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The sparse nature of single-cell omics data makes it challenging to dissect the wiring and rewiring of the transcriptional and signaling drivers that regulate cellular states. Many of the drivers, referred to as “hidden drivers”, are difficult to identify via conventional expression analysis due to low expression and inconsistency between RNA and protein activity caused by post-translational and other modifications. To address this issue, we developed scMINER, a mutual information (MI)-based computational framework for unsupervised clustering analysis and cell-type specific inference of intracellular networks, hidden drivers and network rewiring from single-cell RNA-seq data. We designed scMINER to capture nonlinear cell-cell and gene-gene relationships and infer driver activities. Systematic benchmarking showed that scMINER outperforms popular single-cell clustering algorithms, especially in distinguishing similar cell types. With respect to network inference, scMINER does not rely on the binding motifs which are available for a limited set of transcription factors, therefore scMINER can provide quantitative activity assessment for more than 6,000 transcription and signaling drivers from a scRNA-seq experiment. As demonstrations, we used scMINER to expose hidden transcription and signaling drivers and dissect their regulon rewiring in immune cell heterogeneity, lineage differentiation, and tissue specification. Overall, activity-based scMINER is a widely applicable, highly accurate, reproducible and scalable method for inferring cellular transcriptional and signaling networks in each cell state from scRNA-seq data. The scMINER software is publicly accessible via:https://github.com/jyyulab/scMINER.

Nutrients are emerging regulators of adaptive immunity1. Selective nutrients interplay with immunological signals to activate mechanistic target of rapamycin complex 1 (mTORC1), a key driver of cell metabolism2–4, but how these environmental signals are integrated for immune regulation remains unclear. Here we use genome-wide CRISPR screening combined with protein–protein interaction networks to identify regulatory modules that mediate immune receptor- and nutrient-dependent signalling to mTORC1 in mouse regulatory T (Treg) cells. SEC31A is identified to promote mTORC1 activation by interacting with the GATOR2 component SEC13 to protect it from SKP1-dependent proteasomal degradation. Accordingly, loss of SEC31A impairs T cell priming and Treg suppressive function in mice. In addition, the SWI/SNF complex restricts expression of the amino acid sensor CASTOR1, thereby enhancing mTORC1 activation. Moreover, we reveal that the CCDC101-associated SAGA complex is a potent inhibitor of mTORC1, which limits the expression of glucose and amino acid transporters and maintains T cell quiescence in vivo. Specific deletion of Ccdc101 in mouse Treg cells results in uncontrolled inflammation but improved antitumour immunity. Collectively, our results establish epigenetic and post-translational mechanisms that underpin how nutrient transporters, sensors and transducers interplay with immune signals for three-tiered regulation of mTORC1 activity and identify their pivotal roles in licensing T cell immunity and immune tolerance. CRISPR screening and protein–protein interaction networks identify components and mechanisms of nutrient-dependent mTORC1 signalling in regulatory T cells and reveal how mTORC1 integrates immunological cues and nutrient signals for adaptive immunity.

We present a comprehensive and versatile toolkit, NetBID2, for integrating multi-omics data and exposing hidden drivers that are not genetically altered or differentially expressed at the RNA/protein level by reverse-engineering context-specific interactomes and inferring protein activity. We deploy NetBID2 Viewer, Runner, and Cloud apps with 145 context-specific gene regulatory and signalling networks across normal tissues and paediatric and adult cancers to facilitate real-time interactive visualization, analysis, end-to-end use, and sharing.

T follicular helper (TFH) cells are crucial for B cell-mediated humoral immunity1. Although transcription factors such as BCL6 drive the differentiation of TFH cells2,3, it is unclear whether and how post-transcriptional and metabolic programs enforce TFH cell programming. Here we show that the cytidine diphosphate (CDP)–ethanolamine pathway co-ordinates the expression and localization of CXCR5 with the responses of TFH cells and humoral immunity. Using in vivo CRISPR–Cas9 screening and functional validation in mice, we identify ETNK1, PCYT2, and SELENOI—enzymes in the CDP–ethanolamine pathway for de novo synthesis of phosphatidylethanolamine (PE)—as selective post-transcriptional regulators of TFH cell differentiation that act by promoting the surface expression and functional effects of CXCR5. TFH cells exhibit unique lipid metabolic programs and PE is distributed to the outer layer of the plasma membrane, where it colocalizes with CXCR5. De novo synthesis of PE through the CDP–ethanolamine pathway co-ordinates these events to prevent the internalization and degradation of CXCR5. Genetic deletion of Pcyt2, but not of Pcyt1a (which mediates the CDP–choline pathway), in activated T cells impairs the differentiation of TFH cells, and this is associated with reduced humoral immune responses. Surface levels of PE and CXCR5 expression on B cells also depend on Pcyt2. Our results reveal that phospholipid metabolism orchestrates post-transcriptional mechanisms for TFH cell differentiation and humoral immunity, highlighting the metabolic control of context-dependent immune signalling and effector programs. Enzymes in the cytidine diphosphate–ethanolamine metabolic pathway, which promotes de novo synthesis of phosphatidylethanolamine, are shown to act as post-transcriptional mediators of the differentiation of T follicular helper (TFH) cells, by regulating the chemokine receptor CXCR5.

Regulatory T cells (Treg cells) are essential for immune tolerance1, but also drive immunosuppression in the tumour microenvironment2. Therapeutic targeting of Treg cells in cancer will therefore require the identification of context-specific mechanisms that affect their function. Here we show that inhibiting lipid synthesis and metabolic signalling that are dependent on sterol-regulatory-element-binding proteins (SREBPs) in Treg cells unleashes effective antitumour immune responses without autoimmune toxicity. We find that the activity of SREBPs is upregulated in intratumoral Treg cells. Moreover, deletion of SREBP-cleavage-activating protein (SCAP)—a factor required for SREBP activity—in these cells inhibits tumour growth and boosts immunotherapy that is triggered by targeting the immune-checkpoint protein PD-1. These effects of SCAP deletion are associated with uncontrolled production of interferon-γ and impaired function of intratumoral Treg cells. Mechanistically, signalling through SCAP and SREBPs coordinates cellular programs for lipid synthesis and inhibitory receptor signalling in these cells. First, de novo fatty-acid synthesis mediated by fatty-acid synthase (FASN) contributes to functional maturation of Treg cells, and loss of FASN from Treg cells inhibits tumour growth. Second, Treg cells in tumours show enhanced expression of the PD-1 gene, through a process that depends on SREBP activity and signals via mevalonate metabolism to protein geranylgeranylation. Blocking PD-1 or SREBP signalling results in dysregulated activation of phosphatidylinositol-3-kinase in intratumoral Treg cells. Our findings show that metabolic reprogramming enforces the functional specialization of Treg cells in tumours, pointing to new ways of targeting these cells for cancer therapy. Identification of a metabolic checkpoint involving lipid signalling that is specific to regulatory T cells (Treg cells) in the tumour microenvironment raises the possibility of targeting this checkpoint for treatment of cancer.

The identification of mechanisms to promote memory T cells (T(MEM)) has important implications for vaccination and anti-cancer immunotherapy(1–4). Using a CRISPR-based screen for negative regulators of T(MEM) generation in vivo(5), we discovered multiple components of the mammalian canonical Brg1/Brg-associated factor (cBAF)(6,7). Several components of the cBAF complex are essential for the differentiation of activated CD8(+) T cells into T effector (T(EFF)) cells, and their loss promotes T(MEM) formation in vivo. During the first division of activated CD8(+) T cells, cBAF and c-Myc(8) frequently co-assort asymmetrically to the two daughter cells. Daughter cells with high c-Myc and high cBAF display a cell fate trajectory towards T(EFF) cells, while those with low c-Myc and low cBAF preferentially differentiate towards T(MEM) cells. The cBAF complex and c-Myc physically interact to establish the chromatin landscape in activated CD8(+) T cells. Treatment of naïve CD8(+) T cells with a putative cBAF inhibitor during the first 48 hours of activation, prior to the generation of chimeric antigen receptor T (CAR-T) cells, markedly improves efficacy in a solid tumor model. Our results establish cBAF as a negative determinant of T(MEM) cell fate and suggest that manipulation of cBAF early in T cell differentiation can improve cancer immunotherapy.

Phosphatase and tensin homologue (PTEN) is frequently mutated in human cancer, but its roles in lymphopoiesis and tissue homeostasis remain poorly defined. Here we show that PTEN orchestrates a two-step developmental process linking antigen receptor and IL-23-Stat3 signalling to type-17 innate-like T cell generation. Loss of PTEN leads to pronounced accumulation of mature IL-17-producing innate-like T cells in the thymus. IL-23 is essential for their accumulation, and ablation of IL-23 or IL-17 signalling rectifies the reduced survival of female PTEN-haploinsufficient mice that model human patients with PTEN mutations. Single-cell transcriptome and network analyses revealed the dynamic regulation of PTEN, mTOR and metabolic activities that accompanied type-17 cell programming. Furthermore, deletion of mTORC1 or mTORC2 blocks PTEN loss-driven type-17 cell accumulation, and this is further shaped by the Foxo1 and Stat3 pathways. Collectively, our study establishes developmental and metabolic signalling networks underpinning type-17 cell fate decisions and their functional effects at coordinating PTEN-dependent tissue homeostasis.

The inferior cure rate of T-cell acute lymphoblastic leukemia (T-ALL) is associated with inherent drug resistance. The activating NOTCH1 gene mutations have been reported to cause chemoresistance at the stem cell level1. Direct NOTCH1 inhibition has failed in clinical trials due to a narrow therapeutic window but targeting key oncogenic and metabolic pathways downstream of mutated NOTCH1 may offer novel approaches. We previously reported that rapid transformation of thymocytes at the DN3 differentiation stage into preleukemic stem cells (pre-LSC) requires elevated Notch1 in addition to the presence of Scl/Lmo11. Notably, we showed that cellular metabolism of NOTCH1-mutated T-ALLs depends on Oxidative Phosphorylation (OxPhos) and that OxPhos inhibition using the complex I inhibitor IACS-010759 (OxPhos-i) is efficacious in NOTCH1-mutated T-ALL patient derived xenografts (PDXs)2. Here, we investigated the link between NOTCH1-mutated chemoresistance and OxPhos in pre-leukemic and leukemic cells, utilizing comprehensive molecular and functional assays. We hypothesized that chemotherapy aided by OxPhos-i overcomes chemoresistance, depletes LSCs and combats T-ALL. First, we analyzed the role of OxPhos in downstream Notch1 targets at the pre- and leukemic stage considering four stages of thymocyte differentiation (D1-D4), in a mouse model of human T-ALL1. Gene set enrichment analysis (GSEA) implicated increased expression of Notch1 target genes starting at DN1, and OxPhos target genes were the highest-ranked gene set at DN3. Next, activation of Notch1 by its ligand DL4 and inhibition of OxPhos reduced viability of pre-LSCs, indicating that ligand-dependent activation of Notch1 signaling upregulates the OxPhos pathway and sensitizes pre-LSCs to OxPhos-i. To clarify the role of Notch1 signaling, we examined the effect of IACS-010759 on pre-leukemic thymocytes harboring LMO1, SCL-LMO1, NOTCH1, LMO1-NOTCH1 and SCL-LMO1-NOTCH1 with and without DL4 stimulation. We found that in the absence of DL4, only thymocytes harboring the Notch1 oncogene responded to OxPhos-i, whereas all DL4-stimulated thymocytes responded regardless of Notch1 status (Fig. 1a). In addition, at the leukemic stage, we found elevation of the OxPhos pathway driven by oncogenic Notch1 when we compared transcriptomes of SCL-LMO1 induced T-ALL in the presence or absence of the NOTCH1 oncogene. In line with the murine T-ALL NOTCH1 model, we performed transcriptome analysis of two independent T-ALL patient cohorts prior to chemotherapy, COG TARGET ALL (n=263) and AALL1231 (n=75), comparing transcriptomes of NOTCH1-mutated vs NOTCH1-wt T-ALLs. We found co-segregation of NOTCH1 mutations with significant upregulation of OxPhos and TCA cycle genes and downregulation of apoptosis signaling. Aiming to reverse the NOTCH1-controlled anti-apoptotic program and chemoresistance, we next tested the combination of Vincristine, Dexamethasone and L-Asparaginase (VXL) with IACS-010759. When compared to vehicle, OxPhos-i or VXL alone, only the VXL-OxPhos-i treatment caused an energetic crisis indicated by decreased OCR and ECAR (Seahorse), which translated to a profound reduction of viability (CTG, flow cytometry) in T-ALL cell lines (n=9) and primary T-ALL samples (n=5). Additionally, the IACS-VXL combination in vivo resulted in pan-metabolic blockade, which caused metabolic shut-down and triggered early induction of apoptosis in leukemic cells in peripheral blood, spleen and bone marrow (Fig. 1b). Single cell Proteomic analysis (CyTOF) of spleen showed reduced expression of cell proliferation marker -ki67, c-myc, ERK and p38 proteins, and reduction in number of leukemic cells. Finally, this combination therapy resulted in reduced leukemia burden and extension of overall survival across all three aggressive NOTCH1-mutated T-ALL PDX models (p Disclosures Jabbour: Pfizer: Other: Advisory role, Research Funding; Genentech: Other: Advisory role, Research Funding; BMS: Other: Advisory role, Research Funding; Takeda: Other: Advisory role, Research Funding; Amgen: Other: Advisory role, Research Funding; Adaptive Biotechnologies: Other: Advisory role, Research Funding; AbbVie: Other: Advisory role, Research Funding. Teachey:Sobi: Consultancy; Amgen: Consultancy; Janssen: Consultancy; La Roche: Consultancy. Rezvani:Takeda: Other: Licensing agreement; GemoAb: Membership on an entity's Board of Directors or advisory committees; Adicet Bio: Membership on an entity's Board of Directors or advisory committees; Virogen: Membership on an entity's Board of Directors or advisory committees; Pharmacyclics: Other: Educational grant; Affimed: Other: Educational grant; Formula Pharma: Membership on an entity's Board of Directors or advisory committees. Andreeff:Daiichi-Sankyo; Jazz Pharmaceuticals; Celgene; Amgen; AstraZeneca; 6 Dimensions Capital: Consultancy; Daiichi-Sankyo; Breast Cancer Research Foundation; CPRIT; NIH/NCI; Amgen; AstraZeneca: Research Funding; Centre for Drug Research & Development; Cancer UK; NCI-CTEP; German Research Council; Leukemia Lymphoma Foundation (LLS); NCI-RDCRN (Rare Disease Clin Network); CLL Founcdation; BioLineRx; SentiBio; Aptose Biosciences, Inc: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding. Lorenzi:Precision Pathways: Consultancy. Konopleva:Calithera: Research Funding; Kisoji: Consultancy; AbbVie: Consultancy, Research Funding; Sanofi: Research Funding; Genentech: Consultancy, Research Funding; F. Hoffmann La-Roche: Consultancy, Research Funding; Cellectis: Research Funding; Rafael Pharmaceutical: Research Funding; Eli Lilly: Research Funding; Reata Pharmaceutical Inc.;: Patents & Royalties: patents and royalties with patent US 7,795,305 B2 on CDDO-compounds and combination therapies, licensed to Reata Pharmaceutical; Agios: Research Funding; AstraZeneca: Research Funding; Ablynx: Research Funding; Forty-Seven: Consultancy, Research Funding; Amgen: Consultancy; Stemline Therapeutics: Consultancy, Research Funding; Ascentage: Research Funding.

Dendritic cells (DCs) play a pivotal role in priming adaptive immunity. However, the involvement of DCs in controlling excessive and deleterious T cell responses remains poorly defined. Moreover, the metabolic dependence and regulation of DC function are unclear. Here we show that LKB1 signaling in DCs functions as a brake to restrain excessive tumor-promoting regulatory T cell (Treg) and Th17 cell responses, thereby promoting protective anti-tumor immunity and maintaining proper immune homeostasis. LKB1 deficiency results in dysregulated metabolism and mTOR activation of DCs. Loss of LKB1 also leads to aberrant DC maturation and production of cytokines and immunoregulatory molecules. Blocking mTOR signaling in LKB1-deficient DCs partially rectifies the abnormal phenotypes of DC activation and Treg expansion, whereas uncontrolled Th17 responses depend upon IL-6–STAT3 signaling. By coordinating metabolic and immune quiescence of DCs, LKB1 acts as a crucial signaling hub in DCs to enforce protective anti-tumor immunity and normal immune homeostasis.

Chimeric antigen receptor (CAR)–T-cell therapeutic efficacy is associated with long-term T-cell persistence and acquisition of memory. Memory-subset formation requires T-cell factor 1 (TCF-1), a master transcription factor for which few regulators have been identified. Here, we demonstrate using an immune-competent mouse model of B-cell acute lymphoblastic leukemia (ALL; B-ALL) that Regnase-1 deficiency promotes TCF-1 expression to enhance CAR–T-cell expansion and memory-like cell formation. This leads to improved CAR-T–mediated tumor clearance, sustained remissions, and protection against secondary tumor challenge. Phenotypic, transcriptional, and epigenetic profiling identified increased tumor-dependent programming of Regnase-1–deficient CAR-T cells into TCF-1+ precursor exhausted T cells (TPEX) characterized by upregulation of both memory and exhaustion markers. Regnase-1 directly targets Tcf7 messenger RNA (mRNA); its deficiency augments TCF-1 expression leading to the formation of TPEX that support long-term CAR–T-cell persistence and function. Regnase-1 deficiency also reduces exhaustion and enhances the activity of TCF-1− CAR-T cells. We further validate these findings in human CAR-T cells, where Regnase-1 deficiency mediates enhanced tumor clearance in a xenograft B-ALL model. This is associated with increased persistence and expansion of a TCF-1+ CAR–T-cell population. Our findings demonstrate the pivotal roles of TPEX, Regnase-1, and TCF-1 in mediating CAR–T-cell persistence and recall responses, and identify Regnase-1 as a modulator of human CAR–T-cell longevity and potency that may be manipulated for improved therapeutic efficacy.

Regulatory T cells (T

The Hippo kinase Mst1 enforces the establishment of cellular quiescence for terminal maturation and reciprocal fate decisions between iNKT1 and iNKT17 effector cells, which respectively depend upon Opa1-mediated mitochondrial dynamics and ICOS–mTORC2 signaling., Invariant natural killer T (iNKT) cells acquire effector functions during development by mechanisms that remain poorly understood. Here, we show that the Hippo kinases Mst1 and Mst2 act as molecular rheostats for the terminal maturation and effector differentiation programs of iNKT cells. Loss of Mst1 alone or together with Mst2 impedes iNKT cell development, associated with defective IL-15–dependent cell survival. Mechanistically, Mst1 enforces iNKT cellular and transcriptional quiescence associated with maturation and commitment to iNKT1 cells by suppressing proliferation and Opa1-related mitochondrial metabolism that are dynamically regulated during iNKT cell development. Furthermore, Mst1 shapes the reciprocal fate decisions between iNKT1 and iNKT17 effector cells, which respectively depend upon mitochondrial dynamics and ICOS–mTORC2 signaling. Collectively, these findings establish Mst1 as a crucial regulator of mitochondrial homeostasis and quiescence in iNKT cell development and effector lineage differentiation and highlight that establishment of quiescence programs underlies iNKT cell development and effector maturation.

T follicular helper (Tfh) cells are crucial for B cell-mediated humoral immunity(1). Although transcription factors, such as Bcl6, drive Tfh cell differentiation(2,3), whether and how posttranscriptional and metabolic programs enforce Tfh cell programming are unclear. Here, we show that the cytidine diphosphate (CDP)-ethanolamine pathway coordinates the expression and localization of CXCR5 with Tfh responses and humoral immunity. Using in vivo CRISPR-Cas9 screening and functional validation, we uncover Etnk1, Pcyt2 and Selenoi – enzymes in the CDP-ethanolamine pathway for de novo phosphatidylethanolamine (PE) synthesis – as selective posttranscriptional regulators of Tfh cell differentiation, by promoting CXCR5 surface expression and functional effects. Tfh cells show unique lipid metabolic programs and PE distribution to the plasma membrane outer layer where it co-localizes with CXCR5. De novo PE synthesis via the CDP-ethanolamine pathway coordinates these events to prevent CXCR5 internalization and degradation. Genetic deletion of Pcyt2, but not the CDP-choline pathway enzyme Pcyt1a, in activated T cells impairs Tfh cell differentiation, associated with reduced humoral immune responses. Surface PE levels and CXCR5 expression on B cells also depend upon Pcyt2. Our results reveal that phospholipid metabolism coordinates posttranscriptional mechanisms for Tfh cell differentiation and humoral immunity, highlighting metabolic control of context-dependent immune signaling and effector programs.

c-Myc coordinates context-dependent homeostasis and transitional activation with metabolic programming of regulatory T cells., Regulatory T cell (Treg) activation and expansion occur during neonatal life and inflammation to establish immunosuppression, yet the mechanisms governing these events are incompletely understood. We report that the transcriptional regulator c-Myc (Myc) controls immune homeostasis through regulation of Treg accumulation and functional activation. Myc activity is enriched in Tregs generated during neonatal life and responding to inflammation. Myc-deficient Tregs show defects in accumulation and ability to transition to an activated state. Consequently, loss of Myc in Tregs results in an early-onset autoimmune disorder accompanied by uncontrolled effector CD4+ and CD8+ T cell responses. Mechanistically, Myc regulates mitochondrial oxidative metabolism but is dispensable for fatty acid oxidation (FAO). Indeed, Treg-specific deletion of Cox10, which promotes oxidative phosphorylation, but not Cpt1a, the rate-limiting enzyme for FAO, results in impaired Treg function and maturation. Thus, Myc coordinates Treg accumulation, transitional activation, and metabolic programming to orchestrate immune homeostasis.

Dendritic cells orchestrate the crosstalk between innate and adaptive immunity. CD8α+ dendritic cells present antigens to CD8+ T cells and elicit cytotoxic T cell responses to viruses, bacteria and tumours 1 . Although lineage-specific transcriptional regulators of CD8α+ dendritic cell development have been identified 2 , the molecular pathways that selectively orchestrate CD8α+ dendritic cell function remain elusive. Moreover, metabolic reprogramming is important for dendritic cell development and activation3,4, but metabolic dependence and regulation of dendritic cell subsets are largely uncharacterized. Here we use a data-driven systems biology algorithm (NetBID) to identify a role of the Hippo pathway kinases Mst1 and Mst2 (Mst1/2) in selectively programming CD8α+ dendritic cell function and metabolism. Our NetBID analysis reveals a marked enrichment of the activities of Hippo pathway kinases in CD8α+ dendritic cells relative to CD8α− dendritic cells. Dendritic cell-specific deletion of Mst1/2—but not Lats1 and Lats2 (Lats1/2) or Yap and Taz (Yap/Taz), which mediate canonical Hippo signalling—disrupts homeostasis and function of CD8+ T cells and anti-tumour immunity. Mst1/2-deficient CD8α+ dendritic cells are impaired in presentation of extracellular proteins and cognate peptides to prime CD8+ T cells, while CD8α− dendritic cells that lack Mst1/2 have largely normal function. Mechanistically, compared to CD8α− dendritic cells, CD8α+ dendritic cells exhibit much stronger oxidative metabolism and critically depend on Mst1/2 signalling to maintain bioenergetic activities and mitochondrial dynamics for their functional capacities. Further, selective expression of IL-12 by CD8α+ dendritic cells depends on Mst1/2 and the crosstalk with non-canonical NF-κB signalling. Our findings identify Mst1/2 as selective drivers of CD8α+ dendritic cell function by integrating metabolic activity and cytokine signalling, and highlight that the interplay between immune signalling and metabolic reprogramming underlies the unique functions of dendritic cell subsets. A data-driven analysis helps to identify specific roles of the Hippo signalling kinases Mst1 and Mst2 in integrating metabolic activity and cytokine signalling in dendritic cells, and thereby orchestrating immune cell function.

Regulatory T (Treg) cells derived from the thymus (tTreg) and periphery (pTreg) have central and distinct functions in immunosuppression, but mechanisms for the generation and activation of Treg subsets in vivo are unclear. Here, we show that mechanistic target of rapamycin (mTOR) unexpectedly supports the homeostasis and functional activation of tTreg and pTreg cells. mTOR signaling is crucial for programming activated Treg-cell function to protect immune tolerance and tissue homeostasis. Treg-specific deletion of mTOR drives spontaneous effector T-cell activation and inflammation in barrier tissues and is associated with reduction in both thymic-derived effector Treg (eTreg) and pTreg cells. Mechanistically, mTOR functions downstream of antigenic signals to drive IRF4 expression and mitochondrial metabolism, and accordingly, deletion of mitochondrial transcription factor A (Tfam) severely impairs Treg-cell suppressive function and eTreg-cell generation. Collectively, our results show that mTOR coordinates transcriptional and metabolic programs in activated Treg subsets to mediate tissue homeostasis.

Metabolic reprogramming is recognized as one of the key hallmarks in acquiring aggressive phenotype and chemoresistance in solid tumors and hematologic malignancies. We have previously demonstrated that T-ALL are characterized by significant dependency on oxidative phosphorylation (OxPhos) with ability to utilize glutamine either in oxidative or reductive directions of TCA cycle, when mitochondria are blocked by Complex I Inhibitor (Baran N, et al. ASH 2020). To survive upon Complex I blockade leukemic cells require functional monocarboxylate transporter MCT1, that enables excretion of lactate and permissive pyruvate flux (Fig.1 a). Here we show that metabolic intervention utilizing OxPhos blockade can be potentiated by targeting MCT1 transporter and propose a novel metabolic synthetic lethality that could be exploited to eradicate T-ALL and other OxPhos-dependent malignancies. We first demonstrated that Complex I inhibition leads to increased MCT1 expression; on the contrary, MCT1 transporter blockade forces cells to increase OxPhos. In turn, the combinatorial therapy with Complex I inhibitor (IACS-010759) and MCT1 inhibitor (AZD3965) causes loss of ATP content (Fig. 1b), significant reduction of cell number and massive induction of apoptosis. Mechanistically, the combination treatment further reduced oxygen consumption rate (OCR) (Fig. 1c) and increased extracellular acidification rate, as measured by Seahorse. In concert with those results, dual inhibition led to TCA blockade, accumulation of intracellular lactate and depletion of glutamine, cystathionine and glutathione, indicating severe disruption of redox balance as measured by mass spectrometry and confirmed by significant accumulation of intracellular and mitochondrial reactive oxygen species (ROS) (Fig. 1d), loss of mitochondrial membrane potential (ΔΨ) (Fig. 1e) and subsequent mitochondria swelling. RNAseq data showed simultaneous upregulation of glycolysis and glutathione-related processes as possible mechanisms of metabolic compensation, yet strong upregulation of genes regulating apoptosis related to mitochondria dysfunction (Fig. 1f). Real-time hyperpolarized MRI based metabolic imaging studies with [1-13C]-pyruvate in patient-derived xenografts in vivo revealed significant decrease of lactate-to-pyruvate ratio in mice treated with AZD3965 or IACS-010759 alone, and in mice treated with drug combination. [13C]-Glucose isotope tracing analysis in patient-derived xenografts in vivo revealed an increased intracellular trapping of lactate as a marker of treatment effectiveness in mice subjected to dual blockade. While MCT1 inhibition induced only moderate reduction of leukemia growth in vitro and tumor burden in vivo, combination with IACS-010759 depleted significantly both, circulating and marrow/spleen/liver resident leukemia cells. Mechanistically, inhibition of MCT1 by AZD3965 therapy in leukemia-bearing mice led to lactate accumulation, OCR increase, moderate ROS production and mitochondrial membrane hyperpolarization, while Complex I blockade resulted in upregulation of MCT-1, reduction of OCR, lactate production and increase of ROS ; consequently, combinatorial therapy caused complete mitochondria shut-down and drastic inhibition of tumor growth both in vitro and in vivo in two xenografts models and led to significant extension of overall survival (p Figure 1 Figure 1. Disclosures Skwarska: Halilovich E, Wang Y, Morris E, Konopleva M, Skwarska A.: Patents & Royalties: Combination of a MCL-1 inhibitor and midostaurin, uses and pharmaceutical composition thereof.. Konopleva: Reata Pharmaceuticals: Current holder of stock options in a privately-held company, Patents & Royalties: intellectual property rights; Rafael Pharmaceuticals: Other: grant support, Research Funding; Stemline Therapeutics: Research Funding; Eli Lilly: Patents & Royalties: intellectual property rights, Research Funding; Ascentage: Other: grant support, Research Funding; Genentech: Consultancy, Honoraria, Other: grant support, Research Funding; Ablynx: Other: grant support, Research Funding; AstraZeneca: Other: grant support, Research Funding; AbbVie: Consultancy, Honoraria, Other: Grant Support, Research Funding; Novartis: Other: research funding pending, Patents & Royalties: intellectual property rights; Cellectis: Other: grant support; Sanofi: Other: grant support, Research Funding; KisoJi: Research Funding; Calithera: Other: grant support, Research Funding; Forty Seven: Other: grant support, Research Funding; Agios: Other: grant support, Research Funding; F. Hoffmann-La Roche: Consultancy, Honoraria, Other: grant support.

Spatial heterogeneity of diverse cellular components in the tumor microenvironment (TME) plays a critical role in the reprogramming of tumor initiation, growth, invasion, metastasis, and response to therapies. Systematic knowledge of TME spatial organization with regards to immune infiltration and tumor resource distribution is of high clinical significance. High throughput single-cell RNA sequencing (scRNA-seq) has become a revolutionary approach for studying cell composition and the development of TME. However, the spatial information of cells is lost as the tissue must be dissociated before the sequencing is performed. While various spatial techniques are emerging, their applicability is still rather limited. To address this challenge computationally, we develop a novel de novo framework to reconstruct TME spatial organization from scRNA-seq data. We hypothesized that cell spatial organization in a microenvironment is mainly determined by cell identity and interactions between different cells. In particular, the spatial organization of structural cells and immune cells follow different mechanisms. Neighboring structural cells, which share similar whole transcriptome profiles, form a scaffold of the TME; immune cells, whose activities are influenced by the structural cells, migrate in the scaffold to interact with structural cells and exert their functions. The algorithm models the scaffold of structural cells using adaptive nearest neighbor graph by taking the cell density estimation into the consideration, where the nearest neighbor graph was further augmented by inserting immune cells into the appropriate locations of the scaffold according to the LR similarities. To reconstruct 3D spatial organization while preserving the cell topology represented by the graph, we employed a graph embedding strategy to minimize the discrepancy between the graph topology and the embedded 3D space. We evaluated the framework on two diffuse intrinsic pontine gliomas (DIPG) samples from a mouse model with coupled scRNA-seq and spatial transcriptome (ST, 10x Visium platform) data. The predicted spatial organization successfully separates the major cell types. The T-cell infiltrated tumor, verified by the T-cell spatial spots of the ST image, is well recapitulated. We deconvoluted the ST data by integrating the scRNA-seq data using SPOTlight. The neighborhood enrichment distributions of predicted spatial organization and the spot deconvoluted ST data show high consistency as measured by Kullback-Leibler divergence. We found heterogeneous neighborhood composition of CD8+ T-cells, indicating diverse clonality and functions with respect to their locations in the TME. Citation Format: Liang Ding, Hao Shi, Koon-Kiu Yan, Yogesh Dhungana, Sivaraman Natarajan, John Easton, Jason Chiang, Christopher L. Tinkle, Xiaoyan Zhu, Liming Cai, Suzanne J. Baker, Hongbo Chi, Jiyang Yu. Inferring spatial organization of tumor microenvironment from single-cell RNA sequencing data using graph embedding [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 237.

Karmaus et al. show that loss of mechanistic target of rapamycin complex 1 (mTORC1) signaling impairs myelopoiesis. M-CSF–dependent myelopoiesis requires mTORC1 signaling and anabolic metabolism, which in turn promote expression of M-CSFR and transcription factors PU.1 and IRF8, thereby constituting a feed-forward loop for myelopoiesis., Myelopoiesis is necessary for the generation of mature myeloid cells during homeostatic turnover and immunological insults; however, the metabolic requirements for this process remain poorly defined. Here, we demonstrate that myelopoiesis, including monocyte and macrophage differentiation, requires mechanistic target of rapamycin complex 1 (mTORC1) signaling and anabolic metabolism. Loss of mTORC1 impaired myelopoiesis under steady state and dampened innate immune responses against Listeria monocytogenes infection. Stimulation of hematopoietic progenitors with macrophage colony-stimulating factor (M-CSF) resulted in mTORC1-dependent anabolic metabolism, which in turn promoted expression of M-CSF receptor and transcription factors PU.1 and IRF8, thereby constituting a feed-forward loop for myelopoiesis. Mechanistically, mTORC1 engaged glucose metabolism and initiated a transcriptional program involving Myc activation and sterol biosynthesis after M-CSF stimulation. Perturbation of glucose metabolism or disruption of Myc function or sterol biosynthesis impaired myeloid differentiation. Integrative metabolomic and genomic profiling further identified one-carbon metabolism as a central node in mTORC1-dependent myelopoiesis. Therefore, the interplay between mTORC1 signaling and metabolic reprogramming underlies M-CSF–induced myelopoiesis.

Effector regulatory T (eT(reg)) cells are essential for immune tolerance and depend upon T cell receptor (TCR) signals for generation. The immunometabolic signaling mechanisms that promote the differentiation and maintenance of eT(reg) cells remain unclear. Here, we show that isoprenoid-dependent posttranslational lipid modifications dictate eT(reg)-cell accumulation and function by intersecting with TCR-induced intracellular signaling. We find that isoprenoids are essential for activated T(reg)-cell suppressive activity, and T(reg) cell-specific deletion of the respective farnesylation- and geranylgeranylation-promoting enzymes Fntb or Pggt1b leads to the development of fatal autoimmunity, associated with reduced eT(reg)-cell accumulation. Mechanistically, Fntb promotes eT(reg)-cell maintenance by regulating mTORC1 activity and ICOS expression. In contrast, Pggt1b acts as a rheostat of TCR-dependent transcriptional programming and Rac-mediated signaling for establishment of eT(reg)-cell differentiation and immune tolerance. Therefore, our results identify bidirectional metabolic signaling, specifically between immunoreceptor signaling and metabolism-mediated posttranslational lipid modifications, for the differentiation and maintenance of eT(reg) cells.

Thymocyte egress is a critical determinant of T cell homeostasis and adaptive immunity. Du et al. describe unexpected roles of mevalonate metabolism–fueled protein geranylgeranylation, but not farnesylation, in driving thymocyte egress through modulating Cdc42 and Pak activities., Thymocyte egress is a critical determinant of T cell homeostasis and adaptive immunity. Despite the roles of G protein–coupled receptors in thymocyte emigration, the downstream signaling mechanism remains poorly defined. Here, we report the discrete roles for the two branches of mevalonate metabolism–fueled protein prenylation pathway in thymocyte egress and immune homeostasis. The protein geranylgeranyltransferase Pggt1b is up-regulated in single-positive thymocytes, and loss of Pggt1b leads to marked defects in thymocyte egress and T cell lymphopenia in peripheral lymphoid organs in vivo. Mechanistically, Pggt1b bridges sphingosine-1-phosphate and chemokine-induced migratory signals with the activation of Cdc42 and Pak signaling and mevalonate-dependent thymocyte trafficking. In contrast, the farnesyltransferase Fntb, which mediates a biochemically similar process of protein farnesylation, is dispensable for thymocyte egress but contributes to peripheral T cell homeostasis. Collectively, our studies establish context-dependent effects of protein prenylation and unique roles of geranylgeranylation in thymic egress and highlight that the interplay between cellular metabolism and posttranslational modification underlies immune homeostasis.

Summary Regulatory T (Treg) cells are critical mediators of immune tolerance whose activity depends upon T cell receptor (TCR) and mTORC1 kinase signaling, but the mechanisms that dictate functional activation of these pathways are incompletely understood. Here, we showed that amino acids license Treg cell function by priming and sustaining TCR-induced mTORC1 activity. mTORC1 activation was induced by amino acids, especially arginine and leucine, accompanied by the dynamic lysosomal localization of the mTOR and Tsc complexes. Rag and Rheb GTPases were central regulators of amino acid-dependent mTORC1 activation in effector Treg (eTreg) cells. Mice bearing RagA-RagB- or Rheb1-Rheb2-deficient Treg cells developed a fatal autoimmune disease and had reduced eTreg cell accumulation and function. RagA-RagB regulated mitochondrial and lysosomal fitness, while Rheb1-Rheb2 enforced eTreg cell suppressive gene signature. Together, these findings reveal a crucial requirement of amino acid signaling for licensing and sustaining mTORC1 activation and functional programming of Treg cells.

Adoptive cell therapy represents a new paradigm in cancer immunotherapy, but it can be limited by the poor persistence and function of transferred T cells1. Here we use an in vivo pooled CRISPR-Cas9 mutagenesis screening approach to demonstrate that, by targeting REGNASE-1, CD8+ T cells are reprogrammed to long-lived effector cells with extensive accumulation, better persistence and robust effector function in tumours. REGNASE-1-deficient CD8+ T cells show markedly improved therapeutic efficacy against mouse models of melanoma and leukaemia. By using a secondary genome-scale CRISPR-Cas9 screening, we identify BATF as the key target of REGNASE-1 and as a rheostat that shapes antitumour responses. Loss of BATF suppresses the increased accumulation and mitochondrial fitness of REGNASE-1-deficient CD8+ T cells. By contrast, the targeting of additional signalling factors-including PTPN2 and SOCS1-improves the therapeutic efficacy of REGNASE-1-deficient CD8+ T cells. Our findings suggest that T cell persistence and effector function can be coordinated in tumour immunity and point to avenues for improving the efficacy of adoptive cell therapy for cancer.

How early events in effector T cell (TEFF) subsets tune memory T cell (TMEM) responses remains incompletely understood. Here, we systematically investigated metabolic factors in fate determination of TEFF and TMEM cells using in vivo pooled CRISPR screening, focusing on negative regulators of TMEM responses. We found that amino acid transporters Slc7a1 and Slc38a2 dampened the magnitude of TMEM differentiation, in part through modulating mTORC1 signaling. By integrating genetic and systems approaches, we identified cellular and metabolic heterogeneity among TEFF cells, with terminal effector differentiation associated with establishment of metabolic quiescence and exit from the cell cycle. Importantly, Pofut1 (protein-O-fucosyltransferase-1) linked GDP-fucose availability to downstream Notch-Rbpj signaling, and perturbation of this nutrient signaling axis blocked terminal effector differentiation but drove context-dependent TEFF proliferation and TMEM development. Our study establishes that nutrient uptake and signaling are key determinants of T cell fate and shape the quantity and quality of TMEM responses.

Regulatory T (Treg) cell activation and expansion during neonatal life and in response to inflammation are critical for immunosuppression, yet the mechanisms governing these events are incompletely understood. We report that the oncogene and transcriptional regulator c-Myc (Myc) controls immune homeostasis through regulation of Treg cell accumulation and functional activation. Myc activity is enriched in Treg cells generated during neonatal life and responding to inflammation. Myc-deficient Treg cells show cell-intrinsic defects in overall accumulation and ability to transition to an activated state during early life or acute inflammation. Consequently, loss of Myc in Treg cells results in a rapid, early-onset autoimmune disorder accompanied by uncontrolled effector CD4+ and CD8+ T cell responses. We also provide evidence that Myc regulates mitochondrial oxidative metabolism but is dispensable for fatty acid oxidation (FAO). Indeed, Treg cell-specific deletion of Cox10, which is required for oxidative phosphorylation, but not Cpt1a, the rate-limiting enzyme for FAO, results in impaired Treg cell function and maturation. Thus, Myc coordinates Treg cell accumulation, transitional activation and metabolic programming to orchestrate immune homeostasis.

The interaction between extrinsic factors and intrinsic signal strength governs thymocyte development, but the mechanisms linking them remain elusive. We report that mechanistic target of rapamycin complex 1 (mTORC1) couples microenvironmental cues with metabolic programs to orchestrate the reciprocal development of two fundamentally distinct T cell lineages, the αβ and γδ T cells. Developing thymocytes dynamically engage metabolic programs including glycolysis and oxidative phosphorylation, as well as mTORC1 signaling. Loss of RAPTOR-mediated mTORC1 activity impairs the development of αβ T cells but promotes γδ T cell generation, associated with disrupted metabolic remodeling of oxidative and glycolytic metabolism. Mechanistically, we identify mTORC1-dependent control of reactive oxygen species production as a key metabolic signal in mediating αβ and γδ T cell development, and perturbation of redox homeostasis impinges upon thymocyte fate decisions and mTORC1-associated phenotypes. Furthermore, single-cell RNA sequencing and genetic dissection reveal that mTORC1 links developmental signals from T cell receptors and NOTCH to coordinate metabolic activity and signal strength. Our results establish mTORC1-driven metabolic signaling as a decisive factor for reciprocal αβ and γδ T cell development and provide insight into metabolic control of cell signaling and fate decisions.

A defining feature of adaptive immunity is the development of long-lived memory T cells to curtail infection. Recent studies have identified a unique stem-like T-cell subset amongst exhausted CD8-positive T cells in chronic infection1-3, but it remains unclear whether CD4-positive T-cell subsets with similar features exist in chronic inflammatory conditions. Amongst helper T cells, TH17 cells have prominent roles in autoimmunity and tissue inflammation and are characterized by inherent plasticity4-7, although how such plasticity is regulated is poorly understood. Here we demonstrate that TH17 cells in a mouse model of autoimmune disease are functionally and metabolically heterogeneous; they contain a subset with stemness-associated features but lower anabolic metabolism, and a reciprocal subset with higher metabolic activity that supports transdifferentiation into TH1-like cells. These two TH17-cell subsets are defined by selective expression of the transcription factors TCF-1 and T-bet, and by discrete levels of CD27 expression. We also identify signalling via the kinase complex mTORC1 as a central regulator of TH17-cell fate decisions by coordinating metabolic and transcriptional programmes. TH17 cells with disrupted mTORC1 signalling or anabolic metabolism fail to induce autoimmune neuroinflammation or to develop into TH1-like cells, but instead upregulate TCF-1 expression and acquire stemness-associated features. Single-cell RNA sequencing and experimental validation reveal heterogeneity in fate-mapped TH17 cells, and a developmental arrest in the TH1 transdifferentiation trajectory upon loss of mTORC1 activity or metabolic perturbation. Our results establish that the dichotomy of stemness and effector function underlies the heterogeneous TH17 responses and autoimmune pathogenesis, and point to previously unappreciated metabolic control of plasticity in helper T cells.

Summary Interleukin-2 (IL-2) and downstream transcription factor STAT5 are important for maintaining regulatory T (Treg) cell homeostasis and function. Treg cells can respond to low IL-2 levels, but the mechanisms of STAT5 activation during partial IL-2 deficiency remain uncertain. We identified the serine-threonine kinase Mst1 as a signal-dependent amplifier of IL-2−STAT5 activity in Treg cells. High Mst1 and Mst2 (Mst1−Mst2) activity in Treg cells was crucial to prevent tumor resistance and autoimmunity. Mechanistically, Mst1−Mst2 sensed IL-2 signals to promote the STAT5 activation necessary for Treg cell homeostasis and lineage stability and to maintain the highly suppressive phosphorylated-STAT5+ Treg cell subpopulation. Unbiased quantitative proteomics revealed association of Mst1 with the cytoskeletal DOCK8−LRCHs module. Mst1 deficiency limited Treg cell migration and access to IL-2 and activity of the small GTPase Rac, which mediated downstream STAT5 activation. Collectively, IL-2−STAT5 signaling depends upon Mst1−Mst2 functions to maintain a stable Treg cell pool and immune tolerance.

Regulatory T (Treg) cells derived from the thymus (tTreg) and periphery (pTreg) have central and distinct functions in immunosuppression, but mechanisms for the generation and activation of Treg subsets in vivo are unclear. Here, we show that mechanistic target of rapamycin (mTOR) unexpectedly supports the homeostasis and functional activation of tTreg and pTreg cells. mTOR signaling is crucial for programming activated Treg-cell function to protect immune tolerance and tissue homeostasis. Treg-specific deletion of mTOR drives spontaneous effector T-cell activation and inflammation in barrier tissues and is associated with reduction in both thymic-derived effector Treg (eTreg) and pTreg cells. Mechanistically, mTOR functions downstream of antigenic signals to drive IRF4 expression and mitochondrial metabolism, and accordingly, deletion of mitochondrial transcription factor A (Tfam) severely impairs Treg-cell suppressive function and eTreg-cell generation. Collectively, our results show that mTOR coordinates transcriptional and metabolic programs in activated Treg subsets to mediate tissue homeostasis., The authors previously showed that mTOR controls the function of regulatory T cells. Here they show how this mTOR signaling orchestrates homeostasis of Treg-cell subsets and prevents fatal autoimmunity.