PDF file - 133KB, Immunofluorescence staining (IF) of CD11b+ myeloid cells on spleen and tumor samples (S1). CTX+CD4 AT therapy induces an inflammatory immune milieu (S2). Chemoimmunotherapy leads to myeloid cell expansion in mice with lung metastasis of CT26HA colon cancer (S3). Therapy-induced monocytes can suppress CD4+ T cell activation in response to either antigen-specific or nonspecific stimulation (S4). Dose effect of CTX on myeloid cell induction (S5). Monocytic myeloid suppressor cells can be induced by doxorubicin and melphalan (S6). Low dose gemcitabine following CTX+CD4 AT therapy confers long-term survival benefit to mice with lung metastasis of CT26HA colon cancer (S7). Low dose 5-fluorouracil (5-FU) reduces therapy-induced monocytes (S8).

Reagents that activate the signaling adaptor stimulator of interferon genes (STING) suppress experimentally induced autoimmunity in murine models of multiple sclerosis and arthritis. In this study, we evaluated STING agonists as potential reagents to inhibit spontaneous autoimmune type I diabetes (T1D) onset in non-obese diabetic (NOD) female mice. Treatments with DNA nanoparticles (DNPs), which activate STING when cargo DNA is sensed, delayed T1D onset and reduced T1D incidence when administered before T1D onset. DNP treatment elevated indoleamine 2,3 dioxygenase (IDO) activity, which regulates T-cell immunity, in spleen, pancreatic lymph nodes and pancreas of NOD mice. Therapeutic responses to DNPs were partially reversed by inhibiting IDO and DNP treatment synergized with insulin therapy to further delay T1D onset and reduce T1D incidence. Treating pre-diabetic NOD mice with cyclic guanyl-adenyl dinucleotide (cGAMP) to activate STING directly delayed T1D onset and stimulated interferon-αβ (IFN-αβ), while treatment with cyclic diguanyl nucleotide (cdiGMP) did not delay T1D onset or induce IFN-αβ in NOD mice. DNA sequence analyses revealed that NOD mice possess a STING polymorphism that may explain differential responses to cGAMP and cdiGMP. In summary, STING agonists attenuate T1D progression and DNPs enhance therapeutic responses to insulin therapy.

IDO2 is implicated in tryptophan catabolism and immunity but its physiological functions are not well established. Here we report the characterization of mice genetically deficient in IDO2, which develop normally but exhibit defects in IDO-mediated T-cell regulation and inflammatory responses. Construction of this strain was prompted in part by our discovery that IDO2 function is attenuated in macrophages from Ido1 (-/-) mice due to altered message splicing, generating a functional mosaic with implications for interpreting findings in Ido1 (-/-) mice. No apparent defects were observed in Ido2 (-/-) mice in embryonic development or hematopoietic differentiation, with wild-type profiles documented for kynurenine in blood serum and for immune cells in spleen, lymph nodes, peritoneum, thymus and bone marrow of naive mice. In contrast, upon immune stimulation we determined that IDO1-dependent T regulatory cell generation was defective in Ido2 (-/-) mice, supporting Ido1-Ido2 genetic interaction and establishing a functional role for Ido2 in immune modulation. Pathophysiologically, both Ido1 (-/-) and Ido2 (-/-) mice displayed reduced skin contact hypersensitivity responses, but mechanistic distinctions were apparent, with only Ido2 deficiency associated with a suppression of immune regulatory cytokines that included GM-CSF, G-CSF, IFN-γ, TNF-α, IL-6 and MCP-1/CCL2. Different contributions to inflammation were likewise indicated by the finding that Ido2 (-/-) mice did not phenocopy Ido1 (-/-) mice in the reduced susceptibility of the latter to inflammatory skin cancer. Taken together, our results offer an initial glimpse into immune modulation by IDO2, revealing its genetic interaction with IDO1 and distinguishing its non-redundant contributions to inflammation.

AbstractIn recent years, immune-based therapies have become an increasingly attractive treatment option for patients with cancer. Cancer immunotherapy is often used in combination with conventional chemotherapy for synergistic effects. The alkylating agent cyclophosphamide (CTX) has been included in various chemoimmunotherapy regimens because of its well-known immunostimulatory effects. Paradoxically, cyclophosphamide can also induce suppressor cells that inhibit immune responses. However, the identity and biologic relevance of these suppressor cells are poorly defined. Here we report that cyclophosphamide treatment drives the expansion of inflammatory monocytic myeloid cells (CD11b+Ly6ChiCCR2hi) that possess immunosuppressive activities. In mice with advanced lymphoma, adoptive transfer (AT) of tumor-specific CD4+ T cells following cyclophosphamide treatment (CTX+CD4 AT) provoked a robust initial antitumor immune response, but also resulted in enhanced expansion of monocytic myeloid cells. These therapy-induced monocytes inhibited long-term tumor control and allowed subsequent relapse by mediating functional tolerization of antitumor CD4+ effector cells through the PD-1–PD-L1 axis. PD-1/PD-L1 blockade after CTX+CD4 AT therapy led to persistence of CD4+ effector cells and durable antitumor effects. Depleting proliferative monocytes by administering low-dose gemcitabine effectively prevented tumor recurrence after CTX+CD4 AT therapy. Similarly, targeting inflammatory monocytes by disrupting the CCR2 signaling pathway markedly potentiated the efficacy of cyclophosphamide-based therapy. Besides cyclophosphamide, we found that melphalan and doxorubicin can also induce monocytic myeloid suppressor cells. These findings reveal a counter-regulation mechanism elicited by certain chemotherapeutic agents and highlight the importance of overcoming this barrier to prevent late tumor relapse after chemoimmunotherapy. Cancer Res; 74(13); 3441–53. ©2014 AACR.

Cytosolic DNA sensing activates the stimulator of IFN genes (STING) adaptor to induce IFN type I (IFN-αβ) production. Constitutive DNA sensing to induce sustained STING activation incites tolerance breakdown, leading to autoimmunity. In this study, we show that systemic treatments with DNA nanoparticles (DNPs) induced potent immune regulatory responses via STING signaling that suppressed experimental autoimmune encephalitis (EAE) when administered to mice after immunization with myelin oligodendrocyte glycoprotein (MOG), at EAE onset, or at peak disease severity. DNP treatments attenuated infiltration of effector T cells into the CNS and suppressed innate and adaptive immune responses to myelin oligodendrocyte glycoprotein immunization in spleen. Therapeutic responses were not observed in mice treated with cargo DNA or cationic polymers alone, indicating that DNP uptake and cargo DNA sensing by cells with regulatory functions was essential for therapeutic responses to manifest. Intact STING and IFN-αβ receptor genes, but not IFN-γ receptor genes, were essential for therapeutic responses to DNPs to manifest. Treatments with cyclic diguanylate monophosphate to activate STING also delayed EAE onset and reduced disease severity. Therapeutic responses to DNPs were critically dependent on IDO enzyme activity in hematopoietic cells. Thus, DNPs and cyclic diguanylate monophosphate attenuate EAE by inducing dominant T cell regulatory responses via the STING/IFN-αβ/IDO pathway that suppress CNS-specific autoimmunity. These findings reveal dichotomous roles for the STING/IFN-αβ pathway in either stimulating or suppressing autoimmunity and identify STING-activating reagents as a novel class of immune modulatory drugs.

Activation of Stimulator of Interferon genes (STING) adaptor causes the release of IFN αβ in most of the cells, an activity that is tightly controlled to avoid continuous immune activation that could lead to autoimmunity. Here we show that STING activators can be used systemically to suppress experimental autoimmune encephalitis following myelin oligodendrocyte (MOG) immunization through STING-IFN αβ pathway. DNA nanoparticles (DNPs) attenuated MOG-specific effector responses in CNS and spleen. Therapeutic responses to DNPs are dependent on STING adaptor and IFN αβ receptors as they were abolished in mice lacking those genes. Additionally, indoleamine 2,3 dioxygenase enzyme (IDO) is crucial for therapeutic responses to DNPs as the loss of IDO1 gene in hematopoietic cells and IDO inhibition by 1-methyl-D-tryptophan had ablated those responses. Cyclic diguanylate monophosphate (c-diGMP), a direct STING activator also attenuated EAE progression and disease severity. Thus, Systemic administration of DNPs and c-diGMP can attenuate EAE through STING-IFN αβ-IDO regulatory pathway that is activated in certain immune cells subsets to overcome CNS specific autoimmunity. These findings emphasize a previously unappreciated role of STING activators to attenuate autoimmunity.

Tolerance to apoptotic cells is essential to prevent inflammatory pathology. Though innate responses are critical for immune suppression, our understanding of early innate immunity driven by apoptosis is lacking. Herein we report apoptotic cells induce expression of the chemokine CCL22 in splenic metallophillic macrophages, which is critical for tolerance. Systemic challenge with apoptotic cells induced rapid production of CCL22 in CD169(+) (metallophillic) macrophages, resulting in accumulation and activation of FoxP3(+) Tregs and CD11c(+) dendritic cells, an effect that could be inhibited by antagonizing CCL22-driven chemotaxis. This mechanism was essential for suppression after apoptotic cell challenge, because neutralizing CCL22 or its receptor, reducing Treg numbers, or blocking effector mechanisms abrogated splenic TGF-β and IL-10 induction; this promoted a shift to proinflammatory cytokines associated with a failure to suppress T cells. Similarly, CCR4 inhibition blocked long-term, apoptotic cell-induced tolerance to allografts. Finally, CCR4 inhibition resulted in a systemic breakdown of tolerance to self after apoptotic cell injection with rapid increases in anti-dsDNA IgG and immune complex deposition. Thus, the data demonstrate CCL22-dependent chemotaxis is a key early innate response required for apoptotic cell-induced suppression, implicating a previously unknown mechanism of macrophage-dependent coordination of early events leading to stable tolerance.

ObjectiveDiabetic retinopathy, a major cause of blindness, is characterized by increased expression of vascular endothelial growth factor (VEGF), leukocyte attachment to the vessel walls and increased vascular permeability. Previous work has shown that reactive oxygen species (ROS) produced by the superoxide generating enzyme NOX2/NADPH oxidase play a crucial role in the vascular pathology. The aim of this work was to identify the cellular sources of the damaging NOX2 activity by studies using bone marrow chimera mice. MethodsBone marrow cells were collected from the femurs and tibias of wild type and NOX2 deficient (NOX2-/-) donor mice and injected intravenously into lethally irradiated NOX2-/- and wild type recipients. Following recovery from radiation, mice were rendered diabetic by streptozotocin injections. The following groups of bone marrow chimeras were studied: non-diabetic WT→WT, diabetic WT→WT, diabetic WT→NOX2-/-, diabetic NOX2-/-→WT. After 4 weeks of diabetes, early signs of retinopathy were examined by measuring ROS, expression of VEGF and ICAM-1, leukocyte attachment to the vessel wall and vascular permeability. ResultsThe retinas of the diabetic WT→WT chimeras showed significant increases in ROS as compared with the non-diabetic chimeras. These diabetes-induced alterations were correlated with increases in expression of VEGF and ICAM-1, leukocyte adhesion and vascular permeability. Each of these diabetes-induced alterations were significantly attenuated in the diabetic WT→NOX2-/- and NOX2-/-→WT chimera groups (p<0.05). ConclusionNOX2-generated ROS produced by both bone marrow-derived cells and resident retinal cells contribute importantly to retinal vascular injury in the diabetic retina. Targeting NOX2 in bone marrow and/or retinal cells may represent a novel therapeutic strategy for the treatment/prevention of vascular injury in the diabetic retina.

Abstract Cytoplasmic DNA sensing triggers anti-microbial immunity by inducing interferon type I (IFNαβ) via STING-TBK1 activation but sustained STING activation incites autoimmunity. Systemic DNA nanoparticle (DNP) treatment triggered rapid and potent tolerogenic responses in mice via selective activation of the STING-IFNαβ pathway in myeloid dendritic cells (DCs) to induce indoleamine 2, 3 dioxygenase (IDO) activity. DNPs associated rapidly with splenic marginal zone (MZ) macrophages (MΦs) and some DCs, and IFNαβ and IL-1β were induced soon after DNP injection. IFNβ1 was primarily induced in myeloid (CD11b+) DCs and this response was STING dependent, while IL-1β was induced primarily in granulocytes and was STING independent. IFNαβ-mediated IDO induction caused DCs and regulatory T cells (Tregs) to acquire potent tolerogenic phenotypes. Physiologic depletion of (CD11c+) DCs and STING ablation abolished IDO induction and tolerogenic responses to DNPs, but MZ (CD169+) MΦ depletion did not. Moreover, systemic treatment with the cyclic dinucleotide (c-diGMP) to activate STING directly induced IDO and suppressed antigen-specific Th1 responses. Thus myeloid DCs sense circulating cargo DNA and c-diGMP to induce selective IFNαβ release that promotes dominant tolerogenic responses via IDO. Targeting this distinctive tolerogenic pathway may be an effective strategy to suppress hyper-immune syndromes, including autoimmune diseases incited by excessive IFNαβ release.

Cytosolic DNA sensing via the stimulator of IFN genes (STING) adaptor incites autoimmunity by inducing type I IFN (IFN-αβ). In this study, we show that DNA is also sensed via STING to suppress immunity by inducing IDO. STING gene ablation abolished IFN-αβ and IDO induction by dendritic cells (DCs) after DNA nanoparticle (DNP) treatment. Marginal zone macrophages, some DCs, and myeloid cells ingested DNPs, but CD11b(+) DCs were the only cells to express IFN-β, whereas CD11b(+) non-DCs were major IL-1β producers. STING ablation also abolished DNP-induced regulatory responses by DCs and regulatory T cells, and hallmark regulatory responses to apoptotic cells were also abrogated. Moreover, systemic cyclic diguanylate monophosphate treatment to activate STING induced selective IFN-β expression by CD11b(+) DCs and suppressed Th1 responses to immunization. Thus, previously unrecognized functional diversity among physiologic innate immune cells regarding DNA sensing via STING is pivotal in driving immune responses to DNA.

Tolerance to self-antigens present in apoptotic cells is critical to maintain immune-homeostasis and prevent systemic autoimmunity. However, mechanisms that sustain self-tolerance are poorly understood. Here we show that systemic administration of apoptotic cells to mice induced splenic expression of the tryptophan catabolizing enzyme indoleamine 2,3-dioxygenase (IDO). IDO expression was confined to the splenic marginal zone and was abrogated by depletion of CD169+ cells. Pharmacologic inhibition of IDO skewed the immune response to apoptotic cells, resulting in increased proinflammatory cytokine production and increased effector T-cell responses toward apoptotic cell-associated antigens. Presymptomatic lupus-prone MRLlpr/lpr mice exhibited abnormal elevated IDO expression in the marginal zone and red pulp and inhibition of IDO markedly accelerated disease progression. Moreover, chronic exposure of IDO-deficient mice to apoptotic cells induced a lupus-like disease with serum autoreactivity to double-stranded DNA associated with renal pathology and increased mortality. Thus, IDO limits innate and adaptive immunity to apoptotic self-antigens and IDO-mediated regulation inhibits inflammatory pathology caused by systemic autoimmune disease.

Nanoparticles containing DNA complexed with the cationic polymer polyethylenimine are efficient vehicles to transduce DNA into cells and organisms. DNA/polyethylenimine nanoparticles (DNPs) also elicit rapid and systemic release of proinflammatory cytokines that promote antitumor immunity. In this study, we report that DNPs possess previously unrecognized immunomodulatory attributes due to rapid upregulation of IDO enzyme activity in lymphoid tissues of mice. IDO induction in response to DNP treatment caused dendritic cells and regulatory T cells (Tregs) to acquire potent regulatory phenotypes. As expected, DNP treatment stimulated rapid increase in serum levels of IFN type I (IFN-αβ) and II (IFN-γ), which are both potent IDO inducers. IDO-mediated Treg activation was dependent on IFN type I receptor signaling, whereas IFN-γ receptor signaling was not essential for this response. Moreover, systemic IFN-γ release was caused by TLR9-dependent activation of NK cells, whereas TLR9 signaling was not required for IFN-αβ release. Accordingly, DNPs lacking immunostimulatory TLR9 ligands in DNA stimulated IFN-αβ production, induced IDO, and promoted regulatory outcomes, but did not stimulate potentially toxic, systemic release of IFN-γ. DNP treatment to induce IDO and activate Tregs blocked Ag-specific T cell responses elicited in vivo following immunization and suppressed joint pathology in a model of immune-mediated arthritis. Thus, DNPs lacking TLR9 ligands may be safe and effective reagents to protect healthy tissues from immune-mediated destruction in clinical hyperimmune syndromes.

Marginal zone macrophages (MZMs) play a crucial role in generation of systemic tolerance to apoptotic cell (AC)-associated antigens. However, the mechanism(s) by which MZMs drive tolerogenic responses is not understood. In this report, we show that systemic administration of ACs induces splenic expression of the immunosuppressive enzyme indoleamine 2-3 dioxygenase (IDO) in Marco+SignR1+ MZMs. Moreover, we found abrogation of IDO activity altered immunity to ACs resulting in decreased TGF-β synthesis and increased pro-inflammatory cytokine production associated with a reduction in Treg function and a loss of T cell tolerance towards AC antigens. When pre-symptomatic, lupus-prone MRLlpr/lpr mice were examined we found significant IDO expression in the splenic MZ analogous to the observations in AC challenged mice. When IDO was inhibited, autoimmunity was rapidly accelerated in MRLlpr/lpr mice with a >10-fold increase in anti-dsDNA IgG titers and increased renal pathology. Finally, IDO-/- mice, which do not show signs of autoimmunity, were challenged chronically with ACs. The mice developed high titer serum IgG autoreactivity, kidney inflammation, and increased mortality compared to B6 mice, which did not develop autoimmunity. Thus, the data demonstrate that a novel IDO-dependent regulatory circuit is induced in MZMs upon apoptotic cell phagocytosis providing clues to future therapeutic targets to re-establish tolerance in systemic autoimmune disease.

Dendritic cells (DCs) competent to express the regulatory enzyme IDO in mice are a small but distinctive subset of DCs. Previously, we reported that a high-dose systemic CpG treatment to ligate TLR9 in vivo induced functional IDO exclusively in splenic CD19+ DCs, which stimulated resting Foxp3-lineage regulatory T cells (Tregs) to rapidly acquire potent suppressor activity. In this paper, we show that IDO was induced in spleen and peripheral lymph nodes after CpG treatment in a dose-dependent manner. Induced IDO suppressed local T cell responses to exogenous Ags and inhibited proinflammatory cytokine expression in response to TLR9 ligation. IDO induction did not occur in T cell-deficient mice or in mice with defective B7 or programmed death (PD)-1 costimulatory pathways. Consistent with these findings, CTLA4 or PD-1/PD-ligand costimulatory blockade abrogated IDO induction and prevented Treg activation via IDO following high-dose CpG treatment. Consequently, CD4+CD25+ T cells uniformly expressed IL-17 shortly after TLR9 ligation. These data support the hypothesis that constitutive interactions from activated T cells or Tregs and IDO-competent DCs via concomitant CTLA4→B7 and PD-1→PD-ligand signals maintain the default potential to regulate T cell responsiveness via IDO. Acute disruption of these nonredundant interactions abrogated regulation via IDO, providing novel perspectives on the proinflammatory effects of costimulatory blockade therapies. Moreover, interactions between IDO-competent DCs and activated T cells in lymphoid tissues may attenuate proinflammatory responses to adjuvants such as TLR ligands.

Inflammation stimulates immunity but can create immune privilege in some settings. Here, we show that cutaneous Leishmania major infection stimulated expression of the immune regulatory enzyme indoleamine 2,3 dioxygenase (IDO) in local lymph nodes. Induced IDO attenuated the T cell stimulatory functions of dendritic cells and suppressed local T cell responses to exogenous and nominal parasite antigens. IDO ablation reduced local inflammation and parasite burdens, as did pharmacologic inhibition of IDO in mice with established infections. IDO ablation also enhanced local expression of proinflammatory cytokines and induced some CD4(+) T cells to express interleukin (IL) 17. These findings showed that IDO induced by L. major infection attenuated innate and adaptive immune responses. Thus, IDO acts as a molecular switch regulating host responses, and IDO inhibitor drugs are a potential new approach to enhance host immunity to established leishmania infections.

Foxp3(+) regulatory T (Treg) cells can undergo reprogramming into a phenotype expressing proinflammatory cytokines. However, the biologic significance of this conversion remains unclear. We show that large numbers of Treg cells undergo rapid reprogramming into activated T helper cells after vaccination with antigen plus Toll-like receptor 9 (TLR-9) ligand. Helper activity from converted Treg cells proved essential during initial priming of CD8(+) T cells to a new cross-presented antigen. Help from Treg cells was dependent on CD40L, and (unlike help from conventional non-Treg CD4(+) cells) did not require preactivation or prior exposure to antigen. In hosts with established tumors, Treg cell reprogramming was suppressed by tumor-induced indoleamine 2,3-dioxygenase (IDO) and vaccination failed because of lack of help. Treg cell reprogramming, vaccine efficacy, and antitumor CD8(+) T cell responses were restored by pharmacologic inhibition of IDO. Reprogrammed Treg cells can thus participate as previously unrecognized drivers of certain early CD8(+) T cell responses.

A discrete population of splenocytes with attributes of dendritic cells (DCs) and coexpressing the B-cell marker CD19 is uniquely competent to express the T-cell regulatory enzyme indoleamine 2,3-dioxygenase (IDO) in mice treated with TLR9 ligands (CpGs). Here we show that IDO-competent cells express the B-lineage commitment factor Pax5 and surface immunoglobulins. CD19 ablation abrogated IDO-dependent T-cell suppression by DCs, even though cells with phenotypic attributes matching IDO-competent cells developed normally and expressed IDO in response to interferon γ. Consequently, DCs and regulatory T cells (Tregs) did not acquire T-cell regulatory functions after TLR9 ligation, providing an alternative perspective on the known T-cell regulatory defects of CD19-deficient mice. DCs from B-cell–deficient mice expressed IDO and mediated T-cell suppression after TLR9 ligation, indicating that B-cell attributes were not essential for B-lymphoid IDO-competent cells to regulate T cells. Thus, IDO-competent cells constitute a distinctive B-lymphoid cell type with quintessential T-cell regulatory attributes and phenotypic features of both B cells and DCs.

Background A common procedure in human cytotoxic T lymphocyte (CTL) adoptive transfer immunotherapy is to expand tumor-specific CTLs ex vivo using CD3 mAb prior to transfer. One of the major obstacles of CTL adoptive immunotherapy is a lack of CTL persistence in the tumor-bearing host after transfer. The aim of this study is to elucidate the molecular mechanisms underlying the effects of stimulation conditions on proliferation and survival of tumor-specific CTLs. Methodology/Principal Findings Tumor-specific CTLs were stimulated with either CD3 mAb or cognate Ag and analyzed for their proliferation and survival ex vivo and persistence in tumor-bearing mice. Although both Ag and CD3 mAb effectively induced the cytotoxic effecter molecules of the CTLs, we observed that Ag stimulation is essential for sustained CTL proliferation and survival. Further analysis revealed that Ag stimulation leads to greater proliferation rates and less apoptosis than CD3 mAb stimulation. Re-stimulation of the CD3 mAb-stimulated CTLs with Ag resulted in restored CTL proliferative potential, suggesting that CD3 mAb-induced loss of proliferative potential is reversible. Using DNA microarray technology, we identified that survivin and ifi202, two genes with known functions in T cell apoptosis and proliferation, are differentially induced between Ag- and CD3 mAb-stimulated CTLs. Analysis of the IFN-γ signaling pathway activation revealed that Ag stimulation resulted in rapid phosphorylation of STAT1 (pSTAT1), whereas CD3 mAb stimulation failed to activate STAT1. Chromatin immunoprecipitation revealed that pSTAT1 is associated with the promoters of both survivin and ifi202 in T cells and electrophoresis mobility shift assay indicated that pSTAT1 directly binds to the gamma activation sequence element in the survivin and ifi202 promoters. Finally, silencing ifi202 expression significantly decreased T cell proliferation. Conclusions/Significance Our findings delineate a new role of the IFN-γ signaling pathway in regulating T cell proliferation and apoptosis through upregulating survivin and ifi202 expression.