Mapping T cell antigen-specificity in LGI1 antibody encephalitis

背景自身免疫性脑炎是指由于错误的免疫反应引起的脑炎症。这种情况会导致许多症状，包括记忆丧失，癫痫发作和精神问题。抗富含亮氨酸胶质瘤灭活1（LGI1）的自身抗体可导致LGI1抗体脑炎，这是最常见的自身免疫性脑炎。虽然类固醇和其他免疫疗法是可用的，但患有LGI1抗体脑炎的患者尽管有目前最好的治疗方法，但仍会出现长期的情绪、记忆和疲劳问题。尽管B细胞产生LGI1自身抗体，但有强有力的证据表明，T细胞在LGI1抗体脑炎中也很重要。T细胞是一种免疫细胞，它使用T细胞受体识别称为肽的蛋白质的特定小部分，然后直接或通过激活其他免疫细胞类型产生免疫反应。T细胞可以有效地抵御感染和肿瘤，但当它们与体内天然存在的肽反应时，会引起自身免疫。T细胞在一个称为胸腺的器官中发育，在胸腺中，识别自身肽的T细胞通过一个称为负选择的过程被清除。然而，阴性选择是不完美的，可能导致自身反应性T细胞存在于血液和身体的其他部位。我的目标是在整个T细胞发育过程中研究LGI1抗体脑炎中的LGI1反应性T细胞：从它们在胸腺中的初始产生，到它们在外周血中对LGI 1肽的初始反应，以及它们最终在脑周围的脑脊液（CSF）中的炎症反应。本项目将全面了解T细胞如何在LGI1抗体脑炎中靶向LGI1肽，并最终导致开发新的LGI1特异性T细胞靶向治疗。ApproachI将使用通过将LGI1蛋白分裂成小片段而产生的小肽来激活来自LGI1抗体脑炎患者外周血的T细胞。这将确定哪些LGI1肽是这种情况下T细胞反应的基础。然后，这些肽可以被装载到抗原呈递分子中，并用于从外周血中分离出LGI1反应性T细胞，然后我将利用创新的单细胞测序技术，这使我能够测量单个细胞中每个基因的表达水平，沿着其T细胞受体序列的测序。该方法将用于研究胸腺中的LGI1反应性发育中的T细胞，以及LGI1抗体脑炎患者和对照受试者的外周血和CSF中的LGI1反应性发育中的T细胞。这种方法使我能够同时检查许多蛋白质的丰度和分布。我将利用这一点来了解LGI1肽是如何呈递给发育中的T细胞的，从而了解自身反应性T细胞是如何逃避负选择进入外周血的。我还将展示在LGI1抗体脑炎患者中，T细胞的哪些亚型与LGI1肽反应，并了解这如何导致脑部炎症。这可能揭示LGI1抗体脑炎的新机制，这将导致针对特异性抑制LGI1反应性T细胞的靶向治疗措施，同时使其他T细胞不受影响。这些结果对于理解T细胞在其他神经免疫性疾病中的作用以及T细胞肽反应性在更广泛的自身免疫性疾病、癌症和感染性疾病中的作用也将是重要的。

BackgroundAutoimmune encephalitis refers to brain inflammation due to a misdirected immune response. This condition causes many symptoms including memory loss, seizures and psychiatric issues. Autoantibodies against Leucine Rich Glioma Inactivated 1 (LGI1) cause LGI1 antibody encephalitis, the commonest type of autoimmune encephalitis. Although steroids and other immune therapies are available, patients with LGI1 antibody encephalitis suffer long-term problems with mood, memory and fatigue despite current best treatments.Although B cells produce LGI1 autoantibodies, there is strong evidence that T cells are also important in LGI1 antibody encephalitis. T cells are immune cells that use T cell receptors to recognise particular small sections of proteins called peptides and then generate an immune response either directly or through activating other immune cell types. T cells provide an effective defence against infections and tumours but can cause autoimmunity when they react to peptides naturally present in the body.T cells develop in an organ called the thymus, in which T cells recognising self-peptides are eliminated through a process called negative selection. However, negative selection is imperfect and can result in self-reactive T cells being present in the blood and other parts of the body.I aim to study LGI1-reactive T cells in LGI1 antibody encephalitis throughout the entire development of T cells: from their initial production in the thymus, to their initial reaction against LGI1 peptides in peripheral blood, and to their eventual inflammatory response within cerebrospinal fluid (CSF) surrounding the brain.This project will comprehensively understand how T cells target LGI1 peptides in LGI1 antibody encephalitis, and ultimately lead to the development of new LGI1-specific T cell-targeted treatments.ApproachI will use small peptides generated by splitting the LGI1 protein into small fragments to activate T cells from the peripheral blood of patients with LGI1 antibody encephalitis. This will identify which LGI1 peptides underlie the T cell responses in this condition. These peptides can then be loaded into antigen-presenting molecules and used to isolate LGI1-reactive T cells from peripheral blood.I will then take advantage of innovative single cell sequencing technologies, which allow me to measure the expression level of every gene in an individual cell, along with sequencing its T cell receptor sequence. This method will be used to study LGI1-reactive developing T cells in the thymus, and also in the peripheral blood and CSF from patients with LGI1 antibody encephalitis and control subjects.In parallel, I will use a method called CODEX on thymus samples. This method allows me to examine the abundance and distribution of many proteins simultaneously. I will use this to understand how LGI1 peptides are presented to developing T cells and thus how self-reactive T cells may escape negative selection into the peripheral blood.ImpactThis project will identify how LGI1-reactive T cells escape negative selection in the thymus. I will also show what subtype of T cells react to LGI1 peptides in patients with LGI1 antibody encephalitis and understand how this can result in brain inflammation. This is likely to uncover novel mechanisms underlying LGI1 antibody encephalitis that will lead to targeted treatment measures directed at specifically suppressing LGI1-reactive T cells while leaving other T cells unaffected. These results will also be important in understanding the role of T cells in other neuroimmunological diseases, and T cell peptide-reactivity in autoimmune diseases more widely, in cancer and in infectious diseases.