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Unusual metabolic pathways used by cancer cells offer possible targets for the development of clinical treatments. One such pathway, involving molecules called polyamines, has been found for pancreatic cancer. Pancreatic cancer cells make polyamine molecules by an unusual pathway.

The adoption of Warburg metabolism is critical for the activation of macrophages in response to lipopolysaccharide. Macrophages stimulated with lipopolysaccharide increase their expression of nicotinamide phosphoribosyltransferase (NAMPT), a key enzyme in NAD + salvage, and loss of NAMPT activity alters their inflammatory potential. However, the events that lead to the cells' becoming dependent on NAD + salvage remain poorly defined. We found that depletion of NAD + and increased expression of NAMPT occurred rapidly after inflammatory activation and coincided with DNA damage caused by reactive oxygen species (ROS). ROS produced by complex III of the mitochondrial electron-transport chain were required for macrophage activation. DNA damage was associated with activation of poly(ADP-ribose) polymerase, which led to consumption of NAD + . In this setting, increased NAMPT expression allowed the maintenance of NAD + pools sufficient for glyceraldehyde-3-phosphate dehydrogenase activity and Warburg metabolism. Our findings provide an integrated explanation for the dependence of inflammatory macrophages on the NAD + salvage pathway. Macrophages can shift their cellular metabolism in response to tissue cues and infection. Pearce and colleagues show that lipopolysaccharide-activated ‘inflammatory’ macrophages become depleted of NAD + pools and require the salvage-pathway enzyme NAMPT to sustain cellular redox balance.

During infection, CD8+ T cells initially expand then contract, leaving a small memory pool providing long lasting immunity. While it has been described that CD8+ T cell memory formation becomes defective in old age, the cellular mechanism is largely unknown. Autophagy is a major cellular lysosomal degradation pathway of bulk material, and levels are known to fall with age. In this study, we describe a novel role for autophagy in CD8+ T cell memory formation. Mice lacking the autophagy gene Atg7 in T cells failed to establish CD8+ T cell memory to influenza and MCMV infection. Interestingly, autophagy levels were diminished in CD8+ T cells from aged mice. We could rejuvenate CD8+ T cell responses in elderly mice in an autophagy dependent manner using the compound spermidine. This study reveals a cell intrinsic explanation for poor CD8+ T cell memory in the elderly and potentially offers novel immune modulators to improve aged immunity. In the face of an infection, the immune system mounts an aggressive response by producing many copies of killer immune cells called CD8+ T cells that recognize and destroy any cells infected with the invading pathogen. The number of killer cells produced depends on the extent of the infection. Once the infection has been brought under control, most of the CD8+ T cells die off. The small numbers that are retained—called memory cells—‘remember’ the pathogen, so that if it invades the body again, they can help the immune system to respond more quickly and effectively. Memory cells are also critical to the effectiveness of vaccines, many of which introduce a dead or weakened pathogen into the body. This does not cause an infection, but does allow the immune system to create memory cells that are able to fend off the same pathogen in the future. However, vaccines only work in individuals that are able to produce and maintain memory cells, which many older people are less able to do. An important system that maintains cells, called autophagy, destroys and removes the ‘junk’ and toxic by products that all cells accumulate over time as a result of normal cell functions. Without autophagy, cells become less able to produce energy and they may die. Puleston et al. show that autophagy begins to fail in old mice, which prevents the formation of a proper memory response. In addition, mice that lack an important gene needed for autophagy are unable to produce memory cells after being infected with viruses such as influenza. Puleston et al. found that boosting autophagy in older mice using a chemical called spermidine—which is also found naturally in many tissues—helped to restore the mice's ability to create and maintain memory cells. Spermidine-treated mice developed a stronger immunity to influenza after vaccination compared with other mice of a similar age. Further research is required to better understand how spermidine works to see if it could be developed into a drug that safely boosts the immune system of humans.

Significance Autophagy is an evolutionarily conserved catabolic process essential to maintaining cellular homeostasis through the breakdown and recycling of damaged organelles and long-lived proteins. We report that autophagy plays an essential cell-intrinsic role in maintaining the survival of a subset of innate-like cells known as invariant natural killer T (iNKT) cells. Autophagy deficiency prevents transition to a quiescent state after population expansion of thymic iNKT cells. Hence, autophagy-deficient iNKT cells accumulate mitochondria and oxygen radicals and subsequently die of apoptosis. Autophagy is an evolutionarily conserved cellular homeostatic pathway essential for development, immunity, and cell death. Although autophagy modulates MHC antigen presentation, it remains unclear whether autophagy defects impact on CD1d lipid loading and presentation to invariant natural killer T (iNKT) cells and on iNKT cell differentiation in the thymus. Furthermore, it remains unclear whether iNKT and conventional T cells have similar autophagy requirements for differentiation, survival, and/or activation. We report that, in mice with a conditional deletion of the essential autophagy gene Atg7 in the T-cell compartment (CD4 Cre-Atg7 ⁻/⁻), thymic iNKT cell development—unlike conventional T-cell development—is blocked at an early stage and mature iNKT cells are absent in peripheral lymphoid organs. The defect is not due to altered loading of intracellular iNKT cell agonists; rather, it is T-cell–intrinsic, resulting in enhanced susceptibility of iNKT cells to apoptosis. We show that autophagy increases during iNKT cell thymic differentiation and that it developmentally regulates mitochondrial content through mitophagy in the thymus of mice and humans. Autophagy defects result in the intracellular accumulation of mitochondrial superoxide species and subsequent apoptotic cell death. Although autophagy-deficient conventional T cells develop normally, they show impaired peripheral survival, particularly memory CD8 ⁺ T cells. Because iNKT cells, unlike conventional T cells, differentiate into memory cells while in the thymus, our results highlight a unique autophagy-dependent metabolic regulation of adaptive and innate T cells, which is required for transition to a quiescent state after population expansion.

CD4+ T cells are pivotal cells playing roles in the orchestration of humoral and cytotoxic immune responses. It is known that CD4+ T cell proliferation relies on autophagy, but identification of the autophagosomal cargo involved is missing. Here we create a transgenic mouse model, to enable direct mapping of the proteinaceous content of autophagosomes in primary cells by LC3 proximity labelling. Interleukin-7 receptor-α, a cytokine receptor mostly found in naïve and memory T cells, is reproducibly detected in autophagosomes of activated CD4+ T cells. Consistently, CD4+ T cells lacking autophagy show increased interleukin-7 receptor-α surface expression, while no defect in internalisation is observed. Mechanistically, excessive surface interleukin-7 receptor-α sequestrates the common gamma chain, impairing the interleukin-2 receptor assembly and downstream signalling crucial for T cell proliferation. This study shows that key autophagy substrates can be reliably identified in this mouse model and help mechanistically unravel autophagy’s contribution to healthy physiology and disease. Autophagy is known to impact CD4+ T cell proliferation but the identity of autophagosomal components remain unclear. Here the authors leverage a transgenic mouse model to assess the autophagosomal compartment and identify interleukin-7 receptor-α as a key cargo in proliferating CD4+ T cells.

T cell senescence is thought to contribute to immune function decline, but the pathways that mediate senescence in these cells are not clear. Here, we evaluated T cell populations from healthy volunteers and determined that human CD8+ effector memory T cells that reexpress the naive T cell marker CD45RA have many characteristics of cellular senescence, including decreased proliferation, defective mitochondrial function, and elevated levels of both ROS and p38 MAPK. Despite their apparent senescent state, we determined that these cells secreted high levels of both TNF-α and IFN-γ and showed potent cytotoxic activity. We found that the senescent CD45RA-expressing population engaged anaerobic glycolysis to generate energy for effector functions. Furthermore, inhibition of p38 MAPK signaling in senescent CD8+ T cells increased their proliferation, telomerase activity, mitochondrial biogenesis, and fitness; however, the extra energy required for these processes did not arise from increased glucose uptake or oxidative phosphorylation. Instead, p38 MAPK blockade in these senescent cells induced an increase in autophagy through enhanced interactions between p38 interacting protein (p38IP) and autophagy protein 9 (ATG9) in an mTOR-independent manner. Together, our findings describe fundamental metabolic requirements of senescent primary human CD8+ T cells and demonstrate that p38 MAPK blockade reverses senescence via an mTOR-independent pathway.

CD4 + T cell differentiation requires metabolic reprogramming to fulfil the bioenergetic demands of proliferation and effector function, and enforce specific transcriptional programmes 1 – 3 . Mitochondrial membrane dynamics sustains mitochondrial processes 4 , including respiration and tricarboxylic acid (TCA) cycle metabolism 5 , but whether mitochondrial membrane remodelling orchestrates CD4 + T cell differentiation remains unclear. Here we show that unlike other CD4 + T cell subsets, T helper 17 (T H 17) cells have fused mitochondria with tight cristae. T cell-specific deletion of optic atrophy 1 (OPA1), which regulates inner mitochondrial membrane fusion and cristae morphology 6 , revealed that T H 17 cells require OPA1 for its control of the TCA cycle, rather than respiration. OPA1 deletion amplifies glutamine oxidation, leading to impaired NADH/NAD + balance and accumulation of TCA cycle metabolites and 2-hydroxyglutarate—a metabolite that influences the epigenetic landscape 5 , 7 . Our multi-omics approach revealed that the serine/threonine kinase liver-associated kinase B1 (LKB1) couples mitochondrial function to cytokine expression in T H 17 cells by regulating TCA cycle metabolism and transcriptional remodelling. Mitochondrial membrane disruption activates LKB1, which restrains IL-17 expression. LKB1 deletion restores IL-17 expression in T H 17 cells with disrupted mitochondrial membranes, rectifying aberrant TCA cycle glutamine flux, balancing NADH/NAD + and preventing 2-hydroxyglutarate production from the promiscuous activity of the serine biosynthesis enzyme phosphoglycerate dehydrogenase (PHGDH). These findings identify OPA1 as a major determinant of T H 17 cell function, and uncover LKB1 as a sensor linking mitochondrial cues to effector programmes in T H 17 cells. OPA1 regulates the formation of the distinct mitochondrial morphology observed in T helper 17 cells, which influences cytokine expression via LKB1.

Maturation of conventional dendritic cells (cDCs) is crucial for maintaining tolerogenic safeguards against auto-immunity and for promoting immunogenic responses to pathogens and cancer. The subcellular mechanism for cDC maturation remains poorly defined. We show that cDCs mature by leveraging an internal reservoir of cholesterol (harnessed from extracellular cell debris and generated by de novo synthesis) to assemble lipid nanodomains on cell surfaces of maturing cDCs, enhance expression of maturation markers and stabilize immune receptor signaling. This process is dependent on cholesterol transport through Niemann–Pick disease type C1 (NPC1) and mediates homeostatic and Toll-like receptor (TLR)-induced maturation. Importantly, we identified the receptor tyrosine kinase AXL as a regulator of the NPC1-dependent construction of lipid nanodomains. Deleting AXL from cDCs enhances their maturation, thus improving anti-tumor immunity. Altogether, our study presents new insights into cholesterol mobilization as a fundamental basis for cDC maturation and highlights AXL as a therapeutic target for modulating cDCs. To mature, dendritic cells collect and synthesize cholesterol to construct lipid nanodomains on their membranes. Obstructing this process impairs their ability to prime T cells.

Fever can provide a survival advantage during infection. Metabolic processes are sensitive to environmental conditions, but the effect of fever on T cell metabolism is not well characterized. We show that in activated CD8⁺ T cells, exposure to febrile temperature (39 °C) augmented metabolic activity and T cell effector functions, despite having a limited effect on proliferation or activation marker expression. Transcriptional profiling revealed an up-regulation of mitochondrial pathways, which was consistent with increased mass and metabolism observed in T cells exposed to 39 °C. Through in vitro and in vivo models,we determined thatmitochondrial translation is integral to the enhanced metabolic activity and function of CD8⁺ T cells exposed to febrile temperature. Transiently exposing donor lymphocytes to 39 °C prior to infusion in a myeloid leukemia mouse model conferred enhanced therapeutic efficacy, raising the possibility that exposure of T cells to febrile temperatures could have clinical potential.

How lipidome changes support CD8 + effector T (T eff ) cell differentiation is not well understood. Here we show that, although naive T cells are rich in polyunsaturated phosphoinositides (PIP n with 3–4 double bonds), T eff cells have unique PIP n marked by saturated fatty acyl chains (0–2 double bonds). PIP n are precursors for second messengers. Polyunsaturated phosphatidylinositol bisphosphate (PIP 2 ) exclusively supported signaling immediately upon T cell antigen receptor activation. In late T eff cells, activity of phospholipase C-γ1, the enzyme that cleaves PIP 2 into downstream mediators, waned, and saturated PIP n became essential for sustained signaling. Saturated PIP was more rapidly converted to PIP 2 with subsequent recruitment of phospholipase C-γ1, and loss of saturated PIP n impaired T eff cell fitness and function, even in cells with abundant polyunsaturated PIP n . Glucose was the substrate for de novo PIP n synthesis, and was rapidly utilized for saturated PIP 2 generation. Thus, separate PIP n pools with distinct acyl chain compositions and metabolic dependencies drive important signaling events to initiate and then sustain effector function during CD8+ T cell differentiation. Here the authors show how metabolic alteration of acyl chain composition affects phosphoinositide-driven signaling to initiate and sustain CD8 + T cell effector function during cell differentiation.