Control of T-Cell Activation and Signaling by Amino-Acid Catabolizing Enzymes

Dietary methionine restriction in cancer development and antitumor immunity

Methionine restriction (MR) has been shown to suppress tumor growth and improve the responses to various anticancer therapies. However, methionine itself is required for the proliferation, activation, and differentiation of T cells that are crucial for antitumor immunity. The dual impact of methionine, that influences both tumor and immune cells, has generated concerns regarding the potential consequences of MR on T cell immunity and its possible role in promoting cancer. In this review we systemically examine current literature on the interactions between dietary methionine, cancer cells, and immune cells. Based on recent findings on MR in immunocompetent animals, we further discuss how tumor stage-specific methionine dependence of immune cells and cancer cells in the tumor microenvironment could ultimately dictate the response of tumors to MR.

Cystine deprivation triggers CD36-mediated ferroptosis and dysfunction of tumor infiltrating CD8+ T cells

Cancer cells develop multiple strategies to evade T cell-mediated killing. On one hand, cancer cells may preferentially rely on certain amino acids for rapid growth and metastasis. On the other hand, sufficient nutrient availability and uptake are necessary for mounting an effective T cell anti-tumor response in the tumor microenvironment (TME). Here we demonstrate that tumor cells outcompete T cells for cystine uptake due to high Slc7a11 expression. This competition induces T-cell exhaustion and ferroptosis, characterized by diminished memory formation and cytokine secretion, increased PD-1 and TIM-3 expression, as well as intracellular oxidative stress and lipid-peroxide accumulation. Importantly, either Slc7a11 deletion in tumor cells or intratumoral cystine supplementation improves T cell anti-tumor immunity. Mechanistically, cystine deprivation in T cells disrupts glutathione synthesis, but promotes CD36 mediated lipid uptake due to dysregulated cystine/glutamate exchange. Moreover, enforced expression of glutamate-cysteine ligase catalytic subunit (Gclc) promotes glutathione synthesis and prevents CD36 upregulation, thus boosting T cell anti-tumor immunity. Our findings reveal cystine as an intracellular metabolic checkpoint that orchestrates T-cell survival and differentiation, and highlight Gclc as a potential therapeutic target for enhancing T cell anti-tumor function.

Metabolic waypoints during T cell differentiation

This Review explores the interplay between T cell activation and cell metabolism and highlights how metabolites serve two pivotal functions in shaping the immune response. Traditionally, T cell activation has been characterized by T cell antigen receptor-major histocompatibility complex interaction (signal 1), co-stimulation (signal 2) and cytokine signaling (signal 3). However, recent research has unveiled the critical role of metabolites in this process. Firstly, metabolites act as signal propagators that aid in the transmission of core activation signals, such as specific lipid species that are crucial at the immune synapse. Secondly, metabolites also function as unique signals that influence immune differentiation pathways, such as amino acid-induced mTORC1 signaling. Metabolites also play a substantial role in epigenetic remodeling, by directly modifying histones, altering gene expression and influencing T cell behavior. This Review discusses how T cells integrate nutrient sensing with activating stimuli to shape their differentiation and sensitivity to metabolites. We underscore the integration of immunological and metabolic inputs in T cell function and suggest that metabolite availability is a fundamental determinant of adaptive immune responses.

IDO-triggered swellable polymeric micelles for IDO inhibition and targeted cancer immunotherapy

Indoleamine 2,3-dioxygenase (IDO) has been studied as a promising target for cancer immunotherapy. IDO catalyzes the oxidation of tryptophan into kynurenine, which subsequently activates regulatory T cells, thereby promoting an immunosuppressive microenvironment in the tumor tissue. Due to its overexpression in tumor cells, IDO itself could be a tumor-specific stimulus for targeted cancer therapy. Toward this objective, we developed IDO-triggered swellable micelles for targeted cancer immunotherapy. The micelles are prepared by the self-assembly of amphiphilic polymers containing polymerized tryptophan as a hydrophobic block. The micelles exhibited IDO-responsive behavior via solubility conversion of the hydrophobic core triggered by the oxidation of tryptophan residues into kynurenine. The micelles were internalized into tumor cells and disassembled by overexpressed IDO. Loaded with IDO inhibitor, the micelle presented enhanced therapeutic antitumor effect, and effector T-cells were recruited into the tumor tissue. We demonstrated that overexpressed IDO in cancer cells could be utilized as a tumor-specific stimulus, and utilizing an IDO-responsive drug delivery system holds great promise for targeted cancer therapy and immunomodulation.

Raman Spectroscopy Profiling of Splenic T-Cells in Sepsis and Endotoxemia in Mice

Sepsis is a life-threatening condition that results from an overwhelming and disproportionate host response to an infection. Currently, the quality and extent of the immune response are evaluated based on clinical symptoms and the concentration of inflammatory biomarkers released or expressed by the immune cells. However, the host response toward sepsis is heterogeneous, and the roles of the individual immune cell types have not been fully conceptualized. During sepsis, the spleen plays a vital role in pathogen clearance, such as bacteria by an antibody response, macrophage bactericidal capacity, and bacterial endotoxin detoxification. This study uses Raman spectroscopy to understand the splenic T-lymphocyte compartment profile changes during bona fide bacterial sepsis versus hyperinflammatory endotoxemia. The Raman spectral analysis showed marked changes in splenocytes of mice subjected to septic peritonitis principally in the DNA region, with minor changes in the amino acids and lipoprotein areas, indicating significant transcriptomic activity during sepsis. Furthermore, splenocytes from mice exposed to endotoxic shock by injection of a high dose of lipopolysaccharide showed significant changes in the protein and lipid profiles, albeit with interindividual variations in inflammation severity. In summary, this study provided experimental evidence for the applicability and informative value of Raman spectroscopy for profiling the immune response in a complex, systemic infection scenario. Importantly, changes within the acute phase of inflammation onset (24 h) were reliably detected, lending support to the concept of early treatment and severity control by extracorporeal Raman profiling of immunocyte signatures.

High infiltration of CD209+ dendritic cells and CD163+ macrophages in the peritumor area of prostate cancer is predictive of late adverse outcomes

Introduction

Prostate cancer (PCa) shows considerable variation in clinical outcomes between individuals with similar diseases. The initial host-tumor interaction as assessed by detailed analysis of tumor infiltrating immune cells within the primary tumor may dictate tumor evolution and late clinical outcomes. In this study, we assessed the association between clinical outcomes and dendritic cell (DC) or macrophage (MΦ) tumor infiltration as well as with expression of genes related to their functions.

Methods

Infiltration and localization of immature DC, mature DC, total MΦ and M2-type MΦ was analyzed by immunohistochemistry in 99 radical prostatectomy specimens from patients with 15.5 years median clinical follow-up using antibodies against CD209, CD83, CD68 and CD163, respectively. The density of positive cells for each marker in various tumor areas was determined. In addition, expression of immune genes associated with DC and MΦ was tested in a series of 50 radical prostatectomy specimens by Taqman Low-Density Array with similarly long follow-up. Gene expression was classified as low and high after unsupervised hierarchical clustering. Numbers and ratio of positive cells and levels of gene expression were correlated with endpoints such as biochemical recurrence (BCR), need for definitive androgen deprivation therapy (ADT) or lethal PCa using Cox regression analyses and/or Kaplan-Meier curves.

Results

Positive immune cells were observed in tumor, tumor margin, and normal-like adjacent epithelium areas. CD209⁺ and CD163⁺ cells were more abundant at the tumor margin. Higher CD209⁺/CD83⁺ cell density ratio at the tumor margin was associated with higher risk of ADT and lethal PCa while higher density of CD163⁺ cells in the normal-like adjacent epithelium was associated with a higher risk of lethal PCa. A combination of 5 genes expressed at high levels correlated with a shorter survival without ADT and lethal PCa. Among these five genes, expression of IL12A and CD163 was correlated to each other and was associated with shorter survival without BCR and ADT/lethal PCa, respectively.

Conclusion

A higher level of infiltration of CD209⁺ immature DC and CD163⁺ M2-type MΦ in the peritumor area was associated with late adverse clinical outcomes.

Procyanidin B2 3,3″-di-O-gallate suppresses IFN-γ production in murine CD4+ T cells through the regulation of glutamine influx via direct interaction with ASCT2

Excessive activation of CD4⁺ T cells increases cytokine production substantially and induces immune-mediated diseases. Procyanidins are polyphenols with anti-inflammatory properties. Procyanidin B2 (PCB2) gallate [specifically, PCB2 3,3''-di-O-gallate (PCB2DG)] inhibits cytokine production through the suppression of glycolysis via mammalian target of rapamycin (mTOR) in T cells. Several amino acids play critical roles in T cell activation, especially glutamine, which is important in mTOR signaling and interferon-γ (IFN-γ) production in CD4⁺ T cells. However, the mechanisms underlying the effects of PCB2DG, including its interaction partners, have yet to be clarified. In the present study, the mechanisms underlying the inhibitory effect of PCB2DG on IFN-γ through glutamine metabolism regulation were investigated. We found that PCB2DG treatment reduced intracellular glutamine levels in CD4⁺ T cells, whereas the addition of glutamine abrogated the inhibitory effects of PCB2DG on IFN-γ production. The PCB2DG-induced reduction in intracellular glutamine accumulation led to the upregulated expression of activating transcription factor 4, which was induced by the cytoprotective signaling pathway in the amino acid response. In addition, the mRNA and protein expression levels of alanine serine cysteine transporter 2 (ASCT2), a major glutamine transporter in CD4⁺ T cells, were not altered by PCB2DG treatment. Further analysis using a target identification strategy revealed that PCB2DG binds to ASCT2, suggesting that PCB2DG interacts directly with this major glutamine transporter to inhibit glutamine influx. Overall, this study indicates that ASCT2 is a novel target protein of a dietary polyphenol and provides new insights into the mechanism underlying the immunomodulatory effects of polyphenols.

Metabolite variations in the sera of HIV+ patients after an oral administration of effervescent glutamine and in comparison to non-HIV individuals by NMR

It was demonstrated that effervescent glutamine supplementation in HIV+ individuals treated with antiretroviral therapy (ART) increased CD4+ T lymphocytes, decreased inflammation biomarkers, and brought health benefits. This pilot study aimed to explore serum metabolite variations in the HIV+ group under ART after 30 days of supplementation with glutamine, and in comparison to the matched HIV- group. The group of HIV+ showed lower levels of choline, creatine, pyruvate, glutamate, lysine, and tyrosine when compared to the HIV- group. Glucose, lipids, lactate, glutamine, phenylalanine, threonine, and phenylalanine/tyrosine were higher in HIV+ patients under long ART. Serum metabolome variations were shown to be consistent with the health improvements observed in the HIV+ group after effervescent glutamine supplementation, which might aid in ART in HIV+ individuals.

Multiomics and artificial intelligence enabled peripheral blood-based prediction of amnestic mild cognitive impairment

BACKGROUND

Since dementia is preventable with early interventions, biomarkers that assist in diagnosing early stages of dementia, such as mild cognitive impairment (MCI), are urgently needed.

METHODS

Multiomics analysis of amnestic MCI (aMCI) peripheral blood (n = 25) was performed covering the transcriptome, microRNA, proteome, and metabolome. Validation analysis for microRNAs was conducted in an independent cohort (n = 12). Artificial intelligence was used to identify the most important features for predicting aMCI.

FINDINGS

We found that hsa-miR-4455 is the best biomarker in all omics analyses. The diagnostic index taking a ratio of hsa-miR-4455 to hsa-let-7b-3p predicted aMCI patients against healthy subjects with 97% overall accuracy. An integrated review of multiomics data suggested that a subset of T cells and the GCN (general control nonderepressible) pathway are associated with aMCI.

INTERPRETATION

The multiomics approach has enabled aMCI biomarkers with high specificity and illuminated the accompanying changes in peripheral blood. Future large-scale studies are necessary to validate candidate biomarkers for clinical use.

Metabolic Regulation of CD8+ T Cells: From Mechanism to Therapy

Significance: Cancer immunotherapy has yielded striking antitumor effects in many cancers, yet the proportion of benefited patients is still limited. As key mediators of tumor suppression, CD8⁺ T cells are crucial for cancer immunotherapy. It has been widely appreciated that the modulation of CD8⁺ T cell immunity could be an effective way to further improve the therapeutic benefit of immunotherapy. Recent Advances: Emerging evidence has underlined a close link between metabolism and immune functions, providing a metabolism-immune axis that is increasingly investigated for understanding CD8⁺ T cell regulation. On the other hand, growing findings have reported that tumors adopt multiple approaches to induce metabolic reprogramming of CD8⁺ T cells, leading to compromised immunotherapy. Critical Issues: CD8⁺ T cell metabolism in the tumor microenvironment (TME) is often adapted to diminish antitumor immune responses and thereby evade from immune surveillance. A better understanding of metabolic regulation of CD8⁺ T cells in the TME is believed to hold promise for opening a new therapeutic window to further improve the benefit of immunotherapy. We herein review the mechanistic understanding of how CD8⁺ T cell metabolism is reprogrammed in the TME, mainly focusing on the impact of nutrient availability and bioactive molecules secreted by surrounding cells. Future Directions: Future research should pay attention to tumor heterogeneity in the metabolic microenvironment and associated immune responses. It is also important to include the trending opinion of "precision medicine" in cancer immunotherapies to tailor metabolic interventions for individual patients in combination with immunotherapy treatments. Antioxid. Redox Signal. 37, 1234-1253.

Immunomodulatory Role of Thioredoxin Interacting Protein in Cancer's Impediments: Current Understanding and Therapeutic Implications

Cancer, which killed ten million people in 2020, is expected to become the world's leading health problem and financial burden. Despite the development of effective therapeutic approaches, cancer-related deaths have increased by 25.4% in the last ten years. Current therapies promote apoptosis and oxidative stress DNA damage and inhibit inflammatory mediators and angiogenesis from providing temporary relief. Thioredoxin-binding protein (TXNIP) causes oxidative stress by inhibiting the function of the thioredoxin system. It is an important regulator of many redox-related signal transduction pathways in cells. In cancer cells, it functions as a tumor suppressor protein that inhibits cell proliferation. In addition, TXNIP levels in hemocytes increased after immune stimulation, suggesting that TXNIP plays an important role in immunity. Several studies have provided experimental evidence for the immune modulatory role of TXNIP in cancer impediments. TXNIP also has the potential to act against immune cells in cancer by mediating the JAK-STAT, MAPK, and PI3K/Akt pathways. To date, therapies targeting TXNIP in cancer are still under investigation. This review highlights the role of TXNIP in preventing cancer, as well as recent reports describing its functions in various immune cells, signaling pathways, and promoting action against cancer.

TCR-Independent Metabolic Reprogramming Precedes Lymphoma-Driven Changes in T-cell Fate

Chronic T-cell receptor (TCR) signaling in the tumor microenvironment is known to promote T-cell dysfunction. However, we reasoned that poorly immunogenic tumors may also compromise T cells by impairing their metabolism. To address this, we assessed temporal changes in T-cell metabolism, fate, and function in models of B-cell lymphoma driven by Myc, a promoter of energetics and repressor of immunogenicity. Increases in lymphoma burden most significantly impaired CD4+ T-cell function and promoted regulatory T cell (Treg) and Th1-cell differentiation. Metabolomic analyses revealed early reprogramming of CD4+ T-cell metabolism, reduced glucose uptake, and impaired mitochondrial function, which preceded changes in T-cell fate. In contrast, B-cell lymphoma metabolism remained robust during tumor progression. Finally, mitochondrial functions were impaired in CD4+ and CD8+ T cells in lymphoma-transplanted OT-II and OT-I transgenic mice, respectively. These findings support a model, whereby early, TCR-independent, metabolic interactions with developing lymphomas limits T cell-mediated immune surveillance.

Targeting Metabolic Pathways of Myeloid Cells Improves Cancer Immunotherapy

Tumor-infiltrating myeloid cells are a prominent pro-tumorigenic immune cell population that limit host anti-tumor immunity and present a significant obstacle for many cancer immunotherapies. Targeting the mechanisms regulating myeloid cell function within the tumor microenvironment may overcome immunotherapy resistance in some cancers. Recent discoveries in the emerging field of immunometabolism reveal that the metabolic profiles of intratumoral myeloid cells are rewired to adapt to the nutrition-limited tumor microenvironment, and this shapes their pro-tumor phenotypes. Interestingly, metabolic modulation can shift these myeloid cells toward the immune-stimulating anti-tumor phenotype. In this review, we will highlight the roles of specific metabolic pathways in the activation and function of myeloid cells, and discuss the therapeutic value of metabolically reprogramming myeloid cells to augment and improve outcomes with cancer immunotherapy.

Neuroblastoma Formation Requires Unconventional CD4 T Cells and Arginase-1-Dependent Myeloid Cells

Immune cells regulate tumor growth by mirroring their function as tissue repair organizers in normal tissues. To understand the different facets of immune-tumor collaboration through genetics, spatial transcriptomics, and immunologic manipulation with noninvasive, longitudinal imaging, we generated a penetrant double oncogene-driven autochthonous model of neuroblastoma. Spatial transcriptomic analysis showed that CD4⁺ and myeloid populations colocalized within the tumor parenchyma, while CD8⁺ T cells and B cells were peripherally dispersed. Depletion of CD4⁺ T cells or CCR2⁺ macrophages, but not B cells, CD8⁺ T cells, or natural killer (NK) cells, prevented tumor formation. Tumor CD4⁺ T cells displayed unconventional phenotypes and were clonotypically diverse and antigen independent. Within the myeloid fraction, tumor growth required myeloid cells expressing arginase-1. Overall, these results demonstrate how arginine-metabolizing myeloid cells conspire with pathogenic CD4⁺ T cells to create permissive conditions for tumor formation, suggesting that these protumorigenic pathways could be disabled by targeting myeloid arginine metabolism. SIGNIFICANCE: A new model of human neuroblastoma provides ways to track tumor formation and expansion in living animals, allowing identification of CD4⁺ T-cell and macrophage functions required for oncogenesis.

What role for AHR activation in IL4I1-mediated immunosuppression ?

The amino-acid catabolizing enzyme Interleukin-4 induced gene 1 (IL4I1) remains poorly characterized despite it is emerging as a pertinent therapeutic target for cancer. IL4I1 is secreted in the synaptic cleft by antigen-presenting cells. It inhibits TCR signaling, modulates naïve T cell differentiation and limits effector T cell proliferation. IL4I1 expression in tumors shapes the tumor microenvironment and impairs the antitumor cytotoxic T cell response, thereby facilitating cancer immune escape. Several mechanisms participate in these effects. Recent data suggest a role of new IL4I1 metabolites in activation of the aryl-hydrocarbon receptor (AHR). Here, we observe that expression of IL4I1 is poorly correlated with that of validated targets of AHR in human cancers. Moreover, dendritic cells do not upregulate AHR target genes in relation with IL4I1 expression in vivo. Finally, IL4I1 activity toward tryptophan leading to production of AHR-activating products is very low, and should be negligible when tryptophan-degrading enzymes of higher affinity compete for the substrate. We recently showed that IL4I1 expression by dendritic cells directly regulates immune synapse formation and modulates the repertoire and memory differentiation of responding CD8 T cells after viral infection. Thus, IL4I1 may restrain tumor control through regulating the priming of tumor-specific CD8 T cells, independently of AHR activation.