Understanding T cell immunity in anti-NMDAR encephalitis: Developing therapeutic tools for neurological autoimmunity.

Encephalitis (inflammation of the brain) affects 6000 people in the UK annually. It commonly causes significant disability, including seizures, memory problems, loss of independence and unemployment all of which affect families and carers of patients. While many cases are caused by infection, a large number occur as a result of abnormal immune responses, where cells of the immune system produce antibodies, which attack specific proteins on the surface of healthy brain cells. Currently, while we have some available treatments for immune-mediated encephalitis, often patients are resistant to treatment, respond poorly and need to remain in hospital for several months either on a specialist ward or the intensive care unit. There is a pressing need to understand how and why immune-mediated encephalitis occurs, and to identify new forms of treatment to improve recovery and outcomes for our patients.

It is not known what triggers the generation of autoantibodies that cause encephalitis, but recent evidence has suggested an important role for a specific type of immune cell (T cells) in their generation. In addition, it has recently been observed that some new cancer treatments called 'checkpoint inhibitors' or more generally, 'cancer immunotherapy', which work by affecting T cell function, can cause immune-mediated encephalitis and other immune-mediated neurological complications. These checkpoint inhibitors make normal T cells attack cancer cells more aggressively, but unfortunately, as a side effect, unregulated T cells can cause autoimmunity and also damage healthy body cells including cells in the brain.

The proposed project has 2 broad aims: (i) to characterise the function of T cell responses in patients with immune mediated encephalitis and with neurological complications after checkpoint inhibitor therapy; and (ii) to use state of the art genetic engineering to develop targeted immune suppressive therapies by generating regulatory immune cells (Tregs), which can be activated within the brain to suppress inflammation regardless of it's cause.

For the first aim we will examine the number and function of T cells in healthy volunteers and in patients and investigate whether it is easier to trigger unwanted T cell responses to specific brain proteins (NMDAR peptides) in patients who develop encephalitis and NMDAR autoantibodies.
For the second aim we will explore the use of gene-engineered T cells in the treatment of immune-mediated encephalitis. While some T cells have an 'attack' function, such as those causing disease, others (Regulatory T cells, or Tregs) are immune regulators and can suppress inflammation. We will use state-of-the-art genetic engineering to generate T regs which can become activated on entry into the brain, and switch off abnormal inflammation. Designing a personalised, precision-targeted cellular therapy for encephalitis, could transform the way we think about treating not just encephalitis, but a range of other inflammatory diseases of the brain, such as multiple sclerosis.

Over the last 15 years, University College London has been at the forefront of T cell engineering and now has the largest clinical translation pipeline of genetically engineered immune cells in Europe. Recently gene-engineered T cells have been introduced as a licensed treatment for childhood leukaemias. In the brain, they are also being trialled in patients with glioblastoma, a type of brain tumour. We aim to complete pre-clinical testing of these cells in the laboratory. If successful this could pave the way for a phase I clinical trials in the next 3-5 years.

Using a model of NMDA-receptor (NMDAR) encephalitis, we will investigate the role of effector T cells in initiating antibody-mediated neurological disease. Recent evidence supports a role for T cell help in the production of antibodies to the NMDAR. We will identify antigen-specific T cell responses to the NMDA receptor in healthy controls and in patients with de novo encephalitis or neurological autoimmunity post checkpoint inhibitors. We will complete 'proof of concept' pre-clinical development of genetically engineered regulatory T cells (Tregs) to suppress pathogenic immune responses against neuronal cell surface proteins in vitro.

The following hypotheses will be tested:
(1) Tolerance to NMDAR derived peptides is incomplete and functional antigen-specific T cells can be identified in PBMC isolated from healthy controls and patients.
(2) In the presence of checkpoint inhibitors, the frequency of NMDAR-specific T cell responses increases.
(3) Human Tregs can be genetically engineered to express the myelin basic protein-specific TCR (MBP-TCR), be activated in the presence of MBP (CNS tissue restricted peptide) and demonstrate antigen-specific suppression of pathogenic effector T cell responses in vitro.

T cells from healthy controls and patients will be stimulated using an NMDAR overlapping peptide pool. Peptide-specific responses, including proliferation and cytokine secretion, will be determined by CFSE assays and Luminex. MBP-TCR Tregs will be engineered by established retroviral transduction methods. To demonstrate the ability of the transduced Treg to suppress inflammation in an antigen-dependent manner we will assess suppression in vitro, by titrating doses of MBP-TCR Tregs with NMDAR peptide-specific effector T cells, stimulated with the relevant NMDAR peptide loaded target cells in the presence or absence of MBP peptide pulsed DCs. Mock-transduced Treg will be used as controls.
Ethics approvals are in place for both patients and controls.

Encephalitis affects 6,000 people in the UK per year, and many more worldwide. It can be fatal or cause significant morbidities, including seizures, cognitive disability, unemployment and loss of independence. Autoimmune encephalitis (AE) is being increasingly recognized and many patients who would previously have been diagnosed with 'presumed viral' encephalitis are now being found to have causative autoantibodies, most commonly to the NMDA-receptor. Although current therapies can be effective for some patients with AE, many patients have incomplete responses, or remain refractory to treatment, often spending many months in the hospital or intensive care unit. There is a pressing need to better understand disease mechanisms and identify new targets for treatment, in order to better care for our patients and improve outcomes.

We hypothesize that T cells are important in initiating the break in immune tolerance, required to generate autoantibodies and cause disease. This is supported by recent evidence, which implies an important T cell step in disease initiation. Understanding the triggers for development of self-reactive T cells in the central nervous system (CNS) would have the potential to challenge current understanding of CNS autoimmunity, and provide new targets for treatment, benefiting scientists and clinical academics in this area, in addition to patients and their relatives if new therapeutic strategies were to emerge. Better understanding of neurological autoimmunity would extend beyond encephalitis, into other active areas of research in neuroinflammatory disease.

For the checkpoint inhibitor work, we will be part of a large, multi-disciplinary, clinical and scientific collaboration, conducting a large prospective observational study of patients receiving immune checkpoint inhibitors. This will be of high impact, and have the potential to make many advances in the clinical and immunological understanding of the immune related adverse events both in neurology and other subspecialty areas.

The most exciting and potentially far-reaching part of the proposed project is testing the ability of genetically engineered regulatory T cells (Tregs) to suppress inflammation in the brain. We aim to generate a gene engineered Treg capable of switching off abnormal inflammation in the brain in an antigen-specific manner. If successful, this could radically change the treatment landscape in neuroimmunology, allowing for the development of targeted, personalized approaches to treatment. Other than in patients with glioblastoma, the potential for gene engineered T cells in neurological disease has not yet been explored. The proposed Treg could potentially be used in a range of neuroinflammatory disorders, and would therefore stand to benefit scientific researchers and clinical academics across the whole field, and potentially also in other areas such as in brain injury or neurodegeneration. Furthermore, optimising techniques to generate gene engineered Tregs could benefit researchers studying novel therapeutic mechanisms for other systemic inflammatory disorders.

We will maximize our impact by publishing in peer-reviewed journals and presenting at national/international meetings. We are committed to public and patient involvement, including through the Encephalitis Society, which has been involved in the planning of this project. Dissemination of our results to patients and the public will help increase the profile of these important diseases, and help provide patients with better understanding of why they have been affected and what treatments might help them.