Reduced Numbers and Impaired Function of Regulatory T Cells in Peripheral Blood of Ischemic Stroke Patients

The Aging Immune System: A Critical Attack on Ischemic Stroke

Ischemic stroke caused by cerebrovascular embolism is an age-related disease with high rates of disability and mortality. Although the mechanisms of immune and inflammatory development after stroke have been of great interest, most studies have neglected the critical and unavoidable factor of age. As the global aging trend intensifies, the number of stroke patients is constantly increasing, emphasizing the urgency of finding effective measures to address the needs of elderly stroke patients. The concept of "immunosenescence" appears to explain the worse stroke outcomes in older individuals. Immune remodeling due to aging involves dynamic changes at all levels of the immune system, and the overall consequences of central (brain-resident) and peripheral (non-brain-resident) immune cells in stroke vary according to the age of the individual. Lastly, the review outlines recent strategies aimed at immunosenescence to improve stroke prognosis.

Nanomaterial-Based Strategies for Attenuating T-Cell-Mediated Immunodepression in Stroke Patients: Advancing Research Perspectives

This review article discusses the potential of nanomaterials in targeted therapy and immunomodulation for stroke-induced immunosuppression. Although nanomaterials have been extensively studied in various biomedical applications, their specific use in studying and addressing immunosuppression after stroke remains limited. Stroke-induced neuroinflammation is characterized by T-cell-mediated immunodepression, which leads to increased morbidity and mortality. Key observations related to immunodepression after stroke, including lymphopenia, T-cell dysfunction, regulatory T-cell imbalance, and cytokine dysregulation, are discussed. Nanomaterials, such as liposomes, micelles, polymeric nanoparticles, and dendrimers, offer advantages in the precise delivery of drugs to T cells, enabling enhanced targeting and controlled release of immunomodulatory agents. These nanomaterials have the potential to modulate T-cell function, promote neuroregeneration, and restore immune responses, providing new avenues for stroke treatment. However, challenges related to biocompatibility, stability, scalability, and clinical translation need to be addressed. Future research efforts should focus on comprehensive studies to validate the efficacy and safety of nanomaterial-based interventions targeting T cells in stroke-induced immunosuppression. Collaborative interdisciplinary approaches are necessary to advance the field and translate these innovative strategies into clinical practice, ultimately improving stroke outcomes and patient care.

Decoding the potential role of regulatory T cells in sepsis-induced immunosuppression

Sepsis, a multiorgan dysfunction with high incidence and mortality, is caused by an imbalanced host-to-infection immune response. Organ-support therapy improves the early survival rate of sepsis patients. In the long term, those who survive the "cytokine storm" and its secondary damage usually show higher susceptibility to secondary infections and sepsis-induced immunosuppression, in which regulatory T cells (Tregs) are evidenced to play an essential role. However, the potential role and mechanism of Tregs in sepsis-induced immunosuppression remains elusive. In this review, we elucidate the role of different functional subpopulations of Tregs during sepsis and then review the mechanism of sepsis-induced immunosuppression from the aspects of regulatory characteristics, epigenetic modification, and immunometabolism of Tregs. Thoroughly understanding how Tregs impact the immune system during sepsis may shed light on preclinical research and help improve the translational value of sepsis immunotherapy.

Update on the role of T cells in cognitive impairment

The central nervous system (CNS) has long been considered an immune-privileged site, with minimal interaction between immune cells, particularly of the adaptive immune system. Previously, the presence of immune cells in this organ was primarily linked to events involving disruption of the blood-brain barrier (BBB) or inflammation. However, current research has shown that immune cells are found patrolling CNS under homeostatic conditions. Specifically, T cells of the adaptive immune system are able to cross the BBB and are associated with ageing and cognitive impairment. In addition, T-cell infiltration has been observed in pathological conditions, where inflammation correlates with poor prognosis. Despite ongoing research, the role of this population in the ageing brain under both physiological and pathological conditions is not yet fully understood. In this review, we provide an overview of the interactions between T cells and other immune and CNS parenchymal cells, and examine the molecular mechanisms by which these interactions may contribute to normal brain function and the scenarios in which disruption of these connections lead to cognitive impairment. A comprehensive understanding of the role of T cells in the ageing brain and the underlying molecular pathways under normal conditions could pave the way for new research to better understand brain disorders. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

GPR55 Inactivation Diminishes Splenic Responses and Improves Neurological Outcomes in the Mouse Ischemia/Reperfusion Stroke Model

Although strokes are frequent and severe, treatment options are scarce. Plasminogen activators, the only FDA-approved agents for clot treatment (tissue plasminogen activators (tPAs)), are used in a limited patient group. Moreover, there are few approaches for handling the brain's inflammatory reactions to a stroke. The orphan G protein-coupled receptor 55 (GPR55)'s connection to inflammatory processes has been recently reported; however, its role in stroke remains to be discovered. Post-stroke neuroinflammation involves the central nervous system (CNS)'s resident microglia activation and the infiltration of leukocytes from circulation into the brain. Additionally, splenic responses have been shown to be detrimental to stroke recovery. While lymphocytes enter the brain in small numbers, they regularly emerge as a very influential leukocyte subset that causes secondary inflammatory cerebral damage. However, an understanding of how this limited lymphocyte presence profoundly impacts stroke outcomes remains largely unclear. In this study, a mouse model for transient middle cerebral artery occlusion (tMCAO) was used to mimic ischemia followed by a reperfusion (IS/R) stroke. GPR55 inactivation, with a potent GPR55-specific antagonist, ML-193, starting 6 h after tMCAO or the absence of the GPR55 in mice (GPR55 knock out (GPR55ko)) resulted in a reduced infarction volume, improved neurological outcomes, and decreased splenic responses. The inhibition of GPR55 with ML-193 diminished CD4+T-cell spleen egress and attenuated CD4+T-cell brain infiltration. Additionally, ML-193 treatment resulted in an augmented number of regulatory T cells (Tregs) in the brain post-tMCAO. Our report offers documentation and the functional evaluation of GPR55 in the brain-spleen axis and lays the foundation for refining therapeutics for patients after ischemic attacks.

Traditional Chinese medicines treat ischemic stroke and their main bioactive constituents and mechanisms

Ischemic stroke (IS) remains one of the leading causes of death and disability in humans. Unfortunately, none of the treatments effectively provide functional benefits to patients with IS, although many do so by targeting different aspects of the ischemic cascade response. The advantages of traditional Chinese medicine (TCM) in preventing and treating IS are obvious in terms of early treatment and global coordination. The efficacy of TCM and its bioactive constituents has been scientifically proven over the past decades. Based on clinical trials, this article provides a review of commonly used TCM patent medicines and herbal decoctions indicated for IS. In addition, this paper also reviews the mechanisms of bioactive constituents in TCM for the treatment of IS in recent years, both domestically and internationally. A comprehensive review of preclinical and clinical studies will hopefully provide new ideas to address the threat of IS.

Regulatory T cells: A suppressor arm in post-stroke immune homeostasis

The activation of the immune system and the onset of pro- and anti-inflammatory responses play crucial roles in the pathophysiological processes of ischaemic stroke (IS). CD4+ regulatory T (Treg) cells is the main immunosuppressive cell population that is studied in the context of peripheral tolerance, autoimmunity, and the development of chronic inflammatory diseases. In recent years, more studies have focused on immune modulation after IS, and Treg cells have been demonstrated to be essential in the remission of inflammation, nerve regeneration, and behavioural recovery. However, the exact effects of Treg cells in the context of IS remain controversial, with some studies suggesting a negative correlation with stroke outcomes. In this review, we aim to provide a comprehensive overview of the current understanding of Treg cell involvement in post-stroke homeostasis. We summarized the literature focusing on the temporal changes in Treg cell populations after IS, the mechanisms of Treg cell-mediated immunomodulation in the brain, and the potential of Treg cell-based therapies for treatment. The purposes of the current article are to address the importance of Treg cells and inspire more studies to help physicians, as well as scientists, understand the whole map of immune responses during IS.

Temporal changes in regulatory T cell subsets defined by the transcription factor Helios in stroke and their potential role in stroke-associated infection: a prospective case-control study

BACKGROUND

Regulatory T cells (Tregs) are involved in the systemic immune response after ischemic stroke. However, their role remains unclear, and the effect appears to be both neuroprotective and detrimental. Treg suppressor function may result in immunodepression and promote stroke-associated infection (SAI). Thus we assume that the bidirectional effects of Tregs may be in part attributed to the intracellular transcription factor Helios. Tregs with Helios expression (H+ Tregs) constitute 70-90% of all Treg cells and more frequently than Helios-negative Tregs (H- Tregs) express molecules recognized as markers of Tregs with suppressor abilities.

METHODS AND RESULTS

We prospectively assessed the circulating Treg population with flow cytometry in 52 subjects on days 1, 3, 10 and 90 after ischemic stroke and we compared the results with those obtained in concurrent age-, sex- and vascular risk factor-matched controls. At all studied time points the percentage of H+ Tregs decreased in stroke subjects-D1: 69.1% p < 0.0001; D3: 62.5% (49.6-76.6), p < 0.0001; D10: 60.9% (56.5-72.9), p < 0.0001; D90: 79.2% (50.2-91.7), p = 0.014 vs. controls: 92.7% (81.9-97.0) and the percentage of H- Tregs increased accordingly. In patients with SAI the percentage of pro-suppressor H+ Tregs on post-stroke day 3 was higher than in those without infection (p = 0.03). After adjustment for confounders, the percentage of H+ Tregs on day 3 independently correlated with SAI [OR 1.29; CI 95%: 1.08-1.27); p = 0.02]. Although the percentage of H+ Tregs on day 3 correlated positively with NIHSS score on day 90 (rS = 0.62; p < 0.01) and the infarct volume at day 90 (rS = 0.58; p < 0.05), in regression analysis it was not an independent risk factor.

CONCLUSIONS

On the first day after stroke the proportion of H+ vs. H- Tregs changes in favor of pro-inflammatory H- Tregs, and this shift continues toward normalization when assessed on day 90. A higher percentage of pro-suppressive H+ Tregs on day 3 independently correlates with SAI and is associated positively with NIHSS score, but it does not independently affect the outcome and stroke area in the convalescent phase of stroke.

Amniotic membrane mesenchymal stromal cell-derived secretome in the treatment of acute ischemic stroke: A case report

BACKGROUND

Stroke is the second and third leading cause of death and disability, respectively. To date, no definitive treatment can repair lost brain function. Recently, various preclinical studies have been reported on mesenchymal stromal cells (MSCs) and their derivatives and their potential as alternative therapies for stroke.

CASE SUMMARY

A 45-year-old female suffered an acute stroke, which led to paralysis in the left upper and lower limbs. The amniotic membrane MSC-derived secretome (MSC-secretome) was intravenously transplanted once a week for 4 wk. MSC-secretome-regulated regulatory T cells were investigated for the beneficial effects. The clinical improvement of this patient was accompanied by an increased frequency of regulatory T cells after transplantation.

CONCLUSION

Intravenous administration of MSC-secretome can potentially treat patients who suffer from acute ischemic stroke.

The impact of fingolimod on Treg function in brain ischaemia

Fingolimod has generally shown neuroprotective effects in stroke models. Here, we tested the hypothesis that fingolimod modulates T-cell cytokine production towards a regulatory phenotype. Second, we investigated how fingolimod altered the Treg suppressive function and the sensitivity of effector T cells to regulation. Mice that had underwent the permanent electrocoagulation of the left middle cerebral artery received saline or fingolimod (0.5 mg/kg) daily for 10-days post-ischaemia. Fingolimod improved neurobehavioural recovery compared to saline control and increased Treg frequency in the periphery and brain. Tregs from fingolimod-treated animals had a higher expression of CCR8. Fingolimod increased the frequencies of CD4+ IL-10+ , CD4+ IFN-γ+ and CD4+ IL-10+ IFN-γ+ cells in spleen and blood, and CD4+ IL-17+ cells in the spleen, with only minor effects on CD8+ T-cell cytokine production. Treg from post-ischaemic mice had reduced suppressive function compared to Treg from non-ischaemic mice. Fingolimod treatment rescued this function against saline-treated but not fingolimod-treated CD4+ effector T cells. In conclusion, fingolimod seems to improve the suppressive function of Treg post-stroke while also increasing the resistance of CD4+ effector cells to this suppression. Fingolimod's capacity to increase both effector and regulatory functions may explain the lack of consistent improvement in functional recovery in experimental brain ischaemia.

Potential regulatory effects of stem cell exosomes on inflammatory response in ischemic stroke treatment

The high incidence and disability rates of stroke pose a heavy burden on society. Inflammation is a significant pathological reaction that occurs after an ischemic stroke. Currently, therapeutic methods, except for intravenous thrombolysis and vascular thrombectomy, have limited time windows. Mesenchymal stem cells (MSCs) can migrate, differentiate, and inhibit inflammatory immune responses. Exosomes (Exos), which are secretory vesicles, have the characteristics of the cells from which they are derived, making them attractive targets for research in recent years. MSC-derived exosomes can attenuate the inflammatory response caused by cerebral stroke by modulating damage-associated molecular patterns. In this review, research on the inflammatory response mechanisms associated with Exos therapy after an ischemic injury is discussed to provide a new approach to clinical treatment.

Regulatory T lymphocytes as a therapy for ischemic stroke

Unrestrained excessive inflammatory responses exacerbate ischemic brain injury and impede post-stroke brain recovery. CD4+CD25+Foxp3+ regulatory T (Treg) cells play important immunosuppressive roles to curtail inflammatory responses and regain immune homeostasis after stroke. Accumulating evidence confirms that Treg cells are neuroprotective at the acute stage after stroke and promote brain repair at the chronic phases. The beneficial effects of Treg cells are mediated by diverse mechanisms involving cell-cell interactions and soluble factor release. Multiple types of cells, including both immune cells and non-immune CNS cells, have been identified to be cellular targets of Treg cells. In this review, we summarize recent findings regarding the function of Treg cells in ischemic stroke and the underlying cellular and molecular mechanisms. The protective and reparative properties of Treg cells endorse them as good candidates for immune therapy. Strategies that boost the numbers and functions of Treg cells have been actively developing in the fields of transplantation and autoimmune diseases. We discuss the approaches for Treg cell expansion that have been tested in stroke models. The application of these approaches to stroke patients may bring new hope for stroke treatments.

Naïve-memory regulatory T cells ratio is a prognostic biomarker for patients with acute ischemic stroke

Background

Regulatory T cells (Treg) have been identified as a key modulator of neuroinflammation in stroke. However, little is known about the association of Treg subpopulations with clinical outcome in patients with acute ischemic stroke (AIS).

Methods

Patients within 1 week from stroke onset were prospectively enrolled in this study. Healthy controls were sex-and age-matched 1:1 to AIS patients. The frequencies of Treg and Treg subsets were analyzed by flow cytometry and compared with nonstroke control. Univariate and multivariate logistic regression analysis was performed to investigate the prognostic value of Treg subsets in stroke outcomes.

Results

A total of 328 patients and 328 controls were included in the study. Compared with controls, patients with AIS had higher levels of Treg frequency and memory Treg (mTreg) frequency, but lower levels of naïve Treg (nTreg) frequency and nTreg/mTreg ratio. One hundred twenty-six (38.4%) patients experienced unfavorable outcome (modified Rankin score 2-6). Multivariate regression analysis showed that nTreg/mTreg ratio was negatively associated with unfavorable 90-day outcome (the highest tertile versus the lowest tertile: odds ratio 0.13, 95% confidential interval [CI] 0.05-0.35). The risk estimation of unfavorable 90 day outcome can be significantly improved by adding nTreg/mTreg ratio to the conventional clinical parameters (continuous net reclassification improvement 91.26, 95% CI 69.04-113.5%, p < 0.001; integrated discrimination improvement 22.38, 95% CI 17.16-27.59%, p < 0.001).

Conclusion

This study showed that patients with AIS had elevated Treg frequency and mTreg frequency, but reduced nTreg frequency and nTreg/mTreg ratio. Admission nTreg/mTreg ratio was an independent predictor of unfavorable 90 day outcome in AIS. However, large sample-size cohort studies are needed to confirm our findings.

Inflammatory Responses After Ischemic Stroke

Ischemic stroke generates an immune response that contributes to neuronal loss as well as tissue repair. This is a complex process involving a range of cell types and effector molecules and impacts tissues outside of the CNS. Recent reviews address specific aspects of this response, but several years have passed and important advances have been made since a high-level review has summarized the overall state of the field. The present review examines the initiation of the inflammatory response after ischemic stroke, the complex impacts of leukocytes on patient outcome, and the potential of basic science discoveries to impact the development of therapeutics. The information summarized here is derived from broad PubMed searches and aims to reflect recent research advances in an unbiased manner. We highlight valuable recent discoveries and identify gaps in knowledge that have the potential to advance our understanding of this disease and therapies to improve patient outcomes.

Interleukin-2-inducible T-cell kinase (Itk) signaling regulates potent noncanonical regulatory T cells

Regulatory T cells (Tregs) play an important role in controlling autoimmunity and limiting tissue damage and inflammation. IL2-inducible T cell kinase (Itk) is part of the Tec family of tyrosine kinases and is a critical component of T cell receptor mediated signaling. Here, we showed that either genetic ablation of Itk signaling or inhibition of Itk signaling pathways resulted in increased frequency of "noncanonical" CD4+ CD25- FOXP3+ Tregs (ncTregs), as well as of "canonical" CD4+ CD25+ FOXP3+ Tregs (canTregs). Using in vivo models, we showed that ncTregs can avert the formation of acute graft-versus-host disease (GVHD), in part by reducing conventional T cell proliferation, proinflammatory cytokine production, and tissue damage. This reduction in GVHD occurred without disruption of graft-versus-leukaemia (GVL) effects. RNA sequencing revealed that a number of effector, cell adhesion, and migration molecules were upregulated in Itk-/- ncTregs. Furthermore, disrupting the SLP76: ITK interaction using a specific peptide inhibitor led to enhanced Treg development in both mouse and primary human cells. This peptide inhibitor also significantly reduced inflammatory cytokine production in primary GVHD patient samples and mouse T cells without causing cell death or apoptosis. We provide evidence that specifically targeting Itk signaling could be a therapeutic strategy to treat autoimmune disorders.

Phenotypic and Functional Diversity in Regulatory T Cells

The concept that a subset of T cells exists that specifically suppresses immune responses was originally proposed over 50 years ago. It then took the next 30 years to solidify the concept of regulatory T cells (Tregs) into the paradigm we understand today - namely a subset of CD4+ FOXP3+ T-cells that are critical for controlling immune responses to self and commensal or environmental antigens that also play key roles in promoting tissue homeostasis and repair. Expression of the transcription factor FOXP3 is a defining feature of Tregs, while the cytokine IL2 is necessary for robust Treg development and function. While our initial conception of Tregs was as a monomorphic lineage required to suppress all types of immune responses, recent work has demonstrated extensive phenotypic and functional diversity within the Treg population. In this review we address the ontogeny, phenotype, and function of the large number of distinct effector Treg subsets that have been defined over the last 15 years.

T Cell Response in Ischemic Stroke: From Mechanisms to Translational Insights

Ischemic stroke, caused by a sudden disruption of blood flow to the brain, is a leading cause of death and exerts a heavy burden on both patients and public health systems. Currently available treatments for ischemic stroke are very limited and are not feasible in many patients due to strict time windows required for their administration. Thus, novel treatment strategies are keenly required. T cells, which are part of the adaptive immune system, have gained more attention for its effects in ischemic stroke. Both preclinical and clinical studies have revealed the conflicting roles for T cells in post-stroke inflammation and as potential therapeutic targets. This review summarizes the mediators of T cell recruitment, as well as the temporal course of its infiltration through the blood-brain-barrier, choroid plexus, and meningeal pathways. Furthermore, we describe the mechanisms behind the deleterious and beneficial effects of T cells in the brain, in both antigen-dependent and antigen-independent manners, and finally we specifically focus on clinical and preclinical studies that have investigated T cells as potential therapeutic targets for ischemic stroke.

Reduced frequency and functional potency of CD49d- T regulatory cells in patients with newly diagnosed type 2 diabetes mellitus

This study set out to check the quantitative and qualitative properties of peripheral CD4⁺CD25⁺CD49d^- T regulatory (CD49d^- Treg) cells in type 2 diabetes mellitus (T2DM) patients. This work comprised 35 newly diagnosed patients and 35 healthy controls (HCs). The frequency of FoxP3 expressing CD49d^- Treg cells was determined by flow cytometry. The gene expression of FoxP3 and CD49d was assessed by real-time PCR. Suppression assays with purified CD49d^- Treg cells and CD4⁺CD25^- T conventional (Tconv) cells were done by flow cytometry. The supernatants of Tconv/CD49d^- Treg co-cultures were tested for IFN-γ, IL-4, IL-17, and IL-10 using ELISA. The frequency of CD49d^- Treg cells (by both CD4⁺CD25⁺CD49d^- and CD4⁺CD25⁺⁺CD49d^- phenotypes) observed to be reduced in patients versus HCs. In the patients, decreased protein and gene expression of FoxP3 was seen in CD49d^- Treg cells. Suppressive potency of CD49d^- Treg cells to inhibit Tconv cells proliferation was diminished, and inversely related to fasting plasma glucose and hemoglobin A1c in the patients. Tconv cells from T2DM patients released higher amount of IL-17 and lower concentration of IL-10 versus HCs. In Tconv/CD49d^- Tregs co-cultures, decreased IL-17 and increased IL-10 levels were seen in HCs, but not T2DM patients. CD49d^- Treg cells from the patients have a fundamental defect and Treg cells fail to inhibit the aggressive inflammatory responses.

Immune Cells in the BBB Disruption After Acute Ischemic Stroke: Targets for Immune Therapy?

Blood-Brain Barrier (BBB) disruption is an important pathophysiological process of acute ischemic stroke (AIS), resulting in devastating malignant brain edema and hemorrhagic transformation. The rapid activation of immune cells plays a critical role in BBB disruption after ischemic stroke. Infiltrating blood-borne immune cells (neutrophils, monocytes, and T lymphocytes) increase BBB permeability, as they cause microvascular disorder and secrete inflammation-associated molecules. In contrast, they promote BBB repair and angiogenesis in the latter phase of ischemic stroke. The profound immunological effects of cerebral immune cells (microglia, astrocytes, and pericytes) on BBB disruption have been underestimated in ischemic stroke. Post-stroke microglia and astrocytes can adopt both an M1/A1 or M2/A2 phenotype, which influence BBB integrity differently. However, whether pericytes acquire microglia phenotype and exert immunological effects on the BBB remains controversial. Thus, better understanding the inflammatory mechanism underlying BBB disruption can lead to the identification of more promising biological targets to develop treatments that minimize the onset of life-threatening complications and to improve existing treatments in patients. However, early attempts to inhibit the infiltration of circulating immune cells into the brain by blocking adhesion molecules, that were successful in experimental stroke failed in clinical trials. Therefore, new immunoregulatory therapeutic strategies for acute ischemic stroke are desperately warranted. Herein, we highlight the role of circulating and cerebral immune cells in BBB disruption and the crosstalk between them following acute ischemic stroke. Using a robust theoretical background, we discuss potential and effective immunotherapeutic targets to regulate BBB permeability after acute ischemic stroke.

A hyperacute immune map of ischaemic stroke patients reveals alterations to circulating innate and adaptive cells

Systemic immune changes following ischaemic stroke are associated with increased susceptibility to infection and poor patient outcome due to their role in exacerbating the ischaemic injury and long-term disability. Alterations to the abundance or function of almost all components of the immune system post-stroke have been identified, including lymphocytes, monocytes and granulocytes. However, subsequent infections have often confounded the identification of stroke-specific effects. Global understanding of very early changes to systemic immunity is critical to identify immune targets to improve clinical outcome. To this end, we performed a small, prospective, observational study in stroke patients with immunophenotyping at a hyperacute time point (< 3 h) to explore early changes to circulating immune cells. We report, for the first time, decreased frequencies of type 1 conventional dendritic cells (cDC1), haematopoietic stem and progenitor cells (HSPCs), unswitched memory B cells and terminally differentiated effector memory T cells re-expressing CD45RA (TEMRA). We also observed concomitant alterations to human leucocyte antigen D-related (HLA-DR), CD64 and CD14 expression in distinct myeloid subsets and a rapid activation of CD4+ T cells based on CD69 expression. The CD69+ CD4+ T cell phenotype inversely correlated with stroke severity and was associated with naive and central memory T (TCM) cells. Our findings highlight early changes in both the innate and adaptive immune compartments for further investigation as they could have implications the development of post-stroke infection and poorer patient outcomes.

The effect of fingolimod on regulatory T cells in a mouse model of brain ischaemia

Background

The role of the immune system in stroke is well-recognised. Fingolimod, an immunomodulatory agent licensed for the management of relapsing-remitting multiple sclerosis, has been shown to provide benefit in rodent models of stroke. Its mechanism of action, however, remains unclear. We hypothesised fingolimod increases the number and/or function of regulatory T cells (Treg), a lymphocyte population which promotes stroke recovery. The primary aim of this study was to rigorously investigate the effect of fingolimod on Tregs in a mouse model of brain ischaemia. The effect of fingolimod in mice with common stroke-related comorbidities (ageing and hypercholesteremia) was also investigated.

Methods

Young (15–17 weeks), aged C57BL/6 mice (72–73 weeks), and ApoE^−/− mice fed a high-fat diet (20–21 weeks) underwent permanent electrocoagulation of the left middle cerebral artery. Mice received either saline or fingolimod (0.5 mg/kg or 1 mg/kg) at 2, 24, and 48 h post-ischaemia via intraperitoneal injection. Another cohort of young mice (8–9, 17–19 weeks) received short-term (5 days) or long-term (10 days) fingolimod (0.5 mg/kg) treatment. Flow cytometry was used to quantify Tregs in blood, spleen, and lymph nodes. Immunohistochemistry was used to quantify FoxP3+ cell infiltration into the ischaemic brain.

Results

Fingolimod significantly increased the frequency of Tregs within the CD4+ T cell population in blood and spleen post-ischaemia in all three mouse cohorts compared to untreated ischemic mice. The highest splenic Treg frequency in fingolimod-treated mice was observed in ApoE^−/− mice (9.32 ± 1.73% vs. 7.8 ± 3.01% in young, 6.09 ± 1.64% in aged mice). The highest circulating Treg frequency was also noted in ApoE^−/− mice (8.39 ± 3.26% vs. 5.43 ± 2.74% in young, 4.56 ± 1.60% in aged mice). Fingolimod significantly increased the number of FoxP3+ cells in the infarct core of all mice. The most pronounced effects were seen when mice were treated for 10 days post-ischaemia.

Conclusions

Fingolimod increases Treg frequency in spleen and blood post-ischaemia and enhances the number of FoxP3+ cells in the ischaemic brain. The effect of fingolimod on this regulatory cell population may underlie its neuroprotective activity and could be exploited as part of future stroke therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02083-5.

Regulatory T cells in ischemic stroke

The pathophysiological mechanisms of neuroinflammation, angiogenesis, and neuroplasticity are currently the hotspots of researches in ischemic stroke. Regulatory T cells (Tregs), a subset of T cells that control inflammatory and immune responses in the body, are closely related to the pathogenesis of ischemic stroke. They participate in the inflammatory response and neuroplasticity process of ischemic stroke by various mechanisms, such as secretion of anti‐inflammatory factors, inhibition of pro‐inflammatory factors, induction of cell lysis, production of the factors that promote neural regeneration, and modulation of microglial and macrophage polarization. However, it remains unclear whether Tregs play a beneficial or deleterious role in ischemic stroke and the effect of Tregs in different stages of ischemic stroke. Here, we discuss the dynamic changes of Tregs at various stages of experimental and clinical stroke, the potential mechanisms under Tregs in regulating stroke and the preclinical studies of Tregs‐related treatments, in order to provide a reference for clinical treatment.

Endogenous Regulatory T Cells Promote M2 Macrophage Phenotype in Diabetic Stroke as Visualized by Optical Imaging

Regulatory T cells (Tregs) play an immunosuppressive role in various diseases, yet their function remains controversial in stroke and obscure in diabetic stroke. In the present study, Tregs were found downregulated in the peripheral blood of type 2 diabetes mellitus (T2DM) stroke models and patients compared with controls. In ischemic stroke mice (both T2DM and wild type), endogenous Tregs boosted by CD28SA increased CD206+ M2 macrophage/microglia cells, decreased infarct volumes, and improved neurological recovery. Our results demonstrated the potential of boosting Tregs for treating T2DM stroke. Furthermore, we utilized an optical imaging probe (IRD-αCD206) to target M2 macrophage/microglia cells and demonstrated its effect in visualizing M2 macrophage/microglia cells in vivo in ischemic brain tissue.

Regulatory T cell is critical for interleukin-33-mediated neuroprotection against stroke

Interleukin-33 (IL-33) is known to activate the regulatory T lymphocytes (Tregs), which are negatively correlated with brain damage after ischemic stroke. In this study, we aimed to investigate the role of Tregs in IL-33-mediated neuroprotection and elucidate the underlying mechanisms. In vivo, male C57BL/6 N mice were subjected to 60 min of transient middle cerebral artery occlusion (tMCAO), followed by daily administration of vehicle or IL-33 immediately after injury. Tregs were depleted by intraperitoneal administration of anti-CD25 antibody (anti-CD25Ab). Behavioral changes, brain edema, neuronal injury, Treg percentages, and cytokine expression levels were investigated in each group. In vitro experiments, primary mouse neuronal cells were subjected to oxygen-glucose deprivation (OGD) for 3 h. Vehicle- or drug-conditioned Tregs were applied to the neurons at the time of induction of hypoxia. Neuronal apoptosis and cytokine expression were measured in each group. The results indicate that intraperitoneal administration of anti-CD25Ab reduced CD4 + CD25 + Foxp3+ Tregs, increased infarct volume, enhanced stroke-induced cell death, and decreased sensorimotor functions. Notably, IL-33 increased CD4 + CD25 + Foxp3+ Tregs in the spleen and brain. However, blockading ST2 attenuated these effects of IL-33. The supernatant of the IL-33-treated Treg culture reduced neuronal apoptosis and elevated the production of the Treg cytokines IL-10, IL-35, and transforming growth factor-β (TGF-β). Anti-CD25Ab abrogated the neuroprotective effect of IL-33. Mechanistically, the neuroprotective effects of IL-33 were associated with reduction in apoptosis-related proteins and production of Tregs related cytokines. Overall, these findings showed that IL-33 afforded neuroprotection against ischemic brain injury by enhancing ST2-dependent regulatory T-cell expansion and activation via a mechanism involving anti-apoptosis proteins and cytokines, representing a promising immune modulatory target for the treatment of stroke.

Siponimod (BAF312) Treatment Reduces Brain Infiltration but Not Lesion Volume in Middle-Aged Mice in Experimental Stroke

Background and Purpose- The contribution of neuroinflammation and, in particular, the infiltration of the brain by lymphocytes is increasingly recognized as a substantial pathophysiological mechanism after stroke. The interaction of lymphocytes with endothelial cells and platelets, termed thromboinflammation, fosters microvascular dysfunction and secondary infarct growth. Siponimod is an S1PR (sphingosine-1-phosphate receptor) modulator, which blocks the egress of lymphocytes from lymphoid organs and has demonstrated beneficial effects in multiple sclerosis treatment. We investigated the effect of treatment with siponimod on stroke outcome in a mouse model of cerebral ischemia. Methods- Transient middle cerebral artery occlusion was induced in middle-aged wild-type mice. Animals were either treated with siponimod (3 mg/kg; intraperitoneal) or vehicle for 6 days. Stroke outcome was assessed by magnetic resonance imaging (spleen volume: prestroke, day 3, and day 7; infarct volume: days 1, 3, and 7) and behavioral tests (prestroke, day 2, and day 6). Immune cells of the peripheral blood and brain-infiltrating cells ipsilateral and contralateral were analyzed by VETScan and by flow cytometry. Results- Siponimod significantly induced lymphopenia on day 7 after transient middle cerebral artery occlusion and reduced T-lymphocyte accumulation in the central nervous system. No effect was detected for lesion size. Conclusions- For siponimod administered at 3 mg/kg in transient middle cerebral artery occlusion mouse model, our findings do not provide preclinical evidence for the use of S1PR1/5 modulators as neuroprotectant in stroke therapy.

Regulatory T-cells within bone marrow-derived stem cells actively confer immunomodulatory and neuroprotective effects against stroke

Regulatory T-cells (Tregs) may exert a neuroprotective effect on ischemic stroke by inhibiting both inflammation and effector T-cell activation. Transplantation of human bone marrow-derived stem cells (BMSCs) in ischemic stroke affords neuroprotection that results in part from the cells' anti-inflammatory property. However, the relationship between Tregs and BMSCs in treatment of ischemic stroke has not been fully elucidated. Here, we tested the hypothesis that Tregs within the BMSCs represent active mediators of immunomodulation and neuroprotection in experimental stroke. Primary rat neuronal cells were subjected to an oxygen-glucose deprivation and reperfusion (OGD/R) condition. The cells were re-perfused and co-cultured with Tregs and/or BMSCs. We detected a minority population of Tregs within BMSCs with both immunocytochemistry (ICC) and flow cytometry identifying cells expressing phenotypic markers of CD4, CD25, and FoxP3 protein. BMSCs with the native population of Tregs conferred maximal neuroprotection compared to the treatment conditions containing 0%, 10%, and 100% relative ratio Tregs. Increasing the Treg population resulted in increased IL6 secretion and decreased FGF-β secretion by BMSCs. This study shows that a minority population of Tregs exists within the therapeutic BMSC population, which serves as robust mediators of the immunomodulatory and neuroprotective effect provided by BMSC transplantation.

Perfluorinated substances, risk factors for multiple sclerosis and cellular immune activation

Perfluorinated alkylated substances (PFASs) have immunomodulatory effects but the impact on multiple sclerosis (MS) and cellular immune functions is only sparsely described. In the present study, we found lower concentrations of the long chain PFAS perfluorooctane sulfonic acid (PFOS) in MS than in healthy controls (HC). In HC, we did not detect associations between PFOS concentrations and immune phenotypes. Analyzing the impact of known MS risk factors on cellular immune functions, we found that smoking and Epstein-Barr nuclear antigen 1 antibodies were associated with distinct circulating immune cell changes. In summary, current background PFAS exposure is not an important risk factor for MS.

The Value of a Rapid Test of Human Regulatory T Cell Function Needs to be Revised

CD4⁺CD25⁺FoxP3⁺ human regulatory T_CELLS (T_REG) are promising candidates for reshaping undesired immunity/inflammation by adoptive cell transfer, yet their application is strongly dependent on robust assays testing their functionality. Several studies along with first clinical data indicate T_REG to be auspicious to use for future cell therapies, e.g., to induce tolerance after solid organ transplantation. To this end, T_REG suppressive capacity has to be thoroughly evaluated prior to any therapeutic application. A 7 h-protocol for the assessment of T_REG function by suppression of the early activation markers CD154 and CD69 on CD4⁺CD25⁻ responder T_CELLS (T_RESP) upon polyclonal stimulation via αCD3/28-coated activating microbeads has previously been published. Even though this assay has since been applied by various groups, the protocol comes with a critical pitfall, which is yet not corrected by the journal of its original publication. Our results demonstrate that the observed decrease in activation marker frequency on T_RESP is due to competition for αCD3/28-coated microbeads as opposed to a T_REG-attributable effect and therefore the protocol cannot further be used as a diagnostic test to assess suppressive T_REG function.

Human tissue kallikrein in the treatment of acute ischemic stroke

Acute ischemic stroke (AIS) remains a major cause of death and disability throughout the world. The most severe form of stroke results from large vessel occlusion of the major branches of the Circle of Willis. The treatment strategies currently available in western countries for large vessel occlusion involve rapid restoration of blood flow through removal of the offending blood clot using mechanical or pharmacological means (e.g. tissue plasma activator; tPA). This review assesses prospects for a novel pharmacological approach to enhance the availability of the natural enzyme tissue kallikrein (KLK1), an important regulator of local blood flow. KLK1 is responsible for the generation of kinins (bradykinin and kallidin), which promote local vasodilation and long-term vascularization. Moreover, KLK1 has been used clinically as a direct treatment for multiple diseases associated with impaired local blood flow including AIS. A form of human KLK1 isolated from human urine is approved in the People's Republic of China for subacute treatment of AIS. Here we review the rationale for using KLK1 as an additional pharmacological treatment for AIS by providing the biochemical mechanism as well as the human clinical data that support this approach.

Complex interplay of multiple biological systems that contribute to post-stroke infections

Stroke is a leading contributor of death and disability around the world. Despite its recognised debilitating neurological deficits, a devastating clinical complication of surviving stroke patients that needs more attention is infection. Up to half of the patients develop infections after stroke, and a high proportion of them will die as a direct consequence. Major clinical trials that examined preventive antibiotic therapy in stroke patients have demonstrated this method of prevention is not effective as it does not reduce incidence of post-stroke pneumonia or improve patient outcome. Additionally, retrospective studies evaluating the use of β-blockers for the modulation of the sympathetic nervous system to prevent post-stroke infections have given mixed results. Therefore, there is an urgent need for more effective therapeutic options that target the underlying mechanisms of post-stroke infections. The understanding that infections are largely attributable to the "stroke-induced systemic immunosuppression" phenomenon has begun to emerge, and thus, exploring the pathways that trigger post-stroke immunosuppression is expected to reveal potential new therapeutics. As such, we will outline the impacts that stroke has on several biological systems in this review, and discuss how these contribute to host susceptibility to infection after stroke. Furthermore, the emerging role of the gut and its microbiota has recently come to surface and intensifies the complex pathways to post-stroke infection. Finally, we identify potential avenues to combat infection that target the pathways of stroke-induced systemic immunosuppression to ultimately improve stroke patient outcome.

Regulatory T cells increase after treatment with poly (ADP-ribose) polymerase-1 inhibitor in ischemic stroke patients

BACKGROUND

Regulatory T cells (Tregs) are thought to play a modulatory role in immune responses and to improve outcomes after ischemic stroke. Thus, various strategies for increasing Tregs in animal models of ischemic stroke have yielded successful results. The aim of this study was to examine the potential effect of poly (ADP-ribose) polymerase-1 (PARP-1) inhibitor on Treg proportion in stroke patients.

METHODS

Peripheral blood samples were collected from 12 ischemic stroke patients (within 72 h of stroke onset) and 5 healthy control subjects. Flow cytometry analyses and quantitative reverse transcription polymerase chain reactions (qRT-PCR) were performed on peripheral blood mononuclear cells (PBMCs) before and after treating them with PARP-1 inhibitor (3-AB; JPI-289 1 μm, JPI-289 10 μm) for 24 h.

RESULTS

Treg proportions were significantly higher in healthy controls (median 2.8%, IQR 2.6-5.0%) than ischemic stroke patients (median 1.6%, IQR 1.25-2.2%) (p < 0.001). In the latter, Treg proportions were positively correlated with age (r = 0.595, p = 0.041), but not with infarct volume (r = 0.367, p = 0.241). After PARP-1 inhibitor treatment, Treg proportions among PBMCs increased in response to high dose (10 μm) JPI-289 (median 2.3%, IQR 2.0-2.9%) as did Treg-associated transcription factors such as FoxP3 and CTLA-4 mRNA. PARP-1 inhibitor treatment also decreased pro-inflammatory cytokines (IFN-γ, TNF-α, and IL-17) and increased anti-inflammatory cytokines (IL-4, IL-10, and TGF-β1).

CONCLUSION

Treg proportions are reduced in ischemic stroke patients and increased by treatment with high-dose PARP-1 inhibitor JPI-289. The PARP-1 inhibitor also had a possible anti-inflammatory effect on cytokine levels, and may ameliorate the outcome of ischemic stroke by up-regulating Tregs.

The Dual Role of Treg in Cancer

Regulatory T cells (Tregs) represent a small subpopulation of CD4⁺ cells. Tregs are characterized by the expression of transcription factor Forkhead box protein 3 (FoxP3), also known as scurfin. Tregs are modulators of adaptive immune responses and play an important role in maintaining tolerance to self-antigens, providing the suppression associated with tumour microenvironment as well. These immunomodulatory properties are the main reason for the development of numerous therapeutic strategies, designed to inhibit the activity of cancer cells. However, due to Treg subpopulation diversity and its many functional pathways, the role of these cells in the cancer development and progression is still not fully understood.

Sex differences in stroke across the lifespan: The role of T lymphocytes

Stroke is a sexually dimorphic disease. Ischemic sensitivity changes throughout the lifespan and outcomes depend largely on variables like age, sex, hormonal status, inflammation, and other existing risk factors. Immune responses after stroke play a central role in how these factors interact. Although the post-stroke immune response has been extensively studied, the contribution of lymphocytes to stroke is still not well understood. T cells participate in both innate and adaptive immune responses at both acute and chronic stages of stroke. T cell responses also change at different ages and are modulated by hormones and sex chromosome complement. T cells have also been implicated in the development of hypertension, one of the most important risk factors for vascular disease. In this review, we highlight recent literature on the lymphocytic responses to stroke in the context of age and sex, with a focus on T cell response and the interaction with important stroke risk factors.