Therapeutic complement inhibition: a promising approach for treatment of neuroimmunological diseases

Aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders: progress of experimental models based on disease pathogenesis

Neuromyelitis optica spectrum disorders are neuroinflammatory demyelinating disorders that lead to permanent visual loss and motor dysfunction. To date, no effective treatment exists as the exact causative mechanism remains unknown. Therefore, experimental models of neuromyelitis optica spectrum disorders are essential for exploring its pathogenesis and in screening for therapeutic targets. Since most patients with neuromyelitis optica spectrum disorders are seropositive for IgG autoantibodies against aquaporin-4, which is highly expressed on the membrane of astrocyte endfeet, most current experimental models are based on aquaporin-4-IgG that initially targets astrocytes. These experimental models have successfully simulated many pathological features of neuromyelitis optica spectrum disorders, such as aquaporin-4 loss, astrocytopathy, granulocyte and macrophage infiltration, complement activation, demyelination, and neuronal loss; however, they do not fully capture the pathological process of human neuromyelitis optica spectrum disorders. In this review, we summarize the currently known pathogenic mechanisms and the development of associated experimental models in vitro, ex vivo, and in vivo for neuromyelitis optica spectrum disorders, suggest potential pathogenic mechanisms for further investigation, and provide guidance on experimental model choices. In addition, this review summarizes the latest information on pathologies and therapies for neuromyelitis optica spectrum disorders based on experimental models of aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders, offering further therapeutic targets and a theoretical basis for clinical trials.

Association of plasma sPD-1 and sPD-L1 with disease status and future relapse in AQP4-IgG (+) NMOSD

OBJECTIVE

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune-mediated disorder with aquaporin 4-immunoglobulin G (AQP4-IgG) in most settings. Soluble programmed death-1 (sPD-1) and soluble programmed death ligand 1 (sPD-L1) play key roles in immunomodulation. We aim to assess the association of sPD-1 and sPD-L1 with cytokines and their clinical significance in AQP4-IgG (+) NMOSD.

METHOD

We measured plasma sPD-1, sPD-L1, and 10 cytokines levels of 66 AQP4-IgG (+) NMOSD patients, including 40 patients in attack (attack-NMOSD) and 26 patients in remission (remission-NMOSD) phases, and 28 healthy controls through ultrasensitive Simoa and SP-X platform, respectively. We also performed >2 years (median) of follow-up after testing and analyzed the relationship between the detection index and current and future clinical parameters.

RESULT

Plasma sPD-1 level discriminated attack-NMOSD from remission-NMOSD (AUC = 0.692, p = 0.009). sPD-1 and sPD-L1 levels positively correlated with IL-6 (rsPD-1  = 0.313; rsPD-L1  = 0.508), IFN-γ (rsPD-1  = 0.331; rsPD-L1  = 0.456), and TNF-α (rsPD-1  = 0.451; rsPD-L1  = 0.531) expression, as well as clinical indicators, including the EDSS score (rsPD-1  = 0.331; rsPD-L1  = 0.402), number of attacks (rsPD-1  = 0.431) and segments of spinal cord involvement (rsPD-1  = 0.462; rsPD-L1  = 0.508). The risk of relapse within 2 years after sampling was associated with higher sPD-1/sPD-L1 ratio in attack-NMOSD (p = 0.022; Exp(B) = 1.589).

INTERPRETATION

Plasma sPD-1 and sPD-L1 levels reflected current disease severity and activity, and predicted future relapses in AQP4-IgG (+) NMOSD, suggesting that they hold the potential to guide timely and targeted treatment.

A Comprehensive Review on Neuroimmunology: Insights from Multiple Sclerosis to Future Therapeutic Developments

This review delves into neuroimmunology, focusing on its relevance to multiple sclerosis (MS) and potential treatment advancements. Neuroimmunology explores the intricate relationship between the immune system and the central nervous system (CNS). Understanding these mechanisms is vital for grasping the pathophysiology of diseases like MS and for devising innovative treatments. This review introduces foundational neuroimmunology concepts, emphasizing the role of immune cells, cytokines, and blood-brain barrier in CNS stability. It highlights how their dysregulation can contribute to MS and discusses genetic and environmental factors influencing MS susceptibility. Cutting-edge research methods, from omics techniques to advanced imaging, have revolutionized our understanding of MS, offering valuable diagnostic and prognostic tools. This review also touches on the intriguing gut-brain axis, examining how gut microbiota impacts neuroimmunological processes and its potential therapeutic implications. Current MS treatments, from immunomodulatory drugs to disease-modifying therapies, are discussed alongside promising experimental approaches. The potential of personalized medicine, cell-based treatments, and gene therapy in MS management is also explored. In conclusion, this review underscores neuroimmunology's significance in MS research, suggesting that a deeper understanding could pave the way for more tailored and effective treatments for MS and similar conditions. Continued research and collaboration in neuroimmunology are essential for enhancing patient outcomes.

The role of the complement system in Multiple Sclerosis: A review

The complement system has been involved in the pathogenesis of multiple neuroinflammatory and neurodegenerative conditions. In this review, we evaluated the possible role of complement activation in multiple sclerosis (MS) with a focus in progressive MS, where the disease pathogenesis remains to be fully elucidated and treatment options are limited. The evidence for the involvement of the complement system in the white matter plaques and gray matter lesions of MS stems from immunohistochemical analysis of post-mortem MS brains, in vivo serum and cerebrospinal fluid biomarker studies, and animal models of Experimental Autoimmune Encephalomyelitis (EAE). Complement knock-out studies in these animal models have revealed that this system may have a “double-edge sword” effect in MS. On the one hand, complement proteins may aid in promoting the clearance of myelin degradation products and other debris through myeloid cell-mediated phagocytosis. On the other, its aberrant activation may lead to demyelination at the rim of progressive MS white matter lesions as well as synapse loss in the gray matter. The complement system may also interact with known risk factors of MS, including as Epstein Barr Virus (EBV) infection, and perpetuate the activation of CNS self-reactive B cell populations. With the mounting evidence for the involvement of complement in MS, the development of complement modulating therapies for this condition is appealing. Herein, we also reviewed the pharmacological complement inhibitors that have been tested in MS animal models as well as in clinical trials for other neurologic diseases. The potential use of these agents, such as the C5-binding antibody eculizumab in MS will require a detailed understanding of the role of the different complement effectors in this disease and the development of better CNS delivery strategies for these compounds.

Autoantibodies Against the Complement Regulator Factor H in the Serum of Patients With Neuromyelitis Optica Spectrum Disorder

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune inflammatory disease of the central nervous system (CNS), characterized by pathogenic, complement-activating autoantibodies against the main water channel in the CNS, aquaporin 4 (AQP4). NMOSD is frequently associated with additional autoantibodies and antibody-mediated diseases. Because the alternative pathway amplifies complement activation, our aim was to evaluate the presence of autoantibodies against the alternative pathway C3 convertase, its components C3b and factor B, and the complement regulator factor H (FH) in NMOSD. Four out of 45 AQP4-seropositive NMOSD patients (~9%) had FH autoantibodies in serum and none had antibodies to C3b, factor B and C3bBb. The FH autoantibody titers were low in three and high in one of the patients, and the avidity indexes were low. FH-IgG complexes were detected in the purified IgG fractions by Western blot. The autoantibodies bound to FH domains 19-20, and also recognized the homologous FH-related protein 1 (FHR-1), similar to FH autoantibodies associated with atypical hemolytic uremic syndrome (aHUS). However, in contrast to the majority of autoantibody-positive aHUS patients, these four NMOSD patients did not lack FHR-1. Analysis of autoantibody binding to FH19-20 mutants and linear synthetic peptides of the C-terminal FH and FHR-1 domains, as well as reduced FH, revealed differences in the exact binding sites of the autoantibodies. Importantly, all four autoantibodies inhibited C3b binding to FH. In conclusion, our results demonstrate that FH autoantibodies are not uncommon in NMOSD and suggest that generation of antibodies against complement regulating factors among other autoantibodies may contribute to the complement-mediated damage in NMOSD.

Targeting the complement system in neuromyelitis optica spectrum disorder

INTRODUCTION

Neuromyelitis optica spectrum disorder (NMOSD) is characterized by central nervous system inflammation and demyelination. In AQP4-IgG seropositive NMOSD, circulating immunoglobulin G (IgG) autoantibodies against astrocyte water channel aquaporin-4 (AQP4) cause tissue injury. Compelling evidence supports a pathogenic role for complement activation following AQP4-IgG binding to AQP4. Clinical studies supported the approval of eculizumab, an inhibitor of C5 cleavage, in AQP4-IgG seropositive NMOSD.

AREAS COVERED

This review covers in vitro, animal models, and human evidence for complement-dependent and complement-independent tissue injury in AQP4-IgG seropositive NMOSD. Complement targets are discussed, including complement proteins, regulators and anaphylatoxin receptors, and corresponding drug candidates.

EXPERT OPINION

Though preclinical data support a central pathogenic role of complement activation in AQP4-IgG seropositive NMOSD, they do not resolve the relative contributions of complement-dependent vs. complement-independent disease mechanisms such as antibody-dependent cellular cytotoxicity, T cell effector mechanisms, and direct AQP4-IgG-induced cellular injury. The best evidence that complement-dependent mechanisms predominate in AQP4-IgG seropositive NMOSD comes from eculizumab clinical data. Various drug candidates targeting distinct complement effector mechanisms may offer improved safety and efficacy. However, notwithstanding the demonstrated efficacy of complement inhibition in AQP4-IgG seropositive NMOSD, the ultimate niche for complement inhibition is not clear given multiple drug options with alternative mechanisms of action.Abbreviations: AAV2, Adeno-associated virus 2; ADCC, antibody-dependent cellular cytotoxicity; ANCA, antineutrophilic cytoplasmic autoantibody; AQP4, aquaporin-4; AQP4-IgG, AQP4-immunoglobulin G; C1-INH, C1-esterase inhibitor; C3aR, C3a receptor; C4BP, C4 binding protein; C5aR, C5a receptor; CDC, complement-dependent cytotoxicity; CFHR1, complement factor H related 1; CNS, central nervous system; EAE, experimental autoimmune encephalomyelitis; EndoS, endoglycosidase S; FHL-1, factor-H-like protein 1; GFAP, glial fibrillary acidic protein; Iba-1, ionized calcium-binding adaptor protein-1; IgG, immunoglobulin G; IVIG, intravenous human immunoglobulin G; MAC, membrane attack complex; MBL, maltose-binding lectin; MBP, myelin basic protein; MOG, myelin oligodendrocyte glycoprotein; NK cell, natural killer cell; NMOSD, neuromyelitis optica spectrum disorder; OAP, orthogonal arrays of particles; PNH, paroxysmal nocturnal hemoglobinuria.

Longitudinally Extensive Transverse Myelitis in a Lupus-Neuromyelitis Optica Overlap

Transverse myelitis is an inflammatory lesion of the spinal cord, occurring in different autoimmune, infectious, and traumatic diseases but is the hallmark of neuromyelitis optica (NMO), a rare neurologic autoimmune disease. Patients with systemic lupus erythematosus (SLE) may develop transverse myelitis as a neuropsychiatric complication of active disease; however, at times, NMO co-exists as an additional primary autoimmune condition in a SLE patient. Correct diagnosis of a SLE-NMO overlap is important not only for the different disease course and prognosis compared with SLE-related LETM, but especially for the emerging and highly specific NMO treatment options, not established for SLE-related LETM-such as anti-aquaporin 4 antibodies, anti-VEGF antibodies, complement modulation, or IVIg.

The clinical value of complement proteins in differentiating AQP4-IgG-positive from MOG-IgG-positive neuromyelitis optica spectrum disorders

BACKGROUND

Neuromyelitis optica spectrum disorder (NMOSD) refers to a range of autoimmune inflammatory demyelinating diseases affecting the optic nerves, spinal cord, and periependymal regions of the brain. Classical NMOSD is characterized by the presentation of autoantibodies against the water channel aquaporin-4 (AQP4). However, a subset of patients fulfilling the clinical criteria for NMOSD is negative for AQP4-IgG but positive for autoantibodies against myelin oligodendrocyte glycoprotein (MOG); these patients are associated with different clinical manifestations and pathogenesis.

METHODS

Patients who received a first diagnosis of NMOSD were reviewed retrospectively between April 2015 and December 2018. Patients were classified according to the presence of AQP4-IgG and MOG-IgG in serum and/or cerebrospinal fluid. Clinical characteristics, magnetic resonance imaging findings, disease severity, and serum C3 and C4 levels at the first episode were compared between the groups.

RESULTS

The NMOSD patients with AQP4-IgG and MOG-IgG demonstrated specific, differential clinical features. The AQP4-IgG group featured more women, the presentation of transverse myelitis attacks and simultaneous occurrence of optic neuritis and transverse myelitis were more common, and intrathecal synthesis was more evident. The MOG-IgG group featured younger patients, more acute disseminated encephalomyelitis (ADEM) or ADEM-like attacks, more frequent cerebrospinal fluid pleocytosis, and a better overall outcome. C3 levels were significantly lower in AQP4-IgG-positive patients and higher in MOG-IgG-positive patients relative to healthy controls. C4 levels were significantly lower in the AQP4-IgG-positive NMOSD group when compared to both MOG-IgG-positive patients and controls. C3 and C4 were then combined in a receiver operating characteristic model. The area under the curve of the model was calculated to differentiate the AQP4-IgG-positive group from the MOG-IgG-positive group was 0.787, which was considered moderately predictive.

CONCLUSION

The combination of C3 and C4 could assist in the differential diagnosis of AQP4-IgG-positive NMOSD from MOG-IgG-positive NMOSD.

Therapeutic Inhibition of the Complement System in Diseases of the Central Nervous System

The complement system plays critical roles in development, homeostasis, and regeneration in the central nervous system (CNS) throughout life; however, complement dysregulation in the CNS can lead to damage and disease. Complement proteins, regulators, and receptors are widely expressed throughout the CNS and, in many cases, are upregulated in disease. Genetic and epidemiological studies, cerebrospinal fluid (CSF) and plasma biomarker measurements and pathological analysis of post-mortem tissues have all implicated complement in multiple CNS diseases including multiple sclerosis (MS), neuromyelitis optica (NMO), neurotrauma, stroke, amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). Given this body of evidence implicating complement in diverse brain diseases, manipulating complement in the brain is an attractive prospect; however, the blood-brain barrier (BBB), critical to protect the brain from potentially harmful agents in the circulation, is also impermeable to current complement-targeting therapeutics, making drug design much more challenging. For example, antibody therapeutics administered systemically are essentially excluded from the brain. Recent protocols have utilized "Trojan horse" techniques to transport therapeutics across the BBB or used osmotic shock or ultrasound to temporarily disrupt the BBB. Most research to date exploring the impact of complement inhibition on CNS diseases has been in animal models, and some of these studies have generated convincing data; for example, in models of MS, NMO, and stroke. There have been a few recent clinical trials of available anti-complement drugs in CNS diseases associated with BBB impairment, for example the use of the anti-C5 monoclonal antibody (mAb) eculizumab in NMO, but for most CNS diseases there have been no human trials of anti-complement therapies. Here we will review the evidence implicating complement in diverse CNS disorders, from acute, such as traumatic brain or spine injury, to chronic, including demyelinating, neuroinflammatory, and neurodegenerative diseases. We will discuss the particular problems of drug access into the CNS and explore ways in which anti-complement therapies might be tailored for CNS disease.