Monoclonal Antibodies in NMDAR Antibody Positive Post-HSE

Autoimmune brain inflammation is often caused by antibodies that target patients own nervous tissue. In some patients viral infection (e.g. herpes simplex virus) precedes autoimmune brain inflammation. In those cases, viral structures are thought to trigger the formation of disease- mediating antibodies. The exact mechanisms how viral structures cause the transition from antiviral to disease-mediating antibodies is largely unknown. By investigating the molecular nature of those antibodies we aim to reveal disease-driving mechanisms. The availability of naturally occurring antibodies for research is limited because of their predominant location within the brain and high temporal variability following disease course and therapies. The aim of this proposal is therefore to isolate those immune cells of patients that produce the antibodies. Using highly sophisticated molecular biology methods it will be possible to generate large amounts of the antibodies originating from patients single antibody-producing cells (monoclonal antibodies). Having large amounts of monoclonal antibodies available, it will be possible to investigate the nature of those antibodies in more detail. For example, the degree of antibody maturation can be investigated by mutation analysis, which will shed light into molecular mechanisms driving the disease. Furthermore, it can be determined if viral particles resemble neuronal structures targeted by the antibodies and whether this similarity triggers autoimmune brain inflammation. The isolation and production of monoclonal antibodies from patients with autoimmune diseases is an innovative method, by which unlimited access to hardly accessible antibodies is provided. The technique has never been used for this particular group of patients. Results from the study could serve as a model for further autoimmune diseases, since it is suspected that infections could trigger autoimmunity in various diseases (e.g. Multiple Sclerosis). Once disease-driving mechanisms are better known, more effective therapies can be developed. Moreover, the availability of monoclonal antibodies is also crucial to answer scientific questions in basic research projects in the future.

Monoclonal antibodies in Autoimmune Encephalitis During an immune reaction, various cell types work in concert to protect our body from pathogens, such as viruses. Thereby, T helper cells stimulate B cells, which produce antibodies against viral structures or proteins, so-called antigens. Not only are those antibodies highly specific for their respective target protein, they also have a highly diverse genetic profile, which we are only beginning to understand. In autoimmune diseases, the immune reaction is falsely directed against the body's own proteins, in autoimmune encephalitis these proteins are inside the brain, a highly protected organ, which immune cells usually cannot access. In fact, an immune reaction is initiated in the blood. However, immune cells involved in autoimmune encephalitis affecting the brain are extremely rare in the blood and difficult to capture. Thus, little was known about the nature of these cells. The research aim was to isolate single B cells, specifically enriched to recognize LGI1, from the blood. LGI1 is a neuronal protein important for synaptic transmission, which is also a known target antigen in patients with autoimmune encephalitis. With this novel method it was possible to characterize the genetic profile of monoclonal antibodies produced by individual B cells from patients and to dissect their molecular, potentially pathogenic, mechanisms in detail using in vitro cell cultures and an in vivo animal model. Intriguingly, the observed genetic diversity, along with high mutation frequencies of the isolated LGI1 antibodies suggested a major contribution of T helper cells during affinity maturation. Indeed, antigen-specific T cells reacting to the target protein were also identified in the blood of patients with LGI1 antibody encephalitis. Characterization of the nature of those T cells is ongoing research. In addition, the characterization of the isolated monoclonal antibodies revealed interesting mechanisms of action: while the antibodies targeting the LRR-domain of LGI1 caused internalization of the protein, antibodies targeting the EPTP-domain of LGI1 blocked the interaction of the protein with its interaction partners. Both antibody types impaired long-term potentiation, a sustained amplification of synaptic transmission, and LRR-directed antibodies induced memory impairment as well. Thus, both antibody types contribute to the disruption of synaptic integrity and may cause symptoms typical for LGI1 antibody autoimmune encephalitis. In conclusion, the presence of highly mutated antigen-specific antibodies and T cells support the presence of an underlying autoimmune reaction outside the brain. Two distinct specificities of the antibodies were identified, both with pathogenic potential. Results from this project created new research hypotheses and methods developed are also applicable to other diseases, including other autoimmune diseases and viral infections. The findings will contribute to a better understanding whether and how autoimmunity differs from immunity against viral infections, enabling the development of targeted therapies in the future.