Engagement of the PD-1 immunoinhibitory receptor by a novel B7 family member leads to negative regulation of lymphocyte activation

Plasmacytoid dendritic cell precursors induce allogeneic T-cell hyporesponsiveness and prolong heart graft survival

Dendritic cell (DC) precursors were propagated from C57BL/10 (B10; H2b) mouse bone marrow in fms-like tyrosine kinase 3 ligand. Cosignaling molecule (B7-1/B7-2 and B7-H1) expression and stimulatory capacity of precursor (pre)-plasmacytoid (p)DC (CD11c+B220+CD11b-CD19-) and classic myeloid DC (MDC) for allogeneic (C3H; H2k) T cells were compared. Unstimulated pre-pDC exhibited very low levels of surface MHC class II and classic costimulatory molecules (B7-1/B7-2), whereas a minor population expressed B7-H1 at levels higher than on MDC. The pre-pDC were ineffective T-cell stimulators and induced nonspecific hyporesponsiveness to rechallenge with donor alloantigens in vitro and in vivo. Following stimulation with CpG-oligonucleotide (CpG-ODN), B7 molecule expression was upregulated on pre-pDC, however the ratio between coinhibitory (B7-H1) and costimulatory (B7-1/B7-2) signals was much higher (five- to six-fold) on pre-pDC than MDC. Blockade of B7-H1 expression on pDC increased their T-cell allostimulatory capacity significantly. A single preoperative infusion of C3H hosts with pre-pDC prolonged B10 heart graft survival significantly but nonspecifically compared with untreated mice (median survival times 22 vs. 9 days, respectively). Thus, pre-pDC of donor origin have potential to regulate T-cell responses to alloantigens and can prolong organ graft survival.

Regulation of murine chronic colitis by CD4+CD25- programmed death-1+ T cells

Naturally arising CD4(+)CD25(+) regulatory T (T(R)) cells are engaged in the maintenance of self tolerance and prevention of autoimmune diseases. However, accumulating evidence suggests that a fraction of peripheral CD4(+)CD25(-) T cells also possesses regulatory activity. Programmed death-1 (PD-1) is a new member of the CD28/CTLA-4 family, which has been implicated in the maintenance of peripheral self tolerance. Here, we identified a subpopulation of CD4(+)CD25(-)PD-1(+) T cells in the spleen of naive mice that constitutively expressed CTLA-4 and FoxP3 and was hypoproliferative in response to anti-CD3 antibody stimulation in vitro. However, the CD4(+)CD25(-)PD-1(+) T cells uniquely produced large amounts of IL-4 and IL-10 in response to anti-CD3 and anti-CD28 mAb stimulation, unlike the CD4(+)CD25(+) T(R) cells. The CD4(+)CD25(-)PD-1(+) T cells exhibited a suppressor activity against the proliferation of anti-CD3 antibody-stimulated CD4(+)CD25(-)PD-1(-) T cells in vitro, which was partially abrogated by anti-CTLA-4 mAb, but not by anti-IL-10 or anti-PD-1 mAb. Remarkably, the CD4(+)CD25(-)PD-1(+) T cells inhibited the development of colitis induced by adoptive transfer of CD4(+)CD45RB(high) T cells into C.B17-scid/scid mice, albeit to a lesser extent than CD4(+)CD25(+) T(R) cells, in a CTLA-4-dependent manner. These results indicate that the CD4(+)CD25(-)PD-1(+) T cells contain substantial amounts of T(R) cells that are involved in the maintenance of peripheral tolerance.

Blockade of B7-H1 on Macrophages Suppresses CD4+ T Cell Proliferation by Augmenting IFN-γ-Induced Nitric Oxide Production

PD-1 is an immunoinhibitory receptor that belongs to the CD28/CTLA-4 family. B7-H1 (PD-L1) and B7-DC (PD-L2), which belong to the B7 family, have been identified as ligands for PD-1. Paradoxically, it has been reported that both B7-H1 and B7-DC co-stimulate or inhibit T cell proliferation and cytokine production. To determine the role of B7-H1 and B7-DC in T cell-APC interactions, we examined the contribution of B7-H1 and B7-DC to CD4+ T cell activation by B cells, dendritic cells, and macrophages using anti-B7-H1, anti-B7-DC, and anti-PD-1 blocking mAbs. Anti-B7-H1 mAb and its Fab markedly inhibited the proliferation of anti-CD3-stimulated naive CD4+ T cells, but enhanced IL-2 and IFN-gamma production in the presence of macrophages. The inhibition of T cell proliferation by anti-B7-H1 mAb was abolished by neutralizing anti-IFN-gamma mAb. Coculture of CD4+ T cells and macrophages from IFN-gamma-deficient or wild-type mice showed that CD4+ T cell-derived IFN-gamma was mainly responsible for the inhibition of CD4+ T cell proliferation. Anti-B7-H1 mAb induced IFN-gamma-mediated production of NO by macrophages, and inducible NO synthase inhibitors abrogated the inhibition of CD4+ T cell proliferation by anti-B7-H1 mAb. These results indicated that the inhibition of T cell proliferation by anti-B7-H1 mAb was due to enhanced IFN-gamma production, which augmented NO production by macrophages, suggesting a critical role for B7-H1 on macrophages in regulating IFN-gamma production by naive CD4+ T cells and, hence, NO production by macrophages.

In vivo costimulatory role of B7-DC in tuning T helper cell 1 and cytotoxic T lymphocyte responses

B7-DC, one of the recently described B7 family members, has the capacity to inhibit T cell responses via engagement of the immunoreceptor tyrosine-based inhibitory motif–containing inhibitory PD-1 receptor as well as enhance responses via an as yet unidentified costimulatory receptor. B7-DC is highly homologous to a coinhibitory B7 family member, B7-H1, which also binds PD-1. It is currently unclear which B7-DC function—costimulation or inhibition—predominates in vivo. To study in vivo functions of B7-DC, we evaluated immune responses in B7-DC knockout (KO) mice. Although not eliminated, interferon-γ (IFN-γ) production by CD4 T cells and IFN-γ–dependent humoral responses were reduced in B7-DC KO mice relative to wild type mice. Antigen-specific CD8 T cell responses and cytotoxic T lymphocyte (CTL) activity were also diminished in B7-DC KO mice. Hepatic tumors grew more quickly in B7-DC KO mice, associated with a decrease in intrahepatic tumor-specific CD8 T cells. These results highlight the contrasting in vivo roles of B7-DC and B7-H1 and indicate that B7-DC functions as a tuning molecule, selectively augmenting T helper 1 and CTL responses.

Human Rhinoviruses Inhibit the Accessory Function of Dendritic Cells by Inducing Sialoadhesin and B7-H1 Expression

Dendritic cells (DC) are professional APCs with an unmatched ability to interact with and activate T cells. There is accumulating evidence that DC not only efficiently stimulate T cell activation but also regulate T cell responses. However, little is known about cell surface structures on DC involved in the regulation of T cell responses. We demonstrate that human rhinoviruses (HRV) can efficiently inhibit the accessory function of DC through induction of inhibitory cell surface receptors. We observed that treatment of DC with HRV14 (R-DC), a member of the major group HRV family, diminished their T cell stimulatory capacity and induced a promiscuous and deep anergic state in cocultured T cells despite high levels of MHC molecules as well as costimulatory molecules, e.g., B7-1 (CD80) and B7-2 (CD86), and independent of inhibitory soluble factors such as IL-10. In contrast, expression of inhibitory B7-H1 molecules was up-regulated and R-DC de novo expressed sialoadhesin (Sn). Most importantly, blocking of B7-H1 and Sn on R-DC with specific mAbs against both receptors reverted the inhibitory phenotype. Thus, inhibitory signals delivered from R-DC to T cells via B7-H1 and Sn were critical for the induction of anergy. These observations suggest that an altered accessory molecule repertoire on DC upon interaction with HRV down-modulates adaptive immune responses during the viral infection.

Pathogenic roles of cardiac autoantibodies in dilated cardiomyopathy

Whether autoimmunity could cause dilated cardiomyopathy (DCM) was disputed for more than half a century. Autoantibodies against various cardiac antigens have been found in the sera of patients with DCM but none of these autoantibodies has been shown to have a substantial role in the development of DCM. It was recently reported that the injection of autoantibodies against cardiac troponin I (cTnI) can induce DCM in normal mice. This observation showed that autoantibodies can cause DCM and put an end to the controversy. Clinical trials of immunoglobulin-adsorption therapy for DCM have already started in Germany and the results seem promising. Here, we discuss the recent findings and possibilities of immunoglobulin-adsorption therapy for this deadly disease.

The B7 family revisited

The discovery of new functions for the original B7 family members, together with the identification of additional B7 and CD28 family members, have revealed new ways in which the B7:CD28 family regulates T cell activation and tolerance. B7-1/B7-2:CD28 interactions not only promote initial T cell activation but also regulate self-tolerance by supporting CD4+CD25+ T regulatory cell homeostasis. CTLA-4 can exert its inhibitory effects in both B7-1/B7-2 dependent and independent fashions. B7-1 and B7-2 can signal bidirectionally by engaging CD28 and CTLA-4 on T cells and by delivering signals into B7-expressing cells. The five new B7 family members, ICOS ligand, PD-L1 (B7-H1), PD-L2 (B7-DC), B7-H3, and B7-H4 (B7x/B7-S1) are expressed on professional antigen-presenting cells as well as on cells within nonlymphoid organs, providing new means for regulating T cell activation and tolerance in peripheral tissues. The new CD28 families members, ICOS, PD-1, and BTLA, are inducibly expressed on T cells, and they have important roles in regulating previously activated T cells. PD-1 and BTLA also are expressed on B cells and may have broader immunoregulatory functions. The ICOS:ICOSL pathway appears to be particularly important for stimulating effector T cell responses and T cell-dependent B cell responses, but it also has an important role in regulating T cell tolerance. In addition, the PD-1:PD-L1/PD-L2 pathway plays a critical role in regulating T cell activation and tolerance. In this review, we revisit the roles of the B7:CD28 family members in regulating immune responses, and we discuss their therapeutic potential.

The NOD mouse: a model of immune dysregulation

Autoimmunity is a complex process that likely results from the summation of multiple defective tolerance mechanisms. The NOD mouse strain is an excellent model of autoimmune disease and an important tool for dissecting tolerance mechanisms. The strength of this mouse strain is that it develops spontaneous autoimmune diabetes, which shares many similarities to autoimmune or type 1a diabetes (T1D) in human subjects, including the presence of pancreas-specific autoantibodies, autoreactive CD4+ and CD8+ T cells, and genetic linkage to disease syntenic to that found in humans. During the past ten years, investigators have used a wide variety of tools to study these mice, including immunological reagents and transgenic and knockout strains; these tools have tremendously enhanced the study of the fundamental disease mechanisms. In addition, investigators have recently developed a number of therapeutic interventions in this animal model that have now been translated into human therapies. In this review, we summarize many of the important features of disease development and progression in the NOD strain, emphasizing the role of central and peripheral tolerance mechanisms that affect diabetes in these mice. The information gained from this highly relevant model of human disease will lead to potential therapies that may alter the development of the disease and its progression in patients with T1D.

Bone marrow mesenchymal progenitor cells inhibit lymphocyte proliferation by activation of the programmed death 1 pathway

Bone marrow mesenchymal progenitor cells (BMSC) are used for regenerating tissues of mesodermal origin, as well as tissues of different embryological derivation. Experimental evidence shows that BMSC are able to suppress the activation of the immune response by mechanisms that are still not completely understood. Thus far, in vitro studies carried using human or mouse cells indicate that autologous or allogeneic BMSC strongly suppress proliferation of T lymphocytes, triggered by cellular stimuli, nonspecific mitogenic stimuli, or antigenic peptides. Using cell proliferation and blocking assays, we demonstrated that BMSC inhibited the activation of murine splenocytes, T, and B lymphocytes. Direct contact of BMSC and target cells in a cognate fashion determined the inhibition of cell proliferation via engagement of the inhibitory molecule programmed death 1 (PD-1) to its ligands PD-L1 and PD-L2, leading the target cells to modulate the expression of different cytokine receptors and transduction molecules for cytokine signaling. Soluble factors present on supernatants of BMSC cultures were effective in suppressing proliferation of B cells to a mitogenic stimulus. Taken together, these results highlight the complexity of the role of BMSC in regulating the immune response, asserting the possibility of their therapeutic application in transplantation and autoimmune diseases.

PD-L1 is expressed by human renal tubular epithelial cells and suppresses T cell cytokine synthesis

T cell activation is affected by both stimulatory and inhibitory co-signaling. MHC class II-expressing renal tubular epithelial cells (TEC) can function as APC for T cells. To study the influence of inhibitory ligands on TEC-mediated T cell activation, we examined the expression of programmed death ligand-1 (PD-L1) on human TEC line HK-2 cells, as well as in normal and diseased kidney samples. RT-PCR, FACS, and immunocytochemistry showed that PD-L1 is constitutively expressed on HK-2 cells, and is dramatically upregulated by IFN-gamma. In situ hybridization and immunohistochemical staining revealed constitutive low expression of PD-L1 on proximal tubules at both mRNA and protein levels in normal kidneys, but much higher expression in kidneys with type IV lupus nephritis. In vitro, pretreatment of IFN-gamma-stimulated HK-2 cells with anti-PD-L1 significantly enhanced IL-2 secretion from cocultured, mitogen-activated Jurkat or human peripheral blood T cells. These results suggest that the PD-L1:PD-1 pathway negatively regulates T cell activation by TEC, and may play an inhibitory role in TEC-mediated immune activation and immunopathology in the kidney.

Gene expression characteristics of CD28null memory phenotype CD8+ T cells and its implication in T-cell aging

Accumulation of CD28(null)CD8(+) T cells is considered as one of the hallmarks of aging in the human immune system. However, the precise changes of CD28(null)CD8(+) T cells, compared to those of the precursor CD28(+)CD8(+) memory T cells, have not been determined. In this study, we present an analysis of the global gene expression profiles of CD28(+) and CD28(null) memory phenotype CD8(+) T cells. These two CD8(+) T subsets exhibited an overall similar gene expression profile with only a few dozen genes that were differentially expressed. A wide range of functions, including co-stimulation, effector activity, signaling, and transcription, were possessed by these differentially expressed genes, reflecting significant functional changes of CD28(null) memory phenotype CD8(+) T cells from their CD28(+) counterparts. In addition, CD28(null) memory CD8(+) T cells expressed several natural killer cell receptors and high levels of granzymes, perforin, and FasL, indicating an increasing capacity for cytotoxicity during memory CD8(+) T-cell aging. Interestingly, in vitro culture of these two subsets with interleukin-15 showed that similar gene expression changes occurred in both subsets. Our analysis provides the gene expression portraits of CD28(null) memory phenotype CD8(+) T cells and alteration from their CD28(+) counterparts and suggests potential mechanisms of T-cell aging.

Kinetics of costimulatory molecule expression by T cells and dendritic cells during the induction of tolerance versus immunity in vivo

Steady-state dendritic cells (DC) present peptide-MHC complexes to T cells in a tolerogenic manner, presumably because of deficient costimulation. However, it is clear that the path to tolerance involves initial T cell activation, suggesting that the deficit may lie in late-acting costimulatory molecules. With this in mind we have investigated the kinetics of expression of several costimulatory pairs on DC and OVA-reactive T cells after i.v. injection of mice with peptide and LPS (immunity), or peptide alone (tolerance). We find that T cells up-regulate CD154, OX40, RANKL and PD-1 whether they are destined for tolerance or immunity, although there are some differences in the levels and length of expression. In contrast, when analyzing DC, we found that up-regulation of CD80, CD86, CD40, RANK and PDL-1 occurred only when peptide was co-administered with LPS. These data give a picture of the T cell looking for costimulatory cues that are not forthcoming when pMHC is presented by steady-state DC, leading to tolerance. However, we did see a strong and rapid up-regulation of RANKL on T cells that occurred specifically when peptide was given in the absence of LPS, suggesting a possible positive signal influencing the decision between tolerance and immunity.

Constitutive and inducible expression of b7 family of ligands by human airway epithelial cells

Activated T cells have been implicated in chronic rhinosinusitis (CRS) and asthma and physically interact with epithelial cells in the airways. We now report that human airway epithelial cells display significant constitutive cell-surface expression of costimulatory ligands, B7-H1, B7-H2, B7-H3, and B7-DC. Expression of B7-H1 and B7-DC was selectively induced by stimulation of either BEAS2B or primary nasal epithelial cells (PNEC) with interferon (IFN)-gamma (100 ng/ml). The combination of IFN-gamma and tumor necrosis factor-alpha (100 ng/ml) selectively induced expression better than IFN-gamma alone. Fluticasone treatment (10(-7) M) reduced the baseline expression and inhibited the induction of B7-H1 and B7-DC in BEAS2B cells. In vitro exposure of PNEC to IFN-gamma also resulted in selective induction of B7-H1 and B7-DC. Monoclonal antibody blockade of B7-H1 or B7-DC enhanced IFN-gamma expression by purified T cells in co-culture experiments, suggesting that these two B7 homologs inhibit T cell responses at the mucosal surface. Immunohistochemical staining of human sinonasal surgical tissue confirmed the presence of B7-H1, B7-H2, and B7-H3 in the epithelial cell layer, especially in samples from patients diagnosed with Samter's Triad, a severe form of CRS. Real-time PCR analysis of sinonasal tissue revealed elevated levels of B7-H1 and B7-DC in CRS compared with controls. These results demonstrate that epithelial cells express functional B7 costimulatory molecules and that expression of selected B7 family members is inducible in vitro and in vivo. Epithelial B7 homologs could play a role in regulation of lymphocytic activity at mucosal surfaces.

Organ transplantation—how much of the promise has been realized?

Since the introduction of organ transplantation into medical practice, progress and optimism have been abundant. Improvements in immunosuppressive drugs and ancillary care have led to outstanding short-term (1--3-year) patient and graft survival rates. This success is mitigated by several problems, including poor long-term (>5-year) graft survival rates, the need for continual immunosuppressive medication and the discrepancy between the demand for organs and the supply. Developing methods to induce transplant tolerance, as a means to improve graft outcomes and eliminate the requirement for immunosuppression, and expanding the pool of organs for transplantation are the major challenges of the field.

The B7 family of immune-regulatory ligands

The B7 family consists of structurally related, cell-surface protein ligands, which bind to the CD28 family of receptors on lymphocytes and regulate immune responses via 'costimulatory' or 'coinhibitory' signals.

The role of herpesvirus entry mediator as a negative regulator of T cell-mediated responses

Herpesvirus entry mediator (HVEM), a TNF receptor superfamily member, has been previously described as a T cell costimulatory receptor. Surprisingly, HVEM-/- T cells showed enhanced responses to in vitro concanavalin A (ConA) stimulation when compared with WT T cells. Consistent with these findings, HVEM-/- mice exhibited increased morbidity and mortality as compared with WT mice in a model of ConA-mediated T cell-dependent autoimmune hepatitis. HVEM-/- mice produced higher levels of multiple cytokines, which were dependent on the presence of CD4+ T cells. Furthermore, HVEM-/- mice were more susceptible to MOG peptide-induced experimental autoimmune encephalopathy, and they showed increased T cell proliferation and cytokine production in response to antigen-specific challenge. Taken together, our data revealed an unexpected regulatory role of HVEM in T cell-mediated immune responses and autoimmune diseases.

The role of herpesvirus entry mediator as a negative regulator of T cell-mediated responses

Herpesvirus entry mediator (HVEM), a TNF receptor superfamily member, has been previously described as a T cell costimulatory receptor. Surprisingly, HVEM-/- T cells showed enhanced responses to in vitro concanavalin A (ConA) stimulation when compared with WT T cells. Consistent with these findings, HVEM-/- mice exhibited increased morbidity and mortality as compared with WT mice in a model of ConA-mediated T cell-dependent autoimmune hepatitis. HVEM-/- mice produced higher levels of multiple cytokines, which were dependent on the presence of CD4+ T cells. Furthermore, HVEM-/- mice were more susceptible to MOG peptide-induced experimental autoimmune encephalopathy, and they showed increased T cell proliferation and cytokine production in response to antigen-specific challenge. Taken together, our data revealed an unexpected regulatory role of HVEM in T cell-mediated immune responses and autoimmune diseases.

Various Costimulatory Pathways Are Essential for Induction of Regulatory Cells by Intratracheal Delivery of Alloantigen

BACKGROUND

We previously reported that intratracheal delivery of alloantigen induced regulatory cells in a mouse heart transplantation model. We investigated the roles of costimulatory pathways in the induction of regulatory cells by intratracheal delivery of alloantigen.

METHODS

CBA (H-2k) mice were pretreated with intratracheal delivery of splenocytes (1 x 10(7)) from C57BL/10 (H-2b) mice and administration of monoclonal antibodies (mAb) specific for programmed death (PD)-1 and its ligands, programmed death-ligand (PD-L)1 and PD-L2, CD70, CD134 ligand (CD134L), CD153, CD137L, or receptor activator of nuclear factor-kappaB (NF-kappaB) (RANK). Seven days later, naive CBA mice underwent adoptive transfer of splenocytes (5 x 10(7)) from the pretreated CBA mice and transplantation of C57BL/10 heart.

RESULTS

Adoptive transfer of splenocytes from CBA mice that had been pretreated with intratracheal delivery of C57BL/10 splenocytes significantly prolonged the survival of C57BL/10 allograft (median survival time [MST], 68 days) as compared with adoptive transfer from untreated CBA mice (MST, 12 days). Concomitant administration of control immunoglobulin (Ig)G, anti-PD-L2 mAb, or anti-CD137L along with intratracheal delivery did not significantly affect the prolongation (MST, 72, 68, and 65 days, respectively). In contrast, anti-PD-1, anti-PD-L1, anti-CD70, anti-CD134L, anti-CD153, or anti-RANK mAb abrogated the prolongation induced by adoptive transfer from the pretreated mice with intratracheal delivery (MST, 18, 17, 16, 14, 10, and 18 days, respectively).

CONCLUSION

The PD-1/PD-L1, CD27/CD70, CD134/CD134L, CD30/CD153, and tumor necrosis factor (TNF)-related activation-induced cytokine (TRANCE)/RANK interactions are independently required for generation of regulatory cells by intratracheal delivery of alloantigen.

Inhibitors of mitogen-activated protein kinases differentially regulate costimulated T cell cytokine production and mouse airway eosinophilia

Background

T cells play a dominant role in the pathogenesis of asthma. Costimulation of T cells is necessary to fully activate them. An inducible costimulator (ICOS) of T cells is predominantly expressed on Th2 cells. Therefore, interference of signaling pathways precipitated by ICOS may present new therapeutic options for Th2 dominated diseases such as asthma. However, these signaling pathways are poorly characterized in vitro and in vivo.

Methods

Human primary CD4⁺ T cells from blood were activated by beads with defined combinations of surface receptor stimulating antibodies and costimulatory receptor ligands. Real-time RT-PCR was used for measuring the production of cytokines from activated T cells. Activation of mitogen activated protein kinase (MAPK) signaling pathways leading to cytokine synthesis were investigated by western blot analysis and by specific inhibitors. The effect of inhibitors in vivo was tested in a murine asthma model of late phase eosinophilia. Lung inflammation was assessed by differential cell count of the bronchoalveolar lavage, determination of serum IgE and lung histology.

Results

We showed in vitro that ICOS and CD28 are stimulatory members of an expanding family of co-receptors, whereas PD1 ligands failed to co-stimulate T cells. ICOS and CD28 activated different MAPK signaling cascades necessary for cytokine activation. By means of specific inhibitors we showed that p38 and ERK act downstream of CD28 and that ERK and JNK act downstream of ICOS leading to the induction of various T cell derived cytokines. Using a murine asthma model of late phase eosinophilia, we demonstrated that the ERK inhibitor U0126 and the JNK inhibitor SP600125 inhibited lung inflammation in vivo. This inhibition correlated with the inhibition of Th2 cytokines in the BAL fluid. Despite acting on different signaling cascades, we could not detect synergistic action of any combination of MAPK inhibitors. In contrast, we found that the p38 inhibitor SB203580 antagonizes the action of the ERK inhibitor U0126 in vitro and in vivo.

Conclusion

These results demonstrate that the MAPKs ERK and JNK may be suitable targets for anti-inflammatory therapy of asthma, whereas inhibition of p38 seems to be an unlikely target.

A new haplotype ofPDCD1is associated with rheumatoid arthritis in Hong Kong Chinese

OBJECTIVE

The programmed death 1 (PD-1) molecule is a negative regulator of T cells, and a genetic association between PD-1 and systemic lupus erythematosus and rheumatoid arthritis (RA) in Caucasians has been reported. The aim of this study was to investigate the association of PDCD1 polymorphisms and haplotypes with RA in the Chinese population.

METHODS

Three single-nucleotide polymorphisms (SNPs), PD-1.1 G/A, PD-1.3 G/A, and PD-1.5 C/T, were genotyped in 180 patients with RA and 647 healthy controls in a case-control association study. Analyses of the association of genotypes and alleles with disease, haplotype construction, and linkage disequilibrium (LD) were performed.

RESULTS

We constructed haplotypes with the alleles of markers PD-1.1 G/A and PD-1.5 C/T and found that the GT haplotype was overrepresented in patients with RA (31%) compared with controls (23%) (P = 0.001, odds ratio [OR] 1.54, 95% confidence interval [95% CI] 1.18-1.99). Among GT double homozygotes the risk of RA was increased even further (OR 2.31, 95% CI 1.31-4.08, P = 0.006). We also observed that the AA genotype of SNP PD-1.1 was associated with a decreased risk for developing RA (OR 0.38, 95% CI 0.15-0.99, P = 0.034). No association for SNP PD-1.5 in RA was found, and SNP PD-1.3 was nonpolymorphic in the Chinese population.

CONCLUSION

Our results support the involvement of PDCD1 as a susceptibility gene for RA in the Chinese population.

Identification of a novel splice variant of human PD-L1 mRNA encoding an isoform-lacking Igv-like domain

AIM

To investigate the expression and regulation of PD-1 ligand 1 (PD-L1) in peripheral blood mononuclear cells (PBMC).

METHODS

The cDNA encoding human PD-L1 precursor was cloned from the total RNA extracted from the resting and phorbol dibutyrate plus ionomycin- or phytohemagglutinin-activated PBMC, by reverse transcription polymerase chain reaction (RT-PCR), and independent clones were sequenced and analyzed. The expression and subcellular localization were examined in transiently transfected cells. The PD-L1 gene expression in different PBMC was also analyzed by RT-PCR.

RESULTS

A novel human PD-L1 splice variant was identified from the activated PBMC. It was generated by splicing out exon? encoding an immunoglobulin variable domain (Igv)-like domain but retaining all other exons without a frame-shift. Consequently, the putative translated protein contained all other domains including the transmembrane region except for the Igv-like domain. Furthermore, the conventional isoform was expressed on the plasma surface whereas the novel isoform showed a pattern of intracellular membrane distribution in transiently transfected K562 cells. In addition, the expression pattern of the PD-L1 splice variant was variable in different individuals and in different cellular status.

CONCLUSION

PD-L1 expression may be regulated at the posttranscriptional level through alternative splicing, and modulation of the PD-L1 isoform expression may influence the outcome of specific immune responses in the peripheral tissues.

Interaction of PD-L1 on tumor cells with PD-1 on tumor-specific T cells as a mechanism of immune evasion: implications for tumor immunotherapy

Programmed death receptor ligand 1 (PD-L1, also called B7-H1) is a recently described B7 family member. In contrast to B7-1 and B7-2, PD-L1 does not interact with either CD28 or CTLA-4. To date, one specific receptor has been identified that can be ligated by PD-L1. This receptor, programmed death receptor 1 (PD-1), has been shown to negatively regulate T-cell receptor (TCR) signaling. Upon ligating its receptor, PD-L1 has been reported to decrease TCR-mediated proliferation and cytokine production. PD-1 gene-deficient mice developed autoimmune diseases, which early led to the hypothesis of PD-L1 regulating peripheral tolerance. In contrast to normal tissues, which show minimal surface expression of PD-L1 protein, PD-L1 expression was found to be abundant on many murine and human cancers and could be further up-regulated upon IFN-gamma stimulation. Thus, PD-L1 might play an important role in tumor immune evasion. This review discusses the currently available data concerning negative T-cell regulation via PD-1, the blockade of PD-L1/PD-1 interactions, and the implications for adoptive T-cell therapies.

Expression of B7-H1 and B7-DC on the airway epithelium is enhanced by double-stranded RNA

Viral infection in the airway provokes various immune responses, including Th1 and Th2 responses, which are partly initiated by double-stranded RNA (dsRNA), a viral product for its replication. B7-H1 (PD-L1) and B7-DC (PD-L2) are B7-family molecules that bind to programmed death-1 (PD-1) on lymphocytes and are implicated in peripheral tolerance. We investigated the effect of dsRNA on the expression of B7-H1 and B7-DC on airway epithelial cell lines. B7-H1 and B7-DC were constitutively expressed on the cells, and their expression was profoundly upregulated by stimulation with an analog of viral dsRNA, polyinosinic-polycytidylic acid. B7-H1 and B7-DC were also upregulated by stimulation with IFN-gamma, IL-13, and the supernatant from T cell clones. A relatively high concentration of dexamethasone (1 microM) was required to suppress the upregulation of B7-H1 or B7-DC. These results suggest that epithelial B7-H1 and B7-DC play a role in virus-associated immune responses in the airways.

Low TLR4 expression by liver dendritic cells correlates with reduced capacity to activate allogeneic T cells in response to endotoxin

Signaling via TLRs results in dendritic cell (DC) activation/maturation and plays a critical role in the outcome of primary immune responses. So far, no data exist concerning TLR expression by liver DC, generally regarded as less immunostimulatory than secondary lymphoid tissue DC. Because the liver lies directly downstream from the gut, it is constantly exposed to bacterial LPS, a TLR4 ligand. We examined TLR4 expression by freshly isolated, flow-sorted C57BL/10 mouse liver DC compared with spleen DC. Real-time PCR revealed that liver CD11c+CD8alpha- (myeloid) and CD11c+CD8alpha+ ("lymphoid-related") DC expressed lower TLR4 mRNA compared with their splenic counterparts. Lower TLR4 expression correlated with reduced capacity of LPS (10 ng/ml) but not anti-CD40-stimulated liver DC to induce naive allogeneic (C3H/HeJ) T cell proliferation. By contrast to LPS-stimulated splenic DC, these LPS-activated hepatic DC induced alloantigen-specific T cell hyporesponsiveness in vitro, correlated with deficient Th1 (IFN-gamma) and Th2 (IL-4) responses. When higher LPS concentrations (> or =100 ng/ml) were tested, the capacity of liver DC to induce proliferation of T cells and Th1-type responses was enhanced, but remained inferior to that of splenic DC. Hepatic DC activated by LPS in vivo were inferior allogeneic T cell stimulators compared with splenic DC, whereas adoptive transfer of LPS-stimulated (10 ng/ml) liver DC induced skewing toward Th2 responses. These data suggest that comparatively low expression of TLR4 by liver DC may limit their response to specific ligands, resulting in reduced or altered activation of hepatic adaptive immune responses.

Molecular cloning and characterization of canine ICOS

Inducible costimulatory receptor (ICOS) is one recently identified member of the CD28 family of costimulatory molecules. Evidence suggests ICOS functions as a critical immune regulator and, to evaluate these effects, we employed the canine model system that has been used to develop strategies currently in clinical use for hematopoietic stem cell transplantation. To investigate the effects of blocking the ICOS pathway in the canine hematopoietic cell transplantation model, we tested existing murine and human reagents and cloned the full length of the open reading frame of canine ICOS cDNA to allow the development of reagents specific for the canine ICOS. Canine ICOS contains a major open reading frame of 624 nucleotides, encoding a protein of 208 amino acids, and localizes to chromosome 37. Canine ICOS shares 79% sequence identity with human ICOS, 70% with mouse, and 69% with rat. Canine ICOS expression is limited to stimulated PBMC.

B7-H1 expression on non-small cell lung cancer cells and its relationship with tumor-infiltrating lymphocytes and their PD-1 expression

PURPOSE

B7-H1/PD-L1 (B7-H1) and B7-DC/PD-L2 (B7-DC) are ligands for the receptor PD-1, which is known to negatively regulate T-cell activation. In the present study, we investigated the expression of B7-H1 and B7-DC in tumor specimens of non-small cell lung cancer and their relationships with clinicopathological variables and postoperative survival. Furthermore, we examined the correlation between B7-H1 expression on tumor cells and the number of tumor-infiltrating lymphocytes (TILs) or PD-1 expression on TILs.

EXPERIMENTAL DESIGN

The expression of B7-H1 and B7-DC in 52 surgically resected specimens of non-small cell lung cancer was evaluated immunohistochemically.

RESULTS

Expression of B7-H1 and B7-DC was focally observed in all non-small cell lung cancer tumor specimens. No relationship was found between the expression of B7-H1 or B7-DC and clinicopathological variables or postoperative survival. However, in the same sections evaluated, significantly fewer TILs were identified in B7-H1-positive tumor regions than in B7-H1-negative tumor regions in a subset of five patients (P = 0.01). Moreover, the percentage of TILs expressing PD-1 was significantly lower in B7-H1-positive tumor regions than in B7-H1-negative tumor regions (P = 0.02).

CONCLUSIONS

The expression of B7-H1 on tumor cells in local areas reciprocally correlated with the number of TILs, and this may contribute to negative regulation in antitumor immune responses in non-small cell lung cancer.

Correlation of disease evolution with progressive inflammatory cell activation and migration in the IL-4 transgenic mouse model of atopic dermatitis

Atopic dermatitis is a chronic inflammatory skin disease characterized by inflammatory cell infiltration in the skin. In order to assess the roles of inflammatory cells in this disease, we analysed the activation status and surface markers of various leucocytes in the IL-4 transgenic mouse model of atopic dermatitis, by flow cytometry, immuofluorescence microscopy, and T cell proliferation assays. The studies were performed with a nontransgenic mouse control and transgenic mice at three disease stages: before disease onset, early skin disease, and late skin disease, so that we can delineate the immunological sequence of events. As the skin disease evolves, the skin draining lymph node cells from IL-4-Tg mice show a spontaneous proliferation and a progressively enhanced proliferative response to stimulants including anti-CD3, Con A, PHA, and Staphylococcus enterotoxins A and B. As the disease evolves, the percent of lymphoid organ T cells expressing activation molecules (CD44 and CD69) and costimulatory molecules (ICOS and PD-1) are progressively increased; the percent and total number of T cells are reduced in an incremental manner in the secondary lymphoid organs while the number of T cells infiltrating the skin increases in an incremental fashion; the total number of dendritic antigen presenting cells, macrophages, and NK cells gradually increases in the lymphoid organs. Collectively, our results suggest that there is a continued and progressive migration of activated inflammatory cells from the secondary lymphoid organs into the skin where they participate in immune responses resulting in the pathology associated with inflammation.

Role of the Programmed Death-1 Pathway in Regulation of Alloimmune Responses In Vivo

Programmed death-1 (PD-1), an inhibitory receptor up-regulated on activated T cells, has been shown to play a critical immunoregulatory role in peripheral tolerance, but its role in alloimmune responses is poorly understood. Using a novel alloreactive TCR-transgenic model system, we examined the functions of this pathway in the regulation of alloreactive CD4+ T cell responses in vivo. PD-L1, but not PD-1 or PD-L2, blockade accelerated MHC class II-mismatched skin graft (bm12 (I-Abm12) into B6 (I-Ab)) rejection in a similar manner to CTLA-4 blockade. In an adoptive transfer model system using the recently described anti-bm12 (ABM) TCR-transgenic mice directly reactive to I-Abm12, PD-1 and PD-L1 blockade enhanced T cell proliferation early in the immune response. In contrast, at a later time point preceding accelerated allograft rejection, only PD-L1 blockade enhanced T cell proliferation. In addition, PD-L1 blockade enhanced alloreactive Th1 cell differentiation. Apoptosis of alloantigen-specific T cells was inhibited significantly by PD-L1 but not PD-1 blockade, indicating that PD-1 may not be the receptor for the apoptotic effect of the PD-L1-signaling pathway. Interestingly, the effect of PD-L1 blockade was dependent on the presence of CD4+ CD25+ regulatory T cells in vivo. These data demonstrate a critical role for the PD-1 pathway, particularly PD-1/PD-L1 interactions, in the regulation of alloimmune responses in vivo.

ICOS-B7 Homologous Protein Interactions Are Necessary for Mercury-Induced Autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2(s) mice develop an autoimmune syndrome consisting of the rapid production of IgG autoantibodies that are highly specific for nucleolar autoantigens and a polyclonal increase in serum IgG1 and IgE. In this study, we explore the role of one of the members of the CD28-B7 costimulation families, ICOS-B7 homologous protein (B7h), in the regulation of mercury-induced autoimmunity. The expression of ICOS on T cells was more enhanced in susceptible A.SW mice than in non-responsive C57BL/6 and DBA/2 mice after HgCl(2) treatment. Furthermore, in A.SW mice treated with HgCl(2), administration of a blocking anti-ICOS Ab effectively inhibited anti-nucleolar autoantibodies and total serum IgE production. Taken together, these results indicate that the ICOS-B7h costimulation pathway is required for this autoimmune syndrome and suggest that targeting this pathway might have therapeutic benefits for human autoimmune diseases.

Co-signaling molecules of the B7-CD28 family in positive and negative regulation of T lymphocyte responses

Co-signaling molecules in the B7-CD28 family have been intensively studied over the past decade and have brought much excitement to the field of immune regulation. The discovery of new functions for the classical pathways CD80/CD86/CD28/CTLA-4 and the identification of novel pathways of the family, including B7-H1/B7-DC/PD-1, B7-H2/ICOS, B7-H3, B7-H4 and BTLA, are greatly broadening our understanding of the control of T cell-mediated immune responses and tolerance.

Prevention of Experimental Autoimmune Encephalomyelitis by Transfer of Embryonic Stem Cell-Derived Dendritic Cells Expressing Myelin Oligodendrocyte Glycoprotein Peptide along with TRAIL or Programmed Death-1 Ligand

Experimental autoimmune encephalomyelitis (EAE) is caused by activation of myelin Ag-reactive CD4+ T cells. In the current study, we tested a strategy to prevent EAE by pretreatment of mice with genetically modified dendritic cells (DC) presenting myelin oligodendrocyte glycoprotein (MOG) peptide in the context of MHC class II molecules and simultaneously expressing TRAIL or Programmed Death-1 ligand (PD-L1). For genetic modification of DC, we used a recently established method to generate DC from mouse embryonic stem cells (ES cells) in vitro (ES-DC). ES cells were sequentially transfected with an expression vector for TRAIL or PD-L1 and an MHC class II-associated invariant chain-based MOG epitope-presenting vector. Subsequently, double-transfectant ES cell clones were induced to differentiate to ES-DC, which expressed the products of introduced genes. Treatment of mice with either of the double-transfectant ES-DC significantly reduced T cell response to MOG, cell infiltration into spinal cord, and the severity of MOG peptide-induced EAE. In contrast, treatment with ES-DC expressing MOG alone, irrelevant Ag (OVA) plus TRAIL, or OVA plus PD-L1, or coinjection with ES-DC expressing MOG plus ES-DC-expressing TRAIL or PD-L1 had no effect in reducing the disease severity. In contrast, immune response to irrelevant exogenous Ag (keyhole limpet hemocyanin) was not impaired by treatment with any of the genetically modified ES-DC. The double-transfectant ES-DC presenting Ag and simultaneously expressing immune-suppressive molecules may well prove to be an effective therapy for autoimmune diseases without inhibition of the immune response to irrelevant Ag.

Blockade of B7-H1 and PD-1 by Monoclonal Antibodies Potentiates Cancer Therapeutic Immunity

Contemporary approaches for vaccination and immunotherapy are often capable of eliciting strong T-cell responses against tumor antigens. However, such responses are not parallel to clinical tumor regression. The development of evasion mechanisms within tumor microenvironment may be responsible for poor therapeutic responses. We report here that constitutive or inducible expression of B7-H1, a B7 family molecule widely expressed by cancers, confers resistance to therapeutic anti-CD137 antibody in mice with established tumors. The resistance is accompanied with failure of antigen-specific CD8+ CTLs to destroy tumor cells without impairment of CTL function. Blockade of B7-H1 or PD-1 by specific monoclonal antibodies could reverse this resistance and profoundly enhance therapeutic efficacy. Our findings support that B7-H1/PD-1 forms a molecular shield to prevent destruction by CTLs and implicate new approaches for immunotherapy of human cancers.

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

T cells recognizing self proteins exist without causing autoimmunity in healthy individuals. These autoreactive T cells are kept in check by peripheral tolerance. Using a model for peripheral CD8(+) T cell tolerance resulting from antigen presentation by resting dendritic cells in vivo, we show here that CD8(+) T cell tolerance operates through T cell-intrinsic mechanisms such as deletion or functional inactivation. Peripheral CD8(+) T cell tolerance depended on signaling via the costimulatory molecule PD-1, as an absence of PD-1 converted tolerance induction into priming. Blocking of the costimulatory molecule CTLA-4 resulted in impaired tolerance and enhanced the effect of the absence of PD-1, suggesting that PD-1 and CTLA-4 act synergistically. Thus PD-1 and CTLA-4 are crucial molecules for peripheral CD8(+) T cell tolerance induced by resting dendritic cells.

The balance of immune responses: costimulation verse coinhibition

Many of the B7 superfamily members (e.g., B7-1, B7-2, ICOS-L, B7-H1, B7-DC) were initially characterized as T cell costimulatory molecules. However, more recently it has become clear they can also coinhibit T cell responses. We review many of the B7 family members, with a particular focus on B7-H1, and examine their role in autoimmunity, transplant rejection, and cancer pathogenesis. It is crucial to understand that many B7 family members have opposing effects on an immune response. This cautions against using clinical immunotherapeutic reagents targeted against these molecules until we gain a better understanding of the circumstances that regulate the outcomes of the T cell response.

PD-L2+ dendritic cells and PD-1+ CD4+ T cells in schistosomiasis correlate with morbidity

Dendritic cells (DC) are critical antigen-presenting cells for the induction and control of immune responses. PD-L2 (B7-DC) is a regulatory ligand on subpopulations of DC, and binds to the co-regulatory receptor PD-1, present on some activated T lymphocytes, leading to down-regulation. We now show that very early during experimental schistosomiasis (by 5 weeks) a significantly higher proportion of splenic CD11c+/B220- DC express PD-L2, and by 6 weeks after infection a higher proportion of splenic CD4 T cells express PD-1. In this CBA/J mouse/Schistosoma mansoni chronic infection model we have shown that most mice develop moderate morbidity (Moderate Splenomegaly Syndrome, MSS), while some parallel-infected mice express different immune characteristics and die or develop severe morbidity (Hypersplenomegaly Syndrome, HSS). We now report a positive correlation between the proportion of splenic CD11c+/B220- DC that express PD-L2 and showing MSS. In contrast, there is an inverse correlation between the proportion of splenic CD3+/CD4+ T lymphocytes that express PD-1 and showing MSS. The data demonstrate that schistosomes can induce sustained elevated percentages of PD-L2-expressing, B220-negative DC. Furthermore, when this potentially immunoregulatory environment occurs chronically, infected mice are most likely to have developed MSS, expressing moderate morbidity.

Biliary epithelial cells regulate autoreactive T cells: implications for biliary-specific diseases

The biliary epithelial cell (BEC) is the target for several human immune mediated liver diseases, including primary biliary cirrhosis, but it is not always clear whether the BEC functions as an accessory cell or an antigen presenting cell, although it is well documented that BECs express high levels of human leukocyte antigen Class II, intercellular adhesion molecule-1, and lymphocyte function-associated antigen-3. To examine this issue, we established autoreactive T-cell clones from human leukocyte antigen-DR53 patients with primary biliary cirrhosis and characterized BEC function as a function of the ability of BECs to regulate T-cell activation. We report herein that BEC-mediated T-cell activation occurs partially via programmed death 1 ligands in a cell-contact-dependent manner. Further, such activation occurs via prostaglandin E2 production in a cell-contact-independent fashion. Moreover, the production of prostaglandin E2 was partially controlled by interleukin-1beta and tumor necrosis factor alpha. In conclusion, the regulatory activities of BECs are important for the maintenance of peripheral immune tolerance. Further, modulation of BEC function may be used for therapeutic modulation.

The biology of human lymphoid malignancies revealed by gene expression profiling

Gene expression profiling provides a quantitative molecular framework for the study of human lymphomas. This genomic technology has revealed that existing diagnostic categories are comprised of multiple molecularly and clinically distinct diseases. Diffuse large B-cell lymphoma (DLBCL), for example, consists of three gene expression subgroups, termed germinal center B-cell-like (GCB) DLBCL, activated B-cell-like (ABC) DLBCL, and primary mediastinal B-cell lymphoma (PMBL). These DLBCL subgroups arise from different stages of normal B-cell differentiation, utilize distinct oncogenic mechanisms, and differ in their ability to be cured by chemotherapy. Key regulatory factors and their target genes are differentially expressed among these subgroups, including BCL-6, Blimp-1, and XBP1. ABC DLBCL and PMBL depend upon constitutive activation of the NF-kappaB pathway for their survival but GCB DLBCL does not, demonstrating that this pathway is a potential therapeutic target for certain DLBCL subgroups. In DLBCL, mantle cell lymphoma, and follicular lymphoma, gene expression profiling has also been used to create gene expression-based models of survival, which have identified the biological characteristics of the tumors that influence their clinical behavior. In mantle cell lymphoma, the length of survival following diagnosis is primarily influenced by the tumor proliferation rate, which can be quantitatively measured by a proliferation gene expression "signature." Based on this accurate measure, the proliferation rate can now be viewed as an integration of several oncogenic lesions that each increase progression from the G1 to the S phase of the cell cycle. In DLBCL and follicular lymphoma, gene expression profiling has revealed that the molecular characteristics of non-malignant tumor-infiltrating immune cells have a major influence on the length of survival. The implications of these insights for the diagnosis and treatment of non-Hodgkin lymphomas are discussed.

Paradoxical role of programmed death-1 ligand?2 in Th2 immune responsesin vitro and in a mouse asthma modelin vivo

Programmed death-1 ligand 2 (PD-L2) is a ligand for programmed death-1 (PD-1), a receptor that plays an inhibitory role in T cell activation. Since previous studies have shown up-regulation of PD-L2 expression by Th2 cytokines, and asthma is driven by a Th2 response, we hypothesized that PD-L2 might be involved in regulation of the immune response in this disease. We have found that lungs from asthmatic mice had sustained up-regulation of PD-1 and PD-L2, with PD-L2 primarily on dendritic cells. Although addition of PD-L2-Fc in vitro led to decreased T cell proliferation and cytokine production, administration of PD-L2-Fc in vivo in a mouse asthma model resulted in elevated serum IgE levels, increased eosinophilic and lymphocytic infiltration into bronchoalveolar lavage fluid, higher number of cells in the draining lymph nodes, and production of IL-5 and IL-13 from these cells. Although PD-1 was expressed on regulatory T cells, PD-L2-Fc did not affect regulatory T cell activity in vitro. This study provides in vivo evidence of an exacerbated inflammatory response following PD-L2-Fc administration and indicates a potential role for this molecule in Th2-mediated diseases such as asthma.

Inhibition of T-cell responses by hepatic stellate cells via B7-H1-mediated T-cell apoptosis in mice

In the injured liver, hepatic stellate cells (HSCs) secrete many different cytokines, recruit lymphocytes, and thus participate actively in the pathogenesis of liver disease. Little is known of the role of HSCs in immune responses. In this study, HSCs isolated from C57BL/10 (H2b) mice were found to express scant key surface molecules in the quiescent stage. Activated HSCs express major histocompatibility complex class I, costimulatory molecules, and produce a variety of cytokines. Stimulation by interferon gamma (IFN-gamma) or activated T cells enhanced expression of these molecules. Interestingly, addition of the activated (but not quiescent) HSCs suppressed thymidine uptake by T cells that were stimulated by alloantigens or by anti-CD3-mediated T-cell receptor ligation in a dose-dependent manner. High cytokine production by the T cells suggests that the inhibition was probably not a result of suppression of their activation. T-cell division was also found to be normal in a CFSE dilution assay. The HSC-induced T-cell hyporesponsiveness was associated with enhanced T-cell apoptosis. Activation of HSCs was associated with markedly enhanced expression of B7-H1. Blockade of B7-H1/PD-1 ligation significantly reduced HSC immunomodulatory activity, suggesting an important role of B7-H1. In conclusion, the bidirectional interactions between HSCs and immune cells may contribute to hepatic immune tolerance.

Gamma-aminobutyric acid inhibits T cell autoimmunity and the development of inflammatory responses in a mouse type 1 diabetes model

Gamma-aminobutyric acid (GABA) is both a major inhibitory neurotransmitter in the CNS and a product of beta cells of the peripheral islets. Our previous studies, and those of others, have shown that T cells express functional GABAA receptors. However, their subunit composition and physiological relevance are unknown. In this study, we show that a subset of GABAA receptor subunits are expressed by CD4+ T cells, including the delta subunit that confers high affinity for GABA and sensitivity to alcohol. GABA at relatively low concentrations down-regulated effector T cell responses to beta cell Ags ex vivo, and administration of GABA retarded the adoptive transfer of type 1 diabetes (T1D) in NOD/scid mice. Furthermore, treatment with low dose of GABA (600 microg daily) dramatically inhibited the development of proinflammatory T cell responses and disease progression in T1D-prone NOD mice that already had established autoimmunity. Finally, GABA inhibited TCR-mediated T cell cycle progression in vitro, which may underlie GABA's therapeutic effects. The immunoinhibitory effects of GABA on T cells may contribute to the long prodomal period preceding the development of T1D, the immunological privilege of the CNS, and the regulatory effects of alcohol on immune responses. Potentially, pharmacological modulation of GABAA receptors on T cells may provide a new class of therapies for human T1D as well as other inflammatory diseases.

PD-1 inhibits T-cell receptor induced phosphorylation of the ZAP70/CD3zeta signalosome and downstream signaling to PKCtheta

Engagement of the immunoinhibitory receptor, programmed death-1 (PD-1) attenuates T-cell receptor (TCR)-mediated activation of IL-2 production and T-cell proliferation. Here, we demonstrate that PD-1 modulation of T-cell function involves inhibition of TCR-mediated phosphorylation of ZAP70 and association with CD3zeta. In addition, PD-1 signaling attenuates PKCtheta activation loop phosphorylation in a cognate TCR signal. PKCtheta has been shown to be required for T-cell IL-2 production. A phosphorylated PD-1 peptide, corresponding to the C-terminal immunoreceptor tyrosine-switch motif (ITSM), acts as a docking site in vitro for both SHP-2 and SHP-1, while the phosphorylated peptide containing the N-terminal PD-1 immunoreceptor tyrosine based inhibitory motif (ITIM) associates only with SHP-2.

The deficiency of immunoregulatory receptor PD-1 causes mild osteopetrosis

Recently, the involvement of immune responses in metabolic bone disease and/or local bone destruction has received much attention. Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), a member of the immunoglobulin (Ig) superfamily, negatively regulates T cell activation. The deficiency of CTLA-4 induces profound osteopenia with an increase in osteoclastogenesis, suggesting the important role of activated T cells in osteoclastogenesis. Programmed death-1 (PD-1) is the newly identified immunoregulatory receptor, which also belongs to the Ig superfamily. Both CTLA-4 and PD-1 are induced on activated T cells, however, there are no reports linking PD-1 with osteoclasts. In the present study, we have examined the bone phenotype in PD-1-deficient mice PD-1-/- and the role of PD-1 in osteoclastogenesis and osteoclast function. Both trabecular and cortical bone mineral densities of tibia were significantly increased, as observed in peripheral quantitative computed tomography (pQCT), at 12 weeks of age in PD-1-/- mice. Histomorphometric analysis of the PD-1-/- mice and the age-matched controls at 12 weeks of age showed a 2-fold increase in bone volume (BV/TV) with a 55% decrease in osteoclast number (N.Oc/BS). Bone formation indices were similar in both groups. The number of soluble receptor activator of nuclear factor kappaB ligand (sRANKL)-induced osteoclast-like cells (OCLs) derived from the PD-1-deficient splenocytes was significantly decreased (by 25%). On the other hand, PD-1 deficiency did not affect the bone-resorbing activity of mature osteoclasts. Our results suggest that PD-1 deficiency reduces osteoclastogenesis resulting in an osteopetrotic phenotype. Identical members of the Ig superfamily, CTLA-4 and PD-1, which negatively regulate immune responses, may differentially affect osteoclastogenesis and bone remodeling.

Interferon-beta enhances monocyte and dendritic cell expression of B7-H1 (PD-L1), a strong inhibitor of autologous T-cell activation: relevance for the immune modulatory effect in multiple sclerosis

Antigen-presenting cells (APC) are considered to play a critical role in promoting the (re)activation of potentially autoreactive T cells in multiple sclerosis (MS), an inflammatory demyelinating disorder of the central nervous system (CNS). B7-H1 (PD-L1) is a novel member of the B7 family proteins which exert costimulatory and immune regulatory functions. Here we characterize the expression and functional activity of B7-H1 expressed on monocytes and dendritic cells (DC) of healthy donors and MS patients. B7-H1 is constitutively expressed on monocytes and differentially matured DC, but not on B cells. IFN-beta, the principle immune modulatory agent used for the treatment of MS, strongly enhances B7-H1 expression on monocytes and semi-matured DC, but not B cells, in vitro. Importantly, B7-H1 expressed on APC strongly inhibits autologous CD4 T-cell activation. Neutralization of B7-H1 on monocytes or differentially matured monocyte-derived DC markedly increases the secretion of the pro-inflammatory cytokines, IFN-gamma and IL-2, T-cell proliferation, and the expression of T-cell activation markers. B7-H1 exhibits strong inhibitory effects when expressed on monocytes, immature or semi-mature DC, but less so when expressed on fully matured DC. B7-H1-dependent immune inhibition is in part mediated by CD4/CD25+ regulatory T cells. There is no difference in the baseline expression levels of monocytic B7-H1 between untreated MS patients and healthy donors. However, both groups show a significant concentration-dependent up-regulation of B7-H1 mRNA and protein in response to IFN-beta in vitro. Serial measurements of B7-H1 mRNA in MS patients before and 6 months after initiation of IFN-beta therapy corroborated the relevance of these results in vivo: Nine of nine patients showed a significant increase in B7-H1 mRNA levels after 6 months of IFN-beta therapy (median 1.04 vs. 8.78; p<0.05, two-sided t-test). Accordingly, protein expression of B7-H1 on monocytes was up-regulated after 24 h of IFN-beta application. In summary, B7-H1 expressed on APC acts as a strong inhibitor of autologous CD4 T-cell activation and may thus contribute to the maintenance of peripheral immune tolerance. IFN-beta up-regulates B7-H1 in vitro and in MS patients in vivo and might represent a novel mechanism how IFN-beta acts as a negative modulator on APC T-cell interactions in the periphery.

Dendritic cell-mediated T cell polarization

Effective defense against diverse types of micro-organisms that invade our body requires specialized classes of antigen-specific immune responses initiated and maintained by distinct subsets of effector CD4(+) T helper (Th) cells. Excessive or detrimental (e.g., autoimmune) responses by effector T cells are controlled by regulatory T cells. The optimal balance in the development of the different types of effector and regulatory Th cells is orchestrated by dendritic cells (DC). This review discusses the way DC adapt the T cell response to the type of pathogen, focusing on the tools that DC use in this management of the T cell response.

Blocking Programmed Death-1 Ligand-PD-1 Interactions by Local Gene Therapy Results in Enhancement of Antitumor Effect of Secondary Lymphoid Tissue Chemokine

The negative signal provided by interactions of programmed death-1 (PD-1) and its ligands, costimulatory molecules PD-L1 (also B7-H1) and PD-L2 (also B7-DC), is involved in the mechanisms of tumor immune evasion. In this study, we found that this negative signal was also involved in immune evasion in tumor immunotherapy. When we used different doses of a constructed eukaryotic expression plasmid, pSLC, which expresses functional murine secondary lymphoid tissue chemokine (SLC, CCL21), to treat BALB/c mice inoculated with H22 murine hepatoma cells, the inhibitory effect was enhanced along with the increase of pSLC dosage. Unexpectedly, however, the best complete inhibition rate of tumor was reached when pSLC was used at the dosage of 50 microg but not 100 or 200 microg. RT-PCR and real-time PCR revealed that both PD-L1 and PD-L2 genes were expressed in tumor and vicinal muscle tissues of tumor-bearing mice and the expression level was significantly increased if a higher dosage of pSLC was administered. We then constructed a eukaryotic expression plasmid (pPD-1A) that expresses the extracellular domain of murine PD-1 (sPD-1). sPD-1 could bind PD-1 ligands, block PD-Ls-PD-1 interactions, and enhance the cytotoxicity of tumor-specific CTL. Local gene transfer by injection of pPD-1A mediated antitumor effect and improved SLC-mediated antitumor immunity. The combined gene therapy with SLC plus sPD-1 did not induce remarkable autoimmune manifestations. Our findings provide a potent method of improving the antitumor effects of SLC and possibly other immunotherapeutic methods by local blockade of negative costimulatory molecules.

Murine B7-H3 is a negative regulator of T cells

T cell activation is regulated by the innate immune system through positive and negative costimulatory molecules. B7-H3 is a novel B7-like molecule with a putative receptor on activated T cells. Human B7-H3 was first described as a positive costimulator, most potently inducing IFN-gamma production and cellular immunity. In this study we examined the expression and function of mouse B7-H3. B7-H3 is mostly expressed on professional APCs; its expression on dendritic cells appears to be up-regulated by LPS. In contrast to human B7-H3, we found that mouse B7-H3 protein inhibited T cell activation and effector cytokine production. An antagonistic mAb to B7-H3 enhanced T cell proliferation in vitro and led to exacerbated experimental autoimmune encephalomyelitis in vivo. Therefore, mouse B7-H3 serves as a negative regulator of T cell activation and function.

Shaping phenotype, function, and survival of dendritic cells by cytomegalovirus-encoded IL-10

Human dendritic cells (DCs) are essential for the antiviral immune response and represent a strategically important target for immune evasion of viruses, including human CMV (HCMV). Recently, HCMV has been discovered to encode a unique IL-10 homologue (cmvIL-10). In this study we investigated the capacity of cmvIL-10 to shape phenotype, function, and survival of DCs. For comparison we included human IL-10 and another IL-10 homologue encoded by EBV, which does not directly target DCs. Interestingly, cmvIL-10 strongly activated STAT3 in immature DCs despite its low sequence identity with human IL-10. For most molecules cmvIL-10 blocked LPS-induced surface up-regulation, confirming its role as an inhibitor of maturation. However, a small number of molecules on LPS-treated DCs including IDO, a proposed tolerogenic molecule, showed a different behavior and were up-regulated in response to cmvIL-10. Intriguingly, the expression of C-type lectin DC-specific ICAM-grabbing nonintegrin, a receptor for HCMV infection found exclusively on DCs, was also enhanced by cmvIL-10. This phenotypic change was mirrored by the efficiency of HCMV infection. Moreover, DCs stimulated with LPS and simultaneously treated with cmvIL-10 retained the function of immature DCs. Finally, cmvIL-10 increased apoptosis associated with DC maturation by blocking up-regulation of the antiapoptotic long form cellular FLIP. Taken together, these findings show potential mechanisms by which cmvIL-10 could assist HCMV to infect DCs and to impair DC function and survival.

Blockade of the interaction between PD-1 and PD-L1 accelerates graft arterial disease in cardiac allografts

BACKGROUND

Programmed death-1 (PD-1), a member of the CD28 family, has been identified. PD-1 is involved in the negative regulation of some immune responses. We evaluated the role of PD-ligand 1 (PD-L1) in graft arterial disease (GAD) of cardiac allografts and in smooth muscle cells (SMCs).

METHODS AND RESULTS

C57BL/6 murine hearts were transplanted into B6.C-H2KhEg mice for examination of GAD. PD-L1 was expressed in SMCs of the thickened intima in the graft coronary arteries, and administration of anti-PD-L1 monoclonal antibody (mAb) enhanced the progression of GAD (luminal occlusion: 55+/-5.0% versus 9.8+/-4.3%, P<0.05). The expressions of interferon gamma (IFN-gamma) and tumor necrosis factor alpha of cardiac allografts were upregulated in response to anti-PD-L1 mAb treatment. In vitro, PD-L1 expression was induced in SMCs in response to IFN-gamma stimulation. Sensitized splenocytes increased SMC proliferation, and anti-PD-L1 mAb in combination with IFN-gamma stimulation increased this proliferation.

CONCLUSIONS

The PD-L1 pathway regulates both the proliferation of SMCs and GAD. Thus, control of this interaction is a promising strategy for suppression of GAD.