Resting dendritic cells induce peripheral CD8+ T cell tolerance through PD-1 and CTLA-4

Immunotherapy in advanced gastric cancer, is it the future?

The prognosis of advanced gastric cancer remains extremely poor despite the use of standard therapies such as chemotherapy and biological agents. Blocking immune checkpoint especially programmed cell death-1 (PD-1) and its ligand (PD-L1 or B7-H1), has proven efficacy in several solid cancers, and seems to become a potential option in gastric cancer treatment. This review will focus on data describing the immune microenvironment of gastric tumors on which blocking PD-1/PD-L1 axis may have an anti-tumor efficacy. Then, the encouraging results of clinical trials evaluating anti-PD-1/PD-L1-based therapeutic strategy in first or later-line settings will be discuss. Finally, clinical outcomes according to PD-L1 expression, mismatch repair phenotype and other potential predictive biomarkers of anti-tumor response will be described. Altogether, immunotherapy seems promising in advanced gastric cancer in monotherapy or in combining strategies probably for a specific subgroup of patients who need to be better identified.

A Novel 3D in Vitro Tumor Model Based on Silk Fibroin/Chitosan Scaffolds To Mimic the Tumor Microenvironment

Drug development involves various evaluation processes to ascertain drug effects and rigorous analysis of biological indicators during in vitro preclinical studies. Two-dimensional (2D) cell cultures are commonly used in numerous in vitro studies, which are poor facsimiles of the in vivo conditions. Recently, three-dimensional (3D) tumor models mimicking the tumor microenvironment and reducing the use of experimental animals have been developed generating great interest to appraise tumor response to treatment strategies in cancer therapy. In this study, silk fibroin (SF) protein and chitosan (CS), two natural biomaterials, were chosen to construct the scaffolds of 3D cell models. Human non-small cell lung cancer A549 cells in the SF/CS scaffolds were found to have a great tendency to gather and form tumor spheres. A549 cell spheres in the 3D scaffolds showed biological and morphological characteristics much closer to the in vivo tumors. Besides, the cells in 3D models displayed better invasion ability and drug resistance than 2D models. Additionally, differences in drug-resistant and immune-related protein levels were found, which indicated that 3D models might resemble the real-life situation. These findings suggested that these 3D tumor models composed of SF/CS are promising to provide a valuable biomaterial platform in the evaluation of anticancer drugs.

Inhibitory Receptors and Pathways of Lymphocytes: The Role of PD-1 in Treg Development and Their Involvement in Autoimmunity Onset and Cancer Progression

Regulatory T (Treg) cells represent a subpopulation of suppressor CD4⁺ T cells critically involved in the establishment of peripheral tolerance through the inhibition of effector T (Teff) cells and the suppression of the immune-mediated tissue destruction toward self-antigens. Treg generation, their suppressive properties and also Treg-Teff cell interactions could be modulated at least in part by programmed cell death-1 (PD-1) expression on their surface and through binding between PD-1 and programmed cell death ligand-1 (PD-L1). Defects involving PD-1 and Tregs can lead to the development of pathological conditions, including autoimmune disorders or promote cancer progression by favoring tumor evasion from the host immune response. At the same time, PD-1 and Tregs could represent attractive targets for treatment, as demonstrated by the therapeutic blockade of PD-L1 applied for the management of different cancer conditions in humans. In the present Review, we focus specifically the role of PD-1/PD-L1 on Treg development and activity.

Not All Immune Checkpoints Are Created Equal

Antibodies that block T cell inhibition via the immune checkpoints CTLA-4 and PD-1 have revolutionized cancer therapy during the last 15 years. T cells express additional inhibitory surface receptors that are considered to have potential as targets in cancer immunotherapy. Antibodies against LAG-3 and TIM-3 are currently clinically tested to evaluate their effectiveness in patients suffering from advanced solid tumors or hematologic malignancies. In addition, blockade of the inhibitory BTLA receptors on human T cells may have potential to unleash T cells to effectively combat cancer cells. Much research on these immune checkpoints has focused on mouse models. The analysis of animals that lack individual inhibitory receptors has shed some light on the role of these molecules in regulating T cells, but also immune responses in general. There are current intensive efforts to gauge the efficacy of antibodies targeting these molecules called immune checkpoint inhibitors alone or in different combinations in preclinical models of cancer. Differences between mouse and human immunology warrant studies on human immune cells to appreciate the potential of individual pathways in enhancing T cell responses. Results from clinical studies are not only highlighting the great benefit of immune checkpoint inhibitors for treating cancer but also yield precious information on their role in regulating T cells and other cells of the immune system. However, despite the clinical relevance of CTLA-4 and PD-1 and the high potential of the emerging immune checkpoints, there are still substantial gaps in our understanding of the biology of these molecules, which might prevent the full realization of their therapeutic potential. This review addresses PD-1, CTLA-4, BTLA, LAG-3, and TIM-3, which are considered major inhibitory immune checkpoints expressed on T cells. It provides summaries of our current conception of the role of these molecules in regulating T cell responses, and discussions about major ambiguities and gaps in our knowledge. We emphasize that each of these molecules harbors unique properties that set it apart from the others. Their distinct functional profiles should be taken into account in therapeutic strategies that aim to exploit these pathways to enhance immune responses to combat cancer.

Gemcitabine Synergizes with Immune Checkpoint Inhibitors and Overcomes Resistance in a Preclinical Model and Mesothelioma Patients

PURPOSE

Combination of immune checkpoint inhibitors with chemotherapy is under investigation for cancer treatment.

EXPERIMENTAL DESIGN

We studied the rationale of such a combination for treating mesothelioma, a disease with limited treatment options.

RESULTS

The combination of gemcitabine and immune checkpoint inhibitors outperformed immunotherapy alone with regard to tumor control and survival in a preclinical mesothelioma model; however, the addition of dexamethasone to gemcitabine and immune checkpoint inhibitors nullified the synergistic clinical response. Furthermore, treatment with gemcitabine plus anti-PD-1 resulted in an objective clinical response in two patients with mesothelioma, who were resistant to gemcitabine or anti-PD-1 as monotherapy.

CONCLUSIONS

Thus, treatment of mesothelioma with a combination of gemcitabine with immune checkpoint inhibitors is feasible and results in synergistic clinical response compared with single treatment in the absence of steroids.

Programmed cell death-1 3'-untranslated region polymorphism is associated with spontaneous clearance of hepatitis B virus infection

Hepatitis B virus (HBV)-specific CD8+ T cells play an important role in the clearance of HBV infection. Programmed cell death-1 (PD-1), an immunosuppressive molecule that regulates T-cell activation and peripheral immune tolerance, is increasingly shown to influence the outcome of HBV infection. rs10204525, a single-nucleotide polymorphism in the 3'-untranslated region (3'-UTR) of PD-1, has been associated with susceptibility and disease progression of chronic HBV infection in far-eastern patients. The aim of our study was to assess the impact of rs10204525 variation on HBV infection in Moroccan patients. A total of 236 patients with chronic HBV infection and 134 individuals with spontaneous HBV resolution were genotyped using a Taqman assay. In addition, PD-1 mRNA expression in peripheral blood nuclear cells was determined by quantitative reverse-transcription polymerase chain reaction. We found that the AA genotype is protective (odds ratio, 0.43; 95% confidence interval, 0.19 to 0.97; P = 0.038) against HBV infection. Interestingly, PD-1 messenger RNA (mRNA) expression analysis has revealed that chronic HBV carriers with GG and GA displayed higher levels of PD-1 mRNA compared with corresponding genotypes in resolved subjects (P = 0.031 and 0.014, respectively). Our data suggest that Mediterranean HBV-infected patients carrying PD-1 GG and GA genotypes at rs10204525 have high PD-1 mRNA expression and may be more prone to installation of chronicity.

Description of CD8+ Regulatory T Lymphocytes and Their Specific Intervention in Graft-versus-Host and Infectious Diseases, Autoimmunity, and Cancer

Gershon and Kondo described CD8⁺ Treg lymphocytes as the first ones with regulating activity due to their tolerance ability to foreign antigens and their capacity to inhibit the proliferation of other lymphocytes. Regardless, CD8⁺ Treg lymphocytes have not been fully described-unlike CD4⁺ Treg lymphocytes-because of their low numbers in blood and the lack of specific and accurate population markers. Still, these lymphocytes have been studied for the past 30 years, even after finding difficulties during investigations. As a result, studies have identified markers that define their subpopulations. This review is focused on the expression of cell membrane markers as CD25, CD122, CD103, CTLA-4, CD39, CD73, LAG-3, and FasL as well as soluble molecules such as FoxP3, IFN-γ, IL-10, TGF-β, IL-34, and IL-35, in addition to the lack of expression of cell activation markers such as CD28, CD127 CD45RC, and CD49d. This work also underlines the importance of identifying some of these markers in infections with several pathogens, autoimmunity, cancer, and graft-versus-host disease as a strategy in their prevention, monitoring, and cure.

MicroRNAs as Immunotherapy Targets for Treating Gastroenterological Cancers

Gastroenterological cancers are the most common cancers categorized by systems and are estimated to comprise 18.4% of all cancers in the United States in 2017. Gastroenterological cancers are estimated to contribute 26.2% of cancer-related death in 2017. Gastroenterological cancers are characterized by late diagnosis, metastasis, high recurrence, and being refractory to current therapies. Since the current targeted therapies provide limited benefit to the overall response and survival, there is an urgent need for developing novel therapeutic strategy to improve the outcome of gastroenterological cancers. Immunotherapy has been developed and underwent clinical trials, but displayed limited therapeutic benefit. Since aberrant expressions of miRNAs are found in gastroenterological cancers and miRNAs have been shown to regulate antitumor immunity, the combination therapy combining the traditional antibody-based immunotherapy and novel miRNA-based immunotherapy is promising for achieving clinical success. This review summarizes the current knowledge about the miRNAs and long noncoding RNAs that exhibit immunoregulatory roles in gastroenterological cancers and precancerous diseases of digestive system, as well as the miRNA-based clinical trials for gastroenterological cancers. This review also analyzes the ongoing challenge of identifying appropriate therapy candidates for complex and dynamic tumor microenvironment, ensuring efficient and targeted delivery to specific cancer tissues, and developing strategy for avoiding off-target effect.

Regulatory Role of CD4+ T Cells in Myocarditis

Myocarditis is an important cause of heart failure in young patients. Autoreactive, most often, infection-triggered CD4⁺ T cells were confirmed to be critical for myocarditis induction. Due to a defect in clonal deletion of heart-reactive CD4⁺ T cells in the thymus of mice and humans, significant numbers of heart-specific autoreactive CD4⁺ T cells circulate in the blood. Normally, regulatory T cells maintain peripheral tolerance and prevent spontaneous myocarditis development. In the presence of tissue damage and innate immune activation, however, activated self-antigen-loaded dendritic cells promote CD4⁺ effector T cell expansion and myocarditis. So far, a direct pathogenic role has been described for both activated Th17 and Th1 effector CD4⁺ T cell subsets, though Th1 effector T cell-derived interferon-gamma was shown to limit myocarditis severity and prevent transition to inflammatory dilated cardiomyopathy. Interestingly, recent observations point out that various CD4⁺ T cell subsets demonstrate high plasticity in maintaining immune homeostasis and modulating disease phenotypes in myocarditis. These subsets include Th1 and Th17 effector cells and regulatory T cells, despite the fact that there are still sparse and controversial data on the specific role of FOXP3-expressing Treg in myocarditis. Understanding the specific roles of these T cell populations at different stages of the disease progression might provide a key for the development of successful therapeutic strategies.

The human blood DNA methylome identifies crucial role of β-catenin in the pathogenesis of Kawasaki disease

Kawasaki disease (KD) is a type of acute febrile vasculitis syndrome and is the most frequent cause of cardiac illness in children under the age of five years old. Although the etiology of KD remains largely unknown, some recent genome-wide studies have indicated that epigenetic factors may be important in its pathogenesis. We enrolled 24 KD patients and 24 non-KD controls in this study to access their DNA methylation status using HumanMethylation450 BeadChips. Another 34 KD patients and 62 control subjects were enrolled for expression validation. Of the 3193 CpG methylation regions with a methylation difference ≥ 20% between KD and controls, 3096 CpG loci revealed hypomehtylation, with only 3% being hypermethylated. Pathway buildup identified 11 networked genes among the hypermethylated regions, including four transcription factors: nuclear factor of activated T-cells 1, v-ets avian erythroblastosis virus E26 oncogene homolog 1, runt related transcription factor 3, and retinoic acid receptor gamma, as well as the activator β-catenin. Ten of these network-selected genes demonstrated a significant decrease in mRNA in KD patients, whereas only CTNNB1 significantly decreased in correlation with coronary artery lesions in KD patients. Furthermore, CTNNB1-silenced THP-1 monocytic cells drastically increased the expression of CD40 and significantly increased the expression of both CD40 and CD40L in cocultured human coronary artery endothelial cells. This study is the first to identify network-based susceptible genes of hypermethylated CpG loci, their expression levels, and the functional impact of β-catenin, which may be involved in both the cause and the development of KD.

[Blocking programmed death-ligand 1 attenuates maturation inhibition of dendritic cells by co-cultured breast cancer cells]

OBJECTIVE

To study if programmed death-ligand 1 (PL-L1) expression in breast cancer cell activates PD-L1/PD-1 pathway in dendritic cells to inhibit dendritic cell maturation.

METHODS

Human monocytes were induced to differentiate into immature dendritic cells using GM-CSF and IL-4, and further to mature dendritic cells using TNF-α. PD-L1-expressing breast cancer cell line MDA-MB-231 was co-cultured in contact with the dendritic cells to observe the effects of the breast cancer cells on the maturation of the dendritic cells. A PD-L1 blocking antibody was applied to the co-culture, and the changes in the inhibitory effect of the MDA-MB-231 cells on dendritic cell maturation was observed. TNF-α-induced dendritic cells were treated with a recombinant human PD-L1 protein to study the effect of PD-L1/PD-1 pathway activation on the maturation of dendritic cells. The expression of PD-L1 in MDA-MB-231 cells and the dendritic cell maturation marker HLA-DR and CD83 were analyzed using flow cytometry.

RESULTS

MDA-MB-231 cell line showed PD-L1 positivity on the cell membrane cells at a rate as high as (99.7∓0.15)%. In mature dendritic cells, the positivity rates for HLA-DR and CD83 were (88.8∓6.96)% and (18.36∓3.07)%, respectively, but in the co-culture system, the positivity rates of the dendritic cells were significantly decreased to (42.76∓10.52)% (P<0.01) and (9.93∓2.74)% (P<0.05), respectively, indicating that MDA-MB-231 cells inhibited the maturation of dendritic cells. Following treatment with a PD-L1 antibody isotype control, the percentages of HLA-DR- and CD83-positive cells in the co-culture were (45.17∓10.19)% and (10.15∓2.54)%, which were significantly increased to (63.46∓1.72)% and (16.46∓2.58)% after treatment with PD-L1 antibody, respectively (both P<0.05). Compared with the mature dendritic cell controls, the cells treated with the recombinant human PD-L1 protein exhibited significantly lowered percentages of HLA-DR-positive [from (84.23∓4.18)% to (2.56∓2.39)%, P<0.05] and CD83-positive cells [(87.26∓1.54)% to (60.67∓1.63)%, P<0.05].

CONCLUSION

The effect of PD-L1 antibody therapy on triple negative breast cancer can be partially mediated by blocking PD-L1 expression on breast cancer cell membrane, which attenuates the inhibition of dendritic cell maturation in the cancer microenvironment.

The CXC Chemokine Receptor 3 Inhibits Autoimmune Cholangitis via CD8+ T Cells but Promotes Colitis via CD4+ T Cells

CXC chemokine receptor 3 (CXCR3), a receptor for the C-X-C motif chemokines (CXCL) CXCL9, CXCL10, and CXCL11, which not only plays a role in chemotaxis but also regulates differentiation and development of memory and effector T cell populations. Herein, we explored the function of CXCR3 in the modulation of different organ-specific autoimmune diseases in interleukin (IL)-2 receptor deficiency (CD25^-/-) mice, a murine model for both cholangitis and colitis. We observed higher levels of CXCL9 and CXCL10 in the liver and colon and higher expression of CXCR3 on T cells of the CD25^-/- mice compared with control animals. Deletion of CXCR3 resulted in enhanced liver inflammation but alleviated colitis. These changes in liver and colon pathology after CXCR3 deletion were associated with increased numbers of hepatic CD4⁺ and CD8⁺ T cells, in particular effector memory CD8⁺ T cells, as well as decreased T cells in mesenteric lymph nodes and colon lamina propria. In addition, increased interferon-γ response and decreased IL-17A response was observed in both liver and colon after CXCR3 deletion. CXCR3 modulated the functions of T cells involved in different autoimmune diseases, whereas the consequence of such modulation was organ-specific regarding to their effects on disease severity. Our findings emphasize the importance of extra caution in immunotherapy for organ-specific autoimmune diseases, as therapeutic interventions aiming at a target such as CXCR3 for certain disease could result in adverse effects in an unrelated organ.

Non-invasive assessment of murine PD-L1 levels in syngeneic tumor models by nuclear imaging with nanobody tracers

Blockade of the inhibitory PD-1/PD-L1 immune checkpoint axis is a promising cancer treatment. Nonetheless, a significant number of patients and malignancies do not respond to this therapy. To develop a screen for response to PD-1/PD-L1 inhibition, it is critical to develop a non-invasive tool to accurately assess dynamic immune checkpoint expression. Here we evaluated non-invasive SPECT/CT imaging of PD-L1 expression, in murine tumor models with varying PD-L1 expression, using high affinity PD-L1-specific nanobodies (Nbs). We generated and characterized 37 Nbs recognizing mouse PD-L1. Among those, four Nbs C3, C7, E2 and E4 were selected and evaluated for preclinical imaging of PD-L1 in syngeneic mice. We performed SPECT/CT imaging in wild type versus PD-L1 knock-out mice, using Technetium-99m (^99mTc) labeled Nbs. Nb C3 and E2 showed specific antigen binding and beneficial biodistribution. Through the use of CRISPR/Cas9 PD-L1 knock-out TC-1 lung epithelial cell lines, we demonstrate that SPECT/CT imaging using Nb C3 and E2 identifies PD-L1 expressing tumors, but not PD-L1 non-expressing tumors, thereby confirming the diagnostic potential of the selected Nbs. In conclusion, these data show that Nbs C3 and E2 can be used to non-invasively image PD-L1 levels in the tumor, with the strength of the signal correlating with PD-L1 levels. These findings warrant further research into the use of Nbs as a tool to image inhibitory signals in the tumor environment.

B7-H1 Expression Is Required for Human Endometrial Regenerative Cells in the Prevention of Transplant Vasculopathy in Mice

Vasculopathy is one of the primary pathological changes in chronic rejection of vascularized allograft transplantation. Endometrial regenerative cells (ERCs) are mesenchymal-like stromal cells with immunosuppressive effect. B7-H1 is a negative costimulator that mediates active immune suppression. The aim of this study was to investigate the requirement of B7-H1 in the immunoregulation of ERCs in preventing transplant vasculopathy of aorta allografts. The results showed that B7-H1 expression on ERCs was upregulated by IFN-γ in a dose-dependent manner and it was required for ERCs to inhibit the proliferation of peripheral blood mononuclear cells (PBMCs) in vitro. ERCs could alleviate transplant vasculopathy, as the intimal growth of transplanted aorta was limited, and the preventive effects were correlated with an increase in the percentages of CD11c⁺MHC class II^lowCD86^low dendritic cells, CD68⁺CD206⁺ macrophages, and CD4⁺CD25⁺Foxp3⁺ T cells, as well as a decrease in the percentages of CD68⁺ macrophages, CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells, and donor-reactive IgM and IgG antibodies. Moreover, overexpression of B7-H1 by IFN-γ can promote the immunosuppressive effect of ERCs. These results suggest that overexpression of B7-H1 stimulated by IFN-γ is required for ERCs to prevent the transplant vasculopathy, and this study provides a theoretical basis for the future clinical use of human ERCs.

AllergoOncology: Opposite outcomes of immune tolerance in allergy and cancer

While desired for the cure of allergy, regulatory immune cell subsets and nonclassical Th2-biased inflammatory mediators in the tumour microenvironment can contribute to immune suppression and escape of tumours from immunological detection and clearance. A key aim in the cancer field is therefore to design interventions that can break immunological tolerance and halt cancer progression, whereas on the contrary allergen immunotherapy exactly aims to induce tolerance. In this position paper, we review insights on immune tolerance derived from allergy and from cancer inflammation, focusing on what is known about the roles of key immune cells and mediators. We propose that research in the field of AllergoOncology that aims to delineate these immunological mechanisms with juxtaposed clinical consequences in allergy and cancer may point to novel avenues for therapeutic interventions that stand to benefit both disciplines.

Dendritic cells in the regulation of immunity and inflammation

As potent antigen-presenting cells, dendritic cells (DCs) comprise the most heterogeneous cell population with significant cellular phenotypic and functional plasticity. They form a sentinel network to modulate immune responses, since intrinsic cellular mechanisms and complex external, environmental signals endow DCs with the distinct capacity to induce protective immunity or tolerance to self. Interactions between DCs and other cells of the immune system mediate this response. This interactive response depends on DC maturation status and subtype, as well as the microenvironment of the tissue location and DC-intrinsic regulators. Dysregulated DCs can initiate and perpetuate various immune disorders, which creates attractive therapeutic targets. In this review, we provide a detailed outlook on DC ontogeny and functional specialization. We highlight recent advances on the regulatory role that DCs play in immune responses, the putative molecular regulators that control DC functional responding and the contribution of DCs to inflammatory disease physiopathology.

PD-1/PD-L1 Blockade: Have We Found the Key to Unleash the Antitumor Immune Response?

PD-1–PD-L1 interaction is known to drive T cell dysfunction, which can be blocked by anti-PD-1/PD-L1 antibodies. However, studies have also shown that the function of the PD-1–PD-L1 axis is affected by the complex immunologic regulation network, and some CD8⁺ T cells can enter an irreversible dysfunctional state that cannot be rescued by PD-1/PD-L1 blockade. In most advanced cancers, except Hodgkin lymphoma (which has high PD-L1/L2 expression) and melanoma (which has high tumor mutational burden), the objective response rate with anti-PD-1/PD-L1 monotherapy is only ~20%, and immune-related toxicities and hyperprogression can occur in a small subset of patients during PD-1/PD-L1 blockade therapy. The lack of efficacy in up to 80% of patients was not necessarily associated with negative PD-1 and PD-L1 expression, suggesting that the roles of PD-1/PD-L1 in immune suppression and the mechanisms of action of antibodies remain to be better defined. In addition, important immune regulatory mechanisms within or outside of the PD-1/PD-L1 network need to be discovered and targeted to increase the response rate and to reduce the toxicities of immune checkpoint blockade therapies. This paper reviews the major functional and clinical studies of PD-1/PD-L1, including those with discrepancies in the pathologic and biomarker role of PD-1 and PD-L1 and the effectiveness of PD-1/PD-L1 blockade. The goal is to improve understanding of the efficacy of PD-1/PD-L1 blockade immunotherapy, as well as enhance the development of therapeutic strategies to overcome the resistance mechanisms and unleash the antitumor immune response to combat cancer.

PD-L1

Programmed death ligand 1 (PD-L1) is the principal ligand of programmed death 1 (PD-1), a coinhibitory receptor that can be constitutively expressed or induced in myeloid, lymphoid, normal epithelial cells and in cancer. Under physiological conditions, the PD-1/PD-L1 interaction is essential in the development of immune tolerance preventing excessive immune cell activity that can lead to tissue destruction and autoimmunity. PD-L1 expression is an immune evasion mechanism exploited by various malignancies and is generally associated with poorer prognosis. PD-L1 expression is also suggested as a predictive biomarker of response to anti-PD-1/PD-L1 therapies; however, contradictory evidence exists as to its role across histotypes. Over the years, anti-PD-1/PD-L1 agents have gained momentum as novel anticancer therapeutics, by inducing durable tumour regression in numerous malignancies including metastatic lung cancer, melanoma and many others. In this review, we discuss the immunobiology of PD-L1, with a particular focus on its clinical significance in malignancy.

The Importance of Dendritic Cells in Maintaining Immune Tolerance

Immune tolerance is necessary to prevent the immune system from reacting against self, and thus to avoid the development of autoimmune diseases. In this review, we discuss key findings that position dendritic cells (DCs) as critical modulators of both thymic and peripheral immune tolerance. Although DCs are important for inducing both immunity and tolerance, increased autoimmunity associated with decreased DCs suggests their nonredundant role in tolerance induction. DC-mediated T cell immune tolerance is an active process that is influenced by genetic variants, environmental signals, as well as the nature of the specific DC subset presenting Ag to T cells. Answering the many open questions with regard to the role of DCs in immune tolerance could lead to the development of novel therapies for the prevention of autoimmune diseases.

Tubulointerstitial nephritis as adverse effect of programmed cell death 1 inhibitor, nivolumab, showed distinct histological findings

Immune-checkpoint inhibitor nivolumab (anti-PD-1 antibody) blocks T cell inhibition and stimulate immunologic response toward cancer cells. It was also revealed that PD-1/PD-L1 interaction crucially controls the effector differentiation of auto-reactive T cells to maintain self-tolerance. Therefore, potential autoimmunological side-effect can occur in any organ. Here, we report a case of 67-year-old Japanese male with lung adenocarcinoma treated with nivolumab who developed acute tubulointerstitial nephritis after the third infusion of nivolumab. Kidney biopsy showed distinct histological findings: Proliferation of CD38 positive and IgG positive plasma cells, and affluent infiltration of FoxP3⁺ regulatory T cells. Herein, we do pathological discussion concerning acute tubulointerstitial nephritis occurred in this case based on these histological findings.

T Cell's Sense of Self: a Role of Self-Recognition in Shaping Functional Competence of Naïve T Cells

Post-thymic naïve T cells constitute a key cellular arm of adaptive immunity, with a well-known characteristic of the specificity and robustness of responses to cognate foreign antigens which is presented as a form of antigen-derived peptides bound to major histocompatibility complex (MHC) molecules by antigen-presenting cells (APCs). In a steady state, however, these cells are resting, quiescent in their activity, but must keep full ranges of functional integrity to mount rapid and robust immunity to cope with various infectious pathogens at any time and space. Such unique property of resting naïve T cells is not acquired in a default manner but rather requires an active mechanism. Although our understanding of exactly how this process occurs and what factors are involved remains incomplete, a particular role of self-recognition by T cells has grown greatly in recent years. In this brief review, we discuss recent data on how the interaction of T cells with self-peptide MHC ligands regulates their functional responsiveness and propose that variable strength of self-reactivity imposes distinctly different levels of functional competence and heterogeneity.

Dendritic Cells As Inducers of Peripheral Tolerance

Mechanisms of tolerance initiated in the thymus are indispensable for establishing immune homeostasis, but they may not be sufficient to prevent tissue-specific autoimmune diseases. In the periphery, dendritic cells (DCs) play a crucial tolerogenic role, extending the maintenance of immune homeostasis and blocking autoimmune responses. We review here these essential roles of DCs in orchestrating mechanisms of peripheral T cell tolerance as determined by targeted delivery of defined antigens to DCs in vivo in combination with various genetic modifications of DCs. Further, we discuss how DC functions empowered by specific delivery of T cell antigens could be harnessed for tolerance induction in clinical settings.

Combinatorial drug delivery approaches for immunomodulation

Immunotherapy has been widely explored for applications to both augment and suppress intrinsic host immunity. Clinical achievements have seen a number of immunotherapeutic drugs displace established strategies like chemotherapy in treating immune-associated diseases. However, single drug approaches modulating an individual arm of the immune system are often incompletely effective. Imperfect mechanistic understanding and heterogeneity within disease pathology have seen monotherapies inadequately equipped to mediate complete disease remission. Recent success in applications of combinatorial immunotherapy has suggested that targeting multiple biological pathways simultaneously may be critical in treating complex immune pathologies. Drug delivery approaches through engineered biomaterials offer the potential to augment desired immune responses while mitigating toxic side-effects by localizing immunotherapy. This review discusses recent advances in immunotherapy and highlights newly explored combinatorial drug delivery approaches. Furthermore, prospective future directions for immunomodulatory drug delivery to exploit are provided.

Peripherally Induced Regulatory T Cells: Recruited Protectors of the Central Nervous System against Autoimmune Neuroinflammation

Defects in regulatory T cells (Treg cells) aggravate multiple sclerosis (MS) after its onset and the absence of Treg cell functions can also exacerbate the course of disease in an animal model of MS. However, autoimmune neuroinflammation in many MS models can be acutely provoked in healthy animals leading to an activation of encephalitogenic T cells despite the induction of immune tolerance in the thymus including thymically produced (t)Treg cells. In contrast, neuroinflammation can be ameliorated or even completely prevented by the antigen-specific Treg cells formed extrathymically in the peripheral immune system (pTreg cells) during tolerogenic responses to relevant neuronal antigens. This review discusses the specific roles of Treg cells in blocking neuroinflammation, examines the impact of peripheral tolerance and dendritic cells on a relevant regulation of neuroinflammation, and explores some of the most recent advances in elucidation of specific mechanisms of the conversion and function of pTreg cells including the roles of CD5 and Hopx in these processes.

The role of PD-1 in regulation of macrophage apoptosis and its subversion by Leishmania donovani

Programmed death-1 receptor (PD-1) expressed in many immune cells is known to trigger T-cell exhaustion but the significance of macrophage-associated PD-1 in relevance to macrophage apoptosis is not known. This study is aimed to delineate whether PD-1 pathway has any role in eliciting macrophage apoptosis and, if so, then how the intra-macrophage parasite, Leishmania donovani modulates PD-1 pathway for protecting its niche. Resting macrophages when treated with H₂O₂ showed increased PD-1 expression and apoptosis, which was further enhanced on PD-1 agonist treatment. The administration of either PD-1 receptor or PD-1 ligand-blocking antibodies reversed the process thus documenting the involvement of PD-1 in macrophage apoptosis. On the contrary, L. donovani-infected macrophages showed decreased PD-1 expression concurrent with inhibition of apoptosis. The activation of PD-1 pathway was found to negatively regulate the phosphorylation of pro-survival AKT, which was reversed during infection. Infection-induced PD-1 downregulation led to the activation of AKT resulting in phosphorylation and subsequent inhibition of proapoptotic protein BAD. Strong association of SHP2 (a SH2-containing ubiquitously expressed tyrosine-specific protein phosphatase) with PD-1 along with AKT deactivation observed in H₂O₂-treated macrophages was reversed by L. donovani infection. Kinetic analysis coupled with inhibitor-based approach and knockdown experiments demonstrated that L. donovani infection actively downregulated the PD-1 by deactivating NFATc1 as revealed by its reduced nuclear translocation. The study thus elucidates the detailed mechanism of the role of PD-1 in macrophage apoptosis and its negative modulation by Leishmania for their intracellular survival.

Immune checkpoint inhibition and its relationship with hypermutation phenoytype as a potential treatment for Glioblastoma

Glioblastoma (GBM) is the most common malignant brain tumour in adults. Current prognosis with standard treatment is poor. Immunotherapy is a new paradigm in tumour management. Specifically, recent advances in the field of immune checkpoint molecules have led to dramatic results in many cancers. Inhibition of one particular, programmed cell death-1 (PD-1) has recently been shown to be highly effective in melanoma and non-small cell lung cancer. There has also been recent data to suggest potential benefit in GBM. There also appears to be a relationship between immune checkpoint inhibition and hypermutation, in particular with the mismatch repair process. In this review we look at the current knowledge of immune checkpoint inhibitors with a focus on the PD-1 pathway. We will also review the evidence of PD-1 inhibition in GBM and the role of hypermutation in PD-1 inhibition.

PD-1 gene polymorphic variation is linked with first symptom of disease and severity of relapsing-remitting form of MS

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS), where inflammation, demyelination together with the axonopathy are the cardinal features on pathologic ground, with a combined genetic and environmental background. The associations of PD-1 single nucleotide polymorphisms (SNPs): PD-1.3 (in intron 4), PD-1.5 and PD-1.9 (both in exon 5) with clinical manifestation of MS in 479 south Polish individuals including 203 MS patients were analyzed. Presence of PD-1.5T allele was linked with the first manifestations of disease: diplopia and pyramidal signs - favored pyramidal signs but protected against of diplopia development. Farther, PD-1.3G/PD-1.5C/PD-1.9C haplotype significantly favored whereas GTC protected against diplopia. Besides, GTT haplotype strongly favored non-severe RRMS outcome and ATC haplotype was specific only for these MS patients. Our population-based case-control study, investigating selected three PD-1 SNPs: PD-1.3, PD-1.5 and PD-1.9, revealed that polymorphic variation may be rather disease-modifying than MS risk factor.

Dendritic cells as gatekeepers of tolerance

Dendritic cells (DC) are unique hematopoietic cells, linking innate and adaptive immune responses. In particular, they are considered as the most potent antigen presenting cells, governing both T cell immunity and tolerance. In view of their exceptional ability to present antigen and to interact with T cells, DC play distinct roles in shaping T cell development, differentiation and function. The outcome of the DC-T cell interaction is determined by the state of DC maturation, the type of DC subset, the cytokine microenvironment and the tissue location. Both regulatory T cells (Tregs) and DC are indispensable for maintaining central and peripheral tolerance. Over the past decade, accumulating data indicate that DC critically contribute to Treg differentiation and homeostasis.

Role of PD-1 in Immunity and Diseases

Immunity developed to defend our bodies from foreign particles, including bacteria and viruses. Although effector cells responsible for acquired immunity, mainly T cells, and B cells, are able to distinguish self from non-self, they sometimes attack the body's tissues because of imperfect central tolerance. Several immune check points developed to limit overactivation of these cells. One of the most important immune checkpoints is programmed cell death-1 (PD-1), which is expressed mainly on activated lymphocytes. As its ligands (PD-Ls) are expressed widely in the body and affect the responses against self and foreign antigens, controlling PD-1/PD-L interactions enables the management of several immune-related diseases such as autoimmune disease, virus infection, and cancers. Currently, the strategy of PD-1/ PD-L1 blockade has already been applied to clinical cancer therapy, providing evidences that PD-1 signal is one of the main factors of cancer immune escape in humans. The dramatic efficacy of PD-1 blockade in cancer immunotherapy, promises the control of other immune diseases by PD-1 signal modulation. In this review, we summarize the history of PD-1, subsequent basic studies, and their application to the clinic.

Heme Oxygenase-1-Expressing Dendritic Cells Promote Foxp3+ Regulatory T Cell Differentiation and Induce Less Severe Airway Inflammation in Murine Models

Dendritic cells (DCs) are critical for instructing immune responses toward inflammatory or anti-inflammatory status. Heme oxygenase-1 (HO-1) is known for its cytoprotective effect against oxidative stress and inflammation, suggesting its immune regulatory role in allergic lung inflammation. HO-1 has been implicated in affecting DC maturation; however, its role in DC-mediated T-cell differentiation is unclear. In this study, we demonstrated that HO-1-expressing bone marrow-derived dendritic cells (BM-DCs) displayed tolerogenic phenotypes, including their resistance to lipopolysaccharide (LPS)-induced maturation, high level expression of IL-10, and low T-cell stimulatory activity. In addition, HO-1-expressing DCs were able to induce antigen-specific Foxp3⁺ regulatory T cells (Treg) differentiation in vitro and in vivo. Also, HO-1-expressing DCs modulated the severity of lung inflammatory responses in two murine models of airway inflammation. This study provided evidence supporting the role of HO-1-expressing DCs in tolerance induction and as a potential therapeutic target for allergic asthma as well as other inflammatory diseases.

Dendritic Cells in the Immune System—History, Lineages, Tissues, Tolerance, and Immunity

The aim of this review is to provide a coherent framework for understanding dendritic cells (DCs). It has seven sections. The introduction provides an overview of the immune system and essential concepts, particularly for the nonspecialist reader. Next, the “History” section outlines the early evolution of ideas about DCs and highlights some sources of confusion that still exist today. The “Lineages” section then focuses on five different populations of DCs: two subsets of “classical” DCs, plasmacytoid DCs, monocyte-derived DCs, and Langerhans cells. It highlights some cellular and molecular specializations of each, and also notes other DC subsets that have been proposed. The following “Tissues” section discusses the distribution and behavior of different DC subsets within nonlymphoid and secondary lymphoid tissues that are connected by DC migration pathways between them. In the “Tolerance” section, the role of DCs in central and peripheral tolerance is considered, including their ability to drive the differentiation of different populations of regulatory T cells. In contrast, the “Immunity” section considers the roles of DCs in sensing of infection and tissue damage, the initiation of primary responses, the T-cell effector phase, and the induction of immunological memory. The concluding section provides some speculative ideas about the evolution of DCs. It also revisits earlier concepts of generation of diversity and clonal selection in terms of DCs driving the evolution of T-cell responses. Throughout, this review highlights certain areas of uncertainty and suggests some avenues for future investigation.

Immunoregulation in Fungal Diseases

This review addresses specific regulatory mechanisms involved in the host immune response to fungal organisms. We focus on key cells and regulatory pathways involved in these responses, including a brief overview of their broader function preceding a discussion of their specific relevance to fungal disease. Important cell types discussed include dendritic cells and regulatory T cells, with a focus on specific studies relating to their effects on immune responses to fungi. We highlight the interleukin-10, programmed cell death 1, and cytotoxic T lymphocyte-associated protein 4 signaling pathways and emphasize interrelationships between these pathways and the regulatory functions of dendritic cells and regulatory T cells. Throughout our discussion, we identify selected studies best illustrating the role of these cells and pathways in response to specific fungal pathogens to provide a contextual understanding of the tightly-controlled network of regulatory mechanisms critical to determining the outcome of exposure to fungal pathogens. Lastly, we discuss two unique phenomena relating to immunoregulation, protective tolerance and immune reactivation inflammatory syndrome. These two clinically-relevant conditions provide perspective as to the range of immunoregulatory mechanisms active in response to fungi.

Programmed Death-1 Culls Peripheral Accumulation of High-Affinity Autoreactive CD4 T Cells to Protect against Autoimmunity

Self-reactive CD4 T cells are incompletely deleted during thymic development, and their peripheral seeding highlights the need for additional safeguards to avert autoimmunity. Here, we show an essential role for the coinhibitory molecule programmed death-1 (PD-1) in silencing the activation of high-affinity autoreactive CD4 T cells. Each wave of self-reactive CD4 T cells that escapes thymic deletion autonomously upregulates PD-1 to maintain self-tolerance. By tracking the progeny derived from individual autoreactive CD4 T cell clones, we demonstrate that self-reactive cells with the greatest autoimmune threat and highest self-antigen affinity express the most PD-1. Reciprocally, PD-1 deprivation unleashes high-affinity self-reactive CD4 T cells in target tissues to exacerbate neuronal inflammation and autoimmune diabetes. Reliance on PD-1 to actively maintain self-tolerance may explain why exploiting this pathway by cancerous cells and invasive microbes efficiently subverts protective immunity, and why autoimmune side effects can develop after PD-1-neutralizing checkpoint therapies.

Immunomodulatory Functions of BTLA and HVEM Govern Induction of Extrathymic Regulatory T Cells and Tolerance by Dendritic Cells

Dendritic cells (DCs) initiate immunity and also antigen-specific tolerance mediated by extrathymic regulatory T (Treg) cells, yet it remains unclear how DCs regulate induction of such tolerance. Here, we report that efficient induction of Treg cells was instructed by BTLA⁺DEC205⁺CD8⁺CD11c⁺ DCs and the immunomodulatory functions of BTLA. In contrast, T cell activation in steady state by total CD11c⁺ DCs that include a majority of DCs that do not express BTLA did not induce Treg cells and had no lasting impact on subsequent immune responses. Engagement of HVEM, a receptor of BTLA, promoted Foxp3 expression in T cells through upregulation of CD5. In contrast, T cells activated in the absence of BTLA and HVEM-mediated functions remained CD5^lo and therefore failed to resist the inhibition of Foxp3 expression in response to effector cell-differentiating cytokines. Thus, DCs require BTLA and CD5-dependent mechanisms to actively adjust tolerizing T cell responses under steady-state conditions.

Nutrients and the microenvironment to feed a T cell army

T cells have dramatic functional and proliferative shifts in the course of maintaining immune protection from pathogens and cancer. To support these changes, T cells undergo metabolic reprogramming upon stimulation and again after antigen clearance. Depending on the extrinsic cell signals, T cells can differentiate into functionally distinct subsets that utilize and require diverse metabolic programs. Effector T cells (Teff) enhance glucose and glutamine uptake, whereas regulatory T cells (Treg) do not rely on significant rates of glycolysis. The dependence of these subsets on specific metabolic programs makes T cells reliant on these signaling pathways and nutrients. Metabolic pathways, such as those regulated by mTOR and Myc, augment T cell glycolysis and glutaminolysis programs to promote T cell activity. These pathways respond to signals and control metabolism through both transcriptional or post-transcriptional mechanisms. Epigenetic modifications also play an important role by stabilizing the transcription factors that define subset specific reprogramming. In addition, circadian rhythm cycling may also influence energy use, immune surveillance, and function of T cells. In this review, we focus on the metabolic and nutrient requirements of T cells, and how canonical pathways of growth and metabolism regulate nutrients that are essential for T cell function.

The role of dendritic cells in cancer

Though present in low numbers, dendritic cells (DCs) are recognized as major players in the control of cancer by adaptive immunity. The roles of cytotoxic CD8⁺ T-cells and Th1 helper CD4⁺ T-cells are well-documented in murine models of cancer and associated with a profound prognostic impact when infiltrating human tumors, but less information is known about how these T-cells gain access to the tumor or how they are primed to become tumor-specific. Here, we highlight recent findings that demonstrate a vital role of CD103⁺ DCs, which have been shown to be experts in cross-priming and the induction of anti-tumor immunity. We also focus on two different mediators that impair the function of tumor-associated DCs: prostaglandin E₂ and β-catenin. Both of these mediators seem to be important for the exclusion of T-cells in the tumor microenvironment and may represent key pathways to target in optimized treatment regimens against cancer.

PD-1/PD-L and autoimmunity: A growing relationship

Programmed death 1 (PD-1) and its ligands, namely PD-L1 and PD-L2, are one of the key factors responsible for inhibitory T cell signaling, mediating the mechanisms of tolerance and providing immune homeostasis. Mounting evidence demonstrates that impaired PD-1:PD-L function plays an important role in a variety of autoimmune diseases such as Type 1 diabetes (T1D), encephalomyelitis, inflammatory bowel diseases (IBD), Rheumatoid Arthritis (RA), autoimmune hepatitis (AIH), Behcet's disease (BD), myasthenia gravis (MG), autoimmune uveitis (AU), Sjögren's syndrome (SjS), systemic lupus erythematosus (SLE), systemic sclerosis (SSc), myocarditis, and ankylosing spondylitis (AS). By investigating the candidate genes, genome-wide association studies, and identification of single nucleotide polymorphisms (SNPs) in PD-1 gene in humans, it has been shown that there is a higher risk in relevant genetic associations with developing autoimmune diseases in certain ethnic groups. In this review we have tried to present a comprehensive role of PD-1:PD-L in all recently studied autoimmune diseases.

Novel immunoregulatory role of perforin-positive dendritic cells

The recently described generation of a highly defined population of dendritic cells which express perforin and granzyme A (termed "perf-DCs") and their ability to selectively delete cognate CD8+ T cell has raised the possibility that these cells play a role in the maintenance of peripheral tolerance. Using bone marrow transplantation, we generated mice selectively lacking perforin expressing dendritic cells. These mice progressively gain weight and exhibit features resembling metabolic syndrome as well as an enhanced susceptibility to autoimmunity induction. Interestingly, these pathological phenotypes were reversed upon treatment with CD4/CD8 neutralizing antibodies. Thus, it appears that this rare subpopulation of dendritic cells (perf-DCs) displays a major regulatory role in adipose tissue inflammatory processes and in autoimmunity.

Specific CD8+ T cell response immunotherapy for hepatocellular carcinoma and viral hepatitis

Hepatocellular carcinoma (HCC), chronic hepatitis B (CHB) and chronic hepatitis C (CHC) are characterized by exhaustion of the specific CD8⁺ T cell response. This process involves enhancement of negative co-stimulatory molecules, such as programmed cell death protein-1 (PD-1), cytotoxic T-lymphocyte antigen-4 (CTLA-4), 2B4, Tim-3, CD160 and LAG-3, which is linked to intrahepatic overexpression of some of the cognate ligands, such as PD-L1, on antigen presenting cells and thereby favouring a tolerogenic environment. Therapies that disrupt these negative signalling mechanisms represent promising therapeutic tools with the potential to restore reactivity of the specific CD8⁺ T cell response. In this review we discuss the impressive in vitro and in vivo results that have been recently achieved in HCC, CHB and CHC by blocking these negative receptors with monoclonal antibodies against these immune checkpoint modulators. The article mainly focuses on the role of CTLA-4 and PD-1 blocking monoclonal antibodies, the first ones to have reached clinical practice. The humanized monoclonal antibodies against CTLA-4 (tremelimumab and ipilimumab) and PD-1 (nivolumab and pembrolizumab) have yielded good results in testing of HCC and chronic viral hepatitis patients. Trelimumab, in particular, has shown a significant increase in the time to progression in HCC, while nivolumab has shown a remarkable effect on hepatitis C viral load reduction. The research on the role of ipilimumab, nivolumab and pembrolizumab on HCC is currently underway.

Dendritic cells as therapeutic targets in neuroinflammation

Multiple sclerosis (MS) is the most common chronic inflammatory demyelinating disorder of the central nervous system characterized by infiltration of immune cells and progressive damage to myelin sheaths and neurons. There is still no cure for the disease, but drug regimens can reduce the frequency of relapses and slightly delay progression. Myeloid cells or antigen-presenting cells (APCs) such as dendritic cells (DC), macrophages, and resident microglia, are key players in both mediating immune responses and inducing immune tolerance. Mounting evidence indicates a contribution of these myeloid cells to the pathogenesis of multiple sclerosis and to the effects of treatment, the understanding of which might provide strategies for more potent novel therapeutic interventions. Here, we review recent insights into the role of APCs, with specific focus on DCs in the modulation of neuroinflammation in MS.

Depletion of Regulatory T Cells Induces High Numbers of Dendritic Cells and Unmasks a Subset of Anti-Tumour CD8+CD11c+ PD-1lo Effector T Cells

Natural regulatory T (Treg) cells interfere with multiple functions, which are crucial for the development of strong anti-tumour responses. In a model of 4T1 mammary carcinoma, depletion of CD25⁺Tregs results in tumour regression in Balb/c mice, but the mechanisms underlying this process are not fully understood. Here, we show that partial Treg depletion leads to the generation of a particular effector CD8 T cell subset expressing CD11c and low level of PD-1 in tumour draining lymph nodes. These cells have the capacity to migrate into the tumour, to kill DCs, and to locally regulate the anti-tumour response. These events are concordant with a substantial increase in CD11b⁺ resident dendritic cells (DCs) subsets in draining lymph nodes followed by CD8⁺ DCs. These results indicate that Treg depletion leads to tumour regression by unmasking an increase of DC subsets as a part of a program that optimizes the microenvironment by orchestrating the activation, amplification, and migration of high numbers of fully differentiated CD8⁺CD11c⁺PD1^lo effector T cells to the tumour sites. They also indicate that a critical pattern of DC subsets correlates with the evolution of the anti-tumour response and provide a template for Treg depletion and DC-based therapy.

High-Resolution PET Imaging with Therapeutic Antibody-based PD-1/PD-L1 Checkpoint Tracers

Checkpoint-blocking antibodies like those targeting the PD-1/PD-L1 pathway have revolutionized oncology. We developed radiotracers based on therapeutic checkpoint-blocking antibodies permitting sensitive and high-resolution PET imaging of both PD-1 and PD-L1 in immunocompetent mice. ImmunoPET of naive mice revealed similar overall expression patterns for PD-1 and PD-L1 in secondary lymphoid organs (spleen and lymph nodes). Interestingly, PD-L1 was also detected in brown adipose tissue (BAT), confirming the notion that BAT is immunologically relevant. Under pathophysiological conditions, strong expression of the receptor/ligand pair was also found in non-lymphoid tissues. Both were specifically detected in malignant tumors. PD-1 was readily detected after combined immunoradiotherapy causing massive tumor infiltration by PD-1+ lymphocytes. PD-L1 tracer uptake was reduced in PD-L1 knockout tumors. Moreover, monitoring the expression changes of PD-L1 in response to its main inducer, the effector T cell cytokine IFN-γ, revealed robust upregulation in the lung. This suggests that T cell responses in the lung, a vital organ continuously exposed to a variety of antigens, are strongly restrained by the PD-1 checkpoint. In turn, this could explain the association of PD-1 checkpoint inhibition with potentially fatal immune-mediated pneumonitis and partially also its efficacy in lung cancer.

PD-1 marks dysfunctional regulatory T cells in malignant gliomas

Immunotherapies targeting the immune checkpoint receptor programmed cell death protein 1 (PD-1) have shown remarkable efficacy in treating cancer. CD4⁺CD25^hiFoxP3⁺ Tregs are critical regulators of immune responses in autoimmunity and malignancies, but the functional status of human Tregs expressing PD-1 remains unclear. We examined functional and molecular features of PD-1^hi Tregs in healthy subjects and patients with glioblastoma multiforme (GBM), combining functional assays, RNA sequencing, and cytometry by time of flight (CyTOF). In both patients with GBM and healthy subjects, circulating PD-1^hi Tregs displayed reduced suppression of CD4⁺ effector T cells, production of IFN-γ, and molecular signatures of exhaustion. Transcriptional profiling of tumor-resident Tregs revealed that several genes coexpressed with PD-1 and associated with IFN-γ production and exhaustion as well as enrichment in exhaustion signatures compared with circulating PD-1^hi Tregs. CyTOF analysis of circulating and tumor-infiltrating Tregs from patients with GBM treated with PD-1-blocking antibodies revealed that treatment shifts the profile of circulating Tregs toward a more exhausted phenotype reminiscent of that of tumor-infiltrating Tregs, further increasing IFN-γ production. Thus, high PD-1 expression on human Tregs identifies dysfunctional, exhausted Tregs secreting IFN-γ that exist in healthy individuals and are enriched in tumor infiltrates, possibly losing function as they attempt to modulate the antitumoral immune responses.

Airway responses towards allergens - from the airway epithelium to T cells

The prevalence of allergic diseases such as allergic rhinitis is increasing, affecting up to 30% of the human population worldwide. Allergic sensitization arises from complex interactions between environmental exposures and genetic susceptibility, resulting in inflammatory T helper 2 (Th2) cell-derived immune responses towards environmental allergens. Emerging evidence now suggests that an epithelial dysfunction, coupled with inherent properties of environmental allergens, can be responsible for the inflammatory responses towards allergens. Several epithelial-derived cytokines, such as thymic stromal lymphopoietin (TSLP), IL-25 and IL-33, influence tissue-resident dendritic cells (DCs) as well as Th2 effector cells. Exposure to environmental allergens does not elicit Th2 inflammatory responses or any clinical symptoms in nonatopic individuals, and recent findings suggest that a nondamaged, healthy epithelium lowers the DCs' ability to induce inflammatory T-cell responses towards allergens. The purpose of this review was to summarize the current knowledge on which signals from the airway epithelium, from first contact with inhaled allergens all the way to the ensuing Th2-cell responses, influence the pathology of allergic diseases.