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CD8T细胞因长时间的感染而耗尽 抗原性和炎症刺激。耗尽的CD8T细胞的特征是进行性丧失 能够产生效应性细胞因子并杀死靶细胞，增殖能力差，表达增加 多个抑制性受体。T细胞耗竭首先是在小鼠淋巴细胞模型中表现出来的 脉络膜脑膜炎病毒(LCMV)感染。相当大的努力一直集中在阐明这些机制上。 调节T细胞耗竭，涉及多个因素和途径。封锁PD-1：PD-L1 感染早期的抑制途径可以防止CD8 T细胞耗竭的进展，如果在以后给予 时间点，可以部分挽救功能衰竭的CD8 T细胞。最近的研究结果表明，PD-L1 封锁不会重振所有耗尽的CD8 T细胞，但有选择地扩大耗尽的CD8 T细胞的子集 细胞转化为仅暂时起作用的效应器，恢复到耗尽状态。即使被移除了 在慢性感染环境中，耗尽的CD8T细胞无法分化为有功能的 记忆，表明功能缺陷是在耗尽的T细胞内留下的分子印记。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 二乙酰化组蛋白H3(DiAcH3)在全球和编码效应器的特定位点水平降低 细胞因子，表明这些基因座的开放染色质结构丢失。耗竭T细胞的体外治疗 丙戊酸(VPA)是一种组蛋白去乙酰化酶抑制剂(HDACi)，可恢复diAcH3水平和效应细胞因子 制作。值得注意的是，当过继转移到幼稚的宿主中时，VPA处理的CD8 T细胞“耗尽” 在更长的一段时间内表现出更好的功能，并分化为具有功能的记忆T细胞 具有增强的召回反应。综上所述，这些结果表明表观遗传学在调节 T细胞耗尽，可能掌握着将耗尽的T细胞重新编程为功能效应器的关键 清除慢性感染。在本应用中，我们将测试1)是否采用转移耗尽的CD8 T细胞 通过体外HDACi治疗而获救，将在体内清除已建立的慢性LCMV感染，以及 2)直接用HDACi体内治疗慢性感染小鼠是否能恢复耗尽的CD8 T细胞和 允许病毒清除。我们将研究耗尽的T细胞是如何在表观遗传学和 通过抑制HDAC在转录水平上了解HDACi在解救疲劳中的作用机制。我们会 测试HDACi是否可以重新编程和挽救对PD-L1无效的耗尽CD8T细胞亚群 封锁。我们将研究PD-L1阻断与表观遗传操作是否协同作用以恢复 所有耗尽的CD8T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细胞衰竭的分子机制，并发展 加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.