Tim-3 Relieves Experimental Autoimmune Encephalomyelitis by Suppressing MHC-II

Tim-3, an immune checkpoint inhibitor, is widely expressed on the immune cells and contributes to immune tolerance. However, the mechanisms by which Tim-3 induces immune tolerance remain to be determined. Major histocompatibility complex II (MHC-II) plays a key role in antigen presentation and CD4+T cell activation. Dysregulated expressions of Tim-3 and MHC-II are associated with the pathogenesis of many autoimmune diseases including multiple sclerosis. Here we demonstrated that, by suppressing MHC-II expression in macrophages via the STAT1/CIITA pathway, Tim-3 inhibits MHC-II-mediated autoantigen presentation and CD4+T cell activation. As a result, overexpression or blockade of Tim-3 signaling in mice with experimental autoimmune encephalomyelitis (EAE) inhibited or increased MHC-II expression respectively and finally altered clinical outcomes. We thus identified a new mechanism by which Tim-3 induces immune tolerance in vivo and regulating the Tim-3-MHC-II signaling pathway is expected to provide a new solution for multiple sclerosis treatment.

Autoimmune Regulator (AIRE) Deficiency Does Not Affect Atherosclerosis and CD4 T Cell Immune Tolerance to Apolipoprotein B

Atherosclerosis is a chronic, lipid-driven disease of medium sized arteries which causes myocardial infarction and stroke. Recently, an adaptive immune response against the plaque-associated autoantigen Apolipoprotein B100 (ApoB), the structural protein component of low-density lipoprotein, has been implicated in atherogenesis. In healthy individuals, CD4+ T cells responding to ApoB mainly comprised regulatory T cells, which confer immune tolerance and atheroprotection. Mice and patients with atherosclerosis harbor increased numbers of proatherogenic ApoB-reactive T-helper cell subsets. Given the lack of therapies targeting proatherogenic immunity, clarification of the underlying mechanisms is of high clinical relevance. T cells develop in the thymus, where strong autoreactive T cells are eliminated in the process of negative selection. Herein, we investigated whether the transcription factor autoimmune regulator (AIRE), which controls expression of numerous tissue-restricted self-antigens in the thymus, is involved in mediating tolerance to ApoB and whether Aire deficiency might contribute to atherogenesis. Mice deficient for Aire were crossbred to apolipoprotein E-deficient mice to obtain atherosclerosis-prone Aire−/−Apoe−/− mice, which were fed a regular chow diet (CD) or western-type diet (WD). CD4+ T cells responding to the ApoB peptide p6 were analyzed by flow cytometry. We demonstrate that Aire deficiency influences neither generation nor activation of ApoB-reactive T cells and has only minor and overall inconsistent impacts on their phenotype. Furthermore, we show that atherosclerotic plaque size is not affected in Aire−/−Apoe−/− compared to Aire+/+Apoe−/−, irrespective of diet and gender. In conclusion, our data suggests that AIRE is not involved in regulating thymic expression of ApoB or atherosclerosis. Alternative mechanisms how ApoB-reactive CD4 T cells are selected in the thymus will have to be investigated.

Pentose Phosphate Pathway Regulates Tolerogenic Apoptotic Cell Clearance and Immune Tolerance

The efficient removal of apoptotic cells (ACs), a process termed as efferocytosis, is essential for immune homeostasis. While recent work has established an important interplay between efferocytosis and cellular metabolic changing, underlying mechanisms remain poorly known. Here, we discovered that pentose phosphate pathway (PPP) regulates tolerogenic ACs clearance and immune tolerance. ACs decreased levels of PPP-related genes and metabolites in macrophages. AG1, the agonist of PPP, increased the activity of PPP but greatly reduced macrophage phagocytosis of ACs and enhanced the inflammatory response during efferocytosis. miR-323-5p regulated the expression of PPP-related genes and its levels increased during efferocytosis. miR-323-5p inhibitor greatly promoted levels of PPP-related genes, reduced the macrophage phagocytosis of ACs, and increased inflammatory response during efferocytosis, suggesting that miR-323-5p was essential in regulating PPP activity and ACs clearance in macrophages. Correspondingly, the PPP agonist AG1 exacerbated the lupus-like symptoms in the AC-induced systemic lupus erythematosus (SLE) model. Our study reveals that regulating PPP-dependent metabolic reprogramming is critical for tolerogenic ACs phagocytosis and immune tolerance.

Mechanistic and Biomarker Studies to Demonstrate Immune Tolerance in Multiple Sclerosis

The induction of specific immunological tolerance represents an important therapeutic goal for multiple sclerosis and other autoimmune diseases. Sound knowledge of the target antigens, the underlying pathomechanisms of the disease and the presumed mechanisms of action of the respective tolerance-inducing approach are essential for successful translation. Furthermore, suitable tools and assays to evaluate the induction of immune tolerance are key aspects for the development of such treatments. However, investigation of the mechanisms of action underlying tolerance induction poses several challenges. The optimization of sensitive, robust methods which allow the assessment of low frequency autoreactive T cells and the long-term reduction or change of their responses, the detection of regulatory cell populations and their immune mediators, as well as the validation of specific biomarkers indicating reduction of inflammation and damage, are needed to develop tolerance-inducing approaches successfully to patients. This short review focuses on how to demonstrate mechanistic proof-of-concept in antigen-specific tolerance-inducing therapies in MS.

Chimerism-Based Tolerance to Kidney Allografts in Humans: Novel Insights and Future Perspectives

Chronic rejection and immunosuppression-related toxicity severely affect long-term outcomes of kidney transplantation. The induction of transplantation tolerance – the lack of destructive immune responses to a transplanted organ in the absence of immunosuppression – could potentially overcome these limitations. Immune tolerance to kidney allografts from living donors has been successfully achieved in humans through clinical protocols based on chimerism induction with hematopoietic cell transplantation after non-myeloablative conditioning. Notably, two of these protocols have led to immune tolerance in a significant fraction of HLA-mismatched donor-recipient combinations, which represent the large majority of cases in clinical practice. Studies in mice and large animals have been critical in dissecting tolerance mechanisms and in selecting the most promising approaches for human translation. However, there are several key differences in tolerance induction between these models and humans, including the rate of success and stability of donor chimerism, as well as the relative contribution of different mechanisms in inducing donor-specific unresponsiveness. Kidney allograft tolerance achieved through durable full-donor chimerism may be due to central deletion of graft-reactive donor T cells, even though mechanistic data from patient series are lacking. On the other hand, immune tolerance attained with transient mixed chimerism-based protocols initially relies on Treg-mediated suppression, followed by peripheral deletion of donor-reactive recipient T-cell clones under antigenic pressure from the graft. These conclusions were supported by data deriving from novel high-throughput T-cell receptor sequencing approaches that allowed tracking of alloreactive repertoires over time. In this review, we summarize the most important mechanistic studies on tolerance induction with combined kidney-bone marrow transplantation in humans, discussing open issues that still need to be addressed and focusing on techniques developed in recent years to efficiently monitor the alloresponse in tolerance trials. These cutting-edge methods will be instrumental for the development of immune tolerance protocols with improved efficacy and to identify patients amenable to safe immunosuppression withdrawal.

Prevalence of Inflammatory Pathways Over Immuno-Tolerance in Peripheral Blood Mononuclear Cells of Recent-Onset Type 1 Diabetes

BackgroundChanges in innate and adaptive immunity occurring in/around pancreatic islets had been observed in peripheral blood mononuclear cells (PBMC) of Caucasian T1D patients by some, but not all researchers. The aim of our study was to investigate whether gene expression patterns of PBMC of the highly admixed Brazilian population could add knowledge about T1D pathogenic mechanisms.MethodsWe assessed global gene expression in PBMC from two groups matched for age, sex and BMI: 20 patients with recent-onset T1D (≤ 6 months from diagnosis, in a time when the autoimmune process is still highly active), testing positive for one or more islet autoantibodies and 20 islet autoantibody-negative healthy controls.ResultsWe identified 474 differentially expressed genes between groups. The most expressed genes in T1D group favored host defense, inflammatory and anti-bacterial/antiviral effects (LFT, DEFA4, DEFA1, CTSG, KCNMA1) and cell cycle progression. Several of the downregulated genes in T1D target cellular repair, control of inflammation and immune tolerance. They were related to T helper 2 pathway, induction of FOXP3 expression (AREG) and immune tolerance (SMAD6). SMAD6 expression correlated negatively with islet ZnT8 antibody. The expression of PDE12, that offers resistance to viral pathogens was decreased and negatively related to ZnT8A and GADA levels. The increased expression of long non coding RNAs MALAT1 and NEAT1, related to inflammatory mediators, autoimmune diseases and innate immune response against viral infections reinforced these dataConclusionsOur analysis suggested the activation of cell development, anti-infectious and inflammatory pathways, indicating immune activation, whereas immune-regulatory pathways were downregulated in PBMC from recent-onset T1D patients with a differential genetic profile.

Control of Tumors by Antigen-Specific CD8+ T Cells through PDL1-Targeted Delivery of Antigenic Peptide

Tumor antigen-specific T cell function is limited by immune tolerance in the tumor microenvironment. In the tumor microenvironment, tumor cells upregulate PD-L1 expression to promote T cell exhaustion by PD-1/PD-L1 interactions and undergo mutations to avoid being targeted by tumor antigen-specific T cells. Thus, tumor cells escape the immune surveillance by causing immune tolerance. We reason that a chimeric molecule made of a PD-L1-specific antibody linked to a cleavable antigenic peptide can target the antigenic peptide to the tumor microenvironment, resulting in the blockade of the PD-1/PD-L1 pathway and killing tumor cells through the coating of antigenic peptide. Here, we have generated a therapeutic chimeric protein containing the PD-L1 single-chain variable fragment (scFv) linked to a cleavable model cytotoxic T lymphocyte (CTL) epitope: E7 CTL peptide. Our study demonstrated that our chimeric protein (named PDL1-scFv-Fc-RE7) can target PD-L1-expressing tumor cells and enable E7 presentation by releasing cleavable E7 CTL peptide to coat tumor cells, resulting in tumor clearance by E7-specific CD8+ T cells. The presentation of the E7 peptide by cancer cells can then render tumor cells susceptible to the killing of preexisting E7-specific CD8+ T cells and contribute to tumor clearance. Our finding suggests a synergistic approach to not only enhance antigen-specific tumor clearance but also bypass immune tolerance.

Pregnancy depends on a delicate balance of immune activation and regulation

It is well recognized that immune tolerance is important to prevent semiallografted fetuses from rejection by maternal immunocompetent cells; however, immune activation also plays an important role in placental development and fetal growth. Basic and clinical studies have shown that an imbalance between immune activation and regulation can lead to implantation failure, miscarriage, and preeclampsia. Here, the balance between immunostimulation and immunoregulation in reproduction will be reviewed.