Brain-resident regulatory T cells and their role in health and disease

Frontiers of Neurodegenerative Disease Treatment: Targeting Immune Cells in Brain Border Regions

Neurodegenerative diseases (NDs) demonstrate a complex interaction with the immune system, challenging the traditional view of the brain as an "immune-privileged" organ. Microglia were once considered the sole guardians of the brain's immune response. However, recent research has revealed the critical role of peripheral immune cells located in key brain regions like the meninges, choroid plexus, and perivascular spaces. These previously overlooked cells are now recognized as contributors to the development and progression of NDs. This newfound understanding opens doors for pioneering therapeutic strategies. By targeting these peripheral immune cells, we may be able to modulate the brain's immune environment, offering an alternative approach to treat NDs and circumvent the challenges posed by the blood-brain barrier. This comprehensive review will scrutinize the latest findings on the complex interactions between these peripheral immune cells and NDs. It will also critically assess the prospects of targeting these cells as a ground-breaking therapeutic avenue for these debilitating disorders.

Immune mechanisms and shared immune targets in neurodegenerative diseases

The immune system plays a major part in neurodegenerative diseases. In some, such as multiple sclerosis, it is the primary driver of the disease. In others, such as Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, it has an amplifying role. Immunotherapeutic approaches that target the adaptive and innate immune systems are being explored for the treatment of almost all neurological diseases, and the targets and approaches are often common across diseases. Microglia are the primary immune cells in the brain that contribute to disease pathogenesis, and are consequently a common immune target for therapy. Other therapeutic approaches target components of the peripheral immune system, such as regulatory T cells and monocytes, which in turn act within the CNS. This Review considers in detail how microglia, monocytes and T cells contribute to the pathogenesis of multiple sclerosis, Alzheimer disease, amyotrophic lateral sclerosis and Parkinson disease, and their potential as shared therapeutic targets across these diseases. The microbiome is also highlighted as an emerging therapeutic target that indirectly modulates the immune system. Therapeutic approaches being developed to target immune function in neurodegenerative diseases are discussed, highlighting how immune-based approaches developed to treat one disease could be applicable to multiple other neurological diseases.

[Immunological foundations of neurological diseases]

BACKGROUND

Neurodegenerative diseases represent an increasing challenge in ageing societies, as only limited treatment options are currently available.

OBJECTIVE

New research methods and interdisciplinary interaction of different disciplines have changed the way neurological disorders are viewed and paved the way for the comparatively new field of neuroimmunology, which was established in the early 1980s. Starting from neurological autoimmune diseases, such as multiple sclerosis, knowledge about the involvement of immunological processes in other contexts, such as stroke or traumatic brain injury, has been significantly expanded in recent years.

MATERIAL AND METHODS

This review article provides an overview of the role of the immune system and the resulting potential for novel treatment approaches.

RESULTS

The immune system plays a central role in fighting infections but is also able to react to the body's own signals under sterile conditions and cause inflammation and subsequent adaptive immune responses through the release of immune mediators and the recruitment and differentiation of certain immune cell types. This can be beneficial in initiating healing processes; however, chronic inflammatory conditions usually have destructive consequences for the tissue and the organism and must be interrupted.

CONCLUSION

It is now known that different cells of the immune system play an important role in neurological diseases. Regulatory mechanisms, which are mediated by regulatory T cells or Th2 cells, are usually associated with a good prognosis, whereas inflammatory processes and polarization towards Th1 or Th17 have a destructive character. Novel immunomodulators, which are also increasingly being used in cancer treatment, can now be used in a tissue-specific manner and therefore offer great potential for use in neurological diseases.

Expanding Role of Interleukin-1 Family Cytokines in Acute Ischemic Stroke

Ischemic stroke (IS) is a critical medical condition that results in significant neurological deficits and tissue damage, affecting millions worldwide. Currently, there is a significant lack of reliable tools for assessing and predicting IS outcomes. The inflammatory response following IS may exacerbate tissue injury or provide neuroprotection. This review sought to summarize current knowledge on the IL-1 family's involvement in IS, which includes pro-inflammatory molecules, such as IL-1α, IL-1β, IL-18, and IL-36, as well as anti-inflammatory molecules, like IL-1Ra, IL-33, IL-36A, IL-37, and IL-38. The balance between these opposing inflammatory processes may serve as a biomarker for determining patient outcomes and recovery paths. Treatments targeting these cytokines or their receptors show promise, but more comprehensive research is essential to clarify their precise roles in IS development and progression.

Proteogenomic signature of risk of Alzheimer's disease and related dementia risk in individuals with a history of major depression disorder

The mechanisms linking a history of major depressive disorder (MDD) to an increased risk of Alzheimer's disease and related dementia (ADRD) are not fully understood. Using the UK Biobank available proteomic and genomic data, we evaluated the biological mechanisms linking both conditions. In participants with a history of MDD at baseline (n=3,615), we found that plasma levels of NfL, GFAP, PSG1 were associated with higher risk (HR=1.38; 1.37; 1.34, respectively; all adjusted p-values<0.05), while VGF, GET3, and HPGDS were associated with lower risk of incident ADRD (n=150) (HR=0.73; 0.71; 0.66, respectively; all adjusted p-values<0.05) during a mean follow-up of 13.7 years (SD=2.2). Two-sample Mendelian randomization analysis using cis-pQTLs genetic instruments revealed that a lower protein expression of apolipoprotein E and higher IL-10 receptor subunit B were causally linked to incident ADRD. Finally, we developed a Proteomic Risk Score (PrRSMDD-ADRD), which showed strong discriminative power (C-statistic = 0.84) to identify participants with MDD that developed ADRD upon follow-up. In addition to demonstrating an association between plasma proteins associated with inflammation and future ADRD risk in individuals with MDD, our findings include an element of causality using Mendelian Randomization (MR) and PrRSMDD-ADRD can be useful to identify individuals with the highest risk to develop ADRD in a highly vulnerable population.

Candesartan restores blood-brain barrier dysfunction, mitigates aberrant gene expression, and extends lifespan in a knockin mouse model of epileptogenesis

Blockade of Angiotensin type 1 receptor (AT1R) has potential therapeutic utility in the treatment of numerous detrimental consequences of epileptogenesis, including oxidative stress, neuroinflammation, and blood-brain barrier (BBB) dysfunction. We have recently shown that many of these pathological processes play a critical role in seizure onset and propagation in the Scn8a-N1768D mouse model. Here we investigate the efficacy and potential mechanism(s) of action of candesartan (CND), an FDA-approved angiotensin receptor blocker (ARB) indicated for hypertension, in improving outcomes in this model of pediatric epilepsy. We compared length of lifespan, seizure frequency, and BBB permeability in juvenile (D/D) and adult (D/+) mice treated with CND at times after seizure onset. We performed RNAseq on hippocampal tissue to quantify differences in genome-wide patterns of transcript abundance and inferred beneficial and detrimental effects of canonical pathways identified by enrichment methods in untreated and treated mice. Our results demonstrate that treatment with CND gives rise to increased survival, longer periods of seizure freedom, and diminished BBB permeability. CND treatment also partially reversed or 'normalized' disease-induced genome-wide gene expression profiles associated with inhibition of NF-κB, TNFα, IL-6, and TGF-β signaling in juvenile and adult mice. Pathway analyses reveal that efficacy of CND is due to its known dual mechanism of action as both an AT1R antagonist and a PPARγ agonist. The robust effectiveness of CND across ages, sexes and mouse strains is a positive indication for its translation to humans and its suitability of use for clinical trials in children with SCN8A epilepsy.

Systemic inflammation following traumatic injury and its impact on neuroinflammatory gene expression in the rodent brain

BACKGROUND

Trauma can result in systemic inflammation that leads to organ dysfunction, but the impact on the brain, particularly following extracranial insults, has been largely overlooked.

METHODS

Building upon our prior findings, we aimed to understand the impact of systemic inflammation on neuroinflammatory gene transcripts in eight brain regions in rats exposed to (1) blast overpressure exposure [BOP], (2) cutaneous thermal injury [BU], (3) complex extremity injury, 3 hours (h) of tourniquet-induced ischemia, and hind limb amputation [CEI+tI+HLA], (4) BOP+BU or (5) BOP+CEI and delayed HLA [BOP+CEI+dHLA] at 6, 24, and 168 h post-injury (hpi).

RESULTS

Globally, the number and magnitude of differentially expressed genes (DEGs) correlated with injury severity, systemic inflammation markers, and end-organ damage, driven by several chemokines/cytokines (Csf3, Cxcr2, Il16, and Tgfb2), neurosteroids/prostaglandins (Cyp19a1, Ptger2, and Ptger3), and markers of neurodegeneration (Gfap, Grin2b, and Homer1). Regional neuroinflammatory activity was least impacted following BOP. Non-blast trauma (in the BU and CEI+tI+HLA groups) contributed to an earlier, robust and diverse neuroinflammatory response across brain regions (up to 2-50-fold greater than that in the BOP group), while combined trauma (in the BOP+CEI+dHLA group) significantly advanced neuroinflammation in all regions except for the cerebellum. In contrast, BOP+BU resulted in differential activity of several critical neuroinflammatory-neurodegenerative markers compared to BU. t-SNE plots of DEGs demonstrated that the onset, extent, and duration of the inflammatory response are brain region dependent. Regardless of injury type, the thalamus and hypothalamus, which are critical for maintaining homeostasis, had the most DEGs. Our results indicate that neuroinflammation in all groups progressively increased or remained at peak levels over the study duration, while markers of end-organ dysfunction decreased or otherwise resolved.

CONCLUSIONS

Collectively, these findings emphasize the brain's sensitivity to mediators of systemic inflammation and provide an example of immune-brain crosstalk. Follow-on molecular and behavioral investigations are warranted to understand the short- to long-term pathophysiological consequences on the brain, particularly the mechanism of blood-brain barrier breakdown, immune cell penetration-activation, and microglial activation.

Regulatory T cells as a possible new target in epilepsy?

Epilepsy is a complex chronic brain disorder with diverse clinical features that can be caused by various triggering events, such as infections, head trauma, or stroke. During epileptogenesis, various abnormalities are observed, such as altered cellular homeostasis, imbalance of neurotransmitters, tissue changes, and the release of inflammatory mediators, which in combination lead to spontaneous recurrent seizures. Regulatory T cells (Tregs), a subtype of CD4+Foxp3+ T cells, best known for their key function in immune suppression, also seem to play a role in attenuating neurodegeneration and suppressing pathological inflammation in several brain disease states. Considering that epilepsy is also highly associated with neuronal damage and neuroinflammation, modulation of Tregs may be an interesting way to modify the disease course of epilepsy and needs further investigation. In this review, we will describe the currently available information on Tregs in epilepsy.

T-cells and CD45-cells discovery in the central nervous system of healthy and nodavirus-infected teleost fish Dicentrarchus labrax

To achieve insights in antiviral immune defense of the central nervous system (CNS), we investigated T cells and CD45 cells in the marine fish model Dicentrarchus labrax infected with the CNS-tropic virus betanodavirus. By employing markers for pan-T cells (mAb DLT15) and CD45-cells (mAb DLT22) in immunofluorescence (IIF) of leukocytes from brain, we obtained 3,7 ± 2.3 % of T cells and 7.3 ± 3.2 % of CD45+ cells. Both IIF and immunoelectron microscopy confirmed a leukocyte/glial morphology for the immunoreactive cells. Quantitative immunohistochemistry (qIHC) of brain/eye sections showed 1.9 ± 0.8 % of T+ cells and 2 ± 0.9 % of CD45+ cells in the brain, and 3.6 ± 1.9 % and 4.1 ± 2.2 % in the eye, respectively. After in vivo RGNNV infection the number of T cells/CD45+ leukocytes in the brain increased to 8.3 ± 2.1 % and 11.6 ± 4.4 % (by IIF), and 26.1 ± 3.4 % and 45.6 ± 5.9 % (by qIHC), respectively. In the eye we counted after infection 8.5 ± 4.4 % of T cells and 10.2 ± 5.8 % of CD45 cells. Gene transcription analysis of brain mRNA revealed a strong increase of gene transcripts coding for: antiviral proteins Mx and ISG-12; T-cell related CD3ε/δ, TcRβ, CD4, CD8α, CD45; and for immuno-modulatory cytokines TNFα, IL-2, IL-10. A RAG-1 gene product was also present and upregulated, suggesting somatic recombination in the fish brain. Similar transcription data were obtained in the eye, albeit with differences. Our findings provide first evidence for a recruitment and involvement of T cells and CD45+ leukocytes in the fish eye-brain axis during antiviral responses and suggest similarities in the CNS immune defense across evolutionary distant vertebrates.

Regulatory T cells in the context: deciphering the dynamic interplay with the tissue environment

The delicate balance between protective immunity against pathogens and the prevention of autoimmunity requires finely tuned generation and function of regulatory CD4+ T (Treg) cells. Here, we review recent progress in the understanding of a complex set of cues, which converge on Treg cells in lymphoid and nonlymphoid organs and in tumors and how these cues modulate Treg functions. We highlight the versatility of Treg cells underlying their ability to dynamically adapt to local microenvironments and perform a wide range of functions that extend beyond the archetypal role of Treg cells in moderating adverse effects of immune response-associated inflammation and in suppressing autoimmunity.

Intersecting Pathways: The Role of Metabolic Dysregulation, Gastrointestinal Microbiome, and Inflammation in Acute Ischemic Stroke Pathogenesis and Outcomes

Acute ischemic stroke (AIS) remains a major cause of mortality and long-term disability worldwide, driven by complex and multifaceted etiological factors. Metabolic dysregulation, gastrointestinal microbiome alterations, and systemic inflammation are emerging as significant contributors to AIS pathogenesis. This review addresses the critical need to understand how these factors interact to influence AIS risk and outcomes. We aim to elucidate the roles of dysregulated adipokines in obesity, the impact of gut microbiota disruptions, and the neuroinflammatory cascade initiated by lipopolysaccharides (LPS) in AIS. Dysregulated adipokines in obesity exacerbate inflammatory responses, increasing AIS risk and severity. Disruptions in the gut microbiota and subsequent LPS-induced neuroinflammation further link systemic inflammation to AIS. Advances in neuroimaging and biomarker development have improved diagnostic precision. Here, we highlight the need for a multifaceted approach to AIS management, integrating metabolic, microbiota, and inflammatory insights. Potential therapeutic strategies targeting these pathways could significantly improve AIS prevention and treatment. Future research should focus on further elucidating these pathways and developing targeted interventions to mitigate the impacts of metabolic dysregulation, microbiome imbalances, and inflammation on AIS.

Reconstitution of human microglia and resident T cells in the brain of humanized DRAGA mice

Humanized mouse models are valuable tools for investigating the human immune system in response to infection and injury. We have previously described the human immune system (HIS)-DRAGA mice (HLA-A2.HLA-DR4.Rag1KO.IL-2RgKO.NOD) generated by infusion of Human Leukocyte Antigen (HLA)-matched, human hematopoietic stem cells from umbilical cord blood. By reconstituting human cells, the HIS-DRAGA mouse model has been utilized as a "surrogate in vivo human model" for infectious diseases such as Human Immunodeficiency Virus (HIV), Influenza, Coronavirus Disease 2019 (COVID-19), scrub typhus, and malaria. This humanized mouse model bypasses ethical concerns about the use of fetal tissues for the humanization of laboratory animals. Here in, we demonstrate the presence of human microglia and T cells in the brain of HIS-DRAGA mice. Microglia are brain-resident macrophages that play pivotal roles against pathogens and cerebral damage, whereas the brain-resident T cells provide surveillance and defense against infections. Our findings suggest that the HIS-DRAGA mouse model offers unique advantages for studying the functions of human microglia and T cells in the brain during infections, degenerative disorders, tumors, and trauma, as well as for testing therapeutics in these pathological conditions.

Neuroinflammation in Alzheimer's disease: insights from peripheral immune cells

Alzheimer's disease (AD) is a serious brain disorder characterized by the presence of beta-amyloid plaques, tau pathology, inflammation, neurodegeneration, and cerebrovascular dysfunction. The presence of chronic neuroinflammation, breaches in the blood-brain barrier (BBB), and increased levels of inflammatory mediators are central to the pathogenesis of AD. These factors promote the penetration of immune cells into the brain, potentially exacerbating clinical symptoms and neuronal death in AD patients. While microglia, the resident immune cells of the central nervous system (CNS), play a crucial role in AD, recent evidence suggests the infiltration of cerebral vessels and parenchyma by peripheral immune cells, including neutrophils, T lymphocytes, B lymphocytes, NK cells, and monocytes in AD. These cells participate in the regulation of immunity and inflammation, which is expected to play a huge role in future immunotherapy. Given the crucial role of peripheral immune cells in AD, this article seeks to offer a comprehensive overview of their contributions to neuroinflammation in the disease. Understanding the role of these cells in the neuroinflammatory response is vital for developing new diagnostic markers and therapeutic targets to enhance the diagnosis and treatment of AD patients.

The immune cells in modulating osteoclast formation and bone metabolism

Osteoclasts are pivotal in regulating bone metabolism, with immune cells significantly influencing both physiological and pathological processes by modulating osteoclast functions. This is particularly evident in conditions of inflammatory bone resorption, such as rheumatoid arthritis and periodontitis. This review summarizes and comprehensively analyzes the research progress on the regulation of osteoclast formation by immune cells, aiming to unveil the underlying mechanisms and pathways through which diseases, such as rheumatoid arthritis and periodontitis, impact bone metabolism.

A Search for New Biological Pathways in Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy by Proteomic Research

Background/Objectives: Cerebral Autosomal Dominant Arteriopathy with Subcortical Infarcts and Leukoencephalopathy (CADASIL) is a hereditary small vessel disease leading to significant morbidity and mortality. Despite advances in genetic diagnosis, the underlying pathophysiology remains incompletely understood. Proteomic studies offer insights into disease mechanisms by identifying altered protein expression patterns. Here, we conducted a proteomic analysis to elucidate molecular pathways associated with CADASIL. Methods: We enrolled genetically diagnosed CADASIL patients and healthy, genetically related controls. Plasma samples were subjected to proteomic analysis using the Olink platform, measuring 552 proteins across six panels. The data were analyzed from several approaches by using three different statistical methods: Exploratory Principal Component Analysis (PCA) and Partial Least Squares-Discriminant Analysis (PLS-DA), differential expression with moderated t-test, and gene set enrichment analysis (GSEA). In addition, bioinformatics analysis, including volcano plot, heatmap, and Variable Importance on Projection (VIP) scores from the PLS-DA model were drawn. Results: Significant differences in protein expression were observed between CADASIL patients and controls. RSPO1 and FGF-19 exhibited elevated levels (p < 0.05), while PPY showed downregulation (p < 0.05) in CADASIL patients, suggesting their involvement in disease pathogenesis. Furthermore, MIC-A/B expression varied significantly between patients with mutations in exon 4 versus exon 11 of the NOTCH3 gene (p < 0.05), highlighting potential immunological mechanisms underlying CADASIL. We identified altered pathways using GSEA, applied after ranking the study data. Conclusions: Our study provides novel insights into the proteomic profile of CADASIL, identifying dysregulated proteins associated with vascular pathology, metabolic dysregulation, and immune activation. These findings contribute to a deeper understanding of CADASIL pathophysiology and may inform the development of targeted therapeutic strategies. Further research is warranted to validate these biomarkers and elucidate their functional roles in disease progression.

Non-Tumor Cells within the Tumor Microenvironment-The "Eminence Grise" of the Glioblastoma Pathogenesis and Potential Targets for Therapy

Glioblastoma (GBM) is the most common malignancy of the central nervous system in adults. GBM has high levels of therapy failure and its prognosis is usually dismal. The phenotypic heterogeneity of the tumor cells, dynamic complexity of non-tumor cell populations within the GBM tumor microenvironment (TME), and their bi-directional cross-talk contribute to the challenges of current therapeutic approaches. Herein, we discuss the etiology of GBM, and describe several major types of non-tumor cells within its TME, their impact on GBM pathogenesis, and molecular mechanisms of such an impact. We also discuss their value as potential therapeutic targets or prognostic biomarkers, with reference to the most recent works on this subject. We conclude that unless all "key player" populations of non-tumor cells within the TME are considered, no breakthrough in developing treatment for GBM can be achieved.

Microglia-Dependent Reversal of Depression-Like Behaviors in Chronically Stressed Mice by Administration of a Specific Immuno-stimulant β-Glucan

In recent years, the decline of microglia in the hippocampus has been shown to play a role in the development of depression, and its reversal shows marked antidepressant-like effects. β-glucan is a polysaccharide from Saccharomyces cerevisiae and has numerous beneficial effects on the nervous system, including improving axon regeneration and cognition. Considering its immuno-stimulatory activities in cultured microglia and brain tissues, we hypothesize that β-glucan may be a potential candidate to correct the functional deficiency of microglia and thereby alleviate depression-like behaviors in chronically stressed animals. An expected, our results showed that a single injection of β-glucan 5 h before behavioral tests at a dose of 10 or 20 mg/kg, but not at a dose of 5 mg/kg, reversed the depression-like behavior induced by chronic stress in mice in the tail suspension test, forced swimming test, and sucrose preference test. The effect of β-glucan (20 mg/kg) also showed time-dependent properties that were statistically significant 5 and 8, but not 3, hours after drug injection and persisted for at least 7 days. Fourteen days after β-glucan injection, no antidepressant-like effect was observed anymore. However, this effect was overcome by a second β-glucan injection (20 mg/kg) 14 days after the first β-glucan injection. Stimulation of microglia appeared to mediate the antidepressant-like effect of β-glucan, because both inhibition of microglia and their depletion prevented the antidepressant-like effect of β-glucan. Based on these effects of β-glucan, β-glucan administration could be developed as a new strategy for the treatment of depression.

Augmenting regulatory T cells: new therapeutic strategy for rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, systemic autoimmune condition marked by inflammation of the joints, degradation of the articular cartilage, and bone resorption. Recent studies found the absolute and relative decreases in circulating regulatory T cells (Tregs) in RA patients. Tregs are a unique type of cells exhibiting immunosuppressive functions, known for expressing the Foxp3 gene. They are instrumental in maintaining immunological tolerance and preventing autoimmunity. Increasing the absolute number and/or enhancing the function of Tregs are effective strategies for treating RA. This article reviews the studies on the mechanisms and targeted therapies related to Tregs in RA, with a view to provide better ideas for the treatment of RA.

Mitochondria-Related Candidate Genes and Diagnostic Model to Predict Late-Onset Alzheimer's Disease and Mild Cognitive Impairment

Background

Late-onset Alzheimer's disease (LOAD) is the most common type of dementia, but its pathogenesis remains unclear, and there is a lack of simple and convenient early diagnostic markers to predict the occurrence.

Objective

Our study aimed to identify diagnostic candidate genes to predict LOAD by machine learning methods.

Methods

Three publicly available datasets from the Gene Expression Omnibus (GEO) database containing peripheral blood gene expression data for LOAD, mild cognitive impairment (MCI), and controls (CN) were downloaded. Differential expression analysis, the least absolute shrinkage and selection operator (LASSO), and support vector machine recursive feature elimination (SVM-RFE) were used to identify LOAD diagnostic candidate genes. These candidate genes were then validated in the validation group and clinical samples, and a LOAD prediction model was established.

Results

LASSO and SVM-RFE analyses identified 3 mitochondria-related genes (MRGs) as candidate genes, including NDUFA1, NDUFS5, and NDUFB3. In the verification of 3 MRGs, the AUC values showed that NDUFA1, NDUFS5 had better predictability. We also verified the candidate MRGs in MCI groups, the AUC values showed good performance. We then used NDUFA1, NDUFS5 and age to build a LOAD diagnostic model and AUC was 0.723. Results of qRT-PCR experiments with clinical blood samples showed that the three candidate genes were expressed significantly lower in the LOAD and MCI groups when compared to CN.

Conclusion

Two mitochondrial-related candidate genes, NDUFA1 and NDUFS5, were identified as diagnostic markers for LOAD and MCI. Combining these two candidate genes with age, a LOAD diagnostic prediction model was successfully constructed.

Amyloid-β specific regulatory T cells attenuate Alzheimer's disease pathobiology in APP/PS1 mice

BACKGROUND

Regulatory T cells (Tregs) maintain immune tolerance. While Treg-mediated neuroprotective activities are now well-accepted, the lack of defined antigen specificity limits their therapeutic potential. This is notable for neurodegenerative diseases where cell access to injured brain regions is required for disease-specific therapeutic targeting and improved outcomes. To address this need, amyloid-beta (Aβ) antigen specificity was conferred to Treg responses by engineering the T cell receptor (TCR) specific for Aβ (TCRAβ). The TCRAb were developed from disease-specific T cell effector (Teff) clones. The ability of Tregs expressing a transgenic TCRAβ (TCRAβ -Tregs) to reduce Aβ burden, transform effector to regulatory cells, and reverse disease-associated neurotoxicity proved beneficial in an animal model of Alzheimer's disease.

METHODS

TCRAβ -Tregs were generated by CRISPR-Cas9 knockout of endogenous TCR and consequent incorporation of the transgenic TCRAb identified from Aβ reactive Teff monoclones. Antigen specificity was confirmed by MHC-Aβ-tetramer staining. Adoptive transfer of TCRAβ-Tregs to mice expressing a chimeric mouse-human amyloid precursor protein and a mutant human presenilin-1 followed measured behavior, immune, and immunohistochemical outcomes.

RESULTS

TCRAβ-Tregs expressed an Aβ-specific TCR. Adoptive transfer of TCRAβ-Tregs led to sustained immune suppression, reduced microglial reaction, and amyloid loads. 18F-fluorodeoxyglucose radiolabeled TCRAβ-Treg homed to the brain facilitating antigen specificity. Reduction in amyloid load was associated with improved cognitive functions.

CONCLUSIONS

TCRAβ-Tregs reduced amyloid burden, restored brain homeostasis, and improved learning and memory, supporting the increased therapeutic benefit of antigen specific Treg immunotherapy for AD.

A Stable Micellar Formulation of RAD001 for Intracerebroventricular Delivery and the Treatment of Alzheimer's Disease and Other Neurological Disorders

A large body of evidence, replicated in many mouse models of Alzheimer's disease (AD), supports the therapeutic efficacy of the oral mammalian target of rapamycin inhibitors (mTOR-Is). Our preliminary data show that intracerebroventricular (ICV) administration of everolimus (RAD001) soon after clinical onset greatly diminished cognitive impairment and the intracellular beta amyloid and neurofibrillary tangle load. However, RAD001 shows >90% degradation after 7 days in solution at body temperature, thus hampering the development of proper therapeutic regimens for patients. To overcome such a drawback, we developed a stable, liquid formulation of mTOR-Is by loading RAD001 into distearoylphosphatidylethanolamine-polyethylene glycol 2000 (DSPE-PEG2000) micelles using the thin layer evaporation method. The formulation showed efficient encapsulation of RAD001 and a homogeneous colloidal size and stabilised RAD001, with over 95% of activity preserved after 14 days at 37 °C with a total decay only occurring after 98 days. RAD001-loaded DSPE-PEG2000 micelles were unchanged when stored at 4 and 25 °C over the time period investigated. The obtained formulation may represent a suitable platform for expedited clinical translation and effective therapeutic regimens in AD and other neurological diseases.

Differential roles of regulatory T cells in Alzheimer's disease

Regulatory T (Treg) cells interact with a variety of resident cells and infiltrated immune cells in the central nervous system (CNS) to modulate neuroinflammation and neurodegeneration. Extracellular amyloid-β (Aβ) peptide deposition and secondary persistent inflammation due to activation of microglia, astrocytes, and infiltrated immune cells contribute to Alzheimer's disease (AD)-related neurodegeneration. The majority of evidence supports the neuroprotective effects of Treg cells in AD. In the early stages of AD, appropriate Treg cell activity is required for the induction of microglia and astrocyte phagocytic activity in order to clear A deposits and prevent neuroinflammation. Such neuroprotective impacts were in part attributed to the ability of Treg cells to suppress deleterious and/or boost beneficial functions of microglia/astrocytes. In the later stages of AD, an effective Treg cell activity needs to prevent neurotoxicity and neurodegeneration. Treg cells can exert preventive effects on Th1-, and Th17 cell-related pathologic responses, whilst potentiating Th2-mediated protective activity. The impaired Treg cell-related immunomodulatory mechanisms have been described in AD patients and in related animal models which can contribute to the onset and progression of AD. This review aimed to provide a comprehensive figure regarding the role of Treg cells in AD while highlighting potential therapeutic approaches.

Sex differences in microglia function in aged rats underlie vulnerability to cognitive decline

Aging is associated with a significant shift in immune system reactivity ("inflammaging"), as basal inflammation increases but protective responses to infection are compromised. The immune system exhibits considerable sex differences, which may influence the process of inflammaging, including immune cell activation and behavioral consequences of immune signaling (i.e., impaired memory). Here, we test the hypothesis that sex differences in immune aging may mediate sex differences in cognitive decline. Aged male and female rats received peripheral immune stimulation using lipopolysaccharide (LPS), then molecular, cellular, and behavioral outcomes were assessed. We observed that LPS-treated aged male rats showed cognitive impairment and increased neuroinflammatory responses relative to adult males. In contrast, aged female rats did not display these aging-related deficits. Using transcriptomic and flow cytometry analyses, we further observed significant age- and sex- dependent changes in immune cell populations in the brain parenchyma and meninges, indicating a broad shift in the neuroinflammatory environment that may potentiate these behavioral effects. Ovariectomized aged female rats were also resistant to inflammation-induced memory deficits, indicating that ovarian hormones are not required for the attenuated neuroinflammation in aged females. Overall, our results indicate that males have amplified inflammatory priming with age, which contributes to age-associated cognitive decline. Our findings highlight sexual dimorphism in mechanisms of aging, and suggest that sex is a crucial consideration for identifying therapies for aging and neuroinflammation.

Bibliometric analysis of global research trends on regulatory T cells in neurological diseases

This bibliometric study aimed to summarize and visualize the current research status, emerging trends, and research hotspots of regulatory T (Treg) cells in neurological diseases. Relevant documents were retrieved from the Web of Science Core Collection. Tableau Public, VOSviewer, and CiteSpace software were used to perform bibliometric analysis and network visualization. A total of 2,739 documents were included, and research on Treg cells in neurological diseases is still in a prolific period. The documents included in the research were sourced from 85 countries/regions, with the majority of them originating from the United States, and 2,811 organizations, with a significant proportion of them coming from Harvard Medical School. Howard E Gendelman was the most prolific author in this research area. Considering the number of documents and citations, impact factors, and JCR partitions, Frontiers in Immunology was the most popular journal in this research area. Keywords "multiple sclerosis," "inflammation," "regulatory T cells," "neuroinflammation," "autoimmunity," "cytokines," and "immunomodulation" were identified as high-frequency keywords. Additionally, "gut microbiota" has recently emerged as a new topic of interest. The study of Treg cells in neurological diseases continues to be a hot topic. Immunomodulation, gut microbiota, and cytokines represent the current research hotspots and frontiers in this field. Treg cell-based immunomodulatory approaches have shown immense potential in the treatment of neurological diseases. Modifying gut microbiota or regulating cytokines to boost the numbers and functions of Treg cells represents a promising therapeutic strategy for neurological diseases.

Modulation of Neuroinflammation: Advances in Roles and Mechanisms of the IL-33/ST2 Axis Involved in Ischemic Stroke

Interleukin (IL)-33 was initially recognized as a constituent of the IL-1 cytokine family in 2005. It exerts pleiotropic effects by regulating immune responses via its binding to the receptor ST2 (IL-33R). The IL-33/ST2 pathway has been linked to several inflammatory disorders. In human and rodents, the broad expression of IL-33 in spinal cord tissues and brain indicates its central nervous system-specific functions. Growing evidence supports the protective effects of the IL-33/ST2 pathway in ischemic stroke, along with a better understanding of the underlying mechanisms. IL-33 plays a crucial role in the regulation of the release of inflammatory molecules from glial cells in response to neuropathological lesions. Moreover, IL-33/ST2-mediated neuroprotection following cerebral ischemia may be linked to T-cell function, specifically regulatory T cells. Soluble ST2 (sST2) acts as a decoy receptor in the IL-33/ST2 axis, blocking IL-33 signaling through the membrane ST2 receptor. sST2 has also been identified as a potential inflammatory biomarker of ischemic stroke. Targeting sST2 specifically to eliminate its inhibition of the protective IL-33/ST2 pathway in ischemic brain tissues is a promising approach for the treatment of ischemic stroke.

Assessing the role of T cells in response to retinal injury to uncover new therapeutic targets for the treatment of retinal degeneration

BACKGROUND

Retinal degeneration is a disease affecting the eye, which is an immune-privileged site because of its anatomical and physiological properties. Alterations in retinal homeostasis-because of injury, disease, or aging-initiate inflammatory cascades, where peripheral leukocytes (PL) infiltrate the parenchyma, leading to retinal degeneration. So far, research on PL's role in retinal degeneration was limited to observing a few cell types at specific times or sectioning the tissue. This restricted our understanding of immune cell interactions and response duration.

METHODS

In vivo microscopy in preclinical mouse models can overcome these limitations enabling the spatio-temporal characterization of PL dynamics. Through in vivo imaging, we assessed structural and fluorescence changes in response to a focal injury at a defined location over time. We also utilized minimally invasive techniques, pharmacological interventions, and knockout (KO) mice to determine the role of PL in local inflammation. Furthermore, we investigated PL abundance and localization during retinal degeneration in human eyes by histological analysis to assess to which extent our preclinical study translates to human retinal degeneration.

RESULTS

We demonstrate that PL, especially T cells, play a detrimental role during retinal injury response. In mice, we observed the recruitment of helper and cytotoxic T cells in the parenchyma post-injury, and T cells also resided in the macula and peripheral retina in pathological conditions in humans. Additionally, we found that the pharmacological PL reduction and genetic depletion of T-cells reduced injured areas in murine retinas and rescued the blood-retina barrier (BRB) integrity. Both conditions promoted morphological changes of Cx3cr1+ cells, including microglial cells, toward an amoeboid phenotype during injury response. Interestingly, selective depletion of CD8+ T cells accelerated recovery of the BRB compared to broader depletions. After anti-CD8 treatment, the retinal function improved, concomitant to a beneficial immune response.

CONCLUSIONS

Our data provide novel insights into the adaptive immune response to retinal injury in mice and human retinal degeneration. Such information is fundamental to understanding retinal disorders and developing therapeutics to modulate immune responses to retinal degeneration safely.

Treg cell: Critical role of regulatory T-cells in depression

Depression is a highly prevalent disorder of the central nervous system. The neuropsychiatric symptoms of clinical depression are persistent and include fatigue, anorexia, weight loss, altered sleep patterns, hyperalgesia, melancholia, anxiety, and impaired social behaviours. Mounting evidences suggest that neuroinflammation triggers dysregulated cellular immunity and increases susceptibility to psychiatric diseases. Neuroimmune responses have transformed the clinical approach to depression because of their roles in its pathophysiology and their therapeutic potential. In particular, activated regulatory T (Treg) cells play an increasingly evident role in the inflammatory immune response. In this review, we summarized the available data and discussed in depth the fundamental roles of Tregs in the pathogenesis of depression, as well as the clinical therapeutic potential of Tregs. We aimed to provide recent information regarding the potential of Tregs as immune-modulating biologics for the treatment and prevention of long-term neuropsychiatric symptoms of depression.

Astrocyte-derived extracellular vesicles in stress-associated mood disorders. Does the immune system get astrocytic?

Life stressors can wreak havoc on our health, contributing to mood disorders like major depressive disorder (MDD), a widespread and debilitating condition. Unfortunately, current treatments and diagnostic strategies fall short of addressing these disorders, highlighting the need for new approaches. In this regard, the relationship between MDD, brain inflammation (neuroinflammation), and systemic inflammation in the body may offer novel insights. Recent research has uncovered the crucial role of astrocytes in coordinating the inflammatory response through the release of extracellular vesicles (ADEVs) during different neuroinflammatory conditions. While the contribution of ADEVs to stress and MDD remains largely unexplored, their potential to modulate immune cells and contribute to MDD pathogenesis is significant. In this article, we delve into the immunomodulatory role of ADEVs, their potential impact on peripheral immune cells, and how their microRNA (miRNA) landscape may hold the key to controlling immune cell activity. Together, these mechanisms may constitute an opportunity to develop novel therapeutic pharmacological approaches to tackle mood disorders.

Rapamycin Augmentation of Chronic Ketamine as a Novel Treatment for Complex Regional Pain Syndrome

This case report describes the dramatic clinical response of refractory chronic complex regional pain syndrome to combined immunomodulatory treatment. Ketamine and rapamycin markedly minimized pain historically associated with suicidal behavior, increased baseline activity, and allowed for a reduction in palliative polypharmacy. The piecewise mechanism of action is unclear given multiple postulated targets, such as microglia, astroglia, T-regulatory cells, B-regulatory cells, or neurons. Relevant laboratory and genetic information may allow the application of this treatment to other affected individuals.

Novel therapeutic approaches to target neurodegeneration

Ageing is the main risk factor common to most primary neurodegenerative disorders. Indeed, age-related brain alterations have been long considered to predispose to neurodegeneration. Although protein misfolding and the accumulation of toxic protein aggregates have been considered as causative events in neurodegeneration, several other biological pathways affected by brain ageing also contribute to pathogenesis. Here, we discuss the evidence showing the involvement of the mechanisms controlling neuronal structure, gene expression, autophagy, cell metabolism and neuroinflammation in the onset and progression of neurodegenerative disorders. Furthermore, we review the therapeutic strategies currently under development or as future approaches designed to normalize these pathways, which may then increase brain resilience to cope with toxic protein species. In addition to therapies targeting the insoluble protein aggregates specifically associated with each neurodegenerative disorder, these novel pharmacological approaches may be part of combined therapies designed to rescue brain function.

An open-label multiyear study of sargramostim-treated Parkinson's disease patients examining drug safety, tolerability, and immune biomarkers from limited case numbers

BACKGROUND

The clinical utility and safety of sargramostim has previously been reported in cancer, acute radiation syndrome, autoimmune disease, inflammatory conditions, and Alzheimer's disease. The safety, tolerability, and mechanisms of action in Parkinson's disease (PD) during extended use has not been evaluated.

METHODS

As a primary goal, safety and tolerability was assessed in five PD patients treated with sargramostim (Leukine®, granulocyte-macrophage colony-stimulating factor) for 33 months. Secondary goals included numbers of CD4+ T cells and monocytes and motor functions. Hematologic, metabolic, immune, and neurological evaluations were assessed during a 5-day on, 2-day off therapeutic regimen given at 3 μg/kg. After 2 years, drug use was discontinued for 3 months. This was then followed by an additional 6 months of treatment.

RESULTS

Sargramostim-associated adverse events included injection-site reactions, elevated total white cell counts, and bone pain. On drug, blood analyses and metabolic panels revealed no untoward side effects linked to long-term treatment. Unified Parkinson's Disease Rating Scale scores remained stable throughout the study while regulatory T cell number and function were increased. In the initial 6 months of treatment, transcriptomic and proteomic monocyte tests demonstrated autophagy and sirtuin signaling. This finding paralleled anti-inflammatory and antioxidant activities within both the adaptive and innate immune profile arms.

CONCLUSIONS

Taken together, the data affirmed long-term safety as well as immune and anti-inflammatory responses reflecting clinical stability in PD under the sargramostim treatment. Confirmation in larger patient populations is planned in a future phase II evaluation.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT03790670, Date of Registration: 01/02/2019, URL: https://clinicaltrials.gov/ct2/show/NCT03790670?cond=leukine+parkinson%27s&draw=2&rank=2 .

Molecular and cognitive signatures of ageing partially restored through synthetic delivery of IL2 to the brain

Cognitive decline is a common pathological outcome during aging, with an ill-defined molecular and cellular basis. In recent years, the concept of inflammaging, defined as a low-grade inflammation increasing with age, has emerged. Infiltrating T cells accumulate in the brain with age and may contribute to the amplification of inflammatory cascades and disruptions to the neurogenic niche observed with age. Recently, a small resident population of regulatory T cells has been identified in the brain, and the capacity of IL2-mediated expansion of this population to counter neuroinflammatory disease has been demonstrated. Here, we test a brain-specific IL2 delivery system for the prevention of neurological decline in aging mice. We identify the molecular hallmarks of aging in the brain glial compartments and identify partial restoration of this signature through IL2 treatment. At a behavioral level, brain IL2 delivery prevented the age-induced defect in spatial learning, without improving the general decline in motor skill or arousal. These results identify immune modulation as a potential path to preserving cognitive function for healthy aging.

The potential for treg-enhancing therapies in nervous system pathologies

While inflammation may not be the cause of disease, it is well known that it contributes to disease pathogenesis across a multitude of peripheral and central nervous system disorders. Chronic and overactive inflammation due to an effector T-cell-mediated aberrant immune response ultimately leads to tissue damage and neuronal cell death. To counteract peripheral and neuroinflammatory responses, research is being focused on regulatory T cell enhancement as a therapeutic target. Regulatory T cells are an immunosuppressive subpopulation of CD4+ T helper cells essential for maintaining immune homeostasis. The cells play pivotal roles in suppressing immune responses to maintain immune tolerance. In so doing, they control T cell proliferation and pro-inflammatory cytokine production curtailing autoimmunity and inflammation. For nervous system pathologies, Treg are known to affect the onset and tempo of neural injuries. To this end, we review recent findings supporting Treg's role in disease, as well as serving as a therapeutic agent in multiple sclerosis, myasthenia gravis, Guillain-Barre syndrome, Parkinson's and Alzheimer's diseases, and amyotrophic lateral sclerosis. An ever-broader role for Treg in the control of neurologic disease has been shown for traumatic brain injury, stroke, neurotrophic pain, epilepsy, and psychiatric disorders. To such ends, this review serves to examine the role played by Tregs in nervous system diseases with a focus on harnessing their functional therapeutic role(s).

Early systemic inflammation induces neurodevelopmental disorders: results from ARTEMIS, a French multicenter study of juvenile rheumatisms and systemic autoimmune and auto-inflammatory disorders and meta-analysis

Prenatal immune-mediated events are known risk factors for neurodevelopmental disorders in the offspring (NDD). Although the brain continues to develop for years after birth and many postnatal factors alter the regular trajectory of neurodevelopment, little is known about the impact of postnatal immune factors. To fill this gap we set up ARTEMIS, a cohort of juvenile rheumatisms and systemic autoimmune and auto-inflammatory disorders (jRSAID), and assessed their neurodevelopment. We then complemented our results with a systematic review and meta-analysis. In ARTEMIS, we used unsupervised and supervised analysis to determine the influence of jRSAID age at onset (AO) and delay in introduction of disease-modifying therapy (DMT) on NDD (NCT04814862). For the meta-analysis, we searched MEDLINE, EMBASE, PsycINFO, Cochrane, and Web of Science up to April 2022 without any restrictions on language, or article type for studies investigating the co-occurence of jRSAID and NDD (PROSPERO- CRD42020150346). 195 patients were included in ARTEMIS. Classification tree isolated 3 groups of patients (i) A low-risk group (AO > 130 months (m)) with 5% of NDD (ii) A medium-risk group (AO < 130 m and DMT < 2 m) with 20% of NDD (iii) and a high-risk-group (AO < 130 m and DMT > 2 m) with almost half of NDD. For the meta-analysis, 18 studies encompassing a total of (i) 46,267 children with jRSAID; 213,930 children with NDD, and 6,213,778 children as controls were included. We found a positive association between jRSAID and NDD with an OR = 1.44 [95% CI 1.31; 1.57] p < 0.0001, [I² = 66%, Tau² = 0.0067, p < 0.01]. Several sensitivity analyses were performed without changing the results. Metaregression confirmed the importance of AO (p = 0.005). Our study supports the association between jRSAID and NDD. AO and DMT have pivotal roles in the risk of developing NDD. We plead for systematic screening of NDD in jRSAID to prevent the functional impact of NDD.

Identification of Differentially Expressed Genes Particularly Associated with Immunity in Uremia Patients by Bioinformatic Analysis

Uremia is a common syndrome that happens to nearly all end-stage kidney diseases, which profound have changes in human gene expressions, but the related pathways are poorly understood. Gene Ontology categories and Kyoto Encyclopedia of Genes and Genomes pathways enriched in the differentially expressed genes (DEGs) were analyzed by using clusterProfiler, org.Hs.eg.db, and Pathview, and protein-protein interaction (PPI) network was built by Cytoscape. We identified 3432 DEGs (including 3368 down- and 64 up-regulated genes), of which there were 52 different molecular functions, and 178 genes were identified as immune genes controlled by the four transcription factors (POU domain class 6 transcription factor 1 (POU6F1), interferon regulator factor 7 [IRF7], forkhead box D3 (FOXD3), and interferon-stimulated response element [ISRE]). In the gender research, no significant difference was observed. The top 15 proteins of 178 immune-related genes were identified with the highest degree in PPI network. The DEG analysis of uremia patients was expected to provide fundamental information to relieve pain and add years to their life.

Philosophical Approach to Neural Autoantibodies in Psychiatric Disease-Multi-Systemic Dynamic Continuum from Protective to Harmful Autoimmunity in Neuronal Systems

(1) Background: philosophical views are important to enable a general and multi-systemic view of the potential understanding of autoimmunity in psychiatric disease that is not solely reflected by an immunological viewpoint. (2) Methods: we reviewed current theories of autoimmunity. (3) Results: we propose a novel area view integrating the "self/non-self" and "continuity" model into the expression of varied forms of autoimmunity in psychiatric disease, ranging from protective to harmful autoimmunity consequences framed into micro-systems (nerve cells) and macro-systems (neuronal networks), termed the "multi-systemic dynamic continuum model". (4) Conclusions: autoimmunity's dynamic spectrum is delineated here as something that probably functions as a whole entity to maintain, first of all, human homeostasis in behavior affecting cells or neuronal networks differently, and secondly to prevent psychiatric disease.

Regulatory T Cell Therapeutics for Neuroinflammatory Disorders

A delicate balance of immune regulation exists in the central nervous system (CNS) that is often dysreg-ulated in neurological diseases, making them complicated to treat. With altered immune surveillance in the diseased or injured CNS, signals that are beneficial in the homeostatic CNS can be disrupted and lead to neuroinflammation. Recent advances in niche immune cell subsets have provided insight into the complicated cross-talk between the nervous system and the immune system. Regulatory T cells (Tregs) are a subset of T cells that are capable of suppressing effector T-cell activation and regulating immune tolerance, and play an important role in neuroprotection. Tregs have been shown to be effective therapies in a variety of immune-related disorders including, graft-versus-host disease (GVHD), type 1 diabetes (T1D), and inflammatory bowel disease (IBD), as well as within the CNS. Recently, significant advancements in engineering T cells, such as chimeric antigen receptor (CAR) T cells, have led to several approved therapies suggesting the safety and efficacy for similar engineered Treg therapies. Further, as understanding of the immune system's role in neuroinflammation has progressed, Tregs have recently become a potential therapeutic in the neurology space. In this review, we discuss Tregs and their evolving role as therapies for neuroinflammatory related disorders.