Programmed death 1 (PD-1) is a new member of the CD28/CTLA-4 family, which has been implicated in the maintenance of peripheral tolerance. Two ligands for PD-1, namely, B7-H1 (PD-L1) and B7-DC (PD-L2), have recently been identified as new members of the B7 family but their expression at the protein level remains largely unknown. To characterize the expression of B7-H1 and B7-DC, we newly generated an anti-mouse B7-H1 mAb (MIH6) and an anti-mouse B7-DC mAb (TY25). MIH6 and TY25 immunoprecipitated a single molecule of 43 and 42 kDa from the lysate of B7-H1 and B7-DC transfectants, respectively. Flow cytometric analysis revealed that B7-H1 was broadly expressed on the surface of mouse tumor cell lines while the expression of B7-DC was rather restricted. PD-1 was expressed on anti-CD3-stimulated T cells and anti-IgM plus anti-CD40-stimulated B cells at high levels but was undetectable on activated macrophages or DCs. B7-H1 was constitutively expressed on freshly isolated splenic T cells, B cells, macrophages, and dendritic cells (DCs), and up-regulated on T cells by anti-CD3 stimulation on macrophages by LPS, IFN-γ, GM-CSF, or IL-4, and on DCs by IFN-γ, GM-CSF, or IL-4. In contrast, B7-DC expression was only inducible on macrophages and DCs upon stimulation with IFN-γ, GM-CSF, or IL-4. The inducible expression of PD-1 ligands on both T cells and APCs may suggest new paradigms of PD-1-mediated immune regulation.

Programmed death-1 (PD-1) receptor, an inhibitory costimulatory molecule found on activated T cells, has been demonstrated to play a role in the regulation of immune responses and peripheral tolerance. We investigated the role of this pathway in the development of autoimmune diabetes. PD-1 or PD-L1 but not PD-L2 blockade rapidly precipitated diabetes in prediabetic female nonobese diabetic (NOD) mice regardless of age (from 1 to 10-wk-old), although it was most pronounced in the older mice. By contrast, cytotoxic T lymphocyte–associated antigen 4 (CTLA-4) blockade induced disease only in neonates. Male NOD mice also developed diabetes after PD-1–PD-L1 pathway blockade, but NOR mice, congenic to NOD but resistant to the development of diabetes, did not. Insulitis scores were significantly higher and frequency of interferon γ–producing GAD-reactive splenocytes was increased after PD-1–PD-L1 pathway blockade compared with controls. Interestingly, PD-L1 but not PD-L2 was found to be expressed on inflamed islets of NOD mice. These data demonstrate a central role for PD-1–PD-L1 interaction in the regulation of induction and progression of autoimmune diabetes in the NOD mouse and provide the rationale to develop new therapies to target this costimulatory pathway in this disease.

Summary Although T helper 17 (Th17) cells have been found in human tumor tissues, their function in cancer immunity is unclear. Here we show that IL-17-deficient mice were more susceptible to the development of lung melanoma. Conversely, adoptive T cell therapy with tumor-specific Th17 cells prevented tumor development. Importantly, the donor Th17 cells retained their cytokine expression phenotype and exhibited stronger therapeutic efficacy than Th1 cells. Unexpectedly, therapy using Th17 but not Th1 cells elicited a remarkable activation of tumor-specific CD8+ T cells, which were necessary for the anti-tumor effect. Th17 cells promoted dendritic cell recruitment into the tumor tissues and greatly increased the numbers of CD8α+ dendritic cells containing tumor materials in draining lymph nodes. Moreover, compared to Th1 cells, Th17 cells promoted CCL20 chemokine production in tumor tissues and tumor-bearing CCR6-deficient mice were completely impaired in responding to Th17 therapy. Our data indicate that Th17 cells elicit a protective inflammation that ultimately promotes the activation of tumor-specific CD8+ T cells. These findings have important implications in anti-tumor immunotherapies.

Th17 and regulatory T (Treg) cells play opposite roles in autoimmune diseases. However, the mechanisms underlying their proper migration to inflammatory tissues are unclear. In this study, we report that these two T cell subsets both express CCR6. CCR6 expression in Th17 cells is regulated by TGF-β and requires two nuclear receptors, RORα and RORγ. Th17 cells also express the CCR6 ligand CCL20, which is induced synergistically by TGF-β and IL-6, which requires STAT3, RORγ and IL-21. Th17 cells, by producing CCL20, promote migration of Th17 and Treg cells in vitro in a CCR6-dependent manner. Lack of CCR6 in Th17 cells reduces the severity of experimental autoimmune encephalomyelitis and Th17 and Treg recruitment into inflammatory tissues. Similarly, CCR6 on Treg cells is also important for their recruitment into inflammatory tissues. Our data indicate an important role of CCR6 in Treg and Th17 cell migration.

ICOS is a new member of the CD28 family of costimulatory molecules that is expressed on activated T cells. Its ligand B7RP-1 is constitutively expressed on B cells. Although the blockade of ICOS/B7RP-1 interaction inhibits T cell-dependent Ab production and germinal center formation, the mechanism remains unclear. We examined the contribution of ICOS/B7RP-1 to the generation of CXCR5+ follicular B helper T (TFH) cells in vivo, which preferentially migrate to the B cell zone where they provide cognate help to B cells. In the spleen, anti-B7RP-1 mAb-treated or ICOS-deficient mice showed substantially impaired development of CXCR5+ TFH cells and peanut agglutinin+ germinal center B cells in response to primary or secondary immunization with SRBC. Expression of CXCR5 on CD4+ T cells was associated with ICOS expression. Adoptive transfer experiments showed that the development of CXCR5+ TFH cells was enhanced by interaction with B cells, which was abrogated by anti-B7RP-1 mAb treatment. The development of CXCR5+ TFH cells in the lymph nodes was also inhibited by the anti-B7RP-1 mAb treatment. These results indicated that the ICOS/B7RP-1 interaction plays an essential role in the development of CXCR5+ TFH cells in vivo.

B7-H3 belongs to the B7 superfamily, a group of molecules that costimulate or downmodulate T-cell responses. Although it was shown that B7-H3 could inhibit T-cell responses, several studies -most of them performed in murine systems -found B7-H3 to act in a costimulatory manner. In this study, we have specifically addressed a potential functional dualism of human B7-H3 by assessing the effect of this molecule under varying experimental conditions as well as on different T-cell subsets. We show that B7-H3 does not costimulate human T cells. In the presence of strong activating signals, B7-H3 potently and consistently down-modulated human T-cell responses. This inhibitory effect was evident when analysing proliferation and cytokine production and affected naïve as well as pre-activated T cells. Furthermore, we demonstrate that B7-H3-T-cell interaction is characterised by an early suppression of IL-2 and that T-cell inhibition can be reverted by exogenous IL-2. Since the triggering receptor expressed on myeloid cells like transcript 2 (TREML2/TLT-2) has been recently described as costimulatory receptor of murine B7-H3 we have extensively analysed interaction of human B7-H3 with TREML2/TLT-2. In these experiments we found no evidence for such an interaction. Furthermore, our data do not point to a role for murine TREML2 as a receptor for murine B7-H3. Key words: Costimulatory molecules . Immune regulation . T cells Supporting Information available online IntroductionFor fine-tuning the immune response, several costimulatory and coinhibitory signals are needed, in addition to signal 1 provided via the peptide-MHC/TCR-complex interaction. CD80 (B7-1) and CD86 (B7-2) serve as primary costimulatory ligands. Recently, additional members of the B7 family -the so-called B7 homologshave been identified [1]. The functional role of several of these B7 homologs is still controversially discussed. One of these molecules is B7-H3, which was originally described as a potent costimulatory molecule and inducer of IFN-g in human T cells [2]. In contrast, Ling et al. found human B7-H3 to strongly down-regulate T-cell proliferation and cytokine production [3]. It was suggested that the presence of two B7-H3 receptors with different functions could explain these divergent results [3]. Recent data that showed opposing effects of B7-H3 on resting and cytokine-activated T cells as well as contradicting results on the function of murine B7-H3 would also be in support for such a constellation [4][5][6][7]. Such receptor molecules could either be differentially regulated on T cells or be expressed on different T-cell subsets. Depending on the experimental system used the effects of the costimulatory or the inhibitory receptor could prevail and explain the discrepancies in different studies.Here, we have specifically addressed a potential functional dualism of B7-H3 by studying B7-H3 effects under varying experimental conditions as well as on different subsets of human T cells. Our results point to a potent and consistent inhibitory role of h...

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.

Programmed death-1 (PD-1) and its ligands, B7-H1/PD-L1 and B7-DC/PD-L2, are new CD28-B7 family members that may be involved in the regulation of immune responses. We examined the roles of these molecules in mouse hapten-induced contact hypersensitivity (CH). Administration of anti-PD-1 mAb at sensitization significantly enhanced and prolonged ear swelling. Treatment with anti-B7-H1 mAb, but not anti-B7-DC mAb, also enhanced CH reactions. The anti-PD-1 mAb treatment at sensitization significantly increased the T cell number of draining lymph nodes (DLN). B7-H1 was induced on activated T cells and antigen-presenting cells (APC) in the skin and the DLN, whereas B7-DC expression was restricted to dendritic cells (DC) in the dermis and the DLN. A particular subset of DC, B7-H1 + B7-DC -CD86 low , was found in sensitized DLN. The blockade of B7-H1, but not B7-DC, dramatically enhanced the initial T cell proliferative responses against hapten-pulsed DLN APC, suggesting the preferential contribution of B7-H1 to the T cell-APC interaction. Our results demonstrate the regulatory role of PD-1 and the differential roles of B7-H1 and B7-DC in hapten-induced immune responses. The PD-1-B7-H1 pathway may play a unique role in regulating inflammatory responses.