Exhaustion of chronically stimulated CD8(+) T cells is a significant obstacle to immune control of chronic infections or tumors. Although coinhibitory checkpoint blockade with anti-programmed death ligand 1 (PD-L1) Ab can restore functions to exhausted T cell populations, recovery is often incomplete and dependent upon the pool size of a quiescent T-bet(high) subset that expresses lower levels of PD-1. In a model in which unhelped, HY-specific CD8(+) T cells gradually lose function following transfer to male bone marrow transplantation recipients, we have explored the effect of shifting the balance away from coinhibition and toward costimulation by combining anti-PD-L1 with agonistic Abs to the TNFR superfamily members, OX40 and CD27. Several weeks following T cell transfer, both agonistic Abs, but especially anti-CD27, demonstrated synergy with anti-PD-L1 by enhancing CD8(+) T cell proliferation and effector cytokine generation. Anti-CD27 and anti-PD-L1 synergized by downregulating the expression of multiple quiescence-related genes concomitant with a reduced frequency of T-bet(high) cells within the exhausted population. However, in the presence of persistent Ag, the CD8(+) T cell response was not sustained and the overall size of the effector cytokine-producing pool eventually contracted to levels below that of controls. Thus, CD27-mediated costimulation can synergize with coinhibitory checkpoint blockade to switch off molecular programs for quiescence in exhausted T cell populations, but at the expense of losing precursor cells required to maintain a response.
The interaction of DNA with proteins occurs over a wide range of length scales, and depends critically on its local structure. In particular, recent experimental work suggests that the intrinsic curvature of DNA plays a significant role on its protein-binding properties. In this work, we present a coarse grained model of DNA that is capable of describing base-pairing, hybridization, major and minor groove widths, and local curvature. The model represents an extension of the recently proposed 3SPN.2 description of DNA [D. M. Hinckley, G. S. Freeman, J. K. Whitmer, and J. J. de Pablo, J. Chem. Phys. 139, 144903 (2013)], into which sequence-dependent shape and mechanical properties are incorporated. The proposed model is validated against experimental data including melting temperatures, local flexibilities, dsDNA persistence lengths, and minor groove width profiles.
Nucleosomes provide the basic unit of compaction in eukaryotic genomes, and the mechanisms that dictate their position at specific locations along a DNA sequence are of central importance to genetics. In this Letter, we employ molecular models of DNA and proteins to elucidate various aspects of nucleosome positioning. In particular, we show how DNA's histone affinity is encoded in its sequence-dependent shape, including subtle deviations from the ideal straight B-DNA form and local variations of minor groove width. By relying on high-precision simulations of the free energy of nucleosome complexes, we also demonstrate that, depending on DNA's intrinsic curvature, histone binding can be dominated by bending interactions or electrostatic interactions. More generally, the results presented here explain how sequence, manifested as the shape of the DNA molecule, dominates molecular recognition in the problem of nucleosome positioning.
Survival for patients with glioblastoma, the most common high-grade primary CNS tumor, remains poor despite multiple therapeutic interventions including intensifying cytotoxic therapy, targeting dysregulated cell signaling pathways, and blocking angiogenesis. Exciting, durable clinical benefits have recently been demonstrated for a number of other challenging cancers using a variety of immunotherapeutic approaches. Much modern research confirms that the CNS is immunoactive rather than immunoprivileged. Preliminary results of clinical studies demonstrate that varied vaccine strategies have achieved encouraging evidence of clinical benefit for glioblastoma patients, although multiple variables will likely require systematic investigation before optimal outcomes are realized. Initial preclinical studies have also revealed promising results with other immunotherapies including cell-based approaches and immune checkpoint blockade. Clinical studies to evaluate a wide array of immune therapies for malignant glioma patients are being rapidly developed. Important considerations going forward include optimizing response assessment and identifiying correlative biomarkers for predict therapeutic benefit. Finally, the potential of complementary combinatorial immunotherapeutic regimens is highly exciting and warrants expedited investigation.
Regulatory T (T reg) cells are critical for preventing autoimmunity mediated by self-reactive T cells, but their role in modulating immune responses during chronic viral infection is not well defined. To address this question and to investigate a role for T reg cells in exhaustion of virus-specific CD8 T cells, we depleted T reg cells in mice chronically infected with lymphocytic choriomeningitis virus (LCMV). T reg cell ablation resulted in 10-100-fold expansion of functional LCMV-specific CD8 T cells. Rescue of exhausted CD8 T cells was dependent on cognate antigen, B7 costimulation, and conventional CD4 T cells. Despite the striking recovery of LCMV-specific CD8 T cell responses, T reg cell depletion failed to diminish viral load. Interestingly, T reg cell ablation triggered up-regulation of the molecule programmed cell death ligand-1 (PD-L1), which upon binding PD-1 on T cells delivers inhibitory signals. Increased PD-L1 expression was observed especially on LCMV-infected cells, and combining T reg cell depletion with PD-L1 blockade resulted in a significant reduction in viral titers, which was more pronounced than that upon PD-L1 blockade alone. These results suggest that T reg cells effectively maintain CD8 T cell exhaustion, but blockade of the PD-1 inhibitory pathway is critical for elimination of infected cells.
Chronic graft-versus-host disease (cGVHD) is a leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Having shown that germinal center (GC) formation and immunoglobulin deposition are required for multiorgan system cGVHD and associated bronchiolitis obliterans syndrome (BOS) in a murine model, we hypothesized that T follicular helper (Tfh) cells are necessary for cGVHD by supporting GC formation and maintenance. We show that increased frequency of Tfh cells correlated with increased GC B cells, cGVHD, and BOS. Although administering a highly depletionary anti-CD20 monoclonal antibody (mAb) to mice with established cGVHD resulted in peripheral B-cell depletion, B cells remained in the lung, and BOS was not reversed. BOS could be treated by eliminating production of interleukin-21 (IL-21) by donor T cells or IL-21 receptor (IL-21R) signaling of donor B cells. Development of BOS was dependent upon T cells expressing the chemokine receptor CXCR5 to facilitate T-cell trafficking to secondary lymphoid organ follicles. Blocking mAbs for IL-21/IL-21R, inducible T-cell costimulator (ICOS)/ICOS ligand, and CD40L/CD40 hindered GC formation and cGVHD. These data provide novel insights into cGVHD pathogenesis, indicate a role for Tfh cells in these processes, and suggest a new line of therapy using mAbs targeting Tfh cells to reverse cGVHD.
BRAF-targeted therapy results in objective responses in the majority of patients; however, the responses are short lived (?6 months). In contrast, treatment with immune checkpoint inhibitors results in a lower response rate, but the responses tend to be more durable. BRAF inhibition results in a more favorable tumor microenvironment in patients, with an increase in CD8(+) T-cell infiltrate and a decrease in immunosuppressive cytokines. There is also increased expression of the immunomodulatory molecule PDL1, which may contribute to the resistance. On the basis of these findings, we hypothesized that BRAF-targeted therapy may synergize with the PD1 pathway blockade to enhance antitumor immunity. To test this hypothesis, we developed a BRAF(V600E)/Pten(-/-) syngeneic tumor graft immunocompetent mouse model in which BRAF inhibition leads to a significant increase in the intratumoral CD8(+) T-cell density and cytokine production, similar to the effects of BRAF inhibition in patients. In this model, CD8(+) T cells were found to play a critical role in the therapeutic effect of BRAF inhibition. Administration of anti-PD1 or anti-PDL1 together with a BRAF inhibitor led to an enhanced response, significantly prolonging survival and slowing tumor growth, as well as significantly increasing the number and activity of tumor-infiltrating lymphocytes. These results demonstrate synergy between combined BRAF-targeted therapy and immune checkpoint blockade. Although clinical trials combining these two strategies are ongoing, important questions still remain unanswered. Further studies using this new melanoma mouse model may provide therapeutic insights, including optimal timing and sequence of therapy.
We report that programmed death ligand 2 (PD-L2), a known ligand of PD-1, also binds to repulsive guidance molecule b (RGMb), which was originally identified in the nervous system as a co-receptor for bone morphogenetic proteins (BMPs). PD-L2 and BMP-2/4 bind to distinct sites on RGMb. Normal resting lung interstitial macrophages and alveolar epithelial cells express high levels of RGMb mRNA, whereas lung dendritic cells express PD-L2. Blockade of the RGMb-PD-L2 interaction markedly impaired the development of respiratory tolerance by interfering with the initial T cell expansion required for respiratory tolerance. Experiments with PD-L2-deficient mice showed that PD-L2 expression on non-T cells was critical for respiratory tolerance, but expression on T cells was not required. Because PD-L2 binds to both PD-1, which inhibits antitumor immunity, and to RGMb, which regulates respiratory immunity, targeting the PD-L2 pathway has therapeutic potential for asthma, cancer, and other immune-mediated disorders. Understanding this pathway may provide insights into how to optimally modulate the PD-1 pathway in cancer immunotherapy while minimizing adverse events.
This study investigates current opinions about hospital advertising and compares them to the attitudes expressed 25 years ago. It replicates a survey done in 1985, using the same questionnaire and population to compare responses longitudinally. The study indicates some changes in the public's opinions of hospital advertising. Although the image of hospitals remains positive, most of the 2010 respondents' opinions were rather mixed regarding whether it is proper for hospitals to advertise. The study also confirmed that the quality of service and reputation of hospitals remain more important to the public than price.
Lung squamous cell carcinoma (SCC) is a deadly disease for which current treatments are inadequate. We demonstrate that biallelic inactivation of Lkb1 and Pten in the mouse lung leads to SCC that recapitulates the histology, gene expression, and microenvironment found in human disease. Lkb1;Pten null (LP) tumors expressed the squamous markers KRT5, p63 and SOX2, and transcriptionally resembled the basal subtype of human SCC. In contrast to mouse adenocarcinomas, the LP tumors contained immune populations enriched for tumor-associated neutrophils. SCA1(+)NGFR(+) fractions were enriched for tumor-propagating cells (TPCs) that could serially transplant the disease in orthotopic assays. TPCs in the LP model and NGFR(+) cells in human SCCs highly expressed Pd-ligand-1 (PD-L1), suggesting a mechanism of immune escape for TPCs.
CD80 plays a critical role in stimulation of T cells and subsequent control of infection. To investigate the effect of CD80 on HSV-1 infection, we constructed a recombinant HSV-1 virus that expresses two copies of the CD80 gene in place of the latency associated transcript (LAT). This mutant virus (HSV-CD80) expressed high levels of CD80 and had similar virus replication kinetics as control viruses in rabbit skin cells. In contrast to parental virus, this CD80 expressing recombinant virus replicated efficiently in immature dendritic cells (DCs). Additionally, the susceptibility of immature DCs to HSV-CD80 infection was mediated by CD80 binding to PD-L1 on DCs. This interaction also contributed to a significant increase in T cell activation. Taken together, these results suggest that inclusion of CD80 as a vaccine adjuvant may promote increased vaccine efficacy by enhancing the immune response directly and also indirectly by targeting to DC.
Antigen persistence in chronic infections and cancer up-regulates inhibitory networks, such as the PD-1 and IL-10 pathways, that impair immunity and lead to disease progression. These pathways are attractive targets for immunotherapy, as demonstrated by recent clinical trials of PD-1/PD-L1 blockade in cancer patients. However, in HIV-1 infection not all subjects respond to inhibition of either pathway and the mechanistic interactions between these two networks remain to be better defined. Here we demonstrate that in vitro blockade of PD-L1 and/or IL-10R? results in markedly different profiles of HIV-1-specific CD4 T cell restoration. Whereas PD-L1 blockade leads to balanced increase in IFN-?, IL-2 and IL-13 secretion, IL-10R? blockade preferentially restores IFN-? production. In viremic subjects, combined PD-L1/IL-10R? blockade results in a striking 10-fold increase in IFN-? secretion by HIV-1-specific CD4 T cells that is not observed in subjects with spontaneous (elite controllers) or therapy-induced control of viral replication. In contrast to the dramatic increase in IFN-?, concurrent blockade has a marginal additive effect on IL-2 production, IL-13 secretion and HIV-1-specific CD4 T cell proliferation. IFN-? produced by Thelper cells up-regulates PD-L1, HLA I/II and IL-12 expression by monocytes. The effect of combined blockade on IFN-? was dependent on reciprocal reinforcement through IL-12. These studies provide crucial information on the different immunoregulatory qualities of PD-1 and IL-10 in progressive disease, and link exhausted virus-specific CD4 T cells and monocytes in the regulation of IFN? and IL-12 secretion.
A new 3-Site-Per-Nucleotide coarse-grained model for DNA is presented. The model includes anisotropic potentials between bases involved in base stacking and base pair interactions that enable the description of relevant structural properties, including the major and minor grooves. In an improvement over available coarse-grained models, the correct persistence length is recovered for both ssDNA and dsDNA, allowing for simulation of non-canonical structures such as hairpins. DNA melting temperatures, measured for duplexes and hairpins by integrating over free energy surfaces generated using metadynamics simulations, are shown to be in quantitative agreement with experiment for a variety of sequences and conditions. Hybridization rate constants, calculated using forward-flux sampling, are also shown to be in good agreement with experiment. The coarse-grained model presented here is suitable for use in biological and engineering applications, including nucleosome positioning and DNA-templated engineering.
The success in lung cancer therapy with programmed death (PD)-1 blockade suggests that immune escape mechanisms contribute to lung tumor pathogenesis. We identified a correlation between EGF receptor (EGFR) pathway activation and a signature of immunosuppression manifested by upregulation of PD-1, PD-L1, CTL antigen-4 (CTLA-4), and multiple tumor-promoting inflammatory cytokines. We observed decreased CTLs and increased markers of T-cell exhaustion in mouse models of EGFR-driven lung cancer. PD-1 antibody blockade improved the survival of mice with EGFR-driven adenocarcinomas by enhancing effector T-cell function and lowering the levels of tumor-promoting cytokines. Expression of mutant EGFR in bronchial epithelial cells induced PD-L1, and PD-L1 expression was reduced by EGFR inhibitors in non-small cell lung cancer cell lines with activated EGFR. These data suggest that oncogenic EGFR signaling remodels the tumor microenvironment to trigger immune escape and mechanistically link treatment response to PD-1 inhibition.
Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, play an important role in the maintenance of peripheral tolerance. We explored the role of PD-1 ligands in regulating graft-versus-host disease (GVHD). Both PD-L1 and PD-L2 expression were upregulated in the spleen, liver, colon, and ileum of GVHD mice. Whereas PD-L2 expression was limited to hematopoietic cells, hematopoietic and endothelial cells expressed PD-L1. PD-1/PD-L1, but not PD-1/PD-L2, blockade markedly accelerated GVHD-induced lethality. Chimera studies suggest that PD-L1 expression on host parenchymal cells is more critical than hematopoietic cells in regulating acute GVHD. Rapid mortality onset in PD-L1-deficient hosts was associated with increased gut T-cell homing and loss of intestinal epithelial integrity, along with increased donor T-cell proliferation, activation, Th1 cytokine production, and reduced apoptosis. Bioenergetics profile analysis of proliferating alloreactive donor T-cells demonstrated increased aerobic glycolysis and oxidative phosphorylation in PD-L1-deficient hosts. Donor T-cells exhibited a hyperpolarized mitochondrial membrane potential, increased superoxide production, and increased expression of a glucose transporter in PD-L1-deficient hosts. Taken together, these data provide new insight into the differential roles of host PD-L1 and PD-L2 and their associated cellular and metabolic mechanisms controlling acute GVHD.
CD8? T cells specific for islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) have been implicated in type 1 diabetes in both humans and non-obese diabetic (NOD) mice, in which T cells specific for IGRP??????? are highly prevalent. We sought to manipulate these pathogenic T cells by exploiting the ability of steady-state dendritic cells (DCs) to present antigens in a tolerogenic manner. The endocytic receptor DEC-205 was utilized to deliver an IGRP??????? mimotope to DCs in NOD mice, and the impact of this delivery on a polyclonal population of endogenous islet-reactive cognate T cells was determined. Assessment of islet-infiltrating CD8? T cells showed a decrease in the percentage, and the absolute number, of endogenous IGRP???????-specific T cells when the mimotope was delivered to DCs, compared with delivery of a specificity control. Employing an adoptive transfer system, deletion of CD8? T cells as a result of DEC-205-mediated antigen targeting was found to occur independently of programmed death-1 (PD-1) and its ligand (PD-L1), both often implicated in the regulation of peripheral T-cell tolerance. Given its promise for the manipulation of self-reactive polyclonal T cells demonstrated here, the distinctive characteristics of this antigen delivery system will be important to appreciate as its potential as an intervention for autoimmune diseases continues to be investigated.
Hepatitis C virus (HCV) persistence is facilitated by exhaustion of CD8+ T cells that express the inhibitory receptor programmed cell death 1 (PD-1). Blockade of PD-1 signaling improves in vitro proliferation of HCV-specific T lymphocytes, but whether antiviral function can be restored in infected individuals is unknown. To address this question, chimpanzees with persistent HCV infection were treated with anti-PD-1 antibodies. A significant reduction in HCV viremia was observed in one of three treated animals without apparent hepatocellular injury. Viremia rebounded in the responder animal when antibody treatment was discontinued. Control of HCV replication was associated with restoration of intrahepatic CD4+ and CD8+ T-cell immunity against multiple HCV proteins. The responder animal had a history of broader T-cell immunity to multiple HCV proteins than the two chimpanzees that did not respond to PD-1 therapy. The results suggest that successful PD-1 blockade likely requires a critical threshold of preexisting virus-specific T cells in liver and warrants consideration of therapeutic vaccination strategies in combination with PD-1 blockade to broaden narrow responses. Anti-PD-1 immunotherapy may also facilitate control of other persistent viruses, notably the hepatitis B virus where options for long-term control of virus replication are limited.
To understand the adaptations of costimulatory molecules through mammalian evolution, Forni et al. (Forni et al., 2013) studied evolutionary selection in key costimulatory genes. Their results, presented in this issue of Immunity, suggest that the risk of autoimmmunity is balanced against efficacy of the anti-pathogen immune response.
Outcome for glioblastoma (GBM), the most common primary CNS malignancy, remains poor. The overall survival benefit recently achieved with immunotherapeutics for melanoma and prostate cancer support evaluation of immunotherapies for other challenging cancers, including GBM. Much historical dogma depicting the CNS as immunoprivileged has been replaced by data demonstrating CNS immunocompetence and active interaction with the peripheral immune system. Several glioma antigens have been identified for potential immunotherapeutic exploitation. Active immunotherapy studies for GBM, supported by preclinical data, have focused on tumor lysate and synthetic antigen vaccination strategies. Results to date confirm consistent safety, including a lack of autoimmune reactivity; however, modest efficacy and variable immunogenicity have been observed. These findings underscore the need to optimize vaccination variables and to address challenges posed by systemic and local immunosuppression inherent to GBM tumors. Additional immunotherapy strategies are also in development for GBM. Future studies may consider combinatorial immunotherapy strategies with complimentary actions.
Programmed cell death ligand 1 (PD-L1) is an immunomodulatory molecule expressed by antigen-presenting cells and select tumors that engages receptors on T cells to inhibit T-cell immunity. Immunotherapies targeting the PD-1/PD-L1 pathway have shown durable antitumor effects in a subset of patients with solid tumors. PD-L1 can be expressed by Reed-Sternberg cells comprising classical Hodgkin lymphoma (CHL) and by malignant B cells comprising EBV-positive posttransplant lymphoproliferative disorders (PTLD). We sought to determine whether the expression of PD-L1 represents a general strategy of immune evasion among aggressive B-cell lymphomas and virus- and immunodeficiency-associated tumors.
Tumor progression is facilitated by regulatory T cells (Treg) and restricted by effector T cells. In this study, we document parallel regulation of CD8(+) T cells and Foxp3(+) Tregs by programmed death-1 (PD-1, PDCD1). In addition, we identify an additional role of CTL antigen-4 (CTLA-4) inhibitory receptor in further promoting dysfunction of CD8(+) T effector cells in tumor models (CT26 colon carcinoma and ID8-VEGF ovarian carcinoma). Two thirds of CD8(+) tumor-infiltrating lymphocytes (TIL) expressed PD-1, whereas one third to half of CD8(+) TIL coexpressed PD-1 and CTLA-4. Double-positive (PD-1(+)CTLA-4(+)) CD8(+) TIL had characteristics of more severe dysfunction than single-positive (PD-1(+) or CTLA-4(+)) TIL, including an inability to proliferate and secrete effector cytokines. Blockade of both PD-1 and CTLA-4 resulted in reversal of CD8(+) TIL dysfunction and led to tumor rejection in two thirds of mice. Double blockade was associated with increased proliferation of antigen-specific effector CD8(+) and CD4(+) T cells, antigen-specific cytokine release, inhibition of suppressive functions of Tregs, and upregulation of key signaling molecules critical for T-cell function. When used in combination with GVAX vaccination (consisting of granulocyte macrophage colony-stimulating factor-expressing irradiated tumor cells), inhibitory pathway blockade induced rejection of CT26 tumors in 100% of mice and ID8-VEGF tumors in 75% of mice. Our study indicates that PD-1 signaling in tumors is required for both suppressing effector T cells and maintaining tumor Tregs, and that PD-1/PD-L1 pathway (CD274) blockade augments tumor inhibition by increasing effector T-cell activity, thereby attenuating Treg suppression.
High surface expression of programmed death 1 (PD-1) is associated with T-cell exhaustion; however, the relationship between PD-1 expression and T-cell dysfunction has not been delineated. We developed a model to study PD-1 signaling in primary human T cells to study how PD-1 expression affected T-cell function. By determining the number of T-cell receptor/peptide-MHC complexes needed to initiate a Ca(2+) flux, we found that PD-1 ligation dramatically shifts the dose-response curve, making T cells much less sensitive to T-cell receptor-generated signals. Importantly, other T-cell functions were differentially sensitive to PD-1 expression. We observed that high levels of PD-1 expression were required to inhibit macrophage inflammatory protein 1 beta production, lower levels were required to block cytotoxicity and IFN-? production, and very low levels of PD-1 expression could inhibit TNF-? and IL-2 production as well as T-cell expansion. These findings provide insight into the role of PD-1 expression in enforcing T-cell exhaustion and the therapeutic potential of PD-1 blockade.
The inhibitory receptor programmed cell death 1 (PD-1) plays a major role in functional exhaustion of T cells during chronic infections and cancer, and recent clinical data suggest that blockade of the PD-1 pathway is an effective immunotherapy in treating certain cancers. Thus, it is important to define combinatorial approaches that increase the efficacy of PD-1 blockade. To address this issue, we examined the effect of IL-2 and PD-1 ligand 1 (PD-L1) blockade in the mouse model of chronic lymphocytic choriomeningitis virus (LCMV) infection. We found that low-dose IL-2 administration alone enhanced CD8+ T cell responses in chronically infected mice. IL-2 treatment also decreased inhibitory receptor levels on virus-specific CD8+ T cells and increased expression of CD127 and CD44, resulting in a phenotype resembling that of memory T cells. Surprisingly, IL-2 therapy had only a minimal effect on reducing viral load. However, combining IL-2 treatment with blockade of the PD-1 inhibitory pathway had striking synergistic effects in enhancing virus-specific CD8+ T cell responses and decreasing viral load. Interestingly, this reduction in viral load occurred despite increased numbers of Tregs. These results suggest that combined IL-2 therapy and PD-L1 blockade merits consideration as a regimen for treating human chronic infections and cancer.
There is an unclear relationship between T-cell expression of inhibitory receptors and their ability to control viral infections. Studies of human immune cells have been mostly limited to T cells from blood, which is not always the site of infection. We investigated the relationship between T-cell location, expression of inhibitory receptors, maturation, and viral control using blood and liver cells from patients with hepatitis C virus (HCV) and other viral infections.
Aged individuals have increased morbidity and mortality following influenza and other viral infections, despite previous exposure or vaccination. Mouse and human studies suggest increased senescence and/or exhaustion of influenza virus-specific CD8 T cells with advanced age. However, neither the relationship between senescence and exhaustion nor the underlying transcriptional pathways leading to decreased function of influenza virus-specific cellular immunity in elderly humans are well-defined. Here, we demonstrate that increased percentages of CD8 T cells from aged individuals express CD57 and KLRG1, along with PD-1 and other inhibitory receptors, markers of senescence, or exhaustion, respectively. Expression of T-box transcription factors, T-bet and Eomes, were also increased in CD8 T cells from aged subjects and correlated closely with expression of CD57 and KLRG1. Influenza virus-specific CD8 T cells from aged individuals exhibited decreased functionality with corresponding increases in CD57, KLRG1, and T-bet, a molecular regulator of terminal differentiation. However, in contrast to total CD8 T cells, influenza virus-specific CD8 T cells had altered expression of inhibitory receptors, including lower PD-1, in aged compared with young subjects. Thus, our data suggest a prominent role for senescence and/or terminal differentiation for influenza virus-specific CD8 T cells in elderly subjects.
The majority of HIV-infected individuals fail to produce protective antibodies and have diminished responses to new immunizations. We report here that even though there is an expansion of follicular helper T (TFH) cells in HIV-infected individuals, the cells are unable to provide adequate B cell help. We found a higher frequency of programmed cell death ligand 1 (PD-L1)(+) germinal center B cells from lymph nodes of HIV-infected individuals suggesting a potential role for PD-1-PD-L1 interaction in regulating TFH cell function. In fact, we show that engagement of PD-1 on TFH cells leads to a reduction in cell proliferation, activation, inducible T-cell co-stimulator (ICOS) expression and interleukin-21 (IL-21) cytokine secretion. Blocking PD-1 signaling enhances HIV-specific immunoglobulin production in vitro. We further show that at least part of this defect involves IL-21, as addition of this cytokine rescues antibody responses and plasma cell generation in vitro. Our results suggest that deregulation of TFH cell-mediated B cell help diminishes B cell responses during HIV infection and may be related to PD-1 triggering on TFH cells. These results demonstrate a role for TFH cell impairment in HIV pathogenesis and suggest that enhancing their function could have a major impact on the outcome and control of HIV infection, preventing future infections and improving immune responses to vaccinations.
Human T-cell Immunoglobulin and Mucin-domain containing proteins (TIM1, 3, and 4) specifically bind phosphatidylserine (PS). TIM1 has been proposed to serve as a cellular receptor for hepatitis A virus and Ebola virus and as an entry factor for dengue virus. Here we show that TIM1 promotes infection of retroviruses and virus-like particles (VLPs) pseudotyped with a range of viral entry proteins, in particular those from the filovirus, flavivirus, New World arenavirus and alphavirus families. TIM1 also robustly enhanced the infection of replication-competent viruses from the same families, including dengue, Tacaribe, Sindbis and Ross River viruses. All interactions between TIM1 and pseudoviruses or VLPs were PS-mediated, as demonstrated with liposome blocking and TIM1 mutagenesis experiments. In addition, other PS-binding proteins, such as Axl and TIM4, promoted infection similarly to TIM1. Finally, the blocking of PS receptors on macrophages inhibited the entry of Ebola VLPs, suggesting that PS receptors can contribute to infection in physiologically relevant cells. Notably, infection mediated by the entry proteins of Lassa fever virus, influenza A virus and SARS coronavirus was largely unaffected by TIM1 expression. Taken together our data show that TIM1 and related PS-binding proteins promote infection of diverse families of enveloped viruses, and may therefore be useful targets for broad-spectrum antiviral therapies.
HIV-1 Nef protein down-regulates several cell surface receptors through its interference with the cell sorting and trafficking machinery. Here we demonstrate for the first time the ability of Nef to down-regulate cell surface expression of the negative immune modulator CTLA-4. Down-regulation of CTLA-4 required the Nef motifs DD175, EE155 and LL165, all known to be involved in vesicle trafficking. Disruption of the lysosomal functions by pH-neutralizing agents prevented CTLA-4 down-regulation by Nef, demonstrating the implication of the endosomal/lysosomal compartments in this process. Confocal microscopy experiments visualized the co-localization between Nef and CTLA-4 in the early and recycling endosomes but not at the cell surface. Overall, our results provide a novel mechanism by which HIV-1 Nef interferes with the surface expression of the negative regulator of T cell activation CTLA-4. Down-regulation of CTLA-4 may contribute to the mechanisms by which HIV-1 sustains T cell activation, a critical step in viral replication and dissemination.
An estimated 34 million people are living with HIV worldwide (UNAIDS, 2012), with the number of infected persons rising every year. Increases in HIV prevalence have resulted not only from new infections, but also from increases in the survival of HIV-infected persons produced by effective anti-retroviral therapies. Augmentation of anti-viral immune responses may be able to further increase the survival of HIV-infected persons. One strategy to augment these responses is to reinvigorate exhausted anti-HIV immune cells present in chronically infected persons. The PD-1-PD-L1 pathway has been implicated in the exhaustion of virus-specific T cells during chronic HIV infection. Inhibition of PD-1 signaling using blocking anti-PD-1 antibodies has been shown to reduce simian immunodeficiency virus (SIV) loads in monkeys. We now show that PD-1 blockade can improve control of HIV replication in vivo in an animal model. BLT (Bone marrow-Liver-Thymus) humanized mice chronically infected with HIV-1 were treated with an anti-PD-1 antibody over a 10-day period. The PD-1 blockade resulted in a very significant 45-fold reduction in HIV viral loads in humanized mice with high CD8(+) T cell expression of PD-1, compared to controls at 4 weeks post-treatment. The anti-PD-1 antibody treatment also resulted in a significant increase in CD8(+) T cells. PD-1 blockade did not affect T cell expression of other inhibitory receptors co-expressed with PD-1, including CD244, CD160 and LAG-3, and did not appear to affect virus-specific humoral immune responses. These data demonstrate that inhibiting PD-1 signaling can reduce HIV viral loads in vivo in the humanized BLT mouse model, suggesting that blockade of the PD-1-PD-L1 pathway may have therapeutic potential in the treatment of patients already infected with the AIDS virus.
CD160 is a cell surface molecule expressed by most NK cells and approximately 50% of CD8(+) cytotoxic T lymphocytes. Engagement of CD160 by MHC class-I directly triggers a costimulatory signal to TCR-induced proliferation, cytokine production and cytotoxic effector functions. The role of CD160 in alloimmunity is unknown. Using a newly generated CD160 fusion protein (CD160Ig) we examined the role of the novel costimulatory molecule CD160 in mediating CD4(+) or CD8(+) T cell driven allograft rejection. CD160Ig inhibits alloreactive CD8(+) T cell proliferation and IFN-? production in vitro, in particular in the absence of CD28 costimulation. Consequently CD160Ig prolongs fully mismatched cardiac allograft survival in CD4(-/-), CD28(-/-) knockout and CTLA4Ig treated WT recipients, but not in WT or CD8(-/-) knockout recipients. The prolonged cardiac allograft survival is associated with reduced alloreactive CD8(+) T cell proliferation, effector/memory responses and alloreactive IFN-? production. Thus, CD160 signaling is particularly important in CD28-independent effector/memory CD8(+) alloreactive T cell activation in vivo and therefore may serve as a novel target for prevention of allograft rejection.
CD4 T cells play a critical role in regulating CD8 T-cell responses during chronic viral infection. Several studies in animal models and humans have shown that the absence of CD4 T-cell help results in severe dysfunction of virus-specific CD8 T cells. However, whether function can be restored in already exhausted CD8 T cells by providing CD4 T-cell help at a later time remains unexplored. In this study, we used a mouse model of chronic lymphocytic choriomeningitis virus (LCMV) infection to address this question. Adoptive transfer of LCMV-specific CD4 T cells into chronically infected mice restored proliferation and cytokine production by exhausted virus-specific CD8 T cells and reduced viral burden. Although the transferred CD4 T cells were able to enhance function in exhausted CD8 T cells, these CD4 T cells expressed high levels of the programmed cell death (PD)-1 inhibitory receptor. Blockade of the PD-1 pathway increased the ability of transferred LCMV-specific CD4 T cells to produce effector cytokines, improved rescue of exhausted CD8 T cells, and resulted in a striking reduction in viral load. These results suggest that CD4 T-cell immunotherapy alone or in conjunction with blockade of inhibitory receptors may be a promising approach for treating CD8 T-cell dysfunction in chronic infections and cancer.
The "three sites per nucleotide" (3SPN) model provides a coarse-grained representation of nucleic acids for simulation of molecular processes. Previously, this model has relied on an implicit representation of the surrounding ionic environment at the level of Debye-Hu?ckel theory. In this work, we eliminate this limitation and present an explicit representation of ions, both monovalent and divalent. The coarse-grain ion-ion and ion-phosphate potential energy functions are inferred from all-atom simulations and parameterized to reproduce key features of the local structure and organization of ions in bulk water and in the presence of DNA. The resulting model, 3SPN.1-I, is capable of reproducing the local structure observed in detailed atomistic simulations, as well as the experimental melting temperature of DNA for a range of DNA oligonucleotide lengths, CG-content, Na(+) concentration, and Mg(2+) concentration.
Previous studies have identified the inhibitory role that the programmed death 1 (PD-1) pathway plays during chronic infection. Blockade of this pathway results in rescue of viral-specific CD8 T cells, as well as reduction of viral loads in mice chronically infected with lymphocytic choriomeningitis virus (LCMV). We tested the effect of combining PD ligand 1 (PD-L1) blockade with an agonistic regimen that induces 4-1BB costimulation during chronic LCMV infection. There is a boosting effect in the rescue of LCMV-specific CD8 T cell responses after dual treatment with PD-L1 blockade and 4-1BB agonistic Abs when the amount and timing of 4-1BB costimulation are carefully controlled. When PD-L1-blocking Abs are given together with a single low dose of anti-4-1BB agonistic Abs, there is an enhanced and stable expansion of viral-specific CD8 T cells. Conversely, when blocking Abs to PD-L1 are given with a repetitive high dose of anti-4-1BB, there is an initial synergistic expansion of viral-specific CD8 T cells by day 7, followed by dramatic apoptosis by day 14. Viral control paralleled CD8 T cell kinetics after dual treatment. By day 7 posttreatment, viral titers were lower in both of the combined regimens (compared with PD-L1 blockade alone). However, whereas the high dose of anti-4-1BB plus PD-L1 blockade resulted in rebound of viral titers to original levels, the low dose of anti-4-1BB plus PD-L1 blockade resulted in a stable reduction of viral loads. These findings demonstrate the importance of carefully manipulating the balance between activating and inhibitory signals to enhance T cell responses during chronic infection.
Programmed death-1 ligand 1 (PD-L1) is a coinhibitory molecule that negatively regulates multiple tolerance checkpoints. In the NOD mouse model, PD-L1 regulates the development of diabetes. PD-L1 has two binding partners, programmed death-1 and B7-1, but the significance of the PD-L1:B7-1 interaction in regulating self-reactive T cell responses is not yet clear. To investigate this issue in NOD mice, we have compared the effects of two anti-PD-L1 Abs that have different blocking activities. Anti-PD-L1 mAb 10F.2H11 sterically and functionally blocks only PD-L1:B7-1 interactions, whereas anti-PD-L1 mAb 10F.9G2 blocks both PD-L1:B7-1 and PD-L1:programmed death-1 interactions. Both Abs had potent, yet distinct effects in accelerating diabetes in NOD mice: the single-blocker 10F.2H11 mAb was more effective at precipitating diabetes in older (13-wk-old) than in younger (6- to 7-wk-old) mice, whereas the dual-blocker 10F.9G2 mAb rapidly induced diabetes in NOD mice of both ages. Similarly, 10F.2H11 accelerated diabetes in recipients of T cells from diabetic, but not prediabetic mice, whereas 10F.9G2 was effective in both settings. Both anti-PD-L1 mAbs precipitated diabetes in adoptive transfer models of CD4(+) and CD8(+) T cell-driven diabetes. Taken together, these data demonstrate that the PD-L1:B7-1 pathway inhibits potentially pathogenic self-reactive effector CD4(+) and CD8(+) T cell responses in vivo, and suggest that the immunoinhibitory functions of this pathway may be particularly important during the later phases of diabetogenesis.
The programmed death ligand 1 (PDL1)/programmed death 1 (PD1) costimulatory pathway plays an important role in the inhibition of alloimmune responses as well as in the induction and maintenance of peripheral tolerance. It has been demonstrated recently that PDL1 also can bind B7.1 to inhibit T cell responses in vitro. Using the bm12 into B6 heart transplant model, we investigated the functional significance of this interaction in alloimmune responses in vivo. PD1 blockade unlike PDL1 blockade failed to accelerate bm12 allograft rejection, suggesting a role for an additional binding partner for PDL1 other than PD1 in transplant rejection. PDL1 blockade was able to accelerate allograft rejection in B7.2-deficient recipients but not B7.1-deficient recipients, indicating that PDL1 interaction with B7.1 was important in inhibiting rejection. Administration of the novel 2H11 anti-PDL1 mAb, which only blocks the PDL1-B7.1 interaction, aggravated chronic injury of bm12 allografts in B6 recipients. Aggravated chronic injury was associated with an increased frequency of alloreactive IFN-?-, IL-4-, and IL-6-producing splenocytes and a decreased percentage of regulatory T cells in the recipients. Using an in vitro cell culture assay, blockade of the interaction of PDL1 on dendritic cells with B7.1 on T cells increased IFN-? production from alloreactive CD4(+) T cells, whereas blockade of dendritic cell B7.1 interaction with T cell PDL1 did not. These data indicate that PDL1 interaction with B7.1 plays an important role in the inhibition of alloimmune responses in vivo and suggests a dominant direction for PDL1 and B7.1 interaction.
Defining the T helper functions impaired by programmed death-1 (PD-1) is crucial for understanding its role in defective HIV control and determining the therapeutic potential of targeting this inhibitory pathway. We describe here the relationships among disease stage, levels of PD-1 expression, and reversibility of CD4 T-cell impairment. PD-L1 blockade in vitro enhanced HIV-specific production of Th0 (IL-2), Th1 (IFN-?), Th2 (IL-13), and TFH (IL-21) cytokines by CD4 T cells. PD-L1 blockade caused an early increase in cytokine transcription and translation that preceded cell proliferation. Although the impact of PD-L1 blockade on cytokine expression and, to a lesser extent, cell proliferation was associated with markers of disease progression, restoration of cytokine secretion was also observed in most subjects with undetectable viremia. PD-L1 blockade restored cytokine secretion in both PD-1intermediate and PD-1high sorted CD4 T-cell subsets. Compared with PD-1high HIV-specific CD8 T cells, PD-1high HIV-specific CD4 T cells showed lower expression of the inhibitory molecules CD160 and 2B4, demonstrating marked differences in expression of inhibitory receptors between T-cell subsets. These data show that PD-1 impairs HIV-specific T helper responses both by limiting expansion of these cells and by inhibiting effector functions of multiple differentiated CD4 T-cell subsets.
To design successful vaccines for chronic diseases, an understanding of memory CD8(+) T cell responses to persistent antigen restimulation is critical. However, most studies comparing memory and naive cell responses have been performed only in rapidly cleared acute infections. Herein, by comparing the responses of memory and naive CD8(+) T cells to acute and chronic lymphocytic choriomeningitis virus infection, we show that memory cells dominated over naive cells and were protective when present in sufficient numbers to quickly reduce infection. In contrast, when infection was not rapidly reduced, because of high antigen load or persistence, memory cells were quickly lost, unlike naive cells. This loss of memory cells was due to a block in sustaining cell proliferation, selective regulation by the inhibitory receptor 2B4, and increased reliance on CD4(+) T cell help. Thus, emphasizing the importance of designing vaccines that elicit effective CD4(+) T cell help and rapidly control infection.
Programmed cell death-1 (PD-1) is a member of the CD28 superfamily that delivers negative signals on interaction with its 2 ligands, PD-L1 and PD-L2. We studied the contribution of the PD-1 pathway to regulation of T cells that promote atherosclerotic lesion formation and inflammation.
T cell dysfunction is an important feature of many chronic viral infections. In particular, it was shown that programmed death-1 (PD-1) regulates T cell dysfunction during chronic lymphocytic choriomeningitis virus infection in mice, and PD-1(hi) cells exhibit an intense exhausted gene signature. These findings were extended to human chronic infections such as HIV, hepatitis C virus, and hepatitis B virus. However, it is not known if PD-1(hi) cells of healthy humans have the traits of exhausted cells. In this study, we provide a comprehensive description of phenotype, function, and gene expression profiles of PD-1(hi) versus PD-1(lo) CD8 T cells in the peripheral blood of healthy human adults as follows: 1) the percentage of naive and memory CD8 T cells varied widely in the peripheral blood cells of healthy humans, and PD-1 was expressed by the memory CD8 T cells; 2) PD-1(hi) CD8 T cells in healthy humans did not significantly correlate with the PD-1(hi) exhausted gene signature of HIV-specific human CD8 T cells or chronic lymphocytic choriomeningitis virus-specific CD8 T cells from mice; 3) PD-1 expression did not directly affect the ability of CD8 T cells to secrete cytokines in healthy adults; 4) PD-1 was expressed by the effector memory compared with terminally differentiated effector CD8 T cells; and 5) finally, an interesting inverse relationship between CD45RA and PD-1 expression was observed. In conclusion, our study shows that most PD-1(hi) CD8 T cells in healthy adult humans are effector memory cells rather than exhausted cells.
During infection with the hepatitis A virus (HAV), most patients develop mild or asymptomatic disease. However, a small number of patients develop serious, life-threatening hepatitis. We investigated this variability in disease severity by examining 30 Argentinean patients with HAV-induced acute liver failure in a case-control, cross-sectional, observational study. We found that HAV-induced severe liver disease was associated with a 6-amino-acid insertion in TIM1/HAVCR1 (157insMTTTVP), the gene encoding the HAV receptor. This polymorphism was previously shown to be associated with protection against asthma and allergic diseases and with HIV progression. In binding assays, the TIM-1 protein containing the 157insMTTTVP insertion polymorphism bound HAV more efficiently. When expressed by human natural killer T (NKT) cells, this long form resulted in greater NKT cell cytolytic activity against HAV-infected liver cells, compared with the shorter TIM-1 protein without the polymorphism. To our knowledge, the 157insMTTTVP polymorphism in TIM1 is the first genetic susceptibility factor shown to predispose to HAV-induced acute liver failure. Furthermore, these results suggest that HAV infection has driven the natural selection of shorter forms of the TIM-1 protein, which binds HAV less efficiently, thereby protecting against severe HAV-induced disease, but which may predispose toward inflammation associated with asthma and allergy.
Herpes simplex virus (HSV) infection is a classic example of latent viral infection in humans and experimental animal models. The HSV-1 latency-associated transcript (LAT) plays a major role in the HSV-1 latency reactivation cycle and thus in recurrent disease. Whether the presence of LAT leads to generation of dysfunctional T cell responses in the trigeminal ganglia (TG) of latently infected mice is not known. To address this issue, we used LAT-positive [LAT(+)] and LAT-deficient [LAT(-)] viruses to evaluate the effect of LAT on CD8 T cell exhaustion in TG of latently infected mice. The amount of latency as determined by quantitative reverse transcription-PCR (qRT-PCR) of viral DNA in total TG extracts was 3-fold higher with LAT(+) than with LAT(-) virus. LAT expression and increased latency correlated with increased mRNA levels of CD8, PD-1, and Tim-3. PD-1 is both a marker for exhaustion and a primary factor leading to exhaustion, and Tim-3 can also contribute to exhaustion. These results suggested that LAT(+) TG contain both more CD8(+) T cells and more CD8(+) T cells expressing the exhaustion markers PD-1 and Tim-3. This was confirmed by flow cytometry analyses of expression of CD3/CD8/PD-1/Tim-3, HSV-1, CD8(+) T cell pentamer (specific for a peptide derived from residues 498 to 505 of glycoprotein B [gB(498-505)]), interleukin-2 (IL-2), and tumor necrosis factor alpha (TNF-?). The functional significance of PD-1 and its ligands in HSV-1 latency was demonstrated by the significantly reduced amount of HSV-1 latency in PD-1- and PD-L1-deficient mice. Together, these results may suggest that both PD-1 and Tim-3 are mediators of CD8(+) T cell exhaustion and latency in HSV-1 infection.
PD-1 plays an important role in T cell exhaustion during HIV infection. PD-1 has two ligands: PD-L1, expressed on hematopoietic and nonhematopoietic cells, and PD-L2, limited to DCs and macrophages. Little is known about PD-L1 expression and regulation in human macrophages. Previous reports have found few immediate effects of macrophage exposure to HIV, suggesting that macrophages lack PRRs for this virus. Using quantitative confocal microscopy and a multiplexed cytokine bead array, we measured induction of PD-L1, PD-L2, and innate response cytokines in human MDMs in response to chemically inactivated HIV virions. Consistent with previous reports, no cytokines were induced by HIV virion exposure. Whereas PD-L1 and PD-L2 had low baseline expression, TLR ligands (LPS and CL097) up-regulated PD-L1 but not PD-L2. Unlike what we found for cytokine expression, PD-L1 and PD-L2 were up-regulated in response to exposure with inactivated HIV virions or with replication-competent HIV. Expression of PD-L1 was differentially modulated by IL-10, which induced up-regulation of PD-L1 but not of PD-L2, and IL-10 blockade enhanced only PD-L2 expression. We discuss implications for innate recognition of HIV by macrophages and potential, different roles for PD-L1 and PD-L2 in immunity and pathogenesis.
Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disease characterized by mutations to the ?-L-iduronidase (IDUA) gene resulting in inactivation of the IDUA enzyme. The loss of IDUA protein results in the progressive accumulation of glycosaminoglycans within the lysosomes resulting in severe, multi-organ system pathology. Gene replacement strategies have relied on the use of viral or nonviral gene delivery systems. Drawbacks to these include laborious production procedures, poor efficacy due to plasmid-borne gene silencing, and the risk of insertional mutagenesis. This report demonstrates the efficacy of a nonintegrating, minicircle (MC) DNA vector that is resistant to epigenetic gene silencing in vivo. To achieve sustained expression of the immunogenic IDUA protein we investigated the use of a tissue-specific promoter in conjunction with microRNA target sequences. The inclusion of microRNA target sequences resulted in a slight improvement in long-term expression compared to their absence. However, immune modulation by costimulatory blockade was required and permitted for IDUA expression in MPS I mice that resulted in the biochemical correction of pathology in all of the organs analyzed. MC gene delivery combined with costimulatory pathway blockade maximizes safety, efficacy, and sustained gene expression and is a new approach in the treatment of lysosomal storage disease.
Adaptive immunity is characterized by the expansion of an Ag-specific T cell population following Ag exposure. The precise mechanisms, however, that control the expansion and subsequent contraction in the number of Ag-specific T cells are not fully understood. We show that T cell/transmembrane, Ig, and mucin (TIM)-4, a receptor for phosphatidylserine, a marker of apoptotic cells, regulates adaptive immunity in part by mediating the removal of Ag-specific T cells during the contraction phase of the response. During Ag immunization or during infection with influenza A virus, blockade of TIM-4 on APCs increased the expansion of Ag-specific T cells, resulting in an increase in secondary immune responses. Conversely, overexpression of TIM-4 on APCs in transgenic mice reduced the number of Ag-specific T cells that remained after immunization, resulting in reduced secondary T cell responses. There was no change in the total number of cell divisions that T cells completed, no change in the per cell proliferative capacity of the remaining Ag-specific T cells, and no increase in the development of Ag-specific regulatory T cells in TIM-4 transgenic mice. Thus, TIM-4-expressing cells regulate adaptive immunity by mediating the removal of phosphatidylserine-expressing apoptotic, Ag-specific T cells, thereby controlling the number of Ag-specific T cells that remain after the clearance of Ag or infection.
T cell Ig-like mucin-like-1 (TIM-1) is an important asthma susceptibility gene, but the immunological mechanisms by which TIM-1 functions remain uncertain. TIM-1 is also a receptor for phosphatidylserine (PtdSer), an important marker of cells undergoing programmed cell death, or apoptosis. We now demonstrate that NKT cells constitutively express TIM-1 and become activated by apoptotic cells expressing PtdSer. TIM-1 recognition of PtdSer induced NKT cell activation, proliferation, and cytokine production. Moreover, the induction of apoptosis in airway epithelial cells activated pulmonary NKT cells and unexpectedly resulted in airway hyperreactivity, a cardinal feature of asthma, in an NKT cell-dependent and TIM-1-dependent fashion. These results suggest that TIM-1 serves as a pattern recognition receptor on NKT cells that senses PtdSer on apoptotic cells as a damage-associated molecular pattern. Furthermore, these results provide evidence for a novel innate pathway that results in airway hyperreactivity and may help to explain how TIM-1 and NKT cells regulate asthma.
Allogeneic blood or BM transplantation (BMT) is the most commonly applied form of adoptive cellular therapy for cancer. In this context, the ability of donor T cells to respond to recipient antigens is coopted to generate graft-versus-tumor (GVT) responses. The major reason for treatment failure is tumor recurrence, which is linked to the eventual loss of functional, host-specific CTLs. In this study, we have explored the role of recipient antigen expression by nonhematopoietic cells in the failure to sustain effective CTL immunity. Using clinically relevant models, we found that nonhematopoietic antigen severely disrupts the formation of donor CD8+ T cell memory at 2 distinct levels that operate in the early and late phases of the response. First, initial and direct encounters between donor CD8+ T cells and nonhematopoietic cells blocked the programming of memory precursors essential for establishing recall immunity. Second, surviving CD8+ T cells became functionally exhausted with heightened expression of the coinhibitory receptor programmed death-1 (PD-1). These 2 factors acted together to induce even more profound failure in long-term immunosurveillance. Crucially, the functions of exhausted CD8+ T cells could be partially restored by late in vivo blockade of the interaction between PD-1 and its ligand, PD-L1, without induction of graft-versus-host disease, suggestive of a potential clinical strategy to prevent or treat relapse following allogeneic BMT.
Inhibitory receptors play a crucial role in regulating CD8 T-cell function during chronic viral infection. T-cell Ig- and mucin-domain-containing molecule-3 (Tim-3) is well known to negatively regulate T-cell responses, but its role in CD8 T-cell exhaustion during chronic infection in vivo remains unclear. In this study, we document coregulation of CD8 T cell exhaustion by Tim-3 and PD-1 during chronic lymphocytic choriomeningitis virus infection. Whereas Tim-3 was only transiently expressed by CD8 T cells after acute infection, virus-specific CD8 T cells retained high Tim-3 expression throughout chronic infection. The majority (approximately 65% to 80%) of lymphocytic choriomeningitis virus-specific CD8 T cells in lymphoid and nonlymphoid organs coexpressed Tim-3 and PD-1. This coexpression of Tim-3 and PD-1 was associated with more severe CD8 T-cell exhaustion in terms of proliferation and secretion of effector cytokines such as IFN-gamma, TNF-alpha, and IL-2. Interestingly, CD8 T cells expressing both inhibitory receptors also produced the suppressive cytokine IL-10. Most importantly, combined blockade of Tim-3 and PD-1 pathways in vivo synergistically improved CD8 T cell responses and viral control in chronically infected mice. Taken together, our study defines a parameter for determining the severity of CD8 T cell dysfunction and for identifying virus-specific CD8 T cells that produce IL-10, and shows that targeting both PD-1 and Tim-3 is an effective immune strategy for treating chronic viral infections.
CD8(+) T cells in chronic viral infections such as HIV develop functional defects including loss of interleukin-2 (IL-2) secretion and decreased proliferative potential that are collectively termed exhaustion. Exhausted T cells express increased amounts of multiple inhibitory receptors, such as programmed death-1 (PD-1), that contribute to impaired virus-specific T cell function. Although reversing PD-1 inhibition is therefore an attractive therapeutic strategy, the cellular mechanisms by which PD-1 ligation results in T cell inhibition are not fully understood. PD-1 is thought to limit T cell activation by attenuating T cell receptor (TCR) signaling. It is not known whether PD-1 also acts by upregulating genes in exhausted T cells that impair their function. Here we analyzed gene expression profiles from HIV-specific CD8(+) T cells in individuals with HIV and show that PD-1 coordinately upregulates a program of genes in exhausted CD8(+) T cells from humans and mice. This program includes upregulation of basic leucine transcription factor, ATF-like (BATF), a transcription factor in the AP-1 family. Enforced expression of BATF was sufficient to impair T cell proliferation and cytokine secretion, whereas BATF knockdown reduced PD-1 inhibition. Silencing BATF in T cells from individuals with chronic viremia rescued HIV-specific T cell function. Thus, inhibitory receptors can cause T cell exhaustion by upregulating genes--such as BATF--that inhibit T cell function. Such genes may provide new therapeutic opportunities to improve T cell immunity to HIV.
The TIM (T cell/transmembrane, immunoglobulin, and mucin) gene family plays a critical role in regulating immune responses, including allergy, asthma, transplant tolerance, autoimmunity, and the response to viral infections. The unique structure of TIM immunoglobulin variable region domains allows highly specific recognition of phosphatidylserine (PtdSer), exposed on the surface of apoptotic cells. TIM-1, TIM-3, and TIM-4 all recognize PtdSer but differ in expression, suggesting that they have distinct functions in regulating immune responses. TIM-1, an important susceptibility gene for asthma and allergy, is preferentially expressed on T-helper 2 (Th2) cells and functions as a potent costimulatory molecule for T-cell activation. TIM-3 is preferentially expressed on Th1 and Tc1 cells, and generates an inhibitory signal resulting in apoptosis of Th1 and Tc1 cells. TIM-3 is also expressed on some dendritic cells and can mediate phagocytosis of apoptotic cells and cross-presentation of antigen. In contrast, TIM-4 is exclusively expressed on antigen-presenting cells, where it mediates phagocytosis of apoptotic cells and plays an important role in maintaining tolerance. TIM molecules thus provide a functional repertoire for recognition of apoptotic cells, which determines whether apoptotic cell recognition leads to immune activation or tolerance, depending on the TIM molecule engaged and the cell type on which it is expressed.
Langerhans cells (LCs) are known as "sentinels" of the immune system that function as professional antigen-presenting cells (APCs) after migration to draining lymph node. LCs are proposed to have a role in tolerance and the resolution of cutaneous immune responses. The Programmed Death-1 (PD-1) receptor and its ligands, PD-L1 and PD-L2, are a co-inhibitory pathway that contributes to the negative regulation of T-lymphocyte activation and peripheral tolerance. Surprisingly, we found PD-1 to be expressed on immature LCs (iLCs) in situ. PD-1 engagement on iLCs reduced IL-6 and macrophage inflammatory protein (MIP)-1alpha cytokine production in response to TLR2 signals but had no effect on LC maturation. PD-L1 and PD-L2 were expressed at very low levels on iLCs. Maturation of LCs upon migration from epidermis led to loss of PD-l expression and gain of high expression of PD-L1 and PD-L2 as well as co-stimulatory molecules. Blockade of PD-L1 and/or PD-L2 on migratory LCs (mLCs) and DDCs enhanced T-cell activation, as has been reported for other APCs. Thus the PD-1 pathway is active in iLCs and inhibits iLC activities, but expression of receptor and ligands reverses upon maturation and PD-L1 and PD-L2 on mLC function to inhibit T-cell responses.
Rapid progression to AIDS is a significant problem, especially in developing countries, where the majority of HIV-infected individuals reside. As rapid disease progression is also frequently observed in SIV-infected macaques, they represent a valuable tool to investigate the pathogenesis of this condition in humans. Here, we have shown that pathogenic SIV infection in rhesus macaques resulted in a rapid depletion (as early as week 2) of activated memory B (CD21-CD27+; mBAct) cells that was strongly associated with rapid disease progression. This depletion was progressive and sustained in rapid progressors, but less severe and transient in typical progressors. Because of the rapid and sustained depletion of mBAct cells, rapid progressors failed to develop SIV-specific Ab responses, showed a decline in non-SIV-specific Ab titers, and succumbed faster to intestinal bacterial infections. Depletion of mBAct cells was strongly associated with preferential depletion of mBAct cells expressing programmed death-1 (PD-1), and in vitro blockade of PD-1 improved their survival. Furthermore, in vivo PD-1 blockade in SIV-infected macaques enhanced Ab responses to non-SIV as well as SIV Ags. Our results identify depletion of mBAct cells as a very early predictor of rapid disease progression in pathogenic SIV infection and suggest an important role for the PD-1 pathway in depletion of mBAct cells and impaired humoral immune responses in SIV-infected macaques.
The T cell immunoglobulin mucin (TIM) proteins are a family of cell surface phosphatidyserine receptors that are important for the recognition and phagocytosis of apoptotic cells. Because TIM-4 is expressed by macrophages and dendritic cells in human tissue, we examined its expression in a range of histiocytic and dendritic cell neoplasms and found moderate to strong immunohistochemical staining in cases of juvenile xanthogranuloma and histiocytic sarcoma, and lower level staining in interdigitating dendritic cell sarcoma, Langerhans cell histiocytosis, acute monocytic leukemia (leukemia cutis), and blastic plasmacytoid dendritic cell neoplasm (hematodermic tumor). TIM-3 was first described on activated T(H)1 cells but was recently shown to also be a phosphatidylserine receptor and mediate phagocytosis. We found TIM-3 was expressed by peritoneal macrophages, monocytes and splenic dendritic cells. We found that it, like TIM-4, is expressed in a range of histiocytic and dendritic cell neoplasms, typically with strong immunohistochemical staining. Cases of diffuse large B cell lymphoma, anaplastic large cell lymphoma, metastatic malignant melanoma, and metastatic poorly differentiated carcinoma generally exhibited negative to minimal heterogenous staining for TIM-4 and TIM-3. We conclude that histiocytic and dendritic cell neoplasms consistently express TIM-3 and TIM-4 and that these molecules are new markers of neoplasms derived from histiocytic and dendritic cells.
While the role of PD-1 in inhibiting immunity during chronic infections is well established, its functions during acute infections are much less clear. The PD-1 pathway can dampen CD8 T cell responses during some acute infections and restrain responses by helpless CD8 memory T cells. An emerging role for PD-1 in innate immunity has been revealed by recent studies showing that PD-1 can limit function of DC and macrophages as well as T cell independent B cell responses. Thus, PD-1 can influence adaptive immune responses during acute infections, though precisely how this regulation occurs is only just beginning to be appreciated.
T cell/transmembrane, Ig, and mucin (TIM) proteins, identified using a congenic mouse model of asthma, critically regulate innate and adaptive immunity. TIM-1 and TIM-4 are receptors for phosphatidylserine (PtdSer), exposed on the surfaces of apoptotic cells. Herein, we show with structural and biological studies that TIM-3 is also a receptor for PtdSer that binds in a pocket on the N-terminal IgV domain in coordination with a calcium ion. The TIM-3/PtdSer structure is similar to that of TIM-4/PtdSer, reflecting a conserved PtdSer binding mode by TIM family members. Fibroblastic cells expressing mouse or human TIM-3 bound and phagocytosed apoptotic cells, with the BALB/c allelic variant of mouse TIM-3 showing a higher capacity than the congenic C.D2 Es-Hba-allelic variant. These functional differences were due to structural differences in the BC loop of the IgV domain of the TIM-3 polymorphic variants. In contrast to fibroblastic cells, T or B cells expressing TIM-3 formed conjugates with but failed to engulf apoptotic cells. Together these findings indicate that TIM-3-expressing cells can respond to apoptotic cells, but the consequence of TIM-3 engagement of PtdSer depends on the polymorphic variants of and type of cell expressing TIM-3. These findings establish a new paradigm for TIM proteins as PtdSer receptors and unify the function of the TIM gene family, which has been associated with asthma and autoimmunity and shown to modulate peripheral tolerance.
PURPOSE. Given that dry eye disease (DED) is associated with T cell-mediated inflammation of the ocular surface and that PD-L1 is an important negative or inhibitory regulator of immune responses constitutively expressed at high levels by corneal epithelial cells, the authors studied the expression and function of PD-L1 in DED. METHODS. Dry eye was induced in untreated wild-type mice, PD-L1(-/-) mice, and wild-type mice treated with anti-PD-L1 antibody by exposing these mice to a desiccating environment in the controlled environment chamber modified with subcutaneous administration of scopolamine. Real-time PCR was used to quantify the expression of chemokine gene transcript levels of multiple CC and CXC chemokine ligands and receptors. Epifluorescence microscopy was used to evaluate corneal infiltration of CD3(+) T cells after immunohistochemical staining. RESULTS. The increased expression of specific chemokine ligands and receptors in PD-L1(-/-) corneas of normal mice is associated with significant increases in T-cell homing into these corneas. Similar, and more enhanced, increases in T-cell infiltration were observed in PD-L1(-/-) DED mice or DED mice treated with anti-PD-L1 antibody compared with controls. In addition, the authors found significantly decreased expression of PD-L1 by corneal epithelial cells in DED and significantly increased corneal fluorescein staining score with PD-L1 functional blockade using anti-PD-L1 antibody. CONCLUSIONS. Downregulation of corneal epithelial PD-L1 amplifies dry eye-associated corneal inflammation and epitheliopathy by increasing the expression of chemokine ligands and receptors that promote T-cell homing to the ocular surface.
Tumors have evolved multiple mechanisms to evade immune destruction. One of these is expression of T cell inhibitory ligands such as programmed death-ligand 1 (PD-L1; B7-H1). In this study, we show that PD-L1 is highly expressed on mesothelioma tumor cells and within the tumor stroma. However, PD-L1 blockade only marginally affected tumor growth and was associated with the emergence of activated programmed death-1(+) ICOS(+) CD4 T cells in tumor-draining lymph nodes, whereas few activated CD8 T cells were present. Full activation of antitumor CD8 T cells, characterized as programmed death-1(+) ICOS(+) Ki-67(+) and displaying CTL activity, was only observed when CD4 T cells were depleted, suggesting that a population of suppressive CD4 T cells exists. ICOS(+) foxp3(+) regulatory T cells were found to be regulated through PD-L1, identifying one potentially suppressive CD4 T cell population. Thus, PD-L1 blockade activates antitumor CD8 T cell most potently in the absence of CD4 T cells. These findings have implications for the development of PD-L1-based therapies.
Both the programmed death (PD) 1-PD-ligand (PD-L) pathway and regulatory T (T reg) cells are instrumental to the maintenance of peripheral tolerance. We demonstrate that PD-L1 has a pivotal role in regulating induced T reg (iT reg) cell development and sustaining iT reg cell function. PD-L1(-/-) antigen-presenting cells minimally convert naive CD4 T cells to iT reg cells, showing the essential role of PD-L1 for iT reg cell induction. PD-L1-coated beads induce iT reg cells in vitro, indicating that PD-L1 itself regulates iT reg cell development. Furthermore, PD-L1 enhances and sustains Foxp3 expression and the suppressive function of iT reg cells. The obligatory role for PD-L1 in controlling iT reg cell development and function in vivo is illustrated by a marked reduction in iT reg cell conversion and rapid onset of a fatal inflammatory phenotype in PD-L1(-/-)PD-L2(-/-) Rag(-/-) recipients of naive CD4 T cells. PD-L1 iT reg cell development is mediated through the down-regulation of phospho-Akt, mTOR, S6, and ERK2 and concomitant with the up-regulation of PTEN, all key signaling molecules which are critical for iT reg cell development. Thus, PD-L1 can inhibit T cell responses by promoting both the induction and maintenance of iT reg cells. These studies define a novel mechanism for iT reg cell development and function, as well as a new strategy for controlling T reg cell plasticity.
The PD-1/PD-L pathway plays a major role in regulating T-cell exhaustion during chronic viral infections in animal models, as well as in humans, and blockade of this pathway can revive exhausted CD8(+) T cells. We examined the expression of PD-1 and its ligands, PD-L1 and PD-L2, in multiple tissues during the course of chronic viral infection and determined how the amount of PD-1 expressed, as well as the anatomical location, influenced the function of exhausted CD8 T cells. The amount of PD-1 on exhausted CD8 T cells from different anatomical locations did not always correlate with infectious virus but did reflect viral antigen in some tissues. Moreover, lower expression of PD-L1 in some locations, such as the bone marrow, favored the survival of PD-1(Hi) exhausted CD8 T cells, suggesting that some anatomical sites might provide a survival niche for subpopulations of exhausted CD8 T cells. Tissue-specific differences in the function of exhausted CD8 T cells were also observed. However, while cytokine production did not strictly correlate with the amount of PD-1 expressed by exhausted CD8 T cells from different tissues, the ability to degranulate and kill were tightly linked to PD-1 expression regardless of the anatomical location. These observations have implications for human chronic infections and for therapeutic interventions based on blockade of the PD-1 pathway.
Ongoing antigenic stimulation appears to be an important prerequisite for the persistent expression of programmed death 1 (PD-1), an inhibitory TCR coreceptor of the CD28 family. Although recent publications have emphasized the utility of PD-1 as a marker for dysfunctional T cells in chronic viral infections, its dependence on antigenic stimulation potentially renders it a sensitive indicator of low-level viral replication. To explore the antigenic threshold for the maintenance of PD-1 expression on virus-specific T cells, we compared PD-1 expression on virus-specific and memory T cell populations in controlled and uncontrolled SIV and HIV-1 infection. In both controlled live attenuated SIV infection in rhesus macaques and HIV-1 infection in elite controllers, elevated levels of PD-1 expression were observed on SIV- and HIV-1-specific CD8(+) T cells. However, in contrast to chronic wild-type SIV infection and uncontrolled HIV-1 infection, controlled SIV/HIV-1 infection did not result in increased expression of PD-1 on total memory T cells. PD-1 expression on SIV-specific CD8(+) T cells rapidly decreased after the emergence of CTL escape in cognate epitopes, but was maintained in the setting of low or undetectable levels of plasma viremia in live attenuated SIV-infected macaques. After inoculation of naive macaques with a single-cycle SIV, PD-1 expression on SIV-specific CD8(+) T cells initially increased, but was rapidly downregulated. These results demonstrate that PD-1 can serve as a sensitive indicator of persistent, low-level virus replication and that generalized PD-1 expression on T lymphocytes is a distinguishing characteristic of uncontrolled lentiviral infections.
In immunocompetent individuals, the stability of the herpesvirus-host balance limits opportunities to study the disappearance of a virus-specific CD8(+) T-cell response. However, we noticed that in HLA-A 0201-positive infectious mononucleosis (IM) patients undergoing primary Epstein-Barr virus (EBV) infection, the initial CD8 response targets three EBV lytic antigen-derived epitopes, YVLDHLIVV (YVL), GLCTLVAML (GLC), and TLDYKPLSV (TLD), but only the YVL and GLC reactivities persist long-term; the TLD response disappears within 10 to 27 months. While present, TLD-specific cells remained largely indistinguishable from YVL and GLC reactivities in many phenotypic and functional respects but showed unique temporal changes in two markers of T-cell fate, interleukin 7 receptor alpha (IL-7Ralpha; CD127) and programmed death 1 (PD-1). Thus, following the antigen-driven downregulation of IL-7Ralpha seen on all populations in acute IM, in every case, the TLD-specific population recovered expression unusually quickly post-IM. As well, in four of six patients studied, TLD-specific cells showed very strong PD-1 upregulation in the last blood sample obtained before the cells disappearance. Our data suggest that the disappearance of this individual epitope reactivity from an otherwise stable EBV-specific response (i) reflects a selective loss of cognate antigen restimulation (rather than of IL-7-dependent signals) and (ii) is immediately preceded, and perhaps mediated, by PD-1 upregulation to unprecedented levels.
The ability to induce durable transplantation tolerance predictably and consistently in the clinic is a highly desired but elusive goal. Progress is hampered by lack of appropriate experimental models in which to study resistance to transplantation tolerance. Here, we demonstrate that T helper 1-associated T box 21 transcription factor (Tbet) KO recipients exhibit allograft tolerance resistance specifically mediated by IL-17-producing CD8 T (T17) cells. Neutralization of IL-17 facilitates long-term cardiac allograft survival with combined T cell co-stimulation (CD28-CD80/86 and CD154-CD40) blockade in Tbet KO recipients. We have used this T17-biased Tbet KO model of allograft tolerance resistance to study the impact of targeting a T cell-co-stimulatory pathway, and demonstrate that targeting T cell Ig and mucin domain-1 (Tim-1) with anti-Tim-1 overcomes this resistance by specifically inhibiting the pathogenic IL-17-producing CD8 T17 cells. These data indicate that in the absence of Th1 immunity, CD8 T17 alloreactivity constitutes a barrier to transplantation tolerance. Targeting TIM-1 provides an approach to overcome resistance to tolerance in clinical transplantation.
CD160 is a newly identified ligand for HVEM (herpes virus entry mediator). Previously identified HVEM ligands include BTLA (B- and T-lymphocyte attenuator), LIGHT (lymphotoxin-like, exhibits inducible expression, and competes with herpes simplex virus glycoprotein D for HVEM, a receptor expressed by T lymphocytes) and LTalpha (lymphotoxin-alpha). The binding of LIGHT or LTalpha to HVEM delivers a costimulatory signal, whereas the binding of BTLA or CD160 to HVEM delivers a coinhibitory signal. Thus, HVEM is a bidirectional switch regulating T-cell activation in a costimulatory or coinhibitory fashion whose outcome depends on the ligand engaged. The cysteine-rich domain 1 (CRD1) of HVEM is essential for the binding of coinhibitory ligands CD160 and BTLA but not costimulatory ligand LIGHT. Deletion or blockade of HVEM CRD1 abolishes the binding of CD160 and BTLA, but not LIGHT, and converts HVEM to a dominant costimulatory molecule, possibly through the loss of negative signaling by CD160/BTLA. Therapies targeting the CRD1 of HVEM to block BTLA and CD160 binding are being developed to enhance immune responses and vaccination.
Mammalian programmed cell death (PD)-1 is a membrane-associated receptor regulating the balance between T-cell activation, tolerance, and immunopathology; however, its role in neurons has not yet been defined. The hypothesis that PD-1 signaling actively promotes retinal ganglion cell (RGC) death within the developing mouse retina was investigated.
The generation of humanized BLT mice by the cotransplantation of human fetal thymus and liver tissues and CD34(+) fetal liver cells into nonobese diabetic/severe combined immunodeficiency mice allows for the long-term reconstitution of a functional human immune system, with human T cells, B cells, dendritic cells, and monocytes/macrophages repopulating mouse tissues. Here, we show that humanized BLT mice sustained high-level disseminated human immunodeficiency virus (HIV) infection, resulting in CD4(+) T-cell depletion and generalized immune activation. Following infection, HIV-specific humoral responses were present in all mice by 3 months, and HIV-specific CD4(+) and CD8(+) T-cell responses were detected in the majority of mice tested after 9 weeks of infection. Despite robust HIV-specific responses, however, viral loads remained elevated in infected BLT mice, raising the possibility that these responses are dysfunctional. The increased T-cell expression of the negative costimulator PD-1 recently has been postulated to contribute to T-cell dysfunction in chronic HIV infection. As seen in human infection, both CD4(+) and CD8(+) T cells demonstrated increased PD-1 expression in HIV-infected BLT mice, and PD-1 levels in these cells correlated positively with viral load and inversely with CD4(+) cell levels. The ability of humanized BLT mice to generate both cellular and humoral immune responses to HIV will allow the further investigation of human HIV-specific immune responses in vivo and suggests that these mice are able to provide a platform to assess candidate HIV vaccines and other immunotherapeutic strategies.
Programmed death-1 (PD-1) ligation downregulates active lymphocyte responses. The authors tested whether PD-1 or its ligands are expressed in the posterior segment during active intraocular inflammation.
Chronic immunodeficiency virus infections are characterized by dysfunctional cellular and humoral antiviral immune responses. As such, immune modulatory therapies that enhance and/or restore the function of virus-specific immunity may protect from disease progression. Here we investigate the safety and immune restoration potential of blockade of the co-inhibitory receptor programmed death 1 (PD-1) during chronic simian immunodeficiency virus (SIV) infection in macaques. We demonstrate that PD-1 blockade using an antibody to PD-1 is well tolerated and results in rapid expansion of virus-specific CD8 T cells with improved functional quality. This enhanced T-cell immunity was seen in the blood and also in the gut, a major reservoir of SIV infection. PD-1 blockade also resulted in proliferation of memory B cells and increases in SIV envelope-specific antibody. These improved immune responses were associated with significant reductions in plasma viral load and also prolonged the survival of SIV-infected macaques. Blockade was effective during the early (week 10) as well as late ( approximately week 90) phases of chronic infection even under conditions of severe lymphopenia. These results demonstrate enhancement of both cellular and humoral immune responses during a pathogenic immunodeficiency virus infection by blocking a single inhibitory pathway and identify a novel therapeutic approach for control of human immunodeficiency virus infections.
The B7 family member programmed death-1 ligand (PD-L1) has been shown to play an inhibitory role in the regulation of T cell responses in several organs. However, the role of PD-L1 in regulating tolerance to self-Ags of the small intestine has not been previously addressed. In this study, we investigated the role of PD-L1 in CD8(+) T cell tolerance to an intestinal epithelium-specific Ag using the iFABP-tOVA transgenic mouse model, in which OVA is expressed as a self-Ag throughout the small intestine. Using adoptive transfer of naive OVA-specific CD8(+) T cells, we show that loss of PD-1:PD-L1 signaling, by either Ab-mediated PD-L1 blockade or transfer of PD-1(-/-) T cells, leads to considerable expansion of OVA-specific CD8(+) T cells and their differentiation into effector cells capable of producing proinflammatory cytokines. A fatal CD8(+) T cell-mediated inflammatory response develops rapidly against the small bowel causing destruction of the epithelial barrier, severe blunting of intestinal villi, and recruitment and activation of myeloid cells. This response is highly specific because immune destruction selectively targets the small intestine but not other organs. Collectively, these results indicate that loss of the PD-1:PD-L1 inhibitory pathway breaks CD8(+) T cell tolerance to intestinal self-Ag, thus leading to severe enteric autoimmunity.
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