Aberrant production of soluble inducible T-cell co-stimulator (sICOS) and soluble programmed cell death protein 1 (sPD-1) in patients with chronic hepatitis C

Soluble Programmed Cell Death 1 Protein Is a Promising Biomarker to Predict Severe Liver Inflammation in Chronic Hepatitis B Patients

Background and Aims: Liver inflammation is important in guiding the initiation of antiviral treatment and affects the progression of chronic hepatitis B(CHB). The soluble programmed cell death 1 protein (sPD-1) was upregulated in inflammatory and infectious diseases and correlated with disease severity. We aimed to investigate the correlation between serum sPD-1 levels and liver inflammation in CHB patients and their role in indicating liver inflammation. Methods: 241 CHB patients who underwent liver biopsy were enrolled. The correlation between sPD-1 levels and the degree of liver inflammation was analyzed. Univariate and multivariate logistic regression analyses were performed to analyze independent variables of severe liver inflammation. Binary logistic regression analysis was conducted to construct a predictive model for severe liver inflammation, and the receiver operating characteristic curve (ROC) was used to evaluate the diagnostic accuracy of the predictive model. Results: sPD-1 was highest in CHB patients with severe liver inflammation, which was higher than that in CHB patients with mild or moderate liver inflammation (P < 0.001). Besides, sPD-1 was weakly correlated with AST (r = 0.278, P < 0.001). Multivariable analysis showed that sPD-1 was an independent predictor of severe liver inflammation. The predictive model containing sPD-1 had areas under the ROC (AUROCs) of 0.917 and 0.921 in predicting severe liver inflammation in CHB patients and CHB patients with ALT ≤ 1× upper limit of normal (ULN), respectively. Conclusions: Serum sPD-1 level is associated with liver inflammation in CHB patients, and high levels of sPD-1 reflect severe liver inflammation. Serum sPD-1 is an independent predictor of severe liver inflammation and shows improved diagnostic accuracy when combined with other clinical indicators.

T-Cell Exhaustion in HIV-1/Hepatitis C Virus Coinfection Is Reduced After Successful Treatment of Chronic Hepatitis C

Background

T-cell responses during chronic viral infections become exhausted, which is reflected by upregulation of inhibitory receptors (iRs) and increased interleukin 10 (IL-10). We assessed 2 iRs-PD-1 (programmed cell death protein 1) and Tim-3 (T-cell immunoglobulin and mucin domain-containing protein 3)-and IL-10 mRNAs in peripheral blood mononuclear cells (PBMCs) and their soluble analogs (sPD-1, sTim-3, and IL-10) in plasma in chronic HIV-1/hepatitis C virus (HCV) coinfection and explored the effect of HCV treatment on these markers. We also aimed to establish whether iR expression may be determined by the HCV CD8+ T-cell immunodominant epitope sequence.

Methods

Plasma and PBMCs from 31 persons with chronic HIV-1/HCV coinfection from the Swiss HIV Cohort Study were collected before and after HCV treatment. As controls, 45 persons who were HIV-1 negative with chronic HCV infection were recruited. Exhaustion markers were assessed by enzyme-linked immunosorbent assay in plasma and by quantitative reverse transcription polymerase chain reaction in PBMCs. Analysis of an HCV epitope sequence was conducted by next-generation sequencing: HLA-A*02-restricted NS31073-1081 and NS31406-1415 and HLA-A*01-restricted NS31436-1444.

Results

The study revealed higher plasma sPD-1 (P = .0235) and IL-10 (P = .002) levels and higher IL-10 mRNA in PBMCs (P = .0149) in HIV-1/HCV coinfection. A decrease in plasma sPD-1 (P = .0006), sTim-3 (P = .0136), and IL-10 (P = .0003) and Tim-3 mRNA in PBMCs (P = .0210) was observed following successful HCV treatment. Infection with the HLA-A*01-restricted NS31436-1444 ATDALMTGY prototype variant was related to higher sTim-3 levels than infection with the ATDALMTGF escape variant (P = .0326).

Conclusions

The results underscore the synergistic effect of coinfection on expression of exhaustion markers, their reduction following successful HCV treatment and imply that iR levels may operate on an epitope-specific manner.

Soluble (PD-1) and Autophagy protein (ATG-5) in patients with tuberculosis

mmune checkpoints such as programmed cell death protein (PD-1) and autophagy-related protein 5 (ATG5) can directly affect the immune response and thus, interfere with infection with Mycobacterium tuberculosis (Mtb). This study aimed to determine the role of soluble ATG5 and soluble PD-1 proteins in tuberculosis (TB) patients. The study included a collection of 90 blood samples (47 samples from patients with confirmed tuberculosis and 43 samples from age and gender-matched healthy subjects to estimate the concentration of soluble autophagy (ATG-5) and programmed cell death protein (PD-1). Enzyme-linked immunosorbent assay was used to estimate the serum levels of these markers. The median value of ATG5 level in patients was 2.08 µg/ml, which is higher than the level of the control group (median = 0.93 µg/ml) with a highly significant difference. Similarly, the median value of PD-1 level in patients was 259.4 ng/ml (range 107.76-924.25 ng/ml), which was higher than that of the control (median = 146.4 ng/ml, range = 50.32-1117.1 ng/ml) and with a highly significant difference. It can be concluded that both soluble ATG5 and PD-1 increased significantly in patients with TB compared with controls. Keywords: tuberculosis, M. tuberculosis, Autophagy, Programmed cell death protein-1

Serum soluble programmed cell death 1 levels predict spontaneous functional cure in inactive carriers with chronic hepatitis B

BACKGROUND

Hepatitis B surface antigen (HBsAg) seroclearance is the most important milestone indicating favourable clinical outcomes in patients with chronic hepatitis B (CHB). However, it is difficult to achieve due to the impaired HBV-specific immunity, such as programmed cell death 1 (PD-1)-associated T cell exhaustion. We assessed soluble PD-1 (sPD-1) as a novel seromarker for predicting spontaneous HBsAg loss.

METHODS

Serial serum levels of sPD-1 were evaluated in 1046 untreated hepatitis B e antigen (HBeAg)-seronegative individuals who had achieved undetectable serum HBV DNA. Multiple regression analyses were applied to assess associations among baseline and subsequent sPD-1 levels, HBsAg decline during follow-up, and spontaneous HBsAg seroclearance.

RESULTS

A total of 390 individuals achieved spontaneous HBsAg seroclearance during 6464.4 person-years of follow-up. Baseline sPD-1 levels were inversely associated with baseline HBsAg levels (qHBsAg) as well as a greater decline in qHBsAg during follow-up. Incidence rates of HBsAg seroclearance were 11.5, 61.7, 96.7 and 151.0 per 1000 person-years for sPD-1 levels of ≥4000, 536-3999, 125-535 and <125 pg/mL, respectively (P_trend  < 0.0001). Compared with baseline sPD-1 levels ≥4000 pg/mL, the rate ratio (95% CI) of HBsAg seroclearance was 2.1 (1.1-3.9), 3.0 (1.6-5.5) and 5.1 (2.8-9.5), for baseline sPD-1 levels of 536-3999, 125-535 and <125 pg/mL, respectively, after adjustment for sex, age and serum alanine aminotransferase and HBsAg levels.

CONCLUSION

sPD-1 level is a novel marker which independently predicts spontaneous HBsAg seroclearance of HBeAg-negative inactive CHB patients with undetectable HBV DNA. (word count: 234, <250).

Inducible T-cell co-stimulator (ICOS) and ICOS ligand are novel players in the multiple-myeloma microenvironment

The inducible T-cell co-stimulator (ICOS) is a T-cell receptor that, once bound to ICOS ligand (ICOSL) expressed on several cell types including the B-cell lineage, plays a decisive role in adaptive immunity by regulating the interplay between B and T cells. In addition to its immunomodulatory functions, we have shown that ICOS/ICOSL signalling can inhibit the activity of osteoclasts, unveiling a novel mechanism of lymphocyte-bone cells interactions. ICOS and ICOSL can also be found as soluble forms, namely sICOS and sICOSL. Here we show that: (i) levels of sICOS and sICOSL are increased in multiple myeloma (MM) compared to monoclonal gammopathy of undetermined significance and smouldering MM; (ii) levels of sICOS and sICOSL variably correlate with several markers of tumour burden; and (iii) sICOS levels tend to be higher in Durie-Salmon stage II/III versus stage I MM and correlate with overall survival as an independent variable. Moreover, surface ICOS and ICOSL are expressed in both myeloma cells and normal plasma cells, where they probably regulate different functional stages. Finally, ICOSL triggering inhibits the migration of myeloma cell lines in vitro and the growth of ICOSL⁺ MOPC-21 myeloma cells in vivo. These results suggest that ICOS and ICOSL represent novel markers and therapeutic targets for MM.

Circulating levels of sPD-1 and PD-1 genetic variants are associated with hepatitis B infection and related liver disease progression

BACKGROUND

Programmed cell death-1 (PD-1) variants and circulating levels of soluble PD-1 are associated with susceptibility to malignant and infectious disease. This study aimed to examine the association of PD-1.5 and PD-1.9 variants, and plasma sPD-1 levels with HBV infection and disease progression.

METHODS

The study cohort consists of HBV-infected adults (n=513) stratified by clinical course, including chronic hepatitis B (CHB, n=173), liver cirrhosis (LC, n=134), hepatocellular carcinoma (HCC, n=206), and matched healthy controls (HC, n=196). The PD-1.5 (rs2227981 C/T) and PD-1.9 (rs2227982 C/T) genetic variants were genotyped by Sanger sequencing, and plasma sPD-1 levels were quantified by enzyme immunoassay.

RESULTS

The plasma sPD-1 levels were significantly high among HBV patients. The highest plasma sPD-1 levels were observed in CHB patients, followed by the LC and HCC groups. In addition, the plasma sPD-1 levels correlated positively with liver inflammation (aspartate transaminase, AST: rho=0.57, P<0.0001 and alanine aminotransferase, ALT: rho=0.57, P<0.0001) and were positively correlated with liver fibrosis (AST to Platelet Ratio Index, APRI score: rho=0.53, P<0.0001). The PD-1.9 TT genotype was less frequent in CHB patients compared to LC, HCC and HCC+LC patients in both codominant and recessive models (P<0.01) and was found to be a risk factor for HCC predisposition [HCC vs. non-HCC: OR=2.0 (95% CI: 1.13-3.7), P_adj=0.017]. The PD-1.5 CT genotype was associated with a reduced risk of acquiring HCC [OR=0.6 (95%CI: 0.4-0.9), P_adj=0.031].

CONCLUSION

Our study concludes that sPD-1 levels are associated with liver inflammation and progression of liver fibrosis and the PD-1.5 and PD-1.9 variants are associated with HBV infection and progression of liver disease.

Orthogonal quantification of soluble inducible T-cell costimulator (ICOS) in healthy and diseased human serum

Inducible T-cell costimulator (ICOS), a homodimeric protein expressed on the surface of activated T-cells, is being investigated as a potential therapeutic target to treat various cancers. Recent studies have reported aberrant increases in the soluble form of ICOS (sICOS) in human serum in disease-state patients, primarily using commercial ELISA kits. However, results from our in-house immunoassay did not show these aberrant increases, leading us to speculate that commercial sICOS ELISAs may be prone to interference. We directly tested that hypothesis and found that one widely used commercial kit yields false-positives and is prone to human anti-mouse antibody interference. We then analyzed a panel of healthy, cancer, chronic hepatitis C virus, systemic lupus erythematosus, and diffuse cutaneous systemic sclerosis human serum using our in-house immunoassay and reported the measured sICOS concentrations in these populations. Since even well characterized immunoassay methods are prone to non-specific interference, we also developed a novel sICOS LC-MS/MS method to confirm the results. Using these orthogonal approaches, we show that sICOS is a low abundance soluble protein that cannot be measured above approximately 20 pg/mL in human serum.

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Soluble ICOS is a low-abundance protein that is not detectable above approximately 20 pg/mL in human serum.

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Commercial soluble ICOS kits may be prone to HAMA interference and thus false-positives.

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Off-the-shelf assay kits should be well characterized in order to minimize non-specific interferences.

Serum-soluble PD-L1 may be a potential diagnostic biomarker in sepsis

To investigate whether serum-soluble PD-L1 (sPD-L1) is a potential biomarker for identifying sepsis. This study enrolled 64 septic patients, 29 patients with acute appendicitis, 33 patients with acute pancreatitis and 30 healthy volunteers. Sepsis was defined according to the Sepsis 3.0 criteria.[1] The associated clinical parameters were recorded, blood samples were collected on the first day of diagnosis, and serum sPD-L1 levels were measured using enzyme-linked immunosorbent assays. Compared with the control group, a significant increase in sPD-L1 levels was observed in patients with sepsis (n = 64). Increased sPD-L1 expression correlated strongly with increased clinical inflammatory values (CRP, PCT and WBC) and decreased immunological functional parameters (CD3⁺ , CD4⁺ and CD8⁺ cell counts). The area under the ROC curve (AUC) for sPD-L1 in combination with the sequential organ failure assessment (SOFA) score was superior to the AUC for either sPD-L1 or SOFA score in regard to the diagnosis of sepsis. sPD-L1 may represent a valuable biomarker for the diagnosis of sepsis.

LncRNA XLOC_003810 promotes T cell activation and inhibits PD-1/PD-L1 expression in patients with myasthenia gravis-related thymoma

This study aimed to investigate the effect of long non-coding RNA XLOC_003810 on the activation of CD4⁺ T cells and expression of PD-1/PD-L1 in patients with myasthenia gravis-related thymoma (MG-T). Thymus specimens and thymic mononuclear cells were obtained from MG and MG-T patients or cardiac surgery patients undergoing thoracotomy who were selected as negative controls (NC). XLOC_003810 expression was examined using quantitative real-time PCR (qRT-PCR). Frequency of CD4⁺ T cells and proportion of CD4⁺ PD-1⁺ T cells and CD14⁺ PD-L1⁺ monocytes were quantified by flow cytometry. The release of inflammatory cytokines was measured by qRT-PCR and enzyme-linked immunosorbent assay. Compared with the NC group, expression of XLOC_003810, frequency of CD4⁺ T cells and the production of inflammatory cytokines were increased in patients with MG and MG-T. XLOC_003810 overexpression significantly increased the frequency of CD4⁺ T cells, facilitated the production of inflammatory cytokines and decreased the proportion of CD4⁺ PD-1⁺ T cells and CD14⁺ PD-L1⁺ monocytes in the thymic mononuclear cells. In contrast, XLOC_003810 knockdown exerted the opposite effect. Together, XLOC_003810 promotes T cell activation and inhibits PD-1/PD-L1 pathway in patients with MG-T.

Clinical significance of circulating soluble immune checkpoint proteins in sorafenib-treated patients with advanced hepatocellular carcinoma

In hepatocellular carcinoma (HCC), the clinical significance of soluble immune checkpoint protein levels as predictors of patient outcomes or therapeutic responses has yet to be defined. This study profiled the baseline levels of sixteen soluble checkpoint proteins and their changes following sorafenib treatment for HCC. Plasma samples were obtained from 53 patients with advanced HCC at baseline, week 1, 2 and 4 of sorafenib treatment and tested the concentrations of 16 soluble checkpoint proteins using multiplexed fluorescent bead-based immunoassays. Multivariate analysis showed high sBTLA levels at baseline were an independent predictor of poor overall survival (p = 0.038). BTLA was highly expressed in T cells and macrophages in peritumoral areas. At week 2, sCD27 levels were decreased compared to baseline. By contrast, the concentrations of most inhibitory proteins, including sBTLA, sLAG-3, sCTLA-4, sPD-1, sCD80, sCD86 and sPD-L1, had significantly increased. The fold-changes of soluble checkpoint receptors and their ligands, including sCTLA-4 with sCD80/sCD86, sPD-1 with sPD-L1; and the fold-changes of sCTLA-4 with sBTLA or sPD-1 were positively correlated. sBTLA may be a good biomarker for predicting overall survival in HCC patients. Sorafenib treatment in patients with advanced HCC revealed dynamic changes of soluble checkpoint protein levels.

Programmed death ligand 2 - A link between inflammation and bone loss in rheumatoid arthritis

Objective

Active rheumatoid arthritis (RA) is accompanied by increased appendicular and axial bone loss, closely associated to the degree of inflammation. The programmed death-1 (PD-1) pathway is important for maintaining peripheral tolerance, and its ligand PD-L2 has recently been associated with bone morphogenetic protein activity. Here, we report that PD-L2 plays a central role in RA osteoimmunology.

Methods

Femoral bone mineral density (BMD) and trabecular bone microstructure were evaluated by micro-CT in wild type (WT) and PD-L2^−/− mice. Osteoclasts were generated from RA synovial fluid mononuclear cells and peripheral blood monocytes. The effects of recombinant PD-L2, was evaluated by tartrate-resistant acid phosphatase (TRAP) activity and the development of bone erosions in the presence of anti-citrullinated protein antibodies (ACPA). Plasma soluble (s)PD-L2 levels were measured in patients with early (e)RA (n ​= ​103) treated with methotrexate alone or in combination with the TNF inhibitor Adalimumab.

Results

PD-L2^−/− mice had a decreased BMD and deteriorated trabecular bone microstructure that was not related to the RANKL/OPG pathway. PD-L2 decreased TRAP activity in osteoclasts and decreased ACPA-induced erosions. In the RA synovial membrane PD-L2 was highly expressed especially in the lining layer and plasma sPD-L2 levels were increased in eRA patients and decreased with treatment. One-year sPD-L2 correlated inversely with erosive progression two years after treatment initiation with methotrexate and placebo.

Conclusion

PD-L2 regulates bone homeostasis in RA. Our findings provide new insight into the relationship between the immune system and bone homeostasis, and suggest a potential therapeutic target for limiting inflammatory bone loss in RA.

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PD-L2 is closely related to bone homeostasis in a mouse model.

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PD-L2 inhibits osteoclastogenesis and osteoclast activation in vitro.

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PD-L2 is highly expressed by cells in the synovial membrane of rheumatoid arthritis.

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PD-L2 is associated with less radiographic progression in patients with early rheumatoid arthritis.

Soluble immune checkpoints in cancer: production, function and biological significance

Immune checkpoints play important roles in immune regulation, and blocking immune checkpoints on the cell membrane is a promising strategy in the treatment of cancer. Based on this, monoclonal antibodies are having much rapid development, such as those against CTLA-4 (cytotoxic T lymphocyte antigen 4) and PD-1 (programmed cell death protein 1).But the cost of preparation of monoclonal antibodies is too high and the therapeutic effect is still under restrictions. Recently, a series of soluble immune checkpoints have been found such as sCTLA-4 (soluble CTLA-4) and sPD-1 (soluble PD-1). They are functional parts of membrane immune checkpoints produced in different ways and can be secreted by immune cells. Moreover, these soluble checkpoints can diffuse in the serum. Much evidence has demonstrated that these soluble checkpoints are involved in positive or negative immune regulation and that changes in their plasma levels affect the development, prognosis and treatment of cancer. Since they are endogenous molecules, they will not induce immunological rejection in human beings, which might make up for the deficiencies of monoclonal antibodies and enhance the utility value of these molecules. Therefore, there is an increasing need for investigating novel soluble checkpoints and their functions, and it is promising to develop relevant therapies in the future. In this review, we describe the production mechanisms and functions of various soluble immune checkpoint receptors and ligands and discuss their biological significance in regard to biomarkers, potential candidate drugs, therapeutic targets, and other topics.

Aberrant production of soluble inducible T cell co‑stimulator and soluble programmed cell death protein 1 in patients with chronic hepatitis B

Previous studies demonstrated that immune dysregulation is an important cause of hepatitis B virus (HBV)‑mediated liver damage. Co‑stimulators including programmed cell death protein 1 (PD‑1) and inducible T cell co‑stimulator (ICOS) are involved in the pathogenesis of HBV. In the present study, the serum levels of soluble (s)PD‑1 and sICOS in patients with chronic HBV infections, were investigated, and the association between sPD‑1 and sICOS levels and liver injury degree was investigated. Serum sPD‑1 and sICOS levels were increased in the HBV‑patient group particularly in the HBV external core antigen positive group. In the immune clearance group, sPD‑1 and sICOS were increased compared with the tolerance group. Furthermore, the relative mRNA expression levels were also increased in patients with HBV. However there was no correlation between sPD‑1 and sICOS levels and HBV antibodies or PD‑1/ICOS mRNA copies. The altered sPD‑1 and sICOS serum levels in the different HBV groups may reflect the dysregulation of T cell activation, and may be associated with the HBV pathological process.

Serum sPD-L1, Upregulated in Sepsis, May Reflect Disease Severity and Clinical Outcomes in Septic Patients

We aimed to find the correlation between serum sPD-L1 (soluble programmed cell death L-1 ligand) and sepsis. Totally 91 consecutive patients with sepsis were performed in a 15-bed medical intensive care unit (ICU) of the second affiliated hospital, Xi'an Jiaotong University in Xi'an, China, between February 2015 and May 2016. Healthy controls (HC) consisted of 29 healthy volunteer. Baseline demographic data were recorded. Blood samples were collected through an indwelling central venous or by peripheral venipuncture. Serum sPD-L1 and sPD-1 levels were determined with enzyme-linked immunosorbent assay kits (Elabscience Biotechnology Co. Ltd, Wuhan, China). SPSS19.0 software (SPSS Inc., Chicago, Illinois, USA) was used for statistical analysis. Kaplan-Meier survival analysis and Cox regression analysis were also performed. Serum sPD-L1 levels and sPD-1 levels were significantly increased in septic patients compared with HC (P = 0.000). Serum sPD-L1 levels were significantly increased in non-survivors compared with survivors (P < 0.05), but there was no statistically difference on serum sPD-1 levels between non-survivors and survivors (P > 0.05). Serum sPD-L1 levels were correlated with absolute lymphocyte (ALC), platelets and SOFA scores. Serum sPD-L1/sPD-1 levels were negatively correlated with ALC and platelets, and SOFA scores. The prognostic accuracy of the sPD-L1 level to predict 28-day mortality was similar to that of the APACHE-II scores and SOFA scores. Cox regression analysis showed that sPD-L1 was an independent prognostic factor. Serum sPD-L1 is upregulated in sepsis and may reflect disease severity and clinical outcomes in patients. Serum sPD-L1 may be an independent prognostic factor for sepsis.

Role of soluble programmed death-1 (sPD-1) and sPD-ligand 1 in patients with cystic echinococcosis

The programmed death-1 (PD-1)/PD-ligand 1 (PD-L1) signaling pathway is a negative regulatory mechanism that inhibits T cell proliferation and cytokine production. Soluble PD-1 (sPD-1) and soluble PD-L1 (sPD-L1), are also involved in regulation of the PD-1/PD-L1 signaling pathway. In the present study, the expression levels of sPD-1 and sPD-L1, as well as those of T helper (Th)1 [including interleukin (IL)-2 and interferon gamma], Th2 (including IL-4, IL-6 and IL-10) and Th17 (including interleukin 17) cell cytokines, were measured in the sera of patients with cystic echinococcosis (CE). Measurements were performed prior to and following after surgery and treatment with cyclic albendazole to investigate the effects of sPD-1 and sPD-L1 in patients with CE. Cytokine expression levels were measured using cytokine bead array and the expression levels of sPD-1 and sPD-L1 were measured using ELISA. In addition, in vitro stimulation was used to detect whether sPD-L1 has a negative regulatory effect on cytokine secretion or homeostasis. The present study observed significantly higher levels of sPD-L1 in patients with CE compared with healthy controls. Significantly elevated levels of Th2 cytokines in the sera of patients with CE were also observed. The results also suggest that there is an imbalanced expression of Th1 and Th2 cells during CE. In addition, it was demonstrated that sPD-1 and sPD-L1 are regulatory factors to the PD-1/PD-L1 signaling pathway, each having opposite effect, suggesting that they regulate the immune response to CE infection by creating a dynamic balance. In conclusion, sPD-L1 may play an important role in maintaining homeostasis in hosts with CE.

The PD-1/PD-Ls pathway and autoimmune diseases

The programmed death (PD)-1/PD-1 ligands (PD-Ls) pathway, is a new member of the B7/CD28 family, and consists of the PD-1 receptor and its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273). Recently, it is reported that PD-1, PD-L1 and PD-L2 also have soluble forms aside from their membrane bound forms. The soluble forms increase the diversity and complexity of PD-1/PD-Ls pathway in both composition and function. The PD-1/PD-Ls pathway is broadly expressed and exerts a wider range of immunoregulatory roles in T-cell activation and tolerance compared with other B7/CD28 family members. Studies show that the PD-1/PD-Ls pathway regulates the induction and maintenance of peripheral tolerance and protects tissues from autoimmune attack in physiological conditions. In addition, it is also involved in various diseases mediated by T cells, such as autoimmunity, tumor immunity, chronic viral infections, and transplantation immunity. In this review, we will summarize the relevance of the soluble forms and the latest researches on the role of PD-1/PD-Ls pathway in autoimmune diseases.