B7-H1 expression is upregulated in peripheral blood CD14+ monocytes of patients with chronic hepatitis B virus infection, which correlates with higher serum IL-10 levels

Regulatory B Cells Dysregulated T Cell Function in an IL-35-Dependent Way in Patients With Chronic Hepatitis B

Interleukin (IL)-35-secreting B (IL-35+B) cells are critical regulators in autoimmune and infectious diseases and exert suppressive functions in parallel with IL-10-producing B (B10) cells. However, the role of IL-35+B cells in persistent hepatitis B virus (HBV) infection remains unclear. To elucidate the role of IL-35+B cells in the progress of chronic HBV infection, we determined the frequency of IL-35+B cells and their relationship with the classical human regulatory B cell (Breg) subsets, namely, CD19+CD24^hiCD38^hi and CD19+CD24^hiCD27+. Then, the regulatory effect and mechanism of Bregs on effector T cells were investigated in vitro. Here, we found that compared with healthy controls, the frequency of IL-35+B cells was increased in patients with chronic HBV infection and was enriched in human classical Breg subset CD19+CD24^hiCD38^hi B cells. Moderate correlation was observed between the frequency of IL-35+B cells and alanine aminotransferase levels (Spearman r = 0.401), but only mild correlation was noted between the frequency of IL-35+B cells and HBV DNA level (Spearman r = 0.314). The frequency of IL-35+B cells was negatively correlated with interferon-γ (IFN-γ)-producing CD4+ and CD8+ cells but positively correlated with IL-4-producing T cells. Bregs dysregulated T cell function through an IL-35-dependent mechanism and depended on cell-to-cell contact. In conclusion, IL-35+ B cell was enriched in CD19+CD24hiCD38hi B cell subset during persistent HBV infection and Breg cells exerted dysregulation in T cell function through IL-35 dependent mechanism and depend on cell-to-cell contact.

Expression of PD-1 and PD-Ls in Kaposi's sarcoma and regulation by oncogenic herpesvirus lytic reactivation

Kaposi's sarcoma-associated herpesvirus (KSHV) causes several cancers such as Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). PD-1/PD-Ls immune checkpoint molecules play important roles in cancer cell immune escape. The expression of PD-1/PD-Ls and their regulation by oncogenic viruses, in particular KSHV, remain largely undefined. Here we demonstrate strong PD-1/PD-L1/PD-L2 expression in KS tissues from a cohort of HIV + patients. We found that induction of KSHV lytic reactivation significantly upregulates PD-L1 expression on infected tumor cells, potentially through several major cellular signaling pathways and IL-1β, which may represent a novel mechanism for virus-associated tumor cell immune escape.

Kaposi's Sarcoma-Associated Herpesvirus Increases PD-L1 and Proinflammatory Cytokine Expression in Human Monocytes

Kaposi’s sarcoma-associated herpesvirus (KSHV) is associated with the human malignancy Kaposi’s sarcoma and the lymphoproliferative disorders primary effusion lymphoma and multicentric Castleman’s disease. KSHV establishes lytic infection of monocytes in vivo, which may represent an important cellular reservoir during KS disease progression. KS tumors consist of latently infected endothelial cells; however, lytic phase gene products are important for KS onset. Early KS lesion progression is driven by proinflammatory cytokines supplied by immune cell infiltrates including T cells and monocytes. KSHV-infected monocytes may supply the lytic viral products and the inflammatory milieu conducive to KS tumor progression. To establish successful infection, KSHV extensively modulates the host immune system. KSHV antigens activate both innate and adaptive immune responses including KSHV-specific T cells, but lifelong infection is still established. Programmed death ligand 1 (PD-L1) is a prosurvival cell surface protein that suppresses T-cell-mediated killing. PD-L1 is variably present on various tumor cells and is a targetable marker for cancer treatment. We show that KSHV infection of human monocytes increases PD-L1 expression and transcription in a dose-dependent manner. We also saw evidence of lytic gene expression in the KSHV-infected monocytes. Intact KSHV is needed for full PD-L1 response in human monocytes. KSHV induces a general proinflammatory cytokine milieu including interleukins 1α, 1β, and 6, which have been implicated in early KS lesion progression. KSHV-mediated PD-L1 increase may represent a novel mechanism of KSHV-mediated immune modulation to allow for virus survival and eventually malignant progression.

KSHV is the etiologic agent of Kaposi’s sarcoma and the lymphoproliferative disorders primary effusion lymphoma and multicentric Castleman’s disease. Programmed death ligand 1 (PD-L1) is an immunosuppressive cell surface marker that inhibits T cell activation. We report that KSHV infection of primary human monocytes upregulates PD-L1 transcription and protein expression. Analysis of the cytokine and chemokine milieu following KSHV infection of monocytes revealed that KSHV induces interleukins 1α, 1β, and 6, all of which have been implicated in KS development. Our work has identified another potential immune evasion strategy for KSHV and a potential target for immunotherapy of KSHV-derived disease.

The role of PD-L1 in the radiation response and prognosis for esophageal squamous cell carcinoma related to IL-6 and T-cell immunosuppression

The aim of this study was to assess the significance of programmed cell death 1 ligand 1 (PD-L1) in esophageal squamous cell carcinoma (ESCC) and its association with IL-6 and radiation response. Weretrospectively enrolled 162 patients with ESCC, and examined the correlation between PD-L1 levels and clinical outcomes in esophageal cancer patients. Furthermore, the human esophageal SCC cell line CE81T and TE2 were selected for cellular experiments to investigate the role of PD-L1 in T cell functions and radiation response. Here we demonstrated that PD-L1 expression was significantly higher in esophageal cancer specimens than in non-malignant epithelium. In clinical outcome analysis, this staining of PD-L1 was positively linked to the clinical T4 stage (p=0.004), development of LN metastasis (p=0.012) and higher loco-regional failure rate (p=0.0001). In addition, the frequency of PD-L1 immunoreactivity was significantly higher in IL-6-positive esophageal cancer specimens. When IL-6 signaling was inhibited in vitro, the level of PD-L1 is significantly down-regulated. PD-L1 is a significant predictor for poor treatment response and shorter survival.As demonstrated through in vitro experiments, Irradiation increased PD-L1 expression in human esophageal cancer cells. The inhibition of T cell functions including proliferation and cytotoxicity against tumor cells might be the mechanisms responsible to the role of PD-L1 in radiation response. In conclusion, PD-L1 is important in determining the radiation response and could predict the prognosis of patients with esophageal SCC. Therefore, we suggest inhibition of PD-L1 as a potential strategy for the treatment of esophageal SCC.

Immune checkpoint protein inhibition for cancer: preclinical justification for CTLA-4 and PD-1 blockade and new combinations

Over the last two decades, our understanding of the molecular basis of immunity has revealed the complexity of regulatory pathways involved in immune responses to cancer. A significant body of data support the critical importance of immune checkpoints in the control of the adaptive immune response to malignancy, and suggest that inhibitors of those checkpoints might have significant utility in treating cancer. This has been borne out by the recent US Food and Drug Administration (FDA) approvals of two different antibodies, one against cytotoxic T-lymphocyte antigen-4 (CTLA-4) and one against programmed death-1 (PD-1). Here, we provide a comprehensive review of the literature regarding the preclinical justification for the use of CTLA-4 and PD-1 blockade as monotherapy, and as combination therapy in the treatment of cancer. The animal data strongly supported the use of these drugs in patients, and in many cases suggested strategies that directly led to successful registration trials. In contrast, many of the toxicities, and some of the unusual response patterns seen in patients with these drugs, were not predicted by the preclinical work that we cite, highlighting the importance of early-phase trials with patients to inform future drug development. In addition, we review herein the preclinical data surrounding emerging immune checkpoint proteins, including BTLA, VISTA, CD160, LAG3, TIM3, and CD244 as potential targets for inhibition. The current comprehensive review of the literature regarding CTLA-4 and PD-1, as well as a number of novel checkpoint proteins demonstrates a strong preclinical basis for the use of these antibodies singly and in combination to overcome checkpoint inhibition in the treatment of cancer. We also suggest that the use of these antibodies may augment the efficacy of other activating immune antibodies, cytokines, radiation, and adoptive cell therapy in human cancer.

Mesenchymal stem cells suppress T cells by inducing apoptosis and through PD-1/B7-H1 interactions

Mesenchymal stem cells (MSCs) exert a suppressive role toward T cells which has been widely studied in recent decades. However, the underlying mechanisms utilized by MSCs are still not fully elucidated. Herein, we performed traditional suppressive assays using co-cultured MSCs and conventional CD4(+)CD25(-) T cells (Tconv) with and without transwell systems. We showed that the expression of programmed cell death-1 receptor (PD-1) on activated Tconv was significantly elevated after they were exposed to MSCs. And we demonstrated that PD-1/B7-H1 pathway was involved in the suppression of MSCs on activated Tconv. Further analysis revealed that the up-regulation of PD-1 was related to an increasing apoptosis of activated Tconv. Finally, we demonstrated that the PD-1/B7-H1 pathway was not related to the elevated immunosuppressive cytokines including IL-10 and TGF-β1 which in turn played dispensable roles in the up-regulation of PD-1 on activated Tconv in MSC-Tconv co-culture systems.

Identification and characterization of bovine programmed death-ligand 2

Previous reports from this group have indicated that the immunoinhibitory programmed death (PD)-1 receptor and its ligand, PD-L1, are involved in the mechanism of immune evasion of bovine chronic infection. However, no functional analysis of bovine PD-L2 in cattle has been reported. Thus, in this study, the molecular function of bovine PD-L2 was analyzed in vitro. Recombinant PD-L2 (PD-L2-Ig), which comprises an extracellular domain of bovine PD-L2 fused to the Fc portion of rabbit IgG1, was prepared based on the cloned cDNA sequence for bovine PD-L2. Bovine PD-L2-Ig bound to bovine PD-1-expressing cells and addition of soluble bovine PD-1-Ig clearly inhibited the binding of PD-L2-Ig to membrane PD-1 in a dose-dependent manner. Cell proliferation and IFN-γ production were significantly enhanced in the presence of PD-L2-Ig in peripheral blood mononuclear cells (PBMCs) from cattle. Moreover, PD-L2-Ig significantly enhanced IFN-γ production from virus envelope peptides-stimulated PBMCs derived from bovine leukemia virus-infected cattle. Interestingly, PD-L2-Ig-induced IFN-γ production was further enhanced by treatment with anti-bovine PD-1 antibody. These data suggest potential applications of bovine PD-L2-Ig as a therapy for bovine diseases.

Programmed death ligand-1 over-expression correlates with malignancy and contributes to immune regulation in ovarian cancer

The programmed death-1 (PD-1) pathway is important in the maintenance of peripheral tolerance and homeostasis through suppression of T cell receptor signaling. As such, it is employed by many tumors as a means of immune escape. We have investigated the role of this pathway in human ovarian cancer (OC) to assess its potential role as a diagnostic and/or prognostic marker and therapeutic target, following recent clinical trial success of antibody therapy directed at this pathway. We show programmed death ligand-1 (PD-L1) expression on monocytes in the ascites and blood of patients with malignant OC is strikingly higher than those with benign/borderline disease, with no overlap in the values between these groups. We characterize the regulation of this molecule and show a role of IL-10 present in ascitic fluid. Flow cytometric analysis of T cells present in the ascites and blood showed a correlation of PD-1 expression with malignant tumors versus benign/borderline, in a similar manner to PD-L1 expression on monocytes. Finally, we demonstrate functional links between PD-L1 expression on monocytes and OC tumor cells with suppression of T cell responses. Overall, we present data based on samples obtained from women with ovarian cancer, suggesting the PD-1 pathway may be used as a reliable diagnostic marker in OC, as well as a viable target for use with PD-1/PD-L1-directed antibody immunotherapy.

Regulation of B7-H1 expression on peripheral monocytes and IFN-γ secretion in T lymphocytes by HBeAg

This study is to observe the expression of B7-H1, PD-1 and TLR2 on peripheral blood monocytes (PBMCs) regulated by HBeAg in chronic hepatitis B (CHB), and to illustrate the relation between HBeAg and persistent infection of HBV. In both CHB patients and healthy controls, the expression of B7-H7 was significantly increased on CD14(+) monocytes incubated with HBeAg, while that of TLR2 was significantly reduced; the expression of specific IFN-γ was significantly decreased in CD3(+)CD4(+) T lymphocytes incubated with HBeAg, while IL-6 and IL-10 in conditioned media were significantly increased. HBeAg is able to significantly up-regulate B7-H1, down-regulate TLR2 on monocytes, reduce IFN-γ produced by T lymphocytes and increase Th2-type cytokines secretion. These findings suggest that HBeAg suppresses the specific cellular immunity to clear the virus, and eventually lead to immune tolerance to HBV infection. Therefore, HBeAg plays an important role in immune suppression in chronic HBV patients.

Study of human B7 homolog 1 expression in patients with hepatitis B virus infection

AIM: To further investigate the role of human B7 homolog 1 (B7-H1) in the mechanism of persistent hepatitis B virus (HBV) infection.

METHODS: Peripheral and intra-hepatic B7-H1 expression were compared by flow cytometry and immunochemical staining between two 2 distinct groups, one being chronic HBV tolerance patients (CHB-T) and the other being acute hepatitis B patients (AHB). B7-H1 mRNA expression level was also compared by real time polymerase chain reaction between CHB-T and AHB patients. The location of intra-hepatic B7-H1 and CD40 expression were analyzed by immunofluorescence. The levels of B7-H1 and CD40 expression on cultured myeloid dendritic cells (mDCs) with or without hepatitis B surface antigen (HBsAg) treatment were analyzed dynamically by flow cytometry. Intracellular interferon-γ (IFN-γ) staining and the stimulatory capacity of mDC of cultured mDC with or without HBsAg treatment were also compared by flow cytometry.

RESULTS: Peripheral B7-H1 expression on mDCs was increased significantly in AHB compared to CHB-T patients (P < 0.05). In the liver tissues from CHB-T patients, B7-H1 positive cells were almost absent despite a persistently elevated serum HBsAg load. In contrast, there were indeed increased B7-H1-positive cells in situ in the liver tissue from AHB. In vitro analysis showed the parallel upregulation of B7-H1 and CD40 on CD11c+ mDCs after the onset of stimulation. Addition of recombinant hepatitis B surface antigen (rHBsAg) significantly decreased CD40 expression (P < 0.05 at 16 h, 20 h and 24 h time points). B7-H1 expression was also inhibited by rHBsAg, and the inhibition rate of CD40 was greater than that of B7-H1. This preferential inhibition of CD40 expression on mDCs by rHBsAg resulted in the dysfunction of mDCs and T cells in the mixed leucocyte reaction (MLR) system. With rHBsAg pretreatment, in a carboxyfluorescein diacetate succinimidyl ester (CFSE) labeled MLR system at a ratio of 1:5 responder cell-stimulator cell (R/S), the CFSE^dim percentage of T cells decreased from 85.1% to 25.4% and decreased from 30.3% to 12.0% at 1:10 R/S. IFN-γ production by CD8+ T cells, in the MLR system, was reduced significantly by HBsAg pretreatment. At ratios of 1:5 R/S, the percentage of IFN-γ and CD8 dual positive T cells decreased from 55.2% ± 5.3% to 15.1% ± 3.1% (P < 0.001), and decreased from 35.0% ± 5.1% to 7.3% ± 2.7% at ratios of 1:10 R/S (P < 0.001).

CONCLUSION: B7-H1 is not a signature of immune dysfunction, but an inflammation marker. HBsAg regulate immune response by tipping the balance between B7-H1 and CD40.

Potential role of soluble B7-H3 in liver immunopathogenesis during chronic HBV infection

Immune-mediated mechanisms have been implicated in liver pathogenesis and subsequent progression in hepatitis B virus (HBV) infection. Costimulatory molecules, the important regulators of immune responses, participate in the regulation of liver pathology in HBV infection. However, the role of B7-H3 (CD276, a new member of B7 family) in this process has not been investigated. In this study, we detected abundant soluble B7-H3 (sB7-H3) in the plasma of patients with chronic HBV infections. The increase of the plasma B7-H3 was associated with the progression of liver cirrhosis and accompanied by decreased expression of B7-H3 on hepatocytes. The identification analysis suggests that the plasma B7-H3 might be derived from the membrane-bound B7-H3 on hepatocytes. A functional study showed that immobilized (4Ig) B7-H3Ig fusion protein could inhibit TCR-induced proliferation and IFN-γ secretion of T cells, which could be partially blocked by soluble B7-H3flag fusion protein. These results suggest that the reduced expression of B7-H3 in the livers might temper the inhibition of T-cell responses mediated by B7-H3 expressed on hepatocytes and thus promote the hepatic inflammation and hepatitis progression in the chronic HBV-infected patients.

Phagocytosis, a potential mechanism for myeloid-derived suppressor cell regulation of CD8+ T cell function mediated through programmed cell death-1 and programmed cell death-1 ligand interaction

CD8(+) T cells become exhausted, inducing cell surface protein programmed cell death-1 (PD-1) as chronic virus diseases or tumors progress, but underlying mechanisms of this are unclear. We previously showed that M-CSF is important for developing tolerogenic dendritic cells (DCs) from human CD14(+) monocytes. In this article, we identify M-CSF-derived DCs (M-DCs) after stimulation with IL-10 as myeloid-derived suppressor cells with additional tolerogenic activities to CD8(+) T cells. IL-10 increased PD-1 ligand expression on M-DC, and IL-10-stimulated M-DCs (M-DC/IL-10) induced expression of PD-1 on, and apoptosis of, CD8(+) T cells and phagocytosed CD8(+) T cells. Enhanced phagocytic activity of M-DC/IL-10 required IFN-γ, which further increased PD-1 ligand and PD-2 ligand expression on M-DC/IL-10. IFN-γ-stimulated M-DC/IL-10 cells were phenotypically macrophage-like cells with little or no expression of CD86, a costimulatory molecule, but with high expression levels of CD14, CD200R, and CD80. No phagocytic activity was detected with GM-CSF-derived DCs. We propose that phagocytosis by IFN-γ-stimulated M-DC/IL-10 cells, which may be DCs or, alternatively, a unique subset of macrophages, may be a mechanism by which IFN-γ-producing CD8(+) T cells are tolerized after type 1 immune responses to chronic virus or tumor, and that IFN-γ links effector CD8(+) T cells to their phagocytic clearance.

Kinetics of immune responses to hepatitis B virus infection

The pathogenesis of hepatitis B is mainly triggered by the host's cellular immune responses to hepatitis B virus (HBV) infection, and the immune responses against the virus depends on the interaction of various immune cells. Current research of immunity to hepatitis B infection mainly focuses on understanding the differences between patients who can control HBV infection and those with persistent infection. In this paper, we analyze how immunological events influence the development of innate and adaptive immunity needed to control HBV infection and explore the mechanisms by which high levels of viral antigens, CD4⁺ T cells, programmed death 1 (PD-1), the presence of regulatory T cells, and impaired dendritic cell functions maintain the HBV-specific immunological failure.

Immune checkpoint proteins: a new therapeutic paradigm for cancer--preclinical background: CTLA-4 and PD-1 blockade

Much of the recent excitement in the translational field of tumor immunology and immunotherapy has been generated by the recognition that immune checkpoint proteins can be blocked by human antibodies with profound effects in vitro, in animal tumor systems, and in patients. Promising clinical data have already been generated in melanoma and other tumor types with human antibodies directed against cytotoxic T lymphocyte antigen-4 (CTLA-4) and programmed death-1 (PD-1). The preclinical data that supported the clinical development of these two antibodies will be discussed in detail in this review, showing that many of the therapeutic effects of these two agents were predicted by the animal models, as were the immune-related side effects noted with these drugs. In contrast, much of the early work with anti-CTLA-4 antibodies indicated that it had a potent therapeutic effect only when combined with granulocyte-macrophage colony-stimulating factor (GM-CSF)-transduced tumor vaccines, and that the antibody alone was effective only in the most immunogenic tumor models in mice. Intriguingly, in patients, the drug alone clearly has had important therapeutic effects, but the addition of vaccines has not added to its clinical benefit. Murine experiments also suggested that CTLA-4 abrogation might function via important effects on natural T-regulatory cells that were CD4(+), CD25(+high), and FOXp3(+), but this has not been borne out in experiments using peripheral blood mononuclear cells from patients treated with anti-CTLA-4 antibodies, and unlike in animals, in humans the exact mechanism(s) by which CTLA-4 abrogation induced an anti-tumor effect is still unclear. Abrogation of PD-1 functions via different immune signaling pathways than CTLA-4 and is likely to have a different spectrum of effects than blocking CTLA-4. For PD-1 blockade, murine experiments have suggested that the antibody alone and combined with adoptive cell transfer or vaccine approaches would be therapeutically beneficial, and that clear effects on T-cell proliferation and activation, as well as T-regulatory cell function would be observed in patients. The clinical development of anti-PD-1 antibody so far has shown that it has a potent effect when administered alone, and trials of vaccines with anti-PD-1 are just being initiated to test the idea that the predicted effects of that antibody observed in animal systems also would be seen in patients. These observations support the idea that animal preclinical therapeutic experiments are an important guide to the conduct of trials employing abrogation of immune checkpoint proteins in T cells in patients. Nonetheless, clinical investigators must be flexible and prepared to find that the biology of those systems may be very different in humans compared to mice.

HBcAg induces interleukin-10 production, inhibiting HBcAg-specific Th17 responses in chronic hepatitis B patients

T-helper (Th) 17 cells have been shown to have an important role in host defense against viral infection. However, little is known about the regulation of Th17 cells in hepatitis B virus (HBV) infections. Peripheral blood mononuclear cells (PBMCs) isolated from patients with chronic hepatitis B (CHB) were stimulated with anti-interleukin (IL)-10 antibody or recombinant IL-10. The frequency of hepatitis B core antigen (HBcAg)-specific Th17 cells was characterized and produced cytokines were determined by flow cytometry. A low frequency of Th17 cells and a high frequency of Th1 cells were detected in CHB patients. HBcAg stimulation promoted IL-17A, IL-22, IL-23, IL-6, transforming growth factor (TGF)-β and IL-10 production by PBMCs from CHB patients, but not from healthy controls. Furthermore, endogenous IL-10 inhibited HBcAg-stimulated production of IL-17A, IL-22, IL-6 and IL-23, but not TGF-β. Treatment with IL-10 inhibited the HBcAg-stimulated activation of Th17 cells, whereas anti-IL-10 antibody significantly increased the frequency of Th17 and Th1 cells, but not that of CD4(+)CD25(+) regulatory T cells, associated with upregulating RORγt expression in CD4(+) T cells. HBcAg stimulated the production of IL-10, which negatively regulated HBcAg-specific Th17 cell responses in CHB patients. Our findings may represent one evasion strategy for HBV to subvert specific antiviral responses in humans.

Programmed death-1-induced interleukin-10 production by monocytes impairs CD4+ T cell activation during HIV infection

Viral replication and microbial translocation from the gut to the blood during HIV infection lead to hyperimmune activation, which contributes to the decline in CD4+ T cell numbers during HIV infection. Programmed death-1 (PD-1) and interleukin-10 (IL-10) are both upregulated during HIV infection. Blocking interactions between PD-1 and programmed death ligand-1 (PD-L1) and between IL-10 and IL-10 receptor (IL-10R) results in viral clearance and improves T cell function in animal models of chronic viral infections. Here we show that high amounts of microbial products and inflammatory cytokines in the plasma of HIV-infected subjects lead to upregulation of PD-1 expression on monocytes that correlates with high plasma concentrations of IL-10. Triggering of PD-1 expressed on monocytes by PD-L1 expressed on various cell types induced IL-10 production and led to reversible CD4+ T cell dysfunction. We describe a new function for PD-1 whereby microbial products inhibit T cell expansion and function by upregulating PD-1 levels and IL-10 production by monocytes after binding of PD-1 by PD-L1.

Intrahepatic PD-1/PD-L1 up-regulation closely correlates with inflammation and virus replication in patients with chronic HBV infection

Chronic hepatitis B was characterized by fluctuant immune response to infected hepatocytes resulting in hepatic inflammation and virus persistence. Recently, Programmed Death-1 (PD-1) and its ligand PD-L1 have been demonstrated to play an essential role in balancing antiviral immunity and inflammation in the livers of acute hepatitis B patients, significantly influencing disease outcome. PD-1 up-regulation in peripheral T cells is associated with immune dysfunction in chronic hepatitis B patients. However, the effect of PD-1/PD-L1 on hepatic damage and chronic infective status is still unknown in patients with chronic HBV infection. Here, we report up-regulation of PD-1 and PD-L1 in liver biopsies from 32 chronic HBV patients compared to 4 healthy donors. PD-1/PD-L1 up-regulation was significantly associated with hepatic inflammation and ALT elevation. Moreover, appropriate up-regulation but not overexpression of PD-L1 in the active phase of chronic hepatitis B as well as lower expression of PD-L1 in the inactive phase in liver residential antigen presenting cells (including Kupffer cells and sinusoidal endothelial cells) may contribute to viral inhibition. Our data suggest that the intrahepatic interaction of PD-1 and PD-L1 might play an important role in balancing the immune response to HBV and immune-mediated liver damage in chronic HBV infection.

Dendritic cells and chronic hepatitis B

The immune function disorders in patients with chronic hepatitis B (CHB) lead to persistent damage of their liver cells and have impact on the ability to clear the virus. Dendritic cells (DCs) are the most important antigen-presenting cells in body. They help to generate sufficient immune response by the invasion of pathogens. The quantity and functionality of DCs directly correlate with the normal function of the host's immune response. Not only can DCs be resistant to the virus, but also serve as vehicles for the virus to spread and escape immune injury. Therefore the research on DCs and improving their function under the state of CHB is quite significant.

Active systemic lupus erythematosus is associated with failure of antigen-presenting cells to express programmed death ligand-1

OBJECTIVE

Antigen-presenting cells (APC) play critical roles in establishing and maintaining peripheral tolerance. This is accomplished in part via expression of negative co-stimulatory molecules such as programmed death ligand-1 (PD-L1) on tolerogenic APC, such as immature myeloid dendritic cells (mDC). Several studies have strongly linked dysfunction of APC, including mDC, to the pathogenesis of SLE. The objective of this study was to determine whether APC expressed PD-L1 protein at normal levels during active lupus.

METHODS

Peripheral blood mononuclear cells (PBMC) were isolated from 19 paediatric patients with SLE and from 17 healthy age-matched controls. PBMC from both cohorts were cultured in the absence of exogenously added stimuli, and leucocyte PD-L1 expression was measured by flow cytometry.

RESULTS

Immature mDC and monocytes (Mo) from healthy children expressed little PD-L1 at initial isolation, but spontaneously up-regulated PD-L1 by 24 h. In contrast, both mDC and Mo from patients with active SLE failed to up-regulate PD-L1 over a 5 day time course, expressing this protein only during disease remissions.

CONCLUSIONS

These data are the first to link active lupus with reversibly decreased PD-L1 expression on professional APC, suggesting a novel mechanism for loss of peripheral tolerance in SLE.

PDL-1 upregulation on monocytes and T cells by HIV via type I interferon: restricted expression of type I interferon receptor by CCR5-expressing leukocytes

The programmed death (PD)-1 interacts with its ligand (PDL-1) delivering a negative signal to T cells. During human immunodeficiency virus (HIV)-1 infection PD-1 and PDL-1 expressions are increased. Here we show that monocytes and CCR5(+) T cells of HIV-uninfected donors upregulated PDL-1 upon in vitro exposure to HIV. HIV-induced PDL-1 required interferon (IFN)-alpha, but not IFN-gamma, production. Inhibition of endocytosis, required for HIV-induced IFN-alpha production, prevented PDL-1 upregulation. IFN-alpha-inducing Toll-like receptor (TLR) agonists increased PDL-1 on monocytes and CCR5(+) T cells. CD80 and CD86 were also increased on monocytes and CCR5(+) T cells after HIV exposure, but only CD80 was IFN-alpha-dependent. IFN-alpha-receptor subunit 2 (IFNAR2), was expressed only by CCR5(+) T cells and monocytes, explaining why these leukocytes responded to HIV-induced IFN-alpha. Finally, T cell proliferation was improved by PDL-1 blockade in HIV-treated PBMC. In the setting of HIV infection, IFN-alpha may negatively affect T cell responses by inducing PDL-1.

PD-L1 expression in umbilical cord blood monocytes of neonates born from chronic HBV-infected mothers

AIM: To detect PD-L1 expression in umbilical cord blood monocytes of neonates born from chronic HBV-infected mothers and to determine relationship between serum HBeAg and PD-L1 expression.

METHODS: Cord blood mononuclear cells (CBMC) were collected from umbilical cord of cesarean-delivered neonates born from 31 HBsAg-positive mothers and 10 healthy mothers. CBMC were stained with CD14-FITC and PD-L1-APC to detect the expression rate of PD-L1 using flow cytometry. Cord blood serum HBeAg was detected using microparticle enzyme immunoassay (MEIA).

RESULTS: There was no significant difference with PD-L1 expression in cord blood monocytes between neonates born from HBeAg-negative mothers and those born from healthy mothers. In three cases of chronic HBV carrier mothers with high HBeAg level, PD-L1 expression in cord blood monocytes was significantly higher than that of other groups (22.0 ± 1.6 vs 2.55 ± 3.1, 1.3 ± 1.2, 1.5 ± 0.8, all P = 0.00). Compared with the PD-L1 expression of low HBeAg levels, there were no significant difference between HBeAg-negative mother group and healthy mother group.

CONCLUSION: High HBeAg levels in umbilical cord blood may be related to up-regulation of PD-L1 in cord blood monocytes of neonates born from HBeAg-positive mothers. It might be related to neonatal persistent HBV infection.

Inhibitory B7-family molecules in the tumour microenvironment

The B7 family consists of activating and inhibitory co-stimulatory molecules that positively and negatively regulate immune responses. Recent studies have shown that human and rodent cancer cells, and stromal cells and immune cells in the cancer microenvironment upregulate expression of inhibitory B7 molecules and that these contribute to tumour immune evasion. In this Review, we focus on the roles of these B7 molecules in the dynamic interactions between tumours and the host immune system, including their expression, regulation and function in the tumour microenvironment. We also discuss novel therapeutic strategies that target these inhibitory B7 molecules and their signalling pathways to treat human cancer.

B7-H1 up-regulated expression in human pancreatic carcinoma tissue associates with tumor progression

PURPOSE

Aberrant tumor cell B7-H1 expression, a member of B7 family that can predominantly stimulate interleukin 10 (IL-10) products, contributed to the tumor immune evasion and tumor progression. This study was designed to investigate the expression of B7-H1 and IL-10 in normal pancreas tissues and pancreatic carcinoma samples, and to evaluate clinical significance of B7-H1 expression in pancreatic carcinoma.

METHODS

First, the B7-H1 and IL-10 expression in 40 pancreatic carcinoma samples and 8 healthy pancreas specimens using reverse transcription-PCR (RT-PCR) and western-blotting was detected. Localization of B7-H1 and IL-10 was confirmed by immunohistochemical (IHC) staining. Next, the association between B7-H1 expression and tumor differentiation and tumor stage was analyzed. Finally, the correlation between tumor-associated B7-H1 and IL-10 was evaluated.

RESULTS

Pancreatic carcinoma samples demonstrated the up-regulated expression of B7-H1 and IL-10 at mRNA and protein level compared with normal pancreas tissues. IHC staining revealed that B7-H1 and IL-10 was almost localized in tumor cells. Analysis of relationship between B7-H1 and tumor clinicopathological characteristics showed that B7-H1 expression was significantly associated with poor tumor differentiation (P < 0.01) and advanced tumor stage (P < 0.01). Meanwhile, tumor-associated B7-H1 expression was also correlated with IL-10 products (P < 0.01, R (2) = 0.6985, mRNA level; P < 0.01, R (2) = 0.7236, protein level) in tumor cells.

CONCLUSIONS

Our findings for the first time demonstrated up-regulated B7-H1 expression in human pancreatic carcinoma tissues, which might play a role in tumor progression and invasiveness. This expression seemed to be related to the ability of B7-H1 to promoting IL-10 secretion.

PD-1 and its ligands in tolerance and immunity

Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, deliver inhibitory signals that regulate the balance between T cell activation, tolerance, and immunopathology. Immune responses to foreign and self-antigens require specific and balanced responses to clear pathogens and tumors and yet maintain tolerance. Induction and maintenance of T cell tolerance requires PD-1, and its ligand PD-L1 on nonhematopoietic cells can limit effector T cell responses and protect tissues from immune-mediated tissue damage. The PD-1:PD-L pathway also has been usurped by microorganisms and tumors to attenuate antimicrobial or tumor immunity and facilitate chronic infection and tumor survival. The identification of B7-1 as an additional binding partner for PD-L1, together with the discovery of an inhibitory bidirectional interaction between PD-L1 and B7-1, reveals new ways the B7:CD28 family regulates T cell activation and tolerance. In this review, we discuss current understanding of the immunoregulatory functions of PD-1 and its ligands and their therapeutic potential.

Blocking of monocyte-associated B7-H1 (CD274) enhances HCV-specific T cell immunity in chronic hepatitis C infection

The establishment of a chronic hepatitis C (CHC) infection is associated with defective HCV-specific T cell responses. Recent studies suggest that negative T cell regulators such as programmed death 1 (PD-1) contribute to the impairment of virus-specific T cell functions in chronic viral infections. However, the implication of peripheral monocytes from CHC patients in the inhibition of HCV-specific T cell responses is only partially defined. In this study, we found that B7-H1, a ligand of PD-1, was significantly up-regulated on monocytes of CHC patients. Proliferation of T cells in response to anti-CD3 antibody was directly suppressed by B7-H1+CD14+ monocytes, and this suppression was reversed by addition of antagonistic B7-H1 mAb. Furthermore, blocking of monocyte-associated B7-H1 (moB7-H1) significantly enhanced the frequency of IFN-gamma-producing, HCV-specific CD4+ and CD8+ effector T cells and the production of Th1 cytokines, such as IL-2 but not Th2 cytokines, including IL-4 and IL-10. Upon B7-H1 blockade, production of perforin was also increased in CD8+ T cells stimulated with HCV peptides. Our findings suggest that moB7-H1 inhibits HCV-specific CD4+ and CD8+ T lymphocyte proliferation and suppresses Th1 cytokine production and perforin secretion. Blockade of the B7-H1 pathway thus represents an attractive approach in the treatment of chronic HCV infection.

B7-H1 up-regulation on myeloid dendritic cells significantly suppresses T cell immune function in patients with chronic hepatitis B

Although dysfunctional dendritic cells contribute to inadequate adaptive immunity in chronic hepatitis B (CHB), underlying molecular mechanisms remain largely undefined. In this study, we examined B7-H1 expression on circulating myeloid dendritic cells (mDCs) in 46 CHB patients, 10 autoimmune hepatitis patients, and 10 healthy subjects as control. We found that B7-H1 expression is significantly up-regulated on circulating mDCs of CHB and autoimmune hepatitis patients compared with healthy individuals. The B7-H1 up-regulation was significantly correlated with an elevation of serum alanine aminotransaminase levels and plasma viral load. In addition, in vitro, both IFN-alpha and IFN-gamma could strongly stimulate mDCs to express B7-H1. More importantly, elevated B7-H1 expression is also closely associated with the suppression of T cell immune function. In vitro blockade of B7-H1 signaling could not only down-regulate IL-10 and up-regulate IL-12 production by mDCs, but also enhance mDC-mediated allostimulatory capacity and cytokine production of T cells. Blockade of B7-H1 signaling could improve hepatitis B c Ag-pulsed monocyte-derived DC-induced IFN-gamma production by autologous hepatitis B virus-specific T cells. These new findings suggested that chronic inflammation may contribute to B7-H1 up-regulation on mDCs in CHB patients, which potentially cause defective hepatitis B virus-specific T cell function and viral persistence. Our findings further support the notion that the blockade of B7-H1 may represent a novel therapeutic approach for this disease.