Multiple sclerosis: role of meningeal lymphoid aggregates in progression independent of relapse activity

Recent developments in multiple sclerosis neuropathology

PURPOSE OF REVIEW

Neuropathological studies in human brain tissue are indispensable for our understanding of disease mechanisms in multiple sclerosis (MS). They inform concepts of lesion evolution, tissue regeneration and disease progression, and ideally reveal new disease mechanisms and therapeutic targets. Here we review recent neuropathological studies that have advanced our knowledge of MS pathogenesis.

RECENT FINDINGS

Recent cohort studies support the notion that different clinical MS disease phenotypes share underlying pathological features, and that clinical and pathological heterogeneity is derived from a variable combination of innate and adaptive inflammation, demyelinating activity, and neuroaxonal loss. Importantly, emerging technologies for spatial transcriptome analysis enable an unprecedented glimpse into the cellular composition and molecular mechanisms involved in lesion evolution. These promising technologies will help identify the identification of molecular hubs governing tissue damage and regeneration.

SUMMARY

Recent neuropathological studies helped to identify tissue correlates of disability and disease progression. Substantial progress in molecular brain tissue analysis revealed the complexity of MS-related tissue features. Close collaboration between tissue-based, molecular, bioinformatic, pharmacologic, imaging and clinical experts is needed to continue to advance the field, particularly for the benefit of people with progressive MS.

Progressive multiple sclerosis: Evaluating current therapies and exploring future treatment strategies

Progressive forms of multiple sclerosis (MS) include primary progressive MS (PPMS) and secondary progressive MS (SPMS). Unlike relapsing-remitting MS (RRMS), progressive MS is recognized by relentless progression with accumulating disability, rare to no relapses nor new activity on MRIs. Clinically, neurologic worsening in MS can occur in the relapsing-remitting (RRMS) phase of disease due to incomplete recovery from neuroinflammatory relapses. However, a progressive disease course is the dominant factor related to accumulating disability. There is persistent central nervous system (CNS) compartmentalized inflammation, mitochondrial dysfunction and altered immune responses. Unlike in RRMS, the efficacy of disease modifying agents (DMA) in progressive MS has been limited, highlighting the need for novel therapeutic approaches that address both inflammation and neurodegeneration. This article explores current management of progressive MS, and future directions in targeting the unique pathophysiology of this complex disease.

High efficacy therapy to prevent the formation of meningeal tertiary lymphoid organs after CXCL13 index screening in early multiple sclerosis

Postmortem studies have shown the presence of subpial inflammation with tertiary lymphoid organs (TLO) in the meninges of patients with progressive multiple sclerosis, playing an important role in the pathophysiology of the disease. The chemokine (C-X-C motif) ligand 13 (CXCL13) induces the formation of these lymphoid organs, thus promoting activity of disease. The progression to disability in multiple sclerosis has been reduced, thanks to the effect of disease modifying therapy. However, despite advances in the treatment of disease with immunomodulatory agents, we still lack specific laboratory biomarkers that could indicate the state of activity of disease, either at time of diagnosis or when escalation therapy seems to be mandatory. In patients with multiple sclerosis, MRI studies have not demonstrated the presence of TLO in the CNS, so far. The determination of the CXCL13 index (ICXCL 13), in clinical specimens, could become a reliable biomarker for the verification of the presence and activity of the TLO, thus contributing to improving therapy outcome, with high efficacy therapy, in the clinical setting.

A Window into New Insights on Progression Independent of Relapse Activity in Multiple Sclerosis: Role of Therapies and Current Perspective

In multiple sclerosis (MS), there is significant evidence indicating that both progression independent of relapse activity (PIRA) and relapse-related worsening events contribute to the accumulation of progressive disability from the onset of the disease and throughout its course. Understanding the compartmentalized pathophysiology of MS would enhance comprehension of disease progression mechanisms, overcoming the traditional distinction in phenotypes. Smoldering MS activity is thought to be maintained by a continuous interaction between the parenchymal chronic processes of neuroinflammation and neurodegeneration and the intrathecal compartment. This review provides a comprehensive and up-to-date overview of the neuropathological and immunological evidence related to the mechanisms underlying PIRA phenomena in MS, with a focus on studies investigating the impact of currently available therapies on these complex mechanisms.

Selected Aspects of the Neuroimmunology of Cell Therapies for Neurologic Disease: Perspective

Neurologic disease remains a cause of incalculable suffering, a formidable public health burden, and a wilderness of complex biology and medicine. At the same time, advances in basic science, technology, and the clinical development toolkit bring meaningful benefit for patients along with realistic hope for those whose conditions remain inadequately treated. This perspective focuses on cell-based therapies for neurologic disease, with particular emphasis on neuroimmunologic disorders and on the immunologic considerations of cell therapy for nonimmune conditions. I will consider the use of chimeric antigen receptor (CAR)-T effector cells and regulatory T-cell therapies for autoimmune conditions. I will briefly discuss the immune aspects of pluripotent stem cell (PSC)-derived neuronal therapies. With apologies for the omission, we do not discuss mesenchymal stem cells, glial progenitor cells, or CAR-NK cells, primarily for space limitations.

Serum biomarkers at disease onset for personalized therapy in multiple sclerosis

The potential for combining serum neurofilament light chain (sNfL) and glial fibrillary acidic protein (sGFAP) levels to predict worsening disability in multiple sclerosis remains underexplored. We aimed to investigate whether sNfL and sGFAP values identify distinct subgroups of patients according to the risk of disability worsening and their response to disease-modifying treatments (DMTs). This multicentre study, conducted across 13 European hospitals, spanned from 15 July 1994 to 18 August 2022, with follow-up until 26 September 2023. We enrolled patients with multiple sclerosis who had serum samples collected within 12 months from disease onset and before initiating DMTs. Multivariable regression models were used to estimate the risk of relapse-associated worsening (RAW), progression independent of relapse activity (PIRA) and Expanded Disability Status Scale (EDSS) score of 3. Of the 725 patients included, the median age was 34.2 (interquartile range, 27.6-42.4) years, and 509 patients (70.2%) were female. The median follow-up duration was 6.43 (interquartile range, 4.65-9.81) years. Higher sNfL values were associated with an elevated risk of RAW [hazard ratio (HR) of 1.45; 95% confidence interval (CI) 1.19-1.76; P < 0.001], PIRA (HR of 1.43; 95% CI 1.13-1.81; P = 0.003) and reaching an EDSS of 3 (HR of 1.55; 95% CI 1.29-1.85; P < 0.001). Moreover, higher sGFAP levels were linked to a higher risk of achieving an EDSS score of 3 (HR of 1.36; 95% CI 1.06-1.74; P = 0.02) and, in patients with low sNfL values, to PIRA (HR of 1.86; 95% CI 1.01-3.45; P = 0.04). We also examined the combined effect of sNfL and sGFAP levels. Patients with low sNfL and sGFAP values exhibited a low risk of all outcomes and served as a reference. Untreated patients with high sNfL levels showed a higher risk of RAW, PIRA and reaching an EDSS of 3. Injectable or oral DMTs reduced the risk of RAW in these patients but failed to mitigate the risk of PIRA and reaching an EDSS of 3. Conversely, high-efficacy DMTs counteracted the heightened risk of these outcomes, except for the risk of PIRA in patients with high sNfL and sGFAP levels. Patients with low sNfL and high sGFAP values showed an increased risk of PIRA and achieving an EDSS of 3, which remained unchanged with either high-efficacy or other DMTs. In conclusion, evaluating sNfL and sGFAP levels at disease onset in multiple sclerosis might identify distinct phenotypes associated with diverse immunological pathways of disability acquisition and therapeutic response.

In multiple sclerosis patients a single serum neurofilament light chain (sNFL) dosage is strongly associated with 12 months outcome: data from a real-life clinical setting

BACKGROUND

Neurofilament light chain (NFL) is a neuroaxonal cytoskeletal protein released into cerebrospinal fluid (CSF) and eventually into blood upon neuronal injury. Its detection in serum (sNFL) makes it a promising marker in multiple sclerosis (MS).

OBJECTIVE

To evaluate the usefulness of a single dosage of sNFL in clinical practice.

METHODS

626 consecutive relapsing-remitting (RR) MS patients treated with disease modifying treatments (DMTs) for at least 12 months underwent a single sNFL dosage. 553 patients had NEDA-3 status (no relapses, no disability progression, no new/enlarging or contrast-enhancing lesions on brain magnetic resonance imaging) in the 12 months prior blood sampling. sNFL levels were measured by single molecule array (Simoa™). Association between sNFL levels and NEDA-3 status at 12, 24, and 36 months was evaluated with logistic regression models adjusted for sex, EDSS, disease duration, and type of DMTs.

RESULTS

469 out of the 553 NEDA-3 patients had normal sNFL level, whereas 42 had elevated level. The two groups did not differ regarding baseline characteristics. A very strong association between elevated sNFL levels and loss of NEDA-3 status within 12 months was found, with an odds ratio [OR] of 10.74 (95% CI 4.34-26.57); 15 and 10 patients with normal and elevated sNFL, respectively lost NEDA-3 (p < 0.001). The effect was not detected during the subsequent 13-24 and 25-36 months.

CONCLUSIONS

A single elevated sNFL is strongly associated with NEDA-3 loss within 1 year. Elevated sNFL in apparently stable patients suggests an ongoing disease activity below the detection threshold of standard parameters.

Prognostic significance of paramagnetic rim lesions in multiple sclerosis: A systematic review

The diagnostic potential of paramagnetic rim lesions (PRLs) has been previously established; however, the prognostic significance of these lesions has not previously been consistently described. This study aimed to establish the prognostic role of PRLs in MS with respect to the Expanded Disability Status Scale (EDSS) and rates of disability progression. Databases of PubMed, EMBASE, Scopus and reference lists of selected articles were searched up to 29/04/2023. The review was conducted in accordance with PRISMA guidelines and was registered prospectively on PROSPERO (CRD42023422052). 7 studies were included in the final review. All of the eligible studies found that patients with PRLs tend to have higher baseline EDSS scores. Longitudinal assessments revealed greater EDSS progression in patients with PRLs over time in most studies. However, the effect of location of PRLs within the central nervous system were not assessed across the studies. Only one study investigated progression independent of relapse activity (PIRA) and showed that this clinical entity occurred in a greater proportion in patients with PRLs. This review supports PRLs as a predictor of EDSS progression. This measure has widespread applicability, however further multicentre studies are needed. Future research should explore the impact of PRLs on silent disability, PIRA, take into account different MS phenotypes and the topography of PRLs in prognosis.

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.

Intrathecal IgG and IgM synthesis correlates with neurodegeneration markers and corresponds to meningeal B cell presence in MS

Intrathecal synthesis of immunoglobulins (Igs) is a key hallmark of multiple sclerosis (MS). B cells are known to accumulate in the leptomeninges of MS patients and associate with pathology in the underlying cortex and a more severe disease course. However, the role of locally produced antibodies in MS brain pathology is poorly understood. Here, we quantified the protein levels of IgA, IgM, IgG and albumin in serum and cerebrospinal fluid (CSF) samples of 80 MS patients and 28 neurological controls to calculate Ig indices. In addition, we quantified presence of meningeal IgA+, IgM+ and IgG+ B cells in post-mortem brain tissue of 20 MS patients and 6 controls using immunostainings. IgM and IgG, but not IgA, indices were increased in CSF of MS patients compared to controls, with no observed differences between MS disease types. Both IgM and IgG indices correlated significantly with neurofilament light (NfL) levels in CSF, but not with clinical or radiological parameters of disease. Similarly, IgG+ and IgM+ B cells were increased in MS meninges compared to controls, whereas IgA+ B cells were not. Neuronal loss did not differ between sections with low or high IgA+, IgM+ and IgG+ B cells, but was increased in sections with high numbers of all CD19+ meningeal B cells. Similarly, high presence of CD19+ meningeal B cells and IgG+ meningeal B cells associated with increased microglial density in the underlying cortex. Taken together, intrathecal synthesis of IgG and IgM is elevated in MS, which corresponds to an increased number of IgG+ and IgM+ B cells in MS meninges. The significant correlation between intrathecal IgG and IgM production and NfL levels, and increased microglial activation in cortical areas adjacent to meningeal infiltrates with high levels of IgG+ B cells indicate a role for intrathecal IgM- and IgG-producing B cells in neuroinflammatory and degenerative processes in MS.

Cognitive progression independent of relapse in multiple sclerosis

BACKGROUND

Substantial physical-disability worsening in relapsing-remitting multiple sclerosis (RRMS) occurs outside of clinically recorded relapse. This phenomenon, termed progression independent of relapse activity (PIRA), is yet to be established for cognitive decline.

METHODS

Retrospective analysis of RRMS patients. Cognitive decline was defined using reliable-change-index cut-offs for each test (Symbol Digit Modalities Test, Brief Visuospatial Memory Test-Revised, California Verbal Learning Test-II). Decline was classified as PIRA if the following conditions were met: no relapse observed between assessments nor within 9 months of cognitive decline.

RESULTS

The study sample (n = 336) was 80.7% female with a mean (standard deviation (SD)) age, disease duration, and observation period of 43.1 (9.5), 10.8 (8.4), and 8.1 (3.1) years, respectively. A total of 169 (50.3%) subjects were cognitively impaired at baseline relative to age-, sex-, and education-matched HCs. Within subjects who experienced cognitive decline (n = 167), 89% experienced cognitive PIRA. A total of 141 (68.1%) cognitive decline events were observed independent of EDSS worsening. Cognitive PIRA was more likely to be observed with increased assessments (p < 0.001) and lower assessment density (p < 0.001), accounting for baseline clinical factors.

CONCLUSION

These results establish the concept of cognitive PIRA and further our understanding of progressive cognitive decline in RRMS.

Multiple sclerosis: emerging epidemiological trends and redefining the clinical course

Multiple sclerosis is a chronic, inflammatory, and neurodegenerative disease of the central nervous system and a major cause of neurological disability in young adults. Its prevalence and incidence are increasing, and it has been estimated at over 2.8 million cases worldwide, in addition to recent trends towards a shift in MS prevalence to older ages, with peak prevalence estimates in the sixth decade of life. Although historically the relapsing and progressive phases of the disease have been considered separate clinical entities, recent evidence of progression independent of relapse activity (PIRA) has led to a reconsideration of multiple sclerosis as a continuum, in which relapsing and progressive features variably coexist from the earliest stages of the disease, challenging the traditional view of the disease course. In this Series article, we provide an overview of how the traditional description of the clinical course of MS and epidemiological trends in Europe have evolved. For this purpose, we focus on the concept of PIRA, discussing its potential as the main mechanism by which patients acquire disability, how its definition varies between studies, and ongoing research in this field. We emphasise the importance of incorporating the assessment of hidden clinical manifestations into patient management to help uncover and quantify the PIRA phenomenon and the possible implications for future changes in the clinical classification of the disease. At the same time, we provide insights into overcoming the challenges of identifying and defining PIRA and adopting a new understanding of the clinical course of MS.

Reconciling lesions, relapses and smouldering associated worsening: A unifying model for multiple sclerosis pathogenesis

The failure of relapses and white matter lesions to properly explain long-term disability and progression in multiple sclerosis is compounded by its artificial separation into relapsing remitting, secondary progressive, and primary progressive pigeonholes. The well-known epidemiological disconnection between relapses and long-term disability progression has been rediscovered as "progression independent of relapse activity", i.e. smouldering multiple sclerosis. This smouldering associated worsening proceeds despite early and prolonged use of disease modification therapies, even those that are highly effective at preventing relapses and new/enhancing white matter lesions on MRI. We recognise that smouldering associated worsening and relapse/lesion associated worsening coexist, to varying extents. The extent of cortical demyelination has been shown to correlate significantly with the severity of diffuse injury in normal appearing white matter (post mortem histopathologically (r = 0.55; P = 0.001), and in vivo with MRI (r = -0.6874; P = 0.0006)) and does so independently of white matter lesion burden. Axon loss in the normal appearing white matter explains disability in multiple sclerosis better than focal white matter lesions do. Smouldering associated worsening typically manifests as a length-dependent central axonopathy. We propose a unifying model for multiple sclerosis pathogenesis, wherein accumulation of cortical lesion burden predisposes associated normal appearing white matter to diffuse injury, whilst also intensifying damage within white matter lesions. Our novel two-hit hypothesis implicates cortical disease as a culprit for smouldering multiple sclerosis, abetted by active focal inflammation in the white matter (and vice versa). Substantiation of the two-hit hypothesis would advance the importance of specific therapeutic intervention for (and monitoring of) cortical/meningeal inflammation in people with multiple sclerosis.

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.

Digital Pathology Identifies Associations between Tissue Inflammatory Biomarkers and Multiple Sclerosis Outcomes

BACKGROUND

Multiple sclerosis (MS) is a clinically heterogeneous disease underpinned by inflammatory, demyelinating and neurodegenerative processes, the extent of which varies between individuals and over the course of the disease. Recognising the clinicopathological features that most strongly associate with disease outcomes will inform future efforts at patient phenotyping.

AIMS

We used a digital pathology workflow, involving high-resolution image acquisition of immunostained slides and opensource software for quantification, to investigate the relationship between clinical and neuropathological features in an autopsy cohort of progressive MS.

METHODS

Sequential sections of frontal, cingulate and occipital cortex, thalamus, brain stem (pons) and cerebellum including dentate nucleus (n = 35 progressive MS, females = 28, males = 7; age died = 53.5 years; range 38-98 years) were immunostained for myelin (anti-MOG), neurons (anti-HuC/D) and microglia/macrophages (anti-HLA). The extent of demyelination, neurodegeneration, the presence of active and/or chronic active lesions and quantification of brain and leptomeningeal inflammation was captured by digital pathology.

RESULTS

Digital analysis of tissue sections revealed the variable extent of pathology that characterises progressive MS. Microglia/macrophage activation, if found at a higher level in a single block, was typically elevated across all sampled blocks. Compartmentalised (perivascular/leptomeningeal) inflammation was associated with age-related measures of disease severity and an earlier death.

CONCLUSION

Digital pathology identified prognostically important clinicopathological correlations in MS. This methodology can be used to prioritise the principal pathological processes that need to be captured by future MS biomarkers.

Exploring miRNAs' Based Modeling Approach for Predicting PIRA in Multiple Sclerosis: A Comprehensive Analysis

The current hypothesis on the pathophysiology of multiple sclerosis (MS) suggests the involvement of both inflammatory and neurodegenerative mechanisms. Disease Modifying Therapies (DMTs) effectively decrease relapse rates, thus reducing relapse-associated disability in people with MS. In some patients, disability progression, however, is not solely linked to new lesions and clinical relapses but can manifest independently. Progression Independent of Relapse Activity (PIRA) significantly contributes to long-term disability, stressing the urge to unveil biomarkers to forecast disease progression. Twenty-five adult patients with relapsing-remitting multiple sclerosis (RRMS) were enrolled in a cohort study, according to the latest McDonald criteria, and tested before and after high-efficacy Disease Modifying Therapies (DMTs) (6-24 months). Through Agilent microarrays, we analyzed miRNA profiles from peripheral blood mononuclear cells. Multivariate logistic and linear models with interactions were generated. Robustness was assessed by randomization tests in R. A subset of miRNAs, correlated with PIRA, and the Expanded Disability Status Scale (EDSS), was selected. To refine the patient stratification connected to the disease trajectory, we computed a robust logistic classification model derived from baseline miRNA expression to predict PIRA status (AUC = 0.971). We built an optimal multilinear model by selecting four other miRNA predictors to describe EDSS changes compared to baseline. Multivariate modeling offers a promising avenue to uncover potential biomarkers essential for accurate prediction of disability progression in early MS stages. These models can provide valuable insights into developing personalized and effective treatment strategies.

Early use of high-efficacy therapies in multiple sclerosis in the United States: benefits, barriers, and strategies for encouraging adoption

Multiple sclerosis (MS) is characterized by progressive neuroinflammation and neurodegeneration from disease onset that, if left untreated, can result in the accumulation of irreversible neurological disability. Early intervention with high-efficacy therapies (HETs) is increasingly recognized as the best strategy to delay or mitigate disease progression from the earliest stages of the disease and to prevent long-term neurodegeneration. Although there is growing clinical and real-world evidence supporting early HET intervention, foregoing this strategy in favor of a traditional escalation approach prioritizing lower-efficacy disease-modifying therapies remains a common approach in clinical practice. This review explores potential health care professional- and patient-related barriers to the early use of HETs in patients with MS in the United States. Barriers can include regulatory and reimbursement restrictions; knowledge gaps and long-term safety concerns among health care professionals; and various individual, cultural, and societal factors affecting patients. Potential strategies for overcoming these barriers and encouraging early HET use are proposed.

B cell-targeting chimeric antigen receptor T cells as an emerging therapy in neuroimmunological diseases

BACKGROUND

Neuroimmunology research and development has been marked by substantial advances, particularly in the treatment of neuroimmunological diseases, such as multiple sclerosis, myasthenia gravis, neuromyelitis optica spectrum disorders, and myelin oligodendrocyte glycoprotein antibody disease. With more than 20 drugs approved for multiple sclerosis alone, treatment has become more personalised. The approval of disease-modifying therapies, particularly those targeting B cells, has highlighted the role of immunotherapeutic interventions in the management of these diseases. Despite these successes, challenges remain, particularly for patients who do not respond to conventional therapies, underscoring the need for innovative approaches.

RECENT DEVELOPMENTS

The approval of monoclonal antibodies, such as ocrelizumab and ofatumumab, which target CD20, and inebilizumab, which targets CD19, for the treatment of various neuroimmunological diseases reflects progress in the understanding and management of B-cell activity. However, the limitations of these therapies in halting disease progression or activity in patients with multiple sclerosis or neuromyelitis optica spectrum disorders have prompted the exploration of cell-based therapies, particularly chimeric antigen receptor (CAR) T cells. Initially successful in the treatment of B cell-derived malignancies, CAR T cells offer a novel therapeutic mechanism by directly targeting and eliminating B cells, potentially overcoming the shortcomings of antibody-mediated B cell depletion. WHERE NEXT?: The use of CAR T cells in autoimmune diseases and B cell-driven neuroimmunological diseases shows promise as a targeted and durable option. CAR T cells act autonomously, penetrating deep tissue and effectively depleting B cells, especially in the CNS. Although the therapeutic potential of CAR T cells is substantial, their application faces hurdles such as complex logistics and management of therapy-associated toxic effects. Ongoing and upcoming clinical trials will be crucial in determining the safety, efficacy, and applicability of CAR T cells. As research progresses, CAR T cell therapy has the potential to transform treatment for patients with neuroimmunological diseases. It could offer extended periods of remission and a new standard in the management of autoimmune and neuroimmunological disorders.

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.

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.

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.

The Plasticity of Immune Cell Response Complicates Dissecting the Underlying Pathology of Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative autoimmune disease characterized by the destruction of the myelin sheath of the neuronal axon in the central nervous system. Many risk factors, including environmental, epigenetic, genetic, and lifestyle factors, are responsible for the development of MS. It has long been thought that only adaptive immune cells, especially autoreactive T cells, are responsible for the pathophysiology; however, recent evidence has indicated that innate immune cells are also highly involved in disease initiation and progression. Here, we compile the available data regarding the role immune cells play in MS, drawn from both human and animal research. While T and B lymphocytes, chiefly enhance MS pathology, regulatory T cells (Tregs) may serve a more protective role, as can B cells, depending on context and location. Cells chiefly involved in innate immunity, including macrophages, microglia, astrocytes, dendritic cells, natural killer (NK) cells, eosinophils, and mast cells, play varied roles. In addition, there is evidence regarding the involvement of innate-like immune cells, such as γδ T cells, NKT cells, MAIT cells, and innate-like B cells as crucial contributors to MS pathophysiology. It is unclear which of these cell subsets are involved in the onset or progression of disease or in protective mechanisms due to their plastic nature, which can change their properties and functions depending on microenvironmental exposure and the response of neural networks in damage control. This highlights the need for a multipronged approach, combining stringently designed clinical data with carefully controlled in vitro and in vivo research findings, to identify the underlying mechanisms so that more effective therapeutics can be developed.

Promises of Lipid-Based Nanocarriers for Delivery of Dimethyl Fumarate to Multiple Sclerosis Brain

Multiple sclerosis (MS) is a neurodegenerative autoimmune disorder of the central nervous system (CNS) infecting 2.5 million people worldwide. It is the most common nontraumatic neurological impairment in young adults. The blood-brain barrier rupture for multiple sclerosis pathogenesis has two effects: first, during the onset of the immunological attack, and second, for the CNS self-sustained "inside-out" demyelination and neurodegeneration processes. In addition to genetic variations, environmental and lifestyle variables can also significantly increase the risk of developing MS. Dimethyl fumarate (DMF) and sphingosine-1-phosphate (S1P) receptor modulators that may pass the blood-brain barrier and have positive direct effects in the CNS with quite diverse mechanisms of action raise the possibility that a combination therapy could be successful in treating MS. Lipid nanocarriers are recognized as one of the best drug delivery techniques to the brain for effective brain delivery. Numerous scientific studies have shown that lipid nanoparticles can enhance the lipid solubility, oral bioavailability, and brain availability of the drugs. Nanolipidic carriers for DMF delivery could be derived through vitamin D, tocopherol acetate, stearic acid, quercetin, cell-mimicking platelet-based, and chitosan-alginate core-shell-corona-shaped nanoparticles. Clinical and laboratory diagnosis of MS can be performed mainly through magnetic resonance imaging. The advancements in nanotechnology have enabled the clinicians to cross the blood-brain barrier and to target the brain and central nervous system of the patient with multiple sclerosis.

The murine meninges acquire lymphoid tissue properties and harbour autoreactive B cells during chronic Trypanosoma brucei infection

The meningeal space is a critical brain structure providing immunosurveillance for the central nervous system (CNS), but the impact of infections on the meningeal immune landscape is far from being fully understood. The extracellular protozoan parasite Trypanosoma brucei, which causes human African trypanosomiasis (HAT) or sleeping sickness, accumulates in the meningeal spaces, ultimately inducing severe meningitis and resulting in death if left untreated. Thus, sleeping sickness represents an attractive model to study immunological dynamics in the meninges during infection. Here, by combining single-cell transcriptomics and mass cytometry by time-of-flight (CyTOF) with in vivo interventions, we found that chronic T. brucei infection triggers the development of ectopic lymphoid aggregates (ELAs) in the murine meninges. These infection-induced ELAs were defined by the presence of ER-TR7+ fibroblastic reticular cells, CD21/35+ follicular dendritic cells (FDCs), CXCR5+ PD1+ T follicular helper-like phenotype, GL7+ CD95+ GC-like B cells, and plasmablasts/plasma cells. Furthermore, the B cells found in the infected meninges produced high-affinity autoantibodies able to recognise mouse brain antigens, in a process dependent on LTβ signalling. A mid-throughput screening identified several host factors recognised by these autoantibodies, including myelin basic protein (MBP), coinciding with cortical demyelination and brain pathology. In humans, we identified the presence of autoreactive IgG antibodies in the cerebrospinal fluid (CSF) of second stage HAT patients that recognised human brain lysates and MBP, consistent with our findings in experimental infections. Lastly, we found that the pathological B cell responses we observed in the meninges required the presence of T. brucei in the CNS, as suramin treatment before the onset of the CNS stage prevented the accumulation of GL7+ CD95+ GC-like B cells and brain-specific autoantibody deposition. Taken together, our data provide evidence that the meningeal immune response during chronic T. brucei infection results in the acquisition of lymphoid tissue-like properties, broadening our understanding of meningeal immunity in the context of chronic infections. These findings have wider implications for understanding the mechanisms underlying the formation ELAs during chronic inflammation resulting in autoimmunity in mice and humans, as observed in other autoimmune neurodegenerative disorders, including neuropsychiatric lupus and multiple sclerosis.

Defining progression independent of relapse activity (PIRA) in adult patients with relapsing multiple sclerosis: A systematic review✰

BACKGROUND

Progression Independent of Relapse Activity (PIRA) is heterogeneously described in patients with multiple sclerosis (MS) regarding the frequency and nature of PIRA. This systematic review was conducted to characterise and define the elements of PIRA.

METHOD

This systematic review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A systematic search was conducted of the databases Embase, Medline, Cochrane Central Register of Controlled Trials, Scopus, Web of Science, ClinicalTrials.gov and Google Scholar.

RESULTS

5,812 studies were identified by the initial search. 13 studies satisfied the inclusion criteria and were included in the systematic review. PIRA definitions varied considerably between studies. In the context of these variable definitions, along with other methodological differences relating to disease modifying therapy (DMT) use and follow-up duration, the reported proportion of patients experiencing PIRA varied from 4% to 24%.

CONCLUSIONS

The currently available research supports the presence of PIRA in relapsing MS. Based on review of the existing literature, we propose a definition of PIRA that is clinically relevant and minimises confounding from inclusion of patients who have reached the secondary progressive phase of the disease.

Alterations of Oligodendrocyte and Myelin Energy Metabolism in Multiple Sclerosis

Multiple sclerosis (MS) is a complex autoimmune disease of the central nervous system (CNS), characterized by demyelination and neurodegeneration. Oligodendrocytes play a vital role in maintaining the integrity of myelin, the protective sheath around nerve fibres essential for efficient signal transmission. However, in MS, oligodendrocytes become dysfunctional, leading to myelin damage and axonal degeneration. Emerging evidence suggests that metabolic changes, including mitochondrial dysfunction and alterations in glucose and lipid metabolism, contribute significantly to the pathogenesis of MS. Mitochondrial dysfunction is observed in both immune cells and oligodendrocytes within the CNS of MS patients. Impaired mitochondrial function leads to energy deficits, affecting crucial processes such as impulse transmission and axonal transport, ultimately contributing to neurodegeneration. Moreover, mitochondrial dysfunction is linked to the generation of reactive oxygen species (ROS), exacerbating myelin damage and inflammation. Altered glucose metabolism affects the energy supply required for oligodendrocyte function and myelin synthesis. Dysregulated lipid metabolism results in changes to the composition of myelin, affecting its stability and integrity. Importantly, low levels of polyunsaturated fatty acids in MS are associated with upregulated lipid metabolism and enhanced glucose catabolism. Understanding the intricate relationship between these mechanisms is crucial for developing targeted therapies to preserve myelin and promote neurological recovery in individuals with MS. Addressing these metabolic aspects may offer new insights into potential therapeutic strategies to halt disease progression and improve the quality of life for MS patients.

Bruton's tyrosine kinase inhibition reduces disease severity in a model of secondary progressive autoimmune demyelination

Bruton's tyrosine kinase (BTK) is an emerging target in multiple sclerosis (MS). Alongside its role in B cell receptor signaling and B cell development, BTK regulates myeloid cell activation and inflammatory responses. Here we demonstrate efficacy of BTK inhibition in a model of secondary progressive autoimmune demyelination in Biozzi mice with experimental autoimmune encephalomyelitis (EAE). We show that late in the course of disease, EAE severity could not be reduced with a potent relapse inhibitor, FTY720 (fingolimod), indicating that disease was relapse-independent. During this same phase of disease, treatment with a BTK inhibitor reduced both EAE severity and demyelination compared to vehicle treatment. Compared to vehicle treatment, late therapeutic BTK inhibition resulted in fewer spinal cord-infiltrating myeloid cells, with lower expression of CD86, pro-IL-1β, CD206, and Iba1, and higher expression of Arg1, in both tissue-resident and infiltrating myeloid cells, suggesting a less inflammatory myeloid cell milieu. These changes were accompanied by decreased spinal cord axonal damage. We show similar efficacy with two small molecule inhibitors, including a novel, highly selective, central nervous system-penetrant BTK inhibitor, GB7208. These results suggest that through lymphoid and myeloid cell regulation, BTK inhibition reduced neurodegeneration and disease progression during secondary progressive EAE.

Alzheimer's disease and multiple sclerosis: a possible connection through the viral demyelinating neurodegenerative trigger (vDENT)

Alzheimer's disease (AD) and multiple sclerosis (MS) are two CNS disorders affecting millions of people, for which no cure is available. AD is usually diagnosed in individuals age 65 and older and manifests with accumulation of beta amyloid in the brain. MS, a demyelinating disorder, is most commonly diagnosed in its relapsing-remitting (RRMS) form in young adults (age 20-40). The lack of success in a number of recent clinical trials of immune- or amyloid-targeting therapeutics emphasizes our incomplete understanding of their etiology and pathogenesis. Evidence is accumulating that infectious agents such as viruses may contribute either directly or indirectly. With the emerging recognition that demyelination plays a role in risk and progression of AD, we propose that MS and AD are connected by sharing a common environmental factor (a viral infection such as HSV-1) and pathology (demyelination). In the viral DEmyelinating Neurodegenerative Trigger (vDENT) model of AD and MS, the initial demyelinating viral (e.g., HSV-1) infection provokes the first episode of demyelination that occurs early in life, with subsequent virus reactivations/demyelination and associated immune/inflammatory attacks resulting in RRMS. The accumulating damage and/or virus progression deeper into CNS leads to amyloid dysfunction, which, combined with the inherent age-related defects in remyelination, propensity for autoimmunity, and increased blood-brain barrier permeability, leads to the development of AD dementia later in life. Preventing or diminishing vDENT event(s) early in life, thus, may have a dual benefit of slowing down the progression of MS and reducing incidence of AD at an older age.