Meningeal inflammation is widespread and linked to cortical pathology in multiple sclerosis

Infiltration by monocytes of the central nervous system and its role in multiple sclerosis: reflections on therapeutic strategies

Mononuclear macrophage infiltration in the central nervous system is a prominent feature of neuroinflammation. Recent studies on the pathogenesis and progression of multiple sclerosis have highlighted the multiple roles of mononuclear macrophages in the neuroinflammatory process. Monocytes play a significant role in neuroinflammation, and managing neuroinflammation by manipulating peripheral monocytes stands out as an effective strategy for the treatment of multiple sclerosis, leading to improved patient outcomes. This review outlines the steps involved in the entry of myeloid monocytes into the central nervous system that are targets for effective intervention: the activation of bone marrow hematopoiesis, migration of monocytes in the blood, and penetration of the blood-brain barrier by monocytes. Finally, we summarize the different monocyte subpopulations and their effects on the central nervous system based on phenotypic differences. As activated microglia resemble monocyte-derived macrophages, it is important to accurately identify the role of monocyte-derived macrophages in disease. Depending on the roles played by monocyte-derived macrophages at different stages of the disease, several of these processes can be interrupted to limit neuroinflammation and improve patient prognosis. Here, we discuss possible strategies to target monocytes in neurological diseases, focusing on three key aspects of monocyte infiltration into the central nervous system, to provide new ideas for the treatment of neurodegenerative diseases.

Markers of secondary progression in multiple sclerosis

INTRODUCTION

There is no globally accepted definition of Secondary Progressive Multiple Sclerosis (SPMS) or set of unambiguous clinical, radiological, or other criteria that can accurately identify patients who transition to SPMS. Thus, the SPMS diagnosis is almost always a retrospective and frequently delayed process.

OBJECTIVE

The aim of this study was to elucidate the current understanding of phenotypic changes throughout MS course and provide insights into the detection of SPMS from the available literature on this diagnostic landscape.

METHODS

Comprehensive literature review aiming at detecting the transition from RRMS to SPMS. A search for relevant publications was conducted across different databases, scrutinizing studies that investigated tools and biomarkers for an accurate diagnosis of SPMS.

RESULTS

62 studies from the past two decades were included. The EDSS-plus was shown to be more sensitive than the EDSS alone in identifying disability progression. We found some helpful indicators for diagnosing SPMS, including cognitive impairment, particularly on working memory, information processing speed, and verbal fluency; presence of slowly expanding lesions on MRI; thinning of retinal layers on OCT. Also, glial markers as Glial Fibrillary Acidic Protein and Chitinase-3-like protein 1 might be more suitable to identify the conversion to progressive disease than Neurofilament light chain. Certain subjective symptoms seem to be more prevalent in the SPMS phase, although further studies are needed to understand whether patient reported outcomes' measures (PROMs) and which ones could be useful in detecting the transition to a progressive phenotype.

CONCLUSION

Our review highlights the emergence of useful biomarkers in early detection of progression of MS, such as cognitive impairment, MRI, and glial markers. We are getting closer to revolutionising the SPMS diagnosis and clinical management as we get a deeper understanding of these biomarkers.

Smouldering-Associated Worsening in Multiple Sclerosis: An International Consensus Statement on Definition, Biology, Clinical Implications, and Future Directions

Despite therapeutic suppression of relapses, multiple sclerosis (MS) patients often experience subtle deterioration, which extends beyond the definition of "progression independent of relapsing activity." We propose the concept of smouldering-associated-worsening (SAW), encompassing physical and cognitive symptoms, resulting from smouldering pathological processes, which remain unmet therapeutic targets. We provide a consensus-based framework of possible pathological substrates and manifestations of smouldering MS, and we discuss clinical, radiological, and serum/cerebrospinal fluid biomarkers for potentially monitoring SAW. Finally, we share considerations for optimizing disease surveillance and implications for clinical trials to promote the integration of smouldering MS into routine practice and future research efforts. ANN NEUROL 2024;96:826-845.

Spatial transcriptomics of meningeal inflammation reveals inflammatory gene signatures in adjacent brain parenchyma

While modern high efficacy disease modifying therapies have revolutionized the treatment of relapsing-remitting multiple sclerosis, they are less effective at controlling progressive forms of the disease. Meningeal inflammation is a recognized risk factor for cortical gray matter pathology which can result in disabling symptoms such as cognitive impairment and depression, but the mechanisms linking meningeal inflammation and gray matter pathology remain unclear. Here, we performed magnetic resonance imaging (MRI)-guided spatial transcriptomics in a mouse model of autoimmune meningeal inflammation to characterize the transcriptional signature in areas of meningeal inflammation and the underlying brain parenchyma. We found broadly increased activity of inflammatory signaling pathways at sites of meningeal inflammation, but only a subset of these pathways active in the adjacent brain parenchyma. Subclustering of regions adjacent to meningeal inflammation revealed the subset of immune programs induced in brain parenchyma, notably complement signaling and antigen processing/presentation. Trajectory gene and gene set modeling analysis confirmed variable penetration of immune signatures originating from meningeal inflammation into the adjacent brain tissue. This work contributes a valuable data resource to the field, provides the first detailed spatial transcriptomic characterization in a model of meningeal inflammation, and highlights several candidate pathways in the pathogenesis of gray matter pathology.

Subcortical plaques and inflammation reflect cortical and meningeal pathologies in progressive multiple sclerosis

It remains elusive whether lesions and inflammation in the sub/juxtacortical white matter reflect cortical and/or meningeal pathologies. Elucidating this could have implications for MRI monitoring as sub/juxtacortical lesions are detectable by routine MRI, while cortical lesions and meningeal inflammation are not. By large-area microscopy, we quantified total and mixed active plaque loads along with densities and sizes of perivascular mononuclear infiltrates (infiltrates) in the sub/juxtacortical white matter ≤2 mm from the cortex, intra-cortically and in the meninges. Data were related to ante-mortem clinical parameters in a false discovery rate-corrected analysis. We compared 12 patients with primary progressive multiple sclerosis (PPMS) and 15 with secondary progressive MS to 22 controls. Fifteen patients and 11 controls contributed with hemispheric sections. Sections were stained with haematoxylin-eosin, for myelin and for microglia/macrophages. B cells and T cells were confirmed in a subset. Immunoglobulin G depositions in selected cortical plaques resembled depositions described before in "slowly expanding" plaques in the white matter. We quantified plaque activity by measuring microglia-dominated and macrophage-dominated areas. Sub/juxtacortical plaques (load and activity) reflected plaque activity in the cerebral cortex. Plaque activity and infiltrates were more pronounced in the sub/juxtacortical white matter than in the cerebral cortex while conversely, the total plaque load was highest in the cortex. Infiltrates correlated trans-cortically and sub/juxtacortical plaque activity reflected cortical and meningeal infiltrates. Sub/juxtacortical infiltrate sizes correlated with shorter survival after progression onset. Two patients with PPMS and putatively fatal brain stem lesions argue against incidental findings. Trans-cortical inflammatory flares and plaque activity may be pathogenic in progressive MS. We suggest emphasis on sub/juxtacortical MRI lesions as plausible surrogates for cortical and meningeal pathologies and, when present, as indicators for cognitive testing.

Impairment of spinal CSF flow precedes immune cell infiltration in an active EAE model

Accumulation of immune cells and proteins in the subarachnoid space (SAS) is found during multiple sclerosis and in the animal model experimental autoimmune encephalomyelitis (EAE). Whether the flow of cerebrospinal fluid (CSF) along the SAS of the spinal cord is impacted is yet unknown. Combining intravital near-infrared (NIR) imaging with histopathological analyses, we observed a significantly impaired bulk flow of CSF tracers within the SAS of the spinal cord prior to EAE onset, which persisted until peak stage and was only partially recovered during chronic disease. The impairment of spinal CSF flow coincided with the appearance of fibrin aggregates in the SAS, however, it preceded immune cell infiltration and breakdown of the glia limitans superficialis. Conversely, cranial CSF efflux to cervical lymph nodes was not altered during the disease course. Our study highlights an early and persistent impairment of spinal CSF flow and suggests it as a sensitive imaging biomarker for pathological changes within the leptomeninges.

Meningeal lymphatic function promotes oligodendrocyte survival and brain myelination

The precise neurophysiological changes prompted by meningeal lymphatic dysfunction remain unclear. Here, we showed that inducing meningeal lymphatic vessel ablation in adult mice led to gene expression changes in glial cells, followed by reductions in mature oligodendrocyte numbers and specific lipid species in the brain. These phenomena were accompanied by altered meningeal adaptive immunity and brain myeloid cell activation. During brain remyelination, meningeal lymphatic dysfunction provoked a state of immunosuppression that contributed to delayed spontaneous oligodendrocyte replenishment and axonal loss. The deficiencies in mature oligodendrocytes and neuroinflammation due to impaired meningeal lymphatic function were solely recapitulated in immunocompetent mice. Patients diagnosed with multiple sclerosis presented reduced vascular endothelial growth factor C in the cerebrospinal fluid, particularly shortly after clinical relapses, possibly indicative of poor meningeal lymphatic function. These data demonstrate that meningeal lymphatics regulate oligodendrocyte function and brain myelination, which might have implications for human demyelinating diseases.

Disease-modifying therapies for Parkinson disease: lessons from multiple sclerosis

The development of disease-modifying therapies (DMTs) for neurological disorders is an important goal in modern neurology, and the associated challenges are similar in many chronic neurological conditions. Major advances have been made in the multiple sclerosis (MS) field, with a range of DMTs being approved for relapsing MS and the introduction of the first DMTs for progressive MS. By contrast, people with Parkinson disease (PD) still lack such treatment options, relying instead on decades-old therapeutic approaches that provide only symptomatic relief. To address this unmet need, an in-person symposium was held in Toronto, Canada, in November 2022 for international researchers and experts in MS and PD to discuss strategies for advancing DMT development. In this Roadmap article, we highlight discussions from the symposium, which focused on therapeutic targets and preclinical models, disease spectra and subclassifications, and clinical trial design and outcome measures. From these discussions, we propose areas for novel or deeper exploration in PD using lessons learned from therapeutic development in MS. In addition, we identify challenges common to the PD and MS fields that need to be addressed to further advance the discovery and development of effective DMTs.

Chimeric antigen receptor T-cell therapy for autoimmune diseases of the central nervous system: a systematic literature review

IMPORTANCE

B-cell-targeting monoclonal antibodies have demonstrated safety and efficacy in multiple sclerosis or anti-aquaporin-4 IgG positive neuromyelitis optica spectrum disorder. However, these therapies do not facilitate drug-free remission, which may become possible with cell-based therapies, including chimeric antigen receptor (CAR) T cells. CAR T-cell therapy holds promise for addressing other antibody-mediated CNS disorders, e.g., MOG-associated disease or autoimmune encephalitis.

OBJECTIVE

To provide an overview of the current clinical knowledge on CAR T-cell therapy in central nervous system autoimmunity.

EVIDENCE REVIEW

We searched PubMed, Embase, Google Scholar, PsycINFO, and clinicaltrials.gov using the terms 'CAR T cell' and 'multiple sclerosis/MS' or 'neuromyelitis optica/spectrum diseases/NMOSD' or 'MOG-associated disease/MOGAD 'or' autoimmune encephalitis' or 'neuroimmunology'.

FINDINGS

An ongoing phase I clinical trial has indicated the safety and benefits of anti-BCMA CAR T cells in 12 patients with AQP4-IgG seropositive neuromyelitis optica spectrum disorder. Case reports involving two individuals with progressive multiple sclerosis and one patient with stiff-person syndrome demonstrated a manageable safety profile following treatment with anti-CD19 CAR T cells. Recruitment has commenced for two larger studies in MS, and a phase I open-label basket study is underway to evaluate BCMA-directed CAR T cells in various antibody-associated inflammatory diseases, including MOG-associated disease. Preclinical research on NMDA receptor antibody autoimmune encephalitis treated with chimeric autoantibody receptor T cells generated promising data.

CONCLUSIONS AND RELEVANCE

There is minimal evidence of the benefits of CAR T-cell therapy in individuals with central nervous system-directed autoimmunity. Nevertheless, multicenter controlled clinical trials with a manageable safety profile appear feasible and are warranted due to very promising case experiences.

Association of Levels of CSF Osteopontin With Cortical Atrophy and Disability in Early Multiple Sclerosis

BACKGROUND AND OBJECTIVES

To evaluate CSF inflammatory markers with accumulation of cortical damage as well as disease activity in patients with early relapsing-remitting MS (RRMS).

METHODS

CSF levels of osteopontin (OPN) and 66 inflammatory markers were assessed using an immune-assay multiplex technique in 107 patients with RRMS (82 F/25 M, mean age 35.7 ± 11.8 years). All patients underwent regular clinical assessment and yearly 3T MRI scans for 2 years while 39 patients had a 4-year follow-up. White matter lesion number and volume, cortical lesions (CLs) and volume, and global cortical thickness (CTh) were evaluated together with the 'no evidence of disease activity' (NEDA-3) status, defined by no relapses, no disability worsening, and no MRI activity, including CLs.

RESULTS

The random forest algorithm selected OPN, CXCL13, TWEAK, TNF, IL19, sCD30, sTNFR1, IL35, IL16, and sCD163 as significantly associated with changes in global CTh. OPN and CXCL13 were most related to accumulation of atrophy after 2 and 4 years. In a multivariate linear regression model on CSF markers, OPN (p < 0.001), CXCL13 (p = 0.001), and sTNFR1 (p = 0.024) were increased in those patients with accumulating atrophy (adjusted R-squared 0.615). The 10 markers were added in a model that included all clinical, demographic, and MRI variables: OPN (p = 0.002) and IL19 (p = 0.022) levels were confirmed to be significantly increased in patients developing more CTh change over the follow-up (adjusted R-squared 0.619). CXCL13 and OPN also revealed the best association with NEDA-3 after 2 years, with OPN significantly linked to disability accumulation (OR 2.468 [1.46-5.034], p = 0.004) at the multivariate logistic regression model.

DISCUSSION

These data confirm and expand our knowledge on the prognostic role of the CSF inflammatory profile in predicting changes in cortical pathology and disease activity in early MS. The data emphasize a crucial role of OPN.

Disability independent of cerebral white matter demyelination in progressive multiple sclerosis

The pathogenic mechanisms contributing to neurological disability in progressive multiple sclerosis (PMS) are poorly understood. Cortical neuronal loss independent of cerebral white matter (WM) demyelination in myelocortical MS (MCMS) and identification of MS patients with widespread cortical atrophy and disability progression independent of relapse activity (PIRA) support pathogenic mechanisms other than cerebral WM demyelination. The three-dimensional distribution and underlying pathology of myelinated T2 lesions were investigated in postmortem MCMS brains. Postmortem brain slices from previously characterized MCMS (10 cases) and typical MS (TMS) cases (12 cases) were co-registered with in situ postmortem T2 hyperintensities and T1 hypointensities. T1 intensity thresholds were used to establish a classifier that differentiates MCMS from TMS. The classifier was validated in 36 uncharacterized postmortem brains and applied to baseline MRIs from 255 living PMS participants enrolled in SPRINT-MS. Myelinated T2 hyperintensities in postmortem MCMS brains have a contiguous periventricular distribution that expands at the occipital poles of the lateral ventricles where a surface-in gradient of myelinated axonal degeneration was observed. The MRI classifier distinguished pathologically confirmed postmortem MCMS and TMS cases with an accuracy of 94%. For SPRINT-MS patients, the MRI classifier identified 78% as TMS, 10% as MCMS, and 12% with a paucity of cerebral T1 and T2 intensities. In SPRINT-MS, expanded disability status scale and brain atrophy measures were similar in MCMS and TMS cohorts. A paucity of cerebral WM demyelination in 22% of living PMS patients raises questions regarding a primary role for cerebral WM demyelination in disability progression in all MS patients and has implications for clinical management of MS patients and clinical trial outcomes in PMS. Periventricular myelinated fiber degeneration provides additional support for surface-in gradients of neurodegeneration in MS.

New views on the complex interplay between degeneration and autoimmunity in multiple sclerosis

Multiple sclerosis (MS) is a frequently disabling neurological disorder characterized by symptoms, clinical signs and imaging abnormalities that typically fluctuate over time, affecting any level of the CNS. Prominent lymphocytic inflammation, many genetic susceptibility variants involving immune pathways, as well as potent responses of the neuroinflammatory component to immunomodulating drugs, have led to the natural conclusion that this disease is driven by a primary autoimmune process. In this Hypothesis and Theory article, we discuss emerging data that cast doubt on this assumption. After three decades of therapeutic experience, what has become clear is that potent immune modulators are highly effective at suppressing inflammatory relapses, yet exhibit very limited effects on the later progressive phase of MS. Moreover, neuropathological examination of MS tissue indicates that degeneration, CNS atrophy, and myelin loss are most prominent in the progressive stage, when lymphocytic inflammation paradoxically wanes. Finally, emerging clinical observations such as "progression independent of relapse activity" and "silent progression," now thought to take hold very early in the course, together argue that an underlying "cytodegenerative" process, likely targeting the myelinating unit, may in fact represent the most proximal step in a complex pathophysiological cascade exacerbated by an autoimmune inflammatory overlay. Parallels are drawn with more traditional neurodegenerative disorders, where a progressive proteopathy with prion-like propagation of toxic misfolded species is now known to play a key role. A potentially pivotal contribution of the Epstein-Barr virus and B cells in this process is also discussed.

New Imaging Markers in Multiple Sclerosis and Related Disorders: Smoldering Inflammation and the Central Vein Sign

Concepts of multiple sclerosis (MS) biology continue to evolve, with observations such as "progression independent of disease activity" challenging traditional phenotypic categorization. Iron-sensitive, susceptibility-based imaging techniques are emerging as highly translatable MR imaging sequences that allow for visualization of at least 2 clinically useful biomarkers: the central vein sign and the paramagnetic rim lesion (PRL). Both biomarkers demonstrate high specificity in the discrimination of MS from other mimics and can be seen at 1.5 T and 3 T field strengths. Additionally, PRLs represent a subset of chronic active lesions engaged in "smoldering" compartmentalized inflammation behind an intact blood-brain barrier.

Decoding Gray Matter Involvement in Multiple Sclerosis via Imaging

Multiple sclerosis (MS) is increasingly understood not only as a white matter disease but also involving both the deep and cortical gray matter (GM). GM pathology in people with MS (pwMS) includes the presence of lesions, leptomeningeal inflammation, atrophy, altered iron concentration, and microstructural changes. Studies using 7T and 3T MR imaging with optimized protocols established that GM damage is a principal driver of disease progression in pwMS. Future work is needed to incorporate the assessment of these GM imaging biomarkers into the clinical workup of pwMS and the assessment of treatment efficacy.

Characterization of cortico-meningeal translocator protein expression in multiple sclerosis

Compartmentalized meningeal inflammation is thought to represent one of the key players in the pathogenesis of cortical demyelination in multiple sclerosis. PET targeting the 18 kDa mitochondrial translocator protein (TSPO) is a molecular-specific approach to quantifying immune cell-mediated density in the cortico-meningeal tissue compartment in vivo. This study aimed to characterize cortical and meningeal TSPO expression in a heterogeneous cohort of multiple sclerosis cases using in vivo simultaneous MR-PET with 11C-PBR28, a second-generation TSPO radioligand, and ex vivo immunohistochemistry. Forty-nine multiple sclerosis patients (21 with secondary progressive and 28 with relapsing-remitting multiple sclerosis) with mixed or high affinity binding for 11C-PBR28 underwent 90-min 11C-PBR28 simultaneous MR-PET. Tracer binding was measured using 60-90 min normalized standardized uptake value ratios sampled at mid-cortical depth and ∼3 mm above the pial surface. Data in multiple sclerosis patients were compared to 21 age-matched healthy controls. To characterize the nature of 11C-PBR28 PET uptake, the meningeal and cortical lesion cellular expression of TSPO was further described in post-mortem brain tissue from 20 cases with secondary progressive multiple sclerosis and five age-matched healthy donors. Relative to healthy controls, patients with multiple sclerosis exhibited abnormally increased TSPO signal in the cortex and meningeal tissue, diffusively in progressive disease and more localized in relapsing-remitting multiple sclerosis. In multiple sclerosis, increased meningeal TSPO levels were associated with increased Expanded Disability Status Scale scores (P = 0.007, by linear regression). Immunohistochemistry, validated using in situ sequencing analysis, revealed increased TSPO expression in the meninges and adjacent subpial cortical lesions of post-mortem secondary progressive multiple sclerosis cases relative to control tissue. In these cases, increased TSPO expression was related to meningeal inflammation. Translocator protein immunostaining was detected on meningeal MHC-class II+ macrophages and cortical-activated MHC-class II+ TMEM119+ microglia. In vivo arterial blood data and neuropathology showed that endothelial binding did not significantly account for increased TSPO cortico-meningeal expression in multiple sclerosis. Our findings support the use of TSPO-PET in multiple sclerosis for imaging in vivo inflammation in the cortico-meningeal brain tissue compartment and provide in vivo evidence implicating meningeal inflammation in the pathogenesis of the disease.

Characterization of pathological stages in a mouse model of progressive multiple sclerosis

The purpose of this study was to analyze and elucidate the mechanisms of non-obese diabetes-experimental autoimmune encephalomyelitis (NOD-EAE), an animal model of progressive multiple sclerosis (MS), and to compare the pathological features with those observed in human progressive MS. Pathological analysis, flow cytometry analysis, immunohistochemical staining, and transcriptome analysis were performed at each pathological stage of the NOD-EAE mice to characterize each pathological stage in the lesion. The NOD-EAE mice showed a biphasic pattern of disease progression once in remission. The longitudinal profile of demyelination and inflammatory cell infiltration in the spinal cord was consistent with the pathological score. In the chronic phase of the disease, fibrosis and lymph follicle formation, characteristic of progressive human MS, were observed. Here we describe the pathological profile and transcriptome analysis of the NOD-EAE mice and verify that this model has similar features to those of human progressive MS. Our findings suggest that this model recapitulates lymph follicle formation, a disease hallmark of progressive MS, and fibrosis, a feature complicating the pathogenesis of MS in the chronic phase. This model may be useful for evaluating the efficacy of therapeutic agents and for mechanistic analysis.

Determinants and Biomarkers of Progression Independent of Relapses in Multiple Sclerosis

Clinical, pathological, and imaging evidence in multiple sclerosis (MS) suggests that a smoldering inflammatory activity is present from the earliest stages of the disease and underlies the progression of disability, which proceeds relentlessly and independently of clinical and radiological relapses (PIRA). The complex system of pathological events driving "chronic" worsening is likely linked with the early accumulation of compartmentalized inflammation within the central nervous system as well as insufficient repair phenomena and mitochondrial failure. These mechanisms are partially lesion-independent and differ from those causing clinical relapses and the formation of new focal demyelinating lesions; they lead to neuroaxonal dysfunction and death, myelin loss, glia alterations, and finally, a neuronal network dysfunction outweighing central nervous system (CNS) compensatory mechanisms. This review aims to provide an overview of the state of the art of neuropathological, immunological, and imaging knowledge about the mechanisms underlying the smoldering disease activity, focusing on possible early biomarkers and their translation into clinical practice. ANN NEUROL 2024;96:1-20.

The neuropathobiology of multiple sclerosis

Chronic low-grade inflammation and neuronal deregulation are two components of a smoldering disease activity that drives the progression of disability in people with multiple sclerosis (MS). Although several therapies exist to dampen the acute inflammation that drives MS relapses, therapeutic options to halt chronic disability progression are a major unmet clinical need. The development of such therapies is hindered by our limited understanding of the neuron-intrinsic determinants of resilience or vulnerability to inflammation. In this Review, we provide a neuron-centric overview of recent advances in deciphering neuronal response patterns that drive the pathology of MS. We describe the inflammatory CNS environment that initiates neurotoxicity by imposing ion imbalance, excitotoxicity and oxidative stress, and by direct neuro-immune interactions, which collectively lead to mitochondrial dysfunction and epigenetic dysregulation. The neuronal demise is further amplified by breakdown of neuronal transport, accumulation of cytosolic proteins and activation of cell death pathways. Continuous neuronal damage perpetuates CNS inflammation by activating surrounding glia cells and by directly exerting toxicity on neighbouring neurons. Further, we explore strategies to overcome neuronal deregulation in MS and compile a selection of neuronal actuators shown to impact neurodegeneration in preclinical studies. We conclude by discussing the therapeutic potential of targeting such neuronal actuators in MS, including some that have already been tested in interventional clinical trials.

Association of Complement Factors With Disability Progression in Primary Progressive Multiple Sclerosis

BACKGROUND AND OBJECTIVES

The complement system is known to play a role in multiple sclerosis (MS) pathogenesis. However, its contribution to disease progression remains elusive. The study investigated the role of the complement system in disability progression of patients with primary progressive MS (PPMS).

METHODS

Sixty-eight patients with PPMS from 12 European MS centers were included in the study. Serum and CSF levels of a panel of complement components (CCs) were measured by multiplex enzyme-linked immunosorbent assay at a baseline time point (i.e., sampling). Mean (SD) follow-up time from baseline was 9.6 (4.8) years. Only one patient (1.5%) was treated during follow-up. Univariable and multivariable logistic regressions adjusted for age, sex, and albumin quotient were performed to assess the association between baseline CC levels and disability progression in short term (2 years), medium term (6 years), and long term (at the time of the last follow-up).

RESULTS

In short term, CC played little or no role in disability progression. In medium term, an elevated serum C3a/C3 ratio was associated with a higher risk of disability progression (adjusted OR 2.30; 95% CI 1.17-6.03; p = 0.040). By contrast, increased CSF C1q levels were associated with a trend toward reduced risk of disability progression (adjusted OR 0.43; 95% CI 0.17-0.98; p = 0.054). Similarly, in long term, an elevated serum C3a/C3 ratio was associated with higher risk of disability progression (adjusted OR 1.81; 95% CI 1.09-3.40; p = 0.037), and increased CSF C1q levels predicted lower disability progression (adjusted OR 0.41; 95% CI 0.17-0.86; p = 0.025).

DISCUSSION

Proteins involved in the activation of early complement cascades play a role in disability progression as risk (elevated serum C3a/C3 ratio) or protective (elevated CSF C1q) factors after 6 or more years of follow-up in patients with PPMS. The protective effects associated with C1q levels in CSF may be related to its neuroprotective and anti-inflammatory properties.

Myelin-reactive B cells exacerbate CD4+ T cell-driven CNS autoimmunity in an IL-23-dependent manner

B cells and T cells collaborate in multiple sclerosis (MS) pathogenesis. IgH[MOG] mice possess a B cell repertoire skewed to recognize myelin oligodendrocyte glycoprotein (MOG). Here, we show that upon immunization with the T cell-obligate autoantigen, MOG[35-55], IgH[MOG] mice develop rapid and exacerbated experimental autoimmune encephalomyelitis (EAE) relative to wildtype (WT) counterparts, characterized by aggregation of T and B cells in the IgH[MOG] meninges and by CD4+ T helper 17 (Th17) cells in the CNS. Production of the Th17 maintenance factor IL-23 is observed from IgH[MOG] CNS-infiltrating and meningeal B cells, and in vivo blockade of IL-23p19 attenuates disease severity in IgH[MOG] mice. In the CNS parenchyma and dura mater of IgH[MOG] mice, we observe an increased frequency of CD4+PD-1+CXCR5- T cells that share numerous characteristics with the recently described T peripheral helper (Tph) cell subset. Further, CNS-infiltrating B and Tph cells from IgH[MOG] mice show increased reactive oxygen species (ROS) production. Meningeal inflammation, Tph-like cell accumulation in the CNS and B/Tph cell production of ROS were all reduced upon p19 blockade. Altogether, MOG-specific B cells promote autoimmune inflammation of the CNS parenchyma and meninges in an IL-23-dependent manner.

Single-cell profiling indicates a high similarity between immune cells in the cerebrospinal fluid and in meningeal ectopic lymphoid tissue in experimental autoimmune encephalomyelitis

Background and objectives

B cell depleting anti-CD20 monoclonal antibodies (aCD20 mAbs) are highly effective in treatment of multiple sclerosis (MS) but fail to halt the formation of meningeal ectopic lymphoid tissue (mELT) in the murine model experimental autoimmune encephalomyelitis (EAE). While mELT can be examined in EAE, it is not accessible in vivo in MS patients. Our key objectives were to compare the immune cells in cerebrospinal fluid (CSF), which is accessible in patients, with those in mELT, and to study the effects of aCD20 mAbs on CSF and mELT in EAE.

Methods

Applying single cell RNA sequencing, we compared gene expression profiles in immune cells from (1) CSF with mELT and (2) aCD20 mAbs treated with control treated mice in a spontaneous 2D2xTh EAE model.

Results

The immune cell composition in CSF and mELT was very similar. Gene expression profiles and pathway enrichment analysis revealed no striking differences between the two compartments. aCD20 mAbs led not only to a virtually complete depletion of B cells in the CSF but also to a reduction of naïve CD4+ T cells and marked increase of macrophages. No remarkable differences in regulated genes or pathways were observed.

Discussion

Our results suggest that immune cells in the CSF may serve as a surrogate for mELT in EAE. Future studies are required to confirm this in MS patients. The observed increase of macrophages in B cell depleted CSF is a novel finding and requires verification in CSF of aCD20 mAbs treated MS patients. Due to unresolved technical challenges, we were unable to study the effects of aCD20 mAbs on mELT. This should be addressed in future studies.

Meningeal contrast enhancement in multiple sclerosis: Assessment of field strength, acquisition delay, and clinical relevance

BACKGROUND/PURPOSE

Leptomeningeal enhancement (LME) on post-contrast FLAIR is described as a potential biomarker of meningeal inflammation in multiple sclerosis (MS). Here we report an assessment of the impact of MRI field strength and acquisition timing on meningeal contrast enhancement (MCE).

METHODS

This was a cross-sectional, observational study of 95 participants with MS and 17 healthy controls (HC) subjects. Each participant underwent an MRI of the brain on both a 7 Tesla (7T) and 3 Tesla (3T) MRI scanner. 7T protocols included a FLAIR image before, soon after (Gd+ Early 7T FLAIR), and 23 minutes after gadolinium (Gd+ Delayed 7T FLAIR). 3T protocol included FLAIR before and 21 minutes after gadolinium (Gd+ Delayed 3T FLAIR).

RESULTS

LME was seen in 23.3% of participants with MS on Gd+ Delayed 3T FLAIR, 47.4% on Gd+ Early 7T FLAIR (p = 0.002) and 57.9% on Gd+ Delayed 7T FLAIR (p < 0.001 and p = 0.008, respectively). The count and volume of LME, leptomeningeal and paravascular enhancement (LMPE), and paravascular and dural enhancement (PDE) were all highest for Gd+ Delayed 7T FLAIR and lowest for Gd+ Delayed 3T FLAIR. Non-significant trends were seen for higher proportion, counts, and volumes for LME and PDE in MS compared to HCs. The rate of LMPE was different between MS and HCs on Gd+ Delayed 7T FLAIR (98.9% vs 82.4%, p = 0.003). MS participants with LME on Gd+ Delayed 7T FLAIR were older (47.6 (10.6) years) than those without (42.0 (9.7), p = 0.008).

CONCLUSION

7T MRI and a delay after contrast injection increased sensitivity for all forms of MCE. However, the lack of difference between groups for LME and its association with age calls into question its relevance as a biomarker of meningeal inflammation in MS.

Emergence of the brain-border immune niches and their contribution to the development of neurodegenerative diseases

Historically, the central nervous system (CNS) was regarded as 'immune-privileged', possessing its own distinct immune cell population. This immune privilege was thought to be established by a tight blood-brain barrier (BBB) and blood-cerebrospinal-fluid barrier (BCSFB), which prevented the crossing of peripheral immune cells and their secreted factors into the CNS parenchyma. However, recent studies have revealed the presence of peripheral immune cells in proximity to various brain-border niches such as the choroid plexus, cranial bone marrow (CBM), meninges, and perivascular spaces. Furthermore, emerging evidence suggests that peripheral immune cells may be able to infiltrate the brain through these sites and play significant roles in driving neuronal cell death and pathology progression in neurodegenerative disease. Thus, in this review, we explore how the brain-border immune niches may contribute to the pathogenesis of neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). We then discuss several emerging options for harnessing the neuroimmune potential of these niches to improve the prognosis and treatment of these debilitative disorders using novel insights from recent studies.

The contribution of the meningeal immune interface to neuroinflammation in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of disability and mortality worldwide, particularly among the elderly, yet our mechanistic understanding of what renders the post-traumatic brain vulnerable to poor outcomes, and susceptible to neurological disease, is incomplete. It is well established that dysregulated and sustained immune responses elicit negative consequences after TBI; however, our understanding of the neuroimmune interface that facilitates crosstalk between central and peripheral immune reservoirs is in its infancy. The meninges serve as the interface between the brain and the immune system, facilitating important bi-directional roles in both healthy and disease settings. It has been previously shown that disruption of this system exacerbates neuroinflammation in age-related neurodegenerative disorders such as Alzheimer's disease; however, we have an incomplete understanding of how the meningeal compartment influences immune responses after TBI. In this manuscript, we will offer a detailed overview of the holistic nature of neuroinflammatory responses in TBI, including hallmark features observed across clinical and animal models. We will highlight the structure and function of the meningeal lymphatic system, including its role in immuno-surveillance and immune responses within the meninges and the brain. We will provide a comprehensive update on our current knowledge of meningeal-derived responses across the spectrum of TBI, and identify new avenues for neuroimmune modulation within the neurotrauma field.

Antigen-specific immunotherapy via delivery of tolerogenic dendritic cells for multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system resulting from loss of immune tolerance. Many disease-modifying therapies for MS have broad immunosuppressive effects on peripheral immune cells, but this can increase risks of infection and attenuate vaccine-elicited immunity. A more targeted approach is to re-establish immune tolerance in an autoantigen-specific manner. This review discusses methods to achieve this, focusing on tolerogenic dendritic cells. Clinical trials in other autoimmune diseases also provide learnings with regards to clinical translation of this approach, including identification of autoantigen(s), selection of appropriate patients and administration route and frequency.

Cortical Lesions as an Early Hallmark of Multiple Sclerosis: Visualization by 7 T MRI

OBJECTIVES

Compelling evidence indicates a significant involvement of cortical lesions in the progressive phase of multiple sclerosis (MS), significantly contributing to late-stage disability. Despite the promise of ultra-high-field magnetic resonance imaging (MRI) in detecting cortical lesions, current evidence falls short in providing insights into the existence of such lesions during the early stages of MS or their underlying cause. This study delineated, at the early stage of MS, (1) the prevalence and spatial distribution of cortical lesions identified by 7 T MRI, (2) their relationship with white matter lesions, and (3) their clinical implications.

MATERIALS AND METHODS

Twenty individuals with early-stage relapsing-remitting MS (disease duration <1 year) underwent a 7 T MRI session involving T1-weighted MP2RAGE, T2*-weighted multiGRE, and T2-weighted FLAIR sequences for cortical and white matter segmentation. Disability assessments included the Expanded Disability Status Scale, the Multiple Sclerosis Functional Composite, and an extensive evaluation of cognitive function.

RESULTS

Cortical lesions were detected in 15 of 20 patients (75%). MP2RAGE revealed a total of 190 intracortical lesions (median, 4 lesions/case [range, 0-44]) and 216 leukocortical lesions (median, 2 lesions/case [range, 0-75]). Although the number of white matter lesions correlated with the total number of leukocortical lesions (r = 0.91, P < 0.001), no correlation was observed between the number of white matter or leukocortical lesions and the number of intracortical lesions. Furthermore, the number of leukocortical lesions but not intracortical or white-matter lesions was significantly correlated with cognitive impairment (r = 0.63, P = 0.04, corrected for multiple comparisons).

CONCLUSIONS

This study highlights the notable prevalence of cortical lesions at the early stage of MS identified by 7 T MRI. There may be a potential divergence in the underlying pathophysiological mechanisms driving distinct lesion types, notably between intracortical lesions and white matter/leukocortical lesions. Moreover, during the early disease phase, leukocortical lesions more effectively accounted for cognitive deficits.

Contribution of new and chronic cortical lesions to disability accrual in multiple sclerosis

Cortical lesions are common in multiple sclerosis and are associated with disability and progressive disease. We asked whether cortical lesions continue to form in people with stable white matter lesions and whether the association of cortical lesions with worsening disability relates to pre-existing or new cortical lesions. Fifty adults with multiple sclerosis and no new white matter lesions in the year prior to enrolment (33 relapsing-remitting and 17 progressive) and a comparison group of nine adults who had formed at least one new white matter lesion in the year prior to enrolment (active relapsing-remitting) were evaluated annually with 7 tesla (T) brain MRI and 3T brain and spine MRI for 2 years, with clinical assessments for 3 years. Cortical lesions and paramagnetic rim lesions were identified on 7T images. Seven total cortical lesions formed in 3/30 individuals in the stable relapsing-remitting group (median 0, range 0-5), four total cortical lesions formed in 4/17 individuals in the progressive group (median 0, range 0-1), and 16 cortical lesions formed in 5/9 individuals in the active relapsing-remitting group (median 1, range 0-10, stable relapsing-remitting versus progressive versus active relapsing-remitting P = 0.006). New cortical lesions were not associated with greater change in any individual disability measure or in a composite measure of disability worsening (worsening Expanded Disability Status Scale or 9-hole peg test or 25-foot timed walk). Individuals with at least three paramagnetic rim lesions had a greater increase in cortical lesion volume over time (median 16 µl, range -61 to 215 versus median 1 µl, range -24 to 184, P = 0.007), but change in lesion volume was not associated with disability change. Baseline cortical lesion volume was higher in people with worsening disability (median 1010 µl, range 13-9888 versus median 267 µl, range 0-3539, P = 0.001, adjusted for age and sex) and in individuals with relapsing-remitting multiple sclerosis who subsequently transitioned to secondary progressive multiple sclerosis (median 2183 µl, range 270-9888 versus median 321 µl, range 0-6392 in those who remained relapsing-remitting, P = 0.01, adjusted for age and sex). Baseline white matter lesion volume was not associated with worsening disability or transition from relapsing-remitting to secondary progressive multiple sclerosis. Cortical lesion formation is rare in people with stable white matter lesions, even in those with worsening disability. Cortical but not white matter lesion burden predicts disability worsening, suggesting that disability progression is related to long-term effects of cortical lesions that form early in the disease, rather than to ongoing cortical lesion formation.

Transcript Profiles of Microglia/Macrophage Cells at the Borders of Chronic Active and Subpial Gray Matter Lesions in Multiple Sclerosis

OBJECTIVE

Microglia/macrophages line the border of demyelinated lesions in both cerebral white matter and the cortex in the brains of multiple sclerosis patients. Microglia/macrophages associated with chronic white matter lesions are thought to be responsible for slow lesion expansion and disability progression in progressive multiple sclerosis, whereas those lining gray matter lesions are less studied. Profiling these microglia/macrophages could help to focus therapies on genes or pathways specific to lesion expansion and disease progression.

METHODS

We compared the morphology and transcript profiles of microglia/macrophages associated with borders of white matter (WM line) and subpial gray matter lesions (GM line) using laser capture microscopy. We performed RNA sequencing on isolated cells followed by immunocytochemistry to determine the distribution of translational products of transcripts increased in WM line microglia.

RESULTS

Cells in the WM line appear activated, with shorter processes and larger cell bodies, whereas those in the GM line appear more homeostatic, with smaller cell bodies and multiple thin processes. Transcript profiling revealed 176 genes in WM lines and 111 genes in GM lines as differentially expressed. Transcripts associated with immune activation and iron homeostasis were increased in WM line microglia, whereas genes belonging to the canonical Wnt signaling pathway were increased in GM line microglia.

INTERPRETATION

We propose that the mechanisms of demyelination and dynamics of lesion expansion are responsible for differential transcript expression in WM lines and GM lines, and posit that increased expression of the Fc epsilon receptor, spleen tyrosine kinase, and Bruton's tyrosine kinase, play a key role in regulating microglia/macrophage function at the border of chronic active white matter lesions. ANN NEUROL 2024;95:907-916.

Brain regulatory T cells

The brain, long thought to be isolated from the peripheral immune system, is increasingly recognized to be integrated into a systemic immunological network. These conduits of immune-brain interaction and immunosurveillance processes necessitate the presence of complementary immunoregulatory mechanisms, of which brain regulatory T cells (Treg cells) are likely a key facet. Treg cells represent a dynamic population in the brain, with continual influx, specialization to a brain-residency phenotype and relatively rapid displacement by newly incoming cells. In addition to their functions in suppressing adaptive immunity, an emerging view is that Treg cells in the brain dampen down glial reactivity in response to a range of neurological insults, and directly assist in multiple regenerative and reparative processes during tissue pathology. The utility and malleability of the brain Treg cell population make it an attractive therapeutic target across the full spectrum of neurological conditions, ranging from neuroinflammatory to neurodegenerative and even psychiatric diseases. Therapeutic modalities currently under intense development include Treg cell therapy, IL-2 therapy to boost Treg cell numbers and multiple innovative approaches to couple these therapeutics to brain delivery mechanisms for enhanced potency. Here we review the state of the art of brain Treg cell knowledge together with the potential avenues for future integration into medical practice.

A novel imaging marker of cortical "cellularity" in multiple sclerosis patients

Pathological data showed focal inflammation and regions of diffuse neuronal loss in the cortex of people with multiple sclerosis (MS). In this work, we applied a novel model ("soma and neurite density imaging (SANDI)") to multishell diffusion-weighted MRI data acquired in healthy subjects and people with multiple sclerosis (pwMS), in order to investigate inflammation and degeneration-related changes in the cortical tissue of pwMS. We aimed to (i) establish whether SANDI is applicable in vivo clinical data; (ii) investigate inflammatory and degenerative changes using SANDI soma fraction (fsoma)-a marker of cellularity-in both cortical lesions and in the normal-appearing-cortex and (iii) correlate SANDI fsoma with clinical and biological measures in pwMS. We applied a simplified version of SANDI to a clinical scanners. We then provided evidence that pwMS exhibited an overall decrease in cortical SANDI fsoma compared to healthy subjects, suggesting global degenerative processes compatible with neuronal loss. On the other hand, we have found that progressive pwMS showed a higher SANDI fsoma in the outer part of the cortex compared to relapsing-remitting pwMS, possibly supporting current pathological knowledge of increased innate inflammatory cells in these regions. A similar finding was obtained in subpial lesions in relapsing-remitting patients, reflecting existing pathological data in these lesion types. A significant correlation was found between SANDI fsoma and serum neurofilament light chain-a biomarker of inflammatory axonal damage-suggesting a relationship between SANDI soma fraction and inflammatory processes in pwMS again. Overall, our data show that SANDI fsoma is a promising biomarker to monitor changes in cellularity compatible with neurodegeneration and neuroinflammation in the cortex of MS patients.

CNS Resident Innate Immune Cells: Guardians of CNS Homeostasis

Although the CNS has been considered for a long time an immune-privileged organ, it is now well known that both the parenchyma and non-parenchymal tissue (meninges, perivascular space, and choroid plexus) are richly populated in resident immune cells. The advent of more powerful tools for multiplex immunophenotyping, such as single-cell RNA sequencing technique and upscale multiparametric flow and mass spectrometry, helped in discriminating between resident and infiltrating cells and, above all, the different spectrum of phenotypes distinguishing border-associated macrophages. Here, we focus our attention on resident innate immune players and their primary role in both CNS homeostasis and pathological neuroinflammation and neurodegeneration, two key interconnected aspects of the immunopathology of multiple sclerosis.

Synaptic injury in the inner plexiform layer of the retina is associated with progression in multiple sclerosis

While neurodegeneration underlies the pathological basis for permanent disability in multiple sclerosis (MS), predictive biomarkers for progression are lacking. Using an animal model of chronic MS, we find that synaptic injury precedes neuronal loss and identify thinning of the inner plexiform layer (IPL) as an early feature of inflammatory demyelination-prior to symptom onset. As neuronal domains are anatomically segregated in the retina and can be monitored longitudinally, we hypothesize that thinning of the IPL could represent a biomarker for progression in MS. Leveraging our dataset with over 800 participants enrolled for more than 12 years, we find that IPL atrophy directly precedes progression and propose that synaptic loss is predictive of functional decline. Using a blood proteome-wide analysis, we demonstrate a strong correlation between demyelination, glial activation, and synapse loss independent of neuroaxonal injury. In summary, monitoring synaptic injury is a biologically relevant approach that reflects a potential driver of progression.

Soluble CD27 is an intrathecal biomarker of T-cell-mediated lesion activity in multiple sclerosis

OBJECTIVE

Soluble CD27 is a promising cerebrospinal fluid inflammatory biomarker in multiple sclerosis. In this study, we investigate relevant immune and neuro-pathological features of soluble CD27 in multiple sclerosis.

METHODS

Protein levels of soluble CD27 were correlated to inflammatory cell subpopulations and inflammatory cytokines and chemokines detected in cerebrospinal fluid of 137 patients with multiple sclerosis and 47 patients with inflammatory and non-inflammatory neurological disease from three independent cohorts. Production of soluble CD27 was investigated in cell cultures of activated T and B cells and CD27-knockout T cells. In a study including matched cerebrospinal fluid and post-mortem brain tissues of patients with multiple sclerosis and control cases, levels of soluble CD27 were correlated with perivascular and meningeal infiltrates and with neuropathological features.

RESULTS

We demonstrate that soluble CD27 favours the differentiation of interferon-γ-producing T cells and is released through a secretory mechanism activated by TCR engagement and regulated by neutral sphingomyelinase. We also show that the levels of soluble CD27 correlate with the representation of inflammatory T cell subsets in the CSF of patients with relapsing-remitting multiple sclerosis and with the magnitude of perivascular and meningeal CD27 + CD4 + and CD8 + T cell infiltrates in post-mortem central nervous system tissue, defining a subgroup of patients with extensive active inflammatory lesions.

INTERPRETATION

Our results demonstrate that soluble CD27 is a biomarker of disease activity, potentially informative for personalized treatment and monitoring of treatment outcomes.

Time is myelin: early cortical myelin repair prevents atrophy and clinical progression in multiple sclerosis

Cortical myelin loss and repair in multiple sclerosis (MS) have been explored in neuropathological studies, but the impact of these processes on neurodegeneration and the irreversible clinical progression of the disease remains unknown. Here, we evaluated in vivo cortical demyelination and remyelination in a large cohort of people with all clinical phenotypes of MS followed up for 5 years using magnetization transfer imaging (MTI), a technique that has been shown to be sensitive to myelin content changes in the cortex. We investigated 140 people with MS (37 clinically isolated syndrome, 71 relapsing-MS, 32 progressive-MS), who were clinically assessed at baseline and after 5 years and, along with 84 healthy controls, underwent a 3 T-MRI protocol including MTI at baseline and after 1 year. Changes in cortical volume over the radiological follow-up were computed with a Jacobian integration method. Magnetization transfer ratio was employed to calculate for each patient an index of cortical demyelination at baseline and of dynamic cortical demyelination and remyelination over the follow-up period. The three indices of cortical myelin content change were heterogeneous across patients but did not significantly differ across clinical phenotypes or treatment groups. Cortical remyelination, which tended to fail in the regions closer to CSF (-11%, P < 0.001), was extensive in half of the cohort and occurred independently of age, disease duration and clinical phenotype. Higher indices of cortical dynamic demyelination (β = 0.23, P = 0.024) and lower indices of cortical remyelination (β = -0.18, P = 0.03) were significantly associated with greater cortical atrophy after 1 year, independently of age and MS phenotype. While the extent of cortical demyelination predicted a higher probability of clinical progression after 5 years in the entire cohort [odds ratio (OR) = 1.2; P = 0.043], the impact of cortical remyelination in reducing the risk of accumulating clinical disability after 5 years was significant only in the subgroup of patients with shorter disease duration and limited extent of demyelination in cortical regions (OR = 0.86, P = 0.015, area under the curve = 0.93). In this subgroup, a 30% increase in cortical remyelination nearly halved the risk of clinical progression at 5 years, independently of clinical relapses. Overall, our results highlight the critical role of cortical myelin dynamics in the cascade of events leading to neurodegeneration and to the subsequent accumulation of irreversible disability in MS. Our findings suggest that early-stage myelin repair compensating for cortical myelin loss has the potential to prevent neuro-axonal loss and its long-term irreversible clinical consequences in people with MS.

High Levels of Perivascular Inflammation and Active Demyelinating Lesions at Time of Death Associated with Rapidly Progressive Multiple Sclerosis Disease Course: A Retrospective Postmortem Cohort Study

OBJECTIVE

Analysis of postmortem multiple sclerosis (MS) tissues combined with in vivo disease milestones suggests that whereas perivascular white matter infiltrates are associated with demyelinating activity in the initial stages, leptomeningeal immune cell infiltration, enriched in B cells, and associated cortical lesions contribute to disease progression. We systematically examine the association of inflammatory features and white matter demyelination at postmortem with clinical milestones.

METHODS

In 269 MS brains, 20 sites were examined using immunohistochemistry for active lesions (ALs) and perivenular inflammation (PVI). In a subset of 22, a detailed count of CD20+ B cells and CD3+ T cells in PVIs was performed.

RESULTS

ALs were detected in 22%, whereas high levels of PVI were detected in 52% of cases. ALs were present in 35% of cases with high levels of PVI. Shorter time from onset of progression to death was associated with increased prevalence and higher levels of PVI (both p < 0.0001). Shorter time from onset of progression to wheelchair use was associated with higher prevalence of ALs (odds ratio [OR] = 0.921, 95% confidence interval [CI] = 0.858-0.989, p = 0.0230) and higher level of PVI (OR = 0.932, 95% CI = 0.886-0.981, p = 0.0071). High levels of PVI were associated with meningeal inflammation and increased cortical demyelination and significantly higher levels of B lymphocytes within the PVI.

INTERPRETATION

ALs, a feature of early disease stage, persist up to death in a subgroup with high levels of PVI. These features link to a rapid progressive phase and higher levels of meningeal inflammation and B-cell infiltrates, supporting the hypothesis that chronic inflammation drives progression in MS. ANN NEUROL 2024;95:706-719.

Meningeal contrast enhancement in multiple sclerosis: assessment of field strength, acquisition delay, and clinical relevance

Background/Purpose

Leptomeningeal enhancement (LME) on post-contrast FLAIR is described as a potential biomarker of meningeal inflammation in multiple sclerosis (MS). Here we report a comprehensive assessment of the impact of MRI field strength and acquisition timing on meningeal contrast enhancement (MCE).

Methods

This was a cross-sectional, observational study of 95 participants with MS and 17 healthy controls (HC) subjects. Each participant underwent an MRI of the brain on both a 7 Tesla (7T) and 3 Tesla (3T) MRI scanner. 7T protocols included a FLAIR image before, soon after (Gd+ Early 7T FLAIR), and 23 minutes after gadolinium (Gd+ Delayed 7T FLAIR). 3T protocol included FLAIR before and 21 minutes after gadolinium (Gd+ Delayed 3T FLAIR).

Results

LME was seen in 23.3% of participants with MS on Gd+ Delayed 3T FLAIR, 47.4% on Gd+ Early 7T FLAIR (p = 0.002) and 57.9% on Gd+ Delayed 7T FLAIR (p < 0.001 and p = 0.008, respectively). The count and volume of LME, leptomeningeal and paravascular enhancement (LMPE), and paravascular and dural enhancement (PDE) were all highest for Gd+ Delayed 7T FLAIR and lowest for Gd+ Delayed 3T FLAIR. Non-significant trends were seen for higher proportion, counts, and volumes for LME and PDE in MS compared to HCs. The rate of LMPE was different between MS and HCs on Gd+ Delayed 7T FLAIR (98.9% vs 82.4%, p = 0.003). MS participants with LME on Gd+ Delayed 7T FLAIR were older (47.6 (10.6) years) than those without (42.0 (9.7), p = 0.008).

Conclusion

7T MRI and a delay after contrast injection increased sensitivity for all forms of MCE. However, the lack of difference between groups for LME and its association with age calls into question its relevance as a biomarker of meningeal inflammation in MS.

B cell depletion with anti-CD20 promotes neuroprotection in a BAFF-dependent manner in mice and humans

Anti-CD20 therapy to deplete B cells is highly efficacious in preventing new white matter lesions in patients with relapsing-remitting multiple sclerosis (RRMS), but its protective capacity against gray matter injury and axonal damage is unclear. In a passive experimental autoimmune encephalomyelitis (EAE) model whereby TH17 cells promote brain leptomeningeal immune cell aggregates, we found that anti-CD20 treatment effectively spared myelin content and prevented myeloid cell activation, oxidative damage, and mitochondrial stress in the subpial gray matter. Anti-CD20 treatment increased B cell survival factor (BAFF) in the serum, cerebrospinal fluid, and leptomeninges of mice with EAE. Although anti-CD20 prevented gray matter demyelination, axonal loss, and neuronal atrophy, co-treatment with anti-BAFF abrogated these benefits. Consistent with the murine studies, we observed that elevated BAFF concentrations after anti-CD20 treatment in patients with RRMS were associated with better clinical outcomes. Moreover, BAFF promoted survival of human neurons in vitro. Together, our data demonstrate that BAFF exerts beneficial functions in MS and EAE in the context of anti-CD20 treatment.

The presence of Mott cells in the lymph nodes of rats with experimental autoimmune encephalomyelitis

Mott cells are plasma cells that have multiple spherical Russell bodies packed in their cytoplasm. Russell bodies are dilated endoplasmic reticulum cisternae filled with aggregates of immunoglobulins that are neither secreted nor degraded. Mott cells were observed in our study by light and electron microscope in the lymph nodes of rats with experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Mott cells were detected on hematoxylin and eosin (HE)-stained lymph node sections as vacuolated cells with eccentrically positioned nuclei and large number of faint blue spherical inclusions in the cytoplasm. Electron microscopic investigation revealed the presence of Russell bodies of the "medusa" form inside Mott cells in lymph node ultra-thin sections of EAE animals. Mott cells expressed the plasma cell marker CD138 and either kappa or lambda immunoglobulin light chains, indicating their origin from polyclonally activated B cells. Finally, Mott cells were associated with active EAE, as they were not found in the lymph nodes of EAE-resistant Albino Oxford rats. The presence of Russell bodies implies an excessive production of immunoglobulins in EAE, thus further emphasizing the role of B cells, and among them Mott cells, in the pathogenesis of this animal model of multiple sclerosis.

Comparing the Pathology, Clinical, and Demographic Characteristics of Younger and Older-Onset Multiple Sclerosis

OBJECTIVE

Older people with multiple sclerosis (MS) have a less active radiological and clinical presentation, but many still attain significant levels of disability; but what drives worsening disability in this group?

METHODS

We used data from the UK MS Register to characterize demographics and clinical features of late-onset multiple sclerosis (LOMS; symptom onset at ≥50 years), compared with adult-onset MS (AOMS; onset 18-49 years). We performed a pathology study of a separate MS cohort with a later onset (n = 18, mean age of onset 54 years) versus AOMS (n = 23, mean age of onset 29 years).

RESULTS

In the Register cohort, there were 1,608 (9.4%) with LOMS. When compared with AOMS, there was a lower proportion of women, a higher proportion of primary progressive MS, a higher level of disability at diagnosis (median MS impact scale 36.7 vs. 28.3, p < 0.001), and a higher proportion of gait-related initial symptoms. People with LOMS were less likely to receive a high efficacy disease-modifying treatment and attained substantial disability sooner. Controlling for age of death and sex, neuron density in the thalamus and pons decreased with onset-age, whereas actively demyelinating lesions and compartmentalized inflammation was greatest in AOMS. Only neuron density, and not demyelination or the extent of compartmentalized inflammation, correlated with disability outcomes in older-onset MS patients.

INTERPRETATION

The more progressive nature of older-onset MS is associated with significant neurodegeneration, but infrequent inflammatory demyelination. These findings have implications for the assessment and treatment of MS in older people. ANN NEUROL 2024;95:471-486.

Systemic administration of anti-CD20 indirectly reduces B cells in the inflamed meninges in a chronic model of central nervous system autoimmunity

Anti-CD20 B cell depleting therapies have demonstrated that B cells are important drivers of disease progress in Multiple Sclerosis, although the pathogenic mechanisms are not well understood. A population of B cells accumulates in the inflamed meninges in MS and also some chronic animal models of disease, typically adjacent to demyelinating lesions. The role of these meningeal B cells in disease is not known, nor is their susceptibility to anti-CD20 therapy. Here, we administered anti-CD20 to 2D2 IgHMOG spontaneous experimental autoimmune encephalomyelitis mice in the chronic phase of disease, after the establishment of meningeal B cell clusters. Compared to the circulation, lymph nodes, and spleen, B cell depletion from the meninges was delayed and not evident until 7d post-administration of anti-CD20. Further, we did not find evidence that anti-CD20 accessed meningeal B cells directly, but rather that depletion was indirect and the result of ongoing turnover of the meningeal population and elimination of the peripheral pool from which it is sustained.

Prognostic relevance of MRI in early relapsing multiple sclerosis: ready to guide treatment decision making?

Magnetic resonance imaging (MRI) of the brain and spinal cord plays a crucial role in the diagnosis and monitoring of multiple sclerosis (MS). There is conclusive evidence that brain and spinal cord MRI findings in early disease stages also provide relevant insight into individual prognosis. This includes prediction of disease activity and disease progression, the accumulation of long-term disability and the conversion to secondary progressive MS. The extent to which these MRI findings should influence treatment decisions remains a subject of ongoing discussion. The aim of this review is to present and discuss the current knowledge and scientific evidence regarding the utility of MRI at early MS disease stages for prognostic classification of individual patients. In addition, we discuss the current evidence regarding the use of MRI in order to predict treatment response. Finally, we propose a potential approach as to how MRI data may be categorized and integrated into early clinical decision making.

Role of B Cells in Relapsing-Remitting and Progressive Multiple Sclerosis and Long-Term Effects of B Cell Depletion

Depletion of circulating B lymphocytes using anti-CD20 monoclonal antibodies (mAbs) greatly reduces inflammatory activity in relapsing multiple sclerosis (RMS); it reduces progression to a lesser extent in nonrelapsing progressive MS. Mechanisms whereby anti-CD20 mAbs reduce MRI and clinical relapse activity in people with RMS are still being elucidated. Anti-CD20 agents do not fully protect from nonrelapsing disease progression, possibly due to their inability to cross the blood-brain barrier and inability to ameliorate the full extent of biology of MS progression. Anti-CD20 mAbs have a relatively favorable safety profile, at least in the short-term. Long-term safety studies are still needed.

An update on the role of magnetic resonance imaging in predicting and monitoring multiple sclerosis progression

INTRODUCTION

While magnetic resonance imaging (MRI) is established in diagnosing and monitoring disease activity in multiple sclerosis (MS), its utility in predicting and monitoring disease progression is less clear.

AREAS COVERED

The authors consider changing concepts in the phenotypic classification of MS, including progression independent of relapses; pathological processes underpinning progression; advances in MRI measures to assess them; how well MRI features explain and predict clinical outcomes, including models that assess disease effects on neural networks, and the potential role for machine learning.

EXPERT OPINION

Relapsing-remitting and progressive MS have evolved from being viewed as mutually exclusive to having considerable overlap. Progression is likely the consequence of several pathological elements, each important in building more holistic prognostic models beyond conventional phenotypes. MRI is well placed to assess pathogenic processes underpinning progression, but we need to bridge the gap between MRI measures and clinical outcomes. Mapping pathological effects on specific neural networks may help and machine learning methods may be able to optimize predictive markers while identifying new, or previously overlooked, clinically relevant features. The ever-increasing ability to measure features on MRI raises the dilemma of what to measure and when, and the challenge of translating research methods into clinically useable tools.

White matter paramagnetic rim and non-rim lesions share a periventricular gradient in multiple sclerosis: A 7-T imaging study

BACKGROUND

Paramagnetic rim white matter (WM) lesions (PRL) are thought to be a main driver of non-relapsing multiple sclerosis (MS) progression. It is unknown whether cerebrospinal fluid (CSF)-soluble factors diffusing from the ventricles contribute to PRL formation.

OBJECTIVE

To investigate the distribution of PRL and non-rim brain WM lesions as a function of distance from ventricular CSF, their relationship with cortical lesions, the contribution of lesion phenotype, and localization to neurological disability.

METHODS

Lesion count and volume of PRL, non-rim WM, leukocortical lesion (LCL), and subpial/intracortical lesions were obtained at 7-T. The brain WM was divided into 1-mm-thick concentric rings radiating from the ventricles to extract PRL and non-rim WM lesion volume from each ring.

RESULTS

In total, 61 MS patients with ⩾1 PRL were included in the study. Both PRL and non-rim WM lesion volumes were the highest in the periventricular WM and declined with increasing distance from ventricles. A CSF distance-independent association was found between non-rim WM lesions, PRL, and LCL, but not subpial/intracortical lesions. Periventricular non-rim WM lesion volume was the strongest predictor of neurological disability.

CONCLUSIONS

Non-rim and PRL share a gradient of distribution from the ventricles toward the cortex, suggesting that CSF proximity equally impacts the prevalence of both lesion phenotypes.

Personalized Use of Disease-Modifying Therapies in Multiple Sclerosis

Multiple sclerosis is an important neurological disease affecting millions of young patients globally. It is encouraging that more than ten disease-modifying drugs became available for use in the past two decades. These disease-modifying therapies (DMTs) have different levels of efficacy, routes of administration, adverse effect profiles and concerns for pregnancy. Much knowledge and caution are needed for their appropriate use in MS patients who are heterogeneous in clinical features and severity, lesion load on magnetic resonance imaging and response to DMT. We aim for an updated review of the concept of personalization in the use of DMT for relapsing MS patients. Shared decision making with consideration for the preference and expectation of patients who understand the potential efficacy/benefits and risks of DMT is advocated.

Multiple sclerosis

Multiple sclerosis remains one of the most common causes of neurological disability in the young adult population (aged 18-40 years). Novel pathophysiological findings underline the importance of the interaction between genetics and environment. Improvements in diagnostic criteria, harmonised guidelines for MRI, and globalised treatment recommendations have led to more accurate diagnosis and an earlier start of effective immunomodulatory treatment than previously. Understanding and capturing the long prodromal multiple sclerosis period would further improve diagnostic abilities and thus treatment initiation, eventually improving long-term disease outcomes. The large portfolio of currently available medications paved the way for personalised therapeutic strategies that will balance safety and effectiveness. Incorporation of cognitive interventions, lifestyle recommendations, and management of non-neurological comorbidities could further improve quality of life and outcomes. Future challenges include the development of medications that successfully target the neurodegenerative aspect of the disease and creation of sensitive imaging and fluid biomarkers that can effectively predict and monitor disease changes.

Intruders or protectors - the multifaceted role of B cells in CNS disorders

B lymphocytes are immune cells studied predominantly in the context of peripheral humoral immune responses against pathogens. Evidence has been accumulating in recent years on the diversity of immunomodulatory functions that B cells undertake, with particular relevance for pathologies of the central nervous system (CNS). This review summarizes current knowledge on B cell populations, localization, infiltration mechanisms, and function in the CNS and associated tissues. Acute and chronic neurodegenerative pathologies are examined in order to explore the complex, and sometimes conflicting, effects that B cells can have in each context, with implications for disease progression and treatment outcomes. Additional factors such as aging modulate the proportions and function of B cell subpopulations over time and are also discussed in the context of neuroinflammatory response and disease susceptibility. A better understanding of the multifactorial role of B cell populations in the CNS may ultimately lead to innovative therapeutic strategies for a variety of neurological conditions.

hnRNP A1 dysfunction alters RNA splicing and drives neurodegeneration in multiple sclerosis (MS)

Neurodegeneration is the primary driver of disease progression in multiple sclerosis (MS) resulting in permanent disability, creating an urgent need to discover its underlying mechanisms. Herein, we establish that dysfunction of the RNA binding protein heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) results in differential of binding to RNA targets causing alternative RNA splicing, which contributes to neurodegeneration in MS and its models. Using RNAseq of MS brains, we discovered differential expression and aberrant splicing of hnRNP A1 target RNAs involved in neuronal function and RNA homeostasis. We confirmed this in vivo in experimental autoimmune encephalomyelitis employing CLIPseq specific for hnRNP A1, where hnRNP A1 differentially binds and regulates RNA, including aberrantly spliced targets identified in human samples. Additionally, dysfunctional hnRNP A1 expression in neurons caused neurite loss and identical changes in splicing, corroborating hnRNP A1 dysfunction as a cause of neurodegeneration. Collectively, these data indicate hnRNP A1 dysfunction causes altered neuronal RNA splicing, resulting in neurodegeneration in MS.

Cortical matrix remodeling as a hallmark of relapsing-remitting neuroinflammation in MR elastography and quantitative MRI

Multiple sclerosis (MS) is a chronic neuroinflammatory disease that involves both white and gray matter. Although gray matter damage is a major contributor to disability in MS patients, conventional clinical magnetic resonance imaging (MRI) fails to accurately detect gray matter pathology and establish a clear correlation with clinical symptoms. Using magnetic resonance elastography (MRE), we previously reported global brain softening in MS and experimental autoimmune encephalomyelitis (EAE). However, it needs to be established if changes of the spatiotemporal patterns of brain tissue mechanics constitute a marker of neuroinflammation. Here, we use advanced multifrequency MRE with tomoelastography postprocessing to investigate longitudinal and regional inflammation-induced tissue changes in EAE and in a small group of MS patients. Surprisingly, we found reversible softening in synchrony with the EAE disease course predominantly in the cortex of the mouse brain. This cortical softening was associated neither with a shift of tissue water compartments as quantified by T2-mapping and diffusion-weighted MRI, nor with leukocyte infiltration as seen by histopathology. Instead, cortical softening correlated with transient structural remodeling of perineuronal nets (PNNs), which involved abnormal chondroitin sulfate expression and microgliosis. These mechanisms also appear to be critical in humans with MS, where tomoelastography for the first time demonstrated marked cortical softening. Taken together, our study shows that neuroinflammation (i) critically affects the integrity of PNNs in cortical brain tissue, in a reversible process that correlates with disease disability in EAE, (ii) reduces the mechanical integrity of brain tissue rather than leading to water accumulation, and (iii) shows similar spatial patterns in humans and mice. These results raise the prospect of leveraging MRE and quantitative MRI for MS staging and monitoring treatment in affected patients.

A pilot trial of ocrelizumab for modulation of meningeal enhancement in multiple sclerosis

BACKGROUND

Autopsy data suggests that meningeal inflammation in multiple sclerosis (MS) is driven by CD20+ B-cells. Ocrelizumab is an anti-CD20 monoclonal antibody, and thus could potentially ameliorate meningeal inflammation in MS. Leptomeningeal enhancement (LME) on MRI is suggested as a surrogate biomarker of meningeal inflammation in MS, and thus may be a way of monitoring for this treatment effect.

OBJECTIVES

To determine if ocrelizumab impacts meningeal enhancement (ME) on 7T MRI in MS.

METHODS

Twenty-two patients with MS started on ocrelizumab by their treating physician were enrolled into this single-center, open-label, prospective trial. Participants underwent 7T MRI of the brain prior to first infusion, with screening for the presence of LME. Fourteen patients (48 ± 11 years; 11 women) had LME on the baseline scan and were invited to return for an additional 7T MRI after 1 year of treatment. Fourteen MS patients (49 ± 10 years; 11 women) on non-CD20 treatment from a separate observational cohort of annual 7T MRIs were used for comparison - matched for LME at baseline, age, and sex. Post-contrast FLAIR and subtraction images were reviewed for LME and paravascular and dural enhancement (PDE).

RESULTS

All subjects in the ocrelizumab and comparison groups had LME and PDE on their baseline scan. At the beginning of the study the mean number of foci of LME and PDE in the study group were 2.3 ± 1.7 and 6.6 ± 3.9 respectively. Mean LME and PDE count for the comparison group were 1.7 ± 1.5 and 7.8 ± 5.5. Mean volume of LME in the study group was 50.5 mm3 ± 65.0 mm3 and that of the PDE was 866 mm3 ± 937.9. Mean volume of LME and PDE for comparison group were 28.4 mm3 ± 36.0 and 885 mm3 ± 947.7 respectively. At follow-up, the number of patients with LME decreased to 8 (57 %) in both groups, whereas the proportion of patients with PDE was unchanged. Minimal mean change in the number of LME after 1 year were seen in both the study group (0.07 ± 2.9, p = 0.97) and comparison group (-0.71 ± 1.5, p = 0.08). Minimal mean change was seen in the volume of LME in both the study group (-21.91 mm3 ± 77.66, p = 0.27) and comparison group (3.4 mm3 ± 32.11, p = 0.77). There was minimal change in the mean number of foci of PDE after 1 year in both the study group (-0.71 ± 2.36, p = 0.32) and in the comparison group (-0.17 ± 3.89, p = 0.15). Mean change in volume of PDE was measurable, but not significant in both the study group (-397.1 mm3 ±959.6, p = 0.80) and in the comparison group (-417.0 mm3 ± 922.7) (p = 0.80). Comparisons between the changes in foci count and volume for both LME and PDE in the study versus comparison groups showed no significant differences.

CONCLUSION

In this small pilot trial, ocrelizumab did not significantly reduce the number or volume of foci of LME or PDE in MS patients.