Role of Tim-3 in determining T cell immunity

 描述(申请人提供)：T细胞抑制分子，如CTLA-4、PD-1和TIM-3，是T细胞反应的重要调节者，已成为癌症有价值的免疫治疗靶点。在T细胞抑制分子中，TIM-3现在被认为是癌症中出现的功能失调或耗尽的CD8+T细胞的关键决定因素。事实上，我们是第一个表明TIM-3的表达专门标志着肿瘤组织中存在的最功能失调或耗尽的CD8+T细胞群，以TIM-3为靶点的免疫疗法显著提高了以PD-1为靶点的免疫疗法的疗效，以恢复耗尽的CD8+T细胞的功能，并激发强大的抗肿瘤免疫。我们现在发现，TIM-3的表达也标志着一种高度抑制的CD4+FoxP3+调节性T细胞(Treg)群体，这是肿瘤组织中唯一存在的。我们的初步数据进一步表明TIM-3促进了Treg的抑制功能。因此，TIM-3可通过其在CD8+T细胞和Treg中的作用影响肿瘤免疫。然而，TIM-3在CD8+T细胞中如何发挥作用以抑制其反应，而在Treg功能中如何促进其抑制活性尚不清楚。我们现在发现，TCF-1(T细胞因子1)在表现出功能障碍表型的TIM-3+CD8+肿瘤浸润性淋巴细胞(TIL)中特异性下调。我们的初步数据进一步表明，阻断TIM-3和PD-1信号可以消除T细胞衰竭，恢复TIM-3+CD8+TIL中TCF-1的表达。我们进一步发现TCF-1在TIM-3+中表达下调，但在TIM-3-Treg中不下调，TIM-3/PD-1阻断可恢复TIM-3+Treg中TCF-1的表达。Tcf-1是典型的Wnt信号通路中的关键转录因子。Tcf-1是正常T细胞发育和产生长寿命中央记忆CD8+T细胞所必需的，但Wnt信号和Tcf-1在T细胞功能障碍/衰竭发展中的作用尚未阐明。有趣的是，TCF-1最近被认为与拮抗调节性T细胞功能有关，因此提出了TCF-1的Tim-3驱动的抑制可能是Tim-3+Treg强大的抑制功能的基础。根据我们的初步数据，我们假设TIM-3通过抑制肿瘤内CD8+T细胞和Treg中的Wnt信号和TCF-1来抑制抗肿瘤T细胞反应。我们处于一个独特的位置来剖析TIM-3和TCF-1在确定抗肿瘤T细胞反应中的作用，因为我们有可用的新工具，包括TIM-3和TCF-1条件敲除小鼠，以及选择性地在淋巴细胞中特异性地表达激活和抑制形式的TCF-1的小鼠。我们将使用这些新产生的工具来定义TIM-3决定抗肿瘤免疫的机制以及TCF-1在这一过程中的作用。我们提出的具体目标如下：1)确定TIM-3在CD4+FoxP3+调节性T细胞中的作用；2)确定Wnt信号/TCF-1在TIM-3驱动的抗肿瘤免疫抑制中的作用。

 DESCRIPTION (provided by applicant): T cell inhibitory molecules such as CTLA-4, PD-1, and Tim-3 are important regulators of the T cell response that have emerged as valuable immunotherapeutic targets in cancer. Among T cell inhibitory molecules, Tim-3 is now recognized as a critical determinant of the dysfunctional or exhausted CD8+ T cells that arise in cancer. Indeed, we were the first to show that expression of Tim-3 specifically marks the most dysfunctional or exhausted population of CD8+ T cells present in tumor tissue and that immunotherapy that targets Tim-3 markedly improves the efficacy of immunotherapy that targets PD-1 for restoring function to exhausted CD8+ T cells and eliciting potent anti-tumor immunity. We have now discovered that expression of Tim-3 also marks a highly suppressive population of CD4+ FoxP3+ regulatory T cells (Treg) that is uniquely present in tumor tissue. Our preliminary data further indicate that Tim-3 promotes the suppressor function of Treg. Thus, Tim-3 can impact on tumor immunity through its actions in CD8+ T cells and Treg. However, how Tim-3 may function in CD8+ T cells to dampen their responses while in Treg function to promote their suppressive activity is not known. We have now discovered that TCF-1 (T cell factor 1) is specifically down-regulated in Tim-3+ CD8+ tumor- infiltrating lymphocytes (TILs) that exhibit dysfunctional phenotype. Our preliminary data further show that blockade of Tim-3 and PD-1 signaling, which we have shown abrogates T cell exhaustion, restores expression of TCF-1 in Tim-3+ CD8+ TILs. We have further found that TCF-1 is similarly down-regulated in Tim-3+ but not Tim-3- Treg and that Tim-3/PD-1 blockade restores TCF-1 expression in Tim-3+ Treg. TCF-1 is a key transcription factor in the canonical Wnt signaling pathway. TCF-1 is required for normal T cell development and for the generation of long-lived central memory CD8+ T cells but a role for Wnt signaling and TCF-1 in the development of T cell dysfunction/exhaustion has not been addressed. Interestingly, TCF-1 has recently been implicated in antagonizing regulatory T cell function, thus raising the possibility that Tim-3-drivn repression of TCF-1 underlies the potent suppressor function of Tim-3+ Treg. Based on our preliminary data, we hypothesize that Tim-3 suppresses the anti-tumor T cell response via a mechanism that involves repression of Wnt signaling and TCF-1 in intra-tumoral CD8+ T cells and Treg. We are in a unique position to dissect the role of Tim-3 and TCF-1 in determining the anti-tumor T cell response as we have available novel tools, including Tim- 3 and TCF-1 conditional knock-out mice as well as mice that selectively express activating versus repressive forms of TCF-1 specifically in lymphocytes. We will use these newly generated tools to define the mechanisms by which Tim-3 determines anti-tumor immunity and the role of TCF-1 in this process. We propose the following specific aims: 1) Define the role of Tim-3 in CD4+FoxP3+ regulatory T cells; and 2) Define the role of Wnt signaling/TCF-1 in Tim-3-driven suppression of anti-tumor immunity.