Indoleamine 2,3-dioxygenase Production Research Articles

Effect of apigenin on tryptophan metabolic key enzymes expression in lipopolysaccharide-induced microglial cells and its mechanism

[Aims] Flavonoid apigenin (API) has a wide range of biological functions, particularly anti-inflammation. Indoleamine 2,3-dioxygenase (IDO) and 2-Amino-3-carboxymuconate-6-semialdehyde decarboxylase (ACMSD) are important tryptophan metabolic enzymes that play pivotal roles in the production of toxic metabolite quinolinic acid. However, the relationship between inflammation and ACMSD remains unclear. The present study investigated the relationship between inflammation and tryptophan metabolic key enzymes. Similarly, the anti-inflammatory effect of API on important tryptophan metabolic enzymes was examined in lipopolysaccharide (LPS)-treated microglial cells.[Main methods] MG6 cells were exposed to LPS with or without API treatment for 24–48 h. IDO and ACMSD mRNA expression and production of inflammatory mediators were analyzed. Activation of inflammatory signaling pathways, such as mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB), was also examined to study the mechanism of API in the inflammatory state.[Key findings] LPS suppressed ACMSD expression and enhanced IDO expression. However, API elevated ACMSD mRNA expression and suppressed IDO mRNA expression in LPS-treated MG6 cells. Furthermore, API suppressed interleukin-6 and nitric oxide production, whereas overproduction of inflammatory mediators enhanced IDO expression and assisted tryptophan degradation. API also inhibited activation of extracellular signal-regulated kinase (Erk) and jun N-terminal kinase (JNK) MAPK, and degradation of IκBα.[Significance] These results indicate alteration of ACMSD expression under inflammatory conditions. Moreover, API recovers expression of tryptophan metabolic key enzymes, which may be mediated by inhibition of proinflammatory mediator production via inactivation of Erk, JNK MAPK, and NF-κB pathways in LPS-stimulated microglial cells.

Effectiveness of Soluble CTLA-4-Fc in the Inhibition of Bone Marrow T-Cell Activation in Context of Indoleamine 2.3-Dioxygenase (IDO) and CD4+Foxp3+ Treg Induction.

Rheumatoid arthritis (RA) is a chronic autoimmune disease with systemic inflammation finally resulting in damaged joints. One of the RA development models suggests bone marrow (BM) as a place of inflammation development further leading to disease progression. We aimed to investigate the potential of CTLA-4-Fc molecule in inducing tolerogenic milieu in BM measured as indoleamine 2,3-dioxygenase (IDO) expression, CD4+Foxp3+ Treg induction, and T cell activation control. The expression of IDO-pathway genes was also examined in monocytes to estimate the tolerogenic potential in the periphery. Bone marrow mononuclear cells (BMMC) were stimulated by pro-inflammatory cytokines and CTLA-4-Fc. Next IDO expression, CD4+CD69+ and CD4+Foxp3+ percentage were estimated by PCR and FACS staining, respectively. Enzymatic activity of IDO was confirmed by HPLC in BM plasma and blood plasma. Genes expressed in IDO-pathway were analyzed by NGS in peripheral monocytes isolated from RA patients and healthy controls. We found that CTLA-4-Fc and IFN-γ stimulation results in IDO production by BMMC. CTLA-4-Fc induced tryptophan catabolism can inhibit mitogen-induced CD4+ T cells activation without influencing CD8+ cells, but did not control CD25 nor Foxp3 expression in BM cells. Significantly higher expression of selected IDO-pathway genes was detected on peripheral monocytes isolated from RA as compared to healthy controls. This study sheds light on some immunosuppression aspects present or induced in BM. The potential of IDO-mediated pathways were confirmed in the periphery, what may represent the promising candidates for therapeutic strategies in RA.

B7-H4 reduction induced by Toxoplasma gondii infection results in dysfunction of decidual dendritic cells by regulating the JAK2/STAT3 pathway

BackgroundPrimary infection of Toxoplasma gondii can cause serious abnormal pregnancy outcomes such as miscarriage and stillbirth. Inhibitory molecule B7-H4 is abundantly expressed in dendritic cells (DCs) and plays an important role in maintaining immune tolerance. However, the role of B7-H4 in decidual DCs (dDCs) in T. gondii-induced abnormal pregnancy outcomes is not clear.MethodsWe established T. gondii-infected abnormal pregnancy model in wild-type (WT) and B7-H4 knockout (B7-H4−/−) pregnant mice in vivo and cultured primary human dDCs in vitro. The abnormal pregnancy outcomes were observed and the expression of B7-H4, functional molecules (CD80, CD86, and MHC-II or HLA-DR), indoleamine 2,3-dioxygenase (IDO), cytokines (IL-10 and IL-12), and signaling molecules JAK2/STAT3 in dDCs was detected by flow cytometry and Western blot.ResultsOur results showed that T. gondii infection significantly decreased B7-H4 expression in dDCs. In addition, B7-H4−/− infected pregnant mice showed much more severe abnormal pregnancy outcomes than their counterparts. Importantly, B7-H4−/− infection further regulated the expression of molecules (CD80, CD86, and MHC-II or HLA-DR), enzyme IDO, and cytokines (IL-10 and IL-12) in dDCs. We further discovered that B7-H4−/− infection impairs the JAK2/STAT3 pathway, contributing to dDC dysfunction.ConclusionsTaken together, the results show that reduction of B7-H4 by T. gondii infection significantly modulates the decrease in cytokine IL-10 and enzyme IDO and the increase in cytokine IL-12, contributing to dDC dysfunction. Moreover, the JAK2/STAT3 pathway is involved in the regulation of B7-H4 by T. gondii infection and in the subsequent IDO and cytokine production, which ultimately contributes to abnormal pregnancy outcomes.Graphical

AhR Ligands Modulate the Differentiation of Innate Lymphoid Cells and T Helper Cell Subsets That Control the Severity of a Pulmonary Fungal Infection.

In agreement with other fungal infections, immunoprotection in pulmonary paracoccidioidomycosis (PCM) is mediated by Th1/Th17 cells whereas disease progression by prevalent Th2/Th9 immunity. Treg cells play a dual role, suppressing immunity but also controlling excessive tissue inflammation. Our recent studies have demonstrated that the enzyme indoleamine 2,3 dioxygenase (IDO) and the transcription factor aryl hydrocarbon receptor (AhR) play an important role in the immunoregulation of PCM. To further evaluate the immunomodulatory activity of AhR in this fungal infection, Paracoccidioides brasiliensis infected mice were treated with two different AhR agonists, L-Kynurenin (L-Kyn) or 6-formylindole [3,2-b] carbazole (FICZ), and one AhR specific antagonist (CH223191). The disease severity and immune response of treated and untreated mice were assessed 96 hours and 2 weeks after infection. Some similar effects on host response were shared by FICZ and L-Kyn, such as the reduced fungal loads, decreased numbers of CD11c+ lung myeloid cells expressing activation markers (IA, CD40, CD80, CD86), and early increased expression of IDO and AhR. In contrast, the AhR antagonist CH223191 induced increased fungal loads, increased number of pulmonary CD11c+ leukocytes expressing activation markers, and a reduction in AhR and IDO production. While FICZ treatment promoted large increases in ILC3, L-Kyn and CH223191 significantly reduced this cell population. Each of these AhR ligands induced a characteristic adaptive immunity. The large expansion of FICZ-induced myeloid, lymphoid, and plasmacytoid dendritic cells (DCs) led to the increased expansion of all CD4+ T cell subpopulations (Th1, Th2, Th17, Th22, and Treg), but with a clear predominance of Th17 and Th22 subsets. On the other hand, L-Kyn, that preferentially activated plasmacytoid DCs, reduced Th1/Th22 development but caused a robust expansion of Treg cells. The AhR antagonist CH223191 induced a preferential expansion of myeloid DCs, reduced the number of Th1, Th22, and Treg cells, but increased Th17 differentiation. In conclusion, the present study showed that the pathogen loads and the immune response in pulmonary PCM can be modulated by AhR ligands. However, further studies are needed to define the possible use of these compounds as adjuvant therapy for this fungal infection.

Exosomes-carrying Epstein-Barr virus-encoded small RNA-1 induces indoleamine 2, 3-dioxygenase expression in tumor-infiltrating macrophages of oral squamous-cell carcinomas and suppresses T-cell activity by activating RIG-I/IL-6/TNF-α pathway

ObjectivesAlthough exosomes carrying Epstein-Barr virus-encoded small RNA-1 (EBER-1) are involved in the immunosuppressive tumor microenvironments of EBV-associated head and neck carcinomas, the effects of EBER-1-associated exosomes on tumor-infiltrating macrophages are poorly understood. Materials and methodsThe association between EBV infection and expression of indoleamine 2,3-dioxygenase (IDO) was assessed in 165 paraffin-embedded oral squamous cell carcinoma (OSCC) tissue samples. Using in vitro techniques, we investigated whether stimulation of the RIG-I/IL-6/TNF-α pathway by exosomes carrying EBER-1 is critical for IDO induction in macrophages. We performed a thymidine incorporation and a cell cytolytic assay to test for up-regulated IDO in macrophages that can block the proliferation and function of effector T cells. ResultsSome infiltrated macrophages expressed levels of IDO higher than OSCC cells which was significantly associated with presence of EBV. The production of IDO, tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) in human monocyte-derived macrophages (MDMs) was induced by EBV-associated exosomes in vitro. Mechanistically, the retinoic acid-inducible gene I (RIG-I) pathway in MDMs was stimulated by EBV-encoded small RNA-1 (EBER-1) whereas the inhibition of these pathways by BX-795 almost abolished the production of these two cytokines and IDO induction. Also, the EBER-1-activated IDO in MDMs suppressed the proliferation of T lymphocytes and diminished the cytolytic activity of CD8+ T cells. ConclusionExosomes carrying EBER-1 could induce IDO expression in MDMs, considerably aided by an IL-6 and TNF-α-dependent mechanism via the RIG-I signaling pathway, which might create an immunosuppressive microenvironment affecting T-cell immune responses.

Indoleamine 2,3-dioxygenase in melanoma progression and BRAF inhibitor resistance

Indoleamine 2,3-dioxygenase (IDO) is associated with the progression of many types of tumors, including melanoma. However, there is limited information about IDO modulation on tumor cell itself and the effect of BRAF inhibitor (BRAFi) treatment and resistance. Herein, IDO expression was analyzed in different stages of melanoma development and progression linked to BRAFi resistance. IDO expression was increased in primary and metastatic melanomas from patients’ biopsies, especially in the immune cells infiltrate. Using a bioinformatics approach, we also identified an increase in the IDO mRNA in the vertical growth and metastatic phases of melanoma. Using in silico analyses, we found that IDO mRNA was increased in BRAFi resistance. In an in vitro model, IDO expression and activity induced by interferon-gamma (IFNγ) in sensitive melanoma cells was decreased by BRAFi treatment. However, cells that became resistant to BRAFi presented random IDO expression levels. Also, we identified that treatment with the IDO inhibitor, 1-methyltryptophan (1-MT), was able to reduce clonogenicity for parental and BRAFi-resistant cells. In conclusion, our results support the hypothesis that the decreased IDO expression in tumor cells is one of the many additional outcomes contributing to the therapeutic effects of BRAFi. Still, the IDO production changeability by the BRAFi-resistant cells reiterates the complexity of the response arising from resistance, making it not possible, at this stage, to associate IDO expression in tumor cells with resistance. On the other hand, the maintenance of 1-MT off-target effect endorses its use as an adjuvant treatment of melanoma that has become BRAFi-resistant.

Dose and duration of interferon γ pre-licensing interact with donor characteristics to influence the expression and function of indoleamine-2,3-dioxygenase in mesenchymal stromal cells.

Human mesenchymal stromal cells (MSCs) are a leading cell therapy candidate for the treatment of immune and inflammatory diseases due to their potent regulation of immune cells. MSC expression of indoleamine-2,3-dioxygenase (IDO) upon interferon γ (IFNγ) exposure has been proposed as both a sentinel marker and key mediator of MSC immunomodulatory potency. Rather than wait for in vivo exposure to cytokines, MSCs can be pre-licensed during manufacturing to enhance IDO expression. In this study, we systematically examine the relative role that the dose of IFNγ, the duration of pre-licensing and the donor of origin play in dictating MSC production of functional IDO. We find that across three human MSC donors, MSCs increase their expression of IDO in response to both increased dose of IFNγ and duration of pre-licensing. However, with extended pre-licensing, the expression of IDO no longer predicts MSCs ability to suppress activated peripheral blood mononuclear cells. In addition, pre-licensing dose and duration are revealed to be minor modifiers of MSCs inherent potency, and thus cannot be manipulated to boost poor donors to the levels of high-performing donors. Thus, the dose and duration of pre-licensing should be tailored to optimize performance of specific donors and an emphasis on donor selection is needed to realize significant benefits of pre-licensing.

Altered Indoleamine 2,3-Dioxygenase Production and Its Association to Inflammatory Cytokines in Peripheral Blood Mononuclear Cells Culture of Type 2 Diabetes Mellitus.

Aim:To analyze indoleamine 2,3-dioxygenase (IDO) production in the cell culture supernatant of phytohemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMCs) from type 2 DM (T2DM) patients and investigate IDO’s association to pro- and anti-inflammatory cytokines.Subjects and methods:PBMC samples were collected from 21 T2DM patients and 17 normoglycemic participants, then stimulated with PHA for 3 days. Cytokine and IDO concentrations were measured in the PBMC culture supernatants. In vitro production of TNF-α, IL-6, interferon-γ, and IL-10 were measured using multiplex immunoassay. IDO concentration was assessed using ELISA. To assess how PHA stimulation altered IDO production and to minimize the unstimulated baseline effect of T2DM, we subtracted the PHA-stimulated IDO concentration from the unstimulated one. IBM SPSS version 23 was used for statistical analysis.Results:The IDO concentrations in the PBMC culture supernatants were significantly higher in T2DM patients regardless of whether they were unstimulated (P < .001) or PHA-stimulated (P = .012). Reduced IDO production was observed in 52.8% of T2DM patients and was associated with older age and lower interferon-γ levels. Conversely, 42.8% of T2DM patients showed increased IDO concentrations, which were correlated with the IL-6/IL-10 ratio (r = 0.683, P = .021) and interferon-γ/IL-10 ratio (r = 0.517, P = .077).Conclusion:The interferon-γ level was reduced in the PBMC culture supernatant of T2DM patients with reduced IDO production. Reduced IDO production in T2DM patients following PHA stimulation was associated with older age and, notably, higher baseline IDO concentrations. Since IDO is primarily produced by dendritic cells, reduced IDO production after PHA stimulation may indicate dendritic cell dysfunction.

CARD9 prevents lung cancer development by suppressing the expansion of myeloid-derived suppressor cells and IDO production.

Caspase recruitment domain-containing protein 9 (CARD9) is an adaptor protein and highly expressed in myeloid cells. Our previous study demonstrates a critical protective effect of CARD9 in the development of colitis-associated colon cancer. Nevertheless, the effect of CARD9 in lung cancer remains unclear. Here, using a mouse Lewis lung cancer model, we found the tumor burden of CARD9-/- mice was much heavier than that in wild-type (WT) mice. More myeloid-derived suppressor cells (MDSCs) were accumulated and less cytotoxicity T lymphocyte was found in tumor tissues of CARD9-/- mice, compared to WT mice. Depleting MDSCs using anti-Gr1 antibody can significantly decrease tumor burden in CARD9-/- mice. Furthermore, the noncanonical nuclear factor-kappaB (NF-κB) pathway was activated in CARD9-/- mice-derived MDSCs. Deficiency of CARD9 enhanced expression of indoleamine 2,3-dioxygenase (IDO) in MDSCs via noncanonical NF-κB pathway. Moreover, correlations between CARD9 expressions and MDSCs relative genes (IDO, iNOS-2 and arginase 1 [ARG-1]) were further confirmed in tumor tissues from lung cancer patients. Taken together, we showed a CARD9-NF-κB-IDO pathway in MDSCs which can inhibit the suppressive function of MDSCs and prevent lung cancer development.

The surprising role of Indoleamine 2,3-dioxygenase (IDO) in supporting the survival of bone marrow resident long lived plasma cells (LLPC)

Abstract Long lived plasma cells (LLPC) are a key component of protective humoral immunity. The ability of these cells to maintain longevity and a durable antibody response is largely dependent on the complex nature of the bone marrow (BM) microenvironment in which these cells reside. Our lab has demonstrated that the co-stimulatory receptor, CD28, is essential for the survival and function of LLPC. Furthermore, when CD28 on LLPC ligates with CD80/CD86 expressed on DC, it induces upregulation of the enzyme indoleamine 2,3-dioxygenase (IDO), which catabolizes tryptophan (Trp) into kynurenine (kyn), a well-known ligand of the aryl hydrocarbon receptor (AhR). AhR is a nuclear transcription factor that can modulate immune responses and is highly expressed in plasma cells (PC). Our preliminary data reveals that IDO knock-out (KO) mice in comparison to wild type (Wt) mice have a decrease in bone marrow resident PCs and a decrease in overall Ig levels. Additionally, 15 weeks post vaccination IDO KO mice have significantly less antigen-specific long lived antibody titers compared to Wt. It was also observed that interaction with DC both in vitro and in vivo is needed for LLPC survival and function. Moreover, AhR activation by kyn causes an increase in CD28 mRNA in LLPC. This leads us to propose a model where CD28 interaction with CD80/CD86 induces IDO production, which through its metabolite kyn activates AhR which can then regulate CD28 expression- thus creating a mechanism that promotes LLPC survival and function. These findings challenge the traditional idea of IDO as an inhibitory molecule and provide the rationale for investigating its essential role in maintaining LLPC survival and sustained antibody responses.

Quantitative Assessment of Indoleamine 2,3-Dioxygenase (IDO) Expression at Diagnosis Predicts Clinical Outcome in Patients with Acute Myeloid Leukemia Undergoing Allogeneic Stem Cell Transplantation

IntroductionIndoleamine 2,3-dioxygenase (IDO) is an intracellular heme-containing enzyme that catalyzes the initial rate-limiting step in tryptophan degradation along the kynurenine pathway. IDO is physiologically expressed by a wide variety of human cells in response to several stimuli and it is known to have a crucial role in the induction of immune tolerance during pregnancy, infections, transplantation, autoimmunity and tumors. IDO-mediated tryptophan degradation results in inhibition of T-cell proliferation, increase of T-cell apoptosis and T-reg induction. Several studies demonstrated that IDO production can induce the increase of Regulatory T-cells (Tregs) directly through the conversion of CD25- into CD25+ T cells, even in acute myeloid leukemia (AML) patients. IDO expression can be considered a novel mechanism of leukemia escape from immune control and its inhibition may represent an antileukemia therapeutic strategy. Aim of our work is to analyze IDO mRNA expression in a cohort of AML patients and to investigate the presence of any significant correlation between IDO expression and standard prognostic factors or clinical outcome.MethodsWe analyzed a cohort of 68 adult patients aged 18 years or older, who were diagnosed with de novo or secondary AML. IDO mRNA expression was evaluated by Real-Time (RT)-PCR in blood bone marrow and peripheral blood samples at diagnosis. Patients were then retrospectively stratified according to standard risk factors at diagnosis and to IDO mRNA expression levels.ResultsMedian age of analyzed patients was 57 years (range 21-76). Fifty-nine out of 68 patients (87%) had de novo AML, whereas 9 out of 68 patients (13%) had secondary AML. A comprehensive risk assessment was available for 61 patients. Among these 61 patients who were evaluable for risk stratification, 13 patients (21%) resulted to have a favorable risk AML, 30 (49%) had an intermediate risk AML and 17 patients (30%) were stratified as high-risk AML. Sixty out of 68 patients received intensive, standard, induction chemotherapy regimens. The remaining 8 patients were not candidate to receive intensive chemotherapy mainly because of comorbidities. Twenty-three out of 68 patients (34%) were considered eligible for allogeneic stem cells transplantation (alloSCT) as consolidation therapy, after obtaining complete remission with standard chemotherapy. IDO expression in peripheral blood (PB) samples was between 0.07 and 4272.26 (median 5.60). Conversely, IDO expression in bone marrow (BM) samples was between 0.17 and 243.16 (median 1.21). Our data did not establish any significant correlation between IDO expression and leukemia risk factors at diagnosis, in particular cytogenetics, de novo or secondary AML, leukocytosis. Among the 60 patients who received induction chemotherapy, 35 achieved morphological complete remission (CR), 24 did not respond and 1 patient was not evaluable for response. Response to induction chemotherapy was not influenced by IDO mRNA expression levels. Interestingly, among patients undergoing alloSCT, high levels of IDO mRNA expression in PB samples negatively correlated with patients' overall survival. In particular, high IDO expression of more than 10 was associated with worse overall survival after alloSCT even when adjusted by patients' age and disease status at transplant (log rank P=0.02) (Fig.1). With the limitations of the low number of patients, these results from the group of transplanted patients were not likely due to differences in the incidence and severity of graft-versus-host-disease, whereas high IDO mRNA expression level was predictive of increased incidence of relapse.ConclusionsThis work suggests that IDO mRNA expression levels can be considered as predictive of AML outcome, independently from other risk factors at diagnosis. In our set, higher level of IDO mRNA expression at diagnosis was correlated with worse clinical outcome in patients undergoing alloSCT. Larger studies are warranted in order to establish the real predictive role of IDO mRNA expression in influencing AML outcome. DisclosuresCavo:Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Multiple Myeloma Cell-Derived Interleukin-32gamma Increases the Immunosuppressive Function of Macrophages By Promoting Indoleamine 2,3-Dioxygenase (IDO) Expression

Background: The interaction of multiple myeloma (MM) cells with macrophages (MΦs) in the bone marrow microenvironment contributes to the pathophysiology of MM. In addition to promoting angiogenesis through vasculogenic mimicry, MM-associated MΦs (mMΦs) protect MM cells from spontaneous and chemotherapy-induced apoptosis. mMΦs therefore represent a potential target for myeloma treatment and it is essential to explore the mechanisms underlying normal MΦ polarization to mMΦs. We previously showed that IL-32 is overexpressed in MM patients and is mainly derived from MM cells. The present study was designed to explore the clinical significance of IL-32 in MM and to further elucidate the molecular mechanisms underlying the IL-32-mediated immune function of MΦs.Methods: We examined the expression of IL-32 in bone marrow biopsy samples using immunohistochemistry. Quantitative real-time PCR, western blot analysis and immunofluorescence were applied to measure the expression of IL-32, IDO and proteinase 3 (PR3). We obtained the global transcriptional profile of the IL-32γ-treated MΦs by RNA sequencing (RNA-Seq). Immunoprecipitation (IP) and GST pulldown experiments was applied to confirm the binding affinity of PR3 for IL-32. We created IL-32-knockdown MM cells by transfection of IL-32 shRNA and silenced PR3 expression in MΦs using siRNA targeting PR3. CD4+ T cell proliferation and IL-2, IFN-γ and TNF-α production were measured by flow cytometry.Results: We found that high IL-32 expression in MM patients was associated with advanced clinical stage and high serum β2-microglobulin levels. Several isoforms of IL-32 were detected in MM cells and IL-32γ was the most active subtype. RNA sequencing revealed that IL-32γ significantly induced the production of the immunosuppressive molecule indoleamine 2,3-dioxygenase (IDO) in MΦs and this effect was verified at the protein level. Furthermore, IL-32-knockdown MM cells showed less ability than control MM cells to promote IDO expression. As a binding protein for IL-32, PR3 was universally expressed on the surface of MΦs and knockdown of PR3 or inhibition of the STAT3 and nuclear factor κB (NF-κB) pathways hindered the IL-32γ-mediated stimulation of IDO expression. Finally, IDO-positive IL-32γ-educated MΦs inhibited CD4+ T cell proliferation and IL-2, IFN-γ and TNF-α production in response to activation.Conclusion: Our study showed that MM cell-derived IL-32γ induced IDO production in MΦs through PR3 and the downstream STAT3 and NF-κB pathways, resulting in the suppression of the proliferation and effector function of CD4+ T cells. High IL-32 expression in MM may contribute to an immunosuppressive microenvironment by upregulating IDO production in MΦs and promote MM progression. DisclosuresNo relevant conflicts of interest to declare.

The role of Indoleamine 2,3-dioxygenase (IDO) in the survival of bone marrow resident long lived Plasma cells

Abstract Long lived plasma cells (LLPCs) are essential for sustained antibody responses and protective humoral immunity. How these cells maintain longevity and a durable antibody response is largely dependent on the complex nature of the bone marrow microenvironment in which these cells reside, and the pro survival factors produced in this niche. Previous work in our lab has shown that CD28 is required for LLPC survival, and we know that CD28 back signaling to CD80/86 induces IDO production from dendritic cells (DCs) within the bone marrow microenvironment. IDO is classically known to contribute to an immunosuppressive environment (specifically with respect to T cell activity). However, upon investigation of IDO in the normal setting, we observed fewer plasma cells present in the bone marrow of IDO knockout mice in comparison to wild type mice, as well as fewer antigen-specific plasma cells in the bone marrow following vaccination. Additionally, knowing the role of DCs in IDO production in the bone marrow, we employed the use of CD11c-DTR mice to observe the effects of PC survival upon DC elimination. We found that depletion of DCs significantly decreases the amount of antigen-specific plasma cells in the bone marrow. This leads us to propose a model where CD28, through back signaling to CD80/86 induces IDO production in DCs, a mechanism to maintain the bone marrow niche for long lived plasma cell survival and sustained antibody production.

Abstract IA21: Immune mechanisms in gastrointestinal stromal tumor

Abstract Gastrointestinal stromal tumor (GIST) is the most common sarcoma subtype and typically contains an activating mutation in KIT or, less frequently, PDGFRA. Imatinib mesylate inhibits the KIT and PDGFRA oncoproteins and achieves a partial response or stable disease in over 80% of patients with advanced GIST. Unfortunately, disease progression typically occurs within 2 years, usually due to a secondary KIT mutation. Moreover, while adjuvant imatinib prolongs recurrence-free survival, it does not appear to increase the chance of cure following surgery. Thus, novel therapeutic strategies are needed for GIST, which has led us over the last 8 years to investigate the immune response. In a genetically engineered mouse model of GIST with a Kit deletion, we discovered that imatinib works partly by inhibiting tumor cell production of an immunosuppressive enzyme called indoleamine 2,3-dioxygenase (IDO), which catabolizes L-tryptophan. The downstream tryptophan metabolites are immunosuppressive and promote the development and activation of regulatory T cells (Treg) and suppress effector T cells. Consequently, by decreasing IDO production, imatinib can enhance the antitumor immune response. IDO expression was also found in human GIST specimens. While imatinib alone increased the T-cell immune response, we studied the effects of additional T-cell activation. Anti-CTLA-4 increased the antitumor efficacy of imatinib in the mouse model, which led to an NCI trial (NCT01643278) that tested the combination of ipilimumab and dasatanib in advanced, refractory GIST. Disappointingly, there were no responses by RECIST criteria, although dasatinib has limited activity in resistant GIST and concomitant tyrosine kinase inhibition was necessary in the mouse model. Nevertheless, the importance of intratumoral T cells was also shown by Zitvogel, who found that intratumoral CD8 T cells detected by immunohistochemistry correlated with survival in human GIST. Recently, we analyzed 106 human GISTs and found that intratumoral T cells often had a high-level expression of programmed death 1 (PD-1), and there was tumor expression of its ligand PD-L1. In the mouse model, anti-PD-1 or anti-PD-L1 alone lacked efficacy, but each increased the antitumor effects of imatinib. We also performed a detailed analysis of tumor-associated macrophages (TAMs) in 57 human GISTs. Macrophages are generally categorized as classically (M1) or alternatively (M2) activated, although these terms really just define the extremes of a spectrum. M1 macrophages can lyse tumor cells, secrete IL-12 and TNF, and present antigen to T cells. Meanwhile, M2 macrophages promote tumor growth by secreting IL-10 and supporting angiogenesis. Surprisingly, we found that TAMs in GIST were M1 at baseline, became M2 after imatinib therapy, and reverted to M1 after imatinib resistance developed. Accordingly, transcriptome analysis of purified TAMs revealed that there were no genes expressed more than two-fold between untreated and resistant GISTs. Because the TAMs were M1, it may be preferable to pursue strategies to activate TAMs in GIST, instead of depleting them. Recently, we have found in the GIST mouse model that anti-CD40 therapy increased the antitumor response to imatinib. It is now clear that there is a natural antitumor immune response to GIST, given the presence of M1 TAMs and intratumoral T cells expressing PD-1. However, other aspects of the immune response to GIST remain undefined. Manipulating the immune environment in GIST has potential therapeutic benefit. Several immunotherapy trials are opening in GIST, including those incorporating IDO inhibition and anti-PD-1. Citation Format: Ronald DeMatteo. Immune mechanisms in gastrointestinal stromal tumor [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr IA21.

Hypoxia enhances indoleamine 2,3-dioxygenase production in dendritic cells.

Hypoxia-associated metabolic reprogramming modulates the biological functions of many immune and non-immune cells, and affects immune response types and intensities. Adenosine and indoleamine 2,3-dioxygenase (IDO) are known immunosuppressors, and adenosine is a hypoxia-associated product. We investigated the impact of hypoxia on IDO production in dendritic cells (DCs). We found that hypoxia (1% O2) enhances IDO production in DCs, and this increase was dependent on the adenosine A3 receptor (A3R), but not A2aR or A2bR. A3R blockade during hypoxia inhibited IDO production in DCs, while A2bR blockade further enhanced IDO production. Activating A2aR had no effect on IDO production. Hypoxia (1% O2) upregulated CD86, CD274, HLA-DR, and CD54, and downregulated CD40 and CD83 in DCs as compared to normoxia (21% O2). IDO inhibition in hypoxia-conditioned DCs reversed MHC-II, CD86, CD54, and CD274 upregulation, but further downregulated CD40 and CD83. Our findings offer guidance for pharmacological administration of adenosine receptor agonists or antagonists with the goal of achieving immune tolerance or controlling insulin resistance and other metabolic disorders via IDO modulation.

Indoleamine 2,3-Dioxygenase (IDO) Enzyme Links Innate Immunity and Altered T-Cell Differentiation in Non-ST Segment Elevation Acute Coronary Syndrome.

Atherosclerosis is a chronic inflammatory disease characterized by a complex interplay between innate and adaptive immunity. Dendritic cells (DCs) play a key role in T-cell activation and regulation by promoting a tolerogenic environment through the expression of the immunosuppressive enzyme indoleamine 2,3-dioxygenase (IDO), an intracellular enzyme involved in tryptophan catabolism. IDO expression and activity was analyzed in monocytes derived DCs (MDDCs) from non-ST segment elevation myocardial infarction (NSTEMI) patients, stable angina (SA) patients and healthy controls (HC) by real-time quantitative polymerase chain reaction (RT-qPCR) before and after in vitro maturation with lipopolysaccharide (LPS). The amount of tryptophan catabolite; kynurenine; was evaluated in the culture supernatants of mature-MDDCs by ELISA assay. Autologous mixed lymphocyte reaction (MLR) between mature-MDDCs and naïve T-cells was carried out to study the differentiation towards T-helper 1 (Th1) and induced regulatory T-cells (iTreg). Analysis of IDO mRNA transcripts in mature-MDDCs revealed a significant reduction in cells isolated from NSTEMI (625.0 ± 128.2; mean ± SEM) as compared with those from SA (958.5 ± 218.3; p = 0.041) and from HC (1183.6 ± 231.6; p = 0.034). Furthermore; the concentration of kynurenine was lower in NSTEMI patients (2.78 ± 0.2) and SA (2.98 ± 0.25) as compared with HC (5.1 ± 0.69 ng/mL; p = 0.002 and p = 0.016; respectively). When IDO-competent mature-MDDCs were co-cultured with allogeneic naïve T-cells, the ratio between the percentage of generated Th1 and iTreg was higher in NSTEMI (4.4 ± 2.9) than in SA (1.8 ± 0.6; p = 0.056) and HC (0.9 ± 0.3; p = 0.008). In NSTEMI, the tolerogenic mechanism of the immune response related to IDO production by activated MDDCs is altered, supporting their role in T-cell dysregulation.

The modulation of enzyme indoleamine 2,3-dioxygenase from dendritic cells for the treatment of type 1 diabetes mellitus.

Diabetes mellitus type 1 (DM1) is an autoimmune disease in which β-cells of the pancreas islet are destroyed by T lymphocytes. Specific T cells are activated by antigen-presenting cells, mainly dendritic cells (DCs). It is already known that the regulation of tryptophan pathway in DC can be a mechanism of immunomodulation. The enzyme indoleamine 2,3-dioxygenase (IDO) is present in many cells, including DC, and participates in the metabolism of the amino acid tryptophan. Recent studies suggest the involvement of IDO in the modulation of immune response, which became more evident after the in vitro demonstration of IDO production by DC and of the ability of these cells to inhibit lymphocyte function through the control of tryptophan metabolism. Current studies on immunotherapies describe the use of DC and IDO to control the progression of the immune response that triggers DM1. The initial results obtained are promising and indicate the possibility of developing therapies for the treatment or prevention of the DM1. Clinical trials using these cells in DM1 patients represent an interesting alternative treatment. However, clinical trials are still in the initial phase and a robust group of assays is necessary.

The role of Indoleamine 2,3-dioxygenase (IDO) in the survival of bone marrow resident long lived Plasma cells

Abstract Long lived plasma cells (LLPCs) are essential for sustained antibody responses and protective humoral immunity. How these cells maintain longevity and a durable antibody response is largely dependent on the complex nature of the bone marrow microenvironment in which these cells reside, and the pro survival factors produced in this niche. Work in our lab has shown that CD28 is required for LLPC survival, and that Indoleamine 2,3-dioxygenase (IDO), an enzyme that catabolizes tryptophan, is produced as a result of back signaling from CD28:CD80/86 interactions between plasma cells and bone marrow myeloid derived dendritic cells (DC). IDO is classically known to contribute to an immunosuppressive environment through its depletion of tryptophan (specifically with respect to T cells). However, to our great surprise we found that there are fewer LLPCs present in the bone marrow of IDO knockout mice in comparison to wild type mice. Additionally, live cell numbers of purified plasma cells in vitro in tryptophan free media and IDO conditioned media are greater than in media alone. These conditions also caused autophagy to occur in these plasma cells, a process shown to be required for LLPC survival. This leads us to propose a model where CD28, through back signaling to CD80/86, induces IDO production which leads to depletion of tryptophan and causes induction of autophagy, a mechanism LLPCs use to compete and survive within the bone marrow microenvironment.

The inhibition of indoleamine 2, 3-dioxygenase 1 by connexin 43.

Upregulation of connexin 43 (Cx43) showed potential in enhancing immune surveillance that was suppressed in the tumor microenvironment. The expression of indoleamine 2, 3-dioxygenase (IDO) is one of the crucial factors contributing to tumor immune tolerance by depletion of tryptophan and IDO-mediated tryptophan metabolites. Here, we aim to investigate the role of Cx43 in IDO production in murine tumor by using Cx43 inducers. Resveratrol (trans-3, 5, 4 '-trihydroxystilbene) is a natural plant-derived polyphenol possessing positive effect against cancer. Salmonella enterica serovar choleraesuis (S.C.) was proved to target and inhibit tumor growth. Both of them regulated Cx43 expression in tumor cells and led to either chemosensitizing or immune-activating. In this study, the correlation between Cx43 and IDO were determined by the treatment of resveratrol and S.C. Our data showed an increase in Cx43 while IDO protein and IDO-mediated inhibited effects on T cell decreased after tumor cells are given with resveratrol and S.C. treatments. All of which could be inhibited once the expression of Cx43 was blocked. Cx43 involved in IDO regulation might be useful in developing IDO-targeted cancer immune therapy.

Host Interleukin 6 and Indoleamine 2,3 Dioxygenase Regulate Inflammation in the Brain during Graft Versus Host Disease

Graft versus host disease (GVHD) commonly induces pathological damage in peripheral target organs such as the skin, liver and gastrointestinal tract leading to well characterized organ-specific clinical manifestations. A number of studies, however, have shown that patients with GVHD can also have behavioral and mood alterations that can affect overall cognitive function and lead to significant impairments in quality of life. The extent to which GVHD contributes to cognitive dysfunction and induces inflammation within the central nervous system (CNS), however, has not been critically examined. To address this question, we conducted studies using two well-defined murine GVHD models [C57BL/6(H-2b)→Balb/c (H-2d) and B10.BR(H-2k)→B6 (H-2b)]. We observed that there was a significant increase in the number of donor-derived CD4+ and CD8+ T cells in the brains of GVHD recipients early (days 7 -14) and late (day 42) post transplantation compared to BM controls. Histological studies revealed activated microglial cells and CD3+ T cell infiltration in the periventricular regions of brains in GVHD recipients that were not present in BM animals. Real time q-PCR analysis also demonstrated significant increases in IFN-γ, TNF-α, and IL-6 mRNA expression indicative of a proinflammatory state. Notably, GVHD animals exhibited behavioral changes in the forced swim test and elevated plus maze which are validated assays of stress coping and anxiety, respectively. Since IL-6, in particular, plays a pivotal role in GVHD pathogenesis in murine models and humans, we examined whether blockade of IL-6 signaling altered neuroinflammation. Animals treated with an anti-IL-6R antibody had a significant reduction in the number of donor-derived CD4+ and CD8+T cells in the brain compared to isotype control-treated mice. Anti-IL-6R treatment of GVHD mice also resulted in significant reductions in IFN-γ, TNF-α, and IL-6 mRNA and normalized behavior in the forced swim test, indicative of a decreased inflammatory response. Since IL-6 is produced by a wide variety of cells, including microglial and T cells, both donor and recipient cells have the potential to modulate GVHD severity within the CNS. To define whether donor or host IL-6 production was most critical for inducing neuroinflammation, experiments were conducted employing IL-6-/- mice as either donors or recipients. Whereas the absence of IL-6 in donor-derived cells had no impact on the degree of inflammation within the CNS, recipient animals that lacked IL-6 had a significant decrease in the number of donor-derived T cells which accumulated in the brain as well as a marked reduction in inflammatory cytokines, indicating that host IL-6 production was critical. To define the downstream pathways of IL-6-mediated CNS inflammation, we examined the role of indoleamine 2,3-dioxygenase (IDO) since IL-6 has been shown to upregulate IDO-1 expression under inflammatory conditions. We observed that IDO-1 mRNA levels were significantly increased in the brains of GVHD animals, and that blockade of IL-6 signaling resulted in a marked decrease in IDO mRNA levels. Additionally, transplantation studies using IDO-/- mice revealed that host, but not donor, IDO production was required for maximal inflammatory effects. Serotoninergic projections to the prefrontal cortex (PFC), in particular, are sensitive to inflammation and contribute to stress coping behavior. Therefore, to further interrogate this pathway, we performed quantitative mass spectrometry of brain extracts from the PFC. We found that tryptophan and 5HT concentrations were not different between BM and GVHD groups. However, there was an increase in the IDO product, kynurenic acid, in GVHD recipients consistent with an increase in brain IDO expression. To provide additional support for the premise that IL-6 effects were mediated through the IDO pathway, recipient mice were treated with either 1-methyltryptophan (1-MT), a completive inhibitor of IDO, or a vehicle control. GVHD mice treated with 1-MT had decreased accumulation of T cells in the brain and normal behavior in the forced swim test, demonstrating that inhibition of IDO abrogated CNS inflammation and behavioral changes in the presence of intact IL-6 signaling. In summary, these studies demonstrate that host IL-6 and IDO regulate inflammation and adversely impact behavioral function within the brain during GVHD through the tryptophan metabolic pathway. DisclosuresNo relevant conflicts of interest to declare.