Clinical and experimental studies of potentially pathogenic brain-directed autoantibodies: current knowledge and future directions

Autoimmune encephalitis: recent clinical and biological advances

In 2015, we wrote a review in The Journal of Neurology summarizing the field of autoantibody-associated neurological diseases. Now, in 2023, we present an update of the subject which reflects the rapid expansion and refinement of associated clinical phenotypes, further autoantibody discoveries, and a more detailed understanding of immunological and neurobiological pathophysiological pathways which mediate these diseases. Increasing awareness around distinctive aspects of their clinical phenotypes has been a key driver in providing clinicians with a better understanding as to how these diseases are best recognized. In clinical practice, this recognition supports the administration of often effective immunotherapies, making these diseases 'not to miss' conditions. In parallel, there is a need to accurately assess patient responses to these drugs, another area of growing interest. Feeding into clinical care are the basic biological underpinnings of the diseases, which offer clear pathways to improved therapies toward enhanced patient outcomes. In this update, we aim to integrate the clinical diagnostic pathway with advances in patient management and biology to provide a cohesive view on how to care for these patients in 2023, and the future.

The B cell immunobiology that underlies CNS autoantibody-mediated diseases

A rapidly expanding and clinically distinct group of CNS diseases are caused by pathogenic autoantibodies that target neuroglial surface proteins. Despite immunotherapy, patients with these neuroglial surface autoantibody (NSAb)-mediated diseases often experience clinical relapse, high rates of long-term morbidity and adverse effects from the available medications. Fundamentally, the autoantigen-specific B cell lineage leads to production of the pathogenic autoantibodies. These autoantigen-specific B cells have been consistently identified in the circulation of patients with NSAb-mediated diseases, accompanied by high serum levels of autoantigen-specific antibodies. Early evidence suggests that these cells evade well-characterized B cell tolerance checkpoints. Nearer to the site of pathology, cerebrospinal fluid from patients with NSAb-mediated diseases contains high levels of autoantigen-specific B cells that are likely to account for the intrathecal synthesis of these autoantibodies. The characteristics of their immunoglobulin genes offer insights into the underlying immunobiology. In this Review, we summarize the emerging knowledge of B cells across the NSAb-mediated diseases. We review the evidence for the relative contributions of germinal centres and long-lived plasma cells as sources of autoantibodies, discuss data that indicate migration of B cells into the CNS and summarize insights into the underlying B cell pathogenesis that are provided by therapeutic effects.

The autoantibody-mediated encephalitides: from clinical observations to molecular pathogenesis

The autoimmune encephalitis (AE) syndromes have been characterised by the detection of autoantibodies in serum and/or cerebrospinal fluid which target the extracellular domains of specific neuroglial antigens. The clinical syndromes have phenotypes which are often highly characteristic of their associated antigen-specific autoantibody. For example, the constellation of psychiatric features and the multi-faceted movement disorder observed in patients with NMDAR antibodies are highly distinctive, as are the faciobrachial dystonic seizures observed in close association with LGI1 antibodies. These typically tight correlations may be conferred by the presence of autoantibodies which can directly access and modulate their antigens in vivo. AE remains an under-recognised clinical syndrome but one where early and accurate detection is critical as prompt initiation of immunotherapy is closely associated with improved outcomes. In this review of a rapidly emerging field, we outline molecular observations with translational value. We focus on contemporary methodologies of autoantibody detection, the evolution and distinctive nature of the clinical phenotypes, generalisable therapeutic paradigms, and finally discuss the likely mechanisms of autoimmunity in these patients which may inform future precision therapies.

The role of thymic tolerance in CNS autoimmune disease

The contributions of the peripheral adaptive and innate immune systems to CNS autoimmunity have been extensively studied. However, the role of thymic selection in these conditions is much less well understood. The thymus is the primary lymphoid organ for the generation of T cells; thymic mechanisms ensure that cells with an overt autoreactive specificity are eliminated before they emigrate to the periphery and control the generation of thymic regulatory T cells. Evidence from animal studies demonstrates that thymic T cell selection is important for establishing tolerance to autoantigens. However, there is a considerable knowledge gap regarding the role of thymic selection in autoimmune conditions of the human CNS. In this Review, we critically examine the current body of experimental evidence for the contribution of thymic tolerance to CNS autoimmune diseases. An understanding of why dysfunction of either thymic or peripheral tolerance mechanisms rarely leads to CNS inflammation is currently lacking. We examine the potential of de novo T cell formation and thymic selection as novel therapeutic avenues and highlight areas for future study that are likely to make these targets the focus of future treatments.

Autoantibodies and Psychosis

Research into antibody-mediated disease, in response to immune dysfunction or to tumour development, has rapidly expanded in recent years. Antibodies binding to neuroreceptors can cause psychiatric features, including psychosis, in a minority of patients as well as neurological features. The responsiveness of some of these cases to immunotherapy supports the hypothesis that antibody-associated mechanisms play a role in the pathogenesis of psychotic diseases. The purpose of this chapter is to review autoantibodies that are most likely to be relevant for patients with psychotic symptoms. Herein, we describe receptor structure and mechanism of action, clinical and psychiatric features for the growing number of neuronal surface antibodies, including those to the N-methyl-D-aspartate (NMDA) receptor. The identification of a subgroup of patients with psychiatric features having antibody-mediated disease highlights the importance of considering the diagnosis, particularly in those patients presenting with a first episode of psychosis.

Factors underlying the development of chronic temporal lobe epilepsy in autoimmune encephalitis

PURPOSE

Limbic encephalitis (LE) is an autoimmune condition characterized by amnestic syndrome, psychiatric features and seizures. Early diagnosis and prompt treatment are crucial to avoid long-term sequelae, including psycho-cognitive deficits and persisting seizures. The aim of our study was to analyze the characteristics of 33 LE patients in order to identify possible prognostic factors associated with the development of chronic epilepsy.

METHODS

This is a retrospective cohort study including adult patients diagnosed with LE in the period 2010-2017 and followed up for ≥12 months. Demographics, seizure semiology, EEG pattern, MRI features, CSF/serum findings were reviewed.

RESULTS

All 33 LE patients (19 M/14F, mean age 61.2 years) presented seizures. Thirty subjects had memory deficits; 22 presented behavioural/mood disorders. Serum and/or CSF auto-antibodies were detected in 12 patients. In 31 subjects brain MRI at onset showed typical alterations involving temporal lobes. All patients received immunotherapy. At follow-up, 13/33 had developed chronic epilepsy; predisposing factors included delay in diagnosis (p = .009), low seizure frequency at onset (p = .02), absence of amnestic syndrome (p = .02) and absence/rarity of inter-ictal epileptic discharges on EEG (p = .06).

CONCLUSIONS

LE with paucisymptomatic electro-clinical presentation seemed to be associated to chronic epilepsy more than LE presenting with definite and severe "limbic syndrome".

The clinical features, underlying immunology, and treatment of autoantibody-mediated movement disorders

An increasing number of movement disorders are associated with autoantibodies. Many of these autoantibodies target the extracellular domain of neuronal surface proteins and associate with highly specific phenotypes, suggesting they have pathogenic potential. Below, we describe the phenotypes associated with some of these commoner autoantibody‐mediated movement disorders, and outline increasingly well‐established mechanisms of autoantibody pathogenicity which include antigen downregulation and complement fixation. Despite these advances, and the increasingly robust evidence for improved clinical outcomes with early escalation of immunotherapies, the underlying cellular immunology of these conditions has received little attention. Therefore, here, we outline the likely roles of T cells and B cells in the generation of autoantibodies, and reflect on how these may guide both current immunotherapy regimes and our future understanding of precision medicine in the field. In addition, we summarise potential mechanisms by which these peripherally‐driven immune responses may reach the central nervous system. We integrate this with the immunologically‐relevant clinical observations of preceding infections, tumours and human leucocyte antigen‐associations to provide an overview of the therapeutically‐relevant underlying adaptive immunology in the autoantibody‐mediated movement disorders. © 2018 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Use of intravenous immunoglobulin for the treatment of autoimmune encephalitis: audit of the NHS experience

Objectives

The treatments of limbic and other autoimmune encephalitis include immunosuppression, symptomatic treatment, and in the case of paraneoplastic syndromes, appropriate therapy for underlying neoplasms. When immunotherapy is considered, intravenous immunoglobulin is one option for treatment, either alone or in combination with corticosteroids. To date, however, evidence for the use of intravenous immunoglobulin in this context comes from case series/expert reviews as no controlled trials have been performed. We aimed to analyse the NHS England Database of intravenous immunoglobulin usage, which was designed to log use and guide procurement, to explore usage and therapeutic effect of intravenous immunoglobulin in autoimmune encephalitis in England.

Design

We conducted a retrospective audit and review of the NHS England Database on intravenous immunoglobulin use.

Setting

NHS England Database of intravenous immunoglobulin use which covers secondary and tertiary care prescribing and use of intravenous immunoglobulin for all patients in hospitals in England.

Participants

Hospital in-patients with confirmed or suspected autoimmune/limbic encephalitis between September 2010 and January 2017.

Results

A total of 625 patients who were 18 years of age or older were treated with intravenous immunoglobulin for autoimmune encephalitis, of whom 398 were determined as having 'highly likely' or 'definite' autoimmune/limbic encephalitis. Ninety-six percent were treated with a single course of intravenous immunoglobulin. The availability and accuracy of reporting of outcomes was very poor, with complete data only available in 27% of all cases.

Conclusions

This is the first review of data from this unique national database. Whilst there was evidence for clinical improvement in many cases of patients treated with intravenous immunoglobulin, the quality of outcome data was generally inadequate. Methods to improve quality, accuracy and completeness of reporting are crucial to maximise the potential value of this resource as an auditing tool.

LGI1, CASPR2 and related antibodies: a molecular evolution of the phenotypes

Recent biochemical observations have helped redefine antigenic components within the voltage-gated potassium channel (VGKC) complex. The related autoantibodies may be now divided into likely pathogenic entities, which target the extracellular domains of leucine-rich glioma-inactivated 1 (LGI1) and contactin-associated protein-like 2 (CASPR2), and species that target intracellular neuronal components and are likely non-pathogenic. This distinction has enhanced clinical practice as direct determination of LGI1 and CASPR2 antibodies offers optimal sensitivity and specificity. In this review, we describe and compare the clinical features associated with pathogenic LGI1 and CASPR2 antibodies, illustrate emerging laboratory techniques for antibody determination and describe the immunological mechanisms that may mediate antibody-induced pathology. We highlight marked clinical overlaps between patients with either LGI1 or CASPR2 antibodies that include frequent focal seizures, prominent amnesia, dysautonomia, neuromyotonia and neuropathic pain. Although occurring at differing rates, these commonalities are striking and only faciobrachial dystonic seizures reliably differentiate these two conditions. Furthermore, the coexistence of both LGI1 and CASPR2 antibodies in an individual occurs surprisingly frequently. Patients with either antibody respond well to immunotherapies, although systematic studies are required to determine the magnitude of the effect beyond placebo. Finally, data have suggested that CASPR2 and LGI1 modulation via genetic or autoimmune mechanisms may share common intermediate molecules. Taken together, the biochemical distinction of antigenic targets has led to important clinical advances for patient care. However, the striking syndrome similarities, coexistence of two otherwise rare antibodies and molecular insights suggest the VGKC complex may yet be a common functional effector of antibody action. Hence, we argue for a molecular evolution alongside a clinical and phenotypic re-evaluation.

Seronegative antibody-mediated neurology after immune checkpoint inhibitors

Checkpoint inhibitor medications have revolutionized oncology practice, but frequently induce immune‐related adverse events. During autoimmune neurology practice over 20 months, we prospectively identified four patients with likely antibody‐mediated neurological diseases after checkpoint inhibitors: longitudinally extensive transverse myelitis, Guillain–Barré syndrome, and myasthenia gravis. All patients shared three characteristics: symptoms commenced 4 weeks after drug administration, responses to conventional immunotherapies were excellent, and autoantibodies traditionally associated with their syndrome were absent. However, serum immunoglobulins from the myelitis and Guillain–Barré syndrome patients showed novel patterns of tissue reactivity. Vigilance is required for antibody‐mediated neurology after checkpoint inhibitor administration. This phenomenon may inform the immunobiology of antibody‐mediated diseases.

Innate and adaptive immunity in human epilepsies

Inflammatory mechanisms have been increasingly implicated in the origin of seizures and epilepsy. These mechanisms are involved in the genesis of encephalitides in which seizures are a common complaint. Experimental and clinical evidence suggests different inflammatory responses in the brains of patients with epilepsy depending on the etiology. In general, activation of both innate and adaptive immunity plays a role in refractory forms of epilepsy. Epilepsies in which seizures develop after infiltration of cells of the adaptive immune system in the central nervous system (CNS) include a broad range of epileptic disorders with different (known or unknown) etiologies. Infiltration of lymphocytes is observed in autoimmune epilepsies, especially the classical paraneoplastic encephalitides with antibodies against intracellular tumor antigens. The presence of lymphocytes in the CNS also has been found in focal cerebral dysplasia type 2 and in cortical tubers. Various autoantibodies have been shown to be associated with temporal lobe epilepsy (TLE) and hippocampal sclerosis of unknown etiology, which may be due to the presence of viral DNA. During the last decade, an increasing number of antineuronal autoantibodies directed against membranous epitopes have been discovered and are associated with various neurologic syndromes, including limbic encephalitis. A major challenge in epilepsy is to define biomarkers, which would allow the recognition of patient populations who might benefit from immune-modulatory therapies. Some peripheral inflammatory markers appear to be differentially expressed in patients with medically controlled and medically refractory and, as such, could be used for diagnostic, prognostic, or therapeutic purposes. Establishing an autoimmune basis in patients with drug-resistant epilepsy allows for efficacious and targeted immunotherapy. Although current immunotherapies can give great benefit to the correctly identified patient, there are limitations to their efficacy and they may have considerable side effects. Thus the identification of new immunomodulatory compounds remains of utmost importance.

High prevalence of neuronal surface autoantibodies associated with cognitive deficits in cancer patients

The recent discovery of neuronal cell-surface antibodies profoundly expanded the clinical spectrum of paraneoplastic neurological syndromes. Many of these syndromes are associated with impaired cognitive function, a clinical symptom that is of increasing concern in cancer patients. However, the frequency of these antibodies in cancer patients and their relation to clinical syndromes is currently unknown. Here, we investigated the prevalence of neuronal cell-surface antibodies and associated paraneoplastic neurological syndromes in 323 patients with different cancer types and in 105 controls. Cerebrospinal fluid and serum samples were analysed for a large panel of anti-neuronal antibodies and all patients were screened for cognitive deficits. Blood-brain barrier integrity was assessed using the age-normalized albumin cerebrospinal fluid/serum ratio. Anti-neuronal autoantibodies were observed in 24.5% of cancer patients (in contrast to 3.1% in neurological control patients without cancer and 2.5% in healthy controls) and were almost exclusively detected in serum. The majority of antibodies were directed against cell-surface antigens (75.9%), most frequently IgA/IgM isotypes targeting the N-methyl-D-aspartate (NMDA) receptor. Cognitive deficits and cerebellar syndromes were significantly more prevalent in antibody-positive in comparison with antibody-negative patients (21 vs. 7%, p = 2.7 × 10^-4; 11 vs. 2%, p = 3.0 × 10^-3). Antibody-positive patients with cognitive deficits had a significantly increased albumin cerebrospinal fluid/serum ratio in comparison with antibody-positive patients with other neurological deficits, indicating blood-brain barrier dysfunction (49.1 × 10^-3 vs. 12.0 × 10^-3; p = 0.036). Our results show that anti-neuronal antibodies have a high prevalence in a wide range of different tumour types and are associated with distinct neurological deficits. Specifically, the results suggest a so far undefined cognitive paraneoplastic syndrome in patients with antibodies targeting neuronal surface antigens and concurrent blood-brain barrier dysfunction. Anti-neuronal antibodies might thus serve as a biomarker for potentially treatment-responsive cognitive impairments in cancer patients.

Electroconvulsive therapy and/or plasmapheresis in autoimmune encephalitis?

Autoimmune encephalitis is a poorly understood condition that can present with a combination of neurological and psychiatric symptoms, either of which may predominate. There are many autoantibodies associated with a variety of clinical syndromes - anti-N-Methyl-D-Aspartate receptor (NMDAR) is the commonest. Currently, the most widely used therapy is prompt plasmapheresis and steroid treatment (and tumour resection if indicated), followed by second line immunosuppression if this fails. Given the growing awareness of autoimmune encephalitis as an entity, it is increasingly important that we consider it as a potential diagnosis in order to provide timely, effective treatment. We discuss several previously published case reports and one new case. These reports examined the effects of electroconvulsive therapy (ECT) on patients with autoimmune encephalitis, particularly those in whom psychiatric symptoms are especially debilitating and refractory to standard treatment. We also discuss factors predicting good outcome and possible mechanisms by which ECT may be effective. Numerous cases, such as those presented by Wingfield, Tsutsui, Florance, Sansing, Braakman and Matsumoto, demonstrate effective use of ECT in anti-NMDAR encephalitis patients with severe psychiatric symptoms such as catatonia, psychosis, narcolepsy and stupor who had failed to respond to standard treatments alone. We also present a new case of a 71-year-old female who presented to a psychiatric unit initially with depression, which escalated to catatonia, delusions, nihilism and auditory hallucinations. After anti-NMDAR antibodies were isolated, she was treated by the neurology team with plasmapheresis and steroids, with a partial response. She received multiple sessions of ECT and her psychiatric symptoms completely resolved and she returned to her premorbid state. For this reason, we suggest that ECT should be considered, particularly in those patients who are non-responders to standard therapies.

Clinical characterization of autoimmune LGI1 antibody limbic encephalitis

OBJECTIVE

Autoimmune encephalitis associated with antibodies to leucine-rich glioma inactivated 1 (LGI1) has recently been identified and is characterized by an acute to subacute onset of cognitive impairment and convulsion, faciobrachial dystonic seizures (FBDSs), and psychiatric disturbances. This study analyzed the clinical characteristics and outcomes of 10 patients with LGI1 antibody encephalitis in order to further understand this disease and to improve its therapeutic strategies.

METHODS

Between January 2013 and March 2015, we identified 10 patients with LGI1 antibody encephalitis. We retrospectively analyzed the clinical details, laboratory results, electrophysiological and imaging findings, and the treatment outcomes.

RESULTS

All patients tested had LGI1 antibodies. Immunotherapy was effective in all patients. Seizures in patients with FBDS showed a poor response to antiepileptic drugs. Two patients examined by magnetoencephalogram (MEG) during the acute disease phase showed a small quantity of spike-wave dipoles in the temporal lobe close to the lateral fissure and insular lobe.

CONCLUSION

Patients with LGI1 antibody encephalitis responded well to immunotherapy. We speculate that FBDS is likely a form of insular epilepsy.

Autoantibodies to central nervous system neuronal surface antigens: psychiatric symptoms and psychopharmacological implications

RATIONALE

Autoantibodies to central nervous system (CNS) neuronal surface antigens have been described in association with autoimmune encephalopathies which prominently feature psychiatric symptoms in addition to neurological symptoms. The potential role of these autoantibodies in primary psychiatric diseases such as schizophrenia or bipolar affective disorder is of increasing interest.

OBJECTIVES

We aimed to review the nature of psychiatric symptoms associated with neuronal surface autoantibodies, in the context of autoimmune encephalopathies as well as primary psychiatric disorders, and to review the mechanisms of action of these autoantibodies from a psychopharmacological perspective.

RESULTS

The functional effects of the autoantibodies on their target antigens are described; their clinical expression is at least in part mediated by their effects on neuronal receptor function, primarily at the synapse, usually resulting in receptor hypofunction. The psychiatric effects of the antibodies are related to known functions of the receptor target or its complexed proteins, with reference to supportive genetic and pharmacological evidence where relevant. Evidence for a causal role of these autoantibodies in primary psychiatric disease is increasing but remains controversial; relevant methodological controversies are outlined. Non-receptor-based mechanisms of autoantibody action, including neuroinflammatory mechanisms, and therapeutic implications are discussed.

CONCLUSIONS

An analysis of the autoantibodies from a psychopharmacological perspective, as endogenous, bioactive, highly specific, receptor-targeting molecules, provides a valuable opportunity to understand the neurobiological basis of associated psychiatric symptoms. Potentially, new treatment strategies will emerge from the improving understanding of antibody-antigen interaction within the CNS.

The hippocampus in aging and disease: From plasticity to vulnerability

The hippocampus has a pivotal role in learning and in the formation and consolidation of memory and is critically involved in the regulation of emotion, fear, anxiety, and stress. Studies of the hippocampus have been central to the study of memory in humans and in recent years, the regional specialization and organization of hippocampal functions have been elucidated in experimental models and in human neurological and psychiatric diseases. The hippocampus has long been considered a classic model for the study of neuroplasticity as many examples of synaptic plasticity such as long-term potentiation and -depression have been identified and demonstrated in hippocampal circuits. Neuroplasticity is the ability to adapt and reorganize the structure or function to internal or external stimuli and occurs at the cellular, population, network or behavioral level and is reflected in the cytological and network architecture as well as in intrinsic properties of hippocampal neurons and circuits. The high degree of hippocampal neuroplasticity might, however, be also negatively reflected in the pronounced vulnerability of the hippocampus to deleterious conditions such as ischemia, epilepsy, chronic stress, neurodegeneration and aging targeting hippocampal structure and function and leading to cognitive deficits. Considering this framework of plasticity and vulnerability, we here review basic principles of hippocampal anatomy and neuroplasticity on various levels as well as recent findings regarding the functional organization of the hippocampus in light of the regional vulnerability in Alzheimer's disease, ischemia, epilepsy, neuroinflammation and aging.