Analysis of regulatory CD8 T cells in Qa-1-deficient mice

Food antigens suppress small intestinal tumorigenesis

Food components suppressing small intestinal tumorigenesis are not well-defined partly because of the rarity of this tumor type compared to colorectal tumors. Using Apcmin/+ mice, a mouse model for intestinal tumorigenesis, and antigen-free diet, we report here that food antigens serve this function in the small intestine. By depleting Peyer's patches (PPs), immune inductive sites in the small intestine, we found that PPs have a role in the suppression of small intestinal tumors and are important for the induction of small intestinal T cells by food antigens. On the follicle-associated epithelium (FAE) of PPs, microfold (M) cells pass food antigens from lumen to the dendritic cells to induce T cells. Single-cell RNA-seq (scRNA-seq) analysis of immune cells in PPs revealed a significant impact of food antigens on the induction of the PP T cells and the antigen presentation capacity of dendritic cells. These data demonstrate the role of food antigens in the suppression of small intestinal tumorigenesis by PP-mediated immune cell induction.

Novel Autologous Dendritic Cell Therapy AVT001 for Type 1 Diabetes

BACKGROUND

CD8+ T regulatory (Treg) cells that recognize the nonclassical class 1b molecule Qa-1/human leukocyte antigen E (Q/E CD8+ Treg cells) are important in maintaining self-tolerance. We sought to investigate the role that these T cells play in type 1 diabetes (T1D) pathogenesis and whether an intervention targeting this mechanism may delay T1D progression.

METHODS

We conducted a phase 1/2, randomized, double-blind, placebo-controlled trial of the autologous dendritic cell therapy AVT001 that included participants at least 16 years of age, within 1 year of T1D diagnosis, and with ex vivo evidence of a defect in Q/E CD8+ Treg function. Patients were randomly assigned in a 2:1 ratio to AVT001 or placebo, which was administered in three monthly intravenous infusions. The primary end point was safety; efficacy end points included changes from baseline in C-peptide area under the curve (AUC) during a 4-hour mixed meal, hemoglobin A1c (HbA1c), and insulin dose.

RESULTS

Sixteen patients received AVT001, and nine received placebo. Similar rates and severity of adverse events were observed in both groups. None of the patients in the AVT001 group had serious adverse events through visit day 360. Compared with placebo, treatment with ATV001 was associated with less decline from baseline log-transformed C-peptide AUC (nmol/l), with the treatment effect between AVT001 and placebo at day 150 of 0.09 (95% confidence interval [CI], 0.03 to 0.15) and at day 360 of 0.10 (95% CI, 0.04 to 0.15). No clear differences in change in HbA1c and insulin dose from baseline were observed between groups. Estimated treatment effects of AVT001 versus placebo at day 360 were -0.17% (95% CI, -0.60 to 0.26%) for HbA1c and -0.06 U/kg/day (95% CI, -0.14 to 0.02) for daily insulin dose.

CONCLUSIONS

In this phase 1/2 trial, AVT001 did not result in dose-limiting adverse events. Potential signals of efficacy observed here warrant further evaluation in a fully powered trial. (Funded by Avotres Inc. and the Division of Diabetes, Endocrinology, and Metabolic Diseases; ClinicalTrials.gov number, NCT03895996.).

An angel or a devil? Current view on the role of CD8+ T cells in the pathogenesis of myasthenia gravis

BACKGROUND

Myasthenia gravis (MG) and the experimental autoimmune MG (EAMG) animal model are characterized by T-cell-induced and B-cell-dominated autoimmune diseases that affect the neuromuscular junction. Several subtypes of CD4+ T cells, including T helper (Th) 17 cells, follicular Th cells, and regulatory T cells (Tregs), contribute to the pathogenesis of MG. However, increasing evidence suggests that CD8+ T cells also play a critical role in the pathogenesis and treatment of MG.

MAIN BODY

Herein, we review the literature on CD8+ T cells in MG, focusing on their potential effector and regulatory roles, as well as on relevant evidence (peripheral, in situ, cerebrospinal fluid, and under different treatments), T-cell receptor usage, cytokine and chemokine expression, cell marker expression, and Treg, Tc17, CD3+CD8+CD20+ T, and CXCR5+ CD8+ T cells.

CONCLUSIONS

Further studies on CD8+ T cells in MG are necessary to determine, among others, the real pattern of the Vβ gene usage of autoantigen-specific CD8+ cells in patients with MG, real images of the physiology and function of autoantigen-specific CD8+ cells from MG/EAMG, and the subset of autoantigen-specific CD8+ cells (Tc1, Tc17, and IL-17+IFN-γ+CD8+ T cells). There are many reports of CD20-expressing T (or CD20 + T) and CXCR5+ CD8 T cells on autoimmune diseases, especially on multiple sclerosis and rheumatoid arthritis. Unfortunately, up to now, there has been no report on these T cells on MG, which might be a good direction for future studies.

A narrow T cell receptor repertoire instructs thymic differentiation of MHC class Ib-restricted CD8+ regulatory T cells

Although most CD8+ T cells are equipped to kill infected or transformed cells, a subset may regulate immune responses and preserve self-tolerance. Here, we describe a CD8 lineage that is instructed to differentiate into CD8 T regulatory cells (Tregs) by a surprisingly restricted set of T cell receptors (TCRs) that recognize MHC-E (mouse Qa-1) and several dominant self-peptides. Recognition and elimination of pathogenic target cells that express these Qa-1-self-peptide complexes selectively inhibits pathogenic antibody responses without generalized immune suppression. Immunization with synthetic agonist peptides that mobilize CD8 Tregs in vivo efficiently inhibit antigraft antibody responses and markedly prolong heart and kidney organ graft survival. Definition of TCR-dependent differentiation and target recognition by this lineage of CD8 Tregs may open the way to new therapeutic approaches to inhibit pathogenic antibody responses.

The MHC-E peptide ligands for checkpoint CD94/NKG2A are governed by inflammatory signals, whereas LILRB1/2 receptors are peptide indifferent

The immune checkpoint NKG2A/CD94 is a promising target for cancer immunotherapy, and its ligand major histocompatibility complex E (MHC-E) is frequently upregulated in cancer. NKG2A/CD94-mediated inhibition of lymphocytes depends on the presence of specific leader peptides in MHC-E, but when and where they are presented in situ is unknown. We apply a nanobody specific for the Qdm/Qa-1b complex, the NKG2A/CD94 ligand in mouse, and find that presentation of Qdm peptide depends on every member of the endoplasmic reticulum-resident peptide loading complex. With a turnover rate of 30 min, the Qdm peptide reflects antigen processing capacity in real time. Remarkably, Qdm/Qa-1b complexes require inflammatory signals for surface expression in situ, despite the broad presence of Qa-1b molecules in homeostasis. Furthermore, we identify LILRB1 as a functional inhibition receptor for MHC-E in steady state. These data provide a molecular understanding of NKG2A blockade in immunotherapy and assign MHC-E as a convergent ligand for multiple immune checkpoints.

HELIOS-expressing human CD8 T cells exhibit limited effector functions

Introduction

The transcription factor HELIOS is primarily known for its expression in CD4 regulatory T cells, both in humans and mice. In mice, HELIOS is found in exhausted CD8 T cells. However, information on human HELIOS+ CD8 T cells is limited and conflicting.

Methods

In this study, we characterized by flow cytometry and transcriptomic analyses human HELIOS+ CD8 T cells.

Results

These T cells primarily consist of memory cells and constitute approximately 21% of blood CD8 T cells. In comparison with memory HELIOS- T-BEThigh CD8 T cells that displayed robust effector functions, the memory HELIOS+ T-BEThigh CD8 T cells produce lower amounts of IFN-γ and TNF-α and have a lower cytotoxic potential. We wondered if these cells participate in the immune response against viral antigens, but did not find HELIOS+ cells among CD8 T cells recognizing CMV peptides presented by HLA-A2 and HLA-B7. However, we found HELIOS+ CD8 T cells that recognize a CMV peptide presented by MHC class Ib molecule HLA-E. Additionally, a portion of HELIOS+ CD8 T cells is characterized by the expression of CD161, often used as a surface marker for identifying TC17 cells. These CD8 T cells express TH17/TC17-related genes encoding RORgt, RORa, PLZF, and CCL20.

Discussion

Our findings emphasize that HELIOS is expressed across various CD8 T cell populations, highlighting its significance beyond its role as a transcription factor for Treg or exhausted murine CD8 T cells. The significance of the connection between HELIOS and HLA-E restriction is yet to be understood.

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.

The promiscuous development of an unconventional Qa1b-restricted T cell population

MHC-E restricted CD8 T cells show promise in vaccine settings, but their development and specificity remain poorly understood. Here we focus on a CD8 T cell population reactive to a self-peptide (FL9) bound to mouse MHC-E (Qa-1b) that is presented in response to loss of the MHC I processing enzyme ERAAP, termed QFL T cells. We find that mature QFL thymocytes are predominantly CD8αβ+CD4-, show signs of agonist selection, and give rise to both CD8αα and CD8αβ intraepithelial lymphocytes (IEL), as well as memory phenotype CD8αβ T cells. QFL T cells require the MHC I subunit β-2 microglobulin (β2m), but do not require Qa1b or classical MHC I for positive selection. However, QFL thymocytes do require Qa1b for agonist selection and full functionality. Our data highlight the relaxed requirements for positive selection of an MHC-E restricted T cell population and suggest a CD8αβ+CD4- pathway for development of CD8αα IELs.

Cytokine receptor γc effectuates the generation of proinflammatory innate CD8 T cells by non-classical MHC-I molecules

Innate CD8 T cells correspond to a population of terminally differentiated effector T cells that phenotypically appear as antigen-experienced memory cells and functionally resemble proinflammatory CD8 T cells, expressing copious amounts of IFNγ. Innate CD8 T cells, however, are distinct from conventional effector-memory CD8 T cells as they acquire functional maturity during their generation in the thymus. Understanding the molecular mechanisms that drive their thymic development and differentiation is an intensely studied subject in T cell immunity, and here we identified the cytokine receptor γc as a critical mediator of innate CD8 T cell generation that promotes their selection even in the absence of classical MHC-I molecules. Consequently, overexpression of γc resulted in a dramatic increase of innate CD8 T cells in KbDb-deficient mice. We mapped its underlying mechanism to the expansion of IL-4-producing invariant NKT cells, so that it is the increased availability of intrathymic IL-4 which augments the selection of innate CD8 T cells. Collectively, these results unravel the selection of innate CD8 T cells being mediated by non-classical MHC-I molecules and being modulated by the abundance of the γc cytokine, IL-4.

Chemical compositions of Souliea vaginata (Maxim) Franch rhizome and their potential therapeutic effects on collagen-induced arthritis in rats

ETHNOPHARMACOLOGICAL REVEVANCE

Rheumatoid arthritis (RA) is a global prevalent chronic autoimmune inflammatory disease and acceptable safety drugs are lack for its treatment. The rhizomes of Souliea vaginata (Maxim) Franch (SV) possess anti-inflammatory functions and are used as substitution of Coptis chinensis Franch. SV is also traditional Chinese medicine and Tibetan medicine for the treatment of conjunctivitis, enteritis and rheumatic. For searching complementary and alternative anti-RA drugs, it is necessary to characterize the potential anti-arthritic activity of SV and underlying mechanism involved.

AIM OF THE STUDY

The aim of the study was to test the chemical compositions, evaluate the anti-arthritic effects and underlying mechanisms of SV.

MATERIALS AND METHODS

The chemical compositions of SV were analyzed using liquid chromatography-ion trap-time of flight tandem mass spectrometry (LCMS-IT-TOF). From day 11 to day 31, SV (0.5, 1.0 and 1.5 g/kg body weight) and Tripterygium glycosidorum (TG, 10 mg/kg body weight) were administered orally to the CIA model rats once a day. Thickness of paw and body weights were measured once every two days from day 1 to day 31. Histopathological changes were measured using hematoxylin-eosin (HE) staining. Effects of SV on the levels of IL-2, TNF-α, IFN-γ, IL-4 and IL-10 in serum of CIA rats were measured by enzyme-linked immunosorbent assay (ELISA) kits. CD3⁺, CD4⁺, CD8⁺ and CD4⁺CD25⁺ T cells populations were measured using flow cytometric analysis. To evaluate the possible hepatotoxicity and nephrotoxicity, the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea (UREA) and creatinine (CREA) in CIA rats were also tested using blood auto analyzer.

RESULTS

34 compounds were identified from SV based on LCMS-IT-TOF, and triterpenoids are major anti-arthritic compositions. SV significantly relieved CIA rats' paw swelling without obvious influence on the body weight growth. SV decreased the serum levels of IL-2, TNF-α and IFN-γ in CIA rat, and increased the serum levels of IL-4 and IL-10. SV significantly increased and decreased the percentages of CD4⁺ and CD8⁺, with no significant effects on CD3⁺ in lymphocytes of CIA model rats. Moreover, SV simultaneously decreased thymus and spleen indexes and no hepatotoxicity and nephrotoxicity was observed after short-term treatment.

CONCLUSION

These findings suggest that SV possesses preventive and therapeutic effect on RA by modulating the inflammatory cytokines, T-lymphocyte, thymus and spleen indexes and shows no hepatotoxicity and nephrotoxicity.

Murine cytomegalovirus downregulates ERAAP and induces an unconventional T cell response to self

The endoplasmic reticulum aminopeptidase associated with antigen processing (ERAAP) plays a crucial role in shaping the peptide-major histocompatibility complex (MHC) class I repertoire and maintaining immune surveillance. While murine cytomegalovirus (MCMV) has multiple strategies for manipulating the antigen processing pathway to evade immune responses, the host has also developed ways to counter viral immune evasion. In this study, we find that MCMV modulates ERAAP and induces an interferon γ (IFN-γ)-producing CD8+ T cell effector response that targets uninfected ERAAP-deficient cells. We observe that ERAAP downregulation during infection leads to the presentation of the self-peptide FL9 on non-classical Qa-1b, thereby eliciting Qa-1b-restricted QFL T cells to proliferate in the liver and spleen of infected mice. QFL T cells upregulate effector markers upon MCMV infection and are sufficient to reduce viral load after transfer to immunodeficient mice. Our study highlights the consequences of ERAAP dysfunction during viral infection and provides potential targets for anti-viral therapies.

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.

Dynamics of the gut microbiome, IgA response, and plasma metabolome in the development of pediatric celiac disease

BACKGROUND

Celiac disease (CD) is an autoimmune disorder triggered by gluten consumption. Almost all CD patients possess human leukocyte antigen (HLA) DQ2/DQ8 haplotypes; however, only a small subset of individuals carrying these alleles develop CD, indicating the role of environmental factors in CD pathogenesis. The main objective of this study was to determine the contributory role of gut microbiota and microbial metabolites in CD onset. To this end, we obtained fecal samples from a prospective cohort study (ABIS) at ages 2.5 and 5 years. Samples were collected from children who developed CD after the final sample collection (CD progressors) and healthy children matched by age, HLA genotype, breastfeeding duration, and gluten-exposure time (n=15-16). We first used 16S sequencing and immunoglobulin-A sequencing (IgA-seq) using fecal samples obtained from the same children (i) 16 controls and 15 CD progressors at age 2.5 and (ii) 13 controls and 9 CD progressors at age 5. We completed the cytokine profiling, and plasma metabolomics using plasma samples obtained at age 5 (n=7-9). We also determined the effects of one microbiota-derived metabolite, taurodeoxycholic acid (TDCA), on the small intestines and immune cell composition in vivo.

RESULTS

CD progressors have a distinct gut microbiota composition, an increased IgA response, and unique IgA targets compared to healthy subjects. Notably, 26 plasma metabolites, five cytokines, and one chemokine were significantly altered in CD progressors at age 5. Among 26 metabolites, we identified a 2-fold increase in TDCA. TDCA treatment alone caused villous atrophy, increased CD4+ T cells, Natural Killer cells, and two important immunoregulatory proteins, Qa-1 and NKG2D expression on T cells while decreasing T-regulatory cells in intraepithelial lymphocytes (IELs) in C57BL/6J mice.

CONCLUSIONS

Pediatric CD progressors have a distinct gut microbiota composition, plasma metabolome, and cytokine profile before diagnosis. Furthermore, CD progressors have more IgA-coated bacteria and unique targets of IgA in their gut microbiota. TDCA feeding alone stimulates an inflammatory immune response in the small intestines of C57BJ/6 mice and causes villous atrophy, the hallmark of CD. Thus, a microbiota-derived metabolite, TDCA, enriched in CD progressors' plasma, has the potential to drive inflammation in the small intestines and enhance CD pathogenesis. Video Abstract.

Patients With Severe Multiple Sclerosis Exhibit Functionally Altered CD8+ Regulatory T Cells

BACKGROUND AND OBJECTIVES

Multiple sclerosis (MS) is a chronic inflammatory and demyelinating disease of the CNS. Studies of immune dysfunction in MS have mostly focused on CD4⁺ Tregs, but the role of CD8⁺ Tregs remains largely unexplored. We previously evidenced the suppressive properties of rat and human CD8⁺CD45RC^low/neg Tregs from healthy individuals, expressing Forkhead box P3 (FOXP3) and acting through interferon-gamma (IFN-γ), transforming growth factor beta (TGFβ), and interleukin-34 (IL-34). secretions to regulate immune responses and control diseases such as transplant rejection. To better understand CD8⁺CD45RC^low/neg Tregs contribution to MS pathology, we further investigated their phenotype, function, and transcriptome in patients with MS.

METHODS

We enrolled adults with relapsing-remitting MS and age-matched and sex-matched healthy volunteers (HVs). CD8⁺ T cells were segregated based on low or lack of expression of CD45RC. First, the frequency in CSF and blood, phenotype, transcriptome, and function of CD8⁺CD45RC^low and ^neg were investigated according to exacerbation status and secondarily, according to clinical severity based on the MS severity score (MSSS) in patients with nonexacerbating MS. We then induced active MOG_35-55 EAE in C57Bl/6 mice and performed adoptive transfer of fresh and expanded CD8⁺CD45RC^neg Tregs to assess their ability to mitigate neuroinflammation in vivo.

RESULTS

Thirty-one untreated patients with relapsing-remitting MS were compared with 40 age-matched and sex-matched HVs. We demonstrated no difference of CSF CD8⁺CD45RC^low and CD8⁺CD45RC^neg proportions, but blood CD8⁺CD45RC^low frequency was lower in patients with MS exacerbation when compared with that in HVs. CD8⁺CD45RC^neg Tregs but not CD8⁺CD45RC^low showed higher suppressive capacities in vitro in MS patients with exacerbation than in patients without acute inflammatory attack. In vitro functional assays showed a compromised suppression capacity of CD8⁺CD45RC^low Tregs in patients with nonexacerbating severe MS, defined by the MSSS. We then characterized murine CD8⁺CD45RC^neg Tregs and demonstrated the potential of CD45RC^neg cells to migrate to the CNS and mitigate experimental autoimmune encephalomyelitis in vivo.

DISCUSSION

Altogether, these results suggest a defect in the number and function of CD8⁺CD45RC^low Tregs during MS relapse and an association of CD8⁺CD45RC^low Tregs dysfunction with MS severity. Thus, CD8⁺CD45RC^low/neg T cells might bring new insights into the pathophysiology and new therapeutic approaches of MS.

Neuroinflammation: Extinguishing a blaze of T cells

Inflammation is a biological process that dynamically alters the surrounding microenvironment, including participating immune cells. As a well-protected organ surrounded by specialized barriers and with immune privilege properties, the central nervous system (CNS) tightly regulates immune responses. Yet in neuroinflammatory conditions, pathogenic immunity can disrupt CNS structure and function. T cells in particular play a key role in promoting and restricting neuroinflammatory responses, while the inflamed CNS microenvironment can influence and reshape T cell function and identity. Still, the contraction of aberrant T cell responses within the CNS is not well understood. Using autoimmunity as a model, here we address the contribution of CD4 T helper (Th) cell subsets in promoting neuropathology and disease. To address the mechanisms antagonizing neuroinflammation, we focus on the control of the immune response by regulatory T cells (Tregs) and describe the counteracting processes that preserve their identity under inflammatory challenges. Finally, given the influence of the local microenvironment on immune regulation, we address how CNS-intrinsic signals reshape T cell function to mitigate abnormal immune T cell responses.

Treatment and Relapse Prevention of Typical and Atypical Optic Neuritis

Optic neuritis (ON) is an inflammatory condition involving the optic nerve. Several important typical and atypical ON variants are now recognized. Typical ON has a more favorable prognosis; it can be idiopathic or represent an early manifestation of demyelinating diseases, mostly multiple sclerosis (MS). The atypical spectrum includes entities such as antibody-driven ON associated with neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody disease (MOGAD), chronic/relapsing inflammatory optic neuropathy (CRION), and sarcoidosis-associated ON. Appropriate and timely diagnosis is essential to rapidly decide on the appropriate treatment, maximize visual recovery, and minimize recurrences. This review paper aims at presenting the currently available state-of-the-art treatment strategies for typical and atypical ON, both in the acute phase and in the long-term. Moreover, emerging therapeutic approaches and novel steps in the direction of achieving remyelination are discussed.

Characterization of gene expression profiles in the mouse brain after 35 days of spaceflight mission

It has been proposed that neuroinflammatory response plays an important role in the neurovascular remodeling in the brain after stress. The goal of the present study was to characterize changes in the gene expression profiles associated with neuroinflammation, neuronal function, metabolism and stress in mouse brain tissue. Ten-week old male C57BL/6 mice were launched to the International Space Station (ISS) on SpaceX-12 for a 35-day mission. Within 38 ± 4 h of splashdown, mice were returned to Earth alive. Brain tissues were collected for analysis. A novel digital color-coded barcode counting technology (NanoString^TM) was used to evaluate gene expression profiles in the spaceflight mouse brain. A set of 54 differently expressed genes (p < 0.05) significantly segregates the habitat ground control (GC) group from flight (FLT) group. Many pathways associated with cellular stress, inflammation, apoptosis, and metabolism were significantly altered by flight conditions. A decrease in the expression of genes important for oligodendrocyte differentiation and myelin sheath maintenance was observed. Moreover, mRNA expression of many genes related to anti-viral signaling, reactive oxygen species (ROS) generation, and bacterial immune response were significantly downregulated. Here we report that significantly altered immune reactions may be closely associated with spaceflight-induced stress responses and have an impact on the neuronal function.

Abnormalities of T cells in systemic lupus erythematosus: new insights in pathogenesis and therapeutic strategies

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by loss of immune tolerance and sustained production of autoantibodies. Multiple and profound T cell abnormalities in SLE are intertwined with disease expression. Both numerical and functional disturbances have been reported in main CD4⁺ T helper cell subsets including Th1, Th2, Th17, regulatory, and follicular helper cells. SLE CD4⁺ T cells are known to provide help to B cells, produce excessive IL-17 but insufficient IL-2, and infiltrate tissues. In the absence of sufficient amounts of IL-2, regulatory T cells, do not function properly to constrain inflammation. A complicated series of early signaling defects and aberrant activation of kinases and phosphatases result in complex cell phenotypes by altering the metabolic profile and the epigenetic landscape. All main metabolic pathways including glycolysis, glutaminolysis and oxidative phosphorylation are altered in T cells from lupus prone mice and patients with SLE. SLE CD8⁺ cytotoxic T cells display reduced cytolytic activity which accounts for higher rates of infection and the sustenance of autoimmunity. Further, CD8⁺ T cells in the context of rheumatic diseases lose the expression of CD8, acquire IL-17⁺CD4^-CD8^- double negative T (DNT) cell phenotype and infiltrate tissues. Herein we present an update on these T cell abnormalities along with underlying mechanisms and discuss how these advances can be exploited therapeutically. Novel strategies to correct these aberrations in T cells show promise for SLE treatment.

The nonclassical MHC class I Qa-1 expressed in layer 6 neurons regulates activity-dependent plasticity via microglial CD94/NKG2 in the cortex

During developmental critical periods, circuits are sculpted by a process of activity-dependent competition. The molecular machinery involved in regulating the complex process of responding to different levels of activity is now beginning to be identified. Here, we show that the nonclassical major histocompatibility class I (MHCI) molecule Qa-1 is expressed in the healthy brain in layer 6 corticothalamic neurons. In the visual cortex, Qa-1 expression begins during the critical period for ocular dominance (OD) plasticity and is regulated by neuronal activity, suggesting a role in regulating activity-dependent competition. Indeed, in mice lacking Qa-1, OD plasticity is perturbed. Moreover, signaling through CD94/NKG2, a known cognate Qa-1 heterodimeric receptor in the immune system, is implicated: selectively targeting this interaction phenocopies the plasticity perturbation observed in Qa-1 knockouts. In the cortex, CD94/NKG2 is expressed by microglial cells, which undergo activity-dependent changes in their morphology in a Qa-1–dependent manner. Our study thus reveals a neuron–microglial interaction dependent upon a nonclassical MHCI molecule expressed in L6 neurons, which regulates plasticity in the visual cortex. These results also point to an unexpected function for the Qa-1/HLA-E (ligand) and CD94/NKG2 (receptor) interaction in the nervous system, in addition to that described in the immune system.

Topical application of cannabinoid-ligands ameliorates experimental dry-eye disease

PURPOSE

Dry eye disease (DED) is a multifactorial disease, with limitations regarding efficacy and tolerability of applied substances. Among several candidates, the endocannabinoid system with its receptors (CB1R and CB2R) were reported to modulate inflammation, wound healing and pain, which are also core DED pathomechanisms. This study is to investigate the therapeutic responses of Δ-9 tetrahydrocannabinol (a non-selective agonist) and two selective antagonists, SR141716A (CB1R antagonist) and SR144528 (CB2R antagonist), as a topical application using a DED mouse model.

METHOD

Experimental DED was induced in naïve C57BL/6 mice. Expression of CBR at the ocular surface of naïve and DED mice was determined by qPCR and in-situ hybridization. Either THC or CBR antagonists were compounded in an aqueous solution and dosed during the induction of DED. Tear production, cornea sensitivity, and cornea fluorescence staining were tested. At the end of each experiment, corneas were stained with β3-tubulin for analysis of corneal nerve morphology. Conjunctiva was analyzed for CD4⁺ and CD8⁺ infiltration.

RESULTS

CB1R and CB2R are present at the ocular surface, and desiccating stress increased CBR expressions (p < 0.05). After 10 days of DED induction, treated groups demonstrated a reduced CBR expression in the cornea, which was concurrent with improvements in the DED phenotype including fluorescence staining & inflammation. Applying THC protected corneal nerve morphology, thus maintained corneal sensitivity and reduced CD4⁺ T-cell infiltration. The CB1R antagonist maintained cornea sensitivity without changing nerve morphology.

CONCLUSIONS

Endocannabinoid receptor modulation presents a potential multi-functional therapeutic approach for DED.

Class Ib MHC-Mediated Immune Interactions Play a Critical Role in Maintaining Mucosal Homeostasis in the Mammalian Large Intestine

Lymphocytes within the intestinal epithelial layer (IEL) in mammals have unique composition compared with their counterparts in the lamina propria. Little is known about the role of some of the key colonic IEL subsets, such as TCRαβ⁺CD8⁺ T cells, in inflammation. We have recently described liver-enriched innate-like TCRαβ⁺CD8αα regulatory T cells, partly controlled by the non-classical MHC molecule, Qa-1^b, that upon adoptive transfer protect from T cell-induced colitis. In this study, we found that TCRαβ⁺CD8αα T cells are reduced among the colonic IEL during inflammation, and that their activation with an agonistic peptide leads to significant Qa-1^b-dependent protection in an acute model of colitis. Cellular expression of Qa-1^b during inflammation and corresponding dependency in peptide-mediated protection suggest that Batf3-dependent CD103⁺CD11b^- type 1 conventional dendritic cells control the protective function of TCRαβ⁺CD8αα T cells in the colonic epithelium. In the colitis model, expression of the potential barrier-protective gene, Muc2, is enhanced upon administration of a Qa-1b agonistic peptide. Notably, in steady state, the mucin metabolizing Akkermansia muciniphila was found in significantly lower abundance amid a dramatic change in overall microbiome and metabolome, increased IL-6 in explant culture, and enhanced sensitivity to dextran sulfate sodium in Qa-1b deficiency. Finally, in patients with inflammatory bowel disease, we found upregulation of HLA-E, a Qa-1^b analog with inflammation and biologic non-response, in silico, suggesting the importance of this regulatory mechanism across species.

CD8+ Regulatory T Cell - A Mystery to Be Revealed

Regulatory T cells (Treg) are essential to maintain immune homeostasis and prevent autoimmune disorders. While the function and molecular regulation of Foxp3+CD4+ Tregs are well established, much of CD8+ Treg biology remains to be revealed. Here, we will review the heterogenous subsets of CD8+ T cells have been named "CD8+ Treg" and mainly focus on CD122hiLy49+CD8+ Tregs present in naïve mice. CD122hiLy49+CD8+ Tregs, which depends on transcription factor Helios and homeostatic cytokine IL-15, have been established as a non-redundant regulator of germinal center (GC) reaction. Recently, we have demonstrated that TGF-β (Transforming growth factor-β) and transcription factor Eomes (Eomesodermin) are essential for the function and homeostasis of CD8+ Tregs. In addition, we will discuss several open questions regarding the differentiation, function and true identity of CD8+ Tregs as well as a brief comparison between two regulatory T cell subsets critical to control GC reaction, namely CD4+ TFR (follicular regulatory T cells) and CD8+ Tregs.

The nonclassical immune surveillance for ERAAP function

The peptide repertoire presented by MHC class I molecules on the cell surface is essential for the immune surveillance of intracellular pathogens and transformed cells. The generation of this peptide repertoire is critically dependent on the endoplasmic reticulum aminopeptidase associated with antigen processing (ERAAP). Loss of ERAAP function leads to the generation of a profoundly disrupted peptide repertoire including many novel and immunogenic peptides. Strikingly, a large fraction of these novel peptides on ERAAP-KO cells are presented by the nonclassical MHC Ib molecule, Qa-1^b. One immunodominant Qa-1^b-restricted novel peptide is recognized by a unique CD8⁺ T cell population showing features of both conventional cytotoxic T cells and unconventional innate-like T cells. While much remains to be uncovered, here we summarize the latest discoveries of our lab on the important immune surveillance of ERAAP function mediated by nonclassical MHC Ib molecules and their unusual cognate T cells.

Therapeutic effect of various ginsenosides on rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is an autoimmune disease which causes disability and threatens the health of humans. Therefore, it is of great significance to seek novel effective drugs for RA. It has been reported that various ginsenoside monomers are able to treat RA. However, it is still unclear which ginsenoside is the most effective and has the potential to be developed into an anti-RA drug.

Methods

The ginsenosides, including Rg1, Rg3, Rg5, Rb1, Rh2 and CK, were evaluated and compared for their therapeutic effect on RA. In in vitro cell studies, methotrexate (MTX) and 0.05% dimethyl sulfoxide (DMSO) was set as a positive control group and a negative control group, respectively. LPS-induced RAW264.7 cells and TNF-α-induced HUVEC cells were cultured with MTX, DMSO and six ginsenosides, respectively. Cell proliferation was analyzed by MTT assay and cell apoptosis was carried out by flow cytometry. CIA mice model was developed to evaluate the therapeutic efficacy of ginsenosides. The analysis of histology, immunohistochemistry, flow cytometry and cytokine detections of the joint tissues were performed to elucidate the action mechanisms of ginsenosides.

Results

All six ginsenosides showed good therapeutic effect on acute arthritis compared with the negative control group, Ginsenoside CK provided the most effective treatment ability. It could significantly inhibit the proliferation and promote the apoptosis of RAW 264.7 and HUVEC cells, and substantially reduce the swelling, redness, functional impairment of joints and the pathological changes of CIA mice. Meanwhile, CK could increase CD8 + T cell to down-regulate the immune response, decrease the number of activated CD4 + T cell and proinflammatory M1-macrophages, thus resulting in the inhibition of the secretion of proinflammatory cytokine such as TNF-α and IL-6.

Conclusion

Ginsenoside CK was proved to be a most potential candidate among the tested ginsenosides for the treatment of RA, with a strong anti-inflammation and immune modulating capabilities.

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.

Viral infection modulates Qa-1b in infected and bystander cells to properly direct NK cell killing

Natural killer (NK) cell activation depends on the signaling balance of activating and inhibitory receptors. CD94 forms inhibitory receptors with NKG2A and activating receptors with NKG2E or NKG2C. We previously demonstrated that CD94-NKG2 on NK cells and its ligand Qa-1b are important for the resistance of C57BL/6 mice to lethal ectromelia virus (ECTV) infection. We now show that NKG2C or NKG2E deficiency does not increase susceptibility to lethal ECTV infection, but overexpression of Qa-1b in infected cells does. We also demonstrate that Qa-1b is down-regulated in infected and up-regulated in bystander inflammatory monocytes and B cells. Moreover, NK cells activated by ECTV infection kill Qa-1b-deficient cells in vitro and in vivo. Thus, during viral infection, recognition of Qa-1b by activating CD94/NKG2 receptors is not critical. Instead, the levels of Qa-1b expression are down-regulated in infected cells but increased in some bystander immune cells to respectively promote or inhibit their killing by activated NK cells.

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 Lymphocytes: Crucial Players in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease associated with damage to multiple organs and glands. The most common clinical manifestations are dry eyes, dry mouth, and enlarged salivary glands. Currently, CD4+ T lymphocytes are considered to be key factors in the immunopathogenesis of pSS, but various studies have shown that CD8+ T lymphocytes contribute to acinar injury in the exocrine glands. Therefore, in this review, we discussed the classification and features of CD8+ T lymphocytes, specifically describing the role of CD8+ T lymphocytes in disease pathophysiology. Furthermore, we presented treatment strategies targeting CD8+ T cells to capitalize on the pathogenic and regulatory potential of CD8+ T lymphocytes in SS to provide promising new strategies for this inflammatory disease.

CD8+ T Cells in Atherosclerosis

Atherosclerotic lesions are populated by cells of the innate and adaptive immune system, including CD8⁺ T cells. The CD8⁺ T cell infiltrate has recently been characterized in mouse and human atherosclerosis and revealed activated, cytotoxic, and possibly dysfunctional and exhausted cell phenotypes. In mouse models of atherosclerosis, antibody-mediated depletion of CD8⁺ T cells ameliorates atherosclerosis. CD8⁺ T cells control monopoiesis and macrophage accumulation in early atherosclerosis. In addition, CD8⁺ T cells exert cytotoxic functions in atherosclerotic plaques and contribute to macrophage cell death and necrotic core formation. CD8⁺ T cell activation may be antigen-specific, and epitopes of atherosclerosis-relevant antigens may be targets of CD8⁺ T cells and their cytotoxic activity. CD8⁺ T cell functions are tightly controlled by costimulatory and coinhibitory immune checkpoints. Subsets of regulatory CD25⁺CD8⁺ T cells with immunosuppressive functions can inhibit atherosclerosis. Importantly, local cytotoxic CD8⁺ T cell responses may trigger endothelial damage and plaque erosion in acute coronary syndromes. Understanding the complex role of CD8⁺ T cells in atherosclerosis may pave the way for defining novel treatment approaches in atherosclerosis. In this review article, we discuss these aspects, highlighting the emerging and critical role of CD8⁺ T cells in atherosclerosis.

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.

Innate, non-cytolytic CD8+ T cell-mediated suppression of HIV replication by MHC-independent inhibition of virus transcription

MHC-I-restricted, virus-specific cytotoxic CD8+ T cells (CTLs) may control human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) replication via the recognition and killing of productively infected CD4+ T cells. Several studies in SIV-infected macaques suggest that CD8+ T cells may also decrease virus production by suppressing viral transcription. Here, we show that non-HIV-specific, TCR-activated non-cytolytic CD8+ T cells suppress HIV transcription via a virus- and MHC-independent immunoregulatory mechanism that modulates CD4+ T cell proliferation and activation. We also demonstrate that this CD8+ T cell-mediated effect promotes the survival of infected CD4+ T cells harboring integrated, inducible virus. Finally, we used RNA sequencing and secretome analyses to identify candidate cellular pathways that are involved in the virus-silencing mediated by these CD8+ T cells. This study characterizes a previously undescribed mechanism of immune-mediated HIV silencing that may be involved in the establishment and maintenance of the reservoir under antiretroviral therapy and therefore represent a major obstacle to HIV eradication.

Qa-1-Restricted CD8+ T Cells Can Compensate for the Absence of Conventional T Cells during Viral Infection

The role of non-classical T cells during viral infection remains poorly understood. Using the well-established murine model of CMV infection (MCMV) and mice deficient in MHC class Ia molecules, we found that non-classical CD8⁺ T cells robustly expand after MCMV challenge, become highly activated effectors, and are capable of forming durable memory. Interestingly, although these cells are restricted by MHC class Ib molecules, they respond similarly to conventional T cells. Remarkably, when acting as the sole component of the adaptive immune response, non-classical CD8⁺ T cells are sufficient to protect against MCMV-induced lethality. We also demonstrate that the MHC class Ib molecule Qa-1 (encoded by H2-T23) restricts a large, and critical, portion of this population. These findings reveal a potential adaptation of the host immune response to compensate for viral evasion of classical T cell immunity.

Anderson et al. describe a heterogenous population of non-classical CD8⁺ T cells responding to MCMV. Importantly, this population can protect mice from MCMV-induced lethality in the absence of other adaptive immune cells. Among the MHC class Ib-restricted CD8⁺ T cells responding, Qa-1-specific cells are required for protection.

The murine CD94/NKG2 ligand, Qa-1b, is a high-affinity, functional ligand for the CD8αα homodimer

The immune co-receptor CD8 molecule (CD8) has two subunits, CD8α and CD8β, which can assemble into homo or heterodimers. Nonclassical (class-Ib) major histocompatibility complex (MHC) molecules (MHC-Ibs) have recently been identified as ligands for the CD8αα homodimer. This was demonstrated by the observation that histocompatibility 2, Q region locus 10 (H2-Q10) is a high-affinity ligand for CD8αα which also binds the MHC-Ib molecule H2-TL. This suggests that MHC-Ib proteins may be an extended source of CD8αα ligands. Expression of H2-T3/TL and H2-Q10 is restricted to the small intestine and liver, respectively, yet CD8αα-containing lymphocytes are present more broadly. Therefore, here we sought to determine whether murine CD8αα binds only to tissue-specific MHC-Ib molecules or also to ubiquitously expressed MHC-Ib molecules. Using recombinant proteins and surface plasmon resonance-based binding assays, we show that the MHC-Ib family furnishes multiple binding partners for murine CD8αα, including H2-T22 and the CD94/NKG2-A/B-activating NK receptor (NKG2) ligand Qa-1b We also demonstrate a hierarchy among MHC-Ib proteins with respect to CD8αα binding, in which Qa-1b > H2-Q10 > TL. Finally, we provide evidence that Qa-1b is a functional ligand for CD8αα, distinguishing it from its human homologue MHC class I antigen E (HLA-E). These findings provide additional clues as to how CD8αα-expressing cells are controlled in different tissues. They also highlight an unexpected immunological divergence of Qa-1b/HLA-E function, indicating the need for more robust studies of murine MHC-Ib proteins as models for human disease.

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.

Alloactivation of Naïve CD4+CD8-CD25+T Regulatory Cells: Expression of CD8α Identifies Potent Suppressor Cells That Can Promote Transplant Tolerance Induction

Therapy with alloantigen-specific CD4⁺CD25⁺ T regulatory cells (Treg) for induction of transplant tolerance is desirable, as naïve thymic Treg (tTreg) are not alloantigen-specific and are weak suppressor cells. Naïve tTreg from DA rats cultured with fully allogeneic PVG stimulator cells in the presence of rIL-2 express IFN-gamma receptor (IFNGR) and IL-12 receptor beta2 (IL-12Rβ2) and are more potent alloantigen-specific regulators that we call Ts1 cells. This study examined additional markers that could identify the activated alloantigen-specific Treg as a subpopulation within the CD4⁺CD25⁺Foxp3⁺Treg. After culture of naïve DA CD4⁺CD8⁻CD25⁺T cells with rIL-2 and PVG alloantigen, or rIL-2 without alloantigen, CD8α was expressed on 10–20% and CD8β on <5% of these cells. These cells expressed ifngr and Il12rb2. CD8α⁺ cells had increased Ifngr that characterizes Ts1 cells as well was Irf4, a transcription factor induced by TCR activation. Proliferation induced by re-culture with rIL-12 and alloantigen was greater with CD4⁺CD8α⁺CD25⁺Treg consistent with the CD8α⁺ cells expressing IL-12R. In MLC, the CD8α⁺ fraction suppressed responses against allogeneic stimulators more than the mixed Ts1 population, whereas the CD4⁺CD8⁻CD25⁺T cells were less potent. In an adoptive transfer assay, rIL-2 and alloantigen activated Treg suppress rejection at a ratio of 1:10 with naïve effector cells, whereas alloantigen and rIL-2 activated tTreg depleted of the CD8α⁺ cells were much less effective. This study demonstrated that expression of CD8α by rIL-2 and alloantigen activation of CD4⁺CD8⁻CD25⁺Foxp3⁺T cells was a marker of activated and potent Treg that included alloantigen-specific Treg.

Monalizumab: inhibiting the novel immune checkpoint NKG2A

The implementation of immune checkpoint inhibitors to the oncology clinic signified a new era in cancer treatment. After the first indication of melanoma, an increasing list of additional cancer types are now treated with immune system targeting antibodies to PD-1, PD-L1 and CTLA-4, alleviating inhibition signals on T cells. Recently, we published proof-of-concept results on a novel checkpoint inhibitor, NKG2A. This receptor is expressed on cytotoxic lymphocytes, including NK cells and subsets of activated CD8+ T cells. Blocking antibodies to NKG2A unleashed the reactivity of these effector cells resulting in tumor control in multiple mouse models and an early clinical trial. Monalizumab is inhibiting this checkpoint in human beings and future clinical trials will have to reveal its potency in combination with other cancer treatment options.

Distinct PLZF+CD8αα+ Unconventional T Cells Enriched in Liver Use a Cytotoxic Mechanism to Limit Autoimmunity

Hepatic immune system is uniquely challenged to mount a controlled effector response to pathogens while maintaining tolerance to diet and microbial Ags. We have identified a novel population of innate-like, unconventional CD8αα+TCRαβ+ T cells in naive mice and in human peripheral blood, called CD8αα Tunc, capable of controlling effector T cell responses. They are NK1.1+ (CD161+ in human), express NK-inhibitory receptors, and express the promyelocytic leukemia zinc finger (PLZF) transcription factor that distinguishes them from conventional CD8+ T cells. These cells display a cytotoxic phenotype and use a perforin-dependent mechanism to control Ag-induced or T cell-mediated autoimmune diseases. CD8αα Tunc are dependent upon IL-15/IL-2Rβ signaling and PLZF for their development and/or survival. They are Foxp3-negative and their regulatory activity is associated with a functionally distinct Qa-1b-dependent population coexpressing CD11c and CD244. A polyclonal TCR repertoire, an activated/memory phenotype, and the presence of CD8αα Tunc in NKT- and in MAIT-deficient as well as in germ-free mice indicates that these cells recognize diverse self-protein Ags. Our studies reveal a distinct population of unconventional CD8+ T cells within the natural immune repertoire capable of controlling autoimmunity and also providing a new target for therapeutic intervention.

Future prospects for CD8+ regulatory T cells in immune tolerance

CD8⁺ Tregs have been long described and significant progresses have been made about their phenotype, their functional mechanisms, and their suppressive ability compared to conventional CD4⁺ Tregs. They are now at the dawn of their clinical use. In this review, we will summarize their phenotypic characteristics, their mechanisms of action, the similarities, differences and synergies between CD8⁺ and CD4⁺ Tregs, and we will discuss the biology, development and induction of CD8⁺ Tregs, their manufacturing for clinical use, considering open questions/uncertainties and future technically accessible improvements notably through genetic modifications.

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.

Opposing T cell responses in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis is a model for multiple sclerosis. Here we show that induction generates successive waves of clonally expanded CD4+, CD8+ and γδ+ T cells in the blood and central nervous system, similar to gluten-challenge studies of patients with coeliac disease. We also find major expansions of CD8+ T cells in patients with multiple sclerosis. In autoimmune encephalomyelitis, we find that most expanded CD4+ T cells are specific for the inducing myelin peptide MOG35-55. By contrast, surrogate peptides derived from a yeast peptide major histocompatibility complex library of some of the clonally expanded CD8+ T cells inhibit disease by suppressing the proliferation of MOG-specific CD4+ T cells. These results suggest that the induction of autoreactive CD4+ T cells triggers an opposing mobilization of regulatory CD8+ T cells.

Regulation of Diabetogenic Immunity by IL-15-Activated Regulatory CD8 T Cells in Type 1 Diabetes

Unchecked collaboration between islet-reactive T and B lymphocytes drives type 1 diabetes (T1D). In the healthy setting, CD8 T regulatory cells (Tregs) terminate ongoing T-B interactions. We determined that specific CD8 Tregs from NOD mice lack suppressive function, representing a previously unreported regulatory cell deficit in this T1D-prone strain. NOD mice possess 11-fold fewer Ly-49+ CD8 Tregs than nonautoimmune mice, a deficiency that worsens as NOD mice age toward diabetes and leaves them unable to regulate CD4 T follicular helper cells. As IL-15 is required for Ly-49+ CD8 Treg development, we determined that NOD macrophages inadequately trans-present IL-15. Despite reduced IL-15 trans-presentation, NOD Ly-49+ CD8 Tregs can effectively transduce IL-15-mediated survival signals when they are provided. Following stimulation with an IL-15/IL-15Ra superagonist complex, Ly-49+ CD8 Tregs expanded robustly and became activated to suppress the Ag-specific Ab response. IL-15/IL-15Ra superagonist complex-activated CD8+CD122+ T cells also delayed diabetes transfer, indicating the presence of an underactivated CD8 T cell subset with regulatory capacity against late stage T1D. We identify a new cellular contribution to anti-islet autoimmunity and demonstrate the correction of this regulatory cell deficit. Infusion of IL-15-activated CD8 Tregs may serve as an innovative cellular therapy for the treatment of T1D.

IL-10 producing CD8+ CD122+ PD-1+ regulatory T cells are expanded by dendritic cells silenced for Allograft Inflammatory Factor-1

Allograft Inflammatory Factor-1 (AIF1) is a cytoplasmic scaffold protein that contains Ca²⁺ binding EF-hand and PDZ interaction domains important for mediating intracellular signaling complexes in immune cells. The protein plays a dominant role in both macrophage- and dendritic cell (DC)-mediated inflammatory responses. This study now reports that AIF1 expression in DC is important in directing CD8⁺ T cell effector responses. Silencing AIF1 expression in murine CD11c⁺ DC suppressed antigen-specific CD8⁺ T cell activation, marked by reduced CXCR3, IFNγ and Granzyme B expression, and restrained proliferation. These primed CD8⁺ T cells had impaired cytotoxic killing of target cells in vitro. In turn, studies identified that AIF1 silencing in DC robustly expanded IL-10 producing CD8⁺ CD122⁺ PD-1⁺ regulatory T cells that suppressed neighboring immune effector responses through both IL-10 and PD-1-dependent mechanisms. In vivo studies recapitulated bystander suppression of antigen-responsive CD4⁺ T cells by the CD8⁺ Tregs expanded from the AIF1 silenced DC. These studies further demonstrate that AIF1 expression in DC serves as a potent governor of cognate T cell responses and present a novel target for engineering tolerogenic DC-based immunotherapies.

Current approaches toward identifying a correlate of immune protection from tuberculosis

INTRODUCTION

Mycobacterium tuberculosis kills more people than any other pathogen. Vaccination is the most cost-effective control measure for any infectious disease. Development of an effective vaccine against tuberculosis is hindered by the uncertain predictive value of preclinical animal models, incomplete understanding of protective immunity and lack of validated immune correlates of protection (COP).

AREAS COVERED

Here we review what is known about protective immunity against M.tb, the preclinical and clinical cohorts that can be utilized to identify COP, and COP that have been identified to date.

EXPERT COMMENTARY

The identification of COP would allow the rational design and development of vaccine candidates which can then be optimized and prioritized based on the induction of these immune responses. Once validated in field efficacy trials, such COP could potentially facilitate the development and licensure of vaccines, in combination with human efficacy data. The identification and validation of COP would represent a very significant advance in TB vaccine development. Every opportunity to collect samples and cohorts on which to cross-validate pre-existing COP and identify novel COP should be exploited. Furthermore, global cooperation and collaboration on such samples will ensure that the utility of such precious samples is fully exploited.

New Insights Into the Biology of CD8 Regulatory T Cells

Regulatory T cells are central mediators of immune regulation and play an essential role in the maintenance of immune homeostasis in the steady state and under pathophysiological conditions. Disruption of CD8 Treg-dependent recognition of Qa-1-restricted self-antigens can result in dysregulated immune responses, tissue damage, autoimmune disease and cancer. Recent progress in studies on regulatory T cells of the CD8 lineage has provided new biological insight into this specialized regulatory T cell subpopulation. Identification of the Helios transcription factor as an essential control element for the differentiation and function of CD8 regulatory T cells has led to a better understanding of the unique genetic program of these cells. Recent analyses of T-cell receptor usage and antigen recognition by Qa-1-restricted CD8 Treg have provided additional insight into the unusual biological function of this regulatory CD8 lineage. Here we summarize recent advances in our understanding of CD8 regulatory T cells with emphasis on lineage commitment, differentiation and stability.

Providence of the CD25+ KIR+ CD127- FOXP3- CD8+ T-cell subset determines the dynamics of tumor immune surveillance

CD8⁺ T-regulatory (Treg) cells are emerging as crucial components of immune system. Previous studies have reported the presence of FOXP3⁺ CD8⁺ Treg cells, similar to CD4⁺ Tregs, in cancer patients which produce high levels of the immunosuppressive cytokines, IL10 and TGFβ. At an early stage of tumor development, we have identified a subset of FOXP3^- CD8⁺ CD25⁺ KIR⁺ CD127^- Treg-like cells, which are IFNγ⁺ . However, this early-induced CD8⁺ CD25⁺ CD127^- T-cell subset is certainly distinct from the IFNγ⁺ CD8⁺ T-effector cells. These CD8⁺ CD25⁺ CD127^- T cells express other FOXP3^- CD8⁺ Treg cell signature markers, and can selectively suppress autoreactive HLA-E⁺ T_FH cells as well as tumor-induced CD4⁺ Treg cells. In contrast to FOXP3⁺ CD8⁺ Tregs, this subset does not inhibit effector T-cell proliferation or their functions as they are HLA-E^- . Adoptive transfer of this early-CD8⁺ Treg-like subset restrained tumor growth and inhibited CD4⁺ Treg generation that impedes the immune surveillance and impairs cancer immunotherapy. At the late stage of tumor development, when CD4⁺ Treg cells dominate the tumor-microenvironment, CD4⁺ Tregs mediate the clonal deletion of these tumor-suppressive FOXP3^- IFNγ⁺ CD8⁺ CD25⁺ CD127^- T cells and ensure tumor immune evasion. Our findings suggest that at an early stage of the tumor, this tumor-induced IFNγ-producing FOXP3^- CD8⁺ CD25⁺ CD127^- T-cell subset can potentiate immune surveillance by targeting HLA-E-restricted CD4⁺ Treg cells while leaving the effector T-cell population unaffected. Hence, manipulating their profile can open up a new avenue in cancer immunotherapy.

Immune Response Regulation by Antigen Receptors' Clone-Specific Nonself Parts

Antigen determinants (epitopes) are recognized by the combining sites (paratopes) of B and T cell antigen receptors (BCR/TCR), which again express clone-specific epitopes (idiotopes) that can be recognized by BCR/TCR not only of genetically different donors but also within the autologous immune system. While xenogeneic and allogeneic anti-idiotypic BCR/TCR are broadly cross-reactive, only autologous anti-idiotypes are truly specific and of functional regulatory relevance within a particular immune system. Autologous BCR/TCR idiotopes are (a) somatically created at the third complementarity-determining regions, (b) through mutations introduced into BCRs during adaptive immune responses, and (c) through the conformational impact of both. As these idiotypic characters have no genomic counterparts they have to be regarded as antigen receptor-intrinsic nonself-portions. Although foreign, however, they are per se non-immunogenic, but in conjunction with immunogenicity- and adjuvanticity-providing antigen-induced immune responses, they induce abating regulatory idiotypic chain reactions. The dualistic nature of antigen receptors of seeing antigens (self and nonself alike) and being nonself at the same time has far reaching consequences for an understanding of the regulation of adaptive immune responses.

Ex Vivo Expanded Human Non-Cytotoxic CD8+CD45RClow/- Tregs Efficiently Delay Skin Graft Rejection and GVHD in Humanized Mice

Both CD4⁺ and CD8⁺ Tregs play a critical role in the control of immune responses and immune tolerance; however, our understanding of CD8⁺ Tregs is limited while they are particularly promising for therapeutic application. We report here existence of highly suppressive human CD8⁺CD45RC^low/− Tregs expressing Foxp3 and producing IFNγ, IL-10, IL-34, and TGFβ to mediate their suppressive activity. We demonstrate that total CD8⁺CD45RC^low/− Tregs can be efficiently expanded in the presence of anti-CD3/28 mAbs, high-dose IL-2 and IL-15 and that such expanded Tregs efficiently delay GVHD and human skin transplantation rejection in immune humanized mice. Robustly expanded CD8⁺ Tregs displayed a specific gene signature, upregulated cytokines and expansion in the presence of rapamycin greatly improved proliferation and suppression. We show that CD8⁺CD45RC^low/− Tregs are equivalent to canonical CD4⁺CD25^highCD127^low/− Tregs for suppression of allogeneic immune responses in vitro. Altogether, our results open new perspectives to tolerogenic strategies in human solid organ transplantation and GVHD.