Regulatory T (T reg ) cells are essential for immune tolerance 1 but also drive immunosuppression in the tumour microenvironment (TME) 2 . Therapeutic targeting of T reg cells in cancer requires the identification of context-specific mechanisms for T reg cell function. Here we demonstrate that inhibition of sterol regulatory element-binding protein (SREBP)-dependent lipid synthesis and metabolic signalling in T reg cells unleashes effective antitumour immune responses without autoimmune toxicity. SREBP activity is upregulated in intratumoural T reg cells, and T reg cell-specific deletion of SCAP, an obligatory factor for SREBP activity, inhibits tumour growth and boosts anti-PD-1 immunotherapy, associated with uncontrolled IFN-γ production and impaired function of intratumoural T reg cells. Mechanistically, SCAP/SREBP signalling coordinates lipid synthetic programs and inhibitory receptor signalling in T reg cells. First, de novo fatty acid synthesis mediated by fatty acid synthase (FASN) contributes to functional maturation of T reg cells, and loss of FASN in T reg cells inhibits tumour growth. Second, T reg cells show enhanced Pdcd1 expression in tumours in a process dependent on SREBP activity that further signals to mevalonate metabolism-driven protein geranylgeranylation, and blocking PD-1 or SREBP signaling results in dysregulated PI3K activation in intratumoural T reg cells. Our findings establish that metabolic reprogramming enforces T reg cell functional specialization in tumours, pointing to new avenues to target T reg cells for cancer therapy.

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 in exhausted CD8+ T cells in chronic infection1–3, but it remains unclear whether CD4+ T cell subsets with similar features exist in chronic inflammatory conditions. Among helper T cells, TH17 cells play prominent roles in autoimmunity and tissue inflammation and are characterized by inherent plasticity4–7, although the regulation of plasticity is poorly understood. Here we demonstrate that TH17 cells in autoimmune disease are functionally and metabolically heterogeneous and contain a subset with stemness-associated features but lower anabolic metabolism, and a reciprocal subset with higher metabolic activity that supports the transdifferentiation into TH1 cells. These two TH17 cell subsets are defined by selective expression of transcription factors TCF-1 and T-bet, and discrete CD27 expression levels. Moreover, we identify mTORC1 signaling as a central regulator to orchestrate TH17 cell fates by coordinating metabolic and transcriptional programs. TH17 cells with disrupted mTORC1 or anabolic metabolism fail to induce autoimmune neuroinflammation or develop into TH1-like cells, but instead upregulate TCF-1 expression and activity 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 mTORC1 deletion 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 helper T cell plasticity.

Dendritic cells (DCs) orchestrate the crosstalk between innate and adaptive immunity. CD8α+ DCs present antigens to CD8+ T cells and elicit cytotoxic T-cell responses to viruses, bacteria and tumors1. Although lineage-specific transcriptional regulators of CD8α+ DC development have been identified2, the molecular pathways that selectively orchestrate CD8α+ DC function remain elusive. Moreover, metabolic reprogramming is important for DC development and activation3,4, but metabolic dependence and regulation of DC subsets are unknown. Here, we describe a data-driven systems biology algorithm (NetBID) and an unexpected role of Hippo pathway kinases, Mst1 and Mst2 (Mst1/2), in selectively programming CD8α+ DC function and metabolism. Our NetBID analysis reveals a marked enrichment of the activities of Hippo pathway kinases in CD8α+ DCs relative to CD8α− DCs. DC-specific deletion of Mst1/2, but not Lats1/2 or Yap/Taz that mediate canonical Hippo signaling, disrupts homeostasis and function of CD8+ T cells and anti-tumor immunity. Mst1/2-deficient CD8α+ DCs are impaired in presenting extracellular proteins and cognate peptides to prime CD8+ T cells, while CD8α− DCs lacking Mst1/2 have largely normal function. Mechanistically, compared with CD8α− DCs, CD8α+ DCs show much stronger oxidative metabolism and critically depend upon Mst1/2 signaling to maintain bioenergetic activities and mitochondrial dynamics for functional capacities. Further, CD8α+ DCs selectively express IL-12 that depends upon Mst1/2 and the crosstalk with non-canonical NF-κB signaling. Our findings identify Mst1/2 as selective drivers of CD8α+ DC function by integrating metabolic activity and cytokine signaling, and highlight that the interplay between immune signaling and metabolic reprogramming underlies the unique function of DC subsets.

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 Rac1, 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.

T cells play pivotal roles in shaping host immune responses in infectious diseases, autoimmunity, and cancer. The activation of T cells requires immune and growth factor-derived signals. However, alterations in nutrients and metabolic signals tune T cell responses by impinging upon T cell fates and immune functions. In this review, we summarize how key nutrients, including glucose, amino acids, and lipids, and their sensors and transporters shape T cell responses. We also briefly discuss regulation of T cell responses by oxygen and energy sensing mechanisms.

Chronic inflammation is a major risk factor for cancer, including gastric cancers and other gastrointestinal cancers. For example, chronic inflammation caused by autoimmune gastritis (AIG) is associated with an increased risk of gastric polyps, gastric carcinoid tumors, and possibly adenocarcinomas. In this study, we characterized the progression of gastric cancer in a novel mouse model of AIG. In this model, disease was caused by CD4+ T cells expressing a transgenic T cell receptor specific for a peptide from the H+/K+ ATPase proton pump, a protein expressed by parietal cells in the stomach. AIG caused epithelial cell aberrations that mimicked most of those seen in progression of human gastric cancers, including chronic gastritis followed by oxyntic atrophy, mucous neck cell hyperplasia, spasmolytic polypeptide-expressing metaplasia (SPEM), dysplasia and ultimately gastric intraepithelial neoplasias (GIN). Our work provides the first direct evidence that AIG supports the development of gastric neoplasia, and provides a useful model to study how inflammation drives gastric cancer.

Background & AimsAtrophic gastritis caused by chronic inflammation in the gastric mucosa leads to the loss of gastric glandular cells, including acid-secreting parietal cells. Parietal cell atrophy in a setting of chronic inflammation induces spasmolytic polypeptide expressing metaplasia, a critical step in gastric carcinogenesis. However, the mechanisms by which inflammation causes parietal cell atrophy and spasmolytic polypeptide expressing metaplasia are not well defined. We investigated the role of interleukin-17A (IL-17A) in causing parietal cell atrophy.MethodsA mouse model of autoimmune atrophic gastritis was used to examine IL-17A production during early and late stages of disease. Organoids derived from corpus glands were used to determine the direct effects of IL-17A on gastric epithelial cells. Immunofluorescent staining was used to examine IL-17A receptors and the direct effect of signaling on parietal cells. Mice were infected with an IL-17A-producing adenovirus to determine the effects of IL-17A on parietal cells in vivo. Finally, IL-17A neutralizing antibodies were administered to mice with active atrophic gastritis to evaluate the effects on parietal cell atrophy and metaplasia.ResultsIncreased IL-17A correlated with disease severity in mice with chronic atrophic gastritis. IL-17A caused caspase-dependent gastric organoid degeneration, which could not be rescued with a necroptosis inhibitor. Parietal cells expressed IL-17A receptors and IL-17A treatment induced apoptosis in parietal cells. Overexpressing IL-17A in vivo induced caspase-3 activation and terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling staining in parietal cells. Finally, IL-17A neutralizing antibody decreased parietal cell atrophy and metaplasia in mice with chronic atrophic gastritis.ConclusionsThese data identify IL-17A as a cytokine that promotes parietal cell apoptosis during atrophic gastritis, a precursor lesion for gastric cancer.

The ability to regulate ongoing inflammation using regulatory T cells (Tregs) is under intense investigation. Strategies to induce and expand Ag-specific Tregs are being developed, and whether various types of Tregs are suppressive in the inflammatory conditions associated with ongoing disease needs to be determined. In this study, we report that TGF-β–induced Tregs (iTregs) and expanded Tregs specific for a major self-Ag in autoimmune gastritis suppress inflammation and associated pathology when administered late in the process of ongoing disease. Transferred iTregs localized to the stomach, maintained Foxp3 and suppressor functions, and engaged several distinct mechanisms to alleviate disease progression. In addition to suppressing the production of inflammatory cytokines in the stomach and preventing the destruction of parietal cells, we show that iTregs secrete numerous chemokines and regulate both iTreg and effector T cell trafficking into the stomach. These data support efforts to use iTregs in therapies to treat autoimmunity and inflammatory diseases and provide novel insight into the biological mechanisms of iTreg-mediated immune suppression.