SummaryExpansion and acquisition of Th1 cell effector function requires metabolic reprogramming; however, the signals instructing these adaptations remain poorly defined. Here we found that in activated human T cells, autocrine stimulation of the complement receptor CD46, and specifically its intracellular domain CYT-1, was required for induction of the amino acid (AA) transporter LAT1 and enhanced expression of the glucose transporter GLUT1. Furthermore, CD46 activation simultaneously drove expression of LAMTOR5, which mediated assembly of the AA-sensing Ragulator-Rag-mTORC1 complex and increased glycolysis and oxidative phosphorylation (OXPHOS), required for cytokine production. T cells from CD46-deficient patients, characterized by defective Th1 cell induction, failed to upregulate the molecular components of this metabolic program as well as glycolysis and OXPHOS, but IFN-γ production could be reinstated by retrovirus-mediated CD46-CYT-1 expression. These data establish a critical link between the complement system and immunometabolic adaptations driving human CD4+ T cell effector function.

Effector memory (EM) CD4+ T cells recirculate between normoxic blood and hypoxic tissues to screen for cognate Ag. How mitochondria of these cells, shuttling between normoxia and hypoxia, maintain bioenergetic efficiency and stably uphold antiapoptotic features is unknown. In this study, we found that human EM CD4+ T cells had greater spare respiratory capacity (SRC) than did naive counterparts, which was immediately accessed under hypoxia. Consequently, hypoxic EM cells maintained ATP levels, survived and migrated better than did hypoxic naive cells, and hypoxia did not impair their capacity to produce IFN-γ. EM CD4+ T cells also had more abundant cytosolic GAPDH and increased glycolytic reserve. In contrast to SRC, glycolytic reserve was not tapped under hypoxic conditions, and, under hypoxia, glucose metabolism contributed similarly to ATP production in naive and EM cells. However, both under normoxic and hypoxic conditions, glucose was critical for EM CD4+ T cell survival. Mechanistically, in the absence of glycolysis, mitochondrial membrane potential (ΔΨm) of EM cells declined and intrinsic apoptosis was triggered. Restoring pyruvate levels, the end product of glycolysis, preserved ΔΨm and prevented apoptosis. Furthermore, reconstitution of reactive oxygen species (ROS), whose production depends on ΔΨm, also rescued viability, whereas scavenging mitochondrial ROS exacerbated apoptosis. Rapid access of SRC in hypoxia, linked with built-in, oxygen-resistant glycolytic reserve that functionally insulates ΔΨm and mitochondrial ROS production from oxygen tension changes, provides an immune-metabolic basis supporting survival, migration, and function of EM CD4+ T cells in normoxic and hypoxic conditions.

Transforming growth factor–β (TGF-β) is produced by tumors, and increased amounts of this cytokine in the tumor microenvironment and serum are associated with poor patient survival. TGF-β–mediated suppression of antitumor T cell responses contributes to tumor growth and survival. However, TGF-β also has tumor-suppressive activity; thus, dissecting cell type–specific molecular effects may inform therapeutic strategies targeting this cytokine. Here, using human peripheral and tumor-associated lymphocytes, we investigated how tumor-derived TGF-β suppresses a key antitumor function of CD4+ T cells, interferon-γ (IFN-γ) production. Suppression required the expression and phosphorylation of Smad proteins in the TGF-β signaling pathway, but not their nuclear translocation, and depended on oxygen availability, suggesting a metabolic basis for these effects. Smad proteins were detected in the mitochondria of CD4+ T cells, where they were phosphorylated upon treatment with TGF-β. Phosphorylated Smad proteins were also detected in the mitochondria of isolated tumor-associated lymphocytes. TGF-β substantially impaired the ATP-coupled respiration of CD4+ T cells and specifically inhibited mitochondrial complex V (ATP synthase) activity. Last, inhibition of ATP synthase alone was sufficient to impair IFN-γ production by CD4+ T cells. These results, which have implications for human antitumor immunity, suggest that TGF-β targets T cell metabolism directly, thus diminishing T cell function through metabolic paralysis.

Whether screening the metabolic activity of immune cells facilitates discovery of molecular pathology remains unknown. Here we prospectively screened the extracellular acidification rate (ECAR) as a measure of glycolysis and the oxygen consumption rate (OCR) as a measure of mitochondrial respiration in B cells from patients with primary antibody deficiency (PAD). The highest OCR values were detected in three study participants with persistent polyclonal B cell lymphocytosis (PPBL). Exome sequencing identified germline mutations in SDHA, which encodes succinate dehydrogenase subunit A, in all three patients with PPBL. SDHA gain-of-function led to accumulation of fumarate in PPBL B cells, which engaged the KEAP1-Nrf2 system to drive the transcription of genes encoding inflammatory cytokines. In a single patient trial, blocking the activity of the cytokine IL-6 in vivo prevented systemic inflammation and ameliorated clinical disease. Overall, our study has identified pathological mitochondrial retrograde signaling as a disease modifier in PAD. 3 Primary immunodeficiency disorders (PIDs) are rare genetic syndromes arising from defects in the immune system 1. The majority of PID patients display primary antibody deficiency (PAD) that can develop due to B cell intrinsic defects 2. The causes and genetic background of PADs are complex and pathogenic mutations have been identified only in a minority of cases 3, 4, 5. PADs present with a spectrum of clinical problems, ranging from infections to autoinflammation, autoimmunity, lymphoproliferation and enteropathy. Non-infectious complications are typically unaffected by immunoglobulin replacement therapy and contribute to excess mortality 6. The spectrum of clinical presentation is broad even in patients harboring the same pathogenic mutations, pointing to disease modifiers shaping clinical features 6. Cellular metabolism governs immune cell function 7, 8, 9. Specifically, various facets of glycolysis and glutaminolysis impact the function of B cells 10, 11, 12, 13. Glutaminolysis can contribute to ATP production, and glutamine-derived α-ketoglutarate (α-KG) serves as an anaplerotic source of tricarboxylic acid (TCA) cycle metabolites 14. Mitochondrial oxidative phosphorylation (OxPhos) produces most of the ATP required for anabolic processes in immune cells 15. Non-bioenergetic features of mitochondria also regulate immune cell function. Production of mitochondrial reactive oxygen species (mROS) has been linked to the activation of the transcription factor NFAT in CD4 + T cells and to inhibition of the B cell antigen receptor (BCR) signaling in B cells 16, 17. In T cells, mitochondrial function and epigenetic remodeling are interlinked via pyruvate oxidation and conversion of pyruvate-derived citrate to acetyl-CoA, which is required for histone acetylation 18, 19. Metabolites of the TCA cycle can also directly activate (a-KG), or inhibit (fumarate, succinate) dioxygenases involved in histone and DNA demethylation, thus modulating transcriptional activity. This process of m...