CD4+ T Cells in Acute Versus Chronic HCV Infection

描述（由申请人提供）：CD4 T细胞反应对动物和人类病毒感染的控制至关重要。然而，令人惊讶的是，人们对保护性CD4反应的构成以及导致CD4 T细胞衰竭的机制知之甚少。最近在鉴定和分离病毒特异性CD4 T细胞以及分析少量细胞的功能和转录状态方面的技术进步，现在允许回答关于CD4 T细胞在慢性和急性感染中的作用和命运的基本问题，期望这些结果将使疫苗设计和靶向免疫治疗干预措施的发展成为可能。为了更好地定义CD4 T细胞在人类中直接反应的关键方面，我们将使用丙型肝炎病毒（HCV）感染模型。丙型肝炎病毒在全世界感染了近2亿人，尽管最近在抗病毒治疗方面取得了进展，但在可预见的未来，丙型肝炎病毒仍将是世界上一个紧迫的临床问题。因此，替代治疗方式以及预防性疫苗仍然是一个高度优先事项。最重要的是，HCV允许研究急性和慢性病毒感染，从而研究保护性和无效免疫，因为估计有30%的感染者自行清除病毒，而其余则发展为慢性感染和肝炎。作为我们研究的关键资源，我们建立了一个标本库，其中包括来自1000多名HCV+受试者的30,000多份PBMC和15,000多份血浆样本，其中包括近300名感染后6个月内的个体。根据我们最近的研究发现，几乎所有受试者在HCV感染时都会产生可测量的、典型的多特异性CD4反应，我们假设HCV特异性CD4 T细胞之间的功能差异决定了HCV感染的结果，持续感染通过激活T细胞抑制途径导致CD4耗竭，并且病毒能够通过变异成不易识别的变体来规避CD4反应。因此，在目的1中，我们将测试急性HCV感染中的CD4反应在分泌细胞因子的能力上是否存在差异，这些细胞因子有助于协调免疫系统的不同分支，并在启动与T细胞存活相关的细胞内程序中发挥作用。Aim 2将通过探究不同的T细胞抑制途径的激活是否驱动了hcv特异性CD4 T细胞的不同功能和不同命运来扩展这些研究，并特别考虑肝内CD4 T细胞。在目标3中，我们将定义病毒逃逸突变对HCV持久性的作用。在拟议的研究结束时，我们期望对CD4 T细胞如何帮助控制病毒感染以及保护性CD4免疫与失败CD4反应的区别有一个详细的了解。这些结果可能对慢性病毒感染的预防和治疗产生重大影响，而不仅仅是HCV感染。

DESCRIPTION (provided by applicant): CD4 T cell responses are of critical importance for the control of viral infections in animals and humans. Yet surprisingly little is known about what constitutes a protective CD4 response as well as the mechanisms that lead to CD4 T cell failure. Recent technological advances in identifying and isolating virus-specific CD4 T cells and in analyzing the functional and transcriptional state of small numbers of cells now allow to answer basic questions about the role and fate of CD4 T cells in chronic versus acute infection, with the expectation that the results will enable rationale vaccine design as well as the development of targeted immunotherapeutic interventions. In order to better define critical aspects of the CD4 T cell response directly in humans, we will use the model of hepatitis C virus (HCV) infection. HCV infects almost 200 millions people worldwide and despite recent progress in antiviral therapies will remain a pressing clinical problem in the world for the foreseeable future. Thus alternative therapeutic modalities as well as prophylactic vaccines remain a high priority. Most importantly for this proposal, HCV allows to study both acute and chronic viral infection and thus protective and ineffective immunity, since an estimated 30% of infected subjects clear the virus spontaneously while the rest develop chronic infection and hepatitis. As a critical resource for our studies we have established a specimen bank with more than 30,000 PBMC and over 15,000 plasma samples from cohorts with more than 1000 HCV+ subjects, including almost 300 individuals within 6 months post infection. Based on our recent findings that virtually all subjects prime a measurable and typically multi-specific CD4 response upon HCV infection we hypothesize that functional differences between HCV-specific CD4 T cells define the outcome of HCV infection, that persistent infection gives rise to CD4 exhaustion through the activation of T cell inhibitory pathways and that the virus is able to circumvent the CD4 response by mutating towards less recognizable variants. Thus in aim 1 we will test whether CD4 responses in acute HCV infection differ in their capacity to secrete cytokines that help coordinate the different arms of the immune system and in the initiation of intracellular programs associated with T cell survival. Aim 2 will extend these studies by asking whether different functions and a different fate of the HCV-specific CD4 T cells is driven by the activatio of distinct T cell inhibitory pathways, with special consideration of intrahepatic CD4 T cells. In aim 3 we will define the role of viral escape mutations for persistence of HCV. At the end of the proposed studies we expect to have established a detailed understanding of how CD4 T cells can help to control viral infections and what differentiates protective CD4 immunity from a failed CD4 response. These results could have major implications for the prophylaxis and treatment of chronic viral infections, beyond HCV infection alone.