Role of TIGIT in tumor progression and immune evasion

Recently, dysfunction of antigen-specific T cells is well documented as T-cell exhaustion and has been defined by the loss of effector functions during chronicinfections and cancer in human. The exhausted T cells are characterized phenotypically by the surface expression of immunoinhibitory receptors, such asprogrammed death 1 (PD-1), lymphocyte activation gene 3 (LAG-3), T-cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) and cytotoxic T-lymphocyteantigen 4 (CTLA-4). However, there is still a fundamental lack of knowledge about the immunoinhibitory receptors in the fields of veterinary medicine. Inparticular, very little is known about mechanism of T cell dysfunction in chronic infection in cattle. Recent our studies have revealed that immunoinhibitorymolecules including PD-1/ programmed death-ligand 1 (PD-L1) play critical roles in immune exhaustion and disease progression in case of bovine leukemia virus(BLV) infection, Johne’s disease and bovine anaplasmosis. This review includes some recent data from us.

Vulvovaginal melanoma (VVM) is a rare malignancy with poor prognosis and limited evidence to guide immunotherapy selection. This study aimed to assess the expression and interrelationships of programmed death-1 (PD-1), programmed death ligand-1 (PD-L1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), cluster of differentiation 4 (CD4), and cluster of differentiation 8 (CD8), and their associations with clinicopathological features and outcomes. Fifteen VVM cases were analysed using immunohistochemistry. PD-L1 was evaluated using tumour proportion score (TPS), immune cell score (IS), and combined positive score (CPS), CTLA-4, CD4, and CD8 were scored. Continuous marker values were analysed using Pearson correlation, with additional descriptive and spatial assessment of marker distribution. Survival and treatment data were reviewed when available. Most tumours showed high expression of PD-1, PD-L1 (IS/CPS), CTLA-4, CD4, and CD8, whereas PD-L1 (TPS) was comparatively lower. Significant positive correlations were observed between PD-1 and CD8, PD-1 and PD-L1 (IS/CPS), CD8 and PD-L1 (CPS), and between CTLA-4 and PD-L1 (TPS/CPS), indicating coordinated immune-checkpoint activation. PD-L1 expression was frequently enriched at the tumour-stroma interface. High CD4 expression correlated with increased mitotic rate, while CD8 and CTLA-4 expression correlated with melanin status. Higher PD-1, PD-L1, and CTLA-4 expression generally associated with longer overall survival following immunotherapy. In a case with serial recurrences, PD-1, PD-L1 (TPS, CPS), CTLA-4 expression increased while PD-L1 (IS) and CD4 + /CD8 + ratio decreased, suggesting a progressively immunosuppressive tumour microenvironment. These findings suggest that integrated immune profiling of PD-1, PD-L1, CTLA-4, and T-cell subsets may serve as predictive markers for immunotherapy in VVM.

Pd1 and Pdl1 in Hpv + and Hpv -/Tp53 Mutated Head and Neck Squamous Cell Carcinomas

Several Immune Checkpoint Regulators Are Associated With Poor Prognosis in Salivary Duct Carcinoma Patients.

<div>Abstract<p><b>Purpose:</b> Tyrosine kinase inhibitors are effective in gastrointestinal stromal tumors (GISTs) but often are of transient benefit as resistance commonly develops. Immunotherapy, particularly blockade of the inhibitory receptor programmed death 1 (PD-1) or the ligand programmed death ligand 1 (PD-L1), has shown effectiveness in a variety of cancers. The functional effects of PD-1/PD-L1 blockade are unknown in GISTs.</p><p><b>Experimental Design:</b> We analyzed tumor and matched blood samples from 85 patients with GISTs and determined the expression of immune checkpoint molecules using flow cytometry. We investigated the combination of imatinib with PD-1/PD-L1 blockade in <i>Kit<sup>V558Δ/+</sup></i> mice that develop GISTs.</p><p><b>Results:</b> The inhibitory receptors PD-1, lymphocyte activation gene 3, and T-cell immunoglobulin mucin-3 were upregulated on tumor-infiltrating T cells compared with T cells from matched blood. PD-1 expression on T cells was highest in imatinib-treated human GISTs. Meanwhile, intratumoral PD-L1 expression was variable. In human GIST cell lines, treatment with imatinib abrogated the IFNγ-induced upregulation of PD-L1 via STAT1 inhibition. In <i>Kit<sup>V558Δ/+</sup></i> mice, imatinib downregulated IFNγ-related genes and reduced PD-L1 expression on tumor cells. PD-1 and PD-L1 blockade <i>in vivo</i> each had no efficacy alone but enhanced the antitumor effects of imatinib by increasing T-cell effector function in the presence of KIT and IDO inhibition.</p><p><b>Conclusions:</b> PD-1/PD-L1 blockade is a promising strategy to improve the effects of targeted therapy in GISTs. Collectively, our results provide the rationale to combine these agents in human GISTs. <i>Clin Cancer Res; 23(2); 454–65. ©2016 AACR</i>.</p></div>

<div>Abstract<p><b>Purpose:</b> Tyrosine kinase inhibitors are effective in gastrointestinal stromal tumors (GISTs) but often are of transient benefit as resistance commonly develops. Immunotherapy, particularly blockade of the inhibitory receptor programmed death 1 (PD-1) or the ligand programmed death ligand 1 (PD-L1), has shown effectiveness in a variety of cancers. The functional effects of PD-1/PD-L1 blockade are unknown in GISTs.</p><p><b>Experimental Design:</b> We analyzed tumor and matched blood samples from 85 patients with GISTs and determined the expression of immune checkpoint molecules using flow cytometry. We investigated the combination of imatinib with PD-1/PD-L1 blockade in <i>Kit<sup>V558Δ/+</sup></i> mice that develop GISTs.</p><p><b>Results:</b> The inhibitory receptors PD-1, lymphocyte activation gene 3, and T-cell immunoglobulin mucin-3 were upregulated on tumor-infiltrating T cells compared with T cells from matched blood. PD-1 expression on T cells was highest in imatinib-treated human GISTs. Meanwhile, intratumoral PD-L1 expression was variable. In human GIST cell lines, treatment with imatinib abrogated the IFNγ-induced upregulation of PD-L1 via STAT1 inhibition. In <i>Kit<sup>V558Δ/+</sup></i> mice, imatinib downregulated IFNγ-related genes and reduced PD-L1 expression on tumor cells. PD-1 and PD-L1 blockade <i>in vivo</i> each had no efficacy alone but enhanced the antitumor effects of imatinib by increasing T-cell effector function in the presence of KIT and IDO inhibition.</p><p><b>Conclusions:</b> PD-1/PD-L1 blockade is a promising strategy to improve the effects of targeted therapy in GISTs. Collectively, our results provide the rationale to combine these agents in human GISTs. <i>Clin Cancer Res; 23(2); 454–65. ©2016 AACR</i>.</p></div>

Breast cancer remains the most commonly diagnosed malignancy among women worldwide and continues to pose significant therapeutic challenges, particularly in advanced and refractory disease. Although traditionally considered less immunogenic compared with other solid tumours, growing evidence demonstrates that subsets of breast cancer, particularly triple-negative and HER2-positive subtypes, exhibit immune-responsive features. This recognition has spurred the development and clinical evaluation of immunotherapeutic strategies, with immune checkpoint inhibitors (ICIs) emerging as the most prominent approach. This new class of drugs targeting the programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) axis has demonstrated meaningful clinical activity in select patient populations, leading to regulatory approvals in combination with chemotherapy for advanced triple-negative breast cancer. Despite these advances, response rates remain modest, and the benefits are largely restricted to patients with PD-L1-positive tumours. Ongoing studies are evaluating predictive biomarkers, optimal treatment combinations, and mechanisms of resistance to expand the efficacy of ICIs across broader breast cancer subtypes. Furthermore, novel checkpoint targets such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), lymphocyte-activation gene 3 (LAG-3), and T cell immunoreceptor with immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domains (TIGIT) are under investigation, with the potential to enhance or complement PD-1/PD-L1 blockade. This review summarises the current state of knowledge on breast cancer immunotherapy with an emphasis on ICIs, highlighting key clinical trial findings, as well as emerging biomarkers of response, and strategies to overcome therapeutic resistance, if cancer cells eventually develop resistance. By integrating preclinical insights with clinical progress, we aim to provide a comprehensive overview of the evolving role of checkpoint blockade in breast cancer and outline future directions to optimise patient outcomes.

Tyrosine kinase inhibitors are effective in gastrointestinal stromal tumors (GISTs) but often are of transient benefit as resistance commonly develops. Immunotherapy, particularly blockade of the inhibitory receptor programmed death 1 (PD-1) or the ligand programmed death ligand 1 (PD-L1), has shown effectiveness in a variety of cancers. The functional effects of PD-1/PD-L1 blockade are unknown in GISTs. We analyzed tumor and matched blood samples from 85 patients with GISTs and determined the expression of immune checkpoint molecules using flow cytometry. We investigated the combination of imatinib with PD-1/PD-L1 blockade in KitV558Δ/+ mice that develop GISTs. The inhibitory receptors PD-1, lymphocyte activation gene 3, and T-cell immunoglobulin mucin-3 were upregulated on tumor-infiltrating T cells compared with T cells from matched blood. PD-1 expression on T cells was highest in imatinib-treated human GISTs. Meanwhile, intratumoral PD-L1 expression was variable. In human GIST cell lines, treatment with imatinib abrogated the IFNγ-induced upregulation of PD-L1 via STAT1 inhibition. In KitV558Δ/+ mice, imatinib downregulated IFNγ-related genes and reduced PD-L1 expression on tumor cells. PD-1 and PD-L1 blockade in vivo each had no efficacy alone but enhanced the antitumor effects of imatinib by increasing T-cell effector function in the presence of KIT and IDO inhibition. PD-1/PD-L1 blockade is a promising strategy to improve the effects of targeted therapy in GISTs. Collectively, our results provide the rationale to combine these agents in human GISTs. Clin Cancer Res; 23(2); 454-65. ©2016 AACR.

TPS370 Background: The programmed death-1 (PD-1)/PD-L1 pathway plays an important role in tumor induced immunosuppression. PD-L1 overexpression is observed in approximately 30–60% of esophageal cancers and is associated with poor prognosis. Anti-PD-1 agents demonstrate moderate efficacy in PD-L1-positive esophageal cancer in terms of response rate and overall survival, however, long-term outcomes remain poor due to primary and secondary resistance driven by tumor immune escape. The T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT) is upregulated on T-cells and natural killer cells in multiple solid tumors, which can inhibit anticancer immune responses. Ociperlimab (BGB-A1217) is a novel, humanized, monoclonal antibody that binds TIGIT with high specificity and affinity, blocking the interaction with its ligands on tumor cells. Preclinical and clinical studies suggest that dual targeting with anti-TIGIT and anti-PD-1 antibodies produces synergistic immune cell activation and enhanced antitumor activity. Methods: AdvanTIG-203 is a Phase 2, global, randomized, double-blind, placebo-controlled study (NCT04732494) of patients with unresectable, locally advanced, recurrent or metastatic ESCC, who progressed on or after 1st line systemic therapy and whose tumors express PD-L1 (visually-estimated combined positive score ≥ 10%). After stratification by Eastern Cooperative Oncology Group performance status (0 or 1), number of metastatic sites (≤ 1 or ≥ 2) and region (Asian or non-Asian), 280 patients will be randomized (1:1) to either ociperlimab 900 mg intravenous (IV) plus tislelizumab 200 mg IV every 3 weeks (Q3W), or tislelizumab plus placebo Q3W, until disease progression (per RECIST v1.1), unacceptable toxicity, death or withdrawal of consent. Co-primary endpoints are investigator-assessed overall response rate (ORR) and overall survival (OS) in the intention-to-treat population. A sample size of 280 patients was estimated to provide approximately 94.8% power to detect a 20% difference in ORR at a one-sided significance level of 0.025. With 198 deaths, the study was estimated to provide approximately 86% power to detect a hazard ratio of 0.65 for OS. Secondary endpoints are ORR by independent review, progression-free survival, duration of response, disease control rate, and clinical benefit rate per investigator and independent assessment, cancer-specific health-related quality of life (HRQoL), and safety. Exploratory endpoints include but are not limited to expression of TIGIT, CD226, CD155, CD112, and PD-L1, pharmacokinetics, immunogenicity, and generic HRQoL measures. Clinical trial information: NCT04732494.

TPS4150 Background: The programmed death-1 (PD-1)/PD-L1 pathway plays an important role in tumor induced immunosuppression. PD-L1 overexpression is observed in approximately 30–60% of esophageal cancers and is associated with poor prognosis. Anti-PD-1 agents demonstrate moderate efficacy in PD-L1-positive esophageal cancer in terms of response rate and overall survival, however, long-term outcomes remain poor due to primary and secondary resistance driven by tumor immune escape. The T-cell immunoglobulin and immunoreceptor tyrosine-based inhibition motif domain (TIGIT) is upregulated on T-cells and natural killer cells in multiple solid tumors, which can inhibit anticancer immune responses. Ociperlimab (BGB-A1217) is a novel, humanized, monoclonal antibody that binds TIGIT with high specificity and affinity, blocking the interaction with its ligands on tumor cells. Preclinical and clinical studies suggest that dual targeting with anti-TIGIT and anti-PD-1 antibodies produces synergistic immune cell activation and enhanced antitumor activity. Methods: AdvanTIG-203 is a phase 2, global, randomized, double-blind, placebo-controlled study (NCT04732494) of patients with unresectable, locally advanced, recurrent or metastatic ESCC, who progressed on or after 1st line systemic therapy and whose tumors express PD-L1 (visually estimated combined positive score ≥10%). After stratification by Eastern Cooperative Oncology Group performance status (0 or 1), number of metastatic sites (≤1 or ≥2) and region (Asian or non-Asian), 280 patients will be randomized (1:1) to either ociperlimab 900 mg intravenous (IV) plus tislelizumab 200 mg IV every 3 weeks (Q3W), or tislelizumab plus placebo Q3W, until disease progression (per RECIST v1.1), unacceptable toxicity, death or withdrawal of consent. Co-primary endpoints are investigator-assessed overall response rate (ORR) and overall survival (OS) in the intention-to-treat population. A sample size of 280 patients was estimated to provide approximately 94.8% power to detect a 20% difference in ORR at a one-sided significance level of 0.025. With 198 deaths, the study was estimated to provide approximately 86% power to detect a hazard ratio of 0.65 for OS. Secondary endpoints are ORR by independent review, progression-free survival, duration of response, disease control rate, and clinical benefit rate per investigator and independent assessment, cancer-specific health-related quality of life (HRQoL), and safety. Exploratory endpoints include but are not limited to expression of TIGIT, CD226, CD155, CD112, and PD-L1, pharmacokinetics, immunogenicity, and generic HRQoL measures. Clinical trial information: NCT04732494.

Recently, programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) inhibitors have achieved major breakthroughs in oncology, with 32 drugs approved over the past decade. This advancement has established immunotherapy as the fifth major antitumor modality following surgery, chemotherapy, radiotherapy, and targeted therapy. However, PD-1/PD-L1 inhibitors induce sustained responses in only a limited number of patients, and primary and acquired resistance remain critical challenges in clinical practice. As understanding of the complex crosstalk among cancer cells, the tumor microenvironment, and the host immune system deepens, numerous strategies to overcome PD-1/PD-L1 inhibitor resistance have been proposed. In this review, we examine the current development of PD-1/PD-L1 inhibitors, analyze global approval trends, and evaluate their monotherapy efficacy across various tumor types. As multi-target combination therapy is an essential strategy for overcoming resistance, we analyze key combination targets - such as vascular endothelial growth factor (VEGF), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and lymphocyte activation gene 3 (LAG-3) - and highlight the clinical success of novel dual-target regimens such as ivonescimab (PD-1/VEGF). Furthermore, we discuss potential approaches to overcoming resistance from both microenvironmental (e.g., targeting cancer-associated fibroblasts or utilizing antibody-drug conjugates) and macroenvironmental (e.g., modulating the microbiota or sex hormones) perspectives. This review provides a forward-looking framework for designing precision- and mechanism-driven combination therapies aimed at converting non-responders into responders.

BackgroundMetformin, a drug prescribed for patients with type 2 diabetes, has potential efficacy in enhancing antitumor immunity; however, the detailed underlying mechanisms remain to be elucidated. Therefore, we aimed to identify the inhibitory molecular mechanisms of metformin on programmed death ligand 1 (PD-L1) expression in cancer cells and programmed death 1 (PD-1) expression in immune cells.MethodsWe employed a luciferase reporter assay, quantitative real-time PCR, immunoblotting analysis, immunoprecipitation and ubiquitylation assays, and a natural killer (NK) cell-mediated tumor cell cytotoxicity assay. A mouse xenograft tumor model was used to evaluate the effect of metformin on tumor growth, followed by flow-cytometric analysis using tumor-derived single-cell suspensions.ResultsMetformin decreased AKT-mediated β-catenin S552 phosphorylation and subsequent β-catenin transactivation in an adenosine monophosphate-activated protein kinase (AMPK) activation-dependent manner, resulting in reduced CD274 (encoding PD-L1) transcription in cancer cells. Tumor-derived soluble factors enhanced PD-1 protein stability in NK and T cells via dissociation of PD-1 from ubiquitin E3 ligases and reducing PD-1 polyubiquitylation. Metformin inhibited the tumor-derived soluble factor-reduced binding of PD-1 to E3 ligases and PD-1 polyubiquitylation, resulting in PD-1 protein downregulation in an AMPK activation-dependent manner. These inhibitory effects of metformin on both PD-L1 and PD-1 expression ameliorated cancer-reduced cytotoxic activity of immune cells in vitro and decreased tumor immune evasion and growth in vivo.ConclusionsMetformin blocks both PD-L1 and PD-1 within the tumor microenvironment. This study provided a mechanistic insight into the efficacy of metformin in improving immunotherapy in human cancer.

Immunotherapy is currently one of the most important treatment options for patients with various cancers. It is predominantly based on immune checkpoint inhibitors (ICIs), which are supposed to reverse immune suppression caused by interactions of negative immune checkpoints with their ligands. Cytotoxic T lymphocyte antigen 4 (CTLA-4), programmed death 1 (PD-1), and its ligand, programmed death ligand 1 (PD-L1) are the checkpoints targeted by antibodies registered in various types of cancer to enable effective anti-cancer immune response. Despite numerous possibilities, other molecules belonging to immune checkpoints — T cell immunoglobulin and mucin-domain containing-3 (TIM-3), lymphocyte-activation gene 3 (LAG-3), and T cell immunoreceptor with immunoglobulin and ITIM domain (TIGIT), are being extensively researched, mainly due to their role in cancer progression and resistance to immunotherapy. Recently, the first antibody against LAG-3 — relatlimab has been registered in melanoma, and many others are tested in the final stages of clinical trials. Thus, understanding their intricate functions and developing strategies to use them can create opportunities to apply immunotherapy in cancer treatment. This article describes their characteristics and potential role in solid-tumor treatment with TIM-3, LAG-3, and TIGIT molecules, which have been connected to tumor progression, poor survival, and poor prognosis in many tumor types.

Cutaneous adverse events to immune checkpoint inhibitors in pediatric populations: A retrospective cohort study

We read with great interest the previously published article “Costimulation Blockade in Kidney Transplantation: An Update” written by Malvezzi et al.1 In the setting of solid-organ transplantation, it represents a great progress to explore the blockade of some costimulation pathways as an efficient immunosuppressive tool instead of using calcineurin inhibitors. In the section of targeting costimulation pathways, Malvezzi et al1 summarized main T-cell surface signaling molecules, including costimulation and coinhibition. Cosignaling molecules are controllers of T-cell responses to antigens. By selectively turning on and/or off costimulatory and coinhibitory pathways, the T-cell receptor (TCR) signal could be transiently regulated in positive and negative directions. cluster of differentiation (CD), CD28/CD154(CD40L)/inducible costimulator had a positive regulatory effect on T-cell activation, whereas cytotoxic T-lymphocyte-associated antigen-4/programmed death ligand-1 was negative. Based on this article, we will provide some progress in costimulation pathways over the past few years, as shown in Figure 1.Figure 1.: Major T-cell cosignaling pathways. Black lines indicate stimulating signals on T cells, whereas red lines indicate inhibitory signals. CD, cluster of differentiation; CTLA-4, cytotoxic t-lymphocyte-associated antigen-4; ICOS, inducible costimulator; ICOS-L, ICOS ligand; MHC, major histocompatibility complex; PD-1, programmed death 1; PD-L1, programmed death ligand-1; TCR, T-cell receptor.First, as we all know, programmed death 1 (PD-1) and its ligands, mainly PD-L1 and PD-L2, deliver inhibitory signals that regulate the balance among T-cell activation, tolerance, and exhaustion. PD-1 is a CD28 family member. PD-L1 (B7-H1) and PD-L2 (B7-DC) are B7 family members. Several previous findings pointed out a significant bidirectional inhibitory interaction between B7-1 (CD80) and PD-L1, which added an additional dimension to immunoregulatory functions of the B7:CD28 family.2-5 The competition assays in vitro showed that PD-1 and B7-1 competed for binding to PD-L1 and block each other’s binding.6,7 Extremely low levels of PD-1 are sufficient for potent inhibition in the earliest stages of T-cell activation.8 However, this potent inhibition effect of PD-1 depends on the colocalization of TCR and CD28, which initiate the T-cell activation. Therefore, PD-1 plays an extremely important role in the negative regulation of T cells.9,10 Second, the expression of PD-1 and its ligands is widespread. PD-1 can be expressed on T cells, B cells, natural killer T cells, activated monocytes, and dendritic cells (DCs). PD-1 is not expressed on resting T cells. It is induced to express after activation.3-5,11 The expression of PD-L1 and PD-L2 differ in patterns and vary across species. Research data on PD-L2 exhibited a smaller interspecies gap, whereas PD-L1 had a larger expression gap between mice and humans. PD-L1 is constitutively expressed on mouse T and B cells, DCs, macrophages, mesenchymal stem cells, and bone marrow–derived mast cells. However, it is minimally expressed on resting naive human CD4 and CD8 T cells.12 It is upregulated on several cell types after activation.2,7 Compared with PD-L1, the expression of PD-L2 is increasingly restricted. It is induced to express on DCs, macrophages, and bone marrow–derived mast cells.2,5,9,11 Although PD-1 and PD-L1 are simultaneously expressed on T cells and PD-L1 has a high expression on activated T cells in mouse, and studies revealed that PD-L1 could attenuate TCR-mediated T-cell stimulation, PD-1 is the principal inhibitory molecule after T-cell activation, just like CTLA-4. Binding of PD-1 to its ligand PD-L1 or PD-L2 delivers a negative signal by the recruitment of Src homology 2-domain–containing tyrosine phosphatase 2 to the phosphorylated tyrosine residue in the cytoplasmic region.4 Moreover, the result that PD-L1 fails to inhibit PD-1 deficient T cells indicates that PD-L1 conveys suppression signal via its interaction with PD-1.3 Consequently, PD-1 plays a major role in activated T-cell inhibition. Third, the interaction on T-cell responses is comprehensive complex. It is also related to binding affinity, the expression position, spatial conformation, etc. As far as PD-1 and its ligands are concerned, although PD-1 seems to be an exclusive coinhibitor, PD-L1 and PD-L2 have dual functions of coinhibitors and costimulators. A series of in vivo studies indicate that endogenous PD-L1 could act as coinhibitor2,3,13 or costimulatory,6,14-17 whereas PD-L2 mainly acts as costimulatory.18,19 Some observations strongly suggested that PD-L1 and PD-L2 costimulated T-cell growth through a non–PD-1 receptor.20,21 From an affinity point of view, molecular pairs were ranked according to their binding affinity as B7-1: CTLA-4 > PD-1: PD-L1/PD-L2 > PD-L1: B7-1 > B7-1: CD28,2,7 which implies that interactions between cosignaling pathway participants on T cells are sequential. Between T cells and antigen-presenting cells (APCs), it is possible that PD-L1 mainly on APC cell preferentially binds PD-1 on T cell, whereas B7-1 (mainly on APC cell) preferentially binds CTLA-4 on T cell. When PD-L1 and B7-1 are simultaneously expressed on the same cell or expressed on 2 different cells, their interactions are different in the aspect of spatial conformation. The interaction between PD-L1 and B7-1 occurs in cis when they are located in the same cell.7,22,23 However, binding between PD-L1 and B7-1 on different cells still remains controversial.24 Some reports suggested that PD-L1 and B7-1 on different cells bound in trans,2,23,25 whereas others indicated that the interaction occurred not in trans.7,23 Apart from cosignaling pathway participants (CD28, CD80/86, CTLA-4, PD-1, PD-1 L, and inducible costimulator ligand) mentioned above, several novel negative immune regulation molecules have been introduced over the past few years, such as lymphocyte activation gene-3 (LAG-3 or CD223), T-cell immunoglobulin and mucin-domain–containing-3, T-cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain, V-type immunoglobulin domain-containing suppressor of T-cell activation, and so on.26 These negative regulatory molecules provide new targets for inhibiting T-cell activation and are worth our concern. In summary, there is a dynamic and complex interaction network among PD-1, PD-L1/PD-L2/, B7-1 and CTLA-4. PD-L1 has dual functions as coinhibitor and costimulator.