An interaction between kynurenine and the aryl hydrocarbon receptor can generate regulatory T cells

Neuroinflammation and schizophrenia: The role of Toxoplasma gondii infection and astrocytic dysfunction

Obligate intracellular pathogens such as the protozoan Toxoplasma gondii exploit host cell mechanisms to facilitate their survival and replication. While T. gondii can infect any nucleated mammalian cell, it exhibits a particular affinity for central nervous system cells, including neurons, astrocytes, and microglia. Among these, astrocytes play a pivotal role in maintaining neuroimmune balance, and their infection by T. gondii induces structural and functional alterations. Emerging evidence suggests that these changes may contribute to the pathophysiology of schizophrenia (SCZ). Although a direct causal link between T. gondii-induced astrocytic dysfunction and SCZ remains unproven, infection has been associated with increased kynurenic acid production, elevated dopamine levels, and heightened inflammatory cytokines-all of which are implicated in SCZ pathology. Additionally, T. gondii infection disrupts crucial neurobiological processes, including N-methyl-d-aspartate receptor signaling, blood-brain barrier integrity, and gray matter volume, further aligning with SCZ-associated neuropathology. This review underscores the need for targeted research into T. gondii-mediated astrocytic dysfunction as a potential factor in SCZ development. Understanding the mechanistic links between T. gondii infection, astrocytic alterations, and psychiatric disorders may open new avenues for therapeutic interventions.

Age- and diet-instructed metabolic rewiring of the tumor-immune microenvironment

The tumor-immune microenvironment (TIME) plays a critical role in tumor development and metastasis, as it influences the evolution of tumor cells and fosters an immunosuppressive state by intervening the metabolic reprogramming of infiltrating immune cells. Aging and diet significantly impact the metabolic reprogramming of the TIME, contributing to cancer progression and immune evasion. With aging, immune cell function declines, leading to a proinflammatory state and metabolic alterations such as increased oxidative stress and mitochondrial dysfunction, which compromise antitumor immunity. Similarly, dietary factors, particularly high-fat and high-sugar diets, promote metabolic shifts, creating a permissive TIME by fostering tumor-supportive immune cell phenotypes while impairing the tumoricidal activity of immune cells. In contrast, dietary restrictions have been shown to restore immune function by modulating metabolism and enhancing antitumor immune responses. Here, we discuss the intricate interplay between aging, diet, and metabolic reprogramming in shaping the TIME, with a particular focus on T cells, and highlight therapeutic strategies targeting these pathways to empower antitumor immunity.

Loss of aryl hydrocarbon receptor reduces pancreatic tumor growth by increasing immune cell infiltration

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease which remains poorly understood. Increasing evidence suggests that the aryl hydrocarbon receptor (AHR) plays a role in the pathogenesis of several cancers; however, its role in PDAC is unclear because AHR exhibits both pro- and anti-tumor activities. Here we evaluated the role of AHR in CR705 and K8484 murine PDAC cells in vitro and CR705 cells in vivo. Loss of Ahr did not affect cell proliferation compared with Cas9 control cells and no differences in tumor development between CR705Cas9 and CR705AhrKO cells were observed in immunocompromised mice. Conversely, tumors from CR705AhrKO cells grew more slowly than tumors from CR705Cas9 cells in immune competent mice. RNA sequencing identified 1279 genes upregulated and 586 genes downregulated in CR705AhrKO tumors compared with CR705Cas9 tumors. Pathway analysis identified immunoregulatory interactions, interferon signaling, and chemokine signaling among the top upregulated pathways. Increased infiltration of CD45+ cells and higher numbers of CD8+ T cells and F4/80+ cells were observed in CR705AhrKO tumors. Ahr deficiency in macrophages (LysMCre) or lymphocytes (RorcCre) did not alter tumor development of CR705Cas9 cells compared with Ahrfl/fl mice. CR705AhrKO tumors in RorcCre mice, but not in LysMCre mice had significantly lower tumor weights normalized to body weights compared with CR705AhrKO tumors in WT mice. These findings show that Ahr loss in CR705 pancreatic cancer cells is sufficient to induce proinflammatory gene responses that contribute to increased immune cell infiltration and reduced tumor growth.

Study of immunosenescence in the occurrence and immunotherapy of gastrointestinal malignancies

In human beings heterogenous, pervasive and lethal malignancies of different parts of the gastrointestinal (GI) tract viz., tumours of the oesophagus, stomach, small intestine, colon, and rectum, represent gastrointestinal malignancies. Primary treatment modality for gastric cancer includes chemotherapy, surgical interventions, radiotherapy, monoclonal antibodies and inhibitors of angiogenesis. However, there is a need to improve upon the existing treatment modality due to associated adverse events and the development of resistance towards treatment. Additionally, age has been found to contribute to increasing the incidence of tumours due to immunosenescence-associated immunosuppression. Immunosenescence is the natural process of ageing, wherein immune cells as well as organs begin to deteriorate resulting in a dysfunctional or malfunctioning immune system. Accretion of senescent cells in immunosenescence results in the creation of a persistent inflammatory environment or inflammaging, marked with elevated expression of pro-inflammatory and immunosuppressive cytokines and chemokines. Perturbation in the T-cell pools and persistent stimulation by the antigens facilitate premature senility of the immune cells, and senile immune cells exacerbate inflammaging conditions and the inefficiency of the immune system to identify the tumour antigen. Collectively, these conditions contribute positively towards tumour generation, growth and eventually proliferation. Thus, activating the immune cells to distinguish the tumour cells from normal cells and invade them seems to be a logical strategy for the treatment of cancer. Consequently, various approaches to immunotherapy, viz., programmed death ligand-1 (PD-1) inhibitors, Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) inhibitors etc are being extensively evaluated for their efficiency in gastric cancer. In fact, PD-1 inhibitors have been sanctioned as late late-line therapy modality for gastric cancer. The present review will focus on deciphering the link between the immune system and gastric cancer, and the alterations in the immune system that incur during the development of gastrointestinal malignancies. Also, the mechanism of evasion by tumour cells and immune checkpoints involved along with different approaches of immunotherapy being evaluated in different clinical trials will be discussed.

A TCR nanovesicle antibody for redirecting T cells and reversing immunosuppression as a tumor immunotherapy strategy

T-cell receptor T-cell engagers (TCR-TCE) are soluble bispecific proteins composed of TCR and anti-CD3 antibodies, which can effectively redirect tumor-infiltrating T cells to kill tumor cells. However, TCR-TCE development and clinical application are significantly hindered by the instability of natural TCRs and immunosuppressive tumor microenvironment, underscoring the urgent need for alternative engineering strategies. Here, we describe a strategy that utilizes artificial cell membrane nanoparticle technology to generate a TCR nanovesicle antibody (TPC NV), which presents tumor-specific TCR, anti-CD3, and PD-1 antibodies on its membrane, representing a novel TCR-TCE with therapeutic efficacy against solid tumors. TPC NV binds to tumor cells through TCR, redirects tumor-infiltrating T cells via anti-CD3 antibodies, and reverses immunosuppression with anti-PD-1 antibodies, thereby inducing a broad-spectrum T cell response that effectively eliminates established tumors. Furthermore, epacadostat, an inhibitor of indoleamine 2,3-dioxygenase, can be loaded into TPC NV to suppress regulatory T cell (Treg) generation and enhance dendritic cell (DC) maturation by inhibiting tumor tryptophan metabolism. This dual action amplifies adaptive immune activation and triggers a robust systemic anti-tumor immune response.

Characterization of the aryl hydrocarbon receptor as a potential candidate to improve cancer T cell therapies

The efficacy of T-cell-based cancer therapies can be limited by the tumor microenvironment which can lead to T cell dysfunction. Multiple studies, particularly in murine models, have demonstrated the capacity of the aryl hydrocarbon receptor (AHR) to negatively regulate antitumor T cell functions. AHR is a cytoplasmic receptor and transcription factor that was originally identified as a xenobiotic sensor, but has since been shown to play a significant role in the gene regulation of various immune cells, including T cells. Given the insights from murine studies, AHR emerges as a promising candidate to invalidate for optimizing T cell-based cancer therapies. However, the controversial role of AHR in human T cells underscores the need for a more comprehensive characterization of AHR expressing T cells. This study aims to investigate the regulatory mechanisms of AHR in human T cell biology to better understand its impact on reducing antitumor immune responses. Here, we knocked-out AHR in human T cells using CRISPR-Cas9 technology to characterize AHR's function in an in vitro chronic stimulation model. Engineered T cells exhibited enhanced effector- and memory-like profiles and expressed reduced amount of CD39 and TIGIT. AHR knockout enhanced human CAR-T cells' functionality and persistence upon tumor chronic stimulation. Collectively, these results highlight the role of AHR in human CAR-T cells efficiency.

Reversing the immunosuppressive tumor microenvironment via "Kynurenine starvation therapy" for postsurgical triple-negative breast cancer treatment

Immunotherapy is a potential strategy to suppress the postoperative recurrence and metastasis of triple-negative breast cancer (TNBC). However, the excessive accumulation of kynurenine (Kyn) leads to immunosuppressive tumor microenvironment (TME) and impedes immunotherapeutic efficacy. Herein, a two-pronged approach through "Kynurenine Starvation Therapy" is proposed based on the in-situ hydrogel implantation for postsurgical treatment of TNBC. The hydrogel is constructed via Schiff base reaction between oxidized dextran (ODEX) and 8-arm poly(ethylene glycol) amine (8-arm PEG-NH2), which exhibits excellent biocompatibility and gradual biodegradability. The indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor NLG919 and kynureninase (KYNase) are noncovalently loaded into the hydrogel to prepare NLG919 + KYNase@Gel. The obtained hydrogel can sustainably release NLG919 and KYNase to synergistically deplete Kyn, thereby reversing immunosuppression to enhance the antitumor immunity within TME through "Kynurenine Starvation Therapy". Moreover, a single implantation of NLG919 + KYNase@Gel not only effectively inhibits the postoperative recurrence and metastasis in 4 T1 tumor-bearing mice, but also restrains the growth in an orthotopic TNBC mouse model. These findings highlight an innovative strategy to reinforce the antitumor immune response for the treatment of postsurgical TNBC.

Prognostic and predictive value of IDO expression in metastatic melanoma treated with Ipilimumab

BACKGROUND

The tumor microenvironment is crucial for prognosis and response to immunotherapy in several tumor entities.

METHODS

In a multicenter retrospective study, a total of 86 tumor samples from patients with metastatic melanoma were evaluated for baseline expression of indoleamine 2,3-dioxygenase (IDO) and programmed death ligand 1 (PD-L1). Expression patterns of IDO and PD-L1 on tumor cells and antigen-presenting cells (APCs) as determined by immunohistochemical (IHC) staining of paraffin-embedded tissue sections were correlated with response to ipilimumab and overall survival (OS). Statistical analysis was performed using the Spearman correlation, the Mann-Whitney test and Kaplan-Meier estimator.

RESULTS

IDO expression in tumor cells or APCs was not predictive for treatment response. The median OS was 26 months in IDO-positive and IDO-negative patients, regardless of IDO expression in tumor cells or APCs. A correlation of IHC expression scores of IDO and PD-L1 could not be documented.

CONCLUSION

The exact role of IDO in creating an immunosuppressive tumor environment and its reversal needs to be further elucidated.

Immunomodulatory mechanisms driving tumor escape in glioblastoma: The central role of IDO and tryptophan metabolism in local and systemic immunotolerance

BACKGROUND

Glioblastoma (GBM) is the most aggressive primary brain tumor exhibiting extensive immune evasion mechanisms that hinder effective therapeutic interventions. This narrative review explores the immunomodulatory pathways contributing to tumor escape in GBM, specifically focusing on the role of Tryptophan (TRP) metabolism and its downstream mediators Tryptophan metabolism through the kynurenine pathway (KP) is initiated by indoleamine 2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO2) enzymes and serves as a crucial mechanism for promoting an immunosuppressive microenvironments and systemic immunotolerance. Emerging evidence also indicates a non-enzymatic role for IDO1 signaling in these processes. The downstream effectors interact with immune cells, inducing local immunosuppression within the tumor microenvironment and altering peripheral immune responses.

METHODS

We systematically reviewed databases (MEDLINE via PubMed, Science Direct, and Embase) through October 2024 to highlight the interplay between local immune escape mechanisms and circulating immunotolerance, emphasizing the role of TRP metabolic enzymes in supporting GBM progression.

RESULTS

The literature review identified 99 records. TRP-related mechanisms play a central role in fostering immunotolerance in GBM. These phenomena involve intricate interactions between the infiltrating and circulating myeloid and lymphoid compartments, ultimately shaping a tolerant, pro-tumoral environment and the peripheral immunophenotype.

CONCLUSIONS

The biological activity of IDO1 and TRP metabolites positions these compounds as potential markers of disease activity and promising molecular targets for future therapeutic approaches.

Elevated initial blood kynurenine is associated with increased odds of post-stroke infection: Kynurenine and post-stroke infection

OBJECTIVE

Post-stroke infection is a leading cause of acute ischemic stroke mortality. Tryptophan metabolites can modulate the immune response. This study assesses the association between tryptophan metabolism and post-stroke infection.

METHODS

Whole blood from the University of Colorado Emergency Medicine Specimen Bank of acute ischemic stroke patients was collected within 72 hours of last known well. Mass spectrometry determined concentrations of tryptophan metabolites. Multivariate logistic regression modeled the association between post-stroke infection within 30 days and metabolite concentrations, controlling for age, sex, NIH stroke scale score, time to sample collection, smoking status, dysphagia, history of chronic kidney or end stage renal disease, and history of diabetes mellitus.

RESULTS

Of 73 subjects, 21 (28.8 %) developed a post-stroke infection. Those with or without a post-stroke infection had similar concentrations of tryptophan, kynurenic acid and quinolinic acid. Those who developed a post-stroke infection had higher mean concentrations of kynurenine (2.3μM, standard deviation 1.1μM) compared to those who did not develop a post-stroke infection (1.6μM , standard deviation 0.6μM, p = 0.01). The adjusted odds ratio of a post-stroke infection within 30 days was 3.94 (95 % Confidence Interval 1.40 - 11.11) for every 1μM increase in kynurenine concentration.

CONCLUSIONS

Increasing circulating kynurenine within 72 hours of ischemic stroke onset is associated with increased odds of developing a post-stroke infection within 30 days of emergency department admission. Understanding the causal mechanism of kynurenine promoting post-stroke infection may yield targeted therapeutics that reduce the morbidity and mortality of ischemic stroke.

The AhR/P38 MAPK pathway mediates kynurenine-induced cardiomyocyte damage: The dual role of resveratrol in apoptosis and autophagy

Chronic kidney disease increases the risk of cardiovascular disease, partly due to uremic toxins, such as Kynurenine (KYN). While KYN contributes to tissue damage, its role in cardiomyocyte apoptosis and autophagy remains unclear. Resveratrol (RSV) can protect against oxidative stress and inflammation, whereas its specific effects on KYN-induced cardiomyopathy are less understood. This study aimed to investigate the role of KYN in cardiomyocyte apoptosis and autophagy and examine the protective effects of RSV against KYN-induced damage. H9C2 cardiomyocytes were cultured and treated with KYN in presence or absence of RSV or inhibitors of the AhR/Src/MAPKs pathway. Cell viability, apoptosis, mitochondrial membrane potential, and autophagy were assessed using MTT, TUNEL, JC-1, and autophagy detection assays. KYN induced apoptosis, and autophagy in H9C2 cells. RSV pretreatment reduced apoptosis but enhanced autophagy in KYN-treated cells. Inhibiting autophagy or blocking apoptosis, increased KYN-induced apoptosis and autophagy, respectively. Additionally, KYN treatment enhanced AhR activation and the phosphorylation of Src and MAPKs proteins, whereas RSV pretreatment decreased AhR activation and ERK phosphorylation. Inhibitors of p38 MAPK and JNK reduced expression of apoptotic proteins. AhR inhibition also reduced the phosphorylation of p38 MAPK and expression of apoptotic proteins while it enhanced autophagy-related protein expression in KYN treated H9C2 cells. In conclusion, our findings suggest that KYN induces cardiomyocyte apoptosis via the AhR/p38 MAPK pathway whereas RSV can protect against the KYN-induced apoptosis while promoting autophagy. Given the high cardiovascular risk in CKD patients, these findings provide in-sight into potential therapeutic strategies targeting KYN-induced cardiomyopathy.

The aryl hydrocarbon receptor: a rehabilitated target for therapeutic immune modulation

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor originally identified as the target mediating the toxic effects of environmental pollutants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and dioxins. For years, AHR activation was actively avoided during drug development. However, the AHR was later identified as an important physiological regulator of the immune response. These findings triggered a paradigm shift that resulted in identification of the AHR as a regulator of both innate and adaptive immunity and outlined a pathway for its modulation by the diet, commensal flora and metabolism in the context of autoimmunity, cancer and infection. Moreover, the AHR was revealed as a candidate target for the therapeutic modulation of the immune response. Indeed, the first AHR-activating drug (tapinarof) was recently approved for the treatment of psoriasis. Clinical trials are underway to evaluate the effects of tapinarof and other AHR-targeting therapeutics in inflammatory diseases, cancer and infections. This Review outlines the molecular mechanism of AHR action, and describes how it regulates the immune response. We also discuss links to disease and AHR-targeting therapeutics that have been tested in past and ongoing clinical trials.

Kynurenine promotes the immune escape of colorectal cancer cells via NAT10-mediated ac4C acetylation of PD-L1

BACKGROUND

This study aimed to investigate the role of kynurenine in Colorectal Cancer (CRC) and the underlying mechanism.

METHODS

Enzyme-linked immunosorbent assay was employed to assess the kynurenine concentration. Flow cytometry was utilized to analyze the percentages of CD3+CD4+ and CD3+CD8+ T-cells. Immunofluorescence was used to measure the expression of Programmed Death-Ligand 1 (PD-L1). RNA modification levels in CRC cells were analyzed using a dot blot assay. The interaction between NAT10 and PD-L1 was assessed via RNA immunoprecipitation, dual-luciferase reporter, and immunofluorescence assays. A xenograft tumor rat model was established.

RESULTS

Results indicated that kynurenine suppressed T-cell activation and promoted immune escape. Besides, kynurenine promoted N-Acetyltransferase 10 (NAT10)-mediated N4-acetylcytidine (ac4C) modification. Moreover, NAT10 inhibition improved T-cell activation and suppressed immune escape. Mechanically, NAT10 is bound with the mRNA of PD-L1. Rescue experiments showed that PD-L1 inhibitor treatment reversed the suppressed T-cell activation and the promoted immune escape induced by NAT10 overexpression. In vivo, studies indicated that NAT10 deficiency reversed the promoted tumor growth induced by kynurenine treatment.

CONCLUSION

In conclusion, kynurenine promoted the immune escape of CRC cells via NAT10-mediated ac4C acetylation of PD-L1.

Not Indolamine 2,3-Dioxygenase Polymorphisms, but Low Levels of Indoleamine 2,3-Dioxygenase and IDO2 Are Associated with Behçet's Syndrome

OBJECTIVE

Behçet's syndrome (BS) is a multisystemic disorder with a complex genetic background. Indoleamine 2,3-dioxygenase (IDO) and IDO2, key enzymes in tryptophan metabolism, have immunomodulatory effects. Specific IDO and IDO2 polymorphisms may influence enzymatic activity. This study aimed to explore the association between IDO/IDO2 gene polymorphisms and BS susceptibility, and assess serum levels of IDO and IDO2 in relation to BS.

SUBJECTS AND METHODS

Ninety patients with BS and 52 healthy controls were enrolled in this study. Predetermined single-nucleotide polymorphisms (SNPs) were studied at specific gene loci for IDO and IDO2. Serum IDO and IDO2 levels were determined using ELISA.

RESULTS

No statistically significant differences were observed in the genotype and allele frequencies of IDO (rs7820268 and rs10108662) and IDO2 (rs4503083) between patients with BS and controls. Furthermore, no significant association was found between clinical findings and SNPs, except that the IDO rs7820268 CT genotype was significantly lower in patients with neurological involvement (0% vs. 42%, p = 0.026, OR = 0.147, 95% CI = 0.18-1.231). Serum levels of IDO and IDO2 were significantly lower in BS patients compared to controls (p < 0.0000 and p < 0.0001, respectively).

CONCLUSION

Our research revealed that the serum IDO/IDO2 levels of BS were substantially lower than those in the control group. This finding has the potential to impact IDO activity and reduce immune tolerance. No correlation was observed between IDO/IDO2 polymorphisms and most clinical findings of BS. However, the IDO rs7820268 CT genotype was significantly reduced in neuro-BS, suggesting a protective effect. Larger prospective trials are needed to further explore these findings.

Indoleamine 2,3-dioxygenase 1-mediated immune suppressive status is positively associated with brain metastasis in patients with non-small cell lung cancer

Background

Indoleamine 2,3-dioxygenase (IDO1) activity, measured by kynurenine/tryptophan (K:T) ratio, is known for its association with distant metastasis and overall survival (OS) in patients with non-small cell lung cancer (NSCLC). Here, we aimed to examine whether IDO1 activity is correlated with OS in NSCLC patients with brain metastasis (Bramet) and has negative effect on modulating the anti-tumor functions of immune cells.

Methods

This study was a part of a prospective clinical trial in circulating biomarkers. Blood or tissues from eligible participants were collected for measurement of kynurenine, tryptophan, immune cell subtype, scRNA-seq analysis, and untargeted metabolomics analysis.

Results

A total of 195 patients were enrolled. The median kynurenine to tryptophan (K:T) ratio was 0.18, with consistent values observed among patients with NSCLC Bramet and those without (0.18 and 0.11, respectively). Notably, student's t-test analysis revealed significantly higher kynurenine concentrations in stage IV patients compared to those in stage I (2.3 vs 1.7 µM, P < 0.001). In patients with Bramet, both kynurenine concentrations and K:T ratios were significantly elevated in comparison with those of extra-cerebral metastasis (2.7 vs 1.9 µM, P < 0.001; 0.12 vs 0.095, P = 0.028; respectively). Single-cell analysis further validated a high level of IDO1 expression in stage IV tumors or Bramet lesions, particularly in macrophages, regulated by chemokines such as CXCL11. Additionally, K:T ratios exhibited significant associations with Treg cell percentages and OS in patients with Bramet (P = 0.039). Treatment with kynurenine led to the upregulation of immune-suppressive molecules, including PD-1, in T cells. Finally, untargeted metabolomics analysis further identified that, apart from the IDO1 metabolic pathway, other metabolites, such as those involved in phospholipid pathways, were also implicated in Bramet.

Conclusion

IDO1 metabolites may play immune-suppressive roles in NSCLC patients with Bramet.

Using the Key Characteristics Framework to Unlock the Mysteries of Aryl Hydrocarbon Receptor-Mediated Effects on the Immune System

Initially discovered for its role mediating the deleterious effects of environmental contaminants, the aryl hydrocarbon receptor (AHR) is now known to be a crucial regulator of the immune system. The expanding list of AHR ligands includes synthetic and naturally derived molecules spanning pollutants, phytochemicals, pharmaceuticals, and substances derived from amino acids and microorganisms. The consequences of engaging AHR vary, depending on factors such as the AHR ligand, cell type, immune challenge, developmental state, dose, and timing of exposure relative to the immune stimulus. This review frames this complexity using the recently identified key characteristics of agents that affect immune system function (altered cell signaling, proliferation, differentiation, effector function, communication, trafficking, death, antigen presentation and processing, and tolerance). The use of these key characteristics provides a scaffold for continued discovery of how AHR and its myriad ligands influence the immune system, which will help harness the power of this enigmatic receptor to prevent or treat disease.

Myeloid cells: key players in tumor microenvironments

Cancer is the result of evolving crosstalk between neoplastic cell and its immune microenvironment. In recent years, immune therapeutics targeting T lymphocytes, such as immune checkpoint blockade (ICB) and CAR-T, have made significant progress in cancer treatment and validated targeting immune cells as a promising approach to fight human cancers. However, responsiveness to the current immune therapeutic agents is limited to only a small proportion of solid cancer patients. As major components of most solid tumors, myeloid cells played critical roles in regulating the initiation and sustentation of adaptive immunity, thus determining tumor progression as well as therapeutic responses. In this review, we discuss emerging data on the diverse functions of myeloid cells in tumor progression through their direct effects or interactions with other immune cells. We explain how different metabolic reprogramming impacts the characteristics and functions of tumor myeloid cells, and discuss recent progress in revealing different mechanisms-chemotaxis, proliferation, survival, and alternative sources-involved in the infiltration and accumulation of myeloid cells within tumors. Further understanding of the function and regulation of myeloid cells is important for the development of novel strategies for therapeutic exploitation in cancer.

Discovery and Optimization of Novel Apo-IDO1 Inhibitors by a Pharmacophore-Based Structural Simplification Strategy

Indoleamine 2,3-dioxygenase-1 (IDO1) plays a crucial role in tumor immune escape. However, the limited clinical efficacy of traditional IDO1 inhibitors has impeded their further development. Recently, apo-IDO1 inhibitors that displace the heme to target IDO1 have been discovered, which exhibits a slow dissociation rate reminiscent of irreversible inhibitors. This characteristic suggests sustained target engagement, offering a pharmacodynamic advantage. Therefore, the development of apo-IDO1 inhibitors emerges as a promising strategy in the field of IDO1-related studies. Here, we present the identification of the thienopyrimidine derivative XW-001 through structure-based virtual screening, followed by an iterative optimization process that led to the development of XW-032. XW-032 exhibited remarkable in vitro inhibitory activity against apo-IDO1 (IC50 = 21 ± 5 nM) through a pharmacophore-guided structural simplification approach. Notably, XW-032 (TGI = 63%) exhibited potent in vivo antitumor efficacy in the CT26 syngeneic mouse model, highlighting the benefits of apo-IDO1 inhibitors for tumor immunotherapy.

AHR Agonist ITE Boosted PD1 Antibody's Effects by Inhibiting Myeloid-Derived Cells Suppressive Cells in an Orthotopic Mouse Glioma Model

Background: Glioblastoma is "cold". Consequently, immune checkpoint blockade therapy has failed to improve patients' survival, which is negatively correlated with patients' peripheral MDSC counts. AHR is known to mediate immune-suppressive functions of certain tryptophan metabolites such as kynurenine; yet, there lack of reports on how AHR agonists affect glioma immunity. Methods/Objectives: We hypothesized that ITE could synergize with PD1 antibody as AHR is one major node of immune-suppressive pathways, and tested it using an immune-competent mouse glioma model. Results: The combination of ITE+PD1 antibody glioma MDSC was significantly reduced, along with increased infiltration of the CD4-CD8+ and CD4+CD8+ T cells, leading to extended mouse survival. ITE treatment alone significantly reduces the infiltration of CD11b+Ly6G+Ly6Clo cells, namely PMN-MDSCs, and neutrophils, while the combination with PD1 antibody significantly reduces all MDSCs plus neutrophils. The presence of ITE inhibits the expression of IL11 and the in vitro induction of MDSCs from mouse PBMCs by IL11. The identification of the ITE-AHR-IL11-MDSC pathway provides more mechanistic insights into AHR's effects. The fact that ITE, which is otherwise immune-suppressive, can activate immunity in glioma indicates that searching for drugs targeting AHR should go beyond antagonists.

Construction of a risk model associated with tryptophan metabolism and identification of related molecular subtypes in laryngeal squamous cell carcinoma

Catabolic metabolites of tryptophan (Trp) are considered to be important microenvironmental factors by suppressing anti-tumor immune responses in cancers. Nevertheless, the effect of Trp metabolism (Trp metabolism)-related genes Trp metabolism-related genes on laryngeal squamous cell carcinoma (LSCC) progression is not yet clear. So, in this study, the TCGA-LSCC, GSE27020, and 40 TMRGs were extracted via public databases to explore the effects of TMRGs on laryngeal squamous cell carcinoma. Firstly, Weighted Gene Co-expression Network Analysis (WGCNA) was adopted with LSCC samples in TCGA-LSCC to acquire key module, and differentially expressed genes between LSCC and normal samples from TCGA-LSCC were yielded via differential expression analysis. Next, differentially expressed TMRGs (DE-TMRGs) was obtained in key model and DEGs, and prognostic genes were identifde through multiple algorithms. Five prognostic genes, namely SERPINA1, TMC8, RENBP, SDS and FAM107A were finally identified. A risk model was established based on the expressions of prognostic genes and survival information of LSCC samples while that were divided into high and low risk groups. Obviously, the LSCC immune dysfunction and exclusion score of high-risk patients was dramatically higher than that in low-risk patients, indicating that patients in the high-risk subgroup exhibited reduced responsiveness to immunotherapy. Besides, the drug sensitivity analysis showed that the low -risk subgroup was notably sensitive to Salubrinal, Lenalidomide, Metformin, while high -risk subgroup was more responsive to Docetaxel, AUY922, Embelin. Eventually, two clusters of LSCC samples had notable correlations with LSCC prognosis. The above results indicated that the risk model consisted of TMRGs (SERPINA1, TMC8, RENBP, SDS and FAM107A) was constructed in LSCC, contributing to studies related to the prognosis and treatment of LSCC.

Targeting tumor-associated macrophages in colon cancer: mechanisms and therapeutic strategies

Colon cancer (CC) remains a primary contributor to cancer-related fatalities worldwide, driven by difficulties in early diagnosis and constrained therapeutic options. Recent studies underscore the importance of the tumor microenvironment (TME), notably tumor-associated macrophages (TAMs), in fostering malignancy progression and therapy resistance. Through their inherent plasticity, TAMs facilitate immunosuppression, angiogenic processes, metastatic spread, and drug tolerance. In contrast to M1 macrophages, which promote inflammatory and tumoricidal responses, M2 macrophages support tumor expansion and dissemination by exerting immunosuppressive and pro-angiogenic influences. Consequently, manipulating TAMs has emerged as a potential avenue to enhance treatment effectiveness. This review outlines the origins, polarization states, and functions of TAMs in CC, highlights their role in driving tumor advancement, and surveys ongoing efforts to target these cells for better patient outcomes. Emerging therapeutic strategies aimed at modulating TAM functions - including depletion strategies, reprogramming approaches that shift M2-polarized TAMs toward an M1 phenotype, and inhibition of key signaling pathways sustaining TAM-mediated immunosuppression-are currently under active investigation. These approaches hold promise in overcoming TAM - induced resistance and improving immunotherapeutic efficacy in CC.

Restoring immune tolerance in pre-RA: immunometabolic dialogue between gut microbiota and regulatory T cells

Rheumatoid arthritis (RA) is a complex chronic autoimmune disease that remains incurable for most patients. With advances in our understanding of the disease's natural history, the concept of pre-RA has emerged as a window of opportunity to intervene before irreversible joint damage occurs. Numerous studies have indicated that the key step driving autoimmunity in early pre-RA lies at an extra-articular site, which is closely related to the regulatory T (Treg) cell-established immune tolerance to the gut microbiota. The intricate immunometabolic crosstalk between Treg cells and the gut microbiota is beginning to be understood, with the re-recognition of Treg cells as metabolic sensors in recent years. In the future, deciphering their immunometabolic dialogue may help to elucidate the underlying mechanisms of pre-RA. Identifying novel biological pathways in the pre-RA stage will bring insights into restoring immune tolerance, thereby potentially curing or preventing the onset of RA.

Tryptophan-2,3-Dioxygenase as a Therapeutic Target in Digestive System Diseases

Tryptophan (Trp) is an essential amino acid that must be acquired exclusively through dietary intake. The metabolism of tryptophan plays a critical role in maintaining immune homeostasis and tolerance, as well as in preventing excessive inflammatory responses. Tryptophan-2,3-dioxygenase (TDO2) is a tetrameric heme protein and serves as one of the pivotal rate-limiting enzymes in the first step of tryptophan metabolism. Dysregulation of TDO2 expression has been observed in various digestive system diseases, encompassing those related to the oral cavity, esophagus, liver, stomach, pancreas, and colon and rectum. Digestive system diseases are the most common clinical diseases, with complex clinical manifestations and interrelated symptoms, and have become a research hotspot in the field of medicine. Studies have demonstrated that aberrant TDO2 expression is closely associated with various clinical manifestations and disease outcomes in patients with digestive system disorders. Consequently, TDO2 has garnered increasing recognition as a promising therapeutic target for digestive system diseases in recent years, attracting growing attention. This article provides a brief overview of the role of TDO2 in the tryptophan pathway, emphasizing its significant involvement in diseases of the digestive system. Strategies targeting TDO2 through specific inhibitors suggest considerable promise in enhancing therapeutic outcomes for digestive diseases. Thus, this review concludes by discussing recent advancements in the development of TDO2 inhibitors. We believe that targeted inhibition of TDO2 combined with immunotherapy, the screening of a large number of natural products, and the assistance of artificial intelligence in drug design will be important directions for developing more effective TDO2 inhibitors and improving treatment outcomes in the future.

Impact of immune cell metabolism on membranous nephropathy and prospective therapy

Membranous nephropathy (MN) is a primary glomerular disease commonly causing adult nephrotic syndrome. Characterized by thickened glomerular capillary walls due to immune complex deposition, MN is a complex autoimmune disorder. Its pathogenesis involves immune deposit formation, complement activation, and a heightened risk of renal failure. Central to MN is immune system dysfunction, particularly the dysregulation of B and T cell responses. B cells contribute to renal injury through the production of autoantibodies, particularly IgG targeting the phospholipase A2 receptor (PLA2R) on podocytes, while T cells modulate immune responses that influence disease progression. Metabolic reprogramming alters lymphocyte survival, differentiation, proliferation, and function, potentially triggering autoimmune processes. Although the link between immune cell metabolism and MN remains underexplored, this review highlights recent advances in understanding immune metabolism and its role in MN. These insights may provide novel biomarkers and therapeutic strategies for MN treatment.

Exploring effects of gut microbiota on tertiary lymphoid structure formation for tumor immunotherapy

Anti-tumor immunity, including innate and adaptive immunity is critical in inhibiting tumorigenesis and development of tumor. The adaptive immunity needs specific lymph organs such as tertiary lymphoid structures (TLSs), which are highly correlated with improved survival outcomes in many cancers. In recent years, with increasing attention on the TLS in tumor microenvironment, TLSs have emerged as a novel target for anti-tumor therapy. Excitingly, studies have shown the contribution of TLSs to the adaptive immune responses. However, it is unclear how TLSs to form and how to more effectively defense against tumor through TLS formation. Recent studies have shown that the inflammation plays a critical role in TLS formation. Interestingly, studies have also found that gut microbiota can regulate the occurrence and development of inflammation. Therefore, we here summarize the potential effects of gut microbiota- mediated inflammation or immunosuppression on the TLS formation in tumor environments. Meanwhile, this review also explores how to manipulate mature TLS formation through regulating gut microbiota/metabolites or gut microbiota associated signal pathways for anti-tumor immunity, which potentially lead to a next-generation cancer immunotherapy.

The aryl hydrocarbon receptor controls IFN-γ-induced immune checkpoints PD-L1 and IDO via the JAK/STAT pathway in lung adenocarcinoma

While immunotherapy has shown some efficacy in lung adenocarcinoma (LUAD) patients, many respond only partially or not at all. One limitation in improving outcomes is the lack of a complete understanding of immune checkpoint regulation. Here, we investigated a possible link between an environmental chemical receptor implicated in lung cancer and immune regulation, the AhR, a known but counterintuitive mediator of immunosuppression (interferon (IFN)-γ), and regulation of two immune checkpoints (PD-L1 and IDO). AhR gene-edited LUAD cell lines, a syngeneic LUAD mouse model, bulk and scRNA sequencing of LUADs and tumor-infiltrating T cells were used to map out a signaling pathway leading from IFN-γ through the AhR to JAK/STAT, PD-L1, IDO, and tumor-mediated immunosuppression. The data demonstrate that: (1) IFN-γ activation of the JAK/STAT pathway leading to PD-L1 and IDO1 up-regulation is mediated by the AhR in murine and human LUAD cells, (2) AhR-driven IDO1 induction results in the production of Kynurenine (Kyn), an AhR ligand, which likely mediates an AhR→IDO1→Kyn→AhR amplification loop, (3) transplantation of AhR-knockout LUAD cells results in long-term tumor immunity in most recipients. (4) The 23% of AhR-knockout tumors that do grow do so at a much slower pace than controls and exhibit higher densities of CD8+ T cells expressing markers of immunocompetence, increased activity, and increased cell-cell communication. The data definitively link the AhR to IFN-γ-induced JAK/STAT pathway and immune checkpoint-mediated immunosuppression and support the targeting of the AhR in the context of LUAD.

N-formylkynurenine but not kynurenine enters a nucleophile-scavenging branch of the immune-regulatory kynurenine pathway

Tryptophan catabolism along the kynurenine pathway (KP) mediates key physiological functions ranging from immune tolerance to lens UV protection, but the contributory roles and chemical fates of individual KP metabolites are incompletely understood. This particularly concerns the first KP metabolite, N-formylkynurenine (NFK), canonically viewed as a transient precursor to the downstream kynurenine (KYN). Here, we challenge that canon and show that hydrolytic enzymes act as a rheostat switching NFK's fate between the canonical KP and a novel non-enzymatic branch of tryptophan catabolism. In the physiological environment (37 °C, pH 7.4), NFK deaminated into electrophilic NFK-carboxyketoalkene (NFK-CKA), which rapidly (<2 min) formed adducts with nucleophiles such as cysteine and glutathione, the key intracellular antioxidants. Serum hydrolases suppressed NFK deamination as they hydrolysed NFK to KYN ∼3 times faster than NFK deaminates. Whilst KYN did not deaminate, its deaminated product (KYN-CKA) rapidly reacted with cysteine but not glutathione. The new NFK transformations of a yet to be discovered function highlight NFK's significance beyond hydrolysis to KYN and suggests the dominance of its chemical transformations over those of KYN. Enzyme compartmentalisation and abundance offer insights into the regulation of non-enzymatic KP metabolite transformations such as KYN involved in immune regulation, protein modification, lens aging or neuropathology.

The role of the AHR in host-pathogen interactions

Host-microorganism encounters take place in many different ways and with different types of outcomes. Three major types of microorganisms need to be distinguished: (1) pathogens that cause harm to the host and must be controlled; (2) environmental microorganisms that can be ignored but must be controlled at higher abundance; and (3) symbiotic microbiota that require support by the host. Recent evidence indicates that the aryl hydrocarbon receptor (AHR) senses and initiates signalling and gene expression in response to a plethora of microorganisms and infectious conditions. It was originally identified as a receptor that binds xenobiotics. However, it was subsequently found to have a critical role in numerous biological processes, including immunity and inflammation and was recently classified as a pattern recognition receptor. Here we review the role of the AHR in host-pathogen interactions, focusing on AHR sensing of different microbial classes, the ligands involved, responses elicited and disease outcomes. Moreover, we explore the therapeutic potential of targeting the AHR in the context of infection.

The Kynurenine Pathway and Indole Pathway in Tryptophan Metabolism Influence Tumor Progression

Tryptophan (Trp), an essential amino acid, is solely acquired through dietary intake. It is vital for protein biosynthesis and acts as a precursor for numerous key bioactive compounds. The Kynurenine Pathway and the Indole Pathway are the main metabolic routes and are extensively involved in the occurrence and progression of diseases in the digestive, nervous, and urinary systems. In the Kynurenine Pathway, enzymes crucial to tryptophan metabolism, indoleamine-2,3-dioxygenase 1 (IDO1), IDO2, and Trp-2,3-dioxygenase (TDO), trigger tumor immune resistance within the tumor microenvironment and nearby lymph nodes by depleting Trp or by activating the Aromatic Hydrocarbon Receptor (AhR) through its metabolites. Furthermore, IDO1 can influence immune responses via non-enzymatic pathways. The Kynurenine Pathway exerts its effects on tumor growth through various mechanisms, including NAD+ regulation, angiogenesis promotion, tumor metastasis enhancement, and the inhibition of tumor ferroptosis. In the Indole Pathway, indole and its related metabolites are involved in gastrointestinal homeostasis, tumor immunity, and drug resistance. The gut microbiota related to indole metabolism plays a critical role in determining the effectiveness of tumor treatment strategies and can influence the efficacy of immunochemotherapy. It is worth noting that there are conflicting effects of the Kynurenine Pathway and the Indole Pathway on the same tumor phenotype. For example, different tryptophan metabolites affect the cell cycle differently, and indole metabolism has inconsistent protective effects on tumors in different regions. These differences may hold potential for enhancing therapeutic efficacy.

Immunometabolism of Liver Xenotransplantation and Prospective Solutions

End-stage liver diseases, such as hepatocellular carcinoma or acute liver failure, critically necessitate liver transplantation. However, the shortage of available organ donors fails to meet the rapidly growing transplantation demand. Due to the high similarity of liver tissue structure and metabolism between miniature pigs and humans, xenotransplantation of pig livers is considered as a potentially viable solution to organ scarcity. In the 2024, teams from China first time have successfully transplanted a genetically modified Bama miniature pig liver into a clinically brain-dead man lasting for 10 days. This milestone in human xenotransplantation research not only confirms the feasibility of clinical application of xenotransplantation, but also underscores the daunting and protracted nature of this pathway. Despite advanced gene-editing technologies theoretically circumventing the occurrence of most transplant rejection reactions, patients still face challenges such as chronic immune rejection, coagulation disorders, and thrombotic microangiopathy after receiving xenografts. Moreover, prolonged use of immunosuppressive drugs may induce irreversible immune dysfunction, leading to opportunistic infections and metabolic disorders. This article compares the similarities and differences in livers between humans and pigs, summarizes the immunometabolism of xenotransplantation based on current findings, and provides research perspectives on pre-transplantation and post-transplantation strategies for prolonging the survival time of xenografts.

Metabolic T-cell phenotypes: from bioenergetics to function

It is well known that T-cell metabolism and function are intimately linked. Metabolic reprogramming is a dynamic process that provides the necessary energy and biosynthetic precursors while actively regulating the immune response of T cells. As such, aberrations and dysfunctions in metabolic (re)programming, resulting in altered metabolic endotypes, may have an impact on disease pathology in various contexts. With the increasing demand for personalized and highly specialized medicine and immunotherapy, understanding metabolic profiles and T-cell subset dependence on specific metabolites will be crucial to harness the therapeutic potential of immunometabolism and T cell bioenergetics. In this review, we dissect metabolic alterations in different T-cell subsets in autoimmune and viral inflammation, T cell and non-T-cell malignancies, highlighting potential anchor points for future treatment and therapeutic exploitation.

Cooperative Hedgehog/GLI and JAK/STAT signaling drives immunosuppressive tryptophan/kynurenine metabolism via synergistic induction of IDO1 in skin cancer

BACKGROUND

Pharmacological targeting of Hedgehog (HH)/GLI has proven effective for certain blood, brain and skin cancers including basal cell carcinoma (BCC). However, limited response rates and the development of drug resistance call for improved anti-HH therapies that take synergistic crosstalk mechanisms and immune evasion strategies into account. In previous work, we demonstrated that cooperation of HH/GLI and Interleukin 6 (IL6)/STAT3 signaling drives BCC growth. Whether synergistic HH-IL6 signaling promotes BCC via the activation of immune evasion mechanisms remained unclear.

METHODS

HH-IL6 regulated immunosuppressive genes such as indoleamine 2,3-dioxygenase 1 (IDO1) were identified by gene expression profiling. IDO1 expression was evaluated in human BCC and melanoma models by qPCR and Western blot analyses. The cis-regulatory region of IDO1 was interrogated for HH-IL6-regulated GLI and STAT transcription factor binding and epigenetic modifications by targeted chromatin-immunoprecipitation and bisulfite pyrosequencing. Functional analyses of the immunosuppressive effects of IDO1 involved HPLC-MS measurements of its metabolites and the assessment of T cell proliferation via flow cytometry. Bioinformatic analyses of GLI-STAT cooperation were conducted on published bulk and single-cell RNA-seq data of human BCC and melanoma patients.

RESULTS

We identified IDO1 as a target gene of cooperative GLI-STAT activity in BCC and melanoma. GLI1 and STAT3 transcription factors synergistically enhanced IDO1 expression by jointly binding to the cis-regulatory region of IDO1 and by increasing active chromatin marks at the histone level. In human melanoma cells, inhibition of GLI1 expression prevented the induction of IDO1 expression in response to IL6/STAT3 and IFNγ/STAT1 signaling. Pharmacological targeting of HH/GLI signaling reduced IDO1 expression, resulting in decreased production of the immunosuppressive metabolite kynurenine. Further, inhibition of GLI1 enhanced the efficacy of the selective IDO1 inhibitor epacadostat and rescued T cell proliferation by attenuating IDO1/kynurenine-mediated immunosuppression. Elevated expression of IDO1 correlated with active HH/GLI and JAK/STAT signaling in skin cancer patients supporting the clinical relevance of the mechanistic data presented.

CONCLUSIONS

These results identify the immunosuppressive IDO1-kynurenine pathway as a novel pro-tumorigenic target of oncogenic GLI and STAT1/STAT3 cooperation. Our data suggest simultaneous pharmacological targeting of these signaling axes as rational combination therapy in melanoma and non-melanoma skin cancers.

The Aryl Hydrocarbon Receptor (AHR): Peacekeeper of the Skin

In the last decade, the aryl hydrocarbon receptor (AHR) has emerged as a critical peacekeeper for the maintenance of healthy skin. The evolutionary conservation of AHR implied physiological functions for this receptor, beyond the detoxification of man-made compounds, a notion further supported by the existence of physiological AHR ligands, notably derivates of tryptophan by the host and host microbiome. The UV light-derived ligand, 6-formylindolo[3,2-b]carbazole (FICZ), anticipated a role for AHR in skin, a UV light-exposed organ, where physiological AHR activation promotes a healthy skin barrier and constrains inflammation. The clinical development of tapinarof, the first topical AHR modulating drug for inflammatory skin disease, approved by the FDA for mild-to-moderate psoriasis and poised for approval in atopic dermatitis, supports the therapeutic targeting of the AHR pathway to harness its beneficial effect in skin inflammation. Here, we describe how a tightly controlled, physiological activation of the AHR pathway maintains skin homeostasis, and discuss how the pathway is dysregulated in psoriasis and atopic dermatitis, identifying areas offering opportunities for alternative therapeutic approaches, for further investigation.

The Role of Aryl Hydrocarbon Receptor in Skin Homeostasis: Implications for Therapeutic Strategies in Skin Disorders

The aryl hydrocarbon receptor (AhR), a ligand-activated transcription factor, is extensively expressed in diverse human organs and plays a pivotal role in mediating the onset, progression, and severity of numerous diseases. Recent research has explored the substantial impact of AhR on skin homeostasis and related pathologies. As a multi-layered organ, the skin comprises multiple cell populations that express AhR. In this review, we introduce the role of AhR in various skin cells and its impact on skin barrier function. Furthermore, we explore the involvement of AhR in the development of various skin diseases, highlighting its potential as a therapeutic target for skin disorders. By targeting AhR, we may open new avenues for the development of novel and efficient skin disease treatments.

Constitutive loss of kynurenine-3-monooxygenase changes circulating kynurenine metabolites without affecting systemic energy metabolism

Kynurenic acid (KYNA) and quinolinic acid (QUIN) are metabolites of the kynurenine pathway of tryptophan degradation with opposing biological activities in the central nervous system. In the periphery, KYNA is known to positively affect metabolic health, whereas the effects of QUIN remain less explored. Interestingly, metabolic stressors, including exercise and obesity, differentially change the balance between circulating KYNA and QUIN. Here, we hypothesized that chronically elevated levels of circulating KYNA and reduced levels of QUIN would manifest as differences in whole body energy metabolism. To test this, we used a mouse model lacking the enzyme kynurenine 3-monooxygenase (KMO), thus shunting kynurenine away from QUIN synthesis and toward KYNA production. KMO-deficient and wild-type littermate male and female mice were evaluated under chow and high-fat diets. Comprehensive kynurenine pathway metabolite profiling in plasma showed that the loss of KMO elicits robust changes in circulating levels of kynurenine metabolites. This included a 45-fold increase in kynurenine, a 26-fold increase in KYNA, and a 99% decrease in QUIN levels, depending on the diet. However, despite these changes, loss of KMO did not significantly impact whole body energy metabolism or change the transcriptomic profile of subcutaneous adipose tissue on either diet. With KMO inhibitors being considered therapeutic candidates for various disorders, this work shows that chronic systemic KMO inhibition does not have widespread metabolic effects. Our data also indicate that the beneficial effects of KYNA on metabolism may depend on its acute, intermittent elevation in circulation, akin to transient exercise-induced signals that mediate improved metabolic health.NEW & NOTEWORTHY The kynurenine pathway of tryptophan degradation is influenced by metabolic stressors: exercise raises circulating KYNA levels, while obesity is linked to increased QUIN. We investigated whether a mouse model lacking KMO-leading to increased circulating KYNA and decreased QUIN-would exhibit changes in energy metabolism. We found that energy metabolism was largely unaffected despite robust changes in circulating kynurenine metabolites, suggesting that systemic KMO inhibition may not have widespread metabolic effects.

Type 2 conventional dendritic cell functional heterogeneity: ontogenically committed or environmentally plastic?

Conventional dendritic cells (cDCs) are sentinels of the mammalian immune system that sense a wide range of danger and homeostatic signals to induce appropriately targeted T cell immune responses. Traditionally classified into two main subsets, cDC1 and cDC2, recent research shows that cDC2s exhibit significant heterogeneity and can be further subdivided. Studies in mice and humans show that, beyond their ontogeny, cDC2s acquire dynamic and tissue-specific characteristics that are influenced by local environmental signals, which impact on their functions during homeostasis, inflammation, and infection. The novel concept is proposed that tissue-derived signals and tissue plasticity can override preestablished developmental programming, thereby redefining developmental trajectories and cDC2 functionality. Ultimately, understanding cDC2 heterogeneity and plasticity has important implications for modulating T cell immunity in health and disease.

Navigating the metabolic landscape of regulatory T cells: from autoimmune diseases to tumor microenvironments

Regulatory T cells (Tregs) are essential for maintaining immune homeostasis, playing crucial roles in modulating autoimmune conditions and contributing to the suppressive tumor microenvironment. Their cellular metabolism governs their generation, stability, proliferation, and suppressive function. Enhancing Treg metabolism to boost their suppressive function offers promising therapeutic potential for alleviating inflammatory symptoms in autoimmune diseases. Conversely, inhibiting Treg metabolism to reduce their suppressive function can enhance the efficacy of traditional immunotherapy in cancer patients. This review explores recent advances in targeting Treg metabolism in autoimmune diseases and the metabolic adaptations of Tregs within the tumor microenvironment that increase their immunosuppressive function.

How the early life microbiome shapes immune programming in childhood asthma and allergies

Despite advances in our understanding of their diagnosis and treatment, pediatric allergies impose substantial burdens on affected children, families, and healthcare systems. Further, the prevalence of allergic diseases has dramatically increased over the past half-century, leading to additional concerns and concerted efforts to identify the origins, potential predictors and preventions, and therapies of allergic diseases. Together with the increase in allergic diseases, changes in lifestyle and early-life environmental influences have corresponded with changes in colonization patterns of the infant gut microbiome. The gut microbiome plays a key role in developing the immune system, thus greatly influencing the development of allergic disease. In this review, we specifically highlight the importance of the proper maturation and composition of the gut microbiome as an essential step in healthy child development or disease progression. By exploring the intertwined development of the immune system and microbiome across pediatric allergic diseases, we provide insights into potential novel strategies for their prevention and management.

Aromatic Amino Acid Metabolites: Molecular Messengers Bridging Immune-Microbiota Communication

Aromatic amino acid (AAA) metabolites, derived from tryptophan, phenylalanine, and tyrosine through coordinated host and microbial metabolism, have emerged as critical modulators of immune function. We examine the complex journey of AAAs from dietary intake through intestinal absorption and metabolic transformation, highlighting the crucial role of host-microbe metabolic networks in generating diverse immunomodulatory compounds. This review provides a unique integrative perspective by mapping the molecular mechanisms through which these metabolites orchestrate immune responses. Through detailed analysis of metabolite-receptor and metabolite-transporter interactions, we reveal how specific molecular recognition drives cell type-specific immune responses. Our comprehensive examination of signaling networks-from membrane receptor engagement to nuclear receptor activation to post-translational modifications- demonstrates how the same metabolite can elicit distinct functional outcomes in different immune cell populations. The context-dependent nature of these molecular interactions presents both challenges and opportunities for therapeutic development, particularly in inflammatory conditions where metabolite signaling pathways are dysregulated. Understanding the complexity of these regulatory networks and remaining knowledge gaps is fundamental for advancing metabolite-based therapeutic strategies in immune-mediated disorders.

Functional regulation of cytotoxic T cells by gut microbial metabolites

Metabolites from gut microbes have a wide range of functions within the host body. One important function of these metabolites is to either positively or negatively control CD8+ cytotoxic T lymphocytes (CTLs), which can kill cancer and virus-infected cells. In healthy conditions, gut microbes produce a mixture of metabolites that promote CTL activity but also suppress excessive inflammatory responses. However, gut microbial dysbiosis occurs in patients with cancer, and this leads to changes in the production of gut microbial metabolites that can suppress CTL activity, promote inflammatory responses, and/or aid cancer growth. Decreased levels of CTL-promoting metabolites such as short-chain fatty acids, indole metabolites and polyamines but increased levels of CTL-suppressing metabolites, such as certain bile acids along with oncogenic metabolites, have been observed in patients with cancer. This review summarizes the altered production of major microbial metabolites in patients with cancer and discusses the impact of these changes on anti-cancer CTL responses.

Global Trends in Research of Amino Acid Metabolism in T Lymphocytes in Recent 15 Years: A Bibliometric Analysis

Amino acid metabolism in T cells determines the therapeutic efficacy of T-cell-targeting drugs. To assess the direction of amino acid metabolism in T cells and construct related knowledge structure, we performed a bibliometric analysis aiming at amino acid metabolism in T cells utilizing studies publicized in recent 15 years. Three hundred thirty-seven related studies were downloaded from the Web of Science Core Collection (WoSCC), and the information on countries, institutes, and authors was collected and analyzed. In addition, the present research status and future trends were explored according to the results yielded from the analysis of cited references and keywords. This study revealed that publications regarding amino acid metabolism in T cells gradually increased each year. The USA is the top producer and most influential country in this field. Recent research has focused on the correlation between the metabolism of several amino acids and regulatory T cells (Tregs) and CD8+ T cells. Overall, this research offers a comprehensive exhibition on the field of amino acid metabolism in T cells, which will help researchers to study this domain more effectively and intuitively.

Nanomaterial-enabled metabolic reprogramming strategies for boosting antitumor immunity

Immunotherapy has become a crucial strategy in cancer treatment, but its effectiveness is often constrained. Most cancer immunotherapies focus on stimulating T-cell-mediated immunity by driving the cancer-immunity cycle, which includes tumor antigen release, antigen presentation, T cell activation, infiltration, and tumor cell killing. However, metabolism reprogramming in the tumor microenvironment (TME) supports the viability of cancer cells and inhibits the function of immune cells within this cycle, presenting clinical challenges. The distinct metabolic needs of tumor cells and immune cells require precise and selective metabolic interventions to maximize therapeutic outcomes while minimizing adverse effects. Recent advances in nanotherapeutics offer a promising approach to target tumor metabolism reprogramming and enhance the cancer-immunity cycle through tailored metabolic modulation. In this review, we explore cutting-edge nanomaterial strategies for modulating tumor metabolism to improve therapeutic outcomes. We review the design principles of nanoplatforms for immunometabolic modulation, key metabolic pathways and their regulation, recent advances in targeting these pathways for the cancer-immunity cycle enhancement, and future prospects for next-generation metabolic nanomodulators in cancer immunotherapy. We expect that emerging immunometabolic modulatory nanotechnology will establish a new frontier in cancer immunotherapy in the near future.

Metabolic Signaling in the Tumor Microenvironment

Cancer cells must reprogram their metabolism to sustain rapid growth. This is accomplished in part by switching to aerobic glycolysis, uncoupling glucose from mitochondrial metabolism, and performing anaplerosis via alternative carbon sources to replenish intermediates of the tricarboxylic acid (TCA) cycle and sustain oxidative phosphorylation (OXPHOS). While this metabolic program produces adequate biosynthetic intermediates, reducing agents, ATP, and epigenetic remodeling cofactors necessary to sustain growth, it also produces large amounts of byproducts that can generate a hostile tumor microenvironment (TME) characterized by low pH, redox stress, and poor oxygenation. In recent years, the focus of cancer metabolic research has shifted from the regulation and utilization of cancer cell-intrinsic pathways to studying how the metabolic landscape of the tumor affects the anti-tumor immune response. Recent discoveries point to the role that secreted metabolites within the TME play in crosstalk between tumor cell types to promote tumorigenesis and hinder the anti-tumor immune response. In this review, we will explore how crosstalk between metabolites of cancer cells, immune cells, and stromal cells drives tumorigenesis and what effects the competition for resources and metabolic crosstalk has on immune cell function.

Pathobiont-triggered induction of epithelial IDO1 drives regional susceptibility to Inflammatory Bowel Disease

The structure and function of the mammalian gut vary by region, yet why inflammatory diseases manifest in specific regions and not others remains unclear. We use a TNF-overexpressing Crohn's disease (CD) model (TnfΔARE/+), which typically presents in the terminal ileum (TI), to investigate how environmental factors interact with the host's immune susceptibility to drive region-specific disease. We identified Chlamydia muridarum, an intracellular bacterium and murine counterpart to the human sexually transmitted C. trachomatis, as necessary and sufficient to trigger disease manifestation in the ascending colon (AC), another common site of human CD. Disease manifestation in the AC depends on indoleamine 2,3-dioxygenase (IDO1) activity induced by hypersensitive surface secretory cells in genetically susceptible hosts. Single-cell and microbial analyses of human specimens also implicates this pathobiont-epithelial IDO1 pathway in patients with a history of CD in the AC. Our findings demonstrate that genetic and microbial factors can independently drive region-specific disease and provide a unique model to study CD specific to the AC.

Indoleamine 2,3-Dioxygenase 1/Aryl Hydrocarbon Receptor Feedback Loop Mediates Anti-inflammation in lipopolysaccharide-stimulated Astrocytes to Dampen Inflammatory Neurotoxicity

ABSTRACT

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates cell immune responses in a cell type-specific and ligand-dependent manner. In the central nervous system, astrocytic AhR plays important roles in regulating neuroinflammation by mediating responses to endogenous ligands generated from the inflammation-induced indoleamine 2,3-dioxygenase 1 (IDO1)/kynurenine (KYN) pathway. We previously demonstrated that reduction of AhR expression decreases lipopolysaccharide (LPS)-induced pro-inflammatory responses in microglia. However, the role of AhR in the astrocytic immune responses and its subsequent effects on microglial activation and neurotoxicity remain unclear. In this study, we used LPS-induced neuroinflammation in rat cortical glia-neuron (GN) mix cultures, which increased the expression of tumor necrosis factor-α and interleukin-6 and microglial activation. These proinflammatory responses were attenuated by a specific AhR agonist 6-formylindolo [3,2-b] carbazole (FICZ), but not by the AhR antagonist CH223191. CH223191, which inhibits LPS- and FICZ-induced AhR activation, enhanced neurotoxicity induced by LPS-glutamate co-treatment in GN mix cultures. Furthermore, inhibition of AhR expression and activation enhanced LPS-induced proinflammatory responses, and LPS-induced AhR activation was abrogated by the inhibition of IDO1 expression in astrocytes. Notably, AhR knockdown inhibited the anti-inflammatory effects of KYN while enhancing LPS-induced IDO1 expression in astrocytes, suggesting that AhR mediates the anti-inflammatory effect of KYN and the negative feedback regulation of IDO1 expression. Finally, we examined the role of astrocytic AhR in inflammatory astrogliosis-induced neurotoxicity by treating primary cortical neurons with LPS-treated astrocyte-conditioned medium (ACM). The results revealed that ACM derived from siAhR-transfected astrocytes increased neurotoxicity. In conclusion, inflammation-activated AhR mediates the anti-inflammatory effects and negative feedback regulation of the IDO1/KYN pathway in astrocytes, thereby dampening inflammatory astrogliosis-induced neurotoxicity.

Metabolic targeting of regulatory T cells in oral squamous cell carcinoma: new horizons in immunotherapy

Oral squamous cell carcinoma (OSCC) is a prevalent oral malignancy, which poses significant health risks with a high mortality rate. Regulatory T cells (Tregs), characterized by their immunosuppressive capabilities, are intricately linked to OSCC progression and patient outcomes. The metabolic reprogramming of Tregs within the OSCC tumor microenvironment (TME) underpins their function, with key pathways such as the tryptophan-kynurenine-aryl hydrocarbon receptor, PI3K-Akt-mTOR and nucleotide metabolism significantly contributing to their suppressive activities. Targeting these metabolic pathways offers a novel therapeutic approach to reduce Treg-mediated immunosuppression and enhance anti-tumor responses. This review explores the metabolic dependencies and pathways that sustain Treg function in OSCC, highlighting key metabolic adaptations such as glycolysis, fatty acid oxidation, amino acid metabolism and PI3K-Akt-mTOR signaling pathway that enable Tregs to thrive in the challenging conditions of the TME. Additionally, the review discusses the influence of the oral microbiome on Treg metabolism and evaluates potential therapeutic strategies targeting these metabolic pathways. Despite the promising potential of these interventions, challenges such as selectivity, toxicity, tumor heterogeneity, and resistance mechanisms remain. The review concludes with perspectives on personalized medicine and integrative approaches, emphasizing the need for continued research to translate these findings into effective clinical applications for OSCC treatment.

Macrophages promote pre-metastatic niche formation of breast cancer through aryl hydrocarbon receptor activity

Macrophages that acquire an immunosuppressive phenotype play a crucial role in establishing the pre-metastatic niche (PMN), which is essential for facilitating breast cancer metastasis to distant organs. Our study showed that increased activity of the aryl hydrocarbon receptor (AHR) in lung macrophages plays a crucial role in establishing the immunosuppressive PMN in breast cancer. Specifically, AHR activation led to high expression of PD-L1 on macrophages by directly binding to the promoter of Pdl1. This upregulation of PD-L1 promoted the differentiation of regulatory T cells (Tregs) within the PMN, further enhancing immunosuppressive conditions. Mice with Ahr conditional deletion in macrophages had reduced lung metastasis of breast cancer. The elevated AHR levels in PMN macrophages were induced by GM-CSF, which was secreted by breast cancer cells. Mechanistically, the activated STAT5 signaling pathway induced by GM-CSF prevented AHR from being ubiquitinated, thereby sustaining its activity in macrophages. In breast cancer patients, the expression of AHR and PD-L1 was correlated with increased Treg cell infiltration, and higher levels of AHR were associated with a poor prognosis. These findings reveal that the crosstalk of breast cancer cells, lung macrophages, and Treg cells via the GM-CSF-STAT5-AHR-PD-L1 cascade modulates the lung pre-metastatic niche during breast cancer progression.

Targeting pivotal amino acids metabolism for treatment of leukemia

Metabolic reprogramming is a crucial characteristic of cancer, allowing cancer cells to acquire metabolic properties that support their survival, immune evasion, and uncontrolled proliferation. Consequently, targeting cancer metabolism has become an essential therapeutic strategy. Abnormal amino acid metabolism is not only a key aspect of metabolic reprogramming but also plays a significant role in chemotherapy resistance and immune evasion, particularly in leukemia. Changes in amino acid metabolism in tumor cells are typically driven by a combination of signaling pathways and transcription factors. Current approaches to targeting amino acid metabolism in leukemia include inhibiting amino acid transporters, blocking amino acid biosynthesis, and depleting specific amino acids to induce apoptosis in leukemic cells. Different types of leukemic cells rely on the exogenous supply of specific amino acids, such as asparagine, glutamine, arginine, and tryptophan. Therefore, disrupting the supply of these amino acids may represent a vulnerability in leukemia. This review focuses on the pivotal role of amino acids in leukemia metabolism, their impact on leukemic stem cells, and their therapeutic potential.

Plasticity and Tumor Microenvironment in Pancreatic Cancer: Genetic, Metabolic, and Immune Perspectives

Cancer has long been believed to be a genetic disease caused by the accumulation of mutations in key genes involved in cellular processes. However, recent advances in sequencing technology have demonstrated that cells with cancer driver mutations are also present in normal tissues in response to aging, environmental damage, and chronic inflammation, suggesting that not only intrinsic factors within cancer cells, but also environmental alterations are important key factors in cancer development and progression. Pancreatic cancer tissue is mostly comprised of stromal cells and immune cells. The desmoplasmic microenvironment characteristic of pancreatic cancer is hypoxic and hypotrophic. Pancreatic cancer cells may adapt to this environment by rewiring their metabolism through epigenomic changes, enhancing intrinsic plasticity, creating an acidic and immunosuppressive tumor microenvironment, and inducing noncancerous cells to become tumor-promoting. In addition, pancreatic cancer has often metastasized to local and distant sites by the time of diagnosis, suggesting that a similar mechanism is operating from the precancerous stage. Here, we review key recent findings on how pancreatic cancers acquire plasticity, undergo metabolic reprogramming, and promote immunosuppressive microenvironment formation during their evolution. Furthermore, we present the following two signaling pathways that we have identified: one based on the small G-protein ARF6 driven by KRAS/TP53 mutations, and the other based on the RNA-binding protein Arid5a mediated by inflammatory cytokines, which promote both metabolic reprogramming and immune evasion in pancreatic cancer. Finally, the striking diversity among pancreatic cancers in the relative importance of mutational burden and the tumor microenvironment, their clinical relevance, and the potential for novel therapeutic strategies will be discussed.

Indoleamine 2,3-dioxygenase-1 involves in CD8+T cell exhaustion in glioblastoma via regulating tryptophan levels

Indoleamine 2,3-dioxygenase-1 (IDO-1) is an enzyme that catalyzes the metabolism of tryptophan (Trp). It is expressed in limited amounts in normal tissues but significantly upregulated during inflammation and infection. Various inflammatory factors, especially IFN-γ, can induce the expression of IDO-1. While extensive research has been conducted on the role of IDO-1 in tumors, its specific role in complex central nervous system tumors such as glioblastoma (GBM) remains unclear. This study aims to explore the role of IDO-1 in the development of GBM and analyze its association with tryptophan levels and CD8+T cell exhaustion in the tumor region. To achieve this, we constructed an orthotopic mouse glioblastoma tumor model to investigate the specific mechanisms between IDO-1, GBM, and CD8+T cell exhaustion. Our results showed that IDO-1 can promote CD8+T cell exhaustion by reducing tryptophan levels. When IDO-1 was knocked down in glioblastoma cells, other cells within the tumor microenvironment upregulated IDO-1 expression to compensate for the loss and enhance immunosuppressive effects. Therefore, the data suggest that the GBM microenvironment controls tryptophan levels by regulating IDO-1 expression, which plays a critical role in immune suppression. These findings support the use of immune therapy in combination with IDO-1 inhibitors or tryptophan supplementation as a potential treatment strategy.