Defining the mechanisms of CD4+ T cell help and roles of XCR1+ dendritic cells in CD8+ T cell responses

成功的免疫应答依赖于几种免疫细胞类型的相互作用和协调。抗病毒CD8+ T细胞反应的启动就是一个很好的例子，因为它涉及到CD4+ T细胞、树突状细胞（dc）和CD8+ T细胞的合作。在这种情况下，naïve CD8+ T细胞需要被dc激活，这些dc需要得到CD4+ T细胞的许可才能产生有效的反应，特别是在记忆阶段。虽然CD8+ T细胞应答中对CD4+ T细胞帮助的需求已经确立，但这种“帮助”的确切细胞和分子机制尚不清楚。最近，XCR1+ DC作为参与CD4+ T细胞帮助CD8+ T细胞的中心DC亚群出现，它们专门向CD8+ T细胞交叉呈递抗原。在本项目中，我们将以小鼠皮肤单纯疱疹病毒（HSV）感染为模型系统，从分子角度研究XCR1+ dc和CD4+ T细胞在抗病毒CD8+ T细胞中的作用。皮肤HSV感染是一种独特的感染模式，因为HSV停留在皮肤的局部感染，病毒抗原必须由dc携带到引流淋巴结，这是大多数自然病毒感染的情况。研究表明，与CD4+ T细胞相比，这导致CD8+ T细胞的激活延迟，因为CD8+ T细胞需要将病毒抗原从迁移的dc转移到XCR1+ dc。首先，我们将研究XCR1+ dc和CD4+ T细胞通过消耗XCR1+ dc或CD4+ T细胞在CD8+ T细胞启动和记忆中的作用。其次，我们将研究在抗病毒CD8+ T细胞应答HSV的启动阶段T细胞受体信号传导的动力学和作用。最后，我们将在单细胞水平上分析接受CD4+ T细胞帮助或未接受CD4+ T细胞帮助的CD8+ T细胞之间的基因表达差异，并试图确定与增强记忆潜能相关的基因表达模式。这些研究不仅将改善我们对启动抗病毒CD8+ T细胞反应的细胞和分子事件的理解，而且还将为CD4+ T细胞帮助诱导CD8+ T细胞的变化提供有价值的见解。我们希望这些研究的结果能帮助我们设计出更好的疫苗，诱导出更好的CD8+ T细胞来对抗病毒。

Successful immune responses depend on interaction and coordination of several immune cell types. Initiation of antiviral CD8+ T cell responses is an excellent example for this as it involves the cooperation of CD4+ T cells, dendritic cells (DCs) and CD8+ T cells. In this case, naïve CD8+ T cells need to be activated by DCs and these DCs need to be licensed by CD4+ T cells for an effective response, especially in the memory phase. Although the requirement for CD4+ T cell help in CD8+ T cell responses is well established, the exact cellular and molecular mechanisms of this ‘help’ are not well understood. Recently, XCR1+ DCs, which are specialized in cross presentation of antigens to CD8+ T cells, emerged as the central DC subset involved in CD4+ T cell help to CD8+ T cells.In this project, we will investigate the roles XCR1+ DCs and CD4+ T cells in antiviral CD8+ T cells from a molecular perspective using skin herpes simplex virus (HSV) infection in mice as a model system. Skin HSV infection represents a unique infection model since HSV stays as a local infection in the skin and viral antigens has to be carried to draining lymph node by DCs, which is the case with most natural viral infections. It has been shown that this results in delayed activation of CD8+ T cells compared to CD4+ T cells as CD8+ T cells need viral antigens to be transferred to XCR1+ DCs from migratory DCs. Firstly, we will study the role of XCR1+ DCs and CD4+ T cells in CD8+ T cell priming and memory by depleting XCR1+ DCs or CD4+ T cells. Secondly, we will examine the kinetics and effects of T cell receptor signaling during the priming phase of antiviral CD8+ T cell responses against HSV. Lastly, we will analyze gene expression differences between CD8+ T cells that received CD4+ T cell help or not at the single cell level and try to identify genes expression patterns associated with enhanced memory potential. These studies will not only improve our understating of cellular and molecular events involved in the initiation of antiviral CD8+ T cell responses, but also provide valuable insights into changes induced in CD8+ T cells by CD4+ T cell help. We hope results from these studies to help us to design better vaccines that induce superior CD8+ T cells against viruses.