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The restoration of CD4⁺ T cells, especially T-helper type 17 (Th17) cells, remains incomplete in the gut mucosa of most human immunodeficiency virus type 1 (HIV-1)–infected individuals despite sustained antiretroviral therapy (ART). Herein, we report an increase in the absolute number of CXCR3⁺ T cells in the duodenal mucosa during ART. The frequencies of Th1 and CXCR3⁺ CD8⁺ T cells were increased and negatively correlated with CCL20 and CCL25 expression in the mucosa. In ex vivo analyses, we showed that interferon γ, the main cytokine produced by Th1 and effector CD8⁺ T cells, downregulates the expression of CCL20 and CCL25 by small intestine enterocytes, while it increases the expression of CXCL9/10/11, the ligands of CXCR3. Interleukin 18, a pro-Th1 cytokine produced by enterocytes, also contributes to the downregulation of CCL20 expression and increases interferon γ production by Th1 cells. This could perpetuate an amplification loop for CXCR3-driven Th1 and effector CD8⁺ T cells recruitment to the gut, while impairing Th17 cells homing through the CCR6-CCL20 axis in treated HIV-1–infected individuals.

Microbial pathogens have evolved mechanisms to overcome immune responses and successfully infect their host. Here, we studied how Listeria monocytogenes evades immune detection by peptidoglycan (PGN) modification. By analyzing L. monocytogenes muropeptides, we detected O-acetylated muramic acid residues. We identified an O-acetyltransferase gene, oatA, in the L. monocytogenes genome sequence. Comparison of PGN from parental and isogenic oatA mutant strains showed that the O-acetyltransferase OatA O-acetylates Listeria PGN. We also found that PGN O-acetylation confers resistance to different types of antimicrobial compounds targeting bacterial cell wall such as lysozyme, β-lactam antibiotics, and bacteriocins and that O-acetylation is required for Listeria growth in macrophages. Moreover, oatA mutant virulence is drastically affected in mice following intravenous or oral inoculation. In addition, the oatA mutant induced early secretion of proinflammatory cytokines and chemokines in vivo. These results suggest an important role for OatA in limiting innate immune responses and promoting bacterial survival in the infected host.

How the gut microbiota regulates intestinal homeostasis is not completely clear. Gut microbiota metabolite short-chain fatty acids (SCFAs) have been reported to regulate T-cell differentiation. However, the mechanisms underlying SCFA regulation of T-cell differentiation and function remain to be investigated. CBir1, an immunodominant microbiota antigen, transgenic T cells were treated with butyrate under various T-cell polarization conditions to investigate butyrate regulation of T-cell differentiation and the mechanism involved. Transfer of butyrate-treated CBir T cells into Rag1-/- mice was performed to study the in vivo role of such T cells in inducing colitis. Although butyrate promoted Th1 cell development by promoting IFN-γ and T-bet expression, it inhibited Th17 cell development by suppressing IL-17, Rorα, and Rorγt expression. Interestingly, butyrate upregulated IL-10 production in T cells both under Th1 and Th17 cell conditions. Furthermore, butyrate induced T-cell B-lymphocyte-induced maturation protein 1 (Blimp1) expression, and deficiency of Blimp1 in T cells impaired the butyrate upregulation of IL-10 production, indicating that butyrate promotes T-cell IL-10 production at least partially through Blimp1. Rag1-/- mice transferred with butyrate-treated T cells demonstrated less severe colitis, compared with transfer of untreated T cells, and administration of anti-IL-10R antibody exacerbated colitis development in Rag-/- mice that had received butyrate-treated T cells. Mechanistically, the effects of butyrate on the development of Th1 cells was through inhibition of histone deacetylase but was independent of GPR43. These data indicate that butyrate controls the capacity of T cells in the induction of colitis by differentially regulating Th1 and Th17 cell differentiation and promoting IL-10 production, providing insights into butyrate as a potential therapeutic for the treatment of inflammatory bowel disease.

The cross-talk between immune cells and blood vessel endothelial cells promotes pericyte coverage and decreases hypoxia in mouse tumour models, and correlative evidence suggests that these processes influence cancer prognosis in humans. Normalizing tumour vasculature Tumours often develop with abnormal vasculature, characterized among other things by lower pericyte coverage of blood vessels, as well as leaky vessels that result in a hypoxic environment. Abnormal vessels limit immune infiltration and CD4 T cells can regulate angiogenesis. Using mouse models, the authors further dissect this crosstalk between immune cells and blood vessels in cancer, and describe a role for immune cells in normalizing the vasculature of tumours. The crosstalk between CD4 T cells and endothelial cells promotes pericyte coverage and decreases hypoxia, and correlative evidence suggests that these processes influence cancer prognosis in humans. The authors postulate that interventions that foster CD4 T-cell function, such as immune checkpoint blockade, also have a beneficial effect by normalizing the tumour vasculature. Blockade of angiogenesis can retard tumour growth, but may also paradoxically increase metastasis 1 , 2 . This paradox may be resolved by vessel normalization 3 , which involves increased pericyte coverage, improved tumour vessel perfusion, reduced vascular permeability, and consequently mitigated hypoxia 3 . Although these processes alter tumour progression, their regulation is poorly understood. Here we show that type 1 T helper (T H 1) cells play a crucial role in vessel normalization. Bioinformatic analyses revealed that gene expression features related to vessel normalization correlate with immunostimulatory pathways, especially T lymphocyte infiltration or activity. To delineate the causal relationship, we used various mouse models with vessel normalization or T lymphocyte deficiencies. Although disruption of vessel normalization reduced T lymphocyte infiltration as expected 4 , reciprocal depletion or inactivation of CD4 + T lymphocytes decreased vessel normalization, indicating a mutually regulatory loop. In addition, activation of CD4 + T lymphocytes by immune checkpoint blockade increased vessel normalization. T H 1 cells that secrete interferon-γ are a major population of cells associated with vessel normalization. Patient-derived xenograft tumours growing in immunodeficient mice exhibited enhanced hypoxia compared to the original tumours in immunocompetent humans, and hypoxia was reduced by adoptive T H 1 transfer. Our findings elucidate an unexpected role of T H 1 cells in vasculature and immune reprogramming. T H 1 cells may be a marker and a determinant of both immune checkpoint blockade and anti-angiogenesis efficacy.

Activated CD4 T cells proliferate rapidly and remodel epigenetically before exiting the cell cycle and engaging acquired effector functions. Metabolic reprogramming from the naive state is required throughout these phases of activation 1 . In CD4 T cells, T-cell-receptor ligation—along with co-stimulatory and cytokine signals—induces a glycolytic anabolic program that is required for biomass generation, rapid proliferation and effector function 2 . CD4 T cell differentiation (proliferation and epigenetic remodelling) and function are orchestrated coordinately by signal transduction and transcriptional remodelling. However, it remains unclear whether these processes are regulated independently of one another by cellular biochemical composition. Here we demonstrate that distinct modes of mitochondrial metabolism support differentiation and effector functions of mouse T helper 1 (T H 1) cells by biochemically uncoupling these two processes. We find that the tricarboxylic acid cycle is required for the terminal effector function of T H 1 cells through succinate dehydrogenase (complex II), but that the activity of succinate dehydrogenase suppresses T H 1 cell proliferation and histone acetylation. By contrast, we show that complex I of the electron transport chain, the malate–aspartate shuttle and mitochondrial citrate export are required to maintain synthesis of aspartate, which is necessary for the proliferation of T helper cells. Furthermore, we find that mitochondrial citrate export and the malate–aspartate shuttle promote histone acetylation, and specifically regulate the expression of genes involved in T cell activation. Combining genetic, pharmacological and metabolomics approaches, we demonstrate that the differentiation and terminal effector functions of T helper cells are biochemically uncoupled. These findings support a model in which the malate–aspartate shuttle, mitochondrial citrate export and complex I supply the substrates needed for proliferation and epigenetic remodelling early during T cell activation, whereas complex II consumes the substrates of these pathways, which antagonizes differentiation and enforces terminal effector function. Our data suggest that transcriptional programming acts together with a parallel biochemical network to enforce cell state. Genetic, pharmacological and metabolomics experiments reveal that the malate–aspartate shuttle and mitochondrial citrate export support the differentiation of mouse T helper 1 cells, whereas succinate dehydrogenase enforces their terminal effector function.

Recently, increasing evidence has suggested the association between gut dysbiosis and Alzheimer’s disease (AD) progression, yet the role of gut microbiota in AD pathogenesis remains obscure. Herein, we provide a potential mechanistic link between gut microbiota dysbiosis and neuroinflammation in AD progression. Using AD mouse models, we discovered that, during AD progression, the alteration of gut microbiota composition leads to the peripheral accumulation of phenylalanine and isoleucine, which stimulates the differentiation and proliferation of pro-inflammatory T helper 1 (Th1) cells. The brain-infiltrated peripheral Th1 immune cells are associated with the M1 microglia activation, contributing to AD-associated neuroinflammation. Importantly, the elevation of phenylalanine and isoleucine concentrations and the increase of Th1 cell frequency in the blood were also observed in two small independent cohorts of patients with mild cognitive impairment (MCI) due to AD. Furthermore, GV-971, a sodium oligomannate that has demonstrated solid and consistent cognition improvement in a phase 3 clinical trial in China, suppresses gut dysbiosis and the associated phenylalanine/isoleucine accumulation, harnesses neuroinflammation and reverses the cognition impairment. Together, our findings highlight the role of gut dysbiosis-promoted neuroinflammation in AD progression and suggest a novel strategy for AD therapy by remodelling the gut microbiota.

Intergenic long noncoding RNAs (lincRNAs) regulate gene expression in various tissues. Zhao and colleagues identify 1,524 lincRNA clusters in thymocytes and mature T cell subsets and reveal dynamic and cell-specific patterns of lincRNA expression during T cell differentiation. Although intergenic long noncoding RNAs (lincRNAs) have been linked to gene regulation in various tissues, little is known about lincRNA transcriptomes in the T cell lineages. Here we identified 1,524 lincRNA clusters in 42 T cell samples, from early T cell progenitors to terminally differentiated helper T cell subsets. Our analysis revealed highly dynamic and cell-specific expression patterns for lincRNAs during T cell differentiation. These lincRNAs were located in genomic regions enriched for genes that encode proteins with immunoregulatory functions. Many were bound and regulated by the key transcription factors T-bet, GATA-3, STAT4 and STAT6. We found that the lincRNA LincR- Ccr2 -5′AS, together with GATA-3, was an essential component of a regulatory circuit in gene expression specific to the T H 2 subset of helper T cells and was important for the migration of T H 2 cells.

Leukocyte infiltration plays an active role in controlling tumor development. In the early stages of carcinogenesis, T cells counteract tumor growth. However, in advanced stages, cancer cells and infiltrating stromal components interfere with the immune control and instruct immune cells to support, rather than counteract, tumor malignancy, via cell–cell contact or soluble mediators. In particular, metabolites are emerging as active players in driving immunosuppression. Here we demonstrate that in a prostate cancer model lactate released by glycolytic cancer-associated fibroblasts (CAFs) acts on CD4 + T cells, shaping T-cell polarization. In particular, CAFs exposure (i) reduces the percentage of the antitumoral Th1 subset, inducing a lactate-dependent, SIRT1-mediated deacetylation/degradation of T-bet transcription factor; (ii) increases T reg cells, driving naive T cells polarization, through a lactate-based NF-kB activation and FoxP3 expression. In turn, this metabolic-based CAF-immunomodulated environment exerts a pro-invasive effect on prostate cancer cells, by activating a previously unexplored miR21/TLR8 axis that sustains cancer malignancy.

The balance between T helper type 1 (T H 1) cells and other T H cells is critical for antiviral and anti-tumour responses 1 – 3 , but how this balance is achieved remains poorly understood. Here we dissected the dynamic regulation of T H 1 cell differentiation during in vitro polarization, and during in vivo differentiation after acute viral infection. We identified regulators modulating T helper cell differentiation using a unique T H 1–T H 2 cell dichotomous culture system and systematically validated their regulatory functions through multiple in vitro and in vivo CRISPR screens. We found that RAMP3, a component of the receptor for the neuropeptide CGRP (calcitonin gene-related peptide), has a cell-intrinsic role in T H 1 cell fate determination. Extracellular CGRP signalling through the receptor RAMP3–CALCRL restricted the differentiation of T H 2 cells, but promoted T H 1 cell differentiation through the activation of downstream cAMP response element-binding protein (CREB) and activating transcription factor 3 (ATF3). ATF3 promoted T H 1 cell differentiation by inducing the expression of Stat1 , a key regulator of T H 1 cell differentiation. After viral infection, an interaction between CGRP produced by neurons and RAMP3 expressed on T cells enhanced the anti-viral IFNγ-producing T H 1 and CD8 + T cell response, and timely control of acute viral infection. Our research identifies a neuroimmune circuit in which neurons participate in T cell fate determination by producing the neuropeptide CGRP during acute viral infection, which acts on RAMP3-expressing T cells to induce an effective anti-viral T H 1 cell response. RAMP3, a component of the receptor for the neuropeptide CGRP, has a cell-intrinsic role in T helper type 1 cell fate determination.

CAR-T cell therapy is effective for hematologic malignancies. However, considerable numbers of patients relapse after the treatment, partially due to poor expansion and limited persistence of CAR-T cells in vivo. Here, we demonstrate that human CAR-T cells polarized and expanded under a Th9-culture condition (T9 CAR-T) have an enhanced antitumor activity against established tumors. Compared to IL2-polarized (T1) cells, T9 CAR-T cells secrete IL9 but little IFN-γ, express central memory phenotype and lower levels of exhaustion markers, and display robust proliferative capacity. Consequently, T9 CAR-T cells mediate a greater antitumor activity than T1 CAR-T cells against established hematologic and solid tumors in vivo. After transfer, T9 CAR-T cells migrate effectively to tumors, differentiate to IFN-γ and granzyme-B secreting effector memory T cells but remain as long-lived and hyperproliferative T cells. Our findings are important for the improvement of CAR-T cell-based immunotherapy for human cancers. Antigen-specific IL9-secreting CD4 Th9 and CD8 Tc9 cells have been previously characterized for their anti-tumour properties. Here, the authors show that ex vivo polarized Th9/Tc9 human CAR-T cells display increased anti-tumor activity in pre-clinical haematological and solid cancer models compared to conventional IL-2 activated CAR-T cells.