Osteopontin associates with brain T(RM)-cell transcriptome and compartmentalization in donors with and without multiple sclerosis

[XVI Post-ECTRIMS Meeting: review of the new developments presented at the 2023 ECTRIMS Congress (I)]

The XVI Post-ECTRIMS meeting took place in Seville on 20 and 21 October 2023. This meeting was attended by neurologists specialising in multiple sclerosis (MS) from Spain, who shared a summary of the most interesting innovations at the ECTRIMS congress, which had taken place in Milan the previous week. The aim of this article is to summarise new developments related to the pathogenesis, diagnosis and prognosis of MS. The contributions of innate immunity and central nervous system resident cells, including macrophages and microglia in MS pathophysiology and as therapeutic targets were discussed. Compartmentalised intrathecal inflammation was recognised as central to understanding the progression of MS, and the relationship between inflammatory infiltrates and disease progression was highlighted. Perspectives in demyelinating pathologies were reviewed, focusing on neuromyelitis optica and myelin oligodendrocyte glycoprotein antibody-associated disease, highlighting their pathophysiological and diagnostic differences compared to MS. Advances in neuroimaging were also discussed, and especially the analysis of active chronic lesions, such as paramagnetic rim lesions. In the absence of clinical improvements in trials of remyelinating treatments, methodological strategies to optimise the design of future studies were proposed. Breakthroughs in detecting the prodromal phase of MS, the use of biomarkers in body fluids to assess activity, progression and treatment response, and research on progression independent of flares were addressed. The need to define criteria for radiologically isolated syndrome and to clarify the concept was also discussed.

Profiling of microglia nodules in multiple sclerosis reveals propensity for lesion formation

Microglia nodules (HLA-DR+ cell clusters) are associated with brain pathology. In this post-mortem study, we investigated whether they represent the first stage of multiple sclerosis (MS) lesion formation. We show that microglia nodules are associated with more severe MS pathology. Compared to microglia nodules in stroke, those in MS show enhanced expression of genes previously found upregulated in MS lesions. Furthermore, genes associated with lipid metabolism, presence of T and B cells, production of immunoglobulins and cytokines, activation of the complement cascade, and metabolic stress are upregulated in microglia nodules in MS. Compared to stroke, they more frequently phagocytose oxidized phospholipids and possess a more tubular mitochondrial network. Strikingly, in MS, some microglia nodules encapsulate partially demyelinated axons. Taken together, we propose that activation of microglia nodules in MS by cytokines and immunoglobulins, together with phagocytosis of oxidized phospholipids, may lead to a microglia phenotype prone to MS lesion formation.

Differential Runx3, Eomes, and T-bet expression subdivides MS-associated CD4+ T cells with brain-homing capacity

Multiple sclerosis (MS) is a common and devastating chronic inflammatory disease of the CNS. CD4+ T cells are assumed to be the first to cross the blood-central nervous system (CNS) barrier and trigger local inflammation. Here, we explored how pathogenicity-associated effector programs define CD4+ T cell subsets with brain-homing ability in MS. Runx3- and Eomes-, but not T-bet-expressing CD4+ memory cells were diminished in the blood of MS patients. This decline reversed following natalizumab treatment and was supported by a Runx3+ Eomes+ T-bet- enrichment in cerebrospinal fluid samples of treatment-naïve MS patients. This transcription factor profile was associated with high granzyme K (GZMK) and CCR5 levels and was most prominent in Th17.1 cells (CCR6+ CXCR3+ CCR4-/dim ). Previously published CD28- CD4 T cells were characterized by a Runx3+ Eomes- T-bet+ phenotype that coincided with intermediate CCR5 and a higher granzyme B (GZMB) and perforin expression, indicating the presence of two separate subsets. Under steady-state conditions, granzyme Khigh Th17.1 cells spontaneously passed the blood-brain barrier in vitro. This was only found for other subsets including CD28- cells when using inflamed barriers. Altogether, CD4+ T cells contain small fractions with separate pathogenic features, of which Th17.1 seems to breach the blood-brain barrier as a possible early event in MS.

Ocrelizumab associates with reduced cerebrospinal fluid B and CD20dim CD4+ T cells in primary progressive multiple sclerosis

The anti-CD20 monoclonal antibody ocrelizumab reduces disability progression in primary progressive multiple sclerosis. CD20 is a prototypical B-cell marker; however, subpopulations of CD4+ and CD8+ T cells in peripheral blood and cerebrospinal fluid also express low levels of CD20 (CD20dim). Therefore, direct targeting and depletion of these CD20dim T-cell subpopulations may contribute to the therapeutic effect of ocrelizumab. The aim of this observational cohort study was to compare CD20+ B-cell and CD20dim T-cell distributions between peripheral blood and cerebrospinal fluid of ocrelizumab-treated or ocrelizumab-untreated people with primary progressive multiple sclerosis. Ocrelizumab treatment was associated with depletion of circulating B cells and CD20dim CD4+ and CD20dim CD8+ T cells (P < 0.0001, P = 0.0016 and P = 0.0008, respectively) but, in cerebrospinal fluid, only with lower proportions of B cells and CD20dim memory CD4+ T cells (P < 0.0001 and P = 0.0043, respectively). The proportional prevalence of cerebrospinal fluid CD20dim memory CD8+ T cells was not significantly reduced (P = 0.1333). Only in cerebrospinal fluid, the proportions of CD20dim cells within CD4+ and not CD8+ T cells positive for CCR5, CCR6 and CXCR3 were reduced in ocrelizumab-treated participants. The proportion of CD20dim CD4+ T cells and abundance of CD4+ relative to CD8+ T cells in cerebrospinal fluid correlated positively with age (R = 0.6799, P = 0.0150) and Age-Related Multiple Sclerosis Severity score (R = 0.8087, P = 0.0014), respectively. We conclude that, in contrast to cerebrospinal fluid CD20dim CD8+ T cells, B cells and CD20dim CD4+ T cells are reduced in cerebrospinal fluid of people with primary progressive multiple sclerosis with an ocrelizumab-associated depletion of circulating B cells and CD20dim T cells. Therefore, these cells are likely to contribute to the therapeutic effects of ocrelizumab in people with primary progressive multiple sclerosis.

The immunopathogenesis of narcolepsy type 1

Narcolepsy type 1 (NT1) is a chronic sleep disorder resulting from the loss of a small population of hypothalamic neurons that produce wake-promoting hypocretin (HCRT; also known as orexin) peptides. An immune-mediated pathology for NT1 has long been suspected given its exceptionally tight association with the MHC class II allele HLA-DQB1*06:02, as well as recent genetic evidence showing associations with polymorphisms of T cell receptor genes and other immune-relevant loci and the increased incidence of NT1 that has been observed after vaccination with the influenza vaccine Pandemrix. The search for both self-antigens and foreign antigens recognized by the pathogenic T cell response in NT1 is ongoing. Increased T cell reactivity against HCRT has been consistently reported in patients with NT1, but data demonstrating a primary role for T cells in neuronal destruction are currently lacking. Animal models are providing clues regarding the roles of autoreactive CD4+ and CD8+ T cells in the disease. Elucidation of the pathogenesis of NT1 will allow for the development of targeted immunotherapies at disease onset and could serve as a model for other immune-mediated neurological diseases.

Resident Memory-like CD8+ T Cells Are Involved in Chronic Inflammatory and Neurodegenerative Diseases in the CNS

BACKGROUND AND OBJECTIVES

Resident memory T (Trm) cells are a unique population that can survive and function in a compartmentalized tissue with inflammatory potential. We aim to investigate the alteration of Trm population in acute/chronic inflammatory and neurodegenerative diseases in the CNS.

METHODS

The frequencies of CD4+ and CD8+ T cells expressing both CD69 and CD103, the markers for Trm cells, were quantified in the peripheral blood and CSF (n = 80 and 44, respectively) in a cross-sectional manner. The transcriptional profile of Trm-like population in the CSF was further analyzed using a public single-cell dataset.

RESULTS

The frequency of CD69+CD103+CD8+ T cells was strikingly higher in the CSF than in the peripheral blood (among memory fraction, 13.5% vs 0.11%, difference (mean [SE]): 13.4% [2.9]). This CD69+CD103+CD8+ T-cell population was increased in the CSF from patients with chronic inflammatory diseases including multiple sclerosis and with neurodegenerative diseases such as Parkinson disease and Alzheimer disease compared with controls (11.5%, 13.0%, 8.1% vs 2.9%, respectively). By contrast, the frequency was not altered in acute inflammatory conditions in the CNS (4.0%). Single-cell RNAseq analysis confirmed Trm signature in CD69+CD103+CD8+ T cells in the CSF, supporting their Trm-like phenotype, which was not clear in controls.

DISCUSSION

Collectively, an increase in CD69+CD103+CD8+ Trm-like population in the CSF is related with both chronic neuroinflammatory and some neurodegenerative diseases in the CNS, suggesting a partially shared pathology in these diseases.

The adhesion G protein-coupled receptor GPR56/ADGRG1 in cytotoxic lymphocytes

GPR56/ADGRG1 is an adhesion G protein-coupled receptor connected to brain development, haematopoiesis, male fertility, and tumorigenesis. Nevertheless, expression of GPR56 is not restricted to developmental processes. Studies over the last years have demonstrated a marked presence of GPR56 in human cytotoxic NK and T cells. Expression of GPR56 in these cells is driven by the transcription factor HOBIT, corresponds with the production of cytolytic mediators and the presence of CX3 CR1 and CD57, indicates a state of terminal differentiation and cellular exhaustion, and disappears upon cellular activation. Functional studies indicate that GPR56 regulates cell migration and effector functions and thereby acts as an inhibitory immune checkpoint. We here discuss the current state of knowledge regarding GPR56 in cytotoxic lymphocytes.

A Dual Role of Osteopontin in Modifying B Cell Responses

The occurrence of B cell aggregates within the central nervous system (CNS) has prompted the investigation of the potential sources of pathogenic B cell and T cell responses in a subgroup of secondary progressive multiple sclerosis (MS) patients. Nevertheless, the expression profile of molecules associated with these aggregates and their role in aggregate development and persistence is poorly described. Here, we focused on the expression pattern of osteopontin (OPN), which is a well-described cytokine, in MS brain tissue. Autopsied brain sections from MS cases with and without B cell pathology were screened for the presence of CD20⁺ B cell aggregates and co-expression of OPN. To demonstrate the effect of OPN on B cells, flow cytometry, ELISA and in vitro aggregation assays were conducted using the peripheral blood of healthy volunteers. Although OPN was expressed in MS brain tissue independent of B cell pathology, it was also highly expressed within B cell aggregates. In vitro studies demonstrated that OPN downregulated the co-stimulatory molecules CD80 and CD86 on B cells. OPN-treated B cells produced significantly lower amounts of IL-6. However, OPN-treated B cells also exhibited a higher tendency to form homotypic cell aggregates in vitro. Taken together, our data indicate a conflicting role of OPN in modulating B cell responses.