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The PD1:PD-L1/2 Pathway from Discovery to Clinical Implementation.

ABSTRACT: The immune system maintains a critically organized network to defend against foreign particles, while evading self-reactivity simultaneously. T lymphocytes function as effectors and play an important regulatory role to orchestrate the immune signals. Although central tolerance mechanism results in the removal of the most of the autoreactive T cells during thymic selection, a fraction of self-reactive lymphocytes escapes to the periphery and pose a threat to cause autoimmunity. The immune system evolved various mechanisms to constrain such autoreactive T cells and maintain peripheral tolerance, including T cell anergy, deletion, and suppression by regulatory T cells (TRegs). These effects are regulated by a complex network of stimulatory and inhibitory receptors expressed on T cells and their ligands, which deliver cell-to-cell signals that dictate the outcome of T cell encountering with cognate antigens. Among the inhibitory immune mediators, the pathway consisting of the programed cell death 1 (PD-1) receptor (CD279) and its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273) plays an important role in the induction and maintenance of peripheral tolerance and for the maintenance of the stability and the integrity of T cells. However, the PD-1:PD-L1/L2 pathway also mediates potent inhibitory signals to hinder the proliferation and function of T effector cells and have inimical effects on antiviral and antitumor immunity. Therapeutic targeting of this pathway has resulted in successful enhancement of T cell immunity against viral pathogens and tumors. Here, we will provide a brief overview on the properties of the components of the PD-1 pathway, the signaling events regulated by PD-1 engagement, and their consequences on the function of T effector cells.

SUBMITTER: Bardhan K

PROVIDER: S-EPMC5149523 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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The PD1:PD-L1/2 Pathway from Discovery to Clinical Implementation.

Bardhan Kankana K Anagnostou Theodora T Boussiotis Vassiliki A VA

Frontiers in immunology 20161212

The immune system maintains a critically organized network to defend against foreign particles, while evading self-reactivity simultaneously. T lymphocytes function as effectors and play an important regulatory role to orchestrate the immune signals. Although central tolerance mechanism results in the removal of the most of the autoreactive T cells during thymic selection, a fraction of self-reactive lymphocytes escapes to the periphery and pose a threat to cause autoimmunity. The immune system ...[more]

PMID: 28018338

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Project description:Background Skeletal morbidity in cancer patients has a major impact on quality of life and preserving bone health while improving outcomes is an important goal of modern antitumor treatment strategies. Despite their widespread use in early disease stages, the effects of immune-checkpoint inhibitors (ICI) on the skeleton are still poorly defined. Here, we initiated a comprehensive investigation of the impact of ICI on bone turnover by longitudinal assessment of bone turnover markers (BTM) in cancer patients and by validation in a novel bioengineered 3D model of bone remodeling. Methods Serum markers of bone resorption (C-terminal telopeptide, CTX) and formation (procollagen type I N-propeptide, PINP; and osteocalcin, OCN) were measured before each ICI application (PD1 inhibitors, PD1i or PD-L1 inhibitors, PD1i) for 6 months or until disease progression in patients with advanced cancer and no evidence of bone metastases. To validate the in vivo results, we evaluated osteoclast (OC) and osteoblast (OB) differentiation upon treatment with ICI. In addition, their effect on bone remodeling was assessed by immunohistochemistry, immunofluorescence and proteomics analysis in a dynamic 3D model of the bone multicellular unit (BMU). Results The longitudinal assessment of BTM revealed a significant decrease in CTX levels after 3 weeks, followed by a return to baseline levels within 3 months. In contrast, serum levels of PINP and OCN gradually increased from baseline to the last postbaseline assessment. In vitro, ICI impaired the maturation of preosteoclasts by inhibiting STAT3/NFATc1 signaling, but not JNK, ERK and AKT; while lacking any direct effect on osteogenesis. However, using our novel bioengineered 3D bone model, which enables the simultaneous differentiation of OB and OC precursor cells, we confirmed the uncoupling of the OC/OB activity upon ICI treatment by demonstrating impaired OC maturation along with increased OB differentiation. Conclusion Our study indicates that the inhibition of the PD1/PD-L1 signaling axis interferes with the OB/OC coupling of bone turnover and may potentially exert a protective effect on bone by impairing the differentiation OCs and indirectly promoting osteogenesis.

Project description:Immunocheckpoint proteins of tumor infiltrating lymphocytes play an important role in tumor prognosis in the course of tumor clinicopathology. PD-1 (Programmed cell death protein 1) is an important immunosuppressive molecule. By binding to PD-L1 (programmed cell death-ligand 1), it blocks TCR and its costimulus signal transduction, inhibits the activation and proliferation of T cells, depletes the function of effector T cells, and enables tumor cells to achieve immune escape. In recent years, immunocheckpoint blocking therapy targeting the PD-1/PD-L1 axis has achieved good results in a variety of malignant tumors, pushing tumor immunotherapy to a new milestone, such as anti-PD-1 monoclonal antibody Nivolumab, Pembrolizumab, and anti-PD-L1 monoclonal antibody Atezolizumab, which are considered as potential antitumor drugs. It was found in clinical use that some patients obtained long-term efficacy, but most of them developed drug resistance recurrence in the later stage. The high incidence of drug resistance (including primary and acquired drug resistance) still cannot be ignored, which limited its clinical application and became a new problem in this field. Due to tumor heterogeneity, current limited research shows that PD-1 or PD-L1 monoclonal antibody drug resistance may be related to the following factors: mutation of tumor antigen and antigen presentation process, multiple immune checkpoint interactions, immune microenvironment changes dynamically, activation of oncogenic pathways, gene mutation and epigenetic changes of key proteins in tumors, tumor competitive metabolism, and accumulation of metabolites, etc, mechanisms of resistance are complex. Therefore, it is the most urgent task to further elucidate the mechanism of immune checkpoint inhibitor resistance, discover multitumor universal biomarkers, and develop new target agents to improve the response rate of immunotherapy in patients. In this study, the mechanism of anti-PD-1/PD-L1 drug resistance in tumors, the potential biomarkers for predicting PD-1 acquired resistance, and the recent development of combination therapy were reviewed one by one. It is believed that, based on the complex mechanism of drug resistance, it is of no clinical significance to simply search for and regulate drug resistance targets, and it may even produce drug resistance again soon. It is speculated that according to the possible tumor characteristics, three types of treatment methods should be combined to change the tumor microenvironment ecology and eliminate various heterogeneous tumor subsets, so as to reduce tumor drug resistance and improve long-term clinical efficacy.

Dataset Information

The PD1:PD-L1/2 Pathway from Discovery to Clinical Implementation.

Publications

The PD1:PD-L1/2 Pathway from Discovery to Clinical Implementation.

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