PD-1 and its ligands in T-cell immunity

A potential role for the PD1/PD-L1 pathway in the neuroinflammation of Alzheimer's disease

The interaction between PD1 on T lymphocytes and PD-L1 on antigen presenting cells (APC) modulates the balance between inflammation and tolerance by inducing IL-10 production and apoptosis of antigen-specific cells. We analyzed the PD1/PD-L1 pathway, annexin V (AV)-expression, and proliferation in amyloid-beta (Aβ)-stimulated PBMC of patients with Alzheimer's disease (AD) (N = 35) or mild cognitive impairment (MCI) (N = 30) and of age-matched healthy controls (HC; N = 30). Results showed that PD1-expressing CD4(+) T cells, density of PD-L1 on CD14(+) APC, IL-10 production, and PD-L1-expressing/IL-10-producing CD14(+) APC were significantly reduced in AD and MCI patients compared to HC. Aβ-stimulated PD1/AV-expressing (apoptotic) CD4(+) T cells were also diminished, whereas proliferation was augmented in AD and MCI patients compared to controls. Finally, incubation of cells with PD-L1-neutralizing antibodies significantly decreased apoptosis of Aβ-specific CD4(+) T lymphocytes. An impairment of the PD-L1/PD1 pathway is present in AD and MCI. Such alteration results in reduced IL-10 production and diminished apoptosis of Aβ-specific CD4(+) T lymphocytes; these phenomena could play a role in the neuroinflammation accompanying AD.

CNS expression of B7-H1 regulates pro-inflammatory cytokine production and alters severity of Theiler's virus-induced demyelinating disease

The CNS is a unique organ due to its limited capacity for immune surveillance. As macrophages of the CNS, microglia represent a population originally known for the ability to assist neuronal stability, are now appreciated for their role in initiating and regulating immune responses in the brain. Theiler's murine encephalomyelitis virus (TMEV)-induced demyelinating disease is a mouse model of multiple sclerosis (MS). In response to TMEV infection in vitro, microglia produce high levels of inflammatory cytokines and chemokines, and are efficient antigen-presenting cells (APCs) for activating CD4⁺ T cells. However, the regulatory function of microglia and other CNS-infiltrating APCs in response to TMEV in vivo remains unclear. Here we demonstrate that microglia increase expression of proliferating cell nuclear antigen (PCNA), and phenotypically express high levels of major histocompatibility complex (MHC)-Class I and II in response to acute infection with TMEV in SJL/J mice. Microglia increase expression of the inhibitory co-stimulatory molecule, B7-H1 as early as day 5 post-infection, while CNS-infiltrating CD11b⁺CD11c⁻CD45^HIGH monocytes/macrophages and CD11b⁺CD11c⁺CD45^HIGH dendritic cells upregulate expression of B7-H1 by day 3 post-infection. Utilizing a neutralizing antibody, we demonstrate that B7-H1 negatively regulates TMEV-specific ex vivo production of interferon (IFN)-γ, interleukin (IL)-17, IL-10, and IL-2 from CD4⁺ and CD8⁺ T cells. In vivo blockade of B7-H1 in SJL/J mice significantly exacerbates clinical disease symptoms during the chronic autoimmune stage of TMEV-IDD, but only has minimal effects on viral clearance. Collectively, these results suggest that CNS expression of B7-H1 regulates activation of TMEV-specific T cells, which affects protection against TMEV-IDD.

FOXO3 programs tumor-associated DCs to become tolerogenic in human and murine prostate cancer

The limited success of cancer immunotherapy is often attributed to the loss of antigen-specific T cell function in situ. However, the mechanism for this loss of function is unknown. In this study, we describe a population of tumor-associated DCs (TADCs) in both human and mouse prostate cancer that tolerizes and induces suppressive activity in tumor-specific T cells. In tumors from human prostate cancer patients and transgenic adenocarcinoma of the mouse prostate (TRAMP) mice, TADCs expressed elevated levels of FOXO3 and Foxo3, respectively, which correlated with expression of suppressive genes that negatively regulate T cell function. Silencing FOXO3 and Foxo3 with siRNAs abrogated the ability of human and mouse TADCs, respectively, to tolerize and induce suppressive activity by T cells. Silencing Foxo3 in mouse TADCs was also associated with diminished expression of tolerogenic mediators, such as indoleamine-2,3-dioxygenase, arginase, and TGF-β, and upregulated expression of costimulatory molecules and proinflammatory cytokines. Importantly, transfer of tumor-specific CD4+ Th cells into TRAMP mice abrogated TADC tolerogenicity, which was associated with reduced Foxo3 expression. These findings demonstrate that FOXO3 may play a critical role in mediating TADC-induced immune suppression. Moreover, our results identify what we believe to be a novel target for preventing CTL tolerance and enhancing immune responses to cancer by modulating the immunosuppressive activity of TADCs found in the tumor microenvironment.

Inflammatory signatures for eosinophilic vs. neutrophilic allergic pulmonary inflammation reveal critical regulatory checkpoints

Contrary to the T-helper (Th)-2 bias and eosinophil-dominated bronchial inflammation encountered in most asthmatic subjects, other patients may exhibit neutrophil-predominant asthma subphenotypes, along with Th-1 and Th-17 cells. However, the etiology of many neutrophil-dominated asthma subphenotypes remains ill-understood, in part due to a lack of appropriate experimental models. To better understand the distinct immune-pathological features of eosinophilic vs. neutrophilic asthma types, we developed an ovalbumin (OVA)-based mouse model of neutrophil-dominated allergic pulmonary inflammation. Consequently, we probed for particular inflammatory signatures and checkpoints underlying the immune pathology in this new model, as well as in a conventional, eosinophil-dominated asthma model. Briefly, mice were OVA sensitized using either aluminum hydroxide (alum) or complete Freund's adjuvants, followed by OVA aerosol challenge. T-cell, granulocyte, and inflammatory mediator profiles were determined, along with alveolar macrophage genomewide transcriptome profiling. In contrast to the Th-2-dominated phenotype provoked by alum, OVA/ complete Freund's adjuvants adjuvant-based sensitization, followed by allergen challenge, elicited a pulmonary inflammation that was poorly controlled by dexamethasone, and in which Th-1 and Th-17 cells additionally participated. Analysis of the overall pulmonary and alveolar macrophage inflammatory mediator profiles revealed remarkable similarities between both models. Nevertheless, we observed pronounced differences in the IL-12/IFN-γ axis and its control by IL-18 and IL-18 binding protein, but also in macrophage arachidonic acid metabolism and expression of T-cell instructive ligands. These differential signatures, superimposed onto a generic inflammatory signature, denote distinctive inflammatory checkpoints potentially involved in orchestrating neutrophil-dominated asthma.

HIV-1 impairs in vitro priming of naïve T cells and gives rise to contact-dependent suppressor T cells

Priming of T cells in lymphoid tissues of HIV-infected individuals occurs in the presence of HIV-1. DC in this milieu activate T cells and disseminate HIV-1 to newly activated T cells, the outcome of which may have serious implications in the development of optimal antiviral responses. We investigated the effects of HIV-1 on DC–naïve T-cell interactions using an allogeneic in vitro system. Our data demonstrate a dramatic decrease in the primary expansion of naïve T cells when cultured with HIV-1-exposed DC. CD4⁺ and CD8⁺ T cells showed enhanced expression of PD-1 and TRAIL, whereas CTLA-4 expression was observed on CD4⁺ T cells. It is worth noting that T cells primed in the presence of HIV-1 suppressed priming of other naïve T cells in a contact-dependent manner. We identified PD-1, CTLA-4, and TRAIL pathways as responsible for this suppresion, as blocking these negative molecules restored T-cell proliferation to a higher degree. In conclusion, the presence of HIV-1 during DC priming produced cells with inhibitory effects on T-cell activation and proliferation, i.e. suppressor T cells, a mechanism that could contribute to the enhancement of HIV-1 pathogenesis.

Immunological effects of sublingual immunotherapy: clinical efficacy is associated with modulation of programmed cell death ligand 1, IL-10, and IgG4

Sublingual immunotherapy (SLIT) is an alternate route of administration of allergen-specific immunotherapy with an improved safety profile; to clarify the immune mechanisms elicited by this therapy, we analyzed the clinical and immunologic effects of SLIT in patients with a clinical history of ragweed sensitization. To analyze possible difference among immunotherapeutic protocols, we also compared patients receiving preseasonal, seasonal, or prolonged sublingual therapy (≥ 3 y); patients receiving symptomatic therapy alone were enrolled as well in the study. Clinical and immunological parameters were measured twice in and out of the pollination period. Clinical benefits, as measured by the visual analog scale for symptoms and for use of drugs, were evident in all three groups of individuals receiving immunotherapy, but were significantly better in patients undergoing prolonged SLIT. Immunologically, SLIT resulted in increased IL-10 production, programmed cell death ligand 1 expression, and concentration of allergen-specific IgG4, as well as in the reduction of CD80 and CD86 expression and IL-4 production. SLIT, thus, is associated with modulation of programmed cell death ligand 1 expression and IL-10 synthesis and favors the production of allergen-specific IgG4. These effects are evident from the first pollen season, independently from therapeutic regimen (preseasonal or seasonal) even if a prolonged treatment is necessary to obtain full clinical efficacy. A more detailed understanding of the interaction of allergen and APCs within the oral mucosa will allow improved targeting of allergy vaccine.

Tumor antigen cross-presentation and the dendritic cell: where it all begins?

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that are critical for the generation of effective cytotoxic T lymphocyte (CTL) responses; however, their function and phenotype are often defective or altered in tumor-bearing hosts, which may limit their capacity to mount an effective tumor-specific CTL response. In particular, the manner in which exogenous tumor antigens are acquired, processed, and cross-presented to CD8 T cells by DCs in tumor-bearing hosts is not well understood, but may have a profound effect on antitumor immunity. In this paper, we have examined the role of DCs in the cross-presentation of tumor antigen in terms of their subset, function, migration, and location with the intention of examining the early processes that contribute to the development of an ineffective anti-tumor immune response.

Hepatitis C virus infection: a "liaison a trois" amongst the virus, the host, and chronic low-level inflammation for human survival

This review covers the various aspects of the immune system that allows the relationship between the hepatitis-C virus, the host and chronic low-level inflammation, to be highly flexible and able to defend the host from persistent infections. This ambiguity mainly stems from the property of the immune system that can be both protective and harmful. Immunity cannot be fully protective without producing a certain degree of damage (acute hepatitis resulting in resolving HCV infection). In addition, the balance between protection and tissue damage is critical for the development of chronic HCV infection. The establishment of a state of chronic low-level inflammation is instrumental to limit liver immunopathology, to limit viral spread, and ultimately to ensure a long-lasting survival of the host. It is dictated by a fine equilibrium maintained by multiple immunologic mechanisms, including: sensory perception of innate immunity, virus-specific T and B cell functions, control of immune responses, and finally the balance between immunity and immunopathology that has principally evolved to favor the survival of the species.

A tonsillar PolyICLC/AT-2 SIV therapeutic vaccine maintains low viremia following antiretroviral therapy cessation

BACKGROUND

HIV-infected individuals rely on antiretroviral therapy (ART) to control viral replication. Despite abundant demonstrable benefits, the multiple limitations of ART point to the potential advantages of therapeutic vaccination approaches that could provide sustained host control of viral replication after discontinuation of ART. We provide evidence from a non-human primate model that a therapeutic vaccine applied to the tonsils can maintain low viral loads after cessation of ART.

METHODOLOGY/PRINCIPAL FINDINGS

Animals received 40 weeks of ART initiated 9 weeks after rectal SIVmac239 infection. During ART, animals were vaccinated (or not) with AT-2 inactivated SIVmac239 using CpG-C ISS-ODN (C274) or polyICLC as adjuvants. PolyICLC/AT-2 SIV vaccinated animals maintained viral loads <3×10(3) copies/ml for up to 16 weeks post-ART, whereas the C274/AT-2 SIV vaccinated and non-vaccinated animals' viremia ranged between 1×10(4)-4×10(5) copies/ml (p<0.03). Neutralizing Ab activity in plasma was increased by polyICLC/AT-2 tonsillar vaccination under ART, compared to controls (p<0.03). Subsequent vaccination of all animals with polyICLC/AT-2 SIV in the absence of ART did not alter viral loads. Other immune parameters measured in blood and tissues were comparable between groups.

CONCLUSIONS/SIGNIFICANCE

These results provide support for the potential benefit of mucosally delivered vaccines in therapeutic immunization strategies for control of AIDS virus infection.

Follicular lymphoma prognostic factors in the modern era: what is clinically meaningful?

Follicular lymphomas (FL) account for 30% of non-Hodgkin's lymphomas (NHL). Their evolution is heterogeneous. Some patients present with indolent forms undergoing several relapses while in other patients the disease evolves abruptly toward aggressive NHL. This is why accurate prognostic indices are required so that treatment strategies may be optimized for each patient and so that trials may be conducted in groups of patients that are as homogeneous as possible. The Follicular Lymphoma International Prognostic Index (FLIPI) has been designed to separate patients into 3 groups with significantly different hazard ratios for death. Its accuracy has been confirmed in several studies. The FLIPI2 was designed more recently to separate patients with significantly different hazard ratios for progression/relapse in the era of anti-CD20 monoclonal antibody treatments. Gene profile studies have shown that the prognosis of FL is mainly related to the type, number, and activation of immune cells in the microenvironment of lymphomatous follicles. Immunohistochemical studies suggest that macrophages, CD4+ T cells and among them T-regulatory cells (T-regs) and programed death-1 cells (PD-1 cells) play a major role in the outcome of FLs. However, additional confirmatory studies are required due to discrepancies in results. Up to now, these biological study results are more useful for approaching the pathophysiology of FL rather than to be used as prognostic tools in clinical practice.

Enhanced tumor eradication by combining CTLA-4 or PD-1 blockade with CpG therapy

Tumor immunotherapy aims to break effector T-cell anergy and to block suppressive cell types and ligands allowing effector cells to exert tumor eradication. Previous reports demonstrate that cytotoxic T lymphocyte antigen-4 (CTLA-4)-blocking antibodies promote T-cell activation and render T effector cells resistant to T regulatory cells (Tregs) whereas programmed death receptor-1 (PD-1)/PD-L1 blockade results in loss of peripheral tolerance. Herein, we explored single or combined antibody blockade of CTLA-4 and PD-1 alone or combined with the toll-like receptor agonists CpG or bacillus Calmette-Guérin for treatment of murine experimental bladder cancer. In therapeutic studies, tumors were rejected by anti-CTLA-4 (aCTLA-4) while anti-PD-1 (aPD-1) suppressed tumor growth. The combination had no additive effect compared with aCTLA-4 alone. However, elevated levels of circulating CD107a expressing CD8 T cells were found in the aCTLA-4 plus aPD-1 group. In addition, levels of antinuclear antibodies correlated inversely with tumor size. Next, we combined CpG or bacillus Calmette-Guérin with aCTLA-4, aPD-1, or aPD-L1 and found that CpG in combination with aCTLA-4 or aPD-1 increased the survival of mice, with aPD-1 plus CpG being superior to either agent alone. CpG plus aCTLA-4 or aPD-1 increased the numbers of circulating tumor-specific CD107a expressing CD8 T cells as well as activated (CD25FoxP3-) CD4 splenocytes. Further, we investigated the numbers of Tregs in the tumor area of treated animals and detected decreased levels after aCTLA-4 or aPD-1 plus CpG therapy. Thus, the combination of CpG with CTLA-4 or PD-1 blockade improved long-term survival and led to increased levels of tumor-reactive T cells and reduced numbers of Tregs at the tumor site.

Dendritic cells in chronic mycobacterial granulomas restrict local anti-bacterial T cell response in a murine model

BACKGROUND

Mycobacterium-induced granulomas are the interface between bacteria and host immune response. During acute infection dendritic cells (DCs) are critical for mycobacterial dissemination and activation of protective T cells. However, their role during chronic infection in the granuloma is poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

We report that an inflammatory subset of murine DCs are present in granulomas induced by Mycobacteria bovis strain Bacillus Calmette-guerin (BCG), and both their location in granulomas and costimulatory molecule expression changes throughout infection. By flow cytometric analysis, we found that CD11c(+) cells in chronic granulomas had lower expression of MHCII and co-stimulatory molecules CD40, CD80 and CD86, and higher expression of inhibitory molecules PD-L1 and PD-L2 compared to CD11c(+) cells from acute granulomas. As a consequence of their phenotype, CD11c(+) cells from chronic lesions were unable to support the reactivation of newly-recruited, antigen 85B-specific CD4(+)IFNgamma(+) T cells or induce an IFNgamma response from naïve T cells in vivo and ex vivo. The mechanism of this inhibition involves the PD-1:PD-L signaling pathway, as ex vivo blockade of PD-L1 and PD-L2 restored the ability of isolated CD11c(+) cells from chronic lesions to stimulate a protective IFNgamma T cell response.

CONCLUSIONS/SIGNIFICANCE

Our data suggest that DCs in chronic lesions may facilitate latent infection by down-regulating protective T cell responses, ultimately acting as a shield that promotes mycobacterium survival. This DC shield may explain why mycobacteria are adapted for long-term survival in granulomatous lesions.

Regulation of the induction and function of cytotoxic T lymphocytes by natural killer T cell

Cytotoxic T lymphocytes (CTLs) play a crucial role in the infections and the antitumor immunity. Induction and activation of antigen-specific CTLs is an important strategy in immunotherapy for various diseases, and several researchers have focused on the modulation of CTL induction and function. Natural killer T (NKT) cells are an important focus area of researchers studying immunomodulatory responses to tumors and infectious diseases. CD1d-restricted NKT cells consist of type I NKT cells and type II NKT cells. α-galactosylceramide (α-GalCer)-activated type I NKT cells secrete both Th1 (e.g., IFN-γ) and Th2 cytokines, affect the expression of costimulatory molecules in immune cells, and regulate the host immune system. Type II NKT cells, however, are stimulated by sulfatide, a self-glycolipid derived from myelin, and play an immunosuppressive role in animal model of autoimmune diseases. CTL generation, activation, and suppression are strongly affected by activated type I and type II NKT cells. Thus, the regulation of these NKT cells leads to the modification of CTL function. CTLs contribute to antimicrobial responses, antitumor immune and autoimmune responses. Understanding the role of NKT cells in the regulation of CTL generation, activation, and suppression enable the development of novel treatment strategies for these diseases.

Targeting inhibitory pathways in cancer immunotherapy

The clinical success of adaptive transfer of in vitro expanded antigen-specific CD8(+) T cells isolated from patients' tumors has demonstrated that effector cells of the adaptive immune system can effectively eliminate even large tumor masses. Nevertheless, cancer vaccines that aim to expand such CD8(+) T cells in situ have had remarkably little success in spite of numerous attempts. Recent advances in basic immunology have revealed layers of complexity controlling activation and maintenance of adaptive immune responses that are tightly controlled by immunoinhibitory pathways to avoid horror autotoxicus. During tumor progression the activities of negative pathways increase and together with cancer immune evasion tactics presumably prevent induction of an efficacious immune response by cancer vaccines that solely provide more antigen to an already suppressed system. Cancer vaccines may thus need to readjust the imbalance of the cancer patients' immune system by inhibiting immunoinhibitors; such regimens have shown preclinical efficacy and are now entering clinical trials hopefully ending the Kafkaesque futility of cancer vaccines.

CD8+ Tregs in lupus, autoimmunity, and beyond

While CD4(+)CD25(high) regulatory T cells (Tregs) have garnered much attention for their role in the maintenance of immune homeostasis, recent findings have shown that subsets of CD8(+) T cells (CD8(+) Tregs) display immunoregulatory functions as well. Both CD4(+) Tregs and CD8(+) Tregs appear impaired in number and/or function in several autoimmune diseases and in experimental animal models of autoimmunity, suggesting the possibility of immunotherapeutic targeting of these cells for improved management of autoimmune conditions. Our group has developed a strategy to induce CD8(+) Tregs in autoimmune mice through the use of a tolerogenic self-peptide, and new information has been gained on the phenotype, function and role of induced CD8(+) Tregs in autoimmunity. Here we present an overview of the role and mechanisms of action of CD8(+) Tregs in autoimmunity, with a special focus on lupus. We also discuss the potential role of CD8(+) Tregs in other diseases, including chronic infection and cancer.

The yellow fever virus vaccine induces a broad and polyfunctional human memory CD8+ T cell response

The live yellow fever vaccine (YF-17D) offers a unique opportunity to study memory CD8(+) T cell differentiation in humans following an acute viral infection. We have performed a comprehensive analysis of the virus-specific CD8(+) T cell response using overlapping peptides spanning the entire viral genome. Our results showed that the YF-17D vaccine induces a broad CD8(+) T cell response targeting several epitopes within each viral protein. We identified a dominant HLA-A2-restricted epitope in the NS4B protein and used tetramers specific for this epitope to track the CD8(+) T cell response over a 2 year period. This longitudinal analysis showed the following. 1) Memory CD8(+) T cells appear to pass through an effector phase and then gradually down-regulate expression of activation markers and effector molecules. 2) This effector phase was characterized by down-regulation of CD127, Bcl-2, CCR7, and CD45RA and was followed by a substantial contraction resulting in a pool of memory T cells that re-expressed CD127, Bcl-2, and CD45RA. 3) These memory cells were polyfunctional in terms of degranulation and production of the cytokines IFN-gamma, TNF-alpha, IL-2, and MIP-1beta. 4) The YF-17D-specific memory CD8(+) T cells had a phenotype (CCR7(-)CD45RA(+)) that is typically associated with terminally differentiated cells with limited proliferative capacity (T(EMRA)). However, these cells exhibited robust proliferative potential showing that expression of CD45RA may not always associate with terminal differentiation and, in fact, may be an indicator of highly functional memory CD8(+) T cells generated after acute viral infections.

Down-modulation of programmed death 1 alters regulatory T cells and promotes experimental autoimmune encephalomyelitis

The regulatory role of programmed death 1 (PD-1) was investigated in the development of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Typical EAE could be induced by immunization without pertussis toxin (PTX) in PD-1-null but not in wild-type (WT) mice. However, both strains developed a similar EAE phenotype when immunized with PTX or by adoptive transfer of pathogenic T cells. In WT mice that did not develop EAE after immunization without PTX, the frequency of CD4(+)FoxP3(+) Treg cells was boosted in the periphery but not in the thymus. This increase in Treg frequency was abrogated by PD-1 deficiency or inclusion of PTX. In addition, PD-1 expression was critical to in vitro conversion of naïve myelin-specific CD4 T cells into Treg cells and was directly related to Treg suppressive activity. Finally, PD-1 was markedly down-modulated in the periphery of WT mice after administration of PTX. Therefore, down-modulation of PD-1 in Treg cells may abrogate Treg-mediated immune suppression, permitting the activation of myelin-reactive T cells and induction of EAE.

Enhanced PD-1 expression by T cells in cerebrospinal fluid does not reflect functional exhaustion during chronic human immunodeficiency virus type 1 infection

During chronic viral infections, T cells are exhausted due to constant antigen exposure and are associated with enhanced programmed death 1 (PD-1) expression. Deficiencies in the PD-1/programmed death-ligand 1 (PD-L1) pathway are associated with autoimmune diseases, including those of the central nervous system (CNS). To understand the role of PD-1 expression in regulating T-cell immunity in the CNS during chronic infection, we characterized PD-1 expression in cerebrospinal fluid (CSF) and blood of individuals with chronic human immunodeficiency virus type 1 (HIV-1) infection. PD-1 expression was higher on HIV-specific CD8(+) T cells than on total CD8(+) T cells in both CSF and blood. PD-1 expression on CSF T cells correlated positively with CSF HIV-1 RNA and inversely with blood CD4(+) T-cell counts, suggesting that HIV-1 infection drives higher PD-1 expression on CSF T cells. However, in every HIV-positive individual, PD-1 expression was higher on T cells in CSF than on those in blood, despite HIV-1 RNA levels being lower. Among healthy HIV-negative controls, PD-1 expression was higher in CSF than in blood. Furthermore, frequencies of the senescence marker CD57 were lower on CSF T cells than on blood T cells, consistent with our prior observation of enhanced ex vivo functional capacity of CSF T cells. The higher PD-1 expression level on CSF T cells therefore does not reflect cellular exhaustion but may be a mechanism to downregulate immune-mediated tissue damage in the CNS. As inhibition of the PD-1/PD-L1 pathway is pursued as a therapeutic option for viral infections, potential effects of such a blockade on development of autoimmune responses in the CNS should be considered.

A unifying microenvironment model in follicular lymphoma: outcome is predicted by programmed death-1--positive, regulatory, cytotoxic, and helper T cells and macrophages

PURPOSE

The microenvironment influences outcome in follicular lymphoma. Our hypothesis was that several immune cell subsets are important for disease outcome and their individual prognostic importance should be demonstrable in the same analysis and in competition with clinical factors.

EXPERIMENTAL DESIGN

Seventy follicular lymphoma patients with extreme clinical outcome ("poor" and "good" cases) were selected in a population-based cohort of 197. None of the 37 good-outcome patients died from lymphoma, whereas all the 33 poor-outcome patients succumbed in <or=5 years. Furthermore, the good-outcome patients were followed for a long time and needed no or little treatment. A tissue microarray was constructed from diagnostic, pretreatment biopsies. Cellular subsets were quantified after immunostaining, using computerized image analysis, separating cells inside and outside the follicles (follicular and interfollicular compartments). Flow cytometry data from the same samples were also used.

RESULTS

Independently of the Follicular Lymphoma International Prognostic Index, CD4(+) cells were associated with poor outcome and programmed death-1-positive and CD8(+) cells were associated with good outcome. The prognostic values of CD4(+) and programmed death-1-positive cells were accentuated when they were follicular and that of CD8(+) cells were accentuated when they were interfollicular. Follicular FOXP3(+) cells were associated with good outcome and interfollicular CD68(+) cells were associated with poor outcome. Additionally, high CD4/CD8 and CD4 follicular/interfollicular ratios correlated with poor outcome.

CONCLUSION

There are many important immune cell subsets in the microenvironment of follicular lymphoma. Each of these is independently associated with outcome. This is the first study showing the effect of the balance of the entire microenvironment, not only of individual subsets.

How tolerogenic dendritic cells induce regulatory T cells

Since their discovery by Steinman and Cohn in 1973, dendritic cells (DCs) have become increasingly recognized for their crucial role as regulators of innate and adaptive immunity. DCs are exquisitely adept at acquiring, processing, and presenting antigens to T cells. They also adjust the context (and hence the outcome) of antigen presentation in response to a plethora of environmental inputs that signal the occurrence of pathogens or tissue damage. Such signals generally boost DC maturation, which promotes their migration from peripheral tissues into and within secondary lymphoid organs and their capacity to induce and regulate effector T cell responses. Conversely, more recent observations indicate that DCs are also crucial to ensure immunological peace. Indeed, DCs constantly present innocuous self- and nonself-antigens in a fashion that promotes tolerance, at least in part, through the control of regulatory T cells (Tregs). Tregs are specialized T cells that exert their immunosuppressive function through a variety of mechanisms affecting both DCs and effector cells. Here, we review recent advances in our understanding of the relationship between tolerogenic DCs and Tregs.

PD-L1 regulates the development, maintenance, and function of induced regulatory T cells

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.

Programmed cell death 1 gene polymorphisms is associated with ankylosing spondylitis in Chinese Han population

Programmed cell death 1 (PD-1) has been reported to have a genetic association in several autoimmune diseases. The aim of this study was to investigate the association of PD-1 polymorphisms and haplotypes with ankylosing spondylitis (AS) in Chinese Han population. In a case-control association study, three single-nucleotide polymorphisms (SNP), PD-1.3 G/A, PD-1.5 C/T and PD-1.9 T/C, were genotyped in 216 AS patients and 264 healthy controls using polymerase chain reaction-restriction fragment length polymorphism assay. All genotype distributions in the patients and in the controls were in Hardy-Weinberg equilibrium. The associations of genotypes and alleles with AS were analyzed. The genotype distributions of PD-1.9 were significantly different between the patients with AS and the controls (P = 0.025). The frequencies of TC genotype and T allele of PD-1.9 were higher in the patients than those in the controls (P = 0.026 and 0.004). No association for PD-1.5 in AS was found, and PD-1.3 was non-polymorphic in Chinese Han population. Moreover, the frequency of the CT haplotype (PD-1.5 C/T, PD-1.9 T/C) was significantly higher in AS patients than the controls (21.6 vs. 13.9%, P = 0.002). The CC haplotype was more common in the controls than in the patients (57.1 vs. 44.6%, P = 0.000). The results support a genetic association between the PD-1 polymorphism and susceptibility to AS in Chinese Han population.

Inhibitory TCR coreceptor PD-1 is a sensitive indicator of low-level replication of SIV and HIV-1

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.

Costimulatory molecule programmed death-1 in the cytotoxic response during chronic hepatitis C

Hepatitis C virus (HCV)-specific CD8⁺ T cells play an important role in the resolution of HCV infection. Nevertheless, during chronic hepatitis C these cells lack their effector functions and fail to control the virus. HCV has developed several mechanisms to escape immune control. One of these strategies is the up-regulation of negative co-stimulatory molecules such us programmed death-1 (PD-1). This molecule is up-regulated on intrahepatic and peripheral HCV-specific cytotoxic T cells during acute and chronic phases of the disease, whereas PD-1 expression is low in resolved infection. PD-1 expressing HCV-specific CD8⁺ T cells are exhausted with impairment of several effector mechanisms, such as: type-1 cytokine production, expansion ability after antigen encounter and cytotoxic ability. However, PD-1 associated exhaustion can be restored by blocking the interaction between PD-1 and its ligand (PD-L1). After this blockade, HCV-specific CD8⁺ T cells reacquire their functionality. Nevertheless, functional restoration depends on PD-1 expression level. High PD-1-expressing intrahepatic HCV-specific CD8⁺ T cells do not restore their effector abilities after PD-1/PD-L1 blockade. The mechanisms by which HCV is able to induce PD-1 up-regulation to escape immune control are unknown. Persistent TCR stimulation by a high level of HCV antigens could favour early PD-1 induction, but the interaction between HCV core protein and gC1q receptor could also participate in this process. The PD-1/PD-L1 pathway modulation could be a therapeutic strategy, in conjunction with the regulation of others co-stimulatory pathways, in order to restore immune response against HCV to succeed in clearing the infection.

Human prostate-infiltrating CD8+ T lymphocytes are oligoclonal and PD-1+

BACKGROUND

Prostate-infiltrating CD8(+) T lymphocytes (CD8(+) PIL) are prevalent in men with prostate cancer (PCa), however, it is unclear whether the presence of such cells reflects a non-specific immune infiltrate or an oligoclonal, antigen-driven adaptive immune response.

METHODS

We investigated the complexity of the T-cell receptor (TCR) repertoire in the prostate gland by examining the diversity of CD8(+) TCR beta chain variable region (Vbeta) gene sequences in both the peripheral blood and prostates of cancer patients. Vbeta repertoire analysis was performed by family-specific Vbeta spectratyping and flow cytometry, as well as direct sequence analysis (5' RACE and cloning). Programmed cell death 1 (PD-1 or PDCD1) expression on peripheral blood CD8(+) T cells and CD8(+) PIL was analyzed by flow cytometry.

RESULTS

CD8(+) PIL isolated from cancer patients exhibited restricted TCR Vbeta gene usage, and identical clones were identified in multiple sites within the prostate. Furthermore, CD8(+) PIL express high levels of the inhibitory receptor PD-1, a cell surface protein associated with an "exhausted" CD8(+) T-cell phenotype.

CONCLUSIONS

CD8(+) PIL appear to have undergone clonal expansion in response to an as yet unidentified antigen; however, due to the high expression of PD-1, these cells are likely incapable of mounting an effective immune response. The results provide an important basis for further efforts aimed at the identification of specific antigens involved in prostatic inflammation, and suggest that PD-1 blockade may be useful in immunotherapy for PCa.

Gene expression patterns associated with chicken jejunal development

Jejunal development occurs in a spatio-temporal pattern and is characterized by morphological and functional changes. To investigate jejunal development at the transcriptomic level, we performed microarray studies in 1-21-day-old chickens. Nine gene clusters were identified, each with a specific gene expression pattern. Subsequently, groups of genes with similar functions could be identified. Genes involved in morphological and functional development were highly expressed immediately after hatch with declining expression patterns afterwards. Immunological development can be roughly divided based on expression patterns into three processes over time; first innate response and immigration of immune cells, secondly differentiation and specialization, and thirdly maturation and immune regulation. We conclude that specific gene expression patterns coincide with the immunological, morphological, and functional development as measured by other methods. Our data show that transcriptomic approaches provide more detailed information on the biological processes underlying jejunal development.

Tumor-expressed B7-H1 and B7-DC in relation to PD-1+ T-cell infiltration and survival of patients with cervical carcinoma

PURPOSE

The interaction between programmed cell death 1 (PD-1), expressed by activated effector or regulatory T cells, and B7-H1 (PD-L1) and B7-DC (PD-L2) results in the inhibition of T-cell function. The aim of this study was to determine B7-H1, B7-DC, and PD-1 expression in cervical carcinoma.

EXPERIMENTAL DESIGN

A tissue microarray of a well-defined group of 115 patients was stained with antibodies against B7-H1 and B7-DC. Three-color fluorescent immunohistochemistry was used to study the number and phenotype of tumor-infiltrating T cells expressing PD-1. Additional analyses consisted of in vitro T-cell suppression assays.

RESULTS

B7-H1 was expressed in 19%, and B7-DC was expressed by 29% of the 115 tumors. PD-1 was expressed by more than half of both the infiltrating CD8+ T cells and CD4+Foxp3+ T cells, irrespective of B7-H1 or B7-DC expression by tumors. The expression of B7-H1 did not show a direct impact on patient survival. However, subgroup analysis revealed that patients with a relative excess of infiltrating regulatory T cells displayed a better survival when the tumor was B7-H1 positive (P = 0.033). Additional studies showed that the presence of B7-H1 during the activation of CD4+Foxp3+ regulatory T cells impaired their suppressive function in a functional in vitro assay.

CONCLUSIONS

B7-H1 is expressed on only a minority of cervical cancers and does not influence the survival of patients with cervical cancer. PD-1 is expressed by a vast number of infiltrating CD8 T cells, suggesting that blocking of PD-1 could have therapeutic potential in cervical cancer patients.

Phenotypic and functional markers for 1alpha,25-dihydroxyvitamin D(3)-modified regulatory dendritic cells

The clinical use of dendritic cells (DCs) to induce antigen-specific immune tolerance has been hampered by the lack of a widely acknowledged method for generating human regulatory DCs but even more so by the non-existence of reliable markers. Thus, we set out to find reliable markers that can be measured with simple methods to identify regulatory DCs that are applicable for future clinical studies. Human DCs were generated from peripheral blood monocytes in the presence of 1alpha,25-dihydroxyvitamin D(3) (VD3), which gave rise to a phenotype that resembles immature DCs, with the exception of high CD14 and reduced CD1a on the cell surface. These VD3-treated DCs exert a long-lasting inefficient T cell stimulation and induce T cell hyporesponsiveness with regulatory potential. Importantly, such VD3-treated DCs were readily distinguishable from untreated DCs by low levels of interleukin-23 secretion and low expression of miR-155 upon exposure to maturation stimuli. Furthermore, VD3-treated DCs showed over-expression of miR-378. All these features can be used as robust markers for quality control of VD3-treated regulatory DCs in future clinical studies.

Negative immune regulator Tim-3 is overexpressed on T cells in hepatitis C virus infection and its blockade rescues dysfunctional CD4+ and CD8+ T cells

A number of emerging molecules and pathways have been implicated in mediating the T-cell exhaustion characteristic of chronic viral infection. Not all dysfunctional T cells express PD-1, nor are they all rescued by blockade of the PD-1/PD-1 ligand pathway. In this study, we characterize the expression of T-cell immunoglobulin and mucin domain-containing protein 3 (Tim-3) in chronic hepatitis C infection. For the first time, we found that Tim-3 expression is increased on CD4(+) and CD8(+) T cells in chronic hepatitis C virus (HCV) infection. The proportion of dually PD-1/Tim-3-expressing cells is greatest in liver-resident T cells, significantly more so in HCV-specific than in cytomegalovirus-specific cytotoxic T lymphocytes. Tim-3 expression correlates with a dysfunctional and senescent phenotype (CD127(low) CD57(high)), a central rather than effector memory profile (CD45RA(negative) CCR7(high)), and reduced Th1/Tc1 cytokine production. We also demonstrate the ability to enhance T-cell proliferation and gamma interferon production in response to HCV-specific antigens by blocking the Tim-3-Tim-3 ligand interaction. These findings have implications for the development of novel immunotherapeutic approaches to this common viral infection.

PD-1 signaling in primary T cells

SUMMARY

Programmed death-1 (PD-1) is a cell surface molecule that regulates the adaptive immune response. Engagement of PD-1 by its ligands PD-L1 or PD-L2 transduces a signal that inhibits T-cell proliferation, cytokine production, and cytolytic function. While a great deal is known concerning the biologic roles PD-1 plays in regulating the primary immune response and in T-cell exhaustion, comparatively little is known regarding how PD-1 ligation alters signaling pathways. PD-1 ligation is known to inhibit membrane-proximal T-cell signaling events, while ligation of the related inhibitory molecule cytotoxic T-lymphocyte antigen-4 appears to target more downstream signaling pathways. A major obstacle to an in-depth understanding of PD-1 signaling is the lack of physiologic models in which to study signal transduction. This review focuses on: (i) signaling pathways altered by PD-1 ligation, (ii) factors recruited upon PD-1 phosphorylation, and (iii) exploring the hypothesis that PD-1 ligation induces distinct signals during various stages of immune-cell differentiation. Lastly, we describe models to dissect the function of the PD-1 cytoplasmic tail using primary cells in the absence of agonist antibodies.

T-cell growth, cell surface organization, and the galectin-glycoprotein lattice

Basal, activation, and arrest signaling in T cells determines survival, coordinates responses to pathogens, and, when dysregulated, leads to loss of self-tolerance and autoimmunity. At the T-cell surface, transmembrane glycoproteins interact with galectins via their N-glycans, forming a molecular lattice that regulates membrane localization, clustering, and endocytosis of surface receptors. Galectin-T-cell receptor (TCR) binding prevents ligand-independent TCR signaling via Lck by blocking spontaneous clustering and CD4-Lck recruitment to TCR, and in turn F-actin transfer of TCR/CD4-Lck complexes to membrane microdomains. Peptide-major histocompatibility complexes overcome galectin-TCR binding to promote TCR clustering and signaling by Lck at the immune synapse. Galectin also localizes the tyrosine phosphatase CD45 to microdomains and the immune synapse, suppressing basal and activation signaling by Lck. Following activation, membrane turnover increases and galectin binding to cytotoxic T-lymphocyte antigen-4 (CTLA-4) enhances surface expression by inhibiting endocytosis, thereby promoting growth arrest. Galectins bind surface glycoproteins in proportion to the branching and number of N-glycans per protein, the latter an encoded feature of protein sequence. N-glycan branching is conditional to the activity of Golgi N-acetylglucosaminyl transferases I, II, IV and V (Mgat1, 2, 4, and 5) and metabolic supply of their donor substrate UDP-GlcNAc. Genetic and metabolic control of N-glycan branching co-regulate homeostatic set-points for basal, activation, and arrest signaling in T cells and, when disturbed, result in T-cell hyperactivity and autoimmunity.

Oestrogen modulates experimental autoimmune encephalomyelitis and interleukin-17 production via programmed death 1

The mechanism by which oestrogens suppress experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, is only partially understood. We here demonstrate that treatment with 17beta-oestradiol (E(2)) in C57BL/6 mice boosted the expression of programmed death 1 (PD-1), a negative regulator of immune responses, in the CD4(+) FoxP3(+) regulatory T (Treg) cell compartment in a dose-dependent manner that correlated with the efficiency of EAE protection. Administration of E(2) at pregnancy levels but not lower concentrations also enhanced the frequency of Treg cells. Additionally, E(2) treatment drastically reduced the production of interleukin-17 (IL-17) in the periphery of immunized mice. However, E(2) treatment did not protect against EAE or suppress IL-17 production in PD-1 gene-deficient mice. Finally, E(2) failed to prevent Treg-deficient mice from developing spontaneous EAE. Taken together, our results suggest that E(2)-induced protection against EAE is mediated by upregulation of PD-1 expression within the Treg-cell compartment.

PD-1 is a regulator of NY-ESO-1-specific CD8+ T cell expansion in melanoma patients

The programmed death 1 (PD-1) receptor is a negative regulator of activated T cells and is up-regulated on exhausted virus-specific CD8(+) T cells in chronically infected mice and humans. Programmed death ligand 1 (PD-L1) is expressed by multiple tumors, and its interaction with PD-1 resulted in tumor escape in experimental models. To investigate the role of PD-1 in impairing spontaneous tumor Ag-specific CD8(+) T cells in melanoma patients, we have examined the effect of PD-1 expression on ex vivo detectable CD8(+) T cells specific to the tumor Ag NY-ESO-1. In contrast to EBV, influenza, or Melan-A/MART-1-specific CD8(+) T cells, NY-ESO-1-specific CD8(+) T cells up-regulated PD-1 expression. PD-1 up-regulation on spontaneous NY-ESO-1-specific CD8(+) T cells occurs along with T cell activation and is not directly associated with an inability to produce cytokines. Importantly, blockade of the PD-1/PD-L1 pathway in combination with prolonged Ag stimulation with PD-L1(+) APCs or melanoma cells augmented the number of cytokine-producing, proliferating, and total NY-ESO-1-specific CD8(+) T cells. Collectively, our findings support the role of PD-1 as a regulator of NY-ESO-1-specific CD8(+) T cell expansion in the context of chronic Ag stimulation. They further support the use of PD-1/PD-L1 pathway blockade in cancer patients to partially restore NY-ESO-1-specific CD8(+) T cell numbers and functions, increasing the likelihood of tumor regression.

Membrane estrogen receptor regulates experimental autoimmune encephalomyelitis through up-regulation of programmed death 1

Although estrogens exert a pronounced protective effect on multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), their therapeutic application has been limited by undesirable side effects thought to be mediated primarily through estradiol binding to intracellular estrogen receptor alpha. In this study, we found that signaling through the putative membrane estrogen receptor, G protein-coupled receptor 30 (GPR30), was sufficient to mediate protection against EAE, which was significantly impaired in GPR30 gene-deficient mice. Treatment with G-1, an agonist that selectively activates GPR30 without engagement of the intracellular estrogen receptors, retained the ability of estradiol to protect against clinical and histological EAE without estradiol-associated side effects, deviated cytokine profiles, and enhanced suppressive activity of CD4(+)Foxp3(+) T regulatory cells through a GPR30- and programmed death 1-dependent mechanism. This study is the first to evaluate the protective effect of GPR30 activation on EAE, and provides a strong foundation for the clinical application of GPR30 agonists such as G-1 in multiple sclerosis.

Healthy but not RSV-infected lung epithelial cells profoundly inhibit T cell activation

BACKGROUND

Respiratory viruses, including respiratory syncytial virus (RSV), can cause asthma exacerbations and bronchiolitis. Both conditions are associated with enhanced cognate immune responses and inflammation and reduced immune regulation. Lung epithelial cells (LECs) can contribute to antiviral and allergic immune responses while gut epithelial cells can inhibit effector T cell responses. A study was performed to determine whether healthy LECs regulate antigen-specific T cell responses and if this regulation is lost during RSV infection.

METHODS

LA4 cells, a murine LEC line, infected with RSV or primary murine LECs were co-cultured with ovalbumin-specific T cell receptor transgenic CD4+ T cells from DO11.10 mice and ovalbumin-pulsed bone marrow-derived dendritic cells (DC) to assess T cell proliferation by flow cytometry and cytokine production.

RESULTS

The presence of LECs abrogated DC-induced T cell proliferation and significantly reduced T cell cytokine release. These effects of LECs were predominantly contact-dependent, primarily affected T cells directly and were partly mediated by transforming growth factor beta. Soluble factors and DC-mediated effects also contributed to T cell inhibition. RSV infection of LECs reduced their inhibitory capacity in an infection dose-dependent manner. This was independent of proinflammatory cytokines released by infected LECs, but in part due to Toll-like receptor activation and to infection-induced cell death.

CONCLUSION

Healthy LECs are potent inhibitors of T cell activation, but this regulatory function is lost after RSV infection. These findings suggest a central role for LECs in maintaining the tolerogenic environment of healthy lungs. Loss of this regulatory capacity after viral infection may allow development of excessive cognate immune responses and pulmonary inflammation.

High Numbers of Tumor-Infiltrating Programmed Cell Death 1–Positive Regulatory Lymphocytes Are Associated With Improved Overall Survival in Follicular Lymphoma

Purpose

Tumor microenvironment influences the behavior of follicular lymphoma (FL), although the specific cell subsets involved are not well known. The aim of this study was to determine the impact of programmed cell death 1 (PD-1) –positive inhibitory immunoregulatory lymphoid cells in the clinicobiologic features and outcome of patients with FL.

Patients and Methods

We examined samples from 100 patients (53 men and 47 women; median age, 54 years) at diagnosis, as well as in 32 patients at first relapse, with a recently generated monoclonal antibody against PD-1. The cells were quantified using computerized image analysis. Additional analysis consisted of double immunofluorescence and flow cytometry.

Results

PD-1 expression was alternative to FOXP3 in lymphoid cells from both reactive tonsils and FL. At diagnosis, the median percentage of PD-1–positive cells was 14% (range, 0.1% to 74%). Patients with grade 3 FL, poor performance status, and high serum lactate dehydrogenase showed lower numbers of PD-1–positive cells. After a median follow-up of 6.2 years, patients with PD-1–positive cells ≤ 5% (n = 25), 6% to 33% (n = 50), and more than 33% (n = 25) had a 5-year progression-free survival rate of 20%, 46%, and 48% (P = .038) and overall survival (OS) of 50%, 77%, and 95% (P = .004), respectively. PD-1 and FL International Prognostic Index maintained prognostic value for OS in multivariate analysis. Patients with PD-1–positive cells ≤ 5% showed a higher risk of histologic transformation. At that time, transformed diffuse large B-cell lymphomas had lower percentage of PD-1–positive cells than FL.

Conclusion

A high content of PD-1–positive cells predicted favorable outcome of FL patients, whereas a marked reduction is observed in transformation.

Memory T cells need CD28 costimulation to remember

The activation and expansion of naïve T cells require costimulatory signals provided by CD28 and TNF family members. In contrast, for many years it was believed that memory T cells do not require CD28 costimulation for expansion during secondary responses. This was based on in vitro experiments that suggested the re-activation of memory T cells is somewhat independent of costimulation. Recent in vivo evidence, however, has challenged this and shown that both CD4+ and CD8+ memory T cells require CD28 costimulation for maximal expansion and pathogen clearance. This requirement has important implications for host immunity, vaccine development and immunotherapeutics.

Effect of mucosal fluid from women with bacterial vaginosis on HIV trans-infection mediated by dendritic cells

Women with bacterial vaginosis (BV) have a higher risk of HIV transmission but the cause of risk is unknown. Dendritic cells (DC) are implicated in transmission of HIV and we previously observed that DC mature when exposed to mucosal fluid from women with BV. We hypothesized that maturation of DC by BV mucosal fluid would enhance DC-mediated trans-infection of HIV. Monocyte-derived DC (MDDC) were treated with mucosal fluid, incubated with HIV(Bal), and HIV trans-infection was evaluated. While LPS-treated MDDC increased HIV(Bal)trans-infection, BV fluid reduced trans-infection. HIV(Bal) DNA levels in MDDC were not affected by BV fluid or LPS but productive infection of MDDC was decreased by LPS and BV fluid. Mucosal fluid from women with BV does not increase MDDC-mediated trans-infection suggesting that BV does not increase HIV susceptibility by increasing DC-mediated trans-infection. However, indirect effects of DC maturation on HIV transmission cannot be ruled out.

PD-L1 negatively regulates CD4+CD25+Foxp3+ Tregs by limiting STAT-5 phosphorylation in patients chronically infected with HCV

CD4+CD25+Foxp3+ Tregs suppress autoimmune responses. In addition, they limit T cell responses during chronic infection, thereby minimizing T cell-dependent immunopathology. We sought to investigate how Tregs are regulated in the livers of patients chronically infected with HCV, where they control the balance between an adequate protective immune response and suppression of immunopathology. We found that, despite accumulating and proliferating at sites of infection in the livers of patients chronically infected with HCV, Tregs were relatively less expanded than CD4+CD25+Foxp3- effector T cells. The relative lower expansion of intrahepatic Tregs coincided with their upregulation of programmed death-1 (PD-1). PD-1 expression inversely correlated with both Treg proliferation and clinical markers of immune suppression in vivo. Consistent with the possibility that PD-1 controls Tregs, blockade of the interaction between PD-1 and programmed death-1 ligand 1 (PD-L1) enhanced the in vitro expansion and function of Tregs isolated from the livers of patients chronically infected with HCV. Blockade of the interaction between PD-L1 and B7.1 also improved the proliferation of these cells. Interestingly, both PD-1 and phosphorylated STAT-5 were overexpressed in intrahepatic Tregs in a parallel fashion in steady disease conditions, and in an alternate-fluctuating fashion during the course of severe hepatitis reactivation. Notably, PD-L1 blockade upregulated STAT-5 phosphorylation in Tregs ex vivo. These data suggest that PD-L1 negatively regulates Tregs at sites of chronic inflammation by controlling STAT-5 phosphorylation.