Cellular mechanisms by which exhausted T cell responses are restored

项目摘要 暴露在免疫系统无法迅速清除的致病病毒中会导致慢性病毒感染。 针对此类病毒的细胞毒性T细胞(CTL)反应逐渐采用表观固定、功能低下的 通常被称为T细胞衰竭的状态，被认为可以防止免疫病理组织 由抗病毒CTL引起的持续高水平炎症造成的损害。类似形式的适应也发生在 CTL对恶性肿瘤的反应，并导致提高免疫肿瘤的耐受性。在这两个地方 慢性病毒感染和恶性，抗体阻断所谓的免疫检查点，包括 表达在激活的CTL上的抑制性PD-1受体，往往可以恢复衰竭的CTL反应。然而， 这种恢复发生的机制还不完全清楚。 在单细胞水平上，耗竭T细胞反应效应部位的CTL群由干细胞样细胞组成 表达转录因子TCF-1的记忆细胞以及瞬时表达TCF-1neg效应的细胞 在最终处于功能低下的状态之前，获得完全成熟的效应器和细胞因子分泌功能 末端分化。最近发现，PD-1的阻断并不能恢复终末期的功能 分化的细胞，但主要作用于TCF-1pos类干细胞，导致它们分裂，丢失TCF-1 表达，并产生高度增殖的短暂性效应器样亚群，介导抗病毒或抗 肿瘤控制。 在这个项目的前期工作中，我们已经确定了趋化因子受体CXCR6在 优化短暂性效应型CTL与常规树突状细胞罕见激活状态的相互作用 被称为DC3，它将IL-15转导到CTL，以促进它们在肿瘤组织中的存活和积聚。DC3 密集地聚集在肿瘤间质中的微血管周围，形成血管周围的壁龛，我们认为这可能 作为慢性炎症部位CTL反应的关键把关人。我们建议测试一下 假设这些血管周围壁龛也是维持TCF-1pos干样CTL的部位。 肿瘤组织，并将其转化为效应器样细胞。我们将使用高度多元化的组织成像技术 对整个肿瘤和活体显微镜进行观察，以确定TCF-1pos干细胞- 像CTL这样的人被招募到这些利基市场并在其中保留，并被指导与DC3互动，我们将探索 响应PD-1阻断而形成生态位的机制。

Project Summary Exposure to pathogenic viruses that the immune system cannot rapidly clear leads to chronic viral infections. Cytotoxic T cell (CTL) responses against such viruses gradually adopt a epigenetically fixed, hypofunctional state commonly referred to as T cell exhaustion, which is thought to prevent immunopathological tissue damage from continuous high-level inflammation driven by antiviral CTL. A similar form of adaptation occurs in CTL responses against malignant tumors, and leads to increasing immunological tumor tolerance. In both chronic viral infection and malignancy, antibody blockade of so-called immune checkpoints, including the inhibitory PD-1 receptor expressed on activated CTL, can often restore exhausted CTL responses. However, the mechanisms by which this restoration occurs are incompletely understood. At the single cell level, CTL populations at effector sites of exhausted T cell responses consist of stem-like memory cells that express the transcription factor TCF-1 as well as TCF-1neg effector-like cells that transiently acquire full-fledged effector and cytokine-secreting function before eventually adopt a hypofunctional state of terminal differentiation. It recently emerged that PD-1 blockade does not restore the function of terminally differentiated cells, but acts primarily on TCF-1pos stem-like cells and causes them to divide, lose TCF-1 expression, and give rise to the highly proliferative transitory effector-like subset that mediates anti-viral or anti- tumor control. In prior work for this project we have characterized the critical role of the chemokine receptor CXCR6 to optimize the interaction of transitory effector-like CTL with a rare activated state of conventional dendritic cells called DC3, which trans-present IL-15 to CTL to promote their survival and accumulation in tumor tissue. DC3 densely cluster around micro-vessels in the tumor stroma to form perivascular niches, which we suggest may act as critical gatekeepers for CTL responses at sites of chronic inflammation. We propose to test the hypothesis that these perivascular niches are also sites for the maintenance of TCF-1pos stem-like CTL in tumor tissue, and for their conversion into effector-like cells. We will use highly multiplexed histological imaging of whole tumors and intravital microscopy to identify the chemotactic guidance cues by which TCF-1pos stem- like CTL are recruited to and retained in these niches and directed to interact with DC3, and we will explore the mechanism sby which the niches are formed in response to PD-1 blockade.