Isolation and characterization of CD8+ regulatory T cells in multiple sclerosis

Disruption of IFNγ, GZMB, PRF1, or LYST Results in Reduced Suppressive Function in Human CD8+ T Cells

An imbalance between proinflammatory and regulatory processes underlies autoimmune disease pathogenesis. We have shown that acute relapses of multiple sclerosis are characterized by a deficit in the immune suppressive ability of CD8+ T cells. These cells play an important immune regulatory role, mediated in part through cytotoxicity (perforin [PRF]/granzyme [GZM]) and IFNγ secretion. In this study, we further investigated the importance of IFNγ-, GZMB-, PRF1-, and LYST-associated pathways in CD8+ T cell-mediated suppression. Using the CRISPR-Cas9 ribonucleoprotein transfection system, we first optimized efficient gene knockout while maintaining high viability in primary bulk human CD8+ T cells. Knockout was confirmed through quantitative real-time PCR assays in all cases, combined with flow cytometry where appropriate, as well as confirmation of insertions and/or deletions at genomic target sites. We observed that the knockout of IFNγ, GZMB, PRF1, or LYST, but not the knockout of IL4 or IL5, resulted in significantly diminished in vitro suppressive ability in these cells. Collectively, these results reveal a pivotal role for these pathways in CD8+ T cell-mediated immune suppression and provide important insights into the biology of human CD8+ T cell-mediated suppression that could be targeted for immunotherapeutic intervention.

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

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

CD8 T-cell subsets: heterogeneity, functions, and therapeutic potential

CD8 T cells play crucial roles in immune surveillance and defense against infections and cancer. After encountering antigenic stimulation, naïve CD8 T cells differentiate and acquire effector functions, enabling them to eliminate infected or malignant cells. Traditionally, cytotoxic T cells, characterized by their ability to produce effector cytokines and release cytotoxic granules to directly kill target cells, have been recognized as the constituents of the predominant effector T-cell subset. However, emerging evidence suggests distinct subsets of effector CD8 T cells that each exhibit unique effector functions and therapeutic potential. This review highlights recent advancements in our understanding of CD8 T-cell subsets and the contributions of these cells to various disease pathologies. Understanding the diverse roles and functions of effector CD8 T-cell subsets is crucial to discern the complex dynamics of immune responses in different disease settings. Furthermore, the development of immunotherapeutic approaches that specifically target and regulate the function of distinct CD8 T-cell subsets holds great promise for precision medicine.

Neuro-PASC is characterized by enhanced CD4+ and diminished CD8+ T cell responses to SARS-CoV-2 Nucleocapsid protein

Introduction

Many people with long COVID symptoms suffer from debilitating neurologic post-acute sequelae of SARS-CoV-2 infection (Neuro-PASC). Although symptoms of Neuro-PASC are widely documented, it is still unclear whether PASC symptoms impact virus-specific immune responses. Therefore, we examined T cell and antibody responses to SARS-CoV-2 Nucleocapsid protein to identify activation signatures distinguishing Neuro-PASC patients from healthy COVID convalescents.

Results

We report that Neuro-PASC patients exhibit distinct immunological signatures composed of elevated CD4+ T cell responses and diminished CD8+ memory T cell activation toward the C-terminal region of SARS-CoV-2 Nucleocapsid protein when examined both functionally and using TCR sequencing. CD8+ T cell production of IL-6 correlated with increased plasma IL-6 levels as well as heightened severity of neurologic symptoms, including pain. Elevated plasma immunoregulatory and reduced pro-inflammatory and antiviral response signatures were evident in Neuro-PASC patients compared with COVID convalescent controls without lasting symptoms, correlating with worse neurocognitive dysfunction.

Discussion

We conclude that these data provide new insight into the impact of virus-specific cellular immunity on the pathogenesis of long COVID and pave the way for the rational design of predictive biomarkers and therapeutic interventions.

Learning from the nexus of autoimmunity and cancer

The immune system plays critical roles in both autoimmunity and cancer, diseases at opposite ends of the immune spectrum. Autoimmunity arises from loss of T cell tolerance against self, while in cancer, poor immunity against transformed self fails to control tumor growth. Blockade of pathways that preserve self-tolerance is being leveraged to unleash immunity against many tumors; however, widespread success is hindered by the autoimmune-like toxicities that arise in treated patients. Knowledge gained from the treatment of autoimmunity can be leveraged to treat these toxicities in patients. Further, the understanding of how T cell dysfunction arises in cancer can be leveraged to induce a similar state in autoreactive T cells. Here, we review what is known about the T cell response in autoimmunity and cancer and highlight ways in which we can learn from the nexus of these two diseases to improve the application, efficacy, and management of immunotherapies.

Implications of NKG2A in immunity and immune-mediated diseases

In recent studies, NKG2A is revealed to be a key immune checkpoint for both natural killer (NK) cells and CD8⁺ T cells. It form heterodimer receptors with CD94, and targets the peptide-presenting human leukocyte antigen-E (HLA-E) molecules. Upon crosslinking, NKG2A/CD94 delivers inhibitory signals for NK cells and CD8⁺ T cells, while blocking NKG2A can effectively unleash functions of these cytotoxic lymphocytes. The interaction between NKG2A and HLA-E contributes to tumor immune escape, and NKG2A-mediated mechanisms are currently being exploited to develop potential antitumor therapeutic strategies. In addition, growing evidence shows that NKG2A also plays important roles in other immune-related diseases including viral infections, autoimmune diseases, inflammatory diseases, parasite infections and transplant rejection. Therefore, the current work focuses on describing the effect of NKG2A on immune regulation and exploring its potential role in immune-mediated disorders.

MicroRNAs as T Lymphocyte Regulators in Multiple Sclerosis

MicroRNA (miRNA) is a class of endogenous non-coding small RNA with regulatory activities, which generally regulates the expression of target genes at the post-transcriptional level. Multiple Sclerosis (MS) is thought to be an autoimmune-mediated chronic inflammatory demyelinating disease of the central nervous system (CNS) that typically affect young adults. T lymphocytes play an important role in the pathogenesis of MS, and studies have suggested that miRNAs are involved in regulating the proliferation, differentiation, and functional maintenance of T lymphocytes in MS. Dysregulated expression of miRNAs may lead to the differentiation balance and dysfunction of T lymphocytes, and they are thus involved in the occurrence and development of MS. In addition, some specific miRNAs, such as miR-155 and miR-326, may have potential diagnostic values for MS or be useful for discriminating subtypes of MS. Moreover, miRNAs may be a promising therapeutic strategy for MS by regulating T lymphocyte function. By summarizing the recent literature, we reviewed the involvement of T lymphocytes in the pathogenesis of MS, the role of miRNAs in the pathogenesis and disease progression of MS by regulating T lymphocytes, the possibility of differentially expressed miRNAs to function as biomarkers for MS diagnosis, and the therapeutic potential of miRNAs in MS by regulating T lymphocytes.

Cytolytic CD4+ and CD8+ Regulatory T-Cells and Implications for Developing Immunotherapies to Combat Graft-Versus-Host Disease

Regulatory T-cells (Treg) are critical for the maintenance of immune homeostasis and tolerance induction. While the immunosuppressive mechanisms of Treg have been extensively investigated for decades, the mechanisms responsible for Treg cytotoxicity and their therapeutic potential in regulating immune responses have been incompletely explored and exploited. Conventional cytotoxic T effector cells (Teffs) are known to be important for adaptive immune responses, particularly in the settings of viral infections and cancer. CD4+ and CD8+ Treg subsets may also share similar cytotoxic properties with conventional Teffs. Cytotoxic effector Treg (cyTreg) are a heterogeneous population in the periphery that retain the capacity to suppress T-cell proliferation and activation, induce cellular apoptosis, and migrate to tissues to ensure immune homeostasis. The latter can occur through several cytolytic mechanisms, including the Granzyme/Perforin and Fas/FasL signaling pathways. This review focuses on the current knowledge and recent advances in our understanding of cyTreg and their potential application in the treatment of human disease, particularly Graft-versus-Host Disease (GVHD).

Neuroinflammation in Autoimmune Disease and Primary Brain Tumors: The Quest for Striking the Right Balance

According to classical dogma, the central nervous system (CNS) is defined as an immune privileged space. The basis of this theory was rooted in an incomplete understanding of the CNS microenvironment, however, recent advances such as the identification of resident dendritic cells (DC) in the brain and the presence of CNS lymphatics have deepened our understanding of the neuro-immune axis and revolutionized the field of neuroimmunology. It is now understood that many pathological conditions induce an immune response in the CNS, and that in many ways, the CNS is an immunologically distinct organ. Hyperactivity of neuro-immune axis can lead to primary neuroinflammatory diseases such as multiple sclerosis and antibody-mediated encephalitis, whereas immunosuppressive mechanisms promote the development and survival of primary brain tumors. On the therapeutic front, attempts are being made to target CNS pathologies using various forms of immunotherapy. One of the most actively investigated areas of CNS immunotherapy is for the treatment of glioblastoma (GBM), the most common primary brain tumor in adults. In this review, we provide an up to date overview of the neuro-immune axis in steady state and discuss the mechanisms underlying neuroinflammation in autoimmune neuroinflammatory disease as well as in the development and progression of brain tumors. In addition, we detail the current understanding of the interactions that characterize the primary brain tumor microenvironment and the implications of the neuro-immune axis on the development of successful therapeutic strategies for the treatment of CNS malignancies.

Encephalitogenic and Regulatory CD8 T Cells in Multiple Sclerosis and Its Animal Models

Multiple sclerosis (MS), a neuroinflammatory disease that affects millions worldwide, is widely thought to be autoimmune in etiology. Historically, research into MS pathogenesis has focused on autoreactive CD4 T cells because of their critical role in the animal model, experimental autoimmune encephalomyelitis, and the association between MS susceptibility and single-nucleotide polymorphisms in the MHC class II region. However, recent studies have revealed prominent clonal expansions of CD8 T cells within the CNS during MS. In this paper, we review the literature on CD8 T cells in MS, with an emphasis on their potential effector and regulatory properties. We discuss the impact of disease modifying therapies, currently prescribed to reduce MS relapse rates, on CD8 T cell frequency and function. A deeper understanding of the role of CD8 T cells in MS may lead to the development of more effective and selective immunomodulatory drugs for particular subsets of patients.

Immune Soluble Factors in the Cerebrospinal Fluid of Progressive Multiple Sclerosis Patients Segregate Into Two Groups

Primary-progressive (PP) and secondary-progressive (SP) multiple sclerosis (MS) are characterized by neurological deficits caused by a permanent neuronal damage, clinically quantified by the expanded disability status scale (EDSS). Neuronal tissue damage is also mediated by immune infiltrates producing soluble factors, such as cytokines and chemokines, which are released in the cerebrospinal fluid (CSF). The mechanisms regulating the production of a soluble factor are not completely defined. Using multiplex bead-based assays, we simultaneously measured 27 immune soluble factors in the CSF collected from 38 patients, 26 with PP-MS and 12 with SP-MS. Then, we performed a correlation matrix of all soluble factors expressed in the CSF. The CSF from patients with PP-MS and SP-MS had similar levels of cytokines and chemokines; however, the stratification of patients according to active or inactive magnetic resonance imaging (MRI) unveils some differences. Correlative studies between soluble factors in the CSF of patients with PP-MS and SP-MS revealed two clusters of immune mediators with pro-inflammatory functions, namely IFN-γ, MCP-1, MIP-1α, MIP-1β, IL-8, IP-10, and TNF-α (group 1), and anti-inflammatory functions, namely IL-9, IL-15, VEGF, and IL-1ra (group 2). However, most of the significant correlations between cytokines of group 1 and of group 2 were lost in patients with more severe disability (EDSS ≥ 4) compared to patients with mild to moderate disability (EDSS < 4). These results suggest a common regulation of cytokines and chemokines belonging to the same group and indicate that, in patients with more severe disability, the production of those factors is less coordinated, possibly due to advanced neurodegenerative mechanisms that interfere with the immune response.

CD8+ Tregs revisited: A heterogeneous population with different phenotypes and properties

Regulatory T cells (Tregs) play a key role in the peripheral self-tolerance and preventing autoimmunity. While classical CD4⁺ Foxp3⁺ Tregs are well established, their CD8⁺ counterparts are still controversial in many aspects including their phenotypic identity and their mechanisms of suppression. Because of these controversies and because of only a limited number of studies documenting the immunoregulatory function of CD8⁺ Tregs in vivo, the concept of CD8⁺ Tregs is still not unanimously accepted. We propose that any T-cell subset considered as true regulatory must be distinguishable from other cell types and must suppress in vivo immune responses via a known mechanism. In this article, we revisit the concept of CD8⁺ Tregs by focusing on the characterization of individual CD8⁺ T-cell subsets with proposed regulatory capacity separately. Therefore, we review the phenotype and function of CD8⁺ FOXP3⁺ T cells, CD8⁺ CD122⁺ T cells, CD8⁺ CD28^low/- T cells, CD8⁺ CD45RC^low T cells, T cells expressing CD8αα homodimer and Qa-1-restricted CD8⁺ T cells to show whether there is sufficient evidence to establish these subsets as bona fide Tregs. Based on the intrinsic ability of CD8⁺ Treg subsets to promote immune tolerance in animal models, we elaborate on their potential use in clinics.

CD8+ T cells: The past and future of immune regulation

Regulation of the adaptive immune response is critical for health. Regulatory activity can be found in multiple components of the immune system, however, the focus on particular components of the immune regulatory network has left many aspects of this critical immune component understudied. Here we review the evidence for activities of CD8+ T cells in immune homeostasis and regulation of autoimmune reactivity. The heterogeneous nature of identified CD8+ cell types are examined, and common phenotypes associated with functional activities are defined. The varying types of antigen signal crucial for CD8+ T cell regulatory activity are identified and the implications of these activation pathways for control of adaptive responses is considered. Finally, the promising capacity for transgenic antigen receptor directed cytotoxicity as a mechanism for modulation of autoimmunity is detailed.

B and T Cells Driving Multiple Sclerosis: Identity, Mechanisms and Potential Triggers

Historically, multiple sclerosis (MS) has been viewed as being primarily driven by T cells. However, the effective use of anti-CD20 treatment now also reveals an important role for B cells in MS patients. The results from this treatment put forward T-cell activation rather than antibody production by B cells as a driving force behind MS. The main question of how their interaction provokes both B and T cells to infiltrate the CNS and cause local pathology remains to be answered. In this review, we highlight key pathogenic events involving B and T cells that most likely contribute to the pathogenesis of MS. These include (1) peripheral escape of B cells from T cell-mediated control, (2) interaction of pathogenic B and T cells in secondary lymph nodes, and (3) reactivation of B and T cells accumulating in the CNS. We will focus on the functional programs of CNS-infiltrating lymphocyte subsets in MS patients and discuss how these are defined by mechanisms such as antigen presentation, co-stimulation and cytokine production in the periphery. Furthermore, the potential impact of genetic variants and viral triggers on candidate subsets will be debated in the context of MS.

Resolution of inflammation during multiple sclerosis

Multiple sclerosis (MS) is a frequent autoimmune demyelinating disease of the central nervous system (CNS). There are three clinical forms described: relapsing-remitting multiple sclerosis (RRMS), the most common initial presentation (85%) among which, if not treated, about half will transform, into the secondary progressive multiple sclerosis (SPMS) and the primary progressive MS (PPMS) (15%) that is directly progressive without superimposed clinical relapses. Inflammation is present in all subsets of MS. The relapsing/remitting form could represent itself a particular interest for the study of inflammation resolution even though it remains incomplete in MS. Successful resolution of acute inflammation is a highly regulated process and dependent on mechanisms engaged early in the inflammatory response that are scarcely studied in MS. Moreover, recent classes of disease-modifying treatment (DMTs) that are effective against RRMS act by re-establishing the inflammatory imbalance, taking advantage of the pre-existing endogenous suppressor. In this review, we will discuss the active role of regulatory immune cells in inflammation resolution as well as the role of tissue and non-hematopoietic cells as contributors to inflammation resolution. Finally, we will explore how DMTs, more specifically induction therapies, impact the resolution of inflammation during MS.

Interferon-β corrects massive gene dysregulation in multiple sclerosis: Short-term and long-term effects on immune regulation and neuroprotection

Background

In multiple sclerosis (MS), immune up-regulation is coupled to subnormal immune response to interferon-β (IFN-β) and low serum IFN-β levels. The relationship between the defect in IFN signalling and acute and long-term effects of IFN-β on gene expression in MS is inadequately understood.

Methods

We profiled IFN-β-induced transcriptome shifts, using high-resolution microarrays on 227 mononuclear cell samples from IFN-β-treated MS Complete Responders (CR) stable for five years, and stable and active Partial Responders (PR), stable and active untreated MS, and healthy controls.

Findings

IFN-β injection induced short-term changes in 1,200 genes compared to baseline expression after 4-day IFN washout. Pre-injection after washout, and in response to IFN-β injections, PR more frequently had abnormal gene expression than CR. Surprisingly, short-term IFN-β induced little shift in Th1/Th17/Th2 gene expression, but up-regulated immune-inhibitory genes (ILT, IDO1, PD-L1). Expression of 8,800 genes was dysregulated in therapy-naïve compared to IFN-β-treated patients. These long-term changes in protein-coding and long non-coding RNAs affect immunity, synaptic transmission, and CNS cell survival, and correct the disordered therapy-naïve transcriptome to near-normal. In keeping with its impact on clinical course and brain repair in MS, long-term IFN-β treatment reversed the overexpression of proinflammatory and MMP genes, while enhancing genes involved in the oligodendroglia-protective integrated stress response, neuroprotection, and immunoregulation. In the rectified long-term signature, 277 transcripts differed between stable PR and CR patients.

Interpretation

IFN-β had minimal short-term effects on Th1 and Th2 pathways, but long-term it corrected gene dysregulation and induced immunoregulatory and neuroprotective genes. These data offer new biomarkers for IFN-β responsiveness.

Funding

Unrestricted grants from the US National MS Society, NMSS RG#4509A, and Bayer Pharmaceuticals

Vitamin D enhances responses to interferon-β in MS

Objective

To determine the effect of vitamin D3 on interferon-β (IFN-β) response and immune regulation in MS mononuclear cells (MNCs).

Methods

MNCs from 126 subjects, including therapy-naive patients with different forms of MS, plus patients with MS receiving IFN-β or glatiramer treatment, plus healthy controls were incubated in vitro with IFN-β-1b ± vitamin D3 (calcitriol). Activation of the IFN-β–induced transcription factor, p-Y-STAT1, and antiviral myxovirus A (MxA) protein was measured with flow cytometry and Western blots; serum proteins were measured with a customized 31-protein multiplex assay.

Results

Vitamin D enhanced in vitro IFN responses, as measured by induction of p-Y-STAT1 and MxA in MNCs, T cells, and monocytes. Vitamin D augmentation of IFN responses was seen in untreated and in IFN-β-1b–treated MS. The combination of vitamin D plus IFN-β reduced Th1 and Th17 cytokines, and increased Th2 responses, reversing the effect of IFN-β alone. Exacerbations and progression in untreated patients reduced the vitamin D enhancement of IFN responses. Vitamin D had less effect on IFN response in clinically stable glatiramer-treated than in IFN-β–treated patients.

Conclusion

Vitamin D enhances IFN-β induction of multiple proteins and also reverses the Th1/Th2 bias in MS seen with IFN-β alone. The combination of vitamin D and IFN-β has potential benefit in ameliorating MS.

Towards Clinical Translation of CD8+ Regulatory T Cells Restricted by Non-Classical Major Histocompatibility Complex Ib Molecules

In central lymphoid tissues, mature lymphocytes are generated and pathogenic autoreactive lymphocytes are deleted. However, it is currently known that a significant number of potentially pathogenic autoreactive lymphocytes escape the deletion and populate peripheral lymphoid tissues. Therefore, peripheral mechanisms are present to prevent these potentially pathogenic autoreactive lymphocytes from harming one's own tissues. One such mechanism is dictated by regulatory T (Treg) cells. So far, the most extensively studied Treg cells are CD4+Foxp3+ Treg cells. However, recent clinical trials for the treatment of immune-mediated diseases using CD4+ Foxp3+ Treg cells met with limited success. Accordingly, it is necessary to explore the potential importance of other Treg cells such as CD8+ Treg cells. In this regard, one extensively studied CD8+ Treg cell subset is Qa-1(HLA-E in human)-restricted CD8+ Treg cells, in which Qa-1(HLA-E) molecules belong to a group of non-classical major histocompatibility complex Ib molecules. This review will first summarize the evidence for the presence of Qa-1-restricted CD8+ Treg cells and their regulatory mechanisms. Major discussions will then focus on the potential clinical translation of Qa-1-restricted CD8+ Treg cells. At the end, we will briefly discuss the current status of human studies on HLA-E-restricted CD8+ Treg cells as well as potential future directions.

Frequency of CD8+ regulatory T cells in the multiple sclerosis patients: a systematic review and meta-analysis

Multiple sclerosis (MS) is a neuro-immunological demyelinating disease. From the immunological aspects, it is well accepted that T cells play a pivotal role in the etiology of the disease. T helper (Th) 1 and Th17 cells are thought to be the main pathogenic T cells in the pathogenesis of MS and are known as effector T cells. As the self-reactive T lymphocytes can escape clonal deletion in the thymus and subsequently are released into the periphery, there is an urgent need for peripheral tolerance, which is executed by the specialized regulatory T (Treg) cells. Interestingly, CD8⁺ regulatory T (Treg) cells have also been identified among lymphocyte subtypes. The peripheral CD8⁺ Treg cells frequency in MS subjects in comparison with healthy controls is the objective of the current study using the systematic review and meta-analysis. A systematic literature search was carried out using specialized biomedical databases of Pubmed, Pubmed Central, Medline, Google Scholar, Embase and SCOPUS databases without the beginning date restriction until January 2018 in English language. The results were as follows: OR 15.548 (95% confidence interval 1.954-123.742) using the random-effects model. The P value for test of significance of the total OR was examined by the z test and calculated as 0.010 (clearly considered as statistically significant). Based on our findings, the number of CD8⁺ Treg cells in the blood of MS subjects is significantly different as compared to healthy controls.

Experimental Autoimmune Encephalomyelitis (EAE) as Animal Models of Multiple Sclerosis (MS)

Multiple sclerosis (MS) is a multifocal demyelinating disease of the central nervous system (CNS) leading to the progressive destruction of the myelin sheath surrounding axons. It can present with variable clinical and pathological manifestations, which might reflect the involvement of distinct pathogenic processes. Although the mechanisms leading to the development of the disease are not fully understood, numerous evidences indicate that MS is an autoimmune disease, the initiation and progression of which are dependent on an autoimmune response against myelin antigens. In addition, genetic susceptibility and environmental triggers likely contribute to the initiation of the disease. At this time, there is no cure for MS, but several disease-modifying therapies (DMTs) are available to control and slow down disease progression. A good number of these DMTs were identified and tested using animal models of MS referred to as experimental autoimmune encephalomyelitis (EAE). In this review, we will recapitulate the characteristics of EAE models and discuss how they help shed light on MS pathogenesis and help test new treatments for MS patients.

Effector T Cells in Multiple Sclerosis

Multiple sclerosis (MS) has long been considered a CD4 T-cell disease, primarily because of the findings that the strongest genetic risk for MS is the major histocompatibility complex (MHC) class II locus, and that T cells play a central role in directing the immune response. The importance that the T helper (Th)1 cytokine, interferon γ (IFN-γ), and the Th17 cytokine, interleukin (IL)-17, play in MS pathogenesis is indicated by recent clinical trial data by the enhanced presence of Th1/Th17 cells in central nervous system (CNS) tissue, cerebrospinal fluid (CSF), and blood, and by research on animal models of MS, such as experimental autoimmune encephalomyelitis (EAE). Although the majority of research on MS pathogenesis has centered on the role of effector CD4 T cells, accumulating data suggests that CD8 T cells may play a significant role in the human disease. In fact, in contrast to most animal models, the primary T cell found in the CNS in patients with MS, is the CD8 T cell. As patient-derived effector T cells are also resistant to mechanisms of dominant tolerance such as that induced by interaction with regulatory T cells (Tregs), their reduced response to regulation may also contribute to the unchecked effector T-cell activity in patients with MS. These concepts will be discussed below.

Th17 cells, γδ T cells and their interplay in EAE and multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis (MS) that shares many features with the human disease. This review will focus on the role of IL-17-secreting CD4 and γδ T cells in EAE and MS, the plasticity of Th17 cells in vivo and the application of these findings to the understating of the pathogenesis and the development of new treatments for MS. There is convincing evidence that IL-17-secreting CD4 T cells (Th17 cells) and IL-17-secreting γδ T cells play a critical pathogenic role in central nervous system (CNS) inflammation in EAE and MS. Indeed a significant number of the major discoveries on the pathogenic role of IL-17-secreting T cells in autoimmunity were made in the EAE model. These included the first demonstration that IL-23-activated IL-17-secreting T cells are the key T cells in driving autoimmune disease pathology. Although the early studies on IL-17 focused on Th17 cells, it was later demonstrated that γδ T cells were an important early source of IL-17 and IL-21 that helped amplify IL-17 production by Th17 cells in autoimmune diseases. Furthermore, it emerged that Th1 cells can also have encephalitogenic activity and that there was considerable plasticity in these T cell responses, with Th17 cells reverting to a Th1 phenotype in vivo. This questioned the pathogenic role of IL-17 and suggested that other cytokines, such as IFN-γ, GM-CSF and TNF, may be important. Nevertheless, biological drugs that target the IL-23-IL-17 pathway are highly effective in treating human psoriasis and are showing promise in the treatment of relapsing remitting MS and other T-cell mediated autoimmune diseases.

The influence and impact of ageing and immunosenescence (ISC) on adaptive immunity during multiple sclerosis (MS) and the animal counterpart experimental autoimmune encephalomyelitis (EAE)

The human ageing process encompasses mechanisms that effect a decline in homeostasis with increased susceptibility to disease and the development of chronic life-threatening illness. Increasing age affects the immune system which undergoes a progressive loss of efficiency, termed immunosenescence (ISC), to impact on quantitative and functional aspects of innate and adaptive immunity. The human demyelinating disease multiple sclerosis (MS) and the corresponding animal model experimental autoimmune encephalomyelitis (EAE) are strongly governed by immunological events that primarily involve the adaptive arm of the immune response. MS and EAE are frequently characterised by a chronic pathology and a protracted disease course which thereby creates the potential for exposure to the inherent, on-going effects and consequences of ISC. Collective evidence is presented to confirm the occurrence of established and unendorsed biological markers of ISC during the development of both diseases. Moreover, results are discussed from studies during the course of MS and EAE that reveal a premature upregulation of ISC-related biomarkers which indicates untimely alterations to the adaptive immune system. The effects of ISC and a prematurely aged immune system on autoimmune-associated neurodegenerative conditions such as MS and EAE are largely unknown but current evaluation of data justifies and encourages further investigation.

Enterococcus faecium strain L-3 and glatiramer acetate ameliorate experimental allergic encephalomyelitis in rats by affecting different populations of immune cells

The effect of probiotic Enterococcus faecium strain L-3 was studied in rats with experimental allergic encephalomyelitis (EAE). Glatiramer acetate (GA) was used as control drug. E. faecium strain L-3 and GA both were able to reduce the severity of EAE in a similar fashion. Both approaches increased the proportion of EAE resistant rats and rats with mild disease, prolonged the inductive phase of EAE and reduced the disease duration. Study of the phenotypes of immune cells in blood revealed the differences in immunoregulatory pathways that mediate the protective action of probiotic or GA treatment of EAE. The presence of pronounced protective and immunomodulating effects of the probiotic E. faecium strain L-3 opens an opportunity of its application for the treatment of multiple sclerosis.

CD8(+) T-Cells as Immune Regulators of Multiple Sclerosis

The vast majority of studies regarding the immune basis of MS (and its animal model, EAE) have largely focused on CD4(+) T-cells as mediators and regulators of disease. Interestingly, CD8(+) T-cells represent the predominant T-cell population in human MS lesions and are oligoclonally expanded at the site of pathology. However, their role in the autoimmune pathologic process has been both understudied and controversial. Several animal models and MS patient studies support a pathogenic role for CNS-specific CD8(+) T-cells, whereas we and others have demonstrated a regulatory role for these cells in disease. In this review, we describe studies that have investigated the role of CD8(+) T-cells in MS and EAE, presenting evidence for both pathogenic and regulatory functions. In our studies, we have shown that cytotoxic/suppressor CD8(+) T-cells are CNS antigen-specific, MHC class I-restricted, IFNγ- and perforin-dependent, and are able to inhibit disease. The clinical relevance for CD8(+) T-cell suppressive function is best described by a lack of their function during MS relapse, and importantly, restoration of their suppressive function during quiescence. Furthermore, CD8(+) T-cells with immunosuppressive functions can be therapeutically induced in MS patients by glatiramer acetate (GA) treatment. Unlike CNS-specific CD8(+) T-cells, these immunosuppressive GA-induced CD8(+) T-cells appear to be HLA-E restricted. These studies have provided greater fundamental insight into the role of autoreactive as well as therapeutically induced CD8(+) T-cells in disease amelioration. The clinical implications for these findings are immense and we propose that this natural process can be harnessed toward the development of an effective immunotherapeutic strategy.

Multiple Sclerosis and T Lymphocytes: An Entangled Story

Multiple sclerosis (MS) is the prototypic inflammatory disease of the central nervous system (CNS) characterized by multifocal areas of demyelination, axonal damage, activation of glial cells, and immune cell infiltration. Despite intensive years of research, the etiology of this neurological disorder remains elusive. Nevertheless, the abundance of immune cells such as T lymphocytes and their products in CNS lesions of MS patients supports the notion that MS is an immune-mediated disorder. An important body of evidence gathered from MS animal models such as experimental autoimmune encephalomyelitis (EAE), points to the central contribution of CD4 T lymphocytes in disease pathogenesis. Both Th1 (producing interferon-γ) and Th17 (producing interleukin 17) CD4 T lymphocytes targeting CNS self-antigens have been implicated in MS and EAE pathobiology. Moreover, several publications suggest that CD8 T lymphocytes also participate in the development of MS lesions. The migration of activated T lymphocytes from the periphery into the CNS has been identified as a crucial step in the formation of MS lesions. Several factors promote such T cell extravasation including: molecules (e.g., cell adhesion molecules) implicated in the T cell-blood brain barrier interaction, and chemokines produced by neural cells. Finally, once in the CNS, T lymphocytes need to be reactivated by local antigen presenting cells prior to enter the parenchyma where they can initiate damage. Further investigations will be necessary to elucidate the impact of environmental factors (e.g., gut microbiota) and CNS intrinsic properties (e.g., microglial activation) on this inflammatory neurological disease.

Immune regulation of multiple sclerosis by CD8+ T cells

The role of CD8+ T cells in the process of autoimmune pathology has been both understudied and controversial. Multiple sclerosis (MS) is an inflammatory, demyelinating disorder of the central nervous system (CNS) with underlying T cell-mediated immunopathology. CD8+ T cells are the predominant T cells in human MS lesions, showing oligoclonal expansion at the site of pathology. It is still unclear whether these cells represent pathogenic immune responses or disease-regulating elements. Through studies in human MS and its animal model, experimental autoimmune encephalomyelitis (EAE), we have discovered two novel CD8+ T cell populations that play an essential immunoregulatory role in disease: (1) MHC class Ia-restricted neuroantigen-specific "autoregulatory" CD8+ T cells and (2) glatiramer acetate (GA/Copaxone(®)) therapy-induced Qa-1/HLA-E-restricted GA-specific CD8+ T cells. These CD8+ Tregs suppress proliferation of pathogenic CD4+ CD25- T cells when stimulated by their cognate antigens. Similarly, CD8+ Tregs significantly suppress EAE when transferred either pre-disease induction or during peak disease. The mechanism of disease inhibition depends, at least in part, on an antigen-specific, contact-dependent process and works through modulation of CD4+ T cell responses as well as antigen-presenting cells through a combination of cytotoxicity and cytokine-mediated modulation. This review provides an overview of our understanding of CD8+ T cells in immune-mediated disease, focusing particularly on our findings regarding regulatory CD8+ T cells both in MS and in EAE. Clinical relevance of these novel CD8-regulatory populations is discussed, providing insights into a potentially intriguing, novel therapeutic strategy for these diseases.

Regulatory T cells in B cell follicles

Understanding germinal center reactions is crucial not only for the design of effective vaccines against infectious agents and malignant cells but also for the development of therapeutic intervention for the treatment of antibody-mediated immune disorders. Recent advances in this field have revealed specialized subsets of T cells necessary for the control of B cell responses in the follicle. These cells include follicular regulatory T cells and Qa-1-restricted cluster of differentiation (CD)8⁺ regulatory T cells. In this review, we discuss the current knowledge related to the role of regulatory T cells in the B cell follicle.

From classic to spontaneous and humanized models of multiple sclerosis: impact on understanding pathogenesis and drug development

Multiple sclerosis (MS), a demyelinating disease of the central nervous system (CNS), presents as a complex disease with variable clinical and pathological manifestations, involving different pathogenic pathways. Animal models, particularly experimental autoimmune encephalomyelitis (EAE), have been key to deciphering the pathophysiology of MS, although no single model can recapitulate the complexity and diversity of MS, or can, to date, integrate the diverse pathogenic pathways. Since the first EAE model was introduced decades ago, multiple classic (induced), spontaneous, and humanized EAE models have been developed, each recapitulating particular aspects of MS pathogenesis. The advances in technologies of genetic ablation and transgenesis in mice of C57BL/6J background and the development of myelin-oligodendrocyte glycoprotein (MOG)-induced EAE in C57BL/6J mice yielded several spontaneous and humanized EAE models, and resulted in a plethora of EAE models in which the role of specific genes or cell populations could be precisely interrogated, towards modeling specific pathways of MS pathogenesis/regulation in MS. Collectively, the numerous studies on the different EAE models contributed immensely to our basic understanding of cellular and molecular pathways in MS pathogenesis as well as to the development of therapeutic agents: several drugs available today as disease modifying treatments were developed from direct studies on EAE models, and many others were tested or validated in EAE. In this review, we discuss the contribution of major classic, spontaneous, and humanized EAE models to our understanding of MS pathophysiology and to insights leading to devising current and future therapies for this disease.

TGF-β prevents T follicular helper cell accumulation and B cell autoreactivity

T follicular helper (Tfh) cells contribute to the establishment of humoral immunity by controlling the delivery of helper signals to activated B cells; however, Tfh development must be restrained, as aberrant accumulation of these cells is associated with positive selection of self-reactive germinal center B cells and autoimmunity in both humans and mice. Here, we show that TGF-β signaling in T cells prevented Tfh cell accumulation, self-reactive B cell activation, and autoantibody production. Using mice with either T cell-specific loss or constitutive activation of TGF-β signaling, we demonstrated that TGF-β signaling is required for the thymic maturation of CD44⁺CD122⁺Ly49⁺CD8⁺ regulatory T cells (Tregs), which induce Tfh apoptosis and thus regulate this cell population. Moreover, peripheral Tfh cells escaping TGF-β control were resistant to apoptosis, exhibited high levels of the antiapoptotic protein BCL2, and remained refractory to regulation by CD8+ Tregs. The unrestrained accumulation of Tfh cells in the absence of TGF-β was dependent on T cell receptor engagement and required B cells. Together, these data indicate that TGF-β signaling restrains Tfh cell accumulation and B cell-associated autoimmunity and thereby controls self-tolerance.

How type I interferons work in multiple sclerosis and other diseases: some unexpected mechanisms

Type I interferons (IFNs) are important in innate and adaptive immunity. They are used to treat virus infections, cancer, and multiple sclerosis (MS). There are 5 type I IFN families in humans-IFN-α with 13 subtypes, plus IFN-β, ɛ, κ, and ω. Because their receptor binding affinities vary, these IFNs have different gene induction profiles and quite variable therapeutic effects. IFN-α subtypes may each be specific for certain viruses, but can be neurotoxic. IFN-β induces IFN-α, plus has additional direct effects on target cells. IFN-β was the first therapy approved that could change the course of MS. It has broader specificity than IFN-α, enhances cognition in MS, and may be neuroprotective and can potentially enhance fertility in women. Priming the IFN signaling system with an injection of IFN-β can enhance subnormal type I IFN signals in MS. Many other commonly used drugs and vitamins may potentiate clinical benefits of IFN-β.

HLA-E restricted CD8+ T cell subsets are phenotypically altered in multiple sclerosis patients

BACKGROUND

The importance of Qa-1 restricted CD8(+) T cells in regulating autoreactive T cell responses has been demonstrated in animal models for autoimmune disorders, including multiple sclerosis (MS).

OBJECTIVE

We hypothesize that their human variant, HLA-E restricted CD8(+) T cells, fulfills a similar regulatory role in man and that these cells are of importance in MS.

METHODS

A large cohort of MS patients and healthy controls was genotyped for the two known HLA-E polymorphisms. Flow cytometry was used to determine HLA-E expression kinetics and to phenotype HLA-E restricted CD8(+) T cells. Immunohistochemistry was performed to investigate HLA-E expression in the central nervous system (CNS) of MS patients.

RESULTS

HLA-E is upregulated on immune cells upon in vitro activation and this upregulation is polymorphism-dependent for T and B cells. T and B cells in lesions of MS patients show enhanced HLA-E expression. Furthermore, NKG2C(+)CD8(+) T cells of MS patients have a significantly lower Foxp3 expression, while NKG2A(+)CD8(+) T cells of MS patients produce higher levels of pro-inflammatory cytokines compared to those of healthy individuals.

CONCLUSION

Our study indicates that the HLA-E system is altered in MS and could play a regulatory role in disease.

Disease exacerbation of multiple sclerosis is characterized by loss of terminally differentiated autoregulatory CD8+ T cells

Multiple sclerosis (MS) is an inflammatory, demyelinating disease of the central nervous system (CNS). Although its etiology remains unknown, pathogenic T cells are thought to underlie MS immune pathology. We recently showed that MS patients harbor CNS-specific CD8+ Tregs that are deficient during disease relapse. We now demonstrate that CNS-specific CD8+ Tregs were cytolytic and could eliminate pathogenic CD4+ T cells. These CD8+ Tregs were present primarily in terminally differentiated (CD27-, CD45RO-) subset and their suppression was IFNγ, perforin and granzyme B-dependent. Interestingly, MS patients with acute relapse displayed a significant loss in terminally differentiated CD8+ T cells, with a concurrent loss in expression of perforin and granzyme B. Pre-treatment of exacerbation-derived CD8+ T cells with IL-12 significantly restored suppressive capability of these cells through upregulation of granzyme B. Our studies uncover immune-suppressive mechanisms of CNS-specific CD8+ Tregs, and may contribute to design of novel immune therapies for MS.

The experimental autoimmune encephalomyelitis (EAE) model of MS: utility for understanding disease pathophysiology and treatment

While no single model can exactly recapitulate all aspects of multiple sclerosis (MS), animal models are essential in understanding the induction and pathogenesis of the disease and to develop therapeutic strategies that limit disease progression and eventually lead to effective treatments for the human disease. Several different models of MS exist, but by far the best understood and most commonly used is the rodent model of experimental autoimmune encephalomyelitis (EAE). This model is typically induced by either active immunization with myelin-derived proteins or peptides in adjuvant or by passive transfer of activated myelin-specific CD4+ T lymphocytes. Mouse models are most frequently used because of the inbred genotype of laboratory mice, their rapid breeding capacity, the ease of genetic manipulation, and availability of transgenic and knockout mice to facilitate mechanistic studies. Although not all therapeutic strategies for MS have been developed in EAE, all of the current US Food and Drug Administration (FDA)-approved immunomodulatory drugs are effective to some degree in treating EAE, a strong indicator that EAE is an extremely useful model to study potential treatments for MS. Several therapies, such as glatiramer acetate (GA: Copaxone), and natalizumab (Tysabri), were tested first in the mouse model of EAE and then went on to clinical trials. Here we discuss the usefulness of the EAE model in understanding basic disease pathophysiology and developing treatments for MS as well as the potential drawbacks of this model.

CD8(+) T cells in multiple sclerosis

INTRODUCTION

CD8(+) T cells were originally considered to exert a suppressive role in demyelinating disease because of bias toward the CD4(+) T cell-mediated experimental autoimmune encephalomyelitis, the most common multiple sclerosis (MS) model. However, recent studies of human MS lesion samples and cerebrospinal fluid (CSF) provided compelling evidence about the pathogenic role of CD8(+) T cells. In this article, we discuss the theoretical roles of different CD8(+) T-cell subsets in MS.

AREAS COVERED

A revised focus from CD4(+) to CD8(+) T cell-mediated demyelinating disease is summarized. Clonal expansion of CD8(+) T cells in MS lesions and in vitro evidence that CD8(+) T cells injure every central nervous system (CNS) cell type and transect axons are discussed. The role of CD8(+) T cells in two animal models of MS and of regulatory, interleukin (IL)-17-secreting CD8(+) T cells is reviewed. Lastly, an overview about the pathogenic and/or beneficial role of various CD8(+) T-cell subsets is offered.

EXPERT OPINION

Growing evidence supports the pathogenic role of CD8(+) T cells. Clonally expanded CD8(+) T cells within MS lesions may damage the nervous system. Revealing the specific antigen is critical to design novel efficient treatments with minimal adverse effects. Increasing evidence exists for the role of regulatory, IL-17-secreting CD8(+) T cells in MS.

Characteristic cerebrospinal fluid cytokine/chemokine profiles in neuromyelitis optica, relapsing remitting or primary progressive multiple sclerosis

BACKGROUND

Differences in cytokine/chemokine profiles among patients with neuromyelitis optica (NMO), relapsing remitting multiple sclerosis (RRMS), and primary progressive MS (PPMS), and the relationships of these profiles with clinical and neuroimaging features are unclear. A greater understanding of these profiles may help in differential diagnosis.

METHODS/PRINCIPAL FINDINGS

We measured 27 cytokines/chemokines and growth factors in CSF collected from 20 patients with NMO, 26 with RRMS, nine with PPMS, and 18 with other non-inflammatory neurological diseases (OND) by multiplexed fluorescent bead-based immunoassay. Interleukin (IL)-17A, IL-6, CXCL8 and CXCL10 levels were significantly higher in NMO patients than in OND and RRMS patients at relapse, while granulocyte-colony stimulating factor (G-CSF) and CCL4 levels were significantly higher in NMO patients than in OND patients. In NMO patients, IL-6 and CXCL8 levels were positively correlated with disability and CSF protein concentration while IL-6, CXCL8, G-CSF, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IFN-γ were positively correlated with CSF neutrophil counts at the time of sample collection. In RRMS patients, IL-6 levels were significantly higher than in OND patients at the relapse phase while CSF cell counts were negatively correlated with the levels of CCL2. Correlation coefficients of cytokines/chemokines in the relapse phase were significantly different in three combinations, IL-6 and GM-CSF, G-CSF and GM-CSF, and GM-CSF and IFN-γ, between RRMS and NMO/NMOSD patients. In PPMS patients, CCL4 and CXCL10 levels were significantly higher than in OND patients.

CONCLUSIONS

Our findings suggest distinct cytokine/chemokine alterations in CSF exist among NMO, RRMS and PPMS. In NMO, over-expression of a cluster of Th17- and Th1-related proinflammatory cytokines/chemokines is characteristic, while in PPMS, increased CCL4 and CXCL10 levels may reflect on-going low grade T cell and macrophage/microglia inflammation in the central nervous system. In RRMS, only a mild elevation of proinflammatory cytokines/chemokines was detectable at relapse.

Eye-mediated induction of specific immune tolerance to encephalitogenic antigens

AIMS

Administration of antigens into the anterior chamber (AC) of the eye induces a form of antigen-specific immune tolerance termed anterior chamber-associated immune deviation (ACAID). This immune tolerance effectively impairs host delayed-type hypersensitivity (DTH) responses. We hypothesized that ACAID could be generated in BALB/c mice following AC inoculation of the encephalitogenic antigens myelin oligodendrocyte glycoprotein (MOG) and myelin basic protein (MBP).

METHODS

We used DTH assays and local adoptive transfer (LAT) assays to test whether MOG/MBP-induced ACAID following their administration into the AC, whether they elicited this immune tolerance via CD8(+) T cells, and whether their AC coadministration (MOG/MBP) induced specific immune tolerance to one or both antigens.

RESULTS

We showed that MOG/MBP-induced AC-mediated specific immune tolerance, as evident from impaired DTH responses. This antigen-driven DTH suppression was solely mediated via splenic CD8(+) T cells as confirmed by LAT assays. Finally, a single AC injection with both antigens was sufficient to induce specific immune tolerance to these antigens, as evident from DTH and LAT assays.

CONCLUSION

ACAID T-cell regulation could be used as a therapeutic tool in the treatment of complicated autoimmune diseases that involve multiple antigens such as multiple sclerosis.

Identification of cytolytic CD161- CD56+ regulatory CD8 T cells in human peripheral blood

We previously developed methods for establishing CD8 regulatory T cell (Treg) clones from normal human peripheral blood and demonstrated that these clones were capable of killing T cell receptor (TCR)-activated autologous CD4 T cells. Based on phenotypic and functional characterization of the CD8 Treg clones, we have identified a corresponding population of endogenous CD8 Treg in normal human peripheral blood. These cells appear morphologically as large lymphocytes with abundant cytoplasm and have the following unique phenotype: CD3⁺CD8⁺CD161⁻CD56⁺. The majority of CD8 Treg express CD45RA and CD62L with low or negative expression of CD45RO, CD25, CD27, CD28 and CCR7. The expression of CD94 and NKG2a on CD8 Treg was elevated compared to conventional CD8 T cells. Following in vitro activation, this T cell subset is capable of killing TCR-activated CD4 T cells. These studies identify an endogenous CD8 Treg population in humans and it will now be possible to characterize these cells in a variety of clinical conditions.

Cytotoxic NKG2C+ CD4 T cells target oligodendrocytes in multiple sclerosis

The mechanisms whereby immune cells infiltrating the CNS in multiple sclerosis patients contribute to tissue injury remain to be defined. CD4 T cells are key players of this inflammatory response. Myelin-specific CD4 T cells expressing CD56, a surrogate marker of NK cells, were shown to be cytotoxic to human oligodendrocytes. Our aim was to identify NK-associated molecules expressed by human CD4 T cells that confer this oligodendrocyte-directed cytotoxicity. We observed that myelin-reactive CD4 T cell lines, as well as short-term PHA-activated CD4 T cells, can express NKG2C, the activating receptor interacting with HLA-E, a nonclassical MHC class I molecule. These cells coexpress CD56 and NKG2D, have elevated levels of cytotoxic molecules FasL, granzyme B, and perforin compared with their NKG2C-negative counterparts, and mediate significant in vitro cytotoxicity toward human oligodendrocytes, which upregulated HLA-E upon inflammatory cytokine treatment. A significantly elevated proportion of ex vivo peripheral blood CD4 T cells, but not CD8 T cells or NK cells, from multiple sclerosis patients express NKG2C compared with controls. In addition, immunohistochemical analyses showed that multiple sclerosis brain tissues display HLA-E(+) oligodendrocytes and NKG2C(+) CD4 T cells. Our results implicate a novel mechanism through which infiltrating CD4 T cells contribute to tissue injury in multiple sclerosis.

Working out mechanisms of controlled/physiologic inflammation in the GI tract

The mucosal immune system is distinct from its systemic counterpart by virtue of its enormous antigenic exposure (commensal flora, food antigen, pathogens). Despite this, the mucosal immune system maintains a response defined as controlled or physiologic inflammation. This is regulated by many different mechanisms, among which there are physical, cellular and soluble factors. Our laboratory has focused on unique Tregs in the gut controlled by, in one instance, intestinal epithelial cells that serve as non-professional antigen-presenting cells. We believe that intestinal epithelial cells, expressing classical and non-classical MHC molecules, serve to activate Tregs and thus maintain controlled or physiologic inflammation. In this review, we describe regulatory cytokines and T cells that are one part of the emphasis of our laboratory.

Increased HLA-E expression in white matter lesions in multiple sclerosis

The molecular mechanisms underpinning central nervous system damage in multiple sclerosis (MS) are complex and it is widely accepted that there is an autoimmune component. Both adaptive and innate immune effector mechanisms are believed to contribute to tissue disease aetiology. HLA-E is a non-classical MHC class Ib molecule that acts as the ligand for the NKG2A inhibitory receptor present on natural killer (NK) and CD8+ cells. Peptide binding and stabilization of HLA-E is often considered to signal infection or cell stress. Here we examine the up-regulation of HLA-E in MS brain tissue. Expression is significantly increased in white matter lesions in the brain of MS patients compared with white matter of neurologically healthy controls. Furthermore, using quantitative immunohistochemistry and confocal microscopy, we show increased HLA-E protein expression in endothelial cells of active MS lesions. Non-inflammatory chronic lesions express significantly less HLA-E protein, comparable to levels found in white matter from controls. Increased HLA-E protein levels were associated with higher scores of inflammation. These results suggest the potential for an effect in central nervous system pathogenesis from HLA-E modulation in stressed tissue. Co-localization with infiltrating CD8+ cells implicates a possible role for HLA-E-restricted regulatory CD8+ cells, as has been proposed in other autoimmune diseases.

Epstein-Barr virus peptide presented by HLA-E is predominantly recognized by CD8(bright) cells in multiple sclerosis patients

Multiple sclerosis (MS) is associated with Epstein-Barr virus (EBV) infection, but impaired immune suppression may be part of the disease pathogenesis. CD8(+) T cells that are restricted by HLA-E exert an important immunoregulatory mechanism. To explore how EBV might interfere with immune regulation, we examined the expression of HLA-E and the frequency of CD8(+) cells recognizing HLA-E, presenting either an EBV peptide from the BZLF1 protein or a signal sequence peptide from HLA-A2, in relapsing remitting (MS-RR), primary progressive (MS-PP) MS patients, and healthy controls (HC). Treatment with IFN-α or EBV increased HLA-E expression on CD4(+) cells. However, only MS-PP had increased expression of HLA-E on resting CD4(+) cells when compared with HC (p<0.005). CD8(+) cells were divided into CD8(bright) and CD8(dim) cells by flow cytometry analyses. MS-RR had significantly fewer CD8(dim) cells than HC (p<0.003). Flow cytometry analyses were performed with HLA-E tetramers folded in the presence of the EBV or HLA-A2 peptide to identify HLA-E-interacting cells. MS-RR had increased frequency of CD8(bright) cells recognizing HLA-E/A2 (p=0.006) and HLA-E/BZLF1 (p=0.016). Conversely, MS-RR had fewer CD8(dim) cells that recognized HLA-E/BZLF1 (p=0.001), but this could be attributed to the overall lower number of CD8(dim) cells in MS-RR. Whereas HLA-E/A2 was predominantly recognized by CD8(dim) cells, HLA-E/BZLF1 was predominantly recognized by CD8(bright) cells in MS-RR and MS-PP, but not in HC. As expected, HLA-E/A2 was also recognized by CD8-negative cells in a CD94-dependent manner, whereas HLA-E/BZLF1 was poorly recognized in all groups by CD8-negative cells. These data demonstrate that MS-RR patients have expanded their CD8(bright) cells recognizing HLA-E/BZLF1. Moreover, HLA-E/BZLF1 appears to be recognized by the immune system in a different manner than HLA-E/A2.

Prolongation of prion disease-associated symptomatic phase relates to CD3+ T cell recruitment into the CNS in murine scrapie-infected mice

Prion diseases are caused by the transconformation of the host cellular prion protein PrP(c) into an infectious neurotoxic isoform called PrP(Sc). While vaccine-induced PrP-specific CD4(+) T cells and antibodies partially protect scrapie-infected mice from disease, the potential autoreactivity of CD8(+) cytotoxic T lymphocytes (CTLs) received little attention. Beneficial or pathogenic influence of PrP(c)-specific CTL was evaluated by stimulating a CD8(+) T-cell-only response against PrP in scrapie-infected C57BL/6 mice. To circumvent immune tolerance to PrP, five PrP-derived nonamer peptides identified using prediction algorithms were anchored-optimized to improve binding affinity for H-2D(b) and immunogenicity (NP-peptides). All of the NP-peptides elicited a significant number of IFNγ secreting CD8(+) T cells that better recognized the NP-peptides than the natives; three of them induced T cells that were lytic in vivo for NP-peptide-loaded target cells. Peptides 168 and 192 were naturally processed and presented by the 1C11 neuronal cell line. Minigenes encoding immunogenic NP-peptides inserted into adenovirus (rAds) vectors enhanced the specific CD8(+) T-cell responses. Immunization with rAd encoding 168NP before scrapie inoculation significantly prolonged the survival of infected mice. This effect was attributable to a significant lengthening of the symptomatic phase and was associated with enhanced CD3(+) T cell recruitment to the CNS. However, immunization with Ad168NP in scrapie-incubating mice induced IFNγ-secreting CD8(+) T cells that were not cytolytic in vivo and did not influence disease progression nor infiltrated the brain. In conclusion, the data suggest that vaccine-induced PrP-specific CD8(+) T cells interact with prions into the CNS during the clinical phase of the disease.

Self-tolerance in multiple sclerosis

During the last decade, several defects in self-tolerance have been identified in multiple sclerosis. Dysfunction in central tolerance leads to the thymic output of antigen-specific T cells with T cell receptor alterations favouring autoimmune reactions. In addition, premature thymic involution results in a reduced export of naïve regulatory T cells, the fully suppressive clone. Alterations in peripheral tolerance concern costimulatory molecules as well as transcriptional and epigenetic mechanisms. Recent data underline the key role of regulatory T cells that suppress Th1 and Th17 effector cell responses and whose immunosuppressive activity is impaired in patients with multiple sclerosis. Those recent observations suggest that a defect in self-tolerance homeostasis might be the primary mover of multiple sclerosis leading to subsequent immune attacks, inflammation and neurodegeneration. The concept of multiple sclerosis as a consequence of the failure of central and peripheral tolerance mechanisms to maintain a self-tolerance state, particularly of regulatory T cells, may have therapeutic implications. Restoring normal thymic output and suppressive functions of regulatory T cells appears an appealing approach. Regulatory T cells suppress the general local immune response via bystander effects rather than through individual antigen-specific responses. Interestingly, the beneficial effects of currently approved immunomodulators (interferons β and glatiramer acetate) are associated with a restored regulatory T cell homeostasis. However, the feedback regulation between Th1 and Th17 effector cells and regulatory T cells is not so simple and tolerogenic mechanisms also involve other regulatory cells such as B cells, dendritic cells and CD56(bright) natural killer cells.

Regulation of self-tolerance by Qa-1-restricted CD8(+) regulatory T cells

Mounting an efficient immune response to pathogens while avoiding damage to host tissues is the central task of the immune system. Emerging evidence has highlighted the contribution of the CD8(+) lineage of regulatory T cells to the maintenance of self-tolerance. Specific recognition of the MHC class Ib molecule Qa-1 complexed to peptides expressed by activated CD4(+) T cells by regulatory CD8(+) T cells triggers an inhibitory interaction that prevents autoimmune responses. Conversely, defective Qa-1-restricted CD8(+) regulatory activity can result in development of systemic autoimmune disease. Here, we review recent research into the cellular and molecular basis of these regulatory T cells, their mechanism of suppressive activity and the potential application of these insights into new treatments for autoimmune disease and cancer.

Role of CD8 T cell subsets in the pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system leading to demyelination and axonal/neuronal loss. Cumulating evidence points to a key role for CD8 T cells in this disabling disease. Oligoclonal CD8 T cells reside in demyelinating plaques where they are likely to contribute to tissue destruction. Histopathological analyses and compelling observations from animal models indicate that cytotoxic CD8 T cells target neural cell populations with the potential of causing lesions reminiscent of MS. However, CD8 T cell differentiation results in several subsets of effector CD8 T cells that could be differentially implicated in the mechanisms contributing to tissue damage. Moreover CD8 regulatory T cells arise as important populations involved in restoring immune homoeostasis and in maintaining immune privileged sites. Here we examine the current literature pertaining to the role of CD8 effector and regulatory T cell subsets in the pathogenesis of MS.

Global expression profiling of peripheral Qa-1-restricted CD8αα+TCRαβ+ regulatory T cells reveals innate-like features: implications for immune-regulatory repertoire

Among peripheral regulatory T cells, CD8(+) T cells also play an important role in the maintenance of immune homeostasis. A subset of CD8(+) Treg that express αβ T cell receptor (TCR) and CD8αα homodimers can recognize TCR-derived peptides in the context of the class Ib MHC molecule Qa-1. To gain a better understanding of the nature and phenotype of CD8αα(+)TCRαβ+ Treg, a global gene expression profiling using microarray, real-time quantitative polymerase chain reaction, and flow-cytometric analysis was performed using functional Treg clones and lines. The study findings show that CD8(+) Treg shared gene profile expressed by innate-like lymphocytes, including murine intraepithelial lymphocytes and thymic CD8αα(+)TCRαβ+ T-cell populations. In addition, this subset displays differential expression of several key regulatory molecules, including CD200. CD8αα(+) Treg expressed higher levels of a number of natural killer cell-related receptors and molecules belonging to the TNF superfamily. Collectively, peripheral class Ib-reactive CD8αα(+)TCRαβ+ T cells represent a unique regulatory population different from class Ia major histocompatibility complex-restricted conventional T cells. These studies have important implications for the regulatory mechanisms mediated by the CD8(+) Treg population in general.