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Key Points The immune response against cancer is tightly regulated through a set of stimulatory and inhibitory molecules expressed by cancer cells, stromal cells (including APCs) and haematopoietic cells in the tumour microenvironment. Expression of inhibitory members of the co-stimulatory B7 family, such as B7-H1 and B7-H4, is often up-regulated in the tumour microenvironment by local factors including cytokines. Inhibitory B7 molecules mediate various mechanisms to evade tumour-antigen-specific T-cell immunity, including T-cell apoptosis, anergy and exhaustion, forming a molecular shield to protect tumour cells from lysis, and functional modulations of antigen-presenting cells and regulatory T cells. Expression of inhibitory B7 molecules in the tumour microenvironment correlates with poor prognosis in several types of human cancer. Therefore, these molecules might be potential biomarkers to predict therapeutic outcome. Blockade of signalling through the inhibitory B7 molecules is a promising strategy that might work alone or in combination with other modalities to improve current tumour therapies. This Review describes how the expression of inhibitory members of the B7 family, particularly B7-H1 and B7-H4, by cancer cells, stromal cells and haematopoietic cells in the tumour microenvironment is regulated and acts to inhibit T-cell immunity, as well as the therapeutic implications. 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.

This report describes five patients with treatment-resistant focal segmental glomerulosclerosis and positive B7-1 immunostaining who had a response to abatacept (CTLA-4–Ig), a costimulatory inhibitor that targets B7-1 (CD80). The renal glomeruli are highly specialized structures that ensure selective ultrafiltration of plasma, by which most proteins are retained in the blood. 1 The glomerular filtration barrier consists of the glomerular capillary endothelium, the glomerular basement membrane, and specialized cells, the podocytes, that serve as a final barrier to urinary loss of plasma proteins. 1 Disrupted podocyte function damages the kidney filtration mechanism, resulting in proteinuria and, in some circumstances, the nephrotic syndrome. 1 Proteinuria is common to a heterogeneous group of kidney diseases, including minimal-change disease, FSGS, membranous nephropathy, and diabetic nephropathy, all of which affect millions of persons worldwide and often . . .

Programmed cell death–1 (PD-1)–targeted therapies enhance T cell responses and show efficacy in multiple cancers, but the role of costimulatory molecules in this T cell rescue remains elusive. Here, we demonstrate that the CD28/B7 costimulatory pathway is essential for effective PD-1 therapy during chronic viral infection. Conditional gene deletion showed a cell-intrinsic requirement of CD28 for CD8 T cell proliferation after PD-1 blockade. B7-costimulation was also necessary for effective PD-1 therapy in tumor-bearing mice. In addition, we found that CD8 T cells proliferating in blood after PD-1 therapy of lung cancer patients were predominantly CD28-positive. Taken together, these data demonstrate CD28-costimulation requirement for CD8 T cell rescue and suggest an important role for the CD28/B7 pathway in PD-1 therapy of cancer patients.

Targeted blockade of PD-1 with immune checkpoint inhibitors can activate Tcells to destroy tumors. PD-1 is believed to function mainly at the effector, but not in the activation, phase of T cell responses, yet how PD-1 function is restricted at the activation stage is currently unknown. Here we demonstrate that CD80 interacts with PD-L1 in cis on antigen-presenting cells (APCs) to disrupt PD-L1/PD-1 binding. Subsequently, PD-L1 cannot engage PD-1 to inhibit Tcell activation when APCs express substantial amounts of CD80. In knock-in mice in which cis-PD-L1/CD80 interactions do not occur, tumor immunity and autoimmune responses were greatly attenuated by PD-1.These findings indicate that CD80 on APCs limits the PD-1 coinhibitory signal,while promoting CD28-mediated costimulation, and highlight critical components for induction of optimal immune responses.

Key Points Co-stimulatory and co-inhibitory molecules are cell surface receptors and ligands that are classified into various families on the basis of their structure and functions. After interaction with their specific ligands or counter-receptors that positively and negatively regulate T cell function, co-signalling receptors trigger biochemical signals in T cells. Multiple co-stimulatory and co-inhibitory receptors are expressed differentially during specific phases of T cell differentiation and on specific subsets of T cells to direct T cell regulation and function. Co-stimulatory and co-inhibitory molecules constitute important targets for immune modulation and the treatment of human diseases. The central role of co-stimulatory and co-inhibitory receptors in T cell biology has been proven by the effective therapeutic targeting of some of these molecules. However, the molecular aspects of T cell co-stimulation and co-inhibition are far from being fully understood. Here, the authors discuss emerging concepts in T cell co-signalling. Co-stimulatory and co-inhibitory receptors have a pivotal role in T cell biology, as they determine the functional outcome of T cell receptor (TCR) signalling. The classic definition of T cell co-stimulation continues to evolve through the identification of new co-stimulatory and co-inhibitory receptors, the biochemical characterization of their downstream signalling events and the delineation of their immunological functions. Notably, it has been recently appreciated that co-stimulatory and co-inhibitory receptors display great diversity in expression, structure and function, and that their functions are largely context dependent. Here, we focus on some of these emerging concepts and review the mechanisms through which T cell activation, differentiation and function is controlled by co-stimulatory and co-inhibitory receptors.

Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an essential negative regulator of T cell immune responses whose mechanism of action is the subject of debate. CTLA-4 shares two ligands (CD80 and CD86) with a stimulatory receptor, CD28. Here, we show that CTLA-4 can capture its ligands from opposing cells by a process of trans-endocytosis. After removal, these costimulatory ligands are degraded inside CTLA-4—expressing cells, resulting in impaired costimulation via CD28. Acquisition of CD86 from antigen-presenting cells is stimulated by T cell receptor engagement and observed in vitro and in vivo. These data reveal a mechanism of immune regulation in which CTLA-4 acts as an effector molecule to inhibit CD28 costimulation by the cell-extrinsic depletion of ligands, accounting for many of the known features of the CD28—CTLA-4 system.

Intrinsic malignant brain tumors, such as glioblastomas are frequently resistant to immune checkpoint blockade (ICB) with few hypermutated glioblastomas showing response. Modeling patient-individual resistance is challenging due to the lack of predictive biomarkers and limited accessibility of tissue for serial biopsies. Here, we investigate resistance mechanisms to anti-PD-1 and anti-CTLA-4 therapy in syngeneic hypermutated experimental gliomas and show a clear dichotomy and acquired immune heterogeneity in ICB-responder and non-responder tumors. We made use of this dichotomy to establish a radiomic signature predicting tumor regression after pseudoprogression induced by ICB therapy based on serial magnetic resonance imaging. We provide evidence that macrophage-driven ICB resistance is established by CD4 T cell suppression and T reg expansion in the tumor microenvironment via the PD-L1/PD-1/CD80 axis. These findings uncover an unexpected heterogeneity of response to ICB in strictly syngeneic tumors and provide a rationale for targeting PD-L1-expressing tumor-associated macrophages to overcome resistance to ICB. Modeling patient-individual resistance to immunotherapy is challenging. Here, the authors use a syngeneic experimental hypermutated orthotopic glioma model to define radiological and biological features that can predict or explain the mechanistic differences between responders and non-responders to immunotherapy.

Immune checkpoint blockade of the inhibitory immune receptors PD-L1, PD-1 and CTLA-4 has emerged as a successful treatment strategy for several advanced cancers. Here we demonstrate that miR-424(322) regulates the PD-L1/PD-1 and CD80/CTLA-4 pathways in chemoresistant ovarian cancer. miR-424(322) is inversely correlated with PD-L1, PD-1, CD80 and CTLA-4 expression. High levels of miR-424(322) in the tumours are positively correlated with the progression-free survival of ovarian cancer patients. Mechanistic investigations demonstrated that miR-424(322) inhibited PD-L1 and CD80 expression through direct binding to the 3′-untranslated region. Restoration of miR-424(322) expression reverses chemoresistance, which is accompanied by blockage of the PD-L1 immune checkpoint. The synergistic effect of chemotherapy and immunotherapy is associated with the proliferation of functional cytotoxic CD8+ T cells and the inhibition of myeloid-derived suppressive cells and regulatory T cells. Collectively, our data suggest a biological and functional interaction between PD-L1 and chemoresistance through the microRNA regulatory cascade. Resistance to chemotherapy occurs in many ovarian cancer cases. Here, the authors show that mir-424(322) expression restores the sensitivity of ovarian cancer cells to chemotherapy by blocking the PD-L1 immune checkpoint, and find that combining immunotherapy and chemotherapy has a synergistic effect.

Innate immune cells adjust to microbial and inflammatory stimuli through a process termed environmental plasticity, which links a given individual stimulus to a unique activated state. Here, we report that activation of human plasmacytoid predendritic cells (pDCs) with a single microbial or cytokine stimulus triggers cell diversification into three stable subpopulations (P1–P3). P1-pDCs (PD-L1 + CD80 – ) displayed a plasmacytoid morphology and specialization for type I interferon production. P3-pDCs (PD-L1 – CD80 + ) adopted a dendritic morphology and adaptive immune functions. P2-pDCs (PD-L1 + CD80 + ) displayed both innate and adaptive functions. Each subpopulation expressed a specific coding- and long-noncoding-RNA signature and was stable after secondary stimulation. P1-pDCs were detected in samples from patients with lupus or psoriasis. pDC diversification was independent of cell divisions or preexisting heterogeneity within steady-state pDCs but was controlled by a TNF autocrine and/or paracrine communication loop. Our findings reveal a novel mechanism for diversity and division of labor in innate immune cells. Plasmacytoid dendritic cells (pDCs) are known for their copious IFN-I production. Soumelis and colleagues show that functionally and transcriptomically distinct human pDC populations can be generated from a single microbial or cytokine stimulus.

The unique differentiation of IgE cells suggests unconventional mechanisms of IgE memory. IgE germinal centre cells are transient, most IgE cells are plasma cells, and high affinity IgE is produced by the switching of IgG1 cells to IgE. Here we investigate the function of subsets of IgG1 memory B cells in IgE production and find that two subsets of IgG1 memory B cells, CD80 + CD73 + and CD80 − CD73 − , contribute distinctively to the repertoires of high affinity pathogenic IgE and low affinity non-pathogenic IgE. Furthermore, repertoire analysis indicates that high affinity IgE and IgG1 plasma cells differentiate from rare CD80 + CD73 + high affinity memory clones without undergoing further mutagenesis. By identifying the cellular origin of high affinity IgE and the clonal selection of high affinity memory B cells into the plasma cell fate, our findings provide fundamental insights into the pathogenesis of allergies, and on the mechanisms of antibody production in memory B cell responses. IgE is an important mediator of protective immunity as well as allergic reaction, but how high affinity IgE antibodies are produced in memory responses is not clear. Here the authors show that IgE can be generated via class-switch recombination in IgG1 memory B cells without additional somatic hypermutation.