Specific central nervous system recruitment of HLA-G(+) regulatory T cells in multiple sclerosis

UP-regulated levels of sHLA-G in women with a history of RPL in mid-gestation presumably to achieve ongoing pregnancy

PROBLEM

Recurrent Pregnancy Loss (RPL) is a disorder characterized by two or more pregnancy losses within 20th week of gestation. Globally 1-5% of the couples are affected, 50% of these cases are with unknown etiology. HLA-G, an Immuno-modulatory molecule is a non-classical MHC-1 protein, expressed abundantly on extravillous trophoblastic cells, responsible for spiral artery remodeling, maintaining maternal immune tolerance and fetal growth by adjusting pro and anti-inflammatory milieu during different gestational phases.

METHOD OF STUDY

In the present case-control study CD4+HLA-G+ tTreg cells were enumerated by flow cytometry and estimation of the circulating levels of sHLA-G in the blood samples of 300 mid-gestation pregnant women with (iRPL) and without history of RPL (nRPL) by Enzyme-linked Immunosorbent assay was done. The cases included 92 primary and 58 secondary RPL cases RESULTS: A significant reduction in number of tTregs and elevated levels of circulating sHLA-G in iRPL (.03, 200.9) versus nRPL (.09, 90.32) was observed. Further, the primary cases showed higher circulating sHLA-G and no difference in relation to CD4+HLA-G+ tTregs compared to the secondary cases. Receiver operating curve (ROC) characteristics of sHLA-G (AUC = .8) was superior to CD4+HLA-G+ (AUC = .7) for iRPL patients over nRPL group.

CONCLUSIONS

Our results are suggestive of the over-expression of sHLA-G which may be caused due to its shedding from surface of trophoblast as a compensatory mechanism to save the on-going pregnancy. To realize the present outcome, studies are required on on-going pregnancy follow-up cases with favorable and unfavorable pregnancy outcome.

Induction of pulmonary HLA-G expression by SARS-CoV-2 infection

The non-classical human leukocyte antigen (HLA)-G exerts immune-suppressive properties modulating both NK and T cell responses. While it is physiologically expressed at the maternal-fetal interface and in immune-privileged organs, HLA-G expression is found in tumors and in virus-infected cells. So far, there exists little information about the role of HLA-G and its interplay with immune cells in biopsies, surgical specimen or autopsy tissues of lung, kidney and/or heart muscle from SARS-CoV-2-infected patients compared to control tissues. Heterogeneous, but higher HLA-G protein expression levels were detected in lung alveolar epithelial cells of SARS-CoV-2-infected patients compared to lung epithelial cells from influenza-infected patients, but not in other organs or lung epithelia from non-viral-infected patients, which was not accompanied by high levels of SARS-CoV-2 nucleocapsid antigen and spike protein, but inversely correlated to the HLA-G-specific miRNA expression. High HLA-G expression levels not only in SARS-CoV-2-, but also in influenza-infected lung tissues were associated with a high frequency of tissue-infiltrating immune cells, but low numbers of CD8+ cells and an altered expression of hyperactivation and exhaustion markers in the lung epithelia combined with changes in the spatial distribution of macrophages and T cells. Thus, our data provide evidence for an involvement of HLA-G and HLA-G-specific miRNAs in immune escape and as suitable therapeutic targets for the treatment of SARS-CoV-2 infections.

Suppressor CD4+ T cells expressing HLA-G are expanded in the peripheral blood from patients with acute decompensation of cirrhosis

OBJECTIVE

Identifying components of immuneparesis, a hallmark of chronic liver failure, is crucial for our understanding of complications in cirrhosis. Various suppressor CD4⁺ T cells have been established as potent inhibitors of systemic immune activation. Here, we establish the presence, regulation and mechanism of action of a suppressive CD4⁺ T cell subset expressing human leucocyte antigen G (HLA-G) in patients with acute decompensation of cirrhosis (AD).

DESIGN

Flow cytometry was used to determine the proportion and immunophenotype of CD4⁺HLA-G⁺ T cells from peripheral blood of 20 healthy controls (HCs) and 98 patients with cirrhosis (28 with stable cirrhosis (SC), 20 with chronic decompensated cirrhosis (CD) and 50 with AD). Transcriptional and functional signatures of cell-sorted CD4⁺HLA-G⁺ cells were delineated by NanoString technology and suppression assays, respectively. The role of immunosuppressive cytokine interleukin (IL)-35 in inducing this population was investigated through in vitro blockade experiments. Immunohistochemistry (IHC) and cultures of primary human Kupffer cells (KCs) were performed to assess cellular sources of IL-35. HLA-G-mediated T cell suppression was explored using neutralising antibodies targeting co-inhibitory pathways.

RESULTS

Patients with AD were distinguished by an expansion of a CD4⁺HLA-G⁺CTLA-4⁺IL-35⁺ immunosuppressive population associated with disease severity, clinical course of AD, infectious complications and poor outcome. Transcriptomic analyses excluded the possibility that these were thymic-derived regulatory T cells. IHC analyses and in vitro cultures demonstrate that KCs represent a potent source of IL-35 which can induce the observed HLA-G⁺ phenotype. These exert cytotoxic T lymphocyte antigen-4-mediated impaired responses in T cells paralleled by an HLA-G-driven downregulation of T helper 17-related cytokines.

CONCLUSION

We have identified a cytokine-driven peripherally derived suppressive population that may contribute to immuneparesis in AD.

Regulatory Cells in Multiple Sclerosis: From Blood to Brain

Multiple sclerosis (MS) is a chronic, autoimmune, and neurodegenerative disease of the central nervous system (CNS) that affects myelin. The etiology of MS is unclear, although a variety of environmental and genetic factors are thought to increase the risk of developing the disease. Historically, T cells were considered to be the orchestrators of MS pathogenesis, but evidence has since accumulated implicating B lymphocytes and innate immune cells in the inflammation, demyelination, and axonal damage associated with MS disease progression. However, more recently the importance of the protective role of immunoregulatory cells in MS has become increasingly evident, such as that of myeloid-derived suppressor cells (MDSCs), regulatory T (Treg) and B (Breg) cells, or CD56bright natural killer cells. In this review, we will focus on how peripheral regulatory cells implicated in innate and adaptive immune responses are involved in the physiopathology of MS. Moreover, we will discuss how these cells are thought to act and contribute to MS histopathology, also addressing their promising role as promoters of successful remyelination within the CNS. Finally, we will analyze how understanding these protective mechanisms may be crucial in the search for potential therapies for MS.

The HLA-G Immune Checkpoint Plays a Pivotal Role in the Regulation of Immune Response in Autoimmune Diseases

The human G-leukocyte antigen (HLA-G) molecule is a non-classical major histocompatibility complex (MHC) class I molecule. The pertinence of HLA-G has been investigated in numerous studies which have sought to elucidate the relevance of HLA-G in pathologic conditions, such as autoimmune diseases, cancers, and hematologic malignancies. One of the main goals of the current research on HLA-G is to use this molecule in clinical practice, either in diagnostics or as a therapeutic target. Since HLA-G antigens are currently considered as immunomodulatory molecules that are involved in reducing inflammatory and immune responses, in this review, we decided to focus on this group of antigens as potential determinants of progression in autoimmune diseases. This article highlights what we consider as recent pivotal findings on the immunomodulatory function of HLA-G, not only to establish the role of HLA-G in the human body, but also to explain how these proteins mediate the immune response.

The STING-IFN-β-Dependent Axis Is Markedly Low in Patients with Relapsing-Remitting Multiple Sclerosis

Cyclic GMP-AMP-synthase is a sensor of endogenous nucleic acids, which subsequently elicits a stimulator of interferon genes (STING)-dependent type I interferon (IFN) response defending us against viruses and other intracellular pathogens. This pathway can drive pathological inflammation, as documented for type I interferonopathies. In contrast, specific STING activation and subsequent IFN-β release have shown beneficial effects on experimental autoimmune encephalomyelitis (EAE) as a model for multiple sclerosis (MS). Although less severe cases of relapse-remitting MS (RRMS) are treated with IFN-β, there is little information correlating aberrant type I IFN signaling and the pathologic conditions of MS. We hypothesized that there is a link between STING activation and the endogenous production of IFN-β during neuroinflammation. Gene expression analysis in EAE mice showed that Sting level decreased in the peripheral lymphoid tissue, while its level increased within the central nervous system over the course of the disease. Similar patterns could be verified in peripheral immune cells during the acute phases of RRMS in comparison to remitting phases and appropriately matched healthy controls. Our study is the first to provide evidence that the STING/IFN-β-axis is downregulated in RRMS patients, meriting further intensified research to understand its role in the pathophysiology of MS and potential translational applications.

HLA-G Expressing Immune Cells in Immune Mediated Diseases

HLA-G is a HLA class Ib antigen that possesses immunomodulatory properties. HLA-G-expressing CD4+ and CD8+ T lymphocytes, NK cells, monocytes, and dendritic cells with immunoregulatory functions are present in small percentages of patients with physiologic conditions. Quantitative and qualitative derangements of HLA-G+ immune cells have been detected in several conditions in which the immune system plays an important role, such as infectious, neoplastic, and autoimmune diseases as well as in complications from transplants and pregnancy. These observations strongly support the hypothesis that HLA-G+ immune cells may be implicated in the complex mechanisms underlying the pathogenesis of these disorders.

HLA-G Neo-Expression on Tumors

HLA-G is known to modulate the immune system activity in tissues where physiological immune-tolerance is necessary (i.e., maternal-fetal interface, thymus, and cornea). However, the frequent neo-expression of HLA-G in many cancer types has been previously and extensively described and is correlated with a bad prognosis. Despite being an MHC class I molecule, HLA-G is highly present in tumor context and shows unique characteristics of tissue restriction of a Tumor Associated Antigen (TAA), and potent immunosuppressive activity of an Immune CheckPoint (ICP). Consequently, HLA-G appears to be an excellent molecular target for immunotherapy. Although the relevance of HLA-G in cancer incidence and development has been proven in numerous tumors, its neo-expression pattern is still difficult to determine. Indeed, the estimation of HLA-G's actual expression in tumor tissue is limited, particularly concerning the presence and percentage of the new non-canonical isoforms, for which detection antibodies are scarce or inexistent. Here, we summarize the current knowledge about HLA-G neo-expression and implication in various tumor types, pointing out the need for the development of new tools to analyze in-depth the HLA-G neo-expression patterns, opening the way for the generation of new monoclonal antibodies and cell-based immunotherapies.

Regulatory T Cells in Pregnancy: It Is Not All About FoxP3

In pregnancy, the semi-allogeneic fetus needs to be tolerated by the mother's immune system. Regulatory T cells (Tregs) play a prominent role in this process. Novel technologies allow for in-depth phenotyping of previously unidentified immune cell subsets, which has resulted in the appreciation of a vast heterogeneity of Treg subsets. Similar to other immunological events, there appears to be great diversity within the Treg population during pregnancy, both at the maternal-fetal interface as in the peripheral blood. Different Treg subsets have distinct phenotypes and various ways of functioning. Furthermore, the frequency of individual Treg subsets varies throughout gestation and is altered in aberrant pregnancies. This suggests that distinct Treg subsets play a role at different time points of gestation and that their role in maintaining healthy pregnancy is crucial, as reflected for instance by their reduced frequency in women with recurrent pregnancy loss. Since pregnancy is essential for the existence of mankind, multiple immune regulatory mechanisms and cell types are likely at play to assure successful pregnancy. Therefore, it is important to understand the complete microenvironment of the decidua, preferably in the context of the whole immune cell repertoire of the pregnant woman. So far, most studies have focused on a single mechanism or cell type, which often is the FoxP3 positive regulatory T cell when studying immune regulation. In this review, we instead focus on the contribution of FoxP3 negative Treg subsets to the decidual microenvironment and their possible role in pregnancy complications. Their phenotype, function, and effect in pregnancy are discussed.

Next-Generation Neuroimmunology: New Technologies to Understand Central Nervous System Autoimmunity

Understanding neuroimmunological disorders is essential for developing new diagnostic and therapeutic strategies. Rodent models have provided valuable insights, but are sometimes equated with their human counterparts. Here, we summarize how novel technologies may enable an improved human-focused view of immune mechanisms. Recent studies have applied these new technologies to the brain parenchyma, its surrounding cerebrospinal fluid, and peripheral immune compartments. Therapeutic interventions have also facilitated translational understanding in a reverse way. However, with improved technology, access to patient samples remains a rate-limiting step in translational research. We anticipate that next-generation neuroimmunology is likely to integrate, in the immediate future, diverse technical tools for optimal diagnosis, prognosis, and treatment of neuroimmunological disorders.

Expression of membrane-bound human leucocyte antigen-G in systemic sclerosis and systemic lupus erythematosus

Human leucocyte antigen-G (HLA-G) is a nonclassical class I major histocompatibility complex (MHC) molecule characterized by complex immunoregulatory and tolerogenic functions. Membrane-bound HLA-G is expressed on the surface of different cell populations in both physiological and pathological conditions. Systemic sclerosis (SSc) is a multisystem autoimmune disease characterized by widespread tissue fibrosis, vascular lesions and immunological alterations. Systemic lupus erythematosus is the prototypic systemic autoimmune disease affecting virtually any organ system, such as skin, joints, central nervous system, or kidneys. In SSc and SLE patients, the membrane expression of HLA-G on monocytes (0.88 ± 1.54 and 0.43 ± 0.75, respectively), CD4+ (0.42 ± 0.78 and 0.63 ± 0.48, respectively), CD8+ (2.65 ± 3.47 and 1.29 ± 1.34, respectively) and CD4+ CD8+ double-positive cells (13.87 ± 15.97 and 3.79 ± 3.11, respectively) was significantly higher than in healthy controls (0.12 ± 0.07; 0.01 ± 0.01; 0.14 ± 0.20 and 0.32 ± 0.38, respectively) (p < 0.0001). Our results show that in SSc and SLE the membrane expression of HLA-G by different subpopulations of peripheral blood mononuclear cells (PBMC) is increased, suggesting a potential role of HLA-G molecules in the complex immunological pathogenesis of these two autoimmune disorders.

Non-parametric combination analysis of multiple data types enables detection of novel regulatory mechanisms in T cells of multiple sclerosis patients

Multiple Sclerosis (MS) is an autoimmune disease of the central nervous system with prominent neurodegenerative components. The triggering and progression of MS is associated with transcriptional and epigenetic alterations in several tissues, including peripheral blood. The combined influence of transcriptional and epigenetic changes associated with MS has not been assessed in the same individuals. Here we generated paired transcriptomic (RNA-seq) and DNA methylation (Illumina 450 K array) profiles of CD4+ and CD8+ T cells (CD4, CD8), using clinically accessible blood from healthy donors and MS patients in the initial relapsing-remitting and subsequent secondary-progressive stage. By integrating the output of a differential expression test with a permutation-based non-parametric combination methodology, we identified 149 differentially expressed (DE) genes in both CD4 and CD8 cells collected from MS patients. Moreover, by leveraging the methylation-dependent regulation of gene expression, we identified the gene SH3YL1, which displayed significant correlated expression and methylation changes in MS patients. Importantly, silencing of SH3YL1 in primary human CD4 cells demonstrated its influence on T cell activation. Collectively, our strategy based on paired sampling of several cell-types provides a novel approach to increase sensitivity for identifying shared mechanisms altered in CD4 and CD8 cells of relevance in MS in small sized clinical materials.

Single-Cell High-Throughput Technologies in Cerebrospinal Fluid Research and Diagnostics

High-throughput single-cell technologies have recently emerged as essential tools in biomedical research with great potential for clinical pathology when studying liquid and solid biopsies. We provide an update on current single-cell methods in cerebrospinal fluid research and diagnostics, focusing on high-throughput cell-type specific proteomic and genomic technologies. Proteomic methods comprising flow cytometry and mass cytometry as well as genomic approaches including immune cell repertoire and single-cell transcriptomic studies are critically reviewed and future directions discussed.

Evaluation of membrane-bound and soluble forms of human leucocyte antigen-G in systemic sclerosis

Systemic sclerosis (SSc) is a complex disease characterized by immune dysregulation, extensive vascular damage and widespread fibrosis. Human leucocyte antigen-G (HLA-G) is a non-classic class I major histocompatibility complex (MHC) molecule characterized by complex immunomodulating properties. HLA-G is expressed on the membrane of different cell lineages in both physiological and pathological conditions. HLA-G is also detectable in soluble form (sHLA-G) deriving from the shedding of surface isoforms (sHLA-G1) or the secretion of soluble isoforms (HLA-G5). Several immunosuppressive functions have been attributed to both membrane-bound and soluble HLA-G molecules. The plasma levels of sHLA-G were higher in SSc patients (444·27 ± 304·84 U/ml) compared to controls (16·74 ± 20·58 U/ml) (P < 0·0001). The plasma levels of transforming growth factor (TGF)-β were higher in SSc patients (18 937 ± 15 217 pg/ml) compared to controls (11 099 ± 6081 pg/ml; P = 0·003), and a significant correlation was found between TGF-β and the plasma levels of total sHLA-G (r = 0·65; P < 0·01), sHLA-G1 (r = 0·60; P = 0·003) and HLA-G5 (r = 0·47; P = 0·02). The percentage of HLA-G-positive monocytes (0·98 ± 1·72), CD4+ (0·37 ± 0·68), CD8+ (2·05 ± 3·74) and CD4+ CD8+ double-positive cells (14·53 ± 16·88) was higher in SSc patients than in controls (0·11 ± 0·08, 0·01 ± 0·01, 0·01 ± 0·01 and 0·39 ± 0·40, respectively) (P < 0·0001). These data indicate that in SSc the secretion and/or shedding of soluble HLA-G molecules and the membrane expression of HLA-G by peripheral blood mononuclear cells (PBMC) is clearly elevated, suggesting an involvement of HLA-G molecules in the immune dysregulation of SSc.

Analysis of Lymphocyte Extravasation Using an In Vitro Model of the Human Blood-brain Barrier

Lymphocyte extravasation into the central nervous system (CNS) is critical for immune surveillance. Disease-related alterations of lymphocyte extravasation might result in pathophysiological changes in the CNS. Thus, investigation of lymphocyte migration into the CNS is important to understand inflammatory CNS diseases and to develop new therapy approaches. Here we present an in vitro model of the human blood-brain barrier to study lymphocyte extravasation. Human brain microvascular endothelial cells (HBMEC) are confluently grown on a porous polyethylene terephthalate transwell insert to mimic the endothelium of the blood-brain barrier. Barrier function is validated by zonula occludens immunohistochemistry, transendothelial electrical resistance (TEER) measurements as well as analysis of evans blue permeation. This model allows investigation of the diapedesis of rare lymphocyte subsets such as CD56^brightCD16^dim/- NK cells. Furthermore, the effects of other cells, cytokines and chemokines, disease-related alterations, and distinct treatment regimens on the migratory capacity of lymphocytes can be studied. Finally, the impact of inflammatory stimuli as well as different treatment regimens on the endothelial barrier can be analyzed.

HLA-G+ HIV-1-specific CD8+ T cells are associated with HIV-1 immune control

OBJECTIVE(S)

To assess the frequency and function of HIV-1-specific HLA-G (histocompatibility antigen class I, G) CD8 T cells in HIV-1 controllers and progressors.

DESIGN

We performed an observational cross-sectional cohort analysis in untreated (n = 47) and treated (n = 17) HIV-1 patients with different rates of disease progression and n = 14 healthy individuals.

METHODS

We evaluated the frequency, the proportion and the function of total and virus-specific HLA-G CD8 T cells by tetramer or intracellular cytokine staining, followed by flow cytometric analysis. Cytokine secretion of sorted CD8 T-cell subsets was evaluated by Luminex assays.

RESULTS

The proportion and the absolute frequency of HLA-G HIV-1-specific CD8 T cells were directly associated with CD4 T-cell counts and inversely correlated with viral loads, whereas total or HLA-G-negative HIV-1-specific CD8 T cells were not. In functional assays, HLA-G CD8 T cells from HIV-1-negative individuals had higher abilities to produce the antiviral (C-C chemokine receptor type 5) ligands MIP-1β (macrophage inflammatory protein-1ß), MIP-1α and Rantes.

CONCLUSION

HLA-G HIV-1-specific CD8 T cells may represent a previously unrecognized correlate of HIV-1 immune control.

Rescuing lymphocytes from HLA-G immunosuppressive effects mediated by the tumor microenvironment

Several studies have demonstrated that the antitumor activities of both T and natural killer (NK) effector populations are limited by the immunosuppressive strategies of tumors. In several malignant transformations, the expression of HLA-G by tumor cells rises dramatically, rendering them strongly immunosuppressive. In this study, we postulated that the absence of HLA-G receptors would prevent the immunosuppressive effects of both soluble and membrane-bound HLA-G. Thus, we investigated the therapeutic potential of effector NK cells genetically modified to downregulate the expression of ILT2 (HLA-G receptor) on their cell surfaces. We have shown that the proliferation of modified NK is still dependent on stimulation signals (no malignant transformation). ILT2⁻ NK cells proliferate, migrate, and eliminate HLA-G negative targets cells to the same extent parental NK cells do. However, in the presence of HLA-G positive tumors, ILT2⁻ NK cells exhibit superior proliferation, conjugate formation, degranulation, and killing activities compared to parent NK cells. We tested the effectiveness of ILT2⁻ NK cells in vivo using a xenograft cancer model and found that silencing ILT2 rescued their anti-tumor activity.

We believe that combining ILT2⁻ NK cells with existing therapeutic strategies will strengthen the antitumor response in cancer patients.

Allergen-driven HLA-G expression and secretion in peripheral blood mononuclear cells from allergic rhinitis patients

BACKGROUND

It has been reported that soluble HLA-G serum levels are increased in patients with pollen-induced allergic rhinitis and decrease after immunotherapy. However, no functional study has been conducted so far. The aim of this study was to evaluate the membrane expression and secretion of HLA-G molecules in peripheral blood mononuclear cells from allergic rhinitis patients after in vitro incubation with the causal allergen.

METHODS AND RESULTS

Twenty-two allergic rhinitis patients and ten healthy subjects were enrolled. Membrane HLA-G expression was determined by flow cytometry and soluble HLA-G in culture supernatant was determined by immunoenzymatic assay. HLA-G expression was detected in CD4+ (T-helper-2) cells and monocytes after in vitro stimulation with the causal allergen but not with non specific stimuli and non causal allergens. Accordingly, the release of soluble HLA-G in culture supernatant occurred only after the stimulation with the causal allergen. Collectively, these results were confirmed by Western blot analysis.

CONCLUSIONS

The present study provides the first in vitro evidence that in allergic patients HLA-G expression and secretion is specifically induced by the causal allergen. These data may add new insights into the pathogenetic mechanisms underlying allergic inflammation and allergen specific immunotherapy.

Get It through Your Thick Head: Emerging Principles in Neuroimmunology and Neurovirology Redefine Central Nervous System "Immune Privilege"

The central nervous system (CNS) coordinates all aspects of life, autonomic and sentient, though how it has evolved to contend with pathogenic infections remains, to a great degree, a mystery. The skull and cerebrospinal fluid (CSF) provide protection from blunt force contacts, and it was once thought that the blood-brain barrier (BBB) was a fortress that restricted pathogen entry and limited inflammation. Recent studies, however, have caused a revision of this viewpoint: the CNS is monitored by blood-borne lymphocytes, but can use alternative strategies to prevent or resolve many pathogenic challenges. In this Review, we discuss emerging principles that indicate how the CNS is immunologically unique from peripheral tissues. We focus on developments that include glymphatics, recently characterized brain lymphatic vessels, distinctions in innate and adaptive immune strategies, novel points of entry for neurotropic viruses, and, finally, how the periphery can influence CNS homeostasis and immune responses within the brain. Collectively, these attributes demand a re-evaluation of immunity in the brain: not privileged, but distinct.

ALAIN01--Alemtuzumab in autoimmune inflammatory neurodegeneration: mechanisms of action and neuroprotective potential

BACKGROUND

Alemtuzumab (Lemtrada®) is a newly approved therapeutic agent for relapsing-remitting multiple sclerosis (RRMS). In previous phase II and III clinical trials, alemtuzumab has proven superior efficacy to subcutaneous interferon beta-1a concerning relapse rate and disability progression with unprecedented durability and long-lasting freedom of disease activity. The humanized monoclonal antibody targets CD52, leading to a rapid and long-lasting depletion, especially of B and T cells. Arising from hematopoietic precursor cells a fundamental reprogramming of the immune system restores tolerogenic networks effectively suppressing autoimmune inflammatory responses in the central nervous system (CNS). Despite its favourable effects alemtuzumab holds a severe risk of side effects with secondary autoimmunity being the most considerable. Markers for risk stratification and treatment response improving patient selection and therapy guidance are a big unmet need for MS patients and health care providers.

METHODS/DESIGN

This is a mono center, single arm, explorative phase IV study including 15 patients with highly active RRMS designed for 3 years. Patients will be studied by a high-resolution analysis comprising a repertoire of various immunological assays for the detection of immune cells and their function in peripheral blood as well as the cerebrospinal fluid (CSF). These assays encompass a number of experiments investigating immune cell subset composition, activation status, cytokine secretion, migratory capacity, potential neuroprotective properties and cytolytic activity complemented by instrument-based diagnostics like MRI scans, evoked potentials and optical coherence tomography (OCT).

DISCUSSION

Our study represents the first in-depth and longitudinal functional analysis of key immunological parameters in the periphery and the CNS compartment underlying the fundamental effects of alemtuzumab in MS patients. By combining clinical, experimental and MRI data our study will provide a deeper understanding of alemtuzumab's mechanisms of action (MOA) potentially identifying immune signatures associated with treatment response or the development of secondary autoimmunity. After validation in larger cohorts this might help to improve efficacy and safety of alemtuzumab therapy in RRMS patients.

TRIAL REGISTRATION

NCT02419378 (clinicaltrials.gov), registered 31 March 2015.

CD4(+)HLA-G(+) regulatory T cells: Molecular signature and pathophysiological relevance

The regulation of potentially harmful immune responses by regulatory T (Treg) cells is essential for maintaining peripheral immune tolerance and homeostasis. Especially CD4(+) Treg cells have been regarded as pivotal regulators of autoreactive and inflammatory responses as well as inducers of immune tolerance by using a variety of immune suppressive mechanisms. Besides the well-known classical CD4(+)CD25(+)FoxP3(+) Treg cells, CD4(+) T cells expressing the immune tolerizing molecule human leukocyte antigen G (HLA-G) have been recently described as another potent thymus-derived Treg (tTreg) cell subset. Albeit both tTreg subsets share common molecular characteristics, the mechanisms of their immunosuppressive function differ fundamentally. Dysfunction and numerical abnormalities of classical CD4(+) tTreg cells have been implicated in the pathogenesis of several immune-mediated diseases such as multiple sclerosis (MS). Clearly, a deeper understanding of the various CD4(+) tTreg subsets and also the underlying mechanisms of impaired immune tolerance in these disorders are essential for the development of potential therapeutic strategies. This review focuses on the current knowledge on defining features and functioning of HLA-G(+)CD4(+) tTreg cells as well as their emerging role in various pathologies with special emphasis on the pathogenesis of MS. Furthermore, future research possibilities together with potential therapeutic applications are discussed.

HLA-G Molecules in Autoimmune Diseases and Infections

Human leukocyte antigen (HLA)-G molecule, a non-classical HLA-Ib molecule, is less polymorphic when compared to classical HLA class I molecules. Human leukocyte antigen-G (HLA-G) was first detected on cytotrophoblast cells at the feto-maternal interface but its expression is prevalent during viral infections and several autoimmune diseases. HLA-G gene is characterized by polymorphisms at the 3' un-translated region and 5' upstream regulatory region that regulate its expression and are associated with autoimmune diseases and viral infection susceptibility, creating an unbalanced and pathologic environment. This review focuses on the role of HLA-G genetic polymorphisms, mRNA, and protein expression in autoimmune conditions and viral infections.

Pathology of multiple sclerosis and related inflammatory demyelinating diseases

This article provides a comprehensive overview of the pathology of multiple sclerosis (MS), including recent insights into its molecular neuropathology and immunology. It shows that all clinical manifestations of relapsing and progressive MS display the same basic features of pathology, such as chronic inflammation, demyelination in the white and gray matter, and diffuse neurodegeneration within the entire central nervous system. However, the individual components of the pathological spectrum vary quantitatively between early relapsing and late progressive MS. Widespread confluent and plaque-like demyelination with oligodendrocyte destruction is the unique pathological hallmark of the disease, but axonal injury and neurodegeneration are additionally present and in part extensive. Remyelination of existing lesions may occur in MS brains; it is extensive in a subset of patients, while it fails in others. Active tissue injury in MS is always associated with inflammation, consistent with T-cell and macrophage infiltration and microglia activation. Recent data suggest that oxidative injury and subsequent mitochondrial damage play a major pathogenetic role in neurodegeneration. Finally we discuss similarities and differences of the pathology between classical MS and other inflammatory demyelinating diseases, such as neuromyelitis optica, concentric sclerosis, or acute disseminated encephalomyelitis.

VLA-4 blockade promotes differential routes into human CNS involving PSGL-1 rolling of T cells and MCAM-adhesion of TH17 cells

Schneider-Hohendorf describe expression of adhesion molecules MCAM and PSGL-1 on human CD4⁺ T cells and Th17 T cells in multiple sclerosis patients under long-term natalizumab treatment. The authors identify that despite blockade of VLA-4, MCAM⁺ T cells can migrate through the blood–brain barrier to access the CNS through PSGL-1 and MCAM.

The focus of this study is the characterization of human T cell blood–brain barrier migration and corresponding molecular trafficking signatures. We examined peripheral blood and cerebrospinal fluid immune cells from patients under long-term anti–very late antigen-4 (VLA-4)/natalizumab therapy (LTNT) and from CNS specimens. LTNT patients’ cerebrospinal fluid T cells exhibited healthy central-/effector-memory ratios, but lacked CD49d and showed enhanced myeloma cell adhesion molecule (MCAM) expression. LTNT led to an increase of PSGL-1 expression on peripheral T cells. Although vascular cell adhesion molecule-1 (VLA-4 receptor) was expressed at all CNS barriers, P-selectin (PSGL-1-receptor) was mainly detected at the choroid plexus. Accordingly, in vitro experiments under physiological flow conditions using primary human endothelial cells and LTNT patients’ T cells showed increased PSGL-1–mediated rolling and residual adhesion, even under VLA-4 blockade. Adhesion of MCAM⁺/T_H17 cells was not affected by VLA-4 blocking alone, but was abrogated when both VLA-4 and MCAM were inhibited. Consistent with these data, MCAM⁺ cells were detected in white matter lesions, and in gray matter of multiple sclerosis patients. Our data indicate that lymphocyte trafficking into the CNS under VLA-4 blockade can occur by using the alternative adhesion molecules, PSGL-1 and MCAM, the latter representing an exclusive pathway for T_H17 cells to migrate over the blood–brain barrier.

New insights into HLA-G mediated tolerance

Human Leukocyte Antigen G (HLA-G) is a nonclassical HLA class I molecule with well-characterized immunomodulatory activities. HLA-G was first described as a regulatory molecule that allows the fetus to elude the maternal immune response. In the last decade it has become evident that HLA-G is involved in modulating both innate and adaptive immune responses, in maintaining tolerance in autoimmune and inflammatory diseases and after transplantation, and in promoting immune escape in cancer and infectious diseases. HLA-G exerts its modulatory/regulatory functions directly by interacting with specific inhibitory receptors. The expression of HLA-G is finely tuned by genetic variations in the noncoding region of the locus. The recent discovery of dendritic cells-10 (DC-10) as naturally occurring HLA-G-expressing dendritic cells opens new perspectives in the identification of the molecular and cellular mechanisms underlying HLA-G-mediated tolerance. An overview on the HLA-G-mediated inhibition of innate and adaptive immune cells, on the genetic influence on HLA-G expression, and on HLA-G-expressing DC-10 is presented. Moreover, we discuss the central and critical role of DC-10 in the HLA-G-mediated tolerance.

HLA-G as a tolerogenic molecule in transplantation and pregnancy

HLA-G is a nonclassical HLA class I molecule. In allogeneic situations such as pregnancy or allograft transplantation, the expression of HLA-G has been related to a better acceptance of the fetus or the allograft. Thus, it seems that HLA-G is crucially involved in mechanisms shaping an allogeneic immune response into tolerance. In this contribution we focus on (i) how HLA-G is involved in transplantation and human reproduction, (ii) how HLA-G is regulated by genetic and microenvironmental factors, and (iii) how HLA-G can offer novel perspectives with respect to therapy.

Human CD4+ HLA-G+ regulatory T cells are potent suppressors of graft-versus-host disease in vivo

CD4(+) T cells expressing the immunotolerizing molecule HLA-G have been described as a unique human thymus-derived regulatory T (tTreg) cell subset involved in immunoregulation and parenchymal homeostasis during infectious and autoimmune inflammation. We compared properties and molecular characteristics of human CD4(+)HLA-G(+) with those of CD4(+)CD25(+)FoxP3-expressing tTreg cells using in vitro studies of T-cell receptor (TCR) signaling, single-cell electrophysiology, and functional in vivo studies. Both tTreg populations are characterized by alterations in proximal-signaling pathways on TCR stimulation and a hyperpolarization of the plasma membrane when compared to conventional CD4(+) T cells. However, both clearly differ in phenotype and pattern of secreted cytokines, which results in distinct mechanisms of suppression: While CD4(+)HLA-G(+) cells secrete high levels of inhibitory molecules (IL-10, soluble HLA-G, IL-35), CD4(+)CD25(+)FoxP3(+) cells express these molecules at significantly lower levels and seem to exert their function mainly in a contact-dependent manner via cyclic adenosine-monophosphate. Finally we demonstrate that human CD4(+)HLA-G(+) tTreg cells significantly ameliorated graft-versus-host disease in a humanized mouse model as a first proof of their in vivo relevance. Our data further characterize and establish CD4(+)HLA-G(+) cells as a potent human tTreg population that can modulate polyclonal adaptive immune responses in vivo and thus being a promising candidate for potential clinical applications in the future.

Impact of HLA-G analysis in prevention, diagnosis and treatment of pathological conditions

Human leukocyte antigen-G (HLA-G) is a non-classical HLA class I molecule that differs from classical HLA class I molecules by low polymorphism and tissue distribution. HLA-G is a tolerogenic molecule with an immune-modulatory and anti-inflammatory function on both innate and adaptative immunity. This peculiar characteristic of HLA-G has led to investigations of its role in pathological conditions in order to define possible uses in diagnosis, prevention and treatment. In recent years, HLA-G has been shown to have an important implication in different inflammatory and autoimmune diseases, pregnancy complications, tumor development and aggressiveness, and susceptibility to viral infections. In fact, HLA-G molecules have been reported to alternate at both genetic and protein level in different disease situations, supporting its crucial role in pathological conditions. Specific pathologies show altered levels of soluble (s)HLA-G and different HLA-G gene polymorphisms seem to correlate with disease. This review aims to update scientific knowledge on the contribution of HLA-G in managing pathological conditions.

HLA-G expression on blasts and tolerogenic cells in patients affected by acute myeloid leukemia

Human Leukocyte Antigen-G (HLA-G) contributes to cancer cell immune escape from host antitumor responses. The clinical relevance of HLA-G in several malignancies has been reported. However, the role of HLA-G expression and functions in Acute Myeloid Leukemia (AML) is still controversial. Our group identified a subset of tolerogenic dendritic cells, DC-10 that express HLA-G and secrete IL-10. DC-10 are present in the peripheral blood and are essential in promoting and maintaining tolerance via the induction of adaptive T regulatory (Treg) cells. We investigated HLA-G expression on blasts and the presence of HLA-G-expressing DC-10 and CD4⁺ T cells in the peripheral blood of AML patients at diagnosis. Moreover, we explored the possible influence of the 3′ untranslated region (3′UTR) of HLA-G, which has been associated with HLA-G expression, on AML susceptibility. Results showed that HLA-G-expressing DC-10 and CD4⁺ T cells are highly represented in AML patients with HLA-G positive blasts. None of the HLA-G variation sites evaluated was associated with AML susceptibility. This is the first report describing HLA-G-expressing DC-10 and CD4⁺ T cells in AML patients, suggesting that they may represent a strategy by which leukemic cells escape the host's immune system. Further studies on larger populations are required to verify our findings.

CD4+NKG2D+ T cells exhibit enhanced migratory and encephalitogenic properties in neuroinflammation

Migration of encephalitogenic CD4(+) T lymphocytes across the blood-brain barrier is an essential step in the pathogenesis of multiple sclerosis (MS). We here demonstrate that expression of the co-stimulatory receptor NKG2D defines a subpopulation of CD4(+) T cells with elevated levels of markers for migration, activation, and cytolytic capacity especially when derived from MS patients. Furthermore, CD4(+)NKG2D(+) cells produce high levels of proinflammatory IFN-γ and IL-17 upon stimulation. NKG2D promotes the capacity of CD4(+)NKG2D(+) cells to migrate across endothelial cells in an in vitro model of the blood-brain barrier. CD4(+)NKG2D(+) T cells are enriched in the cerebrospinal fluid of MS patients, and a significant number of CD4(+) T cells in MS lesions coexpress NKG2D. We further elucidated the role of CD4(+)NKG2D(+) T cells in the mouse system. NKG2D blockade restricted central nervous system migration of T lymphocytes in vivo, leading to a significant decrease in the clinical and pathologic severity of experimental autoimmune encephalomyelitis, an animal model of MS. Blockade of NKG2D reduced killing of cultivated mouse oligodendrocytes by activated CD4(+) T cells. Taken together, we identify CD4(+)NKG2D(+) cells as a subpopulation of T helper cells with enhanced migratory, encephalitogenic and cytotoxic properties involved in inflammatory CNS lesion development.

Intrathecal soluble HLA-E correlates with disease activity in patients with multiple sclerosis and may cooperate with soluble HLA-G in the resolution of neuroinflammation

Expression and function of the immunoregulatory molecule HLA-E was investigated in patients with relapsing-remitting (RR) multiple sclerosis (MS). Serum and cerebrospinal fluid (CSF) soluble (s)HLA-E and -G levels were measured by ELISA in 80 RRMS patients. Controls were patients with other inflammatory neurological disorders (OIND, n = 81) and noninflammatory neurological disorders (NIND, n = 86). Serum sHLA-E concentrations were higher in RRMS than in NIND patients only. CSF sHLA-E concentrations were higher in RRMS than controls. Increased CSF sHLA-E levels were detected in MRI inactive and clinically stable RRMS patients. sHLA-E intrathecal synthesis (ITS) was higher in RRMS than controls, and the number of patients with sHLA-E ITS above cut-off was higher i) in MS than controls, and ii) in clinically stable than clinically active MS patients. sHLA-E CSF levels and ITS correlated with i) the same sHLA-G parameters, and ii) disease duration. HLA-E expression and co-expression with CD markers were investigated in MS plaques from three different cases by immunohistochemistry and confocal microscopy, respectively. Infiltrating T lymphocytes and macrophages, as well as resident microglial cells and astrocytes expressed HLA-E. CSF samples from MS patients were finally tested for inhibitory activity of in vitro CTL and NK cell mediated cytotoxicity. sHLA-E⁺ were more effective than sHLA-E⁻ CSF samples in such inhibition. Maximum inhibition was achieved with sHLA-E⁺/sHLA-G⁺ CSF samples In conclusion, increased sHLA-E CSF levels may play an immunomodulatory role in MS, contributing to the inhibition of intrathecal inflammatory response. The potential of sHLA-E as biomarker of MS activity warrants further investigation.

Endothelial TWIK-related potassium channel-1 (TREK1) regulates immune-cell trafficking into the CNS

The blood-brain barrier (BBB) is an integral part of the neurovascular unit (NVU). The NVU is comprised of endothelial cells that are interconnected by tight junctions resting on a parenchymal basement membrane ensheathed by pericytes, smooth muscle cells and a layer of astrocyte end feet. Circulating blood cells, such as leukocytes, complete the NVU. BBB disruption is common in several neurological diseases, but the molecular mechanisms involved remain largely unknown. We analyzed the role of TWIK-related potassium channel-1 (TREK1, encoded by KCNK2) in human and mouse endothelial cells and the BBB. TREK1 was downregulated in endothelial cells by treatment with interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Blocking TREK1 increased leukocyte transmigration, whereas TREK1 activation had the opposite effect. We identified altered mitogen-activated protein (MAP) kinase signaling, actin remodeling and upregulation of cellular adhesion molecules as potential mechanisms of increased migration in TREK1-deficient (Kcnk2(-/-)) cells. In Kcnk2(-/-) mice, brain endothelial cells showed an upregulation of the cellular adhesion molecules ICAM1, VCAM1 and PECAM1 and facilitated leukocyte trafficking into the CNS. Following the induction of experimental autoimmune encephalomyelitis (EAE) by immunization with a myelin oligodendrocyte protein (MOG)35-55 peptide, Kcnk2(-/-) mice showed higher EAE severity scores that were accompanied by increased cellular infiltrates in the central nervous system (CNS). The severity of EAE was attenuated in mice given the amyotrophic lateral sclerosis drug riluzole or fed a diet enriched with linseed oil (which contains the TREK-1 activating omega-3 fatty acid α-linolenic acid). These beneficial effects were reduced in Kcnk2(-/-) mice, suggesting TREK-1 activating compounds may be used therapeutically to treat diseases related to BBB dysfunction.

Functional characterization of HLA-G⁺ regulatory T cells in HIV-1 infection

Regulatory T cells represent a specialized subpopulation of T lymphocytes that may modulate spontaneous HIV-1 disease progression by suppressing immune activation or inhibiting antiviral T cell immune responses. While the effects of classical CD25(hi) FoxP3⁺ Treg during HIV-1 infection have been analyzed in a series of recent investigations, very little is known about the role of non-classical regulatory T cells that can be phenotypically identified by surface expression of HLA-G or the TGF-β latency-associated peptide (LAP). Here, we show that non-classical HLA-G-expressing CD4 Treg are highly susceptible to HIV-1 infection and significantly reduced in persons with progressive HIV-1 disease courses. Moreover, the proportion of HLA-G⁺ CD4 and CD8 T cells was inversely correlated to markers of HIV-1 associated immune activation. Mechanistically, this corresponded to an increased ability of HLA-G⁺ Treg to reduce bystander immune activation, while only minimally inhibiting the functional properties of HIV-1-specific T cells. Frequencies of LAP⁺ CD4 Treg were not significantly reduced in HIV-1 infection, and unrelated to immune activation. These data indicate an important role of HLA-G⁺ Treg for balancing bystander immune activation and anti-viral immune activity in HIV-1 infection and suggest that the loss of these cells during advanced HIV-1 infection may contribute to immune dysregulation and HIV-1 disease progression.

HLA-G 2012 conference: the 15-year milestone update

The non-classical human leukocyte antigen (HLA) Class I molecule HLA-G is best known for its tolerogenic function at the maternal-fetal interface, where it protects the fetus from destruction by the immune system of its mother. Yet, HLA-G has been the topic of intense investigations and its functions reach much further than originally believed. International conferences on HLA-G have taken place every 3 years since 1998, and the Sixth International Conference on HLA-G, that took place in Paris in July 2012. It counted 180 attendees from 28 countries, 35 speakers in plenary sessions, and 63 presentations of research in symposia and poster sessions, bringing new insight in HLA-G research. Here we summarize the major advances on the function and nature of HLA-G molecule that were reported, with particular interest on the findings in new mechanisms of action through regulatory cells, its relevance in cancer as well as in the molecular structure and functions of HLA-G, which are key for its clinical application.

HLA-G expressing DC-10 and CD4(+) T cells accumulate in human decidua during pregnancy

Multiple mechanisms underlie the surprising willingness of mothers to tolerate the semi-allogeneic fetal tissues during pregnancy. Chief among these is the expression of the HLA-G molecules that has been largely demonstrated to be responsible for reprogramming the local maternal immune response towards tolerance. We recently identified a subset of tolerogenic dendritic cells, DC-10 that secrete high amounts of IL-10 and express high levels of HLA-G and its ligand ILT4. DC-10 are present in the peripheral blood and are essential in inducing adaptive regulatory T cells. We investigated the presence of DC-10 and HLA-G-expressing CD4⁺ T cells in human decidua in the first trimester of pregnancy. Results showed that these cells are highly represented in human decidua as compared to the peripheral blood. This is the first report describing decidual DC-10 and CD4⁺HLA-G⁺ T cells, strongly suggesting that they may accumulate or be induced at the fetal maternal interface to promote tolerance.

Role of HLA-G 14bp deletion/insertion and +3142C>G polymorphisms in the production of sHLA-G molecules in relapsing-remitting multiple sclerosis

HLA-G is believed to act as an anti-inflammatory molecule in Multiple Sclerosis (MS). The 3' untranslated region of the HLA-G gene is characterized by two polymorphisms, DEL/INS14bp and +3142C>G, which control soluble HLA-G (sHLA-G) production. The influence of these two HLA-G variants on sHLA-G serum and cerebrospinal fluid (CSF) levels was investigated in 69 Relapsing-Remitting MS patients grouped in magnetic resonance imaging (MRI) inactive and active disease. Serum and CSF sHLA-G levels were more elevated in high than in low DEL/INS 14bp and +3142C>G sHLA-G producers and were different among the various combined HLA-G genotypes in both MRI inactive and active diseases. The highest and the lowest sHLA-G values were identified in MS patients with C/C,DEL/DEL and G/G,INS/INS genotypes, respectively. Our preliminary findings suggest that serum and CSF sHLA-G levels in MS could be influenced by HLA-G polymorphisms irrespective of the inflammatory microenvironment.

The immunosuppressive molecule HLA-G and its clinical implications

Human leukocyte antigen G (HLA-G) is a non-classical major histocompatibility complex (MHC) class I molecule that, through interaction with its receptors, exerts important tolerogenic functions. Its main physiological expression occurs in placenta where it seems to participate in the maternal tolerance toward the fetus. HLA-G has been studied as a marker of pregnancy complications such as abortion or pre-eclapmsia. Although HLA-G is not expressed in most adult tissues, its ectopic expression has been observed in some diseases such as viral infections, autoimmune disorders, and especially cancer. HLA-G neo-expression in cancer is associated with the capability of tumor cells to evade the immune control. In this review, we will summarize HLA-G biology and how it participates in these physiopathological processes. Special attention will be paid to its role as a diagnostic tool and also as a therapeutic target.

CNS recruitment of CD8+ T lymphocytes specific for a peripheral virus infection triggers neuropathogenesis during polymicrobial challenge

Although viruses have been implicated in central nervous system (CNS) diseases of unknown etiology, including multiple sclerosis and amyotrophic lateral sclerosis, the reproducible identification of viral triggers in such diseases has been largely unsuccessful. Here, we explore the hypothesis that viruses need not replicate in the tissue in which they cause disease; specifically, that a peripheral infection might trigger CNS pathology. To test this idea, we utilized a transgenic mouse model in which we found that immune cells responding to a peripheral infection are recruited to the CNS, where they trigger neurological damage. In this model, mice are infected with both CNS-restricted measles virus (MV) and peripherally restricted lymphocytic choriomeningitis virus (LCMV). While infection with either virus alone resulted in no illness, infection with both viruses caused disease in all mice, with ∼50% dying following seizures. Co-infection resulted in a 12-fold increase in the number of CD8⁺ T cells in the brain as compared to MV infection alone. Tetramer analysis revealed that a substantial proportion (>35%) of these infiltrating CD8⁺ lymphocytes were LCMV-specific, despite no detectable LCMV in CNS tissues. Mechanistically, CNS disease was due to edema, induced in a CD8-dependent but perforin-independent manner, and brain herniation, similar to that observed in mice challenged intracerebrally with LCMV. These results indicate that T cell trafficking can be influenced by other ongoing immune challenges, and that CD8⁺ T cell recruitment to the brain can trigger CNS disease in the apparent absence of cognate antigen. By extrapolation, human CNS diseases of unknown etiology need not be associated with infection with any particular agent; rather, a condition that compromises and activates the blood-brain barrier and adjacent brain parenchyma can render the CNS susceptible to pathogen-independent immune attack.

There are many CNS diseases, including multiple sclerosis and amyotrophic lateral sclerosis, which have an inflammatory component, though no direct link has been established between incidence and a CNS-resident infectious agent. We reasoned that peripheral immunogens could play a role in CNS disease by inducing an immune response that is “mis-targeted” to the brain. This hypothesis was based on the immunological principle that, while education and activation of naïve cells is an antigen-driven process, recruitment is primarily antigen-independent. We developed a viral co-infection model using measles virus (MV) as a CNS activator and recruiting signal and lymphocytic choriomeningitis (LCMV) as a peripheral immune response initiator. Co-infection with both viruses resulted in significant morbidity and mortality, coincident with LCMV-specific CD8⁺ T cell trafficking to the brain. Death occurred due to edema, despite an apparent absence of LCMV antigens within the brain, and pathogenesis was CD8⁺ T cell-dependent, but perforin-independent. Thus, recruitment of peripherally activated CD8⁺ T cells to the CNS can potentiate neuroinflammation. This work raises the possibility that concomitant immune challenges may be an important cause of the neuroinflammation of some human CNS diseases, perhaps accounting for the inability to identify a discrete pathogenic trigger within affected brain tissues.

CD8(+) Tregs in autoimmunity: learning "self"-control from experience

Autoreactive CD8(+) regulatory T cells (Tregs) play important roles as modulators of immune responses against self, and numerical and functional defects in CD8(+) Tregs have been linked to autoimmunity. Several subsets of CD8(+) Tregs have been described. However, the origin of these T cells and how they participate in the natural progression of autoimmunity remain poorly defined. We discuss several lines of evidence suggesting that the autoimmune process itself promotes the development of autoregulatory CD8(+) T cells. We posit that chronic autoantigenic exposure fosters the differentiation of non-pathogenic autoreactive CD8(+) T cells into antigen-experienced, memory-like autoregulatory T cells, to generate a "negative feedback" regulatory loop capable of countering pathogenic autoreactive effectors. This hypothesis predicts that approaches capable of boosting autoregulatory T cell memory will be able to blunt autoimmunity without compromising systemic immunity.

The tolerogenic interplay(s) among HLA-G, myeloid APCs, and regulatory cells

Myeloid antigen-presenting cells (APCs), regulatory cells, and the HLA-G molecule are involved in modulating immune responses and promoting tolerance. APCs are known to induce regulatory cells and to express HLA-G as well as 2 of its receptors; regulatory T cells can express and act through HLA-G; and HLA-G has been directly involved in the generation of regulatory cells. Thus, interplay(s) among HLA-G, APCs, and regulatory cells can be easily envisaged. However, despite a large body of evidence on the tolerogenic properties of HLA-G, APCs, and regulatory cells, little is known on how these tolerogenic players cooperate. In this review, we first focus on key aspects of the individual relationships between HLA-G, myeloid APCs, and regulatory cells. In its second part, we highlight recent work that gathers individual effects and demonstrates how intertwined the HLA-G/myeloid APCs/regulatory cell relationship is.

Tregs and infections: on the potential value of modifying their function

CD4(+) T cells, which express a master transcription factor, Foxp3, have been recognized as bona fide Tregs. These cells are essential to maintain immune homeostasis in healthy as well as infected mice and humans. Extensive investigations in the last decade have provided ways to manipulate the Foxp3(+) Treg response therapeutically so the role of such cells in microbe-induced inflammatory reactions can be evaluated. This review focuses on our current understanding of the mechanisms required for the generation and sustenance of Tregs in vivo and the potential value of modulating Tregs to control microbe-induced immunopathological responses.

Immunological and clinical consequences of treating a patient with natalizumab

BACKGROUND

Long-term therapy with natalizumab increases the risk of progressive multifocal leukoencephalopathy (PML).

OBJECTIVES

We present a patient study through therapy, the diagnosis of PML (after 29 infusions), plasma exchange (PE) and development of immune reconstitution inflammatory syndrome (IRIS).

METHODS

Routine diagnostics, magnetic resonance imaging (MRI), immunological status (flow cytometry, T-cell migration assays and T-cell repertoire analysis), and brain biopsy with immunohistological analysis.

RESULTS

CD49d decreased after 12 months of treatment. At PML diagnosis, CD49d expression and migratory capacity of T cells was low and peripheral T-cell receptor (TCR) complexity showed severe perturbations. The distribution of peripheral monocytes changed from CCR5+ to CCR7+. After PE some changes reverted: CD49d increased and overshot earliest levels, migratory capacities of T cells recovered and peripheral TCR complexity increased. With no clinical, routine laboratory or cerebrospinal fluid (CSF) changes, MRI 2 months after PE demonstrated progressive lesion development. Brain histopathology confirmed the presence of infiltrates indicative of IRIS without clinical signs, immunologically accompanied by CCR7/CCR5 recovery of peripheral monocytes.

CONCLUSION

Natalizumab-associated immunological changes accompanying PML were reversible after PE; IRIS can occur very late, remain asymptomatic and be elusive to CSF analysis. Our study may provide insights into the changes under treatment with natalizumab associated with JC virus control.

Regulatory T cells exhibit enhanced migratory characteristics, a feature impaired in patients with multiple sclerosis

Migration of immune cells characterizes inflammation and plays a key role in autoimmune diseases such as MS. CD4(+)Foxp3(+) regulatory T cells (Treg) have the potential to dampen immune responses but show functional impairment in patients with MS. We here show that murine Treg exhibit higher constitutive cell motility in horizontal migration on laminin, surpass non-Treg in transwell assays through microporous membranes as well as across primary brain endothelium and are present in the naïve CNS to a significantly higher extent compared to spleen, lymph nodes and blood. Likewise, human Treg from healthy donors significantly exceed non-Treg in migratory rates across primary human brain endothelium. Finally, we investigated whether the propensity to migrate is impaired as a feature of autoimmunity and therefore tested patients with MS. Treg from patients with stable relapsing-remitting MS show significantly impaired migratory capacity under non-inflammatory conditions compared to healthy donors. We hypothesize that the enhanced propensity to migrate is a feature of Treg that allows for an equilibrium in parenchymal immune surveillance, e.g. of the CNS. Impaired Treg migration across the intact blood-brain barrier, as observed for Treg from patients with MS, indicates a broader functional deficiency hypothetically contributing to early CNS lesion development or phases of MS remissions.

Intracerebral human regulatory T cells: analysis of CD4+ CD25+ FOXP3+ T cells in brain lesions and cerebrospinal fluid of multiple sclerosis patients

Impaired suppressive capacity of CD4(+)CD25(+)FOXP3(+) regulatory T cells (Treg) from peripheral blood of patients with multiple sclerosis (MS) has been reported by multiple laboratories. It is, however, currently unresolved whether Treg dysfunction in MS patients is limited to reduced control of peripheral T cell activation since most studies analyzed peripheral blood samples only. Here, we assessed early active MS lesions in brain biopsies obtained from 16 patients with MS by FOXP3 immunohistochemistry. In addition, we used six-color flow cytometry to determine numbers of Treg by analysis of FOXP3/CD127 expression in peripheral blood and cerebrospinal fluid (CSF) of 17 treatment-naïve MS patients as well as quantities of apoptosis sensitive CD45RO(hi)CD95(hi) cells in circulating and CSF Treg subsets. Absolute numbers of FOXP3(+) and CD4(+) cells were rather low in MS brain lesions and Treg were not detectable in 30% of MS biopsies despite the presence of CD4(+) cell infiltrates. In contrast, Treg were detectable in all CSF samples and Treg with a CD45RO(hi)CD95(hi) phenotype previously shown to be highly apoptosis sensitive were found to be enriched in the CSF compared to peripheral blood of MS patients. We suggest a hypothetical model of intracerebral elimination of Treg by CD95L-mediated apoptosis within the MS lesion.