B7-H1, a recently described member of the B7 family of costimulatory molecules, is thought to be involved in the regulation of cellular and humoral immune responses through the PD-1 receptor on activated T and B cells. We report here that, except for cells of the macrophage lineage, normal human tissues do not express B7-H1. In contrast, B7-H1 is abundant in human carcinomas of lung, ovary and colon and in melanomas. The pro-inflammatory cytokine interferon-gamma upregulates B7-H1 on the surface of tumor cell lines. Cancer cell-associated B7-H1 increases apoptosis of antigen-specific human T-cell clones in vitro, and the apoptotic effect of B7-H1 is mediated largely by one or more receptors other than PD-1. In addition, expression of B7-H1 on mouse P815 tumor increases apoptosis of activated tumor-reactive T cells and promotes the growth of highly immunogenic B7-1(+) tumors in vivo. These findings have implications for the design of T cell-based cancer immunotherapy.

Tumour cells evade immune surveillance by upregulating the surface expression of programmed death-ligand 1 (PD-L1), which interacts with programmed death-1 (PD-1) receptor on T cells to elicit the immune checkpoint response. Anti-PD-1 antibodies have shown remarkable promise in treating tumours, including metastatic melanoma. However, the patient response rate is low. A better understanding of PD-L1-mediated immune evasion is needed to predict patient response and improve treatment efficacy. Here we report that metastatic melanomas release extracellular vesicles, mostly in the form of exosomes, that carry PD-L1 on their surface. Stimulation with interferon-γ (IFN-γ) increases the amount of PD-L1 on these vesicles, which suppresses the function of CD8 T cells and facilitates tumour growth. In patients with metastatic melanoma, the level of circulating exosomal PD-L1 positively correlates with that of IFN-γ, and varies during the course of anti-PD-1 therapy. The magnitudes of the increase in circulating exosomal PD-L1 during early stages of treatment, as an indicator of the adaptive response of the tumour cells to T cell reinvigoration, stratifies clinical responders from non-responders. Our study unveils a mechanism by which tumour cells systemically suppress the immune system, and provides a rationale for the application of exosomal PD-L1 as a predictor for anti-PD-1 therapy.

The B7 family members B7-1 and B7-2 interact with CD28 and constitute an essential T-cell co-stimulatory pathway in the initiation of antigen-specific humoral and cell-mediated immune response. Here, we describe a third member of the B7 family, called B7-H1 that does not bind CD28, cytotoxic T-lymphocyte A4 or ICOS (inducible co-stimulator). Ligation of B7-H1 co-stimulated T-cell responses to polyclonal stimuli and allogeneic antigens, and preferentially stimulated the production of interleukin-10. Interleukin-2, although produced in small amounts, was required for the effect of B7-H1 co-stimulation. Our studies thus define a previously unknown co-stimulatory molecule that may be involved in the negative regulation of cell-mediated immune responses.

We describe here a newly identified member of the human B7 family, designated B7 homolog 3 (B7-H3), that shares 20-27% amino acid identity with other B7 family members. B7-H3 mRNA is not detectable in peripheral blood mononuclear cells, although it is found in various normal tissues and in several tumor cell lines. Expression of B7-H3 protein, however, can be induced on dendritic cells (DCs) and monocytes by inflammatory cytokines and a combination of phorbol myristate acetate (PMA) + ionomycin. Soluble B7-H3 protein binds a putative counter-receptor on activated T cells that is distinct from CD28, cytotoxic T lymphocyte antigen 4 (CTLA-4), inducible costimulator (ICOS) and PD-1. B7-H3 costimulates proliferation of both CD4+ and CD8+ T cells, enhances the induction of cytotoxic T cells and selectively stimulates interferon gamma (IFN-gamma) production in the presence of T cell receptor signaling. In contrast, inclusion of antisense B7-H3 oligonucleotides decreases the expression of B7-H3 on DCs and inhibits IFN-gamma production by DC-stimulated allogeneic T cells.Thus, we describe a newly identified costimulatory pathway that may participate in the regulation of cell-mediated immune responses.