SUMMARY Naïve T cells respond to antigen stimulation by exiting from quiescence and initiating clonal expansion and functional differentiation, but the control mechanism is elusive. Here we describe that Raptor-mTORC1-dependent metabolic programming is a central determinant of this transitional process. Loss of Raptor abrogated T cell priming and Th2 cell differentiation, although Raptor function is less important for continuous proliferation of actively cycling cells. mTORC1 coordinated multiple metabolic programs in T cells including glycolysis, lipid synthesis and oxidative phosphorylation to mediate antigen-triggered exit from quiescence. mTORC1 further linked glucose metabolism to the initiation of Th2 cell differentiation by orchestrating cytokine receptor expression and cytokine responsiveness. Activation of Raptor-mTORC1 integrated T cell receptor and CD28 co-stimulatory signals in antigen-stimulated T cells. Our studies identify a Raptor-mTORC1-dependent pathway linking signal-dependent metabolic reprogramming to quiescence exit, and this in turn coordinates lymphocyte activation and fate decisions in adaptive immunity.

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.

Mitochondrial abnormalities have been noted in lupus, but the causes and consequences remain obscure. Autophagy-related genes ATG5 , ATG7 , and IRGM have been previously implicated in autoimmune disease. We reasoned that failure to clear defective mitochondria via mitophagy might be a foundational driver in autoimmunity by licensing mitochondrial (mt)DNA-dependent induction of type I interferon (IFN-I). Here, we show that mice lacking the GTPase IRGM1 (IRGM homologue) exhibited a type I interferonopathy with autoimmune features. Irgm1 deletion impaired execution of mitophagy with cell-specific consequences. In fibroblasts, mtDNA soiling of the cytosol induced cyclic GMP-AMP synthase (cGAS)–Stimulator of Interferon Genes (STING)-dependent IFN-I, whereas in macrophages, lysosomal TLR7 was activated. In vivo , Irgm1 −/− tissues exhibited mosaic dependency upon nucleic acid receptors. Whereas salivary and lacrimal gland autoimmune pathology were abolished and lung pathology was attenuated by cGAS and STING deletion, pancreatic pathology remained unchanged. These findings reveal fundamental connections between mitochondrial quality control and tissue-selective autoimmune disease.

Significance Enhancing the generation and function of memory T cells represents a crucial strategy to improve protective immunity against pathogens and tumors. The signaling pathway via mechanistic target of rapamycin (mTOR) has been implicated in the regulation of the differentiation of effector and memory T cells, but the upstream regulators or downstream mechanisms remain unclear. In this study, we provide insight into the mechanistic basis that controls mTOR signaling and memory T-cell responses. The deficiency of tuberous sclerosis 1 (Tsc1) in antigen-experienced T cells impairs the differentiation of memory T-cell precursors and the formation of memory T cells, associated with excessive mTOR activity and dysregulated cell metabolism. Our study establishes a molecular mechanism that links mTOR signaling and cell metabolism for memory T-cell development.

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⌬ 9-Tetrahydrocannabinol (⌬ 9 -THC) has been widely established as a modulator of host immune responses. Accordingly, the objective of the present study was to examine the effects of ⌬ 9 -THC on the immune response within the lungs and associated changes in the morphology of the bronchiolar epithelium after one challenge with a nonlethal dose of the influenza virus A/PR/8 (PR8). C57BL/6 mice were treated by oral gavage with ⌬ 9 -THC and/or vehicle (corn oil) for 5 consecutive days. On day 3, mice were instilled intranasally with 50 plaque-forming units of PR8 and/or vehicle (saline) 4 h before ⌬ 9 -THC exposure. Mice were subsequently killed 7 and 10 days postinfection (dpi). Viral hemagglutinin 1 (H1) mRNA levels in the lungs were increased in a dose-dependent manner with ⌬ 9 -THC treatment. Enumeration of inflammatory cell types in bronchoalveolar lavage fluid showed an attenuation of macrophages and CD4 ϩ and CD8 ϩ T cells in ⌬ 9 -THC-treated mice compared with controls. Likewise, the magnitude of inflammation and virus-induced mucous cell metaplasia, as assessed by histopathology, was reduced in ⌬ 9 -THC-treated mice by 10 dpi. Collectively, these results suggest that ⌬ 9 -THC treatment increased viral load, as assessed by H1 mRNA levels, through a decrease in recruitment of macrophages and lymphocytes, particularly CD4 ϩ and CD8 ϩ T cells, to the lung.

The role of cannabinoid receptors, CB1 and CB2, in immune competence and modulation by Delta9-tetrahydrocannabinol (Delta9-THC) was investigated in CB1(-/-)/CB2(-/-) mice. Immunofluorescence analysis of splenic leukocytes showed no significant differences in the percentage of T cell subsets, B cells, or macrophages between wild-type and CB1(-/-)/CB2(-/-) mice. Lymphoproliferative control responses to PHA, phorbol ester plus ionomycin, or LPS and sensitivity to suppression by Delta9-THC showed no profound differences between the two genotypes, although some differences were observed in control baseline responses. Likewise, similar control responses and sensitivity to Delta9-THC were observed in mixed lymphocyte responses (MLR) and in IL-2 and IFN-gamma production in both genotypes. Conversely, humoral immune responses showed a markedly different profile of activity. Delta9-THC suppressed the in vivo T cell-dependent, anti-sheep RBC (anti-sRBC) IgM antibody-forming cell (AFC) response in wild-type but not in CB1(-/-)/CB2(-/-) mice, and the in vitro anti-sRBC IgM response in CB1(-/-)/CB2(-/-) splenocytes was too low to rigorously assess CB1/CB2 involvement in modulation by Delta9-THC. Conversely, comparable in vitro IgM AFC control responses to LPS and CD40 ligand (CD40L) activation were observed in the two genotypes. Interestingly, LPS-induced IgM responses were refractory to suppression by Delta9-THC, regardless of genotype, and CD40L-induced IgM responses were only suppressed by Delta9-THC in wild-type but not in CB1(-/-)/CB2(-/-) B cells. Collectively, we demonstrate differential involvement of CB1 and/or CB2 in immune modulation by Delta9-THC and in some control responses. Moreover, CB1/CB2 involvement was observed in humoral responses requiring CD40-initiated signaling for suppression by Delta9-THC.