Treating chronic viral infection by epigenetic reprogramming of exhausted CD8 T cells

在许多慢性病毒感染期间，病毒特异性CD8 T细胞由于长时间的免疫应答而变得耗竭。 抗原和炎症刺激。耗尽的CD 8 T细胞的特征是CD 8 T细胞的逐渐丧失。 产生效应细胞因子和杀死靶细胞的能力，增殖能力差，表达增加 多种抑制性受体。T细胞耗竭首先在淋巴细胞性白血病小鼠模型中表征。 脉络丛脑膜炎病毒（LCMV）感染。已经作出了相当大的努力， 调节T细胞衰竭，涉及多种因素和途径。阻断PD-1：PD-L1 在感染期间早期的抑制途径可以防止CD8 T细胞耗竭的进展，并且如果在感染后早期给予抑制途径， 时间点，可以部分地拯救耗尽的CD8 T细胞的功能。最近的研究结果表明，PD-L1 阻断并不能使所有衰竭的CD8 T细胞恢复活力，但选择性地扩增衰竭的CD8 T细胞亚群。 细胞转化为效应器，只是暂时发挥作用，恢复到耗尽状态。即使被移除 从慢性感染环境中，耗尽的CD8 T细胞不能分化成功能性T细胞。 记忆，这表明功能缺陷被分子印记在疲惫不堪的T细胞内。我们最近 研究表明，慢性LCMV感染期间CD8 T细胞功能的进行性丧失与 在整体上和在编码效应子的特定基因座处， 细胞因子，表明在这些基因座开放的染色质结构的损失。耗尽的T细胞的体外处理 与丙戊酸（VPA），组蛋白脱乙酰酶抑制剂（HDACi），恢复diAcH3水平和效应细胞因子 生产值得注意的是，当过继转移到幼稚宿主中时，VPA处理的"耗尽" CD8 T细胞 在延长的时间段内表现出改善的功能性并分化成功能性记忆T细胞 增强的回忆反应。总之，这些结果表明，表观遗传学在调节 T细胞耗竭，并且可能是将耗竭的T细胞重编程为能够 清除慢性感染。在本申请中，我们将测试1）是否过继转移具有以下特征的耗尽的CD8 T细胞： 通过体外HDACi治疗挽救的LCMV感染将在体内起作用以清除已建立的慢性LCMV感染，并且 2)如果在体内用HDACi直接治疗慢性感染小鼠可以使耗尽的CD8 T细胞再生， 允许病毒清除。我们将研究耗尽的T细胞是如何表观遗传地重新编程的， 通过HDAC抑制转录来了解HDACi在拯救疲劳中的机制。我们将 测试HDACi是否可以重新编程和拯救对PD-L1没有反应的耗尽的CD8 T细胞亚群 封锁我们将研究PD-L1阻断与表观遗传操作相结合是否能协同恢复 所有耗尽的CD8 T细胞的功能，并实现更快的病毒清除。通过这些研究，我们 希望能更好地了解T细胞耗竭的分子机制， 增强免疫控制和清除慢性病毒感染的最佳策略。

During many chronic viral infections, virus-specific CD8 T cells become exhausted as a result of prolonged antigenic and inflammatory stimulation. Exhausted CD8 T cells are characterized by a progressive loss of the ability to produce effector cytokines and kill target cells, poor proliferative capacity, and increased expression of multiple inhibitory receptors. T cell exhaustion was first characterized in the murine model of lymphocytic choriomeningitis virus (LCMV) infection. Considerable effort has been focused on elucidating the mechanisms that regulate T cell exhaustion, with multiple factors and pathways implicated. Blockade of the PD-1:PD-L1 inhibitory pathway early during infection can prevent progression of CD8 T cell exhaustion and, if given at later time points, can partially rescue the function of exhausted CD8 T cells. Recent results show that PD-L1 blockade does not reinvigorate all exhausted CD8 T cells but selectively expands a subset of exhausted CD8 T cells into effectors that function only temporarily, reverting back to the exhausted state. Even when removed from the chronic infection environment, exhausted CD8 T cells are unable to differentiate into functional memory, indicating that the functional defects are molecularly imprinted within exhausted T cells. Our recent work has shown that progressive loss of CD8 T cell functionality during chronic LCMV infection is associated with decreased diacetylated histone H3 (diAcH3) levels globally and at specific loci encoding effector cytokines, indicating a loss of open chromatin structure at these loci. In vitro treatment of exhausted T cells with valproic acid (VPA), a histone deacetylase inhibitor (HDACi), restores diAcH3 levels and effector cytokine production. Remarkably, when adoptively transferred into naïve hosts, VPA-treated “exhausted” CD8 T cells exhibit improved functionality for an extended period of time and differentiate into functional memory T cells with enhanced recall responses. Together, these results show that epigenetics plays a crucial role in regulating T cell exhaustion and may hold the key to reprogramming exhausted T cells into functional effectors capable of clear chronic infection. In this application, we will test 1) if adoptive transfer of exhausted CD8 T cells that have been rescued by in vitro HDACi treatment will work in vivo to clear an established chronic LCMV infection, and 2) if direct treatment of chronically infected mice with HDACi in vivo can rejuvenate exhausted CD8 T cell and allow for viral clearance. We will examine how exhausted T cells are reprogrammed epigenetically and transcriptionally by HDAC inhibition to understand the mechanisms of HDACi in rescuing exhaustion. We will test whether HDACi can reprogram and rescue subsets of exhausted CD8 T cells that fail to respond to PD-L1 blockade. We will examine if combining PD-L1 blockade with epigenetic manipulation synergizes to restore the functionality of all exhausted CD8 T cells and achieve faster viral clearance. Through these studies, we hope to gain a better understanding of the molecular mechanisms underlying T cell exhaustion and to develop an optimal strategy for enhancing immune control and clearance of chronic viral infection.