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1.  PD-L1 co-stimulation contributes to ligand-induced T cell receptor down-modulation on CD8 T cells 
EMBO molecular medicine  2011;3(10):581-592.
T cell receptor (TCR) down-modulation after antigen presentation is a fundamental process that regulates TCR signal transduction. Current understanding of this process is that intrinsic TCR/CD28 signal transduction leads to TCR down-modulation. Here we show that the interaction between PD-L1 in dendritic cells (DCs) and PD-1 on CD8 T cells contributes to ligand-induced TCR down-modulation. We provide evidence that this occurs via Casitas B-lymphoma (Cbl)-b E3 ubiquitin ligase up-regulation in CD8 T cells. Interference with PD-L1/PD-1 signalling markedly inhibits TCR down-modulation leading to hyper-activated, proliferative CD8 T cells as assessed in vitro and in vivo in an arthritis model. PD-L1 silencing accelerates anti-tumour immune responses and strongly potentiates DC anti-tumour capacities, when combined with MAPK modulators that promote DC activation.
doi:10.1002/emmm.201100165
PMCID: PMC3191120  PMID: 21739608
Dendritic; Down-modulation; Cbl; PD-L1; TCR
2.  Langerhans cells are negative regulators of the anti-Leishmania response 
Langerhans cells suppress the immune response to low-dose Leishmania major infection in part by inducing regulatory T cells.
Migratory skin dendritic cells (DCs) are thought to play an important role in priming T cell immune responses against Leishmania major, but DC subtypes responsible for the induction of protective immunity against this pathogen are still controversial. In this study, we analyzed the role of Langerin+ skin-derived DCs in the Leishmania model using inducible in vivo cell ablation. After physiologically relevant low-dose infection with L. major (1,000 parasites), mice depleted of all Langerin+ DCs developed significantly smaller ear lesions with decreased parasite loads and a reduced number of CD4+ Foxp3+ regulatory T cells (T reg cells) as compared with controls. This was accompanied by increased interferon γ production in lymph nodes in the absence of Langerin+ DCs. Moreover, selective depletion of Langerhans cells (LCs) demonstrated that the absence of LCs, and not Langerin+ dermal DC, was responsible for the reduced T reg cell immigration and the enhanced Th1 response, resulting in attenuated disease. Our data reveal a unique and novel suppressive role for epidermal LCs in L. major infection by driving the expansion of T reg cells. A better understanding of the various roles of different DC subsets in cutaneous leishmaniasis will improve the development of a potent therapeutic/prophylactic vaccine.
doi:10.1084/jem.20102318
PMCID: PMC3092359  PMID: 21536741
3.  Conventional Dendritic Cells Are Required for the Activation of Helper-Dependent CD8 T Cell Responses to a Model Antigen After Cutaneous Vaccination with Lentiviral Vectors 
Cutaneous vaccination with lentiviral vectors generates systemic CD8 T cell responses that have the potential to eradicate tumors for cancer immunotherapy. However, although s.c. immunization with <1 million lentiviral particles clearly primes cytotoxic T cells, vaccination with much higher doses has routinely been used to define the mechanisms of T cell activation by lentiviral vectors. In particular, experiments to test presentation of lentiviral Ags by dendritic cells (DC) require injection of high viral titers, which may result in aberrant transduction of different DC populations. We exploited inducible murine models of DC depletion to investigate which DC prime the lentiviral response after s.c. immunization with low doses of lentiviral particles. In this article, we demonstrate that conventional DC are required to present Ag to CD8 T cells in draining lymph nodes. Langerhans cells are not required to activate the effector response, and neither Langerhans cells nor plasmacytoid DC are sufficient to prime Ag-specific T cells. Immunization drives the generation of endogenous long-lived memory T cells that can be reactivated to kill Ag-specific targets in the absence of inflammatory challenge. Furthermore, lentiviral vaccination activates expansion of endogenous CD4 Th cells, which are required for the generation of effector CD8 T cells that produce IFN-γ and kill Ag-specific targets. Collectively, we demonstrate that after cutaneous immunization with lentiviral particles, CD4-licensed lymph node conventional DC present Ag to CD8 T cells, resulting in the generation of protective endogenous antitumor immunity that may be effective for cancer immunotherapy.
doi:10.4049/jimmunol.1002529
PMCID: PMC3071788  PMID: 21389256
4.  PD-L1 co-stimulation contributes to ligand-induced T cell receptor down-modulation on CD8+ T cells 
EMBO Molecular Medicine  2011;3(10):581-592.
T cell receptor (TCR) down-modulation after antigen presentation is a fundamental process that regulates TCR signal transduction. Current understanding of this process is that intrinsic TCR/CD28 signal transduction leads to TCR down-modulation. Here, we show that the interaction between programmed cell death 1 ligand 1 (PD-L1) on dendritic cells (DCs) and programmed death 1 (PD-1) on CD8 T cells contributes to ligand-induced TCR down-modulation. We provide evidence that this occurs via Casitas B-lymphoma (Cbl)-b E3 ubiquitin ligase up-regulation in CD8 T cells. Interference with PD-L1/PD-1 signalling markedly inhibits TCR down-modulation leading to hyper-activated, proliferative CD8 T cells as assessed in vitro and in vivo in an arthritis model. PD-L1 silencing accelerates anti-tumour immune responses and strongly potentiates DC anti-tumour capacities, when combined with mitogen-activated kinase (MAPK) modulators that promote DC activation.
doi:10.1002/emmm.201100165
PMCID: PMC3191120  PMID: 21739608
Cbl; dendritic cells; PD-1; PD-L1; TCR
5.  Keratinocytes function as accessory cells for presentation of endogenous antigen expressed in the epidermis 
The precise contribution(s) of skin dendritic cells (DCs) to immune responses in the skin has not been well delineated. We developed an intradermal (i.d.) injection model in which CD8+ T (OT-I) cells that express ovalbumin (OVA)-peptide-specific T-cell receptors (Vα2/Vβ5) are delivered directly to the dermis of transgenic (Tg) mice expressing OVA in the epidermis. Following i.d. injection, these mice reliably develop skin GvHD by day 7. To determine the relative contribution of LCs to the ensuing graft-versus-host (GvHD) - like reaction, we generated K14-OVA × Langerin-Diphtheria-Toxin-Receptor (Langerin-DTR) Tg mice to allow conditional ablation of LCs in the epidermis. To delineate the role of dermal dendritic cells (dDCs) in the reaction we also generated K14-OVA Tg chimeras using beta-2-microglobulin-deficient (b2m) congenic donor bone marrow cells. Dermal DCs in these mice cannot present OVA to OT-I cells while the LC are antigen presentation competent. Unexpectedly, OT-I cell injection into diphtheria toxin (DT)-treated b2m→K14−OVA × Langerin-DTR Tg mice resulted in skin GvHD. Thus, in vivo, both LC and dDC appear to be dispensable for induction of keratinocyte-directed, CD8-mediated effector immune responses. Furthermore and surprisingly, OVA-expressing epidermal cells depleted of LCs that could not initiate allogeneic epidermal lymphocyte reactions, activated naïve OT-I cells in vitro. These results indicate that keratinocytes may function as accessory cells-competent to prime naïve skin-reactive T cells.
doi:10.1038/jid.2009.176
PMCID: PMC2784095  PMID: 19554018
Langerhans cells; Dendritic cells; GvHD; Langerin KO mice
6.  Nonhematopoietic antigen blocks memory programming of alloreactive CD8+ T cells and drives their eventual exhaustion in mouse models of bone marrow transplantation  
The Journal of Clinical Investigation  2010;120(11):3855-3868.
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.
doi:10.1172/JCI41446
PMCID: PMC2964967  PMID: 20978352
7.  Clearance of influenza virus from the lung depends on migratory langerin+CD11b− but not plasmacytoid dendritic cells 
The Journal of Experimental Medicine  2008;205(7):1621-1634.
Although dendritic cells (DCs) play an important role in mediating protection against influenza virus, the precise role of lung DC subsets, such as CD11b− and CD11b+ conventional DCs or plasmacytoid DCs (pDCs), in different lung compartments is currently unknown. Early after intranasal infection, tracheal CD11b−CD11chi DCs migrated to the mediastinal lymph nodes (MLNs), acquiring co-stimulatory molecules in the process. This emigration from the lung was followed by an accumulation of CD11b+CD11chi DCs in the trachea and lung interstitium. In the MLNs, the CD11b+ DCs contained abundant viral nucleoprotein (NP), but these cells failed to present antigen to CD4 or CD8 T cells, whereas resident CD11b−CD8α+ DCs presented to CD8 cells, and migratory CD11b−CD8α− DCs presented to CD4 and CD8 T cells. When lung CD11chi DCs and macrophages or langerin+CD11b−CD11chi DCs were depleted using either CD11c–diphtheria toxin receptor (DTR) or langerin-DTR mice, the development of virus-specific CD8+ T cells was severely delayed, which correlated with increased clinical severity and a delayed viral clearance. 120G8+ CD11cint pDCs also accumulated in the lung and LNs carrying viral NP, but in their absence, there was no effect on viral clearance or clinical severity. Rather, in pDC-depleted mice, there was a reduction in antiviral antibody production after lung clearance of the virus. This suggests that multiple DCs are endowed with different tasks in mediating protection against influenza virus.
doi:10.1084/jem.20071365
PMCID: PMC2442640  PMID: 18591406
8.  Inducible ablation of mouse Langerhans cells diminishes but fails to abrogate contact hypersensitivity 
The Journal of Cell Biology  2005;169(4):569-576.
Langerhans cells (LC) form a unique subset of dendritic cells (DC) in the epidermis but so far their in vivo functions in skin immunity and tolerance could not be determined, in particular in relation to dermal DC (dDC). Here, we exploit a novel diphtheria toxin (DT) receptor (DTR)/DT-based system to achieve inducible ablation of LC without affecting the skin environment. Within 24 h after intra-peritoneal injection of DT into Langerin-DTR mice LC are completely depleted from the epidermis and only begin to return 4 wk later. LC deletion occurs by apoptosis in the absence of inflammation and, in particular, the dDC compartment is not affected. In LC-depleted mice contact hypersensitivity (CHS) responses are significantly decreased, although ear swelling still occurs indicating that dDC can mediate CHS when necessary. Our results establish Langerin-DTR mice as a unique tool to study LC function in the steady state and to explore their relative importance compared with dDC in orchestrating skin immunity and tolerance.
doi:10.1083/jcb.200501071
PMCID: PMC2171694  PMID: 15897263
9.  Heterologous expression of the filarial nematode alt gene products reveals their potential to inhibit immune function 
BMC Biology  2005;3:8.
Background
Parasites exploit sophisticated strategies to evade host immunity that require both adaptation of existing genes and evolution of new gene families. We have addressed this question by testing the immunological function of novel genes from helminth parasites, in which conventional transgenesis is not yet possible. We investigated two such novel genes from Brugia malayi termed abundant larval transcript (alt), expression of which reaches ~5% of total transcript at the time parasites enter the human host.
Results
To test the hypothesis that ALT proteins modulate host immunity, we adopted an alternative transfection strategy to express these products in the protozoan parasite Leishmania mexicana. We then followed the course of infection in vitro in macrophages and in vivo in mice. Expression of ALT proteins, but not a truncated mutant, conferred greater infectivity of macrophages in vitro, reaching 3-fold higher parasite densities. alt-transfected parasites also caused accelerated disease in vivo, and fewer mice were able to clear infection of organisms expressing ALT. alt-transfected parasites were more resistant to IFN-γ-induced killing by macrophages. Expression profiling of macrophages infected with transgenic L. mexicana revealed consistently higher levels of GATA-3 and SOCS-1 transcripts, both associated with the Th2-type response observed in in vivo filarial infection.
Conclusion
Leishmania transfection is a tractable and informative approach to determining immunological functions of single genes from heterologous organisms. In the case of the filarial ALT proteins, our data suggest that they may participate in the Th2 bias observed in the response to parasite infection by modulating cytokine-induced signalling within immune system cells.
doi:10.1186/1741-7007-3-8
PMCID: PMC555940  PMID: 15788098
10.  Lipopolysaccharide or Whole Bacteria Block the Conversion of Inflammatory Monocytes into Dendritic Cells In Vivo 
The Journal of Experimental Medicine  2003;198(8):1253-1263.
Monocytes can develop into dendritic cells (DCs) that migrate to lymph nodes (LNs) and present antigens to T cells. However, we find that this differentiation is blocked when monocytes accumulate subcutaneously in response to bacteria or lipopolysaccharide (LPS). The inhibition of DC differentiation is mediated by the bacteria and in conjunction with inflammatory cells recruited at the site of injection. Inhibition of migratory DC development was reversed in Toll-like receptor (TLR)4-mutated mice when LPS, but not whole bacteria, was injected, suggesting that TLR4 is one but not the only mediator of the inhibition. The block imposed by bacteria was partly relieved by the absence of interleukin (IL)-12 p40, but not by individual absence of several cytokines involved in DC differentiation or in inflammation, i.e., IL-6, IL-10, IL-12 p35, and interferon γ. Consistent with the inability of monocytes to yield migrating DCs, and the finding that other DCs had limited access to particulate or bacterial antigens, these antigens were weakly presented to T cells in the draining LN. These results illustrate that bacteria-associated signals can have a negative regulatory role on adaptive immunity and that local innate responses for containment of infectious bacteria can at least initially supersede development of adaptive responses.
doi:10.1084/jem.20030335
PMCID: PMC2194237  PMID: 14568983
Salmonella typhimurium; migration; inflammation; innate immunity; adaptive immunity

Results 1-10 (10)