Synovial T cell hyporesponsiveness to myeloid dendritic cells is reversed by preventing PD-1/PD-L1 interactions

T peripheral helper (Tph) cells, a marker of immune activation in cancer and autoimmune disorders

T peripheral helper (Tph) cells are a newly discovered subtype of CD4+ T cells that have emerged as the counterpart of T follicular helper (Tfh) cells in the peripheral tissues. These two cell types share some common characteristics, such as high levels of PD1 and CXCL13 expression, but differ in the expression of transcription factors and chemokine receptors. Tph cells have been studied in relation to B cells' effector functions, including cytokines production and antibody-mediated immune responses. However, their role in the inflammatory-mediated development of malignancies remains poorly understood. Tph cells were initially identified in the synovium of rheumatoid arthritis patients and have since been found to be expanded in several autoimmune diseases. They have been linked to a worse prognosis in autoimmune conditions, but intriguingly, their presence has been correlated with better outcomes in certain types of cancer. The functions of Tph cells are still being investigated, but recent data suggests their involvement in the assembly of tertiary lymphoid structures (TLS). Furthermore, their interaction with B cells, which have been mainly described as possessing a memory phenotype, promotes their development. In this review, we explore the role of Tph cells in peripheral immune responses during cancer and autoimmune disorders.

Exploring the Role of PD-1 in the Autoimmune Response: Insights into Its Implication in Systemic Lupus Erythematosus

Despite advances in understanding systemic lupus erythematosus (SLE), many challenges remain in unraveling the precise mechanisms behind the disease's development and progression. Recent evidence has questioned the role of programmed cell death protein 1 (PD-1) in suppressing autoreactive CD4+ T cells during autoimmune responses. Research has investigated the potential impacts of PD-1 on various CD4+ T-cell subpopulations, including T follicular helper (Tfh) cells, circulating Tfh (cTfh) cells, and T peripheral helper (Tph) cells, all of which exhibit substantial PD-1 expression and are closely related to several autoimmune disorders, including SLE. This review highlights the complex role of PD-1 in autoimmunity and emphasizes the imperative for further research to elucidate its functions during autoreactive T-cell responses. Additionally, we address the potential of PD-1 and its ligands as possible therapeutic targets in SLE.

A Study on the Immunoregulatory Role of the PD1 Pathway in Juvenile Idiopathic Arthritis

Objectives

To investigate the immunoregulatory role of the Programmed-cell-Death-protein-1 (PD1) pathway, an inhibitory immune checkpoint, in Juvenile Idiopathic Arthritis (JIA).

Methods

The PD1 expression on CD4+ and CD8+ T-cells was determined by flow cytometry and the PD1 soluble form (sPD1) levels by ELISA, in peripheral blood (PB)/serum and synovial fluid (SF) samples of JIA patients and healthy controls (HCs). We searched for any association in-between the biomarkers and with JIA activity.

Results

101 Caucasian patients (69 female), aged 12 (8-15) years, and 20 HCs participated in this study. The PB PD1 expression on T-cells was higher in: a. JIA patients vs HCs (CD4: 1.24% vs 0.32%, p=0.007, CD8: 1.6% vs 0.4%, p=0.002). b. active vs inactive JIA (CD4: 1.44% vs 0.87%, p=0.072, CD8: 2.1% vs 0.93%, p=0.005). The SF PD1 expression on T-cells correlated strongly and positively with the disease activity (CD4: ρ=0.55, p=0.022, CD8: ρ=0.555, p=0.026). The SF PD1 expression on CD8 T-cells was higher in patients on-treatment vs those off-treatment (21.3% vs 5.83% p=0.004). The sPD1 levels were higher in the SF vs the serum (801pg/ml vs 367.2, p=0.013), without an association with disease activity.

Conclusion

These results indicate an up-regulation of the PD1-pathway in JIA, at least quantitatively, especially in active disease. sPD1 is compartmentally produced at the inflamed joints. Further investigation in a larger sample of JIA patients may verify these observations and contribute to unravelling the precise role of the PD1 pathway in the pathogenesis and persistence of the joint inflammation.

The mechanism of dendritic cell-T cell crosstalk in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterised by joint pain and swelling, synovial hyperplasia, cartilage damage, and bone destruction. The mechanisms of dendritic cell (DC) and T cell-mediated crosstalk have gradually become a focus of attention. DCs regulate the proliferation and differentiation of CD4+ T cell subtypes through different cytokines, surface molecules, and antigen presentation. DC-T cell crosstalk also blocks antigen presentation by DCs, ultimately maintaining immune tolerance. DC-T cell crosstalk mainly involves chemokines, surface molecules (TonEBP, NFATc1), the PD-L1/PD-1 signalling axis, and the TGF-β signalling axis. In addition, DC-T cell crosstalk in RA is affected by glycolysis, reactive oxygen species, vitamin D, and other factors. These factors lead to the formation of an extremely complex regulatory network involving various mechanisms. This article reviews the key immune targets of DC-T cell crosstalk and elucidates the mechanism of DC-T cell crosstalk in RA to provide a basis for the treatment of patients with RA.

Emerging phagocytosis checkpoints in cancer immunotherapy

Cancer immunotherapy, mainly including immune checkpoints-targeted therapy and the adoptive transfer of engineered immune cells, has revolutionized the oncology landscape as it utilizes patients' own immune systems in combating the cancer cells. Cancer cells escape immune surveillance by hijacking the corresponding inhibitory pathways via overexpressing checkpoint genes. Phagocytosis checkpoints, such as CD47, CD24, MHC-I, PD-L1, STC-1 and GD2, have emerged as essential checkpoints for cancer immunotherapy by functioning as "don't eat me" signals or interacting with "eat me" signals to suppress immune responses. Phagocytosis checkpoints link innate immunity and adaptive immunity in cancer immunotherapy. Genetic ablation of these phagocytosis checkpoints, as well as blockade of their signaling pathways, robustly augments phagocytosis and reduces tumor size. Among all phagocytosis checkpoints, CD47 is the most thoroughly studied and has emerged as a rising star among targets for cancer treatment. CD47-targeting antibodies and inhibitors have been investigated in various preclinical and clinical trials. However, anemia and thrombocytopenia appear to be formidable challenges since CD47 is ubiquitously expressed on erythrocytes. Here, we review the reported phagocytosis checkpoints by discussing their mechanisms and functions in cancer immunotherapy, highlight clinical progress in targeting these checkpoints and discuss challenges and potential solutions to smooth the way for combination immunotherapeutic strategies that involve both innate and adaptive immune responses.

T-cell exhaustion in immune-mediated inflammatory diseases: New implications for immunotherapy

Immune-mediated inflammatory diseases(IMIDs) are referred to as highly disabling chronic diseases affecting different organs and systems. Inappropriate or excessive immune responses with chronic inflammation are typical manifestations. Usually in patients with chronic infection and cancer, due to long-term exposure to persistent antigens and inflammation microenvironment, T-cells are continuously stimulated and gradually differentiate into an exhausted state. Exhausted T-cells gradually lose effector function and characteristics of memory T-cells. However, existing studies have found that exhausted T-cells are not only present in the infection and tumor environment, but also in autoimmunity, and are associated with better prognosis of IMIDs. This suggests new prospects for the application of this reversible process of T-cell exhaustion in the treatment of IMID. This review will focus on the research progress of T-cell exhaustion in several IMIDs and its potential application for diagnosis and treatment in IMIDs.

Beyond Cancer: Regulation and Function of PD-L1 in Health and Immune-Related Diseases

Programmed Cell Death 1 Ligand 1 (PD-L1, CD274, B7-H1) is a transmembrane protein which is strongly involved in immune modulation, serving as checkpoint regulator. Interaction with its receptor, Programmed Cell Death Protein 1 (PD-1), induces an immune-suppressive signal, which modulates the activity of T cells and other effector cells. This mediates peripheral tolerance and contributes to tumor immune escape. PD-L1 became famous due to its deployment in cancer therapy, where blockage of PD-L1 with the help of therapeutic antagonistic antibodies achieved impressive clinical responses by reactivating effector cell functions against tumor cells. Therefore, in the past, the focus has been placed on PD-L1 expression and its function in various malignant cells, whereas its role in healthy tissue and diseases apart from cancer remained largely neglected. In this review, we summarize the function of PD-L1 in non-cancerous cells, outlining its discovery and origin, as well as its involvement in different cellular and immune-related processes. We provide an overview of transcriptional and translational regulation, and expression patterns of PD-L1 in different cells and organs, and illuminate the involvement of PD-L1 in different autoimmune diseases as well as in the context of transplantation and pregnancy.

Revisiting PD-1/PD-L pathway in T and B cell response: Beyond immunosuppression

The regulation of T cell response depends on co-inhibitory pathways that serve to control immune-mediated tissue damage and resolve inflammation by modulating the magnitude and duration of immune response. In this process, the axis of T-cell-expressed programmed death-1 (PD-1) and its ligands (PD-L1 and PD-L2) play a key role. While the PD-1/PD-L pathway has received considerable attention for its role in the maintenance of T cell exhaustion in cancer and chronic infection, the PD-1/PD-L pathway also plays diverse roles in regulating host immunity beyond T cell exhaustion. In this review, we will discuss emerging concepts in co-stimulatory functions of PD-1/PD-L pathway on T cell- and B cell response and explore the potential underlying mechanisms. In addition, based on the elevated expression of PD-1 and its ligands in local inflamed tissues, we further discussed the role of PD-1/PD-L pathway in autoimmune diseases.

The Effects of Moxibustion on PD-1/PD-L1-Related Molecular Expression and Inflammatory Cytokine Levels in RA Rats

Objective. Rheumatoid arthritis (RA) is an autoimmune disease that starts with inflammation of the synovium. The pain and joint dysfunction caused by RA urgently need an effective treatment to alleviate the inflammatory reaction and delay the progression of the disease. The pathological damage of RA is proposed to associate with the dysfunction of the programmed cell death 1/programmed cell death ligand 1 (PD-1/PD-L1) pathway. Moxibustion, as a main complementary therapy of traditional Chinese medicine (TCM), has been proved effective to reduce chronic inflammatory reaction on RA, but whether the anti-inflammatory effects are mediated by PD-1/PD-L1 pathway is still unclear. Therefore, moxibustion was conducted in the rats with RA to investigate its effect on PD-1/PD-L1. Methods. The rats' right hind paws were injected with Freundʼs complete adjuvant (FCA) to establish the model of RA. Seven days after the injection of FCA, moxibustion therapy was performed on the acupoints of Shenshu (BL23) and Zusanli (ST36) once a day for three weeks. Then, ELISA and immunohistochemical methods were used to analyze the influence of moxibustion on the expression of PD-1/PD-L1. If the moxibustion had an effect on the expression of PD-1/PD-L1-related molecules, we would knock down PD-1 with adenovirus vector. After moxibustion therapy, ELISA and histological analysis were performed to observe the anti-inflammatory effect of moxibustion. Results. The results demonstrated that moxibustion had an effect on the expression of PD-1-related molecules. The results of ELISA manifested that moxibustion decreased the level of IFN-γ and increased the level of IL-4 and IL-10. HE staining revealed that moxibustion alleviated the proliferation of synovial tissue. However, the anti-inflammatory effect and pathological improvement were weakened when PD-1 was blocked. Conclusions. The results indicate that moxibustion affected the expression of PD-1/PD-L1-related molecules and can effectively treat RA damage. The anti-inflammatory effect of moxibustion was weakened when PD-1 was knocked down.

Functionally Mature CD1c+ Dendritic Cells Preferentially Accumulate in the Inflammatory Arthritis Synovium

Objective

To examine the role of synovial CD1c⁺DCs in patients with Inflammatory Arthritis (IA) with a specific focus on the transcriptional and maturation signatures that govern their function.

Methods

RNA sequencing was performed on healthy control (HC) peripheral blood (PB), IA PB, and IA synovial fluid (SF) CD1c⁺DCs. Multiparametric flow-cytometry and SPICE analysis were used to examine site [SF and Synovial Tissue (ST) CD1c+DCs] and disease specific characteristics of CD1c⁺DCs, while functional assays such as antigen processing, activation, and MMP production were also performed.

Results

Increased frequency of CD1c⁺DCs (p<0.01) with a concomitant increase in CD80, CCR7 (p<0.01), and CXCR3 (p<0.05) expression was identified in IA PB compared to HC PB. Enrichment of CD1c⁺DCs was identified in IA synovial tissue (ST) (p<0.01) and IA SF (p<0.0001) compared to IA PB, while RNAseq revealed distinct transcriptional variation between PB and SF CD1c⁺DCs. Flow cytometry revealed increased expression of CD83, CD80, PD-L1, and BTLA (all p<0.05) in IA SF CD1c⁺DCs compared to PB, while SPICE identified synovial cells with unique co-expression patterns, expressing multiple DC maturation markers simultaneously. Functionally, synovial CD1c⁺DCs are hyper-responsive to TLR7/8 ligation (p<0.05), have decreased antigen processing capacity (p=0.07), and display dysregulated production of MMPs. Finally, examination of both synovial CD1c⁺DCs and synovial CD141⁺DCs revealed distinct maturation and transcriptomic profiles.

Conclusion

Synovial CD1c⁺DCs accumulate in the inflamed IA synovium in a variety of distinct poly-maturational states, distinguishing them transcriptionally and functionally from CD1c⁺DCs in the periphery and synovial CD141⁺DCs.

Cellular and molecular regulation of the programmed death-1/programmed death ligand system and its role in multiple sclerosis and other autoimmune diseases

Programmed Cell Death 1 (PD-1) receptor and its ligands (PD-Ls) are essential to maintain peripheral immune tolerance and to avoid tissue damage. Consequently, altered gene or protein expression of this system of co-inhibitory molecules has been involved in the development of cancer and autoimmunity. Substantial progress has been achieved in the study of the PD-1/PD-Ls system in terms of regulatory mechanisms and therapy. However, the role of the PD-1/PD-Ls pathway in neuroinflammation has been less explored despite being a potential target of treatment for neurodegenerative diseases. Multiple Sclerosis (MS) is the most prevalent, chronic, inflammatory, and autoimmune disease of the central nervous system that leads to demyelination and axonal damage in young adults. Recent studies have highlighted the key role of the PD-1/PD-Ls pathway in inducing a neuroprotective response and restraining T cell activation and neurodegeneration in MS. In this review, we outline the molecular and cellular mechanisms regulating gene expression, protein synthesis and traffic of PD-1/PD-Ls as well as relevant processes that control PD-1/PD-Ls engagement in the immunological synapse between antigen-presenting cells and T cells. Also, we highlight the most recent findings regarding the role of the PD-1/PD-Ls pathway in MS and its murine model, experimental autoimmune encephalomyelitis (EAE), including the contribution of PD-1 expressing follicular helper T (TFH) cells in the pathogenesis of these diseases. In addition, we compare and contrast results found in MS and EAE with evidence reported in other autoimmune diseases and their experimental models, and review PD-1/PD-Ls-targeting therapeutic approaches.

Autoreactivity of Peripheral Helper T Cells in the Joints of Rheumatoid Arthritis

Autoreactive CD4 T cells are thought to play pivotal roles in the pathogenesis of rheumatoid arthritis (RA). Recently, a subset of CD4 T cells that express high levels of programmed death-1 (PD-1) but are distinct from follicular helper T cells have been identified in the joints of RA patients and named peripheral helper T (Tph) cells. Because PD-1 is expressed on T cells chronically stimulated with the Ags, we tested a hypothesis that Tph cells are the pathogenic autoreactive CD4 T cells in RA. We found that human Tph cells in RA joints produce proinflammatory effector cytokines, including IFN-γ, TNF-α, and GM-CSF, in addition to B cell-helping cytokines, such as IL-21 and CXCL13. Flow cytometric analysis showed different bias of TCR Vβ usage between PD-1^high Tph cells and PD-1^low/neg CD4 T cells, including Th1 cells, in the joint or memory CD4 T cells in the peripheral blood, whereas there was little difference between the latter two subsets. In line with this, deep sequencing of TCR demonstrated an overlap of expanded clones between peripheral blood memory CD4 T cells and PD-1^low/neg CD4 T cells but not Tph cells in the joint. Interestingly, Tph cells preferentially exhibited autologous MLR in vitro, which required recognition of self-MHC class II and was pronounced by blocking PD-1 signaling. Taken together, these results suggest that Tph cells are the pathogenic autoreactive CD4 T cells in RA, which expand locally in the joints and are regulated by PD-1 signaling.

The PD-1:PD-L1 axis in Inflammatory Arthritis

The activation of antigen specific T cells during an immune response is a tightly regulated process at the level of both costimulatory and coinhibitory receptors. One such coinhibitory receptor or checkpoint inhibitor which has received much attention in the field of oncology is the programmed cell death protein 1 (PD-1). Blockade of PD-1 or its ligand PD-L1 has proven successful in the treatment of a wide variety of cancers, therefore highlighting an important role for this pathway in anti-tumour immune responses. However, a caveat of PD-1 therapy and boosting anti-tumour immune responses is the development of self-reactive T cells which can lead to the induction of various autoimmune or inflammatory diseases, referred to as immune- related adverse events (irAEs). The emergence of rheumatological irAEs such as Inflammatory Arthritis (IA) in recent years has highlighted the importance of PD-1 in maintaining self-tolerance. Furthermore, the emergence of rheumatology related irAEs raises an important question as to how defects in this pathway can contribute to spontaneous rheumatological disease. In this review, we describe the biological distribution, function and regulation of the PD-1 pathway, its potential role in IA and irAE related IA.

The PD-1/PD-L pathway in rheumatic diseases

BACKGROUND/PURPOSE

Autoimmune diseases are diseases in which the body produces an abnormal immune response to self-antigens and damages its own tissues. Programmed death-1 (PD-1) and its ligands (PD-Ls) have been discovered to be important negative regulators of the immune system, playing crucial roles in autoimmunity.

METHODS

We analyzed the existing scientific literature dealing with this issue. In this review, the PD-1/PD-L pathway in the genetic susceptibility to and pathogenesis of rheumatic diseases is discussed. The PD-1/PD-L pathway might be helpful for diagnosing, evaluating the disease activity of and treating rheumatic diseases.

RESULTS

PD-1/PD-L gene polymorphisms are associated with a genetic predisposition to rheumatic disorders, which can provide reference information for diagnosis and disease activity. The conclusion of the crucial role of the PD-1/PD-L pathway in the pathogenesis of rheumatic diseases is consistent, but the details remain controversial. In some animal models, manipulating the PD-1/PD-L pathway could decrease disease severity. PD-1/PD-Ls may enable us to develop new therapeutics for patients with rheumatic diseases in the future.

CONCLUSION

The PD-1/PD-L pathway plays crucial roles in rheumatic disease. More work is needed to provide a better mechanistic understanding of the PD-1/PD-L pathway and to facilitate the precise therapeutic manipulation of this pathway.

Statins can suppress DC-mediated Th2 responses through the repression of OX40-ligand and CCL17 expression

DCs and epithelial cell-derived thymic stromal lymphopoietin (TSLP) have pivotal roles in allergic inflammation. TSLP stimulates myeloid DCs to express OX40-ligand (OX40L) and CCL17, which trigger and maintain Th2 cell responses. We have previously shown that statins, which are HMG-CoA reductase inhibitors, have the ability to suppress type I IFN production by plasmacytoid DCs. Here, we extended our previous work to examine the immunomodulatory effect of statins on allergic responses, particularly the TSLP-dependent Th2 pathway induced by myeloid DCs. We found that treatment of TSLP-stimulated DCs with either pitavastatin or simvastatin suppressed both the DC-mediated inflammatory Th2 cell differentiation and CRTH2+ CD4+ memory Th2 cell expansion and also repressed the expressions of OX40L and CCL17 by DCs. These inhibitory effects of statins were mimicked by treatment with either a geranylgeranyl-transferase inhibitor or Rho-kinase inhibitor and were counteracted by the addition of mevalonate, suggesting that statins induce geranylgeranylated Rho inactivation through a mevalonate-dependent pathway. We also found that statins inhibited the expressions of phosphorylated STA6 and NF-κB-p50 in TSLP-stimulated DCs. This study identified a specific ability of statins to control DC-mediated Th2 responses, suggesting their therapeutic potential for treating allergic diseases.

Pleiotropic functions of plasmacytoid dendritic cells in the pathogenesis of the rheumatoid arthritis

Rheumatoid arthritis is a chronic autoimmune inflammatory disease with an unclear etiology. The disease is characterized by infiltration of synovial tissue with immune cells, among which there are dendritic cells that play multifaceted roles in the pathogenesis of the disease. Here we shall assume that plasmacytoid dendritic cells are able to change their phenotype under the influence of various stimuli, thereby modulating the course of the disease, contributing to both the development of exacerbations and the induction of remissions depending on the phenotype they have acquired. This property can be used to develop new methods of immunotherapy.

Peptide-based and small synthetic molecule inhibitors on PD-1/PD-L1 pathway: A new choice for immunotherapy?

Blockade the interaction of the programmed cell death protein 1 (PD-1) and its ligand, programmed death-ligand 1 (PD-L1) can prevent immune evasion of tumor cells and significantly prolong the survival of cancer patients. Currently marketed drugs targeting PD-1/PD-L1 pathway are all monoclonal antibodies (mAbs) that have achieved great success in clinical trials. With the constantly emerging problems of antibody drugs, small molecule inhibitors have attracted the attention of pharmaceutical chemists due to their controllable pharmacological and pharmacokinetic properties, which make them potential alternatives or supplements to mAbs to regulate PD-1/PD-L1 pathway. However, the insufficient target structure information hinders the development of small molecule inhibitors. Since the publication of human-PD-1/human-PD-L1 (hPD-1/hPD-L1) crystal structure, more and more cocrystal structures of mAbs, cyclopeptides and small molecules with PD-1 and PD-L1 have been resolved. These complexes provide a valuable starting point for the rational design of peptide-based and small synthetic molecule inhibitors. Here we reviewed the non-antibody inhibitors that have been published so far and analyzed their structure-activity relationships (SAR). We also summarized the cocrystal structures with hot spots identified, with the aim to provide reference for future drug discovery.

Inhibitory Receptor Expression on T Cells as a Marker of Disease Activity and Target to Regulate Effector Cellular Responses in Rheumatoid Arthritis

OBJECTIVE

Inhibitory receptors are essential for the regulation of effector immune responses and may play critical roles in autoimmune diseases. We evaluated whether inhibitory receptor expression on T cells from patients with rheumatoid arthritis (RA) were correlated with immune activation, disease activity, and response to treatment, as well as whether inhibitory receptor-mediated pathways were functional.

METHODS

Using flow cytometry, we performed extensive phenotypic and functional evaluation of CD4+ and CD8+ T cells from the blood and synovial fluid (SF) of RA patients ex vivo and after culture. The relationship of each parameter with the Disease Activity Score in 28 joints using the erythrocyte sedimentation rate (DAS28-ESR) and response to treatment was examined.

RESULTS

In RA patients with low levels of T cell activation, inhibitory receptor expression showed an inverse relationship with the DAS28-ESR. The frequency of T cells expressing multiple inhibitory receptors was reduced in untreated RA patients but returned to normal levels in treated patients. RA patients who responded to treatment showed an augmented frequency of inhibitory receptor-expressing T cells that correlated with reduced inflammatory cytokine production in comparison to nonresponders. Higher frequencies of effector and memory T cells that expressed multiple inhibitory receptors were seen in SF than in peripheral blood. Notably, inhibitory pathways were operative in blood and synovial T cells from all RA patients, although cells from nonresponder patients were less sensitive to inhibition.

CONCLUSION

Inhibitory receptor expression on T cells from RA patients is inversely correlated with effector T cell function and disease activity and may predict response to treatment. Furthermore, different inhibitory pathways are functional and cooperatively suppress synovial T cells, providing a rationale for new treatment strategies to regulate acute local inflammation.

Expansion and activation of monocytic-myeloid-derived suppressor cell via STAT3/arginase-I signaling in patients with ankylosing spondylitis

Background

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease. The dysregulated immune system plays an important role in the pathogenesis of AS. Myeloid-derived suppressor cells (MDSCs) play a key immunoregulatory role in autoimmune arthritis. The aim of this study was to clarify the underlying immunoregulatory mechanism of MDSCs in patients with AS.

Methods

Flow cytometry was used to analyze the phenotype of MDSCs among peripheral blood mononuclear cells (PBMCs) from 46 patients with AS and 46 healthy control subjects. The correlation between MDSC frequency and the disease index of patients with AS was evaluated. A T cell proliferation experiment was used to evaluate the immunosuppressive function of MDSCs.

Results

Polymorphonuclear (PMN) and monocytic (M)-MDSCs were significantly elevated in the PBMCs of patients with AS, when compared with levels in healthy controls. Additionally, M-MDSC levels correlated positively with the clinical index of AS, including the Bath ankylosing spondylitis disease activity index (BASDAI) score, erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels. M-MDSCs derived from patients with AS suppressed T cell responses, and this effect was dependent on the induction of arginase-I. Furthermore, AS-derived M-MDSCs showed high levels of phosphorylated STAT3. Stattic, a STAT3-specific inhibitor, and STAT3-targeted siRNA abrogated the immunosuppressive function of M-MDSCs. Inhibition of STAT3 signaling also resulted in decreased arginase-I activity.

Conclusions

STAT3/arginase-I signaling plays an important role in both the expansion and activation of M-MDSCs in patients with AS. This information may be beneficial in developing novel therapeutic strategies for preventing AS.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1654-4) contains supplementary material, which is available to authorized users.

Smoking Is Associated With Low Levels of Soluble PD-L1 in Rheumatoid Arthritis

Background

Smoking is a risk factor for developing rheumatoid arthritis (RA), but the mechanism remains uncertain. We previously demonstrated that smoking lowers the T cell activation threshold by limiting programmed death protein 1 (PD-1) expression.

Aim

To investigate how smoking influence the levels of soluble PD-1 ligand (sPD-L1).

Method

Serum levels of sPD-L1 were measured in 246 RA patients and in 168 healthy subjects. The analysis was done with respect to inflammation, smoking, treatments, and autoantibody status. The effect of therapeutic TNF-inhibiting antibodies (TNFi) on sPD-L1 was studied in 16 RA patients at their first infliximab infusion. The expression of Fcγ-receptor (FcγR) subclass IIB and IIIA was analyzed with quantitative polymerase chain reaction in peripheral blood mononuclear cells (PBMCs) from 12 RA patients and 15 healthy controls, and in healthy PBMC exposed to IgG containing antibodies to cyclic citrullinated peptides (aCCP).

Results

The negative association between smoking and sPD-L1 in RA patients was established by multiple logistic regression (OR = 0.52, p = 0.038). Other covariates in the regression model were serum levels of IL-1β representing inflammation (OR = 1.6, p = 0.0076) and aCCP positivity (OR = 1.9, p = 0.047). First infliximab infusion repressed sPD-L1 (p = 0.023) in patients, and low levels of sPD-L1 were found in patients with early RA treated with TNFi (p = 0.018). Treatment with TNFi was associated with higher sPD-L1 in patients with long disease duration (p = 0.041) and restored levels in smokers. In vitro exposure to aCCP+ IgG suppressed sPD-L1 (p = 0.036), but aCCP+ patients with long disease duration had higher sPD-L1 (p = 0.016). High ratio of the inhibitory FcγR subclass IIB over the stimulatory IIIA resulted in low sPD-L1 release (p = 0.029). Smoking was associated with a higher FcγR IIB/IIIA ratio (p = 0.00062) and lower levels of sPD-L1 (p = 0.013).

Conclusion

In RA, serum sPD-L1 was related to systemic inflammation and aCCP positivity. Smoking altered the expression of FcγRs and limited sPD-L1 in RA patients, permitting inappropriate T cell responses. Differential regulation of sPD-L1 during the early and late RA may indicate transposition from acute to chronic inflammation.

Immune checkpoint inhibitor PD-1 pathway is down-regulated in synovium at various stages of rheumatoid arthritis disease progression

Immune checkpoint blockade with therapeutic anti-cytotoxic T lymphocyte-associated antigen (CTLA)-4 (Ipilimumab) and anti-programmed death (PD)-1 (Nivolumab and Pembrolizumab) antibodies alone or in combination has shown remarkable efficacy in multiple cancer types, concomitant with immune-related adverse events, including arthralgia and inflammatory arthritis (IA) in some patients. Herein, using Nivolumab (anti-PD-1 antagonist)-responsive genes along with transcriptomics of synovial tissue from multiple stages of rheumatoid arthritis (RA) disease progression, we have interrogated the activity status of PD-1 pathway during RA development. We demonstrate that the expression of PD-1 was increased in early and established RA synovial tissue compared to normal and OA synovium, whereas that of its ligands, programmed death ligand-1 (PD-L1) and PD-L2, was increased at all the stages of RA disease progression, namely arthralgia, IA/undifferentiated arthritis, early RA and established RA. Further, we show that RA patients expressed PD-1 on a majority of synovial tissue infiltrating CD4⁺ and CD8⁺ T cells. Moreover, enrichment of Nivolumab gene signature was observed in IA and RA, indicating that the PD-1 pathway was downregulated during RA disease progression. Furthermore, serum soluble (s) PD-1 levels were increased in autoantibody positive early RA patients. Interestingly, most of the early RA synovium tissue sections showed negative PD-L1 staining by immunohistochemistry. Therefore, downregulation in PD-1 inhibitory signaling in RA could be attributed to increased serum sPD-1 and decreased synovial tissue PD-L1 levels. Taken together, these data suggest that agonistic PD1 antibody-based therapeutics may show efficacy in RA treatment and interception.

PD-1/PD-L1 in disease

Aim: Expression of PD-1 on T/B cells regulates peripheral tolerance and autoimmunity. Binding of PD-1 to its ligand, PD-L1, leads to protection against self-reactivity. In contrary, tumor cells have evolved immune escape mechanisms whereby overexpression of PD-L1 induces anergy and/or apoptosis of PD-1 positive T cells by interfering with T cell receptor signal transduction. PD-L1 and PD-1 blockade using antibodies are in human clinical trials as an alternative cancer treatment modality. Areas covered: We describe the role of PD-1/PD-L1 in disease in the context of autoimmunity, neurological disorders, stroke and cancer. Conclusion: For immunotherapy/vaccines to be successful, the expression of PD-L1/PD-1 on immune cells should be considered, and the combination of checkpoint inhibitors and vaccines may pave the way for successful outcomes to disease.

Elevated expression of PD‑1 on T cells correlates with disease activity in rheumatoid arthritis

It is well known that lymphocytes are important in rheumatoid arthritis (RA). Programmed cell death-1 (PD‑1) is one of the immunosuppressive costimulatory molecules, which mediates an inhibitory effect. However, its role in RA remains to be fully elucidated. In the present study, the expression levels of PD‑1 on T cells in the peripheral blood (PB) and synovial fluid (SF) were determined using flow cytometry. In addition, the expression levels of PD‑1 on T cells in the PB and SF of patients with RA were further analyzed to determine correlation with markers of the autoimmune response, inflammation and disease activity in RA. Compared with healthy controls, the expression of PD‑1 on T cells in the PB was significantly elevated in patients with RA (P<0.0001). The expression of PD‑1 on T cells in the SF of patients with RA was significantly increased, compared with that in the autologous PB (P<0.0001). It was also found that the expression of PD‑1 on T cells in the PB of patients with RA was increased significantly in subjects with a high rheumatoid factor titer, high levels of inflammatory markers and a high disease activity score 28 (DAS28). The expression of PD‑1 on T cells in the SF of patients with RA was increased significantly in subjects with a high DAS28. These data showed that the expression of PD‑1 on T cells was elevated in patients with RA and was correlated with the disease activity.

Extracellular Vesicles Transfer the Receptor Programmed Death-1 in Rheumatoid Arthritis

Introduction

Extracellular vesicles (EVs) have been recognized as route of communication in the microenvironment. They transfer proteins and microRNAs (miRNAs) between cells, and possess immunoregulatory properties. However, their role in immune-mediated diseases remains to be elucidated. We hypothesized a role for EVs in the rheumatoid arthritis (RA) joint, potentially involving the development of T cell exhaustion and transfer of the co-inhibitory receptor programmed death 1 (PD-1).

Methods

Synovial fluid mononuclear cells (SFMCs) and peripheral blood mononuclear cells (PBMCs) from RA patients were investigated for PD-1 and other markers of T cell inhibition. EVs were isolated from RA plasma and synovial fluid. In addition, healthy control (HC) and RA PBMCs and SFMCs were cultured to produce EVs. These were isolated and investigated by immunogold electron microscopy (EM) and also co-cultured with lymphocytes and PD-1 negative cells to investigate their functions. Finally, the miRNA expression profiles were assessed in EVs isolated from RA and HC cell cultures.

Results

Cells from the RA joint expressed several T cell co-inhibitory receptors, including PD-1, TIM-3, and Tigit. ELISA demonstrated the presence of PD-1 in EVs from RA plasma and synovial fluid. Immunogold EM visualized PD-1 expression by EVs. Co-culturing lymphocytes and the PD-1 negative cell line, U937 with EVs resulted in an induction of PD-1 on these cells. Moreover, EVs from RA PBMCs increased proliferation in lymphocytes when co-cultured with these. All EVs contained miRNAs associated with PD-1 and other markers of T cell inhibition and the content was significantly lower in EVs from RA PBMCs than HC PBMCs. Stimulation of the cells increased the miRNA expression. However, EVs isolated from stimulated RA SFMCs did not change their miRNA expression profile to the same extend.

Conclusion

EVs carrying both the PD-1 receptor and miRNAs associated with T cell inhibition were present in RA cell cultures. Upon stimulation, these miRNAs failed to be upregulated in EVs from RA SFMCs. This was in line with increased expression of T cell co-inhibitory markers on SFMCs. In conclusion, we suggest EVs to play a significant role in the RA microenvironment, potentially favoring the progression of T cell exhaustion.

Elevated Expression of Immunoreceptor Tyrosine-Based Inhibitory Motif (TIGIT) on T Lymphocytes is Correlated with Disease Activity in Rheumatoid Arthritis

Background

It is well known that lymphocytes play an important role in rheumatoid arthritis (RA). T cell immunoreceptors with immunoglobulin (Ig) and immunoreceptor tyrosine-based inhibitory motif (TIGIT) have immunosuppressive co-stimulatory molecules that mediate inhibitory effects, but their roles in RA are poorly understood.

Material/Methods

Were recruited 76 patients with RA and 33 healthy controls (HC). Clinical manifestations, laboratory measurements, physical examination, and medical history of RA patients were recorded. The expression of TIGIT on CD3⁺ T lymphocytes, B lymphocytes, monocytes, neutrophils, CD3⁺CD4⁺ T lymphocytes, and CD3⁺CD8⁺ T lymphocytes was determined using flow cytometry. The expression of TIGIT on T lymphocytes in patients with RA was further analyzed to investigate its correlations with markers of autoimmune response, inflammation, and disease activity in RA.

Results

Compared with HC, the expression levels of TIGIT on CD3⁺CD4⁺ T lymphocytes and CD3⁺CD8⁺ T lymphocytes were significantly increased in patients with RA (P < 0.01). The frequency of TIGIT-expressing CD3⁺CD4⁺ T lymphocytes was positively correlated with RF, increased ACPA, ESR, and CRP levels. The frequency of TIGIT-expressing CD3⁺CD8⁺ T lymphocytes was positively correlated with RF and ESR levels. Furthermore, the expression level of TIGIT on CD3⁺CD4⁺ T lymphocytes was positively correlated with the DAS28 score in RA.

Conclusions

The expression levels of TIGIT on T lymphocytes were elevated and correlated with disease activity in RA.

The function of myeloid dendritic cells in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease that causes joint pain, inflammation, and loss of function. Disease pathogenesis involves activation and proliferation of autoreactive pro-inflammatory effector T cells. While the details of RA onset and progression remain controversial, dendritic cell (DC) numbers dramatically increase in the synovial joint tissues of RA patients. Based on their key functions as antigen-presenting cells and inducers of T cell differentiation, DCs may play an important role in the initiation of joint inflammation. Myeloid DC contributions are likely central to the development of RA, as they are more efficient at antigen presentation in comparison with their closely related cousins, plasmacytoid DCs. Synovial fluid in the joints of RA patients is enriched with pro-inflammatory cytokines and chemokines, which may stimulate or result from DC activation. Epidemiological evidence indicates that smoking and periodontal infection are major environmental risk factors for RA development. In this review, factors in the synovial environment that contribute to altered myeloid DC functions in RA and the effects of environmental risk factors on myeloid DCs are described.

Endogenous programmed death ligand-1 restrains the development and onset of Sjӧgren's syndrome in non-obese diabetic mice

Programmed death-ligand 1 (PD-L1) down-modulates various immune responses by engaging the co-inhibitory receptor programmed death-1. Expression of PD-L1 and programmed death-1 is elevated in the salivary glands of patients with Sjögren’s syndrome (SS). The objective of this study is to define the role of endogenous PD-L1 in SS pathogenesis in non-obese diabetic (NOD) mouse model of this disease. We inhibited endogenous PD-L1 function by intraperitoneal administration of a blocking antibody to 6 week-old female NOD/ShiLtJ mice repeatedly during a 9-day period. PD-L1 blockade accelerated leukocyte infiltration and caspase-3 activation in the submandibular gland (SMG), production of antinuclear and anti-M3 muscarinic acetylcholine receptor (M3R) autoantibodies and impairment of saliva secretion, indicative of accelerated development and onset of SS. The effect of PD-L1 blockade was associated with increased T- and B cells and T helper 1 cytokine IFN-γ in the SMG. Local administration of exogenous IFN-γ to the SMG led to impaired salivary secretion accompanied by down-regulation of aquaporin 5 and an increase in anti-M3R autoantibodies. Conversely, neutralization of IFN-γ markedly improved salivary secretion and aquaporin 5 expression in anti-PD-L1-treated NOD/ShiLtJ mice. Hence, endogenous PD-L1 hinders the development and onset of SS in NOD mice, in part by suppressing IFN-γ production.

Soluble PD-1 aggravates progression of collagen-induced arthritis through Th1 and Th17 pathways

INTRODUCTION

The programmed cell death 1 (PD-1) protein is a critical regulator of T-cell activation and is also an important therapeutic target for autoimmune diseases. Little is known about the regulation and functional properties of the soluble PD-1 (sPD-1) variant. The aim of this study was to examine the role of sPD-1 in the regulation of human and murine rheumatoid arthritis (RA).

METHODS

Expression of cytokines and sPD-1 in sera, synovial fluid, and peripheral blood (PB) mononuclear cells of patients with RA were analyzed by enzyme-linked immunosorbent assay and quantitative polymerase chain reaction. PD-1 function was assessed in PB T cells after stimulation of the cells with anti-CD3 and PD-L1-Fc to crosslink PD-1. Recombinant PD-1-Fc was injected intraperitoneally into DBA/1 mice with collagen-induced arthritis (CIA) to analyze the function of sPD-1 in vivo.

RESULTS

High concentrations of sPD-1 were found in sera and synovial fluid of patients with RA. The levels of serum sPD-1 were significantly correlated with titers of rheumatoid factor (RF) (r = 0.306, p = 0.005) and 28-joint Disease Activity Score (r = 0.545, p < 0.001). Further characterization of sPD-1 revealed that it functionally blocked the inhibitory effect of membrane-bound PD-1 on T-cell activation. Interferon γ, tumor necrosis factor α, and interleukin 17A were identified as inducers of sPD-1 in vitro. Moreover, PD-1-Fc enhanced proinflammatory cytokine expression, generation of Th1 cells and Th17 cells, and joint pathology in a CIA model.

CONCLUSIONS

sPD-1 regulates peripheral T-cell responses in both human and murine RA. Thus, sPD-1 may represent an additional biomarker or target in immunomodulatory therapy for RA.