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

T cell quiescence is essential for maintaining a broad repertoire against a large pool of diverse antigens from microbes and tumors, but the underlying molecular mechanisms remain largely unknown. We show here that CD8α is critical for the maintenance of CD8+ T cells in a physiologically quiescent state in peripheral lymphoid organs. Upon inducible deletion of CD8α, both naïve and memory CD8+ T cells spontaneously acquired activation phenotypes and subsequently died without exposure to specific antigens. PILRα was identified as a ligand for CD8α in both mice and humans, and disruption of this interaction was able to break CD8+ T cell quiescence. Thus, peripheral T cell pool size is actively maintained by the CD8α-PILRα interaction in the absence of antigen exposure.

The immature and dysfunctional vascular network within solid tumors poses a substantial obstacle to immunotherapy because it creates a hypoxic tumor microenvironment that actively limits immune cell infiltration. The molecular basis underpinning this vascular dysfunction is not fully understood. Using genome-scale receptor array technology, we showed here that insulin-like growth factor binding protein 7 (IGFBP7) interacts with its receptor CD93, and we subsequently demonstrated that this interaction contributes to abnormal tumor vasculature. Both CD93 and IGFBP7 were up-regulated in tumor-associated endothelial cells. IGFBP7 interacted with CD93 via a domain different from multimerin-2, the known ligand for CD93. In two mouse tumor models, blockade of the CD93/IGFBP7 interaction by monoclonal antibodies promoted vascular maturation to reduce leakage, leading to reduced tumor hypoxia and increased tumor perfusion. CD93 blockade in mice increased drug delivery, resulting in an improved antitumor response to gemcitabine or fluorouracil. Blockade of the CD93 pathway triggered a substantial increase in intratumoral effector T cells, thereby sensitizing mouse tumors to immune checkpoint therapy. Last, analysis of samples from patients with cancer under anti-programmed death 1/programmed death-ligand 1 treatment revealed that overexpression of the IGFBP7/CD93 pathway was associated with poor response to therapy. Thus, our study identified a molecular interaction involved in tumor vascular dysfunction and revealed an approach to promote a favorable tumor microenvironment for therapeutic intervention.

Lymphocyte-activation gene 3 (LAG-3) is an immune inhibitory receptor, with major histocompatibility complex class II (MHC-II) as a canonical ligand. However, it remains controversial whether MHC-II is solely responsible for the inhibitory function of LAG-3. Here, we demonstrate that fibrinogen-like protein 1 (FGL1), a liver-secreted protein, is a major LAG-3 functional ligand independent from MHC-II. FGL1 inhibits antigen-specific T cell activation, and ablation of FGL1 in mice promotes T cell immunity. Blockade of the FGL1-LAG-3 interaction by monoclonal antibodies stimulates tumor immunity and is therapeutic against established mouse tumors in a receptor-ligand inter-dependent manner. FGL1 is highly produced by human cancer cells, and elevated FGL1 in the plasma of cancer patients is associated with a poor prognosis and resistance to anti-PD-1/B7-H1 therapy. Our findings reveal an immune evasion mechanism and have implications for the design of cancer immunotherapy.

The central nervous system (CNS) is an immune-privileged organ with the capacity to prevent excessive inflammation. Aside from the blood-brain barrier, active immunosuppressive mechanisms remain largely unknown. We report that a neuron-specific molecule, synaptic adhesion-like molecule 5 (SALM5), is a crucial contributor to CNS immune privilege. We found that SALM5 suppressed lipopolysaccharide-induced inflammatory responses in the CNS and that a SALM-specific monoclonal antibody promoted inflammation in the CNS, and thereby aggravated clinical symptoms of mouse experimental autoimmune encephalomyelitis. In addition, we identified herpes virus entry mediator as a functional receptor that mediates SALM5's suppressive function. Our findings reveal a molecular link between the neuronal system and the immune system, and provide potential therapeutic targets for the control of CNS diseases.

B7-H3 is a cell surface molecule in the immunoglobulin superfamily that is frequently upregulated in response to autoantigens and pathogens during host T cell immune responses. However, B7-H3's role in the differential regulation of T cell subsets remains largely unknown. Therefore, we constructed a new B7-H3 deficient mouse strain (B7-H3 KO) and evaluated the functions of B7-H3 in the regulation of Th1, Th2, and Th17 subsets in experimental autoimmune encephalomyelitis (EAE), experimental asthma, and collagen-induced arthritis (CIA); these mouse models were used to predict human immune responses in multiple sclerosis, asthma, and rheumatoid arthritis, respectively. Here, we demonstrate that B7-H3 KO mice have significantly less inflammation, decreased pathogenesis, and limited disease progression in both EAE and CIA mouse models when compared with littermates; these results were accompanied by a decrease in IFN-γ and IL-17 production. In sharp contrast, B7-H3 KO mice developed severe ovalbumin (OVA)-induced asthma with characteristic infiltrations of eosinophils in the lung, increased IL-5 and IL-13 in lavage fluid, and elevated IgE anti-OVA antibodies in the blood. Our results suggest B7-H3 has a costimulatory function on Th1/Th17 but a coinhibitory function on Th2 responses. Our studies reveal that B7-H3 could affect different T cell subsets which have important implications for regulating pathogenesis and disease progression in human autoimmune disease.

The B7/CD28 family has profound modulatory effects in immune responses and constitutes an important target for the development of novel therapeutic drugs against human diseases. Here we describe a new CD28 homologue (CD28H) that has unique functions in the regulation of the human immune response and is absent in mice. CD28H is constitutively expressed on all naive T cells. Repetitive antigenic exposure, however, induces a complete loss of CD28H on many T cells, and CD28H negative T cells have a phenotype of terminal differentiation and senescence. After extensive screening in a receptor array, a B7-like molecule, B7 homologue 5 (B7-H5), was identified as a specific ligand for CD28H. B7-H5 is constitutively found in macrophages and could be induced on dendritic cells. The B7-H5/CD28H interaction selectively costimulates human T-cell growth and cytokine production via an AKT-dependent signalling cascade. Our study identifies a novel costimulatory pathway regulating human T-cell responses.

T cell cosignaling pathways regulate T cell activation and control the fate of T cell responses. They consist of complex receptor-ligand interactions on cell surface between T cell and antigen presenting cell. The effort to identify co-signaling interactions has been hampered by low expression levels and weak affinities. We generated a comprehensive receptor array system in which over 2,500 human transmembrane proteins of hematopoietic system are expressed individually at high level and could be screened in a high throughput format to determine the binding partner of a fluorescence-labeled target protein. We report here the identification and characterization of two new interactions in the B7-CD28 family. Firstly, B7-H2, formerly known as the ligand for ICOS, is identified as the third ligand for CD28 and CTLA-4 in human. B7-H2 interacts with CD28 through a non-overlapping domain as B7-1 and B7-2. B7-H2-CD28 interaction is essential for the costimulation of human T cells’ primary responses to allogeneic antigens and memory recall responses. B7-H2-CD28 costimulation upregulates survival factor Bcl-xL, suppresses cell cycle inhibitor p27kip1 and induces signaling cascade of ERK and AKT kinases-dependent pathways. Secondly, B7-1 is identified as an inhibitory counter-receptor on T cell for B7-H1. Our study reveals new cosignaling interactions as potential targets for immune-modulation and provides a platform to rapidly discover receptor-ligand interactions in a large scale.

CD28 and CTLA-4 are cell surface cosignaling molecules essential for the control of T cell activation upon the engagement of their ligands B7-1 and B7-2 from antigen-presenting cells. By employing a receptor array assay, we have demonstrated that B7-H2, best known as the ligand of inducible costimulator, was a ligand for CD28 and CTLA-4 in human, whereas these interactions were not conserved in mouse. B7-H2 and B7-1 or B7-2 interacted with CD28 through distinctive domains. B7-H2-CD28 interaction was essential for the costimulation of human T cells' primary responses to allogeneic antigens and memory recall responses. Similar to B7-1 and B7-2, B7-H2 costimulation via CD28 induced survival factor Bcl-xL, downregulated cell cycle inhibitor p27kip1, and triggered signaling cascade of ERK and AKT kinase-dependent pathways. Our findings warrant re-evaluation of CD28 and CTLA-4's functions previously attributed exclusively to B7-1 and B7-2 and have important implications in therapeutic interventions against human diseases.

Antigen-specific memory T cells (Tms) are essential in the immune surveillance of residual and metastatic tumors. Activation of Tms requires designing vaccines based on tumor rejection antigens, which are often not available to cancer patients. Therefore, it is desirable to have a general applicable approach to activate Tms without extensive knowledge of tumor antigens. Here, we report that activation of antigen-specific Tms could be achieved by the administration of agonistic anti-CD137 monoclonal antibody without additional tumor vaccination, leading to the prevention of recurrence and metastases after surgical resection of primary tumors in mouse models. By reconstitution with CD137-deficient Tms, we demonstrate that expression of CD137 on antigen-specific Tms is only partially required for the effect of anti-CD137 antibody. Other host cells, including those from hematopoietic and nonhematopoietic origins, are also important because ablation of CD137 from these cells partially but significantly eliminates antitumor effect of anti-CD137 antibody. Our findings implicate a potential new approach to prevent recurrence and metastases in cancer patients.

Finding an association between soluble B7-H4 and rheumatoid arthritis severity, Lieping Chen and colleagues use a mouse model to show that the soluble form blocks the inhibitory function of cell-surface B7-H4.

B7-H4 is an immunoglobulin superfamily molecule and shown to be inhibitory for T-cell responses. To explore physiologic roles of B7-H4, we created B7-H4-deficient (KO) mice by genetic targeting. B7-H4KO mice are healthy and their T- and B-cell responses to polyclonal antigens are in normal range. However, B7-H4KO mice are more resistant to infection by Listeria monocytogenes than their littermates. Within 3 days after infection, bacterial colonies in livers and spleens are significantly lower than the controls, suggesting a role of B7-H4 in enhancing innate immunity. Further studies demonstrate that neutrophils increase in peripheral organs of B7-H4KO mice more so than their littermates but their bactericidal functions remain unchanged. Augmented innate resistance is completely dependent on neutrophils, even in the absence of adaptive immunity. In vitro B7-H4 inhibits the growth of bone marrow-derived neutrophil progenitors, suggesting an inhibitory function of B7-H4 in neutrophil expansion. Our results identify B7-H4 as a negative regulator of the neutrophil response to infection and provide a new target for manipulation of innate immunity.

SummaryLeucocyte‐associated immunoglobulin‐like receptor‐1 (LAIR‐1) is a membrane receptor of the immunoglobulin (Ig) superfamily that is expressed on most types of haematopoietic cells, and delivers inhibitory signals through interacting with collagens. In order to elucidate the immunological functions of LAIR‐1 in vivo, we established transgenic mice expressing a chimeric protein composed of the extracellular domain of LAIR‐1 fused with an Ig tag (LAIR‐1–Ig), which acts as a decoy by competing with endogenous LAIR‐1. The transgenic mice showed an increased susceptibility for development of contact hypersensitivity (CHS), an experimental model of allergic contact dermatitis, in association with enhanced hapten‐specific T‐cell responses. When T cells from the hapten‐sensitized donor mice were transferred into non‐sensitized recipients, treatment of either donor mice or recipient mice with LAIR‐1–Ig protein accelerated CHS, suggesting a potentially negative role of LAIR‐1 in both the sensitization and the elicitation of hapten‐reactive T cells. In vitro assays revealed that LAIR‐1 decreased the production of interleukin‐6 and interleukin‐12 in dendritic cells, and inhibited the proliferation and cytokine production of naïve and memory T cells along with G0/G1 cell cycle arrest. Collectively, our findings suggest that LAIR‐1 plays a crucial inhibitory role in CHS by regulating antigen‐presenting cell and T‐cell functions.

Programmed death one (PD-1) is an inducible molecule belonging to the immunoglobulin superfamily. It is expressed on activated T and B lymphocytes and plays pivotal roles in the negative regulation of adaptive immune responses. We report here an unexpected finding: that PD-1 could also be induced on splenic dendritic cells (DCs) by various inflammatory stimuli. Adoptive transfer of PD-1-deficient DCs demonstrates their superior capacity to wild-type DCs in innate protection of mice against lethal infection by Listeria monocytogenes. Furthermore, PD-1-deficient mice are also more resistant to the infection than wild-type controls, even in the absence of T and B cells, accompanied by elevated production of DC-derived interleukin-12 and tumor necrosis factor-alpha. Our results reveal a novel role of PD-1 in the negative regulation of DC function during innate immune response.

B7-H1 is an immunoglobulin-like immune suppressive molecule broadly detectable on the majority of human and rodent cancers, and its functions have been attributed to delivering an inhibitory signal to its counter-receptor programmed death-1 (PD-1) on T cells. Here we report that B7-H1 on cancer cells receives a signal from PD-1 to rapidly induce resistance against T cell-mediated killing because crippling signaling capacity of B7-H1 but not PD-1 ablates this resistance. Importantly, loss of B7-H1 signaling is accompanied by increased susceptibility to immune-mediated tumoricidal activity. In addition to resistance against T-cell destruction, B7-H1+ cancer cells also become refractory to apoptosis induced by Fas ligation or the protein kinase inhibitor Staurosporine. Our study reveals a new mechanism by which cancer cells use a receptor on immune cells as a ligand to induce resistance to therapy.

CD137 has long been recognized as a costimulatory receptor for growth and functional maturation of recently activated T cells in the presence of T-cell receptor signal. In this report, we present the fact that, in the absence of MHC and antigen, triggering of CD137 by an agonist monoclonal antibody induces vigorous growth of both CD8(+) and CD4(+) T cells with memory phenotype, whereas it does not affect naive T cells. Moreover, T cells with memory phenotype accumulate progressively in transgenic mice overexpressing CD137 ligand. CD137-mediated proliferation of memory T cells is directly through CD137 on T cells and does not require IL-15 and IFN-gamma. Our results define a new role of CD137 signal in the growth of memory T cells.

B7-H4 is a recently identified B7 family member. We previously showed that ovarian tumor and associated macrophages expressed B7-H4; tumor B7-H4(+) macrophages and CD4(+)CD25(+)FOXP3(+) regulatory T cells (Treg cells) suppressed tumor-associated antigen-specific T-cell immunity. To determine the pathologic relationship between B7-H4, macrophages, and Treg cells in the tumor environment, in addition to Treg cell numbers, we quantified B7-H4 expression in the tumor and tumor-associated macrophages in 103 patients with ovarian carcinoma. We observed that the intensity of B7-H4 expression in macrophages was significantly correlated with Treg cell numbers in the tumor. Further, both Treg cells and macrophage B7-H4, but not tumor B7-H4, were negatively associated with patient outcome. Tumor Treg cells enabled macrophages to spontaneously produce interleukin (IL)-10 and IL-6. Tumor macrophages stimulated B7-H4 expression in an autocrine manner through IL-10 and IL-6. Our previous work showed that tumor-associated macrophages spontaneously produced chemokine CCL22 to mediate Treg cell trafficking into tumor, and Treg cells induced B7-H4 on antigen-presenting cells (APC) including macrophages. Altogether, our data support the concept that there is a mechanistic interaction between Treg cells and macrophage, and that Treg cells may convey the suppressive activity to APCs through B7-H4 induction in human ovarian cancer.

Decoy lymphotoxin beta receptor (LTbetaR) has potent immune inhibitory activities and thus represents a promising biologic for the treatment of inflammation, autoimmune diseases, and graft-versus-host disease (GVHD). As this reagent interrupts multiple molecular interactions, including LTbeta-LTbetaR and LIGHT-HVEM/LTbetaR, underlying molecular mechanisms have yet to be fully understood. In this study, we demonstrate that blockade of the LIGHT-HVEM pathway is sufficient to induce amelioration of GVHD in mouse models. Anti-host cytotoxic T lymphocyte (CTL) activity following in vivo transfer of allogeneic lymphocytes was completely abrogated when LIGHT- or HVEM-deficient (KO) T cells were used as donor cells. Accordingly, survival of the recipient mice following the transfer of allogeneic bone marrow cells plus LIGHT-KO or HVEM-KO T cells was significantly prolonged. In the absence of LIGHT-HVEM costimulation, alloreactive donor T cells undergo vigorous apoptosis while their proliferative potential remains intact. Furthermore, we prepared a neutralizing monoclonal antibody (mAb) specific to HVEM and showed that administration of anti-HVEM mAb profoundly ameliorated GVHD and led to complete hematopoietic chimerism with donor cells. Collectively, our results demonstrate an indispensable role of LIGHT-HVEM costimulation in the pathogenesis of GVHD and illustrate a novel target for selective immunotherapy in allogeneic bone marrow transplantation.