 成功操纵TCR Catch债券(发表在今年的《科学》杂志上)，但这是通过 筛选文库，对作用机制不了解。因此，我们缺乏对武力的预测模型 TCR中的依赖行为，以及这如何影响生物学，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，我们开发了一个全面的框架来识别、操纵和预测力 TCR-pMHC相互作用中的依赖行为。与以前的努力不同，我们的框架直接解决 机制。在这里，我们将进一步开发、细化和应用我们的框架。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，即如何以及为什么 捕捉债券出现在TCR中，允许对其进行理性预测和操纵，并允许进行武力考虑 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 力相关TCR行为的机制框架；2)解释如何产生捕捉键的变化 TCR界面的自然变异以及Catch键如何调节T细胞生物学；以及3)使用合理的Catch键 基因工程以更好地控制小鼠的病毒感染。总体而言，这项提案中的工作将照亮不透明的 作为T细胞机械生物学基础的机制，将捕捉结合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.