Mapping T cell antigen-specificity in LGI1 antibody encephalitis

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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.