PD-1 blockage reverses immune dysfunction and hepatitis B viral persistence in a mouse animal model

Persistent hepatitis B viral (HBV) infection results in chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC). Recent studies in animal models of viral infection indicate that the interaction between the inhibitory receptor, programmed death (PD)-1, on lymphocytes and its ligand (PD-L1) play a critical role in T-cell exhaustion by inducing T-cell inactivation. High PD-1 expression levels by peripheral T-lymphocytes and the possibility of improving T-cell function by blocking PD-1-mediated signaling confirm the importance of this inhibitory pathway in inducing T-cell exhaustion. We studied T-cell exhaustion and the effects of PD-1 and PD-L1 blockade on intrahepatic infiltrating T-cells in our recently developed mouse model of HBV persistence. In this mouse animal model, we demonstrated that there were increased intrahepatic PD-1-expressing CD8+ and CD4+ T cells in mice with HBV persistence, but PD-1 upregulation was resolved in mice which had cleared HBV. The Intrahepatic CD8+ T-cells expressed higher levels of PD-1 and lower levels of CD127 in mice with HBV persistence. Blockade of PD-1/PD-L1 interactions increased HBcAg-specific interferon (IFN)-γ production in intrahepatic T lymphocytes. Furthermore, blocking the interaction of PD-1 with PD-L1 by an anti-PD-1 monoclonal antibody (mAb) reversed the exhausted phenotype in intrahepatic T lymphocytes and viral persistence to clearance of HBV in vivo. Our results indicated that PD-1 blockage reverses immune dysfunction and viral persistence of HBV infection in a mouse animal model, suggesting that the anti-PD-1 mAb might be a good therapeutic candidate for chronic HBV infection.     

Contribution of the PD-L1/PD-1 pathway to T-cell exhaustion: an update on implications for chronic infections and tumor evasion

Recent clinical data support ideas of Programmed death receptor-ligand 1 (PD-L1; also called B7-H1, CD274) playing an important role in immune evasion of tumor cells. Expression of PD-L1 on tumors strongly correlates with the survival of cancer patients. PD-L1 on tumors interacts with the co-inhibitory molecule Programmed death receptor-1 (PD-1, CD279) on T cells mediating decreased TCR-mediated proliferation and cytokine production. In animal tumor models, blockade of PD-L1/PD-1 interactions resulted in an improved tumor control. In addition, exhausted T cells during chronic viral infections could be revived by PD-L1 blockade. Thus, targeting PD-L1/PD-1 interactions might improve the efficacy of adoptive cell therapies (ACT) of chronic infections as well as cancers. Obstacles for a general blockade of PD-L1 might be its role in mediating peripheral tolerance. This review discusses the currently available data concerning the role of PD-L1 in tumor immune evasion and envisions possibilities for implementation into ACT for cancer patients. This article is a symposium paper from the conference “Cancer Immunotherapy 2006 Meets Strategies for Immune Therapy,” held in Mainz, Germany, on 4–5 May 2006.     

Correlation between PD-1/PD-L1 expression and polarization in tumor-associated macrophages: A key player in tumor immunotherapy

Tumor immunotherapy, such as PD-1/PD-L1 blockade, has shown promising clinical efficacy in patients with various types of tumors. However, the response to PD-1/PD-L1 blockade in a majority of malignancies is limited, indicating an urgent need for a deeper understanding of the mechanisms of PD-1/PD-L1 axis-mediated tumor tolerance. As the most abundant immune cells in the tumor stroma, macrophages display multiple phenotypes and functions in response to the stimuli of the tumor microenvironment. PD-1/PD-L1 has been demonstrated to be highly expressed in tumor-associated macrophages (TAMs), and TAM polarization has been shown to be important during tumor progression. In this review, we outline the relationship between TAM PD-1/PD-L1 expression and polarizations, summarize the involvement of M2 TAMs in PD-1/PD-L1-mediated T-cell exhaustion, and discuss improved approaches for overcoming PD-1/PD-L1 blockade resistance by inducing M2/M1 switching of TAMs.     

Blocking of the PD-1/PD-L1 interaction by a novel cyclic peptide inhibitor for cancer immunotherapy

The interaction of PD-1/PD-L1 allows tumor cells to escape from immune surveillance. Clinical success of the antibody drugs has proven that blockade of PD-1/PD-L1 pathway is a promising strategy for cancer immunotherapy. Here, we developed a cyclic peptide C8 by using Ph.D.-C7 C phage display technology. C8 showed high binding affinity with h PD-1 and could effectively interfere the interaction of PD-1/PD-L1. Furthermore, C8 could stimulate CD8+T cell activation in human peripheral blood mononuclear cells(PBMCs). We also observed that C8 could suppress tumor growth in CT26 and B16-OVA, as well as anti-PD-1 antibody resistant B16 mouse model. CD8+T cells infiltration significantly increased in tumor microenvironment, and IFN-γ secretion by CD8+T cells in draining lymph nodes also increased. Simultaneously, we exploited T cells depletion models and confirmed that C8 exerted anti-tumor effects via activating CD8+T cells dependent manner. The interaction model of C8 with h PD-1 was simulated and confirmed by alanine scanning. In conclusion, C8 shows anti-tumor capability by blockade of PD-1/PD-L1 interaction, and C8 may provide an alternative candidate for cancer immunotherapy.     

Development of Search Strategy for Peptide Inhibitors of Immune Checkpoints

Current strategy for the blockade of molecules inhibiting T-cell immunity, the immune checkpoints (ICP), such as CTLA-4, PD-1, and B7-H1(PD-L1), using monoclonal antibodies (mAbs), showed significant clinical effects in cancer immunotherapy. In this kind of therapy, antibodies do not kill tumor cells directly, but block inhibitory signals for T lymphocytes, resulting in activation of the immune response cascade that eliminate malignant cells and lead to tumor degradation. However, the mAb preparations have some limitations, and the development of new low-molecular-weight antagonists (for example, peptides) is an important issue. In this study, we used peptide microarrays and phage display libraries to search for peptides that interact with the immune checkpoints. We found peptides that specifically bind CTLA-4, PD-1, B7-1, B7-2 and B7-H1(PD-L1) which play important role in the regulation of the immune responses. These synthetic peptides can be applied to the development of new immunomodulating drugs for cancer immunotherapy.     

Deubiquitinating enzyme OTUB1 promotes cancer cell immunosuppression via preventing ER-associated degradation of immune checkpoint protein PD-L1

Upregulation of programmed death ligand 1 (PD-L1) helps tumor cells escape from immune surveillance, and therapeutic antibodies targeting PD-1/PD-L1 have shown better patient outcomes only in several types of malignancies. Recent studies suggest that the clinical efficacy of anti-PD-1/PD-L1 treatments is associated with PD-L1 levels; however, the underlying mechanism of high PD-L1 protein levels in cancers is not well defined. Here, we report that the deubiquitinase OTUB1 positively regulates PD-L1 stability and mediates cancer immune responses through the PD-1/PD-L1 axis. Mechanistically, we demonstrate that OTUB1 interacts with and removes K48-linked ubiquitin chains from the PD-L1 intracellular domain in a manner dependent on its deubiquitinase activity to hinder the degradation of PD-L1 through the ERAD pathway. Functionally, depletion of OTUB1 markedly decreases PD-L1 abundance, reduces PD-1 protein binding to the tumor cell surface, and causes increased tumor cell sensitivity to human peripheral blood mononuclear cells (PBMCs)-mediated cytotoxicity. Meanwhile, OTUB1 ablation-induced PD-L1 destabilization facilitates more CD8⁺ T cells infiltration and increases the level of IFN-γ in serum to enhance antitumor immunity in mice, and the tumor growth suppression by OTUB1 silencing could be reversed by PD-L1 overexpression. Furthermore, we observe a significant correlation between PD-L1 abundance and OTUB1 expression in human breast carcinoma. Our study reveals OTUB1 as a deubiquitinating enzyme that influences cancer immunosuppression via regulation of PD-L1 stability and may be a potential therapeutic target for cancer immunotherapy.Subject terms: Proteins, Immune evasion     

免疫检查点程序性细胞死亡蛋白配体-1翻译后修饰及其在免疫治疗中的应用前景

免疫检查点程序性细胞死亡蛋白配体-1（programmed cell death 1 ligand 1,PD-L1）是一种主要表达于肿瘤细胞表面的免疫抑制性分子,其可与T淋巴细胞表面的程序性细胞死亡蛋白-1（programmed cell death protein 1,PD-1）结合,抑制T淋巴细胞的激活,发挥免疫抑制性功能。基于这一原理所开发的PD-1/PD-L1免疫阻断疗法,已在临床广泛应用于多种实体瘤的治疗,使诸多病人受益。与此同时,随着对PD-L1调控机制研究的深入,PD-L1的多种翻译后修饰形式陆续得到了鉴定,包括糖基化、磷酸化、泛素化和棕榈酰化等。研究表明,这些翻译后修饰过程可影响PD-L1的蛋白质稳定性与生理功能。因此,翻译后修饰成了PD-L1研究新的切入点。目前,PD-L1翻译后修饰靶向药物已在免疫治疗中展现出良好的应用前景。通过靶向PD-L1翻译后修饰过程,进而调控由PD-L1介导的肿瘤免疫逃逸,成了提高免疫治疗应答率的新思路和新策略。本文将对PD-L1翻译后修饰的研究进行系统总结,并陈述其在免疫治疗领域中的应用前景,希望为未来针对PD-L1翻译后修饰的研究提供理论支持。     

PD-1/PD-L1 immune checkpoint: Potential target for cancer therapy

Recent studies show that cancer cells are sometimes able to evade the host immunity in the tumor microenvironment. Cancer cells can express high levels of immune inhibitory signaling proteins. One of the most critical checkpoint pathways in this system is a tumor-induced immune suppression (immune checkpoint) mediated by the programmed cell death protein 1 (PD-1) and its ligand, programmed death ligand 1 (PD-L1). PD-1 is highly expressed by activated T cells, B cells, dendritic cells, and natural killer cells, whereas PD-L1 is expressed on several types of tumor cells. Many studies have shown that blocking the interaction between PD-1 and PD-L1 enhances the T-cell response and mediates antitumor activity. In this review, we highlight a brief overview of the molecular and biochemical events that are regulated by the PD-1 and PD-L1 interaction in various cancers.     

Programmed cell death protein 1 activation preferentially inhibits CD28.CAR–T cells

Targeted adoptive immunotherapy with engineered T cells is a promising treatment for refractory hematologic malignancies. However, many patients achieving early complete remissions ultimately relapse. Immunosuppressive ligands are expressed on tumor and supportive cells in the tumor microenvironment (TME). When activated, T cells express associated “checkpoint” receptors. Binding of co-inhibitory ligands and receptors may directly contribute to T-cell functional exhaustion. It is not known whether all T cells engineered to express chimeric antigen receptors (CARs) are subject to checkpoint-mediated regulation. It is also unknown whether distinct CAR signaling moieties modulate T-cell responsiveness to these inhibitory pathways. We have, therefore, directly compared functional co-inhibition in engineered T cells identically targeted to the tumor-associated antigen CD123, but distinct in their mode of T-cell activation: via the endogenous T-cell receptor (ENG), or downstream of CD28 or 41BB-containing CARs. In all cases, we have observed antigen-independent T-cell activation associated with upregulation of the co-inhibitory receptors programmed cell death protein 1 (PD-1, CD279), Tim-3 and Lag-3. Notably, CD28.CAR T cells were uniquely susceptible to PD-1/PD-L1 mediated checkpoint inhibition. Together, our data indicate that PD-1/PD-L1 checkpoint blocking agents may be considered clinically when CD28.CAR T cells do not perform optimally in human trials.     

B7-DC-Ig Enhances Vaccine Effect by a Novel Mechanism Dependent on PD-1 Expression Level on T Cell Subsets

Programmed death receptor 1 (PD-1) is an important signaling molecule often involved in tumor-mediated suppression of activated immune cells. Binding of this receptor to its ligands, B7-H1 (PD-L1) and B7-DC (PD-L2), attenuates T cell activation, reduces IL-2 and IFN-γ secretion, decreases proliferation and cytotoxicity, and induces apoptosis. B7-DC-Ig is a recombinant protein that binds and targets PD-1. It is composed of an extracellular domain of murine B7-DC fused to the Fc portion of murine IgG2a. In this study, we demonstrate that B7-DC-Ig can enhance the therapeutic efficacy of vaccine when combined with cyclophosphamide. We show that this combination significantly enhances Ag-specific immune responses and leads to complete eradication of established tumors in 60% of mice and that this effect is CD8 dependent. We identified a novel mechanism by which B7-DC-Ig exerts its therapeutic effect that is distinctly different from direct blocking of the PD-L1-PD-1 interaction. In this study, we demonstrate that there are significant differences between levels and timing of surface PD-1 expression on different T cell subsets. We found that these differences play critical roles in anti-tumor immune effect exhibited by B7-DC-Ig through inhibiting proliferation of PD-1(high) CD4 T cells, leading to a significant decrease in the level of these cells, which are enriched for regulatory T cells, within the tumor. In addition, it also leads to a decrease in PD-1(high) CD8 T cells, tipping the balance toward nonexhausted functional PD-1(low) CD8 T cells. We believe that the PD-1 expression level on T cells is a crucial factor that needs to be considered when designing PD-1-targeting immune therapies.     

The effect of Curcumin on multi-level immune checkpoint blockade and T cell dysfunction in head and neck cancer

BackgroundDespite recent advances in understanding the complex immunologic dysfunction in the tumor microenvironment (TME), fewer than 20% of patients with head and neck squamous cell carcinoma (HNSCC) respond to immune checkpoint blockade (ICB). Thus, it is important to understand how inhibitory IC receptors maintain the suppressed dysfunctional TME, and to develop more effective combination immunotherapy. This study evaluated the immune-modulating effects of Curcumin, which has well-established anti-cancer and chemopreventive properties, and its long-term safety as a phytochemical drug.MethodsWe carried out the western blot and small interfering RNA (siRNA) transfection assay to evaluate the effects of Curcumin on IC ligands and IC ligands function in HNSCC. Through T-cell cytotoxicity assay and measurements of cytokine secretion, we assessed the effects of combination of Curcumin with programmed death-ligand 1 (PD-L1) Ab on cancer cell killing. Flow cytometry were used to analyze the effects of Curcumin on the expression of programmed cell death protein 1 (PD-1) and T-cell immunoglobulin and mucin-domain3 (TIM-3) on CD4, CD8 and Treg. Immunofluorescence, immunohistochemistry and western blot were used to detecte the cytokine (IFN-γ, Granzyme B), IC receptors (PD-1 and TIM-3) and its ligands (PD-L1, PD-L2, Galectin-9) in xenograft mouse model and 4-nitroquinoline-1-oxide (4-NQO) oral cancer model.ResultsWe found that Curcumin decreased the expression of IC ligands such as PD-L1, PD-L2, and Galectin-9 in HNSCC, leading to regulation of epithelial-to-mesenchymal transition-associated tumor invasion. Curcumin also effectively restored the ability of CD8⁺ cytotoxic T cells to lyse cancer cells. To evaluate the effect of Curcumin on the TME further, the 4-NQO oral cancer model was used. Curcumin increased T-cell proliferation, tumor-infiltrating lymphocytes (TILs), and effector cytokines, and decreased the expression of PD-1, TIM-3, suppressive IC receptors and their ligands (PD-L1, PD-L2, and Galectin-9) in the TME, implying reinvigoration of the exhausted CD8⁺ T cells. In addition, Curcumin inhibited expression of CD4⁺CD25⁺FoxP3⁺ Treg cells as well as PD-1 and TIM-3.ConclusionsThese results show that Curcumin reinvigorates defective T cells via multiple (PD-1 and TIM-3) and multi-level (IC receptors and its ligands) IC axis suppression, thus providing a rationale to combine Curcumin with conventional targeted therapy or ICB as a multi-faceted approach for treating patients with HNSCC.     

Crystal clear: visualizing the intervention mechanism of the PD-1/PD-L1 interaction by two cancer therapeutic monoclonal antibodies

Antibody-based PD-1/PD-L1 blockade therapies have taken center stage in immunotherapies for cancer, with multiple clinical successes. PD-1 signaling plays pivotal roles in tumor-driven T-cell dysfunction. In contrast to prior approaches to generate or boost tumor-specific T-cell responses, antibody-based PD-1/PD-L1 blockade targets tumor-induced T-cell defects and restores preexisting T-cell function to modulate antitumor immunity. In this review, the fundamental knowledge on the expression regulations and inhibitory functions of PD-1 and the present understanding of antibody-based PD-1/ PD-L1 blockade therapies are briefly summarized. We then focus on the recent breakthrough work concerning the structural basis of the PD-1/PD-Ls interaction and how therapeutic antibodies, pembrolizumab targeting PD-1 and avelumab targeting PD-L1, compete with the binding of PD-1/PD-L1 to interrupt the PD-1/PD-L1 interaction. We believe that this structural information will benefit the design and improvement of therapeutic antibodies targeting PD-1 signaling.     

Adoptive Transfer of siRNA Cblb-Silenced CD8(+) T Lymphocytes Augments Tumor Vaccine Efficacy in a B16 Melanoma Model

The ubiquitin ligase Cbl-b is an established regulator of T cell immune response thresholds. We recently showed that adoptive cell transfer (ACT) of cblb(-/-) CD8(+) T cells enhances dendritic cell (DC) immunization-mediated anti-tumor effects in immune-competent recipients. However, translation of cblb targeting to clinically applicable concepts requires that inhibition of cblb activity be transient and reversible. Here we provide experimental evidence that inhibition of cblb using chemically synthesized siRNA has such potential. Silencing cblb expression by ex vivo siRNA transfection of polyclonal CD8(+) T cells prior to ACT increased T cell tumor infiltration, significantly delayed tumor outgrowth, and increased survival rates of tumor-bearing mice. As shown by ex vivo recall assays, cblb silencing resulted in significant augmentation of intratumoral T cell cytokine response. ACT of cblb-silenced polyclonal CD8(+) T cells combined with DC-based tumor vaccines predominantly mediated anti-tumor immune responses, whereas no signs of autoimmunity could be detected. Importantly, CBLB silencing in human CD8(+) T cells mirrored the effects observed for cblb-silenced and cblb-deficient murine T cells. Our data validate the concept of enhanced anti-tumor immunity by repetitive ACT of ex vivo cblb siRNA-silenced hyper-reactive CD8(+) T cells as add-on adjuvant therapy to augment the efficacy of existing cancer immunotherapy regimens in clinical practice.     

Exosomes-delivered PD-L1 siRNA and CTLA-4 siRNA protect against growth and tumor immune escape in colorectal cancer

ObjectiveThis study aims to dissect impacts of exosomes-delivered PD-L1 and CTLA-4 siRNAs on colorectal cancer (CRC) progression and immune responses.MethodsExosomes containing PD-L1 siRNA and CTLA-4 siRNA were prepared and utilized to treat CRC cells to evaluate their effects. A tumor-bearing mouse model was established for verification.ResultsExosomes containing PD-L1 siRNA and CTLA-4 siRNA repressed malignant features of CRC cells and restrained tumor growth and activated tumor immune responses in vivo. Co-culture of CRC cells treated with exosomes containing PD-L1 siRNA and CTLA-4 siRNA with human CD8⁺ T cells increased the percentage of CD8⁺ T cells, decreased the apoptotic rate of CD8⁺ T cells, elevated IL-2, IFN-γ, and TNF-α expression in cell supernatants, reduced adherent density of CRC cells, augmented the positive rate of CRC cells, and subdued tumor immune escape.ConclusionExosomes containing PD-L1 siRNA and CTLA-4 siRNA suppressed CRC progression and enhanced tumor immune responses.     

Role of the programmed death-1 pathway in regulation of alloimmune responses in vivo

Programmed death-1 (PD-1), an inhibitory receptor up-regulated on activated T cells, has been shown to play a critical immunoregulatory role in peripheral tolerance, but its role in alloimmune responses is poorly understood. Using a novel alloreactive TCR-transgenic model system, we examined the functions of this pathway in the regulation of alloreactive CD4+ T cell responses in vivo. PD-L1, but not PD-1 or PD-L2, blockade accelerated MHC class II-mismatched skin graft (bm12 (I-Abm12) into B6 (I-Ab)) rejection in a similar manner to CTLA-4 blockade. In an adoptive transfer model system using the recently described anti-bm12 (ABM) TCR-transgenic mice directly reactive to I-Abm12, PD-1 and PD-L1 blockade enhanced T cell proliferation early in the immune response. In contrast, at a later time point preceding accelerated allograft rejection, only PD-L1 blockade enhanced T cell proliferation. In addition, PD-L1 blockade enhanced alloreactive Th1 cell differentiation. Apoptosis of alloantigen-specific T cells was inhibited significantly by PD-L1 but not PD-1 blockade, indicating that PD-1 may not be the receptor for the apoptotic effect of the PD-L1-signaling pathway. Interestingly, the effect of PD-L1 blockade was dependent on the presence of CD4+ CD25+ regulatory T cells in vivo. These data demonstrate a critical role for the PD-1 pathway, particularly PD-1/PD-L1 interactions, in the regulation of alloimmune responses in vivo.     

Generation of autologous tumor-specific T cells for adoptive transfer based on vaccination, in vitro restimulation and CD3/CD28 dynabead-induced T cell expansion

Adoptive cell transfer (ACT) of in vitro expanded autologous tumor-infiltrating lymphocytes (TIL) has been shown to exert therapeutic efficacy in melanoma patients. We aimed to develop an ACT protocol based on tumor-specific T cells isolated from peripheral blood and in vitro expanded by Dynabeads? ClinExVivo?CD3/CD28. We show here that the addition of an in vitro restimulation step with relevant peptides prior to bead expansion dramatically increased the proportion of tumor-specific T cells in PBMC-cultures. Importantly, peptide-pulsed dendritic cells (DCs) as well as allogeneic tumor lysate-pulsed DCs from the DC vaccine preparation could be used with comparable efficiency to peptides for in vitro restimulation, to increase the tumor-specific T-cell response. Furthermore, we tested the use of different ratios and different types of Dynabeads? CD3/CD28 and CD3/CD28/CD137 T-cell expander, for optimized expansion of tumor-specific T cells. A ratio of 1:3 of Dynabeads? CD3/CD28 T-cell expander to T cells resulted in the maximum number of tumor-specific T cells. The addition of CD137 did not improve functionality or fold expansion. Both T-cell expansion systems could generate tumor-specific T cells that were both cytotoxic and effective cytokine producers upon antigen recognition. Dynabeads?-expanded T-cell cultures shows phenotypical characteristics of memory T cells with potential to migrate and expand in vivo. In addition, they possess longer telomeres compared to TIL cultures. Taken together, we demonstrate that in vitro restimulation of tumor-specific T cells prior to bead expansion is necessary to achieve high numbers of tumor-specific T cells. This is effective and easily applicable in combination with DC vaccination, by use of vaccine-generated DCs, either pulsed with peptide or tumor-lysate.     

PD-1 regulates self-reactive CD8+ T cell responses to antigen in lymph nodes and tissues

PD-1, an inhibitory receptor expressed on activated lymphocytes, regulates tolerance and autoimmunity. We tested the role of PD-1:PD-1 ligand (PD-L) interactions in cross-presentation and the generation and control of CD8(+) responses against self-Ag. Ag-naive PD-1(-/-) OVA-specific OT-I CD8(+) T cells exhibited exacerbated responses to cross-presented Ag in mice expressing soluble OVA under the control of the rat insulin promoter (RIP-ova(high)). Following adoptive transfer into RIP-ova(high) recipients, PD-1(-/-) OT-I T cells expanded in the pancreatic lymph node. In contrast to wild-type OT-I cells, PD-1(-/-) OT-I T cells secreted IFN-gamma and migrated into the pancreas, ultimately causing diabetes. Loss of PD-1 affected CD8(+) cells intrinsically, and did not significantly alter the responses of wild-type OT-I T cells adoptively transferred into the same RIP-ova(high) recipient mouse. PD-1:PD-L interactions also limited CD8(+) effector cells, and PD-L1 expression on parenchymal tissues protected against effector OT-I T cell attack. Finally, we found that the loss of PD-1 on effector OT-I cells lowers the threshold for Ag recognition in peripheral tissues. These findings indicate two checkpoints where PD-1 attenuates self-reactive T cell responses: presentation of self-Ag to naive self-reactive T cells by dendritic cells in the draining lymph node and reactivation of pathogenic self-reactive T cells in the target organ.     

Programmed death (PD)-1:PD-ligand 1/PD-ligand 2 pathway inhibits T cell effector functions during human tuberculosis

Protective immunity against Mycobacterium tuberculosis requires the generation of cell-mediated immunity. We investigated the expression and role of programmed death 1 (PD-1) and its ligands, molecules known to modulate T cell activation, in the regulation of IFN-gamma production and lytic degranulation during human tuberculosis. We demonstrated that specific Ag-stimulation increased CD3+PD-1+ lymphocytes in peripheral blood and pleural fluid from tuberculosis patients in direct correlation with IFN-gamma production from these individuals. Moreover, M. tuberculosis-induced IFN-gamma participated in the up-regulation of PD-1 expression. Blockage of PD-1 or PD-1 and its ligands (PD-Ls: PD-L1, PD-L2) enhanced the specific degranulation of CD8+ T cells and the percentage of specific IFN-gamma-producing lymphocytes against the pathogen, demonstrating that the PD-1:PD-Ls pathway inhibits T cell effector functions during active M. tuberculosis infection. Furthermore, the simultaneous blockage of the inhibitory receptor PD-1 together with the activation of the costimulatory protein signaling lymphocytic activation molecule led to the promotion of protective IFN-gamma responses to M. tuberculosis, even in patients with weak cell-mediated immunity against the bacteria. Together, we demonstrated that PD-1 interferes with T cell effector functions against M. tuberculosis, suggesting that PD-1 has a key regulatory role during the immune response of the host to the pathogen.     

Program death-1 engagement upon TCR activation has distinct effects on costimulation and cytokine-driven proliferation: attenuation of ICOS,IL-4, and IL-21, but not CD28, IL-7, and IL-15 responses

The program death 1 (PD-1) receptor and its ligands, PD-1 ligand (PD-L)1 and PD-L2, define a novel regulatory pathway with potential inhibitory effects on T, B, and monocyte responses. In the present study, we show that human CD4(+) T cells express PD-1, PD-L1, and PD-L2 upon activation, and Abs to the receptor can be agonists or antagonists of the pathway. Under optimal conditions of stimulation, ICOS but not CD28 costimulation can be prevented by PD-1 engagement. IL-2 levels induced by costimulation are critical in determining the outcome of the PD-1 engagement. Thus, low to marginal IL-2 levels produced upon ICOS costimulation account for the greater sensitivity of this pathway to PD-1-mediated inhibition. Interestingly, exogenous IL-2, IL-7, and IL-15 but not IL-4 and IL-21 can rescue PD-1 inhibition, suggesting that among these cytokines only those that activate STAT5 can rescue PD-1 inhibition. As STAT5 has been implicated in the maintenance of IL-2Ralpha expression, these results suggest that IL-7 and IL-15 restore proliferation under conditions of PD-1 engagement by enhancing high-affinity IL-2R expression and hence, IL-2 responsiveness.     

PD-1/PD-L1与Treg细胞相关性的研究新进展

PD-1和PD-L属于B7家族的共刺激分子,介导免疫反应的负性调节信号。Treg细胞是一个具有免疫调节作用的T细胞亚群,在机体的免疫耐受和免疫稳定中具有重要作用。本文就PD-1/PD-L1与Treg细胞的免疫调节作用及相关性研究进展作简要综述。