Biophysical analysis of T-cell discrimination among classes of self-ligands

描述（由申请人提供）：在自然界中，细胞毒性T细胞负责识别展示外源抗原的细胞并杀死它们。然而，T细胞不仅对典型的外源抗原完全应答，而且在自身免疫或有效的抗肿瘤应答的情况下，还以共激动剂活性（其中某些宿主自身配体可以与激动剂配体协同触发T细胞受体复合物以引发信号传导）或明显的激动剂活性的形式显示对外周中自身的应答。一种潜在的策略是通过增加TCR-CD 8-肽-MHC结合亲和力来补偿无效的抗肿瘤应答。然而，目前还不清楚如何增加系统的效力，以介导更大的T细胞活性，而不介导危险的自身反应性宿主抗原。我们的长期目标是修改T细胞活化阈值，使得这些免疫效应物介导对疾病相关的自身（肿瘤）抗原的有效免疫应答，同时保持对宿主的非肿瘤相关的自身抗原无应答。本申请中提出的实验的目的是通过确定T细胞如何区分不同类别的自身配体（定义为肿瘤（自身）和宿主（自身）配体）的生物物理机制来朝着该目标迈出重要一步。本申请的中心假设是，具有共激动剂活性的自身配体与介导自我破坏性应答的自身配体之间的功能区分是通过由TCR和CD 8共受体的联合作用介导的动力学阈值来实现的。在强有力的初步数据的指导下，将通过追求三个具体目标来检验该假设：1）确定针对特定肽-MHC配体的TCR-⑶ 8结合亲合力与这些配体的共激动剂相对于效应物诱导活性之间的定量关系; 2）确定TCR亲和力，其限定维持对效应物诱导配体的特异性的阈值; 3）确定CD 8亲和力的改变将如何影响T细胞维持自身配体类别之间的区分的能力。为了实现这些目标，我们将使用完善的模型系统来识别“真正的”自身抗原，其涉及在小鼠CD 8 + T细胞上表达人自身/肿瘤反应性HLA-A2限制性受体。我们将使用新的分子荧光成像和生物物理技术来研究配体识别和功能反应的生物物理之间的关系。最后，我们将使用体外噬菌体展示来选择出高亲和力TCR和CD 8分子，这将使我们能够获得比使用天然存在的TCR和CD 8分子更大的动力学窗口。所提出的研究的基本原理是在正常组织共激动剂和弱肿瘤激动剂之间存在足够大的亲和力窗口，使得增强对后者的结合TCR-CD 8亲合力可以改善效应器应答而不产生不期望的抗组织应答。与人类健康的相关性：我们相信这个问题对于理解和增强癌症免疫力非常重要，并可能导致对这种疾病更有效的治疗。公共卫生相关性：我们期望我们的研究将提供洞察我们如何能够通过增加TCR-CD 8-肽-MHC相互作用的亲和力来操纵免疫应答，以介导更有效地识别肿瘤（自身）抗原，同时避免自身反应性。所获得的知识在产生高亲和力TCR或CD 8分子方面将是重要的，所述TCR或CD 8分子在转移到CD 8 + T细胞中时可以用于有效的过继免疫疗法转移疗法并且仍然保留特异性。或者，也可以修饰具有明确特异性的可溶性TCR以递送放射性核素、毒素或免疫调节分子，从而更有效地杀死肿瘤细胞。

DESCRIPTION (provided by applicant): In nature, cytotoxic T-cells are responsible for identifying cells that display foreign antigens and killing them. However, T-cells do not only respond fully to typical foreign antigens but also show responses to self in the periphery in the form of co-agonist activity (wherein certain host self-ligands can synergize with agonist ligands in triggering the T-cell receptor complex to initiate signaling) or overt agonist activity in the case of autoimmunity or effective anti-tumor responses. One potential strategy is to compensate for ineffective anti- tumor responses by increasing TCR-CD8-peptide-MHC binding affinity. However, it is still not clear how much one can increase the potency of the system in order to mediate greater T-cell activity without mediating dangerous auto-reactivity to host antigens. Our long-term goal is to modify the T-cell activation threshold so that these immune effectors mediate efficient immune responses to disease-associated, self (tumor)-antigens while remaining unresponsive to the host's non-tumor associated self-antigens. The objective of the experiments proposed in this application is to make a major step towards this goal by determining the biophysical mechanism underlying how T-cells discriminate between different classes of self-ligands defined as tumor (self) and host (self) ligands. The central hypothesis of the application is that functional discrimination between self-ligands with co-agonist activity and those that mediate self-destructive responses is achieved by kinetic thresholding mediated by the conjoint action of the TCR and the CD8 co-receptor. Guided by strong preliminary data, this hypothesis will be tested by pursuing three specific aims: 1) Determine the quantitative relationship between TCR-CD8 binding avidity for specific peptide-MHC ligands and the co-agonist verses effector-inducing activity of these ligands; 2) Determine the TCR affinity that defines the threshold for maintaining specificity to effector-inducing ligands; 3) Determine how alterations in CD8 affinity will affect the ability of the T-cells to maintain discrimination among self-ligand classes. To achieve these aims we will use a well-established model system for recognition of "true" self-antigens involving expression of human self/tumor- reactive HLA-A2 restricted receptors on mouse CD8+ T-cells. We will use novel molecular fluorescent imaging and biophysical techniques to investigate the relationship between the biophysics of ligand recognition and functional responses. Finally, we will use in vitro phage display to select out high-affinity TCR and CD8 molecules which will allow us to access a larger kinetic window than available using naturally occurring TCR and CD8 molecules. The rationale for the proposed research is that a sufficiently large affinity window exists between normal tissue co-agonists and weak tumor agonists such that enhancing the conjoint TCR-CD8 avidity for the latter can improve effector responses without engendering undesirable anti-tissue responses. Relevance to human health: We believe this issue is important in understanding and enhancing cancer immunity and could lead to more effective therapies for this disease. Public Health Relevance: We expect that our studies will provide insight into how we can manipulate the immune response by increasing the affinity of the TCR-CD8-peptide-MHC interaction to mediate more effective recognition of tumor (self) antigens while avoiding self-reactivity. The knowledge obtained would be important in terms of generating high-affinity TCR or CD8 molecules that when transferred into CD8+ T-cells could be used for effective adoptive immunotherapy transfer therapies and still retain specificity. Alternatively, soluble TCRs with well-defined specificities could also be modified to deliver radionuclides, toxins or immunomodulatory molecules for more efficient killing of tumor cells.