B7-DC (PD-L2) costimulation of CD4+ T-helper 1 response via RGMb.

The role of B7-DC in T-cell responses remains controversial because both coinhibitory and costimulatory functions have been reported in various experimental systems in vitro and in vivo. In addition to interacting with the coinhibitory receptor PD-1, B7-DC has also been shown to bind repulsive guidance molecule b (RGMb). The functional consequences of the B7-DC/RGMb interaction, however, remain unclear. More than a decade ago, we reported that replacement of a murine B7-DC mutant lysine with serine (K113S) at positive 113 resulted in a loss of binding capacity to PD-1. Nevertheless, K113S remained costimulatory for T cells in vitro, implicating a dual functionality for B7-DC in T-cell responses. Here we show that recombinant K113S protein interacts with RGMb with a similar affinity to wild-type B7-DC. More importantly, K113S costimulates CD4+ T-cell responses via RGMb and promotes Th1 polarization. RGMb is expressed on the surface of naive mouse T cells, macrophages, neutrophils and dendritic cells. Finally, K113S/RGMb costimulation suppresses Th2-mediated asthma and ameliorates small airway inflammation and lung pathology in an experimental mouse model. Our findings indicate that RGMb is a costimulatory receptor for B7-DC. These findings from the K113S variant provide not only a possible explanation for the B7-DC-triggered contradictory effects on T-cell responses, but also a novel approach to investigate the B7-DC/PD-1/RGMb axis. Recombinant K113S or its derivatives could potentially be developed as an agonist for RGMb to costimulate the Th1 response without triggering PD-1-mediated T-cell inhibition.

Oral Squamous Carcinoma Cells Express B7-H1 and B7-DC Receptors in Vivo.

B7-H1 and B7-DC ligands are members of the B7 family with important regulatory functions in cell-mediated immune response. Both receptors are ligands of the programmed death receptor PD-1. B7-H1 expression has been detected in the majority of human carcinomas in vivo. B7-H1 mediated signals are able to negatively regulate activated T cell functions and survival, and enable tumor cells to overcome host response. The aim of this study was to investigate the expression of B7-H1 and B7-DC proteins in oral squamous cell carcinomas (OSCC) in vivo. Tissues from 15 samples were cryo-sected and following histological routine staining (HE), incubated with antibodies against human B7-H1 and B7-DC. Immuno-staining of pan-cytokeratin was performed to ascertain the epithelial origin of the tissue and CK 19 to demonstrate the proliferating stage. Confocal laser scanning microscopy confirmed the presence of both B7-H1 and B7-DC in all 15 OSCC. The B7-H1 and B7-DC staining was located in areas of the tissue that were identified as cancerous lesions in the previously stained HE sections before. Staining with Pan-CK and CK19 provided evidence for the epithelial origin and the proliferating stage of the tissue. The in vivo expression of the B7-H1 and B7-DC receptors in oral squamous cell carcinomas suggest that general mechanisms for immune evasion of tumors are also found in OSCC.

Blockade of the B7-H1/PD-1 pathway for cancer immunotherapy.

The aim of cancer immunotherapy is to treat malignant disease by inducing or enhancing cancer specific immune responses. With the identification of tumor-associated antigens (TAAs) in the 1990s, cancer immunotherapy research largely focused on inducing immune responses against TAAs but achieved limited success. More recently, the underlying mechanisms and molecular pathways that cancers manipulate to subvert immune-mediated destruction have been identified, including a set of molecules with potent coinhibitory functions. Coinhibitory molecules are expressed on the surface of immune cells, cancer cells, and stromal cells and negatively regulate immune responses to cancer. In particular, one of these ligand-receptor coinhibitory interactions, B7-H1/PD-1, is critical for modulating immune responses to cancer. This knowledge led to the design of revolutionary new immunotherapeutics based on the manipulation of these molecular pathways. Monoclonal antibodies (mAbs) are the primary immunotherapeutic modality used to promote immune function via antagonism or agonism of inhibitory or stimulatory molecular pathways, respectively. Here, we review current knowledge on the function of the B7-H1/PD-1 pathway in mice and humans, its role in the subversion of immune responses in cancer, and clinical evidence that mAb targeting of this pathway results in profound immune anti-cancer effects.

Kinetic expressions of PD-L1 and PD-L2 on the surface of human lymphocytes and monocytes / 中国病理生理杂志

AIM: To investigate the expression kinetics of PD-L1 and PD-L2 on the surface of the resting and activated B/T cells as well as monocytes from healthy human peripheral blood.METHODS: Fluorescent antibody staining together with flow cytometry were used to detect the percentages of the resting as well as the activated B cells and T cells that expressed PD-L1 and PD-L2.Meanwhile the percentages of the resting and activated monocytes that expressed PD-L2 were determined.RESULTS: Both resting B cells and T cells did not express PD-L1 on their surface,however PD-L1 expression was significantly up-regulated on the surface of the activated B cells after 6 h stimulation with LPS or pokeweed mitogen(PWM),and the percentages of B cells that expressed PD-L1 reached a plateau at 24 h,which were(46.26?10.71)% with LPS and(43.67?6.14)% with PWM stimulation,respectively.No markedly change of PD-L1 expression on the surface of the activated T cells after stimulation with LPS was observed,but upregulation of PD-L1 expression was observed when stimulation with PWM.The percentages of T cells that expressed PD-L1 reached a plateau at 24 h,which was(25.42?9.23)%.PD-L2 expression was not found on the resting as well as the activated B cells and T cells.In addition,the resting monocytes did not express PD-L2.Combination of INF-? plus LPS markedly induced the PD-L2 expression,and the percentages of monocytes that expressed PD-L2 reached a peak at 48 h,which was(28.70?14.22)%.CONCLUSION: The activated lymphocytes only express PD-L1,reaching a plateau at 24 h.PD-L2 is expressed on the surface of the activated monocytes,reaching a peak at 48 h.