The Molecular Mechanism of Tim-3-mediated T Cell Dysfunction

描述(申请人提供)：我们克隆了TIM-3，作为一种在产生干扰素-γ的Th1/Tc1细胞上差异表达的分子，最近发现TIM-3也在致病的促炎Th17细胞上表达。我们鉴定Galectin-9是TIM-3的配体，并发现Galectin-9与TIM-3的相互作用导致细胞死亡，随后终止Th1/Tc1反应。这些研究结合其他体内对可溶性TIM-3的阻断研究表明，TIM-3是抑制效应分子Th1/Tc1免疫所必需的抑制分子。令人兴奋的新数据表明，Tim-3也参与了诱导T细胞衰竭的过程。在慢性病毒感染(如HIV)和癌症中，效应T细胞上TIM-3的表达增加，使其功能障碍，而在人类自身免疫性疾病中，效应T细胞上的TIM-3表达缺失，使其高度促炎和致病。因此，TIM-3在多种人类疾病中发挥着重要作用，但令人惊讶的是，人们对TIM-3的功能生物学知之甚少：尚不清楚是什么诱导T细胞表达TIM-3，以及它是如何介导其抑制作用的。要了解细胞内的 为了进一步研究介导TIM-3功能的途径，我们进行了酵母双杂交筛选，鉴定了BAT3(人类白细胞抗原B相关转录本3)是一个与TIM-3细胞质尾部结合的分子。当BAT3结合到Tim-3的尾巴上时，它就像一个分子守门人一样，调节Tim-3的抑制功能。为了解决这一假设，我们提出了以下具体目标：1)确定 TIM-3信号进入T细胞诱导T细胞功能障碍/衰竭的分子机制。由于我们已经确定BAT3是TIM-3尾巴的结合伙伴，我们将分析条件缺失BAT-3是否会导致T细胞功能障碍，并研究BAT3与TIM-3结合是如何调节CD3-TCR信号的。这项拟议的研究将确定TIM-3在T细胞中介导其抑制功能的分子机制，这些机制可用于调节自身免疫反应。虽然增强Tim-3信号可以抑制自身免疫性疾病，但抑制Tim-3功能可以增强慢性病毒感染(如HIV)和癌症的免疫反应。

DESCRIPTION (provided by applicant): We cloned Tim-3 as a molecule differentially expressed on IFN-gamma producing Th1/Tc1 cells and more recently found that Tim-3 is also expressed on pathogenic pro-inflammatory Th17 cells. We identified Galectin-9 as the Tim-3 ligand, and found that the interaction of galectin-9 with Tim-3 led to cell death and subsequent termination of Th1/Tc1 responses. These studies, together with other in vivo blockade studies with soluble Tim- 3, suggested that Tim-3 is inhibitory molecule necessary for dampening of effector Th1/Tc1 immunity. Exciting new data suggests that Tim-3 is also involved in inducing T cell exhaustion. Tim-3 expression is increased on effector T cells in chronic viral infections (e.g HIV) and cancers, rendering them dysfunctional, however in human autoimmune diseases there is loss of Tim-3 expression on effector T cells making them highly proinflammatory and pathogenic. Therefore, Tim-3 plays an important role in multiple human diseases, yet surprisingly little is known about the functional biology of Tim-3: it is not clear what induces Ti-3 expression on T cells and how it mediates its inhibitory effects. To understand the intracellular pathways that mediate Tim-3 function, we undertook a yeast two-hybrid screen and identified Bat3 (HLA-B associated transcript 3) as a molecule that binds to the Tim-3 cytoplasmic tail. Bat3, when bound to the Tim-3 tail, acts as a molecular "gate-keeper" that regulates Tim-3 inhibitory functions. To address this hypothesis we propose the following specific aim: 1) Identify molecular mechanisms by which Tim-3 signals into T cells to induce T cell dysfunction/exhaustion. Since we have identified Bat3 as a binding partner for the Tim-3 tail, we will analyze whether conditional loss of Bat-3 will induce T cell dysfunction and study how Bat3 bound to Tim-3 regulates proximal CD3-TcR signaling. The proposed studies will identify the molecular mechanisms by which Tim-3 mediates its inhibitory function in T cells that could be exploited to regulate autoimmune responses. While boosting Tim-3 signals could dampen autoimmune disease, repressing Tim-3 function could augment immune responses in chronic viral infections (e.g. HIV) and cancer.